Deciphering pyritization-kerogenization gradient for fish soft-tissue preservation

Gabriel L Osés,Evandro P Da Silva,Gustavo M E M Prado,Isaac D Rudnitzki,Fabio Rodrigues,Elidiane C Rangel,Setembrino Petri,Cibele G Voltani,Marcia A Rizzutto,Paula A Sucerquia,M L A F Pacheco,Douglas Galante

doi:10.1038/s41598-017-01563-0

Abstract

Soft-tissue preservation provides palaeobiological information that is otherwise lost during fossilization. In Brazil, the Early Cretaceous Santana Formation contains fish with integument, muscles, connective tissues, and eyes that are still preserved. Our study revealed that soft-tissues were pyritized or kerogenized in different microfacies, which yielded distinct preservation fidelities. Indeed, new data provided the first record of pyritized vertebrate muscles and eyes. We propose that the different taphonomic pathways were controlled by distinct sedimentation rates in two different microfacies. Through this process, carcasses deposited in each of these microfacies underwent different residence times in sulphate-reduction and methanogenesis zones, thus yielding pyritized or kerogenized soft-tissues, and a similar process has previously been suggested in studies of a late Ediacaran lagerstätte.

Highlights

Preserved fossils have palaeobiological novelties that are not often encountered elsewhere in the geological record
BL microfacies most probably corresponds to laminated limestones (LL)[12]
GL are composed of 1–3-mm-thick layers[12] and have microfaults (Supplementary Figure 2)

Summary

Introduction

Preserved fossils have palaeobiological novelties that are not often encountered elsewhere in the geological record. Housed in deposits known as Konservat-Lagerstätten[1], investigation of fossil soft-tissues may provide unique insights into ancient biology and palaeoenvironmental conditions. Among these deposits, the Mesozoic rocks from the Santana Formation (Araripe Basin, northeast Brazil) stand out for their often exquisitely preserved and diverse fossil content, including plants, vertebrates (e.g., fishes, pterosaurs, dinosaurs, turtles and lizards), and invertebrates (e.g., insects, arachnids, and crustaceans)[2]. The results of our analyses confirmed that the fish were either pyritized or kerogenized in different sedimentary microfacies. We suggest that the Crato Member fish fossilization occurred through a process similar to the kerogenization-pyritization gradient model for Neoproterozoic-Palaeozoic metazoan preservation[7, 8]

Methods

Results

Conclusion