Charcoal and fossil wood from palaeosols,sediments and artificial structures indicating Late Holocene woodland decline in southern Tibet (China)

Charcoal and fossil wood taken from palaeosols, sediments and artificial structures were analysed in order to evaluate the regional pedoanthracological potential and to obtain information on Holocene environmental changes, particularly on possible past tree occurrences in southern Tibet. This research was initiated by the question to what extent this area is influenced by past human impact. Even recent evaluations have perceived the present treeless desertic environment of southern Tibet as natural, and the previous Holocene palaeoenvironmental changes detected were predominantly interpreted to be climate-determined. The material analysed – comprising a total of 53 botanical spectra and 55 radiocarbon datings from 46 sampling sites (c. 3500–4700 m a.s.l.) – represents the largest systematically obtained data set of charcoal available from Tibet so far. 27 taxa were determined comprising trees, (dwarf-) shrubs and herbs as well as grasses. The predominant tree taxa were Juniperus, Hippophae, Salix and Betula. According to their present-day occurrence in the region, the genera Juniperus and Hippophae can be explicitly attributed to tree species. Further, less frequently detected tree taxa were Populus, Pinus, Quercus, Taxus and Pseudotsuga. Charcoal of Juniperus mainly occurred on southern exposures, whereas Betula was associated with northern exposures. In contrast, the (partly) phreatophytic taxa Hippophae and Salix showed no prevalent orientation. The distribution of radiocarbon ages on charcoal revealed a discontinuous record of burning events cumulating in the Late Holocene (c. 5700–0 cal BP). For southern Tibet, these results indicated a Late Holocene vegetation change from woodlands to the present desertic pastures. As agrarian economies in southern and south-eastern Tibet date back to c. 3700 and 5700 cal BP, respectively, and the present-day climate is suitable for tree growth up to c. 4600 m a.s.l., we concluded that the Late Holocene loss or thinning out of woodlands had been primarily caused by humans.     

Pseudotachylite associated with a bedding-parallel fault zone between the Witwatersrand and Ventersdorp Supergroups,South Africa

A Proterozoic bedding-parallel fault zone is described from the Witwatersrand basin in South Africa. The fault zone is dominated by pseudotachylite, the youngest tectonite present, but also contains quartz veins and cataclasites which post-date the spatially associated mylonites. Both tectonic eliminations and duplications are caused by the fault zone which is dominated by a northerly to westerly overthrusting. The fault rocks probably did not form during a single event but as a result of a minimum of two periods of activation of the fault zone separated in time by at least the period required to deposit in excess of 4 km of sediments belonging to the lower part of the Transvaal Sequence. Equivocal evidence suggests that the pseudotachylites, which probably formed as a result of frictional fusion on fault planes, may have formed at similar depths to the mylonites. Consequently the related parameters of pressure and temperature are not considered to be as important in determining whether brittle or ductile deformation occurs, as are pore fluid pressure and strain rate. The age, direction of tectonic transport and a characteristic enrichment in lead all suggest that there may be a genetic link between the pseudotachylites in this fault zone and the type pseudotachylites at Vredefort, 60 km to the south.     

Seismic investigations in the vicinity of the great Sphinx of Giza,Egypt

An integrated suite of seismic geophysical surveys including seismic refraction, refraction tomography, and high resolution reflection was utilized in the areas within the Sphinx Enclosure, the Sphinx Temple, and in the surrounding desert areas to the east and south of the Sphinx. The purposes of the investigations were to analyze the depth and distribution of weathering in the exposed limestone bedrock, search for voids/cavities around and under the Sphinx, and describe the bedrock configuration where buried by sands in the adjacent desert areas. The survey discovered that subsurface weathering below the floor of the Sphinx Enclosure is not uniform, suggesting varied periods of subaerial exposure for different portions of the excavation. A series of cavities on each side of the Sphinx, as well as between its paws, was defined. Further, the sand-buried bedrock surface in the desert area shows evidence of several excavated, or possibly downfaulted, structures.     

Sediment sequences and paleosols in the Kyichu Valley, southern Tibet (China), indicating Late Quaternary environmental changes

Abstract The Tibetan Plateau is highly sensitive to environmental changes and affects the settings of a far larger territory in Central Asia and beyond. Thus, knowledge on past environmental changes in that area is essential. Even though the Kyichu (Lhasa River) Valley and its tributaries is an easily accessible area, the Late Quaternary landscape evolution of southern Tibet is in general scarcely known. Therefore, 12 sedimentary sections in the middle and lower catchment were subjected to multidisciplinary analyses (sedimentology, paleopedology, AMS ¹⁴C and luminescence dating, and charcoal determination) aiming at results on regional paleoenvironmental changes. At the altitude studied (3600–4000 m above sealevel), no glacial relics could be detected, indicating that the valley positions have been unglaciated since the Last Interglacial. The lack of fluvial–lacustrine structures above the floodplain is due to the aggradational character of this tectonically (sub‐)active valley, which caused an alluvial burying of older valley bottoms. During the Late Pleistocene the mouth area of the Kyichu was occupied by a lake which was part of a larger dam‐lake in the superordinate Yarlung Zhangbo Valley. On the valley flanks, loesses were predominantly deposited before the Last Glacial Maximum (LGM), whereas eolian sands were predominantly deposited around and after the LGM. Paleosols of Last Interglacial, Last Glacial and Holocene ages regularly occur at terrestrial sites representing temperate to cool and humid to semiarid conditions during soil formation. Ages of colluvial sediments indicate that the widespread barren valley slopes were primarily formed by Late Pleistocene erosion followed by a secondary Holocene erosion phase. Charcoal spectra indicate a Late Holocene change from a forest environment to a pastoral environment with sparse grasses, herbs and dwarf shrubs. It is assumed that the Late Holocene environmental changes, such as loss of forests/woodlands and erosion, have at least been reinforced by humans, enhancing a regional climatic aridification and cooling trend.     

Time-series modeling of reservoir effects on river nitrate concentrations

Saylorville Reservoir is a 24.1 km² impoundment of the Des Moines River located approximately 10 km north of the City of Des Moines, Iowa, USA. Surface water from the Des Moines River used for drinking water supply is impaired for nitrate–nitrogen. Monthly mean nitrate concentration data collected upstream and downstream of the reservoir for a 30-year period (1977–2006) were selected for time-series analysis. Our objectives were to (1) develop a model describing nitrate concentrations downstream of the reservoir as a function of the concentrations entering the reservoir and (2) use the model to provide a 1-month ahead forecast for downstream water quality. Results indicated that downstream nitrate can be effectively modeled using a transfer function approach that utilized inflow concentrations during the current and previous month as input variables. Inflow concentrations were modeled using an AR(20) model, with the higher order model consistent with temporal correlation noted by others. The transfer function model suggested that the reservoir is reducing nitrate concentrations by 22 ± 6%, a reduction that greatly exceeds previous estimates. Monthly nitrate forecasted with the model were nearly all within a 95% prediction interval of their actual measured values and did not appear greatly affected by flow variations.     

An Estuarine Habitat Classification for a Complex Fjordal Island Archipelago

Spatial patterns of estuarine biota suggest that some nearshore ecosystems are functionally linked to interacting processes of the ocean, watershed, and coastal geomorphology. The classification of estuaries can therefore provide important information for distribution studies of nearshore biodiversity. However, many existing classifications are too coarse-scaled to resolve subtle environmental differences that may significantly alter biological structure. We developed an objective three-tier spatially nested classification, then conducted a case study in the Alexander Archipelago of Southeast Alaska, USA, and tested the statistical association of observed biota to changes in estuarine classes. At level 1, the coarsest scale (100–1000’s km²), we used patterns of sea surface temperature and salinity to identify marine domains. At level 2, within each marine domain, fjordal land masses were subdivided into coastal watersheds (10–100’s km²), and 17 estuary classes were identified based on similar marine exposure, river discharge, glacier volume, and snow accumulation. At level 3, the finest scale (1–10’s km²), homogeneous nearshore (depths <10 m) segments were characterized by one of 35 benthic habitat types of the ShoreZone mapping system. The aerial ShoreZone surveys and imagery also provided spatially comprehensive inventories of 19 benthic taxa. These were combined with six anadromous species for a relative measure of estuarine biodiversity. Results suggest that (1) estuaries with similar environmental attributes have similar biological communities, and (2) relative biodiversity increases predictably with increasing habitat complexity, marine exposure, and decreasing freshwater. These results have important implications for the management of ecologically sensitive estuaries.     

The stratigraphic interpretation of a highly deformed proterozoic region in central bushmanland,South Africa: First correlation of structurally separated metasediments of the aggeneys subgroup

It is demonstrated that highly deformed and structurally separated Proterozoic metasediments, which have previously defied stratigraphic and sedimentological classification, may be correlated and characterised. This is done by using a multidisciplinary approach, including stratigraphic and structural mapping and sedimentological interpretation, developed during the Geodynamics Programme in Western Namaqualand (1975–1980). The metasediments under consideration belong to the economically important Aggeneys Subgroup, which hosts stratabound massive sulphide deposits at Aggeneys and Gamsberg (Gams). Four isolated areas are considered and it is shown that the Dabenoris, Kabas and Pella Formations, and the lower part of the Achab Formation are equivalent to the lower part of the Wortel Formation, and that the upper part of the stratigraphic column is composed of the upper units of the Achab Formation, the Gams Formation and the Blomhoek Formation. The Zuurwater Formation is, for the most part, equivalent to the lower portion of the Wortel Formation, but the uppermost strata are correlated with the Blomhoek Formation. These results illustrate that it is possible to obtain the information necessary for a palaeobasin analysis from even the most complex Proterozoic regions.     

Historische Entwicklung einer Sedimentbelastung: Gedächtnis einer Industrieregion Historical Trends of Sediment Loads: Memory of an Industrial Region

The chronologies are shown of sediment load on the banks of a river of the Ruhr district (Lippe) with radionuclides of radium, lead and cesium and preliminary chemical measurements for lead, zinc, arsenic, mercury, cadmium, barium, PAHs, PCDDs, PCDFs, PCBs, TOC, AOX and EOX. A new method of dating is developed and proved, which is especially suitable for rivers with radioactivity from coal mines. The method improves the well-known excess-²¹⁰Pb-dating for the use with rivers in industrial regions and allows the preparation of load histories (chronologies). Conclusions are made on the historical trend of emissions in the region from the trend of the sediment load of known age and regular sedimentation without perturbation.     

Petrochemical evidence on the probable origin of ferriferous metasediments in western Bushmanland

The mineralized Proterozoic metasediments of Bushmanland are characterized by the presence of ferriferous rocks. This includes banded and unbanded iron formations and various types of gossans. These units are not laterally extensive and occur in different stratigraphic levels. The prevalent minerals in the ferriferous rocks are hematite, magnetite, quartz, garnet, muscovite, biotite and sillimanite, but less common occurrences of graphite, alunite, plumbojarosite, gahnite and dufrenite have been noted. The chemical variation (wt%) is extensive: total Fe₂O₃ (1.3–93.5), SiO₂ (4–93), Al₂O₃ (0.2–14.0), CaO (0.02–20.7), MnO (0.0–14.3), MgO (0.0–5.7), TiO₂ (0.0–4.4), Na₂O (0.0–2.0), K₂O (0.0–1.5) and P₂O₅ (0.1–7.0). The preliminary nature of the data set precludes, however, firm conclusions regarding stratigraphic control of the chemical composition. The trace-element contents (ppm) extend over several orders of magnitude: Zn (0–7,000), Ba (0–5,200), Cu (0–1,400), Pb (0–1,070) and Ni (6–540). Collectively, the data indicate that most of the ferriferous rocks represent highly metamorphosed sediments.