Two-billion-year-old evaporites capture Earth’s great oxidation

Abstract

Major changes in atmospheric and ocean chemistry occurred in the Paleoproterozoic era (2.5 to 1.6 billion years ago). Increasing oxidation dramatically changed Earth's surface, but few quantitative constraints exist on this important transition. This study describes the sedimentology, mineralogy, and geochemistry of a 2-billion-year-old, ~800-meter-thick evaporite succession from the Onega Basin in Russian Karelia. The deposit consists of a basal unit dominated by halite (~100 meters) followed by units dominated by anhydrite-magnesite (~500 meters) and dolomite-magnesite (~200 meters). The evaporite minerals robustly constrain marine sulfate concentrations to at least 10 millimoles per kilogram of water, representing an oxidant reservoir equivalent to more than 20% of the modern ocean-atmosphere oxidizing capacity. These results show that substantial amounts of surface oxidant accumulated during this critical transition in Earth's oxygenation.

Redox Chemistry and Molybdenum Burial in a Mesoproterozoic Lake

“…Located in LH (Figure b), the MIS is a 23‐m‐deep karst feature wherein low‐oxygen high‐sulfate groundwater seeps into the sinkhole, resulting in low (<5%) dissolved oxygen and 7.8 mM sulfate that persists 1–3 m above the sediment‐water interface (Ruberg et al, ). This water chemistry is comparable to proposed levels for mid‐Proterozoic waters, which are inferred to have little to no oxygen (e.g., Lyons et al, ; Shen et al, ), and sulfate concentrations in the range of <2 to ~10 mM (Blättler et al, ; Olson et al, ). As a result of this water chemistry, dynamic microbial mats grow at this interface, including cyanobacteria that conduct both oxygenic and anoxygenic photosynthesis (Voorhies et al, ), and are therefore similar to the versatile cyanobacteria proposed to have dominated Proterozoic aquatic systems (Johnston et al, ; Voorhies et al, ).…”

Cr isotopic insights into ca. 1.9 Ga oxidative weathering of the continents using the Beaverlodge Lake paleosol, Northwest Territories, Canada

“…The duration of the oxygen overshoot is imprecisely known, but it has been linked to the Lomagundi Event, a period of high δ 13 C values in marine carbonate sediment dated between ~2.32 and 2.06 Ga, which is interpreted as a period of enhanced organic carbon burial. Bedded marine sulfate deposits are preserved from this time (Melezhik, Fallick, Rychanchik, & Kuznetsov, 2005), and there is widespread evidence for pseudomorphs after gypsum preserved in marine sedimentary rocks, thus pointing to a sizeable marine sulfate reservoir in the oceans (Bachon & Kump, 2015;Planavsky, Bekker, Hoffman, & Owens, 2012;Reuschel et al, 2012), estimated by Blattler et al (2018) to reflect 20% of the modern oxidizing capacity of the oceans and atmosphere.…”

“…Bedded marine sulfate deposits are preserved from this time (Melezhik, Fallick, Rychanchik, & Kuznetsov, ), and there is widespread evidence for pseudomorphs after gypsum preserved in marine sedimentary rocks, thus pointing to a sizeable marine sulfate reservoir in the oceans (Bachon & Kump, ; Planavsky, Bekker, Hoffman, & Owens, ; Reuschel et al., ), estimated by Blattler et al. () to reflect 20% of the modern oxidizing capacity of the oceans and atmosphere.…”

“…Paleosols formed before the GOE, such as the Archean Saganaga Tonalite (Driese et al., ), are depleted in iron, having sustained weathering losses of soluble ferrous iron beneath a reducing atmosphere, while those formed after the GOE, such as the Neoproterozoic Baltic laterite paleosol (Liivamägi et al., ), are enriched in iron due to the immobility of ferric iron beneath an oxidizing atmosphere. The Beaverlodge Lake paleosol is also enriched in iron (Shakotko, ), but it is unclear whether it formed at a time of lingering high atmospheric levels originating during the 2.3–2.06 Ga “oxygen overshoot” (up to 100% PAL; Bekker & Holland, ; Blattler et al., ; Harada, Tajika, & Sekine, ), or the lower atmospheric levels inferred for the boring billion (0.01%–1% PAL; Lyons, Reinhard, & Planavsky, ; Reinhard et al., ; Harada et al., ).…”

Searching for dark matter with paleo-detectors

“…from ultra-deep boreholes used for geological R&D and oil exploration (see, e.g. [44][45][46]). This would offer an overburden of up to O(12) km rock, corresponding to O(30) km.w.e., making backgrounds induced by cosmic rays negligible.…”