Dinosaurs, spherules, and the “magic” layer: A new K-T boundary clay site in Wyoming

Bohor, B. F.; Triplehorn, Don M.; Nichols, Douglas J.; Millard, H.T.

doi:10.1130/0091-7613(1987)15<896:dsatml>2.0.co;2

Cited by 96 publications

(41 citation statements)

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“…Note: References: 1-Lerbekmo et al (1987); 2-Lerbekmo et al (1996); 3-Sweet et al (1999); 4-Sweet and Braman (2001); 5-Sweet and Braman (1992); 6-Eberth and O'Connell (1995); 7-Therrien et al(2007); 8-Hildebrand and Boynton (1988); 9-Bohor and Izett (1986); 10-Bohor et al (1987a); 11-Bohor et al (1987b); 12-Grieve and Alexopoulos (1988); 13-Lerbekmo and Coulter (1984); 14-McIver and Basinger (1993); 15-Belcher et al (2003); 16-Nichols et al (1986); 17-Kamo and Krogh (1995); 18-Sweet and Cameron (1991).…”

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confidence: 96%

A paleoclimatic and paleoatmospheric record from peatlands accumulating during the Cretaceous-Paleogene boundary event, Western Interior Basin, Canada

Jerrett

Price

Grimes

et al. 2015

Geological Society of America Bulletin

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Petrological and δ 13 C analyses were under taken on contiguous specimens of coal and intercalated minor organicrich clastic sedi ments collected from coal seams spanning the CretaceousPaleogene boundary in the Alberta and Saskatchewan portions of the Western Interior Basin. The generally high smectite content of the coal suggests that the original mires were largely small, discon nected, and rheotrophic, readily receiving abundant waterborne detrital clastic mate rial of largely volcanic origin. Nevertheless, using the distinctive claystone that marks the CretaceousPaleogene boundary as a regional datum , it is possible to correlate cycles in the vitrinite and inertinite compo sition of the coals over >500 km. Estimates of peat accumulation rates suggest that the cycles in vitrinite and inertinite composi tion represent regional, cyclic fluctuations in wildfire and oxi da tion of the peatlands and overlying canopy at a frequency of hundreds to thousands of years. The likely causes of these fluctuations were cyclic, regionalscale changes in temperature. The Cretaceous Paleogene boundary event occurred early during a phase of gradually increasing tem perature and/or decreasing rainfall, but peak wildfire and desiccation of peat occurred up to 14,000 yr later than the Cretaceous Paleogene boundary, and the mires did not experience significant water stress in the im mediate aftermath of the extinction event. A persistent, 1.5‰-3.0‰ negative δ 13 C excur sion occurs across the CretaceousPaleogene boundary, but it cannot be readily separated from four, further negative excursions later in the earliest Danian. The negative carbon isotope excursion linked to the Cretaceous Paleogene boundary began a few hundred years before the event itself, and recovery occurred within 21 k.y., and possibly in as little as just a few thousand years, consistent with recently calibrated shallowmarine δ 13 C records. Hence, the atmospheric and surface ocean carbon pools were coupled at this time. The absence of evidence for catastrophic change in the climatic regime at the time of the CretaceousPaleogene extinction in these mires supports the notion that the negative shift in atmospheric δ 13 C was brought about by changes in the δ 13 C composition of the sur face ocean. This is consistent with the greater magnitude of extinction experienced by ma rine fauna relative to the terrestrial realm.

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confidence: 96%

A paleoclimatic and paleoatmospheric record from peatlands accumulating during the Cretaceous-Paleogene boundary event, Western Interior Basin, Canada

Jerrett

Price

Grimes

et al. 2015

Geological Society of America Bulletin

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“…Proteacidites, disappears abruptly at this horizon (this same genus has been reported from Tertiary rocks in other parts of North America), while most other floral taxa continue with little change into the Tertiary (Tschudy and Tschudy, 1986). In Wyoming, Bohor et al (1987b) report a fern spore spike in the claystone immediately below the impct layer, with a dominance of angiosperm pollen immediately above the layer. According to Izett's (1987) interpretation of the microstratigraphy of the nonmarine boundary clays, this implies that fern dominance preceeded the impact event at this site.…”

Section: Discussionmentioning

confidence: 99%

“…Unfortunately, many of the K/T boundary sites in the western interior do not allow a direct test of the synchronicity between termination of the dinosaurs and the impact layer. Only in Wyoming and Canada, where dinosaur bones have been found 1 to 4 m below the impact layer (Bohor et al, 1987b;Lerbekmo et al, 1987), and 'unreworked' dinosaur teeth 1.3 m above the Ir anomaly (Sloan et al, 1986) can evidence for and against synchronicity be cited. Outside of North America, evidence for synchronous extinctions of the dinosaurs seems to be lacking (references cited in Sloan et aI., 1986).…”

Section: Discussionmentioning

confidence: 99%

“…This thin shocked layer also appears to correspond to the peak in Ir concentrations in the U.S. nonmarine K/T boundary sections (Pillmore and Flores, 1987;Bohor et al, 1987b). The shocked layer, along with the underlying kaolinitic bed, also correlates with the sudden disappearance of the morphologically exotic pollen genera Aquilapollenites and Proteacidites in western North America, and has been associated with a 'spike' in fern spore abundance, considered as diagnostic a recolonization following ecological catastrophy Nichols et al, 1986).…”

Section: Shocked Quartz and Feldsparmentioning

confidence: 99%

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A critical review of the case for, and against, extraterrestrial impact at the K/T boundary

Cisowski

1990

Surv Geophys

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The discovery of an excess of Ir and other noble metals in approximately chondritic proportions at numerous sites, synchronous with the Cretaceous/Tertiary (K/T) boundary, provided hard evidence for earlier suggestions that extraterrestrial events may have coincided with many global geologic boundaries. Further support for the impact hypothesis arose from the identification of abundant microspherules and shocked quartz in K/T boundary marine and nonmarine deposits, respectively, and the discovery of an apparent periodicity in the megaextinction event record. However continuing doubts about the impact origin of the K/T spherical forms and associated geochemical anomalies, uncertainty about the range and extent of the shocked quartz distribution, and the lack of a large, suitably-aged crater, has led to an alternative hypothesis calling upon purely endogenic processes to account for the boundary layer phenomena. Advocates of this opposing theory generally call upon large scale, possibly periodic injection of mantle material directly into the lithosphere. While a number of arguments can be made from the existing data base for and against both competing theories, other evidence suggests that additional phenomena, including sudden changes in the physical and chemical conditions of the oceans, natural combustion on a global scale, and/or widespread sediment-contaminated volcanism, may have contributed to the dramatic transition recorded in the K/T boundary rock record.

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“…According to Johnson and Melosh (2012b), these spherical particles are most likely to be found within 4000 km of the impact site, and to be chemically related to the target material, and not to the impactor. Such materials are reported across North America as Type 1 spherules (Bohor et al, 1987), sometimes referred to as microtektites. Since these spherules are not global, they likely were not as relevant to climate as the Type 2 spherules.…”

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confidence: 99%

Designing global climate and atmospheric chemistry simulations for 1 and 10 km diameter asteroid impacts using the properties of ejecta from the K-Pg impact

2016

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Dinosaurs, spherules, and the “magic” layer: A new K-T boundary clay site in Wyoming

Cited by 96 publications

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A paleoclimatic and paleoatmospheric record from peatlands accumulating during the Cretaceous-Paleogene boundary event, Western Interior Basin, Canada

A paleoclimatic and paleoatmospheric record from peatlands accumulating during the Cretaceous-Paleogene boundary event, Western Interior Basin, Canada

A critical review of the case for, and against, extraterrestrial impact at the K/T boundary

Designing global climate and atmospheric chemistry simulations for 1 and 10 km diameter asteroid impacts using the properties of ejecta from the K-Pg impact

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Dinosaurs, spherules, and the “magic” layer: A new K-T boundary clay site in Wyoming

Cited by 96 publications

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A paleoclimatic and paleoatmospheric record from peatlands accumulating during the Cretaceous-Paleogene boundary event, Western Interior Basin, Canada

A paleoclimatic and paleoatmospheric record from peatlands accumulating during the Cretaceous-Paleogene boundary event, Western Interior Basin, Canada

A critical review of the case for, and against, extraterrestrial impact at the K/T boundary

Designing global climate and atmospheric chemistry simulations for 1 and 10 km diameter asteroid impacts using the properties of ejecta from the K-Pg impact

Contact Info

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Designing global climate and atmospheric chemistry simulations for 1 and 10 km diameter asteroid impacts using the properties of ejecta from the K-Pg impact