Frontiers and Opportunities in Antarctic Geosciences * Certosa di Pontignano * 29-31 July 2004
Ice Sheet Load, Erosion and Deposition Effects on Sedimentation:
A Geophysical and Geological Integrated Approach
L. DE SANTIS, F. ACCAINO, G. BOHM, G. BRANCOLINI, S. CERAMICOLA, U. TINIVELLA, V. VOLPI
Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS, Borgo Grotta Gigante 42/c, 34010 Sgonico (Trieste), Italy
*Corresponding author (ldesantis@ogs.trieste.it)
N. CORRADI, R. IVALDI
Dipartimento per lo Studio del Territorio e delle sue Risorse DIP.TE.RIS. Università di Genova, corso Europa 26,16132 Genova, Italy
The criteria to univocally reconstruct the volume and the extension of the ice sheet during its growth in the late
Cenozoic and to recognise its polar rather than temperate character remain contentious because of the difficulties in
dating the glacial record and because of the still limited onshore and offshore data.
The offshore stratigraphy is relatively more continuous than the onshore record and it has been better preserved in thick
prograding wedges bounding the Antarctic continent. Studies based on reflection seismic profiles and drill sites reveal a
drastic change in sedimentation pattern in the Mid- Late-Miocene to early Pliocene, likely due to a significant shift in
the ice sheet configuration.
Typical glacial process signature in the margin architecture linked to continental size ice sheet expansion and retreat are
topset beds lying on erosional, over-deepened paleo-sea floor surfaces, steep foreset wedges pinching out at the base of
the continental slope.
Up to now, only limited areas of the Antarctic margin have been investigated with an extensive low and high
resolution seismic surveys, which for the most part have not been properly tied to the stratigraphic information
obtained from drill site. Stratigraphic information obtained from the few drill site data in four sectors of the Antarctic
margin (Ross Sea, Antarctic Peninsula, and Prydz Bay), indicate that usually the topset beds are comprised of poorly
sorted, gravelly diamictites with only a few thin layers of diatomaceous, in some cases stratified mud or coarse sand. In
some cases these diamictites appear to be overcompacted, in other cases they are normally consolidated. The different
physical/mechanical character of the subglacial sediments has been interpreted as a result of the dynamic, rehology and
thickness of the ice sheet as well as strictly linked to climate variability (temperate vs. polar character of the ice sheet
since the Miocene)
We propose the investigation of two areas of the Antarctic margin (Prydz Bay and Ross Sea) focusing on the effects of
ice sheet load, erosion and deposition on subglacial sediments over glacial banks and troughs, since the early Miocene:
This study will be accomplished by using an integrated geophysical and geological approach. In particular the sediment
texture and the quantification and areal distribution of the sediment overcompaction by the ice load will be attempted
by:
1) direct geotechnical and physical properties analysis on the subglacial sediments from the existing drill site record;
2) indirect estimate of the sediment physical properties by re-processing of multichannel seismic data in order to
preserve the amplitude, Amplitude versus Offset analysis, acoustic impedance estimate, tomographic inversion, and prestack migration on existing multichannel seismic profiles collected across the drill sites;
3) characterization of sediments through seismic attribute analysis in order to obtain the distribution of the petrophysical
properties around the well locations.
A model showing the original morphology and palaeo sea bed reconstructions of the most significant Cenozoic time
slice will be finally produced by the application of 2-D and 3-D backstripping technique, using estimated sediment
properties, regional markers and palaeo-bathymetries . The final product of this investigation is inteded to provide new
insights on the dynamic regulating ice sheet configuration and its evolution through Cenozoic.