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The Miocene Monterey Formation

The Miocene Monterey Formation. Sedimentology, Diagenesis, & Paleoceanographic Significance. By Lisa White. Miocene Monterey Formation 16-6 MYA. Background. Geol & Geog. Setting. Lithology & Composition. Paleo- oceanography. Diagenesis. Petroleum. Geologic Setting.

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The Miocene Monterey Formation

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  1. The Miocene Monterey Formation Sedimentology, Diagenesis, & Paleoceanographic Significance By Lisa White

  2. Miocene Monterey Formation 16-6MYA Background Geol & Geog. Setting Lithology & Composition Paleo- oceanography Diagenesis Petroleum

  3. Geologic Setting • Deposited during the Miocene Period(16-6MYA) • Deposited in pull-apart or wrench-faulted basins • Middle bathyal depths (ocean environment 200-4000m) of accumulation

  4. Geographic Extent LOCAL: • Discontinuous North-South extension of 1700km • Typically 300-500m thick • Upper facies is siliceous (diatomaceous) sediments

  5. Neogene Basins

  6. Deposition • Range: • lower middle bathyal (1500-2300m) to upper middle bathyal (500-1500m) • Oxygen-deficient environment • Basin plains, slopes, banktops, shelf edges • mid-water oxygen minimum zone

  7. Lithology & Composition • Calcareous facies: • 16-15MYA ; lower/basal layer • Carbonate: coccoliths & foraminifers • Phosphatic facies: • 15-14MYA ; middle/transitional layer • phosphate, shale, & mudstones • Siliceous facies: • 14-6MYA; upper member/layer • diatoms & radiolarians

  8. Geographic Extent GLOBAL: • Discontinuous belt throughout North Pacific Rim (and South) • Onshore and offshore equivalents (ODP and DSDP sites)

  9. Lithology & Composition • Diatomaceous Units

  10. Lithology & Composition • High diatomaceous and organic rich deposits •  plankton productivity =  upwelling;  terrigenous input =  sediment starvation; =>  relative proportions of Silica, OM, Phosphate, or Carbonate

  11. Lithology & Composition

  12. Lithology & Composition

  13. Silica Diagenesis

  14. Diagenesis: Silica • 2-Step Alteration: Opal-A  Opal-CT Opal CT  Diagenetic Quartz • Process of Alteration: • Complete dissolution • Re-precipitation

  15. Diagenesis: Silica • Transformation controlled by temp. & burial depth, bulk composition & rock properties (porosity & permeability) • 2 narrow temp. ranges & burial depth: 40-50ºC & 0.5-2km (Opal-A  Opal-CT) 65-80ºC & 1.5-3km (Opal CT  Quartz) • Purest sediments alter early: hard, brittle Opal-CT (2-33ºC) & quartz cherts (36-76ºC)

  16. Silica Diagenesis

  17. Paleoceanographic Significance

  18. Paleo- Significance • Deposited within important transition in: • Cenozoic cooling associated with Antartic Ice Sheet expansion • Increased upwelling associated with thermohaline circulation reorganization • Accelerated CO2 drawdown associated with Himalayan uplift

  19. Paleo- Significance • Major changes: ocean circulation, global climate, tectonic transition Upwelling & Nutrients (Diatom Blooms) Cooling (Antarctic Ice Sheet) CO2 Drawdown  (Weathering) Burial & Preservation (Organic Matter)

  20. Miocene Monterey Formation 16-6MYA Background Geol Setting & Geog Extent Lithology & Composition Paleo- Environment Diagenesis Petroleum

  21. Petroleum Resources Source • Significance: both oil source & reservoir • 1º source rock of hydrocarbons in Cal • Oil source generated in immature or marginally mature rocks • May largely come from organic-rich carbonates and phosphates • TOC: can be as much as 23%, but averages at 2% - 5%

  22. Petroleum ResourceReservoirs • Non-commercial reservoirs - lack effective porosity (ne) & permeability (k) in composition of fine-grained, organic-rich rock • Reservoirs generally consist of: • Adjacent or interfringed sandstone beds, members or formations • Naturally fractured, brittle diagenetic siliceous & dolomitic rocks

  23. Summary • Vast extent, deposited at different times and stages. • Diagenesis stages relate to original rock composition and depth of burial. • Petroleum source and reservoir. • Formation of carbonate, phosphate, and silica facies reflect global oceanic conditions.

  24. Internet References • http://www.sci.sdsu.edu/pacsepm/SEPMpastfldtrips.htm • http://www.ucmp.berkeley.edu/tertiary/mio/monterey.html • http://www.seis.natsci.csulb.edu/rbehl/Mont.htm

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