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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 965

Last Page: 965

Title: Waulsortian Mounds and Lithoherms Compared: ABSTRACT

Author(s): A. Conrad Neumann

Article Type: Meeting abstract


Lithified bioherms (lithoherms) in the northern Straits of Florida have been compared with the Waulsortian mounds of the Early Carboniferous of Europe. The lithoherms occur at 400 to 600 m in the presence of moderate bottom currents. A zoned coral-octacoral-crinoid community appears to build into the current as concomitant cementation provides a diagenetic framework. Coral debris, pelagics, bank-derived muds and cements compose the mound material. Exposed downcurrent surfaces are undergoing bioerosion.

The ancient mounds in the Belgium type area are composite structures with a lower (Tournaisian) sparry "blue vein" facies of fenestellid bryozoans cemented by marine calcite crusts and relatively little micrite. This is overlain by a Visean phase of micritic facies, still rich in fenestellids, with steep depositional slopes suggestive of subsea cementation. Outside Belgium, the mounds are predominantly micritic. They contain stromatactoid cavities which have also been associated with marine cementation. Work by others suggest that filamentous algae, including Girvanella, had some part in local generation of lime mud. Mound facies pass laterally into shaly limestones and shales with chert, which locally may be rich in algae.

Early Carboniferous continental reconstructions place the ancient mounds in a general equatorial carbonate margin or near margin. The paleo-oceanographic consequences suggest a light shallow mixed layer within which shallow equatorial upwelling could maintain moderate surface biologic productivity while not mixing deeply enough to fully oxygenate the slope and basin bottoms.

Ancient mounds, in contrast to the modern lithoherms, appear to have accumulated largely from submarine cementation of products of in-situ origin, in a setting of slower currents and possibly reduced oxygen levels on a bottom that may have been shallow enough to extend at times into the lower photic zone.

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Copyright 1997 American Association of Petroleum Geologists