The Red Coloration of Goikoetxe Cave's Speleothems (Busturia
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Quaternary International 566-567 (2020) 141–151 Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint The red coloration of Goikoetxe Cave’s speleothems (Busturia, Spain): An indicator of paleoclimatic changes T ∗ V. Martínez-Pilladoa,b, , I. Yustaa, E. Iriartec, A. Álvarod, N. Ortegad, A. Aranburua, J.L. Arsuagab,e a Departamento de Mineralogía y Petrología, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU. Barrio Sarriena s/n, 48940, Leioa, Bizkaia, Spain b Centro Mixto de Evolución y Comportamiento Humanos UCM-ISCIII. Avda. Monforte de Lemos 5, Pabellón 14, 28029, Madrid, Spain c Laboratorio de Evolución Humana, Dpto. de Historia, Geografía y Comunicación, Universidad de Burgos. Plaza Misael Bañuelos s/n, Edificio de I+D+i, 09001, Burgos, Spain d Centro Nacional de Investigación sobre la Evolución Humana (CENIEH). Paseo Sierra de Atapuerca, 3. 09002, Burgos, Spain e Departamento de Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid. C/ José Novais, 12. 28040, Madrid, Spain ARTICLE INFO ABSTRACT Keywords: The most commonly used paleoclimatic proxies in speleothem studies are the carbon and oxygen stable isotopes Speleothem color and the trace elements of calcite. However, assessing the incorporation of other components, such as organic Organic matter matter, may also be of interest in interpreting and reconstructing the climate during speleothem growth. In this Spectroscopy work, the incorporation of humic and fulvic acids derived from overlying soils is proposed as the cause of the red Fluorescence coloration of speleothems from the Goikoetxe Cave (Busturia, Bizkaia). Through the application of petrological studies combined with X-ray fluorescence, UV luminescence, Raman spectroscopy and Fourier-transform in- frared spectroscopy (FTIR) analysis, it has been possible to correlate a variation of organic content in the overlying soils and the red coloration, being this stain a main proxy to study and reconstruct the seasonal paleoclimatic parameters during the speleothem formation. 1. Introduction analyzed, and it is correlated with the petrological characteristics pre- sented by these stalagmites, providing additional information on the Speleothems are one of the main records for establishing paleocli- climatic conditions during their formation. matic and paleoenvironmental sequences during the Quaternary, as their formation may be related to different climatic variables that un- 2. Regional settings dergo changes over time. For its study, the most commonly used proxies are the stable isotopes of carbon and oxygen (eg. Dorale et al., 1998; The Goikoetxe cave, also known as the "Malloku System", is located Genty et al., 2003; Baldini et al., 2008), and the incorporation of trace within the karst of Peña Forua, in the municipality of Busturia elements in the carbonate structure (eg. Treble et al., 2003; Johnson (Bizkaia), within the Urdaibai Biosphere Reserve (Fig. 1A). The Peña et al., 2006; Fairchild et al., 2007; Fairchild and Treble, 2009; Osácar Forua karst is located on the northern flank of the Gernika diapiric et al., 2013). However, studying the incorporation of other components, anticline (Morales-Juberías and Fernández de Valderrama, 2010). It is such as organic matter, may also be of interest in interpreting and re- developed on reef limestones from the Lower Cretaceous (Aptian-Al- constructing the climate (eg. Baker et al., 1996; McGarry and Baker, bian) in the Urgonian facies (Fig. 1B), emerged and deformed during 2000; van Beynen et al., 2001; Blyth et al., 2008). the Alpine orogeny, from the Eocene to the Miocene (García-Mondéjar Despite the fact that iron is generally assigned as the main re- et al., 1985), when the process of karstification began, giving rise to a sponsible of the red color in both geological and archaeological mate- well-defined cone-doline-type landscape (Aranburu et al., 2015). The rials, it has been found that organic matter can be a main source of main entrance to the system is located inside the Goikoetxe barn (from speleothem color (e.g. Caldwell et al., 1982). which the cave takes its name), at a distance of about 6.5 km from the In this work, the cause of the red coloration that characterizes most mouth of the Oka river (Fig. 1B). of the speleothems formed in the Goikoetxe Cave (Busturia, Bizkaia) is The karstic system presents a principal network of galleries along ∗ Corresponding author. Departamento de Mineralogía y Petrología, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU. Barrio Sarriena s/n, 48940, Leioa, Bizkaia, Spain. E-mail address: [email protected] (V. Martínez-Pillado). https://doi.org/10.1016/j.quaint.2020.04.006 Received 31 January 2020; Received in revised form 3 April 2020; Accepted 4 April 2020 Available online 11 April 2020 1040-6182/ © 2020 Elsevier Ltd and INQUA. All rights reserved. V. Martínez-Pillado, et al. Quaternary International 566-567 (2020) 141–151 Fig. 1. A) Peña Forua karst location (red star) within, Bizkaia province (Spain) and the Urdaibai Biosphere Reserve. B) Geological map of the Peña Forua karst area (modified from Aranburu et al., 2015). C) Longitudinal cave profile and location of the Sala Roja (modified from Aranzabal and Maeztu, 2011). D) Malloku System with the three karst levels (modified from Aranburu et al., 2015). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 3400 m with N–S orientation (Fig. 1C). It comprises three subhorizontal fluvial origin mainly at the base (Edeso et al., 2011), and chemical levels (Fig. 1D) of marked phreatic origin that present abrupt changes calcite precipitates (flowstones, stalagmites and stalactites) in the upper in the direction of the galleries due to intense structural control. In the part. The speleothem formation in this chamber occurs through long upper level (at about 80 m asl), which is practically full of sediments, it cracks in the ceiling, causing the alignment of the stalactites and sta- has been possible to explore only a few meters (Aranzabal and Maeztu, lagmites along the cavity (Fig. 2A). 2011). The intermediate level (about 50 m asl) constitutes 80% of the The most distinctive feature of the speleothems in the Sala Roja is karst system, and includes abundant speleothems and terrigenous de- the coexistence of abundant colored formations, from honey to red hues posits of different granulometry. The active level of the karst (at about (Fig. 2A), with some white stalagmites and thin colorless tubular sta- 30 m asl) receives water from the area of recharge, marked by a large lactites. This coloration in the speleothems could be related to the development of drains, as well as non-native water from the siliciclastic presence of cations incorporated during the crystalline growth, al- massifs draining through small water courses that run laterally to the though it could also be due to inclusions of other minerals or to the karst. presence of crystalline defects. Vadillo and Barberá (2011) carried out a The Sala Roja (“Red Chamber”), located on the intermediate karstic study of the chemistry of the dripping water along the second level of floor, presents a sequence of mixed filling formed by gravel and sands of the Goikoetxe cave, collected under stalactites of different colors to look 142 V. Martínez-Pillado, et al. Quaternary International 566-567 (2020) 141–151 Fig. 2. A) General view of the Sala Roja, where reddish speleothem formation is abundant. Note the alignment of red spe- leothems with the fractures in the ceiling. Picture from Grupo Espeleológico ADES. B) General stratigraphic outline of the Sala Roja and relationship between the different endokarstic infillings. Unscaled drawing. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) for a correlation between their colour and the concentration of metals (Fe, Mn and Al) by means of ICP-MS. The results did not show any difference that would allow differentiating the composition of the wa- ters over the red and white stalagmites. Neither the study of dissolved total organic carbon in the dripping water (which varies between 0.68 and 1.38 mg/L over red and 0.38–1.38 mg/L over white speleothems, yielding mean values of 0.94 and 0.9 mg/L respectively) gave results that allowed relating the reddish coloring of some of the speleothems with the inclusion of organic matter from the vegetation cover of the massif (Vadillo and Barberá, 2011). Based on allostratigraphic criteria, at least two growth phases of drip speleothems in this cavity have been determined (Aranburu et al., 2015). The first one was developed over a wide flowstone that went broken and tilted, and where the second speleothem generation grew after its fall (Fig. 2B). Both generations contain red stalagmites, in- dicating that the coloration of these speleothems has been a continuous process over the years and not punctual. 3. Material and methods In order to identify the cause of the characteristic reddish coloration of the Goikoetxe cave stalagmites, and given the existence of white speleothems from the same precipitation phase coexisting with the red ones in the Sala Roja, four stalagmites of different colors belonging to the two speleothem generations have been selected (Moreno, Antuá, Gorri and Zuri, Fig. 3) as well as two small tubular modern stalactites. The Moreno stalagmite, with the most intense red color, was col- lected in situ from the last speleothem generation (Generation II, Fig. 2B). The Antuá stalagmite, with an amberine-reddish color, was collected in situ from the Generation I (Fig. 2B). The Gorri and Zuri stalagmites, with reddish and white colorations respectively, were Fig. 3. Studied stalagmites from the Sala Roja of Goikoetxe's cave to determine found broken and displaced from their original positions, and they are the factors influencing the different colorations.