Investigation of the grain size, shape, and texture of the Perseverance Drift, Antarctic Peninsula: Sediment transport history and Holocene variability

The Perseverance Drift, on the northern Antarctic Peninsula continental shelf, records changes in ocean and ice conditions throughout the Holocene. This study uses the sedimentary archive contained in a 25.81m jumbo piston core taken from a ~100m thick sedimentary drift deposit. The drift deposit is composed of laminated, black- to olive-colored diatomaceous mud and ooze; several horizons of ikaite crystals occur throughout the section. Grain size, grain shape, and grain textures of sediments in the drift deposit can be used to determine sediment transport history and assess variations in the relative proportions of current-transported, iceberg-rafted, and aeolian-transported sediment. Based on grain size and lithologic description, four sediment facies were assigned. Facies 1 and Facies 3 contain a high abundance of terrigenous material brought to the site by strong currents and aeolian processes to sea ice. The presence of sea ice causes a decrease in phytoplankton growth. The lack of biogenic material amplifies the terrigenous signal. Facies 2 and Facies 4 are dominated by biogenic sedimentation; in these two facies terrigenous sediment is delivered by currents and ice rafting. In all facies, there is an input of terrigenous sediment by aeolian processes. Ikaite occurs throughout the core, and there is no direct correlation between ikaite intervals and the facies. Based on the four facies, two units are assigned to the site: Unit 1, representing a warmer, open marine environment, and Unit 2, representing an open marine environment with varied sea ice. These are interpreted to be a Warm Period, from present to 1,700 cal. yr. BP, and the Neoglacial, from 1,700 to >3,375 cal. yr. BP. The end of the Neoglacial in the Bransfield Basin to the west of the Perseverance Drift occurs at nearly the same time. Grain microtextures show a very high abundance of silica precipitation, covering textures that would give clues about the transport history to the site. The silica precipitation is interpreted to form quickly and in situ. The high-resolution grain-shape results are inconclusive because authogenically precipitated silica obscures the original shape of the grain.