Hiatus-related processes: Paleokarst, paleosol, and a transgressive rocky shore from the Mississippian-Pennsylvanian unconformity in northwestern Arkansas
- Texas A and M Univ., College Station, TX (United States). Dept. of Geology
Unconformities are often considered only as stratigraphic gaps or sequence boundaries despite the evidence of climate- and paleogeography-linked hiatus processes that they may preserve. In northwestern Arkansas, progressively older Paleozoic strata are truncated to the north and west by the Mississippian-Pennsylvanian unconformity. In southern Washington County, Arkansas, the partly truncated Chesterian Pitkin Limestone is unconformably overlain by the Cane Hill Member of the Morrowan Hale Formation. The top of the Pitkin Limestone locally consists of cryptokarst with abundant solution pipes and lithoclasts formed by dissolution fragmentation. These lithoclasts, and surrounding clay dissolution residue, form regolith that is increasingly altered by pedogenic calcretization towards the top. The basal conglomerate of the overlying Cane Hill Member is interpreted as a transgressive boulder shore deposit. Conglomerate clasts consist of Pitkin cobbles and boulders that were derived from the erosion of local Pitkin highs.'' Most clasts are heavily bored on all sides by a variety of Trypanites and acrothoracian barnacle borings. Encrusting bryozoans and the encrusting tabulate coral, Michelinia, complete the rocky shore fauna. Preservation of paleokarst and poorly-indurated paleosol in low-lying areas around the eroded Pitkin highs,'' suggests that: (1) the vast majority of missing Pitkin was removed from the section by karstification during the hiatus, and not by erosion during the subsequent transgression; (2) transgression was too rapid to effectively scour the transgressed surface to bed rock; and (3) the net nearshore sediment transport direction was shoreward as the sea transgressed.
- OSTI ID:
- 5882387
- Report Number(s):
- CONF-921058--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 24:7; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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