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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 484

Last Page: 484

Title: Rudists as Historians--Smoky Hill Chalk Member (Upper Cretaceous), Kansas: ABSTRACT

Author(s): Donald E. Hattin


Remains of Smoky Hill rudists yield a wide spectrum of data relating to growth attitude, nature of substrate, death, and postmortem events. Well-preserved skeletal remains of these organisms occur mainly in the lower half of the Smoky Hill Chalk Member, and are most common in a highly fossiliferous interval that lies approximately 23 m (75 ft) above the base of a recently established reference section. Early records of Great Plains explorations suggest that extensive collecting accounts in part for low apparent specimen density. Among the many Durania specimens examined during this study, including numerous nearly intact lower valves, few have closely similar morphology. Specimens are solitary or compound, thin walled to thick walled, tall-conical to short-discoidal, symm trical to highly asymmetrical in lateral aspect, and have little to extreme lateral expansion of last-formed parts of the valve wall. Wide morphological variability manifests adaptation to unstable substrate conditions, and compensation for gradual tilting or abrupt toppling as specimens approached adult size. Distribution of epizoans, particularly oysters, permits assessment of specimen orientation during life and after death, especially by defining sediment-water interfaces. Epizoan distribution also furnishes evidence of pre-burial fragmentation of Smoky Hill rudists. Texture and structure of enclosing chalky sediments are consistent with a low-energy depositional environment, so wave or current damage is unlikely. Pre-burial fragmentation of some specimens, fragments oriented contrar to normal gravitational settling, overturned specimens, and possible tooth marks combine to suggest that large vertebrates left in their wake the wreckage of extensive predation.

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