Deciphering processes controlling mid-Jurassic coccolith turnover

Western Tethys Early and Middle Jurassic calcareous nannofossil biostratigraphy

“…However, a decrease in δ 13 C values is observed from the NJT9 Zone coeval with the Watznaueria speciation. This radiation reflects the decrease in abundance of Lotharingius species already observed in other works (e.g., Ferreira et al, 2015;Giraud et al, 2016;Aguado et al, 2017;Wiggan et al, 2018), particularly that of L. crucicentralis whose RD happens at the temperature minimum, and of L. velatus. The Watznaueria radiation and its subsequent ecological dominance was not made at the expenses of other genera but through its integration in the coccolithophore community (Suchéras-Marx et al, 2015).…”

“…The expansion of Watznaueria occurred in two separate steps: first, during the latest Aalenian and earliest Bajocian, where morphotypes with a cross in their central area such as W. colacicchii, W. contracta and W. aff. W. contracta dominated (Suchéras-Marx et al, 2015;Giraud et al, 2016;Wiggan et al, 2018); and second, during the early Bajocian when species lacking a central cross, those with a central bar and those with a closed central area such as W. aff. W. manivitiae and W. manivitiae increased their abundance (Giraud et al, 2016).…”

“…W. contracta dominated (Suchéras-Marx et al, 2015;Giraud et al, 2016;Wiggan et al, 2018); and second, during the early Bajocian when species lacking a central cross, those with a central bar and those with a closed central area such as W. aff. W. manivitiae and W. manivitiae increased their abundance (Giraud et al, 2016). The Watznaueria upsurge roughly coincides with the Propinquans positive excursion, when δ 13 C values steadily and consistently increase by ~1 ‰.…”

Early Jurassic climatic trends in the south-Tethyan margin

“…Thus, apart from the data dispersion (Fig. 5) also reported from brachiopod isotope composition in other time intervals (e.g., Giraud et al, 2016), some prominent excursions are observed in the present work for δ 13 C and δ 18 O values from NW Algeria (i.e., Sinemurian-Pliensbachian boundary, Pliensbachian-Toarcian boundary, early Toarcian Anoxic Event). These excursions can likely be related to palaeoclimatic and palaeoceanographic events, once proven the primary nature of the isotopic signal.…”

“…SEM images were used to evaluate the preservation of the microstructures of the secondary layer, the shell microstructures are considered to be well preserved when smooth fibrous surfaces of secondary layer occur, similarly to those observed in living specimens (Brand et al, 2003;Suan et al, 2008a). Diagenetically-altered structures of the secondary layer of brachiopod shells are identified by the poor individualization of calcite fibres (Suan et al, 2008a;Giraud et al, 2016). In specimens showing a good preservation of the calcite fibres of the secondary layer under SEM, the primary character of the stable carbon and oxygen isotope composition of the brachiopod shells was tested using the concentrations of strontium and manganese, which are known to be sensitive to diagenetic alteration (Brand and Veizer, 1980;Brand et al, 2003).…”