Comment on "Orbitally forced climate and sea-level changes in the Paleoceanic Tethyan domain (marl–limestone alternations, Lower Kimmeridgian, SE France) " by S. Boulila, M. de Rafélis, L. A. Hinnov, S. Gardin, B. Galbrun, P.-Y. Collin [Palaeogeography Palaeoclimatology Palaeoecology 292 (2010) 57–70] Emanuela Mattioli ⁎, Claude Colombié, Fabienne Giraud 1 , Nicolas Olivier, Bernard Pittet Laboratoire CNRS UMR 5125 “PaléoEnvironnements & PaléobioSphère”, Université Claude Bernard Lyon 1, Campus de la Doua, F-69622 Villeurbanne, France abstract article info Article history: Received 8 June 2010 Received in revised form 1 December 2010 Accepted 16 December 2010 Available online 27 April 2011 Keywords: Oxfordian–Kimmeridgian Marl-limestone alternations Calcareous nannofossils Basin-platform correlations Carbonate production A recent paper by Boulila et al. (2010) reports on orbitally-forced cycles recorded as marl-limestone alternations in one Lower Kimmeridgian section, Chateauneuf d'Oze (SE France, Tethyan domain). In an attempt to illustrate the in situ (i.e., pelagic) origin of carbonates in marls and limestones, the authors challenged the results of previous work concerning sections from other Tethyan areas of similar age, which demonstrate that nannofossil abundance is originally higher in marls than in limestones. Boulila et al. (2010) present data acquired with optical and Scanning Electron microscopes estimating nannofossil contribution to the rocks. However, their selected illustrations do not support a high contribution of the nannofossils to the carbonate fraction of their samples or their interpretation of the finest fraction of the rocks (micarbs). Furthermore, according to their data on carbonate content of the rocks, they did not analyse true marl- limestone alternations, but slightly argillaceous limestones and limestones. Boulila et al. (2010) also criticize earlier work providing a sequence stratigraphy interpretation of the Chateauneuf d'Oze section. However, contrarily to these earlier works, they did not consider platform-to-basin correlations that are essential in order to understand the sedimentary dynamics at the basin-wide scale. This comment challenges the work by Boulila et al. (2010) that largely underestimates the role of carbonate production on shallow platforms and its subsequent export basinwards as a major mechanism controlling the sedimentation in epicontinental basins. © 2011 Elsevier B.V. All rights reserved. The work by Boulila et al. (2010) presents magnetic susceptibility, geochemical (wt% CaCO 3 , Mg content, carbon and oxygen stable isotopes), and micropalaeontological (calcareous nannofossils) re- sults from a 8.5 m thick interval of the Chateauneuf d'Oze section (Lower Kimmeridgian, SE France). These authors show orbitally- driven cycles expressed in the lithology and in the geochemical signal. They infer a depositional model of combined climate and sea-level cycles forced in concert by Earth's orbital parameters, and suggest an antagonism between marine surface productivity (i.e., nannofossils) and detrital flux. The aim of micropalaeontological analysis of the Boulila et al. paper is to have a rapid estimate of the nannofossil contribution to CaCO 3 content in marl-limestone alternations. The semi-quantitative analysis of calcareous nannofossils they performed with an optical microscope reveals that the contribution of nannofossils is higher in marls than in limestones. The authors consider that this difference is essentially the result of a stronger diagenesis, and a higher fragmentation of nannofossils in limestones than in marls. But, they analysed calcareous nannofossils only in twelve samples with poorly contrasted lithologies, namely from ~72 to 97% CaCO 3 , with average values for marls at 78% CaCO 3 and for limestones at 90% CaCO 3 . We doubt that this difference in wt% CaCO 3 is important enough to have a significantly different fragmentation during sample processing. Boulila et al. (2010) document abundances of 107 nannofossils in 25 fields of view (FOV) under optical microscope in a sample with 87.5 wt% CaCO 3 , and 194 nannofossils per 25 FOV in a sample with 84 wt% CaCO 3 . Does this mean that a 3.5% difference in CaCO 3 is important enough to have a ~50% reduction of nannofossil abun- dances either due to diagenesis or to fragmentation during sample preparation? Concerning the preservation of nannofossils, Boulila et al. (2010) refer to one single paper stating that the presence of clay minerals exerts a protective function against dissolution and overgrowth of Palaeogeography, Palaeoclimatology, Palaeoecology 306 (2011) 249–251 DOI of original article: 10.1016/j.palaeo.2010.03.026. ⁎ Corresponding author. E-mail address: emanuela.mattioli@univ-lyon1.fr (E. Mattioli) 1 Université Joseph Fourier LGCA - ISTERRE Maison des Géosciences Domaine universitaire BP 53 38041, Grenoble Cedex 9, France. Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo 0031-0182/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.12.028