Chemostratigraphy of the early Pliocene diatomite interval from MIS AND-1B core (Antarctica): Palaeoenvironment implications

Abstract

The AND-1B drill core (1285 m-long) was recovered, inside the ANDRILL (ANtarctic geological DRILLing) Program, during the austral summer of 2006/07 from beneath the floating McMurdo Ice Shelf. Drilling recovered a stratigraphic succession of alternating diamictites, diatomites and volcaniclastic sediments spanning about the last 14 Ma. A core portion between 350 and 480 mbsf, including a 80 m-thick diatomite interval recording the early Pliocene warming event, was investigated in term of opal biogenic content and element geochemistry. Across the diatomite interval, in spite of the lithological uniformity, a fluctuating biogenic opal profile mirrors the δ 18O record, testifying a decrease in productivity when temperature drops as a consequence of small glacial fluctuations. The comparison of biogenic opal data with Chaetoceros spp. abundances from Konfirst et al. (2012) documents alternations between periods of high primary productivity in stratified surface waters and of enhanced terrigenous input in ice-free conditions. Cluster analysis discriminates elements associated to terrigenous input from those subject to biogenic control. Further separation in sub-cluster was interpreted in term of different element response to changes in provenance but also to depositional/early diagenetic conditions at the seafloor. Whilst K and Ti are related to different sediment sources confirming previous studies from the same interval, V, Zn and, to a lesser extent, Fe, document reducing/anoxic conditions during the diatomites deposition (in particular in 400-460 mbsf interval). Mg, Sr and Mn contents are related to authigenic carbonate precipitation whilst Ba is interested by nonsteady-state processes leading to local peaks of barium below the sulphate-rich/sulphate-poor pore water boundary where generally the low degree of barite saturation is responsible for Ba remobilization. Such alteration in depositional dynamics, responsible of the precipitation of an oxygen-depleted barium phase, was probably induced by change in sedimentation rate and/or in palaeoenvironmental conditions.

Stratigraphic architecture of the Cenozoic succession in the McMurdo Sound region, Antarctica: An archive of polar palaeoenvironmental change in a failed rift setting

“…), the dominant lithologies are diamictites (recording glacial maxima) and fine‐grained rocks, particularly biochemical oozes (diatomites) that record glacial minima, with subordinate proportions of other facies (Naish et al ., , ; McKay et al ., ). One particularly long interval of diatomite from 438 to 376 mbsf records the interval 3·6 to 3·4 Ma (Naish et al ., ) and indicates a time of sustained, largely ice‐free conditions in that part of the basin (Konfirst et al ., ; Scopelliti et al ., ). This and the overlying interval (440 to 280 mbsf) also contain robust Zoophycos and other marine trace fossils (Miller et al ., ) that are reminiscent of the Oligocene succession.…”

Fossil proxies of near-shore sea surface temperatures and seasonality from the late Neogene Antarctic shelf

“…In the early Pliocene, (seasonally) open-water conditions lasted through a series of orbital cycles. Best estimates suggest that these ice-free periods in the western Ross Sea lasted for hundreds of thousands of years in intervals between 4.5 and 3.4 Ma (Scopelliti et al 2013). Although many circumstances could have caused cooling between the early and late Pliocene (e.g.…”