Biochemostratigraphy of the Upper Frasnian in the Namur–Dinant Basin, Belgium: Implications for a global Frasnian–Famennian pre-event

Abstract

a b s t r a c tThe Upper Frasnian sequence of the Namur-Dinant Basin in southern Belgium consists of mixed siliclasticcarbonate succession of a ramp setting, where the sequence spans the rhenana-linguiformis conodont zones. Earlier studies investigated the chemostratigraphic variations during the Frasnian-Famennian event, but little has been yet known about the nature of the counterpart variations that immediately preceded that time interval. Despite the scarcity of well-preserved brachiopods, sixty-one calcitic shells were collected mainly from beds of the Neuville and Les Valisettes formations (Lower and Upper rhenana zones), to investigate biochemostratigraphic profiles of oxygen-, carbon-isotope and rare earth element (REE) variations of 18 13 Upper Frasnian Namur-Dinant Basin Belgium the time interval immediately before the Frasnian-Famennian boundary. The δ O and δ C values of the well-preserved shells range from − 9.5 to − 5.6‰ VPDB (− 7.7 ± 1.1, n = 33) and from − 1.8 to 3.8‰ VPDB (1.1 ± 1.7, n = 33), respectively, which are within the documented global values. The C-and O-isotope profiles exhibit parallel shifts, particularly at the top of the Neuville Formation (top of the Lower rhenana Zone), which are associated with a sea-level rise and shrinkage in the brachiopod community. Also, the Th/U (0.9 ± 0.6, n = 16) and Ce/Ce* (2.2 ± 0.5, n = 16) ratios suggest deposition under reducing conditions consistent with sea transgression.

Neotethys seawater chemistry and temperature at the dawn of the end Permian mass extinction

“…The ΣREE of the brachiopods ranges from 2.2 to 13.5 ppm, which brackets the values documented for modern and fossil shells with minimum alteration (Azmy et al, , 2012Brand et al, 2012a), and the whole rock ΣREE data from Tibet ranges from 10.6 to 94.9 ppm. The Ce/Ce* anomaly values (De Baar et al, 1988;Bau and Dulski, 1996;Azmy et al, 2011, Brand et al, 2012a for the brachiopods ranges from 0.310 to 0.578, which is matched by the Ce/Ce* values of the enclosing rock ranging from 0.237 to 0.655 before the event, and of 0.276 for whole rock in the estimated extinction interval (Appendix 3).…”

“…the influence of diagenetic alteration (e.g., Azmy et al, 2011Azmy et al, , 2012Brand et al, 2012b). ).…”

Geochemistry of rare earth elements and cerium anomaly in sedimentary marine carbonates: modern concepts

“…Однако не так давно было показано, что на самом деле такая строгая линейная зависимость отсутствует: изменения Се аном хорошо отражают переход к бескислородным обстановкам, но не очень чувствительны к вариациям концентраций О 2 в кислородной среде в целом (Ling et al, 2013;Cao et al, 2022). Тем не менее вариации значений Ce/Ce* в карбонатных последовательностях позволяют отслеживать интервалы глобальных аноксидных событий, имеющих высокий корреляционный потенциал (Schröder, Grotzinger, 2007;Azmy et al, 2012;Bodin et al, 2013;Мизенс и др., 2014 и др. ).…”

Comment on the Kaiho et al., paper “A forest fire and soil erosion event during the Late Devonian mass extinction” [Palaeogeography, Palaeoclimatology, Palaeoecology 392 (2013): 272–280]

“…Thus, C-isotope composition of organic matter would be very helpful (Joachimski et al, 2001;Chen et al, 2005), especially since Azmy et al (2012) discovered in nearby Belgian localities an enigmatic "global F-F pre-event".…”