The Cretaceous/Paleogene Boundary Deposits on Gorgonilla Island   

Hermann Darío BERMÚDEZ, Ignacio ARENILLAS, José Antonio ARZ, Vivi VAJDA, Paul R. RENNE, Vicente GILABERT, and José Vicente RODRÍGUEZ

https://doi.org/10.32685/pub.esp.37.2019.01

Citation is suggested as: 

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 Geológico Colombiano, Publicaciones Geológicas Especiales 37, p. 1–19. Bogotá. https://doi.org/10.32685/pub.esp.37.2019.01​

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Abstract 

A ca. 20 mm thick spherule bed representing Chicxulub impact ejecta deposits and marking the Cretaceous/Paleogene (K/Pg) boundary was recently discovered on Gorgonilla Island (Gorgona National Natural Park, Pacific of Colombia). This discovery represents the first confirmed record of the K/Pg event in Colombia, South America, and the eastern Pacific Ocean. The deposit consists of extraordinarily well–preserved glass spherules (microtektites and microkrystites) reaching 1.1 mm in diameter. Importantly, the Gorgonilla spherule bed is unique relative to other K/Pg boundary sites in that up to 90% of the spherules are intact and not devitrified, and the bed is virtually devoid of lithic fragments and microfossils. The spherules were deposited in a deep marine environment, possibly below the calcite compensation depth. The preservation, normal size–gradation, presence of fine textures within the spherules, and absence of bioturbation or traction transport indicate that the Gorgonilla spherules settled within a water column with minimal disturbance. The spherule bed may represent one of the first parautochthonous primary deposits of the Chicxulub impact known to date. ⁴⁰Ar/³⁹Ar dating and micropaleontological analysis reveal that the Gorgonilla spherule bed resulted from the Chicxulub impact. Intense soft–sediment deformation and bed disruption in Maastrichtian sediments of the Gorgonilla Island K/Pg section provide evidence for seismic activity triggered by the Chicxulub bolide impact, 66 million years ago. It is also notable that the basal deposits of the Danian in the Colombian locality present the first evidence of a recovery vegetation, characterized by ferns from a tropical habitat, shortly following the end–Cretaceous event.

Keywords: K/Pg boundary, Chicxulub, microtektites, seismites, Gorgonilla Island, Colombia.

Resumen

Una capa de aproximadamente 20 mm de espesor con depósitos de eyecta del impacto de Chicxulub, que marca el límite Cretácico–Paleógeno (K/Pg), fue recientemente descubierta en la isla Gorgonilla (Parque Nacional Natural Gorgona, Pacífico colombiano). 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 (microtectitas y microcristitas) de hasta 1,1 mm de diámetro extraordinariamente bien preservadas. 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 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 representar uno de los primeros depósitos paraautóctonos primarios del impacto de Chicxulub conocidos hasta el momento. Dataciones ⁴⁰Ar/³⁹Ar y resultados de análisis micropaleontológicos 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.

Abbreviations 

SEM                   Scanning electron microscope 

CCD                   Carbonate compensation depth 

K/Pg                 Cretaceous/Paleogene

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