Tafonomy of macroinvertebrates and Albian marine ingression as recorded by the Romualdo Formation (Cretaceous, Araripe Basin, Brazil)

Ludmila Alves Cadeira Do Prado,Gelson Luís Fambrini,Alcina Magnólia Franca Barreto

doi:10.1590/2317-4889201820180048

Ludmila Alves Cadeira Do Prado, Gelson Luís Fambrini + Show 1 more

Open Access

https://doi.org/10.1590/2317-4889201820180048

Copy DOI

Abstract

The Romualdo Formation, Araripe Basin, crops out in the municipality of Exu, Pernambuco State, exposing coquinas. Fauna survey, taphonomic analysis of the macrobenthos, and identification of sedimentary facies of the outcrop were carried out to contribute to paleoenvironmental understanding of the Romualdo Formation. The association of molluscs (Cerithium sp., Tylostoma ranchariensis, Aguileria dissita, Brachidontes araripensis and unidentified cassiopids) and echinoids of the species Bothryopneustes araripensis suggests sedimentation in the marine environment. The taphonomic similarities made possible the grouping of coquinas into two types. Coquinas type 1 exhibit characteristics of transport and reworking of bioclast generated by storms in proximal setting. Coquinas type 2 demonstrates echinoids in situ and articulated with spines connected to shells, suggesting a fast sedimentation by distal tempestite. Regarding sedimentary facies, the concentrations of invertebrates would have been formed in the transitional offshore zone of siliclastic platform. The results presented here evidence a broader distribution of echinoids and expand the geographic limits of the shallow marine environment in the Romualdo Formation.

Highlights

Taphonomic analysis based on concentrations formed by molluscs and echinoids has frequently been used to aid in the interpretation of paleoenvironment and fossilization processes (García and Aguirre 2004, Olóriz et al 2008)
Echinoid-bearing coquinas had only been found in the west border of the basin, Araripina county, Pernambuco State, Brazil (Beurlen 1966, Prado et al 2015, 2016) (Fig. 1)
At the Cedro site, the Romualdo Formation shows a succession of fossil-bearing shales interfingered by sandstone strata with planar and climbing ripple laminations, and thin layers of coquinas (Cq), labeled Layers of Cedro-LCE

Summary

Introduction

Taphonomic analysis based on concentrations formed by molluscs and echinoids has frequently been used to aid in the interpretation of paleoenvironment and fossilization processes (García and Aguirre 2004, Olóriz et al 2008). Toward the top of the Romualdo Formation, there are different limestone and calciferous sandstones strata, mostly forming coquinas, which occur widespread in the Araripe Basin and can reach one meter in thickness (Sales 2005, Assine et al, 2014). These shell-rich rocks are formed by marine molluscs and echinoderms, cleary suggesting a marine ingression in the basin (Beurlen 1966, 1971, Assine 1992, 2007, Sales 2005, Assine et al 2014). Sedimentological studies interpreted coquinas as residual lags originated above ravine surface and analyzed as a stratigraphic framework (Assine 2007)

Methods

Results

Discussion

Conclusion