Diagenesis of a mixed siliciclastic/evaporitic sequence of the Middle Muschelkalk (Middle Triassic), the Catalan Coastal Range, NE Spain |
| |
Authors: | S MORAD I S AL-AASM† F J LONGSTAFFE‡ R MARFIL§ L F DE ROS H JOHANSEN¶ M MARZO |
| |
Institution: | edimentary Geology Research Group, Institute of Earth Sciences, Uppsala University, S-752 36 Uppsala, Sweden;Department of Geology, University of Windsor, Windsor, Ontario N9B 3P4, Canada;Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada;Departamento de Petrología y Geoquímica, Universidad Complutense, 28040 Madrid, Spain;Institutt for Energiteknikk, Instituttveien 18, N-2007 Kejeller, Norway;Universitat de Barcelona, Departament de Geologia Dinàmica, Geofísica i Paleontologia, Facultat de Geologia, Zona Universitària de Pedralbes, 08028 Barcelona, Spain |
| |
Abstract: | The Middle Muschelkalk (Middle Triassic) of the Catalan Coastal Range (north-east Spain) comprises sandstone, mudstone, anhydrite and minor carbonate layers. Interbedded sandstones and mudstones which are dominant in the north-eastern parts of the basin are terminal alluvial fan deposits. South-westward in the basin, the rocks become dominated by interbedded evaporites and mudstones deposited in sabkha/mudflat environments. The diagenetic and pore water evolution patterns of the Middle Muschelkalk suggest a strong facies control. During eodiagenesis, formation of microdolomite, anhydrite, baryte, magnesite, K-feldspar and mixed-layer chlorite/smectite was favoured within and adjacent to the sabkha/mudflat facies, whereas calcite, haematite, mixed-layer illite/smectite and quartz formed mainly in the alluvial facies. Low δ18OSMOW values for microdolomite (+23.7 to +28.4%) and K-feldspar overgrowths (+17.3 to +17.7%) suggest either low-temperature, isotopic disequilibrium or precipitation from low-18O porewaters. Low-18O waters might have developed, at least in part, during low-temperature alteration of volcanic rock fragments. During mesodiagenesis, precipitation of quartz overgrowths and coarse dolomite occurred in the alluvial sandstones, whereas recrystallization of microdolomite was dominant in the sabkha/mudflat facies. The isotopic compositions of these mesogenetic phases reflect increasing temperature during burial. Upon uplift and erosion, telogenetic calcite and trace haematite precipitated in fractures and replaced dolomite. The isotopic composition of the calcite (δ18OSMOW=+21.5 to +25.6%o; δ13C= 7.7 to - 5.6%o) and presence of haematite indicate infiltration of meteoric waters. |
| |
Keywords: | |
|
|