Guest “Geolithic!” by David Middleton
Impact Crater off the coast of Africa may be linked to Chicxulub
The underwater crater, discovered incidentally in commercial observations of seafloor sediments, is thought to have formed in close resemblance to the famous Cretaceous-Paleogenian collision event.
By Katherine Kornei
September 19, 2022In the world of impact craters, Chicxulub is a celebrity: The 180-kilometer-diameter ape, in the Gulf of Mexico, was created by a cataclysmic asteroid impact in the late Cretaceous that led to the extinction of most dinosaurs. But researchers have now discovered another crater off the coast of Guinea that may be Chicxulub’s cousin. The newly discovered feature, although much smaller, is also about 66 million years old. It’s a strange coincidence and scientists are now wondering if the two colliding structures could be linked. Perhaps Chicxulub and the newly discovered feature – known as the Nadir crater – were formed from the breakup of the parent asteroid or were part of a cluster of collisions, the team suggests. These results are published year Scientific advance.
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The newly discovered Nadir crater appears to have formed around the same time as that cataclysm. Uisdean Nicholson, a sedimentary geologist at Heriot-Watt University in Edinburgh, Scotland, and his colleagues discovered the candidate crater while they were studying observations of the original seafloor sediments. collected for oil and gas exploration. The team discovered the structure about 8 km wide in seismic reflection image data obtained off the coast of West Africa. “It was a pure coincidence,” Nicholson said.
This hypothetical crater was buried about 300 meters under sediment, topped by 900 meters of water, and its appearance suggests it was created by a supersonic impact, Nicholson said. For starters, it has a rounded shape, with a pronounced rim. Second, it contains a small vertex in the middle, a feature Usually occurs in large impact craters. And perhaps most importantly, there is clear evidence of deformed sediments – by faulting and folding – that exist hundreds of meters below what would be the crater. “There are a lot of things that suggest it was an impact,” said Gavin Kennya geochemist at the Swedish Museum of Natural History in Stockholm, who was not involved in the study.
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Paper, Nicholson et al., 2022, well worth reading and the full text is available. The crater was identified in 2d seismic surveys conducted by WesternGeco (1999) and TGS (2017). I see a lot of interesting geology on 3d seismic data every day, mostly related to salt tectonics, but I’ve never seen anything as interesting as a very well photographed impact crater on Figure 1B…
(One) Regional depth map of the Guinea Plateau and Guinea Topography showing the 2D seismic reflectance location and well data used in this study. JS, Jane Seamount; NS, Nadir Seamount; PS, Porter Seamount. The white dashed line shows the NE extent of the discontinuous high-amplitude seismic facies at the Maastrichtian peak interpreted as ejecta and associated tsunami deposits. The northeastern limit of this facies closely corresponds to the break of the Maastrichtian shelf flank at the mainland edge of Guinea Terrace. Inset map showing a paleontological reconstruction of the Atlantic Ocean near the end of the Cretaceous period, ~66 Ma, performed using GPlates software (58). Ch, Chicxulub Crater; Nd, Nadir Crater; Bo, Boltysh Crater. (REMOVE). Area-composited 2D seismic reflectance profiling extending from well GU-2B-1 in the east to the deep Atlantic basin in the west, revealing the structural and stratigraphic features of the Guinea Plateau and the Stratigraphy Guinea. (OLD) North-South seismic profile from the salt basin in the north to the Nadir Sea, south of the Guinea Fault Zone. Data provided by the Republic of Guinea and TGS. (Nicholson et al., 2022)
Figure 2 from the article zoom in on the crater on the TGS line (black rectangle on Figure 1B) and the WesternGeco line. This is a great textbook example of integrating geological and geophysical data…
MATERIALS AND METHODS
The seismic-stratigraphic framework is based on an extensive 2D seismic reflection dataset and three industrial wells drilled in the southeast of the plateau (Figure 1). 2D data is collected and processed by TGS and WesternGeco. Survey NWAAM-17 in Guinea and Guinea Bissau was acquired by TGS in 2017 in Guinea and Guinea Bissau; data was collected in 2017 at water depths between 15 and 4600 meters. Acquisition parameters include a 12 km transmitter length pulled at a depth of 18 m, with 960 hydrophone channels with a group length of 12.5 m and a firing point distance of 25 m, for full data coverage. screen 240 times. Total record length is 14 s with 2 ms sampling rate for all lines. The sound source was a 4310 in3 rig pulled at 8 m and fired every 25 m using the Bigshot control system. Data is processed using pre-stacked time-migration (PSTM) sequencing, with a subset of data processed using pre-stack depth-first migration, providing depth and domain data time. The seismic frequency at the top of the crater is about 45 Hz, and the interval velocity is ~1800 m/s, giving an adjustable thickness (seismic resolution) of about 10 m.
The GWG99 survey in Guinea was purchased by WesternGeco in 1999 at water depths between 150 and 4500 m. Acquisition parameters include a 6 km transmitter length pulled at a depth of 8 m, with 480 hydrophone channels with a group length of 12.5 m and a firing point distance of 25 m, for full data coverage. screen 120 times. Total record length is 10 s with 2 ms sampling rate for all lines. The sound source is a 2000 in3 array pulled at 6 m and fired every 25 m. Data were processed using PSTM sequencing, with a subset of the data reprocessed in 2017 to improve images and reduce multiples and noise. The seismic frequency at the top of the crater is about 45 Hz, and the interval velocity is ~1800 m/s, giving an adjustable thickness (seismic resolution) of about 10 m.
Seismic interpretation was performed using Schlumberger Petrel 2020 software, including horizon mapping, structural composition mapping, velocity analysis, and seismic-well relationships. The petrographic, physical, and biostratigraphic data from exploration wells are used to limit the stratigraphic and petrographic age of seismic reflections. The seismic-well relationship is based on survey photograph surveys, with the relationship further improved by constructing synthetic seismic images using density log data and sound. Reconstruction of the structure of the pre-impact stratigraphy and the shape of the transient crater was performed by seismic flattening of the Top Maastrichtian and KU1 horizons, respectively. On the basis of ~10 m vertical seismic resolution for the top of Nadir Crater, the age uncertainty for individual seismic reflections is estimated to be 0.5 Ma for the Cretaceous upper (700 m thick deposited on 34 Ma = 20 m/Ma, 10/20 = 0.5 Ma) and 0.8 Ma for Paleogene (400 m thick deposited on 32 Ma = 12 m/Ma, 10/12 ,5 = 0.8 Ma).
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Presenter
Kornei, K. (2022), Impact crater off the coast of Africa possibly associated with Chicxulub, Eos, 103, https://doi.org/10.1029/2022EO220454. Published on September 19, 2022.
Nicholson U, Bray VJ, Gulick SPS, Aduomahor B. Nadir Crater off West Africa: A Cretaceous-Paleogenic Impact Structure Candidate. Science Fiction Adv. 2022 August 19; 8 (33): eabn3096. doi: 10.1126 / sciadv.abn3096. Episode 2022 August 17. PMID: 35977017; PMCID: PMC9385158.
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