The Cretaceous/Paleogene (K‐Pg) boundary at the J Anomaly Ridge, Newfoundland (IODP Expedition 342, Hole U1403B)

Abstract

We present results of an in‐situ geochemical study using laser‐ablation inductively coupled plasma–mass spectrometry (LA‐ICP‐MS) analyses along a ~4.3 cm long section across the K‐Pg event bed, drilled during IODP Expedition 342 at J Anomaly Ridge south of St. John's, Newfoundland. This section comprises the Maastrichtian with a sharp boundary to the graded, between 1.5 and 1.8 cm thick ejecta layer with totally altered impact glass spherules, which in turn is topped by Danian sediments. The porous and clayey material required elaborate preparation in order to yield reliable data. The ejecta bed shows a highly variable depletion in rare earth elements that even results in strongly subchondritic concentrations. The Ce/Ce* varies strongly (0.81–34), Ni/Cr ranges from 0.38 to 2.79. The maximum platinum group elements (PGE) concentrations are located in one LA‐spot exactly at the basis of the ejecta layer; they amount (in μg g−1) to 0.35 (Rh), 1.64 (Pd), 2.79 (Pt), and 0.86 (Au). The Nb/Ta ratio increases in the Ma from ~10 to 35.9 toward the ejecta horizon, which itself has higher Nb, Ta, Zr, and Hf concentrations than the background sedimentation, combined with low Nb/Ta (~5–10), and low Zr/Hf (~20–30). The overall result is that alteration processes changed totally the original geochemical characteristics of this K‐Pg spherule bed. To explain the exorbitant element mobility at distances of hundreds of μm, we discuss a combination of mostly reducing redox processes and interaction with organic compounds. This study demonstrates the high potential of in‐situ analyses with high spatial resolution at complex geological materials. Moreover, our results indicate that some caution is necessary in determining the projectile type in impactites via PGE ratios.

­The End-Triassic Extinction as Recorded in the Deep-Sea Archive of the Budva Basin, Dinarides, Montenegro

“…9C). In contrast, marine K-Pg sites show trace element patterns that lack a relative HREE enrichment (see e.g., Ebihara and Miura, 1996;Shrivastava et al, 2013;Loroch et al, 2016;Sial et al, 2018). This shows a strong contrast between the trace element enrichments of the extinction horizon at Čanj to that of K-Pg sections.…”

Geochemical records of the end-Triassic Crisis preserved in a deep marine section of the Budva Basin, Dinarides, Montenegro.

“…9C). In contrast, marine K-Pg sites show trace element patterns that lack a relative HREE enrichment (see e.g., Ebihara and Miura, 1996;Shrivastava et al, 2013;Loroch et al, 2016;Sial et al, 2018). This shows a strong contrast between the trace element enrichments of the extinction horizon at Čanj to that of K-Pg sections.…”

Application of laser ablation-ICP-MS to determine high-resolution elemental profiles across the Cretaceous/Paleogene boundary at Agost (Spain)

“…Recently, LA-ICP-MS analysis was used to studied the geochemistry and textural characteristics of glass spherules in proximal (Belza et al, 2015;Ritter et al, 2015) and distal sites (Belza et al, 2017) and LA-ICP-MS analyses have furthermore been undertaken in intermediate sites of KPgB (Berndt et al, 2011;Loroch et al, 2016), but merely oriented towards the analysis of individual spots, not in the continuous highresolution laser mode as used here.…”