Young, Grant M.; Nesbitt, H. Wayne (1996): Are continental glaciations induced by orogeny? Evidence from major element geochemistry of Cenozoic muds and ancient glacial deposits. Geological Society of America (GSA), Boulder, CO, United States, In: Anonymous, Geological Society of America, 28th annual meeting, 28 (7), 505, georefid:1997-039965
Abstract:
Mountain uplift and glaciation in low latitudes may have played a significant role in deterioration of global climate over the last 40Ma. Upward-increasing Sr ratios in marine carbonates are thought to reflect increased silicate weathering, attributed to comminution of minerals during transport in mountain glaciers and subsequent fluvial transport to lower altitudes. To further investigate this question, a Chemical Index of Alteration (CIA), which provides a proxy for silicate weathering, was calculated for samples of Cenozoic siliciclastic muds from DSDP drill sites in both low (Sites 146,149) and high latitudes (Site 328). The low latitude samples show clear evidence of upward-increasing weathering during the last 40 Ma. Samples from Site 328, by contrast, show upward-decreasing values (decreasing weathering) that correspond closely to existing oxygen isotope data and other evidence of Cenozoic climatic deterioration. These results provide strong evidence that (orogenically-induced?) increases in low latitude weathering occurred at the same time as global climatic cooling and development of continental glaciers in high latitudes. Widespread preservation and the unweathered nature of materials (low CIA values) in many ancient glacial deposits such as the Paleoproterozoic Gowganda Formation indicate that they formed under conditions comparable to those of Recent low latitude continental glaciers. By analogy with the Cenozoic, such Proterozoic glaciations may have formed in response to cryptic, orogenically-induced (end-Archean, Pan African) mountain glaciations. Deposits formed as a result of such alpine glaciations in low latitudes would be physically and chemically unrecognizeable in the geological record because the glaciogenic materials would be reworked by fluvial systems and would undergo chemical weathering at low altitudes.
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West: -95.0000 East: -36.3931 North: 57.0000 South: -49.4841
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