Proximate environmental forcing in fine-scale geochemical records of calcareous couplets (Upper Cretaceous and Palaeocene of the Basque-Cantabrian Basin, eastern North Atlantic) Álvaro Jiménez Berrocoso a, ⁎, Javier Elorza b , Kenneth G. MacLeod c a School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, UK b Departamento de Mineralogía y Petrología, Universidad del País Vasco, Apartado 644, 48080 Bilbao, Spain c Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA abstract article info Article history: Received 20 August 2012 Received in revised form 16 November 2012 Accepted 19 November 2012 Available online 28 November 2012 Editor: B. Jones Keywords: Calcareous couplets Oxygen and carbon stable isotopes Alternating climates Oxygen-rich water masses Late Cretaceous and Palaeocene Basque Cantabrian Basin Calcareous couplets are key elements in reconstructing the evolution of a sedimentary basin due to the influence of forcing mechanisms such as climate, sea level and tectonism on their depositional patterns. Proposed forcing mechanisms, however, are often not mutually exclusive and even constraining the relative importance of differ- ent processes is problematic. Added to the question of discriminating forcing mechanisms, a major challenge is to produce high-sampling density so that observations lie within temporal resolutions equal to or finer than the timescales on which different forcing operates. Here, we show fine-scale (1 sample/~2 cm) CaCO 3 , δ 18 O and δ 13 C records and sedimentological observations from three different sites (Isla de Castro, Sopelana-Ma, and Sopelana-Da) with calcareous couplets in the Basque Cantabrian Basin (eastern North Atlantic) to illustrate the potential of fine-sampling strategies to help distinguish proximate environmental forcing. Partial redistribu- tion of carbonate during burial diagenesis has been proposed for these sediments. Our CaCO 3 , δ 18 O and δ 13 C data could thus be dismissed as diagenetic signals if only one sample was collected from each bed. Detailed observa- tions of the fine-scale geochemical records, however, challenge purely diagenetic explanations. Combined with sedimentology, the CaCO 3 , δ 18 O and δ 13 C values, partially altered by diagenesis, are interpreted to have resulted from alternating climates. The proximate forcing through which alternating climates caused the geochemical patterns, though, was different in each section, due to their specific palaeogeographic positions in the basin and the properties of the seawater masses. The proximity of continental areas of high relief to the Isla de Castro section supported a high continental influence during its deposition. The Sopelana-Ma sediments are assigned to a transgressive system tract, a condition that is interpreted to have promoted a high influence of oceanic process- es in its depositional setting. Finally, a relatively cool, oxygen-rich water mass with high oxidation potential influenced the geochemical and depositional patterns of Sopelana-Da. Beyond the climatic and oceanographic dynamics inferred for a basin that linked the western Tethys with Boreal domains during major marine trans- gressions of the Late Cretaceous to Palaeocene, an implication of our work is that if similar fine-scale geochemical records were applied to calcareous couplets spanning major events in Earth's history (e.g., ocean anoxic events), alternative forcing scenarios leading to and out of these events could be discriminated. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Alternations of marls, marly limestones and limestones (herein calcar- eous couplets) constitute remarkable features of the Phanerozoic strati- graphic record. Examples span this Eon and represent a wide range of depositional settings. These deposits often contain biostratigraphically important fossils and can record temporal changes in and interactions among climate, sea level and tectonism. However, because there are multiple pathways by which calcareous couplets can be formed, interpre- tations are not always straightforward. Calcareous couplets are often interpreted as a result of periodic cli- matic fluctuations producing variations in terrigenous inputs (dilution cycles) and/or carbonate production (productivity cycles) (Einsele, 1982; Arthur et al., 1984; Einsele et al., 1991). These climatic fluctua- tions are generally related to Milankovitch cycles (~20–400 kyr) and indicate ultimate forcing by periodic changes in Earth's surface insola- tion due to cyclic solar-terrestrial orbital variations (Barron et al., 1985; Fischer and Bottjer, 1991; de Boer and Smith, 1994; Elder et al., 1994; House, 1995; Dinarès-Turell et al., 2003, 2010). In successions where orbital variations force lithological variations and where deposi- tion is relatively continuous, cyclostratigraphic analyses can yield Sedimentary Geology 284–285 (2013) 76–90 ⁎ Corresponding author at: Repsol Exploration, Méndez Álvaro 44, Madrid 28045, Spain. E-mail addresses: alvaro.jimenezberrocoso@manchester.ac.uk, alvaro.jimenez.b@repsol.com (Á. Jiménez Berrocoso). 0037-0738/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sedgeo.2012.11.007 Contents lists available at SciVerse ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo