Marine or freshwater? Accessing the paleoenvironmental parameters of the Caldas Bed, a key marker bed in the Crato Formation (Araripe Basin, NE Brazil)

The Aptian Crato Formation is world renowned for its well-preserved fossils in microbially-induced laminated limestones, which are regarded as one of the main Cretaceous Konservat-Lagerstätte geological record. Detailed stratigraphic investigation and mapping up to 90-m-thick at eastern border Araripe Plateau allowed recognition a regionally persistent fossil-bearing muddy interval, herein defined Caldas Bed. At type locality, it an 2-m-thick coarsening-upward succession grey/green mudstone interbedded sandy siltstone claystone. 0.85- interval was recognized several localities along outcrop belt, bounded by sharp, lower (Konservat-Lagerstätte limestone) upper (sandstone heterolithic facies) contacts. Despite previous literature data suggesting presence marine mollusks, bed contains freshwater bivalves, small gastropods, spinicaudatans, plant remains, trace fossils, rare ostracods. Bed records benthic paleocommunities representing short-term isochronous regional freshening event, marked abrupt changes sedimentation pattern, bathymetry, salinity, oxygenation water chemistry.