DIATOMACEOUS SEDIMENTS FROM THE MIOCENE MONTEREY FORMATION CALIFORNIA- A LAMINA-SCALE INVESTIGATION OF BIOLOGICAL, ECOLOGICAL, AND SEDIMENTARY PROCESSES

Finely laminated diatomaceous sediments from the Miocene Monterey Form ation, Lompoc, Santa Barbara County, California, record the mutualisti c coupling of life processes and environmental evolution at subannual and subseasonal resolution. In this study we present a new classificat ion of lamina and couplet styles based on couplet bimodality, lamina t hickness, compositional domination, lamina spacing, and cyclicity. We also describe five distinct lamina types with emphasis on paleoenviron mental settings, paleoecological associations, and biologically mediat ed sedimentary / taphonomic processes. Detrital laminae, consisting of silt, clay, and robust diatoms, were deposited from continental runof f during rainy seasons. Thin biosiliceous laminae consist of either mo derately preserved high-diversity diatom assemblages, or well-preserve d monogeneric phytoplankton assemblages. Most thick, continuous diatom aceous laminae are composed of well-preserved monogeneric and monospec ific diatom assemblages that likely experienced biologically induced a ggregation and rapid sedimentation without grazing. Thick, discontinuo us diatomaceous laminae consist of either Thalassiothrix longissima ma ts or Chaetoceros setae. Mat laminae reflect stratified water conditio ns and high biomass conditions developed via vertically migrating diat om mats. Setae laminae are problematic to interpret. Macerated biosili ca laminae, consisting of closely packed and highly fragmented biosili ca from a: variety of taxa, reflect intense zooplankton maceration and dissolution of diverse phytoplankton assemblages. Our results illustr ate how different Lamina types and associations can be used to proxy s pecific ecological and oceanographic conditions. This study provides a foundation for developing a high-resolution time series of paleoenvir onmental variability recorded by biological event strata in hemipelagi c sediments.