Crinoids, hardgrounds, and community succession: The Silurian Laurel—Waldron contact in southern Indiana

Authors

  • MARGARET S. HALLECK

    1. Department of Geophysical Sciences, University of Chicago, Chicago, Illinois 60637, U.S.A.
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    • 2

      Northern Branch, The University of New Mexico, Los Alamos, New Mexico 87544]


Abstract

Halleck, Margaret S.: Crinoids, hardgrounds, and community succession: The Silurian Laurel-Waldron contact in southern Indiana.

The uppermost surface of the Silurian Laurel Limestone at its contact with the Waldron Shale in southeastern Indiana was a hardground lithified prior to the deposition of the Waldron. Evidence for this conclusion is the presence of attached palmate crinoid roots, auloporid corals, and craniid brachiopods on the Laurel surface; the irregularity of the contact with the Waldron; and a pyritic veneer at this contact. The hardground apparently had a submarine origin. In addition to the attached epifauna mentioned above, algal-sediment ‘clods’ formed on this surface. Some of these accumulated around the crinoid stems, causing them to produce cirral extensions. The resulting community was a crinoid ‘meadow’ with algal growths forming sediment traps around and between the crinoids. Later stages of Waldron Shale deposition led to the development of a soft-bottom community.

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