Seawater lithium isotope excursion across the K-Pg boundary; Chicxulub Impact vs. Deccan Traps

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Author(s): Misra, Sambuddha; Froelich, Philip N.
Author Affiliation(s): Primary:
University of Cambridge, Department of Earth Sciences, Cambridge, United Kingdom
Froelich Education Services, United States
Volume Title: Goldschmidt 2012 abstract volume
Source: Mineralogical Magazine, 76(6), p.1720; Goldschmidt 2012, Montreal, QC, Canada, June 24-29, 2012. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X CODEN: MNLMBB
Note: In English. 1 refs.
Summary: A 4ppm drop in the 7Li/6Li ratio of seawater (δ7LiSW), from about 29ppm in the Late Cretaceous to 25ppm in the early Paleocene, occurs within less than 0.5 Ma across the Cretaceous-Paleogene boundary (K-PgB, 65.68 Ma). Because δ7LiSW is sensitive to both very large Li-isotope fractionation factors and to changes in silicate sources and sinks on time scales of the Li residence time in seawater (τ Li ∼ 1.2 Ma), this negative excursion must reflect a large and fast influx of 6Li to the ocean, presumably from continental or seafloor silicates, the primary Li-reservoirs in the Earth's crust. It can not be due to rapid addition of isotopically light Li from (a) the Chicxulub bolide itself nor its impact crater, even if pulverized and instantaneously dissolved in the ocean, or from (b) congruent weathering of the simultaneously erupted Deccan Traps Large Igneous Province (δ7LiBasalt ∼3.4ppm). One possibility is that estimates of the volume of Deccan basaltic lavas "missing" in the Geologic Record is an order of magnitude too low. Another possibility is that the conflagration from the Chicxulub impact deforested large portions of the continents and induced rapid acid-rain chemical weathering of incinerated continental soils that then washed into the ocean. In any event, the cause of this large fast δ7LiSW drop across the K-Pg boundary remains enigmatic. The lithium and strontium isotope records were recovered from forams in the same drill cores at ODP sites 1262 and 1267. Osmium isotope data are from Peucker-Ehrenbrink & Ravizza (GTS 2012) DOI: 10.1126/science.1214697
Year of Publication: 2012
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Alkali metals; Asia; Atlantic Ocean; Cenozoic; Chemical composition; Chicxulub Crater; Cretaceous; Deccan Traps; India; Indian Peninsula; Isotope ratios; Isotopes; K-T boundary; Leg 208; Li-7/Li-6; Lithium; Lithostratigraphy; Lower Paleocene; Mesozoic; Metals; Mexico; ODP Site 1262; ODP Site 1267; Ocean Drilling Program; Paleo-oceanography; Paleocene; Paleogene; Sea water; South Atlantic; Stable isotopes; Stratigraphic boundary; Tertiary; Upper Cretaceous; Walvis Ridge; Yucatan Peninsula
Coordinates: S271100 S271100 E0013500 E0013400
S280600 S280600 E0014300 E0014200
Record ID: 2014030944
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland