--> ABSTRACT: Bioturbation in Freshwater vs. Marine Deposits, by Molly F. Miller, Trent A. McDowell, Yu Shyr, Noel Kemp, and John Isbell; #90906(2001)
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Molly F. Miller1, Trent A. McDowell2, Yu Shyr3, Noel Kemp4, John Isbell5

(1) Vanderbilt University, Nashville, TN
(2) Vanderbilt university, Nashville, TN
(3) Vanderbilt University
(4) Tasmanian Museum and Art Gallery, Hobart, Australia
(5) University of Wisconsin, Milwaukee, Milwaukee, WI

ABSTRACT: Previous HitBioturbationNext Hit in Freshwater vs. Marine Deposits

The amount and style of Previous HitbioturbationNext Hit is different in freshwater vs. marine deposits. We compared the amount of Previous HitbioturbationNext Hit on bedding planes and vertical surfaces of fluvial (channel and subaqueous floodplain) and lacustrine facies in rocks of Permian-Jurassic age exposed in the Shackleton Glacier area, Antarctica, and Colorado Plateau to that in Permian marine rocks in Tasmania and in marine, high-energy sandstones, as reported in the literature.

Amount of Previous HitbioturbationNext Hit in freshwater facies is low. Most vertical surfaces observed (94%) showed no Previous HitbioturbationNext Hit (NB). The percentage of unbioturbated (NB) bedding planes of all freshwater facies is 65% but differs significantly between facies (p<0.001; Fisher's Exact Test [FET}); Previous HitbioturbationNext Hit is least in channel and greatest in lacustrine deposits. The Antarctic fluvial deposits are more bioturbated than the lower paleolatitude Colorado Plateau deposits, suggesting climatic control of the amount of Previous HitbioturbationNext Hit.

Amount of Previous HitbioturbationNext Hit on both vertical and bedding surfaces of Permian marine sandstones in Tasmania is statistically significantly greater (p<0.001; FET) than that in the freshwater deposits. All observed surfaces of marine rocks were bioturbated, and 34% had the highest level of Previous HitbioturbationNext Hit (60-100%) vs. only 0.2% of the freshwater deposits. The data from Tasmania are limited, but the high level of Previous HitbioturbationNext Hit is consistent with that reported in lower Paleozoic marine sandstones deposited in high energy environments (only 33% NB; 14% were 60-100% bioturbated) (Droser and Bottjer, 1990). The marine Previous HitbioturbationNext Hit contrasts with the low Previous HitbioturbationNext Hit in high energy fluvial channel deposits (99% NB), and underscores the potential utility of Previous HitbioturbationTop in distinguishing between marine and freshwater deposits.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado