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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 257

Last Page: 258

Title: Compactional Features in Cambro-Ordovician Carbonates of Central Appalachians and Their Significance: ABSTRACT

Author(s): Robert K. Goldhammer, Lawrence A. Hardie, Chou Nguyen

Article Type: Meeting abstract


Compactional features are well known from siliciclastic rocks, but it is generally believed that carbonates have undergone little burial compaction. However, in the 3.5-km thick Cambrian-Ordovician carbonates of the Central Appalachians, many small-scale compaction features have been recognized. Evidence for differential compaction is: (1) wrapping of thin beds around meter-scale early-cemented algal bioherms and (2) sedimentary boudinage and pinch-and-swell features in interlayered thin beds of carbonate grainstone and mudstone. The grainstone layers have deformed in a brittle manner (cracking or yielding boudins), whereas mudstone layers behave ductily (flowing and bending around boudins), indicating that at the time of burial, grainstone layers were lithified but mudst ne layers were unlithified. Burrows and shells in sandy layers are preserved, but burrows are deformed and shells broken in muddy layers. Pervasive, rather than differential, compaction in muddy carbonates is evidence by flattened burrows, rotation of platy allochems parallel with

End_Page 257------------------------------

bedding, telescoping of mudcracks, and anastomosing wispy argillaceous seams. Pervasive compaction in peloidal grainstone is evidenced by warping and cracking of internal layers that are outlined by wispy seams. Ooid and skeletal grainstones and algal bioherms do not show these compaction features.

Time lines in these Cambrian-Ordovician carbonates converge across depositional strike from east to west, and this coincides with a change in facies from shelf-margin algal bioherms and grainstones showing little compaction to lagoon-peritidal mudstones with abundant compaction features. Volume reduction by compaction is clearly facies controlled and also has influenced the geometry of the time lines.

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Copyright 1997 American Association of Petroleum Geologists