ژئومورفولوژی شیب و خیز قاره ای
Abstract
۱٫ Introduction
۲٫ Data and methods
۳٫ Results
۴٫ Discussion
۵٫ Conclusions
Declaration of Competing Interest
Acknowledgments
References
Abstract
The continental slope and rise seaward of the Totten Glacier and the Sabrina Coast, East Antarctica features continental margin depositional systems with high sediment input and consistent along-slope current activity. Understanding their genesis is a necessary step in interpreting the paleoenvironmental records they contain. Geomorphic mapping using a systematic multibeam survey shows variations in the roles of downslope and along slope sediment transport influenced by broad-scale topography and oceanography. The study area contains two areas with distinct geomorphology. Canyons in the eastern part of the area have concave thalwegs, are linked to the shelf edge and upper slope and show signs of erosion and deposition along their beds suggesting cycles of activity controlled by climate cycles. Ridges between these canyons are asymmetric with crests close to the west bank of adjacent canyons and are mostly formed by westward advection of fine sediment lofted from turbidity currents and deposition of hemipelagic sediment. They can be thought of as giant levee deposits. The ridges in the western part of the area have more gently sloping eastern flanks and rise to shallower depths than those in the east. The major canyon in the western part of the area is unusual in having a convex thalweg; it is likely fed predominantly by mass movement from the flanks of the adjacent ridges with less sediment input from the shelf edge. The western ridges formed by accretion of suspended sediment moving along the margin as a broad plume in response to local oceanography supplemented with detritus originating from the Totten Glacier. This contrasts with interpretations of similar ridges described from other parts of Antarctica which emphasise sediment input from canyons immediately up-current. The overall geomorphology of the Sabrina Coast slope is part of a continuum of mixed contourite-turbidite systems identified on glaciated margins.
Introduction
Studies of the Antarctic margin have shown that the continental slope and rise are the major sink for sediment removed from the continent for at least 34 Ma of episodic glaciation (Cooper and O’Brien, 2004). The expression of this long history on the slope and rise is an array of geomorphic features that have only been well documented in a few areas (e.g. Rebesco et al., 1996, Dowdeswell et al., 2006, Gales et al., 2013, Amblas and Canals, 2016, Larter et al., 2016). Where the Antarctic slope and rise have been well studied, their geomorphology reflect high sediment input from the continent and persistent along slope current activity producing a set of deposits included in the facies model for contourites (Rebesco et al., 1996). The Antarctic slope and rise are important sites for recovery of paleoclimate records so understanding depositional processes are an essential step in deciphering climate history. In addition, understanding Antarctic margin sedimentation can shed light on other settings with high sediment input and lateral current activity, including margins where ancient deposits have resource potential (e.g. Fonnesu et al., 2020). The East Antarctic margin is particularly important because it reflects the history of the longest-lived ice sheet on earth which is also the largest ice mass at present. Previous studies have relied mostly on single beam bathymetry and seismic reflection profiles (Kuvaas and Leitchenkov, 1992, Escutia et al., 2000) with multibeam coverage of the Antarctic Peninsula and George V Land margins (Rebesco et al., 2007, Amblas and Canals, 2016, Beaman et al., 2011). Areas seaward of large outlet glaciers of the East Antarctic Ice Sheet have not been surveyed with multibeam. These large outlet glaciers are potential barometers of wider ice sheet behaviour and points of vulnerability to warming climate (Pritchard et al., 2012). One of these is the Totten Glacier which flows through the Sabrina Coast between 112°E and 120°E.