Frontiers and Opportunities in Antarctic Geosciences * Certosa di Pontignano * 29-31 July 2004
Sedimentary Record and Glacial History of
the Antarctic Continental Margin
G. BRANCOLINI
Istituto Nazionale di Oceanografia e Geofisica Sperimentale (OGS), B.go Grotta Gigante 42/C, 34010 Trieste
gbrancolini@ogs.trieste.it
Sediments distribution, composition and sea floor morphologies on the Antarctic margins recorded the complex
interaction between tectonics, palaeoceanography and ice sheet growth and evolution. Similarly to all the continental
margins, the Antarctic margin can be subdivided in three main domains represented by the continental shelf, slope and
rise, dominated by different depositional processes and strongly influenced by the ice sheet dynamic, during the
Cenozoic.
The continental shelf contains the more direct record of the ice sheet growth and variability. Stratigraphic data provided
by several drill sites, seismic facies, seismic attributes and backstripping techniques have been widely used to
reconstruct the configuration of the ice sheet through time. Unfortunately, sediments on the shelf have been deeply
eroded by different advances and retreats of grounded ice and the stratigraphic record is largely discontinuous. The
results obtained from the Ross Sea and Antarctic Peninsula data analyses, led to the conclusion that glacial features on
the shelf can be detected since early Miocene, but the overdeepening and the landward dipping profile characterized the
shelf only since late Miocene or early Pliocene. One of the most recent and promising frontiers on the geology of the
Antarctic shelf is the discovery of expanded and undisturbed Holocene sequences. These sequences, usually deposited
within confined basins, are mainly composed by siliceous mud and diatomaceous ooze and can provide an expanded
paleo-environmental record of the last interglacial periot.
The continental slope is formed by steep (more than 7°) prograding clinoforms. From ODP Site 1167 located on the
Prydz Bay trough-mouth fan, we know that the formation of the fan started in early to mid-Pliocene time and it has
growth most during periods when the Lambert Glacier has grounded near or at the shelf edge, delivering basal debris.
The material was then redistributed by sediment gravity flows and melt water plumes.
The continental rise deposits form giant asymmetric ridges, roughly orthogonal to the margin. Ridges are the product of
the the interplay between turbiditic and conturitic processes. ODP site 1165 on the Prydz Bay rise recorded a continuos
decreasing in sedimentation rates throughout the Cenozoic (from 120 m/My in early Miocene to 15 m/My in the
Pleistocene). Similar results have been obtained from ODP site 1068 on the Antarctic Peninsula rise. These data are
congruent with seismic facies that
indicate that the main growth phases of the sediment ridges occured under
polythermal glacial conditions, when a wet based ice sheet was grounded on the continental shelf, delivering large
quantities of sediments on the rise. The progressive upward attenuation of wavy geometries, with filling and draping of
the pre-existing reliefs, have been related to the ice sheet evolution from polithermal to truly polar, with the progressive
sediment starvation of the continental rise.
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