The Santa Filomena meteorite shower: Trajectory,classification, and opaque phases as indicators of metamorphic conditions

On August 19, 2020, at 13:18—UTC, a meteor event ended as a meteorite shower in Santa Filomena, a city in the Pernambuco State, northeast Brazil. The heliocentric orbital parameters resulting from images by cameras of the weather broadcasting system were semimajor axis a = 2.1 ± 0.1 au, eccentricity e = 0.55 ± 0.03, and inclination i = 0.15^o ± 0.05. The data identified the body as an Apollo object, an Earth-crossing object with a pericenter interior to the Earth's orbit. The chemical, mineralogical, and petrological evaluations, as well as the physical analysis, followed several traditional techniques. The meteorite was identified as a H5-6 S4 W0 ordinary chondrite genomict breccia. The large amount of metal in the meteorite made a metallographic evaluation based on the opaque phases possible. The monocrystalline kamacite crystals suggest a higher petrological type and the distorted Neumann lines imply at least two different shock events. The absence of the plessite phase shows that the meteorite did not reach the highest shock levels S5 and S6. The well-defined polycrystalline taenite is indicative of petrologic types 4 and 5 due to the conserved internal tetrataenite rim at the boundaries. The presence of polycrystalline taenites and the characteristics of the Agrell Effect suggest that the Santa Filomena meteorite did not reheat above 700°C. The absence of martensite confirms reheating temperatures <800°C and a slow cooling rate. The Ni contents and sizes of the zoned taenite particles indicate a slow cooling rate ranging from 1 to 10 K Myr⁻¹.     

The distribution and characteristics of the igneous complexes in the northern East China Sea Shelf Basin and their implications for hydrocarbon potential

This paper presents results of two-dimensional seismic mapping of the northern East China Sea Shelf Basin. Various igneous features such as sills, volcanic edifices and stocks were identified by the geophysical exploration. The sills are most common, and are observed at more than 90 locations. Most mapped sills in the study area are characterized by high-amplitude continuous reflections with distinct terminations. Saucer- and cup-shaped sills are observed locally. The stocks are discordant (nearly vertical) igneous bodies and they are characterized by seismic transparency, with upturned host rocks and uplifted overburden. The volcanic edifices and/or necks consist of irregular mounds and peaks and are characterized by strong positive top reflections with chaotic internal facies. The oldest igneous activity in the northern East China Sea Shelf Basin is Early Cretaceous (123.3 ± 3.7). This igneous activity coincides with those observed in eastern China which has been related mainly to the subduction of the Pacific Plate beneath Eurasia Plate. The Miocene igneous activity is well constrained based on seismic stratigraphic relationships within the folded stratigraphy, age dating, and the occurrence of igneous sills. The timing of this intrusion is coincident with the intensive igneous activity as previously suggested for the eastern China. Igneous rocks can produce hydrocarbon traps, reservoirs and they can act as a seal, and therefore are of great importance in petroleum study.     

Water level changes in Lake Van,Turkey, during the past ca. 600 ka: climatic,volcanic and tectonic controls

Sediments of Lake Van, Turkey, preserve one of the most complete records of continental climate change in the Near East since the Middle Pleistocene. We used seismic reflection profiles to infer past changes in lake level and discuss potential causes related to changes in climate, volcanism, and regional tectonics since the formation of the lake ca. 600 ka ago. Lake Van’s water level ranged by as much as 600 m during the past ~600 ka. Five major lowstands occurred, at ~600, ~365–340, ~290–230, ~150–130 and ~30–14 ka. During Stage A, between about 600 and 230 ka, lake level changed dramatically, by hundreds of meters, but phases of low and high stands were separated by long time intervals. Changes in the lake level were more frequent during the past ~230 ka, but less dramatic, on the order of a few tens of meters. We identified period B1 as a time of stepwise transgressions between ~230 and 150 ka, followed by a short regression between ca. 150 and 130 ka. Lake level rose stepwise during period B2, until ~30 ka. During the past ~30 ka, a regression and a final transgression occurred, each lasting about 15 ka. The major lowstand periods in Lake Van occurred during glacial periods, suggesting climatic control on water level changes (i.e. greatly reduced precipitation led to lower lake levels). Although climate forcing was the dominant cause for dramatic water level changes in Lake Van, volcanic and tectonic forcing factors may have contributed as well. For instance, the number of distinct tephra layers, some several meters thick, increases dramatically in the uppermost ~100 m of the sediment record (i.e. the past ~230 ka), an interval that coincides largely with low-magnitude lake level fluctuations. Tectonic activity, highlighted by extensional and/or compressional faults across the basin margins, probably also affected the lake level of Lake Van in the past.