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Along the lower course of the Rioni and several minor rivers, more than 70 settlement mounds (local name: Dikhagudzuba) have been identified by field surveys and remote sensing techniques. They give evidence of a formerly densely populated landscape in the coastal lowlands on the Colchian plain (western Georgia) and have been dated to the Bronze Age. As yet, limited information is available on their internal architecture, the chronology of the different layers and their palaeoenvironmental context. Based on archaeological sources, remote sensing measurements of three mounds and sediment cores from one mound and its closer surroundings, our study presents a review of the relevant literature and reveals the internal structure, distribution and spatial extent of the mounds. Geochemical and sedimentological analyses of element contents (X‐ray fluorescence) and granulometry helped to identify different stratigraphical layers and differentiate between natural facies and anthropogenic deposits; using the Structure‐from‐Motion technique the mounds' dimensions were calculated. The studied settlement mounds had relatively small dimension (varying from 30 to 100 m in diameter) and were similar in their stratigraphy. Measurement of elements that can identify types of human activity, notably metals and phosphorus, suggest changing intensities of human occupation, pastoral agriculture and metalworking through the occupation sequence. According to the 14C chronology, the formation of the settlements occurred during the first half of the second millennium B.C., which confirms the archaeological interpretation of their Bronze Age origin. The narrow age difference between the lowermost and uppermost anthropogenic layers indicates an intentional construction of the mounds, rather than a successive accumulation of construction debris due to the disintegration of loam bricks by weathering. Therefore, they are indeed mounds and not tells. It is most likely that the characteristic circular moats that surround them were the source of their construction material. Fluvial and alluvial processes in a warm and humid climate dominated the environment of the mounds. [ABSTRACT FROM AUTHOR]

Soils in hyper‐arid climates, such as the Chilean Atacama Desert, show indications of past and present forms of life despite extreme water limitations. We hypothesize that fog plays a key role in sustaining life. In particular, we assume that fog water is incorporated into soil nutrient cycles, with the inland limit of fog penetration corresponding to the threshold for biological cycling of soil phosphorus (P). We collected topsoil samples (0–10 cm) from each of 54 subsites, including sites in direct adjacency (<10 cm) and in 1 m distance to plants, along an aridity gradient across the Coastal Cordillera. Satellite‐based fog detection revealed that Pacific fog penetrates up to 10 km inland, while inland sites at 10–23 km from the coast rely solely on sporadic rainfall for water supply. To assess biological P cycling we performed sequential P fractionation and determined oxygen isotope of HCl‐extractable inorganic Pδ18OHCl−Pi$$ \mathrm{P}\ \left({\updelta}^{18}{\mathrm{O}}_{\mathrm{HCl}-{\mathrm{P}}_{\mathrm{i}}}\right) $$. Total P (Pt) concentration exponentially increased from 336 mg kg−1 to a maximum of 1021 mg kg−1 in inland areas ≥10 km. With increasing distance from the coast, soil δ18OHCl−Pi$$ {\updelta}^{18}{\mathrm{O}}_{\mathrm{HCl}-{\mathrm{P}}_{\mathrm{i}}} $$ values declined exponentially from 16.6‰ to a constant 9.9‰ for locations ≥10 km inland. Biological cycling of HCl‐Pi near the coast reached a maximum of 76%–100%, which could only be explained by the fact that fog water predominately drives biological P cycling. In inland regions, with minimal rainfall (<5 mm) as single water source, only 24 ± 14% of HCl‐Pi was biologically cycled. We conclude that biological P cycling in the hyper‐arid Atacama Desert is not exclusively but mainly mediated by fog, which thus controls apatite dissolution rates and related occurrence and spread of microbial life in this extreme environment. [ABSTRACT FROM AUTHOR]

A complete annual cycle of the dynamics of fine-grained sediment supplied by the Omo and smaller rivers is simulated for Lake Turkana, one of the world's large lakes, with the hydrodynamic, wave and sediment transport model Delft3D. The model is forced with river liquid and solid discharge and wind data in order to simulate cohesive sediment transport and resuspension. It simulates stratification due to salinity, wave generation and dissipation, and sediment advection and resuspension by waves and currents, with multiple cohesive sediment fractions. A comparison of the simulation results with remotely-sensed imagery and with available in-situ sediment deposition rates validates the model. By devising simulation scenarios in which certain processes were switched on or off, we investigated the contribution of waves, wind-induced surface and bottom currents, salinity-induced stratification and river jet, in resuspending and transporting fine sediments in the lake basin. With only the wind or river influence, most of the sediment deposition occurs in the first 10 km off the Omo River mouth and at a depth < 10 m. When waves are switched on, increased bed shear stresses resuspend most of the fine sediments, that are then deposited further and deeper in the first 30 km, in water depths > 30 m. This study sheds new light on sediment transport in Lake Turkana and in great lakes in general, favouring the view that wind-waves can be the main agent that transports sediment away from river mouths and to deeper areas, as opposed to river-plume or gravity-driven transport. [ABSTRACT FROM AUTHOR]

Phoenicians were the first to systematically develop the area surrounding the Strait of Gibraltar at the end of the 9th century B.C. Following pioneering studies in the Río Guadiaro estuary (Málaga/Cádiz) in the 1980s, a German‐Spanish cooperation project focussed on the role of indigenous people in the Phoenician colonisation trading networks at Los Castillejos de Alcorrín (Manilva, Málaga), one of the most important Early Iron Age settlements in southwestern Iberia. In the recent past, combined with systematic archaeological surveys, geoarchaeological research embedded in the interdisciplinary project 'Archeostraits' aimed at (i) deciphering palaeoenvironmental and coastal changes in the surroundings of Los Castillejos de Alcorrín throughout the mid‐ to late Holocene; (ii) constraining palaeoenvironmental conditions during early Phoenician colonisation; and (iii) better understanding human–environment interactions during the Final Bronze and Early Iron Age (i.e., end of 9th and 8th centuries B.C.). Coring transects along the Río Guadiaro allowed for differentiating successive palaeoenvironments and for establishing a chrono‐stratigraphy for the Holocene sedimentary infill of the valley. Based on these results, the deposition of shallow marine sands, overlying deltaic deposits of alternating sand and mud, and the subsequent development of lagoonal conditions in the lower Guadiaro valley took place before the Phoenicians established the first settlements along the coast. [ABSTRACT FROM AUTHOR]

Wave-transported boulders represent important records of storm and tsunami impact over geological timescales. Their use for hazard assessment requires chronological information on their displacement that in many cases cannot be achieved by established dating approaches. To fill this gap, this study investigated, for the first time, the potential of optically stimulated luminescence rock surface exposure dating (OSL-RSED) for estimating cliff-detachment ages of wave-transported coastal boulders. The approach was tested on calcarenite clasts at the Rabat coast, Morocco. Calibration of the OSL-RSED model was based on samples with rock surfaces exposed to sunlight for ∼ 2 years, and OSL exposure ages were evaluated against age control deduced from satellite images. Our results show that the dating precision is limited for all targeted boulders due to the local source rock lithology which has low amounts of quartz and feldspar. The dating accuracy may be affected by erosion rates on boulder surfaces of 0.02–0.18 mm yr -1. Nevertheless, we propose a robust relative chronology for boulders that are not affected by significant post-depositional erosion and that share surface angles of inclination with the calibration samples. The relative chronology indicates that (i) most boulders were detached from the cliff by storm waves; (ii) these storms lifted boulders with masses of up to ∼ 24 t; and (iii) the role of storms in the formation of boulder deposits along the Rabat coast is more significant than previously assumed. Although OSL-RSED cannot provide reliable absolute exposure ages for the coastal boulders in this study, the approach has large potential for boulder deposits composed of rocks with larger amounts of quartz or feldspar and less susceptibility to erosion. [ABSTRACT FROM AUTHOR]

Chronostratigraphic investigations on coastal sedimentary records such as washover fans or beach‐ridge sequences may be used to reconstruct storm chronologies on centennial to millennial time scales. However, modern analogs are pivotal in interpreting depositional processes and reducing uncertainty in evaluating the complex chronostratigraphic architecture of these landforms. Such a modern analog was provided by category 3 tropical cyclone (TC) Olwyn in 2015, which caused a significant storm surge in the Exmouth Gulf (Western Australia). Pre‐ and post‐TC Olwyn geomorphological surveys and high‐resolution drone‐derived topographical data of a large washover fan document a detailed history of erosion and deposition during the event. The modern analog deposits provided an excellent opportunity to evaluate the use of luminescence‐based proxies (luminescence inventories) for tracing event‐related sediment source environments and understanding transport processes. Sediments deposited during Olwyn show a systematic relationship between luminescence characteristics and washover fan position. Seaward and central washover sections are indicated by well‐bleached deposits due to the beach as the dominant source and/or long transport distances. Lateral washover deposits are characterized by rather local source areas and short transport distances, resulting in higher remnant ages of 70–140 a. Our data show that the combination of sediment source environments and sediment transport length across the fan represents the main control in resetting the luminescence signal and enabling reliable depositional ages to be calculated. It documents the benefit of investigating luminescence inventories when establishing chronologies from complex sedimentary records, thereby demanding a careful consideration of local processes and source areas when interpreting sedimentary TC records. Key Points: We investigated deposits of tropical cyclone Olwyn by combining drone‐derived digital elevation models and single grain luminescence dataHigh‐resolution pre‐ and post‐TC Olwyn DEMs helped to quantify the complex pattern of erosion and deposition in a large washover fanThe single grain luminescence data revealed differences in sediment source areas and transport distances of the washover deposits [ABSTRACT FROM AUTHOR]

In the southernmost part of the Colchian plain (Georgia), the Supsa and Rioni rivers represent important catchments for reconstructing Holocene landscape changes. Using granulometric methods, geochemical analyses and radiocarbon dating, we demonstrate that significant palaeoenvironmental changes have taken place in the surroundings of the Supsa fan since at least 4000 BCE. The initial foothill fan accumulation was prolonged by delta plain progradation. Due to continued fluvial sediment supply, mainly from the Rioni, the lagoon silted up and extended peat bogs formed east of the beach ridge complex. The Supsa fan first prograded northwards (since the third millennium BCE) and later shifted westwards, eventually following an avulsion of the Rioni. While Supsa deposits remain limited to the area of the fan and the modern estuary, the alluvial fines of the Rioni dominate the surrounding areas. The relative sea-level (RSL) index points of the region suggest a gradual RSL rise from ∼-9 m between 4000 and 3500 BCE to -3 / -2 m below the modern sea level in the second half of the first millennium BCE, the period during which Greek colonization and Colchian settlements are attested by archaeological remains. Kurzfassung: Im südlichsten Teil der kolchischen Tiefebene (Georgien) stellen die Einzugsgebiete von Rioni und Supsa wichtige Areale zur Rekonstruktion des holozänen Landschaftswandels dar. Mittels granulometrischer und geochemischer Analysen sowie Radiokohlenstoffdatierungen lässt sich der signifikante Landschaftswandel im Bereich des Supsa-Schwemmfächers seit etwa 4000 v. Chr. nachweisen. Das Areal wurde von einer Sandbarre vom offenen Meer getrennt, hinter der sich große Stillwasserbereiche bildeten. Der anhaltende fluviale Sedimenteintrag, hauptsächlich durch den Rioni, begünstigte die allmähliche Verlandung und die Entstehung von Torfmooren. Gleichzeitig baute sich – zunächst nach Norden (etwa ab dem 3. Jahrtausend v. Chr.) und später durch den Rioni nach Westen abgelenkt – der Schwemmfächer des Supsa vor. Während sich die Supsa-Ablagerungen im Wesentlichen auf den Schwemmfächer und die aktuelle Mündung beschränken, dominieren die feinkörnigen Ablagerungen des Rioni die Umgebung. Die Indexpunkte für den relativen Meeresspiegel deuten auf einen anhaltenden Anstieg des Meeres hin, ausgehend von etwa -9 m unter dem heutigen Niveau um 4000 bis 3500 v. Chr. auf -3 bis -2 m in der zweiten Hälfte des 1. Jahrtausends v. Chr. Für den letztgenannten Zeitraum sind kolchische und griechische Siedlungen durch archäologische Funde in der Umgebung der Supsa-Mündung belegt. [ABSTRACT FROM AUTHOR]

Abstract Quartz is the preferred dosimeter for luminescence dating of Holocene sediments as optically stimulated luminescence (OSL) signals reset rapidly upon light exposure, and are stable over time. However, feldspar is required where quartz luminescence properties are inappropriate for dating, as is often the case in geologically young mountain ranges and areas with young volcanism. Here we aim to evaluate the potential of single grain feldspar luminescence dating applied to late Holocene cyclone and tsunami deposits, for which complete signal resetting can a priori not be guaranteed. To address potential problems of feldspar dating of such deposits associated with heterogeneous bleaching, remnant doses and anomalous fading, we use a low-temperature post infrared infrared stimulated luminescence protocol (pIRIR 150) on single grains. For most samples, good agreement between fading corrected IR 50 and non-fading corrected pIRIR 150 ages is observed. Both feldspar ages generally also show good agreement with age control provided by historical data and quartz luminescence ages. pIRIR 150 remnant ages in modern analogue samples are shown to be < 50 years, indicating that dating accuracy might be negatively affected by insufficient signal zeroing only for sediments younger than ∼500 years. As these minor remnant ages are interpreted as being caused by unbleachable luminescence residuals, slight age overestimation for young samples can be overcome by subtracting the remnant ages. The good agreement between pIRIR 150 , IR 50 and quartz ages, indicates that a significant number of grains must have experienced relatively complete signal resetting during or immediately prior to transport, as the three signals are known to bleach at different rates. Since light exposure during the event is expected to be limited, we deduce that a significant portion of the grains in the cyclone and tsunami deposits was already bleached prior to the event of interest. These well-bleached grains were likely eroded at the beach, while other grains with larger remnant ages probably originate from the shallow subtidal, coastal barriers or even further inland sources. Additional signal resetting during storm and tsunami transport is indicated by slightly younger quartz than feldspar ages for grains with incomplete pre-transport resetting that were eroded at the Holocene coastal barrier. Highlights • Feldspar single grain dating of tsunami and cyclone deposits younger than 3000 years. • Both fading corrected IR 50 ages and uncorrected pIRIR 150 ages agree with age control. • Well-bleached grains due to pre-transport resetting of source material from the beach. • Multi-luminescence-signal approach informs about sediment transport processes in coastal zone. • OSL indicates mixture of well-bleached grains from beach and incompletely reset sediment from barrier. [ABSTRACT FROM AUTHOR]

Abstract: Situated between the Enguri and Khobistskali rivers, more than 30 settlement mounds (locally named Dikhagudzuba) provide evidence for a relatively densely populated landscape in the coastal lowlands of western Georgia during the Bronze Age. Compared to older mounds in eastern Georgia and other regions, these mounds differ not only in age but also in their average size and spatial distribution. Based on the interpretation of nine sediment cores, drone survey and structure‐from‐motion photogrammetry techniques, our study aims at (i) establishing a chronostratigraphic framework for the mounds based on 14C dating; (ii) reconstructing possible phases and gaps in human occupation; (iii) determining potential source areas of the mounds’ construction material; and (iv) identifying the environmental conditions at the time of their use. The three investigated mounds are similar in dimension and stratigraphy. Anthropogenic layers could clearly be identified and separated from the natural alluvial deposits below. According to the 14C age estimates, the mounds date to the first half of the 2nd millennium B.C.; this confirms the archaeological interpretation of their Bronze Age origin. While only one construction phase is assumed for two of the mounds, stratigraphic analysis suggests a successive enlargement of a third mound over at least 470 years. Paleoenvironmental conditions in the vicinity of the mounds were dominated by swampy, fluvial (channel) to alluvial (overbank) processes, as attested by river‐bank deposits and floodplain alluvium. [ABSTRACT FROM AUTHOR]

Prehistoric storm records are relatively scarce in most parts of the world. This article presents storm records derived from coral rubble-based geological archives of the Houtman Abrolhos Archipelago located off the west coast of Australia, where the southernmost coral reefs of the Indian Ocean are found. Winter storm swell from the circum-Antarctic 'Brave Westerlies', as well as tropical cyclone waves, have left numerous ridge systems on dozens of islands of the archipelago, all composed of coral rubble from adjacent reefs. At three islands, seven ridge systems were dated by three different methods: U-series (68 dates), radiocarbon (64 dates), electron spin resonance (7 dates); 139 radiometric dates span the last 5500 years of the Holocene. In contrast to the geomorphological interpretation, the age sequences show 'inversions', hiatuses and different ages for the same ridge, all pointing to complicated ridge formation processes. Time gaps, some exceeding 1000 years, are interpreted as phases of erosion and not as phases without storm activity. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study investigates synthetic aperture radar (SAR) time series of the Sentinel-1 mission acquired over the Atacama Desert, Chile, between March 2015 and December 2018. The contribution analyzes temporal and spatial variations of Sentinel-1 interferometric SAR (InSAR) coherence and exemplarily illustrates factors that are responsible for observed signal differences. The analyses are based on long temporal baselines (365–1090 days) and temporally dense time series constructed with short temporal baselines (12–24 days). Results are compared to multispectral data of Sentinel-2, morphometric features of the digital elevation model (DEM) TanDEM-X WorldDEM™, and to a detailed governmental geographic information system (GIS) dataset of the local hydrography. Sentinel-1 datasets are suited for generating extensive, nearly seamless InSAR coherence mosaics covering the entire Atacama Desert (>450 × 1100 km) at a spatial resolution of 20 × 20 meter per pixel. Temporal baselines over several years lead only to very minor decorrelation, indicating a very high signal stability of C-Band in this region, especially in the hyperarid uplands between the Coastal Cordillera and the Central Depression. Signal decorrelation was associated with certain types of surface cover (e.g., water or aeolian deposits) or with actual surface dynamics (e.g., anthropogenic disturbance (mining) or fluvial activity and overland flow). Strong rainfall events and fluvial activity in the periods 2015 to 2016 and 2017 to 2018 caused spatial patterns with significant signal decorrelation; observed linear coherence anomalies matched the reference channel network and indicated actual episodic and sporadic discharge events. In the period 2015–2016, area-wide loss of coherence appeared as strip-like patterns of more than 80 km length that matched the prevailing wind direction. These anomalies, and others observed in that period and in the period 2017–2018, were interpreted to be caused by overland flow of high magnitude, as their spatial location matched well with documented heavy rainfall events that showed cumulative precipitation amounts of more than 20 mm. [ABSTRACT FROM AUTHOR]

The hyperarid parts of the Atacama Desert, N Chile, are among the driest places on Earth, and a number of studies have emphasized the remarkable slowness of earth surface processes since the late Tertiary. Nevertheless, geomorphic processes such as overland flow or flash flood activity, salt-driven shrink-swell processes, dust deposition, or seismic shaking have significantly contributed to the landscape formation in the Atacama. Hitherto, the study of Owen et al. (2013) represents the only study with detailed investigations on the enigmatic and Atacama-specific zebra stripes, which are contour-parallel, thin lateral bands of rather angular gravels on hillslopes, characterized by grain sorting and a specific wavelength. While these authors suggest that zebra stripes represent fossil evidence of overland flow, recent investigations on the formation of the Atacama boulder fields emphasized the significance of seismicity in shaping Atacama landscapes, thereby challenging the water-related evolution of zebra stripes.Based on UAV-derived high-resolution aerial photos, geomorphological surveys and sediment sampling, this contribution adds important new and contrary data on zebra stripe patterns, which may be conducive in their better understanding. We document a wider distribution of zebra-type stone stripes than previously published, and a rather high variability of zebra stripe characteristics with regard to stripe orientation, sorting-patterns and bedding properties. Stripes are poorly to well sorted, and surface gravel units may be multi-grained and up to 10 cm thick, loosely bedded, and entirely uncemented. At most locations, stripe orientation seems to be oblique rather than parallel to contour lines. In addition, stripe fronts at numerous locations consist of multiple bulges of 0.5-2 m width showing lateral and downslope coarsening patterns. Based on the form-concordance between these zebra stripes and experiments on segregation-induced granular fingering, we propose a combination of seismic shaking and dry granular free surface flows as the most likely mechanism for the formation of zebra stripes, rather than (palaeo-) overland flow. As such, our findings may complicate the geomorphic interpretation of zebra stripes and the inference of related geomorphic processes. [ABSTRACT FROM AUTHOR]

Fields of wave-emplaced blocks and boulders represent impressive evidence of cyclone and tsunami flooding over Holocene time scales. Unfortunately, their use for coastal hazard assessment is in many cases impeded by the absence of appro-priate dating approaches, which are needed to generate robust chronologies. The commonly applied AMS-14C, U/Th or ESR dating of coral-reef rocks and marine organisms attached to the clasts depends on a – mostly hypothetical – coincidence between the organisms' death and boulder displacement, and inferred event chro-nologies may be biased by the marine 14C-reservoir effect and reworked orga-nisms. Here we discuss the potential of the recently developed optically stimulat-ed luminescence (OSL) surface exposure dating technique to directly date the relocation process of wave-emplaced boulders. Exposure dating may even allow to decipher more complex transport histories of boulders that were relocated and overturned repeatedly, thus experiencing multiple phases of exposure and burial.For this, we sampled 11 coastal boulders from the Rabat coast, Morocco, which were either relocated by tsunami-induced flooding (e.g. during the 1755 Lisbon tsunami and similar events) or by exceptional North Atlantic winter storms. All sampled boulders (i) show clear indication of overturning during wave transport in the form of downward-facing bio-eroded surfaces; (ii) are composed of sand-stones that contain quartz with adequate luminescence signals; (iii) are of Holo-cene age and, therefore, in the dating range of OSL surface exposure dating. The measured signal-depth profiles indicate time-dependent resetting of luminescence signals in the freshly exposed post-transport surfaces of all investigated boulders. Calibration samples with known exposure ages of 2 years are used to determine local values for light attenuation in the rock and signal resetting at the rock sur-face. These parameters are required to transform signal-depth profiles of sampled boulders into exposure ages. Results so far indicate that dating accuracy of most boulders is significantly affected by post-transport erosion of the surfaces. How-ever, the approach nevertheless provides relative age differences for boulder dislo-cation, and the observed patterns agree with the relative chronology expected due to the macroscopic appearance of the boulder surfaces. Thereby, it promises to overcome some of the limitations of existing dating techniques and will provide first chronological information on the frequency-magnitude relationship of ex-treme wave events at the Rabat coast. [ABSTRACT FROM AUTHOR]

Working with a large temporal dataset spanning several decades often represents a challenging task, especially when the record is heterogeneous and incomplete. The use of statistical laws could potentially overcome these problems. Here we apply Benford's Law (also called the 'First-Digit Law') to the traveled distances of tropical cyclones since 1842. The record of tropical cyclones has been extensively impacted by improvements in detection capabilities over the past decades. We have found that, while the first-digit distribution for the entire record follows Benford's Law prediction, specific changes such as satellite detection have had serious impacts on the dataset. The least-square misfit measure is used as a proxy to observe temporal variations, allowing us to assess data quality and homogeneity over the entire record, and at the same time over specific periods. Such information is crucial when running climatic models and Benford's Law could potentially be used to overcome and correct for data heterogeneity and/or to select the most appropriate part of the record for detailed studies. [ABSTRACT FROM AUTHOR]