November 4, 2013 at 3:54 pm

Gierlowski-Kordesch Presents on Continental Carbonates, New Stratigraphic Correlative Tool

Ohio University faculty made an impact with 23 presentations at the Geological Society of America’s 125th Anniversary Annual Meeting & Exposition Oct. 27–30 in Denver.

Dr. Elizabeth Gierlowski-Kordesch presented on CLASSIFICATION OF CONTINENTAL CARBONATES. Gierlowski-Kordesch is Professor of Geological Sciences in the College of Arts & Sciences.

The types of continental carbonates that are described in the literature seem to represent a plethora of origins and textures. These nonmarine carbonates are documented from all latitudes so climate is a minor control on deposition. A classification of these carbonates should involve an understanding of the depositional environment as well as the hydrologic controls of water or calcium ion input. Large quantities of water with carbonate load, whether dissolved load, suspended load, or bedload, are needed to accumulate significant carbonate deposits in subaerial and subaqueous continental environments since time is short in the context of geologic time and landscape evolution. Provenance is key to predicting patterns of deposition as well, especially for eolian carbonate deposits. Microbialites are components of many of these carbonate types and require significant input of Ca-rich water, especially groundwater. Classification categories for depositional environments include: (1) soil, (2) palustrine to playa, (3) lacustrine, (4) fluvial above and at the regional springline, (5) fluvial below the springline and (5) eolian. Inputs include: (1) surface water, (2) groundwater, and (3) wind. Input directly by precipitation occurs but is very minor and difficult to distinguish. Types of continental carbonates can be (1) pedogenic carbonates and calcrete, (2) groundwater calcrete, (3) spring/seep deposits at or above the regional springline, (4) artesian spring/seep deposits, (5) subaqueous lacustrine carbonates, (6) palustrine margin carbonates of perennial lakes, (7) palustrine-playa carbonates of ephemeral lakes, (8) spring/seep deposits at ephemeral and perennial lake margins, including beachrock, (9) carbonate pond sediments on sheetflood plains containing pedogenic mud aggregates, (10) lacustrine delta carbonates, (11) eolian carbonates, (12) carbonate lake deposits on anastomosing river floodplains, and (13) carbonate eolianites.


The continental Pennsylvanian and Permian rocks of southeastern Ohio display poor lateral continuity because of the lack of diagnostic flora and fauna, rapid lateral facies changes, and paleosols with many erosional incisions. With no prominent marker beds, such as coal and marine limestones, correlation across the area of the mudrocks, sandstones, and nonmarine limestones, interpreted originally as cyclothems, is difficult. A geochemical correlative tool is needed to precisely identify similar beds across the region. Strontium isotopic ratios (87Sr/86Sr) from the nonmarine limestone units have been used to reconstruct the tectonic history of these Late Paleozoic rocks, though sampling to date has been restricted to one sample per unit to observe changes over time. Because Sr isotopic ratios are seemingly unique to each limestone unit, it is probable that they reflect the signal of the drainage area rocks at the time of deposition and can be used as a correlative tool. More precise stratigraphic correlation will facilitate more detailed paleoenvironmental reconstructions across the region.

To test the applicability of Sr isotopes as a correlative tool, ten limestone samples were collected across the bottom of a limestone layer in the Monongahela Group (Pennsylvanian) exposed near Macksburg, OH in northern Washington County to see if the Sr isotopic ratios were similar across this nonmarine unit. Sr isotopic ratios ranged from 0.710414 to 0.710441. The non-parametric Kolmogorov-Smirov statistical test confirmed that these data reflect one population. The next field test is to compare these data with that from a probable correlated unit in Athens County to the west. Detailed petrographic work on the nonmarine limestones shows that they are palustrine carbonates developed on a siliciclastic fluvial floodplain of a probable anastomosing river system sourced from the east.


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