Abstract: What Laminated Sediments Mean: Illustrations from ODP Cores and the Miocene Monterey Formation

GRIMM, KURT A., ALICE S. CHANG, and KRISTEN M. JOHNSON

The optimal analytical approach to laminated sediments unites stratigraphic trends in composition and sediment fabric, with a microstratigraphic (lamination-scale) subsampling and analytical method that integrates sedimentological, paleoecological and multi-tracer geochemical measurements. Ongoing research integrates biological and sediment trap data with outcrop and subsurface stratigraphies in the Japan Sea, Santa Barbara Basin, Saanich Inlet and the Miocene Monterey Formation (MF). Conclusions to date are listed below: 1) Hemipelagic sedimentation is a biologically-mediated process. 2) Primary laminae record discrete sedimentation events; Secondary laminae - typified by phosphatic, dolomitic and siliceous laminae in the MF - arise by diagenetic enhancement of primary variability, by dissolution, pressure solution, and/or authigenic mineral precipitation. 3) Laminated hemipelagic sediments are part of a genetic continuum between distinctly laminated, indistinctly laminated and non-laminated sediments. 4) Heterogeneities in the texture and/or composition of sediment supply are necessary for the production of laminated sediments; the absence of hydraulic and biological reworking permits their preservation (i.e. the sole persistence of "anoxic" conditions at or near the sediment/water interface is insufficient to produce distinctly-laminated sediment). 5) Variations in lamination style record the heterogeneity of biologically-mediated, hemipelagic sediment flux.

Our integrative approach is providing unique insights into organic carbon richness and speciation, and their relationship to detrital influx, primary production, water column paleoecology, seafloor and pore water redox conditions and stratigraphic changes in sediment composition and texture. All of these factors influence rock fabric and composition of the MF; in turn they govern petrophysical characteristics of hydrocarbon migration, entrapment and recovery.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California