Microbial mound growing on grainstones and buried by grainstones.

Abstract 1835:
Carbonate mounds within the Chesterian (Mississippian) Bangor Limestone in north Alabama and east Tennessee are few in number, but diverse in character. Fourteen known mounds in this area can be assigned to five categories: 1) stromatolitic, 2) mud, 3) bryozoan-crinoid-coral, 4) bryozoan-crinoid, and 5) coral. Stromatolitic and mud mounds are microbial, bryozoan-crinoid-coral mounds are biodetrital, and coral mounds and some bryozoan-crinoid mounds are biohermal (reefal). Three lensoid stromatolites within crinkly-laminated dolomudstone comprise a single mound horizon about 0.5 m thick east of Monteagle, Tennessee. Near Haletown, Tennessee, the Bangor Limestone contains two mud mounds. The largest measures 8.2 m across and contains articulated bivalves and brachiopods, and intact fenestrate bryozoans. The mound's upper surface is bored. The mud matrix appears to contain tubular microfossils resembling Renalcis. A single bryozoan-crinoid-coral mound has been identified in Lawrence County, Alabama. It is approximately 25 m wide, up to 1.6 m thick, and had a maximum of 45 cm of synoptic relief. This mound is dominated by in situ colonies of the large rugosan Caninia sp. in a matrix of fenestrate bryozoan and echinoderm debris. A bryozoan-crinoid mound about 0.7 m thick and 1.5 m wide near Blount Springs, Alabama, contains a framework of fenestrate bryozoans and serpulids, spar-filled voids, and skeletal debris dominated by echinoderm ossicles. Bryozoan-crinoid mounds about 2 m thick have been reported from the Bangor-Pennington transition zone east of Monteagle. Five mounds up to 15 m wide and up to 1.5 m thick that are constructed entirely by Caninia sp. are known near Blount Springs and Lacon, Alabama.   Bangor mounds are relatively rare and small, suggesting environmental stress. The mounds we examined are mostly underlain by packstone/grainstone, which suggests that the principal stressor might have been a mobile substrate coupled with periodic smothering. However, the Lawrence County mound is underlain by oolitic grainstone that had first been indurated during a period of early subaerial exposure. Early diagenesis or other stabilization mechanisms probably occurred at the other mound sites as well. 