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Abstract

Discuss alternative models for deposition.

  1. 1.

    Parasequence model. Deposits represent normal progradation and transgression of lacustrine deltas, interrupted by occasional base level fall and basinward shift in facies. Base level driven, and the vertical facies succession in Kirmaky Valley is a result of lateral shifts in facies belts.

    • a.

      Kirmaky Suite - sublacustrine distributary channels in background of lacustrine mudstones.

    • b.

      Lack of well developed paleosols. Only brief exposure periods.

    • c.

      Interpreted distributary mouth bar facies in lower net to gross intervals in cores.

    • d.

      Coarsening and shallowing up of the upper portion of Kirmaky Suite into overlying Nad Kirmaky Sandstone (NKP) sandstones.

  2. 2.

    Climatically driven lake model. Sandstones primarily represent humid phases and abundant sediment supply whereas mudstone intervals primarily represent lowered inputs of both sediment and water. Sediment and water supply driven, and much of the vertical facies succession results from different depositional environments associated with different climatic settings.

    • a.

      Nad Kirmaky Shale (NKG) Suite — One of the most continuous mudstone intervals in basin—regional pressure seal, yet abundant mud cracks, and palynology indicates arid climate (terminal fan?).

    • b.

      Shales within Fasila and Balakhany at Kir-maky Valley similar to NKG.

    • c.

      Extensive flooding shales at top of Balakhany and Sabunchy in offshore contain thin evaporites.

    • d.

      Laterally extensive sand sheets.

    • e.

      Lack of large-scale progradational cycles on well logs or seismic.

    • f.

      Apparent, near-horizontal time lines.

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