Termination of carbonate slope progradation: An example from the Carnian of the Dolomites, Northern Italy

Lorenz Keim, Rainer Brandner, Leopold Krystyn, Wolfgang Mette

Veröffentlichungen: Beitrag in FachzeitschriftArtikelPeer Reviewed

Abstract

The demise of carbonate platforms during Carnian time is a widespread phenomenon of the Western Tethys, but the controlling factors are not well-understood. The Dolomites of the Southern Alps (Northern Italy) are well-known for their large-scale Ladinian and Carnian prograding carbonate platforms. Platform growth stopped during the Early Carnian and both platforms and basinal areas were subsequently covered by mixed carbonate-siliciclastic sediments (Raibl Group). We present a carbonate platform, whose slope progradation came to a halt prior to draping by the siliciclastic sediments. Judging from the height of the clinoforms a platform-to-basin relief of at least 100 m existed during the final stage of progradation. This paleoslope was colonized by coral patches draped by skeletal packstones to microbial bindstones, forming typically lens-shaped mounds on the steep slope. The formation of mounds on the platform flank was only possible, because the downslope transport of detritus from the platform and/or upper slope was stopped. The sedimentary evolution in the adjacent basin indicates a poorly oxygenated environment with abundant brackish water ostracods of low diversity. Based on the inherited platform-to-basin relief and the lithofacies of the basin fill a local sea-level drop in the order of 60-80 m is postulated. With rising sea level the accommodation space between former basin and platform became filled by shallow-marine, mixed carbonate-siliciclastic sediments. The abundance of epibenthic suspension feeders of the basin fill such as megalodonts suggests increased nutrient supply. The termination of slope progradation was a multiphased process triggered by a stagnation of the regional subsidence, a reduction of water circulation, followed by a sea level-drop, the influx of freshwater and the input of siliciclastics. Fluctuating salinity caused intermittently a biotically stressed environment. Π2001 Elsevier Science B.V. All rights reserved.
OriginalspracheEnglisch
Seiten (von - bis)303-323
Seitenumfang21
FachzeitschriftSedimentary Geology
Jahrgang143
Ausgabenummer3-4
PublikationsstatusVeröffentlicht - 2001

ÖFOS 2012

  • 105118 Paläontologie

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