GEOL 4010 QUATERNARY GEOLOGY Instructor: Dr' Hester Jiskoot

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GEOL 4010QUATERNARY GEOLOGYInstructor Dr.
Hester Jiskoot
LECTURE 10
Glacio- isostacy eustacy
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SEA LEVELS SINCE LAST INTERGLACIAL
World-wide LGM sealevel 100-135 m. below present
http//www.homepage.montana.edu/geol445/hyperglac
/eustasy1/index.htm
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EUSTATIC SEA LEVEL Redistribution water
storage Ice ? Oceans
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SISScandinavian ice sheet LISLaurentide ice
sheet

• LIS melted by 5000 y BP
• last 10 m of sea level rise not explained by ice
  sheet decay.
• Thermal expansion of ocean waters isostatic
  uplift of the shallow North Sea and Hudson Bay
  (spilling into the larger oceans), are the most
  likely explanations

Decay LIS
Younger Dryas
Decay SIS
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RECORD OF SEA LEVEL
Datable marine terraces (raised beaches) in
regions of tectonic uplift Datable coral reefs in
regions of emergence or submergence
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RAISED SEA LEVELS, SKORBEEVKA, RUSSIA
(Moermansk Bay)
Last 7000 yrs
92 m aslmarine limit
55 m asl
22 m aslHolocene transgression max.
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GLOBAL CURVE OF EUSTATIC SEALEVEL
Terraces on rapidly uplifting New Guinea, dated
by Uranium-series on coral. High stands are
well-dated - falls are estimated.
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PRE-QUATERNARY EUSTATIC SEALEVEL
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ANOMALIES IN SEA LEVEL CURVES
SOUTHERN HEMISPHERE Numerous episodes of very
rapid sea level rise. Indication of complete or
partial ice sheet collapses. Complete collapse
WAIS would raise global sea level an additional
6m -has happened at least once since the ice
sheet formed.
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LAND VS. MARINE BASED ICE SHEET
WAIS concern
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MODELLED COLLAPSE OF WAIS
Simulated history of West Antarctic ice-sheet
volume calculated by a coupled basal-till/ice-flow
model (MacAyeal, D., Nature, 359, 29-32 1992).
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ISOSTATIC SEA LEVEL Crustal movement
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GLACIO-ISOSTACY
Lithosphere depresses under weight (
visco-elastic) ? Delayed response to loading
Depression Hice(?ice/?mantle)
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ISOSTATIC REBOUND
Exponentially declining rate with half-recovery
time of thousands of years

• Uplift former ice centres (Hudson Bay/Baltic
  Sea) still ongoing
• Negative gravity anomalies

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Isobase maps of uplift to present Canada,
Scandinavia, Scotland Note the 3 dome
structure of the LIS
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Isobases Hudson Bay
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Residual isostatic uplift Fenno-Scandinavia
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GRAVITY ANOMALIES DUE TO ISOSTACY
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Spatial variation in the Earths gravity field
Blue Lower than average Red Higher than
Average
From Simmons and Hager, 1997 Nature
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SEA-LEVEL CURVES and REBOUND
Total recovery
Rebound-residual
CRUST glacioisostacy hydroisostacy Depression
Hice(?ice/?mantle)
Rebound-postglacial
Amount of crustal rebound
Rebound-restrained
?Time since deglaciation
WATER glacio eustacy geoidal eustacy steric
(ocean warming)
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NOW COMBINED eustatic isostatic sea level
curves
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Reading for Friday pages 94-104