CENOZOIC SIERRA NEVADA TILTING: THE BIG STORY FROM CENTRAL VALLEY STRATIGRAPHY

Many approaches have been taken to quantifying the Cenozoic tilt history of the Sierra Nevada crustal block. Inferring block tilting from the inclinations of Cenozoic strata in the Central Valley basin fill is one of the most productive because the fill extends the length of the Valley, allowing reconstruction of tilt for the entire length of the mountain range, and because the fill was deposited throughout the Cenozoic, allowing a history of tilt to be reconstructed.

I have used this technique to reconstruct the tilt history from the Eocene to the present. The reconstruction shows that south of the San Joaquin River the range has tilted continuously, but that the rate accelerated substantially at ~5 Ma, producing 2 to 4 km of crest uplift since the Eocene. North of the San Joaquin River tilting was very slow until a pulse of tilting began at ~5 Ma and lasted until ~1.5 Ma, producing 1.0 to 1.5 km crest uplift. If erosion is taken into account, this tilt history is consistent with previous studies showing that the crest elevation of the northern Sierra in the Eocene was similar to the present elevation.

The tilt history of the southern range is consistent with predictions based on geophysical and geochemical observations that indicate convective removal of the lithospheric root of the Sierra Nevada batholith in the late Cenozoic. The cause of the brief pulse of tilting of the northern range is more speculative, but the temporal correlation of the initiation of tilting with the southern range suggests an explanation also involving lithospheric convection.

Comparison of the uplift magnitude of the crest along the length of the range with the depth of the Central Valley to the west and the depth of the down-faulted basins in the Great Basin to the east shows substantial similarity. This indicates that late Cenozoic tilting of the Sierra Nevada crustal block controls the configurations of the very large basins on either side of the Sierra.