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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)


Journal of Sedimentary Petrology
Vol. 63 (1993)No. 3. (May), Pages 488-494

Quasi-Planar-Laminated Sandstone Beds of the Lower Cretaceous Bootlegger Member, North-Central Montana: Evidence of Combined-Flow Sedimentation

R. W. C. Arnott


Lower-shoreface to shallow-shelf strata of the Bootlegger Member of the Lower Cretaceous Blackleaf Formation are characterized by interbedded sandstone and mudstone. Sandstone beds are characterized by a peculiar planar lamination showing a subtle although perceptible undulation; spacing-to-height ratios of the undulation are generally 100 or more. Typically the undulation shows no evidence of lateral accretion but only vertical aggradation, and as a result most beds consist of a single laminaset. Aspects of quasi-planar-laminated beds indicate single-event storm sedimentation, and paleocurrent data indicate offshore sediment transport.

By its sedimentary characteristics and its similarity with a bed configuration generated in un experimental wave duct, quasi-planar lamination is produced by high-energy combined flows. This style of stratification should be common in the shallow-marine stratigraphic record, and its recognition should aid in interpreting high-energy, combined-flow depositional events.

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