--> ABSTRACT: High-Frequency Transgressive Episodes Punctuate Shoreline Regression in the Upper Cretaceous Dalton Sandstone, New Mexico, by S. Gupta; #91021 (2010)

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High-Frequency Transgressive Episodes Punctuate Shoreline Regression in the Upper Cretaceous Dalton Sandstone, New Mexico

GUPTA, SANJEEV


Progradational shore zone deposits in the Upper Cretaceous Dalton Sandstone of New Mexico are segmented by multiple, laterally discontinuous ravinement surfaces. The geometry and lateral distribution of these surfaces allows reconstruction of the patterns of high-frequency shoreline migration within a 20 km long dip-oriented regressive succession.

The Dalton Sandstone of northwestern New Mexico is a northeastward-prograding clastic wedge of late Coniacian to earliest Santonian age deposited in a ramp-type bathymetric setting in the Cretaceous Western Interior Basin. Individual progradational shoreface units (parasequences) can be traced for several kilometers from their landward pinchouts to their seaward pinchouts in marine shales. They comprise stacked amalgamated HCS sandstone units that are separated from each other by ravinement surfaces that have length scales of several kilometers (< 5 km). The ravinement surfaces are commonly characterized by pebble conglomerate beds containing sharks teeth, that are interpreted as transgressive lags. Transgressive deposits comprising thin-bedded piano-convex HCS beds are frequently preserved above ravinement surfaces, beneath the overlying prograded shoreface. Successive shorefaces are observed to onlap landwards onto the depositional surface of the underlying shoreface clinotherm.

A shoreline trajectory plot was constructed by measuring the progradational extents of successive shoreface units and the landward distance of transgression associated with the ravinements separating them. This indicates that seaward advance of the Dalton Sandstone shoreline over distances of tens of kilometers has been accomplished in short episodic steps during which the shoreline prograded several kilometers, then retreated over the underlying shoreface, after which progradation was resumed. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.