(1) Department of Environmental Sciences, Barnard College, Columbia University, NY, NY 10027 USA (jliddico@barnard.edu), (2) Department of History, Xiamen University, Xiamen 361005, China, (3) Institute of Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China, (4) Paleomagnetism and Geochronology Laboratory, Institute of Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Detailed paleomagnetic investigations conducted on the Malan loess (L1) at a well‐dated section (Weinan) in the Chinese Loess Plateau revealed two distinct anomalous directional intervals (ADI) accompanied by lower relative paleointensity. Rock magnetic properties and anisotropy of magnetic susceptibility (AMS) of samples taken from sedimentary horizons carrying the anomalous directions are similar to those taken from outside the anomalous directional intervals. Thus, the anomalous directions are interpreted as geomagnetic excursions. Based on 14 C and TL data, the excursions occurred at 27.1–26.0 and 46.8–37.4 kyr B.P; the ages are consistent with the ages assigned to the Mono Lake excursion (MLE) and Laschamp excursion (LE), respectively. The result indicates that the MLE and LE were independent geomagnetic excursions. The morphology of LE at this section suggests that the LE might be an aborted geomagnetic reversal.
The timing of the Jiufotang Formation remains speculative despite recent progress in the study of the Jehol Biota. In this paper we contribute to this topic with 40 Ar/ 39 Ar dating on K‐feldspar (sanidine and orthoclase) from tuffs interbedded within the fossil‐bearing shales of the Jiufotang Formation, from the upper part of the Jehol Group in Chaoyang, Liaoning, northeastern China. 40 Ar/ 39 Ar step heating analyses of K‐feldspar and the SHRIMP U‐Pb zircon data indicate that tuffs at the Shangheshou section erupted at 120.3 ± 0.7 million years ago. This result confirms an Aptian age for the Jiufotang Formation that was mainly based on biostratigraphic evidence. It also places stringent controls on the age of the fossils from the formation, providing a minimum age (120 Ma) for the four‐winged dinosaur, Microraptor , and the seed‐eating bird, Jeholornis .
Martian meteorites are the only samples from Mars available for extensive studies in laboratories on Earth. Among the various unresolved science questions, the question of the Martian atmospheric composition, distribution, and evolution over geological time still is of high concern for the scientific community. Recent successful space missions to Mars have particularly strengthened our understanding of the loss of the primary Martian atmosphere. Noble gases are commonly used in geochemistry and cosmochemistry as tools to better unravel the properties or exchange mechanisms associated with different isotopic reservoirs in the Earth or in different planetary bodies. The relatively low abundance and chemical inertness of noble gases enable their distributions and, consequently, transfer mechanisms to be determined. In this review, we first summarize the various in situ and laboratory techniques on Mars and in Martian meteorites, respectively, for measuring noble gas abundances and isotopic ratios. In the second part, we concentrate on the results obtained by both in situ and laboratory measurements, their complementarity, and the implications for the Martian atmospheric dynamic evolution through the last billions of years. Here, we intend on demonstrating how the various efforts established the Mars-Martian meteorites connection and its significance to our understanding of the red planet.
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