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The Record of Pliocene SeaThe Record of Pliocene Sea--Level Change At Level Change At EnewetakEnewetak AtollAtoll

Bruce W. Bruce W. WardlawWardlaw and Terrence M. Quinnand Terrence M. QuinnQuarternaryQuarternary Science ReviewsScience Reviews, Vol. 10, pp. 247, Vol. 10, pp. 247--258, 1991.258, 1991.

Steven Steven ScyphersScyphersGeological OceanographyGeological Oceanography

3/20/20083/20/2008

When?When?

Pleistocene: 1.8 Ma to 11.5 KaPleistocene: 1.8 Ma to 11.5 Ka

Pliocene: 5.3 Ma to 1.8 MaPliocene: 5.3 Ma to 1.8 Ma

Where is PEACE?Where is PEACE?PurposePurpose

Reconstruct sea level based upon Reconstruct sea level based upon stratigraphicstratigraphicdistribution of major distribution of major disconformitiesdisconformities that that coincide with resolvable age differences in the coincide with resolvable age differences in the biochronologybiochronology

StratigraphyStratigraphy= study of distributions, = study of distributions, deposition, and age of sedimentary deposition, and age of sedimentary rocksrocks

Litho= physical and Litho= physical and petrographicpetrographic propertiesproperties

Chemo= dating marine sediments/rocks using trace Chemo= dating marine sediments/rocks using trace elements, molecular fossils, isotopic ratioselements, molecular fossils, isotopic ratios

Seismic= Reflection character analysisSeismic= Reflection character analysis

Bio= based upon fossil content Bio= based upon fossil content

Disconformities= surface between successive Disconformities= surface between successive strata, representing a missing interval in strata, representing a missing interval in geologic timegeologic time

OverviewOverview

Previous studies: Previous studies: Single Bore HoleSingle Bore HoleSingle Isotope (Single Isotope (SrSr))

Discrepancies due with intraDiscrepancies due with intra--lagoon variability when lagoon variability when compared with compared with biochronologybiochronology

This study: Six Bore HolesThis study: Six Bore HolesMultiple ApproachesMultiple Approaches

-- Sequence Sequence StratigraphyStratigraphy ModelModel-- Isotope ModelIsotope Model

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Seismic Seismic StratigraphyStratigraphy

-utilizes equipment that produces vibrations and allows their behavior in the substrate to be recorded

Seismic Seismic StratigraphyStratigraphy

Results:Results: 9 Major Disconformities in 9 Major Disconformities in PEACE BoreholesPEACE Boreholes

6 within the 6 within the PlioPlio--Pleistocene Pleistocene

2 Shallow Reflections correlate exactly with 2 Shallow Reflections correlate exactly with disconformitiesdisconformities

ChemostratigraphyChemostratigraphy

Literature on sediments states:Literature on sediments states:Holocene = unaltered aragonite Holocene = unaltered aragonite PlioPlio--Pleistocene= mixed mineralogy of Pleistocene= mixed mineralogy of aragonite/calcitearagonite/calcitePliocene= altered calcite Pliocene= altered calcite

Low Low δδ1313 C and C and δδ1818 O relate to meteoric O relate to meteoric calcitizationcalcitization

ChemostratigraphyChemostratigraphy

BiostratigraphyBiostratigraphy

------------ Upper and Lower Upper and Lower PaleoPaleo Lines of Lines of CorrelationCorrelation

_____ Line of Correlation_____ Line of Correlation

Windows of Correlation Windows of Correlation define distance between define distance between disconformitiesdisconformities

Sea Level Sea Level HighStandHighStand ModelsModels

25 and 40 m/Ma Subsidence Rates for Isotope Proxy Model and Sequence Stratigraphy Model

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Sea Level EstimatesSea Level Estimates

Considering minor disconformities, Sea Level Falls were probably less than the depth of the Lagoon.

PlioPlio--Pleistocene Ice Volume, Antarctic Pleistocene Ice Volume, Antarctic Climate, and the Global Climate, and the Global δδ1818 O RecordO Record

M.E. M.E. RaymoRaymo, L.E. , L.E. LisieckiLisiecki, K.H. , K.H. NisanciogluNisanciogluScience. Science. Vol. 313. 28 July 2006Vol. 313. 28 July 2006

Steven Steven ScyphersScyphersGeological OceanographyGeological Oceanography

3/20/20083/20/2008

ObjectivesObjectives

Present a simple model of ice volume Present a simple model of ice volume change that predicts sea level change and change that predicts sea level change and δδ1818 OO that matches geological record.that matches geological record.

Evaluate the relative Evaluate the relative importancesimportances of of obliquity and precession to obliquity and precession to cyclicitycyclicity..

AssertionsAssertions

23k year orbital precession cancels out 23k year orbital precession cancels out globally.globally.

41k year in41k year in--phase phase obiquityobiquity is the is the component of component of insolationinsolation that dominates that dominates the records.the records.

ObliquityObliquity

The angle of axial tiltThe angle of axial tilt

Lower Obliquity Lower Obliquity

Lower Solar Lower Solar RadationRadationat Polesat Poles

Increased Increased GlaciationGlaciation

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PrecessionPrecession--dV/dtdV/dt = (i + V)/ = (i + V)/ t

Relationship of Relationship of accumulation and accumulation and abrasionabrasion

Milankovitch Model Output

ConclusionsConclusions

Obliquity and Precession are both factorsObliquity and Precession are both factorsObliquity in phase between polesObliquity in phase between polesPrecession out of phase between polesPrecession out of phase between poles

LongLong--term cooling could transition term cooling could transition primarily land based to marine based East primarily land based to marine based East AnarcticaAnarctica Ice SheetIce Sheet

ConclusionConclusion

Small Changes in Small Changes in AnarcticAnarctic Ice Mass could Ice Mass could cancel out much larger changes in N.H.cancel out much larger changes in N.H.

The TerrestrialThe Terrestrial--Marine Shift could result in Marine Shift could result in strengthening of the 23k cycle in the strengthening of the 23k cycle in the marine marine δδ1818 O O