Middle Jurassic Tethyan–Boreal ostracod faunal links: a case study from the Callovian of Portugal

Pais, Vanessa; Cabral, Maria Cristina; Lord, Alan; Azerêdo, Ana C.; Gallagher, Liam

doi:10.1144/jmpaleo2015-035

Cited by 2 publications

(1 citation statement)

References 38 publications

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“…The well exposed coastal section at Pedrógão beach (Fig. 1B) exhibits an Upper Callovian-Oxfordian succession that has been described in detail by Azerêdo et al (2002a, b) and further addressed in several thematic works on microfossil groups, namely ostracods (Cabral et al, 1998;Azerêdo et al, 2002a;Pais et al, 2016), charophytes (Grambast-Fessard and Ramalho, 1985;Pereira et al,1998Pereira et al, , 2003Azerêdo et al, 2002a) and palynomorphs (Barron et al, 1999;Barron and Azerêdo, 2003). Azerêdo and Cabral (2004), using a range of palaeontological (chiefly the ostracod associations) and sedimentological data, identified in the Oxfordian deposits four facies/palaeoecological subdivisions, which are here labelled Units 1-4, updated and taken as independent background to test the facies interpretations of the present study ( Fig.…”

Section: Pedrógão Sectionmentioning

confidence: 58%

Testing whether early diagenesis of skeletal carbonate is different in non-marine settings: Contrasting styles of molluscan preservation in the Upper Jurassic of Portugal

Wright

Cherns

Azerêdo

et al. 2018

Palaeogeography, Palaeoclimatology, Palaeoecology

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This study tests the hypothesis that the early diagenesis of aragonite shells should differ fundamentally between marine and freshwater environments. This is predicted to be the case because aragonite is highly susceptible to dissolution in the TAZ (Taphonomically Active Zone) in low energy marine settings due to acidity caused largely by the oxidation of H2S generated by sulphatereducing bacteria, but reduced sulphide activity in freshwater settings should result in less early dissolution of aragonite. To test this hypothesis a range of fresh-brackish-hypersaline and marine limestones were sampled from the Upper Jurassic (mid Oxfordian) Cabaços Formation of central western Portugal. In these freshwater and brackish deposits, molluscs are preserved mostly as sparite shell replacements indicating that the original aragonite was preserved through the TAZ and was later replaced during subsequent burial by calcite cement. In limestones deposited in more marine to hypersaline settings, molluscan remains mostly consist of the calcitic layers of bimineralic bivalves, as shell where the original was wholly calcitic, or as gastropod steinkerns. Exceptions occur and reflect other factors such as higher energy conditions during deposition whereby organic matter, as the drive for microbial decay processes, was removed. The implications for molluscan preservation including some hydrocarbon reservoirs are discussed.

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Section: Pedrógão Sectionmentioning

confidence: 58%