Geology topics

D. A. Handwerger

Publications and source records attributed to D. A. Handwerger.

3 recordsLinked to original sources

USGS2004

Prydz channel fan and the history of extreme ice advances in Prydz Bay

During the late Neogene, the Lambert Glacier-Amery Ice Shelf drainage system flowed across Prydz Bay in an ice stream that reached the shelf edge and built a trough mouth fan on the upper continental slope. The adjacent banks saw mostly subglacial till deposition beneath slower-moving ice. The fan consists mostly of debris flow deposits derived from the melting out of subglacial debris at the grounding line at the continental shelf edge. Thick debris flow intervals are separated by thin mudstone horizons deposited when the ice had retreated from the shelf edge. Age control at Ocean Drilling Program Site 1167 indicates that the bulk of the trough mouth fan was deposited prior to ~780 ka with as few as three debris flow intervals deposited since then. This stratigraphy indicates that extreme advances of the Lambert Glacier-Amery Ice Shelf system ceased during the mid-Pleistocene. Possible causes for this change are progressive over-deepening of the inner shelf, a reduction in maximum ice volumes in the interior of the East Antarctic Ice Sheet caused by temperature change, and a change in the interaction of Milankovich cycles and the response time of the ice sheet.

Prydz Bay↗

USGS2004

Seismic stratigraphic correlations between ODP sites 742 and 1166: Implications for depositional paleoenvironments in Prydz Bay, Antarctica

New high-resolution seismic reflection data recorded between Ocean Drilling Program Sites 1166 and 742 are interpreted to link acoustic features to lithologic units at the two drill sites. New findings include: (1) Site 1166 drilled a deeper (older) section than Site 742; (2) Paleogene units mostly do not extend between the two sites, except the deformed sand unit (Units III [1166] and VI [742]); (3) the preglacial to glacial unconformity sampled at Site 1166 lies ~50 m below Site 742; (4) the Paleogene flooding surface at Site 1166 lies on top of Unit III, not within, as previously reported; and (5) Pliocene diatomaceous horizons correlated between the sites based on downhole logging cannot be traced between the two sites in seismic data. For the study region, we infer a progression from a preglacial setting on a low-relief alluvial plain to glaciomarine and subglacial settings. Late Cretaceous alluvial plain and lagoonal environments evolved to a late Eocene broad fluvial channel system or outwash plain. Marine transgression infilled and buried the channel system with glacial deposits that were extensively eroded during the Oligocene to late Miocene. Late Neogene environments were mostly subglacial with episodes of reduced ice and biogenic deposition.

Proceedings of the Ocean Drilling Program: Scienti↗

USGS2004

Synthetic seismograms linking ODP sites to seismic profiles, continental rise and shelf of Prydz Bay, Antarctica

Synthetic seismograms provide a crucial link between lithologic variations within a drill hole and reflectors on seismic profiles crossing the site. In essence, they provide a ground-truth for the interpretation of seismic data. Using a combination of core and logging data, we created synthetic seismograms for Ocean Drilling Program Sites 1165 and 1166, drilled during Leg 188, and Site 742, drilled during Leg 119, all in Prydz Bay, Antarctica. Results from Site 1165 suggest that coring penetrated a target reflector initially thought to represent the onset of drift sedimentation, but the lithologic change across the boundary does not show a change from predrift to drift sediments. The origin of a shallow reflector packet in the seismic line across Site 1166 and a line connecting Sites 1166 and 742 was resolved into its constituent sources, as this reflector occurs in a region of large-scale, narrowly spaced impedance changes. Furthermore, Site 1166 was situated in a fluvio-deltaic system with widely variable geology, and bed thickness changes were estimated between the site and both seismic lines.

Proceedings of the Ocean Drilling Program: Scienti↗