A carbonate palustrine system with marshes and shallow ephemeral lakes (Campanian, northeastern Iberian Basin)

Abstract

The sedimentary and stratigraphic features of the low-gradient slope carbonate palustrine system of the Fortanete Formation (northeast Spain) during the early Campanian have been studied. The succession of the Fortanete Fm provides depositional record of a progressive transition to continental settings in an area that was predominantly marine for most of the Late Cretaceous. Palustrine systems can be developed in a wide variety of environments, however, modern analogues are scarce. The Fortanete Fm thus presents a great opportunity to study the stratigraphy, the sedimentary features and isotopic composition of a palustrine–marine influenced system. A total of 10 stratigraphic sections distributed along a 40 km wide and 80 km long area have been carried out in order to decipher the facies distribution in the system. This study led to the differentiation of three palaeoenvironments based on predominant lithofacies and sedimentary structures: (1) marshes and shallow low-gradient slope lakes; (2) ephemeral lakes, lake margins and prairies with variable water level and marine influence; and (3) mudflats with evaporites and fine siliciclastic input. The Fortanete Fm serves as an excellent case study for palustrine environments with the presence of typical palustrine features such as pseudomicrokarst, brecciation, black pebbles, desiccation cracks, nodules, Microcodium, and fenestral fabric. Most palustrine systems are associated with continental freshwater settings, whereas the Fortanete Fm displays evidence of intermittent marine influence in the distal studied sections. Carbon and oxygen isotope composition is within the range of typical freshwater lake carbonates and also corresponds to isotope composition of palustrine carbonates with marine influence. The Fortanete Fm shares a number of characteristics with freshwater continental and freshwater modern analogues. Comparison with these systems provides new insights on how modern analogues can be used to decipher the complexity of the processes developing these systems in the past.