Climate in Earth History Studies in Geophysics (1982) / Chapter Skim
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15 Interpreting Paleoenvironments, Subsidence History, and Sea-Level Changes of Passive Margins from Seismic and Biostratigraphy
15 Interpreting Paleoenvironments, Subsidence History, and Sea-Level Changes of Passive Margins from Seismic and Biostratigraphy
Pages 139-153
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From page 139... ...
Retracing the interaction of ecstatic changes and basement subsidence from the sedimentary record is efficiently handled by the geohistory analysis techmque. This technique integrates the stratigraphic and paleubathymetric data in a time-depth framework and reproduces the subsidence of basement as a rests t of basement faulting, crustal and mantle cooling, and sediment loading.
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From page 140... ...
rid rs E , 0 E— _ _ JON HARDENBOL,PETERR.VAIL, and 1 FERRER This total subsidence also includes the apparent vertical movement effects of sediment compaction and eustatic sealevel changes. By quantification of he effects of sediment compaction, sediment loading, and thermal subsidence, the eustatic changes can be determined.
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From page 141... ...
''~~ —f _ K ,2 :: :. ~ | 133 O S KM 1 1 l O SMILES WB = WATER BOTTOM MULTIPLE 141 E 0 _ 1 jest 3 o r - 54 A - i EIGUF~E 15.3 Seismic section from offshore northwest Africa showing interpreted seismic stratigraphic sequences The sequence boundaries are determined by cycle terminations indicated by arrows.
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From page 142... ...
Gechistory diagrams show effectively the interaction between sedbnent supply, eustatic sea-level changes, and basement subsidence through time, Correchons for sediment compaction (Horowitz, 1976) are necessary to obtain a correct total subsidence history.
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From page 143... ...
' i.'~, —S/S- — SHELF/SLOPE BREAK HSH — BASINAL MARINE SHALE BLS — BASINAL LIMESTONE AND SHALE SSD — SHELF SANDSTONE AND SHALE RB7143 O 7 5 7 6 . p SKM O SMILES SCA — SHELF CARBONATES SSH — SHELF MARINE SHALE RF — REEF RB — CONTINENTAL RED BEDS FIGURE IS.S Seismic r ction from offshore northwest Africa showing interpret d seismic stratigraphic sequences with reirmic facies interpreted from the nature of the wquenoe boundaries and the internal reflection characteristics within the sequence For sequence designations, r e Figure IS.
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From page 144... ...
~ . ~ t~ E esenl Sea Level F7CURE 15.7 GeDhistory analysis diagram with stratigraphic and pale bathymetric histories for a oombined weU and seism subsidence Curve depiots tbe subsidence of the Early 3urassic base through time.
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From page 145... ...
, even though the positions of the data points in the example are affected by eustatic changes of sea level. The initial rifting phase along the northwest African mar gin probably started in the Triassic, whereas the age of the earliest oceanic crust is generally quoted as 180 Ma (Pitman and TaLvani, 1972, Hayes and Rabinowitz, 1975)
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From page 146... ...
This assumes that the observed thermotectonic subsidence curve represents on y thermal subsidence with long-term eustatic departures that started immediately after the formation of the first oceanic crust. The geohistory diagram (Figure 15.10)
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From page 147... ...
The distance between the thermotectonic subsidence curve and the 60 percent model subsidence curve in Figure l S.10 is a measure of the long-term eustatic sea-level change in the Jurassic and Early Cretaceoms. Sea level is rising in the late Middle Jurassic and begins falling in the latest Jurassic and Berriasian.
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From page 148... ...
Thermotectonic subsidence histories for Georges Bank and Baltimore Canyon COST wells suggest considerable tectonic activity in the Early Cretaceous and Middle Terhary. IDENTIFICATION OF SHORT-TERM EUSTATIC CHANGES Previous sections of this paper discussed the palenenvironments, subsidence history, and long-term sea-level changes determined from a well located on seismic line C, offshore northwestern Africa.
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From page 149... ...
· MA TO D IBIS GAPER CAICUUYO tGI.I S G IGtNr U SWGt CAICUIAIEO tUSIAIIC slAle.Tl GuANGtS FICURE IS. 12 Comparison of eustatic so ia-level changes dctermiued from the subsidence history of the northwest African margin with previously published estimates for global changes of sea level.
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From page 150... ...
1.) Seismic line perpendicular to the shelf edge, offshore northwest Africa, showing major erosional paHerns in the Tertiary.
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From page 151... ...
The rapid change from shallow shelf to upper bathyal water depths ( ~ 50 to 300 m) from the Bathonian to the Callovian must have taken place 151 FIGURE 15.15 Offshore northwest Africa seismic line showing prograding Callovian she f margin.
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From page 152... ...
DISCUSSION The magnitude of long-term, sea-level changes between the Early Cretaceous and the present, as determined from the subsidence history of a basin offshore northwest Africa, is in line with previously published estimates. Values obtained by Hays and Pitman (1973)
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From page 153... ...
. Seismic stratigraphy and global changes of sea level, Part 8: Identification of Upper Triassic, Jurassic and Lower Cretaceous seismic sequences in Gulf of Mexico and offshore west Africa, in Seismic Stratigraphy—Application to Hydrocarbon E ploration C
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