Trace Fossils from Brackish-Marine Shales, Upper Pennsylvanian of Kansas, U.S.A.
William G. Hakes, 1985. "Trace Fossils from Brackish-Marine Shales, Upper Pennsylvanian of Kansas, U.S.A.", Biogenic Structures: Their Use in Interpreting Depositional Environments, H. Allen Curran
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Several trace fossil assemblages from the clastic members of three Upper Pennsylvanian cyclothems in the state of Kansas are considered to represent marginal marine (brackish-marine) environments. Trace fossils were collected from several lenticular- or flaser-bedded siltstone and fine-grained sandstone horizons within the Rock Lake Shale, Timberhill Siltstone, and Lawrence Shale. These units were commonly thought to be nonmarine (freshwater to subaerial exposure) due to the general lack of marine body fossils. Common trace fossils are Asteriacites, Lingulichnus. lsopodirhnus. Chondrites, Didymaulichnus, Pelecypodichnus, and Planolites. The trace fossil assemblages are characterized by the following: (1) small-sized members; (2) excellent preservation; (3) high to moderate diversity; (4) moderate abundance; (5) no preferential preservation; and (6) all ethological groups except grazing trails. The small size of these trace fossils is related to a lowering of salinity as a result of freshwater influx into a shallow marine environment accompanying the deposition of the silts and sands upon which the ichnofauna is preserved. These trace fossils may have been overlooked because of their small size, and it is proposed that they could be found elsewhere within similar shallow water stratigraphic sequences.
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Organisms of one sort or another today inhabit virtually every sediment environment on Earth, and the rock record tells us that this has been the case through the greater part of our planet’s history. Furthermore, organisms leave their mark in most sedimentary settings, either directly in the form of body fossils or indirectly as biogenic structures. In addition to their often profound modifying effects on substrates, ancient biogenic structures preserve a record of organism behavioral activity in response to substrate and other paleoenvironmental controls. Thus, biogenic structures can be highly useful as facies indicators and can provide valuable clues to the interpretation of paleodepositional environments. The purpose of this volume is to present a broad spectrum of case-book examples of the use of biogenic structures in the interpretation of depositional environments.