Palaeoenvironmental reconstruction of a middle Miocene alluvial fan to cyclic shallow lacustrine depositional system in the Calatayud Basin (NE Spain)

摘要: The middle Miocene sedimentary fill of the Calatayud Basin in north-eastern Spain consists proximal to distal alluvial fan-floodplain and shallow lacustrine deposits. Four main facies groups characteristic different environments are recognized: (1) medial fan that comprise clast-supported gravel subordinate sandstone mudstone, latter exhibiting incipient pedogenic features; (2) facies, formed mainly massive carbonate-rich palaeosols local carbonate pond deposits; (3) lake margin which show two distinct lithofacies associations depending on their distribution relative system, i.e. front (lithofacies A), comprising siliciclastic mudstone tabular carbonates, or lateral B) showing laminated and/or alternating with beds; (4) mudflat–shallow a remarkable cyclical alternation green-grey red units white dolomitic beds. cyclic succession, as exposed Orera composite section (OCS), is dominantly composed small-scale mudstone–carbonate/dolomite cycles. intervals cycles interpreted result sedimentation from suspension by sheet floods, deposits evolving either under subaerial exposure water-saturated conditions, location mudflat climate. dolomite accumulated during lake-level highstands Mg-rich waters becoming increasingly concentrated. Lowstand highstand changes indicated mudstone/dolomite reflect climate control (from dry wet conditions) area. spatial implies deposition smallscale took place low-gradient, basin located an interfan zone. development was constrained gradual aggradation. Additional support for palaeoenvironmental interpretation derived isotopic compositions carbonates various wide range δ18O δ13C values varying )-7.9 3.0‰ PDB -9.2 -1.7‰ respectively. More negative lakemargin extended systems, whereas more positive correspond beds deposited environment. results clear trend enrichment centre basin, thereby also demonstrating evolved hydrologically closed conditions.