Sedimentology of Upper Paleocene-Lower Eocene Sepultura Formation near Colonet, Baja California, Mexico
Upper Paleocene-lower Eocene braided-stream conglomerate of the Sepultura Formation crops out extensively within a paleovalley incised into the Cretaceous Peninsular Ranges batholith and the Alisitos Formation volcanics. The paleovalley trends just north of west as shown in 22-km long exposures within the modern San Telmo Canyon. Remnants of Sepultura fluvial-conglomerate infill reach a maximum thickness of 250 m and widths of 5-10 km. Conglomerate-clast assemblages are dominated by volcanic clasts (68-81%) along with the metamorphic (12-20%) and plutonic (2-8%) stones. The clast assemblage of andesitic and dacitic porphyries, volcaniclastics, granodiorites, aplites, and various metasediments appears to have been locally derived; all clasts are similar to the basement rocks exposed in the paleostream drainageway or just to the east of the metasedimentary belt. The Sepultura Formation contains none of the exotic, far-travelled, ultradurable rhyolitic gravels analogous to the Poway clasts that mark the time-equivalent deposits of the Mt. Soledad Formation in the San Diego area 220 km to the north. The Sepultura fluvial system supplied a gravel-rich braid delta that prograded westward over the inner shelf. Outcrops are up to 15 km wide and 23 km long, spanning braid-delta, transition-zone, and shallow-marine facies. Excellent exposures of reworked gravelly and biotite-rich sandy marine facies, some of which exhibit hummocky cross-stratification, occur in the vicinity of Punta Colonet. A late Paleocene age is indicated by the presence of turritella peninsularis. A late Paleocene age is indicated by the presence of Turritella peninsularis. A late Paleocene-early Eocene age is suggested by a sparse foraminiferal fauna (Ceratiopsos sp., Lanternosphaeridum lappaceum, Deflandrea speiosa, and Spindinium sp.).
- Research Organization:
- San Diego State Univ., CA (USA)
- OSTI ID:
- 6633921
- Report Number(s):
- CONF-8804144-
- Journal Information:
- AAPG Bull.; (United States), Vol. 72:3; Conference: AAPG SEPM-SEG Pacific Section and SPWLA annual convention, Santa Barbara, CA, USA, 17 Apr 1988
- Country of Publication:
- United States
- Language:
- English
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