Palynological investigations of the WX James Ross Island basin and Robertson Island, Antarctic Peninsula , N

R. A. ASKIN

Geology Department Colorado School of Mines Golden, Colorado 80401

Stratigraphically well-controlled outcrop samples, with ap- A parently continuous sedimentation across the Cretaceous/Terti- ary (KIT) boundary, show a gradually changing succession at 4 Seymour Island of both marine and non-marine fossil pal- PIWO, ynomorphs. Peridinioid and other dinoflagellates record evolu- tion from an upper Maestrichtian assemblage into a "transi- tional boundary zone" which spans the presumed K/T boundary and is replaced by a distinctive Paleocene assemblage. Rich palynomorph assemblages, including marine micro- phytoplankton (dinoflagellate cysts, acritarchs) and pollen and spores, were found in samples collected by two expeditions to 1) the James Ross Island basin, the first in February and March 1982 (Askin and Fleming 1982), and the second in December 1983 and January 1984. Frederic C. Barbis and James M. Robin- son collected over 320 samples for palynological study during this second expedition to Seymour Island, concentrating on the uppermost part of the Lopez de Bertodano Formation (samples .4 collected at 0.5-meter intervals over the KIT boundary) and C sections at Cape Wiman. In addition, samples were collected from Robertson Island further south along the Antarctic Penin- Figure 2. Photomicrographs of dinoflagellate cysts from uppermost sula (figure 1). Lopez de Bertodano Formation, Seymour Island. A. Spinidinium In central and southern Seymour Island, between about 25 macmurdoense (Wilson) Lentin and Williams, x 1000; B. Phe- and 10 meters below the presumed KIT boundary, the Isab- lodinium sp.ct. P magnificum (Stanley) Stover and Evitt, x 500; C. elidinium n.sp.1—I. n.sp.2 dinoflagellate complex is gradually Isabelidinium druggil (Stover) Lentin and Williams, x 500; D. De- replaced by the Isabelidinium druggii (Stover) Lentin and flandrea sp.cf. D. medcalfii Stover, x 500. Williams—I. seelandicum (Lange) Lentin and Williams complex. This latter peridinioid dinoflagellate complex, along with com- the peridinioid species Phelodinium sp.cf. P. magnificum (Stanley) Stover (figure mon Exochosphaeridium bifidum (Clarke and Verdier) Clarke et al. Stover and Evitt and Deflandrea sp.cf. D. med caifli and Exochosphaeridium sp. 1, dominates the marine component 2). Both species become more numerous above the KIT of the "transition zone" which spans the boundary. In its lower boundary. part the "transition zone" includes the first rare occurrences of The top of the "transition zone" is marked by the disap- pearance of the I. druggii–I. seelandicum complex and E. bifidum, and by the appearance, sometimes in great abundance, of Sene- 62"Wc9 -L-- galinium sp.cf. S. obscurum (Drugg) Stover and Evitt, and Spin- idinium macmurdoense (Wilson) Lentin and Williams. De- so flandreoid dinoflagellates with diagnostic excystment aper- tures (wide hexa archeopyles) become abundant among the 0 marine forms up through the Paleocene section. 0 km 100 bQ p Confirmation of a Maestrichtian age for the lower part of the • Vega Island "transition zone" is provided by the ammonite Pachydiscus n.sp. Ross Is (Macellari and Zinsmeister 1983), foraminifera, and other mi- Seymour Is. crofossils (Huber, Harwood, and Webb 1983). At the top of its Snow Hill Is. range the ammonite is associated with I. drugii–I. seelandicum 6 CP and E. bifidum. Wilson (1978) described I druggii–I. seelandicum assemblages immediately below (rare) and above (abundant) the KIT boundary dated by foraminifera at Woodside Creek, Robertson Island New Zealand. As Wilson noted, I. drugii and I. seelandicum are apparently restricted to the Late MaestrichtianlEarly Danian Figure 1. Locality map for James Ross Island basin and Robertson interval worldwide. They occur in the type Danian at Stevns Island. Klint, Denmark (Lange 1969). E. bifidum is not known above the

ANTARCTIC JOURNAL Maestrichtian outside Seymour Island. P. tnagnificum occurs in References Maestrichtian and Danian strata (e.g., Stanley 1965; Drugg Askin, R.A. 1983. Campanian palynomorphs from James Ross and 18(5), 1967) and D. medcalfii in Paleocene/Early Eocene strata in Aus- Vega Islands, Antarctic Peninsula. Antarctic Journal of the U.S., tralia (Stover 1973). Among the species occurring above the 63-64. Askin, R.A., and R.F. Fleming. 1982. Palynological investigations of "transition zone" S. was described from Maestrich- obscurum Campanian to lower Oligocene sediments on Seymour Island, Ant- from tian/Danian rocks (Drugg 1967) and S. macrnurdoense arctic Peninsula. Antarctic Journal of the U.S., 17(5), 70-71. Lower Tertiary (? Eocene) erratics in McMurdo Sound, Ant- Drugg, W.S. 1967. Palynology of the upper Moreno Formation (Late arctica (Wilson 1967). The latter species also occurs in the Cretaceous-Paleocene) Escarpado Canyon, California. Palaeon- Eocene of Seymour Island. "Wide hexa" species of Deflandrea tographics, 12013, 1-71. characterize Paleocene and younger strata. Huber, B.T., D.M. Harwood, and P.N. Webb. 1983. Upper Cretaceous In summary, there does not appear to be any evidence for an microfossil biostratigraphy of Seymour Island, Antarctic Peninsula. abrupt change in the marine or non-marine palynomorph rec- Antarctic Journal of U.S., 18(5), 72-74. Lange, D. 1969. Mikroplankton aus dem Fischton von Stevns Klint auf ord at Seymour Island at the KIT boundary. A gradual ap- 24-25 (III), 110-121. (In German.) pearance of new non-marine plant species, particularly an- Seeland. Beitrage zur Meereskunde, Macellari, C.E., and W.J. Zinsmeister 1983. Sedimentology and mac- giosperms, is evident through the Campanian/Maestrichtian/ ropaleontology of the Upper Cretaceous to Paleocene sequence of Paleocene section. Seymour Island. Antarctic Journal of the U.S., 18(5), 69-71. Samples from further southwest at Robertson Island contain Stanley, E.A. 1965. Upper Cretaceous and Paleocene plant microfossils non-marine and some marine species in common with Campa- and Paleocene dinoflagellates and hystrichosphaerids from north- nian assemblages previously found at Vega Island (Askin 1983). western South Dakota. Bulletins of American Paleontology, 49(222), They show some compositional differences in the marine com- 1-384. ponent, however, and probably record different marine facies in Stover, L.E. 1973. Paleocene and Eocene species of Deflandrea (Dino- these correlative intervals. phyceae) in Victorian coastal and offshore basins, Australia. Geo- I appreciate the care and quality of sample collecting by logical Society of Australia. (Special Publication No. 4.) 167-188. Wilson, G.J. 1967. Some new species of Lower Tertiary dinoflagellates Frederic C. Barbis and James M. Robinson and the support of from McMurdo Sound, Antarctica. New Zealand Journal of Botany, 5(1), other members of the Seymour expedition and the captain and 57-83. crew of the USCGC Westwind. I thank Stephen R. Jacobson for Wilson, G.J. 1978. The dinoflagellate species Isabelia druggii (Stover) and helpful discussion and Kenneth C. Pill for sample preparations. I. seelandica (Lange): Their association in the Teurian of Woodside This research is supported by National Science Foundation Creek, Marlborough, New Zealand. New Zealand Journal of Geology grant DPP 80-20095. and Geophysics, 21(1), 75-80.

echinoids, bivalves, gastropods, and arthropods occur in these Late Cretaceous marine reptiles from sediments, indicating Campanian to Maestrichtian age (Rinaldi Antarctica et al. 1978). Fossil reptiles are usually found scattered in hard concretion- ary boulders of sandstone. Nowhere could these sandstone S. CHATTERJEE, layers be located in situ. As a result, articulated skeletons are B.J. SMALL, and M.W. NICKELL extremely rare. So far two partial skeletons of plesiosaurs have been found in the unconsolidated silty sandstones. Except for The Museum isolated braincases and jaw fragments, the rest of the material Texas Tech University represents postcranial skeletons of several individuals. Lubbock, Texas 79409 Because most of the bones were found in the hard, non- calcareous sandstone, preparation of the material will be en- Chatterjee and Zinsmeister (1982) reported the discovery of tirely mechanical and thus a time-consuming process. At this plesiosaurs, mosasaurs, bony fish, and sharks from Seymour stage, the identification of taxa is tentative, and finer diagnosis Island, Antarctic Peninsula. Further vertebrate assemblages must wait until the preparation of the material is completed. have been recovered from the same island during the 1983-1984 From the shoulder girdle and paddle it appears that the austral summer. The material was found in the late Cretaceous plesiosaurs from Seymour Island are very similar to elas- Lopez de Bertodano Formation of the Marambio Group. The mosaurs. These long-necked giant reptiles reached a length of lithologies include loosely consolidated sandstones and silty 15 meters. Among mosasaurids, both plioplaticarpines and sandstones which crop out in the southern two-thirds of tylossaurines were present. These forms are characterized by Seymour Island. Abundant invertebrates such as ammonites, short bodies and long, pointed tails.

1984 REVIEW