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A Cool Temperate Climate on the Antarctic Peninsula Through the Latest Cretaceous to Early Paleogene

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A Cool Temperate Climate on the Antarctic Peninsula Through the Latest Cretaceous to Early Paleogene A cool temperate climate on the Antarctic Peninsula through the latest Cretaceous to early Paleogene David B. Kemp1*, Stuart A. Robinson2, J. Alistair Crame3, Jane E. Francis3, Jon Ineson4, Rowan J. Whittle3, Vanessa Bowman3, and Charlotte O’Brien2 1Environment, Earth and Ecosystems, Centre for Earth and Planetary Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK 2Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK 3British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK 4Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen, Denmark ABSTRACT ous times from the Maastrichtian to Eocene, although the stratigraphic Constraining past fl uctuations in global temperatures is cen- resolution of these data is coarse, so the absence of climatic variability tral to our understanding of the Earth’s climatic evolution. Marine could be an artifact. A complementary approach for reconstructing past proxies dominate records of past temperature reconstructions, continental climates is based on the methylation index and cyclization whereas our understanding of continental climate is relatively poor, ratio of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in particularly in high-latitude areas such as Antarctica. The recently bacterial membrane lipids (Weijers et al., 2007), known as the MBT/ developed MBT/CBT (methylation index of branched tetraethers/ CBT paleothermometer. It has the advantage over macrofl oral proxies in cyclization ratio of branched tetraethers) paleothermometer offers that the analyses can be carried out on relatively small quantities of bulk an opportunity to quantify ancient continental climates at temporal sediment sampled at high temporal resolutions, and it is, therefore, not resolutions typically not afforded by terrestrial macrofl oral prox- reliant on the presence and discovery of well-preserved fl ora. ies. Here, we have extended the application of the MBT/CBT proxy To further our understanding of Late Cretaceous to early Paleogene into the Cretaceous by presenting paleotemperatures through an climate evolution on Antarctica, we present here MBT/CBT–derived expanded sedimentary succession from Seymour Island, Antarctica, continental paleotemperature estimates through the latest Cretaceous to spanning the latest Maastrichtian and Paleocene. Our data indicate Paleocene of Seymour Island (paleolatitude ~65°S; Fig. 1). We com- the existence of a relatively stable, persistently cool temperate cli- pare these new continental paleotemperature estimates with estimates mate on the Antarctic Peninsula across the Cretaceous-Paleogene derived from existing paleofl oral proxies and sea-surface temperature boundary. These new data help elucidate the climatic evolution of (SST) data, and discuss our fi ndings in the context of circum-Antarctic Antarctica across one of the Earth’s most pronounced biotic reorga- climate evolution through the Late Cretaceous and early Paleogene. nizations at the Cretaceous-Paleogene boundary, prior to major ice- sheet development in the late Paleogene. Our work emphasizes the MATERIALS AND METHODS likely existence of temporal and/or spatial heterogeneities in climate Seymour Island contains one of the most expanded Cretaceous– of the southern high latitudes during the early Paleogene. Paleogene (K-Pg) successions known. Our studied interval comprises ~700 m of predominantly shallow-marine deltaic to estuarine sediments INTRODUCTION deposited in a large backarc basin fed from the Antarctic Peninsula mag- The latest Cretaceous to early Paleogene (70–41 Ma) was an inter- matic arc (Crame et al., 1991). The K-Pg boundary occurs in the up- val of signifi cant climatic and biotic reorganization. Central to our under- permost part of the López de Bertodano Formation, where it is marked standing of climatic evolution through this interval is the quantifi cation by a minor iridium anomaly (Elliot et al., 1994; Fig. 2). An unconfor- of global temperatures. The temperature record of the Late Cretaceous mity separates the López de Bertodano Formation from the overlying and early Paleogene is now reasonably well constrained for oceanic bot- Sobral Formation, which is early Paleocene in age (Bowman et al., 2012, tom waters (e.g., Cramer et al., 2009), whereas current knowledge of continental temperatures is substantially poorer. Notably, the true nature 30 S EARLY PALEOGENE o of terrestrial climate changes that may have infl uenced the major biotic New Zealand reorganizations associated with the end-Cretaceous mass extinction is debated (e.g., Wilf et al., 2003). Moreover, the Cretaceous–Paleogene 60 So climate evolution of high-latitude areas such as Antarctica is highly un- certain owing to a paucity of accessible study sites and inadequate dat- 1172 ing of existing data. Accurately quantifying past Antarctic temperatures U1356 is important, however, for assessing the veracity of paleoclimate models, Australia Antarctica and because of the key role that the continent played, and continues to PRESENT DAY 60°W play, in modulating global climate. Antarctic The Antarctic Peninsula is an area of specifi c interest to modern Peninsula and past climatic studies, as it seems particularly sensitive to change 65°S (e.g., Bowman et al., 2013). Continental paleotemperature estimates for SEYMOUR the Cretaceous–early Paleogene interval are reliant on relatively sparse ISLAND 250 km and isolated paleofl oral-derived data (Greenwood and Wing, 1995; Francis and Poole, 2002; Poole et al., 2005). These data suggest that Figure 1. Paleogeographic and present-day maps showing loca- the Antarctic Peninsula experienced cool temperate climates at vari- tion of Seymour Island, Antarctic Peninsula, and other localities discussed in text. Paleogeographic map is redrawn after Bijl et al. *E-mail: [email protected]. (2009). 1172 and U1356 are ocean drilling sites discussed in the text. GEOLOGY, July 2014; v. 42; no. 7; p. 583–586; Data Repository item 2014205 | doi:10.1130/G35512.1 | Published online 22 May 2014 GEOLOGY© 2014 Geological | July Society2014 | ofwww.gsapubs.org America. Gold Open Access: This paper is published under the terms of the CC-BY license. 583 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/42/7/583/3545208/583.pdf by guest on 02 October 2021 BIT index MBT’ CBT Soil pH Soil MAT ( o C) 0.4 0.6 0.8 1.0 0.3 0.5 0.7 0.9 1.1 1.3 5 5.5 6 6.5 7 04812162206 10 14 18 Strat.Formation age Height (m)Lithology 200 150 100 50 Cross Valley Valley Fm. Cross U P . A L E O 0 350 300 * * * 250 * 200 150 ** Sobral Formation 100 50 * L O W E R P A L O C N L O * K-Pg boundary 0 * -50 * -100 M A A S T . M A S * -28 -26 -24 -22 cl. svffmcvc 13 ( = Glauconite) δ organic ( VPDB) López de BertodanoLópez Fm. * C Figure 2. Organic geochemistry and paleotemperature data from Seymour Island, Antarctica. Methylation index of branched tetraeth- ers (MBT′), cyclization ratio of branched tetraethers (CBT), soil pH, and mean annual air temperature (MAT) are calculated using equa- tions of Peterse et al. (2012). Error bars equate to the ±5 °C uncertainty inherent in MBT′/CBT calibration data set (Peterse et al., 2012). BIT—branched and isoprenoid tetraether; MAAST.—Maastrichtian; UP.—Upper; PALEO.—Paleogene; cl.—clay; s—silt; vf—very fi ne sand; f—fi ne sand; m—medium sand; c—coarse sand; vc—very coarse sand. 1 and references therein; Fig. 2; see also the GSA Data Repository ). The dex values (mean of 0.56) preclude the use of the TEX86 proxy for marine Cross Valley Formation unconformably overlies the Sobral Formation, paleotemperature determination owing to the risk of terrestrially derived infi lling a deeply incised valley. Marine palynological data indicate that isoprenoid GDGTs biasing calculated TEX86 values (Weijers et al., 2006). δ13 ′ the Cross Valley Formation is late Paleocene in age (Wrenn and Hart, BIT index, Corg, MBT , CBT, soil pH, and calculated temperature are 1988; Fig. 2; see the Data Repository). plotted in Figure 2 against a composite log of the studied interval. MBT/CBT paleotemperatures were determined on 41 samples. For Our data demonstrate that MATs from the López de Bertodano and glycerol dialkyl glycerol tetraethers (GDGT) analysis, 8–20 g of sediment Sobral Formations average 12.4 ± 5 °C (Fig. 2). Within the Cross Valley was solvent extracted ultrasonically following the methods outlined by Formation this average decreases to 8.7 ± 5 °C, which includes one mark- Schouten et al. (2007). Extracts were analyzed for GDGT abundance us- edly lower value of 3.6 °C (Fig. 2). This value and four other relatively ing an Agilent 1200 HP-LC-MS online to a G6130A single quadrupole low temperatures (7–10 °C) calculated from the Cross Valley Formation δ13 mass spectrometer. Soil pH and mean annual air temperature (MAT) were are associated with organic matter with markedly higher Corg values calculated from analysis of MBT and CBT abundances using the calibra- than determined from samples elsewhere in the succession (>2‰ differ- tion equations of Peterse et al. (2012) (see the Data Repository). This latest ence; Fig. 2). It is thus possible that the organic matter in these samples calibration uses an MBT quantifi cation distinct from that originally pre- was at least partly derived from soils formed in a region distinct from ′ δ13 sented in Weijers et al. (2007), hereafter referred to as MBT (see Peterse that of the rest of the succession. However, Corg does not correlate with et al., 2012, for details). Repeat analysis of standards and samples yielded temperature or any other measured index in the succession, and samples MBT′ and CBT uncertainties that equated to absolute temperature errors associated with these relatively low temperatures are not associated with of <0.5 °C. This analytical uncertainty is well within the calibration error consistently different BIT indices or pH, MBT′, or CBT values. of ±5 °C (Peterse et al., 2012).
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