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R Rocchia - One of the best experts on this subject based on the ideXlab platform.
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the stratigraphic distribution of ni rich spinels in cretaceous tertiary Boundary rocks at el kef tunisia caravaca spain and hole 761c leg 122
Earth and Planetary Science Letters, 1991Co-Authors: E Robin, D Boclet, Ph Bonte, L Froget, C Jehanno, R RocchiaAbstract:Abstract Ni-rich spinels have been found throughhout the world at the Cretaceous-Tertiary Boundary. These minerals have no counterparts in terrestrial rocks but have been observed in meteoroid ablation material and impact debris, suggesting that the Cretaceous-Tertiary Boundary spinels result from an extraterrestrial event. Their stratigraphic distribution, which has been observed at the Cretaceous-Tertiary Boundary sites of El Kef (Tunisia), Caravaca (Spain) and Hole 761C (ODP Leg 122, Indian Ocean), are markedly different from site to site and are all much less extended than the Ir anomalies. Regional differences in Ni-rich spinel distibution are entirely explained by a brief event recorded under different bioturbation conditions. The wider stratigraphic dispersion of Ir is attributed to postdepositional chemical processes. At El Kef, the site which appears to be the least affected by bioturbation and which has the highest sedimentation rate, the 1–2 mm thick Ni-rich spinel spike indicates that the deposition time did not exceed an upper limit of 100 years. This upper limit is consistent only with the collision of an asteroid or a comet at the close of the Cretaceous.
Ahmed F A Tmalla - One of the best experts on this subject based on the ideXlab platform.
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stratigraphic position of the cretaceous tertiary Boundary in the northern sirt basin libya
Marine and Petroleum Geology, 1992Co-Authors: Ahmed F A TmallaAbstract:Abstract Biostratigraphic analysis reveals that the contact of the Kalash Limestone with the Hagfa Shale does not coincide with the Cretaceous-Tertiary Boundary as previously used in the subsurface geology of the Sirt Basin. In well A1a-NC29A, in the northern Sirt Basin, the Cretaceous-Tertiary Boundary lies within the uppermost part of the Kalash Limestone. This is based on a study of the foraminiferal assemblages below and above this Boundary. Key species of both planktonic and benthic foraminifera are used to illustrate this conclusion. The local Eoglobigerina minutula Zone is here proposed for the earliest Palaeocene biostratigraphic interval which lies between the Cretaceous-Tertiary Boundary and the Subbotina pseudobulloides Zone.
E Robin - One of the best experts on this subject based on the ideXlab platform.
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the stratigraphic distribution of ni rich spinels in cretaceous tertiary Boundary rocks at el kef tunisia caravaca spain and hole 761c leg 122
Earth and Planetary Science Letters, 1991Co-Authors: E Robin, D Boclet, Ph Bonte, L Froget, C Jehanno, R RocchiaAbstract:Abstract Ni-rich spinels have been found throughhout the world at the Cretaceous-Tertiary Boundary. These minerals have no counterparts in terrestrial rocks but have been observed in meteoroid ablation material and impact debris, suggesting that the Cretaceous-Tertiary Boundary spinels result from an extraterrestrial event. Their stratigraphic distribution, which has been observed at the Cretaceous-Tertiary Boundary sites of El Kef (Tunisia), Caravaca (Spain) and Hole 761C (ODP Leg 122, Indian Ocean), are markedly different from site to site and are all much less extended than the Ir anomalies. Regional differences in Ni-rich spinel distibution are entirely explained by a brief event recorded under different bioturbation conditions. The wider stratigraphic dispersion of Ir is attributed to postdepositional chemical processes. At El Kef, the site which appears to be the least affected by bioturbation and which has the highest sedimentation rate, the 1–2 mm thick Ni-rich spinel spike indicates that the deposition time did not exceed an upper limit of 100 years. This upper limit is consistent only with the collision of an asteroid or a comet at the close of the Cretaceous.
J. D. Macdougall - One of the best experts on this subject based on the ideXlab platform.
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Seawater Sr isotopes at the Cretaceous/Tertiary Boundary
Earth and Planetary Science Letters, 1991Co-Authors: Ellen E Martin, J. D. MacdougallAbstract:Abstract Seawater 87 Sr/ 86 Sr values increase abruptly by 28 × 10 −6 across the Cretaceous/Tertiary Boundary (KTB). This small, but rapid shift is superimposed on the larger scale structure of the seawater Sr isotope curve. The time scale of radiogenic Sr addition appears to be too rapid to reconcile with sources associated with volcanism, and we show that the amount of Sr required to produce even this small increase is too large to be derived from: (1) a KT bolide of the size constrained by the Ir anomaly, (2) continental crust ejecta from the impact of such a bolide, (3) soot from global wildfires initiated by an impact, or (4) any combination of these sources. The probable source of the radiogenic Sr is enhanced continental weathering, but the high rate of increase appears to rule out processes such as sea level regression, glaciation or tectonism. A plausible mechanism for rapid addition of radiogenic Sr to the oceans is enhanced weathering associated with globally distributed acid rain (pH ∼ 1) which is a proposed by-product of a bolide impact [51, EPSL Vol. 83].
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Fine-Scale Structure of the Seawater Strontium Isotope Curve at the Cretaceous/Tertiary Boundary: ABSTRACT
AAPG Bulletin, 1990Co-Authors: E.e. Martin, J. D. MacdougallAbstract:The fine-scale structure of the seawater strontium isotope curve near the Cretaceous/Tertiary Boundary is of particular interest because it may reflect some of the unusual events that occurred at that time. The authors report an attempt to document that record, emphasizing experimental aspects relevant to strontium isotope stratigraphy. They used very small, well-documented samples of hand-picked foraminifera typically containing about 20 ng Sr. Thus, a fragment of one individual can be analyzed for large specimens, or several individuals for smaller ones. This makes it possible to examine each foram using the scanning electron microscope and reject obviously recrystallized samples. Furthermore, each sample represents a specific point in time rather than an average. However, definition of the curve is limited by age determinations and mechanical reworking. Reproducibility of each data point is well within the precision determined from repeat analyses of NBS 987. This was verified by 10 sets of duplicates and 18 intercore comparisons of samples with similar ages. Also, seven individually analyzed forams from one sample yielded a variation around the mean equivalent to the standard uncertainty. Applying this technique, they have found a statistically significant step function increase in {sup 87}Sr/{sup 86}Sr at the Cretaceous/Tertiary Boundary. Recovery frommore » this perturbation was much faster than expected from the residence time of Sr in seawater, suggesting an influx of less radiogenic Sr, possibly from weathering of Cretaceous carbonates.« less
Ph Bonte - One of the best experts on this subject based on the ideXlab platform.
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Formation of spinels in cosmic objects during atmospheric entry: a clue to the Cretaceous-Tertiary Boundary event
Earth and Planetary Science Letters, 1992Co-Authors: Eric Robin, Ph Bonte, L Froget, C Jehanno, Robert RocchiaAbstract:Abstract Magnetic spinels produced by oxidation of extraterrestrial objects in the atmosphere have a composition distinct from terrestrial spinels. They are characterized by a high iron oxidation state, arising from crystallization under high oxygen fugacities, and a high nickel concentration due to the relatively high abundance of this element in extraterrestrial material. The iron oxidation state increases from micrometeorites, to meteoroid ablation material and to impact-generated products. This reflects a progressive increase of the oxygen fugacity, corresponding to decreasing altitudes of crystallization. Spinels found at the Cretaceous-Tertiary Boundary are similar to those that crystallized from meteoroid ablation material and impact-generated products, supporting the view that a collisional event did occur at the end of the Cretaceous.
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the stratigraphic distribution of ni rich spinels in cretaceous tertiary Boundary rocks at el kef tunisia caravaca spain and hole 761c leg 122
Earth and Planetary Science Letters, 1991Co-Authors: E Robin, D Boclet, Ph Bonte, L Froget, C Jehanno, R RocchiaAbstract:Abstract Ni-rich spinels have been found throughhout the world at the Cretaceous-Tertiary Boundary. These minerals have no counterparts in terrestrial rocks but have been observed in meteoroid ablation material and impact debris, suggesting that the Cretaceous-Tertiary Boundary spinels result from an extraterrestrial event. Their stratigraphic distribution, which has been observed at the Cretaceous-Tertiary Boundary sites of El Kef (Tunisia), Caravaca (Spain) and Hole 761C (ODP Leg 122, Indian Ocean), are markedly different from site to site and are all much less extended than the Ir anomalies. Regional differences in Ni-rich spinel distibution are entirely explained by a brief event recorded under different bioturbation conditions. The wider stratigraphic dispersion of Ir is attributed to postdepositional chemical processes. At El Kef, the site which appears to be the least affected by bioturbation and which has the highest sedimentation rate, the 1–2 mm thick Ni-rich spinel spike indicates that the deposition time did not exceed an upper limit of 100 years. This upper limit is consistent only with the collision of an asteroid or a comet at the close of the Cretaceous.