A 1284.87-m-long sediment core (AND-1B) from beneath the McMurdo sector of the Ross Ice Shelf provides the most complete single section record to date of fluctuations of the Antarctic Ice Sheets over the last 13 Ma. The core contains a succession of subglacial, glacimarine, and marine sediments that comprise ~58 depositional sequences of orbitalscale duration. These cycles are constrained by a chronology based on biostratigraphic, magnetostratigraphic, and 40Ar/39Ar iso topic ages. Each sequence represents a record of a grounded ice-sheet advance and retreat cycle over the AND-1B drill site, and all sediments represent sub glacial or marine deposystems with no subaerial exposure surfaces or terrestrial deposits. On the basis of characteristic facies within these sequences, and through comparison with sedimentation in modern glacial environments from various climatic and glacial settings, we identify three facies associations or sequence " motifs" that are linked to major changes in ice-sheet volume, glacial thermal regime, and climate. Motif 1 is documented in the late Pleistocene and in the late Middle Miocene intervals of AND-1B, and it is dominated by diamictite of subglacial origin overlain by thin mudstones interpreted as ice-shelf deposits. Motif 1 sequences lack evidence of subglacial meltwater and represent glaciation under cold, " polar" -type conditions. Motif 2 sequences were deposited during the Pliocene and early Pleistocene section of AND-1B and are characterized by sub glacial diamictite overlain by a relatively thin proglacial-marine succession of mudstone-rich facies deposited during glacial retreat. Glacial minima are represented by diatom-bearing mudstone, and diatomite. Motif 2 represents glacial retreat and advance under a " subpolar" to " polar" style of glaciation that was warmer than present, but that had limited amounts of subglacial meltwater. Motif 3 consists of subglacial diamictite that grades upward into a 5to 10-m-thick pro glacial retreat succession of stratified diamictite, graded conglomerate and sandstone, graded sandstone, and/or rhythmically stratified mudstone. Thick mudstone intervals, rather than diatomite-dominated deposition during glacial minima, suggest increased input of meltwater from nearby terrestrial sources during glacial minima. Motif 3 represents Late Miocene "subpolar"-style glaciation with significant volumes of glacially derived meltwater. © 2009 Geological Society of America.

Mckay, R., Browne, G.H., Carter, L., Cowan, E., Dunbar, G., Krissek, L., et al. (2009). The stratigraphic signature of the late Cenozoic Antarctic Ice Sheets in the Ross Embayment. GEOLOGICAL SOCIETY OF AMERICA BULLETIN, 121(11-12), 1537-1561 [10.1130/B26540.1].

The stratigraphic signature of the late Cenozoic Antarctic Ice Sheets in the Ross Embayment

TALARICO, F. M.;
2009

Abstract

A 1284.87-m-long sediment core (AND-1B) from beneath the McMurdo sector of the Ross Ice Shelf provides the most complete single section record to date of fluctuations of the Antarctic Ice Sheets over the last 13 Ma. The core contains a succession of subglacial, glacimarine, and marine sediments that comprise ~58 depositional sequences of orbitalscale duration. These cycles are constrained by a chronology based on biostratigraphic, magnetostratigraphic, and 40Ar/39Ar iso topic ages. Each sequence represents a record of a grounded ice-sheet advance and retreat cycle over the AND-1B drill site, and all sediments represent sub glacial or marine deposystems with no subaerial exposure surfaces or terrestrial deposits. On the basis of characteristic facies within these sequences, and through comparison with sedimentation in modern glacial environments from various climatic and glacial settings, we identify three facies associations or sequence " motifs" that are linked to major changes in ice-sheet volume, glacial thermal regime, and climate. Motif 1 is documented in the late Pleistocene and in the late Middle Miocene intervals of AND-1B, and it is dominated by diamictite of subglacial origin overlain by thin mudstones interpreted as ice-shelf deposits. Motif 1 sequences lack evidence of subglacial meltwater and represent glaciation under cold, " polar" -type conditions. Motif 2 sequences were deposited during the Pliocene and early Pleistocene section of AND-1B and are characterized by sub glacial diamictite overlain by a relatively thin proglacial-marine succession of mudstone-rich facies deposited during glacial retreat. Glacial minima are represented by diatom-bearing mudstone, and diatomite. Motif 2 represents glacial retreat and advance under a " subpolar" to " polar" style of glaciation that was warmer than present, but that had limited amounts of subglacial meltwater. Motif 3 consists of subglacial diamictite that grades upward into a 5to 10-m-thick pro glacial retreat succession of stratified diamictite, graded conglomerate and sandstone, graded sandstone, and/or rhythmically stratified mudstone. Thick mudstone intervals, rather than diatomite-dominated deposition during glacial minima, suggest increased input of meltwater from nearby terrestrial sources during glacial minima. Motif 3 represents Late Miocene "subpolar"-style glaciation with significant volumes of glacially derived meltwater. © 2009 Geological Society of America.
Mckay, R., Browne, G.H., Carter, L., Cowan, E., Dunbar, G., Krissek, L., et al. (2009). The stratigraphic signature of the late Cenozoic Antarctic Ice Sheets in the Ross Embayment. GEOLOGICAL SOCIETY OF AMERICA BULLETIN, 121(11-12), 1537-1561 [10.1130/B26540.1].
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11365/8274
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