Extraterrestrial Metallic Iron in the Lacustrine, Epicontinental and Oceanic Sediments: A Review of Thermomagnetic and Microprobe Analyzes Data

Abstract

The article represents an overview and generalization of the microprobe and thermomagnetic data on the distribution, content and composition of metallic iron in Pleistocene lacustrine sediments of the Darhad Basin, northern Mongolia, in the Upper Miocene sediments of Lake Baikal, epicontinental sediments of Miocene-Late Jurassic, and Early Cambrian ages in different regions of North Eurasia and in Miocene-Late Jurassic oceanic sediments of North- Western Atlantic. Iron particles percentage varies from ~10-5 to 0.05%, their distribution is bimodal with the distinct zero mode, and the accumulation of iron particles is inversely linked with the rate of sedimentation. Pyrite and pyrrhotite are widespread in the studied sediments, and the distribution of metallic iron does not depend on the presence of pyrite (i.e., on redox conditions). The variations in the Curie temperature of iron from 700°C up to 780°C. The nickel admixture in native iron forms three groups, 1) pure iron (main part of particles), 2) iron with mode 5-6% Ni (kamacite), and 3) Fe-Ni alloy with mode 50% Ni (rare), were found in all studied sections. The global pattern of the distribution and composition of the iron particles clearly indicates that their origin is associated with interplanetary cosmic dust. At the same time, the particles of Fe-Ni alloy are very rare, and their concentration does not correlate with the content of other iron particles. Most likely, the particles of Fe-Ni alloy are mainly due to impact events. Correlation between the concentrations of iron particles and terrestrial minerals (magnetite) is absent as a rule. Such correlation (r=0.3-0.7) testifies the redeposition of iron particles.