Refined Ordovician timescale reveals no link between asteroid breakup and biodiversification

Abstract

The catastrophic disruption of the L chondrite parent body in the asteroid belt c. 470 Ma initiated a prolonged meteorite bombardment of Earth that started in the Ordovician and continues today. Abundant L chondrite meteorites in Middle Ordovician strata have been interpreted to be the consequence of the asteroid breakup event. Here we report a zircon U-Pb date of 467.50±0.28 Ma from a distinct bed within the meteorite-bearing interval of southern Sweden that, combined with published cosmic-ray exposure ages of co-occurring meteoritic material, provides a precise age for the L chondrite breakup at 468.0±0.3 Ma. The new zircon date requires significant revision of the Ordovician timescale that has implications for the understanding of the astrogeobiologic development during this period. It has been suggested that the Middle Ordovician meteorite bombardment played a crucial role in the Great Ordovician Biodiversification Event, but this study shows that the two phenomena were unrelated.

An Image Mapping Approach to U‐Pb LA‐ICP‐MS Carbonate Dating and Applications to Direct Dating of Carbonate Sedimentation

“…It was determined on a part of the valve that appeared to be least altered as suggested by minor and trace element compositions and by SEM imaging. The obtained date is in good agreement with the biostratigraphic range of the brachiopod (Aseri on the Baltoscandian scale; c. 465.2 to 463.2 Ma—Lindskog et al, ), and we consider this U‐Pb date a close age estimate for the brachiopod shell and for deposition of the host sediment. The results furthermore suggest the feasibility of the LA‐ICP‐MS U‐Pb dating technique to dating biogenic carbonate materials, particularly brachiopods which typically grow shells of primary calcite (most mollusk shells are composed mainly of aragonite which is metastable on the Earth's surface and inverts to calcite over geological time).…”

A Gondwanan perspective on the Ordovician Radiation constrains its temporal duration and suggests first wave of speciation, fuelled by Cambrian clades

“…; Lindskog et al . ). This main pulse of the GOBE is temporally synchronous globally being detected with high precision in the Dapingian–middle Darriwilian interval where a marked peak occurs in the lower–middle Darriwilian ( Lenodus variabilis–Yangtzeplacognatus crassus Zones) of Baltica (Rasmussen et al .…”

Lower–Middle Ordovician carbon and oxygen isotope chemostratigraphy at Hällekis, Sweden: implications for regional to global correlation and palaeoenvironmental development

“…() calculated a net depositional rate for the ‘orthoceratite limestone’ (see below) at Kinnekulle of ~3.3 mm/ka, and Lindskog et al . () calculated ~4 mm/ka.…”