the range contain more rocks of intermediate com- Geological investigations position than previously thought (Daiziel et al., 1974a). The volcanics thus may represent a rem- on Seymour Island, nant arc behind the Lower Cretaceous marginal Antarctic Peninsula basin recently recognized in the Southern Andes (Daiziel et al., 1974b).

(3) Andean Precordillera. Detailed structural map- D. H. ELLIOT 1 , C. RINALDI 2 , W. J . ZINSMEISTER1, ping of the east-west trending part of the Precor- T. A. TRAUTMAN 1 , W. A. BRYANT 3 , and dillera north of Cordillera Darwin was begun by R. DEL VALLE4 Ms. Winslow, assisted by Linda Raedeke, University of Washington. Institute of Polar Studies and (4) Patagonian batholith. Dr. Stern, assisted by Department of Geology and Mineralogy Janet Stroup, Lamont-Doherty Geological Obser- The Ohio State University vatory, and by M. Alexandra Skewes, Universidad Columbus, Ohio 43210 de Chile, traversed the Patagonian batholith north of the Strait of Magellan to collect samples for 2Comisi6n Nacional de Energia Atómica later petrologic and geochemical studies. Buenos Aires, Argentina (5) Cenozoic and Recent igneous bodies. Dr. Stern Department of Geology and party also studied and collected from such late Northern Illinois University Cenozoic plutons of the Andean Precordillera as DeKalb, Illinois 60115 Cerro Paine, and the recently active volcanoes, such as Monte Burney. 4Direcc16n Nacional del Antártico Instituto Antártico Argentino We thank Captain Pieter Lenie and the crew of Buenos Aires, Argentina RIV Hero for their enthusiastic support of Dr. de Wits party. The work in Chile was supported by the Empresa Nacional del Petróleo. The assistance Seymour Island, about 100 kilometers southeast of Srs. Eduardo Gonzalez, Salvador Harambour, of the Antarctic Peninsula (figure 1), has the only Bernardo Bergman, and Raül Cortés was in- known exposed marine Lower Tertiary in Antarc- valuable. Finally, we thank the Chilean navy for tica. The island, first sighted by James Clark Ross transportation in the Beagle Channel. in 1843, has considerable historical interest. An This project is supported by National Science O expedition under Norwegian whaling captain C. A. Foundation grants pp 74-21415, Gx-34410, and Larsen visited the island in 1893 and made the first DES 75-04076. collections of Tertiary fossils (Sharman and New- ton, 1894, 1898); it was more extensively sampled by the Swedish South Polar Expedition (1901 to References 1903), which discovered fossil plants, penguins, and Cretaceous invertebrates, and also established an Daiziel, I. W. D. 1971. Structural studies in the Scotia Arc: the South Orkney Islands. WV Hero Cruise 71-I. Antarctic Jour- outline of the geologic history of the northern nal of the U.S., VI(4): 124-126. Antarctic Peninsula (Andersson, 1906; Norden- Dalziel, I. W. D. 1974. Evolution of the margins of the Scotia skjöld, 1905, 1913). Sea. In: The Geology of Continental Margins (Burk, C. A., and The island was examined briefly in 1953 and C. L. Drake, editors). New York, Springer-Verlag. 567-579. Daiziel, I. W. D., R. Caminos, K. F. Palmer, F. Nullo, and R. 1954 by members of the Falkland Islands Depen- Casanova. 1974a. Southern extremity of the Andes: geology dencies Survey (now the British Antarctic Survey) of Isla de los Estados, Argentine Tierra del Fuego. Ameri- (Adie, 1958), but no extensive studies were con- can Association of Petroleum Geologists. Bulletin, 58(12): ducted until the 1973-1974 season when geologists 2502-2512. Dalziel, I. W. D., and R. Cortés. 1972. Tectonic style of the from the Instituto Antártico Argentino mapped southernmost Andes and the Antarctandes. 24th Internaitonal most of the island. Four geologists from the Insti- Geological Congress, Montreal, August 1972. 316-327. tute of Polar Studies, The Ohio State University, Dalziel, 1. W. D., M. J . de Wit, and K. F. Palmer. 1974b. A fossil and from Northern Illinois University, were invited marginal basin in the southern Andes. Nature, 250: 291-294. Dalziel, I. W. D., David P. Price, and Gerry L. Stirewalt. 1970. Structural studies in the Scotia Arc: Elephant Island, Gibbs Island, Hope Bay, and Livingston Island. Antarctic Journal Isla Vicecomodoro Marambio is the name given on Argentine of the U.S., V(4): 100-101. maps.

182 ANTARCTIC JOURNAL

by the Instituto Antártico Argentino to participate sandstones in which fossils are concentrated; as ex- in their 1974-1975 field project on Seymour Island. pected, the shell banks are diachronous and die out The U.S. groups objective was to do a detailed study laterally. The shell banks of unit V do not appear of the stratigraphy, sedimentary petrology, and to differ except in their fossil content, and the inter- paleontology of the Tertiary strata to complement vening sands may also contain scattered molluscs. studies made the previous year by Argentine The bulk of the section is unconsolidated and con- geologists. sists of the following: laminated, fine-grained, gray sand alternating with dark, silty clay layers; light gray, well-sorted fine sand; mottled brownish gray Stratigraphy. Tertiary strata crop out on the north- to greenish gray bioturbated silty sand. ern part of the island and are centered about a Throughout the section the loose sands contain meseta with an elevation of about 200 meters concretionary horizons that may be laterally very (figure 2). The Tertiary is in fault contact with extensive. The concretions range in size up to 1.5 possible Cretaceous beds at the islands northern meters across, and some contain shell fragments point. The contact with the Cretaceous south of in their centers. Sheet-like pebble beds are very the meseta in Cross Valley is also faulted, though sparsely distributed throughout the section and in two places in a fault sliver an unconformity may consist of well-rounded clasts of volcanic, plutonic, be exposed. and sedimentary rocks. The clasts range up to 30 The Tertiary strata (figure 3) appear to be dis- centimeters across. The clasts indicate a provenance posed in a broad syncline with maximum dips on similar to the terrain now exposed to the north- the northeast limb attaining 10°; the syncline west, on the Antarctic Peninsula: the upper Paleo- plunges very gently to the southeast. The structure zoic Trinity Peninsula Series, acidic volcanic rocks is partly obscured by slumping. Probable Tertiary probably of Late Jurassic age, and "Andean" plu- strata also crop out in the fault slivers in Cross tonic rocks that may range in age from Early Juras- Valley; their relation to the rest of the Tertiary sic to Tertiary (Adie, 1972). sequence is uncertain, although it seems likely that Sedimentary structures include ripple-drift they are older. cross-lamination sets (figure 6), planar cross bed- The older (?) Tertiary strata (figure 4, unit I) con- ding, oscillation ripple marks, and both small- and sist of about 80 meters of immature, coarse sand large-scale cut and fill channels. Direction of sedi- that passes up into prominent pebbly bluffs. Above ment transport is inferred to have been south- the coarse sand and pebbly unit there are about easterly and away from a northeast to southwest- 22 meters of loose sand and clayey sand with sparsely distributed resistant beds. The loose sand has pronounced yellow limonitic (?) staining, con- tains sparse concretions, and locally carries fossil 58W -56W wood and coalified plant debris. The thin resistant tille sandstone beds also contain plant and wood debris. st(ott field Hope The remainder of the Tertiary sequence crops Boy out around the meseta. The oldest beds are exposed along a coastal cliff at the northwest end of Cross Valley, but because of faulting and the apparently unfossiliferous character of the beds the thickness there is difficult to determine. Much better expo- Erebus and sures occur at the northern end of the island where iij11j 2 about 150 meters of very poorly consolidated, thinly _J rf\$ASI) Terror Gulf bedded, fine-grained sand and silty sand (figure 4, 64S " 64S unit II) crop out below the lowest of the fossil shell ( banks that characterize much of the overlying unit JamesJo Ross L- (unit III). The remainder of the section, more 9 than 200 meters thick, can be divided into three Seymour units (figure 4, units III, IV, and V). Unit III is Island characterized by shell banks up to 1.5 meters thick Snow Hill Weddell that have abundant and very well preserved inver- Island Cope Longing Sea tebrate faunas (figure 5). Unit IV lacks shell banks, 9 50 km whereas unit V includes thin shell banks; the fossils 58W 56W in unit V are less abundant, and in many cases more restricted in type, than in unit III. The shell banks Figure 1. Location map for the James Ross and Seymour in unit III are pebbly to cobbly, medium to coarse islands area.

July/August 1975 183 - measured stratigraphic section 560 4k W Cape Wlman -- fault, location approximate, fault trace generalized

-9 Strike and dip of strata U 0 Upper Tertiary to Quaternary glacial deposits on top of the meseta

Lower Tertiary strata

Cretaceous strata• Bodman beds near Cape Wiman Point are provisionally given this age

640 15 S 5 S

Figure 2. Location and re- U connaissance geological U sketch map of Seymour Is- Seymou land (Argentine maps give alternate names for some features). The age of the Istand beds adjacent to Cape WI- man is uncertain, but here the beds are provisionally assigned to the Creta- ceous. The faulting in Cross Valley is much more complex than illustrated, 0 km 5 and fault slivers include 56°45 W both Cretaceous and Ter- tiary strata. trending shoreline. These clastic sediments were island were examined and consist of about 230 probably deposited in a high-energy, nearshore meters of very poorly consolidated sand with sparse deltaic and shallow marine environment. Observa- resistant sandstone beds and concretionary hori- tions along the southeast-facing coastal cliffs sug- zons. Cross bedding on a 1-meter scale was ob- gest periods of slumping of loose wet sediment served in the upper 110 meters. Resistant beds are down the delta front, the formation of submarine more abundant in the interval from 120 to 175 valleys up to 500 meters across and 100 meters meters; above this a prominent interval of varie- deep, and subsequent filling and repetition of the gated beds carries abundant wood and plant debris, process in adjacent locations. and is overlain by more loose sand. One Cretaceous The Cretaceous (?) strata at the north end of the section south of the meseta was measured for petro- logical sampling and comparison with the Tertiary. The measured section lies stratigraphically above the highest ammonite-bearing horizon and is itself overlain by an uncertain thickness of unmeasured Cretaceous. About 240 meters of section were meas- ured and in the lower part consist of very poorly . 4..,. . , . consolidated sand with occasional concretionary All horizons and thin resistant sandstone beds, some of which are glauconitic. The upper part consists of similar loose sand with very sparse cross-bedded units and resistant sandstone beds. Fossils through- ,- out this section and that at the islands north end are confined to a few poorly preserved plant re- mains and invertebrates.

-.-; Paleontology. Seymour Island contains an excep- Figure 3. Tertiary strata cropping out on the southwest side tionally abundant and diverse Upper Cretaceous- of the meseta (view toward the northwest). Tertiary invertebrate fauna together with a limited

184 ANTARCTIC JOURNAL flora and vertebrate fauna. The emphasis this season was placed on the Tertiary exposed around the meseta at the islands north end. Much effort was placed on the accurate geographic and strati- M Unit graphic location of all the fossil material collected. Molluscs represent the most abundant inverte- brate element in the Tertiary. The earliest data concerning the molluscan fauna are recorded in two short notes by Sharman and Newton (1894, 1898) on the material collected by the Larsen expe- dition. A more extensive account of the molluscan fauna was given by Wilckens (1912), who described and figured the material collected by the Swedish South Polar Expedition. He enlarged the known fauna to a total of 28 species, of which 22 were known only from the Antarctic. The remaining members of the fauna were also known to occur in South America. During 1974-1975, a large amount of material was obtained. Preliminary examination IL!4 of the molluscan fauna reveals the following: (1) molluscan fauna are considerably more diverse than originally thought, (2) the fauna can be tenta- tively divided into three biostratigraphic units based on evolutionary changes within the gastro- pod Struthiolarella nordenskjöldi lineage, and (3) many of the new species are closely related to simi- lar forms in the Lower Tertiary of New Zealand. It is apparent that the faunal similarities in the Cre- "U taceous between South America, Antarctica, and New Zealand persisted well into the Tertiary. The presence of an undescribed species ofAturia similar to the Eocene A. bruggeni Ihering from Tierra del Fuego tends to support the assignment (Simpson, 1971) of an Eocene age for the marine sequence on Seymour Island. The precise field location of the sample from HI which Granwell (1959, 1969) obtained plant micro- fossils that have been assigned a possible Maastrich- tian to Paleocene age remains uncertain, although the Tertiary beds in the fault slivers are the likely part of the section. Study of the foraminifera by Peter Webb and the palynomorphs by Stephen Hall, both of Northern Illinois University, may resolve this point; more precise age determina- tions for this and other parts of the section hope- Shell bank fully will be possible. Pebble horizon A small amount of fossil penguin, shark, and whale bone material was collected incidentally to Conglomerate the other studies. Most of this bone material ap- Resistant sandstone pears to consist of the remains of penguins, and Unconsolidated sand Unconsolidated sand, it is presumed to be similar to that described by silty clay, clayey sand Wiman (1905), Marples (1953), and Simpson (1971). Penguin bones appear to be scattered Scale iti meters (m) throughout the upper two-thirds of the section; near the top of the section one loosely consoli- Figure4. Generalized stratigraphic column for the Lowerler- dated sandstone contained a large number of bone tiary strata on Seymour Island. Unit I has been recognized only in the fault slivers in Cross Valley. The diagonal break in fragments. This fossiliferous horizon was en- unit II represents 100 meters of section that does not differ countered in several places. All material collected from that illustrated.

July/August 1975 185 than previously thought; the contact relations with the Cretaceous are complex; the section is Early g(c Tertiary in age and in part probably Eocene, as suggested by Simpson (1971); the provenance of the sediments was a terrain probably similar to the present Antarctic Peninsula; the sediments were deposited in a high-energy, shallow marine (pos- sibly deltaic) environment. The unusual combination of excellent exposures and abundant fossil material from a number of dif- ferent plant and animal groups on Seymour Island should give important new data concerning the Early Tertiary geologic history of the Antarctic Peninsula.

We express our gratitude to Argentinas Dirección Figure 5. Shell bank in unit lii of the Tertiary section; the large Nacional del Antártico and Instituto Antártico Ar- bivalves all belong to the genus Cucullaea. gentino for the support that afforded us the oppor- tunity to participate in the geological investigation occurred as float, and no attempt was made to of Seymour Island. This research was also sup- quarry or to bring back large bulk samples. A small ported by National Science Foundation grants oii 74-21509 to the Ohio State University and oii 74- whale skeleton (Zeuglodon) (?) was found, however; fragments of the lower jaw containing teeth should 22 894 to Northern Illinois University. yield valuable information concerning the whales early evolution. Large quantities of plant material occur near the References base of the Tertiary section (unit I) south of Cross Adie, R. J . 1958. Geological investigations in the Falkland Valley. Most of the plant material consists of car- Islands Dependencies since 1940. Polar Record, 9(58): 3-17. bonized wood fragments. Several tree trunks in this Adie, R. J . 1972. Recent advances in the geology of the Ant- vicinity were 10 meters long; small fragments of arctic Peninsula. In: Antarctic Geology and Geophysics (R. J. limbs and trunks occur throughout the entire sEc- Adie, editor). Oslo, Universitetsforlaget. 121-124. Andersson, J . G. 1906. On the geology of Graham Land. Bul- tion. Leaf material is locally abundant near the letin of the Geological Institute of the University of Upsala, 7: 19-7 1. base of the section. Cranwell, L. M. 1959. Fossil pollen from Seymour Island, Ant- arctica. Nature, 184(4701): 1782-1785. Cranwell, L. M. 1969. Antarctic and circum-Antarctic palynolo- Summary. The limited survey conducted in the gical contributions. AntarcticJournal of the U.S., IV(5): 197-198. 1974-1975 season and preliminary examination of Marples, B. J . 1953. Fossil penguins from the mid-Tertiary of the field data has shown the following: the Ter- Seymour Island. Falkland Islands Dependencies Survey. Scientific report, 5. 15p. tiary sequence is much thicker (about 500 meters) Nordenskjöld, 0. 1905. Petrographische Untersuchungen aus dem west Antarktischen Gebiete. Bulletin of the Geological Institute of the University of Upsala, 6: 234-246. Nordenskjold, 0. 1913. Antarktis. In: Handbuch der Re_gionalen Geologie (G. Steinmann and 0. Wilckens, editors). Heidelberg, Carl Winters Universitätsbuch handlung, 8(6): 1-29. Sharman, G., and E. J. Newton. 1894. Notes on some fossils from Seymour Island, in the antarctic regions, obtained by Dr. V Donald. Transactions of the Royal Society of Edinburgh, 37, part 3(30): 707-709. Sharman, G., and E. T. Newton. 1898. Notes on some additional fossils collected at Seymour Island, Grahams Land, by Dr. I ) nald and Captain Larsen. Proceedings of the Royal Society () Edinburgh, 22(1): 58-61. SI1I1}son, G. G. 1971. Review of fossil penguins from Seymour Island. Transactions of the Royal Society of London, series b, 178: 357-387. Wilckens, 0. 1912. Die Mollusken der antarktischen Tertiär- formation. Wi.ssen.cchaftliche Ergebnisse der Schwedischen Süd- polarexpedition, 1901-1903, 3(13): 1-62. Wiman, C. 1905. Uber die alttertiären vertebraten der Seymour- Figure 6. Ripple-drift cross-lamination in the unconsolidated Insel. Wusenschaftlzche Ergebnisse der Schwedzschen Sudpolar- sands of unit IV of the Tertiary section. expedition, 1901-1 903, 3(1): 1-37.

186 ANTARCTIC JOURNAL