Karoo Basin

8/18/2019 Karoo Basin

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Facultatea de Geologie si Geofizica

Universitatea Bucuresti

Geologie istorica

Evolution of the Karoo

sedimentary basin

Autori: Dobrin Sebastian 303B Olteanu Dan-Cristian 302A

Ene Vlad 302A Voiculescu Alexandru 302B


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Abstract

The main purpose of this paper is to present the evolution of the Karoo sedimentary basin,

from its inception to it’s extinction. Situated in South Africa, it is a retroarc foreland basin developed

in front of the Cape Fold Belt, wich is made up of rock formations from Late Carboniferous to Early

Jurassic. In fact, it forms the thickest and stratigraphically most complete megasequence of several

depositories of Permo-Carboniferous to Jurassic age in south-western Gondwana.

Due to it being a foreland basin, there is a clear distinction between the southern and the

northern part. The southern part is close to the CFB, and thus it is considered proximal, while the

northern part is distal. A lack of correlation between formations can be observed, and also a thinning

of the formations from south to north

The climates in wich the deposition took places was quite different in Karoo’s history, andthus a shift from glaciar to deep water, shallow water and finally arid depositional system can be

observed. Accomodation was also affected by different processes at different moments in Karoo’s

history.

The Karoo basin is famous for being rich in fossil-bearing rocks having quite an importance in

dating some formations.


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Tectonic settings

The Karoo basins (fig 1) of south-central Africa evolved during the first-order cycle of supercontinent

assembly and breakup of Pangea,under the influence of two distinct tectonic regimes sourced fromthe southern and northern margins of Gondwana.

The southern tectonic regime was related to processes of subduction and orogenesis along the

Panthalassan (palaeo-Pacific) margin of Gondwana, which resulted in the formation of a retroarc

foreland system known as the ‘‘main Karoo’’ Basin, with the primary subsidence mechanisms

represented by flexural and dynamic loading. This basin preserves the reference stratigraphy of the

Late Carboniferous –Middle Jurassic Karoo time, which includes the Dwyka, Ecca, Beaufort and

Stormberg lithostratigraphic units.


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North of the main Karoo Basin, the tectonic regimes were dominated by extensional or

transtensional stresses that propagated southwards into the supercontinent from the divergent

Tethyan margin of Gondwana.

Superimposed on the tectonic control on basin development, climatic fluctuations also left a mark on

the stratigraphic record, providing a common thread that links the sedimentary fill of the Karoobasins formed under different tectonic regimes. As a general trend, the climate changed from cold

and semi-arid during the Late Carboniferous –earliest Permian interval,to warmer and eventually hot

with fluctuating precipitation during the rest of Karoo time.

Due to the shifts in tectonic and climatic conditions from the southern to the northern margins of

Africa during the Karoo interval,the lithostratigraphic character of the Karoo Supergroup also

changes significantly across the African continent.

For this reason, the Karoo basins sensu stricto(fig.1), which show clear similarities with the main

Karoo Basin of South Africa, are generally restricted tosouth-central Africa, whereas the Karoo-agesuccessions preserved to the north of the equator are distinctly different.

The Cape and Karoo basins formed within the continental interior of Gondwana. Subsidence resulted

from the vertical motion of rigid basement blocks and intervening crustal faults. Each basin episode a

three-stage evolution consisting of crustal uplift, fault-controlled subsidence, and long periods of

regional subsidence largely unaccompanied by faulting or erosional truncation. The large-scale

episodes of subsidence were probably the result of lithospheric deflection due to subduction-driven

mantle flow. (fig 2)

The Karoo basin is a cratonic cover that mimics the underlying basement blocks. The Permian Ecca

and lower Beaufort groups were deposited in a southward-deepening ramp syncline by extensional

decoupling on the intra-crustal decollement. Reflection seismic and deep-burial diagenetic studies

indicate that the Cape orogeny started in the Early Triassic. Deformation was partitioned into

basement-involved strike-slip faults and thin-skinned thrusting. Uplift of the Namaqua basement

resulted in erosion of the Beaufort cover.

East of the Cape fold belt, contemporaneous subsidence and tilting of the Natal basement created a

late Karoo transtensional foreland basin, the Stormberg depocentre. Early Jurassic tectonic resetting

and continental flood basalts terminated the Karoo basin.

2. Accumulation of Karoo aged successions in Africa corresponds to the Pangean first-order cycle of

supercontinent assembly and breakup.


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The tectonic regime during Karoo time was defined by

compression and accretion along the southern margin

of Gondwana coeval with extension propagating into

the supercontinent from its Tethyan margin

(Wopfner, 1994, 2002). This unique combination of

tectonic stresses sourced from the convergent and

divergent margins of Gondwana resulted in the

formation of different basin types across Africa, with

accommodation generated by tectonic and dynamic

loads in the south, and riftingto the north. The

extensional field in central and northern Africa during

Karoo time is explained by the updoming caused by

the self-induced Pangean heat anomaly that followed

the onset of supercontinent assembly (Wopfner,

1990, 1994; Veevers and Powell, 1994). Tensionalregimes initiated during that time resulted in the

formation of the early Tethyan spreading centre, and

continued to govern the Karoo deposition until the

breakup of Gondwana in the Middle Jurassic. Starting

with the onset of the Late Carboniferous, tensional

stresses propagated gradually to the south from the

Tethyan margin,controlling the deposition of Karoo

sediments in grabens and subsequent rift structures.

The age of the extensional structures in southern

Africa is thus inferred to be younger than in central

and northern Africa (e.g., Bordy and Catuneanu,

2002c).

Fig 2. Model evolution of Cape and Karoo

basins


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Discussion and conclusions

The formation of the Karoo-age basins of Africa took place during the Late Paleozoic –Early Mesozoic

interval,when the Pangea supercontinent reached its maximum extent.Tectonism was the primarycontrol on accommodation in the Karoo basins, with subsidence mechanisms (fig.3) ranging from

flexural in the south, in relation to processes of subduction and orogenesis along the palaeo-Pacific

margin,to extensional in the north, propagating southwards from the divergent Tethyan margin. The

interplay of these tectonic mechanisms, combined

with the influence exerted by the inherent structures

of the underlying Precambrian basement, resulted in

the formation of discrete depozones that follow

regional tectonic trends. Sedimentation patterns in

these Karoo basins were further influenced by a shift

in climatic regimes, from early cold conditions during

the Late Carboniferous –earliest Permian interval, to

warmer and eventually hot climates with fluctuating

precipitation during the rest of Karoo time. The

climatic background provided a common thread for

the sedimentary fill of all Karoo basins, which resulted

in the development of similar depositional trends

across much of south-central Africa in spite of the

change in tectonic regimes.

The lacuna which followed the coalescence of

Pangea led to extensive denudation and

peneplanation of central and eastern African cratonic

regions. The first release of heat from the self-induced

Pangean heat anomaly (Veevers et al., 1994a,b)

caused updoming, followed by rifting in the eastern

African and Malagasy region. Rust (1975) and

subsequently Tewari and Veevers (1993) suggested

that the shape of Pangean basins (like the Karoo

basins) was largely determined by the structure of the

basement.

Syneclisic type Karoo basins formed by flexure and

thermal sagging over isotropic, mainly Archean

basement (e.g., Congo Craton), whereas linear, east

African type basins developed 246 O. Catuneanu et al.

/ Journal of African Earth Sciences 43 (2005) 211 –253

by fracturing over anisotropic, mainly Proterozoic fold

belts (Wopfner, 1993, 1994). Similarly, Radelli (1975)that

syn-depositional faulting within the MorondavaBasin followed old zones of weaknesses within the

underlying Mozambique Fold Belt. More recently, Visser and Praekelt (1996) suggested a similar

Fig 3. Geodynamic history of the Cape

and Karoo basins.


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model for the breakup between East Africa and Madagascar/India.Whilst the concept of rift

directions being inherited from tectonic trends within the underlying basement holds true in a

general way, there are a number of cases where Karoo rifts cut right across older fold structures. One

of the best examples is the Ruhuhu Basin, the rift structures of which cut the fold fabric of the

Palaeoproterozoic Ubendian Metamorphic Complex almost at a right angle (Wopfner and Diekmann,

1996)

Although the dominant trend of the eastern African and Malagasy graben structures is northeast,

there are a number of shorter structures with northerly or even northwesterly trends. Some of them

may be simple accommodation faults, but the great thickness of sediments accumulated against

some of them suggests a pull-apart mechanism. It may be concluded therefore that East

African/Malagasy rifts were not just simple tensional systems but that they were governed by a

transtensional stress field with a clear left-lateral component (Wopfner et al., 1993).North of Kenya,

at the point where later in the Jurassic the northwest trending, failed rift of the Anza Trough

developed (Reeves et al., 1986), the Karoo rift system deviated from the trend of the Mozambique

Belt altogether and presumably continued northeastward to southern Oman.Such a continuation is

indicated not only by various palaeobiological assemblages (see Wopfner et al., 1993;Wopfner, 1994,

1999, 2002 for references) but also by the relationship of the glacigene deposits of southern Oman to

the Huqh-Haushi uplift (Lee, 1990). Permian pillow lavas overlain by radiolarian cherts in the Oman

Mountains show that here the intracratonic rift of the Malagasy Trough merged with the

Neotethyan Ocean.In summary it can be stated that the formation of the Karoo rift basins of eastern

Africa resulted from left lateral transtension between India/Madagascar and Africa.

Although the onset of rifting was triggered by an anomalous heat accumulation under the insulating

blanket of the vast continental crust, transtension was the controlling mechanism for the

establishment of rift directions. The forces were created by the opening of Neotethys combined with

the right-lateral rotation between Gondwana and Laurasia (Veevers et al., 1994a). The release of

heat from the self-induced heat anomaly is considered the cause for the sagging and the formation

of the syneclise-type basins on the western side of African Gondwana.At the same time with the

manifestation of dominantly extensional or transtensional tectonic regimes across much of

Gondwana, the evolution of the southern part of the supercontinent was primarily linked to the

formation of the Pan-Gondwanian fold-thrust belt, which provided the supracrustal load for the

flexural subsidence recorded in the main Karoo Basin. Flexural loading, coupled with dynamic

subsidence related to the process of subduction beneath Gondwana, conferred the main Karoo Basin

of southern Africa unique characteristics that set it apart from all other Karoo-age basins of Africa.This retroarc foreland basin preserves the reference stratigraphy for the Late Carboniferous – Middle

Jurassic interval of Gondwana, which includes the regionally correlatable Dwyka, Ecca, Beaufortand

Stormberg lithostratigraphic units.


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Distribution of the main lithostratigraphic units

Fig.4. Distribution of the main lithostratigraphic units of the Main Karoo Basin

Dwyka Group

The initiation of sedimentary processes of the Dwyka Group was estimated at about 300 Myr

(Moscovian) after a 30 Myr sedimantation break (Visean). The Dyka facies (tillites, cyclically grading

upwards into finer-grainde clastic rocks) indicates a glacial environment, with deposition from both

grounded and floating ice. The trend in which grounded and floating ice is separated is from north,

respectively south, althought alternate deposition from grounded and floating ice has been recorded

throughout the Karoo Basin. The foredeep accumulated about 800 m of silt-dominated marinediamictites with dropstones (Fig. 5) derived from the floating ice. In the south part of the basin the

thickness of the fining-upward cycles varies from 60 to 100 metres featuring an uniform character

and lateral continuity of the layers, suggesting that deposition from floating ice was taking place

within a large marine basin, each cycle displaying a transition from terrestrial to subaqueous

moraines at the base, to glaciolacustrine shales at the top. A general feature of the foredeep

succession is the uniform character and lateral continuity of the diamictite layers, suggesting

deposition from suspension in a relatively low energy environment, a large marine basin. Processes

of resedimentation of the initial fallout deposits by debris flows have also been documented in this

glacio-marine environment.


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Fig.5. Dropstone

Contrasting to the Dwyka succesion in the south, in the

north, the lateral correlation of the facies were very difficult

to comprehend due to the irregularity in thickness and

complex facies relationships of the succession. Despite this,

two finning-upwards cylces have been identified, each of

them comprising a basal massive till, a result of continental

glaciation, grading upwards into a stratified terminal zone

deposited from floating ice. Another interesting aspect is

that in the north part the top glacial-formed layers are

younger than the southern top of the Dwyka group,

meaning that the continental glaciation could have last

longer in the north due to a higher altitude than in thesouth where the climate was warmer because of the

marine environment during the Early Permian deglaciation.

As the result of deglaciation of the northern zone of the

basin, the uppermost layer of Dwyka succesion is

compound by coal-bearing fluviodeltaic sequences.

In the north, the limit is represented by ravinement surface generated during the marine

transgression of the Ecca Sea. In the south, a precise boundary between Dwyka and Ecca Groups is

difficult to trace as the transition between glaciomarine and marine environments is gradual, the

percentage of dropstones gradually deacreases upwards in parallel with the disintegration of the

floating ice.

Ecca Group

The term Ecca was first used to descrise argillaceous sedimentary strata exposed in the Ecca pass, in

the Eastern Cape Province, South Africa. The Ecca group occurs between the Late Carboniferous

Dwyka Group and the Late Permian-Middle Triassic Beaufort Group, encompassing the Permian time

slot of the Karoo lithologies. Its maximum thickness is located in the southern part of the Karoo

basin, in the foredeep, being of aproximately 3000 m. Most age determinations are based of fossil

wood biostratigraphy and palynology. The absolute ages are generally in agreement with the 290 Ma

aged inferred from palynomorphs. The Ecca group is mainly composed of mixed clastic sediments

with some minor carbonates.

The Ecca Group is diachronous, meaning that the distal region is younger than the proximal region,

making the Volkrust Fm. correlative with the lowermost Adelaide Subgroup – Koonap Formation (Fig.

6). With that being known, the age of the proximal region of the Ecca Group is from Artinskian to

Kazanian, and in the distal region, the Ecca Group begins in Kungurian and finishes somewhere in

Tatarian (Fig. 6). In the proximal region, the sedimentary processes was dominated by deep marine

conditions, forming Bouma sequences in Collingham Formation. The Collingham Formation is made

up of alternating siltstone and shale with yellowish layers of up. It is interpreted as a distal submarine


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fan facies associated with pelagic sedimentation and wind-blown interbedded volcanic ash. The age

is Late Permian, probably Ufimian.

The Fort Brown Formation hasbeen formed in a shallow water,

coresponding with a regressive

marine environment in the Late

Permian. This formation is

represented by greenish-grey shale

with subordinate sandstone

becoming more prominent

upwards. It comprises two

coarsening-upward-sequences.

Both are several 100 m thick. Their

basal parts consist of dark pelites

and rhythmic alternating sand- and

mudstones layers of a prodelta.

They pass over into sandy distal

bar and distributary mouth bar

deposits of the deltafront. The age

of the Fort Brown Formation is

Late Permian.

Fig. 6. Lithostratigrahy of the Karoo

Supergroup, along the profile

shown on Fig. 4

In the northern part of the basin, the Pietermaritzburg Fm. consists mainly of shales accumulated in

a moderate to deep marine environment, of Kungurian age. The Vryheid Formation consist of

fluviodeltaic deposition, containing the only nonmarine sedimentary deposits of the Ecca Group.Contrary to this, the correlation with the proximal Ecca Group is made with Whitehill Formation,

apparently the deepest marine environment from this period, being recorded at Kungurian age. The

Volkrust Fm. is accumulated in a deep to shallow marine environment, and is made up

predominantly of dark shales with intercalations of fine-grained sandstone. The age of this formation

is estimated as Umifian to Tatarian. The transgression of the Ecca Sea over the Vryheid Fm. formed

an uncomformable boundary between the fluviodeltaic facies and the marine transgressive facies of

Volkrust Fm.

The history of the Ecca formation is quite hard to understand due to the complexity of structures

and depositional enviromanets. After the Dwyka glaciation, the main facies types are meltwater rain-deposits, glaciofluvial and glaciolacustrine deposits, found in the norther Karoo, with deep-water


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marine sedimentation in the foredeep. This is still in the underfilled settings of the basin, where the

foredeep accumulates pelagic to gravity flow sediments. Accomodation is obtained by dynamic

subsidence wich outpaces the rates of flexural uplift, leading to the lowering of the peripheral bulge

below the sea level and the manifestation of the basin-wide transgressions of the interior seaway. At

a higher frequency level, fluctuations in sediment supply and in the balance between the rates of

flexural tectonics and dynamic loading may result in forced regressions on the side of the basin that

is subject to flexural uplift, coeval with transgressions or normal regressions of the opposite shoreline

of the interior seaway.

The latter is the case with the age-equivalent Ripon and Vryheid formations in the Karoo

Basin, when submarine fans in the foredeep formed at the same time as the progradation of fluvial –

deltaic sequences over the forebulge. The filled foreland stage is represented by the Fort Brown and

the Volkrust Formations, when the deep-water environment specific to the foreland is replaced by a

shallow-marine environment. Also the forebulge is lowered below sea leve wich means that the

dynamic subsidence is outpacing the rates of flexural uplift, which in turn implies base level rise

across the entire foreland and sedimentation rates that are within the range of variaton of the rates

of base level rise.

The boundary between Ecca Group and Adelaide Subgroup is comformable, both in proximal and

distal regions.

Beaufort Group

The term Beaufort “Beds” was first introduced to describe

sedimentary rocks of the lower part of the Karoo series at

Beaufort West in South Africa, but has been expanded toinclude a wider range of fluviatile deposited Permo-Triasic

rocks in the main Karoo. The absolute age of the Beaufort

Group is not preciselly placed but the wealth of fossils

tetrapods has allowed biostratigraphic subdvisions into eight

biozones which have allowed the correlation with other

better dated fossil bearing successions in the world.

These rocks cover about 200000 square kilometers,

making up about 20% of the local surface area of South

Africa, with a maximum thickness of 7000 m in the

foredeep, thinning rapidly northwards. Beaufort Group

strata consist predominantly of mudstones and siltstones

with subordinate lenticular and tabular

Fig.7. Beaufort shale

sandstones deposited by a variety of fluvial systems (Fig. 7).The boundary with the underlying Ecca

Group is transitional and diachronous, recording a gradual change from deltaic to fluvial depositional

systems. The climates had become semi-arid with seasonal rainfall. The presence of desert rose-

gypsum, dessication cracks, palustrine carbonate beds and pedogenic carbonate horizons is a direct


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indicator of a semi-arid region. Lower Beaufort sediments came from different margins of the Karoo

basin, giving rise to pebbly sandstones in the north and fine-grained sandstones elsewhere. The

Beaufort Groups is divided into two major subgrops : the Adelaide and Tarkastad Subgroups.

Adelaide Subgroup

By the time the Adelaide Subgroup had formed the nonmarine conditions of sedimentation were

established in all Karoo Basin. The proximal facies of the Adelaide Subgroup includes the Koonap,

Middleton and Balfour Formations being the correspondent for Tatarian age and the distal facies is

represented by Normandien Fm. – Upper Tatarian – Lower Scythian (Fig. 6). The base of the Adelaide

Subgroup is conformable with the lower Ecca Group in both distal and proximal facies, due to the

transition marine-nonmarine environment; however the subgroup in its lower part is diachronous.

The Koonap Formation has been formed in high-energy systems (braided river) grading upwards

innto lower energy meandering systems. It is made up of greenish silty mudstones and sandstones.

The Middleton Fm. composed by a finning-upward succesion made up of marron and greenish-grey

mudstones interbedded with sandstones and is deposited in low-energy meandering and lacustrine

systems. The Contact between the Middleton and the overlying Balfour Fm. is unconformable due to

the changes in the facies and sedimentation energy rate, from low-energy meandering facies to high-

energy braided facies. Similar to the lower sequence of Koonap and Middleton Formations, the

Balfour Fm. presents changes in the depositional environment fom braided rivers grading upwards

into meadnering systems. It also represents a finnin-up sequence, bounded by subaerial

unconformities both at the top and at the base. They are composed of yellowish and bluish-greenish-grey sandstones interbedded with dark mudstones, and their age is Tatarian to early Scythian. The

presence of calc-alkaline volcaniclastic detritus and ‘‘cherts’’ of tuffaceous origin (Ho-Tun, 1979)

suggests that the provenance rocks in the southwest may have included an active andesitic volcanic

chain located on the eastern side of the Andean Cordillera in South America and West Antarctica.

The Normandien Formation is also the result of a fluviatile system, but showing evidence of wide

semiarid floodplains, being made up of interbedded sandstones and mudstones deposited by

meandring streams with channels flanked by this semiarid floodplains. It correlates with the upper

part of the Balfour Fm., and therefore the age is tartarian-Early Scythian.

Tarkastad Subgroup

The Tarkastad proximal facies is composed of the Katberg and Burgersdorp formations. The distal

facies is made up of the Driekoppen and Verkykerskop formations. It's age is Scythian to early

Anisian.

The Katberg is made up of thick, laterally extensive, light olive grey, coarse-grained sandstones,

composed of transverse and longitudinal bar macroforms, which are internally structuredpredominantly by horizontal and trough cross-stratification. It unconformably overlays the Balfour


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Formation. It was deposited in a shallow braided environment with pulsatory discharge. Abandoned

channel fills are also present and are represented by thin sequences of red-olive yellow mudstones.

The Burgersdrorp Formation conformably overlies the Katberg Formation and consists

predominantly of thick fining-upward units of laterally inextensive, olive grey, fine to medium

grained sandstones overlain by red-maroon coloured siltstones and mudstones. These fining-upwardsequences are thought to represent mixed-load meandering river and floodplain deposits and

preserve a fauna assignable to the Cynognathus Assemblage Zone. The source area is composed

predominantly of granitic, metamorphic and alkaline volcanic rocks.

The Verkykerskop Fomation consists predominantly of thin, laterally extensive, medium to fine

grained sandstones dominated by transverse bar macroforms wich are internally structured by

planar cross-bedding. It is the northern equivalent of the Katberg formation. The Driekoppen

formation is composed of thin fine-grained channel sandstones, internally structured by horizontal

stratification, overlain by thick, massive to diffusely laminated siltstones and mudstones. They are

believed to represent suspended-load-dominated meandering river deposits.

The Tarkastad Subgroup may be regarded as a single finning-upward sequence : sandstone

dominated braidplain deposits at the base, grade upwards into mudstone-dominated floodplain

deposits associated with meandering river systems.

The Beaufort Group marks the begging of the overfilled basin stage of the Karoo basin. Overfilled

foreland systems are dominated by non-marine environments, and reflect stages in the evolution of

the basin when sediment supply outpaces the available accommodation. The accommodation in this

case is only achieved through tectonic processes.

Stormberg Group

A major stratigraphic gap, corresponding to the late Anisian-Ladinian interval separates these strata

from underlying Tarkastad. In contrast to the other groups, there are no proximal or distal facies.

Nevertheless, the entire group may be considered a distal facies for the Stormberg Group did not

extend to the Cape Fold Belt. Furthermore, studies show that Dwyka, Ecca and Beaufort rocks are the

sediment sources for the Stormberg Group, reworking this older Karoo sequences. The base-Moltenoangular unconformity, well developed in many basins, indicates a significant tectonic event across

the region to usher in Stormberg sedimentation.

The sequence discussed here is constituted by tree different formations: Molteno, Elliot and

Clarens, from Middle Triassic to Middle Jurassic. (Fig. 6)

The Molteno Fm. is composed by two coarsening upward sequences that formed deposits

interpreted as the fills of abandoned channel tracks and within ponded bodies of water on the

braidplain. The formation is composed predominantly of tabular sheets of medium to coarse grained

sandstone internally structured by horizontally and cross-stratified macroforms. Siltstone, mudstone

and coal deposits also occur but are far less abundant. The Bamboesberg Member is dominated byolive grey fine to medium grained sandstones, internally structured


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equally by horizontal and trough cross-stratification. The overlying Indwe Sandstone Member is also

dominated by sandstone, internally structured predominantly by trough cross-stratification. Other

distinctive features of the two members include the presence of dm-scale clasts

of Witteberg quartzites within the sandstones (especially in the uppermost Bamboesberg and Indwe

Sandstone members), and the large (mm-to cm-scale) crystals of feldspar within the Indwe sand-

stones (Turner, 1975; Christie, 1981). The Transitional Member also coarsens upwards with the

contact between the Molteno and overlying Elliot Formation marked by

the top of the uppermost coarse sandstone. This contact also marks a sharp palaeontological break

in that it coincides with the first occurrence of fossils assignable to the lowermost biozone of the

Elliot Formation, the Euskelosaurus Assemblage Zone.

The Elliot Formation (Norian –Early Jurassic, Fig. 8) is dominated by floodplain mudstones with

subordinate channel and crevasse splay sandstones, probably representing a meandering system. In

addition to the fluvial sediments, an aeolian loessic dust component is apearing on the upper part of

the formation, increasing in the top, showing a transition not only in sedimentation processes, but

also in the climate change, a more arid tipe of climate. The occurrence of aeolian sandstones starts as

m-scale thick intercalations in the upper part of the Elliot Formation, before the definitive

establishment of the aeolian environment, showing cyclical changes in climate or aeolian sediment

input in the transition interval between the Elliot and Clarens environments.

Fig.8. Elliot and Clarens Formations

In the Clarens Fm. (Early to Middle Jurassic, Fig.6) consists of cream or yellow fine grained

sandstones, sandy siltstones and mudstones with subordinate coarse-grained sandstones. Theclimate discussed previously intensified in the first period, and then a moderate tipe of climate with a

more abundent rainfall takes place. Considering the stratigraphic conformity and the gradual

character of the transition between the fluvial-dominated (Elliot) and the aeolian-dominated

(Clarens) environments, the Elliot and Clarens formations may be taken together as one coarsening-

upward sequence. The upper contact with the lavas suggests synchronous desert sedimentation and

early volcanism, particularly in the Huab and main Karoo basin.


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Fig.9 Idealized structure and process of the evolution of theforeland system which is influenced by cycles of orogenic

loading and unloading

Drakensberg

The Karoo Igneous Province consists of several remnant floodbasalt accumulations, sills and vast

dyke swarms . From the geochemical stratigraphy it appears that the tholeiitic lavas onceformed an extensive carapace centred on the 1800 m thick Lesotho remnant. 40Ar/39Ar dates on the

flood basalts and intrusives record a 185 –180 Ma duration of magmatism. Continental flood basalts

are commonly associated with continental breakup, such as the extensional basins that developed

along the margin of the Namaqua plate. Synrift sediments of Kimmeridgian age have been drilled in

the Outeniqua basin and Middle Jurassic age in the conjugate North Falkland basin. Magmatism and

the start of extension were more or less contemporaneous.

Interpretation

A crucial issue in the analysis of

the Karoo Basin is the

identification of the flexural

foredeep and forebulge

characteristics, as well as the

migration trends through time.

The stages of orogenic loading

and unloading represent animportant influence on the

migration of the hinge line

between phases of

sedimentation, controlling also

the subsidence and the uplift of

the foreland system flexural

profile (Fig.9)

Flexural processes combined with

sedimentation determine theposition of the basin depocentre

in the proximal region during

orogenic loading, and in the distal

region during orogenic unloading.

The out of phase base-level

changes between the proximal

and the distal regions result in

contrasting stratigraphies (Fig.6),

which may explain the

stratigraphic hinge lines in

Dwyka, Ecca and Beaufort


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Fig.10 Variation of the stratigraphic hinge line through time

Groups (Fig.10). The hinge line

shifted towards the craton

during the Late Carboniferous-

Permian interval, and back

towards the orogen during the

Triassic-Middle Jurassic. As

contrasting stratigraphies

develop in response to ut of

phase base-level changes

between the proximal and the

distal regions of the foreland

system, the pattern of hinge

line migration reflects a

correspondig migration of the

flexural foredeep andforebulge.

The data of the studies of the

Karoo Basin suggest that the

cratonward migration of the

foreland system (Late

Carboniferous-Permian)

occured during a time of

orogenic loading in the CapeFold Belt. Although the first

order orogenic loading lasted

until the end of the Middle

Triassic, which was continued

with a low-rate shift in the

same direction during the Late

Triassic-Middle Jurassic stage

of first order orogenic

unloading. The figures.... offer

a precise and detailed image

of the variation of the changes

that have been occured in

sedimentation, relanshionship

between proximal and distal

regions depending on the

flexural characteristics and

paleoclimatic trend of a

specific region. The

progradation of the foreland

system is attributed to the

Fig.11 Schematic model for the evolution of the Karoo

sedimentar basin


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progradation of the orogenic fron during stages of orogenic loading. For the Late Carboniferous-

Permian interval, when the progradation of the Karoo foreland system took place, evidence for the

gradual advance of the CFB against the basin is supplied by the Dwyka, Ecca and lower Beaufort

strata that are incorporated within the orogenic structures in the proximity of the orogenic front. The

geology of the CFB indicates that no further progradation of the orogenic front occured after the end

of the Permian, although the first-order orogenic loading continued until the end of the Middle

Triassic. The subsequent low-rate retrogradation of the foreland system during the Late Triassic-

Middle Jurassic stage of first-order orogenic unloading is attributed to the erosion of the orogenic

front leading to a slow retrogradation of the centre of weight in the orogenic belt. Such stages of

low-rate retrogradation of the foreland system due to the erosion of the Fig. Schematic model for the

evolution of the Karoo sedimentary basin orogenic front probably took place during all quiescence

stages of the CFB first order cycle.

The depocentre of the Karoo basin is alternately the foredeep, during orogenic loading, and the

foresag during which the retrogradation of the orogenic load due to the erosion of the orogenic front

may cauze an orogenward migration of the foresag. The depocentre of the Karoo basin is alterately

the foredeep during orogenic loading, and the foresag, during orogenic unloading. In Fig.11 , time

step (1) suggest the coeval deposition of marine and nonmarine Dwyka facies, as well as the debut of

the Ecca Sea (lower Prince Albert Formation) restricted to the southern part of the basin, which

explains the diachroneity of

the Dwyka-Ecca contact.

The Ecca-Beaufort contact

is also diachronous, which

is explained by the

persistence of the Ecca Seawithin the foresag area

coeval with the debut of

fluvial aggradation in the

more proximal region

during time-step (5).The

basin is underfilledduring

time-steps (1)-(4), with

deep marine

sedimentation, it reaches afilled phase during time

step (5), with shallow

marine=nonmarine

sedimentation and evolves

into an overfilled phase

during time-step (6), with

fully nonmarine

sedimentation across the

entire basin.

Fig.11 Schematic model for the evolution of the Karoo -

sedimentary basin (continuation)


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In the period Triassic-Middle Jurrasic the orogenward migration of the peripheral bulge/sag may

either be attributed to the retrogradation of the orogenic load due to the erosion of the orogenic

front during times of quiescence. The basin is overfilled with fully nonmarine sedimentation during

the stages presented at Fig. . As a function of the relative position between the equilibrium drainage

profile and the flexural profile, areas of sedimentation, bypass or erosion are separated within the

basin.


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Paleontology

Fossil Potential:

* Dwyka Formation: a glacial deposit (tillite) containing no fossils.

* Ecca Group: in this southern part of the basin, some fossil wood and fragmentary plant material is

found. In addition, rare fish fossils have also been found (Jubb and Gardiner, 1975), as well as trace

fossils in the form of burrows, feeding track and fish-fin drag marks at the interface of bedding

planes.

* Beaufort Group: these predominantly terrestrial sediments have, throughout South Africa, yielded

a large number of vertebrate fossils in the form of amphibians, early primitive reptiles (the

captorhinids), mammal-like reptiles (therapsids), and fish. Minor freshwater invertebrates (molluscs)

and plant fossils have also been recovered. For the most part, however, the fossils found in the

Beaufort sediments are rare, particularly in the lowermost part of the succession, just above the

Ecca- Beaufort contact.

The Beaufort Group is subdivided into eight biozones (Fig.12) (Rubidge, 1995) on the basis.

Fig. 12 Beaufort Group


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-The Eodicynodon Assemblage Zone:

Eodicynodon (Fig. 13 ) was a therapsid reptile of the Capitanian stage (266-260 million years ago) of

the Permian Period. It measured about 30 cm. (11.8 inches) long. The length of the skull was 9 cm.

(3.5 inches).

Fig. 13 Eodicynodon reconstruction

-The Tapinocephalus Assemblage Zone:

Tapinocephalus (Fig.14) is a genus of large herbivorous dinocephalian that lived during the Middle

Permian Period 250 million years ago. These stocky, barrel-bodied animals were characterised by a

massive bony skull roof and short weak snout. It is thought that, like the rest of the members of its

family, the animals engaged in head-butting intraspecific behavior, possibly for territory or mates.

The fossil remains (skull and postcranial elements) of Tapinocephalus are known from the Lower,Middle, and Upper part of the Tapinocephalus Assemblage Zone ( Capitanian age) of the Lower

Beaufort Beds of the South African Karoo. Only the type species, T. atherstonei is now considered

valid for this genus.

In life, these animals were over 3 meters (10 ft) in length and weighed around 1.5 to 2 metric tonnes

(1.6 to 2 short tons), making them among the largest animals of their time.They died off in the

Triassic-Jurassic extinction about 200 million years ago, which opened the door to dinosaur

domination of the earth.

http://en.wikipedia.org/wiki/Therapsidhttp://en.wikipedia.org/wiki/Capitanianhttp://en.wikipedia.org/wiki/Capitanianhttp://en.wikipedia.org/wiki/Faunal_stagehttp://en.wikipedia.org/wiki/Faunal_stagehttp://en.wikipedia.org/wiki/Million_years_agohttp://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Genushttp://en.wikipedia.org/wiki/Herbivorehttp://en.wikipedia.org/wiki/Dinocephaliahttp://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Family_%28biology%29http://en.wikipedia.org/wiki/Agonistic_behaviorhttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Skullhttp://en.wikipedia.org/wiki/Postcraniahttp://en.wikipedia.org/wiki/Tapinocephalus_Assemblage_Zonehttp://en.wikipedia.org/wiki/Capitanianhttp://en.wikipedia.org/wiki/Beaufort_Grouphttp://en.wikipedia.org/wiki/Beaufort_Grouphttp://en.wikipedia.org/wiki/South_Africahttp://en.wikipedia.org/wiki/Karoohttp://en.wikipedia.org/wiki/Type_specieshttp://en.wikipedia.org/wiki/Metrehttp://en.wikipedia.org/wiki/Foot_%28length%29http://en.wikipedia.org/wiki/Metric_tonnehttp://en.wikipedia.org/wiki/Short_tonhttp://en.wikipedia.org/wiki/Short_tonhttp://en.wikipedia.org/wiki/Metric_tonnehttp://en.wikipedia.org/wiki/Foot_%28length%29http://en.wikipedia.org/wiki/Metrehttp://en.wikipedia.org/wiki/Type_specieshttp://en.wikipedia.org/wiki/Karoohttp://en.wikipedia.org/wiki/South_Africahttp://en.wikipedia.org/wiki/Beaufort_Grouphttp://en.wikipedia.org/wiki/Beaufort_Grouphttp://en.wikipedia.org/wiki/Beaufort_Grouphttp://en.wikipedia.org/wiki/Capitanianhttp://en.wikipedia.org/wiki/Tapinocephalus_Assemblage_Zonehttp://en.wikipedia.org/wiki/Postcraniahttp://en.wikipedia.org/wiki/Skullhttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Agonistic_behaviorhttp://en.wikipedia.org/wiki/Family_%28biology%29http://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Dinocephaliahttp://en.wikipedia.org/wiki/Herbivorehttp://en.wikipedia.org/wiki/Genushttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Million_years_agohttp://en.wikipedia.org/wiki/Faunal_stagehttp://en.wikipedia.org/wiki/Capitanianhttp://en.wikipedia.org/wiki/Therapsid


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Fig. 14 Tapinocephalus reconstruction

-The Pristerognathus Assemblage Zone :

Pristerognathus (Fig.15) a genus of Therocephalian mammal-like reptile, whose fossils have been

found in that structure. These animals were roughly cat-sized, and are characterized by long, narrow

skulls with large canines. They are likely to have preyed on smaller therapsids and millerettids of the

time.

Fig. 15 Pristerognathus reconstruction

http://en.wikipedia.org/wiki/Pristerognathushttp://en.wikipedia.org/wiki/Pristerognathushttp://en.wikipedia.org/wiki/Therocephaliahttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Therapsidshttp://en.wikipedia.org/wiki/Millerettidshttp://en.wikipedia.org/wiki/Pristerognathushttp://en.wikipedia.org/wiki/Pristerognathushttp://en.wikipedia.org/wiki/Millerettidshttp://en.wikipedia.org/wiki/Therapsidshttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Therocephaliahttp://en.wikipedia.org/wiki/Pristerognathus


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-The Tropidostoma Assemblage Zone is a geological stratum and a faunal zone of the Beaufort

Group, of the South African Karoo. The name refers to Tropidostoma, a genus of dicynodont

mammal-like reptile, whose fossils have been found in that structure.

The Cistecephalus Assemblage Zone The name refers to Cistecephalus, a genus of small burrowing,

mole-like reptile, whose fossils have been found in that structure.

Cistecephalus (Fig. 16) was a small, specialised, burrowing dicynodont, possibly with habits similar to

a modern mole. The head was flattened and wedge-shaped, the body short, and the forelimbs very

strong, with similarities in structure to the forelimb of modern burrowing mammals.Cistecephalus is

so far known from the Cistecephalus Assemblage Zone of the South African Karoo, as well as from

Zambia and India. Cistecephalus was about 33 centimetres (13 in) in length.

Fig. 16a A trace of Cistecephalus

Fig. 16b Cistecephalus reconstruction

http://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Stratumhttp://en.wikipedia.org/wiki/Biozonehttp://en.wikipedia.org/wiki/Beaufort_Grouphttp://en.wikipedia.org/wiki/Beaufort_Grouphttp://en.wikipedia.org/wiki/South_Africahttp://en.wikipedia.org/wiki/Karoohttp://en.wikipedia.org/wiki/Tropidostomahttp://en.wikipedia.org/wiki/Dicynodonthttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Cistecephalushttp://en.wikipedia.org/wiki/Reptilehttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Dicynodonthttp://en.wikipedia.org/wiki/Mole_%28animal%29http://en.wikipedia.org/wiki/Cistecephalus_Assemblage_Zonehttp://en.wikipedia.org/wiki/South_Africahttp://en.wikipedia.org/wiki/Karoohttp://en.wikipedia.org/wiki/Zambiahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Zambiahttp://en.wikipedia.org/wiki/Karoohttp://en.wikipedia.org/wiki/South_Africahttp://en.wikipedia.org/wiki/Cistecephalus_Assemblage_Zonehttp://en.wikipedia.org/wiki/Mole_%28animal%29http://en.wikipedia.org/wiki/Dicynodonthttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Reptilehttp://en.wikipedia.org/wiki/Cistecephalushttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Dicynodonthttp://en.wikipedia.org/wiki/Tropidostomahttp://en.wikipedia.org/wiki/Karoohttp://en.wikipedia.org/wiki/South_Africahttp://en.wikipedia.org/wiki/Beaufort_Grouphttp://en.wikipedia.org/wiki/Beaufort_Grouphttp://en.wikipedia.org/wiki/Beaufort_Grouphttp://en.wikipedia.org/wiki/Biozonehttp://en.wikipedia.org/wiki/Stratumhttp://en.wikipedia.org/wiki/Geology


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The Dicynodon Assemblage Zone :

The name refers to Dicynodon (Fig. 17), a genus of mammal-like reptile, that flourished in the

Permian Period and whose fossils have been found in that structure. Is a type of herbivorous

mammal-like reptile that flourished during the Permian Period. This animal was toothless, except for

prominent tusks, hence the name. It probably cropped vegetation with a horny beak, much like atortoise, while the tusks may have been used for digging up roots and tubers.

Dicynodon was a medium sized and advanced member of the Dicynodont group. It had an average

length of 1.2 metres (3.9 ft), although size differed among species. Its fossil remains have been found

in sediments of latest Permian age in South Africa, Tanzania, Russia, and China.

Fig. 7 Dicynodon reconstruction

The Lystrosaurus Assemblage Zone The name refers to Lystrosaurus, a genus of mammal-like reptile,

a dominant life form of the Early Triassic Period, whose fossils have been found in that structure.

Lystrosaurus ( Fig. 18) was a genus of Late Permian and Early Triassic Period dicynodont therapsids,

which lived around 250 million years ago in what is now Antarctica, India, and South Africa. Four to

six species are currently recognized.Being a dicynodont, Lystrosaurus had only two teeth, a pair of

tusk-like canines, and is thought to have had a horny beak that was used for biting off pieces of

vegetation. Lystrosaurus was a heavily-built, herbivorous animal, approximately the size of a pig. The

structure of its shoulders and hip joints suggest that Lystrosaurus moved with a semi-sprawling gait.

The forelimbs were even more robust than the hindlimbs, and the animal is thought to have been apowerful digger that nested in burrows.

Lystrosaurus was by far the most common terrestrial vertebrate of the Early Triassic, accounting for

as many as 95% of the total individuals in some fossil beds. It has often been suggested that it had

anatomical features that enabled it to adapt better than most animals to the atmospheric conditions

that were created by the Permian –Triassic extinction event and which persisted through the Early

Triassic—low concentrations of oxygen and high concentrations of carbon dioxide. However recent

research suggests that these features were no more pronounced in Lystrosaurus than in genera that

perished in the extinction or genera that survived but were much less abundant than Lystrosaurus.

http://en.wikipedia.org/wiki/Dicynodonhttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Herbivorehttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Lystrosaurushttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Triassichttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Genushttp://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Triassichttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Dicynodonthttp://en.wikipedia.org/wiki/Therapsidhttp://en.wikipedia.org/wiki/Antarcticahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/South_Africahttp://en.wikipedia.org/wiki/Dicynodonthttp://en.wikipedia.org/wiki/Tuskhttp://en.wikipedia.org/wiki/Canine_toothhttp://en.wikipedia.org/wiki/Herbivorehttp://en.wikipedia.org/wiki/Pighttp://en.wikipedia.org/wiki/Terrestrial_locomotionhttp://en.wikipedia.org/wiki/Early_Triassichttp://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_eventhttp://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_eventhttp://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_eventhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_eventhttp://en.wikipedia.org/wiki/Early_Triassichttp://en.wikipedia.org/wiki/Terrestrial_locomotionhttp://en.wikipedia.org/wiki/Pighttp://en.wikipedia.org/wiki/Herbivorehttp://en.wikipedia.org/wiki/Canine_toothhttp://en.wikipedia.org/wiki/Tuskhttp://en.wikipedia.org/wiki/Dicynodonthttp://en.wikipedia.org/wiki/South_Africahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Antarcticahttp://en.wikipedia.org/wiki/Therapsidhttp://en.wikipedia.org/wiki/Dicynodonthttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Triassichttp://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Genushttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Triassichttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Lystrosaurushttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Herbivorehttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Period_%28geology%29http://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Dicynodon


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Fig. 18 Lystrosaurus

The Cynognathus Assemblage Zone. The name refers to Cynognathus, a genus of eucynodontian

mammal-like reptile, whose fossils have been found in that structure.

Cynognathus (Fig. 19) was a heavily built animal, and measured around 1 metre (3.3 ft) in body

length. It had a particularly large head, 30 centimetres (1.0 ft) in length, with wide jaws and sharp

teeth. Like hind limbs were placed directly beneath the body, as in mammals, but the fore-limbs

sprawled outwards in a reptilian fashion.

The dentary was equipped with differentiated teeth that show this animal could effectively process

its food before swallowing. The presence of a secondary palate in the mouth indicates that

Cynognathus would have been able to breathe and swallow simultaneously.

The lack of ribs in the stomach region suggests the presence of an efficient diaphragm: an important

muscle for mammalian breathing. Pits and canals on the bone of the snout indicate concentrations of

nerves and blood vessels. In mammals, such structures allow hairs (whiskers) to be used as sensory

organs.

Fig. 19 Cynognathus

http://en.wikipedia.org/wiki/Cynognathushttp://en.wikipedia.org/wiki/Eucynodontiahttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Dentaryhttp://en.wikipedia.org/wiki/Secondary_palatehttp://en.wikipedia.org/wiki/Diaphragm_%28anatomy%29http://en.wikipedia.org/wiki/Nervehttp://en.wikipedia.org/wiki/Whiskershttp://en.wikipedia.org/wiki/Whiskershttp://en.wikipedia.org/wiki/Nervehttp://en.wikipedia.org/wiki/Diaphragm_%28anatomy%29http://en.wikipedia.org/wiki/Secondary_palatehttp://en.wikipedia.org/wiki/Dentaryhttp://en.wikipedia.org/wiki/Fossilhttp://en.wikipedia.org/wiki/Mammal-like_reptilehttp://en.wikipedia.org/wiki/Eucynodontiahttp://en.wikipedia.org/wiki/Cynognathus


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Fun Fact

The Permian –Triassic (P –Tr) extinction event, informally known as the Great Dying, was an

extinction event that occurred 251.4 million years ago, forming the boundary between the Permian

and Triassic geologic periods. It was the Earth's most severe extinction event, with up to 96% of all

marine species and 70% of terrestrial vertebrate species becoming extinct It is the only known mass

extinction of insects.

Distinct assemblages of paleosols above and below the Permian –Triassic boundary in the Karoo

Basin of South Africa are evidence for reorganization of ecosystems following this greatest of all

mass

extinctions. The Permian –Triassic boundary is recognized from the last appearance of Dicynodon and

from a series of negative excursions in the isotopic composition of carbon within therapsid

tusks,

pedogenic carbonate nodules, and organic matter.

Causes of the end-Permian mass extinction

The changes in fluvial style in the Karoo Basin at the end of the Permian were initially thought to

be triggered by a pulse of thrusting in the southerly source area, which brought about rapid

progradation of a large sandy braided fan system (the Katberg Fm.) into the central parts of the basin

.Ward suggested an alternative that better fits the observed palaeoclimatic changes. They proposed

that the switch in fluvial regime was a consequence of the extinction event rather than the cause.

The global aridification and con comitant de-vegetation of the continental interiors caused unstable

channel banks and increased run-off that is reflected by the onset of gullying of the floodplains and

the switch from high to low sinuosity channel pattern.

Stable isotopic analyses of pedogenic nodules and teeth taken from embedded fossils through

the extinction interval at the Bethulie section revealed an anomalous negative excursion within the

boundary laminites.This anomaly is interpreted as having been caused by a relatively rapid release of

methane or CO2

into the atmosphere over a period of some 150 kyr. The greenhouse effect from these emissions,

whether they originated from the Siberian volcanism or oceanic overturn , could have caused the

observed global aridification of continental interiors .

Recovery fauna

Only four genera (31%) survived the extinction: the dicynodont Lystrosaurus and the

therocephalian genera Tetracynodon,Moschorhinus and Ictidosuchoides. However, none of the

therocephalian genera survived into the succeeding Early Triassic Katberg Formation, because they

died out in the upper Palingkloof some 160 kyr after the main extinction event during what could be

interpreted as a second pulse of extinctions amongst the ‘survivor fauna’.Out of the ten taxa

recovered from Earliest Triassic

http://en.wikipedia.org/wiki/Extinction_eventhttp://toolserver.org/~verisimilus/Timeline/Timeline.php?Ma=251.4http://en.wikipedia.org/wiki/Permianhttp://en.wikipedia.org/wiki/Triassichttp://en.wikipedia.org/wiki/Geologic_periodhttp://en.wikipedia.org/wiki/Marine_biologyhttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Terrestrial_ecoregionhttp://en.wikipedia.org/wiki/Vertebratehttp://en.wikipedia.org/wiki/Extinctionhttp://en.wikipedia.org/wiki/Insectshttp://en.wikipedia.org/wiki/Insectshttp://en.wikipedia.org/wiki/Extinctionhttp://en.wikipedia.org/wiki/Vertebratehttp://en.wikipedia.org/wiki/Terrestrial_ecoregionhttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Marine_biologyhttp://en.wikipedia.org/wiki/Geologic_periodhttp://en.wikipedia.org/wiki/Triassichttp://en.wikipedia.org/wiki/Permianhttp://toolserver.org/~verisimilus/Timeline/Timeline.php?Ma=251.4http://en.wikipedia.org/wiki/Extinction_event


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strata, directly above the PTB, seven taxa originate within 30 m of the boundary. The first new taxon

to appear almost immediately above the boundary is the archosauriform Proterosuchus .

This taxon is closely followed by the amphibian Micropholis and the procolophonoid

‘Owenetta’kitchingorum (soon to be placed in a new genus, the dicynodonts Lystrosaurus murrayi

and L.declivis, and the cynodonts Thrinaxodon l iorhinus and Galesaurus. The amphibian, Lydekkerina., the procolophonoid)

Procolophon and the therocephalian Scaloposaurus appear stratigraphically higher in the Katberg

Formation, with Lydekkerina appearing firstat approximately 37 m above the boundary.

Procolophonwas previously regarded as originating just abovethe PTB , but our collecting has

repeatedly shown this taxon makes its first appearance approximately 60m above the PTB,

thereafter it then occurs in abundance.


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Conclusions

Due to the flexural behaviour of the foredeep and forebulge of the basin, controlled by the orogenic

loading and unloading processes. As a result, the depocentre of the foreland system alternatedbetween the depositional foresag, during orogenic unloading, and the depositional foredeep, during

orogenic loading, so the orogenic tectonism played a crucial role in creating the stratigraphic

arhitecture. The first-order CFB orogenic cycle icludes a Late Carboniferous-Middle Triassic orogenic

loading stage followed by a Late Triassic-Middle Jurassic unloading stage. The Karoo foreland system

migrated towards the craton during the Late Carboniferous-Permian, and back towards the orogen

during the Triassic-Middle Jurassic. The cratonward migration of the foreland system is controlled by

the progradation of the orogenic front during orogenic loading. The retrogradation of the centre of

weight in the orogenic belt is probably attributed to the erosion the orogenic front.

Bibliography

The Karoo basins of south-central Africa - O. Catuneanu a,*, H. Wopfner b, P.G. Eriksson c, B.

Cairncross d, B.S. Rubidge e, R.M.H. Smith f, P.J. Hancox e

Tectonic evolution of the Cape and Karoo basins of South Africa - Anthony Tankard a,*, HermanWelsink b, Peter Aukes c, Robert Newton d, Edgar Stettler e

The recovery of terrestrial vertebrate diversity in the South African Karoo Basin after the end-

Permian extinction - Roger Smith *, Jennifer Botha

Fluvial style variations in the Late Triassic –Early Jurassic Elliot formation, main Karoo Basin, South

Africa - Emese M. Bordy *, P. John Hancox, Bruce S. Rubidge

Reciprocal flexural behavior and contrasting stratigraphies: a new basin development model for the

Karoo retroarc foreland system, South Africa – O. Catuneanu, P. J. Hancox, B. S. Rubidget

Evolution of the Karoo basin - ??

Wikipedia.org

Different geology sites for small questions.

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