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An Early Paleogene Pollen and Spore Assemblage from the Sabrina Coast, East Antarctica

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An Early Paleogene Pollen and Spore Assemblage from the Sabrina Coast, East Antarctica Palynology ISSN: 0191-6122 (Print) 1558-9188 (Online) Journal homepage: https://www.tandfonline.com/loi/tpal20 New species from the Sabrina Flora: an early Paleogene pollen and spore assemblage from the Sabrina Coast, East Antarctica Catherine Smith, Sophie Warny, Amelia E. Shevenell, Sean P.S. Gulick & Amy Leventer To cite this article: Catherine Smith, Sophie Warny, Amelia E. Shevenell, Sean P.S. Gulick & Amy Leventer (2019) New species from the Sabrina Flora: an early Paleogene pollen and spore assemblage from the Sabrina Coast, East Antarctica, Palynology, 43:4, 650-659, DOI: 10.1080/01916122.2018.1471422 To link to this article: https://doi.org/10.1080/01916122.2018.1471422 Published online: 12 Dec 2018. Submit your article to this journal Article views: 116 View related articles View Crossmark data Citing articles: 1 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=tpal20 PALYNOLOGY 2019, VOL. 43, NO. 4, 650–659 https://doi.org/10.1080/01916122.2018.1471422 New species from the Sabrina Flora: an early Paleogene pollen and spore assemblage from the Sabrina Coast, East Antarctica Catherine Smitha, Sophie Warnyb, Amelia E. Shevenella, Sean P.S. Gulickc and Amy Leventerd aCollege of Marine Science, University of South Florida, St. Petersburg, FL, USA; bDepartment of Geology and Geophysics and Museum of Natural Science, Louisiana State University, Baton Rouge, LA, USA; cInstitute of Geophysics and Department of Geological Sciences, University of Texas at Austin, Austin, TX, USA; dDepartment of Geology, Colgate University, Hamilton, NY, USA ABSTRACT KEYWORDS Palynological analyses of 13 samples from two sediment cores retrieved from the Sabrina Coast, East Paleocene; Eocene; Aurora Antarctica provide rare information regarding the paleovegetation within the Aurora Basin, which Basin; Sabrina Coast; East today is covered by the East Antarctic Ice Sheet. The assemblages, hereafter referred to as the Sabrina Antarctica; Gambierina; Flora, are dominated by angiosperms, with complexes of Gambierina (G.) rudata and G. edwardsii rep- Battenipollis resenting 38–66% of the assemblage and an abundant and diverse Proteaceae component. The Sabrina Flora also includes Battenipollis sectilis, Forcipites sp. and Nothofagidites (N.) spp. (mostly belonging to the N. cf. rocaensis-cf. flemingii complex), along with a few fern spores, including Laevigatosporites ovatus, a moderate presence of conifers, and previously undescribed angiosperm morphospecies. Two of these, Battenipollis sabrinae sp. nov. and being Gambierina askiniae sp. nov., are described herein. A majority of the assemblage is interpreted as deposited contemporaneously with sedimentation, including Gambierina spp., which is traditionally assigned a Cretaceous–earliest Eocene age range. However, our age diagnosis for the Sabrina Flora, based on key morphospecies, indicates that sediment was most likely deposited between the latest Paleocene to early–middle Eocene, and that Gambierina rudata and G. edwardsii extended longer than previously proposed. 1. Introduction sequence, marine sediment cores were collected from out- cropping seismic reflectors in the lower part of the sequence The Aurora Subglacial Basin (ASB), one of the three largest and surrounding the regional unconformity at the base of subglacial basins in East Antarctica, is drained by large outlet Megasequence III. These data reveal a history of Cenozoic cli- glaciers terminating at the Sabrina Coast (115˚ to 121E and mate and environmental change within the ASB catchment, 67 S), East Antarctica (Figures 1 and 2, Ferraccioli et al. 2009; including a record of ice advance and retreat that suggests Young et al. 2011; Fretwell et al. 2013; Rignot et al. 2013; the EAIS is more sensitive to climate change than tradition- Greenbaum et al. 2015; Aitken et al. 2016). The region is ally thought (Gulick et al. 2017). presently sensitive to climate change, as indicated by the Two jumbo piston cores (JPC; NPB 14-02 JPC-54 and JPC- thinning and retreat of local outlet glaciers influenced by 55, see Figures 1–3 for locations) retrieved from the lower- warm modified Circumpolar Deep Water driven onto the most preglacial Sabrina Coast sediments (Megasequence I) Sabrina Coast continental shelf as westerly winds shift south- contain an abundant, diverse, and well-preserved terrestrial ward (Rintoul et al. 2016; Greene et al. 2017). Past regional palynomorph assemblage, as first reported in Gulick et al. climate sensitivity is also suggested by ice sheet and climate (2017). Here we detail this new terrestrial palynological models and marine geological observations, which indicate assemblage, termed the Sabrina Flora, and describe two pre- that ice caps may have nucleated in the Gambertsev viously undescribed species discovered in the Sabrina Coast Mountains and first reached the Sabrina Coast and Prydz Bay sediments. The Sabrina Flora provides a rich paleobotanical prior to continental scale Antarctic glaciation in the latest archive of the ASB catchment before and during ice sheet Eocene (DeConto and Pollard 2003; Gulick et al. 2017). development and adds to the available Paleogene East In 2014, the first marine seismic and geological investiga- Antarctic margin terrestrial palynomorph records from Prydz tions of Sabrina Coast continental shelf sediments were con- Bay (e.g. Macphail and Truswell 2004; Hannah 2006; Truswell ducted as part of the United States Antarctic Program RV/IB and Macphail 2009), the Shackleton Ice Shelf region (Truswell Nathaniel B. Palmer cruise NBP 14-02. From the resulting geo- 1983, 2012), the Wilkes Land margin (Domack et al. 1980; physical data, Gulick et al. (2017) identified three seismic Truswell 1983; Schrum et al. 2004; Pross et al. 2012; stratigraphic intervals, termed Megasequence I, II, and III Contreras et al. 2013), and the Ross Sea region, including the (Figure 3), interpreted to reflect pre-glacial, meltwater-rich McMurdo Erratics (Askin 2000; Levy and Harwood 2000) and glacial, and polar glacial environments, respectively. To con- McMurdo Sound (Truswell 1983; Mildenhall 1989; Hannah strain the age of the Sabrina Coast shelf sedimentary et al. 1998; Askin and Raine 2000; Raine and Askin 2001; CONTACT Sophie Warny [email protected] Geology and Geophysics, E235 Howe Russell Geoscience Complex, Baton Rouge 70803, US ß 2018 AASP – The Palynological Society Published online 12 Dec 2018 PALYNOLOGY 651 90°E 120°E Eucla Australia Indian Bremer Ocean Bremer Eyre Bight C ed 60°S una NBP14-02 JPC-54, -55 1166 Prydz Murray Bay Otway 60°E Aurora Subglacial U1356 150°E Basin Gi NBP01-01 Ba ppsland s s DF79-38 Sorell South Tasman Rise Antarctica Pacific 30°E 50 Ma Ocean McMurdo erratics 600 km Figure 1. Paleogeographic reconstruction of the Australo-Antarctic Gulf at 50 Ma (modified from the Ocean Drilling Stratigraphic Network (ODSN); Hay et al. 1999; van Hinsbergen et al. 2015). Sedimentary basins, including those with published pollen records of equivalent age, are indicated. Study location indicated by an open circle. respectively (Figure 3). Both cores recovered 20–40 cm of late Quaternary greenish gray diatom-rich mud (Unit I) with a sharp lower contact separating Unit I from Unit II (Figure 4). In core JPC-54, Unit II consists of sandy mud to diamict with angular igneous clasts interpreted as ice-rafted debris (IRD) (Gulick et al. 2017), while Unit II in JPC-55 consists of mica- rich mud with siderite concretions, including one 10 cm in diameter, and pyrite nodules (Figure 4). The sediments in both cores were recovered from strata stratigraphically below the first seismic evidence of grounded ice on the Sabrina continental shelf (Gulick et al. 2017). Thus, core JPC-55 sediments record the pre-glacial environment in the Aurora Basin prior to regional glaciation, while those in core JPC-54 reflect a environment where marine terminating gla- ciers were present, but ice had yet to advance onto the shelf. 3. Methods 3.1. Palynology To quantify absolute abundance of terrestrial palyno- Figure 2. Multibeam bathymetry of Sabrina Coast continental shelf collected during NBP14-02 (modified from Gulick et al. 2017; Fernandez et al. 2018). morphs and assign ages to Unit II in cores JPC-54 and JPC- Locations of sediment cores JPC-54 and JPC-55 (black circles) and seismic line 55, nine and eight samples, respectively, were split and 17 (black line) are indicated. Inset: Map of the Sabrina Coast shelf with location processed at Global Geolab Limited (Alberta, Canada) to and orientation of the NBP14-02 study area indicated by the multibeam data and sesimic survey lines. MUIS ¼ Moscow University Ice Shelf. (modified from extract terrestrial palynomorphs. Note that the two top Fretwell et al. 2013). samplesineachcorearenotdiscussedinthispaperas these represent modern deposition above an erosional sur- Prebble et al. 2006; Warny et al. 2009; Feakins et al., 2012; face (Figure 4). For each sample, 5 g of dried sediment Griener et al. 2013; Griener and Warny 2015). was processed using standard techniques. Acid soluble minerals (carbonates and silicates) were digested in HCl, 2. Stratigraphic context HF, followed by controlled oxidation. The residues were then rinsed to neutrality. Residues were concentrated by Cores JPC-54 (121 cm) and JPC-55 (170 cm) were collected filtration on a 10 lm mesh sieve and spiked with a known above and below a prograding clinoform in Megasequence I, quantity of Lycopodium spores to allow quantitative 652 C. SMITH ET AL. CDP 500 1500 2500 3500 4500 5500 6500 7500 8500 9500 10500 11500 12500 Line 17 landward MS-III 0.50 first grounded JPC-55 clinoforms JPC-54 ice MS-II MS-I 0.75 multiple 1.00 Two-way traveltime (sec) Two-way SSW NNE km 0 6.25 12.50 18.75 25.00 31.25 37.50 Figure 3. Seismic image collected on NBP14-02 utilized to target JPC-54 and 55 sites. Seismic line NBP14-02 Line 17 illustrates erosional surfaces and clinoforms. JPC-54 and JPC-55 are above and below these clinoforms, respectively.
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