Subsidence History of Great Valley: Forearc Basin Evolution During Laramide Orogeny: ABSTRACT

Abstract

Geohistory analysis was performed on 25 surface and subsurface stratigraphic sections from the Sacramento and northern San Joaquin basins. These geohistory curves document in detail the subsidence history of the Great Valley forearc basin, and permit correlation of forearc basin events with plate motion reconstructions and with events in the arc and subduction complex. Furthermore, the geohistory curves present a model that could be integrated with thermal history data to assess maturation of potential source rocks in the basin. Interpretation of the subsidence history curves and sedimentary facies distribution patterns shows five phases of basin evolution, punctuated by tectonic and/or eustatic events. 1) The earliest phase (Tithonian to mid-Cenomanian, 152-95 Ma) consists of distal turbidite sedimentation, but cannot be reliably interpreted due to a paucity of data. 2) Great Valley Group turbidites accumulated during a mid-Cenomanian to latest Campanian (95-74.5 Ma) phase of rapid tectonic subsidence and submarine fan sediment accumulation. The Maestrichtian (74.5-66.4 Ma) represents a transition between the Late Cretaceous and Paleogene phases, with localized gentle uplift of the western basin margin displacing the depocenter progressively eastward. 3) Structural disruption of the basin, locally subaerially exposing the western basin margin and forming a complex intrabasin borderland topography of more » rapidly subsiding subbasins and stable blocks, characterized the Paleogene phase (66.4-36 Ma). Subsidence curves show two periods of rapid subsidence (60-56 Ma and 52-47 Ma) alternating with basin-filling or uplift periods; these basin evolution signatures may reflect movement along a proto-San Andreas fault. 4) A widespread unconformity, induced partially by eustatic sea level fall, characterized the Oligocene (36-24 Ma). 5) Subbasins continued to evolve separately during the Miocene to holocene phase (24-0 Ma). « less