The Miocene Monterey The Miocene Monterey FormationFormation

Sedimentology, Sedimentology, Diagenesis, & Diagenesis, &

Paleoceanographic Paleoceanographic SignificanceSignificance

By Lisa White

Miocene Monterey FormationMiocene Monterey Formation16-616-6MYAMYA

Lithology &Lithology &CompositionComposition

PetroleumPetroleumDiagenesisDiagenesis

BackgroundBackground

Paleo-Paleo-oceanographyoceanography

Geol & Geog.Geol & Geog.SettingSetting

Geologic SettingGeologic Setting

• Deposited during the Miocene Deposited during the Miocene Period(16-6Period(16-6MYAMYA))

• Deposited in pull-apart or Deposited in pull-apart or wrench-faulted basinswrench-faulted basins

• Middle bathyal depths (ocean Middle bathyal depths (ocean environment 200-4000m) of environment 200-4000m) of accumulationaccumulation

Geographic ExtentGeographic Extent

LOCAL:LOCAL:• Discontinuous North-South Discontinuous North-South

extension of 1700kmextension of 1700km• Typically 300-500m thickTypically 300-500m thick• Upper facies is siliceous Upper facies is siliceous

(diatomaceous) sediments(diatomaceous) sediments

Neogene Basins

DepositionDeposition

• Range: Range: lower middle bathyal (1500-2300m) to lower middle bathyal (1500-2300m) to

upper middle bathyal (500-1500m)upper middle bathyal (500-1500m)• Oxygen-deficient environmentOxygen-deficient environment• Basin plains, slopes, banktops, shelf edgesBasin plains, slopes, banktops, shelf edges• mid-water oxygen minimum zonemid-water oxygen minimum zone

Lithology & Lithology & CompositionComposition

• Calcareous facies:Calcareous facies: – 16-15MYA ; lower/basal layer16-15MYA ; lower/basal layer– Carbonate: coccoliths & foraminifersCarbonate: coccoliths & foraminifers

• Phosphatic facies:Phosphatic facies: – 15-14MYA ; middle/transitional layer15-14MYA ; middle/transitional layer– phosphatephosphate, shale, & mudstones, shale, & mudstones

• Siliceous facies:Siliceous facies:– 14-6MYA; upper member/layer14-6MYA; upper member/layer– diatoms & radiolariansdiatoms & radiolarians

Geographic ExtentGeographic Extent

GLOBAL:GLOBAL:• Discontinuous belt throughout Discontinuous belt throughout

North Pacific Rim (and South)North Pacific Rim (and South)• Onshore and offshore Onshore and offshore

equivalents (ODP and DSDP equivalents (ODP and DSDP sites)sites)

Lithology & Lithology & CompositionComposition

• Diatomaceous Diatomaceous Units Units

Lithology & Lithology & CompositionComposition

• High diatomaceous and organic rich High diatomaceous and organic rich depositsdeposits

plankton productivity = plankton productivity = upwelling; upwelling;

terrigenous input = terrigenous input = sediment sediment starvation; starvation;

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

Lithology & Lithology & CompositionComposition

Lithology & Lithology & CompositionComposition

SilicaDiagenesis

Diagenesis: SilicaDiagenesis: Silica

• 2-Step Alteration: 2-Step Alteration: Opal-A Opal-A Opal-CT Opal-CT

Opal CT Opal CT Diagenetic Quartz Diagenetic Quartz

• Process of Alteration:Process of Alteration:– Complete dissolution Complete dissolution

– Re-precipitationRe-precipitation

Diagenesis: SilicaDiagenesis: Silica

• Transformation controlled by temp. & Transformation controlled by temp. & burial depth, bulk composition & rock burial depth, bulk composition & rock properties (porosity & permeability)properties (porosity & permeability)

• 2 narrow temp. ranges & burial depth:2 narrow temp. ranges & burial depth:40-50ºC & 0.5-2km (Opal-A 40-50ºC & 0.5-2km (Opal-A Opal-CT) Opal-CT)

65-80ºC & 1.5-3km (Opal CT 65-80ºC & 1.5-3km (Opal CT Quartz) Quartz)

• Purest sediments alter early:Purest sediments alter early: hard, brittle hard, brittle Opal-CT (2-33ºC) & quartz cherts (36-76ºC) Opal-CT (2-33ºC) & quartz cherts (36-76ºC)

Silica Diagenesis

PaleoceanographicSignificance

Paleo- SignificancePaleo- Significance

• Deposited within important transition in:Deposited within important transition in: Cenozoic Cenozoic coolingcooling associated with associated with

Antartic Ice Sheet expansionAntartic Ice Sheet expansion Increased Increased upwellingupwelling associated with associated with

thermohaline circulation thermohaline circulation reorganizationreorganization

Accelerated Accelerated COCO22 drawdown associated drawdown associated with Himalayan upliftwith Himalayan uplift

Paleo- SignificancePaleo- Significance

• Major changes: ocean circulation, global Major changes: ocean circulation, global climate, tectonic transitionclimate, tectonic transition

Upwelling &Upwelling &NutrientsNutrients

(Diatom Blooms)(Diatom Blooms)CoolingCooling

(Antarctic Ice Sheet)(Antarctic Ice Sheet)

Burial &Burial &PreservationPreservation

(Organic Matter)(Organic Matter)

COCO22 Drawdown Drawdown

(Weathering)(Weathering)

Miocene Monterey FormationMiocene Monterey Formation16-616-6MYAMYA

Lithology &Lithology &CompositionComposition

PetroleumPetroleumDiagenesisDiagenesis

BackgroundBackground

Paleo-Paleo-EnvironmentEnvironment

Geol Setting &Geol Setting &Geog ExtentGeog Extent

Petroleum Resources Petroleum Resources SourceSource

• Significance: both oil source & reservoirSignificance: both oil source & reservoir• 1º source rock of hydrocarbons in Cal 1º source rock of hydrocarbons in Cal • Oil source generated in immature or Oil source generated in immature or

marginally mature rocksmarginally mature rocks• May largely come from organic-rich May largely come from organic-rich

carbonates and phosphatescarbonates and phosphates• TOC: can be as much as 23%, but TOC: can be as much as 23%, but

averages at 2% - 5%averages at 2% - 5%

Petroleum ResourcePetroleum ResourceReservoirsReservoirs

• Non-commercial reservoirs - lack Non-commercial reservoirs - lack effective porosity (neffective porosity (nee) & permeability ) & permeability (k) in composition of fine-grained, (k) in composition of fine-grained, organic-rich rockorganic-rich rock

• Reservoirs generally consist of:Reservoirs generally consist of:1.1. Adjacent or interfringed sandstone beds, Adjacent or interfringed sandstone beds,

members or formationsmembers or formations2.2. Naturally fractured, brittle diagenetic Naturally fractured, brittle diagenetic

siliceous & dolomitic rockssiliceous & dolomitic rocks

SummarySummary

• Vast extent, deposited at different times Vast extent, deposited at different times and stages.and stages.

• Diagenesis stages relate to original rock Diagenesis stages relate to original rock composition and depth of burial.composition and depth of burial.

• Petroleum source and reservoir.Petroleum source and reservoir.• Formation of carbonate, phosphate, and Formation of carbonate, phosphate, and

silica facies reflect global oceanic silica facies reflect global oceanic conditions.conditions.

Internet ReferencesInternet 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/http://www.seis.natsci.csulb.edu/rbehl/Mont.htmMont.htm