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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 49 (1965)

Issue: 1. (January)

First Page: 113

Last Page: 114

Title: Symmetry, Stratigraphy, and Petrography of Cyclic Cretaceous Deposits of San Juan Basin: ABSTRACT

Author(s): Floyd F. Sabins, Jr.

Article Type: Meeting abstract


Late Cretaceous strata of the San Juan basin consist of cyclically interstratified non-Previous HitmarineNext Hit, nearshore Previous HitmarineNext Hit, and offshore Previous HitmarineNext Hit clastic sediments which were deposited during Previous HitmarineNext Hit transgressions and regressions. Thickness of the transgressive and regressive parts of these cyclic sequences varies, permitting subdivision into two types of cycles: symmetrical and asymmetrical. In symmetrical cycles the thickness of transgressive and regressive parts are nearly equal; in asymmetrical cycles the transgressive sandstone is thin or absent.

The Hosta-Point Lookout wedge is an example of a symmetrical cycle. At its base the transgressive Previous HitmarineNext Hit Hosta Sandstone overlies non-Previous HitmarineNext Hit strata of the Crevasse Canyon Formation. The Hosta Sandstone grades upward into the offshore Previous HitmarineNext Hit Satan Shale. The Satan Shale marks the mid-point of the cycle and the maximum Previous HitmarineNext Hit inundation; it grades upward into the regressive Previous HitmarineNext Hit Point Lookout Sandstone. The Point Lookout is overlain by the non-Previous HitmarineNext Hit Menefee Formation. Southwestward, toward the former shoreline, the Satan Shale pinches out and the transgressive and regressive sandstones merge into a single massive sandstone, which is also called the Point Lookout Sandstone. Still farther southwestward this massive sandstone grades into non-Previous HitmarineNext Hit strata of the Crevasse Canyon and Mene ee Formations.

The Mulatto-Dalton cycle is asymmetrical for it lacks a basal transgressive sandstone. Instead, the offshore Mulatto Shale directly overlies the non-Previous HitmarineNext Hit Dilco Coal with only scattered Previous HitmarineNext Hit sand lenses at the contact. The Mulatto Shale grades southwestward (toward the former shoreline) and upward into the regressive Previous HitmarineNext Hit Dalton Sandstone, which in turn grades southwestward into, and is overlain by, non-Previous HitmarineTop deposits of the Crevasse Canyon Formation.

Petrography is closely related to the sandstone depositional environments as follows.


End_Page 113------------------------------


These petrographic properties may be used to identify and correlate units in problem areas.

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Copyright 1997 American Association of Petroleum Geologists