Controls on Early Cretaceous desert sediment provenance in south-west Gondwana,Botucatu Formation (Brazil and Uruguay)     

Gabriel Bertolini  Juliana C. Marques  Adrian J. Hartley  Atila A. S. Da-Rosa  Claiton M. S. Scherer  Miguel A. S. Basei  José C. Frantz 《Sedimentology》2020,67(5):2672-2690

The Lower Cretaceous Botucatu Formation records the development of widespread dry–aeolian desert sedimentation throughout the Paraná Basin in south-west Gondwana. To reconstruct the provenance of the aeolian sediment, petrography, granulometric analysis, U-Pb detrital zircon ages have been determined from along the southern basin margin in Rio Grande do Sul state (southern Brazil) and Uruguay (Tacuarembó region). The dataset reveals a mean composition Qt₈₉F₈L₃, comprising very fine to medium-grained quartozose and feldspatho-quartzose framework. Heavy mineral analysis reveals an overall dominance of zircon, tourmaline and rutile grains (mean ZTR_0.84) with sporadic garnet, epidote and pyrolusite occurrences. The detrital zircon U-Pb ages are dominated by Cambrian to Neoproterozoic (515 to 650 Ma), Tonian to Stenian (900 to 1250 Ma) and Orosirian to Rhyacian (1.8 to 2.2 Ga) material. The detrital zircon dataset demonstrates a significant lateral variation in sediment provenance: Cambrian to Neoproterozoic detrital zircons dominate in the east, while Tonian to Stenian and Orosirian to Rhyacian ages predominate in the west of the study area. Sandstones are quartz-rich with dominantly durable zircon, tourmaline and rutile heavy mineral suite, with subtle but statistically significant along-strike differences in heavy mineral populations and detrital mineralogy which are thought to record local sediment input points into the aeolian system. The similar age spectra of Botucatu desert with proximal Paraná Basin units, the predominance of quartzose, and zircon, tourmaline and rutile components, suggests that recycling is the mechanism responsible for the erg feeding.  相似文献   

Compositional Variations and Tectonic Settings of Podiform Chromitites Associated with Ultramafic Rocks of the Pan-African Proterozoic Ophiolites from South Eastern Desert, Egypt     

Mohamed Metwaly ABU ANBAR  Fernando GERVILLA 《《地质学报》英文版》2020,94(Z1):40-42

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Relating 27-Day Averages of Solar,Interplanetary Medium Parameters,and Geomagnetic Activity Proxies in Solar Cycle 24     

Castillo  Yvelice  Pais  Maria Alexandra  Fernandes  João  Ribeiro  Paulo  Morozova  Anna L.  Pinheiro  Fernando J. G. 《Solar physics》2021,296(7):1-30

Solar Physics - During solar minimum, the Sun is relatively inactive with few sunspots observed on the solar surface. Consequently, we observe a smaller number of highly energetic events such as...  相似文献   

Late pleistocene/early holocene environments and climates,fauna, and human occupation in the argentine altiplano     

Jorge Fernndez  Vera Markgraf  Hctor O. Panarello  Miguel Albero  Fernando E. Angiolini  Susana Valencio  Mirta Arriaga 《Geoarchaeology》1991,6(3):251-272

The Barro Negro site (23°S lat., 65°37′W long.) in the Altiplano (Puna) of northwestern Argentina contains a well stratified sequence of remains of Hippidion, the American extinct horse, camelids, and archaeological materials, which is the focus of this study. In addition to establishing a reliable chronology, paleoenvironmental information was obtained based on analyses of pollen and stable isotopes (oxygen and carbon) from bone and marl. The data indicate that Hippidion was present at the site between 12,000 and 10,000 yr B. P., at a time when Altoandean grasslands had expanded to lower elevations. By 10,000 yr B.P., when modern semi-arid sub-puna scrub had replaced the Altoandean grasslands, only camelids (Lama or Vicugna) were present, simultaneous with the first evidence of local human occupation. This suggests that a climatic shift from cool and moist (winter rain regime) to warm and dry (summer rain regime) conditions took place simultaneously with the disappearance of the American horse and the appearance of camelids and man.  相似文献