Abstract

This article presents (1) a process-oriented description of an outcrop analog for epeiric successions; (2) a discussion of fundamental characteristics of epeiric basin fills; and (3) a generic depositional model, which may be used for improved reservoir prediction in epeiric settings. The case study focuses on the upper Ladinian, mixed siliciclastic-carbonate Lower Keuper Formation. It is composed of storm-generated, tide-generated, and bioturbated facies. Paleogeographically the succession shows an unusual lateral energy zonation comprising a seaward low-energy zone close to wave base; an intermediate, reservoir-prone, high-energy zone within wave base; and a landward low-energy zone above wave base. Stratigraphically the Lower Keuper Formation is subdivided into meter-scale transgressive-regressive cycles, correlatable over distances of more than 500 km. Cycle boundaries are interpreted to be isochronous. Within the resulting chronostratigraphic framework, facies distributions have been mapped out in three dimensions, revealing that reservoir-prone facies are most extensive in shoreline-detached positions. Reservoir bodies are thin, have sheetlike geometries but extend for several tens of kilometers, and are stacked in an aggradational facies architecture. Additionally, the reservoir-prone facies is thicker developed in zones of stronger subsidence, a few kilometers wide, linked to underlying basement blocks.

Resulting unconventional reservoir prediction strategies for similar shallow-marine epeiric settings should target shoreline-detached high-energy facies belts that are preferentially developed within zones of stronger subsidence, controlled by basement tectonics.

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