Diatomaceous sediments from the Miocene Monterey Formation, California; a lamina-scale investigation of biological, ecological, and sedimentary processes

Abstract

Finely laminated diatomaceous sediments from the Miocene Monterey Formation, Lompoc, Santa Barbara County, California, record the mutualistic coupling of life processes and environmental evolution at subannual and subseasonal resolution. In this study we present a new classification of lamina and couplet styles based on couplet bimodality, lamina thickness, compositional domination, lamina spacing, and cyclicity. We also describe five distinct lamina types with emphasis on paleoenvironmental settings, paleoecological associations, and biologically mediated sedimentary/taphonomic processes. Detrital laminae, consisting of silt, clay, and robust diatoms, were deposited from continental runoff during rainy seasons. Thin biosiliceous laminae consist of either moderately preserved high-diversity diatom assemblages, or well-preserved monogeneric phytoplankton assemblages. Most thick, continuous diatomaceous laminae are composed of well-preserved monogeneric and monospecific diatom assemblages that likely experienced biologically induced aggregation and rapid sedimentation without grazing. Thick, discontinuous diatomaceous laminae consist of either Thalassiothrix longissima mats or Chaetoceros setae. Mat laminae reflect stratified water conditions and high biomass conditions developed via vertically migrating diatom mats. Setae laminae are problematic to interpret. Macerated biosilica laminae, consisting of closely packed and highly fragmented biosilica from a variety of taxa, reflect intense zooplankton maceration and dissolution of diverse phytoplankton assemblages. Our results illustrate how different lamina types and associations can be used to proxy specific ecological and oceanographic conditions. This study provides a foundation for developing a high-resolution time series of paleoenvironmental variability recorded by biological event strata in hemipelagic sediments.