Upper Cretaceous microfossil biostratigraphy of ...

Upper Cretaceous microfossil biostratigraphy of Seymour Island, Antarctic Peninsula BRIAN T. HUBER, DAVID M. HARWOOD,

and

PETER N. WEBB

Department of Geology and Mineralogy

and

Institute of Polar Studies The Ohio State University Columbus, Ohio 43210

During the 1982 Ohio State University expedition to Seymour Island, we sampled and measured detailed sections in the Upper Cretaceous Lopez de Bertodano Formation. Approximately 200 samples were collected from three sections, the thickest being 1,460 meters (figure 1). The purpose of this study is to document the microfossil assemblages from this locality and to use these assemblages to develop a biostratigraphic zonation and establish Southern Hemisphere correlations. Foraminifera are the responsibility of B. T. Huber and calcareous nannoplankton and diatoms of D. M. Harwood. The Cretaceous stratigraphy of Seymour Island (figure 1) has been described by Andersson (1906), Bibby (1966), and Mac-

ellari and Huber (1982), and formations were named by Rinaldi (1982). The Lopez de Bertodano Formation was considered (on the basis of ammonite evidence) to be Campanian to possibly Maastrichtian age by Spath (1953), whereas Howarth (1966) and Olivero (1981) suggested a middle to late Campanian age. Although the conformably overlying Sobral Formation lacks ammonites, Rinaldi (1982) considered it to be uppermost Cretaceous to lower Tertiary. Prior to the 1982 field season, documentation of marine microfossils from Upper Cretaceous strata of the James Ross Basin was very limited; Holland (1910) described two agglutinated foraminiferal taxa and Macfadyen (1966) described 17 other poorly preserved taxa. The foraminifera were considered Senonian based on their co-occurrence with ammonites of this age. Calcareous nanno plankton. Well preserved calcareous nannoplankton assemblages are dominated by Braarudosphaera bigellowi and include the following Late Cretaceous species: Microrhabdulus decoratus, Cribrosphaerella ehrenbergii, Eiffellithus turriseiffeli, Prediscosphaera cretacea, Kamptnerius magnificus, and Arkhangelskiella cymbiformis. Three Maastrichtian species occur: Braarudosphaera turbinae (late Maastrichtian), Nephrolithus frequens (late Maastrichtian), and N. corystus Wind (latest Campa-

nian—middle Maastrichtian) (figure 2). A more thorough treatment of the nannoplankton is in progress (Harwood in preparation). Nephrolithus frequens has a bipolar distribution and is most abundant in higher latitudes, often comprising 20 percent of

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Figure 1. Geologic map of Seymour Island showing sections measured by Rinaldi et al. (1978) and Macellari and Huber (1982). Sample localities referred to in the text are also shown. 72

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floral assemblages south of 50°S latitude (Thierstein 1981). Latitude controls the stratigraphic range of N. frequens, because its first occurrence is older toward the poles. Therefore, the maximum stratigraphic range is assumed on Seymour Island. Although commonly regarded as late Maastrichtian, the oldest reported occurrence of this taxon is latest middle Maastrichtian at Deep Sea Drilling Project site 249 (Wind 1979). Worsley most likely included N. car ystus in his N. frequens 'et al" category, because he reports N. frequens "et al" from the lower Maastrichtian in polar shelf sections (Worsley 1974, figure 10). The assemblage of Late Cretaceous taxa from Seymour Island belongs to the Nephrolithus frequens province of Worsley and Martini (1970) and the Falkland Island nannofossil province of Wind (1979). This study extends the known range of each of these provinces southward by more than 13° latitude. Foraminifera. Over 157 foraminiferal species have been recovered from the Lopez de Bertodano Formation on Seymour Island. Low diversity agglutinated assemblages alternate with assemblages of mixed calcareous benthic, planktonic, and agglutinated forams. The absence of calcareous taxa in many levels of the formation may be due to subaerial leaching. We believe that the variations noted in foraminiferal faunas reflect a wide variety of paleoenvironmental conditions. Dominant taxa in the agglutinated assemblages include species of Rhabdamm ma, Bath ysiphon, Hyperammina, Psamrnosphaera,

C



e

Ammodiscus, Reophax, Haploph ragmo ides, Cyclammina, Trochammina, Cribrostornoides, Spiroplectamrnina, and Ammobaculites.

Large agglutinated taxa, some attaining diameters of 3 millimeters, occur in the lower third of the sections. Fluctuations in abundance and diversity of praebuliminids and members of the family Chilostomellinae can be correlated across sections I, II, and III (figure 1). The buliminids present include species of Praebulirnina, Pyramidina, Neobulimina, and Bulim inc/la. Other notable calcareous benthics include Eouvigerina hispida, Bolivina incrassata, B. decurrens, and Anomalinoides piripaua. Numerous species of the families Caucasiniidae, Nonionidae, Alabamindae, Osangulariidae, and Anomalinidae are also represented. A single well preserved specimen of Frondicularia rakauroana (Finlay) was found in sample 101. This taxon was reported previously only from the upper part of the Haumurian stage (upper Maastrichtian) of New Zealand (Webb 1971, 1972). All three sections contain a variety of well preserved globigerinids. Hedbergella holrndelensis and Globigermnelloides mu!tispinatus are quite common whereas Hedhergella rnonmouthensis, Globotruncanella havanensis, Rugoglobigerina rugosa, R. rotundata, R. macrace phala, Heterohelix globuloso, H. glabrans, and Gumbe! itria cretacea occur in low abundance. The above taxa gener-

ally range from the late Campanian through Maastrichtian (Pessagno 1967; Webb 1971; Sliter 1976). The foraminiferal faunas resemble Maastrichtian assemblages from southern South America (Charrier and Lahsen 1968), New Zealand (Webb 1971), and particularly site 327 on the Falkland Plateau (Sliter 1976). Diatoms. Rare fragments of diatoms were encountered during examination of calcareous nannofossil preparations. Since few Upper Cretaceous diatom localities are known in the world, an intensive study of diatoms is underway. Diatoms will be thoroughly examined in the future (Harwood in preparation). Sample 70 (figure 1) from the upper part of the Lopez de Bertodano Formation contains a rich assemblage of Paleogene marine diatoms including: Goniothecium odontella, Pterotheca pokrovskajae, P. danica, Eunotogramma weissi, Chasea bicornis, C.

1983 REVIEW

Figure 2. Photographs of microfossils from the Lopez de Bertodano Formation on Seymour Island. (a) Hedberge!la holmde!ensis from sample 28; (b) Globotruncanella monmouthensis from sample 38; (c-d) Braarudosphaera turbinae from sample 148; (e) Glob igerinelloides multispinatus from sample 28b; (f-h) Nephrolithus corystus from sample 28b; (i-k) Nephrolithus frequens from sample 148.

oronata, Rh izosolen ia cretacea, Step1ianopixis spp. Acan tliodiscus schmidtii, Hemiaui!us kondai, H. glescri, and others. Sample 76

(110 meters higher in the section) contains a slightly different diatom assemblage including: Pterothcca crucifera, P. coriluta,

Pseudopyxillia aculeata, Pseudoru tila na mon ilL', Hcmiau/us schmidtmi, H. echinulatus, Trincaria arietnium, Arachnoidiscus chrenbcrgii, Kent rodiscus armatus, Corbisema geometrica (silicoflagellate), and

others. Many of these taxa are reported from the Cretaceous and Paleogene. However, the absence of the characteristic Late Cretaceous genus Gladius and silicoflagellates Ltram u/a furcula and Valacerta hortonii and V. tumidula (all of which are present lower in the section) is significant. Discussion. The calcareous nannoplankton provide the greatest degree of age resolution. In this preliminary report, we separate the Lopez de Bertodano Formation into four broad subdivisions as stated below. Examination of these subdivisions is continuing and this will further refine the positions of biostratigraphic boundaries. 73

The presence of Nephrolithus corystus and the absence of N. frequens in sample 28b (figure 1) suggests an upper Campanian-lower middle Maastrichtian age (Wind 1979, 1983) for this sample and the section below it. Sample 38 contains both N. corystus and N. frequens suggesting an uppermost middle Maastrichtian age as noted in Deep Sea Drilling Project site 249 by Wind (1979). Sample 148 is upper Maastrichtian as indicated by the occurrence of N. frequens and Braarudosphaera turbinae. The above information enables placement of the Campanian/ Maastrichtian boundary below sample 38 and the middle/upper Maastrichtian boundary between samples 38 and 148. The last occurrence of ammonites (Zinsmeister and Macellari Antarctic Journal, this issue) and foraminifera 20 meters below sample 70 and the absence of characteristic Late Cretaceous diatoms and silicoflagellates in sample 70 and above suggests that the Cretaceous/Tertiary boundary may occur in the uppermost part of the Lopez de Bertodano Formation on Seymour Island. The Lopez de Bertodano Formation has the potential to be one of the more continuous Cretaceous/Tertiary sequences. An extremely rapid sedimentation rate (equal to approximately 200 meters per million years) and the detrital nature of this sequence is exceptional as most other boundary sequences are carbonate-rich and contain an hiatus. This study was supported by National Science Foundation grants DPP 80-20096 to D. H. Elliot and W. J . Zinsmeister (fieldwork) and DPP 80-18749 AOl to P. N. Webb (laboratory work).

Macfadyen, W. A. 1966. Foraminifera from the Upper Cretaceous of James Ross Island. British Antarctic Survey Bulletin 8, 75-87. Olivero, E. G., 1981. Esquema de zonación de ammonites del Cretácico Superior del Grupo de Islas James Ross, Antártida. Viii Congreso Geólogico Argentino, San Luis, September 20-27, 1981. Acta, 311, 897-907. Pessagno, E. A., Jr. 1967. Upper Cretaceous planktonic foraminifera from western Gulf Coastal Plain. Palaeontographica Americana, 5, 245-445. Rinaldi, C. A. 1982. The Upper Cretaceous in the James Ross Island Group. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Rinaldi, C., A. Massabie, J. Morelli, L. Roseman, and R. del Valle. 1978. Geologia de la Isla Vicecomodoro Marambio. Contribuciones del inSt it uto Antdrtico Argentino, 217, 1-37. Sliter, W. V. 1976. Cretaceous foraminifera from the southwestern Atlantic Ocean, Leg 36, Deep Sea Drilling Project. In P. F. Barker and I.W.D. Daiziel (Eds.), Initial Reports of the Deep Sea Drilling Project, Vol. 28. Washington, D.C.: U.S. Government Printing Office. Spath, L. F. 1953. The Upper Cretaceous cephalopoda fauna of Graham Land. Falkland islands Dependancies Survey Scientific Reports, 3, 1-60. Thierstein, H. R. 1981. Late Cretaceous nannoplankton and the change at the Cretaceous-Tertiary boundary. In J. Warme et al. (Eds.), The Deep Sea Drilling Project: A decade of progress. (Society of Economic Paleontologists and Mineralogists Special Publication 32) Tulsa, Oklahoma. Wind, F. H. 1979. Maastrichtian-Campanian nannofloral provinces of the southern Atlantic and Indian Oceans. In M. Talwani, W. Hay, and

References

Geophysical Union. Wind, F. H. 1983. The genus Nephrolithus Górka, 1957 (Coccolithophoridae). Journal of Paleontology, 57, 157-161. Worsley, T. R. 1974. The Cretaceous-Tertiary boundary event in the ocean. In W. W. Hay (Ed.), Studies in Paleo-oceanography. (Society of Economic Paleontologists and Mineralogists Special Publication 20.) Tulsa, Oklahoma. Worsley, T. R., and E. Martini, 1970. Late Maastrichtian nannoplankton provinces. Nature, 225, 1242-1243. Webb, P. N. 1971. New Zealand Late Cretaceous (Haumurian) foraminifera and stratigraphy: A summary. New Zealand Journal of Geology and Geophysics, 14(4), 795-828. Webb, P. N. 1972. A redescription of Frondicularia rakauroana (Finlay) from the Late Cretaceous (Maastrichtian) of New Zealand. Micropaleontology, 18(1), 94-100. Zinsmeister, W. 1.' and C. E. Macellari. 1983. Changes in the macrofossil faunas at the end of the Cretaceous on Seymour Island, Antarctic Peninsula. Antarctic Journal of the U.S., 18(5).

Andersson, J. C. 1906. On the geology of Graham Land. Bulletin of the Geological Institute of Uppsala, 7, 19-71. Bibby, J. S. 1966. The stratigraphy of part of north-east Graham Land and the James Ross Island Group. British Antarctic Survey Report, 53 1-37. Charrier, R. G., and A. A. Lahsen. 1968. Contribution a l'étude de la limite Crétacé-Tertiaire de la Province de Magellan, extrême-sud du Chili. Revue de Micropaleontologie, 11(2), 111-120. Harwood, D. M., In preparation. Upper Cretaceous calcareous nannoplankton and diatoms from Seymour Island, Antarctic Peninsula. Holland, R, 1910. The fossil foraminifera. Wissenshaftliche Ergehenisse der Schwedischen Sudpolar-expedition, Sudpolarexped., 3(9), 1-11. Howarth, M. K. 1966. Ammonites from the Upper Cretaceous of the James Ross Island Group. British Antarctic Survey Bulletin, 10, 55-69. Macellari, C. and Huber, B. T. 1982. Cretaceous stratigraphy of Seymour Island, east Antarctic Peninsula. Antarctic Journal of the U. S., 17(5), 68-70.

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W. B. F. Ryan (Eds.), Deep Drilling in the Atlantic Ocean: Continental Margins and Paleoenvironment. Washington, D.C.: American

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