Controls on stratal cyclicity in a shelf to basin transition, middle Eocene, southern California
Conference
·
· AAPG Bulletin (American Association of Petroleum Geologists); (USA)
OSTI ID:6720583
- Colorado School of Mines, Denver, CO (USA)
The Narizian (middle Eocene) stage in the Topatopa Mountains of southern California is represented by parts of the Matilija, Cozy Dell, and Coldwater formations - siliciclastic strata that filled a marine fore-arc basin. Facies representing shelf, slope, and basin environments record three orders of stratal cyclicity: (1) individual bedsets, (2) progradational units (parasequences) comprised of multiple bedsets and bound by deepening events, and (3) seismic-scale sequences (depositional sequences) comprised of multiple parasequences and bound by unconformities, stratal geometries, parasequence stacking patterns, and facies distributions document five depositional sequences: (1) the middle Matilija (Na1), (2) upper Matilija and Cozy Dell (Na2), (3) lower Coldwater (Na3), (4) middle Coldwater (Na4), and (5) upper Coldwater (Na5). Transgressive surfaces of erosion cap sequences Na2 and Na5 and separate discordant strata or changes in porosity. Regressive surfaces of erosion cap sequences Na1 and Na4. Also, a sand-rich parasequence in the Cozy Dell half-sequence indicates an increase in the sand/shale ratio of sediment entering the basin, even though paleosoils and geohistory diagrams indicate that Narizian deposition in southern California was characterized by decreasing sedimentation rates. Depositional patterns are attributed to combined tectonic and eustatic controls. Formation of sequences Na2 and Na4 was followed by increased rates of basin subsidence, which created transgressive surfaces of erosion and drowned the sequence capping disconformities.
- OSTI ID:
- 6720583
- Report Number(s):
- CONF-900605--
- Conference Information:
- Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 74:5
- Country of Publication:
- United States
- Language:
- English
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