Abstract

The regressive Miocene succession of offshore Louisiana comprises 10 third-order sequences and no fewer than 58 fourth-order sequences, which average approximately 1.1 and 0.19 m.y. in duration, respectively, comparable to durations measured in the Gulf Coast Basin and basins worldwide. Upper lower to middle Miocene distal third-order sequences comprise mostly lowstand prograding-wedge, slope-fan, and basin-floor-fan deposits. In contrast, middle to upper Miocene medial sequences record progressively more landward systems tracts: (1) the lateral transition between on-shelf incised-valley fills and the proximal parts of basinward-thickening, lowstand prograding wedges and (2) cyclic on-shelf highstand and transgressive systems tracts. Upper Miocene inner-shelf and marginal marine systems tracts and more abundant incised valleys dominate the thinner proximal third-order sequences.

This genetic framework has a major influence on hydrocarbon distribution. Although a strong structural-trapping component is present in the fields, more than 90% of cumulative production originates where fourth-order systems tracts stack to form third-order lowstand systems tracts in all 10 third-order sequences. The development of a high-frequency sequence framework for the prolific Miocene succession and the discovery that hydrocarbons are pooled within the Miocene third-order lowstand systems tracts yield a focused model for the development of abundant undiscovered Miocene reserves in the mature northern Gulf of Mexico shelf province.

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