2009 Portland GSA Annual Meeting (18-21 October 2009)
Paper No. 35-5
Presentation Time: 9:00 AM-6:00 PM


SMITH, Casey J., Physical Sciences, Kutztown University, 425 Boehm P.O. Box 730, Kutztown, PA 19530, csmit036@live.kutztown.edu, MORAN, Kelli L., Physical Sciences, Kutztown, 425 Boehm P.O. Box 730, Kutztown, PA 19530, FILLMORE, David L., Physical Sciences, Kutztown University, 424 Boehm Hall, Kutztown, PA 19530, SIMPSON, Edward L., Physical Sciences, Kutztown University of Pennsylvania, 424 Boehm, Kutztown, PA 19530, and LUCAS, Spencer G., New Mexico Museum of Natural History and Science, 1801 Mountain Road N.W, Albuquerque, NM 87104

The middle member of the Mississippian/Visean Mauch Chunk Formation that crops out in eastern Pennsylvania has produced a diverse assemblages of both invertebrate and vertebrate trace fossils that span a critical juncture in the evolution of terrestrial ecosystems. Analysis of the facies succession from the middle to upper member indicates that these deposits developed in an ephemeral-braided stream shifting to a more perennial setting. Within this depositional system, the presence or absence of the mudstone-draped ripple facies is the factor that controls the taphonomic filtering of this important paleoecosystem.

Fining-upwards, stacked channel sequences characterize the middle member. Vertically, the channel fills are characterized by: 1) scoured base, 2) either medium-grained, trough cross-bedded or structureless sandstones with intense bioturbation, 3) intermittently occurring parallel laminated sandstones, 4) ripple deposits with various climb angles commonly preserving bedforms with mudstone drapes increasing in abundance upwards and the preservation of rain drop impressions, mud cracks, roots, as well as vertebrate footprints including Palaeosauropus and Batrachichnus, and 5) mudstones with pedogenic Bk horizons. This vertical facies succession is best interpreted as the product of an ephemeral-braided stream system. In the upper member, the coarsest sediment size is gravel. Channel-fill bases are deeply cut and filled with several upward-fining sequences that are characterized by massive, clast-supported or trough cross-bedded conglomerate, overlain by trough cross-bedded sandstone that fines upward. Tops of smaller-scale fining-upward cycles may be overlain by mudstone. The channel sequences are capped with massive mudstones that lack, or have weakly developed, Bk horizons. Vertebrate tracks are not present where the mudstone-draped ripple facies are not present or well developed. This depositional system is best interpreted as a higher-gradient braided stream system with mud sedimentation restricted to overbank flooding events. Our study indicates that terrestrial mudstone-draped sandstone should be explored extensively to discover ichnofossils that fill gaps in our understanding of vertebrate and invertebrate evolution.

2009 Portland GSA Annual Meeting (18-21 October 2009)
General Information for this Meeting
Session No. 35--Booth# 230
Sediments, Clastic: New Insights on Old Problems (Posters)
Oregon Convention Center: Hall A
9:00 AM-6:00 PM, Sunday, 18 October 2009

Geological Society of America Abstracts with Programs, Vol. 41, No. 7, p. 119

© Copyright 2009 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.