Introduction

The Crato Formation comprises a series of laminated limestones inter-bedded with sandstones, marls and clays, sandwiched between a highly variable sequence of strata in the mainly Mesozoic Araripe Basin. Its distribution has not been completely mapped as an integral stratigraphic unit, although some beds of limestone were mapped by the Projeto Santana team in the 1970s (Moraes et al., 1976). The formation has never been formally defined, although Martill and Wilby (1993) proposed a type section in the river at Cascata near Crato, but exposures of the upper part of the Crato Formation sequence are only poorly exposed here compared with elsewhere. There have been a few attempts to define the unit (e.g. Martill and Wilby, 1993; Berthou et al., 1994), but it is not always clear what authors are referring to when discussing the Crato sedimentary unit, partly due to terminology and partly due to concept. Here we consider the Crato Formation to comprise a heterolithic suite of strata lying above the Rio da Batateiras Formation of Ponte and Appi (1990) and beneath a unit of evaporites termed the Ipubi Formation by Martill and Wilby (1993) (Figure 3.1). Its base is defined as the first appearance of laminated limestones and its top by the first appearance of the evaporites of the overlying Ipubi Formation (see Figures 3.4 and 3.8, respectively, below).