Middle Pleistocene Glaciations in the Southern Hemisphere.

A. CORONATO; RABASSA, J

The Encyclopedia of Quaternary Science

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013; p. 187 - 190

Introduction Middle Pleistocene glaciations are understood to be one of the consequences of climatic cooling forced by solar radiation variation during the 100-ka period cycles driven by Earth?s orbit eccentricity. The marine isotope stage (MIS) curves reflect high frequency and intensive periods of low d18O since 0.88 Ma (MIS 22) and throughout the subsequent Brunhes Normal magnetic polarity chron. According to Ehlers and Gibbard (2007), MIS 22 is the first of the colder events in which critical d18O values (5.55%) were reached, which allowed continental ice cap formation in mid-latitudes, thus defining the critical conditions during the following middle Pleistocene times. This time spans the period between 780 ka, when the magnetic polarity changed from reverse to normal, and 130 ka, when the last interglacial period began. Although there are fewer land masses in the Southern Hemisphere in comparison to the Northern Hemisphere, evidence for the middle Pleistocene glaciations has been recognized, mostly through geomorphological mapping and cosmogenic exposure dating. The latter uses 10Be, 26Al, and 36Cl, as well as 39Ar?40Ar incremental heating techniques on basaltic rocks related to till units. The dates obtained have been correlated with the d18O MIS or with Antarctic temperature curves, depending on the author?s decisions. This work shows how the cosmogenic and 39Ar?40Ar dates presented herein correspond to the cold periods in the MIS curve produced by Lisiecki and Raymo (2005), in which the benthic d18O records of 57 globally distributed sites were averaged. Knowledge of these glaciations has been improved by recent work in the Central Andes (Bolivia and Peru), as well as on the eastern slope of the Southern Andes (Patagonia, Argentina), in the New Zealand Alps, and in the western ranges of Tasmania. As this contribution is an updated review of Coronato and Rabassa (2007), only post-2005 findings and the literature not previously considered is presented herein. For previous work and other references, the reader should consult the authors? article in the first edition of the Encyclopedia of Quaternary Science.