--> Abstract: Does Climate Affect Amount of Bioturbation? Comparison of Ichnofabric in Low vs. High Latitude Triassic Fluvial Sandstones, by G. M. Galloway and M. F. Miller; #90937 (1998)
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Abstract: Does Climate Affect Amount of Previous HitBioturbationNext Hit? Comparison of Ichnofabric in Low vs. High Latitude Triassic Fluvial Sandstones

GALLOWAY, GARY M., MOLLY F. MILLER, Department of Geology, Vanderbilt University

Amount of Previous HitbioturbationNext Hit primarily is controlled by the rate of physical reworking relative to rate of biological reworking and by chemical conditions (e.g. salinity, oxygen availability). A potentially important, but unknown influence on the rate of biologic activity is climate, particularly temperature. If a sedimentary sequence was deposited in a low temperature regime at high latitudes, and if biological activity were inhibited by cold temperatures, the deposit would be less bioturbated than if it had accumulated under more benign conditions. Paucity of Previous HitbioturbationNext Hit could lead to an erroneous interpretation of the physical depositional regime.

To isolate the effect of climate on the preserved record of biological activity, we compared the amount of Previous HitbioturbationNext Hit in Triassic fluvial sandstones deposited at low latitudes with the amount of Previous HitbioturbationNext Hit in sandstones of approximately the same age deposited under similar conditions at high latitudes. The low latitude sequences include the Moenkopi and Chinle Formations of the Colorado Plateau; the high latitude sandstones, deposited at latitudes greater than 60¯ south, are included in the Fremouw Formation exposed in the Shackleton Glacier area of the Central Transantarctic Mountains (Antarctica).

Previous HitBioturbationNext Hit was assessed both on bedding plane and vertical exposures using the semiquantitative methods of Miller and Small (1997) for bedding plane exposures and Droser and Bottjer (1986) for vertical exposures. Because of extensive bedding plane exposures in Antarctica and the Colorado Plateau, the bedding plane data sets consist of thousands of observations; this large size of the data sets minimizes the effects of local variation that might obscure broad trends.

Preliminary analysis indicates that a small percentage (< 20%) of bedding plane observations show some Previous HitbioturbationNext Hit, but that the level of Previous HitbioturbationNext Hit is low. Where Previous HitbioturbationNext Hit is observed, typically less than 10% of the area is disturbed, and only rarely is more that 40% of the area disturbed. The preliminary results also suggest that high latitude fluvial sandstones are more bioturbated than equivalent low latitude sandstones, although this difference may not hold up in the complete statistical analysis of the final data set. However, this method provides a method for evaluating the role of climate as a factor controlling amount of Previous HitbioturbationTop.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah