[The Journal of Geology, 2007, volume 115, p. 601–608]  2007 by The University of Chicago. All rights reserved. 0022-1376/2007/11505-0007$15.00. DOI: 10.1086/519780 601 GEOLOGICAL NOTE Global Aridity during the Early Miocene? A Terrestrial Paleoclimate Record from the Ebro Basin, Spain Jessica M. M. Hamer, 1 Nathan D. Sheldon, 2 and Gary J. Nichols 3 Geology Department, Royal Holloway, University of London, Egham, Surrey TW20 0EX, United Kingdom (e-mail: j.hamer@gl.rhul.ac.uk) ABSTRACT Paleosols are an important tool in the paleoclimatic and paleoenvironmental interpretation of continental deposits and can provide a high-resolution proxy for paleoclimate. Results from geochemical climofunctions applied to Early Miocene strata exposed in the Ebro Basin, Spain, demonstrate that mean annual precipitation was the dominant control on paleosol type and indicate that the paleoclimate was considerably wetter during the Early Miocene, by up to 1150 mm yr -1 , in comparison to modern values, placing it in a subhumid climatic regime rather than an arid- semiarid regime as previously suggested by sedimentological and paleontological approaches. By making comparisons with published data on paleoclimate during the Early Miocene, this article stresses the importance of regional climatic changes in global paleoclimatic interpretation. Introduction Paleosols are an effective and underused proxy for paleoclimatic interpretation, and their use, partic- ularly when there is a dearth of other proxies, can provide quantitative and detailed paleoclimatic in- formation. By using a combination of detailed out- crop studies and geochemical analyses, this article describes paleoclimatic trends within the Early Miocene that are preserved in distal fluvial deposits within the Huesca Fluvial Distributary System, Ebro Basin in northern Spain (fig. 1). Paleoenvironmental and paleoclimatic data for the Early Miocene of the Ebro Basin are limited. Studies of Late Oligocene fluvial and lacustrine de- posits of the Calf and Mequinenza sequences, which form part of a separate fluvial system found in the southeastern Ebro Basin, have suggested an arid to semiarid climate, based on sedimentary and paleobiological observations (e.g., Cabrera et al. 2002). Similarly, micromammal biostratigraphy based on faunal composition has provided some low-resolution paleoclimatic information within Manuscript received October 16, 2006; accepted January 26, 2007. 1 Author for correspondence. 2 E-mail: n.sheldon@gl.rhul.ac.uk. 3 E-mail: g.nichols@gl.rhul.ac.uk. the Huesca system that suggests decreasing tem- peratures and increasing aridity from the Late Ol- igocene to the Middle-Late Miocene (A ´ lvarez Sierra et al. 1990). Field observations made by Nichols and Hirst (1998) conversely infer a relatively humid cli- mate during the Late Oligocene–Early Miocene of the Huesca Fluvial Distributary System, which was not found during this study. However, this conclu- sion is based on the absence of calcrete profiles and, ambiguously, on the identification of Vertisol-like paleosols, which have shown to be absent from sec- tions studied (Hamer et al. 2007). A decrease in aridity is suggested from studies within lake de- posits of the central Ebro Basin during the Early to Middle Miocene (e.g., Arenas and Pardo 2000). A dearth of organics and pedogenic carbonates has meant that paleoclimatic interpretations of Late Oligocene–Early Miocene clastic sediments within the Ebro Basin have been based on field ob- servations alone or are of low temporal resolution (e.g., A ´ lvarez Sierra et al. 1990; Nichols and Hirst 1998; Cabrera et al. 2002). This article provides a new, higher-resolution proxy that refines previous interpretations of the terrestrial paleoclimate rec- ord of the Ebro Basin and highlights the importance