Precipitation of dolomite from seawater on a Carnian coastal plain (Dolomites, northern Italy)

Autor(en)
Maximilian Rieder, Wencke Wegner, Monika Horschinegg, Stefanie Klackl, Nereo Preto, Anna Breda, Susanne Gier, Urs Kloetzli, Stefano M. Bernasconi, Gernot Arp, Patrick Meister
Abstrakt

The geochemical conditions conducive to dolomite formation in shallow evaporitic environments along the Triassic Tethyan margin are still poorly understood. Large parts of the Triassic dolomites in the Austroalpine and the southern Alpine realm are affected by late diagenetic or hydrothermal overprinting, but recent studies from the Carnian Travenanzes Formation (southern Alps) provide evidence of primary dolomite. Here a petrographic and geochemical study of dolomites intercalated in a 100 m thick Carnian sequence of distal alluvial plain deposits is presented to gain better insight into the conditions and processes of dolomite formation. The dolomites occur as 10 to 50 cm thick homogeneous beds, millimetre-scale laminated beds, and nodules associated with palaeosols. The dolomite is nearly stoichiometric with slightly attenuated ordering reflections. Sedimentary structures indicate that the initial primary dolomite or precursor phase consisted largely of unlithified mud. Strontium isotope ratios (

87Sr/

86Sr) of homogeneous and laminated dolomites reflect Triassic seawater composition, suggesting precipitation in evaporating seawater in a coastal ephemeral lake or sabkha system. However, the setting differed from modern sabkha or coastal ephemeral lake systems by being exposed to seasonally wet conditions with significant siliciclastic input and the inhibition of significant lateral groundwater flow by impermeable clay deposits. Thus, the ancient Tethyan margin was different from modern analogues of primary dolomite formation.

Organisation(en)
Department für Lithosphärenforschung, Institut für Geologie
Externe Organisation(en)
Università degli Studi di Padova, Eidgenössische Technische Hochschule Zürich, Universität Wien, Georg-August-Universität Göttingen
Journal
Solid earth
Band
10
Seiten
1243-1267
Anzahl der Seiten
25
ISSN
1869-9510
DOI
https://doi.org/10.5194/se-10-1243-2019
Publikationsdatum
07-2019
Peer-reviewed
Ja
ÖFOS 2012
105105 Geochemie
Schlagwörter
ASJC Scopus Sachgebiete
Earth-Surface Processes, Geochemistry and Petrology, Geology, Geophysics, Soil Science, Palaeontology, Stratigraphy
Link zum Portal
https://ucris.univie.ac.at/portal/de/publications/precipitation-of-dolomite-from-seawater-on-a-carnian-coastal-plain-dolomites-northern-italy(9aeed35c-e3fc-4d12-9106-3339b896fd5c).html