Palynostratigraphy and palynofacies of the Upper Triassic Streppenosa Formation (SE Sicily, Italy) and inference on the main controlling factors in the organic rich shale deposition S. Cirilli a, ⁎, N. Buratti a , L. Gugliotti b , A. Frixa b a Dipartimento di Fisica e Geologia, Università di Perugia, Via Pascoli, 06123 Perugia, Italy b Eni E&P, Via Emilia 1, San Donato Milanese, Milano, Italy abstract article info Article history: Received 23 April 2014 Received in revised form 16 September 2014 Accepted 17 October 2014 Available online xxxx Keywords: Triassic Palynofacies Palynostratigraphy Organic matter Sicily Streppenosa Formation This paper focuses on the Upper Triassic Streppenosa Formation, penetrated by the Pachino 4 on-shore well, (Southern Sicily, Italy) in order to find stratigraphic age constrains and to reconstruct the paleoenvironmental evo- lution of this basin within the Upper Triassic palaeogeographic scenario of the western Tethys. Pachino 4 is one of the wells drilled by Eni Exploration and Production in the south-eastern Hyblean plateau with the purpose to better define the time and space distribution of reservoirs and source rocks in an area characterized by considerable sub- sidence and strong tectonic activity, balanced by high sedimentation rate. The Streppenosa Formation depocenter consists of a thick sequence (N 2500 m) of organic rich shales, turbiditic limestones and marly limestones, grouped into three members (Lower, Middle and Upper). The well diversified microflora assemblages allow the dating of the upper part of the Lower Member and the Middle Member as Norian and the Upper Member as Rhaetian. The palynofacies variations across the Streppenosa Formation show significative changes in the relative abundances of the organic debris that, associated with the lithological and sedimentological features, allowed a reconstruction of the depositional facies successions and a hypothesis for the forcing mechanisms driving the black shale deposi- tion. We considered that the deposition of the Streppenosa Formation occurred in an epeiric basin, under oxygen- depleted bottom waters, with different depth that varied through time in response to the sedimentation rates, eustatic sea level changes, and basin subsidence. The integration of palynofacies and lithofacies data suggests a crucial role for river runoff, responsible for water stratification and for primary productivity increase in the water column. The process was triggered by warmer and wetter climate conditions as documented in many Upper Triassic successions of the western Tethys realm. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Large fluctuations in the early Mesozoic climate are usually linked to widespread deposition of organic carbon rich sediments. In the western Tethys evidence of increasing humidity and seasonality around the Triassic–Jurassic (Tr–J) boundary have been documented by the large amount of enriched organic matter and shaly sediments deposited within low dysoxic–anoxic basins (e.g., Hallam, 1985; Berra and Cirilli, 1997; Cirilli et al., 1999; Wignall, 2001; Buratti and Cirilli, 2007; Bonis et al., 2010a). The beginning of black shale deposition seems to coincide with the onset of a negative δ 13 C excursion (Kürschner et al., 2007; Bonis et al., 2010a, 2010b; Ruhl et al., 2011) just before the Tr–J boundary. This boundary is marked by major environmental and biotic changes assumed to be coeval with perturbations of the global carbon cycle, thus suggesting sudden input into the ocean–atmosphere system of large amount of CH 4 or CO 2 . Two distinct negative organic Carbon Isotope Excursions (CIE) both in carbonates and organic matter were recorded in many sections within and outside the Tethys Ocean (Hesselbo et al., 2002; Galli et al., 2007; McElwain et al., 2007; Götz et al., 2009; Clemence et al., 2010; Deenen et al., 2010; Michalík et al., 2010; Ruhl et al., 2011; Schaller et al., 2011; Steinthorsdottir et al., 2011; Lindström et al., 2012; Dal Corso et al., 2014). The short-lived “initial” CIE concurs with the major end-Triassic biotic turnover and is separated from the longer-lived “main” CIE by a return to Rhaetian base values (Hesselbo et al., 2002). The onset of the main CIE coincides with the base of the Jurassic, which is defined by the first occurrence of the Psiloceras spelae ammonite species (von Hillebrandt et al., 2007). At the Tr–J transition it has been recently ar- gued that changes in the bulk C-isotope composition of the sedimentary organic matter are largely controlled by changes in type of organic matter (van de Schootbrugge et al., 2008). Still matter of debate is instead the forcing mechanisms that have been invoked to explain the environmental and biological changes at the Tr–J transition. According to several re- searchers the onset of the Central Atlantic Magmatic Province (CAMP), related to the break-up of Pangaea, could have triggered the biotic crisis by releasing of volcanic gases (mainly CO 2 and SO 2 ) into the ocean– Review of Palaeobotany and Palynology xxx (2015) xxx–xxx ⁎ Corresponding author. E-mail address: simonetta.cirilli@unipg.it (S. Cirilli). PALBO-03593; No of Pages 13 http://dx.doi.org/10.1016/j.revpalbo.2014.10.009 0034-6667/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Review of Palaeobotany and Palynology journal homepage: www.elsevier.com/locate/revpalbo Please cite this article as: Cirilli, S., et al., Palynostratigraphy and palynofacies of the Upper Triassic Streppenosa Formation (SE Sicily, Italy) and inference on the main controlling..., Rev. Palaeobot. Palynol. (2015), http://dx.doi.org/10.1016/j.revpalbo.2014.10.009