The spread of marine anoxia on the northern Tethys margin during the Paleocene-Eocene Thermal Maximum

Abstract

Records of the paleoenvironmental changes that occurred during the Paleocene-Eocene Thermal Maximum (PETM) are preserved in sedimentary rocks along the margins of the former Tethys Ocean and Peri-Tethys. This paper presents new geochemical data that constrain paleoproductivity, sediment delivery, and seawater redox conditions, from three sites that were located in the Peri-Tethys region. Trace and major element, iron speciation, and biomarker data indicate that water column anoxia was established during episodes when inputs of land-derived higher plant organic carbon and highly weathered detrital clays and silts became relatively higher. Anoxic conditions are likely to have been initially caused by two primary processes: (i) oxygen consumption by high rates of marine productivity, initially stimulated by the rapid delivery of terrestrially derived organic matter and nutrients, and (ii) phosphorus regeneration from seafloor sediments. The role of the latter process requires further investigation before its influence on the spread of deoxygenated seawater during the PETM can be properly discerned. Other oxygen-forcing processes, such as temperature/salinity-driven water column stratification and/or methane oxidation, are considered to have been relatively less important in the study region. Organic carbon enrichments occur only during the initial stages of the PETM as defined by the negative carbon isotope excursions at each site. The lack of observed terminal stage organic carbon enrichment does not support a link between PETM climate recovery and the sequestration of excess atmospheric CO 2 as organic carbon in this region; such a feedback may, however, have been important in the early stages of the PETM.

The effects of metamorphism on iron mineralogy and the iron speciation redox proxy

“…Although most early iron speciation studies did not screen for pyrrhotite or AVS, this has become a more standard practice now and many studies note very low or no detectable AVS in their samples (e.g. Dickson et al, 2014;Gilleaudeau and Kah, 2015;Johnston et al, 2012;Och et al, 2016;Planavsky et al, 2011;Sperling et al, 2013). However, when pyrrhotite is detected, the analysis and interpretations that follow vary.…”

Ocean Circulation in the Toarcian (Early Jurassic): A Key Control on Deoxygenation and Carbon Burial on the European Shelf

“…The high TOC/P ratios (Figure ) indicate a strong recycling of P that may have further sustained primary productivity. Such recycling of P likely played a key role in the development of ocean anoxia during various periods of Earth history including Cretaceous OAEs and the PETM (Dickson et al, ; Kraal et al, ; Mort et al, ; Ruvalcaba Baroni et al, ; Tsandev & Slomp, ). In contrast, river input to the southern EES was likely to have been small during the T‐OAE.…”

Environmental Change in the Deep Ocean

“…Such conditions have been linked to major extinction events affecting shallow and also deep-water ecosystems [e.g., end Cambrian (83), end Ordovician (84), end Permian (85), early Jurassic (86), and Paleocene-Eocene thermal maximum (87)]. The latest of these events, the Paleocene-Eocene thermal maximum, was specifically associated with an extinction of deep-water foraminifera (87,88). In addition to its association with extinctions, climate change has also been involved in creating the conditions for invasion by various groups of animals and radiation into the deep ocean, mainly during the onset of cool conditions that drive the thermohaline circulation.…”