Late Pleistocene alluvial fan evolution along the coastal Atacama Desert (N Chile)

Due to their sensitivity to both tectonic activity and climatic variations, coastal alluvial fans (CAF) along the western flank of the Coastal Cordillera in the Atacama Desert (northern Chile) are important geo-archives for unravelling Quaternary environmental change. Our study focuses on terrestrial and marine deposits of five CAF complexes between 20 degrees and 25 degrees S along the coastal zone of the Atacama to identify phases of alluvial fan activity during the Late Quaternary. Based on a combination of luminescence dating and Be-10 cosmogenic nuclide exposure dating as well as existing chronological data in the area, insights into climatic variations along the hyperarid coast are presented for the Late Pleistocene derived from CAF morphodynamics. Activity of alluvial fans could be documented during time spans 95-80 ka, 60-45 ka, 35-20 ka, as well as the Holocene. Numerical dating of marine terrace deposits gives insights into the tectonic uplift of the Coastal Plain in northern Chile during the Late Quaternary period, for which estimated uplift rates between similar to 0.06 and similar to 0.57 m/ka were derived. While tectonic activity induces base-level changes, long-term tectonic activity rather indirectly controls alluvial fan activity. We suggest that alluvial fan activity is mainly controlled by atmospheric changes from the Pacific Ocean. Based on our observations, CAF in the hyper-arid Atacama Desert serve as suitable geo-archives for reconstructing climate changes during the Quaternary. In particular, the usefulness of alluvial fan systems in a water-limited environment is important for understanding the palaeoenvironmental evolution in a coastal desert

Violet stimulated luminescence as an alternative for dating complex colluvial sediments in the Atacama Desert

Luminescence dating has become a key tool in studies of the Quaternary. The typically stable luminescence response of quartz grains and the absence of a significant internal dose, make quartz minerals the preferred dosimeter for monitoring the burial dose in sediments. Unfortunately, the reliability of conventional OSL (optically stimulated luminescence) dating, based on blue stimulation, can be compromised when the luminescence decay is not dominated by a rapidly decaying and stable part of the luminescence signal (i.e. the fast component). On the other hand, standard methods in luminescence dating are limited to ages of a few hundred kiloyears. In this study, violet stimulated luminescence (VSL) has been used as a means to overcome both problems, applied to a series of colluvial deposits in the Atacama Desert, Chile. Quartz from this region, characterized by poor blue-OSL response, showed a reproducible and stable VSL signal capable of recovering given doses up to -500 Gy and a saturation dose twice as high as conventional OSL. The VSL response from these samples has been studied in detail and the estimated ages have been compared with an already established chronology for the same site, based on IRSL of potassium feldspar single grains. Results agree for the dose range of the profile studied, -100-250 Gy, equivalent to ages of 29-79 ka confirming the suitability of VSL for dating sedimentary quartz with unreliable blue-OSL response and to extend the age range of conventional OSL dating

Taken from the sea, reclaimed by the sea: The fate of the closed harbour of Elaia, the maritime satellite city of Pergamum (Turkey)

During Hellenistic times, when the Pergamenian kingdom was prospering, Pergamum was operating an important harbour, used by merchants and military at the city of Elaia. This paper focuses on the development, utilisation and decay of the closed harbour of Elaia, which is discussed in the context of the landscape evolution of the environs of the ancient settlement. Based on geoarchaeological, archaeological and literary evidence, the construction of two harbour moles in order to provide shelter against wave action and enemies can be attributed to the early Hellenistic period. Geoelectric measurements revealed the construction profile of the moles. Coring evidence indicated that together with mole construction, a greater area of the formerly shallow marine and sublittoral terrain was consolidated, most probably to create space for harbour installations. The closed harbour basin was used intensely during Hellenistic and Roman times. Later, continued siltation hindered further usage. In combination with the decline of the city of Elaia in Late Antiquity, this was the reason why the harbour was abandoned. Scenarios for the time of the maximum transgression of the sea around 2500 BC, the early Hellenistic times around 300 BC, and Late Antiquity AD 500, are presented. (C) 2013 Elsevier Ltd and INQUA. All rights reserved

Gradients in climate, geology, and topography affecting coastal alluvial fan morphodynamics in hyperarid regions - The Atacama perspective

Along the coast of the hyperarid Atacama Desert, late Quaternary alluvial fans emerge from the Coastal Cordillera to the Pacific Ocean between 20.5 degrees S and 25.5 degrees S. Coastal alluvial fans (CAF) show, in comparison to the interior fans of the Atacama Desert, pronounced recent activity. However, the complex interplay between climate, lithology, and tectonics affecting the CAF morphodynamics in such hyperarid coastal settings needs to be better understood. We therefore aim at assessing the major factors driving CAF activity and evaluate their effects along gradients. We conducted an extensive study relating climatic, lithologic, and tectonic characteristics to fan and catchment geomorphology of 123 CAF. Geomorphometric analyses are based on the 12.5 m TanDEM-X WorldDEM (TM), catchment lithology and faults are extracted from 13 regional geological maps, and the frequency of heavy rainfall events capable of activating CAF is derived from a Weather Research and Forecasting (WRF) regional climate model. Our results point to a primary climatic control on CAF morphodynamics shown in functional relationships with catchment hydromorphometric characteristics reflecting a high susceptibility to debris flows - the main CAF-constructing process. Catchment properties along the latitudinal gradient reflect the source of significant precipitation events: frontal systems and cut-off lows which mainly originate in the extratropics and become increasingly rare towards the north. The frequency of precipitation extremes can only be correlated to the hydromorphometry and geomorphic maturity of catchments that feature a high degree of sediment transport potential and generally do not cut back far into the Coastal Cordillera. Related to the strongly reduced influence of the Pacific precipitation source towards the east, this additional climatic transition is governed by the orographic effect of the steep W-E gradient in topography. In contrast, source-area lithology is of negligible relevance for CAF catchment morphometry and fan activity. An important indirect influence of tectonics, however, can be seen in the long-term (neo)tectonic activity within the Coastal Cordillera, which in turn shapes catchments and controls the topography

Unravelling fluvial deposition and pedogenesis in ephemeral stream deposits in the vicinity of the prehistoric rock shelter of Ifri n'Ammar (NE Morocco) during the last 100 ka

Our study focuses on the ephemeral stream deposits of Wadi Selloum to identify phases of morphodynamic stability (pedogenesis) and activity (flooding) in the direct vicinity of the rock shelter of Ifri n'Ammar (NE Morocco). As one of the oldest settlement sites of anatomically modern humans (AMH) in North Africa, Ifri n'Ammar documents periodical occupations since similar to 170 ka. Since the discontinuous settlement record may reflect climate forcing with subsequent landscape changes, we aim at reconstructing the palaeoenvironmental variability recorded in the ephemeral stream deposits. In addition to the use of micromorphological, seditnentological, geochemical and mineralogical methods, the geochronological framework of ephemeral stream deposits was established by the application of different luminescence dating techniques. The deposition ages between 102 +/- 8 ka and 13 +/- 0.2 ka span different morphodynamically stable and active phases. Periods of enhanced aggradation occurred around similar to 100 ka, similar to 75 ka, similar to 55 ka, after the LGM, and during the Holocene, whilst sedimentation ended after similar to 13 ka. The Wadi Selloum might be characterised by enhanced flooding during humid phases. Pedogenesis may be used as environmental indicator for more humid climate conditions during MIS 3 (palaeo-Calcisol), the early Holocene (Calcisol) and the late Holocene (Fluvisol). This study thus provides first insights into the palaeoenvironmental changes around the rock shelter of Ifri n'Ammar during the last glacial-interglacial cycle. (C) 2016 Elsevier B.V. All rights reserved

Testing the potential of K-feldspar pIR-IRSL and quartz ESR for dating coastal alluvial fan complexes in arid environments

Coastal alluvial fans (CAF) are important geo-archives due to their sensitivity to both tectonic activity and climatic changes. Thus, they can give key insights for geomorphic and sedimentary processes. In this study we test the potential of K-feldspar post infrared-infrared stimulated luminescence (pIR-IRSL) and quartz electron spin resonance (ESR) methods for dating alluvial fan complexes in arid environments. The existing chronological data from marine terraces that interact with CAF make the Atacama Desert in northern Chile an excellent setting for this research. Samples have been collected from alluvial, marine and aeolian sediments embedded in the CAF complexes, allowing evaluation of the different signal properties and bleaching characteristics of the pIR-IRSL and ESR signals over Late Pleistocene time scales. pIR-IRSL dose distributions of clast-rich alluvial fan samples are characterised by higher scatter and demonstrate heterogeneous bleaching, while matrix-rich alluvial fan deposits show rather homogeneous poor bleaching in the dose dispersion as indicated by a modern analogue sample. In contrast, marine and aeolian deposits are homogeneously well bleached, supported by a modern littoral sample. Following the quartz multiple centre (MC) ESR dating approach (Al and Ti centres), bleaching of the different centres prior to deposition has been achieved. While the Ti-H centre provides mostly lower doses than the Ti-Li centre, in most cases the Al centre provides the highest dose values. This pattern is consistent with their respective bleaching kinetics and suggests that the Ti centre signals most likely provide the closest estimate to the true burial dose for samples with doses > 200 Gy. ESR and pIR-IRSL ages are consistent at 2 sigma for the marine, aeolian and clast-rich debris-flow deposits, which is in agreement with existing chronological data in this area. It appears that the mode of sediment transport on alluvial fans, either as matrix- or clast-rich flows, plays an important role in sediment bleaching. While clast-rich alluvial fan deposits are likely better bleached, we cannot exclude insufficient bleaching during matrix-rich alluvial fan flows; our dating results suggest that both pIR-IRSL and ESR dating overestimate the true burial age. The combination of pIR-IRSL and MC ESR dating can be considered as a promising tool for deciphering alluvial fan formation over (Late) Pleistocene time scales

Luminescence dating of ephemeral stream deposits around the Palaeolithic site of Ifri n'Ammar (Morocco)

The prehistoric site of Ifri n'Ammar is situated in northeastern Morocco, in the northern prolongation of the Middle Atlas Mountains. It is a key location in unravelling the history of anatomically modern humans (AMH) in northern Africa as it reveals Middle and Late Palaeolithic occupation phases since similar to 170 ka. Whilst the archaeological sequence within the rock shelter has been well studied, the timing of landscape dynamics around Ifri n'Ammar is still poorly understood. This study therefore aims to establish a detailed chronology of the Wadi Selloum profile at the apron of the shelter, based on optically stimulated luminescence (OSL) dating of ephemeral stream deposits. Coarse-grain quartz was used for single-grain and multiple-grain dating procedures to investigate the luminescence properties of these deposits and to get more accurate age information concerning the phases of human occupation. Continuous wave OSL (CW-OSL) revealed a dominant fast component for all quartz samples. The dose distribution of the uppermost samples showed overdispersion values >25% and significant positive skewness. We identified partial bleaching as the main source of scatter in the equivalent dose (D-e) distribution. The lowermost sample appeared to be close to signal saturation. The shapes of the dose response curve varied widely between aliquots and coarse quartz grains exhibited therefore very different dose saturation behaviours among aliquots. With fully saturated dose response curves (DRCs), meaningful D-0 values were assumed for D-e estimation. The eight OSL samples yielded stratigraphically consistent ages ranging from 1.3 +/- 0.2 ka to 76 +/- 5 ka, thus reaching the Middle Palaeolithic period. Moreover, a pottery shard dated to 7.4 +/- 0.6 ka (Early Neolithic period) by thermoluminescence (TL), perfectly matched the Holocene OSL samples extracted at the same depth of the profile. In summary, our results point to fluvial aggradation during OIS 5.1, the late glacial period, and the Holocene. (C) 2015 Elsevier B.V. All rights reserved

Identification of humid periods in the Atacama Desert through hillslope activity established by infrared stimulated luminescence (IRSL) dating

Geological records indicate that the hyper-aridity in the Atacama Desert has prevailed since at least the mid-Miocene, with shorter periods of increased humidity punctuating long-term aridity. The 7-m-high accumulation of colluvial sediments at the Salar Grande (21 degrees S/70 degrees W) studied here provides a key palaeoclimate record to understand hillslope dynamics and its relation to humid periods. While 1 degrees Be surface exposure ages point to long-term surface stability of the flat upslope surface, a combination of humidity-driven soil creep, overland flow and soil creep related to seismic shaking, caused denudation of the hillslope and accumulation of several metres of colluvium over much shorter timescales during the last 130 ka. A robust chronology for the hillslope sediments has been established by using Infrared Stimulated luminescence (pIR-IR225 protocol) on K-feldspar extracts from nine samples collected within the accumulation. A series of tests has been carried out to confirm the suitability of the method. The estimated ages indicate accelerated sedimentation at 35-80 ka, and 100-130 ka, which are interpreted as periods with more humid climate conditions than present. These findings agree with climate variations in the hyper-arid Atacama indicated by the activity of coastal alluvial fans and river catchments

A primaquine-chloroquine hybrid with dual activity against Plasmodium liver and blood stages

We present a new class of hybrid molecules consisting of the established antiplasmodial drugs primaquine and chloroquine. No drug is known to date that acts comparably against all stages of Plasmodium in its life cycle. Starting from available precursors, we designed and synthesized a new-generation compound consisting of both primaquine and chloroquine components, with the intent to produce agents that exhibit bioactivity against different stages of the parasite's life cycle. In vitro, the hybrid molecule 3 displays activity against both asexual and sexual P. falciparum blood stages as well as P. berghei sporozoites and liver stages. In vivo, the hybrid elicits activity against P. berghei liver and blood stages. Our results successfully validate the concept of utilizing one compound to combine different modes of action that attack different Plasmodium stages in the mammalian host. It is our hope that the novel design of such compounds will outwit the pathogen in the spread of drug resistance. Based on the optimized synthetic pathway, the compound is accessible in a smooth and versatile way and open for potential further molecular modification