The Chicxulub ejecta deposit at Demerara Rise (western Atlantic); dissecting the geochemical anomaly using laser ablation-mass spectrometry

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doi: 10.1130/G31599.1
Author(s): Berndt, Jasper; Deutsch, Alexander; Schulte, Peter; Mezger, Klaus
Author Affiliation(s): Primary:
Westfälische Wilhelms-Universität Münster, Institut für Mineralogie, Munster, Germany
Other:
Universität Erlangen, Germany
Volume Title: Geology (Boulder)
Source: Geology (Boulder), 39(3), p.279-282. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0091-7613 CODEN: GLGYBA
Note: In English. With GSA Data Repository Item 2011096. 21 refs.; illus., incl. sketch map
Summary: We analyzed in situ the trace-element distributions in the pristine 2-cm-thick spherule-rich Cretaceous-Paleogene (K-Pg) event bed at Ocean Drilling Program (ODP) Leg 207 Site 1259C (Demerara Rise, western Atlantic) using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) with a spot diameter of 235 µm, corresponding to a sample volume of ∼8.6×105 µm3. Unparalleled so far, this high resolution pinpoints the fallout of the Chicxulub projectile to the uppermost 2 mm of the K-Pg bed. Most of the Ni is not of extraterrestrial origin, as indicated by low, typical upper-crustal Ni/Cr ratios. Very low Zr/Hf and Nb/Ta ratios are confined exclusively to the K-Pg bed, indicating that storms and flooding spilled highly fractionated supracrustal material off the Guiana craton to reach the seafloor contemporaneously with the now-altered glass spherules. Chicxulub ejecta volumetrically dominate the K-Pg bed but contributed only minimally to the trace-element budget, as indicated by the very low rare earth element concentrations. At the top of the ejecta layer, together with the fallout of Pt from the impactor (∼0.1 ppm), a pronounced Pb enrichment (up to 1500 ppm) occurs, which is interpreted to derive from the Guiana craton. Both elements obviously were contained in submicrometer-size particles that could only reach the seafloor attached to larger particles, the sedimentation of which may have occurred up to a year after the Chicxulub impact event. Our high-resolution analysis of the K-Pg event bed allows us, for the first time, to differentiate among the contributing components in detail, as well as assess the settling time frame of this geologically important boundary deposit.
Year of Publication: 2011
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; Cenozoic; Chicxulub Crater; Cretaceous; Demerara Rise; Ejecta; Equatorial Atlantic; Experimental studies; Geochemical anomalies; Geochemistry; High-resolution methods; ICP mass spectra; K-T boundary; Laboratory studies; Laser ablation; Laser methods; Leg 207; Lower Paleocene; Marine sediments; Mass spectra; Mesozoic; North Atlantic; Northwest Atlantic; ODP Site 1259; Ocean Drilling Program; Paleocene; Paleogene; Sediments; Spectra; Stratigraphic boundary; Tertiary; Trace elements; Upper Cretaceous; West Atlantic
Coordinates: N091800 N091800 W0541200 W0541200
Record ID: 2011028211
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