[Papers in Palaeontology, Vol. 6, Part 1, 2020, pp. 1–29] NEW FOSSIL WOODS FROM LOWER CENOZOIC VOLCANO-SEDIMENTARY ROCKS OF THE FILDES PENINSULA, KING GEORGE ISLAND, AND THE IMPLICATIONS FOR THE TRANS-ANTARCTIC PENINSULA EOCENE CLIMATIC GRADIENT by CHANGHWAN OH1 , MARC PHILIPPE2 , STEPHEN MCLOUGHLIN3 , JUSUN WOO4,MARCELOLEPPE5 ,TERESATORRES6, TAE-YOON S. PARK4 and HAN-GU CHOI7 1Department of Earth & Environmental Sciences, Chungbuk National University, Cheongju 28644, Korea; [email protected] 2Universite Lyon 1 & CNRS, UMR 5023, 7 rue Dubois, F69622 Villeurbanne, France; [email protected] 3Department of Palaeobiology, Swedish Museum of Natural History, Box 50007, S-104 05 Stockholm, Sweden; [email protected] 4Division of Polar Earth-System Sciences, Korea Polar Research Institute, Incheon 21990, Korea; [email protected], [email protected] 5Instituto Antartico Chileno (INACH), Plaza Munoz~ Gamero 1055 Punta Arenas, Chile; [email protected] 6Facultad de Ciencias Agronomicas Casilla 1004, Universidad Chile, Santiago, Chile; [email protected] 7Division of Polar Life Sciences, Korea Polar Research Institute, Incheon 21990, Korea; [email protected] Typescript received 14 August 2018; accepted in revised form 22 November 2018 Abstract: Ten embedded fossil logs sampled in situ from assemblages from Seymour Island, on the western and east- the middle Eocene volcano-sedimentary rocks close to Suf- ern sides of the Antarctic Peninsula respectively, are inter- field Point in the Fildes Peninsula, King George Island, preted to result from environmental and climatic gradients Antarctica, are assigned to Protopodocarpoxylon araucarioides across the Peninsula Orogen during the early Palaeogene. In Schultze-Motel ex Vogellehner, Phyllocladoxylon antarcticum particular, a precipitation gradient inferred across the Penin- Gothan, Agathoxylon antarcticum (Poole & Cantrill) Pujana sula at that time might have been induced by a rain-shadow et al., A. pseudoparenchymatosum (Gothan) Pujana et al. and effect. an unidentified angiosperm wood. Differences in the taxo- nomic representation and growth-ring characters of the Key words: fossil woods, Eocene, Antarctica, growth-ring Eocene woods on King George Island and coeval analysis, rainfall gradient, palaeoclimate. A LTHOUGH Antarctica is largely covered by an ice sheet The Antarctic Peninsula has been the subject of intense today, terrestrial plants flourished there from the Devo- palaeontological study because it represents the northern- nian (Grindley et al. 1980; Woolfe et al. 1990; McLough- most extent of Antarctica and has yielded abundant Cre- lin & Long 1994; Xu & Berry 2008), via the late taceous and Cenozoic terrestrial fossils (Cantrill & Poole Palaeozoic (Taylor et al. 1989; McLoughlin et al. 1997; 2005a). King George Island, the largest of the South Shet- Slater et al. 2012, 2015; Tewari et al. 2015), Mesozoic land Islands to the west of the Antarctic Peninsula (Jefferson 1982; Garland et al. 2007; Frobisch€ et al. 2010; (Fig. 1), is well known for occurrences of various terres- Escapa et al. 2011; Bomfleur et al. 2011a, b; Coria et al. trial fossils from Upper Cretaceous to Palaeogene depos- 2013) and into the Palaeogene (Goin et al. 1999; Ash- its. These records include invertebrate trace fossils (Yang worth & Kuschel 2003; Cantrill & Poole 2005a, b). Inten- & Shen 1999), bird tracks and feather prints (Covacevich sified cooling and ice-sheet development after the & Lamperein 1972; Covacevich & Rich 1982; Li & Zhen isolation of Antarctica and the establishment of the South 1994; Mansilla et al. 2012, 2014), numerous ferns, coni- Circumpolar Current at the end of the Eocene saw a dra- fers and angiosperm leaf impressions (Orlando 1963, matic decline in terrestrial vegetation there through the 1964; Birkenmajer & Zastawniak 1986; Tokarski et al. remainder of the Cenozoic (Coxall et al. 2005; Anderson 1987; Chun et al. 1994; Zhou & Li 1994a, b; Li & Zhou et al. 2011). 2007; Fontes & Dutra 2010), fossil woods (Lucas & Lacey © The Palaeontological Association doi: 10.1002/spp2.1256 1 2 PAPERS IN PALAEONTOLOGY, VOLUME 6 FIG. 1. Geographical and geological maps showing the study area and collecting site. A, geographical map of the Antarctic Peninsula with principal study areas indicated by arrows; AB transect see Figure 11. B, geographical map of King George Island with study area indicated by rectangle. C, geological map of the Fildes Peninsula with collecting site indicated by arrow (A, Artigas Station, Uruguay; B, Bellingshausen Station, Russia; F, Frei Station, Chile; E, Escudero Station, Chile; G, Great Wall Station, China; from Shen 1999). 1981; Torres 1984; Chun & Chang 1991; Zhang & Wang most investigations have used transported (reworked) 1994; Poole et al. 2001) and spore-pollen assemblages woody pebbles or loose blocks released by melting glaciers (Cao 1992, 1994). (Torres 1984; Zhang & Wang 1994; Poole et al. 2001). Much useful information about the Antarctic palaeoen- During the January 2015 field season, ten fossil logs vironments and palaeoclimate (Birkenmajer & Zastawniak embedded in volcano-sedimentary rocks were sampled 1989; Zastawniak 1994; Dutra & Batten 2000) has been in situ from close to Suffield Point on the Fildes Penin- gleaned from the fossil records. Growth-ring characters of sula, King George Island (Fig. 1). One of these logs had fossil woods from this region are particularly important already been noted by previous researchers (Torres 1990), for understanding southern high-latitude climates during but no anatomical study had been undertaken. Here we the Eocene, since other austral regions (e.g. Victoria Land, describe the anatomical features and identify these woods. New Zealand, Australia) host only sparse occurrences of We also compare the growth parameters of the Eocene permineralized woods of this age (Leisman 1986; Bamford wood assemblages from King George Island with woods & McLoughlin 2000; Francis 2000; Lee et al. 2012). In par- documented by other researchers (Gothan 1908; Torres ticular, fossil wood, which is quite abundant on King 1990; Torres et al. 1994; Pujana et al. 2014) from coeval George Island, has provided cursory information about strata on Seymour Island to the east of the Antarctic the composition of the high-latitude Palaeogene vegetation Peninsula in order to assess whether there were distinctive (Torres 1984, 1990; Poole et al. 2001). Although fossil vegetational and climatic differences between the western wood has long been known from the island, relatively little (forearc) and eastern (backarc) sides of the Antarctic research has been conducted on such material and, of that, Peninsula during the early Palaeogene. OH ET AL.: EOCENE WOODS FROM THE ANTARCTIC PENINSULA 3 GEOLOGICAL BACKGROUND researchers have employed a more detailed stratigraphical scheme for the FPG. Zheng & Liu (1990) subdivided the The Antarctic Peninsula region has a complex tectonic FPG into two formations and four members. Shen (1994) history, summarized in numerous studies (Barker 1982; reassigned these units to five formations: the Half Three Lawver et al. 1992; Maldonado et al. 1994; Robertson Point Formation of Late Cretaceous age, Jasper Hill and Maurice et al. 2003; Poblete et al. 2011), involving Gond- Agate Beach formations of Paleocene age, Fossil Hill and wanan breakup and subsequent convergence with palaeo- Block Hill formations of Eocene age, and Suffield Point Pacific crustal segments. From the mid-Cretaceous to Volcanics of Miocene age. Subsequently, Shen (1999) sub- Miocene, convergence of the Phoenix Plate from the west divided the Fossil Hill Formation into two members: the generated tholeiitic to calc-alkaline magmatism that pro- Great Wall Bay Member and Rocky Cove Member gressively migrated towards the outer portions of the (Figs 1, 2). peninsula producing a mountainous spine extending Although many researchers have attempted to refine the northwards in the direction of South America (Domack stratigraphic succession of the FPG, it remains poorly et al. 2003; Poblete et al. 2011). Rifting in the Bransfield resolved, because of strong local faulting, the lack of well- Strait (between the Antarctic Peninsula and South Shet- exposed continuous sections (Birkenmajer 1989), sediment land Islands) associated with roll-back of the Phoenix homogeneity and conflicting past stratigraphic unit defini- Plate beneath the South Shetland Islands began in the tions (see Hunt 2001; Cantrill & Poole 2012). Overall, the Oligocene (Birkenmajer 1994) or late Miocene and per- radiometric and biostratigraphic ages proposed for the FPG sists to the present (Barker 1982; Barker et al. 2003; Solari generally range from Late Cretaceous to Eocene. However, et al. 2008). Thus, upper Mesozoic to Palaeogene deposits the upper FPG might include some strata as young as late on King George Island (and other parts of the South Oligocene or early Miocene (Pankhurst & Smellie 1983; Shetland Islands chain) record sedimentation in a forearc Smellie et al. 1984; Fensterseifer et al. 1988; Birkenmajer & basin to the west of the emerging spine of the Antarctic Zastawniak 1989; Cao 1994; Shen 1994, 1999; Wang & Shen Peninsula. Since the Late Cretaceous, the Antarctic Penin- 1994). The K–Ar age of rocks at Suffield Point, nearby the sula region has been located at roughly the same latitude fossiliferous strata sampled in this study, is middle Eocene of 60–65°S (Lawver et al. 1992). (43 Æ 1–44 Æ 1 Ma; Smellie et al. 1984). The stratigraphy of the Fildes Peninsula, King George