Abstract

Microdeltas produced by slope-controlled runoff are useful emergence indicators in cross-bedded, tidal, and fluvial sandstones because they occur abundantly, have high preservation potential, and are identifiable in cross-section. Each microdelta normally consists of a lenticular-shaped, linguoid cross-bed that sits within a scour at the base of a larger cross-bed. Delta thickness approximates the relief on the base of the overlying set, while their lateral extent is normally less than 1 m. The deltas are closely associated with reactivation surfaces in the overlying set and are generally oriented perpendicular to the over- and underlying cross-beds. The lowest occurrence of microdeltas in a sequence provides an estimate of the low-water level, the identification of which should greatly aid in the quantification of paleotidal or stage-fluctuation ranges.

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