Sequence stratigraphy, micropaleontology, and foraminiferal geochemistry, Bass River, New Jersey paleoshelf, USA: Implications for Eocene ice-volume changes

Micropaleontological faunal studies coupled with foraminiferal geochemical analyses from the Bass River Site (Ocean Drilling Program [ODP] Leg 174AX; New Jersey, USA) reveal rapid changes in relative sea level due to million-year-scale glaciations during the early to middle Eocene, a time previously thought to have been mainly ice free. We examine benthic foraminiferal assemblages, stable isotopes (δ18O and δ13C), Mg/Ca, planktonic foraminiferal abundances, and ostracod abundances in eight lower to middle Eocene sequences at Bass River to reconstruct paleo–water depth and paleoceanographic changes within a sequence stratigraphic framework on the New Jersey paleo–continental shelf. Distinct benthic foraminiferal biofacies are identified and interpreted for paleodepth and environmental changes. Certain dominant species (e.g., Uvigerina spp., Cibicidoides eocaenus, Spiroplectammina alabamensis, Siphonina claibornensis, and Cibicidoides pippeni) indicate changes in water depth and/or environmental conditions. We estimate middle to outer neritic (50–100+ m) paleodepths for much of the early to middle Eocene, with maximum water depths (~150 ± 25 m) occurring in the early Eocene. We integrate these results with ostracod abundances and diversity, planktonic foraminiferal abundances, lithofacies, downhole logs, and core erosional surfaces to create a sequence framework for the early Eocene to early late Eocene of the New Jersey coastal plain. We compare the relationships among these sequences to foraminiferal biofacies of coreholes of the New Jersey Coastal Plain Drilling Project (Island Beach, Atlantic City, and ACGS#4), showing coeval hiatuses associated with regional base-level lowerings. Benthic and planktonic foraminifera δ18O coupled with low-resolution Mg/Ca measurements provide a first-order correlation of sequence boundaries and δOseawater variations, indicating glacioeustatic changes associated with the growth and decay of small ice sheets on the order of 20–30 m sea-level equivalent during the Eocene. INTRODUCTION The cause of eustatic changes has been widely debated (e.g., Moucha et al., 2008). Global mean sea level (GMSL) is controlled by fluctuations in either the ocean basin size or the volume of water in the ocean (e.g., Miller et al., 2005a), whereas relative sea level (RSL) is described by changes in accommodation space due to changes in (1) GMSL and/or (2) subsidence and/or uplift (Posamentier and Vail, 1988). The growth and decay of continental ice sheets produces rapid and large-scale changes in the volume of water (up to 40 m/k.y. and 200 m respectively), whereas water temperature and variations in groundwater and lake storage occur at high rates (10 m/k.y.) yet low amplitudes (~5–10 m) (e.g., Miller et al., 2005a). Fluctuations in ocean basin volume are controlled by slow (>1 m.y.) variations in sea-floor spreading rates, sedimentation, and continental collision (e.g., Miller et al., 2005a). Therefore, the only known mechanism that can explain large (>25 m) and rapid (<1 m.y.) changes in GMSL is the growth and decay of ice sheets (glacioeustasy). Glacioeustasy in a Greenhouse World The onset of continent-wide Antarctic glaciation occurred around the Eocene-Oligocene transition (EOT) and is marked by a prominent δ18O increase at 34–33.5 Ma (e.g., Kennett and Shackleton, 1976; Miller et al., 1991, 2008; Zachos et al., 1996; Coxall et al., 2005; Katz et al., 2008; Lear et al., 2008; Carter et al., 2017). The EOT is associated with a fall of atmospheric CO2 (e.g., DeConto and Pollard, 2003a; Pearson et al., 2009; Pagani et al., 2005, 2011) and/or a change in ocean circulation (e.g., Exon et al., 2004; Stickley et al., 2004; Scher and Martin, 2006; Livermore et al., 2007; Borrelli et al., 2014). In the first scenario, cooling caused by falling pCO2 allowed snow to accumulate and ice sheets to expand over Antarctica at high elevations (e.g., DeConto and Pollard, 2003a). In the second scenario, the opening of two gateways resulted in the development of the Antarctic Circumpolar Current (ACC) and led to Antarctic glaciation: (1) the Drake Passage, which isolated Antarctica from South America (Scher and Martin, 2006; Livermore et al., 2007); and (2) the Tasman Rise, which isolated Antarctica from Australia (Exon et al., 2004; Stickley et al., 2004). Although there is a consensus for the glaciation of much, if not all, of the Antarctic continent in the Oligocene, the period leading up to Antarctic glaciation remains poorly constrained. The overall cooling trend that led to the EOT began following the sustained warming period of the Early Eocene GEOSPHERE GEOSPHERE, v. 15, no. 2 https://doi.org/10.1130/GES01652.1 14 figures; 1 table; 1 set of supplemental files CORRESPONDENCE: fungm3@rpi.edu; megankfung @gmail.com CITATION: Fung, M.K. , Katz, M.E. , Miller, K.G. , Browning, J.V. , and Rosenthal, Y. , 2019, Sequence stratigraphy, micropaleontology, and foraminiferal geochemistry, Bass River, New Jersey paleoshelf, USA: Implications for Eocene ice-volume changes: Geosphere, v. 15, no. 2, p. 502–532, https://doi.org/10.1130 /GES01652.1. Science Editor: Raymond M. Russo Associate Editor: Cinzia Cervato Published online 19 February 2019 This paper is published under the terms of the CC-BY-NC license. © 2019 The Authors Received 21 December 2017 Revision received 11 October 2018 Accepted 9 January 2019 Downloaded from https://pubs.geoscienceworld. org/gsa/geosphere/article-pdf/4663947/502.pdf by guest on 31 October 2019