Magnetostratigraphy and biochronology of the San Timoteo Badlands, southern California, with implications for local Pliocene-Pleistocene tectonic anddepositional patterns

Authors
Citation
Lb. Albright, Magnetostratigraphy and biochronology of the San Timoteo Badlands, southern California, with implications for local Pliocene-Pleistocene tectonic anddepositional patterns, GEOL S AM B, 111(9), 1999, pp. 1265-1293
Citations number
73
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
GEOLOGICAL SOCIETY OF AMERICA BULLETIN
ISSN journal
0016-7606 → ACNP
Volume
111
Issue
9
Year of publication
1999
Pages
1265 - 1293
Database
ISI
SICI code
0016-7606(199909)111:9<1265:MABOTS>2.0.ZU;2-F
Abstract
The San Timoteo Badlands expose nearly 2000 m of nonmarine sedimentary rock s ideally situated temporally and spatially to address questions regarding major tectonic events that occurred in southern California from latest Mioc ene to medial Pleistocene time. These events include development of the San Andreas-San Jacinto fault system and uplift of the Transverse Ranges. The badlands sequence also spans three of the four most recent North American L and Mammal "ages" and therefore coincides with important trans-Beringian an d Neotropical mammal dispersal events. No other terrestrial sequence in Nor th America records relatively continuous deposition over this interval of t ime. Magnetostratigraphy and mammalian biochronology provide a temporal framewor k that allows greater resolution of the geologic and biotic events recorded within the sequence than previous studies on this region, Data show that t he sequence extends from chron C3An.2n, ca, 6.3 Ma, at the lowest part of t he section in the study area, to within the Brunhes chron, or younger than 0.78 Ma, near the top. Refined age estimates for geologic and biotic events recorded within the sequence indicate that (1) a Peninsular Ranges basemen t source south of the badlands region dominated deposition from before 6.3 Ma to about 4.6 Ma, after which time the provenance shifted to a San Gabrie l Mountains basement source from the north; (2) deposition of San Gabriel M ountains-type material continued until as recently as ca, 0.70 Ma, although sediments from the San Bernardino Mountains appeared in the northwesternmo st area of the badlands ca, 1.5 Ma; (3) the late Hemphillian Mount Eden Loc al Fauna is dated as 5.6 Ma, compared,vith previous estimates of 5.0-5.4 Ma ; (4) the early Irvingtonian Fl Casco Local Fauna is 1.3-1.4 Ma; and (5) th e Shutt Ranch Local Fauna is ca, 0.7-0.99 Ma, Paleomagnetic data show that the badlands region may be slightly rotated in a counterclockwise direction , contrary to previous models predicting clockwise rotation in right-latera l shear zones.