Volume 3 Quaternary Chapter 1 Neogene https://doi.org/10.32685/pub.esp.37.2019.01 The Cretaceous/Paleogene Boundary Deposits Published online 11 October 2019 on Gorgonilla Island Paleogene Hermann Darío BERMÚDEZ1* , Ignacio ARENILLAS2 , José Antonio ARZ3 , Vivi VAJDA4 , Paul R. RENNE5 , Vicente GILABERT6 , and José Vicente RODRÍGUEZ7 1 [email protected] Grupo de Investigación Paleoexplorer Abstract A ca. 20 mm thick spherule bed representing Chicxulub impact ejecta deposits 4690 W. Eldorado parkway, apt 1016, McKinney, Texas Cretaceous and marking the Cretaceous/Paleogene (K/Pg) boundary was recently discovered on 75070 USA Gorgonilla Island (Gorgona National Natural Park, Pacific of Colombia). This discovery 2 [email protected] Universidad de Zaragoza represents the first confirmed record of the K/Pg event in Colombia, South America, Instituto Universitario de Ciencias and the eastern Pacific Ocean. The deposit consists of extraordinarily well–preserved Ambientales de Aragón Departamento de Ciencias de la Tierra glass spherules (microtektites and microkrystites) reaching 1.1 mm in diameter. Impor- E–50009 Zaragoza, Spain Jurassic tantly, the Gorgonilla spherule bed is unique relative to other K/Pg boundary sites in 3 [email protected] Universidad de Zaragoza that up to 90% of the spherules are intact and not devitrified, and the bed is virtually Instituto Universitario de Ciencias devoid of lithic fragments and microfossils. The spherules were deposited in a deep Ambientales de Aragón Departamento de Ciencias de la Tierra E–50009 Zaragoza, Spain marine environment, possibly below the calcite compensation depth. The preservation, Triassic normal size–gradation, presence of fine textures within the spherules, and absence of 4 [email protected] Swedish Museum of Natural History bioturbation or traction transport indicate that the Gorgonilla spherules settled within Departament of Palaeobiology a water column with minimal disturbance. The spherule bed may represent one of Stockholm, Sweden 5 [email protected] the first parautochthonous primary deposits of the Chicxulub impact known to date. Berkeley Geochronology Center (BGC) 40Ar/39Ar dating and micropaleontological analysis reveal that the Gorgonilla spherule 2455 Ridge Road, Berkeley, CA 94709, USA Permian University of California, Berkeley bed resulted from the Chicxulub impact. Intense soft–sediment deformation and bed Department of Earth and Planetary Science disruption in Maastrichtian sediments of the Gorgonilla Island K/Pg section provide Berkeley, CA, 94720, USA 6 [email protected] evidence for seismic activity triggered by the Chicxulub bolide impact, 66 million years Universidad de Zaragoza Departamento de Ciencias de la Tierra ago. It is also notable that the basal deposits of the Danian in the Colombian locality E–50009 Zaragoza, Spain Carboniferous present the first evidence of a recovery vegetation, characterized by ferns from a trop- 7 [email protected] ical habitat, shortly following the end–Cretaceous event. 4690 W. Eldorado parkway, apt 1016, McKinney, TX, 75070 Keywords: K/Pg boundary, Chicxulub, microtektites, seismites, Gorgonilla Island, Colombia. * Corresponding author Resumen Una capa de aproximadamente 20 mm de espesor con depósitos de eyecta del Devonian impacto de Chicxulub, que marca el límite Cretácico–Paleógeno (K/Pg), fue recientemen- te descubierta en la isla Gorgonilla (Parque Nacional Natural Gorgona, Pacífico colombia- no). Este es el primer registro confirmado del evento K/Pg en Colombia, Suramérica y el Pacífico oriental. El depósito consiste en una acumulación de esferulitas de vidrio (mi- Silurian crotectitas y microcristitas) de hasta 1,1 mm de diámetro extraordinariamente bien pre- servadas. La capa de esferulitas de Gorgonilla es única entre los depósitos conocidos de eyecta de Chicxulub; hasta un 90 % de las esférulas está aún completamente vitrificadas y la capa está prácticamente desprovista de líticos o microfósiles. Las esferulitas fueron depositadas en un paleoambiente marino de aguas profundas, posiblemente por debajo Ordovician Citation: Bermúdez, H.D., Arenillas, I., Arz, J.A., Vajda, V., Renne, P.R., Gilabert, V. & Rodríguez, J.V. 2019. The Cretaceous/Paleogene boundary deposits on Gorgonilla Island. In: Gómez, J. & Mateus–Zabala, D. (editors), The Geology of Colombia, Volume 3 Paleogene – Neogene. Servicio Cambrian Geológico Colombiano, Publicaciones Geológicas Especiales 37, p. 1–19. Bogotá. https://doi. org/10.32685/pub.esp.37.2019.01 1 Proterozoic BERMÚDEZ et al. del nivel de compensación de la calcita. La preservación, gradación normal, presencia de estructuras delicadas dentro de las esférulas y ausencia de evidencias de bioturbación o de transporte indican que la capa de esferulitas de Gorgonilla se asentó a través de la columna de agua con mínima perturbación subsecuente. Esta capa puede represen- tar uno de los primeros depósitos paraautóctonos primarios del impacto de Chicxulub conocidos hasta el momento. Dataciones 40Ar/39Ar y resultados de análisis micropaleon- tológicos muestran que la capa de esférulas de Gorgonilla fue producida por el impacto del asteroide que formó el cráter de Chicxulub. Adicionalmente, la intensa deformación sinsedimentaria y la perturbación de las capas del Maastrichtiano en la sección K/ Pg de la isla Gorgonilla proporcionan evidencia de la actividad sísmica producida por el impacto de Chicxulub hace 66 millones de años. Es también notable que las capas basales del Daniano en la localidad colombiana muestran las primeras evidencias de la recuperación de la vegetación, representada por helechos de un hábitat tropical, justo después del evento del fin del Cretácico. Palabras clave: límite K/Pg, Chicxulub, microtectitas, sismitas, isla Gorgonilla, Colombia. 1. Introduction and Gertsch et al. (2013) concluded that there is no evidence supporting the impact origin of those spherules. The breccia The Cretaceous/Paleogene (K/Pg) boundary marks one of the unit, interpreted as a tsunamite, is composed of intraformational five major mass extinctions in Earth’s history and has long lime– and marlstone clasts but also contains bones, phosphatic been associated with the Chicxulub impact in the Yucatán Pen- lumps, phosphatized foraminifera, glauconite, and small pyrite insula, 66 million years ago (Alvarez et al., 1980; Hildebrand concretions, which indicate reworking and erosion from near– et al., 1991; Pope et al., 1991; Schulte et al., 2010). However, shore areas (Stinnesbeck & Keller, 1996). Gertsch et al. (2013) some authors question this vast evidence, suggesting that the suggested that this unit represented a gravity flow formed Chicxulub impact predated the K/Pg boundary by several hun- during the latest Maastrichtian lowstand. dred thousand years and that it was not responsible for the K/ A new pristine K/Pg section has been discovered on Gor- Pg mass extinction (Keller, 2011; Keller et al., 2001, 2003a, gonilla Island, in the Pacific of Colombia (Bermúdez et al., 2003b; Stinnesbeck et al., 1997, 2002). 2016). Although most of the glass spherules formed during the Ejecta deposits containing melt droplets in the form of tiny Chicxulub impact are now devitrified and have been altered to glass spherules, with a similar chemical composition as the secondary clay minerals, such as smectite, the spherules from glass from the Yucatán impact breccia, have been document- Gorgonilla Island are virtually unaltered and represent the most ed throughout Central and North America and the Caribbean pristine K/Pg boundary spherules known to date. This unique (Keller et al., 2013; Norris et al., 1999; Ocampo et al., 1996; boundary section is the first confirmed record of this event in Olsson et al., 1997; Schulte et al., 2010; Smit et al., 1992; Colombia, South America, and the eastern Pacific Ocean and Wigforss–Lange et al., 2007). However, in South America, K/ it has been studied with respect to stratigraphy, sedimentol- Pg boundary sections are exceedingly rare, and only two sec- ogy, mineralogy, chemistry, micropaleontology, palynology, tions have been formally associated with the Chicxulub impact and 40Ar/39Ar geochronology (Renne et al., 2018). The present event. In the Neuquén Basin, Argentina, Scasso et al. (2005) paper is a summary of an international interdisciplinary re- described a coarse–grained sandstone bed, which occurs in a search project, still in progress, and condenses the information homogeneous shallow shelf mudstone sequence. The authors available to date. suggested that this siliciclastic unit represents a tsunami depos- it, triggered by the Chicxulub impact. In a subsequent analysis 1.1. Location and Geological Setting from the same section, however, Keller et al. (2007) suggested that the deposition of the sandstone occurred 500 ky after the The Gorgonilla Island K/Pg section (2º 56’ N, 78º 12’ W) is K/Pg hiatus and is unrelated to the Chicxulub impact. At Poty located in Gorgona National Natural Park, south of the Playa quarry, Pernambuco, Northeast Brazil, Albertão & Martins del Amor, SW coast of Gorgonilla Island, approximately 35 (1996) described a shallow–marine marl and limestone suc- kilometers off the Colombian Pacific coast (Figure 1a). The cession with impact–derived exotic products (microtektite–like island is 0.5 to 1 km in diameter and is located approximately microspherules and shock–metamorphosed quartz), associated 500 m SW of the larger Gorgona Island. Rock units only crop with a possible impact–generated tsunamite. However, subse- out along the coast at both