The Quaternary Climatic and Tectonic Development of the Murat River Valley (Muş Basin, Eastern Turkey) as Recorded by Fluvial Deposits Dated by Optically Stimulated Luminescence

The paper describes climatic and tectonic effects on fluvial processes of East Anatolia. This study from the Muş Basin contains three alluvial terrace levels (T3-T1) ranging from 30–35 m to 3–5 m above the present Murat River in its middle section. In order to provide a chronology for the evaluation of the significant, effects of climatic changes and tectonic uplift, we used optically stimulated luminescence (OSL) dating of the river deposits of the youngest (T3) and medium terrace (T2). The ages from these terrace deposits show that the T3 has formed approximately 6.5 ka ago, i.e., during the last part of the Holocene (MIS 1) and T2 has formed nearly 25 ka ago, i.e., during MIS 2 at the ending of the last glacial period. According to these results, it appears that the Murat River established its terrace sequences both in cold and warm periods. The variations in climate oriented fluvial evolution between the East Anatolia fluvial system and the temperate-periglacial fluvial systems in Europe may be the conclusion of different vegetation cover and melting thicker snow coverings in cold periods.

Trifolium vesiculosum (Fabaceae) in Ukraine: a new find and historical overview

Trifolium vesiculosum is listed in the current floristic inventories as a species native to Ukraine. In order to clarify the native versus alien status of this taxon, we studied historical and recent literature and herbarium data.We also report here our new record of the species. We found T. vesiculosum in 2020 in Mykolayiv Region (Mykolayiv District, Andriivka village, on the alluvial terrace of the Southern Bug River valley), in a disturbed habitat with predominantly synanthropic and alien species. Previous finds of T. vesiculosum in Ukraine were reported mainly in publications of the 19th century and were based on a few herbarium specimens from the present-day territory of Odesa Region. Due to characteristics of these records, dates and localities of the finds of T. vesiculosum in Ukraine, we have traced its probable introductions during the 19th century in the port of Odesa, on the sand deposits of the Danube River, in the German settlements, and therefore we can confirm the conclusion of Paczoski (1921) who assumed the alien status of the species in Ukraine. Thus, T. vesiculosum is classified as a kenophyte (introduced before 1808). Taking into account the current climatic changes in Ukraine, we emphasize the need for further monitoring of the species, changes in its dispersal strategy, and for registration of its introduction and dispersal pathways.

Steady-state valley width revealed by alluvial terrace sequences

<div> <p>Lateral erosion by rivers drives valley widening and controls valley-bottom width. The current lack of a comprehensive valley-widening model complicates the reproduction of the full range of valley shapes that we find in nature as well as the prediction of valley evolution under different climatic and tectonic boundary conditions. Field data have shown that water discharge and valley wall lithology control lateral erosion rates. However, order-of magnitude variations in valley width formed in uniform lithology and under similar discharge conditions suggest additional, so far unquantified controls on valley width.</p> <p>Fluvial terrace sequences offer an opportunity to study valley-width evolution under comparable discharge and lithologic conditions. Alluvial terraces are composed of flat surfaces and steep walls carved into previously deposited river sediments. They form where a river alternates between phases of lateral valley widening by lateral planation and vertical incision and terrace formation. In order to form an entire terrace staircase, such alternations have to repeat and many Quaternary terrace staircases are interpreted to be driven by cyclic climate changes. Because Quaternary climate cycles have had comparable amplitudes and durations, individual surfaces in paired climate-driven terrace sequences preserve the widths of valleys that have formed under similar discharge conditions, lithologies and over comparable time-intervals. We use a global compilation of 16 climatically formed alluvial terrace sequences to investigate controls on valley width.</p> <p>Between 90 and 99% of the variance in valley width can be explained by a linear relationship of the width with the total valley depth. Hence, at least one of the missing controls on valley width must scale (close to) linearly with valley depth. Ruling-out a preservation bias and a number of parameters that are unrelated to valley depth, we propose a model that relates valley width to a competition between the sediment supplied from valley walls and the river’s capacity to rework sediment, such that a lateral sediment-flux steady state is reached. According to our model the valley width-depth relationship is controlled by (1) the horizontal hillslope-erosion rate, (2) the lateral sediment-transport capacity of the river and (3) the valley-width which forms in the absence of lateral-sediment input. Hence, the model allows to predict valley width when all of the above parameters are quantified in the field. Alternatively, any of the three parameters can be predicted when valley width is measured. The new model is able to reproduce the first-order trend observed in terrace-derived valley widths and it can explain the evolution of paired terrace sequences, which has so far been a major challenge.</p> </div>

Deciphering the Enigmatic Origin of Guyana's Diamonds

Diamonds have long been mined from alluvial terrace deposits within the rainforest of Guyana, South America. No primary kimberlite deposits have been discovered in Guyana, nor have there been previous studies on the mineralogy and origin of the diamonds. Paleoproterozoic terranes in Guyana are prospective to diamond occurrences because the most productive deposits are associated spatially with the eastern escarpment of the Paleoproterozoic Roraima Supergroup. Geographic proximity suggests that the diamonds are detrital grains eroding from the <1.98 Ga conglomerates, metamorphosed to zeolite and greenschist facies. The provenance and paragenesis of the alluvial diamonds are described using a suite of placer diamonds from different locations across the Guiana Shield. Guyanese diamonds are typically small, and those in our collection range from 0.3 to 2.7 mm in diameter; octahedral and dodecahedral, with lesser cubic and minor macle forms. The diamonds are further subdivided into those with abraded and non-abraded surfaces. Abraded diamonds show various colors in cathodoluminescence, whereas most non-abraded diamonds appear blue. In all populations, diamonds are predominantly colorless, with lesser brown to yellow and very rare white. Diamonds are predominantly Type IaAB and preserve moderate nitrogen aggregation and total nitrogen concentrations ranging from trace to ~1971 ppm. The kinetics of nitrogen aggregation indicate mantle-derived residence temperatures of 1124 ± 100 °C, assuming residence times of 1.3 and 2.6 Ga for abraded and non-abraded diamonds, respectively. The diamonds are largely sourced from the peridotitic to eclogitic lithospheric upper mantle based on both δ13C values of –5.82 ± 2.45‰ (VPDB-LSVEC) and inclusion suites predominantly comprised of forsterite, enstatite, Cr-pyrope, chromite, rutile, clinopyroxene, coesite, and almandine garnet. Detrital, accessory minerals are non-kimberlitic. Detrital zircon geochronology indicates diamondiferous deposits are predominantly sourced from Paleoproterozoic rocks of 2079 ± 88 Ma.

Structural and textural features of genetic types of the massive and ice wedges, and the conditions of their formation in the lower reaches of the Gyda River

In the structure of the frozen thickness of the 2nd lake-alluvial terrace of the Gyda River were detected polygonal-wedge, lens massive and lensoid ice were. A detailed analysis of structural and textural peculiarities in the layers was carried out for the first time for these morphological types of underground ice. Based on the cryolithological structure of host rocks and structural-textural features of ice, the main mechanisms of deposit formation – polygonal-wedge, infiltration-segregational, and congelation were determined. The development of polygonal-wedge ice occurred in an alluvial floodplain setting of sedimentation accompanied by the climate fluctuations in the end of the Late Pleistocene and Holocene. The growth of ice wedge in the second half of the Sartan Period was interrupted under the reservoirs with shallow talik waters, after freezing of which there formed infiltration-segregational lensoid formation ices. The structure of frozen thickness was complicated by the lenses of congelation ice formed in thermoerosive niches in the Holocene optimum of about 6.5 thousand years ago. At the present time is possible the formation of similar types of ice on various sections of the relief. The established peculiarities of cryogenic structure are important for the creation of paleogeographic reconstructions and forecasting the dynamics of permafrost-facies environments accompanied by the modern changes in the depth of the seasonal thaw layer and the development of thermokarst.

Structure and formation of ice-ground veins of the second lake-alluvial terrace in the North of Gydan in the late Neopleistocene–Holocene

The syngenetic ice and ice-ground composite veins in khasyrey (alas) and interalas plateaus were studied on the second lake-alluvial terrace located in the North of the Gydan Peninsula near the village of Gyda. On the basis of the radiocarbon dating, the time of formation of deposits containing veins from was established – from 16 640 to 854 BP. The peat deposits are mainly represented by the following species: Carex sp., Eriophorum sp., Betula nana, Equisetum sp., Calamagrostis sp., Vaccinium vitis-idaea, Drepanocladus sp., Empetrum sp., Vaccinium uliginosum, Rubus arcticus, Petasites sp. It is established that the polygonal-veined ice of khasyrey and interalas plateaus, except for vertical-striped «clean» ice, contain areas with vertical wavy streaks of ice-ground. Ice of elementary veins and segregation ice were revealed in the composition of veins according to structural and textural features in polarized light. Elementary ice veins compose «clean» ice sections of veins and segregation ice which are their ice-ground sections. Elementary veins are indicative of the predominance of the process of frost cracking during the formation of polygonal-vein ices. The presence of inclusions of ice-ground in the structure of veins points is evidence of a manifestation of local thermokarst processes under the growth of polygonal-vein ice. Ice-ground veins were formed by repeated thawing of the initial ice veins. The formation of ice-ground veins during syngenetic freezing of sediments of the second lake-alluvial terrace is related to uneven manifestation of thermokarst in different facies situations and and climate changes at the Early Pleistocene and Holocene.