Abstract

The lower-middle part of the Pennsylvanian Haymond Formation in the Marathon Basin, west Texas, consists of interbedded sandstone, siltstone, and shale, which have been traditionally interpreted as turbidites deposited in deep water. Comparisons of the internal structures and mean grain size of the turbiditelike sandstone to Bouma's (1962) classical turbidite sequence suggest important dissimilarities. The majority of the Haymond turbidite-like sandstone beds displays only one kind of internal structure — cross-lamination, which can be subdivided into trough and flaser subtypes. Other turbiditelike sandstones in which two kinds of internal structure are found appear to have some similarities to Bouma's sequence; however, their general lack of normal grading indicates that turbidity currents played only a very minor depositional role.

On the bases of the internal structures, grain-size distributions, and mineralogic and bed-thickness variations, it is suggested that the sandstone was probably deposited on a sloping, delta-front platform on which currents generated by waves, tide, and wind have constantly acted upon the sediments that were periodically flushed from nearby distributary channels. During flood stages in distributary channels or during storms, high-velocity currents and turbulence may have developed, thus modifying depositional processes on the platform to produce turbiditelike sedimentation.

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