Late Cretaceous-early Tertiary paleoceanography and cyclic sedimentation along the California margin: Evidence from the Moreno Formation

Upper Maestrichtian through Danian laminated biosiliceous and phosphatic sediments of the upper Moreno Formation in San Joaquin Valley, California provide a high resolution record of coastal upwelling and productivity along the Pacific margin of North America during a period of global climate change. Stratigraphic, sedimentologic, geochemical, and micropaleontologic analysis of organic-rich sediments characterizing the Marca Shale member of the formation indicate that variations in productivity of siliceous phytoplankton, influx of terrigenous sediments, and intensity of oxygen minima were the primary controls on sedimentation. Episodic occurrence of phosphates, glauconite, bioturbated sediments, continuous laminations, and distribution of trace-metals and specific biomarkers indicate the Marca Shale was deposited under predominantly sub-oxic denitrifying conditions on the upper-slope of the Cretaceous California margin. Laminated Marca sediments include depositional couplets composed of light and a dark colored laminae representing annual varves. SEM micrographs and variations in content of biogenic silica emphasize differences in the abundance and composition of siliceous phytoplankton within laminae. Seasonal humid periods resulted in laminae dominated by terrigenous components whereas dry periods and associated vigorous upwelling resulted in deposition of diatom-rich laminae. Image analysis was used to quantify variations in texture and thickness of laminae allowing recognition of high frequency cyclicity, including eleven-year cycles. Sedimentologic observations, gamma ray spectrometry, and bulk chemical analysis indicate the presence of four short term depositional cycles within the Marca Shale. Spectral analysis suggests Milankovitch band climatic oscillations influenced Marca depositional cycles as late Cretaceous climate cooled. Finally, detailed analysis of the Cretaceous/Tertiary boundary layer at the contact between the Marca Shale and overlying Dos Palos Shale revealed the presence of goyazite spherules and a condensed layer containing high abundances of rare earth elements similar to patterns recorded across the K/T boundary at other localities.