Magnetostratigraphic Chronology of a Cenozoic Sequence From DSDP Site 274, Ross Sea, Antarctica

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.

A Song of Ice and a Warm Southern Ocean

“…e lower part, cores 35-43, has a very low recovery and is prone to normal polarity directions. Magnetostratigraphic results for the upper Oligocene generally agree with those recently published by Jovane et al (2020), as shown in Figure 2. For the lower part of the record, our biostratigraphic results provide new tie points that indicate a lower-Oligocene age, instead of the previously published upper-Eocene age (Hayes et al, 1975;Jovane et al, 2020).…”

“…Magnetostratigraphic results for the upper Oligocene generally agree with those recently published by Jovane et al (2020), as shown in Figure 2. For the lower part of the record, our biostratigraphic results provide new tie points that indicate a lower-Oligocene age, instead of the previously published upper-Eocene age (Hayes et al, 1975;Jovane et al, 2020). e presence of the marker dinocyst Malvinia escutiana (FO = 33.7 Ma; Houben et al, 2011Houben et al, , 2019 in the lowermost sediment sample (Core 43, 404.66 mbsf), directly overlying the basement, indicates an Early-Oligocene age of the lowermost sediment that was also suggested from the age of the underlying ocean crust (Cande et al, 2000).…”

“…A few biostratigraphic constraints, including middle-Miocene radiolarian species in Core 19 (Hayes et al, 1975), indicate that the latest Oligocene and Oligocene-Miocene transition is missing in a large hiatus of ~7 Myr between cores 19 and 20 (181.23 mbsf). We abstain from correlating the normal magnetozone of Core 19 to a speci c chron, due to the limited biostratigraphic markers; thus, we support Jovane et al (2020), who suggested Langhian to Burdigalian ages. Extrapolating linearly between chrono and biostratigraphic tie points (Figure 2b, Table 2), we calculate the average sedimentation rate in the Oligocene to be 2.4 cm/kyr.…”

Miocene Phosphatization of Rocks From the Summit of Rio Grande Rise, Southwest Atlantic Ocean

“…Thus, the Miocene was a significant time for phosphogenesis globally. Important global phosphogenesis events coincided with two significant global climatic shifts: (a) during the Eocene-Oligocene boundary (∼34 Ma), when climate shifted from a warmer to a glacial Earth and (b) the late Oligocene-early Miocene transition (∼27-21 Ma) during a shift from a glacial to warmer Earth (Hein et al, 1993;Hyeong et al, 2013;Jovane et al, 2020;Schöllhorn et al, 2019). According to Sheldon (1980), major climatic shifts initiated phosphogenesis in the oceans because they promoted intense oceanic vertical mixing that mobilized high amounts of phosphorus stored in the deep ocean after long periods of sluggish vertical mixing.…”

Temperate Oligocene surface ocean conditions offshore of Cape Adare, Ross Sea, Antarctica

“…The abbreviations of the dinocysts species can be found in Table 1. The data were plotted in the C2 software program (Juggins, 2007). The analysis scores are provided in Table S4.…”