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Volume 14, issue 8 | Copyright
Clim. Past, 14, 1147-1163, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Aug 2018

Research article | 10 Aug 2018

Mid-Cretaceous paleoenvironmental changes in the western Tethys

Cinzia Bottini and Elisabetta Erba Cinzia Bottini and Elisabetta Erba
  • Dipartimento di Scienze della Terra “A. Desio”, Università degli Studi di Milano, 20133 Milan, Italy

Abstract. We present a continuous record of surface water temperature and fertility variations through the latest Barremian–Cenomanian interval (ca. 27Myr) based on calcareous nannofossil abundances from the western Tethys. The nannofossil temperature index, calibrated with TEX86 sea surface temperatures, suggests that warmest (34–36°C) conditions were reached during oceanic anoxic event (OAE) 1a onset, the Aptian–Albian boundary interval hyperthermals (113, Kilian level and Urbino level OAE 1b) and during a ca. 4Myr long phase in the middle Albian. Coolest temperatures (29°C) correspond instead to the late Aptian. Generally warm conditions characterized the Albian followed by a progressive cooling trend that started in the latest Albian (at the Marne a Fucoidi–Scaglia Bianca Formation transition). Temperate conditions occurred in the Cenomanian with frequent short-term variations highlighted by abundance peaks of the cold-water nannofossil species E. floralis and R. parvidentatum. Mid-Cretaceous surface water fertility was rather fluctuating and mostly independent from climatic conditions as well as from black shales intervals. Intense warming and fertility spikes were systematically associated only with black shales of OAE 1a and of the Aptian–Albian boundary hyperthermals. The Albian–Cenomanian rhythmic black shales are, in fact, associated with varying long-term climatic and fertility conditions. The similarity of western Tethys climatic and fertility fluctuations during OAE 1a, OAE 1b, the middle Albian and OAE 1d with nannofossil-based records from other basins indicated that these paleoenvironmental conditions were affecting the oceans at supra-regional to global scale.

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Short summary
The mid-Cretaceous (ca. 121 to 94 Ma) was characterized by a generally warm climate punctuated by supra-regional to global phenomena of widespread ocean anoxia. In this work we present the first complete record of temperature and fertility variations through the mid-Cretaceous in the western Tethys based on calcareous nannofossils. The new record indicates that temperatures and fertility were rather fluctuating but mostly independently, and they were not systematically associated with anoxia.
The mid-Cretaceous (ca. 121 to 94 Ma) was characterized by a generally warm climate punctuated...