AMS 14C ages of Yamato achondritic meteorites

Terrestrial ^C ages of some Yamato achondrites and other meteorites, have been determined by accelerator mass spectrometry (AMS). Samples of meteorites previously studied for ^C are reported, as are new measurements on Yamato achondrites. Results on a number of meteorites from the Yamato-79 series shows longer terrestrial ages than expected for this site, where young ages predominate. A new ^C age on Y-74037 confirms the younger age for this diogenite similar to Y-74097,whereas Y-74010 is older (15kyr) and these two data suggest there may be more than one diogenite fall in the Yamato-74 group

Annual radiocarbon record indicates 16th century BCE date for the Thera eruption

The mid-second millennium BCE eruption of Thera (Santorini) offers a critically important marker horizon to synchronize archaeological chronologies of the Aegean, Egypt, and the Near East and to anchor paleoenvironmental records from ice cores, speleothems, and lake sediments. Precise and accurate dating for the event has been the subject of many decades of research. Using calendar-dated tree rings, we created an annual resolution radiocarbon time series 1700–1500 BCE to validate, improve, or more clearly define the limitations for radiocarbon calibration of materials from key eruption contexts. Results show an offset from the international radiocarbon calibration curve, which indicates a shift in the calibrated age range for Thera toward the 16th century BCE. This finding sheds new light on the long-running debate focused on a discrepancy between radiocarbon (late 17th–early 16th century BCE) and archaeological (mid 16th–early 15th century BCE) dating evidence for Thera

Radiocarbon Dating | Plant Macrofossils

International audienc

Mammoth Extinction and Radiation Dose: A Comment

Recently, an article was published in this journal, discussing evidence for a solar flare cause of faunal extinction during the Late Pleistocene. The article is based on the hypothesis that an increase in atmospheric radiocarbon concentration might have been produced by a giant solar proton event (SPE). This proposed SPE would deliver a lethal radiation dose of at least 3–6 Sv to the surface of the Earth, causing termination of the Pleistocene megafauna.

Signatures of global climatic events and forcing factors for the last two millennia from the active mudflats of Rohisa, southern Saurashtra, Gujarat, western India

The limited extent of instrumental records going back in time and control of various climatic variables on Indian Summer Monsoon (ISM) has reinvigorated the unprecedented effort in documenting climate changes for the last two millennia. Although extensive studies on late Holocene ISM reconstruction are available, comprehensive understanding on the influence of natural forcing factors on ISM and their plausible signatures is not arrived at till date. In view of this, the present study attempts to address the ISM variations during the last two millennia with special emphasis on natural forcing factors (solar and volcanic) and climate variables (ocean-atmospheric processes). The Saurashtra peninsula of Gujarat in western India receives majority of rainfall during ISM and hence it provides an ideal test-bed to study the ISM variability. A multiproxy approach has been adopted on a sediment core retrieved from the active mudflat of Southern Saurashtra which was chronologically supported by Pb-210, Cs-137 and C-14. The present study demonstrates vacillating climate with strengthened ISM during Roman Warm Period and Medieval Warm Period (2000 - 950 cal yr BP) as a result of increased solar irradiance interrupted by reduced ISM during Dark Ages of Cold Period (similar to 1500 cal yr BP). The plausible occurrence of volcanic eruption before the onset of Little Ice Age (500- 200 cal yr BP) caused the southward migration of Intertropical Convergence Zone (ITCZ) leading to enhanced western disturbances in the study area thereby resulting in cool and wet climate in the region. The study also emphasizes the increased El Nino events with gradual decline in the ISM since Little Ice Age. Further, the study underscores a climate warming during the last two centuries that corroborates well with the instrumental records. Thus, the present study has implication towards understanding the significant role of volcanic activity and solar variability in controlling the millennia scale climate oscillations with additional feedback mechanisms.Ministry of Earth Sciences24 month embargo; published online: 21 February 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Exposure History of Shergottites Dar Al Gani 476/489/670/735 and Sayh Al Uhaymir 005

Four basaltic shergottites, Dar al Gani (DaG) 476, 489, 670, and 735 were found in the Libyan Sahara [1-3]; two basaltic shergottites, Sayh al Uhaymir (SaU) 005 and 008 were found in Oman [4]. Recently SaU 051 was also recognized as a possible pair of SaU 005/008. Although the collection sites were different, the texture, bulk chemical compositions, and noble gas compositions of these shergottites are similar [e.g. 4]. However, cosmic-ray-produced noble gases alone cannot unambiguously constrain the irradiation history for these objects. From a combination of cosmogenic stable- and radionuclides, exposure histories, and ejection conditions from the hypothesized Martian parent body, and genetic relationships between the Martian meteorites can be determined. In addition to those nuclides produced by galactic cosmic rays (GCR) are those produced by solar cosmic rays (SCR). Radionuclides produced by SCRs reside in the uppermost few centimeters of extraterrestrial bodies and their presence in meteorites indicates the degree to which a meteorite has been ablated. Previous work shows ablation is less than 1-2 cm in at least three shergottites, ALH 77005, Shergotty, and EETA79001 [e.g. 5] and so it is possible some SCR signal may be observed in these meteorites. This suggests that the atmospheric entry velocity and/or entry angle of these shergottites is much lower than the velocity and/or entry angle of most ordinary chondrites. We report here preliminary results of cosmogenic nuclides, {sup 14}C (half-life = 5,730 yr), {sup 36}Cl (3.01 x 10{sup 5} yr), {sup 26}Al (7.05 x 10{sup 5} yr), and {sup 10}Be(1.5 x 10{sup 6} yr)