Supplementary material to “Antarctic Sedimentary Basins: Key to Understanding Glacial Processes”

Fred Davey, GNS Science, Lower Hutt, New Zealand

Citation:
Davey, F. (2007), ROSSMAP workshop, Eos Trans. AGU, 88(39), 384. [Full Article (pdf)]

Workshop to establish an integrated seismic stratigraphy for the Ross Sea, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Trieste, Italy, 18–20 June 2007

The Cenozoic history of the Antarctic is largely recorded in the sequences contained in sedimentary basins of the Antarctic continental shelf. These records are particularly important in defining the development of the cryosphere over the past 35 Ma, as direct sampling of the sediments is limited to core from only a few drill holes. The geometry and character of the seismic stratigraphy are use to infer glacial processes and the age of these events. In order to have a consistent circum-Antarctic interpretation of past glacial and tectonic events, a consistent stratigraphy is needed. To address this issue and to develop an accessible electronic data base of the marine stratigraphy, an IPY project was developed—ROSSMAP—to take a first step by developing an integrated seismic stratigraphy for the Ross Sea—a complex region containing several major sedimentary basins. The ROSSMAP project is a project of the SCAR Antarctic Climate Evolution (ACE) programme. Several groups are using marine seismic data in the Ross Sea for various geoscience outcomes and the ROSSMAP Steering Committee consider it important to come to a consensus on the correlation between various seismic data sets and with the limited drill-hole data in the region. The first meeting of the ROSSMAP group was a workshop to study and resolve these correlation issues in marine seismic stratigraphy of the Ross Sea. It was held in mid-June at the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale—OGS, in Trieste, Italy.

The format of the workshop consisted of a series of summary overviews of their work by several research groups working in the region to ensure that all participants were aware of the whole range of research that had been undertaken and the problems and issues that people had encountered. Chris Sorlien of UCSB covered the work the UCSB group had done, outlining their data and interpretations from the Eastern basin and Roosevelt basin of eastern Ross Sea and from the margin of the Ross Ice shelf in central Ross Sea. Chiara Sauli (OGS) outlined her largely completed digital compilation of existing data from the Victoria Land basin (the PNRA Vilmar project). Stuart Henrys summarised the interpretation and new data in southern Victoria Land basin by the GNS (Stuart Henrys), OSU (Terry Wilson) and UNL (Chris Fielding). Phil Bart (LSU) reviewed his group’s work on the younger sequences in north-western Ross Sea. Riccardo Geletti (OGS) presented some reprocessed seismic data over northern Victoria Land basin. Roi Granot (SIO) and Fred Davey (GNS) presented correlations of the continental shelf sediments to a DSDP site (274) on the lower continental rise.

The second part of the workshop involved task groups to work on two major issues—Firstly sequences, sequence boundaries and their seismic expression, and secondly correlation to drill sites and uncertainties in these correlations. The Ross Sea contains three major basin systems—the Eastern basin and Roosevelt sub-basin in the east, the Central trough in central Ross Sea and the Northern basin and Victoria Land basin in the west—which, with the western continental slope and rise, were discussed in detail. A common agreement on what are the major seismic sequence boundaries, how well they can be mapped within a basin and between basins, and what is the effect of different resolution seismic acquisition systems, is essential. In addition, a number of seismic stratigraphic columns have been published with different nomenclature. Some rationalisation is essential to ensure a common understanding. However, until an event can be correlated between basins unequivocally, the workshop considered that a different nomenclature should be used for each basin. It was recommended that type (seismic) sections should be set up for each major basin system on which the seismic stratigraphic units are defined, but a simple stratigraphy should be adopted until an adequate correlation is achieved between basins. The major reflectors for each basin were identified. However, a major problem exists is correlating between basin systems with critical areas identified as i) western Victoria Land basin (VLB), north to south past Drygalski Ice Tongue, ii) west to east VLB, iii) VLB to Northern basin, iv) Eastern VLB to Central trough to Eastern basin, v) the older section—below about 30 Ma (sub “RSU-6”). On a more positive note, it was generally agree that there are Ross Sea wide sequence boundaries in the younger part of the section.

The second topic discussed was correlation to drill sites and age control. Seismic data have been correlated with major events/sequence boundaries at drill sites and hence an age for a seismic event derived. Drill sites exist in eastern Ross Sea (DSDP 270, 271, 272), central Ross Sea (DSDP 273), western Ross Sea (CRP 1,2,3, CIROS 1, 2, MSSTS 1), and the western Ross Sea continental rise (DSDP 274). A number of issues were discussed including identifying the associated seismic events, their characteristics, and continuity; real uncertainty in ages, confidence in correlation to a drill site (twt, m), priorities for new drill sites, and priorities for reprocessing seismic sections. A number of critical ages were identified for close examination and included the Neogene record, the Eocene/Oligocene onset of glaciation, and regional tectonic events at about 20Ma, 35 Ma and 45 Ma.

The final session focussed on the future direction and work program for ROSSMAP. Two main components were agreed, in the short term to work towards an integrated seismic stratigraphic interpretation of the Ross Sea with outputs in electronic format, and in the longer term to expand the coverage of the project to other circum Antarctic continental shelf regions. Dr Chiara Sauli (OGS) was elected convenor of the ROSSMAP group until the next workshop. People interested in the future work of the ROSSMAP group should contact Dr Sauli at csauli@ogs.trieste.it