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- BERMÚDEZ,, Hermann Darío, et al.
(författare)
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The Cretaceous/Paleogene boundary deposits on Gorgonilla Island
- 2018
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Ingår i: The Geology of Colombia: Volume 3 Paleogene – Neogene. - Bogota : Servicio Geológico Colombiano. ; , s. 1-34
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Bokkapitel (refereegranskat)abstract
- A ~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. Thus, 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.
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| 2. |
- Renne, Paul R, et al.
(författare)
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Multi-proxy record of the Chicxulub impact at the Cretaceous-Paleogene boundary from Gorgonilla Island, Colombia
- 2018
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Ingår i: Geology. - Denver : Geological Society of America. - 0091-7613 .- 1943-2682. ; 46, s. 547-550
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Tidskriftsartikel (refereegranskat)abstract
- A 40 m stratigraphic section at Gorgonilla Island, Colombia, provides a unique deepmarine, low-latitude, Southern Hemisphere record of events related to the end-Cretaceous Chicxulub impact and the global Cretaceous/Paleogene boundary (KPB). The KPB is marked by a 20-mm-thick, densely packed spherule bed as defined by planktic foraminifera, in contrast to complex relationships found in high-energy, impact-proximal sites in the Gulf of Mexico and Caribbean basins. The absence of basal Danian foraminiferal Zone P0 may indicate a possible hiatus of <10 ka immediately above the spherule bed, but is most probably an artifact of deposition below the calcite compensation depth as suggested by the nearly complete absence of calcareous fossils for 20 m below the Zone Pα. A weighted mean 40Ar/39Ar age of 66.051 ± 0.031 Ma for 25 fresh glassy spherules unequivocally establishes both their derivation from Chicxulub, and the association between the impact and the KPB. The spherule bed, and Maastrichtian strata below it, display soft-sediment deformation features consistent with strong seismic motion, suggesting that seismic activity in the immediate aftermath of the Chicxulub impact continued for weeks. We discovered a fern-spike immediately above the spherule bed, representing the first record of this pioneer vegetation from the South American continent, and from a low-latitude (tropical) environment.
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