Visitor “Geology Rocks!” by David Middleton
Impression Crater off the African Coast Could Be Linked to Chicxulub
The underwater crater, noticed serendipitously in business observations of seafloor sediments, is believed to have shaped at roughly the identical time because the well-known Cretaceous-Paleogene impression occasion.
By Katherine Kornei
19 September 2022On the planet of impression craters, Chicxulub is a celeb: The 180-kilometer-diameter maw, within the Gulf of Mexico, was created by a cataclysmic asteroid impression on the finish of the Cretaceous that spelled the demise of most dinosaurs. However researchers have now uncovered one other crater off the coast of Guinea which may effectively be Chicxulub’s cousin. The newly found characteristic, albeit a lot smaller, can be about 66 million years previous. That’s a curious coincidence, and scientists at the moment are questioning whether or not the 2 impression buildings could be linked. Maybe Chicxulub and the newly found characteristic—dubbed Nadir crater—shaped from the breakup of a mother or father asteroid or as a part of an impression cluster, the crew prompt. These outcomes had been revealed in Science Advances.
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The newly found Nadir crater seems to have shaped proper across the identical time as that cataclysm. Uisdean Nicholson, a sedimentary geologist at Heriot-Watt College in Edinburgh, Scotland, and his colleagues found the candidate crater whereas they had been poring over observations of seafloor sediments initially collected for oil and gasoline exploration. The crew noticed the roughly 8-kilometer-wide construction in seismic reflection imaging knowledge obtained off the coast of West Africa. “It was pure serendipity,” mentioned Nicholson.
The putative crater is buried underneath roughly 300 meters of sediments topped by 900 meters of water, and its look strongly suggests it was created by a hypervelocity impression, mentioned Nicholson. For starters, it’s round in form, with a pronounced rim. Second, it incorporates a small central peak, a characteristic that usually arises in massive impression craters. And maybe most necessary, there’s clear proof of deformed sediments—brought on by faulting and folding—persisting a whole bunch of meters under what could be the crater ground. “There’s quite a lot of issues that recommend it’s an impression,” mentioned Gavin Kenny, a geochemist on the Swedish Museum of Pure Historical past in Stockholm who was not concerned within the analysis.
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The paper, Nicholson et al., 2022, is well-worth studying and the complete textual content is obtainable. The crater was recognized on 2nd seismic surveys shot by WesternGeco (1999) and TGS (2017). I see quite a lot of cool geology on 3d seismic knowledge day-after-day, principally associated to salt tectonics., however I’ve by no means seen something as cool because the very well-imaged impression crater on Determine 1B…
(A) Regional bathymetry map of the Guinea Plateau and Guinea Terrace exhibiting location of 2D seismic reflection and effectively knowledge used on this research. JS, Jane Seamount; NS, Nadir Seamount; PS, Porter Seamount. The white dashed line reveals the NE extent of high-amplitude discontinuous seismic facies on the prime Maastrichtian interpreted as ejecta deposits and related tsunami deposits. The north-east restrict of this facies intently corresponds with the Maastrichtian shelf-slope break on the landward margin of the Guinea Terrace. Inset map reveals a paleogeographic reconstruction of the Atlantic close to the tip of the Cretaceous, ~66 Ma in the past, made utilizing GPlates software program (58). Ch, Chicxulub Crater; Nd, Nadir Crater; Bo, Boltysh Crater. (B). Regional composite 2D seismic reflection profile extending from the GU-2B-1 effectively within the east to the deep Atlantic basin within the west, exhibiting the structural and stratigraphic character of the Guinea Plateau and Guinea Terrace. (C) North-South seismic profile from the salt basin within the north to the Nadir Seamount, south of the Guinea Fracture Zone. Knowledge courtesy of the Republic of Guinea and TGS. (Nicholson et al., 2022)
Determine 2 from the paper zooms in on the crater on the TGS line (black rectangle on Determine 1B) and a WesternGeco line. This can be a nice textbook instance of integrating geological and geophysical knowledge…
MATERIALS AND METHODS
The seismic stratigraphic framework is predicated on an in depth 2D seismic reflection dataset and three trade wells drilled on the southeast of the plateau (Fig. 1). The 2D knowledge had been acquired and processed by TGS and WesternGeco. The NWAAM-17 survey in Guinea and Guinea Bissau was acquired in 2017 by TGS in Guinea and Guinea Bissau; knowledge had been acquired in 2017 in water depths of 15 to 4600 meters. Acquisition parameters embody a 12-km streamer size towed at a depth of 18 m, with 960 hydrophone channels of 12.5-m group size and a 25-m shot level spacing, giving a 240 full-fold knowledge protection. Whole document size was 14 s with a 2-ms pattern charge for all traces. The sound supply was one 4310 in3 array towed at 8 m and firing each 25 m utilizing a Bigshot controller system. Knowledge had been processed utilizing a pre-stack time migration (PSTM) sequence, with a subset of knowledge processed utilizing a pre-stack depth migration sequence, offering knowledge in depth and time area. Seismic frequency on the prime of the crater is round 45 Hz, and interval velocity is ~1800 m/s, giving a tuning thickness (seismic decision) of round 10 m.
The GWG99 survey in Guinea was acquired in 1999 by WesternGeco in water depths of 150 to 4500 m. Acquisition parameters embody a 6-km streamer size towed at a depth of 8 m, with 480 hydrophone channels of 12.5-m group size and a 25-m shot level spacing, giving a 120 full-fold knowledge protection. Whole document size was 10 s with a 2-ms pattern charge for all traces. The sound supply was one 2000 in3 array towed at 6 m and firing each 25 m. Knowledge had been processed utilizing a PSTM sequence, with a subset of knowledge reprocessed in 2017 to enhance imaging and cut back multiples and noise. Seismic frequency on the prime of the crater is round 45 Hz, and interval velocity is ~1800 m/s, giving a tuning thickness (seismic decision) of round 10 m.
Seismic interpretation was carried out utilizing Schlumberger Petrel 2020 software program, together with horizon mapping, structural component mapping, velocity evaluation, and seismic-to-well ties. Lithological, petrophysical, and biostratigraphic knowledge from the exploration wells had been used to constrain the stratigraphic age and lithology of seismic reflections. Seismic-to-well ties had been primarily based on checkshot surveys, with the tie additional improved by developing artificial seismograms utilizing sonic and density log knowledge. Structural reconstructions of the preimpact stratigraphy and the geometry of the transient crater had been carried out by seismic flattening of the Prime Maastrichtian and KU1 horizons, respectively. On the premise of a vertical seismic decision of ~10 m for the highest of the Nadir Crater, the age uncertainty for particular person seismic reflections is estimated at 0.5 Ma for the Higher Cretaceous (700 m thick deposited over 34 Ma = 20 m/Ma, 10/20 = 0.5 Ma) and 0.8 Ma for the Paleogene (400 m thick deposited over 32 Ma = 12 m/Ma, 10/12.5 = 0.8 Ma).
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References
Kornei, Ok. (2022), Impression crater off the African coast could also be linked to Chicxulub, Eos, 103, https://doi.org/10.1029/2022EO220454. Revealed on 19 September 2022.
Nicholson U, Bray VJ, Gulick SPS, Aduomahor B. The Nadir Crater offshore West Africa: A candidate Cretaceous-Paleogene impression construction. Sci Adv. 2022 Aug 19;8(33):eabn3096. doi: 10.1126/sciadv.abn3096. Epub 2022 Aug 17. PMID: 35977017; PMCID: PMC9385158.
