ORIGINAL PAPER Coastal sediments from the Algarve: low-latitude climate archive for the Aptian-Albian Ulrich Heimhofer Æ Thierry Adatte Æ Peter A. Hochuli Æ Stefan Burla Æ Helmut Weissert Received: 27 September 2006 / Accepted: 28 February 2007 / Published online: 3 April 2007 Ó Springer-Verlag 2007 Abstract The Late Aptian to Early Albian transition has previously been identified as a possible example of sub- stantial climate cooling within the mid-Cretaceous green- house period. To study the response of continental weathering and terrestrial vegetation to this cooling epi- sode at low- to mid-latitudes, marine nearshore deposits from the Algarve Basin (SW Portugal) have been investi- gated with a combined approach including palynology, clay mineralogy and bulk-rock geochemistry. In the Lower Aptian part of the succession, quartz-rich sandstone facies is accompanied by high abundances of early diagenetic kaolinite, which is interpreted to reflect episodes of en- hanced humidity and high meteoric flow-through. In con- trast, the Late Aptian to Early Albian deposits are characterized by high abundances of detrital clay minerals (mica and chlorite) indicating the dominance of physical weathering processes in the source area, most probably related to low precipitation rates in conjunction with tec- tonically enhanced erosion. Palynological data show a strong dominance of Classopollis pollen associated with low pteridophyte spore abundances, suggesting warm semi-arid to arid palaeoenvironments. Changes in sedi- mentation patterns from varicoloured lagoonal marls to thick-bedded shallow-water carbonates are neither ex- pressed in the spore-pollen assemblages nor in the distri- butions of clay minerals which both remain essentially stable throughout the Late Aptian to Early Albian. These relatively stable patterns are in contrast with various lines of evidence, predominantly from high-latitude areas, that suggest a significant cooling during this time interval. Our study demonstrates that terrestrial environments of low- to mid-latitude regions were not significantly affected by the Late Aptian - Early Albian ‘‘cold snap’’. Keywords Early Cretaceous Á Algarve Basin Á Palaeoclimate Á Palynology Á Clay mineralogy Introduction The mid-Cretaceous is generally referred to as a period of extreme global warmth and represents one of the best examples of ‘‘greenhouse’’ conditions in the geological record. However, the stability of the Cretaceous green- house is still a matter of debate and the long-held view of an equable and stable Cretaceous climate has been ques- tioned (e.g. Kemper 1987). The Aptian to Early Albian interval (121–106 Ma, Gradstein et al. 1995) has been identified as a possible period of substantial climatic change within the mid-Cretaceous greenhouse period (Fig. 1). Mean temperature estimates derived from d 18 O measurements of phosphatic fish remains (Puce ´at et al. 2003), rudist shells (Steuber et al. 2005), benthic forami- U. Heimhofer (&) Institute for Geology, Mineralogy and Geophysics, Ruhr-Universita ¨t Bochum, Universita ¨tsstr. 150, Bochum 44801, Germany e-mail: ulrich.heimhofer@rub.de T. Adatte Institute of Geology, University of Neucha ˆtel, Emile-Argand 11, Case Postale 158, Neucha ˆtel CH2009, Switzerland P. A. Hochuli Palaeontological Institute, University of Zu ¨rich, Karl Schmid-Strasse 4, Zu ¨rich 8006, Switzerland S. Burla Á H. Weissert Geological Institute, ETH Zu ¨rich, Sonneggstr. 5, Zu ¨rich 8092, Switzerland 123 Int J Earth Sci (Geol Rundsch) (2008) 97:785–797 DOI 10.1007/s00531-007-0186-y