Facies patterns of a tectonically-controlled Upper Triassic platform-slope carbonate depositional system (Carnian Prealps, Northeastern Italy) |
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Authors: | Andrea Cozzi |
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Institution: | (1) Institut für Geologie, ETH Zentrum, Sonneggstrasse 5, CH-8092 Zürich |
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Abstract: | Summary Upper Triassic (Middle-Upper Norian) shallow-water carbonates of the Dolomia Principale and its deep-water counterparts (Forni
Dolomite) have been studied in the Carnian Prealps (northeastern Italy). The Dolomia Principale was a storm-dominated carbonate
platform; in the Mt. Pramaggiore area, along a well-preserved 3.5 km-long platform-to-basin transition, the inner platform
facies of the Dolomia Principale, characterized by m-scale shallowing upward cycles, give way seaward to open marine storm-dominated
shallow subtidal lagoon deposits with frequent hardgrounds and evidence of microbial stabilization of the bottom sediment.
The margin of the Dolomia Principale platform was colonized by meter-scale stromatolites and serpulid-microbial mounds that
thrived due to the local highly stressed environment, characterized by drastic salinity fluctuations and turbid waters, that
excluded the Upper Triassic coral-sponge communities. The Forni Dolomite slope-basin complex was characterized by an upper
slope facies with debris flows, megabreccias, turbidites and serpulid-microbial mounds. The lower slope and basinal facies
show thinning and fining trends. After restoring the original geometry of the slope, the depositional angles of the clinoforms
range between 11 and 36 degrees, reflecting closely the coarse-grained character of the Forni Dolomite slope complex, which
can be interpreted as a slope apron that, as a model, can be extended to steeply inclined carbonate slopes. The onset of synsedimentary
extensional tectonics at the Middle-Late Norian boundary affected the platform-slope depositional system via: 1) localized
inner platform collapses and the formation of an intraplatform anoxic depression at Mt. Valmenone, 2) a switch from platform
lateral progradation during the Middle Norian to vertical aggradation in the Late Norian, reflected in an increase in platform
relief, steeper foreslope angles and coarser-grained slope facies, and 3) controlling the spatial orientation of the margin
of the Dolomia Principale. |
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Keywords: | Platform-to-basin transition Synsedimentary extensional tectonics Carnian Prealps (North-Eastern Italy) Dolomia principale Forni dolomite Upper triassic |
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