Fire & Global Change During Key Intervals of the Late Triassic & Early Jurassic with a Focus on the Central Polish Basin

Abstract

Core from modern-day Poland recovering fluvial and paralic strata provides an excellent record of climatic and environmental changes in the Central Polish Basin during two key intervals of the Early Jurassic. Thick successions of Rhaetian-Hettangian and Pliensbachian-Toarcian age are examined using a number of techniques in order to understand the wildfire activity history, carbon-cycle interactions, and organic matter composition of sediments at two sites in the Central Polish Basin. Physical and geochemical proxies for wildfire activity show evidence of increased wildfire activity both prior to and after the Toarcian Oceanic Anoxic Event (OAE) at the Kazewy-1 site, with suppression of wildfire activity during the negative carbon-isotope excursion of the OAE. Correlation with published wildfire activity proxy records from additional sites in the Tethyan realm shows that this pattern was not limited to the Central Polish Basin, but is part of a wider, regional change. Additionally, new wildfire activity proxy records show increased wildfire activity across the Triassic-Jurassic Boundary at the Kaszewy-1 and Niekłań PIG-1 sites in the Central Polish Basin, correlating with other contemporaneous proxy records from Denmark and Greenland. New carbon-isotope records generated from terrestrial organic matter from the Niekłań PIG-1 core show trends towards heavier δ¹³C values immediately after the Triassic-Jurassic Boundary, providing evidence of a perturbation to the carbon-cycle at this time. Exploratory investigation of sediments from the Kaszewy-1 core provides a new record of BIT indices of Early Jurassic sediments, surpassing the oldest-known use of this terrestrial organic matter input proxy. Additionally, a newly-developed technique is used to investigate carbon-isotope variability in fossil terrestrial organic matter across the Toarcian Oceanic Anoxic Event carbon-isotope excursions. A new record of individual phytoclast δ¹³C values demonstrates that, despite δ¹³C variability between phytoclasts from a single horizon, larger overall trends in δ¹³C values can be identified from single phytoclast δ¹³C measurements.Core from modern-day Poland recovering fluvial and paralic strata provides an excellent record of climatic and environmental changes in the Central Polish Basin during two key intervals of the Early Jurassic. Thick successions of Rhaetian-Hettangian and Pliensbachian-Toarcian age are examined using a number of techniques in order to understand the wildfire activity history, carbon-cycle interactions, and organic matter composition of sediments at two sites in the Central Polish Basin. Physical and geochemical proxies for wildfire activity show evidence of increased wildfire activity both prior to and after the Toarcian Oceanic Anoxic Event (OAE) at the Kazewy-1 site, with suppression of wildfire activity during the negative carbon-isotope excursion of the OAE. Correlation with published wildfire activity proxy records from additional sites in the Tethyan realm shows that this pattern was not limited to the Central Polish Basin, but is part of a wider, regional change. Additionally, new wildfire activity proxy records show increased wildfire activity across the Triassic-Jurassic Boundary at the Kaszewy-1 and Niekłań PIG-1 sites in the Central Polish Basin, correlating with other contemporaneous proxy records from Denmark and Greenland. New carbon-isotope records generated from terrestrial organic matter from the Niekłań PIG-1 core show trends towards heavier δ¹³C values immediately after the Triassic-Jurassic Boundary, providing evidence of a perturbation to the carbon-cycle at this time. Exploratory investigation of sediments from the Kaszewy-1 core provides a new record of BIT indices of Early Jurassic sediments, surpassing the oldest-known use of this terrestrial organic matter input proxy. Additionally, a newly-developed technique is used to investigate carbon-isotope variability in fossil terrestrial organic matter across the Toarcian Oceanic Anoxic Event carbon-isotope excursions. A new record of individual phytoclast δ¹³C values demonstrates that, despite δ¹³C variability between phytoclasts from a single horizon, larger overall trends in δ¹³C values can be identified from single phytoclast δ¹³C measurements.