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Ichnological Analysis of the Bidart and Sopelana Cretaceous/Paleogene (K/Pg) Boundary Sections (Basque Basin, W Pyrenees): Refining Eco-Sedimentary Environment

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Ichnological Analysis of the Bidart and Sopelana Cretaceous/Paleogene (K/Pg) Boundary Sections (Basque Basin, W Pyrenees): Refining Eco-Sedimentary Environment Sedimentary Geology 234 (2011) 42–55 Contents lists available at ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo Ichnological analysis of the Bidart and Sopelana Cretaceous/Paleogene (K/Pg) boundary sections (Basque Basin, W Pyrenees): Refining eco-sedimentary environment F.J. Rodríguez-Tovar a,⁎, A. Uchman b, X. Orue-Etxebarria c, E. Apellaniz c, Juan I. Baceta c a Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, 18002 Granada, Spain b Jagiellonian University, Institute of Geological Sciences, Oleandry Str. 2a, PL-30-063 Kraków, Poland c Departamento de Estratigrafía y Paleontología, Facultad de Ciencia y Tecnología, Universidad del País Vasco, E-48080 Bilbao, Spain article info abstract Article history: Ichnological analysis of two Cretaceous–Paleogene boundary sections at Bidart (SE France) and Sopelana (N Received 12 August 2010 Spain) has been conducted in order to refining eco-sedimentary environment, and to a make comparison with Received in revised form 23 October 2010 previous interpretations based on microfossils. In both sections, trace fossil assemblage is low diverse, Accepted 22 November 2010 consisting of Chondrites, Planolites, Thalassinoides, Trichichnus, Zoophycos, and ?Phycosiphon, ascribed to the Available online 1 December 2010 Zoophycos ichnofacies, however, with distinct differences. In the Bidart section, early Danian dark-filled trace Editor: M.R. Bennett fossil assemblage is more abundant in large Thalassinoides, Zoophycos and larger Chondrites, and less abundant in Trichichnus and small Chondrites in comparison to the Sopelana section. Sopelana is thus interpreted as a Keywords: more offshore, deeper section than Bidart although both were located in the upper bathyal zone of the basin. Trace fossils Oxygenation below the sediment–water interface was enough to favour a generalized total bioturbation of Cretaceous/Paleogene boundary sediments. The presence of chemichnia and trace fossils which tracemakers sequestered sediments from the Zoophycos ichnofacies sea floor in deep burrows (Zoophycos) suggests at least periodical food deficiency. The distribution and Eco-sedimentary conditions content of trace fossils across the K/Pg boundary do not change significantly, revealing minor incidence of the Bidart K/Pg boundary event on the macrobenthic environment. The K/Pg boundary transition, including the Sopelana boundary layer, is nearly totally bioturbated; hence a redistribution of microbiotic and abiotic components by tracemakers is possible. © 2010 Elsevier B.V. All rights reserved. 1. Introduction 1984; Ekdale and Stinnesbeck, 1998). However, in the last years ichnological analyses conducted in several K/Pg sections, reveal that The Cretaceous–Paleogene (K/Pg) boundary event is one of the the boundary layer is bioturbated, containing diverse trace fossils, most spectacular phenomenon in the Phanerozoic history of the which help to refine several aspects in the interpretation of the Earth causing a global major extinction. In pelagic environments it is palaeoenvironmental conditions that prevailed during sedimenta- recorded in the so-called boundary layer, which is a thin, usually 5– tion of the K/Pg boundary event interval (Rodríguez-Tovar, 2005; 10 cm thick, dark and calcium carbonate depleted claystone or Rodríguez-Tovar and Uchman, 2004a,b, 2006, 2008; Rodríguez- marlstone. Commonly, the base of the boundary layer is defined by a Tovar et al., 2002, 2004, 2006). millimeter-thick rusty layer which contains the iridium and other In the Basque Basin (western Pyrenees) several outcrops of deep geochemical anomalies related with the extraterrestrial bolide marine (hemi)pelagic facies has been studied, revealing the well impact at the northern Yucatan peninsula (Schulte et al., 2010; developed, expanded and relatively complete K–Pg boundary Smit, 1999)whichdefine the formal position of the K/Pg boundary interval (see Apellaniz et al., 1997; Pujalte et al., 1998). These (Molina et al., 2006). Publications showing the presence of trace favourable features determined the numerous studies conducted in fossils at the K/Pg boundary interval are scarce (see Rodríguez-Tovar the uppermost Maastrichtian–lowermost Danian sediments of this and Uchman, 2008 for a review), especially those including a area, involving sequence stratigraphic, mineralogical, isotopic, detailed ichnological characterization (e.g., Ekdale and Bromley, geochemical, magnetostratigraphical and biostratigraphical analy- ses (see Alegret, 2007 for a recent review). In this exhaustive research, however, detailed ichnological analysis has been only recently initiated (Rodríguez-Tovar et al., 2010). In this paper we ⁎ Corresponding author. Tel.: +34 958 242724; fax: +34 958 248528. present the ichnological analysis of two of the best-preserved K/Pg E-mail addresses: [email protected] (F.J. Rodríguez-Tovar), [email protected] (A. Uchman), [email protected] (X. Orue-Etxebarria), boundary sections, Bidart, in SW France, and Sopelana, in N Spain [email protected] (E. Apellaniz), [email protected] (J.I. Baceta). (Figs. 1 and 2). Their ichnological features have been investigated in 0037-0738/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2010.11.004 F.J. Rodríguez-Tovar et al. / Sedimentary Geology 234 (2011) 42–55 43 Fig. 1. A) Paleogeographic map of the Pyrenean Basin, with location of Bidart, Sopelana and Zumaia sections. B) Schematic lithologic logs of the Bidart and Sopelana sections, including sequence stratigraphic distribution (bottom). Note: The Zumaia section is included for comparison. order to show some biogenic and sedimentary phenomena through 2. Location and setting the K/Pg boundary interval, and to define the similarities and differences between these two sections. The latter aspect is of special The late Cretaceous and Paleogene in the Pyrenees are represented interest, because in deep basins that presumably record homoge- by a wide variety of sedimentary rocks, including continental alluvial neous hemipelagic sediment supply, ichnological features may clastics, shallow marine carbonates and deep-water hemipelagites become a powerful tool to recognize subtle lateral changes in the and turbidites accumulated in a broad E–W elongated embayment sedimentation regime and the palaeoenvironmental conditions at opened into the Bay of Biscay and the North Atlantic (Baceta, 1996; the sea floor. Baceta et al., 2004; Plaziat, 1981; Pujalte et al., 1998). Basinal 44 F.J. Rodríguez-Tovar et al. / Sedimentary Geology 234 (2011) 42–55 Fig. 2. Lithological columns of the Sopelana B and Bidart sections with sample locations and range of trace fossils. hemipelagites and turbidites were deposited in the central part of the The best known K/Pg boundary sections being of the Basque Basin embayment, the so-called Basque Basin (Pujalte et al., 1998), at are located in coastal cliffs between the north of Bilbao and the south depths ranging from 1000 to1500 m (Fig. 1). of Baiona. Up to twelve of these K/Pg sections can be identified, the The late Maastrichtian–earliest Ypresian was a phase or relative Zumaia section being the reference for all of them (see Apellaniz et al., tectonic quiescence, during which turbidite deposition was reduced 1997 for a synthesis). Bidart and Sopelana, the two K/Pg sections and the Basque Basin became dominated by regular alternations of selected for ichnological analysis, are 100 km apart (see Fig. 1 for hemipelagic limestones and marls, usually grouped in bedding correlation with the Zumaia section according the most significant couplets and bundles as representative of precession and short- correlation levels a to e). The Bidart section is located in south- eccentricity climatic cycles (Dinarès-Turell et al., 2003, 2007). western France, in a long beach few kilometres to the north of the F.J. Rodríguez-Tovar et al. / Sedimentary Geology 234 (2011) 42–55 45 Bidart town (43º27′N and 1º35′E), within an upper Cretaceous– of white and reddish bioturbated limestones with thin (2–3 cm) Eocene succession that dips 15–35º to the north. The Sopelana section marlstone interbeds. is located north of Bilbao, in northern limb of the Cretaceous– The Bidart section can be considered, together with the classical Paleogene Byscay Sinclinorium (Fig. 1, 43º23′N and 2º59′W). The Zumaia section (Fig. 1), as one of the most complete land-based K/Pg upper Cretaceous–Paleocene basinal succession of the Sopelana boundary sections exposed in the eastern margin of the Atlantic section is affected by reverse and strike-slip faults, which cause Ocean (Apellaniz et al., 1997; Haslett, 1994; Seyve, 1990), as recently stratigraphic repetitions and the existence of three different K/Pg corroborated by magnetostratigraphic, calcareous nannofossils and boundary outcrops. Two of these sections have been analysed: planktic foraminifera analyses (Galbrun and Gardin, 2004; Gallala et Sopelana A (Sopelana Beach) and Sopelana B (above the cliff) al., 2009). These works reveal a continuous sedimentation across the sections, which in previous papers were labelled, respectively, as K/Pg boundary transition, without any biostratigraphically significant Sopelana III (Apellaniz, 1998) and Sopelana I (Orue-Etxebarria, 1983, hiatus. The planktic foraminifera biozonation (Gallala et al., 2009), 1984, 1985). is as follow: a) at the Upper Maastrichtian, the Abathomphalus mayaroensis Zone is differentiated, b) the Guembelitria cretacea Zone
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