--> Abstract: Diverse Tectonic Histories in the Stratigraphic Record of Crustal Blocks in the Eastern California Coast Ranges: Evidence for Long-Lived and Reactivated Structures, by J. Weber-Band, D. L. Jones, and T. V. McEvilly; #90958 (1995).

Datapages, Inc.Print this page

Abstract: Diverse Tectonic Histories in the Stratigraphic Record of Crustal Blocks in the Eastern California Coast Ranges: Evidence for Long-Lived and Reactivated Structures

J. Weber-Band, D. L. Jones, T. V. McEvilly

Are the active structures in the modern California Coast Ranges, namely the through-going strike-slip faults, entirely new and a simple response to the change in tectonic regime from convergent to transform in the mid-Miocene? Most geoscientists have assumed this to be the case. Our recent work in the eastern Central Coast Ranges suggests an alternative view of the roles of the major faults in the context of a changing tectonic regime.

The composite stratigraphic sections within the studied area show distinctly different sources and local depositional environments. The sequence an each "stratigraphic assemblage" tells a unique tectonic history for that crustal block as it responded to tectonic stresses over time. Assemblages are bounded by major faults, primarily strike-slip and thrust faults. Noticeably absent is the offset along strike-slip faults of originally continuous sedimentary basins. While such examples may have been removed through uplift and erosion, we find the evidence much more compelling for the separation of stratigraphic assemblages by more or less the same faults that are active today, i.e., the Concord, Calaveras, and Green Valley faults in the study area. The stratigraphic assemblage in the Delt area demonstrates it was a long-lived structural low where successive submarine canyons emptied from the shelf onto the slope. The oldest assemblages, of which the Delta area is one, show independent movement as far back as the Late Cretaceous, well before the transform regime predominated.

If faults are viewed merely as weak zones between relatively strong crustal blocks, then we can: (1) use the stratigraphic history of individual blocks to reconstruct margin tectonics, and (2) predict the existence of subsurface structures based on basin geometry. The relative movement of the blocks along the faults (in response to large-scale tectonic forces) resulted in a series of distinct upper crustal basins and highs, each recording a unique tectonic and sedimentary history. A geometric arrangement of lozenge-shaped crustal blocks along the California margin would very efficiently respond to reversing tectonic forces.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California