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BENTHIC FORAMINIFERA RESPONSE TO METHANE RELEASEIN AN ADRIATIC SEA POCKMARK

GIULIANA PANIERI

Receit,ed Awgust 13,2002; acceptecl May 12,2003

Key uords. Benthìc foreminifera, methane release (pockmark),ò''C, foraminiferal taxonomy, Bonaccia field, Adriatic Sea, Italy.

Abstrdct. The presence of methane-bearing shallow sedimentsin the Adriatic Sea has been known sìnce the fifties, but little is knownabout the benthic foraminiferal assemblages associated with them. Oneseep and two conrrol cores were collected in the Bonaccia field (cen-tral Adriatic Sea) at a warer depth of 8O m to investigate the possibleinfluence of the reiease of gas from marine reservoìrs on these fo-raminiferal assemblages. The seep core was drilled inside a pockmarkìn the vicìnìty of an active mud-volcano. Two control cores were col-lected in nearbv areas unaffected by presence of methane. Benthic fo-raminiferal assemblages from the seep core are comparable to thosefrom the seep-free cores and are composed of species common in thecentral Adriatic Sea. However, foraminìferal density in the seep-coreis remarkably lower than in tbe control ones cores. Besides, calcìticforaminiferal tests from the seep core revealed unusual trends in stablecarbon isotope composition. Even though not within the same range, asimilar trend was observed throughout the seep core for the ò,rC val-ues oÍ Gat,elinopsis lobatulus, Cassìd.ulina carìnata, and Bu/ìmìna mar,ginata.In partìcular, negariye carbon isotope values qrere recorded forGaoelinopsis lobatulus at the top of the core where merhane seeps y/eredetected and deep inside the core sediments (50 cm). These findingsseefir to point to temporal variations in seep activit,v, proving that the6''C values of foraminiferal tests reflect hydrocarbon release and mayhence be used to reconstruct seep activity history.

Ridssunto. La presenza di metano nei sedìmenti di alcune areedel mare Adriatico è nota da tempo, ma i suoi effetti sulle associazionia foraminiferi bentonici sono ancora poco conosciuti. A quesro scoposono state studiate, sia dal punto di vista micropaleontologico sia iso-topico, tre carote prelevate nell'Adriatico centrale ad una profondità di80 m, una in prossimità di una zona influenzata dalla risalita di metanoe due in un'area dove esso è assente. I risultati di questa ricerca hannomesso in evidenza che nella carota inreressata dalla risalita di metano. ladensità microfaunistica è fortemente rìdotta e i valori degli isotopi sta-bilj del carbonio nei ioraminiferi bentonici (in particolare Gavelinopsislobatulus) registrano risalita di merano. I segnali isotopici dei foramini-feri possono quindi essere vllizzati per ricostruire la storia dell'attivitàdelle luorru.cire di idrocarburi.

Introduction

Shallow marine sediments containing gas have beenreported from several areas of the Adriatic Sea. The Bo-naccia field (central Adriatic Sea, Italy) represenrs oneof the most important of these areas, wirh a significantamount of gas-related features such as seeps and pock-marks (Fig. 1). Oil companies have often performed hy-drocarbon-related studies in the area. Lirerarure on thesubject is however still scant. The survey carried ourduring this study ìn 1995 revealed the presence of pock-marks, mud volcanoes, abundant amounts of authigeniccarbonates (crusrs, hard grounds and mounds) (Fig. i),and methane presence in sub-bottom sedimenrs, in ec-cordance with previous observations by Curzi 8r Veggiani(1985), Mazzoni er al. (1987), Colantoni er al. (1997),and Taviani et aL. (1997).

As clearly emerged from the discussion of sever-al participants ar the "Third International Congress onEnvironmental Micropaleontology, Microbiology andMeiobenthology" held in Vienna (Austria) in Septem-ber 2Aa2, there is great inreresr in the response of benthicforaminifera to various pollution sources (heary metaland/ or hydrocarbon) in srress environmenrs. Given thatbenthic foraminifera represenr one of the most usefultools for paleoenvironmenral and paleoceanographicstudy (Gooday 1994; Van der Zwaan et al. 1999 amongothers), investigators have recently also begun to ex-plore the ecological role of these protists in hydrocar-bon-based environmenrs. Findings, however, have so farnot been univocal. In order to have a reliable record ofthe response of fossil and recent benthic foraminiferalassemblages from methane rich sediments, rhree cores

Dipartin-rento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Via Zamboni 67 - 4a126 Bologna, ItalyE-m:ìl: p:nieri,o geomin.unrbo.ir

550

were investigated. One was taken from a pockmark de-

pression in the vicinity of a mud-volcano in the presence

of methane release source, while the other two from gas-

free areas in the Bonaccia field in the central Adriatic Sea.

The top 1O cm of the cores contained sandy mud withgrey mud below, down to the bottom.

The study set out to determine: 1) possible varia-tions in the benthic foraminiferal taxonomy; 2) the rela-tionship between methane seep and stable isotopic com-position of benthic foraminifera; 3) the viability of usingthe isotopic signature of benthic foraminifera to recon-struct the hi.tory of reep rctivity.

Study area

The hydrocarbon seep considered in the presentstudy is located in the Bonaccia gas-field in the centralAdriatic Sea about 35 km off the Conero Promontoryr, at

a warer depth of 80 m (Fig. 1). Gas-fields in the area are

present in Plio-Pleistocene turbidite sequences (Mattavelliet aI. 1991).In this part of the Adriatic basin, thin sandy

deposits called relict sands were deposited durine the Ver-

silian Transgression and Holocene mud belts (Van Straaten

1920; Colantoni et al. 1979) were deposited as a high-stand

Fig. 1 - Location of the cores in the

Bonaccia field (central Adri-atic Sea). Captions: 1) lsobaths

(0.5 m interval); 2) Coarse bio-genic sediments; 3) Hard bot-rom. crrbonrre' biogenìc con-cretions;'1) Gravit)' cores loca-

tlon.

system tract (Trincardi et al. 1994).The Holocene mudbelt in this area is diffusely impregnated by biogenic gas,

mainly rnelhane lCrbbianelli, pers. comm.).Seismic sur-veys performed during this study exhibit

characteristics that may be interpreted as relating to nat-ural gas seeping from the Plio-Pleistocene turbidite intoHolocene sequences. Sediments diffusely charged withlocal1y rising gas were observed in the sub-bottom profileof the site from which core GAB2 was taken (Fig. 2). Theseismic profile exhibited a 2-5 m-thick layer of sandy siltsediment lying over a peat and clay lens of continental ortransitional environments. The fine-grained gas charged

sediment pores were observed to be partially filled withpore warer and free gas (Gabbianelii, pers. comm.). Gas

quantity was presumed to be relatively low, being con-tained in the sediment as a millimetre scale bubble so as

to rule out any sienificant reworking. Geochemical analy-

ses (Mattavelli et al. 1991) proved the biogenic origin ofthe methane in the area.

Materials and methods

Three Kullenberg cores (with an inner diameter of 10 cn)drilled in the ' icinitv of rhc pockn-rark of the study area (Fig. 1) were

;rn:rlysecl. Corc GABl (lat 43 35'26"/long 11 2I' 35") was drilled at

G. Panieri

z

the bese of thc pockrnrrk, core GAB2 (lat .13 35' 25"/long 14 21' 35")n-as taken close to the nrud volcano at the centrc of the pockmark, andcore CABS (lat ,{3 35' 23"/long 11 2\' 25") in the nearby :re'l unr{-fected bv methane seeps.

Onc-centimetre-thick sedin-rent samples taken at 1O cm jn-tervals aìong the entire cores u'ere used for foranriniferal ancl geo-chemjcel analyses. After drr.ing and weighìne, unconsolidated sam-ples were soaked in r.ater for 1-2 davs. Each sample was u.ashedthrough a 63pm mesh sjeve, dried, an.l rhen,h. ..rld.r", were splitinto aliquots containing about 3OO benthic foraminìfera. Benthic fo-rarninifera were ìdentified and counted (Appendix). Simple speciespercentases over the total assemblage (see the Online BackgroundDataset. http://www.go.terra.unimi.itlrivista/ 1 O9n3.htm) and mì-cropeleontologìcal densitl' expressed as number of specìnens pergram drr.weight were determined on the basis of benthic foraminif-eral specirnen counts (Appendix).

To avoid the erroneous estimation due to the occurrence orabsence of rare specimens, diversìtr'trras nor determined on the basisof the number of species in the sample (S) but on the number of spe-cies and their frequencv according to the Shannon-\fiener formula,H{,t) - -If.,p, lnp,, r.herep. is thc proportion of the nth species (Ap-pendix). Statistical analvsis u'as conducted so as to gaìn more detailedinforrrrrtjon (,n en\ ironrrenl:ì rr:bilrr1.

Foraminiferal specimens for isotopic analyses were sampled fromcore GAB2. Different species of benthic foran-rinifera (BuLìmitta ntar-ginata, Cassidu/ina carinata, and Gatelinopsis Iobatu/uí) were selected.To minimiz-e the possibility of conramination by calcite overgrowihsor carbonate erains, each specimen underrvenr screening by binocularmicroscopy to detect xn). traces of carbonate incrustation on the tcsts.

Diffractometric (XRD) analyses s.ere performed by means ofa Philips P\f3Z:10 X-ra1- powder dìffractor.r.reter on abour 100 tests ofGai:elhopsis letbatu/us sampled from the GAB2 core. The scanninq an-gular range was from 25" to l1'(20) with an acquisition time of 60tììinute\ ir rr s1.111.q i.rl rnerninc.

Benthic foraminifera as indicators of hydrocarbon release

The release of methane from marine reservoirs inrooverlyine sediments is known to affect carbon isotope ra-tios at the sediment-water interface (Graber er al. 1990).For instance, ò'tC values of bicarbonate and dissolved in-organìc carbon (DIC) may diminish (Roberts & Aharon1994). Generall,v, the chemistry of benthic foraminifera is

a reliable proxy for numerous environmental paramerersxs rhe lesrs rre secrered in isotopic equilibrium wirh rhesea-water (Grossman 1987). It has also been obser-ved that

Benthic foraminifera response to methane release 5s1

Fig. 2 - Details of a 3.5 kHz sub-bot-rom profrle. .hoq irr!, rhe rol-cano n-irh rìding gas detected

and the GAB2 position in theBonaccia field. See location inFigure 1.

the carbon isotopic signature of this group of Protista is

more negative in hydrocarbon seeps than in hydrocarbonfree-areas (Sen Gupta & Aharon 1994; Sen Gupta et al.1992). Negative excursions in òLrC values of fossil ben-thic foraminifera in Quaternary sediments (Cannariato &Kennett 1 996; Kennet r et al. 7996,2000; Wefer et aI. 1994)and near the Paleocene/Eocene boundary (Dickens et al.

1995,1997) have been relared ro merhane release causedby gas hydrate dissociation during cooling episodes. Inparticular, cooler episodes favour a drop in sea level andthe subsequent decrease in hydrostatic pressure mry al-low the release of considerable quantities of methane fromgas hydrate dissociations. Cr.tor-r ciata referred ro ben-thic foraminifera from the Northern California marginsuggest that methane release may be related ro temporalvariations in seep activity caused by temperature varia-tions (Rathburn er al. 2000).

Results

Benthic foraminifera. The species found in thebenthic foraminiferal assemblages of the rhree cores ex-amined are well-documenred in the literature on rhis areaof the Adriatic Sea (Jorissen 1988). The resuks of eachcore examined are reported below.

GABl - Between 41 and 19 taxa per sample wereidentified in the GABl core (Appendix). The Shannon-Wiener index ranges from 3.39 to 3.19. After an increasefrom the base up ro 50 cm, where the highest value wasreached (5.39), a decrease was observed followed by a

slow increase up-core (Fig. 3).Microfaunal densitl. values were found to increese

from the base up-core reaching 61,25 ar the top of thecore (Fig. 4).

The benthic foraminiferal assemblage (Fig. 5) is

characterized by Cassidulina cdrinata, n'hich was seento slowly increase up-core reaching 14.6"/. at rhe top.Bulimìna marginatd exhibited a marked increase at ,lO

cm (11%) and two marked drops at 30 cm (ca 7.k) andat the top of the core where the lowe st value (4.47o) was

H(S)

(Diversity of Shannon-Wiener)

3.1 3.2 3.3 3.4 ?E

Depth(cm)

552

Fio I Stratigraphic variations in diversity H(S) Shannon-\Vicner

index in core GABl, GAB2, and GAB3.

reached. Cribroelpbid.ium decipiens rose throughout thecore reachin g ca 13'% at the top, u,hllst Cribroelphidiumgranosum exhibited relatively stable occurrences (ca 77o).

Gat,elinopsis lobatulus increased from the base to 10 cm

where a small peak (7.7"/.) was seen to be followed by a

strong decrease up to the top (2.7%). Globocassidulinasubglobosa was found to increase from the base up to 3O

cm (ce 9"/o) and fronr 20 cm to the top where it reached

6.8%. An accessory species that was seen to decrease up-core \À/rs Bigenerina n,Ldosaria.

GAB2 - In this core between ,10 to 47 taxa werefound per sample with the Shannon-\íiener index rang-ing from 3.13 to 3.27 (Appendix). The H(S) remainedalmost constant from the bottom up to 30 cm, althougha small decrease at 50 cm was obser-ved (3.18), where a

small peak was followed by a marked decreasing trend upto the core top (Fig. 3). The lowest H(S) vras in fact ob-

Fio 4 Stratigraphic variations in microfaunal density (number o{

specirnens per I gnm drv-weight) in core GABl (triangle),GAB2 (squarc) and GABI (rumble) from the Bonaccia field(central Adrìatìc Sea).

served at the top (3.13), where the presence of methaneu-as detected by seismic profile.

Microfaunal density values were at their lowestin the CA82 core (Fig.4;. Alter slo*ly decrersing up-

core throughout the core, the low.est value of 4166 was

reached at the top.Figure 5 shows the temporal distribution of the

significant GAB2 core. Benthic foraminiferal assemblage

was found to be dominated by the genera Cassìdulina (C.

carinata and C. crassa) and by Bulimina marginata. Cas-

sidwlina carinata increased from the core base reaching

ca 14"/o at 50 cm and ca l5"k at 2O cm. After the last peak

it decreased up to the top. The quantity of Cassidulinacrassa slowly diminished towards the core top. Buliminamarginata frequency diminished from the base to 40 cm

(7 .1%), and then increased up to 20 cm. A new drop at 1O

cm was followed by a strong peak at the top of the core

G. Paniert

Microfaunal density

(n' specimenslgr dry sediment)

2000 4000 6000 8000

90

100

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A ^o 5 io 15 o 5 10 i5 o 5 ro 15 o b 10 o

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where the species reached its highest value of l4'k. Cri-broelphidium granosum, which was seen to generally in-crease up-core, exhibited two peaks ol tA.l "/. and 11 .3"/"at 5O and 30 cm, respectively. After decreasing up to 6O

cm, Bigenerina nodosaria was found to increase up to 40

cm (8.4%), decrease up to 20 cm, and then increase againup to 10 cm, where it was most abundant of al1 (ca 10%).Gaoelinopsis lobatulus showed marked peaks of 5.33 and6"/" at 5A cm and at the core-top, respectively.

GAB3 - Taxa count values in the core ranged from4A to 17 (Appendix). Strong variations were recorded inthe Shannon-'$f iener diversity index H (S). After increas-ing from the bottom to 80 cm, the index reached its low-est value at 50 cm (3.13), newly increasing to 1O cm where

Benthic foraminifera response to metbane release 553

Fìs.5 - Srrnrmrrv clirlrrm of benrh-^_5'"

ic foraminifera frequencl' ofsome species (> 5%) plottedagainst the depth. 5A - Fre-

quencf in core GABI' 58 -

Frequencf in core GAB2. 5C- Frequency in core GAB3.

it reached 3.42, and finally dropping once more to 3.26I /-'

.t fhè .^ra f^n / tsrd \ ì

Microfaunal density increased up-core, although a

slight drop was observed between 50 and 30 cm (Fìg.4).Foraminiferal assemblage showed (Fig. 5) Cassl-

dulina carinata initially increasing and peaking at 5O cm

(18.8%) before decreasing at the top. Cassidwlina crassa

was found to decrease from the core base to 60 cm andthen to slowly increase to 20 cm where it reached9.2"k,before decreasing again up to the top. After a small peakat 1OO cm (12.4%), Bulimina marginata was seen to de-

crease up to 60 cm (7.6%). At 50 cm another small peakwas recorded followed by a drop up to 10 cm (6.8%), witha final increase x1 1[s.^- ^{.Lo.^,o t1î706). Despite

Sediment depth(c-)0-1

9- 10

19-20

29-30

39-40

49-50

59-60

69-70

79-80

òrc

-0.14

-0.14<41

-0.66

-3.4 1

-0.08

0.s6

-0.51

-0.32

-0.95

-0.35

-0.03

-0.94

0.70

-0.46

-0.47

0.07

0.24

-0.61

1 .81

-0.51

0.05

1.37

ò'ro ldentification

1.54 Buliminamarginctla

1.87 Cassidulinacarinatt,

0.54 Gavelinopsislohattrlus

0.75 Buliminamarginata

0.16 Gavelinopsislobatulu.s

2.09 Buliminamarginata1.1I Cassidttlinacarinala

0.69 Gavelinopsislobatttlu.s

1.63 Buliminamarginata-1.44 Cassidttlinacarinattt

i24 GavelinopsislobatttÌu.s

0.52 Btliminamarginata

0.96 Cassidttlinacarinatu

0.60 Gavelinopsislobuîulus

2.00 Buliminàmarginata-0.60 Cassidtrlinacarinatu

-0.14 Gavelinopsislobatultts

1.35 Buliminamarginaîa

1.37 Cassidulinacarinatu

1.27 Buliminan'targinata

Cassidulina carinatu

0.98 Buliminamlrginlto2.37 Cassidulinacarinata

0.3 7 Guvel lctburulus

554

Tab. 1 - Stable isotopic values (7"o relative PDB) from GAB2 core

taxa. Sample which generated variable isotope oxygen sìg-

nals (standard deviation of >0.05%.) are not ìndicated.

Bigenerina nodosaria's odd up-and-down pattern cyclicincreases and decreases, its occurrence was fairly stabÌe

at about 6'k. Cribroelphidium decìpiens increased up core

with a peak of 8.6"/" at 10 cm, u,hrlst Cribroelphidiumgranosum, quantitatively constant from the base up to 70

cm, peaked at 60 cm (8.8%) and at the core top (8.8%).Accessory species that were seen to increase up core

include Miliolinella subrotunda and Rosalina globularis,while the decreasing ones were found to be Lobatula lo-batula and Spiroplectammina urigbti.

Stable isotopes. Carbon and oxygen isoropic ana-

lyses (Tab.1) were performed on three species of benth-ic foraminifera collected every 10 cm in the GAB2 core.

B ulimina marginata, Cassidulina carinata, and G acelinop -

sis lobatulus v/ere selected because present in relativelyquantities throughout.

Sncri-".. {^rr..l ,t ,ho "^r" tnn /O- | e m\ urcre(vH \v

considered as representing the modern sea floor and thepresent-day environment. Changes in 6"C for each ana-

lysed highlighted a similar isotopic pattern throughoutalmost ail the core (Fig. 0).

Bwlimina marginata ò'tC values were seen to range

from -0.74 ro 0.a7"k". A slight shift was observed in theò''C values of the species from positive Q.A7%) at 60 cm

to negative (-0.74%) ones at the core top, with a gener-

al decrease up-core. Bulimina margindtd ò"O values ex-

hibited only a positive spread, becoming more positivefrom the base (0.98%o) up to 50 cm (2%") (Tab. t;. ,tless positive ò"O vaÌue was recorded at 40 cm followed byan increase up to the top, with peaks at 2A cm (2.a9"k")and at rhe core top (l.54ooo).

Carbon isotope signature values for Cassidwlina

carinata ranged from -0.95 to 1.817oo, initially increas-ing (1.81%.) up to Z0 cm and then markedly dropping(A.95%.) up to 30 cm. A positive peak at 20 cm Q.56'/"")n'as followed by a new drop to negative values at the core

top (-0.95). Further variations were observed in E'*O val-ues, with the most negative at 50 and 30 cm (-0.600/oo and

-1.4 4"/"", respectiveÌy).Gar.,elinopsis lobatulus E"C values exhibited even

greater var;ations, with the largest changes to more nega-

tive values being recorded at 50 cn (-2.92"/oo) and at thecore top (-5.27%.). As isotope data was not obtainableat 60 and 7a cm, a diminishing trend from the core base

up to 50 cm may be presumed - (Fig. 6) . Oxygen iso-tope values for Gaoelinopsis lobatwlws are quantitativelyconstant (ca 0.6'k") along the core except a smail peak(1.24%") recorded at 30 cm.

Discussion

General faunal characteristics. Progress in as-

sessing the effect of hldr<rcarbon release on benthic fo-raminiferal communities has been considerable over thelast few years, even though the exact interaction affectingthe taxonomic structure of this group of organisms is stillunder debate. The findings of the study on the three cores

from the central Adriatic Sea are a further contributionfor interpreting the effects of the methane seepage.

All the species identified in the cores are well-documented in the literature of the Adriatic Sea (Joris-sen 1988). The findings of the study were hence in ac-

cordance with those of previous Authors (Sen Gupta et

al. 1997; Bernhard et al.2001), so that unlike what was

observed for a group of megafaunal components by Sibuet

& Olu (1998), the absence of endemic species in hydro-carbon-based environments was confirmed.

Benthic foraminiferal assemblage composition was

found to be similar in all three cores. The lack of any trueassemblage differences between the GAB2 methane-af-fected and the GAB1 and GAB3 control cores may be as-

cribed to insufficient andl or short/intermittent durationof methane seepages. This is probably why a distinctivemethane-seep association was not observed, with differ-ences in microfaunal density and H(S) values only be-

ing recorded for complex situations. Microfaunal density(number of benthic foraminiferal specimens in one gram

of dry sediment) was found to be severely reduced in the

GAB2 seep-core. At the same water depth and hence overthe same interval of time the lowest values were in factrecorded in this core compared to the control ones. Ben-

G. Panieri

Benthic foraminifera response to metl'tane release

Downcore stable isotope (6''C) records in GAB2 core obtained fron Bulimina marginata, Cassidulina carinata, and Ga.r,elinopsis lo-batulus.

Fig. 6

thic foraminiferal density has been observed to be linkedto the trophic structure (i.e. food and oxygen levels) ofthe habitat. A number of studies have pointed our thar rhesize of foraminiferal population is controlled by oxygencontent at ocean floor level and in sediment pore waters(e.g. Lohmann 1978 Perez-Cruz & Machain-Castillo 1990;

Sen Gupta 8c Machain-Castillo 1993; Loubere 1.994), as

well as by organic carbon availability (Althenbach & Sarn-thein 1989; Herguera i992; Jorissen et a1. 1995; Corliss &Emerson 1990; Gooday 1996; Rathburn et al. 1996). Thesimilar upward trend in microfaunal density observed inall analysed cores suggests a general improvement in thearea. But the reduced microfaunal density reported for theGAB2 core, which appeared especially marked at the core-top where methane was detected during the survey (Fig.2), suggests the presence of an unusual ecosystem ascrib-able to methane release and characterised by reduced oxy-gen content and high quantities of organic matter. Thesefindings are in line with those recently reported by Yanko& Flexer (1991) for a study in the Odessa Bay area, andby Sen Gupta er aI. QA)l for a study on cold seeps in theGulf of Mexico based on a 24 cm-long push core takenat a site characterised by present-day hydrate dissociarìonand gas expulsion.

The H(S) Shannon-Wiener index permits an overalldescription of faunal diversity and hence affords a detailedaccount of environmental stability. Given that foraminif-

era population diversity distribution is a function of en-vironmental dynamics and variability (Gibson 1966), theiowest values recorded in the GAB2 seep core may be rea-

sonably presumed to depend on the seep-induced stressundergone by benthic foraminifera population. In fact,in all likeiihood the seep makes for an unsrable ecosys-tem as the very presence of seeping fluid and its variabil-ity due to changing fluid flow intensities favour reducedoxygen availability and organic compound build up. Thedecreasing up-core trend obserued in the upper interwalof GAB2, that terminates with the absolute lowest val-ue, suggests seepage intensification in terms of quantityand/ or duration at the core top. Similar results have beenreported by Sen Gupta et al. (Z.OOZ) according to whomthe reduced diversity observed by them in a methane -hy-drate affected area of the Gulf of Mexico was ascribableto seepage onset or intensification.

At specific leve\, Bulimina marginata belong to a

genera usually considered capable of coping with highenvironmental stress, especially 1ow oxygen content (e.g.

Van der Zwttn 1982; Murray 1991; Sen Gupta & Mach-ain-Castillo 1993), and their presence has been reportedin most seep data sets (Akimoto et a1. 1994; Sen Guptaet aL. 1997; Rathburn et al. 2000; Bernhard et al. zoot;.In the GAB2 core an up-core increase of the species was

observed, with values at the top greater than those of theother cores. This enhanced frequency, that proved detri-

613c (PDB) ò13c (PDB) ò13c (pDB)

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0,4 -2 -1 0 1 2 -6 -5 -4 -3 -2 -1 0 1 z

10

40

50

80

E Bttlimina marginata Cassidulina cQrinata

.

i

I

)

:

!

is lobatulus

556

mental to other species, appears to be closely related todepleted oxygen content as the species does not seem

to be at al1 adversely affected by dysoxic conditions, un-der which it is also capable of reproducing itself (Bern-hard & Sen Gupta 1999).The species may hence be pre-sumed to be pre-adapted to thrive in methane-saturatedenvironments.

Gaoelinopsis lobatwlus, which, as suggested by itsisotopic signatures and discussed below, is of considerableimportance, peaks at 50 cm and at the core-top. Gupta(1999) reported this species in an assemblage from DSDPSite 214 in the East Indian Ocean characterised by highenergy, good oxygenation, and probably 1ow organic c"rr-

bon content and ascribed these conditions to its presence.

The conditions prevailing at the GAB2 core site were such

that Gupta's assumption as to Gapelinopsis lobatulus en-

vironmental affinity cannot be confirmed. Furthermore,the relatively low frequency of the species and the preva-lence of taxa (for instance, Cassidulina spp. and Bulimi-na spp.) marking environmental conditions that are thereverse of those reported by Gupta make for a differentinterpretation of the abundance peaks observed at 50 cm

and at the core-top that would hence appear ascribable

to other factors.

Stable isotopes. Being extremely useful as indica-tors of paleoenvironmental and paleoceanographic con-ditions the stable isotopic composition of benthic fo-raminifera has been recently utilized also in seep envi-ronments. According to the literature, hydrocarbons af-fect the carbon isotope values of benthic foraminifera at

seep sites (Sen Gupta & Aharon 1994; Sen Gupta et al.

1997; Rathburn et al. 2000; Kennett et al. 2000; \íefer er

aI. 1994). In hydrocarbon release sites the increased levels

of DIC (dissolved inorganic carbon) caused by microbialprocesses involving sulphate reduction and hydrocarbonoxidation are characterizedby negative ò"C values (Rob-erts & Aharon1994). Calcite tests of foraminifera accord-ing to Sen Gupta & Aharon (1994) and Sen Gupta et al.

\1997) appear reliable for yielding such results. Moreo-ver, determining the time and extent of methane release

on the basis of the isotopic records of methane-affectedforaminifera caused by cold episodes occurring at differ-ent times in the climate cycle, also in case of methane re-lease being caused by dissociated clathrates (Wefer et al.

1994; Kennett et a1. 1996,2AaA: Cannariato & Kennett1996;Zachos et al. 1994; Dickens et al. 1995,1997) has

been deemed to be a viable method.Despite the partial findings of the present study,

some of the carbon isotopic values reported here stronglyagree with those of the literature cited above. The isotop-ic results obtained f or Gaaelinopsis lobatulus, Cassidulinacarinata and Bwlimina marginata exhibit the same patternthroughout almost the full length of the GAB2 core even

though with different magnitudes. Such inter species cov-ariance suggests that the ò'tC values are a record of varia-

tions in environmental conditions that trigger changes inforaminiferal isotopic signature. Negative ò'tC values forGaaelinopsis lobatulus were recorded at the top, at 10, and

at 5O cm of core depth. Similar results were also reportedfor Cassidu/ina carinata and Bwlimina marginata (no value

was recorded Îor Cassidulina carinata at 10 cm).A salient finding of the present study is the

verw neqrrive E'rC v;lues recorded for the well-knownGa'oelinopsis lobatulus. The oxidation of organic míÌtterrich in ''C may determine such negative ò"C values in fo-raminiferal tests (McCorkle et ai. 1985, 1990) . The iso-

topic values recorded here for Gavelinopsìs lobatulus may

be ascribable to such a factor. This assumption cannothowever be confirmed given the lack of other support-ing evidence. The lack of information on species living inenvironments rich in decomposing org.rnic matter is 1eta further obstacle to making viable comparisons.

In a study by Rathburn et al. (t990) in the Sulu

Sea relative PDB values for Gavelinopsis lobatwlus werefound to be negative, ranging from -2.96 ro -3.57"/"o .Thefinding was explained by the authors on the basis of thefact th.rt "unexpectedly low" ò'tC values were yielded bythe aragonitic test made on the species. Given the crucialimportance to the present study of the isotopic values ofspecies, diffractometric analyses were made to determinethe nature of the test. Results pointed to a calcite testfor Gavelìnopsis lobatulus, so that the obser-ved depletionmust be accounted for byother causes.

Bearing in mind that ò'rC excursions of up to 57oo

have only been reported for specimens collected in meth-ane-affected environments (Sen Gupta 8e Aharon 1994;

Vefer et aI. 1994; Kennett et al. 1996; Sen Gupta et al.

i99Z; Rathburn et al. 2000) and that the GAB2 site con-sidered in the present study was very close to the seep, itmay be presumed that the very low ò"C values recordedfor Gavelinopsis lobatulus in the initial centimetres of thecore length are ascribable to the presence of methane. Itwould seem that the ò''C values of the Gaoelinopsis lo-batulus tests record the high levels of dissolved inorganiccarbon (DIC), the very negative values being attributableto methane oxidation. If this is so, then the stratigraph-ic interval at 5O cm, where Bulimina marginata and Cas-

sidulina carinata carbon isotopic values were also seen

to diminish, is further evidence of of 1.et further meth-ane release.

It may be presumed that this temporal distributionof carbon isotopic composition reflects changes in the

quantity of seeped methane. If so, the finding is in line

with that of other studies that consider methane seepage

to be a viable explanation of temporal changes record-ed by shifts to more negative foraminiferal 6''C values

(\flefer et aI. 1994:' Kennerr et aL. 1996). On the otherhand, according to Williams et al. (2002) in a study on live

(rose Bengal stained) foraminifera associated with meth-ane seeps in the California Margin off the Eel River and

in Monterey Bay, the carbon isotopic signatures of ben-

G. Panieri

thic foraminifera were not in line with the very negativemethane-influenced values of the pore water, while thepresence of methane affected instead the carbon isotopicvariability between seep foraminifera (2.9"k" measured

for Globobulimina pacifica and ca 1.95o/oo for Uvigerinaperegrina). Be it as it may, the results of the present studyagree with Sen Gupta et aI. (1997) and Rathburn et a1.

(2000). According to these authors large excursions of 3

to 4"/oo in isotopic signatures for the same species livingin the same area over a short amount of time are evidence

of methane effects.Considering that the Gavelinopsis lobatulws calcite

test record methane in sediments, it is difficult to explainwhy only this species shows negative carbon values. Theinterspecific differences among taxa in the same intervaiare difficult to explain. Ir is also interesting ro note rhatGaoelinopsis lobatwlus has an epifaunal habitat, while Cas-

sidulina carinata and Bulimina marginata have a shallowinfaunal one. According to McCorkle et aI. (199a, D97)the ò'rC values of epifaunal species (i.e., those species thatlive on or within the upper 1 cm in the sediments) reflectthe òrrC values of the bottom-water DIC, whereas thoseof infaunal species (i.e., those species capable of livingdeeper in sediment) reflect the more negative ò"C valuesof pore waters. But the results of the present study didnot confirm these conclusions at all. In fact, the more de-

pleted carbon values were reported for the epifaunal spe-cies. As borne out by previous studies (Voodruff et al.

1980; Grossman 1984; McCorkle et al. 1990; Loubere etal. 1995; Rathburn et aI. 1996), the differences in isotopiccomposition among benthic foraminifera taken from thesame interval may be reasonably assumed to depend ona number of joint causes such as viability, microhabitat,food preference, and vertical movement within the sedi-ment. Be it as it may, the relationship between the isoropiccomposition and ecological behaviour of foraminifera is

still. however, an open queslion.According to DeNiro & Epstein (1978) the ò''C of

foraminiferal calcite formed from metabolic CO. may be

strongiy influenced by the ò''C of the food source. Zahnet al. (1986) conciuded that the "habitat effecr" mightalso strongly influence the carbon isotopic signature ofbenthic foraminifera, and seasonal movement has been

Benthic foraminifera response to methane release

observed for some species inet al.1992).

557

the Adriatic Sea (Jorissen

6''O values for Gavelinopsis lobatulus, Buliminamarginata, and Cassid.ulina carinata were found to be

usually invariable throughout the core. The values are inline with the literature (Rathburn et aI. 1996) also for theAdriatic Sea (Asioli 1996).

Comparison between carbon and oxygen isotopepresent data suggests that no relation can be determinedand it is unlikely that the two isotope systems are con-trolled by independent factors.

Conclusions

The following conclusions may be drawn fromthis study.

(1) Several species of benthic foraminifera live insediments in proximity to methane seep sites in the Adri-atic Sea. The species are cosmopolitan and not endemicto these particular ecosystems.

(2) The chief response of the foraminifera to hy-drocarbon presence in sediments of the analysed sites was

a drastic drop in density and diversity H(S).(3) Additional proof that foraminifera are capable

of living and growing in hydrocarbon seep site sedimentswas the negative carbon-13 shifts recorded in the species

examined, especially in Gaaelinopsis lobatulus.(4) Isotopic results showed that the carbon iso-

topic signatures of benthic foraminifera provide/afforda useful record of methane release events and hence ofseep activity history.

AclenowLedgmenrs. I wish to thank Barun K. Sen Gupta and PaulAharon for useful discussion, Roberto Barbieri for comments and a care-

ful rer.ier. of earlier r.ersion of the manuscript, Sara D'Onofrio for dis-cussions on species identification, Teodoro Ricchiuto and GeochemicalLaboratory of Agip for several isotopic analyses, and Giovanni Valdròfor diffractometric (XRD) analyses. I also thank Sih'ia Spezz-aferri andRodolfo Coccioni for their helpful reviews of the manuscript. The mr-terial was kindly provided by Giovanni Gabbianelli through the cour-tesr. of Pìetro Vittorio Curzi. This research was partially supported byMURST er 60% (Giovanni Gabbianelli).

558 G. Panieri

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s60

Number ofbenthic foraminifera from GABlcore samples

G. Panieri

Depth (cm)

A mma n ia b ec cari i Linnae$

Annonia peilucida (Heron-Allen & Earland)

A mmo nia tep ida (Cnshman)

A mp h i c a ry n a s c ú | a ù' (B atsch)

A ngu lo ge rina an gu los a (Williamson)

A s te rigerínd ta nan il la (Willìarnson)

Ast e ù ge rína ta p I ano I b is (d' Oîbigny)

E igener í no nodos a r ia d' Orbtgny

B ilocul i n e Ia glo bu la (B omemanr)

B ilo& t in e l I d I ab ìdta (Schlumberger)

B o lirina a I bat ro s s i Cr$hman

Bol iv ina pseudopli cota Heron,Allen & Earìand

B o l iv i nú pun ctata d' Orbi gny

B o I tu ina su b spin e s ce ns Cnshtaan

B r iza I Ìna ala ra (Segtenza)

B rizal ì n a dilatah (.Reúss)

B rízal in a spa t hu lat a (W illiamsoa)

Buccel la granulata (di Napolì Alliata)

Bu I iùín a el a ngat a d' Orbigny

B u I imína e Ínea Se4uetza

B u I imlna nar g in a ta d' Orbigny

B u I inina su b l imb ar a P anizza

Coss idu I iù d car inat a Sil\ esú

Caes iùl in a c ras s a d' Orbigny

Co r nu s píra ín vo lv e ns (Reuss)

C r i b roe lph idium a ft ícillalan (d'Orbigny)

C r i brce lp h i d iu n decip i e ns (Costa)

C r i b ne lp h idin m gr a nosrm (d'Orbigny)

E lp h idiu n at1 ve nu m (Cushman)

E Ìp h itl iu m cr ispu m (Linnaets)

Elphídium macellum (Fichiel & Moll)

E p is ro míne I I a erigu a (Brady)

F ìs su r i na ap icila ta (Reuss)

F b sil r ina c.ts tanea (F lint)

F it sil r ina p s euda r bí gnyaza (Buchner)

F is su h na s rap hyilear i a (Schw ager)

Fu rs en ko in a st hrei be r s iana (Czjzek)

G ayel in ops is lo b atu lus (P aft)

C lo bocas s ídu | í n a s u b g loóosd (Brady)

Hanzm aia bou ean a (d' Orbigny)

Haynesina depressttla (Walker & Jacob)

Hd y n e i i n a g er tn a n i c a (Ehr etb ery)

Hya I ínea b a lt hic a (Schr oeter)

La gena úríaf d (d' Oîbigny)

Lobatula lobahtla (Walker & Jacob)

Me la n is bar leea num (W illtamson)

Miliolids

Mi I ia I in e I la s u b n ta nda (Moilta,èt)

N e oc o n a rb i na k rq u emí (Rzehak)

N o n io n e l l a xr rgida (W rlliamson)

O o I in a hexago na (W illuamson lP lano úù | in a nedi ter r arensn d'Orbigny

Pu I I enía q ua d r i lo b a Retss

Py r go bu l I o ìt1 * (d' Ot6gny)

Pt rya a b lo nga (d' Orbìeny)

Qu in que lo cu I i na ú sp erula Seguenza

Qu í n q ue lo cu I ì na b ic afi nard d'Orbigny

Qil ì nqù e lo. u lí na í n a equaln d'Orbigny

Qu in qúe loLu I i na paLia n a P ercontg

Quinq uelacu lina seniúrlril (Linné)

.Re"sse//d .jP t,,/.,sd (Reuss)

Rosa lino glohularis d' Otbi9ny

S igna i I in ha t e nu is (Czjzek)

Sigma ilops is elota (Costa)

Signo ilopsÚ schl u nbe rgel, (Sjlvestri)

Sip horexht lar ia aflìni s (F ornasini)

S p ir a I oc u I ìn a c a n d I iL u I a/ú d'Orbigny

Sp i to p I et tanm í n d w I i glli (Silvesti)

Spircpthdl mldiun acuîimaryo encara (W iesnei)

T6 tulari o ac icu ldtù d'Orbi9ny

Terlu lar i a sag útul a Delrarce

Texril lario roldan iì F omas;ri

Urigerina ne.1i leffdned HofKel

Others

Tolal specimens counted

(s)

H(S)

Microfaunal densiry

L2

4

I

22

I

31

2

1t

29

2

t2

I

1

l

13

28

3

I

1

2

7

5

3

1

l

z2t54166t28644t8 13 28

Ì

I

tlI

421314 Ìt 12

z

44 30 3l

54235 34 30

l0 8 ls

I

25 16 25

18 23 19

5349127

3117

tlz5

1

l

2

I

4

l0

2

I

I

1

76l7 13

4134

2

56l

997l

22I

t

Ì

I

l

31Ì3 8 13 6

5 1 9 l0

t0223l111253

rt5lt3l3l1810221 I

122

3t3rl52651

310 314 322 304

46 4t 47 48

3,28 l.l9 3,39 3,33

21t9 3413.04 3500 1471

Appendix - Number, roràl number of ben-thic foraminifera counted, (S),

H(S), and microfaunal densityfor benthic foraminiferal raxa

in the '63 micron size frac-tions from GABI, GAB2 and

GAB3 cores.

t2

I

12

2

11

I

I

212I

42841

4 6- 3

1

l3

4

43

4

3

L

30 33

5 lt32 46

6',75t

38 l9 15

18 2',7 24

153128l4

I

I

131I

8 24 18

z0 12 12

222rll

8

2

ll21

t3 5

21

6

433

2315

2

4l

llt0

2

2

i

5

2

I

2

2

n2

20

2

I

6182127 t5 t0

12

2

t421

2

,7

4122t4 I

294 312 126

49 45 43

3,30 3,35 3,24

6t25 5319 l2ó0

Benthic foraminifera response to metbane release

Number ofbenthic foraminifera from GAB2 core samples.

561

Dcpth (cml

A I a ba m i n e I la wedde I I ensis (Earland)

A milonía beccdrii Li\naers

4nnnn'2 pa,J,',,7o 1r" on-Allen & Ealmo)

A m no n i a tep ida (Cushnan)

Amp hico ryna s u I aris (Batsch)

A ngu lo ger i na a ngu lo sa (Wìlliamson)

As te ríge rína ta mami I la (Williamson)

As te rige r i na ta p lano r bis (d'Orbigny)

A s tra no n ion s I e I | íge ru m (d'Orbigny)

B i ge ner in a no da s ar ia d' O(bi gny

B i I oat I ine | | a gl o bu I a (Bomenann)

B i l a cu I ineil a I a b i ara (Schlumbe€er)

B o I iv i n a su b spínes ce ns Ctshmat

B r iza I ina di I atat a (Reúss)

B r iza I ina s p at hu la td (W tlltatnson)

B ilc c eila gran u I ata (di Napoli Alliata)

Bul imì na etnea Segtenza

B u I i m i na narginata.J' Orhieny

B ul im ina su b I i m b at a (P ^n;zza)

Casr idu I in a c ar i nata Slly esúi

Cas s í du I in a c r as s a d' Orbigny

Co mu: p it a lnyo lyen s (Re[ss)

C r i b r oe lp hid iu n a r t icu lanm (d' Orhigny)

C r i b ro e lp hid iu n dec i p i ens (CosIa\

Cribrcelp hi diun grdnosaz (d'Orbìgny)

E I p h ì d i u m a d v e n u n (Ctslttut)

E lp h ì díum c r i spu m (Linnaers\

Elphidiun úacellum (Fichtel & Moll)

E p is ro m ine I I a exíEu d (Brady)

F í s s ur iùa mar gí nata (Montagù)

F is s ur in d ps eudor b i gry)ard (Buchner)

Fìs,tu rind staphyl ledrid (Schwager)

G a v el in op s ís I o b a tu I us (P ar)G la bocass idu lina o bl a nga (Reùss)

G lo boc a s s i du I ina su b g I oòosa (Brady)

G f r a i d i n o i.1e s úúbo n atrs (Silveski)

H an za w a i a bou ana (d' Orbì gny)

Ílqlne.îina depressula (Walker & Jacob)

H a y n er ì na g e m a n i c a (Ehr enb eî gJ

H! a I ine a b a h h ica (Sclroeter)

Lagena sulcata (Walker & Iacob\

Lobatuta lobatula (Walker & Jacob)

Mel on is ba r I eeanun (\4 ìlliamson)

Miliolids

Mi I io | í ne l I ù su bro tund a (M onfa9n)

N o nio ne I / a tu r gída (W il1ìamson)

O o I i n a hem go nd (\N illiamson)

P [a na r blt I i n a med i t e r ra"e"rts d'Oibigny

P s eudoc lavu I i na c rus tard Cushman

Pu I len i a qn i nque loba (Re$s)

Pyr go bu I I o i des (d' Orbigny)

4t rga o b I o n ga (d' Oîbigry)

Qu i nq u e I ocù I i n a as p e rula Seguenza

Quí nq ue la c ul iila i n a eq ualls d'Orbigny

QLt I n q ue lo c u I i n a p ad a n a P erconig

Q u i n q u e 1o c u I i na s em ì nu lu n (Linné )Rersselld s/i"r/osd (Reuss)

Rosa I i n a g I o hu I a ú s d' Orbigny

Signa il ina s igno idea (Bftdy)

S i g n a i I in úa I en u i s (Czjzek)

S igno ilopr i s ce lata (CosI^)

S ìgnoilops i s sc h lu nbergeri (Silvestri)

S i p h o tex I u I o t i a a/li n í s (F otnasinl)

Sp i r i I li na v irìpata Etuenbery

S p í ro I oca ! in.r u n a I i c n I ald d'Orbigny

Sp irop le. tomm i na ||ù gl?/i (Silvestrì)

S p irop t h a I n i d i u m a cur i md rgo co nc aya (\N tesner )

Textu lario acicltÌ a ta d'Orbigny

Terîu La / ia s agì ttu l a Defiance

U v i ge fi na n ed i Í erra n e d H ofl(e(

Y a hu ! i n e r i0 h r ady a n a (F ornas;nj)

Others

Total specimens counîed

(s)

H(S)

\,4'crofàuî"1 de ì.iì

I

3tl 3

I

52'1 65308 300 301 306 312

40 42 45 44 42

3.24 3,18 3,20 3,2r 3,15

I12I 2114 23 Ì5 2000 I t56

4

2

t

I

20

2

5

I

I

2/

I

22

tl33

2

2

2

3

1

I

33

9

43

19

I

l

1

4

l1

I

2

3

42

1

32

t6

2

l8

ll1

I

t

3

I

\7

l

l

5

t

l

il7

l5

2

l

t

I

Ì

5

6

4

3

IO

2

I

I

4

2

3

300

46

l,l34167

32

3

It0

3

30

8

38

32

I

i5

30

6

3

5

3

15

1

2

l

5

4

1

4

I

3

I

I

I

I

2

2l23

l3

2

Ì0

2

I

2

4

15

2

5

2

l3

I

32

9

26

28

9

3

17

2

5

3

lt6

3

3

6

ó

5

26

2

I

1',l

21

t9

8

9

I

1

2

9

3

32

t0

l6l3

I

23

23

8

1

3

12

I

34

2

39

l6

4

18

l81l

1

I

1

6

2

20

t5

40

27

2

Ì

9

2

t

12

l

,7

8

31

8

39

29

4

1

19 20

32 2r

I I t2

4t

I

2l

16 ll

44t2ttI

4321'7 11

5t2l

1

I

6

2

3

l4

3

'7

I

2

l

t

6

)

l1

3

I

12 t0

32

I

ll

2

I

3

t4

3

I

t5

I

t

E

I

I

6

2

2

3

8

6

t

2

I

I

4

3

l0

,7

6

3

2

3

l

ll

42 4l3,15 3,18

3242 2341

I

302

47

2378

562 G. Panieri

Number ofbenthic foraminifera from GAB3 core samples.

Defrh (cm) r00

Anmonìa be.carii Liúaers

Anma n ia pa t kinsonìand d'Orbigny

Annania perluci.ld (.Heron Allen & Earland)

An na nia tepidd (Ctshmai)

A tnp h it oryn a s t:a I ar i t (.Batsch)

A n gú lager inu angul osa (Willianxon)

A s teri ge i nata nanill a (Williamson)

A stefi ge ti nata planorb ir (d'Orbigny)

Astronon ian s te I I i ge r11n (d'Orbigny)

B i ge ne t i no n o do s ar i a d' OÍblgny

B i I oc u Ì ì n e I I a g I o bu I a (Bonemann)

B o I i v i n a a I bat ro s s i Crshman

B a I i ú ttu \ u b s p i n e, c e n s C$hm!t1

Brì zd li n a di Io tdta ( Rer6s)

Brizal ina spathu latú (\N tllinnson)

Btrct el la granula ta (di NapoÌi Alìiata)

Bulinina ehea Segrcnza

Bu lin in a margindtu d'Otbigny

B u I i n i n a s u h I i n h a t a (.P

^nizzà)Cds s itlu I i n a & r i na I a Stl\ eslîl

Cd.rsi.{/ilrd ./a.$d d'OÍbigny

Cornrrpira irrohers (Reuss)

C r i b ro e lp h ì d i un de. i p i e n s (Costa\

Cri brae I ph i dìrm gruno.v/r? (d'Ofbigny)

El phldù! n adve n u tn (Cùshnan)

E I p h idiu m u 6 pu n (Ltnnaevs)

Eryhír1ùtm ndcellun lFichÌcl & Moll)

E p i s to m ine I I a e x i gù a (B ndy)

Fìssurina apiculdta (Re$s)

F ìs snr inLl mdrgi natd (Montagt)

l- ì s s u ri n a p s eud a r b i gnlana (Buchneù

F i ssLt I i na rdphyll earì d (Schwaget)

Gave I i nop: is la hdhl us (Pan)

G I a boess i rlù | i nct sil bgloòora (Brady)

G)'to i.1 ina ìdes il nbonatrr (Silvestrì)

Hanzawaia houeana (d' Orbrgny)

Havnesina deprevuld (Walkcr & Jacob)

H a), ne s i na ge m a n í c o (.Ehteiberg]'

Hya li n ea balrhi( a (Schrcereî)

Lagena apiopleura Loebììch and Tappan

Lagend st idtd (d Otbtgny)

adger./ rrlcdld (WaLkcr & Jacob)

Lobatula lobantla (.\\alker & Jacob)

Me ! o n i s h a r l e e a n u n l\N rlliamson)

Miliolids

M ì l i o I in e | | a s il h r o ht n da lMoiagu)N o n i a ne I I a tu r f: i d a (W illiamsor)

Oolird &ci.rgora (Wiìliamson)

P la no I hu I ì na nedi terrunensis d'Orbigny

P:euLlo( laru lin d trus lal4 Cushman

P yrgo o h I a n ga (d' Orbtgny)

Qu i nq ùel otil I i na aspetrla Seguenza

Qil i nqilel ocu I i nd inae.t lrdltr d'Orbigny

Qu i nq ue lot u I ina o hl o ngr (Montagu)

Qu in q u e I ocl! I i n a p a.l o n a P eîcontg

Quh q uelo.u I ina \ em ì nu lt1 h1 (Linre)

Reassel/a rpirrlosa ( Reuss)

Rosú I i nu glo hu lúr is d' Othtgùy

Signoì | ì n i td ten u i ! (Czjzek)

Sigmoibpsìt elata (Cosra)

Signo i lapt i s tch hùn hergeri (Sihestri)

S iphotexru laria allì n i t (F onastni)

Spi li I I ino tìr i pd ra Ehreibery

Sp ilIil ocù I i nu ca nd I i c u ldld d'Orbigny

Sp il oplectamtn i na v ri ghri (Silvcstri)

Sp i ropt hd I n idi ù n atu r i n tt rgo con cava (\N tesrcr)

Textil ldr id oc ic il | oîa d' Orbtgtly

Terîu I drid s dgi I tu I d L)eÍiaìce

Tt ì I acil l i na tr itarinatd d'Otbtgny

Uv igerina n?di terran ed HolKer

Otbers

'Iotal specimens counted

(s)

H{S)

I

5

)l

86 lll

t9

l1)

2

4

I

I

812991101

4423511

1583l

l

I

t0 8 19 l1

36313 8 l0 7

887tli2

lÌ

l

L

I

3t9 15 1 1

85756422ll

I 5 t6

52lt

1119 l,l 13 19

lllli15

ll

I

I

l4

l

I

l

2

l

33

l0

43

9

2

t6

2',7

3

5

l

i

I

3

,1

4

l

1

l3

2

ll3

I

I

5

2

)2

2.2

tÌ3E

t0

9

28

l9

5

3

3

4

1

9

4

2

I

I1

I

21

9

48

28

1

23

t2

8

6

4

3

1

2

9

I

I

l

I

t8

I

I

Ì

2

30

22

2

25

l3

4

3

19

29,7

5

5

I

3

I

8

29

2

l

2

I

l0

I

8

2

32

I

I

tò

\'7

2,7

lI

I

L

2

4

5

I

38

t0

60

36

t8

l8

1

2.

7

4

2

3

2

1

38

6

49

21

ll0

t8

5

5

2

ll33030020121996

l

12

l2

2

1

11

I8

2

l

2

2l

I

4

3

f

34 33

4555 58

25 19

3

17924 12

ll423l24ll

28

5

36

3

1l

1',7

Il

2

5

9

1

l06

42.

5

I

l

3

l5

2

28

9

43

11

20 12

3t9 14

832223

51219 15

10934tl

I

2

22574r0ll

1

,7

3

il5

I

2

2

I

2

8

5

7

5

2

L2

2

8

I

l5

6

4

I

l0

)

10

I

4

1

l

2

3

l1

I

2

L

I

1482).

l0

1l I

21

ll12 15

I

1

I

2t34'/13Ìl308 325 304 313 335 308 329 313 315 361

43 48 1't 14 19 42 13 44 41 4'l

3.26 3.42 3.25 3,23 3,24 r.l3 3.19 3,24 3.26 3,15

307 :09

42 4l

l.r3 3.12

Microfaunal densitv 68,14 4514 4903 3130 3384 .1338 ,1700 4113 2242