--> --> Milankovitch stratigraphy in the Miocene-Quaternary marine succession of offshore coastal California

AAPG Pacific Section and Rocky Mountain Section Joint Meeting

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Milankovitch stratigraphy in the Miocene-Quaternary marine succession of offshore coastal California

Abstract

The Miocene Monterey Formation and related hemipelagic sediments of the California margin display pronounced lithologic cycles on scales from millimeters to tens of meters in thickness, with much speculation on their time significance and forcing functions. We have demonstrated the profound influence of Milankovitch cyclicity from eccentricity to precession time scales, on the upper Miocene to Pleistocene stratigraphy of the Santa Maria Basin of the central California margin and its usefulness as a refined dating and correlation tool. Previously, the development of high-resolution age scales for the fine-grained, homogeneous sediments of the Upper Neogene-Lower Pleistocene Monterey and Sisquoc formations and related successions was difficult due to the absence or discontinuous occurrence of useful microfossils in many successions.

We have applied astrochronology to the Ocean Drilling Program (ODP) Hole 1016A gamma ray well logs, 150 km offshore, to develop a new refined age-depth scale (1.2 to 5.8 Ma), to correlate sedimentary sequences to other more proximal wells in the basin, to refine sedimentation and mass accumulation rates, to identify intervals of condensed section, to show geographic trends in sedimentation rates along the paleomargin, to identify potential previously unknown productivity events, and to suggest possible refinements to dating of Late Neogene radiolaria of the central California margin.

The success of this project suggests that astrochronology is a valuable approach to refining dating along the central California margin for precise chronostratigraphic correlation of distinct facies that change laterally across or between basins. We are currently applying these astrochronoloical techniques to inland sites in more proximal basins that also show evidence of Milankovitch cyclicity.