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Three-dimensional stratal development of a carbonate-siliciclastic sedimentary regime, Northern Carnarvon Basin, Northwest Australia [electronic resource] /

by Cathro, Donna Louise

Abstract (Summary)
Verification of a global sea level curve for the Cenozoic based upon seismic stratigraphic analysis demands in-situ geological evidence of synchronous global sea level change. We tie sequence biostratigraphic analyses from industry wells in the Northern Carnarvon Basin (NCB) to seismic stratigraphic interpretations from an exceptional set of 3D and 2D seismic data. The biostratigraphic database is constructed from ~250 analyses of sidewall cores and ditch cuttings from Eocene to Pliocene intervals. A synthesis of some 286 benthic and 73 planktic taxa of foraminifera is supplemented with quantitative stratigraphic observations of other fossil groups, e.g., ostracods and fragments of bryozoans, corals and mollusks, and lithological components, such as, authigenic calcite, opaque minerals and quartz sands of variable maturity. Preservation of foraminiferal assemblages is extremely variable in Oligocene to latest Miocene stratigraphy, depending upon location of wells and interval investigated. Problems associated with sampling bias from facies control and poor preservation, inherent in studies of foraminiferal distribution in shallowmarine settings, are taken into account. Nonetheless, consistent, detectable faunal signals correlate between wells; some also correlate with prominent seismic horizons. A cluster of planktonic events above seismic horizon DLS4 in the middle Miocene, coincident with turnover in benthic foraminifera, is interpreted to record a regional flooding event and regression. We also suggest that observed diagenesis, particularly evident in Goodwyn 6, is a primary indicator of subsurface water mixing zones and possible emergence, associated shallowing 263 upward trend that dominated the NCB from the middle Miocene to the Pliocene. These detailed analyses of episodic diagenesis and faunal patterns provide evidence of higher-frequency sea level fluctuations (0.5-3Ma) within a secondorder (3-10Ma) major transgressive-regressive cycle. In summary, they suggest that the identified horizons are sequence stratigraphically significant. We compare these results to other, similar records on the southern Australian margin, the New Jersey Shelf and the Great Bahama Bank. Such comparisons are an essential step to understanding perturbations in global climate, including the likely eustatic response to an enhanced greenhouse effect. 264
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School:The University of Texas at Austin

School Location:USA - Texas

Source Type:Master's Thesis

Keywords:geology stratigraphic

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