Palaeogene Macrofossils from CRP-3 Drillhole, Victoria Land Basin, Antarctica
Istituto cli Gcologia Marina. Consiglio Na~ionale (Idle Ricerche. via Gobclli 101. 1-40129 Bologna - Italy
~nstitutc of Geological & Nuclear Sciences. P.O. B o x 30 308. Lower Hutt - New Zealand Received 5 March 200 1 : accf,p/ec/ in rcri.sed form 3 July 2001
Abstract - C R P - 3 cored Palaeogene strata to 8 2 3 metres below the sea floor (mbsf). before passing through Devonian bedrock (Beacon Siipcrgroup) to a depth of 9 3 9 mbsf. Palaeogene body fossils have been identified at 239 horizons in the core. The best preserved macrofossils from the core help elucidate the taxonomy.
chronology and biogeography of Cenozoic ecosystems of Antarctica. although poor p r e s e r v a t i o n p r e v e n t s i d e n t i f i c a t i o n to s p e c i e s level in most c a s e s . T h e l i t h o s t r a t i g r a p h i c unit ( L S U ) o f t h e c o r e t o p ( L S U I . I ) c o n t a i n s an a l m o s t inonospecific modiolid assemblage, similar to mussel beds recovered in the bottom part of the CRP-212A core. These semi-infauna1 mussels appear to be conspecific,
apparently indicating the same age (Early Oligocene) and environment, i.e., a deep muddy shelf characterized by high turbidity and dysoxiclanoxic bottom conditions (high H,S sediment content). L S U 1.2 contains reasonably diverse assemblages representing innerlmiddle shelf environments dominated by e p i f a ~ i n a l suspension feeders. LSU 2.1 contains low-diversity assemblages of suspension feeders (bivalves. brachiopods and bryzoans), probably indicating innerlmiddle shelf environments. LSU 3.1 contains assemblages including infaunal and epifaunal suspension feeders (bivalves, including a scallop, ?Ada/71;(ssium n.sp.. and solitary corals) and infaunal deposit-feeders, possibly indicating deposition on a deep muddy shelf. Both the coral and the scallop previously have been recorded from Oligocene to Miocene rocks in Antarctica. Inner to middle shelf environments a r e suggested by macrofossils in L S U 5 . 1 . mostly infaunal and epifaunal suspension-feeding bivalves. A similar environment is suggested for L S U 6.1, which contains epifaunal scallops and gastropods and infaunal bivalves. LSU 8.1 contains a relatively diverse macrofa~ina of infauna1 suspension feeding bivalves and semi-infaunal/epifaunal gastropods, probably indicating middle shelf environments. ?Aclc~m~~,~sium n.sp. occurs lowest in LSU 8.1, establishing an Oligocene age for CRP-3 down to 320.43 mbsf. One poorly preserved gastropod at 359.07 mbsf indicates marine deposition for LSU 9.1.
The only ~nacrofossil below this is one modiolid mussel in LSU 13.2. The species apparently is different from that observed i n the top of C R P - 3 . An Eocene age f o r this mussel is possible but uncertain. T h e presence of relatively warm-water taxa in the diamicton-dominated part of the CRP-3 core indicates that these taxa did not become extinct abruptly with the onset of Antarctic glaciation, but progressively decreased in diversity as sea-temperatures gradually decreased.
INTRODUCTION
CRP-3 hole, drilled at 77.01 1° and 163.640°E about 12 km east of Cape Roberts, in the Ross Sea, r e a c h e d 9 3 9 metres below s e a f l o o r (mbsf). w i t recovered a thick Palaeogene (Oligocene-?Eocene) succession capping Palaeozoic (Devonian) rocks of the Beacon Supergroup (Cape Roberts Science Team.
2000).
239 macrofossiliferous horizons have been identified in core from CRP-3. Horizons initially identified at the C a p e R o b e r t s L a b o r a t o r y w e r e inspected in the Crary Science & Engineering Center at McMurdo Station. Macrofossil material not suitable for further palaeontological investigation was either sampled for geochemical (oxygen and carbon stable isotope composition, Ss-chronology) and diagenetic studies or stored to be shipped to the Cape Roberts
Project c o r e repository facility in Bremerhaven (Germany). Macrofossils suitable for more detailed palaeontological study were cleaned at the Crary Science & Engineering Center at McMurdo Station using dental tools and delicate specimens hardened using a solution of water and dilute PVA glue.
This report is based on a selection of the best preserved and most identifiable body macrofossils.
Even so, most fossils are minute, highly fragmented andlor highly decalcified, and their poor preservation state made their identification challenging. As in previous reports on CRP macropalaeontology, many taxa from CRP-3 have not been identified to specific or even generic level. The collection is temporarily retained as a d i s c r e t e entity in the Institute of Geological and Nuclear Sciences, Lower Hutt.
Macrofossils are common in the Oligocene section of t h e core, providing further palaeontological
"Correspondiq author (taviani@igm.bo.cnr.it)
doc~imentation of marine macroinvertebrates for this epoch in Antarctica. The CRP-3 drill core adds new data to the growing palaeobiological information for the Oligocene epoch in Antarctica, which combines results from previous drilling operations in the Ross S e a region: DSDP Leg 28 (Dell & Fleming, 1975).
CIROS-1 (Beu & Dell, 1989). and CRP-212A (Taviani et al., 2000) and from erratics at McMurdo Sound ( l Iarwood & Levy, 2000: Stilwell & Feldmann, 2000).
A few CRP-3 macrofossils, however, originated from sedin~entary units of uncertain age and depositional
environment low i n the core (LSU 9.1 a n d l . \ . ? ) , U i c s e m a y prove to be o f d i a g n o s t i c v ; i I ~ i t , ,
considering the overall scarcity of palaeontoloi~ic~al information in the lower past of the core.
TAPHONOMY
D i a ~ p n e s i s . Most carbonate is in an advancril stage o f dissolution (Cape Roberts S c i e n c e 'l'i-iiii~.
2000). I n general, only calcitic fossils of peelini(1
S i l l sand travel
. . . .
. .:.
. . .
-,.A
6. Br>ozoan
7>.
~ e a f -. . . . . . .-* * * * . P--:-
- -
$SO-'.. .:. 1 ,
-: ;
-
.:. . *... :L- . . . . . . .: - - L.' . . . . -+. . . -. - . . . . - . . .
j O O Ã ‘ . ' . . " KEY
""'7 Clam
. 0 Scrpuiid ^' Echinoid ,F-, . Cirripcd :;, Plant
'CG fiagment
Fig. 1 - Litliostratigraphical summary of the CRP-3 drill core showing position and composition - . of the major macrofossil assemblages (slightly modified from Cape Roberts Science Team. 2000).
I'c~lacopcn~' Mcicrolossi Is from ('RP-.! Drillholr 425 bivalves (i.e.. ?Aclamussiuni n.sp. ). worms (scrpiil id
polycliaetes) and ecliinoids are well preserved. Most aragonitic bivalves and gastropods show advancecl decalcil'icii~ion and are represented by moulds. some of which retain a veneer of chalky carbonate. Shell breakage ;ind fragmentation is common i n the CRP-3 core but we are unsure whether i t is mostly linked to skeletal dissolution (as we suspect) o r to rev,!orkiiig.
CaCO:; concretioning has been observed around bivalves and gastropods at 141.20 a n d 359.07 mbsf a n d i n the sediment matrix infilling serpulid polycliiicte tubes (e.g., at 3 8 . 5 3 mbsf). Pyritized moulds o f bivalves occur in LSU 1.3 at 64.42 mbsl'.
8.1 as uni~len~ii'iecl bivalves (Cape Roberts Science 'I'eani, 2000). Barnacles (('irripedia) have only rarely been reported from the CXeno/.oic of Antarctica (Zullo
ct i l l . . 1988: Biickcridgc. 2000) ;ind the S~ibantarctic
(Carriol ci (it., 1992: (iirct et al.. 1994). The CRP-3 material consists of a very small fi~agiiient of the
~ i i a r ~ i n of a sti.oiigly ribbed shell at 168.39 mbsf.
(presumably a friigment of a barnacle plate. recorded in the Initial Report as "small crenulate shell fragment"), a n d one sm;ill. incomplete but well- prescrvei-1 balanoicl barnacle plate. plus several fragments of other plates. at 308.68 mbsf (recorded in the Initial Report as "many small fragments o f unidentified bivalves").
TAXONOMY
Eight phyla of marine Invertebrata have been identified positively in the CRP-3 drill core. They are, in order of relative abundance, Mollusca, Annelida, Cnidaria. Brachiopoda. Crustacea, Bryozoa, Echinodennata and Porifera (Fis. 1). Re-examination of the inferred Vertebrata (fish remains) recorded in the Initial Report at 406.36 and 406.38 mbsf (Cape Roberts S c i e n c e Team, 2000) reveals that such macrofossils a r e very likely plant fragments.
Macroplant remains were also identified in CRP-3, as leaves (Nothofagus sp.) and stems (Cape Roberts Science Team, 2000, fig. 5.9d, 111) and are discussed in detail by Cantrill (this volume). The organic nature of putative macrofossils from LSU 12.3 (465.77, 509.16 and 533.47 mbsf: Cape Roberts Science Team, 2000) could not be confirmed.
Macrofossils from CRP-3 have been treated in s o m e detail in the Initial Report ( C a p e Roberts Science Team. 2 0 0 0 ) and the best preserved specimens are figured there. The present article offers an updated perspective of the macrofossil assemblages with special r e f e r e n c e to Mollusca, and their ecological and biogeographical significance. Annelida are also discussed here.
Mollusca a r e by f a r the dominant group and include, conservatively, at least 15 species of Bivalvia, 6 o f Gastropoda and 1 of Scaphopoda. C n i d a r i a (scleractinian corals) are discussed by Stolarski &
Taviani (this volume).
Brachiopoda, Echinodermata, and Bryozoa are under consideration for a detailed systematic study in the near future and only limited information is given h e r e . Brachiopoda a r e represented by a s m o o t h punctate species, presumably a terebratulid, reaching at least 20 mm in height (e.g. 62.61, 121.19 mbsf).
Echinodei-mata are represented by echinoid debris (including a crushed shell) at 44.12, 114.23 and 121.4 1 mbsf. An undetermined encrusting bryozoan partially envelops a l o n e s t o n e at 88.19 m b s f . Crustacea (a group not recorded in the Initial Report) is added to the list of taxa on the basis of barnacle plates previously recorded from LSU 5.1 and LSU
BIVALVIA WUCULIDAE
?N~/cula sp.
- 122.22-1 22.24 mbsf: One very small. articulated, chalky bivalve. hinge not visible.
Remarks: Small Nuculidae occur in the Cretaceous- Palaeogene of Antarctica. including the Ross Sea region (Beu & Dell, 1989; Stilwell, 2000: Taviani et al., 2000).
SAREPTIDAE
?Yolcliella sp.
- 120.34-120.37 mbsf: Incomplete left valve of small, elongate, smooth protobranch bivalve, taxodont hinge visible, aff. Yoldiella.
- 122.22-122.24 n ~ b s f : One small left valve of a s m o o t h pi-otobranch(?) bivalve, shaped as in Ti~iclc~ria, Jupiferia, etc., hinge not visible; outline most nearly resembles those of Yoldiella antarctica (Thiele) and Y. prof~indora (Melvill & Standen) (Dell, 1990, figs. 17, 21).
- 124.93-124.96 mbsf: Several small bivalves, at least 3 valves, smooth, chalky, no hinges visible, but presumably the same taxon as a b o v e ; another smaller, moderately elongate, weakly rostrate, rather thick-shelled protobranch bivalve, also a ?Yolcliella sp., ventral margin strongly a b r a d e d before fossilisation. indeterminable.
- 124.96-125.01 mbsf: 6-7 small bivalves, rather poor and chalky, no hinges visible but apparently all smooth, rostrate protobranchs, the same two species as above (a smaller and a larger ?Yoldiella species).
- 125.18-125.20 mbsf: 5-6 more small fragments of apparently the same, larger ?Yoldiella sp. as in the above three samples.
- 126.40-126.42 mbsf: Two bivalve fragments; (a) from the shape, one is probably ?Yoldiella sp., as above; (b) the other is very small, indeterminable.
- 127.34-127.36 mbsf: One poor, chalky valve of
?Yoldiella s p . , as above, p l u s two s m a l l , unidentifiable bivalve fra_ oments.
Remarks: Members of this family inhiihit cold. deep waters world-wide. including modern Antarctica (Dell, 1990): Yoldiella has been recorded recently from Eocene erratics at Mt Discovery. McMurdo Sound, by Stilwell (2000).
7LIMOPSIDAE
?l^inwpsis sp.
- 200.12-200.14 mbsf: Two fragments of one valve of a relatively thick-shelled, symmetrical, s ~ i b c i r c ~ ~ l a r bivalve with weak cornmarginal sculpture; small area of s y m m e t r i c a l , serrated hinge visible in profile; probably Limopsis sp.
Remarks: T h e small species L i m o p s i , ~ a ~ i f a r c f o m i n ~ / t a has been described from Eocene erratics in the McMurdo Sound (Stilwell. 2000): the extant, large circum-Antarctic taxon L. ~~iurionensis occurs in the Pleistocene deposits of Cape Barne, Ross Island (personal observations).
MYTILIDAE
?Modiolus sp. 1 (Cape Roberts Science Team, 2000, fig. 5.9a)
- 6.80-6.88 mbsf: One decalcified shell.
- 10.80-10.85 mbsf: One articulated mould.
- 10.88-10.89 mbsf: Two articulated, decalcified shells.
Remarks: This species is the same as that recovered in the Early Oligocene sediments of the CRP-212A drill core (Taviani et al., 2000, fig. 6). The muddy lithologies of L S U 1.1 of core CRP-3 contain some articulated mussels, mostly decalcified.
?Modiolux sp. 2 (('iipc Roberts Science Tea111, 2000, fig. 5.911)
- 7 8 1.34-78 1.36 m17sf: One a r t i c u l a t e d , highly decalcified shell.
Remarks: The single specimen (Fig. 2a) rcprt.-senis the lowermost occurrence of marine macrol'ossils in CRP-3. The poorly preserved shell b e l o n g s 1 0 :i
species o f Mytilidac tentatively a s c r i b e d to Mocliolus s.1. Because of advanced decalcil'icatioii, n o important shell characters are v i s i b l e . Some growth lines are evident near the edge of the right valve. The shell consists of articulated valves lying parallel to bedding ( i n a p o l y m i c t i c , coiirse sandstone) but it is difficult to ascertain whether the shell is in life position or has suffered s o m e minor displacement. Comparison with other mussels in Antartica suggests that ?Modiol~i.s sp. 2 is dilTcrent from any other Mytilidae described so far from {lie Cenozoic rocks of Antarctica (Zinsmeistcr. 1084;
Stilwell & Zinsmeister. 1992; Stilwell, 2000).
PECTINIDAE
?AcIamussi~i17i n. sp.
- 2 9 . 9 4 - 2 9 . 9 6 mbsf: Fresh broken v a l v e ( C a p e Roberts S c i e n c e Team, 2000: f i g . 5.913) with auricles.
- 38.8 1-38.82 mbsf: Broken fragment, fresh.
- 41.61-41.63 mbsf: Two fresh, broken valves.
- 47.55-47.57 mbsf: One fragment.
- 83.95-83.97 mbsf: Fragments of a smooth pectinid
(?); no unibo or auricles; apparently ?Adam~/.s.sii//~i
n. sp. as in CRP-I and CRP-212A.
Fig. 2 - M a c r o f o s s i l s from C R P - 3 drill c o r e : ( a ) M o d i o l i d mussel (?Modiolns s p . 2) from 781.34 mbsf; note that the highly decalcified specimen is an articulated shell, slightly gaping (age uncertain: Early Oligogene-?Late Eocene): (b) bivalve-scleractinian assemblage at 140.69 mbsf: CY = articulated carditid bivalve (Cyclocardia sp.), SC = solitary scleractinian coral (FIubelliim rariseptatiim). both probably in life position ( A g e : Early Oligocene): ( c ) well preserved serpulid polychaete tube aggregates ( ? S u p 1 0 sp.) from 38.53 rnbsf: this taxon shows distinct growth wrinkles and rings (arrow).
- 1 14.10- 1 14.22 mbsf Fragments.
- 190.20 100.3 1 inbsl Fragments.
- 308.20 3 0 8 . 2 5 mbsf: One articulated shell a n d fragments (Cape Roberts Science Team, 2000: fig.
5.9i).
- 309.20-309.33 mbsf: Two broken. well preserved valves ( C a p e Roberts Science Team, 2000: fig.
5.91).
- 3 2 0 . 4 0 - 3 2 0 . 4 3 mbsf: Fragment, probably 7Acl11111iixxium 11. sp.
Remarks: T h i s taxon evidently is the s a m e
?Adcuinissium n. sp. as in C R P - l and CRP-2/2A and discussed in detail by Jonkers & Taviani (1998) a n d Taviani et al. ( 2 0 0 0 ) . T h e stratigraphic significance of pectinids in the Cenozoic of Antarctica has been discussed by Jonkers (1998).
Pectinidae sp.
- 3 8 . 8 1-38.83 mbsf: A small fragment (severely damaged during core preparation, less than a quarter of the disc; but 2 0 mm in longest dimension) of an external mould of the exterior of the disc of a strongly radially costate pectinid, shell material chalky; many very fine radial costellae on surface of radial costae. A latex cast confirms that this is from a pectinid with wide, convex-crested costae and narrow costal interspaces.
Remarks: This pectinid has not been reported from Antarctica before (Dell & Fleming, 1975; Dell, 1990; Stilwell & Zinsmeister, 1992; Jonkers, 1998;
Jonkei-s & Taviani, 1 9 9 8 ; S t i l w e l l , 2000) and probably is unnamed, but the material is too poor f o r further coniment. The auricle was abraded off before fossilisation, an indication that the fossil underwent transport or reworking.
PLIMIDAE
?Lima sp.
- 1 6 3 . 6 5 - 1 6 3 . 6 8 mbsf: Part of an incomplete, articulated specimen of a bivalve, perhaps ?Lima s p . ; superficially similar to the narrowly ribbed Cyclocardia sp. that is common above this level, but differs in being ( a ) apparently originally calcitic, rather than aragonitic; (b) larger; and (c) with costae that diverge at a much lower angle, i.e., this specimen originally was significantly taller and narrower than Cyclocardia.
Remarks: If confirmed, this is the first record of Limidae in the Oligocene of Antarctica, although t h i s family is known f r o m L a t e C r e t a c e o u s (Zinsmeister & Macellari, 1988) and Eocene beds of Seymour Island (Zinsmeister & Stilwell, 1992;
S t i l w e l l & G a z d i c k i , 1 9 9 8 ) , a s well a s from Pleistocene deposits of McMurdo Sound (Cape Barne: Speden, 1962; and personal observations) and the Ross Sea (Taviani et al., 1998). Limidae are also among the most conspicuous elements of the Recent Antarctic shelf fauna ( e . g . , Bullivant, 1967; Dell, 1990).
I ,D("lNll)AIi 1 ,t~cini(iiic spp.
- 190.90 197.02 nibsf.: One small piece ol' an incomplete valve (umbonal area lost during core prepai'ation) of a fairly thick-shelled. weakly inf'hilcd l~ivalve with a n almost circular shell and prominent, narrow. widely spaced cornmarginal amcl lac; possibly the lucinid Liicinoma.
- 127.84- 127.87 mbsf: One very poor, chalky, weakly inflated. s~iperficially smooth, s~~bcirculai-, irticulated bivalve, Lucinidae?, not determinable.
Remarks: Lucinids (Sa.voliicinu, Miltha) previously have been recorded from Eocene rocks o f the Antarctic Peninsula and McMurdo Sound (Zinsmeiste~-, 1984; Stilwell & Zinsmeister, 1992;
Stilwell, 2000).
CARDITlDAE Cyclocardia spp.
-
6 . 4 8 - 6 . 5 1 inbsf: O n e chalky fragment from a radially ribbed, subtriangular bivalve, probably Cyclocardia sp.- 120.34-120.37 inbsf: C\clocardia sp., with narrow, well defined radial costae, as in CRP-2/2A (Taviani et al., 2000), one small valve.
-
120.43-120.47 mbsf: One fragment of a fairly thick shell with prominent radial sculpture and weaker commarginal sculpture; presumably Cyclocardia sp.- 120.58-120.60 mbsf: Two fragments (part and counterpart of one fragment?) of Cyclocardia sp., as above.
- 120.60- 120.62 mbsf: One slightly incomplete valve of Cyclocardia sp., as at 120.34-120.37 m, and probably the same as at 120.58-120.60 inbsf.
- 1 2 1 . 1 9 - 1 2 1 . 2 2 mbsf: O n e small fragment of a coarsely radially sculptured bivalve, probably C\clocardia.
- 121.23-121.27 mbsf: Cyclocardia sp., as above, and as at 120.34. 120.58 and 120.60 inbsf, one fairly complete (but very chalky) valve, one incomplete
"merits.
articulated pair (chalky), and a few fra-
- 121.29 mbsf: Cyclocarclia s p . , a s above, one articulated but opened pair (part and counterpart on broken faces of core) and one good fragment with relatively undisturbed sculpture.
- 121.49-121.51 inbsf: Cyclocardia sp. (as above), one articulated pair, sawn through in preparing core;
shell chalky.
- 126.48-126.51 mbsf: Fragments of one valve of a narrowly ribbed Cyclocardia sp., as above.
- 126.66-126.69 nibsf: Fragments of two valves of a narrowly ribbed Cyclocardia sp., as above.
- 127.84-127.87 inbsf: O n e fairly good but very chalky, articulated specimen of Cyclocc~i~dic~ sp., as above.
- 128.58-128.60 m b s f : One small fragment of a narrowly ribbed Cyclocmlia.
- 1 3 6 . 3 5 - 1 3 6 . 3 8 m b s f : O n e very chalky, poor, incomplete, articulated specimen of a narrowly ribbed C\clocardia sp.
- 1 37.33-1 37.35 mbsf One small, chalky fragment of a narrowly ribbed C\cli)c.tirclici sp., as above.
140.02-140.04 mbsf: Fragments of the umbonal area of a chalky, articulated specimen of a narrowly ribbed Cyclocc~rcliu sp.. as above.
- 140.11 -140.14 mbsf: One poor, chalky fragment of a narrowly ribbed Cyclo(~~rclic~ sp.. as above.
- 1 4 0 . 6 9 - 1 4 0 . 7 4 mbsf: Fragments a n d shells (including articulated ones) of 7-8 specimens of the narrowly ribbed Cyclociirdia s p . ( F i g . 2 b ) . a s above.
- 140.79-140.8 1 nibsf: One chalky, poor valve (and fragments from the same specimen) of the narrowly ribbed Cyclocardia sp.. as above.
- 1 4 1 . 9 2 - 1 4 1 . 9 5 nibsf: Part of o n e very poorly preserved. chalky valve of the narrowly ribbed Cjclocardia sp., as above.
- 165.66- 165.68 nibsf: Narrowly ribbed Cyclocardia sp., as above: one incomplete. chalky, articulated specimen. cut in preparing core,
- 319.97-319.99 mbsf: Poor, chalky fragments of an articulated specimen of a narrowly ribbed bivalve, presumably the s a m e Cxclocardici s p . as is s o common above.
Remarks: Two different species seems to be present of the cosmopolitan genus Cyclocardia Conrad, 8 6 7 , which is well represented in the Cenozoic and Recent of the palaeoaustral region, including Antarctica (Hendy et al., 1969; Beu & Maxwell, 1990; Dell, 1990; Stilwell & Zinsmeister. 1992;
Taviani et al., 1998: Stilwell, 2000; Taviani et al., 2000). One species, characterized by a subcircular outline. seems conspecific with Cycloca~dici s p . identified i n the L a t e O l i g o c e n e of CRP-212A (Taviani et al., 2000; fg. 2c); the second species has a more elongate shell (Fig. 2; and Cape Roberts Science Team. 2000, fig. 5.9f).
VENEROIDEA
- 127.94-127.97 mbsf: One very poor, incomplete, chalky bivalve, severely compressed diagentically, apparent posterior-un~bonal ridge probably produced entirely by c o m p r e s s i o n ; w e a k c o m m a r g i n a l sculpture; shape resembles a venerid, but identity not determinable.
- 139.46-1 39.47 n ~ b s f : One indeterminate, chalky bivalve fragment; shape resembles a venerid, but no useful characters visible.
- 197.85-197.86 mbsf: Small fragment of the posterior area of a small bivalve; presence of a weak radial posterior-umbonal a n g u l a t i o n and of l o w commarginal s c u l p t u r e s u g g e s t s t h a t this is a veneroidean, but family not identifiable; appears to be the same taxon as above.
Remarks: Absent from the Antarctic Recent fauna.
Stilwell, 2 0 0 0 ) . An undescribed species ;ilso Ims been repoi'tcd f'rom Laic Oligocenc sediments in ~ l i r ('RP-212A drill core (Taviani et al.. 2000).
?PliRIPI .OMATIDAE iff. P~~i~i/)loiiid sp.
- 62.61-62.69 nibsf: Fragments of moulds (with sonic chalky shell material remaining) of ca. 2 0 nun long. very thin-shelled, weakly biconvex hiviilvr with two valves articulated, and with weak, roundc(t commargiinal folds, aff. Periploma or similar'.' hut n o umbonal area or outline visible. indeterminable.
- 120.34-120.37 mbsf: Fragment of a small. t h i n - shelled bivalve with one valve almost flat, the other more convex.
cf.
Periploma?~ but smaller and morc inflated than usual for Periploma.'1011s Remarks: Taviani et al. (2000) discussed p r e ~ ' records of Pei~iplonui from the Cenozoic rocks of Antarctica, to which must be added t h e rcccnl report from McMurdo Sound erratics by Stilwcll (2000).
7LATERNULIDAE aft. Later~iiila sp.
- 140.69-140.74 mbsf: One large fragment (c(/. 24 m m long) of a very thin-shelled, f r a g i l e ( n o w severely distorted) bivalve with weak commarginal growth ridges (aff. LciternuW).
Remarks: The extant species Laterniila elliptic(/
(King & Broderip, 183 1) is one the most common shallow-water circum-Antarctic bivalves. It also is recorded from a number of Pleistocene outcrops (Berkmann et al., 1998), but the pre-Pleistocenc history of this family is obscure.
7THRACIIDAE
?T/~mcic/ sp.
- 7 5 . 5 4 mbsf: Partial. chalky, crushed, elongate, articulated bivalve w i t h weak comniarginal sculpture, damaged in core preparation, no hinge visible. Indeterminable but possibly Thracia s p . ?
- 76.03-76.04 mbsf: At least three articulated (but all slightly t o s e v e r e l y i n c o m p l e t e and chalky) s p e c i m e n s of a s m a l l ( m . 1 0 - 1 2 m m long).
elongate, moderately inflated (but right valve less strongly inflated than left), weakly con~n~arginally sculptured bivalve, with rounded anterior end and weakly rostrate, truncated posterior end, possibly Thracia sp.?
Remarks: T h e Cenozoic record of Thraciidae in Antarctica p r e v i o u s l y h a s been l i m i t e d to P l e i s t o c e n e r e c o r d s of t h e extant taxon T.
m e r i d i o n a l i s S m i t h , 1 8 8 5 (e.g., S p e d e n , 1962, listing earlier records; Berckmann et al., 1998).
veneroid bivalves were in contrast. common in the Indeterminate bivalves:
warmer Palaeogene waters around this continent Indeterminable fragments (mostly chalky moulds) (Zinsmeister, 1984: Stilwell & Zinsmeister. 1992; of bivalves were recognised at the following depths:
I'alaropcnc Macrol'ossils froin CRP-3 Drillliolc 429
the nacreous internal layer confirms the superfamily this one is even more poorly preserved.
10.88- 10.99 mbsf
(cf.
Macornu, h l e r n u l a ) ; 50.46- 50.48 nihsf: 5 1.20-5 1.23 nibsf; 64.42-64.43 nibsf';8 9 . 0 2 - 8 9 . 0 3 mbsf; 96.27-96.29 mbsf: 94.37- 94.38 inhsf; 98.31-98.33 mbsf ('.' aff. l/nnopxis. but shell thin): 99.59-99.61 mbsf (?Veiicriclac): 1 15.43- l 15.45 mhsf (?Pectinidae); 1 19.08- 1 19. 10 nibsf (;ifS.
Thrcicin" o r Yolclia?); 119.45- 1 19.47 nibsf (aff.
Tl~racici'? o r Yoldia?); 120.75-120.79 mbsf (cu. 8 small (8-10 m m ) bivalves, Y o h i i e l l d ) : 12 1.29 mbsf':
122.22 inbsf: 126.32-126.35 inbsf; 126.45- 126.47 m b s f ; 127.34-1 2 7 . 3 6 inbsf: 127.84- 127.87 nibsf; 128.58-128.60 mbsf (Lucinidae or Veneridac?): 128.64-1 2 8 . 6 6 mbsf; 157.7 1 - 157.75 nibsf; 274.27-274.3 1 mbsf (?Pcctinidae. but with widely spaced commarginal grooves); 308.68- 308.71 mbsf; 3 1 5 . 6 6 - 3 1 5 . 6 9 mbsf (taxondont);
320.40-320.43 mbsf.
SCAPHOPODA DENTAL1 IDAE
aff. Dentalium sp.
- 38.44-38.45 mbsf : Chalky fragments of a straight, approximately cylindrical calcareous tube, now conlpressed. One fragment of exterior shows both irregular commarginal rings (growth ridges?) and longitudinal costae; evidently a scaphopod
Remarks: Scaphopods identified in the Oligocene successions at Cape Roberts (CRP-212A: Taviani et a l . , 2000; C R P - 3 : this paper) a r e all poorly preserved but belong to at least two different taxa, o n e with a smooth shell (CRP-2/2A), the other costate, like the specimen collected at 157.83 mbsf (see below). Scaphopods, including Dentaliz~m, have been recorded previously from Cenozoic beds of Antarctica and Subantai-ctica (Pugaczewska, 1984;
Stilwell & Zinsmeister, 1992; Stilwell, 2000).
Scaphopod. not determinable
- 1 5 7 . 8 3 - 1 5 7 . 8 6 mbsf: Short length of a gently tapering, cylindrical tube, cut during c o r e preparation; not compressed: very chalky. not determinable, but certainly a scaphopod.
GASTROPODA TROCHOIDEA
Trochoidea, family not determinable:
- 198.88-198.89 inbsf: Small fragment of the outer lip and base of a nacreous indeterminable gastropod (PTrochidae) w i t h s c u l p t u r e of numerous low, narrow, close spiral ridges.
Remarks: T h e p o o r l y preserved m o u l d s a n d fragnients of trochoidean shells recorded so far in the Cenozoic successions at Cape Roberts (CRP- 2/2A: Taviani et al., 2000; CRP-3: this paper) are difficult to classify even at family level, although
position. Troclioiilea are among the most conspicuous elements ol' the Recent Antarctic macrofauna (Smith. 1902: Dell. 1990; Hain, 1990) a n d have a continuous record i n Antarctica since at least Eocene time (Stilwell & Zinsmeister, 1992;
Stilwell. 2000).
TURRITELLIDAE
Tiirrifellci (sensii Icito) sp. (Cape Roberts Science Team. 2000. fig. 5.911)
- 3 1 1.25-3 1 1.27 mbsl Fragment, at least 20 mm high.
and formerly >35 m m high and ca. 8-10 mm in diameter, of the interior of a calcitic replacement of a very high-spired, almost flat-sided t~irritellid(?) gastropocl. The large number (6-7) of primary spiral ridges and several orders of secondary and tertiary ridgelets suggest that i t might be a previously unknown genus of Turritellidae.
Remarks: Members of Family T ~ ~ ~ r i t e l l i d a e occur quite commonly in Cenozoic outcrops of Antarctica and Subantarctica. Colposigma euthenici Stilwell &
Zins~neister 1992. is common in the Late Eocene macrofauna of La Meseta Formation, Seymour Island (Stilwell & Zinsmeister 1992). Karczewski (1987) mentioned three species from the Miocene Cape Melville Formation of King George Island (South Shetlands), including the European Neogene Arc11i111edielIc~ cf .s~~bangiilafci (Brocchi, 18 14), a inisintepretation. A turritellid is also recorded from the Miocene of Kerguelen (Giret et al.. 1994).
More recently, two species of Turritellidae have been identified by Stilwell (2000) in McMurdo S o u n d en'atics: C. euthenia (erratics from Mt.
Discovery, Middle to Late Eocene; see Harwood &
Levy, 2000) and Zeacolpiis? sp. (erratics from Mt.
Discovery, age not specified; see Harwood & Levy, 2000) but both appear to be different from the CRP-3 taxon.
7CALYPTRAEIDAE
?Sigapafellci sp.
- 6 6 . 6 4 - 1 6 6 . 6 6 inbsf: Good internal mould of a calyptraeid gastropod, similar to Sigapatella.
Remarks: The single CRP-3 specimen has a taller spire than any Sigcipafellci species w e know of, with the possible exception of S. colossa recently described by Stilwell (2000) from PEocene (age not reported) erratics in McMurdo Sound.
NATICIDAE
Naticidae, indeterminable
- 198.50-198.53 mbsf: Poor, chalky specimen of a naticid gastropod (Cape Roberts Science Team, 2000; fig. 5.9g); not identifiable, but the moderately thick shell and moderately exert spire suggest aff.
Polinices or Amai/ropsis (etc.) rather than Bulbiis (cf. Dell, 1990).
- 3 1 7 . 8 8 - 3 17.92 inbsf: I n d e t e r m i n a b l e naticid gastropod; comments as for specimen above, but
Fig. 3 - Undetermined gastropod from LSU 9.1 at 359.07 mbsf: the original ~nacrofossil is a highly decalcified shell sliced by core splitting and embedded in a coarse sandy matrix: camera liiciela hand drawing (M.T.) elaborated by Alessandro Remia.
- 326.72-326.78 mbsf: Incomplete internal a n d external mould of a large, indeterminable naticid(?) gastropod, ca. >40 mm in diameter, cut through by the drill.
Remarks: Members of family Naticidae have been recorded frequently from the Cenozoic of Antarctica and S u b a n t a r c t i c a (Dell & Fleming, 1 9 7 5 ; Gazdzicki & Pugaczewska, 1984; Giret et al., 1994;
Stilwell & Zinsmeiester, 1992; Stilwell, 2000;
Taviani et al., 2000).
7PYRAMIDELLIDAE
?Pyramidellidae sp.
- 157-76-157.83 mbsf Internal mould of a gastropod protoconch, apparently heterostrophic. possibly
?Pyramidellidae, genus indeterminable.
Remarks: O u r determination is uncertain; this family of ectoparasitic opisthobranch gastropods has an extremely p o o r fossil record in Antarctica (Pleistocene of Cape Barne, Ross Island: Hedley, 1916) and very few modern representatives (Dell, 1990).
Indeterminable gastropods:
- 197.29-197.32 mbsf: Internal view of the spire of a low-spired g a s t r o p o d , poor, very c h a l k y ; indeterminable.
359.07-359.1 1 mbsf: Internal view of high-spired gastropod, very poorly preserved, longitudinally sliced by core splitting (Fig. 3).
Remarks: Not much can be said a b o u t t h i s gastropod (from 359.07-359.11 mbsf) because of its extremely p o o r preservation. T h i s finding i s , however, of some relevance since it represents one
of the few fossils recorded in this part of (lie ( ' R I ' 3 core. I t is important to note that the s[x-cinn.'ii resembles a turritcllid or similar tall-spirctl inariiu' 8 - o ~ i p of gastropods. I t therefore probably i nd i r i i k ~ a marine depositional setting for LSU 9.1.
Mollusca incertue s a i l s
166.64-166.66 mbsf: Part of one v a l v e o f ;\
strange bivalve(?) with a calcitic o u t e r layer (particularly shown o n the counterpart) and ;I chalky (presumably aragonitic) inner layer, a n d with sculpture of low coinrnarginal folds, surface otherwise smooth; the alternative hypothesis of belonging to :I t h e c o s o n ~ a t o ~ ~ s pteropod (such as C a v o l i n i a or
Diacria?) should be also taken into account.
319.09-319.10 mbsf: Another fragment with the same shell structure as above; apparently the same taxon.
ANNELIDA Polychaeta
Calcareous polychaete tubes are scattered within the upper part of the CRP-3 drill core. Reasonably well preserved tubes occur in L S U 1 . 2 a n d 3.1.
associated with predominantly sandy a n d m u d d y lithologies respectively. Possible polycliacke bioturbation is also indicated by burrow-fillings of en.
3-5 111111 diameter (e.g., 50.46 and 62.62 mbsf).
?SerpuIa sp.
- 38.44-38.45 mbsf: Fragments.
- 38.53-38.66 mbsf: Various tubes, well preserved, aggregated (Cape Roberts Science Team, 2000.
fig. 5.14 g and Fig. 2c).
- 50.42-50.43 mbsf: One short length of a relatively large, almost smooth, now severely compressed, thin-shelled, cylindrical calcareous tube; with very fine commarginal growth ridges, but the thinness and finely fibrous shell structure suggest it is a polychaete tube rather than a s c a p h o p o d . Preservation better than at 38.53-38.66 mbsf, shell material pale brown; sulfides in matrix perhaps suggest a different diagenetic history at this level from that above and below.
- 94.37-94.38 mbsf: Two fragments from a mould of a small tube, c a . 2 m m diameter, presumably formerly calcareous (polychaete?).
120.60-120.62 mbsf: One moderately large ( c a . 7 mm diameter) calcareous tube, smooth apart from growth ridges, relatively thin, slightly compressed;
evidently a polychaete tube.
1 2 1 . 0 6 - 1 2 1 . 0 7 mbsf: O n e badly c r u s h e d , cylindrical, smooth calcareous tube, presumably a polychaete.
Remarks: The best preserved material consists of an aggregation of various s p e c i m e n s (>3) at 3 8 . 5 3 mbsf ( F i g . 2 c ) . B a s e d on t u b e f e a t u r e s ,
Palaeogene Macrofossils from Cl<l'-:3 Drillhole 43 1 including raised collars and growth rings, similar to
those of the extant Antarctic species Sprpiilci nan'oi~(~iisis Baird, 1865 (</: Hartmann, 1966; Knox
& Ctiiiicron, 1998), we tentatively attribute this material to Serpula. Serpulid polychaetes, very similar to the CRP-3 tubes, have been identified in Early O l i g o c e n e to Early M i o c e n e s e d i m e n t s previously cored at Cape Roberts (Jonkers &
Taviani. 1998; Taviani et al., 2000).
Serpulidac, indeterminate
- 39.00-39.01 mbsf: Two large, slightly chalky, now slightly compressed fragments of one calcareous.
cylindrical tube, sawn through in preparing the core; this specimen (unlike that at 38.44- 38.45 ni) is smooth externally, and has a prominent, regrown break halfway along; apparently a polychaete tube.
- 4 1 . 8 4 - 4 1 . 8 5 mbsf: Two m o r e f r a g m e n t s of a smooth. compressed, presumed polychaete tube, as above.
- 4 3 . 7 0 - 4 3 . 7 2 mbsf: One fragment of a s m o o t h , compressed, presumed polychaete tube, as above.
Incertae sedis
- 124.93-1 24.96 mbs: One small, circular, calcitic(?) bivalve, or possibly a non-punctate brachiopod bracliial valve, apparently lacking a normal bivalve hinge after careful excavation.
- 165.50-165.53 mbsf: Small fragment of a very small tube, < 1 mm diameter; structure is radially fibrous; non-biological? Perhaps a foraminiferan?
- 324.35-324.39 mbsf: Unidentifiable shell fragment.
- 533.47-533.48 mbsf: Small fragment of a solid, probably cylindrical, calcareous o b j e c t with c o n c e n t r i c s t r u c t u r e . T h i s s h o w s s u p e r f i c i a l sinlilarities to an echinoid spine, and confirmation would be important because of the depth in the core (within the unfossiliferous interval). However, removal from the matrix demonstrated that it is definitely a clast.
PALAEOENVIRONMENTS
The lithostratigraphic unit of the core top (LSU 1 . 1 ) contains a l m o s t m o n o s p e c i f i c m o d i o l i d assemblages, correlatable with mussel beds recovered in the bottom part of the CRP-2/2A core (Taviani et al., 2000). These undescribed semi-infaunal mussels appear to b e conspecific, indicating t h e s a m e a,ge (Early Oligocene) and environment postulated for CRP-2/2A (i.e., a deep muddy shelf characterized by h i g h turbidity a n d , very likely, p e c u l i a r b o t t o m conditions such as a high H,S sediment content). Unit L S U 1.2 contains reasonably diverse assemblages that indicate innerlmiddle shelf environments dominated by epifaunal suspension feeders, including gregarious serpulid polychaetes (Serpula), scallops (?Adamussium n . s p . ) . s c a p h o p o d s ( ? D e n t a l i u m ) , t e r e b r a t u l i d brachiopod, and aragonitic bivalves. Unit 2.1 contains
asscinhliigcs of low diversity. consistingof epifaunal ('?Alidini~,v.si~iiii n . s p . . terebratulid brachiopods, c n e r u s t i n g b r y o ~ ~ i i n s ) a n d infauna1 (bivalves) suspension feeders, probably indicating inner/middle shell' environments. Unit LSU 3.1 c o n t a i n s in~icrof'ossil asscmbhigcs possibly indicati~i~leposilion o n 21 deep muddy shelf, characterized by moderate water activity and turbidity and enrichment in organic matter. T h e macrobenthic assemblages i n c l u d e infaunal and epifaunal suspension feeders, such a s bivalves (Cyclocardic~, lucinid) and solitary corals (Fluhelium iriiise/~/cifum), as well as infa~~nal dcposit- feeders. such as protobranch bivalves (Yoldiella).
Inner to middle shelf environments are suggested by macrofossils in 1,SU 5.1, most of which are infauna1 (Cy(,locardia) and epifaunal (?Liwa) suspension- f e e d i n g bivalves. A s i m i l a r environment is a l s o suggested for LSU 6.1, based on the occurrence o f e p i f a u n a l scallops (?Adamussium n . s p . ) and gastropods (trochid, naticid) and infauna1 bivalves ( l ~ ~ c i n i d ) . Unit LSU 8.1 contains a relatively diverse macrofauna consisting of infauna1 suspension feeders (Cyclocardia) and semi-infaunal/epifaunal gastropods (naticid, turritellid), probably indicating deposition in middle shelf environments. LSU 8.1 also includes the lowest occurrence of ?Ac/ai~i~~~vsi~im n.sp. in CRP-3, indicating a relatively low sedimentation rate.
The likely climatic conditions reconstructed for the E a r l y Oligocene of E a s t Antarctica have been presented in our previous study on C R P - 2 / 2 A niacrofossil assemblages (Taviani et al., 2000) and are not repeated here. It is sufficient to say that the presence of such macrofossils as turritellids, modiolid mussels and veneroidean bivalves suggests that the climate was warmer than at present, comparable to that of the present-day Subantarctic.
M a r i n e macrofossils appear again in L S U 9.1 (359.07 mbsf: undetermined gastropod), and finally in LSU 13.2 at 781.34 mbsf with the single occurrence of an undescribed modiolid mussel. T h e palaeo- climatic significance of modiolid mussels in Antartica has been discussed in detail by Taviani et al. (2000).
I t is possible that this mussel inhabited d e e p m a r i n e (slope? b a s i n ? ) , o r g a n i c - r i c h s e d i m e n t s , sporadically influenced by gravity mass flows. This r e c o n s t r u c t i o n d i f f e r s f r o m t h e depositional e n v i r o n m e n t i n t e r p r e t e d f r o m physical- sedimentological arguments, which imply instead a near-shore, deltaic setting, possibly above wave base ( C a p e Roberts Science Team, 2000: Fig. 7 . 4 ) . At present, we consider that neither interpretation can be taken as definitive. F o r now, w e point o u t s o m e arguments that support our alternative hypothesis of a deep setting rather than a shallow one, at least for the part of the core containing the mussel.
ues are Environment: Modiolid niussel assemblaa often associated with "turbiditic" environnlents where h y d r o g e n sulfide a n d l o r m e t h a n e s e e p a g e from d e c o m p o s i n g o r g a n i c m a t t e r may take place, providing sustenance for the bivalves, and of course
t h e y a r e well-known members of t h e d e e p - s e a hyclothermal vent comminiity (briefly reviewed by ('osel & Oki. 1998, p . 660: and others references therein).
Coi;11;1;(11ity". I t is true that today such peculiar iniissel-supporting environments o c c u r i n a w i d e spectrum of water depths, from brackish-lagoonal t o a b y s s a l . However. in the c a s e of s h a l l o w c o m m u n i t i e s , mussels a r c but o n e of many components of such assemblages. while in the CRP-3 core (as in many deep-sea mussel communities) there is n o sign of a c c o m p a n y i n g m a c r o f o s s i l s . Furthermore, nearshore environments are normally m a r k e d by a substantial s i g n a t u r e of a d j a c e n t terrestrial biota (such as phytoliths), but this is not the s i t u a t i o n in t h e C R P - 3 drill c o r e . T h i s s e e m s t o indicate that deposition took place at a significant distance from reservoirs of terrestrial biota.
Historical r e c o r d : O u r k n o w l e d g e of t h e biodiversity of macsoinvertebrates inhabiting shallow A n t a r c t i c waters d u r i n g the P a l a e o g e n e i s now relatively advanced. None of the mussel taxa so far d e s c r i b e d a p p e a r s to be c o n s p e c i f i c ( o r even c o n g e n e r i c ) with t h e C R P - 3 m u s s e l , a p o s s i b l e indication of CRP-3 environmental settings decidely d i f f e r e n t f r o m t h e s h a l l o w - w a t e r o n e s r e p o r t e d elsewhere in Antarctica.
O u r interpretation of the lithostratigraphic unit containing this mussel as possibly deposited in a d e e p - s e a d y s o x i c l a n o x i c e n v i r o n m e n t h a s s o m e important implications for determining the age of this critical part of the CRP-3 core.
BIOGEOGRAPHICAL AND CHRONOLOGICAL IMPLICATIONS
T h e l i t h o s t r a t i g r a p h i c u n i t of t h e c o r e t o p ( L S U 1.1) contains almost monospecific modiolid assemblages, correlatable with mussel beds recovered in the bottom part of the CRP-212A core (Taviani et al., 2000), consistent with this part of the core being the same age (Early Oligocene) as that postulated for CRP-212A.
Units L S U 1 . 2 a n d 2.1 c o n t a i n t h e p e c t i n i d
? A ~ C L I T I L / , Y S ~ L / ~ I I n.sp., whose known stratigraphic range e x t e n d s f r o m t h e O l i g o c e n e to t h e M i o c e n e o f A n t a r c t i c a (Taviani et a l . , 2 0 0 0 ) . U n i t L S U 3 . 1 contains the solitary coral Flabellum rariseptatum and
?Ac/a1-11iissiiim n.sp., with a known stratigraphic range extending from the Oligocene to the Early Miocene of Antarctica. L S U 8.1 represents the lowerniost occurrence of ? A c / c ~ ~ ; ~ i ( s s i ~ ~ i ~ ~ n.sp., establishing a n Oligocene age for the CRP-3 core down to 320.43 mbsf.
Macrofossils reappear in LSU 13.2 with the single m u s s e l , a s p e c i e s different f r o m t h e m o d i o l i d observed in the top of the CRP-3 drill core and from o t h e r m u s s e l s r e c o r d e d f r o m t h e P a l a e o g e n e o f Antarctica (Zinsmeister, 1984; Stilwell & Zinsmeister,
1002: Sli lwell. 2000). This macrofossil may prove 01' ci'itic;il importance not only for the c~ivii-oiiiiit~i~~;il interpretation oiitlincd above. but a l s o l'or i ~ i
hiochronologiciil potential. Its apparent iil>~em'i.- Iron) sedinients of established Oligocene age in ~ l i c K o s s Sea re"o11 possibly indicates an older age, k-aviny open (lie possibility that it is Eocene. However, t h i s ptirticiilar mussel is n o t recorded from a n y l+n~i.~iitt o u t c r o p s in Antarctica, neither on the A n t i i r c ~ i r Peninsula (Stilwell & Zinsmeister, 1992) n o r i n ilu5 McMurdo Sound erratics (Stilwcll, 2 0 0 0 ) . I f ' our environmental interpretion is correct, however. ils absence from other Eocene rocks could rel'lcd tinx lack of c o m p a r a b l e d e p o s i t i o n a l s e t t i n g s ; other Antarctic Palaeogene r o c k s apparently a l l vvci'r deposited in shallow water. CRP-3 may represeiit tli'
first record of "deep-sea" Eocene sediments extiiiiiii~~d so far in Antarctica. A possible Eocene age
for
('RP3at c a . 7 8 0 mbsf is not in conflict with t h e oilier available palaeontological evidence.
An interesting aspect of the CRP-3 n~acrof';uina lor the history of the Antarctic fauna is its preservation i n diamicton-doininated rocks. Relatively wasni-water taxa (such as turritellid gastropods, modiolid mussels and veneroidean bivalves), not now living arountl Antarctica, apparently still lived there after the onsct of Antarctic glaciation. A still more diverse iiiolliisc;iii f a u n a inhabited A n t a r c t i c a d u r i n g E o c e n e time (Stilwell & Zinsnieistes, 1 9 9 2 ; S t i l w e l l , 2 0 0 0 ) . i n c l ~ ~ d i n g diverse mussels, mactrid bivalves, diverse Veneridae, s h a l l o w - w a t e r T r o c h i d a e , a n d large, shallow-water tuKid and volutid gastropods. It seems that, rather than undergoing an abrupt extinction with the onset of major Antarctic glaciation, these taxa that are not present around Antarctica today progressively w e r e lost f r o m t h e S o u t h e r n Ocean as sea temperatures continued gradually to decrease. Rather t h a n being e x p e l l e d s u d d e n l y with the o n s e t of slaciation (a "mass extinction"), the Antarctic biota
U
may have waned gradually to its present impoverished diversity.
CONCLUSIONS
Identified m a r i n e m a c r o f o s s i l s i n c o r e C R P - 3 belong to eight phyla of marine I n ~ e ~ t e b r a t a which a r e , i n o r d e r of r e l a t i v e a b u n d a n c e . M o l l u s c a . Annelida, Bryozoa, Cnidaria, Crustacea. Brachiopoda, Echinodermata and Porifera. Mollusca are by far the d o m i n a n t g r o u p a n d i n c l u d e , conservatively, 15 s p e c i e s of B i v a l v i a , 6 of Gastropods a n d 1 of Scaphopoda. Unfortunately, the poor preservation of t h e available material m e a n s that most taxa must remain unidentified at the generic and specific level.
Mussel-dominated beds from the core top unit (LSU 1.1) are correlatable with mussel assemblages f r o m CRP-212A b o t t o m u n i t s , suggesting similar environmental conditions (deep sea muddy shelflslope.
warmer-than-present sea water conditions and peculiar H$-enriclicd sediments) and age (Early Oligocene).
Macrol'ossiliferous horizons arc common in CRP-3 down to c(/. 325 mbsf (LSU 1.2 to 8.1 ) ancl contain fossils whose stratigraphic range does not extend e a r l i e r than Early O l i g o c e n e ( t h e pectinid
?Aclcimii,ssIiim n . s p . a n d t h e scleractinian coral Flc~belliini ra r i , ~ e p t a j z i m ) . T h e s e assemblages arc interpreted a s d e p o s i t e d in shelf settings. most typically muddy, organic-rich middle-outer shclf e n v i r o n m e n t s . as testified by the d o m i n a n c e of infauna1 deposit- and suspension-feeding bivalvcs (largely, carditids and protobranchs).
Below 325 mbsf the macrofossil content is limited to single o c c u r r e n c e s of m a r i n e molluscs: a n undetermined gastropod at 359.07 mbsf (LSU 9.1) and an articulated modiolid mussel at 78 1.34 mbsf (LSU 13.2). The latter is significant, as it is one of t h e few fossils f o u n d w i t h i n a c a . 3 5 0 m-thick sedimentary succession at the base of the core, almost barren of fossils, of uncertain age and problematic depositional setting (LSU 9.1 to 13.2). It is possible t h a t this mussel lived o n a relatively d e e p s l o p e influenced by gravity flows, and it is compatible with a (?Late) Eocene age.
Taxa of relatively warm-water affinities that do not n o w live a r o u n d A n t a r c t i c a a r e p r e s e n t in t h e diamicton-dominated rocks of CRP-3, and evidently continued to live around Antarctica after the onset of major glaciation. The Antarctic biota apparently did not undergo a "mass extinction" with the onset of glaciation, but progressively waned to its present impoverished diversity as sea temperatures gradually continued to fall.
ACKNOWLEDGEMENTS - All on-ice colleagues of the Cape Roberts Project during the 1999-2000 drilling season are warmly thanked for their stimulating conversations a b o u t environmental and chronological issues and. in particular, David Harwood. Michele Claps, Chris Fielding.
F a b i o Florindo, Peter-Noel Webb. Peter Barrett, Ross Powell. Rosemary Askin, John Simes. Massimo Sarti and Malcom Laird. Mark Lavelle is gratefully acknowledged for his painstaking activity spotting macrofossil horizons in the CRP-3 drill core at the Cape Roberts Campsite laboratory.
Tom Janacek and Matt Curren assisted with sampling and handling of the macrofossil samples. We are indebted to Alessandro Remia. Barbara Gualandi. Paolino Ferrieri.
Stefano Parisini. Vanessa Thorn. and Bruno Sabelli who helped at various stages of the manuscript with photography and figure preparation. We are also grateful to John Simes.
Adam Harris and Luciano Perrozzi for technical support.
We are grateful to the referees. Ian Raine, Ewan Fordyce, Hamish Campbell and an anonymous referee, for helpful improvements to the manuscript. This study was partially supported by the Italian Programma Nazionale di Ricerche in Antarticle and the New Zealand Foundation for Research.
Science and Technology. This is IGM scientific contribution n. 1255. and Institute of Geological and Nuclear Sciences contribution no. 21 32.
licrckmann P.A.. Andrews .l.'!'.. Biocrck S.. Collioun E.A.. Emslie S . D . . Goodwill I D . . Hall H I , , . II;iri C.P.. Hirakawa K . . Igarashi A.. Ingocl t'sson 0.. I .opc~-M:ii-tine/. l . . Berry Lyons W., Mahin M.C.G.. Quilty P.C;.. Taviani M . & Yoshida Y..
0 9 8 . Circuin-Antcirctic co;isi;il ciiviroiiinci~al shifts during the L a i c Q u a t e r n a r y rcl'lccictl b y c m c r ~ c c l marine d e p o s i t s . ¥\iil(ii'r/i Science. 10. 345-362.
Bcu A . G . & D d l R . K . . 1989. Molluscc~. I n : l3;irreIt P.J. (eel.).
A n t a r c t i c C c n o ~ o i c history from the C I R O S - l d r i l l h o l e . iVIcMui-clo Sound. /\Icir Zc,tiliiiiil Dcptii.lineiil of Scientific and Industrial Rcwircli Hidlclin. 245. 135- 14 1 .
Ben A . G . & Maxwell P.A.. 1990. Ceno/.oic Mollusca of New Zealand. Drawings by R. C. B r a ~ i c r . /\/cn. Z'/.cl(iad Geological 5'11n'c'y Pcilc~~oiilolo~ccil Bulletin. 58. 5 18 p.
Biickcriclge J . St. J . S.. 2000. A new species of Aii.\troba!ann.\
(Cirripedia. Thoracica) Sroni Eocene erraties, Mount Discovery.
M c M u r d o S o u n d . East ant arc tic;^. In: Palacobioloey and Palaeoenvimnments o f Eocenc Rocks. McMnrdo Soiind. East Antarctica. Antarctic Research Series. 76. 329-333.
Bullivant J.S.. 1967. Ecology of the Ross Sea benthos. The Fauna o f t h e R o s s S e a , New Z e a l a n d Oceiino,yrop/iic I n s t i t u t e Memoir. 32. 49-77.
Cantrill D.J.. 2001. Early Oligocenc / \ ~ o / h o f ~ s from CRP-3.
A n t a r c t i c a : Implications f o r the Vegetation History. T h i s volume.
Cape Roberts Science Team. 2000. Studies from the Cape Roberts Project, Ross Sea. Antarctica. Initial Report on CRP-3. T e r m Antiirticci, 7. 1-209.
c . 'unol . ' R.-P,. Leyrit H. & Giret A.. 1992. Balanoidea (Crustacea.
Cin'ipedia) du Miocene des Kerguelen. Geol~ios, 25. 383-388.
Cosel. R . v011 & Oki, K.. 1998. Gigantism i n Mytilidae. A new Bathymodioliis from cold seeps on the Barbados accretionary p r i s m . C o m p t e Renclii d e I ' A c a d h i e d e s S c i e n c e s , P a r i s , Sciences de lei Vie, 321. 655-663.
Dell R.K.. 1990. Antarctic Mollusca. with special reference to the f a u n a of the Ross S e a . T h e R o y a l Society o f New Z e a l a n d Buiilletin. 27. 3 11 p.
Dell R . K . & Fleniing C . A . , 1975. Oligocene-Miocene bivalve Mollusca and other macrofossils from Sites 270 and 272 (Ross Sea). DSDP. leg 28. Initial Reports of the Deep Sea Drilling Project. 28. 693-703.
G a z d z i c k i A . & Pugaczewska H . . 1 9 8 4 . Biota of t h e "Pecten conglon~erate" (Polonez Cove Formation. Pliocene) of King G e o r g e Island (South Shetland Islands. Antarctica). S t u d i o Geologica Polonica. 79. 59-120.
Giret A.. Leyrit H.. Lauriat-Rage A.. Carriol R.-P. & Lozouet P..
1994. Mioccne des Kcrguelcn: la fauna marine du Mont Rond e t s e s implications geologiques e t palaeoclimatologiques.
Coniptes Rendns de I'Academie des Scieiice de Paris. serie 11.
319. 719-726.
Hain S.. 1990. Die beschalten bentliischen Mollusken (Gastropoda u n d B i v a l v i a ) des Weddellmeeres. Antarktis. T h e b e n t h i c s e a s h e l l s ( G a s t r o p o d a a n d B i v a l v i a ) of the Weddell S e a . Antarctica. Alfred Wegener Institute for Polar and M a r i n e Research. Germany, Bericlzte ;U;Â Polorforschiing (Reports o n Polar Research). 70. 181 p.
H a r w o o d D . M . & Levy R . H . . 2 0 0 0 . T h e M c M u r d o E r r a t i c s : introduction and overview. In: Stilwell J.D. & Feldmann R.M.
(eds.). Palaeobiology and pnieieoeiivironment.~ of Eocene rocks, M c M n r d o Sound, East Antcirctica. Antarctic Research Series.
76. 1-18.
Hartman 0 . . 1966. Polychaeta Myzostomidae and Sedentaria of Antarctica. Antarctic Research Series. 7. 158 p.
Hedley C.. 1916. Report on Mollusca from elevated marine beds ("Raised B e a c h e s ) of M c M u r d o S o u n d . R e p o r t s of t h e Scientific Investigcitions, British Antarctic Expedition, 1907-9, Geology, 2. 85-88.
H e n d y C . H . . Neall V.E. & Wilson A.T.. 1969. R e c e n t m a r i n e deposits from Cape Barne. McMurdo Sound. Antarctica. New Zealand Joi(ri7cil o f Geolosy and Geophysics. 12. 707-712.
J o n k e r s H . A . . 1 9 9 8 . S t r a t i g r a p h y of A n t a r c t i c l a t e C e n o z o i c pectinid-bearing deposits. Antarctic Science. 10. 161-170.
p. 1, o e n v i r o n m c n i i , o f Eoccne Rocks. McMurdo S o u i ~ l . h s i A > ~ ~ a r c i i c i t . Anmrmc / < ~ ~ , s ~ w r d ~ .Swi<>,~, 76, 372 l>.
S i i l w c l l J.11. & Xi1,s8,,cislcr, 1992. M ~ ~ l l ~ ~ s c ~ ~ ~ ~ s y s i m : t l i c s l ~ i ~ ~ s l r : ~ i i g r ~ s ~ ~ l ~ y . 1,nwcs 'Tcrii;~ry 1.2, h4csci8 1 : ~ ~ r n x ~ i i m . Scyal~>$tv l s l ~ ~ ~ ~ ~ l , AnIasc1ic llc~,insulz~. An,tric'z%~, ( j c o p t ~ y s i c : ~ l 1Jnins1, Wns1iingi~)ii D.C.. Ani<irtlic l i r s m r r h Series. 55. 192 p.
Sloliirski J. & Taviani M,. 2001. Oligocene S c l c r a c i i n i a ~ ! Corals fmm CR1'-3 I > i i l l l n ~ l c . V i c u n i a I . a i ~ l Ba-.il>. A ~ l l a r c l i c ; ~ . Tliii ..., >,L,,<,,,,<.
,
l ' u g t t c ~ e n s k a H.. 1984. 'Tertiary Bi\mIvia ztncl S c q ~ l ~ ~ ~ x x l a fron, i M , , 13e,, ,,,G. 1
,
,t)r< c;., ] 9 9 8 . l,lcis i<>cc,,e gIz3cinn1>winc ~ I ~ ~ ~ ~ ~ s i l s :M ;MagIa N ~ t n a l a k . Ki11g Gewge lsl>!~,<In i a c r o f o s s i l s f r o m C R P - I D r i l l h o l e . V i c i o r i a 1-;,nil B a s i n . ( S n u I l ~ S l ~ c l l ~ ~ ~ ~ ~ l i s l ~ ~ ~ ~ ~ l s , A n l s r c l i c z ~ ) . . S ~ u ~ l i o (;~oI<,,qico
A~,r,tsclic:t. 'Tllis \,ol~~sne.
I'olimicii, 79, 53-58.
Taviatii M,, 13eu ,\.G. & J u n k e r H . A . , 2000. M a c r o f o s s i l s from S n ~ i l l ~ I < . A . , 1902. I?<,/>O~I m, 11ze ~ ~ ~ o / n ~ , ~ t ~ r ~ , l ~ l l /ri,s~,~ry ~ ~ ~ ~ i ~ ~ ~ ~ . ~
CI<l'-?/2A V i c l < ~ r i a I-;~II~ 13asiz1, A ~ ~ l a c c i i c : ~ . ?i,rr,t ,\ntor,ic~!. 7, ..,
Z i n s m e i s ~ e r W.J.. 1984. Lale Eocene bivalves IMolltisca) from 11x 1.a M e s e i a F o r m a i i o i i , e o l l e c i e d during i l i c 1 9 7 4 - 7 5 i u i i i i A r g c ~ ~ l i ~ > e - A ~ ~ ~ c r i c a v , c x ] x ~ l i i i ~ ~ x , i n S t y n ~ o t ~ r l s l z ! ~ ~ l , Anlz%rclic l'eninsiiki. Jumicd i,/'l-'aitmnt~a/tw~. 58. 1497-1527.
/insmeislcr W.J. & Macellnri C.E., 1988. Bivsilvisi (Molluscs) from Seynunir Island, A m a r c l i c 1'enii1sula I n : 1t.M. F e l d i i ~ a n n &
M . O . Woodburn (cds.). Gro/o,qy çnr P a k r n ~ m i l o ~ of .Se?imnr l . ~ / o ~ ~ d , Aul<trc!ic / ' ~ ~ ~ ~ i r r . s z ~ l ~ , , t i ~ ~ o l o , q i c ~ , / .S,xi<,l? o/Arn<>ric<r Memoir, 169, 253-284.
Z u l l o V.A., l  ¥ ' e k l m ! m ~ R . M . & Wieclmni, L.,\.. 1988. Balnnomoipl, C i n i p c d i i i f r o m the Hocenc I.;, M c s c l a l-'oriniition. In: R . M . F c k l m i i n i , & M . O . W o o d b u r n (eels.), Gro/n,qy n,zd / ' ~ ~ / ~ , ~ ~ ~ , , r l ~ ~ / , , ~ y <>.f s<,y,2,t,,,r 1.s1,<,,<1, ,iu,orc,ic l',~,,i,,.,,,l,t, Ciffilogiciil Sot-iw of America M i w o i r . 169, 459.464.
