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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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the miocene monterey formation

The Miocene Monterey Formation

Sedimentology, Diagenesis, &

Paleoceanographic Significance

By Lisa White

slide2

Miocene Monterey Formation

16-6MYA

Background

Geol & Geog.

Setting

Lithology &

Composition

Paleo-

oceanography

Diagenesis

Petroleum

geologic setting
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
geographic extent
Geographic Extent

LOCAL:

  • Discontinuous North-South extension of 1700km
  • Typically 300-500m thick
  • Upper facies is siliceous (diatomaceous) sediments
deposition
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
lithology composition
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
geographic extent11
Geographic Extent

GLOBAL:

  • Discontinuous belt throughout North Pacific Rim (and South)
  • Onshore and offshore equivalents (ODP and DSDP sites)
lithology composition12
Lithology & Composition
  • Diatomaceous Units
lithology composition13
Lithology & Composition
  • High diatomaceous and organic rich deposits
  •  plankton productivity =  upwelling;

 terrigenous input =  sediment starvation;

=>  relative proportions of Silica, OM, Phosphate, or Carbonate

slide16

Silica

Diagenesis

diagenesis silica
Diagenesis: Silica
  • 2-Step Alteration:

Opal-A  Opal-CT

Opal CT  Diagenetic Quartz

  • Process of Alteration:
    • Complete dissolution
    • Re-precipitation
diagenesis silica18
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)
slide20

Paleoceanographic

Significance

paleo significance
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
paleo significance22
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)

slide23

Miocene Monterey Formation

16-6MYA

Background

Geol Setting &

Geog Extent

Lithology &

Composition

Paleo-

Environment

Diagenesis

Petroleum

petroleum resources source
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%
petroleum resource reservoirs
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
summary
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.
internet references
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