T242 The Geology of Colombia

Wednesday, 7 November 2018
8:00 AM - 12:00 PM
Room 243

BIOTIC RECOVERY FOLLOWING THE END-CRETACEOUS ASTEROID IMPACT RECORDED FROM GORGONILLA ISLAND, COLOMBIA

Paper number: T242-7
Program: Technical Sessions
Time: 9:30 AM – 9:45 AM

Authors

Abstract

A 2 cm thick spherule bed representing Chicxulub impact ejecta depos­its and marking the Cretaceous/Paleogene (K/Pg) boundary was recently discovered on the Gorgonilla Island, Colombia. In this presentation we focus on the biotic signal, extinction and recovery successions in the sedimentary record spanning the spherule bed dated to 66.051 ±0.031 Ma.

Except for very scarce specimens in some levels, planktic foraminifers are absent within and below the spherule bed, suggesting that Maastrichtian succesions were deposited below CCD. The absence also of terrestrially derived pollen and spores indicates off-shore conditions for the Maastrichtian. However, the post-impact deposit, occurring above the spherule layer at Gorgonilla, shows an interesting recovery succession representing both marine and terrestrial assemblages. Planktic foraminifers are also absent in the first 5 cm above the spherule bed, suggesting these sediments were still deposited below the CCD. However, in the following 110 cm planktic foraminifers belonging to the lowermost Danian Zone Pα are preserved, indicating a pronounced deepening of the local CCD.

The vegetation recovery is represented by fern spores, more specifically by ground fern taxa such as Gleicheniaceae and Dictyophyllum, together with abundant occurrence of the aquatic fern Azolla. These interestingly co-occur with fungal spores and hyphae. A so-called fern-spike has previously been described from New Zealand K/Pg boundary clay coincident with the iridi­um-enriched layer and interpreted as a response to short term darkness. The genus Azolla consistently characterizes warm-climate lacus­trine environments and ranges of many Azolla species span the K/Pg boundary at other sites. The identification in Colombia of Azolla microspores and massulae directly above the K/Pg boundary at the Gorgonilla locality shows their potential to endure altered environmental conditions.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-322027

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