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4. EOCENE-OLIGOCENE PLANKTONIC FORAMINIFERAL

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Hine, A.C., Feary, D.A., and Malone, M.J. (Eds.)Proceedings of the Ocean Drilling Program, Scientific Results Volume 182

4. EOCENEOLIGOCENE PLANKTONIC FORAMINIFERAL BIOSTRATIGRAPHY OF SITES 1126, 1130, 1132, AND 1134, ODP LEG 182, GREAT AUSTRALIAN BIGHT1

Qianyu Li,2 Brian McGowran,2 and Noel P. James3

ABSTRACT

Planktonic foraminiferal results indicate that Paleogene sedimentsrecovered at Sites 1126, 1130, 1132, and 1134 in the Great AustralianBight are of middle Eocenelate Oligocene age, in intervals equivalentto (sub)tropical Zones P12P22. The southern temperate assemblagehosted several subtropical species in the middlelate Eocene and lateOligocene as immigrants probably transported by a warm-water systemsimilar to the present-day Leeuwin Current. The four major hiatusesrecognized or inferred fall (1) between Zones P1213 and P15 in themiddle Eocene, (2) within Zone P15, (3) between Zones P16 and P18across the Eocene/Oligocene boundary, and (4) between Zones P19 andP20 and Subzone P21b in the mid-Oligocene. These unconformitiesrepresent region-wide events across the southern Australian margin,corresponding to global sequence boundaries Part-1 (39.1 Ma), Pr1 +Pr2 (37.136.0 Ma), Pr4/Ru1 (33.7 Ma), and Ru4/Ch1 (28.5 Ma), respec-tively. Unconformities at Site 1130 had a longer duration as lower Oli-gocene ooze with Zone P18P19 species overlying a middle Eocenesandy limestone of Zone P12 age and the whole Oligocene were con-densed to only half as thick as the coeval sediments from up- anddownslope, indicating stronger erosion at this upper slope locality dur-ing the late Eocene. The biostratigraphic results confirm previous stud-ies of the neritic record, reporting that carbonate deposition began in

1Li, Q., McGowran, B., and James, N.P., 2003. EoceneOligocene planktonic forminiferal biostratigraphy of Sites 1126, 1130, 1132, and 1134, ODP Leg 182, Great Australian Bight. In Hine, A.C., Feary, D.A., and Malone, M.J. (Eds.), Proc. ODP, Sci. Results, 182, 128 [Online]. Available from World Wide Web: . [Cited YYYY-MM-DD]22Department of Geology and Geophysics, The University of Adelaide, Adelaide SA 5005, Australia. Correspondence author: [email protected] of Geological Sciences, Queens University, Kingston ON K7L 3N6, Canada.

Initial receipt: 2 April 2001Acceptance: 30 September 2002Web publication: 3 February 2003Ms 182SR-006

mailto:[email protected]

Q. LI ET AL.EOCENEOLIGOCENE PLANKTONIC FORMINIFERAL BIOSTRATIGRAPHY 2

the middle Eocene probably as a response to global warming and mar-ginal subsidence because of the accelerated seafloor spreading betweenAustralia and Antarctica at ~43 Ma.

INTRODUCTION

During Ocean Drilling Program (ODP) Leg 182, Paleogene sedimentswere recovered at Sites 1126, 1128, 1130, 1132, and 1134 in waterdepths between 218 m (Site 1132) and 3875 m (Site 1128) from thewestern Great Australian Bight (Fig. F1). The siliciclastic sequence ofprelate Eocene age, at which most holes terminated, is poorly fossilif-erous and could be fluvial to deltaic in origin. The overlying middleEocene limestones grade upward to wackestones and calcareous oozesof younger ages (Feary, Hine, Malone, et al., 2000). Core recovery is low,

Q. LI ET AL.EOCENEOLIGOCENE PLANKTONIC FORMINIFERAL BIOSTRATIGRAPHY 3

Species identification was made by reference mainly to Blow (1979)and Bolli et al. (1985). Key species for biostratigraphy are discussed andillustrated. The timescale and zonal scheme of Berggren et al. (1995)were correlated with relevant datum levels of species found widely insouthern Australia (Fig. F2). We used the calibrated first occurrence (FO)and last occurrence (LO) datums of many species given in Berggren etal. (1995) and updated by the Shipboard Scientific Parties of Leg 181(Carter, McCave, Richter, Carter, et al., 1999; table T3 in Shipboard Sci-entific Party, 2000a) and Leg 182 (Feary, Hine, Malone, et al., 2000; ta-ble T3 in Shipboard Scientific Party, 2000b).

PLANKTONIC FORAMINIFERAL DATUMS AND ZONES

Figure F2 summarizes the integrated Paleogene geochronostratigra-phy, emphasizing standard planktonic foraminiferal zones and datumlevels from the (sub)tropics. The P-zonation of Berggren et al. (1995)has been correlated with the southern mid-latitude zones identified byJenkins (1966, 1971, 1993) and important datum levels found in south-ern Australia (McGowran, 1986, 1991; McGowran et al., 1997a). To-gether with those used in defining the P-zones, many calculateddatums provide the basic framework for the regional biostratigraphy.Local biozonations are not applied in this study for the same reason asstated in McGowran (1986; p. 250) that it is easier to shuffle the inven-tory of biostratigraphic events than to redefine zones and subzoneseach time there is a new discovery, a correction, or a modest step for-ward in our understanding (of the distribution of species). Apart fromthese datum levels, major components of the planktonic foraminiferalassemblages also provide evidence for changes in age and environment.Species associations help determine if datums are in situ or displaced.Biostratigraphic results from previous studies of neritic sediments aresummarized below.

Eocene

The Paleoceneearly Eocene marine record in southern Australia issparse, and the Kings Park section near Perth and the coastal PebblePoint section to the southwest of Melbourne are the only two outcropswith good planktonic and benthic foraminifers of that age (McGowran,1964, 1965). In contrast, middlelate Eocene carbonates rich in plank-tonic foraminifers are more widespread along the coast of southernAustralia (Quilty, 1969, 1981; McGowran, 1979, 1990, 1991, 1992). Theplanktonic foraminiferal assemblages have these characteristics.

1. Prominent in the Eocene assemblage are Globigerinatheka index,Acarinina primitiva, Acarinina bullbrooki, Acarinina collactea, Tur-borotalia spp., Subbotina linaperta, and Chiloguembelina cubensis.

2. Most (sub)tropical species, especially those zonal markers listedin Fig. F2, are absent. Morozovella is rare and present mostly inZone P10 or older intervals. Hantkenina is sporadic in Zones P15lower P16.

3. The middle Eocene sediments can be subdivided on the follow-ing evidence. Planorotalites australiformis last appears withinZone P11. Assemblages with A. bullbrooki, Acarinina densa, and G.

30

24

26

28

32

34

36

38

40

42

44

46

48

50

52

54

56

58

60

62

64

66

b

b

NP19/20

NP25

NN1

NP24

NP23

NP22NP21

NP18

NP17

NP16

NP15

NP14

NP13

NP12

NP11NP10

NP9

NP8NP6

NP5

NP4

NP3NP2NP1

c

a

a

P & PO

M1aN4 a

P. eugubina (64.9-65.0)S. triloculinoides (64.5)

Gq. dehiscens (23.2)Pg. kugeri s.s. (23.8)Gs. primordius acme (24.3)

Pg. opima (27.1)

Ch. cubensis (28.5)G. angulisuturalis (29.4) T. ampliapertura (30.3)

Pseudohastigerina (32.0)

T. cerroazulensis (33.8)C. inflata (34.0)

T. cunialensis (35.2)

Po. semiinvoluta (38.4)

Gb. beckmanni (40.1-40.5)

Gb. kugleri (45.8)

M. aragonensis (43.6)

M. aragonensis (52.3)

H. nuttalli (49.0)

P. palmerae (50.4)M. formosa (50.8)

M. lensiformis (54.0)M. velascoensis (54.7)M. subbotinae (55.9)P. pseudomenardii (55.9)A. soldadoensis (56.5)A. subsphaerica (57.1)

A. subsphaerica (59.2)P. pseudomenardii (59.2)Ig. albeari (60.0) M. angulata (61.0)Pr. uncinata (61.2)

Pr. inconstans (63.0)P. sompressa (63.0)

{

{

{

M. formosa (54.0){

Ch. cubensis

M. velascoensis

P. pseudomenardii

SP15

SP14

SP13

SP12

SP11

SP10

SP9

SP8

SP7

SP6

SP5

SP4

SP3

SP1SP2

Gq. dehiscens (23.2)

Gt. brazieri

Ch. cubensis (28.5)

S. angiporoides (30.0)

Gt. brevis

A. aculeata

Gk. index (42.9)

M. crater

P. pseudomenardii (59.2)

Gt. brevis

A. primitiva (39.0)

M. crater

M. velascoensis (55.9)

{

{

{

P & PO

M1aN4a

Geochonostratigraphy Nanno-plankton

Planktonic foraminifers Southern mid-latitude Southern Australia

65.0

60.9

57.9

54.8

49.0

41.3

37.0

33.7

28.5

23.8

Pg. opima (30.6)

Age

(M

a)

Acarinina aculeataChiloguembelina cubensis

Chattian

Rupelian

Priabonian

Bartonian

Lutetian

Ypresian

Thanetian

Selandian

Danian

Olig

ocen

eE

ocen

eP

aleo

cene

early

late

early

late

mid

dle

early

late

C6CC7

C8

C9

C10

C11

C12

C13

C15C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

C26

C27

C28

C29

C7A

P. wilcoxensis

T. euapertura

S. angiporoides

Gt. brevis

S. linaperta

T. inconspicua

Gk. index

A. primitiva

M. crater

S. triloculinoides

G. pauciloculata

Gt. brazieri

G. daubjergensis

P. wilcoxensis (54.5)

G. daubjergensis

G. pauciloculat

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