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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 44 (1974)No. 1. (March), Pages 181-189

Positive-Relief Bedforms on Modern Tidal Flat that Resemble Molds of Flutes and Grooves; Implications for Geopetal Criteria and for Origin and Classification of Bedforms

Gerald M. Friedman, John E Sanders

ABSTRACT

Bedforms having positive relief and molded into shapes resembling counterparts of flutes and grooves sculpted in mud have been created by sheetflow of the incoming tide across pelletal carbonate sediments on a tidal flat at Abu Dhabi. The flute-like bedforms, for which the new name setulfs is proposed, are 4 to 5 cm long, 2 to 3 cm wide, and about 1 cm high; their long axes are parallel to the direction of current flow. Setulfs have high pointed ends on their upcurrent sides and flare out and become lower on their downcurrent sides. They were observed as the only bedforms along a traverse about 100 m long at right angles to the shore; they display no obvious large-scale organization. The groove-like linear ridges, 3 to 30 cm long, about 5 to 6 mm wide and 2 to 3 mm high, are parallel o direction of flow. The internal structures of these features are not known.

These positive-relief bedforms, setulfs and ridges, presumably grew in response to complex patterns of flow lines in a shallow current. Secondary flows and flow separations are thought to have been involved, but in a way unlike that in which these characteristics of currents have eroded negative-relief forms in cohesive muds. The striking resemblance between the morphology of the positive-relief setulfs and ridges of the Abu Dhabi tidal flat and the negative-relief forms eroded into cohesive muds is all the more astonishing in view of the diametrically opposite conditions of origin (i.e., positive relief in cohesionless sediment vs. negative relief in cohesive sediment).

The setulfs and linear ridges from the Abu Dhabi tidal flat require new categories to be erected in the classification of sedimentary bedforms and introduce complications into the environmental interpretation of sediments based on sole markings. If the setulfs and linear ridges here described were to be buried by mud, both layers lithified, tilted on edge, and the mudstone eroded away, then the positive original relief forms, at the true top of the bed, could easily be confounded with fillings, on the base of the bed ("sole markings"), of negative relief features originally scoured in the now-vanished and supposedly underlying mud.


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