Porosity and density of the AND-1B sediment core

• Main Authors: Niessen, Frank, Gebhardt, Andrea Catalina, Kuhn, Gerhard, Magens, Diana, Monien, Donata
• Format: Other/Unknown Material
• Language: English
• Published: PANGAEA 2013
• Subjects: AND1-1B; AND-1B; ANDRILL; Antarctic Geological Drilling; AWI_Paleo; DRILL; Drilling/drill rig; McMurdo Ice Shelf; McMurdo Station; MIS; Paleoenvironmental Reconstructions from Marine Sediments @ AWI; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; SPP1158; Antarc*; Antarctic; Antarctica; Ice Shelf; McMurdo Sound; Sea ice
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.834619; https://doi.org/10.1594/PANGAEA.834619

A study of density and porosity is presented for the 1285-m-long AND-1B core recovered from a flexural moat in the McMurdo Sound (Antarctica) in order to interpret sediment consolidation in an ice-proximal location on the Antarctic shelf. Various lithologies imply environmental changes from open marine to subglacial, and are numerically expressed in high-resolution whole-core wet-bulk density (WBD). Grain density data interpolated from discrete samples range from 2.14 to 3.85 g/cm3 and are used to calculate porosity from WBD in order to avoid the 5%-15% overestimation and underestimation of porosities obtained by standard methods. The trend of porosity extends from 0.5 near the top (Pleistocene) to 0.2 at the bottom (Miocene). Porosity fluctuations in different lithologies are superimposed with 0.2-0.3 in sequences younger than ca. 1 Ma and 0.5-0.8 in Pliocene diatomites. The AND-1B porosities and void ratios of Pliocene diatomites and Pleistocene mudstones exhibit a large negative offset compared to modern lithological analogs and their consolidation trends. This offset cannot be explained in terms of the effective stress at the AND-1B site. The effective stress ranges from 0 to 4000 kPa in the upper 600 m, and reaches 13,000 kPa at the base of the AND-1B hole. We suggest an excess of effective overburden stress of ~1700 and ~6000 kPa to explain porosities in Pliocene diatomites and Pleistocene mudstones, respectively. This is interpreted as glacial preconsolidation by subsequently grounded ice sheets under subpolar to polar, followed by colder polar types of glaciations. Information on Miocene consolidation is sparse due to alteration by diagenesis.