Isotope excursions

In geochemistry, paleoclimatology, archaeology, and paleoceanography '''δC''' (pronounced "delta carbon thirteen") is a normalized ratio of the two stable isotopes of carbon—C and C—reported in parts per thousand (per mille, ‰).

anoxic extinction events in the Cretaceous period, occurring at 91.5 ± 8.6 Ma

In geochemistry, paleoclimatology and paleoceanography '''δ18O or delta-O-18''' is a measure of the deviation in ratio of stable isotopes oxygen-18 (18O) and oxygen-16 (16O). It is commonly used as a measure of the temperature of precipitation, as a measure of groundwater/mineral interactions, and as an indicator of processes that show isotopic fractionation, like methanogenesis. In paleosciences, 18O:16O data from corals, foraminifera and ice cores are used as a proxy for temperature.

mass extinction event in the Ludfordian age of the Silurian period, ca. 424 Ma

cyclical variations in the ratio of the abundance of oxygen

first of three relatively minor extinction events (the Ireviken, Mulde, and Lau events) during the Silurian period; occurred at the Llandovery/Wenlock boundary

anoxic event causng mass extinctions, coinciding with a global drop in sea level, and is closely followed by an excursion in geochemical isotopes, during the Silurian period