Citation:

odp.proc.sr.113.161.1990

Name: Geochemical studies of the Cretaceous-Tertiary boundary in ODP Holes 113-689B and 113-690C
Published: 1990
License: https://creativecommons.org/licenses/by/3.0/

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Abstract:

In a study of ODP Hole 689B no iridium (Ir) anomaly was found in Sections 1 through 6 of Core 25X or in Core 26X from the top down to section 2, 3-12 cm. The background Ir abundance averaged 11 parts per trillion (ppt) and a clay-enriched region had nearly the same average, 26 ± 12 ppt. If the Cretaceous-Tertiary (K-T) contact is in the region studied, then sedimentation was not continuous, and the K-T boundary was probably either not deposited or it was eroded away.

In a study of Cores 15X and 16X of ODP Hole 690C, an iridium peak with a maximum abundance of 1566 ± 222 ppt was found in Section 4 of Core 15X at 39-40 cm with a half-width of 6.6 cm. Background abundances were ~15 ppt and distinctly higher Ir abundances were observed from 119 cm below to 72 cm above the main peak. The Ir distribution below the main peak is attributed to bioturbation by organisms with burrows extending at least 0.4 m. The Ir distribution above the main peak may be due to the same cause but other explanations may be significant.

There are variable enrichments of clay in the mainly CaCO3 sediment of Core 15X, and the stratigraphically lowest part of the most abundant clay deposits is found (within 2 cm) in the same position as the main Ir peak. The clay deposit, which is estimated to be about 50% of the sediment, extends upward ~19 cm and then slowly decreases to a background level of 10% over 1 m. The degree of homogeneity of the clay-rich interval suggests it was not due to episodic volcanism but may have been due to a decrease of the CaCO3 deposition rate which was possibly triggered by the impact of a large asteroid or comet on the Earth.

Project(s):

Ocean Drilling Program (ODP)

Coverage:

Median Latitude: -64.838500 * Median Longitude: 2.152350 * South-bound Latitude: -65.160000 * West-bound Longitude: 1.204800 * North-bound Latitude: -64.517000 * East-bound Longitude: 3.099900

Date/Time Start: 1987-01-16T08:00:00 * Date/Time End: 1987-01-23T20:30:00

Event(s):

113-689B * Latitude: -64.517000 * Longitude: 3.099900 * Date/Time Start: 1987-01-16T08:00:00 * Date/Time End: 1987-01-18T06:45:00 * Elevation: -2091.0 m * Penetration: 297.3 m * Recovery: 229.45 m * Location: South Atlantic Ocean * Campaign: * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 33 cores; 297.3 m cored; 0 m drilled; 77.2 % recovery

113-690C * Latitude: -65.160000 * Longitude: 1.204800 * Date/Time Start: 1987-01-21T07:00:00 * Date/Time End: 1987-01-23T20:30:00 * Elevation: -2925.0 m * Penetration: 321.2 m * Recovery: 177.19 m * Location: South Atlantic Ocean * Campaign: * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 23 cores; 200.6 m cored; 0 m drilled; 88.3 % recovery

License:

Creative Commons Attribution 3.0 Unported (CC-BY-3.0)

Size:

4 datasets

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Datasets listed in this publication series

Michel, HV; Asaro, F; Alvarez, W et al. (1990): (Table 3) Abundances of elements other than iridium in selected parts of the K-T region of ODP Hole 113-689B. https://doi.org/10.1594/PANGAEA.754255
Michel, HV; Asaro, F; Alvarez, W et al. (1990): (Table 1) Background iridium abundances in K-T region of ODP Hole 113-689B. https://doi.org/10.1594/PANGAEA.754253
Michel, HV; Asaro, F; Alvarez, W et al. (1990): (Table 6) Abundances of elements in the K-T region of ODP Hole 113-690C. https://doi.org/10.1594/PANGAEA.754256
Michel, HV; Asaro, F; Alvarez, W et al. (1990): (Table 4) Background iridium abundances in K-T region of ODP Hole 113-690C. https://doi.org/10.1594/PANGAEA.754254