Abstract
New paleomagnetic results from the late Eocene-Middle Miocene samples from Deep Sea Drilling Project Site 274, cored during Leg 28 on the continental rise off Victoria Land, Ross Sea, provide a chronostratigraphic framework for an existing paleoclimate archive during a key period of Antarctic climate and ice sheet evolution. Based on this new age model, the cored late Eocene-Middle Miocene sequence covers an interval of almost 20 Myr (from ∼35 to ∼15 Ma). Biostratigraphic constraints allow a number of possible correlations with the Geomagnetic Polarity Time Scale. Regardless of correlation, average interval sediment accumulation rates above 260 mbsf are ∼6 cm/kyr with the record punctuated by a number of unconformities. Below 260 mbsf (across the Eocene/Oligocene boundary) interval, sedimentation accumulation rates are closer to ∼1 cm/kyr. A major unconformity identified at ∼180 mbsf represents at least 9 Myr accounting for the late Oligocene and Early Miocene and represent non-deposition and/or erosion due to intensification of Antarctic Circumpolar Current activity. Significant fluctuations in grain size and magnetic properties observed above the unconformity at 180 mbsf, in the Early Miocene portion of this sedimentary record, reflect cyclical behavior in glacial advance and retreat from the continent. Similar glacial cyclicity has already been identified in other Miocene sequences recovered in drill cores from the Antarctic margin.
Highlights
Deep Sea Drilling Program (DSDP) Leg 28 (Figure 1) was designed to explore the long-term climatic, biostratigraphic and geological history of Antarctica and its environments (Hayes and Frakes, 1975)
Magnetic susceptibility and rock magnetic analyses were conducted at the Centro Oceanográfico de Registros Estratigráficos (CORE) at the Instituto Oceanográfico da Universidade de São Paulo (IO USP) using a Microtrac Bluewave-SIA, an AGICO MFK1-FA Kappabridge, and a Vibrating Sample Magnetometer (VSM) MicroMag 3,900 Princeton-Lake Shore Cryotronics, respectively
We present a new magnetostratigraphic chronology for an upper Eocene to Middle Miocene sedimentary section cored during DSDP Leg 28 (Site 274) on the continental rise off Victoria Land, Ross Sea
Summary
Deep Sea Drilling Program (DSDP) Leg 28 (Figure 1) was designed to explore the long-term climatic, biostratigraphic and geological history of Antarctica and its environments (Hayes and Frakes, 1975) Such geological records provide insights into modern and future climate sensitivity estimates, for time periods characterized by the presence of continental ice sheets and a paleogeography similar to modern (e.g., Markwick, 2007; Farnsworth et al, 2019). 23 Ma), characterized by a ∼1‰ positive excursion in marine benthic foraminiferal δ18O records (e.g., Wilson et al, 2009; Beddow et al, 2016) and associated with a large-scale Antarctic ice sheet expansion at the Oligocene-Miocene transition This event was dramatic in scale, with the East Antarctic Ice Sheet (EAIS) estimated to have grown from 50 to 125% of its present-day size (e.g., Pekar et al, 2006). As in the Oligocene, the cooling during the Miocene was not monotonic, but characterized by swings between cooler and warmer climate (e.g., Miller et al, 1991; Zachos et al, 1997; Zachos et al, 2001; Lear et al, 2004; Holbourn et al, 2005; Shevenell et al, 2008; Holbourn et al, 2013; Holbourn et al, 2014; Holbourn et al, 2015; Lear et al, 2015; Holbourn et al, 2018; Liebrand et al, 2017; Westerhold et al, 2020)
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