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Comparison of Attributes and Formation of Stratal Carapaces Versus Halokinetic Sequences

Katherine A. Giles
Institute of Tectonic Studies, New Mexico State University, Las Cruces, NM

Stratal carapaces and halokinetic sequences are distinctive stratigraphic packages associated with near surface salt diapir rise and provide the basis for interpretation of diapiric history. Stratal carapaces are defined as subparallel, conformable strata originally deposited semi-conformably over bathymetrically raised broad salt domes, canopies and sheets. Halokinetic sequences are angular unconformity-bounded growth strata deposited directly adjacent to and over the margins of bathymetrically raised salt domes, canopies and sheets. During deposition isopachous carapace strata transition laterally into expanding halokinetic sequence wedges and thus form a linked system whose character is influenced by diapiric rise and sediment accumulation.

Carapaces become isolated and rotated from adjacent strata by post-depositional lateral flow of salt from underneath the package. Carapace facies tend to be condensed and homogenous due to accumulation on top of the rising diapir, sheltered from sediment fairways. In contrast, halokinetic sequences are syndepositionally, progressively rotated by the rise of salt and complimentary sediment subsidence (i.e. downbuilding process). The facies record the complex interplay of local variations in sediment accumulation versus diapiric rise rate and include basal sediment gravity flow units, overlain by onlap and overlap sand-prone facies. Tabular shape and abrupt termination of the isopachous carapace layers results from lateral salt flow breakout at the diapir top /margin transition. Tapering carapace edge shape and expanding termination strata indicate lateral breakout at the diapir margin/minibasin transition. Rotated carapace blocks may be onlapped by wedge shape growth strata that are not considered halokinetic sequences because they are not generated at the salt sediment interface.