Preto, N., Agnini, C., Rigo, M., Sprovieri, M. and Westphal, H. (2013) The calcareous nannofossil Prinsiosphaera achieved rock-forming abundances in the latest Triassic of western Tethys: consequences for the δ13C of bulk carbonate. Biogeosciences Discussions, 10 (5). pp. 7989-8025. DOI https://doi.org/10.5194/bgd-10-7989-2013.

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Abstract

The onset of pelagic biomineralization was a mile-stone in the history of the long-term inorganic carbon cy-cle: as soon as calcareous nannofossils became major lime-stone producers, the pH and supersaturation state of theglobal ocean were stabilized (the so-called mid-Mesozoicrevolution). But although it is known that calcareous nan-nofossils were abundant already by the end of the Triassic,no estimates exist on their contribution to hemipelagic car-bonate sedimentation. With this work, we estimate the vol-ume proportion ofPrinsiosphaera, the dominant late Trias-sic calcareous nannofossil, in hemipelagic and pelagic car-bonates of western Tethys. The investigated Upper Trias-sic lime mudstones are composed essentially of microsparand tests of calcareous nannofossils, plus minor bioclasts.Prinsiosphaerahad become a significant component of limemudstones since the late Norian, and was contributing up toca. 60 % of the carbonate by the late Rhaetian in periplat-form environments with hemipelagic sedimentation. The in-creasing proportion ofPrinsiosphaerain upper Rhaetianhemipelagic lime mudstones is paralleled by an increase of the δ13C of bulk carbonate. We interpreted this isotopic trendas related to the diagenesis of microspar, which incorporatedrespired organic carbon with a lowδ13C when it formed dur-ing shallow burial. As the proportion of nannofossil testsincreased, the contribution of microspar with low δ13C di-minished, determining the isotopic trend. We suggest that asimilar diagenetic effect may be observed in many Mesozoiclimestones with a significant, but not yet dominant, propor-tion of calcareous plankton.

Document Type:	Article
Programme Area:	UNSPECIFIED
Research affiliation:	Biogeochemistry and Geology > Geoecology & Carbonate Sedimentology
Refereed:	Yes
Open Access Journal?:	Yes
DOI:	https://doi.org/10.5194/bgd-10-7989-2013
ISSN:	1810-6285
Date Deposited:	16 Aug 2019 15:39
Last Modified:	01 Oct 2020 12:59
URI:	http://cris.leibniz-zmt.de/id/eprint/2675

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