The Loess “Cave” Near the Village of Surduk - an Unusual Pseudokarst Landform in the Loess of Vojvodina, Serbia

Loess “caves” (piping caverns, wells, tunnels) exposed in loess cliffs are rare pseudokarst landforms that can be regarded as morphological equivalents to collapse dolines or sinkholes formed in classical karst terrains. This study presents the results of an investigation into a loess cave exposed in a loess cliff on the right bank of the Danube River near the village of Surduk in the Vojvodina region, Serbia. This study provides a first detailed morphologic description of this young pseudokarstic landform formed by piping erosion, probably partly supported with carbonate dissolution. The loess “cave” has a height of approximately 12 m and average diameter of around 3.5 m. In the middle of the cave ceiling there is a window. Observations indicate that over the last several years, the morphological characteristics of the landform have been stable. The main aim of this study is to provide a better understanding of the evolution of the piping process in the thick loess-paleosol sequences in the Vojvodina region, northern Serbia. A key role in the genesis of this landform was the short distance between an initial loess doline and a cliff exposing loess sediments, providing the possibility for the lateral removal of loess material. The presence of Robinia pseudoakacia trees around the initial depression modulated the evolution of the doline and provides support for the loess cavern roof. The nature of the dynamic erosional processes on the steep cliffs of the soft loess sediment indicates a very limited lifetime of this pseudokarstic landform

Geologie, Paläontologie und Geochronologie des Eem-Beckens Neumark-Nord 2 und Vergleich mit dem Becken Neumark-Nord 1 (Geiseltal, Sachsen-Anhalt)

Den Schwerpunkt dieser Arbeit bilden die Ergebnisse sedimentologischer, palynologischer, malakologischer und chronometrischer Untersuchungen an Sedimenten aus dem Zentralbereich des Paläoseebeckens Neumark-Nord 2. Die interdisziplinären Untersuchungen an dem 11 m mächtigen Hauptprofil A und benachbarten Profilen zeigen übereinstimmend, dass die limnische Sedimentation vom Ende des Saale-Komplexes über die Eem-Warmzeit bis in die Weichsel-Kaltzeit erfolgte. Das Profil lässt Seespiegelschwankungen mit einer generellen Tendenz der Verflachung und Verlandung sowie wechselnde Sedimentationsraten erkennen. Durch die palynologischen Untersuchungen sind außerdem mit Erosion und Sedimentumlagerungen verbundene Hiaten festgestellt worden. Eine von Laurat et al. (2006) und Mania et al. (2008, 2010) im Profil ausgewiesene zusätzliche Warmzeit, die durch eine Kaltphase von der Eem-Warmzeit separiert und zudem jünger als das Interglazial von NN1 sein soll, existiert nicht. Vor allem die palynostratigraphische, aber auch die malakologische Koinzidenz der Becken NN1 und NN2 belegt die Gleichaltrigkeit der Ablagerungen. Somit ist in Neumark-Nord zwischen der Saale-Grundmoräne der Zeitz-Phase und den periglaziären Bildungen der Weichsel-Kaltzeit nur eine Warmzeit nachweisbar, das Eem. Dies wird durch neue geochronologische Daten eindeutig verifiziert. Daher können die zuletzt von Mania et al. (2010) dokumentierten Lagerungsbeziehungen, nach denen die Beckenfolge von NN2 über der von NN1 liegen soll, nicht bestätigt werden. In Neumark-Nord werden die klimatischen Besonderheiten des Mitteldeutschen Trockengebietes während der Eem-Warmzeit deutlich. Insofern bietet der Vergleich der Eem-Vorkommen von Neumark-Nord, Gröbern und Grabschütz ein Lehrbeispiel für die standortspezifische Variabilität benachbarter synchroner Warmzeitprofile.researc

Active Tectonics Around Almaty and along the Zailisky Alatau Rangefront

This is the author accepted manuscript. The final version is available from Wiley via http://onlinelibrary.wiley.com/doi/10.1002/2017TC004657/abstractThe Zailisky Alatau is a >250-km-long mountain range in Southern Kazakhstan. Its northern rangefront around the major city of Almaty has more than 4 km topographic relief, yet in contrast to other large mountain fronts in the Tien Shan, little is known about its Late Quaternary tectonic activity despite several destructive earthquakes in the historical record. We analyse the tectonic geomorphology of the rangefront fault using field observations, differential GPS measurements of fault scarps, historical and recent satellite imagery, metre-scale topography derived from stereo satellite images, and decimetre-scale elevation models from UAV surveys. Fault scarps ranging in height from ~2 m to >20 m in alluvial fans indicate surface rupturing earthquakes occurred along the rangefront fault since the Last Glacial Maximum (LGM). Minimum estimated magnitudes for those earthquakes are M6.8- 7. Radiocarbon dating results from charcoal layers in uplifted river terraces indicate a Holocene slip rate of ~1.2-2.2 mm/a. We find additional evidence for active tectonic deformation all along the Almaty rangefront, basinward in the Kazakh platform, and in the interior of the Zailisky mountain range. Our data indicate the seismic hazard faced by Almaty comes from a variety of sources, and we emphasize the problems related to urban growth into the loess-covered foothills and secondary earthquake effects. With our structural and geochronologic framework we present a schematic evolution of the Almaty rangefront that may be applicable to similar settings of tectonic shortening in the mountain ranges of Central Asia

Loess as a Quaternary paleoenvironmental indicator

Loess (aeolian silt) is widespread in Eurasia and the Americas. Paleowind direction and wind strength can be reconstructed from spatial and temporal trends of loess thickness and particle size. Fossil land snails in loess can reveal much about past climate and vegetation. Loess is aeolian sediment that is dominated by silt-sized particles. Unlike either coarser dune sand or finer-grained, long-rangetransported dust, loess is relatively poorly sorted, reflecting a combination of transport processes, including saltation, low suspension, and high suspension. Loess can be readily identified in the field; deposits range in thickness from a few centimeters to many tens of meters, and are found over large areas of Eurasia, South and North America (Fig. 1), and smaller areas of New Zealand, Australia, Africa and the Middle East. Loess covers approximately 10% of the Earth’s land surface and is therefore one of the most important terrestrial archives of paleoenvironmental change during the Quaternary. In many regions, loess sections consist of deposits of mostly unaltered sediment with intercalated paleosols. Paleosols represent periods of landscape stability when loess deposition ceased altogether, or at least slowed significantly. Loess can be dated directly using luminescence, radiocarbon, and amino acid geochronology methods

Sediment transport by tropical cyclones recorded in a submarine canyon off Bangladesh

Frequent cyclones originating in the Bay of Bengal landfall on the delta coast of the Ganges and Brahmaputra rivers. The cyclones are well recorded in the sediments of a canyon that is deeply incised into the shelf offshore Bangladesh. The large mud supply by the two rivers forms temporary deposits on the innermost shelf, where they are mobilized by waves and currents during the passage of cyclones. The resulting, highly concentrated fine sand-silt-clay suspension is moved by wind-induced currents and eventually plunges into the shelf canyon. These gravity flows are deposited as graded beds on the broad canyon floor. In a 362-cm-long section of a dated sediment core covering the period from 2006 to 1985, nearly all 59 graded beds can be correlated with 42 cyclones observed in that period. The threefold decrease in the sedimentation rate of the last decade compared to the period from 1994 to 1954 is due to the decreased number and power of cyclones. Compared to the sediment transfer by cyclones, the input by local sediment slumps, tidal currents, and monsoonal floods is small. Thus, cyclones dominate the mobilization and distribution of sediment on the Bangladesh shelf. This sediment dispersal mechanism is probably also typical for other shelf areas crossed by tropical cyclones

Eolian dust input to the Subarctic North Pacific

Eolian dust is a significant source of iron and other nutrients that are essential for the health of marine ecosystems and potentially a controlling factor of the high nutrient-low chlorophyll status of the Subarctic North Pacific. We map the spatial distribution of dust input using three different geochemical tracers of eolian dust, 4He, 232Th and rare earth elements, in combination with grain size distribution data, from a set of core-top sediments covering the entire Subarctic North Pacific. Using the suite of geochemical proxies to fingerprint different lithogenic components, we deconvolve eolian dust input from other lithogenic inputs such as volcanic ash, ice-rafted debris, riverine and hemipelagic input. While the open ocean sites far away from the volcanic arcs are dominantly composed of pure eolian dust, lithogenic components other than eolian dust play a more crucial role along the arcs. In sites dominated by dust, eolian dust input appears to be characterized by a nearly uniform grain size mode at ∼4 μm. Applying the 230Th-normalization technique, our proxies yield a consistent pattern of uniform dust fluxes of 1–2 g/m2/yr across the Subarctic North Pacific. Elevated eolian dust fluxes of 2–4 g/m2/yr characterize the westernmost region off Japan and the southern Kurile Islands south of 45° N and west of 165° E along the main pathway of the westerly winds. The core-top based dust flux reconstruction is consistent with recent estimates based on dissolved thorium isotope concentrations in seawater from the Subarctic North Pacific. The dust flux pattern compares well with state-of-the-art dust model predictions in the western and central Subarctic North Pacific, but we find that dust fluxes are higher than modeled fluxes by 0.5–1 g/m2/yr in the northwest, northeast and eastern Subarctic North Pacific. Our results provide an important benchmark for biogeochemical models and a robust approach for downcore studies testing dust-induced iron fertilization of past changes in biological productivity in the Subarctic North Pacific