Browsing by Subject "Sabrina Coast"
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Item Seismic stratigraphy and paleo-glaciology of Sabrina Coast, East Antarctica and Bering Trough, Gulf of Alaska(2015-05) Montelli, Aleksandr; Gulick, Sean P.S.; Blankenship, Donald; Mohrig, DavidExamination of the sedimentary record in areas occupied by fast flowing outlet glaciers and ice streams is critical for understanding ice sheet dynamics on millennial timescales. We use high-resolution seismic data together with log data and foraminiferal- based radiocarbon and isotope data from Integrated Ocean Drilling Program (IODP) Expedition 341 cores to examine the evolution of the Cordilleran Ice Sheet (CIS) in southeast Alaska. Evidence for at least seven advances of the Bering Glacier to the shelf break since the end of Middle Pleistocene Transition (MPT) are interpreted from the seismic data. Seismic data demonstrate two distinctive patterns of slope sedimentation, which are: (1) dominated by sediments bypassing a steep paleo-slope or (2) dominated by glacigenic debris flows (GDFs) that form a trough mouth fan (TMF) on a lower slope. Integration of seismic, well, and age data suggests that the TMF was formed as a result of three advances to the shelf break since ca. 140 ka, implying extreme (average > 4m/ka) rates of sediment delivery. Extraordinarily high sediment flux played a key role in the development of the margin architecture resulting from a temperate, highly aggressive Bering Glacial System and abundant source of erodible bedrock onshore (St. Elias orogeny). We use the first high-resolution seismic data acquired on the Sabrina Coast, East Antarctica, together with core data, to examine major transitions in glacial regime of East Antarctic Ice Sheet. Three large-scale megasequences represent changes in the dominant pattern of sedimentation: Megasequence I shows signs of Eocene fluvial and possibly glacio-fluvial sedimentation; Megasequence II provides evidence of Oligocene-Miocene polythermal glacial sedimentation with significant amount of meltwater; Megasequence III overlies the regional erosional surface that marks major Miocene ice sheet expansion and transition into polar (cold- based) ice sheet glacial regime with no significant evidence of subglacial meltwater preserved. Megasequence II exhibits preserved record of EAIS evolution starting from its first expansion. Seismic stratigraphic analysis suggests a dynamic glacial late Paleogene-early Neogene evolution including expansions of the EAIS across the shelf at least eight times, which is marked by erosional surfaces and chaotic acoustic character of overlying strata. We report on finding the first conclusive seismic evidence of deep, extensive tunnel valley systems incised into sedimentary substrate from Antarctic continental margins. The Sabrina Coast tunnel valley system was presumably formed during Oligocene as a result of the second major EAIS shelf expansion. Shallower erosion events observed in the upper part of Megasequence II suggest more extensive glaciations in the Oligocene compared to the Miocene.Item Submarine sedimentary basin analyses for the Aurora and Wilkes Subglacial Basins and the Sabrina Coast Continental Shelf, east Antarctica(2015-08) Frederick, Bruce Child; Blankenship, Donald D.; Dalziel, Ian W; Gulick, Sean P; Wilson, Clark R; Young, Duncan AThis dissertation focuses on the Wilkes Land region of the East Antarctic Ice Sheet (EAIS) that is predominantly characterized by two large subglacial basins, the Aurora Subglacial Basin (ASB) to the east and the Wilkes Subglacial Basin (WSB) to the west and immediately adjacent to the Transantarctic Mountains (TAM). The ASB and WSB are expansive covering an estimated 750,000 and 980,000 square kilometers, respectively. In addition, their bedrock geometry places them an average of 1.25 km below present day sea level, raising the possibility of fundamental instability through grounding line retreat. Subglacial sediment deformation has long been known to facilitate faster ice flow and significantly impact basal ice conditions including geothermal heat flux, groundwater flow, and frictional heat flux. Recently acquired aerogeophysical data over the interior ASB and WSB document extensive subglacial sedimentary basins that can be distinguished as smaller subbasins, each associated with adjacent topographic highlands and EAIS dynamics. The volumes of these interior subglacial subbasins vary between 26,349 +/- 10,885 km³ and 398,082 +/- 164,454 km³ in the ASB and 7,188 +/- 2,940 km³ and 128,094 +/- 52,399 km³ in the WSB (based upon 20% porosity values). Notably, the character of the basins varies substantially between the more southern ASB and WSB interiors and the more marginal, northern ASB and WSB reflective of different dynamic ice histories across geologic time. ASB sedimentary basin volumes, derived from airborne gravity and magnetic data with ice-penetrating radar constraints, are contrasted with recently acquired highresolution marine seismic sequence stratigraphy collected on the Sabrina Coast continental shelf. With targeted geologic sampling of outcropping strata, megasequence sediment volumes are estimated for a finite area adjacent to the Totten Glacier/Moscow University Ice Shelf catchment draining the ASB interior. Preglacial, temperate/polythermal glacial, and polar glacial sediment volumes of 278.6 +/- 148.8 km³ , 570.6 +/-51.9 km³ , and 1,658 +/- 389 km³, respectively, combined with a multitude of diagnostic glacial tunnel valleys, unconformities, and geologic data, reinforce recent dynamic Pliocene EAIS hypotheses for the Wilkes Land margin.