Geochemical and isotopic characterization of trace fossil infillings: New insights on tracemaker activity after the K/Pg impact event
Introduction
The Cretaceous–Paleogene (K/Pg) boundary, recently dated as ≈ 66.04 Ma ago (Husson et al., 2014, Vandenberghe et al., 2012), is associated with the second most relevant mass extinction taking place during the Phanerozoic, with 40% of genus extinction (Bambach, 2006) and the disappearance of about 70% of the marine and continental species existing at this time (D'Hondt, 2005). Currently, the hypothesis of an extraterrestrial impact (Alvarez et al., 1980, Smit and Hertogen, 1980) causing the end-Cretaceous mass extinction is widely accepted (Molina, 2015, Schulte et al., 2010). The synchronicity of the Chicxulub impact and the mass extinction at the K/Pg boundary has also been widely demonstrated (e.g., Pälike, 2013, Renne et al., 2013 and references therein).
Over recent decades numerous literature on this topic has provided details about the impact site on the Yucatan peninsula in Mexico (Hildebrand et al., 1991); the size of the meteorite, around 10 ± 4 km in diameter (Donaldson and Hildebrand, 2001, Kyte and Wasson, 1982); its nature, of carbonaceous chondritic type CM or CO (Goderis et al., 2013, Kyte, 1998, Shukolyukov and Lugmair, 1998); and the amount and nature of debris ejected to the atmosphere that led to major environmental perturbations (Kring, 2007 and reference therein).
The impact event also resulted in geochemical anomalies worldwide, recognized both in marine and continental depositional environments. The extraterrestrial effects are particularly evident in marine distal sections, located further than 7000 km from the Chicxulub crater (Smit, 1999). In these sections, trace metals of extraterrestrial origin show higher concentrations than in proximal and intermediate sections, wherein the extraterrestrial contribution is highly diluted by target rocks (Berndt et al., 2011, Martínez-Ruiz et al., 2001).
Major environmental perturbations (i.e., nitric and sulfuric acid rain, widespread dust and blackout, destruction of the stratospheric ozone layer, greenhouse effect, temperature increase), followed the K/Pg event (Alegret and Thomas, 2005, Peryt et al., 2002). Diverse geochemical redox proxies, commonly used to reconstruct paleo-oxygen conditions (e.g., Calvert and Pedersen, 2007, Tribovillard et al., 2006), indicate anoxic conditions across the K/Pg boundary transition, mostly promoted by the enhanced contribution of metals to the basins (extraterrestrial contamination and terrestrial elements derived from increasing chemical alteration in emerged areas), as well as a higher input of both terrestrial and marine organic material. An abrupt spike in biomarkers such as dibenzofuran, biphenyl and cadalene evidences the increasing input of terrestrial organic material (Mizukami, Kaiho, & Oba, 2014).
The biotic response to the K/Pg impact event, including the post-event recovery, is still a matter of debate. Several contradictory hypotheses postulate the effects on planktonic vs. benthic organisms, K- vs. r-strategists, or deposit vs. suspension feeders (Labandeira et al., 2015, Molina, 2015, Powell and MacGregor, 2011, Schulte et al., 2010). In the past decade, relevant information has been provided by ichnological data. The trace fossil analysis of K/Pg boundary sections reveals a minor impact of K/Pg environmental changes on the deep-sea macrobenthic tracemaker community, as well as its rapid recovery (Monaco et al., 2015, Rodríguez Tovar et al., 2004, Rodríguez Tovar et al., 2006, Rodríguez-Tovar et al., 2011, Rodríguez-Tovar, 2005, Rodríguez-Tovar and Uchman, 2006, Rodríguez-Tovar and Uchman, 2008). As pointed out by Sosa-Montes de Oca, Martínez-Ruiz, and Rodríguez-Tovar (2013), this unusual biotic recovery could be explained by a rapid response (some few hundred years) of bottom water oxygenation that reestablished shortly after the K/Pg event. Ichnological analyses furthermore revealed the importance of the bioturbational redistribution by tracemakers, which may have affected original signatures and therefore should be considered so as to prevent possible misinterpretations (Kędzierski et al., 2011, Rodríguez-Tovar et al., 2010).
In order to evaluate and corroborate the hypothesis of the rapid recovery of the macrobenthic tracemaker community and the bioturbational disturbance, further analyses have been performed. In particular, geochemical and isotopic analyses of the K/Pg boundary deposits at the Caravaca section (southeast of Spain) included the infilling material of trace fossils as well as the upper Maastrichtian and lower Danian host rocks.
Section snippets
Geological setting and the study section
The K/Pg boundary section at Caravaca (38°04′36.39″N, 1°52′41.45″W) is located on the NW side of road C-336, in the Barranco del Gredero, about 4 km southwest of the town of Caravaca (Murcia, Spain) (Fig. 1). It belongs to the Jorquera Formation (lower Maastrichtian-lower Eocene), around 225 m-thick, which consists of intercalated marls, marly limestones and occasional turbidites. Geologically, this outcrop belongs to the External Subbetic of the Betic Cordillera, corresponding to a
Materials and methods
For this study we selected a 11-cm-thick interval, involving Maastrichtian materials from 8.0-cm below the K/Pg boundary, and Danian rocks to 3.0-cm above the boundary. According to the sedimentation rate of 3.1 cm kyr−1 estimated for the Maastrichtian deposits, and of 0.8 cm kyr−1 calculated for the boundary clay layer (Kaiho et al., 1999), the studied transition would span a time interval of around 6330 years —from 2580 years prior to the K/Pg boundary to 3750 years afterward. Deposition of
Geochemical analysis
Geochemical data are presented in Table 1. The normalized concentrations of Cr, Co and Ni are plotted in Fig. 2, in which the diverse sedimentary intervals are marked: i) the ejecta layer (CA K–Pg) (data from Sosa-Montes de Oca et al., 2013), ii) the host rock from the lower Paleogene, at 2.8–3.0-cm above the K/Pg boundary (previous data from Sosa-Montes de Oca et al., 2013), iii) the infilling material of several trace fossils analyzed, and iv) the Cretaceous deposits hosting trace fossils (
Discussion
As previously indicated, numerous paleontolological studies have been conducted on the K/Pg boundary at the Caravaca section in order to evaluate the effect of the K/Pg boundary event on the biota, in particular on the micropaleontological assemblages. Micropaleontological studies involving planktonic (i.e., Arenillas and Molina, 1997, Arz et al., 2000, Canudo et al., 1991, Kaiho and Lamolda, 1999, Molina et al., 1998, Molina et al., 2001, Smit, 1990) and benthic foraminifera (Coccioni et al.,
Conclusions
Geochemical and isotopic analyses conducted on the Cretaceous–Paleogene boundary transition at the Caravaca section have provided significant information on the macrobenthic tracemaker activity after the K/Pg boundary event.
In particular, the Cr/Al, Co/Al and Ni/Al ratios from the infilling of trace fossils are higher than those of the upper Maastrichtian and lower Danian deposits, but lower than those corresponding to the ejecta layer, indicating a mixture of the sedimentary material due to
Acknowledgments
This research was funded through Project CGL2012-33281 and CGL2012-32659 (Secretaría de Estado de I + D + I, Spain), Project RNM-05212 and Research Group RNM-178 and RNM-179 (Junta de Andalucía) and FEDER funds. The research of Sosa-Montes de Oca was supported by a pre-doctoral grant (BES-2013-064406) by MINECO. We are likewise grateful to E. Holanda for laboratory assistance. Analyses were performed at the Centre for Scientific Instrumentation (CIC), University of Granada (Spain).
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Calcareous microfossils and paleoenvironmental changes across the Cretaceous-Paleogene (K-Pg) boundary at the Cerro Azul Section, Neuquén Basin, Argentina
2021, Palaeogeography, Palaeoclimatology, PalaeoecologyCitation Excerpt :Rb is assumed to mainly replace K in the structure of clay minerals (Calvert and Pedersen, 2007) and, therefore, is used to normalize Cr and Co counts for terrigenous influx. Meanwhile, Cr and Co are moderate siderophile elements (Goderis et al., 2013) with reported increased abundances in K-Pg ejecta layers related to the end-Cretaceous asteroid impact (Goderis et al., 2013; Açikalin et al., 2015; Oca et al., 2015). The Cerro Azul Section records diverse and well-preserved calcareous microfossil assemblages.