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KOPASKA-MERKEL, DAVID C., Geological Survey of Alabama, Tuscaloosa, AL; DIETER SCHMID, Ludwig-Maximilians-Universitaet, Muenchen, Germany

Abstract: New (?) Bioherm-Building Tubular Organism in Jurassic Smackover Formation, Alabama

Microbiohermal carbonate bodies made by a tubular microorganism have been found in two cores of the Smackover Formation in Alabama. The cores (State Oil and Gas Board Permit No. 2943, IJAMS 19-2 No. 2 and Permit No. 4971, T. R. Miller Mill Co. Unit 17-4 No. 1) are located on the northern flanks of the Wiggins arch and Conecuh embayment, respectively.

The IJAMS core, 18.6 m thick, consists of dolomitic mixed-particle wacke-pack-grainstone and undolomitized microbioherms ("microherms") up to 0.32 m thick and 5 cm to more than 9 cm wide. Microherms average 16% of the core by volume and were constructed chiefly by tubular microorganisms. Microherms and their enclosing matrix in the IJAMS core may have been deposited in a decameter-scale carbonate mound representing a previously unknown Jurassic reef type.

Most or all microherms in the IJAMS core consist of micritic tubules embedded in radial fibrous calcium-carbonate cement. Preservation of the tubules is attributed to early cementation that insulated the interiors of the microherms from subsequent diagenesis. The tubules are cylindrical, sparsely branched with "Y"-shaped junctions, and average 42 to 57 micrometers in diameter. Tubules are septate; septa are convex upward in longitudinal section, and are spaced 14 to 42 micrometers apart. Tubule walls and septa average 10 micrometers thick; cement coats range from about 15 to 35 micrometers in thickness. Some septa appear to consist of two parallel microcrystalline laminae separated by a thin layer of calcium-carbonate cement. The tubules resemble Renalcis and other microorganisms that have been interpreted as cyanobacteria or foraminifera. 

See page 1356 of PDF for this abstract.

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AAPG Search and Discovery Article #90924©1999 GCAGS Annual Meeting Lafayette, Louisiana