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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 292

Last Page: 292

Title: Porosity Evolution in Salem Limestone (Mississippian) of South-Central Indiana: ABSTRACT

Author(s): Morgan R. Newton

Article Type: Meeting abstract


The Salem Limestone (Valmeyeran) is represented in Monroe and northern Lawrence Counties, Indiana, by a complex assemblage of bioclastic packstone-grainstones capped by dolomitic rocks. Modal analysis indicates intervals where porosity exceeds 20%. However, the evolution of this porosity is not well documented. Optical and cathodoluminescence petrography reveal primary porosity in coarse echinoderm-bryozoan and diverse-fauna grainstones. In the porous zones, cement occurs as (1) fibrous to sparry cement filling intragranular areas (foraminifer chambers and fenestrate bryozoan zooecia), (2) isopachous crusts on the exterior of polycrystalline and coated grains, (3) syntaxial rims on uncoated echinoderm grains, and (4) rudimentary syntaxial cement on "bald spots" where grai coats have been spalled by compaction. Porosity in analagous bioclastic grainstones composed of uncoated echinoderm fragments is thoroughly occluded with syntaxial cement.

Cathodoluminescence reveals that rudimentary cement under spalled grain coats postdates the earliest cements on uncoated grains. From oldest to youngest, luminescence zonation for well-developed syntaxial rims progresses from nonluminescent, through dully luminescent, through brightly luminescent, to dully luminescent. The rudimentary syntaxial cement under spalled coats is commonly brightly luminescent.

Tightly cemented, fine-grained, bioclastic packstone-grainstones overlie these porous intervals, apparently serving as aquacludes that prevented more thorough cementation. Secondary porosity also is common in the Salem Limestone and occurs as gastropod molds, vugs, and solution-enlarged fractures.

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