Inferring Glacial Dynamics From Temperate Glacimarine Grounding-Line Deposits
Abstract
Reconstruction of glacial dynamics from the glacimarine sediment record is dependent on our understanding of sedimentary and glacigenic processes. Development of positive relief grounding-line deposits in the marine record is a product of the rate of glacial retreat and the net sediment flux to the grounding-line deposystem. These deposits are consequently key for reconstructing past glacial dynamics. In temperate glacimarine systems, such as those along the southern coast of Alaska, high sediment flux is maintained during advance and retreat phases. This produces a sedimentary record that is temporally continuous but spatially discontinuous due to subglacial erosion and the point-source nature of grounding-line sediment flux. Here we present high-resolution seismic reflection data that record glacial dynamics within two Alaskan fjord systems (Muir Inlet and Disenchantment-Yakutat Bay) and two continental shelf glacial systems (Yakutat Sea Valley and Bering Trough). Collectively, these systems represent glacimarine sediment deposition throughout the entirety of the glacial cycle. The geometry of grounding-line deposits is interpreted to record the transition from laterally confined upper-fjord systems to the unconfined continental shelf/shelf-edge systems. As in most deposystems, sediment preservation increases offshore. The inner portions of fjords are scoured to bedrock, whereas their distal segments contain remnant, partially preserved glacial sequences buried beneath deposits from younger advances. Grounding-line deposits within the confined fjord setting consist of mounded morainal-bank deposits that are often stacked in a retrogradational pattern. The sheet-like geometry of older grounding-line deposits within Yakutat Bay is indicative of modern shelf environments, supporting earlier hypotheses that the present coastal plain is the result of progadation onto an inner paleo-shelf. The shelf edge systems tracts are characterized by grounding-line deposits that prograde over the shelf-break during glacial advance. This record of sediment preservation supports earlier interpretations regarding the redistribution of mass along a glaciated continental margin as sediment is eroded from fjords and redeposited on the shelf slope and abyssal plain. During glacial retreat, sediment accumulates on the shelf and within the fjords where it is stored until a glacial readvance. Interpreting sedimentary records that are chronologically well-constrained allows sediment flux across the margin to be quantified and provides a high-resolution record of glacial dynamics. Such records are necessary if we are to understand past climate dynamics and its potential relationship with tectonic processes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.C23C0505W
- Keywords:
-
- 0720 CRYOSPHERE / Glaciers;
- 3025 MARINE GEOLOGY AND GEOPHYSICS / Marine seismics;
- 3045 MARINE GEOLOGY AND GEOPHYSICS / Seafloor morphology;
- geology;
- and geophysics;
- 9315 GEOGRAPHIC LOCATION / Arctic region