Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Howard, J. L. Search for Related Content GeoRef GeoRef Citation

Provenance of quartzite clasts in the Eocene–Oligocene Sespe Formation: Paleogeographic implications for southern California and the ancestral Colorado River

¹ Department of Geology, Wayne State University, Detroit, Michigan 48202, USA

Quartzite clasts in fluvial Sespe Formation conglomerates of the Santa Monica Mountains were compared petrographically with potential source rocks in the Basin and Range and Transition Zone provinces to determine their provenance. Modal analysis indicates that Sespe orthoquartzite clasts are mainly quartzofeldspathic and derived from source rocks with craton-interior provenance. Such clasts were probably derived from Stirling Quartzite and Wood Canyon Formation sources in the northern Mojave Desert. The Mazatzal Peak Quartzite of central Arizona is the probable source of quartzolithic orthoquartzite clasts containing abundant detrital jasper grains. Sespe metaquartzite clasts are mainly from sources in the southern Mojave Desert, but some may be from the Yavapai terrane of central Arizona. The dual provenance of orthoquartzite clasts suggests that the Sespe paleoriver was a bifurcating system tapping both Mojave Desert and Sonora Desert sources. After compensating for Neogene displacement along the San Andreas fault, a paleogeographic reconstruction shows that there is a general spatial coincidence between Sespe (and other Cenozoic) paleodelta deposits around Los Angeles that contain exotic clasts, and the inferred location of the mouth of the Colorado River (assuming that it existed during the Eocene). Thus, the Colorado River may be much older than previously thought (as old as late Paleocene), and perhaps was once part of an ancient fluvial connection with the Mojave Desert interior.

Key Words: California • Cenozoic • conglomerate • Los Angeles • modal analysis • Mojave Desert • provenance

This article has been cited by other articles:

				J. E. Spencer, G. R. Smith, and T. E. Dowling Middle to late Cenozoic geology, hydrography, and fish evolution in the American Southwest Geological Society of America Special Papers, January 1, 2008; 439(0): 279 - 299. [Abstract] [Full Text] [PDF]

				K. A. Howard, S. C. Lundstrom, D. V. Malmon, and S. J. Hook Age, distribution, and formation of late Cenozoic paleovalleys of the lower Colorado River and their relation to river aggradation and degradation Geological Society of America Special Papers, January 1, 2008; 439(0): 391 - 410. [Abstract] [Full Text] [PDF]