Mid-Holocene palaeohydrochemistry and palaeohydrology of Yamdrok Yumtso, southern Tibetan Plateau, reconstructed from δ18O and δ13C of fossil shells of the gastropod Radix auricularia

Palaeohydrochemical and palaeohydrological changes of lakes have seldom been reconstructed from the fossil shells of the gasropod Radix auricularia, which is a new, and potentially high-resolution environnmental archive. We conducted a geochemical and stable isotope study of the shells of Radix from the exposed fluvio-lacustrine sediments near Lake Yamdrok Yumtso in the southern Tibetan Plateau. Our aims were to determine the sedimentary environment, palaeo-lake hydrochemistry and hydrological status. AMS 14C and OSL dating indicates that a lake-level stage of Yamdrok Yumtso higher than that of today occurred during ~4.7–1.2 cal. kyr BP. Results of Sr/Ca, δ13C and δ18O analysis of the fossil shells of Radix auricularia indicate that the lake-level fluctuations were mainly controlled by changes of the Indian Summer Monsoon; decreasing evaporation during the mid- to late-Holocene was also responsible. In addition, based on the geochemical relationship between Radix sp. shells and the ambient water in lakes, the values of δ18OPalaeo-water and Sr/CaPalaeo-water reconstructed using the fossil shells of Radix auricularia are −8.2‰ to −5.1‰ and 0.0012 to 0.0057, respectively. Further, based on the values of δ18Oshell, together with geomorphological evidence, we infer that Yamdrok Yumtso was a closed lake system, and we estimate its possible extent during the interval of high lake-level. In addition, we speculate that the water level of Yamdrok Yumtso at this time exceeded 4448.9 m a.s.l., but was less than 4451 m a.s.l., and that the major separation of various components of the Yamdrok Yumtso system occurred after 1.2 kyr BP.

Isotope hydrology model and stable isotopes in sediment records from Balkan lakes

<p>Isotope mass balance in lake systems is strongly correlated with several climatic factors such as temperature, evaporation, precipitation and air moisture. On the other hand, the sedimentary budget of lake basins driven by climate, tectonic and/or human impact is an essential pool of environmental records. Precipitation, springs and lake water δD and δ18O isotope data were used in order to understand the key factors for the hydrological balance of Balkan lakes in West Macedonia. In general, it is concluded that the open lake Ohrida and the semi-closed lake Kastoria are more buffered hydrological as karst systems and less sensitive to evaporation effect, in contrast to the closed lake system of Prespes that present a strong dependence on climate seasonality. Based on oxygen isotopes in bulk sediments, it is concluded that in Kastoria lake basin an increased run-off on the land surface, probably under a more humid period, in 2.4 kyr BP disturbed the transition to a drier regime from mid/late Holocene to present.</p>

Boom, Bust, and Recovery in Early Chicago, 1835–1850

This chapter looks at the start of construction on the long-anticipated portage canal that would link Chicago with the westward-flowing Des Plaines River in 1836. It mentions Judge Theophilus Smith of the Illinois Supreme Court who predicted that Chicago would boast 20,000 inhabitants in twenty years and 50,000 in fifty years. The chapter describes the enthusiasm of the local residents of Chicago that were wildly optimistic about the town's prospects and their expectation of Chicago to grow quickly into a frontier metropolis. It also talks about the level-headed observers that had every reason to reject the prospects of Chicago dominating the Old Northwest since it was considered small, dirty, and unattractive in 1836. It describes Chicago's winters that were bitter and long, in which the ice closed Lake Michigan to shipping for at least one-third of every year.

Self-purification ability of natural waters in the arid zones

The paper presents the analysis of literature data and research results on self-purification and self-purification ability of natural waters at arid zones (on example of closed Lake Balkhash). The self-purification processes are a combination of all natural (hydrodynamic, chemical, microbiological and hydrobiological) processes in contaminated natural waters. A large number of pollutants and specific (physical and geographical) conditions of reservoirs causes the complexity and variety of cleaning processes of natural waters. Large amounts of pollutants discharged into water reservoirs and drains impede the self-purification processes. It has been established that the sediments and clay of Lake Balkhash absorb the metal ions. Thus, the process of absorption of Mn2+ ions by clay minerals mainly occurs within the first three hours of contact, whereas sorption by slits continues until 10-15 days. The sediments are good absorbents for cadmium (90%), zinc (86%) and copper (78%). The sorption properties in the dynamic mode decreases in the row of zeolite (SEC = 1.02·10-3), then Fe (OH)3 (SEC = 0.28·10-3) and Al (OH)3 (SEC = 0.10·10-3 mmol-eq/g) with respect to Mn+2 ion with concentrations from 5.0 to 100 μg/L.

The sedimentary structure and petroleum geologic significance of the ring belt of the closed lake basin: An integrated interpretation of well and seismic data of the Kong2 Member in Cangdong Sag, Central Bohai Bay Basin, China

Cangdong is a typical oil-rich sag in the Bohai Bay Basin, China. After more than 50 years of exploration and development, the Kong2 Member (the major hydrocarbon play in the sag) still has considerable residual oil and gas resource potential. To pursue replacement areas of oil and gas exploration and development, the basic geology of the entire Kong2 Member in Cangdong Sag as a unit has been reexamined, and the findings have been used to guide the secondary exploration deployment. In this study, the characteristics of sedimentary reservoirs, source rocks, and oil and gas distribution in the Kong2 Member have been systematically studied, and a sedimentary model of the ring belt-circle layer of the closed lake basin in the Kong2 Member of the Cangdong Sag, with three segments (high, middle, and low) on the profile, three ring belts (outer, middle, and inner) on the plane, and three circle layers (outer, middle, and inner) in space has been established. The ring belt and circle layer are jointly controlled by water-body differentiation in the closed lake basin, source-material supply, depositional accommodation space, and deposition base-level cycle, and they can be in round, oval, long strip, and irregular shapes. The outer ring (circle), located near the basin margin, mainly has delta-front subfacies conventional coarse-grained medium-thick sandstone and near-source structural and stratigraphic-lithologic reservoirs; the middle ring (circle), the transitional zone from the basin margin to the central basin, is dominated by fine sandstone, siltstone, and lacustrine carbonates of front delta subfacies, and it mainly contains isolated lithologic reservoirs and unconventional tight oil; the inner ring (circle) is the high-quality hydrocarbon source-rock development zone in the center of the closed lake basin, featuring a high abundance of shale, where the dolomite and siltstone of distal gravity flow right next to source rock, and fine-grained diamictite of the source reservoir in one area rich in tight oil, whereas the high-abundance shale of frequent source-reservoir interbeds is rich in shale oil. The strategy of oil and gas exploration deployment is to look for structural, stratigraphic-lithologic reservoirs in the outer circle (outside source), lithologic reservoirs in the middle circle (near source), and retained tight oil and shale oil in the inner ring (inside source). In recent years, major discoveries have been made in oil and gas exploration in the three circle layers of the Kong2 Member in the Cangdong Sag through drilling, especially in tight-oil exploration in the inner-circle layer: two sandstone sweet-spot intervals of greater than 60 m and three dolomite sweet-spot intervals of greater than 100 m have been confirmed. The maximum daily oil production of vertical wells after fracturing is up to 50 t; several hundred square kilometers of favorable exploration area has been delineated, with an estimated oil geologic resource of 100 million tons.