New insights in the pattern and timing of the Early Jurassic calcareous nannofossil crisisPalaeogeography, Palaeoclimatology, Palaeoecology

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Authors
Marie-Emilie Clémence, Silvia Gardin, Annachiara Bartolini
Year
2015
DOI
10.1016/j.palaeo.2015.03.024
Subject
Earth-Surface Processes / Ecology, Evolution, Behavior and Systematics / Oceanography / Palaeontology

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Received 27 April 2014

Received in revised form 10 March 2015

Accepted 17 March 2015

Keywords:

Early Toarcian

Calcareous nannofossils

Biocalcification crisis

Carbonate production 1. Introduction nannofossil biocalcification crisis (e.g., Mattioli and Pittet, 2004; e, organic matter and al., 2007; Suan et al., fossil crisis is a fundaPalaeogeography, Palaeoclimatology, Palaeoecology 427 (2015) 100–108

Contents lists available at ScienceDirect

Palaeogeography, Palaeocli e lsPliensbachian is rapidly marked by a carbonate production crisis during the early Toarcian Oceanic Anoxic Event (T-OAE). Marine depositional settings across Europe shows evidence for a near disappearance of mental key point in the understanding of the relative roles of intrinsic (dynamic of the community) and extrinsic (environmental changes) processes as drivers of the crisis, and to decipher causal mechanismscalcareous dinoflagellates were the only planktonic organisms able to bio-calcify in the oceanic photic zone and to participate to both the organic-carbon pump and carbonate counter-pump (Rost and

Riebsel, 2004). However, this diversification event starting in the late cursion (CIE) measured in bulk rock carbonat in fossil wood (e.g., Jenkyns, 1988; Hesselbo et 2008a; Hermoso et al., 2009).

Assessment of the timing of calcareous nannoProfound environmental change occurred in the Early Jurassic along with one of the most significant diversification phase in the history of calcareous nannoplankton (Jenkyns, 1988; Bown et al., 2004). At that time, calcareous nannoplankton (coccoliths and nannoliths) and

Tremolada et al., 2005), suggesting a re-organisation of planktonic communities in response to major environmental changes. The T-OAE corresponded to an interval of widespread organic matter burial, global warming and prominent carbon cycle perturbation in the ocean– atmosphere, as testified by a prominent negative carbon-isotope ex-shallow-water platforms (e.g., Dromart et al., in calcium carbonate contents in basinal su ⁎ Corresponding author. Tel.: +43 512/507 5676.

E-mail address:Marie-Emilie.Clemence@uibk.ac.at (M http://dx.doi.org/10.1016/j.palaeo.2015.03.024 0031-0182/© 2015 Published by Elsevier B.V.The Toarcian calcareous nannofossils crisis associated with the early Toarcian Oceanic Anoxic Event (T-OAE) in the Early Jurassic period is thought to represent one of the most important biocalcification crises during the

Mesozoic, occurring simultaneously with profound disturbance of the carbon cycle. However, the causes are still under debate, particularly with regard to the pattern, timing of the biocalcification crisis, relative roles of intrinsic and extrinsic processes as drivers of the crisis, and also causal mechanisms of the T-OAE.

In this study, a new quantification of Toarcian calcareous nannofossil abundance and size is presented for the

Sancerre borehole (Paris Basin, France). Beyond the recognition of a severe biocalcification crisis defined by the major drop in abundance, and the reduction in size of the most important pelagic carbonate producer

Schizosphaerella punctulata, for the first time, this study proposes an insight into the pace and timing of the nannoplankton crisis. At Sancerre, the carbonate production of the lower Toarcian sediments previously attributed to obliquity forcing of climate allows estimating a duration of ~210 kyr for the biocalcification crisis and of ~120 kyr for the shift towards lower carbon isotope values. The onset of the biocalcification crisis marked by a fertility event lasted ~60 kyr, and the calcium carbonate values remained low for ~150 kyr; the subsequent recovery of carbonate and nannoplankton lasted ~60 kyr and N550 kyr, respectively. Additionally, a link between the biocalcification crisis, the seawater palaeotemperature, and the carbon isotope steps can be demonstrated.

This covariance provides compelling evidence of fundamental change in the response of the climatic warming and the carbon cycle systems triggering the biocalcification crisis. These observations indicate that the biocalcification crisis can be regarded as a direct or indirect consequence of a global warming. Moreover, a deficiency of the biological pump is proposed here, as a complementary causal mechanism for explaining the negative carbon-isotope excursion. © 2015 Published by Elsevier B.V.Article history:a b s t r a c ta r t i c l e i n f oNew insights in the pattern and timing of nannofossil crisis

Marie-Emilie Clémence a,⁎, Silvia Gardin b, Annachiara a University of Innsbruck, Institute of Geology, Faculty of Geo- and Atmospheric Sciences, Innra b CR2P Centre de Recherche sur la Paléobiodiversité et les Paléoenvironnements, UMR 7207 CN c CR2P Centre de Recherche sur la Paléobiodiversité et les Paléoenvironnements, UMR 7207 CN j ourna l homepage: www.1996), a significant drop ccessions and a drastic .-E. Clémence).e Early Jurassic calcareous rtolini c 2, Innsbruck 6020, Austria

UPMC, MNHN, Sorbonne Université, 4 place Jussieu, 75252 Paris, cedex 05, France

UPMC, MNHN, Sorbonne Université, 8 rue Buffon, CP38 Paris, cedex 05, France matology, Palaeoecology ev ie r .com/ locate /pa laeoof the T-OAE. Many aspects of calcareous nannofossil crisis have been undertaken, but none have been attempted to estimate its tempo because of a poorly constrained Toarcian timescale (Pálfy et al., 2000;

Hinnov and Ogg, 2007) and because the duration of the negative CIE remains still debated (Kemp et al., 2005, 2011; Suan et al., 2008b;

Huang and Hesselbo, 2013). The recent astronomical calibration of the

Sancerre core performed by Boulila et al. (2014) alongwith stable isotopic and biostratigraphic proxy data provide a strong insight into the pace and timing of the nannoplankton crisis.

In this study, quantitative estimates of calcareous nannofossil abundance and size, and palaeoecological analysis from the lower Toarcian sediments of the Paris Basin (France) are presented. These new data, coupled with published geochemical and cyclostratigraphic data (Hermoso et al., 2009, 2012; Boulila et al., 2014) allow addressing significant questions concerning the pattern and timing of the calcareous nannofossil response to T-OAE environmental changes, the drivers of the biocalcification crisis, and the dynamic of Schizosphaerella, which was the main pelagic carbonate producer of Early Jurassic oceans. The study is based on core samples from the Sancerre–Couy borehole. The succession provides an exceptionally well-preserved pelagic carbonate whichmay serve as a suitable archive formicropalaeontological investigations, representing a key stratigraphic framework for this study. 2. The Sancerre Borehole: geological setting and paleogeography of the Paris Basin