Coexistence of siliceous basin and shallow-water carbonate sedimentation in the Oxfordian of the central Northern Calcareous Alps, Austria - a major step for the understanding of the early history of the Plassen Carbonate Platform
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Sedimentation
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Paleogene
Carbonate platform
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Progradation
Aggradation
Carbonate platform
Sequence Stratigraphy
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Carbonate platform
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Section (typography)
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Paleogeographic analyses and plate reconstructions indicate that the Upper Jurassic series of the Carpathian foreland accumulated on the Eurasian shelf of the Tethys Ocean. In the Carpathian foreland of southern Poland, marine Upper Jurassic carbonate series, exceeding 1000 m in thickness, are covered by Tertiary Molasse series or by thrust units of the Outer Carpathians. From a lithostratigraphic point of view, six facies units can be recognized in these Oxfordian to Tithonian carbonates, namely calcareous plankton, calcareous sponge, algal-oolitic, calcareous-marly coquina, dolomitic-calcareous, and upper algal series. During the lower part of the Upper Jurassic, deeper neritic conditions prevailed (calcareous plankton series). These gave way to upward shoaling conditions (calcareous sponge series, deeper basin calcareous-marly series) and a final shallow water environment (algal-oolitic and younger series). Thickness changes of the calcareous-marly series and the diachronous character of the facies boundary between the Oxfordian and Kimmeridgian show that the basin deepened to the south. Barrier reefs and associated fore-reef and back-reef facies occur within the algal-oolitic series. These trend northwest-southeast and reach 30-50 m in thickness. The reefs were mainly built by algae. Algal reefs under the Molasse and Carpathian thrust sheets are potential hydrocarbon exploration targets. The paleogeographic position of themore » Jurassic of the Carpathian foreland lies within the Tethys realm, which contains a large part of the world's producible oil reserves; this lends encouragement to this play.« less
Molasse
Carbonate platform
Diachronous
Tethys Ocean
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Carbonate platform
Paleoecology
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Carbonate platform
Cenomanian
Aptian
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Abstract In the Transdanubian Range (Hungary), a wide spectrum of Triassic dolomites is known. Mechanism of dolomitization of the platform carbonate successions was subject of a number of studies but the study of dolomitization of basinal carbonates is very limited. Petrographical and isotope–geochemical characteristics of the Upper Triassic dolomitized carbonate deposits, formed in a fault-controlled intraplatform basin, and interpretation of the dolomite-forming processes are presented in the current paper. From the latest Carnian to Middle Norian under semi-arid climatic conditions density-driven flux of seawater derived mesohaline fluids was the dominant mechanism of the near-surface pervasive dolomitization of the thick platform carbonate succession. In the late Middle Norian incipient rifting of the Alpine Tethys led to establishment of an extensional structural regime and onset of the formation of the Kössen Basin. In the study area, above the dolomitized platform carbonate succession, platform-derived carbonate sediments were accumulated in a fault-bounded, semi-restricted sub-basin of the Kössen Basin, whereas talus breccias and debrites were deposited near a basin-bounding master fault. The basin deposits (lower and upper members of the Rezi Dolomite Formation) were subject of early diagenetic dolomitization in shallow burial setting. Enhanced salinity seawater was the dolomitizing fluid; the synsedimentary fracturing may have promoted the fluid flow and thereby the dolomitization. Thick-bedded carbonates (middle member of the Rezi Dolomite Formation) representing a progradational tongue of the ambient platform are intercalated between the basin deposits. The dolomitization of this unit can be explained by the reflux model.
Dolomitization
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Cenomanian
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