Major middle Miocene global climate change: Evidence from East Antarctica and the Transantarctic Mountains

Abstract

We present a glacial record from the western Olympus Range, East Antarctica, that documents a permanent shift in the thermal regime of local glaciers, from wet-to coldbased regimes, more than 13.94 m.y. ago. This glacial record provides the fi rst terrestrial evidence linking middle Miocene global climate cooling to a permanent reorganization of the Antarctic cryosphere and to subsequent growth of the polar East Antarctic Ice Sheet. The composite stratigraphic record constructed from fi eld mapping and analyses of 281 soil excavations shows a classic wetbased till (Circe till, including an extensive melt-out facies), overlain by a weathered colluvial deposit (Electra colluvium), and then a series of stacked tills deposited from cold-based ice (Dido drift). Chronologic control comes from 40 Ar/ 39 Ar analyses of concentrated ash-fall deposits interbedded within glacial deposits. The shift from wetto cold-based glaciation refl ects a drop in mean annual temperature of 25-30 °C and is shown to precede one or more major episodes of ice-sheet expansion across the region, the youngest of which occurred between 13.62 and 12.44 Ma. One implication is that atmospheric cooling, following a relatively warm mid-Miocene climatic optimum ca. 17 to 15 Ma, may have led to, and thus triggered, maximum ice-sheet overriding.

Viscous flow lobes in central Taylor Valley, Antarctica: Origin as remnant buried glacial ice

“…If we assume that this age is valid and that evidence for cryoturbation and water reworking would be preserved in the stratigraphic record, then the combined results suggest that for the last ∼7.9 Myr the average summertime atmospheric temperatures in Mullins Valley have not increased by more than ∼5°C above present values for an extended period of time (e.g., the difference in mean December atmospheric temperature at the Stocking and Mullins glaciers; Table 1). This assertion is consistent with the notion of enduring, extremely cold and hyper-arid conditions at high elevations in the MDV since at least mid-to late-Miocene time (Marchant et al, 1993Lewis et al, 2007).…”

Modeling vapor diffusion within cold and dry supraglacial tills of Antarctica: Implications for the preservation of ancient ice

“…clasts are brought together via sublimation of intervening ice (e.g., Lewis et al, 2007). Ultimately, the clasts are stacked precariously at the buried ice surface, each with minimal grain contacts, and hence fall readily from the surface of exposed soil pit walls.…”

Regolith transport quantified by braking block, McMurdo Dry Valleys, Antarctica

“…Marchant et al, 1993a;Lewis et al, 2007). between modeled and measured braking block topography suggests that the model captures the essence of the regolith transport and shows that the topography surrounding the surveyed boulder has reached the steady state.…”

“…Prior research has revealed a number of 40 Ar/ 39 Ar dated volcanic ashes that are preserved in their primary depositional locations covering regolith in the Dry Valleys (Marchant et al, 1993a(Marchant et al, , b, 1996Sugden et al, 1995;Lewis et al, 2006Lewis et al, , 2007. The oldest of these ashes ranges between 6.4 and 11.3 M yrs old, suggesting almost perfect preservation of regolith surfaces.…”