Abstract
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 of the geological record. Detailed stratigraphic investigation and mapping of the up to 90-m-thick Crato Formation at the eastern border of the Araripe Plateau allowed recognition of a regionally persistent fossil-bearing muddy interval, herein defined as the Caldas Bed. At its type locality, it is defined as an up to 2-m-thick coarsening-upward succession of grey/green mudstone and interbedded sandy siltstone and claystone. The 0.85- to 2-m-thick interval was recognized in several localities along the outcrop belt, and it is bounded by sharp, lower (Konservat-Lagerstätte limestone) and upper (sandstone and heterolithic facies) contacts. Despite previous literature data suggesting the presence of marine mollusks, the bed contains freshwater bivalves, small gastropods, spinicaudatans, plant remains, trace fossils, and rare ostracods. The Caldas Bed records benthic paleocommunities representing a short-term isochronous regional freshening event, marked by abrupt changes in sedimentation pattern, bathymetry, salinity, oxygenation and water chemistry.
Highlights
The Aptian Crato Formation of the Santana Group, Araripe Basin, northeastern Brazil, is worldwide renowned for its exceptionally well-preserved fossils, which are found in lacustrine laminated limestones (Heimhofer et al 2010, Varejão et al 2019a)
Spinicaudatan crustaceans, ostracods and other non-marine fossils in some particular strata (e.g., Coimbra et al 2002, Neumann et al 2003), the Crato Formation is interpreted as a mixed carbonate-siliciclastic succession exclusively deposited in a lacustrine system (Martill et al 2007a)
Martill and Wilby (1993), and Martill et al (2005, 2007a, 2007b) were the first authors to clearly state that the bivalves of the Crato Formation occur in mudstones stratigraphically above the top of the fossil-bearing laminated limestones from the base of the unit
Summary
The Aptian Crato Formation of the Santana Group (sense Assine et al 2014, Neumann and Assine 2015), Araripe Basin, northeastern Brazil, is worldwide renowned for its exceptionally well-preserved fossils, which are found in lacustrine laminated limestones (Heimhofer et al 2010, Varejão et al 2019a). The Crato Formation, an up to 90-m-thick succession of interbedded limestone, shale, mudstone and sandstone, is one of the most-studied Aptian units of the Araripe Basin due to its fossil content
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