Large scale facies change in the middle Eocene South-Pyrenean foreland basin: The role of tectonics and prelude to Cenozoic ice-ages Damien Huyghe a, b, c, ⁎, Sébastien Castelltort d, f , Frédéric Mouthereau a, b , Josep Serra-Kiel e , Pierre-Yves Filleaudeau a, b , Laurent Emmanuel a, b , Benoît Berthier a, b , Maurice Renard a, b a UPMC Univ Paris 06, UMR 7193, ISTeP, F-75005, Paris, France b CNRS, UMR 7193, ISTeP, F-75005, Paris, France c Laboratoire des Fluides Complexes et leurs Réservoirs, I.P.R.A. Université de Pau, BP 1155, 64013 Pau Cedex, France d ETH-Zürich, Geological Institute, Sonneggstrasse 5, 8092 Zürich, Switzerland e Departament de Estratigrafía i Paleontología, Facultat de Geología, Universitat de Barcelona, E-08071, Barcelona, Spain f Section of Earth Sciences, University of Geneva, Rue des Maraîchers 13, 1205 Geneva, Switzerland abstract article info Article history: Received 22 February 2011 Received in revised form 16 December 2011 Accepted 10 January 2012 Available online 18 January 2012 Editor: G.J. Weltje Keywords: Lutetian Pyrenees Foraminifers Carbonates Ice-sheets Erosion The present study reports a sedimentological analysis of the Guara Limestone Formation deposited during the Lutetian in the Sierras Exteriores, in the South-Pyrenean foreland basin. We provide a detailed facies anal- ysis of the carbonates to precise the paleoenvironmental context during their deposition. We show that those limestones are mainly composed of shallow-water foraminifers and were deposited in relative shallow-water environments (b 120 m) during the whole Lutetian (SBZ 13 to SBZ 16). The Guara Limestone Formation rep- resents the last occurrence of carbonate platform in the South-Pyrenean foreland basin and disappeared def- initely at the Lutetian to Bartonian transition. The demise of carbonate producers at the end of the Lutetian could be related to an increase of continental erosion, due to tectonic and/or climatic forcing. We illustrate that in the Jaca basin, this event correlates with a marked increase in subsidence rate. However, this deforma- tion event is local and the carbonate systems in the Pyrenean foreland resisted to many deformation events during the whole basin history before. Paleobathymetric reconstructions in the Jaca basin, where shallow ma- rine sections outcrop, suggest an increase of the amplitude of high-frequency sea-level cycles. This increase is contemporaneous with several climatic evidences, which suggest the appearance of early ice-sheets near the Lutetian–Bartonian boundary. The demise of carbonate producers seems, therefore, to be the result of a major environmental shift in the basin accompanying increased subsidence rates, switching from low nutrient oli- gotrophic conditions – favourable for shallow water benthic foraminifers – to eutrophic conditions due to the increase of erosion and terrigenous nutrient input associated with higher-frequency sea-level changes and river destabilization. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Carbonate platforms can be deposited in different tectonic settings and can present various morphologies (e.g. Bosence, 2005). In fore- land basins settings, carbonate platforms develop on the distal part of the flexural basin and show typical ramp morphologies on the dis- tal part of the flexural basin, (Dorobek, 1995; Bosence, 2005). Based on the French–Swiss alpine foreland basin example, Sinclair (1997) defined a tectonostratigraphic model for underfilled peripheral fore- land basins in which shallow-water carbonate platforms correspond to the lower unit of an underfilled trinity. In this type of setting, strat- igraphic units of this trinity present a diachronous migration towards the external part of the underlying pre-orogenic strata, thus shaping a so-called basal flexural unconformity with the underlying rocks (Crampton and Allen, 1995; Allen et al., 2001). In this context, the de- mise of carbonates ramps results from the progressive drowning of the area of deposition illustrated by the deepening of the sedimentary facies (Sinclair, 1997; Allen et al., 2001) as the orogenic load pro- gresses towards the foreland. The transition from an underfilled to an overfilled stage and the demise of carbonate ramps can be caused by the increase of shortening and thrust stacking including a pulse in erosional exhumation and the increase of sediment supplied from the thrust wedge or/and an increase of the flexural rigidity of the under- lying cratonic plate (see Sinclair, 1997). However, attempts to repro- duce the evolution of carbonate platforms in foreland basins through modelling of the stratigraphic architecture often assume the climate as stable during the period considered (Crampton and Allen, 1995; Allen et al., 2001). Our understanding of the importance of the cli- mate factor in driving the demise of carbonate platforms in foreland basins remains therefore largely underestimated and still need to be established in such orogenic settings. Sedimentary Geology 253–254 (2012) 25–46 ⁎ Corresponding author. E-mail address: damien.huyghe@univ-pau.fr (D. Huyghe). 0037-0738/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2012.01.004 Contents lists available at SciVerse ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo