Pleistocene geocryogenic structures at 38°S.L., 60°W. and 200 M above sea level, Gonzalez Chavez, Buenos Aires Province, Argentina
DOI:
https://doi.org/10.26485/BP/1976/25/3Keywords:
ice wedge casts, gelifluction covers, calcium carbonate precipitates, upper PleistoceneAbstract
After reviewing the knowledge on Pleistocene geocryogenic effects in the· southern Hemisphere and in Argentina, the authors are presenting two types of Pleistocene Permafrost Geocryogenic effects at 38° S. L., 60°W and 200 m above sea level and under a present mean year temperature of + 14.5°C.
The two types of geocryogenic features are: (a) ice wedge casts and (b) gelifluction covers. Ice wedge casts are observed in sandstones, siltstones of upper Paleozoic age and in Ioess deposits of upper Quaternary age. The gelifluction covers are observed in loess deposits which also contain ice wedge casts; making them a sure geocryogenic evidence. This geocryogenic stage is placed in the upper Pleistocene. This is the northernmost location of fossil ice wedges in the southern Hemisphere. It is also the first report which indicates ice wedge casts filled mainly with calcium carbonate precipitates. This also gives important information for paleoecological; paleo-climatic conditions: after a dry, cold, continental climate stage, with a mean annual temperature of - 5°C., -6°C or lower, in which ice-wedges grew, there was a stage of dry and warmer conditions in which ice wedges melted and calcium carbonate with some sand, silt and clay filled the wedge. Temperature increase, therefore, with respect to present temperature since ice wedge formation is about 20°C.
This temperature increase derived from land evidence is in agreement with research on oceanic cores from the shelf region in the south-western Atlantic.
This rigorous climatic conditions might help to explain certain faunal changes in the upper Quaternary.
Some recommendations are given for an extension and improvement of the present information.
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