Did massive glacial dewatering modify sedimentary structures on the Amundsen Sea Embayment shelf, West Antarctica?

Abstract

Multichannel seismic reflection lines collected in the western Amundsen Sea Embayment (ASE) provide an insight into the sedimentary cover on the shelf, which documents glacial processes. Numerous columnar, reflection-poor structures penetrating the sedimentary sequences on the middle shelf form the focus of this study. The features range between 50 and 500 m in width, and from a few metres up to 500 m in height. The columns originate and end at different depths, but do not seem to penetrate to the seafloor. They show well-defined vertical boundaries, and reflection signals can be identified below them. Hence, we exclude gasbearing chimneys. Based on the general seismic reflection characteristics we suggest that the columns originate from dewatering processes which occur close to glaciated areas where fluids are pressed out of rapidly loaded sediments. Likely several mud-diapirs rise from water-rich mud layers within a mixed sedimentary succession and penetrate overlying denser and coarse-grained sediment strata. The presence of fluidescape veins indicates a glacial origin and overprinting of the older sedimentary sequences on the ASE. The locations of the structures indicate that grounded ice sheets reached at least onto the middle shelf during former glacial periods.

Seismic stratigraphic record of the Amundsen Sea Embayment shelf from pre-glacial to recent times: Evidence for a dynamic West Antarctic ice sheet

“…1). Oceanward dipping mid-shelf strata north of outcropping basement are observed in seismic data from the Dotson-Getz Trough collected in 1999 and 2006 (Wellner et al, 2001;Graham et al, 2009;Weigelt et al, 2009Weigelt et al, , 2012 and exhibit alternating sequences of low and high reflectivity, which Weigelt et al (2009) interpret as episodes of major glacial advances and retreat in the Miocene.…”

“…Wellner et al (2001), Anderson (2002, 2003) and Dowdeswell et al (2006) described SCS datasets collected along Pine Island Trough and the Dotson-Getz Trough during RV Nathaniel B. Palmer cruise NBP9902 in 1999. More SCS data were collected on the outer shelf and the middle shelf of the western ASE during RRS James Clark Ross cruise JR141 in early 2006 Graham et al, 2009), followed by MCS data recorded on RV Polarstern cruise ANT-XXIII/4 in the same season of 2006 (Gohl, 2007;Uenzelmann-Neben et al, 2007;Weigelt et al, 2009Weigelt et al, , 2012. Due to unusually favorable sea-ice conditions in the season of early 2010, we were able to acquire more than 3500 km of MCS data from the middle to outer shelf, the slope and the continental rise of the Amundsen Sea during RV Polarstern expedition ANT-XXVI/3 (Gohl, 2010).…”

Early glaciation already during the Early Miocene in the Amundsen Sea, Southern Pacific: Indications from the distribution of sedimentary sequences

“…Intraplate volcanism at 65-56 Ma led to the formation of the Marie Byrd Seamounts (Kipf et al, 2013). The crystalline basement is covered by up to 4 km of sedimentary strata, which have been extensively reworked by oceanic currents in the deep sea (Yamaguchi et al, 1988;Nitsche et al, 2000;Uenzelmann-Neben and Gohl, 2012) and by advance-retreat cycles of the ice sheet on the shelf (Lowe and Anderson, 2002;Dowdeswell et al, 2006;Nitsche et al, 2007;Uenzelmann-Neben et al, 2007;Graham et al, 2009;Weigelt et al, 2009;Weigelt et al, 2012;Gohl et al, 2013;Hochmuth and Gohl, 2013).…”

Sedimentation and potential venting on the rifted continental margin of Dronning Maud Land

“…Geletti and Busetti (2011) related seismic chimneys to the presence of gas hydrates, whose presence they interpreted from Bottom-Simulating Reflectors (BSR) in their seismic records in the Ross Sea. In contrast, Weigelt et al (2012) suggested that the reflection-poor vertical pipe-like structures in sedimentary sequences on the middle shelf of the Amundsen Sea Embayment represent mud-diapirs rising from water-rich sediments, and suggested that their formation has been strongly influenced by glacial/interglacial cycles.…”

“…the Vøring and Møre margin basins, or the Ulleung Bain (Planke et al 2005;Horozal et al 2009). Around Antarctica, seismic chimneys have also been observed in basins of the Amundsen Sea and Ross Sea Embayment (Geletti and Busetti 2011;Weigelt et al 2012). Geletti and Busetti (2011) related seismic chimneys to the presence of gas hydrates, whose presence they interpreted from Bottom-Simulating Reflectors (BSR) in their seismic records in the Ross Sea.…”