T234 Greenhouse to Icehouse Transition: Global Events of the Devonian, Carboniferous, and Early Permian I

Wednesday, 7 November 2018
8:00 AM - 12:00 PM
Room 140

INTENSIFIED OCEANIC CIRCULATION DURING EARLY CARBONIFEROUS COOLING EVENTS: EVIDENCE FROM CARBON AND NITROGEN ISOTOPES

Paper number: T234-14
Program: Technical Sessions
Time: 11:20 AM – 11:35 AM

Authors

Abstract

The Early Carboniferous climate transition to the Late Paleozoic Ice Age was marked by a long-term cooling trend punctuated by short glaciations in the mid-Tournaisian and Visean. Here, we generated organic carbon and nitrogen isotope profiles for two widely separated Lower Carboniferous sections (Arrow Canyon Range, Nevada, and Namur-Dinant Basin, Belgium) in order to assess the global nature and timing of changes in the carbon-nitrogen cycles linked to oceanic productivity and redox conditions during this climate transition. Both sections record major carbon- and nitrogen-cycle perturbations during the mid-Tournaisian and Visean. The mid-Tournaisian event (TICE) is marked by increases of 5-7 ‰ in δ13Ccarb, 1-5 ‰ in δ13Corg, and 9-11 ‰ in δ15Nbulk, and the Visean event (VICE) is marked by increases of 2-4 ‰ in δ13Ccarb, 2-5 ‰ in δ13Corg, and 5-8 ‰ in δ15Nbulk. The positive excursions in all three isotopic records are consistent with increased organic carbon burial and enhanced denitrification, implying intensification of marine productivity and expansion of hypoxia in the global ocean. Given that each event coincided with lowering of sea-surface temperatures and increased glaciation (as documented from published conodont δ18O and sea-level records), we hypothesize that global cooling led to intensified oceanic circulation and upwelling on continental margins, triggering increased marine productivity and attendant redox changes within the affected upwelling zones. Our results provide new insights into changes in Early Carboniferous oceanic conditions in response to the initial stages of cooling leading into the Late Paleozoic Ice Age.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-319617

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