MP9: Chapter 7: Ichnology and Sedimentology of an Eocene Greensand in Texas: Behavioural Response to the Middle Eocene Climate Optimum (MECO)
by S.C. Harding and A.A. Ekdale.
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This chapter is from GAC's Miscellaneous Publication 9: "Ichnology: Papers from Ichnia III" editted by Dr. Duncan McIlroy. To purchase the entire book on disc, please see the Miscellaneous Publications section of our bookstore at http://www.gac.ca/publications/view_pub.php?id=262.
Although rarely employed in paleoclimate studies, ichnologic information may offer some useful insights about climatic conditions during a global warm interval. The Main Glauconite Bed (MGB) of the Middle Eocene Stone City Member, Crockett Formation, in eastern Texas displays multiple ichnocoenoses and demonstrates a sea-level change during the Middle Eocene Climatic Optimum (MECO). The intensely bioturbated, pelleted, central MGB represents an environment probably dominated by infaunal annelid worms. The MGB top, marked by prominent concretionary burrows, represents a shallower environment associated with a firmground omission suite of trace fossils. Spongeliomorpha (showing scratch traces on burrow walls) along with Thalassinoides and Gyrolithes were produced by burrowing decapod crustaceans. A postomission ichnocoenosis is evident where open burrows at the MGB top were filled with sediment and then reoccupied by burrowers. The top of the MGB exhibits a composite ichnofabric including pre-omission, omission and post-omission suites of trace fossils. This bed contains abundant odinite, a green clay mineral that is indicative of the tropical verdine facies. The MGB represents the response of a diverse benthic community to changing seafloor conditions and climatic warming during shoreline regression and expansion of the tropics in the Middle Eocene Climatic Optimum.
Geological Association of Canada
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