Download or read book Mechanisms for Exceptional Preservation in the Fezouata Lagerstätte (Early Ordovician, Morocco) written by Farid Saleh and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Fezouata Shale is the most diverse Lower Ordovician unit with exceptional fossil preservation. Fossils from this formation altered our understanding of early metazoan communities at the transition between the Cambrian Explosion and the Ordovician Radiation. The paleontology and the general sedimentological context of the Fezouata Shale are well established. However, little was done to understand the interaction between both, and studies regarding fossil preservation remain scarce. In this thesis, we investigate the general conditions and mechanisms responsible for soft-tissue preservation in the Fezouata Shale. Comparing brachiopod, bivalve, and trilobite size fluctuations between sites allowed us to constrain burial rates in this formation. This permitted the discovery of a relative post-mortem burial tardiness in sites where exceptional fossil preservation occurred. Moreover, mineralogical investigations showed a correlation between particular chlorite phases (i.e. chamosite/berthierine) and preserved soft parts. This mineralogy may have slowed down oxic decay and its deposition was most probably due to periods with high seasonality. Furthermore, we hypothesized for the first time, a possible implication of biomolecules (i.e. ferritin) in the preservation of soft parts. This, if confirmed, would resolve the observed discrepancies between the fossil record preserving nervous systems to the exclusion to everything else, and decay experiments showing that nervous tissues are among the first structures to decay and disappear in laboratory conditions. Additionally, we show that metamorphism was not operational in the Fezouata Shale. However, modern weathering leached organic material from surface sediments and transformed pyrite into iron oxides. This finding infers that the original mode of preservation of the Fezouata Shale comprises both carbonaceous compressions and accessory authigenic pyritization. The direct implication of this work was shown through a comparison of enigmatic patterns preserved in three groups of echinoderms. It appears that some of these patterns in eocrinoids and somasteroids do not reflect original anatomies and are preservation artifacts. However, it is certain that the structures preserved in stylophorans are real, closing a long-standing debate on the affinity of this animal group. Finally, a general comparison between the Fezouata Shale and Cambrian Lagerstätten allowed us to decipher the implication of the suggested taphonomic pathway on fossil preservation. It appears that the Fezouata Shale mechanism for preservation failed to preserve completely cellular organisms (e.g. chordates, ctenophores, medusoids) implying a possible underestimation of the original Fezouata Biota and confirming that the Cambrian Explosion and the Ordovician Radiation are one single episode of anatomical innovation. Thus, all these results have implications on understanding ecosystems, and evolution at the dawn of animal life and may contribute in the future to the development of a predictive approach for the discovery of exceptionally preserved biotas.