Sedimentary Geology, 27 (1980) 1--81 1 © Elsevier Scientific Publishing Company , Ams te rdam -- Printed in The Netherlands

PRE-PERMIAN DEPOSITIONAL ENVIRONMENTS AROUND THE BRABANT MASSIF

IN BELGIUM, THE NETHERLANDS AND GERMANY

M.J.M. BLESS I J. BOUCKAERT 2, R CONIL 3, E. GROEBSENS 2 W. KASIG 4

E. PAPROTH 5, E. POTY 6, M. VAN STEENWINKEL 7, M. STREEL 8 and R. WALTER 4

I Geological Bureau, Netherlands Geological Survey, Heerlen (the Netherlands)

2Geological Survey of Belgium, Brussels (Belgium)

3Lab. Paleontology, University of Louvain, Louvain-la-Neuve (Belgium)

4RWTH Aachen, Aachen (F.R. Germany)

5Geological Survey Nerthrhine-Westphalia, Krefeld (F.R. Germany)

6Lab. Paleozoology, University of Liege, Liege (Belgium)

7Lab. Paleontology, University of Leuven, Leuvan (Belgium) 8 Lab. Paleobotany and Palynology, University of Liege, Liege (Belgium)

(Received 15 March 1980)

ABSTRACT

Bless, M.J.M., Bouckaert, J., Conil, R., Grsessens, E., Kasig, W., Paproth, E., Poty, E., Steenwinkel, M. van, Streel, M. and Walter, R., 1980.

Pre-Permian depositianal environments around the Brabant Massif in Belgium, the Netherlands and Germany. Sediment. Geol.,27:1--81.

Pre-Permian sedimentation in northwestern Europe has been controlled by the structural evolution of this area. Cambro-Silurian deposition has been influenced by partly synsedimentary movements (among others Ordovician- Silurian uplift south of the Brabant/Condroz zone, such as the £tavelot-Venn Massif).

Presence, respectively absence of important late Caledonian deformation has subdivided northwestern Europe into three major sedimentary environments during the Devono-~arbonifarous: the Caledonian fold belt and the Cornwall- Rhenish Basin which are separated by the Belgo-Dutch platform.

Subsequently, the Hercynian or Variscan orogenies have gradually reduced the sedimentary area end produced the overall withdrawal of the marine environment. Eventually, large-scale overthrusts - such as the Dinant Nappe - masked parts of the original sedimentary basins.

INTRODUCTION

Our knowledge about the Pre-Permian deposits around the Brabant Massif in

Belgium, the Netherlands and Germany (Fig. I) varies from rather good for the

Paleozoic outcrops in the Ardennes and the Rhenish Massif to very incomplete

for the areas to the north where only few boreholes have penetrated the rocks

below the coal-bearing Upper Carboniferous.

The investigations on the Pre-Psrmian in the subsurface south of the

Brabant Massif during the pa~ ten to fifteen years have increased our kn~w-

ledge about the southward extension of the Midi Overthrust, the allochLhonous

nature of the Dinant Synclinorium (here called Dinant Nappe),as well as Lh~

sediments below this Dinant Nappe. But they have also created many new

problems because the facts observed during these studies did not fit into the

old concepts hitherto accepted as classic.

Also, the first published results of the exploration of the Pre-Permian ~n

the North Sea have in part b~en quite surprising and force the geologist ~m

develop new working hypotheses about the structural and sedimantological

evolution of that area. The present paper summarizes several conoepts which

are based upon these new findings. It should be stressed, however, that many of

+,++ , , , , -

LO

@ D minim, I; ' l

• o°ale~ ° oo

-,AI O - : : . D • o ": ' :: ' ; ..:-:.-y:.":: ::.

Fig. I. Location of the Brabant Massif and the Pre-Psrmian outcrops of the Ardennes and Rhenish Massif.

these ideas do not pretend to be anything more than working models that need

to be checked and revised by future exploration.

Structural complication: Oinant Nappe

The evolution of northwestern Europe during Pre-Permian times can only be

understood if we restore the allochthonous deposits of the Dinant Nappe to

their original position. The allochthonous nature of the sediments in the

Dinant Synclinorium was already suggested by Fourmarier (1913), who believed

the Namur Basin to extend south of Dinant below the Midi Overthrust. This is

supported by several seismic surveys recently carried out in northern France

(Clement, 1963), the Famenne area of southern Belgium (non-published reports

of the Geological Survey of Belgium, 1976-1978; Bless et al., ~977a, b), and

in the Stavelot-Venn Massif southeast of Aachen in the F.R.G. (Bartelsen &

Meissner, 1979; M. & R. TeichmUller, 1979). These investigations prove a

minimum extension of the Midi Overthrust of 175x40 km (Fig. 2). However, it

seams reasonable to believe that this overthrust extends beyond the area

studied thus far.

Thrust-folded I B I o c k - f a u t e d a u t o c h t h o n o u s d e p o s i t s allochthonous rocks I

6 cP

F i g , 2. C a r t o o n showing the p roven e x t e n s i o n o f t he D i n a n t Nappe, (From B l e s s et al., Ig8Ob.)

The hypotheses, that the overthrust does not extend across the metamorphic

Ardennan Belt (Bless et al., 1977a, b; R. & M. TeichmUller, 1979) seems alrea

dy out of date since the thrust plane has been traced below the Stavelot-Venn

Massif (Barteleen & Meieener, 1979). It appears more acceptable to suppose

nowadays that the whole Dinant Nappa was derived from the northern flanks of

the Armorican-Mid German Highs. This might imply that the Cambro-Silurian

rocks of the Ardannee and Btavelot-Venn Massif and most of the Lower Devonian

deposits in the Dinant Nappe once formed the western extension of, say, the

Taunus-HunsrUck! This hypothesis also implies that the eastern border of the

Dinant Nappe might coincide more or less with the N-S trending Eifel Zone.

It is worthwhile to compare the N-S trending Eifel Zone and the N-S trenoing

Ems Low, occurring farther north, which may be remnants of the same old 3inea

merit. Little can be said about the western extension of the nappe structure,

since this is covered by a thick sequence of Mesozoic strata.

If we can only speculate about the real extension of the overthrust plane,

we should say less about the possible displacement along the same. One may

imagine that large parts of the Dinant Nappe rest directly upon Cambro-

Silurian or even Precambrian basement. But, on the other hand, it cannot be

excluded without further study that Devono-Carboniferous deposits reach fez

to the south below the overthrust as might be deduced from thick - partly

coal-bearing - Silesian strata in the autochthonous sequence of the Jeumont

Borehole in northern France, as well as from the hypothetical extension o5

Devono-Dinantian avaporite deposits (recognized in several boreholes:

Annappes-1, Leuze, Tournai and St.-Ghislain) below the Famenne and Ourbuy

region (Bouckaert st al., 1977; Bless et el., 1977b, 1980a).

Stratigraphical complication: reworked microfoseils

Exact knowledge of the age of sediments is indispensable for the con-

struction of reliable paleogeographic maps. Frequently, the age is deter-

mined by means of microfossils. Often, microfossils are only considered as

useful stratigraphic tools. From that viewpoint, the occurrence of reworked

specimens (derived from stratigraphically older deposits) in a microfossil

assemblage may be considered as a 'contamination' that may complicate the

age determination. However, such reworked microfossils can also be regaroed

as a special kind of 'accessory mineral grains' in the sediment. In that

case, they may help in tracing the origin of (part of) the sediment, in ~

similar way as - for instance - heavy mineral associations.

The most commonly occurring reworked microfossils are palynomorphs. The

ages of sediments containing reworked palynomorphs are not distributed random~

ly on the geological time scale (Fig. 3). Distinct peaks occur in the Quater-

nary, Lower Tertiary, Neoeomian, Rhaet/Dogger, Westphalian, Upper Devonian/

Dinantian and Lower Devonian. The fact that these peaks become smaller - ano

therefore perhaps less convincing at first sight - is easily explained if

we consider the circumstance that the number of papers dealing with palyno~

morphe is much lower for older than for younger deposits.

We do not believe that this curious distribution of the reworked palyno--

morph record is due to a haphazard literature compilation. It rather suggests

that there were periods in geological history during which the reworking pro-

case was intensified by geological phenomena. We presume that a correlation

Geological Time Table

Quaternary Holocene Pleistocene

Tertiary

Cretaceous

Jurassic

Triassic

Pliocene Miocene Oligocene Eocene Paleocene Senonian Turonian Cenomanian Albian Aptian Barremian Neocomian (incI.Wealden) Maim Dogger Lias Rhaet Keuper Muschelkalk Buntsandstein Thuringian Saxonian Autunian

Permian

Stephanian Westphalian

Carboniferous Narnurian Dinantian Upper

Devonian Middle Lower Ludlovian/Pridolian

Silurian Wenlockian Llandoverian

Ordovician

Cambrian

Main orogenic events

IIIIIIIIIIlUlIIIIIIIIII~ [Changes of base level) Illllllllllll"lllllllllll/ ( Olaciahons )

I Iiiin IIIIIIIIIIII '~ II i i i i i i i i i i i i / Loramian/

I II / 'Subhercyn ian IIII

Iiiii I III III

I Late K i m m e r i a n

I IIII11) III /

I, )

Early Kirnmerian

Asturian

Bretonian

Late Caledonian

Fig. 3. Tentative correlation between recorded ages of deposits containing reworked palynomorphs and main orogenic events, as well as glaciations and sea level changes in the Quaternary. (From Streel & Bless, Ig80.)

can be made between these peaks and the main orogenic events inasmuch as

Tertiary and older deposits are concerned, and with glaciations and base

level changes (sea level changes) during the Ouaternary.

Important reworked palynomorphs assemblages in the Pre-Permian deposits

around the Brabant Massif have been described from the Silurian, Lower

Devonian and Upper Weatphalian (Streel & Bless, 1980). These can be re-

lated to - respectively - Late Caledonian and Late Variscan movements in

north-western Europe. The presence or absence of important amounts of

reworked palynomorphs in the sediment has been used as one of the arguments

for recognizing the presence or absence of areas with a high relative relief

Presumably, a high relative relief points to orogenic movements in the area,

6

whereas a low relative relief suggests the absence of important orogenic

movements.

It is believed that further investigations on reworked micrefossil

occurrences may considerably improve our knowledge of the structural-

depositional history of the Pre-Permian in northwestern Europe.

CAMBRO-SILURIAN

Cambrian, Ordovician and Silurian rocks are exposed at many locations

or are encountered by shallow borings - in the Brabant Maaeif an~ its southern

adjoining areas (Fig. 4). Nevertheless, a comprehensive paleogeographic in~

terpretation of this area is rather difficult. This is due to the lithologic

monotony of the almost purely clastic rock sequence, to unreliable dating ef

some formations, and to the absence of comparable outcrops in the surroundings,

Therefore, the stratigraphic and paleogeographic correlation with more distant

occurrences of Lower Paleozoic rocks - for instance in the British

Caledonides and in the Baltic area - is problematic. A concise interpretation

of the Lower Paleozoic history of the Brabant Massif would, however, enable

a better understanding of the paleogeogrephic conditions in the adjacent areas

of the Netherlands, northern Germany and the North Sea.

The paleogeographic history of the Brabant Massif end its southern ad-

joining areas is even more complicated by the subsequent shortening of the

Old Paleozoic deposits during the Caledonian and, partly, the Hercynian ore-

geneses. The different facies zones show considerable shortening in N-S

direction. A particular problem is the original location of the Lower

Paleozoic of the Stavelot-Venn Maeaif. The facies correlation of the Con~roz

Anticline with the Ebbs Anticline for the Ordovician period reveals that the

Salm facies of Stavelot-Venn is situated at least 10 to 20 km too far to the

north. Probably, this phenomenon can be explained by local far-reaching

overthrusts (M. & R. TeichmOller, 1979). In the paleogeographic maps of

fig. 5-10 such a displacement has been aaeumed. Consequently, the sediments

of the Stavelot-Venn have been placed on these maps some 20 km to the south.

Cambrian

Detailed paleogeographic concepts of the Cambrian in the Brabant Massif

and the neighbouring Ardenne Massif have been preaented by Beugnies at al~

(1976) and Colbeau et el. (1977). They confirm the general peleogeographical

pattern established for Central and Western Europe by Dor~ (1977) and for

the northern parts of Central Europe by Walter (1978). The Deville Series

which here belong - at least partly - to the Lower Cambrian, are initially

~\ ~ ~ --.__.___ _.~..~,r,,,~..~:~'e~l ~ \ ~x_s ;r~ellerwalo Y~ ~ " ~ ~ Skave/o~ MASSIF'

Givonne]V[ ~ ' / - J " ~ " ~ t

~p Possibly allochthonous o 5o loo km /

Fig. 4. Outcrops and borings with Lower Paleozoic rocks in the Brabant Massif and adjoin~g areas.(From Walter, 1980.)

characterized by psammitic and coarse-psammitic rocks deposited in a coastal

shallow-water environment. Sedimentation started with pure sands as, for

instance, the Assise de Dongelberg in the Brabant Massif, the massive light-

colored Dvl-quartzites of the Stavelot-Venn Massif and the quartzites of the

Aseise de la Longue Hale in the Rocroi Massif. The overlying sandy-clayey

sediments still include coarse-grained, partly feldspar-rich duartzites and

sandstone-series (feldspar-rich sandstones and arkoses of the Assise de

Tubize, reddish and green sandstones and quartzites of the Dv2 in the

Stavelot-Venn Massif, arkoees and fine-conglomeratic quartzites in the Assise

de Quatre Fils Aymon in the northern Rocroi Massif). But in the Stavelot-Venn

Massif and, particularly, in the Rocroi Massif pure pelites also occur (roof

slates of the Veine St. Anne and the Veine Renaissance). All these layers

contain Oldhamie, e trace-fossil characteristic for turbiditic sedimentation.

They represent deposits of a slowly deepening, well-aerated shelf area.

Despite mostly homogeneous depesitional conditions in all massifs, Beugnies

et al. (1976) have established a subdivision for the upper sequence of the

Deville Group (Lower Cambrian) of the Brabant and Ardenne Massifs. The arkose

facies of the Assise de Tubize passes from the Brabant Massif in southeastern

BRABANT MASSIF CONDROZ RIDGE STAVELOT ROCROI

D E V O N I A N ~ ' "/~ PEWOI~KED O¢~OOVlClAN "~ 4 000 m '~ ~ - - ~ ACI~ITAI~CHS

Postludlow - ~ ? O NO DEWORKED Ot~DOVICIAN Z . - . I_" .--_'-:-_L E---:-* - - " - - . ' - - . . ~ . ~ ' _ A s s d e C o U b e a u ' ~ x j t ACI~ITAI~CH~; I < LUO,OW J- - . - - - - . - - -~ - -Asp__de~uq~.~ .e_=o- -_= . oO- -AssdeTh imenssr td .~ '~ r -~J j ~Z) " --=----__" ~oZ_---__" . . . . . . . . . . ~ - A s s de J o n q u o i ~ I p ' ~ - - Wenlock I Ass de c'xv,.t.~ . . . . ~ " --J ----'~ ~ ' : = . . . . . . "- '~- '- ~ - - "A ASS de Nennine-~--~--~ "~ !

. . . . . . . . . . . .

AshgiIl J ~ - ~ - - " - - ~ ~ . .~Ass de F 0 s s e ' " ~ - - - - - ~ - - ~ "1

............. I I - -- -- ----- ~ - - T E --'=~'=~'"'--~"~- ....... --'--. ~.--.

o-- -- o . = . . . . . . . . . . , , t . . . . . ~ . . . . . . . . . . . . . I LlandeH0 , o Ass.de Gemb,oux - - Ass de V,tr, va l - Br.uyere " - - " Sm3 . . . . '

~ LI . . . . . . I ^ - - - - - - - - - - I I Z--~'T=-----As~'~Ri~ e"ae--" - - _ _ - - - - ~ s ] ~ ; T - - £ - - - . . . . --" C:= ' /

Arenig " " " ASS de fribolll~ . . . . . . . . . . . . . . ^ ..-7~ . . . .

O , -Ass de Huy Sml ~ , Tremadoc ' " ~ - - '_--Ass.de Laroche_-- . . . . . . . . . . . . . . . . .

Upper .;, " ~ . . - ~ " ._?L __ ~ - - - ' ~ - ' " ~ v S - - ? ~ A ~ s s ~ e V e u x M 0 u h n d e rh

I . . . . . . - - - - . . . . . . 1 - - A ssis e-'de'~ g ' o----- Rv 3 o . . . . -~_.,~1~.,-~±--~-----_-~" • o~-~-~> -- - Ass d Ao~hs~ - I

Middle ~-------Oisqu-~" "~.~-----..------ "~ ,~._o~ ~ ~ --P- . . . . I ----------~'- ~ ~-- ~ . . . . . ~v :" "-'::" " ~ T ASS de {e Roche - & - SePt - I

'~- Cambr,an I ~ = - - ' . - . - - ~ - . ~ - - - : - - &=~'-=-" "~'-" "_%/_~ "'-'"'-Z." "~'_"~-H ~ " <~ - - ~ - - ~ C ~ ~ Rv 1 - - - -Ass .de Transit ion C.) Lower " .. --- ?

~ - , - - A s . s.de Tubize . . . . . ¢, - -- Cambrian . . . . E---=.'Dv 2,,..=. E" Ass de Quatre Fds Ayrnon ~ % _ " . . . . ~ ".','" - " '-" . . . . . . . _ o :~:.'" ~ " '..:.=" - ' - • - • : o _'" • " ~ - .'_:- - - _ = _ - - z _ - : . z _

• ~ .Ass:de . u o . ~ n g e l b e r ~ . ::- . . . . . . o. , , ,~. . .DDv 1 , . . . . o . Ass.de L0n ug.~. Heye- - - PRECAMBRIAI~ .~ A ? A ,~

Fig. 5. Stratigraphic scheme of the Lower Paleozoic in the Brabant Massif and adjoining areas. (From Walter, Ig80.)

direction into a quartzite-feldspar-facies and a quartzite-facies, respective-

ly extending from the eastern parts of the Brabant Massif through the Stavelot-

Venn Massif to the northern parts of the Rocroi Massif. Further south in the

Rocroi Massif a third, predominantly sandy-clayey facies of the higher Oeviiie

Group has been found.

The lateral facies changes from north to south indicate an increasing

distance from the source area. Mortelmans (1955) has postulated north-south

transport directions for the Deville sediments in the Brabant Massif because

of cross-bedding features. Sediment-petrographical observations also indicate

that the feldspar and quartz of the arkoses and quartzites of the Deville

Group in the Brabant Massif and in the massifs of Stavelot-Venn and Rocroi

originate from a northern source area (Beugnies et al. 1976; Colbeau st al.

1977).The exact position and extension of this northern source area, and a

probably subordinate southern source, is still questionable.

Thus the beginning of the Cambrian is cha~act~ized by a stable shelf sea

being filled mainly from a large northern high. The successive subsidence ef

the shelf area was more or less compensated by the sedimentation.

With the beginning of the Ravin, the depositional environment of the

Brabant Massif and of the Ardenne Massif became deeper. The greyish-green,

J

..... 4 <J

/ " ' - - @n.d s h a l e s - ~ - - - - ~ - - ' ~

LATE PRECAMBRIAN/LOWER CAMBRIAN / (DEVlLLE) ~__..~o ~ookml

I

Fig. 6. Lower Cambrian - Lithology and paleogeography in the Brabant Massif and adjoining areas. (From Walter, 1980.)

sandy-clayey layers (base) and the massive siltstones (top) of the Assise

d'Oisquerq in the central and western parts of the Brabant Massif still

represent deposits of a well-aerated outer shelf sea. The contemporary black,

mostly pelitic rocks with sub-ordinate arenaceous intercalations and some

lydites and black limestones are definitely sediments of a less aerated,

though still shallow, pelagic basin. According to Beugnies (1963), similar

pelagic conditions have to be assumed as normal for the Revin sediments in

the Ardenne Massifs. The continuous roof slate horizons of several metres

thickness in the Rocroi Massif and the very homogeneous argillaceous series

of the highest Revin (Rv5) indicate episodes of pelitic sedimentation. Typi-

cal for major parts of the Ardenne massifs, however, are Revin sediments with

rhythmic intercalations of dark pyritic sandstones and quartzites which, cer-

tainly, developed under similar reducing conditions to the pelites. Contrary

to the normal pelitic sedimentation, they always represent short events of

reworking of still unconsolidated sediments from the rims of the Revin basin

into its central parts (Beugnies et al., 1976). Indications for this type

of displacement are to be seen in subaquatic slWd~ngs and turbiditic features

as, for instance, slumping, graded bedding, flute marks etc. (Beugnies, 1963;

1 0

J /

S~ f J - . . . . . . . -~., ,,' ~, "? , i~ ~ • q ! "4 r ' ;,

. . ~ ' .p..~. ? little or no deposit ion ~

? ~

* Vol . . . . . m and d#rk q u a r t z i t e s ~

M I D D L E / U P P E R C A M B R I A N ? posit ive area ? ~, ( R E V t N ) o . . . . . . . 50 ,, , o o k ~

I

Fig. 7. Middle and Upper Cambrian - Lithology and paleogeography in the Brabant Massif end adjoining areas. (From Walter, 1980.)

Geukens, 1963a; Love and Vanguestaine, 1973; Albrecht, 1971; Mortelmans,

1977). Additionally, in many cases the petrographic composition of the

Ravin quartzites matches sub-greywackea rather than orthoquartzites. The

influx of psammitic sediments in the central portion of the basin increased

during two periods, the lower and higher Revin (Assise de la Roche-~-Sept-

Heures and Assise de la Petite Commune of the Rocroi-Massif end the beds ~ the

Rv2 and Rv4 of the Stavelot-Venn Massif~ as can be deduced from widely ex-

tended quartzite-dominated intervals. In this last quartzitic interval the

quartzite layers are particularly thick and they extend to the north, proba-

bly as far as the eastern Brabant Massif (Assise de Jodoigne). Quiet deposi-

tional conditions predominated again at the end of the Upper Cambrian (pure

pelitic rocks of the Rv5 beds in the Stavelot-Vsnn Massif and their lithologic

equivalents in the other Ardenne Massifs.

The available sedimentologic data are still insufficient to define the

shape of the Revin basin end the exact position of the source areas. Obser-

vations in the northern Stavelot-Venn Massif suggest transport directions

for the Rv4 sands f~om southern or southwestern supply areas. The northern

source area had almost lost its influence. According to Beugnies at al. (1976),

the greeter part of the quartz minerals in the Ravin quartzites still

11

originated from the 'North Continent'. This would, however, not contradict

a predominant filling of the deepening Ardennan basin from a southern supply

area if repeated displacements of unconsolidated sediments by turbidity

currents are accepted.

Ordovician

Incoherent exposures and insufficient stratigraphic data and correlations

of the Lower and Middle Ordcvician obscure the paleogeographic history of

the Brabant Massif.

Important interruptions of sedimentation can certainly be excluded for

the Tremadoc-Caradoc. The laminated shales of the Assise de Laroche in the

southern Brabant Massif, and of the Assise de Huy and the Assise de Sart

Bernard in the Condroz Anticline confirm the classic interpretation of both

areas belonging to one basin, even with comparable sedimentation rates in

the beginning (Martin, 1968; Michot, 1978). A gradual increase of the sand

percentage in the shale sequence in the Condroz Anticline indicates a

growing mobility of the southern part of this depression. Lower and Middle

Ordovician sediments in the northwestern Brabant Massif have scarcely been

investigated. Anyhow, no observations exclude the possibility that the

Brabant depression extended far beyond the northern border of the actual

Brabant Massif.

A direct contact with the equivalent deposits in southeastern England is

quite probable although the Ordovician sedimentary history in that area is

as yet incompletely known. Since the bulk of the Ordcvician rocks in south-

eastern England have been dated as Tremadoc and Llanvirn, marine conditions

can very likely be presumed there for the whole Lower and Middle Ordovician.

Only because of the analogy with the Stavelot-Venn Massif, continuous

marine sedimentation from the Upper Cambrian into the Lower Ordovician may

be assumed for the southern Ardennan massifs of Rccroi, Serpont and Givonne.

After a short period of nondeposition near the Revin/Salm limit (postulated

by Geukens, Ig63b), about 1000 m of alternating clays and sands, partly of

flysch habitue, were deposited from Tremadoc to Caradoc. The lower Salm in

particular shows local intercalations of mica-rich fine-grained sandstones

with flute casts at the base, graded bedding, ripple marks and convolute

bedding structures.

A distinction by Schmidt (1956) between a northern sedimentary province

with increasing proportions of sandstones in eastern direction, and a

southern province rich in roof slate horizons, does not necessarily pre-

suppose a northern continent. An increasing palectectonic mobility of the

area with development of independent sub-basins may have produced the

12

h '

- - ,(> ~ S "

~ - :da rk graptol i t ic s h a l e s L ~ _ ----~j~. . ( " ~ . - ~ u n d f inegrained sandstones ~ ~ , , ,.~ ..-,

/,~ ~ - 2 : C . L 2 2 2 - - 2 - T = - _ - T - : ~ i - \ local upmt r

/ / ~ [ D ) E ~ [ ~ I ~ = = s h a l e s and - qua r t zdes - ~- turMdite sandst.ones

l ? posit ive area ? T R E M A D O C - LLANDEILO 0 50 100 krn

Fig. 8. Lower Ordovician - Lithology and paleogeography in the Brabant Massif and adjoining areas. (From Walter, 1980.)

observed changes of facies. Richter & Scholz (1972) postulate for the

south-western Stavelot-Venn Massif a direction of sediment transport from

the south to the north. The intercalated characteristic red pslites of the

higher Salm - representing deposits of strongly oxidizing environment -

indicate the gradual shallowing of the basin (Fransolet et al., 1977). The

quartzite coticules, intercalated in the same shales, have been interpreted

as turfs altered by halmyrolysis (Kramm, 1976). Probably, some of the dyke-

shaped magmatitss in the Lower Paleozoic of the Stavelot-Venn Massif, may

be related with these volcanic events (Scherp, 1960; Geukens, 1976).

In the Rhenish Massif the oldest outcropping Ordovician rocks are

of Llanvirn age. The pelagic character of the Plettenbmrger B~nderschiefer

and the Unterer Tonschieferhorizont of the Ebbe Anticline, however, suggest

similar depositional conditions as for the Brabant Massif and the $ambre-

Meuse area. A direct conned~on between these areas is quits likely.

During the Upper Ordoviclan a considerable change and differentiation of

the paleoenvironment took place, at least for shorter intervals. The observed

unconformity within the Caradoc of the Condroz Anticline proves a local

emersion of the sea floor for the middle Caradoc. Further west, indications

13

~ ~o~ ~ ~ -

p [ . / . / ~ / ~ ,

- - ~ - - - d a r ~ : g~ap[ohtlc shales "t -- /

~ " " ~ c ~ o a ~ p / i i ~ e s~"~st°£~X ? pos,t,ve area / ~ ? p o s i t i v e a r e a ? ~ ~

~ o l c a s

? p o s i t i v e a r e a C A R A D O C - A S H G I L L " o . . . . . ~o, ,ookm,

t

Fig. g. Upper Ordovician - Lithology and paleogeagraphy in the Brabant Massif and adjoining areas. (From Walter, 1980.)

of submarine ridges are the occurrence of intercalated conglomerates, sudden

lithologic changes from pure pslites to carbonate shallow-water sediments and

some coarse sand layers. Uniform pelitic sediments in the surroundings (and

during the Ashgill in the entire Condroz zone) prove that this paleotectonic

mobility represents only local and limited events. They are explained as

synchronous phenomena of an 'Intra-Caradocian orogenesis', which took place

further south in the southern Ardenne Massifs, although definitive evidence

for a true Caradocian orogenesis could not yet be established from immediate

observations in these massifs. Increased paleotectonic mobility of the

central and western part of the Brabant Massif is suggested for the Upper

Ashgill by the accumulation of acid volcanites. This mobility is reflected

in shallow-water sediments which contrast with the normal graptolite-shale

facies of the Ashgill. These facies differences have repeatedly been inter-

preted as local unconformities (Fourmarier, 1954; Legrand, 1968). The Upper

Ordovician volcanism comprised eruption of lava, ignimbritss and tuffs and

various intrusives such as the Quenast Porphyry and the Lessines Porphyry.

In the Rhenish Massif (Ebbs Anticline, Soest-Erwitte borehole), the

pelagic basin sedimentation of the Llanvirn continued with minor variations

14

probably throughout Caradocian and perhaps even into Ashgillian time. The

open-sea connection with the Brabant Massif and the Condroz Anticline, ~]-

ready suggested for the Lower Ordovician, very likely continued. The same

applied for the southeastern England depression.

Silurian

During the Silurian period more or less uniform sedimentary conditions

prevailed in the northwestern part of Central Europe. In the Brabant Massif

and in the Condroz Anticline mainly dark, laminated clays with only a few

sand and silt intercalations have been deposited. These are relatively thick.

The Llandoverian and Wsnlockian deposits have a thickness of up to 1150 m in

the Brabant Massif and up to 500 m in the Condroz Anticline. The similar

lithology and the great thickness in both areas support the idea of a

coherent depression, however, with greater rate of subsidence in the Brabant

Massif. Similar to the Ordovician, the differentiated subsidence in south-

north direction was associated with acidic and basic lavas and tuffs in the

Southern Brabant Massif and in the Condroz Anticline. An overall pelagic

environment can be postulated for the pelites in the Brabant Massif, whereas

in the Condroz Anticline several indications for a southern uplift are

present. In the Upper Llandoverian and Wenlockian, massive sandstone inter-

calations with turbiditic character appear. The same sequence contains rework~

Ordovician acritarchs of excellent preservation. Their occurrence can only

be explained by the reworking of non-consolidated sediments from the south

(Martin, 1968, Martin et el., 1970). Reworked acritarchs have not been found

in the Brabant Massif. In addition, other sedimentary features confirm the

presence of a southern source area for the bulk of the psammites in the

Brabant and Condroz areas (8eugnies in: Martin et el., 1970).

The northern extension of the Silurian basin cannot be defined. Until now,

no characteristic facies changes or other indications for a naighbouring

northern high have been observed. According to the frequency of Silurian sha-

les in borings in southeastern England, the sedimentary province of the

Brabant Massif and Sambre-Mause zone obviously reached far to the west.

In the northeastern Rhenish Massif, the uppermost Ordovician and the Lower

and Middle Silurian have orobably never been deposited. This would suggest

an emersion of this area comparable with the local uplifts of the western

Sambre-Meuse zone and of the Ardenne massifs in early Caledonian time.

If a Silurian age of the laminated shale beds in the Soest-Erwitte bore-

hole could be confirmed, this would imply that the Brabant Depression con-

tinues in eastern direction immediately north of that Sauerland High. Also

for the Upper Silurian (Ludlowian, Post-Ludlowian), an open sea connection

I VAI#rL[

""~?----~--~----: [~ [~ [~ ~[~ ~. ~__~_~ _~_[~] ~,oca, uplift ?

? posirwe area ? . . . . . . . . . "b shallow water

Velc~ s

15

I graptotitic shales LLANIDO'VERY- LUDLOW I o 5o lookm

Fig. 10. Silurian - Lithology and paleogeography in the Brabant Massif and adjc~ning areas. (From Walter, 1980.)

has to be assumed from southeastern England to Central Europe, still with the

highest subsidence rates north of the present Ardenne mountains and the

Rhenish Massif. The northern limit towards an epicontinental complex was

situated probably far in the north. To the south this NW European depression

was limited by the residual Ardenne Uplift. The terrestrial supply from

this direction obviously ceased during the Ludlowian and Post-Ludlowian-

period. At the end of the Silurian the Ardenne Uplift was again partly

covered by a shallow sea. This is suggested by the predominance of calcare-

ous shallow-sea deposits with a rich shelly fauna in the Ebbe Anticline and

the Remscheid-Altena Anticline.

Uppermost Silurian strata appear in similar facies in the western exten-

sion of the Condroz Anticline near Li~vin. After strong Late-Caledonian

dislocations of the Sambre-Meuae zone and the Brabant Massif, the southern

border of a broad North-West-European Caledonian platform matched the

southern rim of the present Ardenne mountains.

16

Conclusions

The available data on lithology and stratigraphy of the Lower Peleozoic

rocks in the Brabant Massif and its surroundings do not permit of establis~ng

a differentiated picture of the paleogeographic-paleotectonic history of

this Caledonian dislocation area, which is important for NW-Central Europe.

Comparison of the Lower Paleozoic sedimentary sequences of the Brabant

Massif, the Condroz anticline and the Ardenne Massifs suggest deposition in

a marginal trough south of a Pre-Cambrian stable high which was presumably

located in the southern North Sea.

The Lower Cambrian continues the Late Pre-Cambrian epicontinental develop-

ment with shallow-sea sediments, being distributed on a large stable shelf

area. Its rate of subsidence increases during the Middle Cambrian, particu-

larly in the south, and the sediment transport from a northern high dimi-

nishes gradually. Depositional conditions of deep-neritic to bathyal environ-

ments prevail. Maximum sedimentation rates were reached in the Ardenne

massifs during the Middle end Upper Cambrian and Lower Ordovician. In the

Brabant Massif maximum rates of sedimentation are observed in the higher

Ordovician end, mainly, in the Silurian.

The development of depressions was each time followed by important dis-

locations. At the verge of the Ordovician, the paleegeographic situation in

the south was changed by the uplift of the Ardennan area. Immediately aftel

the Silurian, new paleogeographic conditions were produced by the Late

Caledonian dislocation of the Ordovician-Silurian Brabant Depression.

The Caledonian sedimentary history and tectogenesis of the Brabant Massif

and the Ardenne Massifs cannot be compared with the orogenic development

of the British-Scandinavian Caledonides. It matches, however, the Early

Paleozoic history of the Danish-Polonian marginal depression st the south-

western border of the East-European Platform. The paleotectonic development

of the latter area during the Early Paleozoic is relatively well known from

borings in northern Poland and from exposures in the Holy-Cross Mountains.

Reliable indications for the nature and extension of a NW-European foreland

north of the Brabant Massif - analogous to the East-European platform - are

still miesing and there is still no information about the southern border with

the Central-European Paleozoic geosyncline. The monotonous lithology and

great thickness of the Lower Paleozoic and the subordinate magmatic activi-

ties in the Brabant Maseif and in the Ardenne massifs suggest subsidence and

uplift of Pre-Cambrian basement block-complexes rather than the development

of an autonomous NW-Central-European Caledonian orthogeosyncline. This

assumption is supported by the absence of an intensive metamorphosis and of

a subsequent significant molasse-develepment.

17

DEVONO-CARBONIFEROUS: TECTONIC FRAMEWORK

The three main depositional environments which can be distinguished

in NW Europe during the Devono-Carboniferous are:

- the Caledonian fold belt running from Norway into Great Britain (with

Devonian Old Red Sandstone deposits and Caledonian trends of basins and highs

characterizing Carboniferous sedimentary pattern),

- the Cornwall-Rhenish Basin (with epicontinental shale-dominated deposits

in the Devonian and 'foredeep' facies in the Carboniferous), and

- the Belgo-Dutch Platform (that may be considered as a micro-craton ori-

ginally belonging to the Fenno-Scandian Shield and NE European Platform).

C~ ~ BELGO- DUTCH ~ 4/

PLATFORM /

Fig. 11. Cartoon of the tectonic framework for the Devono-Carboniferous of NW Europe, (From Bless at al., Ig8Ob).

Caledonian fold belt

The main belt runs from Ireland through northern England and Scotland to

Norway. Secondary branches in NW Europe are found in between Pre-Cambrian

blocks of Cornubian-Armorican-Mid German Highs, the Belgo-Dutch Platform and

the Fenno-Scandian Shield.

Denudation of the Caledonian fold belt since Silurian times took place in

epicontinental and intramontane fault-bounded basins with active volcanism

along faults. The main belt in Britain is marked by fault-bounded basins

18

?

fault-bounded linear basins since Middle Devonian. . ,

. \ \ i l', / ~ e n . ~ , ,

s u b s ~ ~

/ "\

Fig. 12. Cartoon of the tectonic framework for Devonian sedimentation in NW Europe. (From Bless et el., 1980b.)

with non-marine Old Red Sandstone deposits. The gradual decrease of the

relative relief during the Devonian can be deduced from comparison of, e.g.,

the thickness of Lower and Upper Old Red Sandstone deposits (respectively

up to about 4000 m and about 400 m) in the Midland Valley. Continued subsidence

of basinal areas in the Carboniferous can be deduced from Caledonian trends of

the Carboniferous basins matching the position of the Devonian depositional

areas.

Cornwall-Rhenish Basin

This basin was bounded to the south by the Cornubian-Armorican-Mid German

Highs. The bulk of the sediments in this basin must have been derived from

1 9

w i t h i n t e r m i t t e n t n o n - d e p o s i t i o n

o g

e C t

e ~ o e n

Fig. 13. Cartoon of the tectonic framework for Carboniferous sedimentation in NW Europe. (From Bless et al., 1980b.)

these highs. The basin preumably has to be subdivided into several sub-basins

(Paproth, 1976). Local shoals with a cover of shelf carbonates occur since the

Middle Devonian (Gotthardt et al., 1978). Rapid subsidence is marked by ex-

tremely thick siliciclastic epicontinental deposits. Active volcanism occurred

along several faults.

A continuous northward shift of the main basin axes and gradual incorpora-

tion of the southern border of the same within the Variscan belt, followed

by eventual uplift and rapid denudation since the late Famennian is presumed.

Beige-Dutch Platform

With this term is indicated an area extending from northern France into

northwestern Germany with a complex block-mosaic of horst areas separated

20

~,~,9 ¢ ~itW:':;-"';¢.,~. .~ -,~/;~i".:'..!-~-"' ",~ ,,,~.

m

FRASNIAN . . . . . .

P R E D O M I N A N T L Y C A R B O N A T E S

• - - . ~ . " , ~ P R E D O M I N A N T L Y M A R I N E S I L I C t C L A S T I C 5

• ~ . . ~_ . . . . . . . . . I ~ - ~ . " : - . : . . I PREDOMINANTLY P A R A L / C SILICICLASTICS

• . . . . . - - . . L - -

S I L I C I C L A S T / C S

~ EVAPORITE5

Fig. 14. Idealized concept of the evolution of the sedimentary pattern during the Devono-Carboniferous in NW Europe. The Devonian period is characterized by localized deposition in valleys within the Caledonian fold belt. As the re- lative relief of this belt degraded at the end of the Devonian the depositio- nal conditions of the Caledonian fold belt and the Belgo-Dutch Platform b~came more comparable because of the similar relative relief in both areas.

21

by quickly subsiding linear fault-bounded basins, marked by a relatively

mild Caledonian deformation restricted to narrow zones, and by the practical

absence of Variscan deformation (except for its southern border with the

Cornwall-Rhenish Basin which is now incorporated in the Dinant Nappe). This

means, that the Pre-Cambrian or Cambrian rocks are generally overlain by

practically undeformed, mainly non-metamorphic deposits.

Angular unconformities within the Paleozeic sequence - such as those

suggested by Legrand (1968) for the Brabant Massif - may be explained by

rotational tilting of blocks masked by anticlinal draping of overlying strata

Permian Silesi~ Dinantian

Famennian

Eifelian-Frasnian

Lower Devonian

REGRESSION ~ == TRANSGRESSION

-- u'~ ~ S I L I C I C L A S T I C S

~ ~ ~ R R O N A T E S ON SHELF AREA; ~; EVAPORITES IN EYAM, HATHERN (G.B.),ST. GHISLAIN, .,~ ~. ORNEAU (BELGIUM) /

...... OZ FACIES"

~ S ON SHELF AREA; EVAPORITES "~ IN ANNAPPES-I(N.FRANCE),TOURNAI, LEUZE, .~

/ NON-MARINE TO MARINE SILICICLASTICS

C a m b r ~ MENTS

Fig. 15. Simplified sedimentary history of the Belgo-Dutch Platform and Cornwall-Rhenish Basin during Devono-Carboniferous, with special reference to evaporite occurrences. The origin of some reworked sediments (mainly based on studies an reworked palynomorphs and other microfossila) is also indicated.(From Bless et al., IgGOb.)

22

The absence of a strong Caledonian deformation in the Beige-Dutch Platform

and of the corresponding high relative relief may be deduced from the apparent

absence of an important denudation area north of the Brabant Massif during the

Ordovician and Silurian (Walter, 1980), from the apparent absence of basins

with Lower Devonian depoeits~ and from the fact that only few sediments have

been derived from the same during the Devono-Carboniferous.

During the Lower Devonian, the Beige-Dutch Platform separated the non-

marine depositional environment of the British Caledonian fold belt (thickness

of Lower Old Red Sandstone locally up to 4000 m in Midland Valley) from the

epicontinental deposits of the Cornwall-Rhenish Basin (thickness of Lower

Devonian deposits up to about 4000 m in Dinant Nappe).

During the marine transgression of the Eifelian-Frasnian period, the p~at-

form is characterized by widespread carbonate deposits, whereas the British

Caledonides and the Cornwall-Rhenish Basin show a predominance of, respective-

ly, non-marine and marine siliciclestics.

Since the late Famennian/early Dinantian, denudation had lowered the

relative relief of the British Caledonian fold belt so far, that this relief

becomes comparable to that of the Beige-Dutch Platform. From that moment

onwards, only the Caledonian and Armorican trends of depositional areas

reflect the different evolution of these fault-bounded horsts and basins.

The structural subdivision of both the Beige-Dutch Platform and the

British Caledonian fold belt seems to have been rather persistent throughout

the Deveno-Carboniferous. Thick, relatively complete sequences are found in

the basins, whereas thin, often incomplete deposits characterize the positive

areas (fig. 15). The boundary fault systems separating positive and negative

sedimentation areas existed since at least late Caledonian times.

DEVONO-CARBONIFEROUS: DEPOSITIONAL ENVIRONMENTS

Lower Devonian

Lower Devonian sediments occur in the Cornwall-Rhenish Basin and in intra-

montane, non-marine troughs within the Caledonian fold belt. Presumably, they

are practically absent on the Beige-Dutch Platform. Continuous deposition of

marine sediments from Silurian into Lower Devonian times occurred only in

some parts of the Cornwall-Rhenish Basin (e.g. Li~vin borehole in northern

France; Lecompte, 1967). Normally, more or less important sedimentary gaps

are observed, which can be attributed to late Caledonian movements.

Along the flanks of the Beige-Dutch Platform end on local shoals within

the Cornwall-Rhenish Basin, Lower Devonian basal conglomerates seem to rest

discordantly on the Cambro-Silurian rocks. Several, possibly non-marine

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U FAMENNIAN N -':::._~.~,._ _.~, .0] ' ' C O N O R o Z S p . . . . . . . . . . . . . . . . . . . . . . . . z

P ~z ~ M A T A G N E ~ ~] r • i . . . .

O E FRASNIAN I z ~ ~ J_ rL . l _L# , , , I , f B A R R I E R ~ - - - - ~ - - <z I E R ~o<c ' ~" ~ - - "" -- ---"--- C'~'~'~'~ - - - - == ~cm ~ ° , ~ ,.,.. " ~ ' . ~ / _ . . O d ' . ~ " [ ~ -_~_.~REEFS "'~- ~._~:=E ~_....~_.._-- I v M ~ T - r . o O _ 0°o: - ~ ; ' ~ , ~ ; ~ : d ~ = ~ = h 0 DI GIVETIAN i ~ - ..O 0 ~ o ~ j . . I ~ : ~ , ~ _ _ F ? ~ _ ~ / : ~ c~ ~JI

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(~ REWORKED SILURIAN ACRITARCHS PRESUMABLY DERIVED FROM THE NORTH (~) PREDOMINANCE OF REWORKED ORDOVICIAN ACRITARCHS PRESUMABLY DERIVED FROM THE SOUTH

Fig. 17. Stratigraphic scheme of the Devonian around the Brabant Massif.

intercalations (containing a.o. vertebrate fossils: Pteraspis) in the

essentially shallow-marine siliciclastic Lower Devonian deposits of the

Ardennes and the Rhenish Massif suggest the proximity of land. The strong

increase of the thickness of the deposits from north to south in the

Ardennee (from 0 to about 4000 m) and in the Rhenish Massif (from less

than 500 m up to more than 3000 m in the Siegen Trough) suggests that the

bulk of the sediments was derived from southern sources. This hypothesis

is partly corroborated by the results of a first study on reworked

Ordovician and Silurian acritarchs occurring Siegenian and Emsian deposits

of Belgium by Vanguestaine (1979). Vanguestaine suggested that the

Silurian acritarch assemblages (which occur in locations along the northern

flank of the Dinant Nappe) might have been derived from the Brabant Massif.

He argumented that an even more northern source area (Norway) - postulated

by Michot (1976) - is not very likely. The same author presumed that the

reworked Ordovician acritarch assemblages (which are predominant in loca-

tions further to the south within the Dinant Nappe) had been introduced in

the basin from southern supply areas ('Mid German High'?).

The Cornwall-Rhenish Basin should not be considered as a huge, uniform

depositional area. Detailed studies in the Rhenish Massif (cf. Paproth,

1976) have shown that several short-living sub-basins can be distinguished

(Fig. 18). These sub-basins have been interpreted as inversion troughs (sensu vl

Dvorak, 1973) which are characterized by a high rate of sedimentation of

36

• . . . . . - . ~ ~ . . . . , , , '"" " V I "; ~ ' ; ' - " . . ' - _ ~ ~ - - - _ ,,,,',' ,

- .---- - -Z- -~- - -2- - - - :I IIII111 ! ,i I _:?:-:---

\ )

0 lOOkm L I

H

1 0BERBERGI$CH-$AUERLAI1D TROUGH (GEDINNIAbl) II 31EGEH TROUGH (51EGEI'IIAN) III NASSAU TROUGH (LOWER EMSIAN) IV 05T-5AUERLAI1D TROUGH (LOWER EIFELIAN) V LEIIlIE TROUGH (UPPER EIFELIAN-LOWER GIVETIAN) VI VELBERT TROUGH (UPPER GIVETIAN-UPPER

DEVONIAN)

Fig. 18. Inversion troughs of Devonian age within the Rhenish Massif. (After Paproth, 1976.)

mainly shallow-marine deposits in a quickly subsiding trough. In a second

phase, an abrupt reduction of the rate of subsidence, matched by a tempo-

rarely increased heat flow, produced strong coalification and even anchi-

metamorphosis. At the same time, the basinal axis was shifted to neigh-

bouring areas where the same process of quick subsidence and rapid

deposition was repeated. Apparently, these inverted basins remained rela-

tively stable shoals in younger Devono-Carboniferous times as can be de-

duced from the low degree of coalification of e.g. Middle Devonian spores

derived from these shoals during the late Westphalian (Bless & Streel,

lg76). The inverted sub-basins of Devonian age are distinghuished from more

stable areas by the tremendous thickness of the mainly shallow-marine

deposits and the high rank of coalification of the same.

The shallow-marine environment that predominated in the Ardennes and

Rhenish Massif during the Lower Devonian is characterized by the repeated

occurrence of carbonatic sediments containing prolific, thick-shelled

benthos (Aaselberghs, 1946). This environment has been described as the

'Rhenish facies'. More condensed, pelagic sediments which lack a prolific

benthonic fauna have been attributed to the 'Hercynian facies' (Schmidt,

1962).

/,,,.

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u ~

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Argyll ,',

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Fig.

19

. Middle

Devonian

- Lithology

and paleogeography

of northern

Europe.

(After

Gotthardt

et al

.,

1978.)

38

A rather peculiar environment occurred in Normandy (northwestern France)

during the Middle Siegenian. Early diagenetic dolomites and stromatolites

pass laterally into anhydrites (Poncet, 1967), suggesting sabkha-like depp-

sits in that area along the southern flank of the Cornwall-Rhenish Basin.

Middle Devonian and Frasnian

A widespread marine transgression across the 8elgo-Dutch Platform durino

the Middle Devonian and Frasnian is marked by the frequent occurrence of

thin basal conglomerates or (sometime plant-bearing) arenites overlying th~:i~

Cambro-Silurian basement, which are followed by more marine, often carbonatin

deposits. Non-marine environments persisted in the intramontane troughs of

the Caledonian fold belt. Within the Cornwall-Rhenish Basin, fine-grained

siliciclastics (mainly derived from southern sources) predominateo except

for regional shoals which were covered by carbonatic sediments.

i 0 lkm

I.L couwN " I

IA MATAgN E ',~ i ! .......

IIIIIIIIII1111tl 11 t11I lllllllllllll ;;'; ;i;t;!;'; lllllllilllliVVWtllllll I tv r Fig. 20. Frasnian bioherms in the Frasnes-Couvin area of southern Belgium. (After Tsien, Ig71, 1975.) A: simplified geological map. B: schematic cross- section showing the peculiar arrangement of the bioherms on top of each other

39

Bioherm facies on southern slope of Beige-Dutch Platform

On the southern slope of the Beige-Dutch Platform adjacent to the

Cornwall-Rhenish Basin numerous isolated build-ups developed during the

Eifelian-Frasnian period. These biohermal reef complexes grew in a shale-

dominated environment. They consist of relatively pure limestones with

abundant massive globular or lamellar stromatoporoids and rugose corals.

On the flanks a talus of organoclastic limestones with a rich benthos in-

cluding branched corals and stromatoporoids as well as brachiopods and

crinoids was developed. In the southern part of the Dinant Nappe in the

Frasnes-Couvin area (some 75 km south of Brussels) several Frasnian bicherm

complexes can be observed which apparently grew on top of each other (Fig.

20). This phenomenon suggests that the occurrence of these bisherms was

linked to repeated uplift of the same tectonic unit in the basement. In-

creased influx of pelitic material into the basin from southern sources

presumably killed these reefs.

The southern origin of the Eifelian-Frasnian pelites in the southern

part of the Beige-Dutch Platform and its slope to the Cornwall-Rhenish

Basin has often been questioned. Some geologists have suggested that the

pelites had been produced by the Old Red Continent in the north. They in-

vented a complex mechanism of currents that should have 'filtered' the

fine-grained siliciclastics through the carbonate shelf that separated the

presumed northern source area from the Cornwall-Rhenish Basin. It is un-

likely, however, that this suggestion is true since the main horst areas

within the Beige-Dutch Platform (e.g. the Brabant Massif) were covered by

marine carbonates during the acme of the Eifelian-Frasnian transgression.

Therefore, a northern supply area for these pelites can be excluded.

Barrier reef facies

Further to the north on the edge of the platform, a barrier reef occurred

that separated the shale-dominated pelagic environment of the basin from a

more protected carbonate shelf facies with biastromes and patch reefs. The

barrier reef environment was best developed during the acme of the trans-

gression in Lower Frasnian times. During that period, the barrier reef ex-

tended over s distance of at least more than 200 km in a narrow belt sub-

parallel to the southern slope of the Beige-Dutch Platform (Tsien, 1974).

Usually, the carbonates of the barrier reef complex have been dolomitized.

40

Protected carbonate shelf facies

North of the barrier reef complex carbonates were deposited in more or

less protected back-reef to sublageonal or lagoonal environments. Coral-

stromatoporoid biostromes extended over vast areas. Frequently, a rhythmic

or cyclic arrangement of the sediments can be observed. Kesig (1980a) des-

cribed examples of Givetian-Frasnian carbonate cycles in the Aachen region.

He distinguished an ideal cycle composed of three phases (Fig. 2!).

/ |~------~r-. ~ - , , , - _ _ ,,, " ' • s~ruc~ureless

3 ~-... ~ ~ , f - - _--I--~ calcilutites with birdseye Fabrics

2

1

3 Phase

- - I l l - - - - III I1:--I----

_ _ *11 I I I I | 1 ~

StromaEoporoid bios~rome

Amphipora .~asen"

Fig. 21. Scheme of ideal cycle in the Upper Givetian and Frasnian carbonate of the Aachen region, Federal Republic of Germany. (From Kasig, 19BOa.)

The basal bed is dominated by dendroid stromatoporoids, like Amphipors,

which trapped the lime mud. This bed is usually relatively thin. It is

overlain by a much thicker sequence of massive globular etromatoporoids

which must have lived in a high energy environment since most of the

specimens do not occur in life-position. This bed is followed by often

finely laminated, practically non-fossiliferous calcilutitae with birds-

eye fabrics, characteristic of lagoonal facies. These cycles could be

followed over a distance of more than 25 km in the Aachen area.

Within the restricted marine environment south of the Brabant Massif,

a trough with a relatively high rate of subsidence matched by quick depo-

sition of shallow marine carbonates and claetics developed since at least

the Middle Devonian. This can be deduced from the increased thickness of

A N N A P P E S ARGYLL SOUMAGNE

z :.:.:::::.:~i

=" . . . . . , ooo ,,,,, c:~ F r ' ' . . . . . . . . '

, 3 0 0 "A'~" " "" I I I • o . , , o . .

c:~"' " . . . . . . . . . . . . . AX'A~,'~ Fa :X::~:.A: I . ~ Fa " • " .^1 IW:z i .~z l +-~£L~ o ' ~

, , ' ~ 2 9 2 1 0 0 cx. ^ X " . l / z z ~ z l ~

=l:Z~:': ' : == == - " / l n w ~ r i'~r~'+'*,. ~, " . ' o . o o" r . . . . " . . t { . ~ . . ~ " . 4 .~ ,

~ " ' ' e e e , : , . , : : ~ - 3 o o o Devoman i r . ~ . . . ~}... ,-., . . . . . . . 5 o o ^ ^ ^ ^ ^ .

i i = ~ = . • _ _ • _ • _ :

' ' - ' T.D. [ " , % 1

'~ GV 6oo

z i ~ - z = / i i i !

~'~-k-~l

~:^== ~700 .... .. C o n g l o m e r a t e AAAAA |

,~T, ̂ T I " ' ~ v.'.'.'.v S a n d s t o n e

-,- ' .~ , , L i m e s t o n e - - • , , 800 I , I , I

Z - ' - ' - " 7- z t, D o l o m i t e ~ ~'1- A^^^^

-r ~: ^ ^ ^ ^ ^ A n h y d r i t e " I -T

T T -900 E i r "':.:""::

i i lur ian

41

Fig. 22• Simplified sections of some Middle Devonian-Frasnian sequences on the Belgo-Dutch Platform which contain anhydrite intercalations•

42

Middle Devonian deposits (about 500 m) in the Annappes borehole in northerr~

France (Fig. 22) as compared with the thickness of sediments of the same age

in the autochthonous sequence of the Jeumont borehole (presumably less thar~

200 m). This trough is called here St.-Ghislain Trough after the St.-Ghislaif~

borehole (southwestern Belgium) where increased thicknesses of Upper Devonian,

Dinantian and Namurian strata have been observed (of. Fig. 16). Remarkable is

the occurrence of several anhydrite intercalations in the Givetian sequence

of the Annappes borehole. Similar anhydrite intercalations have been described

from the Givetian of the Tournai and Leuze boreholes of southwestern Belgium

on the northern flank of this trough.

Evaporitic environments are not restricted to the Givetian of the

St.-Ghislain Trough. Graulich (1977) described nodular anhydrite intercal~ted

in Frasnian shales and dolomites of the Soumagne borehole southeast of the

Brabant Massif (Fig. 22). Anhydritea ere also interbedded in Givetian and

Frasnian shales end siltstones of the Argyll borehole in the Central North

Sea (Oeegan & Skull, 1977) where they suggest deposition in a sabkha-like

environment (Fig. 22).

Brabant Massif

Although at least minor quantities of erosion products were derived from

the Brabant Massif during the Lower Devonian (Vanguestaine, 1979), it is

believed that this area was characterized by an essentially low relative

relief. Also during the Middle Devonian and basal Frasnian period, the

Brabant Massif was never completely flooded by the marine transgression.

This is deduced from the occurrence of greenish and reddish conglomerates

and arenites along both its southern and northern flanks. Frequently, these

deposits contain large fragments of land-plants. A good example of this

littoral facies has been described from the Booischot borehole (LegranO,

1964; Streel, 1965; Fig. 23). Only in the Middle to Upper Frasnian the

transgression across the Brabant Massif may have become completed.

Campine-Brabant Massif

North of the Brabant Massif, the Campine-Brabant Basin became into

existence sometime during the Middle Oavonian. Apart from the conglomeratic

Givetian-Frasnian deposits of the Booischot area, we know that biostromal

limestones of the same age developed along the northeastern border of the

Brabant Massif in the Vis~-Puth area of northeastern Belgium and the

southernmost Netherlands (Graulich, 1975; Fig. 23). It has been suggested

(Bless et al., 1980a) that evaporites of Middle Devonian age might be found

43

BOOISCHOT HERMALLE MUNSTERLAND S.ARGENTEAU

=~ Fr2 T I

Z 9 0 0

- . . - . I t "

' " ~ ~ -" ~-- ~ ' I / I ! . . . . . . ~7.4e~.?. ~. ; • " . ' . ' . % % 1 I I I I X " N I aDinanUan 17 71 .... z~Z~ l e o eo @ I 0 ~ Frt ~ . ~ . ~ . ~ : ~ 1 0 o o ~ I ~ I ..... . . . 'H-s.A

: ' ,, • I Fa 700 =- '.-..'.-'.._'..'.;:...'1', Iz zl-5 = " -:~£-.li F r ~ Z /

• o ° ° °me% I I I I I / "~ : : t ' : ' : ' : ' t l l ~ ~nn Fr

- - - - o e O O l O . . . . . ~ - - - - " - : : : "U ,,oo I:h¢¢4 • " - ' ~ - ' ~ - I 1 ~ I . u , u . J ~;&~-" • . , I J , , 1 5 0 ~ ' n J i n n

• %%'~%'41 / , , , , , ° :o ~ - : " I , / ~ , n , ]

" o r .To r . ' ~ l I . ~ I i I I I O J P l I I I I I I

: " . % ' . % : 1 / ~ t , . n ' " ----¢';--;I / \ [ ' ' , I

G v ? . ' . ' . ' . ' . ' 4 1200 - . i , , i

:~.",'.;rl / \ I , ,1 5900 ' - ' : . : . : . . : " - . I £ . . . . . , / \ ! ' , , : , !

. . . . ? ~ T . D . S i l u r i a n

C y c l o p e a n B r e c c i o ° . . . ' . ° . " o ' . "

• . v . : : : S o n d s t o n e

,T--,C-q,. . . . . . C o n g l o m e r o t e , , , L i m e s t o n e

; ; ; , , , , D o l o m i t e

Fig. 23. Simplified Middle-Devonian-Frasnian sections of some boreholes on the northern flank of the Brabant Massif as compared with that of the MBnsterland-1 borehole in northwestern Germany.

in the Campine-Brabant Basin. This hypothesis can only be checked by future

exploration.

Zandvoort-Krefeld High

Presumably, the Campine-Brabant Basin was bordered to the north by a

horst complex. The southern portion of this horst area has been named the

Zandvoort-Krefeld High and is believed to match more or less the actual

structural highs in the central part of the Netherlands such as Zandvoort,

Maasbommel and Krefeld. The complete horst complex (including the Zandvoort

Krefeld High) is called the Mid Netherlands High.

Ouring the Givetian, the Zandvoort-Krefeld High may have been subjected

44

to erosion as can be deduced from the occurrence of coarse GiVetian conglo-

merates (containing pebbles with a diameter of up to 50 cm!) in the

Schwarzbachtal (Fig. 19), which pass into marine carbonates to the east.

south and west.

MOnsterland-1 borehole

The northernmost published occurrence of Givetian-Frasnian carbonates

on the continent is in the M~nsterland-1 borehole (Figs. 19 and 23). The

Middle Devonian sequence is incompletely known. The lowermost bad in this

borehole is a quartzitic sandstone of possibly Givetian age. It is over-

lain by massive limestones of Givetian and Lower Frasnian age which are

followed by Upper Frasnian to Lower Famennian dolomitic shales (Kelch, !g61~)

One of the main problems that remains to be solved is the connection of

the Givetian marine environmentsof M~nsterland and Argyll in the Central

North Sea. Although several communications may have been possible, we pre-

sume that a contact between these two areas preferably followed through the

Campine-Brabant Basin or through an as yet hypothetical graben north of the

Mid Netherlands High (Fig. 19).

Famennian

The Famennian is marked by an important regression that started during

the late Frasnian with the deposition of clays and siltstones (Matagne

Shales and equivalents), and culminated in the Upper Fammennian.

Non-marine environments persisted in the intramontane troughs of the

Caledonian fold belt. Erosion products of this belt may have spread across

the northwestern parts of the Belgo-Dutch Platform where red beds occur

a.o. in the Argyll borehole. A marine environment characterized the

Cornwall-Rhenish Basin that was filled with fine-grained, mostly turbidi~c

siliciclastics. These sediments practically lack benthonic faunas, but

contain pelagic fossil assemblages, such as cephalopods and sntomozoan

ostracodes which serve as reliable guides for long-distance correlations.

Sources for these turbidites are regional shoals on the Belgo-Dutch Platform

as well as southern supply areas. Minor quantities of sediment were derived

from local shoals within the basin.

The sedimentary environment on the Belgo-Dutch Platform is known as the

Condroz facies. This magnafacies includes a variety of alluvial to marine

infretidal shelf environments (Fig, 24). Sedimentation was essentially

rhythmic. Minor rhythms, frequently combined in major rhythms, have been

recognized. These show both fining-upward and coarsening-upward tendencies

45

as has been described by Becker et al. (1974) and Thorez et al. (1977).

Siliciclastics predominate. But early diagenetic, fine-grained dolomites

(characteristic of lagoonal facies), cryptitic limestones and coarse-grained

detrital limestones are intercalated locally in the sequence. Frequent occur-

rence of plant debris suggests the existence of land areas on the platform.

Presumably, some erosion took place on the Brabant Massif and possibly on

the Mid Netherlands High. Passage from the Condroz shelf facies into the

more turbiditic basinal environment can be observed in the northwestern part

of the Rhenish Massif and in the southern portion of the Dinant Nappe.

Fig. 24. Scheme showing the ideal relationship between alluvial to infra- tidal environments within the Condroz facies. ~rom Thorez et al., 1977). I) Alluvio-distal facies; 2) Alluvio-lagoonal facies; 3) Lagoonal facies with early diagenetic dolomites; 4) Tidal lagoon facies; 5) Barrier complex with massive sandstones; 6) Fore-barrier facies with tidal flats; 7) Fore-barrier facies with a predominantly intertidal environment; 8) Proximal subtidal facies; g) Distal subtidal facies with fluxo-turbidites; 10) Subtidal to infratidal facies with turbidites and limestone nodules; 11) Pelite-dominated infratidal facies.

Dinantian

Widespread transgressions started in latest Devonian time ('Strunian' or

'Etroeungt') and reached their acme during the late Dinantian period. These

transgressions spread across the Caledonian fold belt from southern directions

At the same time the Old Red Facies was pushed back to the north and to iso-

lated horst areas. This transgression was completed in the Lower Tournaisian.

The horst areas within the Caledonian fold belt influenced the thickness and

facies of the Dinantian sediments, but they practically ceased to produce

terrigeneous detritus. Only the area north of the Midland Valley in Scotland

was marked by a slightly higher relative relief. That area was the main

source for siliciclastic arenites and pelites which predominate in the

Dinantian sequences of northern England, Scotland and the Central North Sea,

46

where a paralic environment was established during the Visean. Sedimentation

in that paralic area was essentially rhythmic (Yoredale rhythms). The rhythms

consist of seat-earth, coal, (marine limestone), shale and sandstone. The

shales may contain thin resinous algal layers and serve as a source rock fo:

hydrocarbons (oil shales).

The marine Dinantian deposits in the Caledonian fold belt are predominantiy

carbonatic on the shoals, whereas thick pelitic sequences - intercalated by

local reef limestones - occur in the troughs.

S STEPHANIAN I L UPPER E WESTPHALtAN

S LOWER I WESTPHALIAN A N NAMURIAN

D I VISEAN N

NA TOURNAISIAN T.

STRUNIAN

NORTH-WEST! MID- J CAMPINE- J CORNWALL- GERMAN NETHERLANDS BRA@ANT ORABANT FRENCH RHEN ISH

BASIN ] HIGH BASIN MASSIF BASIN BASIN •...~:~,,

@ - - - - - - ~ . . . . . . - . . . • . I . . . . \ ~ , :;:.::--,,."...., a ~/-.-.":i:!.-:i:..~.O 0/.-.:~#,,_0 ,- * . • . , . . . . " ' . ' . ; ,~ ~ / . ' . , . ' , . . ' . " . ,x /~ - ' . . . . . . . ,.¢

v ~ - ~ ' ; ~ ~ . , , . . . . __~ .~ : z - . T : ~:.-.~.-.--~b .-.-..<..-~..~: ~:..'.".~ ~ A E 6 I R M. e. - - \ ~ '

. ' - - - - " X ' - - - T ' - - - • - - _ ' - E Z . . - - : - . - - _ ' ~ - - . - - - - . - - : - ~ : _ . - - - - : - : - ~ Z . . - - : . ~ T ~ ~ ~ .----" . - : - - - ~ - - . - - : _ - - : ' . - - ' I ' . : _ ' : ' _ L . - - _ : " ~ - - . ~ ' . . T : : , . ' . ~ : ~ . ' . ~ : ~ . ' ~ . . ~ . ~ ' o o ~ . .

i r a - - - - - - - S A R N S R A N K M B;..~_ ~ . . ',

I--:---------- L-. . . ,~, - .~ a : ~ , , ",- - - - ,-~,'~ : . . .~- : . - - -_--~ I L - . " ~ . ~ . _ v ~ , ' , ' , ' , ' , ' , " i - - r ' - - r ' - - - ~ " [ " A _ ~ ^ ~ - - - - . : . . h - " " ~ " - l i ' i i + i ~ i , i , ~ I , I , I i l i i i I i I / % ' ~ - - i - - p ' l - , - - ~ - - - - " , : : : 1

F _ - - - - - - , , ' , ' , ' , : ' , ' , ' , ' , ' ' , ' , ' , ' , 0 , ' ~ - - : - " ~ 1

I - : . . . . ' i ' , ' ~ " ~ : Z - A - - % - L ~ - ~ - - - - - - . : . : L _ . " - - ~ " ~ t i ! ~ ~ " @ r [ ,' , ' "-- -- -:.'. [ - - - - I. I I , ~7 - , , , I - - - - - . ' . v I I - - - - - - - - - - - - - - Z - - T r - - - r - _ . ~ : ~ . : 1 '~ ] :E . - - - - - - - - - - - - - - : : : ' . I

Fig. 25. Btratigraphic scheme of the Strunian and Carboniferous around the Brabant Massif. The term French Basin was proposed by Bless et al. (1977a~ for the Silesian deposits in Belgium and northern France, south of the Brabant Massif.

The Cornwall-Rhenish Basin continued to receive siliciclastics from the

south. Two main environments can be distinguished: a proximal Kulm greywacke

environment in the southern parts of the basin and a distal Kulm shale facies

along its northern borders.

The Belgo-Outch Platform shows a predominance of shallow-marine carbonates.

However, it is not excluded that pelitic sediments occurred in the central

portions of some troughs.

Kulm facies

Within the Cornwall-Rhenish Basin the Kulm sediments have been preserved

in southwestern England and to the east and west of the Rhenish Massif.

"POSIDONIA SHALE5 11 WITH

INTERCALATION5 OF TU__F FS

31LICEOU3 SHALE3 10 AND CHERTS WITH

ITN/FERsCALATI ON5 OF

51LICEOU3 LIME3TONE

BLACK CHERT3

47

NODULAR LIME§TONE

TRAHSIT]ONAL 61=05 ~ FAULT

3iLICEOU5 BLACK SHALI=S WITH MINOR INTERBED5 OF BLACK - - CHI:RT

BLACK 5HALE

ALLODAPlC L1M ESTONE

BLACK 5HALE

UPPER PART

-,~ FAULT

8REENISH 51LTY SHALES

LOWER PART

Fig. 26. Section through the Dinantian Kulm shale at Riascheid (Wuppertal) in the northwestern part of the Rhenish Massif. (From Zimmerle et al., 1980.)

48

Kulm greywackes predominate in the area east of the Rhenish Massif. They

have been derived from the Mid German High in the south and southeast. The

SW-NE axis of the basin in which they were deposited shifted rapidly to the

northwest. This i8 suggested by the northwestward migration of the successi~Je

greywscke lithoaomes (Kulick, 1960). The thickness of the deposits may be

more than 2000 m.

S T A R V E D B A S I N C A R B O N A T E S H E L F

J ~ ANOXIC ou, ,

S H A L L O W M S H A L L O W M A R I N E

t N FLUX OF DETRITAL CA~I~ONATES

FROM ,SHELF

q3",~ '" "L , ~ i ~ ~ 3 s / "", !

t I I ""1, , . , . , 1"...t,~) I , ~ ~" -- :-" -"[ . ^ -- 1-- __!. t.,...""~,.'"." ~:~:z.i. I "., ..-"~ i ~ _1 _~ ~ 4.,'"..".

o.4:.-. .." ..r ' k , - _ - E _ - . - ~: i : I ' I ~ ~ ' i I I v ~ 3 5 : T H I C K N E S S OF D N A N I " I A N ( M )

Fig. 27. Upper Dinantian - kithology and paleogeography north of the Brabant. and Rhenish Massifa. (After Bless et el., 1976; Zimmerle et el,, 1980.)

A rapid change from Kulm greywackes into more pelitic deposits is observed

north of the Rhenish Massif. The thickness of the Kulm shales is usually much

lees than 200 m (Fig. 27). The facies of these Kulm shales is representative

of an euxinic environment of the substratum in a starved basin. This doesn't

indicate necessarily a deep water facies. The typical rock association con-

sists of black shales, lydites or cherts, allodapic limestones, nodular lime-

stones, siliceous limestones, tuffaceous vslcaniclastics and phosphorite

nodules. Arenites are rare or absent. The ano×ic facies is indicated by the

high organic carbon and pyrite content. A good example is the Rieecheid

section at Wuppertal in the northwestern part of the Rhenish Massif

I ~D

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50

(Zimmerle et el., 1980; Fig. 26).

Local increase of the sediment thickness may be due to the occurrence ~:~

detrital (allodapic) limestones derived from the carbonate shelf (Fig. 27!.

The most important of these is the Flaggy Limestone ('Kulm-Plattenkalk')

with a thickness of slightly more than 100 m (Bless et el., 1976).

The Kulm deposits of the Cornwall-Rhenish Basin in northern France were

either eroded in late Variscan times or they may still exist below the

Mesozoic cover of the Paris Basin. A transitional environment from this

shale-dominated Kulm basin to the carbonate environment of the Dinant Shez~f

is found in the Dinant area of southern Belgium where shales are interbedded

in the otherwise carbonatic sequence of the Lower Oinantian Hasti~re Lime-

stone (Fig. 28; Van Bteenwinkel, 1980).

Very finegrained calcilutites with algal mats and birdseye fabrics

Mainly calcilutites partly laminated, with thin bituminous horizons, very rich in ostracodes

Calcilutites and calcarenites with lenses of coated grams and oncolite - horizons. near the base intraclasts

Calcarenites with coated grains ~-~ca'Te~es end ~ t c - ~ u ~ s - rich in intraclastS, with foraminifera /

Sedimentary breccta. partly like olistostromes

v) 4) "5 >,,

C

5

4)~J

-- I l c~ ® j ' 2

~5 p h a s e l

Fig. 29. Scheme of an ideal carbonate cycle in the Visean strata of the Aachen Shoal, Federal Republic of Germany. (From Kasig, 1980b.)

Carboniferous Limestone facies

Carbonatic sediments were deposited in a shallow to very shallow-marine

environment (Carboniferous Limestone facies) on the Beige-Dutch Platform and

in an important part of the Caledonian fold belt. The thickness of the

deposits may be extremely variable and presumably depends on variations in

the local rate of subsidence.

Sedimentation was often rhythmic. Minor and major cycles can be distin-

guished. The boundaries between major cycles are often erosion levels which

may be followed over hundreds of kilometres. These can be attributed to

widespread sea level changes (Ramsbottom, 1973; Conil & Lys, 1977; George,

1978a).

Minor cycles may be followed over tens of kilometres. They are often

characterized by fining-upward seouences which start with fossiliferous

calcarenites or calcirudites followed by practically non-fossiliferous

calcilutites which may contain birdseye fabrics. Representative examples

of these have been described by Pirlet (1964) from the autochthonous Namur

Basin along the southern flank of the Brabant Massif, and by Kasig (1980b)

from the allochthonous Aachen Shoal (Fig. 29). These minor cycles character-

ize deposition in an intertidal to supratidal environment.

Widespread carbonate mudmounds developed in deeper water on the outer

shelf. These have been called 'Waulsortian bryozoan reefs' because of the

frequent occurrence of fenestellid bryozoans in these deposits. They are

characterized by - often dolomitized - micritic limestones with cavity-

fillings of calcite spar. Whether the fenestellid bryozoans have trapped

the carbonate mud and acted as reef-constructing organisms is still

problematic. Other important inhabitants of the Waulsortian environment

were crinoids and - usually small - brachiopods. Lees et al. (1977) suggest

that these mudmounds have been formed in water depths of 250 to 300 m,

'perhaps up to many tens of kilometrss from the shoreline'.

Evaporite facies

Evaporites (anhydrite and subordinate gypsum) have been described from

several areas within the Belgo-Dutch Platform. The most significant occur-

rence is in the St.-Ghislain borehole south of the Brabant Massif, where

massive and nodular anhydrite is intercalated in the Dinantian succession

(total thickness of anhydrite beds more than 500 m; Dejonghe et al., 1976;

Groessens et al., 1980). Other important occurrences of anhydrite are known

from the Lower Dinantian sequence north of the London-Brabant Massif in

central England (George et al., 1976). Nodular anhydrite and/or gypsum

crystals have been recognized in several locations along the southern

flanks of the Wales-Brabant Massif (George, 1978b; Hance& Hennebert, 1980).

Nodular anhydrite and authigenic gypsum may be indicative of sabkha-type

sequences. Massive, finely laminated anhydrite may have been deposited under

standing water conditions in a lagoonal or sublagoonal environment.

Other evaporites, such as rock salt, have not yet been recognized in the

Dinantian of northwestern Europe. It is suggested that even rock salt may

occur in the deeper parts of the Campine-Brabant and Namur Basins. Schenk,

(1969), Hacquebard (1972) and Geldsetzer (1977) have reported Dinantian rock

52

salt deposits from the Fundy Basin of Nova Scotia, Canada. The rock salt

posses laterally through anhydrites into solution breccias. It is worth-

while to observe that the stratigraphical position of the most importan~

anhydrite intercalations in the Upper Dinantian of the St.-Ghislain boreho~e

is occupied by widespread breccias along both the southern and northern

flanks of the Brabant Massif (Fig. 30)~ A tentative model of the lateral

passage of these breccias into evaporites north of the Brabant Massif has

been proposed by Bless et al, (1980b). This model (Fig. 31) can only be

checked by future exploration.

LOEJ@~OUT TURNHOUT RIJSBERGEN-1

! 1 1

.... : " " "~" ......... " N ...... A M .... U ........ R ....... I A N ...................... s H ...... A ......... L ....... E S . . . . . .

. . . .

~ C A M B R O - ! S I L U R I A N ~ ~ '-..EV,;" v v

× x × × × x × × × × × x ~ ~ ~ i ~ " - . . ~ " ' < " r , - ~ " " ~- x x x x x x x x x x x x ; I \ ' ~ \ ~ ' ~-.~

i x × x x , , x x

Fig. 31. Tentative cross-section along northern flank of the Brabant Massif at the end of Namurian time (not to scale). The increase of the thickness of the Dinantian carbonates between Loenhout and Turnhout has been proven by boreholes. Also the increase of the thickness of the Namurian between Turnhout and Rijsbergen has been checked by boreholes. It is suggested that the breccia horizon in the Upper Dinantian of Turnhout (and Loenhout?) may pass into evaporitem towards the canter of the basin. (From Bless et al., 1980b.)

C a m p i n e - B r a b a n t B a s i n

The isopach map of the Strunio-Dinantian deposits around the Brabant

Massif (Fig. 32) is based on relatively few - partly even incomplete -

sections. Three main depositional areas are recognized (Camplne-Brabant,

*pp. 29--34.

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54

Namur and Diment)which are separated by shoals: Brabant Massif and JeumonL

Shoal. It is suggested that sub-basins or troughs may be distinguished within

the Campine-Brabant and Nsmur Basins, whereas small shoals occur on the

Dinant Shelf. A synthesis of possible basins end highs during the Dinanti~n

time is presented in Fig. 33.

North of the Brabant Massif, only the Loenhout or Heibaart borahole has

yielded a complete sequence of Dinantian strata with overlying Namurian and

underlying Famennian rocks. Woensdrecht, Turnhout, Helen and Wijvenheide

penetrated the Dinantian strata below overlying Namurian and proved the

existence of a sedimentary/erosional gap between the Dinantian and Namur~n

which become more important to the west (Bless et al., ~976). These boreheles

did not reach the base of the Dinsntian° However, the evidence seems to point

to an overall thinning of the deposits from Halenthrough Turnhout and Heibaart

to Weensdrecht. This implSes progressive relative subsidence of the basin

floor from Woensdrecht to Halen even during the late Dinantian/early Namurian

regression (Fig. 31 and 41).

TDOD~, ~ ~ ) ~ SO~DON-SOUM~

O I N A N T S H E L F "-'~....~N~a?L"b"~.-/ tWAULSORTIAN CARBONATE MUD-MOUNDS)

- S H A L E - 0 0 M I N A T E D - - - - - - - - K U L M B. A S I N . . . .

A _ _ - - 5

D f N A N T S H E L F (WAULSORTIAN CARBONATE MUD-MOUNDS)

- - - K U L M B A $ I N . . . .

Fig. 33. Tentative palinspestic maps for Strunio-Dinantian deposits on part of the Beige-Dutch Platform (not to scale). Two different interpretations are shown. In Fig. 33A, the Balland, Soiron end Soumagne d~poeits (l~wermost tec- tonic sheets in boreholgs) are considered as (par-)autochthoneus, in Fig 33B as allochthonous end rgstored to an Original position in the eastern extension of the Jeumont Shoal. (From Bless at el., 1980c.)

UPPER V3c ERMALLE-SOUS-ARGFNTEAU RICHELLE "F'L"N"QUARRlES SOUVRi LA FOLIE

E TRANSGRESSION

KAASTIFICATION FAMENNIAN

UPLIFT UPPER FRASNIAN(?)

SEA LEVEL

UPLIFT

Fig. 34. Hypothetical. reconstruction of the paleogeographic events in the Vise area during the Frasnian to late Visean period. (From Poty, 1960.)

56

The Devonian-Dinantian boundary was only recognized by the Heibaart en

Booischot boreholes. At Booischot, the Upper Dinantien and Namurian strata

have been removed by post-Carboniferous denudation. But the existence of

pelacsols and terrigenss in the relatively thin Lower Dinantian carbonates

(thin in comparison with the VI of Halen anO Turnhout) suggests relatively

slow subsidence of the Booischot area with a nearoy erosional higm. The

lithology of the nearby,very short ano incomplete Kessel section (reo seas

and terrigenes intercalated in the carbonates) suggests similar paleogeo-

graphic conditions as for Booischot.

Boreholes and outcrops in the Vis~-Villers area have yielded evidence

that this region belongs to the Campine-Brabant Basin. A direct communication

of this basin with the Pennines and Ireland alonq the northern flanks

of the Wales-London-Brabant Massif seems likely because of the ~ersiatent

occurrence of Paleotethys (~fro-Asian) faunas in the Visean strata of tne

Vis~-Villers area (Kimpe et al., 1978). Such faunas have not been recognized

in the more endemic fossil assemblages south of the Brabent Massif. Thick-

ness ano facies of the Dinantian in the Vis~-Villers area suggest deposition

on a shoal on the northern flank of tne Brebsnt Massif with a karst tooo-

graphy that was only completely drowned in late Visean time. ~ reconstruction

of this karst landscape has been presented by Poty (1980, Fig. 341.

Immediately north of the Vis~ area, a gravity minimum suggests that the

basement may occur at increased depth. This might imply an increased thick-

neas for the Devono-Dinantian strata (Fig. 35) and possibly the occurrence

of evaporite deposits comparable to those of the St.-Ghislain area in South-

western Belgium and northern trance (Bless et al., 1977b, "980a). Therefore,

the crowdino of the isopachs in the Vis~-Puth area on Fig. 32 and 33 seems

justified.

The overali ~W-SE trend of the isopachs in the eastern part of the

Campine-Brabant Basin is closely matched by the homotexial shorelines of

the Namurian transgression (Bouckaert, 1967; Bless et el., 1976), tne iso-

pachs of the Westphalian C strata (Bless et el., 1977a), the southern moroeF

of the Lower to Middle Jurassic sediments and by the NW-SE trending faults

along the southwestern boroar of the actual Roar Valley Graben (Fig. 36).

It is hardly believable that these are mere coincidences. Therefore, it is

presumeo that the actual Roer Valley Graben border faults are rejuvenations

of much older (Peleozoic) fault systems which orlginally separated fragments

of the basin ?loot with differential subsidence. Inverse movements of this

part of the Campine-Brebent Basin caused uplift an~ erosion during the late

Mesozoic followed by renewed subsidence during the Cenozoic.

Practically no information has been published yet on the western part of

the Campine-Brabant Basin. It has been suggested that it more or less

57

s _ _~_ ~ ~. ~ , ~ ° ~ .

V3 V3

v l ~ ¢ - ~ o o ~ , o ~ ~ " ©~Oo o_r-,_ ~-"---~-.-.--~v-v v2

~":: Tn

/ / ~ V ~ v . / / x x x x x x x × I - ~ t ~:. ," :?}~'v v

x × × / × × x x × × × x i × × x × ! \ × × / × × × × × × × × × ~× × ×!× ~."< . ~ . ~ ' ~

i × X B A S E M | E N T i X I I ~ ~ " ~ x x ~ i x x x x x : i x '

x x I x x x x x x x x x • ~x x ' i x x x

Fig. 35. Tentative cross-section (not to scale) across the northern flank of the Brabant Massif in the Vis~ area at the end of Dinantian time. (From Bless et al., 1980b.)

coincides with the Westphalian C-D deposits exposed at the Pre-Permian sub-

crop. Strong subsidence of that part of the Campine-Brabant Basin during

Mesozoic-Cenozoic time is known (Western Netherlands Basin). Although this

should not be considered as a proof or even an indication for a western sub-

basin, it might be worthwhile to investigate the possibility to distinguish

two sub-basins or troughs within the Campine-Brabant Basin during the

Dinantian.

Namur Basin

The boundary between the Campine-Brabant and Namur Basins can be located

between Moha and Horion (Fig. 32), where a change in facies and fossil assem-

blages occurs. A progressive increase of the thickness of Dinantian deposits

to the west can be observed. This suggests that the distance to the northern

border of the Namur Basin increases from Moha to Tournai. Thus, a NW-SE trent

for the isopachs seems the most logical one. This trend coincides with the

isopachs and facies strikes on the Visean maps of Pirlet (1968).

More problematic is the iscpach strike between St.-Ghislain, Jeumont and

W@pion where several interpretations are possible. The interpretation proposed

58

DI.$TRIBUTIO["I OF LOWEI~MIDDL[ I ,JenAss~c SEO|~EeTS

uPPEe WESTPHALIAM C Z 15opAc,s 3 I'IAMURIAN HOMOTAXlAL

SI'IORELINF5 D IrlAPITIAPI I$OPACHS

5 ROER VALLtrY GRABEN 80UItDARY FAULTS

¥

Fig. 36. Comparison of trends in Dinantian, Namurian and Westphalian sedi- ments along northern flank of Brabant Massif with trends of Roer Valley Graben boundary faults and distribution of some Mesozoic deposits. (From Bless et el., 19BOc.)

on Figure 32 is based on accepting a concordant strike for isopachs and

facies during the Lower Dinantian ~Bless et el., 1980c). The isopachs strong~

ly suggest the existence of a relatively narrow trough (St.-Ghislain Trough)

that reached eastward into the Orneau area and separated the Brabant Massif

in the north from a shoal in the south, the Jeumont Shoal. Both the St.-

Ghislain Trough and the Jeumont Shoal seem to nave come into existence

during the Middle Devonian (see above). The strikes of the Brabant Massif,

the Jeumont Shoal and the intermediate St.-Ghislain Trough would be more

or leas WNW-ESE. This trend is partly matched by the trenO of actual dome

atruetures and solution phenomena in the Heine region of southwestern

Belgium. Domes and solution phenomena h~ve meen interprete~ as the result

of halokinesis and the aolution of under3ying Devono-Dinantian evaporites

(Delmer, 1972).

In the ESE prolongation of the St.-Ghislein Trough a aeoono trough or

59

sub-basin is postulated here. Nowadays, this sub-basin is masked by the

Midi Overthrust. If we believe that the lower tectonic sheets explored

by the boreholes Bolland, Soiron and Saumagne are autochthonous or par-

autochthonous, Bolland might be located on the eastern extension of the

Brabant Massif, and Soiron and Soumagne on its southern flank adjacent to

a hypothetical Soiron-Soumagne Trough. However, if we presume that these

tectonic sheets are allochthonous, Bolland (and also the nearby outcrops

of Booze and Ls Val-Dieu) might represent as well the eastern (ESE) exten-

sion of the Jeumont Shoal. In the latter case, Soiron and Soumagns would

be located on the northern flank of the Dinant Shelf, south of the 3sumont-

Booze-Le Val Dieu Shoal.

Oinant Shelf

The Strunio-Dinantian deposits of the Dinant Nappe have been thrusted

over the Namur Basin and mask the Oeumont Shoal. The thickness of the

Dinantian carbonates at Jeumont (some 575 m) is distinctly less than in

the Dinant Nappe, where their thickness increases from some 750 m at

W6pion to about 900 m near Dinant. Waulsortian carbonate mud-mounds occur

in the Dinant area.

This increasing thickness might point to a slightly higher rate of

subsidence for the southern part of the Dinant Shelf (outer shelf area).

9

f sr

p~.';.~ HASTE N RAT H ®(~ QQ

0 5 lOkm I I I

HASTENRATH SANDSTONE

~ VAUGHANITES OOLITE

~ VISEAN LIMESTONE

COMMUNICATION TO OPEN MARINE SHELF

Fig. 37. Basal Visean paleogeography of the Aachen region, Federal Republic of Germany. (From Kasig, 1980b.)

Thickness and facies trends of the Dinantian deposits in the Aachen region

(mean thickness 200-250 m; Kasig, 1980b) suggest deposition on a shoal with

a slope to the north or northwest (Fig. 37). This idea is corroborated by

the existence of important breaks in the Dinantian sedimentation. Analysis

of fossil assemblages has not yet advanced enough to permit deductions about

60

the original position of the Aachen Shoal. Faunas seem to have strong

relationship with those of the Dinmnt Nappe. Thus, it cannot be excluded

on forehand that this was a shoal on the Dinant Shelf. Of course, it ±s

tempting to consider the Stavelot-Venn Massif as the basement of this

shoal. But more work is needed in order to unravel the intricate structu-

ral relationships between the Stavelot-Venn Massif, the Aachen region and

the Dinant Nappe.

Also the Avesnes area in northern France (cf. Fig. 28) shows a reduced

thickness of the Tournaisian strata and includes a sedimentary gap of

Tn2c-Tn3b (Conil, 1973). The Vieean of the Avesnes area has been truncated

by poet-Carboniferous erosion. We suggest that this region was also a shoal

on the Dinant Shelf during the Dinantian period.

Namurian

The stratigrmphic subdivision of the Namurian in northwestern Europe

(Fig. 38) is based on goniatites which occur in over fifty marine bands.

Several of these provide excellent marker horizons which can be traced

from Ireland into Czechoslovakia and even beyond that area.

old

C

e ta [ ~es

new

YEAOONIAN

MARSDENIAN KINDERSCOUTIAN

ALPORTIAN CHOKIERIAN

ARNSBERaIAN PENDLEIAN

goniatite zones

GI (Goniatit~tes)

R2 (Reticuloceras) RI

H2 (Homoceras) HI

E2 (Eumorphoceras) El

Fig. 38. Subdivision of the Namurian.

The Namurisn period started with a widespread regression coinciding with

the orogenic movements of the Sudetic phase. Only baeinal areas were not

directly affected by this regression. The subsequent transgression gradually

spread across the shoals but was only completed in Upper Namurian (Kinder-

scoutian) times as can be deduced from the example of the Brabant Massif

(Figs. 39-41).

The depositional environment changes from predominantly merine in the

Lower Namurian to paralic in the Upper Namurian. This regressive tendency

continued in the Weetphalian when incursions became rare and practically

ceased in the late westphalian.

WOENSORECHT

6I

/

k_.j

8R4 8A N T SHOAL

HEIBAART \

BRUSSELS 0

\

CHERTAL,

~SIPPENAEKEN

j ~ BLATON RONET

*SOIRON .~.,.~.~THEUX

MIO\ ~ ERTH~ ~ST

L,-, ,J

VIONCEAU

/ \.__,

CQUIER ~,

* DISSOLUTION HOLES IN THE TOP VISEAN

R RADIOACTIVITY OCCURRENCE

Fig. 39. Namurian transgression across the Brsbant Massif (shown by homotaxial shorelines), based on age of lowermost marine - goniatite-bearing - horizon overlying the Dinantian deposits (after Bouckaert, 1967).

MASS F

\ ~ ~ E 2c ~._~. . . . . ._ . .~

Fig. 40. Offlap and onlap of late Dinantian and early Namurian deposits along northern flank of Brabant Massif. (After Bless et al., 1980c.)

62

200m

BIOUL MONCEAU MALONNE L OIfE@MEE

E262

E2bl

CHERrAL

R1: T 7 t

I I I i

( i

JAYA . j "--..----1 j , m ~ . . :

~~____./ ~ "~ \ c::~ s.,,,e SANOSrOME u M c s r o N e COAL SEAM

tJ GONIATtTES

Fig. 41. Stratigraphic sections south of the Brabant Massif showing graduai~ transgression of Namurian. (After Bouckaert, 1971.)

Namurian sediments are almost exclusively siliciclastic. Isolated, thin

carbonate lenses occur locally in the lower portion of the Namurian succession,

whereas economically important coal seams appear usually in the upper part.

Sedimentary cycles in the Namurian have been described by many authors.

Van Lsckwijck (1964) distinguished an ideal cycle with a mean thickness of

60 m that can be subdivided into four phases (in descending order):

Phase d - several rootlet beds which may be overlain by coal seams Phase c - sand-dominated succession Phase b - shale-dominated succession (frequently with non-marine fossils) Phase a - shales with one or mere important marine bands

The basal marine shales of several of these cycles contain the diagnostic

goniatite faunas which serve for long-distance correlations. Within these 60

m cycles, Van Leckwijck recognized up to eight minor (10 m) cycles, which in

turn could be subdivided into so-called 4 m cycles.

French Basin

This term was introduced by Bless et al. (1977a) for the Upper Carbonife-

rous (Silesian) deposits bordered in the north by the Brabsnt Massif and in

the south by the mobile Variscan belt. To the west, the French Basin was con-

nected with the sedimentary area of southwest England and South Wales, to the

68

I 1 ST.GHISLAIN 0 2 JEUMONT 3 COMBLE-NORB /., CHERTAL 5 SOUMAGNE (POSSIBLY

ALLOCHTHONOUS) 6 INDE AREA (ALLOCHTHONOUS)

i '7 TURNHOUT 8 RIJSBERGEN g MUNSTERLAND

10 STENDEN ~!i!iii~THICKNESS IN M

50km I

J

0

......... ~,~ .............. i:ii:::i!ii:~iiiiiiii!!~ili!iiiiiiiii~: v.\ .~.:

........... k ........................................ :~u.,::::u:: =:: % ~, !!!iii!Si!i:i :iiai!iiiii~!i~i!5!i! :::::: ~P~80

........ ~q!!iiiiii!iiiiiii!~iii~i~iiiiiiiiiiiii~:

1 5,,..170 ~ 660 3-*~n :~iiiiiii!iiiii!iii!i~!iiiililiiii!iii~, 400,

/,.

/ " to" /"'230 H /

1OOO ISOPACH OF NAMURIAN

MAIN SEDIMENT TRANSPORT

.6o o

: 6

...:h ° \ /

\~3ooo . " , o / . .

I U . : \ \ \ % _ _ .

x<~::ii~., , 290~_---"/k 5 --- ~)~ ,

i i iiNiiiiSiHii!i!!iiiiiii ii i ,ii..: ,i..i!..:i ] : iii i!!! i!iiii? i! !iiiii !!i iiiiii iiiiiiiiiiiiiii!ii!iiiiiiiii1i ii!i!iiiiiiii ;"

/ / / ALLOCHTHONOUS DEPOSITS (FgE@II~ l~Ulil))

:i !i iii iii i! ?! ~i ii ~! i! ~! i! ! i! i! POSITIVE AREA

Fig. 42. Namurian - Paleogeography and isopach trends around the Brabant Massif.

east there existed a communication with the Campine-Brabant Basin north of

the Brabant Massif.

The sedimentary history and the thickness development of Silesian strata

within the French Basin arm incompletely known. This is due to post-Variscan

erosion of the outcropping Silesian strata in the Dinant Nappe and Namur

Basin as well as to the fact that possibly important parts of the autoch-

thonous Silesian deposits in the Namur Basin below the Dinant Nappe have not

yet been investigated by boreholes.

The thickness of the Namurian deposits in Jeumont, St.-Ghislain and

Comble-Nord (Fig. 42) indicates that the St.-Ghislain Trough (cf. Fig. 16

and 32) persisted in Namurien times. The same seems true for the Jeumont

Shoal to the south of this trough. Indications for a sub-basin southeast of

the Brabant Massif are found in a gradual increase of the thickness of the

Namurian beds from Chertal trough Soumagns into the Inde area.

Important parts of the Devono-Dinantian Cornwall-Rhenish Basin became

incorporated within the northward shifting front of the mobile Variscan belt.

These were uplifted by the Sudetic movements and eroded subsequently.

64

This can be deduced from the intercalation of conglomerates in the Namurien

strata in the southeastern Dart of the French Basin. These ~onglomerates con

tain pebbles reworked from Dinantian ane older deeosits (Klerkx, 19661

Thorez & Bless, 1977). It is curious to observe the (allochthonous) conglo-

merate fans in the Aachen region (Fig. 43) which occupy the geographic Posi-

tion of local sand deoosits at the case of the Vissan on the Aachen shoal

(Fig. 37). Presumably, both the Visean sand and the ~amurian conglomerates

have been derived from the same source area.

m e 1

;" 2

- - 3

E~]AACHEN

®

~.~,0

® o o

0 0 ~ 0 - o o~o ° o _ --o ~o o_o--

, " , u 0 0 o 0 0 _ _ - - HASTENRATH [ ~ c o " o o - - - ~ o . . oo, o %o o _ . .Oo oO-----o o~

[ [ ]AACHEN - - Z , , O o O me ,\ ° ° o 0 O 0 ~ ' wOO 0

ooOo 0 ~./ @O

0 ~

I ,, I

Fig. 43. Extension of Namurian conglomerate fans in the Inde area. (After Hahne & Seidel, 1936.) A: Burgholz or Walhorn Conglomerate; B: Geoau or Ardenne Conglomerate. Compare the position of these fans with that of the basal Visean Hastenrath Sandstone in Fig. 37. ~) Mean diameter of pebbles > 15 mm; 2) mean diameter of pebbles 10-15 mm; 3) mean diameter of pebbles <10 mm.

Campina-Brabant Basin

Our knowledge about the Namurian deposits in the Campine-Brabant Basin

is restricted to the southern flank of the same. Shales and siltstones

predominate. Thickness varation in the boreholes sub-parallel to the pre-

sumed border of the Brabant Massif is relatively small (550-680 m over e

distance of moran than 100 km). But the Namurian succession becomes signi-

ficantly thicker towards the central parts of the basin as can deduced from

the more than 1800 m thick sequence of the Rijsbsrgen-1 borehole. It is

likely, that the thickness in the centre of the Campine-Brabant Basin is

comparable to that recognized in the Central Province in Great Britain (cf~

Ramsbottom, 1957) or the Ruhr Basin in Germany (cf. Hedemann & TeichmUller,

1971), where a thickness of 3000 m or more has been observed° The northern

border of the Campine-Brabent Basin is virtually unknown. However, it is

believed that this may match the actual structural highs of Zandvoort,

Measbommel and Krefeld. A reduced thickness of the Namurian strata on the

66

Krsfeld High in Stenden (about 800 m) was suggested by Elberskirch &

Wolburg (1962). This means that there is good evidence for a shoal at the

position of the actual Krefeld High during the Namurian.

Ruhr Basin

The northward shift of the basinal axis of the Cornwall-Rhenish Basin in

Germany - that had started during the Vissan - continued in Namurian times.

The thickest Namurian deposits are found in the Ruhr Basin that may be con-

sidered as the northern part of the Cornwall-Rhenish Basin. It coincides

with the area that was predominated by an anoxic starved basin environment

during the Dinantian. The quickly growing mobile Variscan belt in the south

was the most important source area for the more than 3000 m thick Namurian

sediments. This is indicated by conglomerate intercalations in the Namurian

succession along the southern flank of the Ruhr Basin (Kulick, 1960). The

rapid sedimentation was prohibitive for the growth of important vegetations.

However, the occurrence of lenses of allochthonous coal and plant debris (in-

cluding trunk fragments) suggest the existence of local, short-lived swamps

which were practically not preserved in the sedimentary record. Only in Upper

Namurian times, the environmental conditions favoured the development of

widespread vegetations.

Westphalian

Correlation of the Westphalian deposits in northwestern Europe is based

on the occurrence of widespread marine bands, which represent short incur-

sions of the sea in a non-marine to paralic environment. The relative fre-

quency of these marine incursions gradually diminished and finally ceased

in Upper Westphalian time. The number of these marine bands in Great Britain

seems to exceed that in the Netherlands and Germany, where usually less

prolific marine fossil assemblages have been recorded. All these observati-

ons suggest that the marine incursions originated from the west or south-

west and eventually were restricted to parts of Britain. Only during the

most important transgressions, a direct communication with marine environ-

ments in the U.S.S.R. seems to have existed (Bless & Winkler Prios, 1972).

Sedimentation during the Westphalian was characterized by a cyclothemic

development. The cycles are comparable to the 60 m cycles of the Namurian

and consist of seat-earth, coal, shale and sandstone. Incomplete cycles are

frequent. Van Wijhe & Bless (1974) distinguished three main types in the

Wesphalian of South Limburg (southeaeternmost part of the Netherlands).

These are represented in Fig. 4~.

66

LOWER UPPER WESTPHALIAN A WESTPHALIAN B

Fig. 44. Schematized cyclothems in the Westphalian A-C of Limburg (the Netherlands) with simplified lithological classification adopted by Bless (1973). Lithologies b, f, l, m, and o are extremely rare and can be ne- glected in practice. Key to symbols: a) coal; b) pseudocannel coal; c) shale with coalstreaks; d) shales and siltetones with rootlets (in- cluding seat-earth or underclay); e) slightly sandy sediments with root- lets; f) sandy sediments with rootlets; g) sandy sediments; h) slightly sandy sediments (including striped beds); i) shales and siltstenes; k) shales and siltstones w~th non-marine fauna; l) slightly sandy sedi- ments with non-marine fauna; m) sandy sediments with non-marine fauna; o) conglomerate; p) shales and siltstones with marine fauna. (From Van Wijhe & Bless, 1974.)

Cycles with a marine to brackish phase immediately overlying the (usu-

ally thin) coal and with widespread sheet sands practically without erosio-

nal channels. These developed in an alluvia-deltaic environment with short-

lived coastal marshes.

Cycles with a brackish to non-marine phase above the (often well-developed)

coal and isolated channel sands in a shale-dominated succession. These re-

present a back swamp facies at relatively longer distance to the shoreline.

- Cycles with a non.marine phase immediately above the coal (often of irre-

gular thickness and limited lateral extension) and widespread sheet sands

alternating with channel sands. Most likely, these cycles are characteris-

tic of fluvial plains with relatively high rates of sedimentation and local,

often short-lived swamps or open moors.

Comparable cycles have been described from Westphalian deposits elsewhere

in northwestern Europe (e.g. Delmer, 1952; Jessen, Kremp & Michelau, 19S2)

and from North America (Weller, 1930; Wanlese, 1969).

The Westphalian D deposits north of the Brabant and Rhenish Massife are

frequently characterized by fining-upward sequences with a relatively coarse

sandstone at the base that passes into siltstones or shales at the top of

6?

the rhythm. The base of such rhythms may be an erosion surface.

Carbonates are extremely rare or absent in the northwestern European basins.

Occasionally, so-called roof-balls occur in the marine horzons, whereas coal-

balls typically occur in some coal seams with a marine roof (Evans & Amos,

1961; Moore, 1968). According to Moore, coal-balls have been formed in areas

at about sea level.

A common feature of the Westphalian deposits is the "wash-outs", which cut

down through one or more sedimentary cycles. These are fluviatile channels

filled with coarse sand fining-upward to silt or clay. Wash-outs in coal

seams appear to be preferably filled with silt or clay. Their thickness,

width and length is quite variable. Frequently, several small wash-outs run

parallel to each other suggesting a braided river system in a swamp facies.

Van Wijhe & Bless (1974) adopted an environmental model for the Westphalian

of northwestern Europe (fig. 45) that assumes a vast sedimentary basin with

an extremely low relief. In such a situation sea level fluctuations could

affect important parts of the depositional area. The progressive withdrawal

DECI~EASING HUMIDITY BECAUSE Of CHAMGIttG CLIMATE

Fig. 45. Environmental model for the Westphalian in northwestern Europe. Idealized relationship between sedimentary facies and vegetational pattern, in time and space. Different vegetation types are indicated by some charac- teristic miospore genera. Of course, these were not restricted to the indi- cated areas and time. (From Van W~he & Bless, 1974.)

68

of the marine influence to the west was matched by a gradual change of the

climate that became more arid in the younger Westphalian.

This more arid climate was prohibitive for the growth of extensive vege-

tations and is marked by the appearance of red beds. A general migration ~f

the arid climate towards the south is illustrated by the fact that the firs~

occurrence of these red beds is much later in the south than in the north

(e.g. Lower Westphalian C in Scotland; Upper Westphalian D in Campine-Brabant

Basin). Local climatic variations between positive areas and basins are

reflected in the slightly earlier appearance of red beds on horst complexes

and by the occurrence of so-called "hinterland" floras which presumably pre-

ferred a somewhat drier habitat. Examples of such "hinterland" floras have

been described from the eastern borders of the Mid Netherlands High (Bless

et el., 1977c).

Lower Westphalian

Presumably, the Brabant Massif has been covered by Upper Namurian and

Lower Westphalian sediments. But thickness variations of the Westphalien

north and south of the Brabant Massif suggest that the downwarp of this ara~

was much slower than that of the French Basin to the south and the Campine-

Brabant Basin to the north. Bless (1973) suggested that the Brabant Massif

was an island during the Lower Westphalian A Finefrau Nebenbank transgres-

sion and may have supplied some sediment into the basin during that peried

(Fig. 46).

The information about the possible existence of a shoal at the place of

the Zandvoort-Krefeld High is inconclusive, although comparison of the thick-

ness of the Westphelian A in the Oostzaan-1 borehole (western Netherlands)

with that of e.g. Steenwi]kerwald-1 (some 80-90 km to the northeast) doesn't

contradict such a suggestion,

Upper Westphalian

The ~egir Marine Band at the base of the Upper Westahalian C represents

the last important marina incursion on the northwestern European continent.

This is in contrast to the situation in Great Britain, where several important

marine incursions followed during the Lower Wastphalian C. It is believed,

that the Brabant massif and the Mid Netherlands High became more or less

non-depositional areas that at intervals acted as erosive highs. This idea

is supported by the isopach pattern for the Upper Westphalian C (Fig. 47).

Presumably, the dlfFerantiation into basins and horst areas was much more

pronounced during the Upper Wastphalian.

69

g Gon/eN/es, P/er /o/ds . .o /[-shore / a u n a 0 _--~-_- *" A, - - ¢

p Pleno/i/es neer-5•ore facieJ .,( %7

-_-Z--- Marine days a n d sz'/t5 ............ ~ ~ \~..~[: ' -_~__- ooo Norlhern ~order o/ @tea w/lh coal-~al/5 end roof-hefts .... "%<, -'-=

..... /n/erred boundary Z~elween near-shore and oil-shore £ecles ,,'~"'* V 0

.~" --4--

¢% ,,/

-:-- i"" ',...: -2~- O F F _ S .--r_ ._ ~ " - - " " _ - -4- H 0 R E -~-~ -- "X,," " "

~t ,**

---:--_4 . . . . . . . . . . . ~ : ~ ~. . _ ~ - j / :/.--" "- ..... ;: ', N E A R - S H O R E "-~.-. ...... '~CI~.s ? i,, "::~....~:.. ,";

A o , --.. J . ._ . .,.:...-- ,,~ OF S~b~. .~ . ~

i

: o~ tTA'-J/'.,' ---_~_---#~.~7. Maas~richt . .!'PI~AIN ' -~-~,~--~ ,~I ~_- ' ~"~ ~

M A S S I F ?"'::"" ' /ransg"ress/ '°n ' l "

~ / / , , ~ ,/ ~ o °

~ , o ~ ~ S ~ - _--zL.d" ~--- ---

0 ~ ~ " 0 14 8kin t I I

De/ta b u l l / ~ p du r i nq oe~ress iye s /age o f ffne/rez/ He~in~ank aee

Fig. 46. Westphalian A - Paleogeography of area around eastern spur of Brabant Massif during Finefrau Nebenbank Time. (From Bless, 1973.)

The Mid Netherlands High should not be regarded as one large tectonic

block. The term is used here for a complex of several smaller blocks which

are distinguished from the surrounding basinal area by a relatively slower

subsidence or even uplift. These blocks may have moved independently (at

70

PARALIC DEPOSITS

POSITIVE AREA

--300-- ISOPACH OF UPPER WESTPHALIAN C

MAIN SEDIMENT TRANSPORT

~_-Z~" MINOR SEDIMENT TRANSPORT

ALLOCHTHONOUS DEPOSITS (FRENCH BASIN)

Fig. 47. Upper Westphalian C - Paleogeography and thickness variations around the Brabant Massif and Mid Netherlands High. (After Bless et el., 1977a; Van Staalduinen et al., 1979.)

least at intervals) and with different rates of subsidence and/or uplift

(Fig. 48). However, these differences are not expressed in the sedimentary

record because of the fragmentary information from bereholes or outcrops.

The same holds for the basinal areas which also may consist of several tec-

tonic blocks with different rates of subsidence. A good example of a complex

high is the Alston-Askrigg Block in Great Britain, whereas the Plzen Basin

in Czechoslovakia illustrates the chess-board structure in a generally sub-

siding basin. It is suggested that the Mid Netherlands High and the Zandvoort

Krefeld High formed a similar complex structure during the Deveno-Carbonife-

rous. Future exploration may reveal the existence of narrow troughs in this

complex during that time-interval.

71

Fig. 48. Chess-board structure of idealized high (horizontal line screen) and basin (blank). (From Bless at al., 1977a.)

Sources of sediment

The principal source area for the Wastphalian sediments was the mobile

Variscan belt. This is illustrated a.o. by the overall increase of rudaceous

material from the north towards the south and by the decrease of the thickness

of Upper Wsstphalian C deposits from the mobile Variscan belt towards the

Fenno-Bcandian Platform in the north.

More specific arguments for a southern origin of the Westphalian deposits

have been forwarded by M. & R. Taichm~llar (1950) and Mackowsky & K~tter

(1962) for the NW German Basin, by Bless & Strael (1976) for the Campine-

Brabant Basin, and by Barroie (1910) and Barrois at al.(193B) for the French

Basin.

M. & R. TeichmOller (1950) recognized reworked coal pebbles in a sandstone

overlying the Lower Westphalian C Iduna coal seam (NW German Basin), which

according to their coalification rank ("Esskohle") had been derived from

Lower Westphalian A rocks along the northern border of the Rhenish Massif,

where a similar rank of cealification characterizes rocks of that age (cf.

Patteisky & TeichmQller, 1962). Mackowsky & K~tter (1962) described reworked

coal pebbles from a sandstone overlying the Lower Wsstphalian Midgart coal

seam (NW German Basin), which according to their coalification ("Magerkohla")

had been derived from the Upper Namurian rocks along the northern border of

the Rhenish Massif, where a similar coalification degree characterizes rocks

of that age (cf. Psttaisky & TaichmUller, 1962).

72

Bless & Streel (1976) described rich rsworked miospore assemblages from

Upper Wsatphalian sediments in the southeastern part of the Campine-Brabant

Basin. These miosporss might have been derived from basal Middle Devonian

to Lower Westphalian rocks which presumably covered the Rhenish Massif and

northeastern portion of the Dinant Nappe until they became eroded during

or immediately after the Malvernlen movements in that area.

Barrois (1910) and Barrels et el. (Ig30) analyzed pebbles occurring in

Upper Westphalien coal seams and in the Upper Westphalian Roucourt Conglo-

merate in the French Basin. They counted some 50% of pebbles and blocks

of Lower Westphelian (mainly sandstones and some coaly shales) and Namurian

(Ardanne Arkose, phthanitas) age and about 40% of Dinantian limestones (both

Tournaisian and Visean) with s.c. brachiopods, against only some 10% of older

rocks (notably Frasnian and Famannian). The extreme size of some of the Lower

Wastphalian sandstone blocks in the Roucourt Conglomerate (more than 4 tons!)

suggests a nearby southern origin for these deposits.

A significant aspect of these observations is, that in all cases Devono-

Carboniferous sediments were reworked from these southern source areas.

Repeated recycling of Devono-Dinantian deposits along the northern border

of the mobile Variscan belt has been suggested also by Hasmmann (1975), who

noted a difference in maturity between Dinantian, Namurian and Wsstphalian

arenites in the NW German Basin. The Dinantian greywackas - deposited in

the foredaep north of the Mid German High - are characterized by a high

content of rock fragments (more than 25%). The Namurian and Westphalian

sediments show an overall change from greywackes through sub-greywackes to

relatively well-sorted sandstones in the Westphalien C. These Wmstphalian C

sandstones contain only some 5-8% of rock fragments and usually less than

15% of feldspars. Feldspars make up more than 25% in the Dinantian gray-

wackes.

This repasted recycling process since the Dinantian illustrates the con-

tinuous northward shift of the southern border of the sedimentary area of

the Cornwall-Rhenish Basin under influence of the Variscan movements (Fig. 49)

The coalification rank of reworkad phytoclasts (coal pebbles and miospo-

res) in the Westphalian C deposits of the NW German Basin and Campine-Brabant

Basin may be used for calculating the relative uplift of the supply areas

during the late Variscan movements.

The coalification rank of reworked Upper Namurian and Lower Wastphalian

coal pebbles in the NW German Basin appears to be distinctly higher than

that of the enclosing Lower Waetphalian C sediments: "Esakohle" to "Magsr-

kohla" (Rm: 1.6-2.2) ~or the coal pebbles, and "Flammkohle" (Rm: about 0.7)

for the Wsatphalian C sediments. The relatlvaly high coalification rank of

the reworkad coal suggests that this was buried at considerable depth (1000-

?3

N _ S e d i m e n I : a r y Basin

Z ¢I O0 LU .J

o1

UJ O. O-

Z

U} LW ..J u~ IX I l l

o ..J

Z

¢I

Z Cl

Z

r~

Z

Z 0 I l l 0

r¢ LU O. O.

NoRthern erosive area

MATURE SANDS

%

SUBGREYWACKES

GREYWACKES

Katazonal Mesoper~h/te

>_ ~,~, Mob i le (erosive) Varisean BelE

~, M/Jd/e Oeyon/,~n m/ospores ' " ~p/to~2a/ FeldspO,"s ~,

~ ' ~ _ Malvernian • Asluric ~ ~. AAAAAAAAAAAAAAA

Phases

T 3ude{ic + Erzgebirgian

AAAAAAAAA Phases

\

~J J

S e d f m e n t a r ~, [ba s i n oF " l w ~ l llll lIE U r O p e

Fig. 49. Strongly idealized and simplified scheme of recycling of deposits within the sedimentary basin of northwestern Europe. The relative amount of detritus involved in the recycling process is indicated by the relative width of the arrows. (From Thorgz & Bless, 1977.)

S

~n

-l-

z :

n ,

:onnlc AAA Phase

74

2000 m) before uplift and erosion took place in the Lower Westphalian C.

This means that important inverse movements must have affected the northern

border of the Rhenish Massif from where the oebbles seem to have been derived

(M. & R. TeichmUller, ~950; Mackowsky & K~tter, "962).

The reworked Middle Devonian to Lower Westphalian miospores in the Upper

Wsstphalian C sediments of the Campine-Brabsnt Basin show the same trans-

lucency as the extent Upper Westphalian C miosoores in the studied samples.

This suggests that the coalification rank of the rocks from which these had

been derived was lower than (or equal to) that of the snvelopping Upper

Wsetphalian C sediments ("Gaskohle" to "Gaaflammkohle", Rm: 0.75-1.25)o

It is worthwile to note, that the coalification of the Middle Devonian rock~

in the presumable source area of the Rhenish Massif (Paffrath-Eifel area,

cf. Fig. 50) is relatively low (Rm: ~). This fact corroOorates the sugges-

tion that the miospores nave seen derived from that area. It also indicates

that the Upper Devonian to Lower Westohalian sedimentary cover in that area

was relatively reduced (possibly less than 500 m). This means that the cen-

tral portion of the Rhenish Massif remained a shoal since the Middle Devonian

and that its relative uplift during the Westohalian C was considerably less

important than that of the northern part.

Stephanian

Btephanian deposits have not been recognized in the French Basin, nor in

the Campine-Brabant Basin. These occur in the southern part of the North

Sea, where the up to 600 m thick sequence includes thin carbonate beds with

echinoderm debris. This suggests that marine incursions may have affected

important parts of northwestern Europe during the Stephanian.

Stephanian strata are also known from a small area along the northern

part of the German-Dutch frontier. There, the about 200-300 m thick succes-

sion of red coloured shales and sandstones is separated from the underlying

Westphalian rocks by an important sedimentary gap. Coal seams are absent,

but the occurrence of rare plant debris suggests the existence of a sparse

vegetation in an essentially non-marine environment. It is not impossible

that this area was isolated from the more paralic sequence in the southern

North Sea.

I

Mi.JNSTERLAND-1 VERSMOLD-1 o O

X\ . . . . ~.~7 °/o''" ~ ~ - - - - - - ~ . . . . "-.. \ \

I \ \\

~\ ~ ~ , " , ' , SOEST-ERWITTE, o \ " \ x k X \ \ \ - -

I \

A ( £ It

_ J

/ / ' ~ , - - / /

'x'd'~ \ \ \ '---. ~"~. f / /

I

Y ' f / . . . . - ( , ~).-..,~

: , . . . . . , . 4 . . / , . . . . . . . _

. ~ . - : : : . : : . . . . ~ :~-..)b':.::: • x,.?.

:: ::!:; ~.!.i:- Q.2 ' : . : C . : "x4~/

i:!: i ~ 7

'o. : ' . : . \

J J

.~L¢.~ .~:'~

?5

SUGGESTED ISOAPOSTILBES (=lines of equal reflectance) IN GIVETIAN SEDIMENTS

0 25KM

Fig. 50. Coalification map for Givetian sediments of the Rhenish Massif and surrounding areas. (Modified after Paproth & Wolf, 1973.)

CONCLUSIONS

The Belgs-Dutch Platform is distinguished from the Caledonian fold belt

and the Cornwall-Rhenish Basin by its depositional history during the Devono-

Carboniferous. Practically no Old Red sediments seem to have been deposited

in this area during the Devonian, this in contrast to the situation in the

Caledonian fold belt.

During the Eifelian-Frasnian and Dinantian transgressions carbonate facies

characterize the platform whereas siliciclastics predominate in the Cornwall-

Rhenish Basin.

The Variscan deformation was largely restricted to the Cornwall-Rhenish

76

Basin that became incorporated in the mobile Variscan belt during the Car-

boniferous period.

Linear, fault-bounded basins with an overall ENE-SWS trend separated com-

plex horst areas on this platform since at least the Middle Devonian. Dif-

ferential subsidence of basins and horsts is reflected in rapid lateral

changes of the thickness of the sediments. Several of the fault systems se-

parating these Peleozoic basins and horsts seem to have been rejuvenated

in Mesozoic and Cenozoic times.

Climatic conditions favoured reef growth during the Eifelian-Frasnian

and Dinantian transgressions, and the formation of extensive peats during

the Silesian. The climate favoured also the repeated occurrence of red bed

and evaporite facies during the Devono-Carboniferous.

The structural-depositional history of the Belgo-Dutch Platform can be

compared into detail with that of the North American Crston. Presumably,

both areas were located in between the same paleoletitudes.

The comparable geology of the Dsvono-Carboniferous rocks in North America

and the Belgo-Dutch Platform have often drawn the attention of petroleum

geologists. The Devono-Carboniferous rocks of North America include important

hydrocarbon resources. These have not yet been recognized in northwestern

Europe. However, large portions of the Devono-Carboniferous rocks on the

Beige-Dutch Platform are covered by thick sequences of younger deposits and

remain to be explored by deep borsholes. Maybe, it is only a Question of time

before economically important hydrocarbon occurrences are detected in this area

ACKNOWLEDGEMENTS

We wish to express our sincere gratitude to a team of enthusiastic col-

laborators. Without their skilful technical assistance the present paper

would never have been possible: Messrs. H.F.J. Bisschoff, G.M.A. Geeraedts,

2.H.L. Jansen, H.J. Kastermans, J.P.M.Th. Meessen, H.M.J. Ruyters, A.J. Schaaf

and Mrs. C.A.M. Willems-Oreszen.

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