--> ABSTRACT: Relationships Between Parasequences and Microplankton in the Ferron Sandstone (Late Cretaceous) of Central Utah, by Christopher N. Denison; #91019 (1996)

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Relationships Between Parasequences and Microplankton in the Ferron Sandstone (Late Cretaceous) of Central Utah

Christopher N. Denison

Canyons that dissect the western flanks of the San Rafael Swell in central Utah provide extensive outcrops of the Ferron Sandstone. Seven stratigraphic cycles or parasequences (SC1 to SC7) developed during the interplay of long and short term base level cycles. Each cycle shows a NE to SW transition from mud dominated distal facies, to nearshore deltaic sandstones, to proximal fluvial and coal swamp deposits.

In distal mudrock facies, marine microplankton abundance (40% of the palynomorph population) and diversity are at their highest. In nearshore area, microplankton are rare (<10%) in flooding surface shales. In a proximal setting, ? Subtilisphaera sp. is common (30%) at the base of flooding surface shales, but 1.0m higher only very rare (<1.0%) deflandreoid cysts are present. The same deflandreoid cysts are very rare (<1.0%) in washover sandstones and extremely rare (<0.1%) in bay shales.

Features of microplankton populations from such outcrop examples can be applied to facies analysis of hydrocarbon reservoirs in analogous settings. Cores through deltaic reservoir successions often contain very rare marine microplankton, although sedimentological evidence may indicate marine processes. Despite the rarity of these microplankton, considerable weight must be given to their presence as corroborative evidence of marine depositional processes.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California