Revision of the late Pleistocene stratigraphy of Bermuda

Abstract

The Quaternary stratigraphy of Bermuda is one of the world's most complete sedimentary records of interglacial highstands, representing at least the past million years. Yet in terms of the last interglacial (Rocky Bay Formation), marine isotope substage (MIS) 5e, only scanty deposits are preserved. In contrast, MIS 7, generally regarded as a diminutive interglaciation, exposes widespread emergent subtidal deposits of the Belmont Formation indicating a prolonged sea level highstand at ca. + 2.5 F 0.3 m. This ''Belmont paradox'' has prompted a reexamination of the geology of key sites along the South Shore of Bermuda.This revision of the late Quaternary stratigraphy of Bermuda is based on geological field observations; primarily the questionable origin of red soil-like deposits. It is concluded here that there is no physical evidence of the exposure of the upper Belmont surface for a full glacial cycle ( f 70 -100 ka), and that interbedded, reddish soil-like, lenticular deposits are the result of colluvial activity during mid-MIS 5e. Reexamination of previously published uranium-series (U/Th) ages indicates that several '' + 3-m notches'' contain a mix of ca. 125 ka and older coral ages. Contrary to previous works, this study favors an early MIS 5e interpretation of the coral ages from the + 2.5-m Belmont shoreline, which is further supported by amino acid racemization (AAR) ratios on whole-rock, Poecilozonites, Glycymeris, and Brachiodontes samples from shore and notch deposits. An updated AAR kinetic model demonstrates that the bulk of epimerization occurred during warm interglacial intervals between 130 and 80 ka and the last 10 ka of the Holocene. This revised stratigraphy of Bermuda now falls into accordance with a more general view of middle and late Pleistocene sea level history. D

PRESERVATION OF TRACE FOSSILS AND MOLDS OF TERRESTRIAL BIOTA BY INTENSE STORMS IN MID-LAST INTERGLACIAL (MIS 5c) DUNES ON BERMUDA, WITH A MODEL FOR DEVELOPMENT OF HYDROLOGICAL CONDUITS

“…Sea level was well above the platform margin, however, as platform flooding is required for substantial bioclastic sediment formation and subsequent transport to the shore (, 220 m). These observations are supported by previous studies on Bermuda that identified a sea level during MIS 5c at , 210 to 215 m (Vollbrecht, 1990;Hearty, 2002).…”

“…This lithologic unit correlates with the Hungry Bay Formation (HBF), formerly the Pembroke Member of the Rocky Bay Formation (Table 1; Fig. 3) (see discussion in Hearty, 2002). The Charles Island deposits yield an equivalent WR mean of 0.27 6 0.01 (N 5 2).…”

“…2; Table 2) correlate with Poecilozonites from the Southampton Formation (0.40 6 0.04 (N 5 36) (Hearty et al, 1992), which, along with marine facies, are correlated with MIS 5a (Vacher and Hearty, 1989;Ludwig et al, 1996;Dorale et al, 2010). The Harrington Member postdates MIS 5e (120 ka) and is correlated with a sea level regression during late MIS 5e, 5d and perhaps into MIS 5c (Hearty, 2002). Thus, the preferred correlation of the HBF, including the former Pembroke Member and Charles Island deposits, is with MIS 5c around 100 ka ago, based on stratigraphy and AAR values.…”

“…Below, we revive the original bottom-up interpretation of palmetto stumps as the external molds of tree trunks (Hearty, 2002) that were later filled with a mixture of sediment types. Curran and White (2001) and Curran et al (2008) investigated the extent of terrestrial trace and body fossils on several islands in the Bahamas, while Kindler et al (2008) described bird trackways in Eleuthera.…”

“…The island formations mapped by were later correlated with marine isotope stages (MIS) through independent U/Th dating (Harmon et al, 1983;Ludwig et al, 1996) and aminostratigraphic techniques (Hearty et al, 1992(Hearty et al, , 2004Hearty and Olson, 2010), with some subsequent minor modifications of the stratigraphic column (Hearty, 2002; Table 1). A litho-, chrono-, and biostratigraphic framework based on limestones and fossils (Hearty et al, 1992;Hearty and Olson, 2010) provides a reliable means to correlate and date most of the deposits from the island.…”