Sequential Paleogeographic Models of the San Andreas Fault System ~70 to ~2 MA
Independent research, Oakland, CA, [email protected]
Paleogeographic reconstructions at ~70-30 Ma, ~11 Ma, ~5 Ma, and ~2 Ma juxtapose more than 60 previously published pairs of correlative features.
Eight pairs of correlatives reported by Dibblee, 1966; Cummings, 1968; Wakabayashi and Hengesh, 1995; and McLaughlin et al., 1996 indicate only ~30 km lateral offset across the section of the San Andreas fault between its intersections with the Calaveras and San Gregorio faults. The Cretaceous-Pleistocene ages of these correlatives indicate dextral offset of this section of the San Andreas fault was not initiated until after 3-4 Ma (McLaughlin et al., 1996).
The 315 km offset of the San Andreas fault from Pinnacles to Neenach volcanics is partitioned between ~30 km offset of the San Andreas fault north of the Calaveras fault intersection, and ~285 km offset of the San Andreas-Calaveras-Hayward-(Rodgers Creek?)-Maacama fault. Offset distance of the Calaveras-fault leg of this partition is verified by paleogeographic juxtaposition (~70-21.3 Ma) (Burnham, 2006, 2009) of Wakabayashi’s (1999) Skaggs Springs Schist near Healdsburg and Pacheco Pass. Dextral offset of the San Andreas-Calaveras-Hayward-(Rodgers Creek?)-Maacama fault commenced after 21.3 Ma, and slipped at least 77 km before 11 Ma.
The ~205 km offset of the northernmost San Andreas fault from the Delgada fan to the Wilson Grove Formation is partitioned between ~180 km offset of the San Gregorio-northern San Andreas fault and ~30 km offset of the San Andreas fault south of the San Gregorio fault intersection. Dextral offset of the San Gregorio-northern San Andreas fault began after ~19 Ma and had slipped at least 70 km before 5.3 Ma.
The Hosgri-San Gregorio-northern San Andreas fault and the San Andreas-Calaveras-Hayward-Maacama fault moved separately in parallel before they were connected by formation of the San Francisco peninsula section of the San Andreas fault and the fault system began to resemble its modern configuration.
AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009