Glaciomarine Sediment Facies: Using Geomorphic Contexts and Multi-Proxy Analysis to Build Ice-Sheet Retreat Models

Existing glaciomarine facies models provide a framework for interpreting deglacial stratigraphic sequences, but lack geomorphic contexts that can further constrain ice behavior. Recently improved high-resolution multibeam swath bathymetric technology allows us to revisit these models with a geomorphic understanding. Recently acquired data from the Ross Sea reveals numerous ice-sheet retreat features, iceberg furrows, and subglacial meltwater channels not clearly observable in lower resolution datasets. This dataset is coupled with targeted sediment cores to refine facies models. Using detailed grain-size analysis, geotechnical properties, and microfossil analyses, we identify distinct units and infer facies based on relationships to geomorphic features. Key retreat facies include grounding line proximal, open marine, and subglacial meltwater deposits. With the addition of legacy cores, we have a dense dataset for examining spatial constraints of facies. We find evidence for multiple grounding line proximal processes ranging from passive basal melt to subglacial meltwater expulsion, identified by varying degrees of sorting and sand content. The open marine facies is composed of diatomaceous sandy silt that is either barren or contains only agglutinated foraminifera. Subglacial meltwater deposits are distinguished by sorted fine silt with little to no coarse material, display a massive to laminated character, and are found within other retreat facies. We do not recognize a distinct sub-ice shelf facies. Rather, sediments found in the sub-ice shelf environment consist of grounding line proximal deposits, meltwater deposits, and advected open marine material. Calcareous benthic and some planktonic foraminifera occur in grounding line proximal deposits while open marine deposits contain only arenaceous foraminifera. Preliminary examination of Pine Island Bay and Marguerite Bay cores indicate similar facies character and distribution patterns, including widespread meltwater deposits. This revised facies model will be useful for understanding processes that influence grounding line stability, and for interpreting cores without geomorphic context, such as drill core and surface sediment cores from early cruises.