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