Reprint of: Late Neogene climate and glacial history of the Southern Victoria Land coast from integrated drill core, seismic and outcrop data☆
Introduction
In December 2006, the ANDRILL (Antarctic Geological Drilling) Program completed its first drill hole (AND-1B) during the McMurdo Ice Shelf Project (Naish et al., 2007b, Naish et al., 2009), coring to 1238 m below the sea floor from a floating ice shelf platform (Falconer et al., 2007). The upper 600 m of the AND-1B core preserves a late Neogene (Pliocene to Recent) history of Antarctic Ice Sheet behavior recording a sequence of sediment and rock that reflects West Antarctic ice sheet oscillation in response to orbital forcing (Naish et al., 2009). The successful recovery of AND-1B adds to the existing set of drill cores in the McMurdo Sound region (Fig. 1) and provides additional paleoenvironmental data from a key ‘offshore’ geographic location. Integration of geologic data from these drill cores allows regional evaluation of stratigraphic packages in the context of ice sheet history and tectonic events. The successful recovery of AND-1B provides offshore data in a geologic transect from the McMurdo Dry Valleys to eastern McMurdo Sound, and allows an examination of the interaction of ice flowing into McMurdo Sound from West Antarctica and from the East Antarctic Ice Sheet via outlet glaciers that cut through the Transantarctic Mountains. In order to utilize the drill core data and construct an accurate geologic history for the region, robust correlation models are required to tie the drill cores and identify isochronous horizons and overlapping stratigraphic intervals. Magnetostratigraphic data and radiogenic isotope ages from volcanogenic material, including primary ash and reworked clasts support the primary correlation tool provided by diatom biostratigraphy. Our ability to correlate using diatom event stratigraphy is enhanced due to the large dataset available from the circum-Antarctic. Demonstration of this ability is a focus of the present paper.
Over the past 35 years, the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) have undertaken fourteen legs in sub-Antarctic and Antarctic waters to recover rock and sediment cores from the ocean basins and continental shelves around the continent. In addition to drilling in the deep ocean basins and on the outer continental shelf, records from locations proximal to the modern Antarctic coast have also been recovered by international drilling efforts including the Dry Valley Drilling Project (DVDP), Cenozoic Investigations in the Western Ross Sea (CIROS) Project, Cape Roberts Project (CRP), and ANDRILL (Fig. 1). Many of these drilling projects recovered sections of late Neogene strata, which contain excellent records of siliceous microfossils including marine diatoms. Detailed analysis of many of these sections has led to the development of a robust diatom taxonomy and biostratigraphy for the circum-Antarctic and continental shelf (Harwood and Maruyama, 1992, Censarek and Gersonde, 2002, Zielinski and Gersonde, 2002, Bohaty et al., 2003, Stickley et al., 2004, Olney et al., 2007, Winter et al., 2010b). While these biostratigraphic studies established key datums and several studies established zonation schemes (e.g. Harwood and Maruyama, 1992, Winter and Harwood, 1997, Censarek and Gersonde, 2002, Zielinski and Gersonde, 2002; Winter et al., 2012-this volume), age resolution has remained limited.
A re-examination of published diatom occurrences and a quantitative analysis of the data under constrained optimization (CONOP) were conducted by Cody et al. (2008). Highest Occurrence (HO) and Lowest Occurrence (LO) data for 116 diatom species from 32 Neogene sequences were integrated with paleomagnetic data to construct a composite standard sequence of First and Last Appearance Datums (FAD's and LAD's). The study produced two models with independent estimates of local occurrences and total ranges of fossil diatoms in the southern high latitudes. Time-calibration of the diatom event data produced an effective resolution between 0.11 and 0.13 m.y., greatly enhancing the age resolution provided by existing zonal schemes. An additional 64 taxa, several paleomagnetic reversals, and three age events (dates on volcanic ash and clasts) have been incorporated into the latest version of the CONOP models, including new data from the AND-1B core (Cody et al., 2012--this volume).
In this study we utilized a new “hybrid model” of Cody et al. (2012-this volume) to re-examine age–depth models for the coastal drill cores in McMurdo Sound. Furthermore, we integrated the coastal cores with the AND-1B drillcore sequence, seismic data, and geologic outcrop from the Dry Valleys region in order to produce a regional correlation model. We then used this new correlation model to examine climatic evolution and tectonic history inferred from distinct chronostratigraphic intervals. A central goal of this work was to better understand the behavior of the West Antarctic Ice Sheet and margins of the East Antarctic Ice Sheet under varying climate.
Section snippets
Establishing a robust chronostratigraphic framework
A high-resolution age model that allows robust correlation between different sites is required to develop a coherent Neogene history of the Antarctic continental margin and the ice sheets. The ability to identify coeval points between sites with a high level of confidence is critical, although achieving this can be problematic due to inherent limitations in the biostratigraphic record. Quantitative biostratigraphy provides objective, statistical solutions to the correlation problem. In this
Late Neogene drillcores from the McMurdo Sound Region
Over the past 30 years several drilling projects have successfully recovered core from locations across the McMurdo Sound region including the Dry Valley Drilling Project (McGinnis et al., 1972, McGinnis, 1981), Eastern Taylor Valley Project (Robinson et al., 1984), Cenozoic Investigations in the Ross Sea (McKelvey, 1975, Barrett and Scientific Staff, 1985, Barrett, 1989), McMurdo Sound Stratigraphic and Tectonic Studies (Barrett, 1986), Cape Roberts Project (Barrett et al., 1998, Barrett and
Biostratigraphic constraints and identification of the Line of Correlation (LOC)
In this paper we present age–depth plots that were developed using diatom event data (Table 1) from a new CONOP-derived hybrid age model v. 4.14 (Cody et al., 2012--this volume). We also incorporated other available geologic data including lithostratigraphy and paleomagnetic reversal stratigraphy, where available. A correlation to the Global Paleomagnetic Time Scale (GPTS) of Gradstein et al. (2004) is proposed for each of the four drill sites (Fig. 2, Fig. 3). A single Line of Correlation
Chronostratigraphic framework and event history
The primary goals of this study are to establish an integrated chronostratigraphic framework for Neogene geologic data from Southern Victoria Land, produce an event history for the region, and place this history within the context of climate-tectonic evolution through the last five million years. To achieve this goal we integrated results from the CONOP-based hybrid model into revised age models (Fig. 2, Fig. 3 and section 4 above) and incorporated a broader regional geologic dataset to include
Regional synthesis, local tectonic processes, and links to global climate records
The integrated geological framework developed in this study provides a platform on which to base a regional synthesis and interpret local observations in terms of broader regional and global change. Large scale mechanisms that influence the geologic record of environmental variability in southern Victoria Land include climate change and tectonics. In the following section we present a summary of key global climate events, synthesize the local geologic records, and correlate these records with
Conclusions
In this study we utilized results from a new iteration of diatom-based age models developed via Constrained Optimization of a large southern ocean database (Cody et al., 2008; this volume) to update age–depth models for drill cores recovered from McMurdo Sound. A new hybrid range model established by Cody et al., (2012-this volume) was used to constrain the age–depth correlations. This new model was used as it accommodates biological and geological controls on the circum-Antarctic diatom data
Acknowledgments
The ANDRILL Program is a multinational collaboration between the Antarctic Programs of Germany, Italy, New Zealand and the United States. Antarctica New Zealand is the project operator, and has developed the drilling system in collaboration with Alex Pyne at Victoria University of Wellington and Webster Drilling and Enterprises Ltd. Scientific studies are jointly supported by the US National Science Foundation (Cooperative Agreement no. 0342484 to the University of Nebraska—Lincoln), NZ
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An error resulted in this article appearing in the wrong issue. The article is reprinted here for the reader's convenience and for the continuity of the special issue. For citation purposes, please use the original publication details: Levy, R., et al., Late Neogene climate and glacial history of the Southern Victoria Land coast from integrated drill core, seismic and outcrop data, Glob. Planet. Change (2011), doi:10.1016/j.gloplacha.2011.10.002.