<p>The shape of soil-mantled hillslopes is typically attributed to erosion rate and... more <p>The shape of soil-mantled hillslopes is typically attributed to erosion rate and the transport efficiency of the various processes that contribute to soil creep. While climate is generally hypothesized to have an important influence on soil creep rates, a lack of uniformity in the measurement of transport efficiency has been an obstacle to evaluating the controls on this important landscape parameter. We addressed this problem by compiling a data set in which the transport efficiency has been calculated using a single method, the analysis of hilltop curvatures using 1-m LiDAR data, and the erosion rates have also been determined via a single method, in-situ  <sup>­</sup>cosmogenic <sup>10</sup>Be concentrations. Moreover, to control for lithology, we chose sites that are only underlain by resistant bedrock. The sites span a range of erosion rates (6 – 1373 mm/kyr), annual precipitation (31 – 320 cm/yr), and aridity index (0.08 – 1.38). Surprisingly, we find that hilltop curvature varies with the square root of erosion rate, whereas previous studies predict a linear relationship. In addition, we find that the inferred transport coefficient also varies with the square root of erosion rate but is insensitive to climate. We explore various mechanisms that might link the transport coefficient to the erosion rate and conclude that present theory regarding soil-mantled hillslopes is unable to explain our results and is, therefore, incomplete. Finally, we tentatively suggest that bedrock processes may be responsible for the shape of hillslope profiles at our sites.</p>
Polygonal patterned grounds are common surface expressions of subsurface dynamics in periglacial ... more Polygonal patterned grounds are common surface expressions of subsurface dynamics in periglacial and Martian environments. In the Periglacial these structures are typically associated with vertically laminated wedges in the subsurface being the product of cryogenic processes. These landscape features similarly occur in arid to hyperarid environments, such as in the Atacama Desert. Due to the salt-dominated soil of the Atacama Desert, haloturbation and salt heave mechanisms control the formation of wedges and polygons under arid conditions. We present x-ray diffraction and x-ray fluorescence analyses of wedges from the central Atacama Desert that contain various calcium-sulfate phases as potential drivers for the wedge-growth activity. The formation of these wedges is connected to varying water activity. Hydration-and dehydration-induced phase transitions of calcium-sulfate phases result in significant volumetric changes in the soils. In combination with crystallisation pressure of (re-)precipitated salts from infiltrated solutions, these processes significantly contribute to the subsurface stress field. The upward stress release is assumed to express in a microtopographic signature of the surface, such as the polygonal patterned ground. In order to investigate the polygon-wedge system under arid conditions, we will present a combination of sedimentological, mineralogical, and geochemical analyses of subsurface wedges from the central Atacama Desert. We also present data constraining the formation age of calcium sulfate-dominated wedges that formed within the El Diablo Formation of Miocene age.
Polygonal patterned grounds are common surface expressions of subsurface dynamics in periglacial ... more Polygonal patterned grounds are common surface expressions of subsurface dynamics in periglacial and Martian environments. In the Periglacial these structures are typically associated with vertically laminated wedges in the subsurface being the product of cryogenic processes. These landscape features similarly occur in arid to hyperarid environments, such as in the Atacama Desert. Due to the salt-dominated soil of the Atacama Desert, haloturbation and salt heave mechanisms control the formation of wedges and polygons under arid conditions. We present x-ray diffraction and x-ray fluorescence analyses of wedges from the central Atacama Desert that contain various calcium-sulfate phases as potential drivers for the wedge-growth activity. The formation of these wedges is connected to varying water activity. Hydrationand dehydration-induced phase transitions of calcium-sulfate phases result in significant volumetric changes in the soils. In combination with crystallisation pressure of (r...
We established a new laboratory for noble gas mass spectrometry that is dedicated to the developm... more We established a new laboratory for noble gas mass spectrometry that is dedicated to the development and application to cosmogenic nuclides at the University of Cologne (Germany). At the core of the laboratory are a state-of-the-art high-mass-resolution multicollector Helix MC Plus (Thermo Fisher Scientific) noble gas mass spectrometer and a novel custom-designed automated extraction line. The mass spectrometer is equipped with five combined Faraday multiplier collectors, with 10 12 and 10 13 preamplifiers for faraday collectors. We describe the extraction line and the automated procedure for cosmogenic neon and the current performance of the experimental setup. Performance tests were conducted using gas of atmospheric isotopic composition (our primary standard gas), as well as CREU-1 intercomparison material, containing a mixture of neon of atmospheric and cosmogenic composition. We use the results from repeated analysis of CREU-1 to assess the performance of the current experimental setup at Cologne. The precision in determining the abundance of cosmogenic 21 Ne is equal to or better than those reported for other laboratories. The absolute value we obtain for the concentration of cosmogenic 21 Ne in CREU is indistinguishable from the published value.
Water is the defining feature of the habitable Earth; it is essential for all life as we know it.... more Water is the defining feature of the habitable Earth; it is essential for all life as we know it. Evolution of life in extremely water limited environments, which cover significant portions on of the Earth, is not well understood. Akin to life, water-driven processes leave unique marks on the Earth's surface. Mars is the only other planet known to bear the marks of water-driven surface processes, albeit fossil and of great age. The slow surface processes that may operate even in the virtual absence of liquid water are essentially unknown. What is evident is that transient episodes of increased water availability leave long lasting traces in extremely water limited environments. Intriguingly those traces of bursts in Earth surface evolution have rarely been related to bursts in biological colonization/evolution, and vice versa, although both relate to the same trigger: water. The objective of the presented Coordinated Research Centre (CRC 1211; http://sfb1211.uni-koeln.de/), involving twenty projects conducted at the Universities of Cologne, Bonn and Aachen, the Research Centre Jülich, and partner institutions in Chile (UCN Antofagasta; Univ. Antofagasta; CEAZA, La Serena; PUC Santiago), is to investigate the mutual evolutionary relationships between Earth surface processes and biota. The target areas are arid to hyper-arid systems, where both biota and Earth surface process are severely and predominantly limited by the availability of water. The initial target is the Atacama Desert (7/2016-6/2020), in a possible second phase (7/2020-6/2024) research in the Atacama would be joined by comparative research the Namib Desert. Primary research aims are to isolate the key fingerprints of biological activity at the (water) limit of the habitable Earth, and to characterize the Earth surface processes operating in the (virtual) absence of liquid water. We aim to characterize thresholds for biological colonization and concurrent fluvial transformation of landscapes, the tipping point(s) of biotically and abiotically controlled Earth surface systems, and establish detailed long-term terrestrial climatic records of the oldest and most arid zones on Earth. Chronometric and spatial information on the colonization and radiation of biota will be related to the landscape evolution and their common driver; climate.
The Mejillones Peninsula is a promontory extending spectacularly from the northern Chilean coastl... more The Mejillones Peninsula is a promontory extending spectacularly from the northern Chilean coastline. The peninsula is marked by well preserved marine terraces extending from just above sea-level to greater than 400 m. These staircased planar expressions result from a combination of glacioeustatic sea-level fluctuation and tectonic uplift. It has been shown by several studies that such terraces are formed during interglacial marine high-stands and are preserved because of abandonment in intervening sea-level low-stands. Post Mid Pleistocene transition high-stands (MIS 1 to 19) were within 10 m of the current sea-level (Siddall et al. 2006). We present cosmogenic Be exposure ages from marine pebbles deposited on the surface of the terraces when they were at sea-level in order to constrain the uplift history of the northwestern highland part of the peninsula. Based on the mean age (n=10) of the oldest terrace measured (∼140 m) we obtain an average uplift rate of ∼0.3 m/ka for the last...
Abstract. We established a new laboratory for noble gas mass spectrometry that is dedicated to th... more Abstract. We established a new laboratory for noble gas mass spectrometry that is dedicated to the development and application to cosmogenic nuclides at the University of Cologne (Germany). At the core of the laboratory are a state-of-the-art high-mass-resolution multicollector Helix MC Plus (Thermo Fisher Scientific) noble gas mass spectrometer and a novel custom-designed automated extraction line. The mass spectrometer is equipped with five combined Faraday multiplier collectors, with 1012 and 1013 Ω pre-amplifiers for faraday collectors. We describe the extraction line and the automated procedure for cosmogenic neon and the current performance of the experimental set-up. Performance tests were conducted using gas of atmospheric isotopic composition (our primary standard gas), as well as CREU-1 intercomparison material, containing a mixture of neon of atmospheric and cosmogenic composition. We use the results from repeated analysis of CREU-1 to assess the performance of the curren...
Neogene constriction in the northern chilean Coastal Cordillera: Neotectonics and surface dating ... more Neogene constriction in the northern chilean Coastal Cordillera: Neotectonics and surface dating using cosmogenic 21Ne. This work documents fault activity and the Neogene’s strain fi eld in northern Chilean Coastal Cordillera. Fault activity is expressed as a group of fault scarps and fault-bend fold scarps whose orientation defi nes three main domains WNW-ESE, N-S and NNW-SSE. The WNW-ESE and N-S faults show reverse kinematics, and NNW-SSE faults shows dextral-reverse kinematics. Exposure ages using cosmogenic Ne show that the faults disrupt an Oligocene-Miocene landscape preserved at the Coastal Cordillera. Inactive valleys incised in this landscape are offset by the faults showing that faults were active after 4 and 2 Ma. Ar/Ar chronology of displaced volcanic tuffs and the deformation of Late Pleistocene sediments indicate that fault activity remain still active during the Quaternary. The deformation regime is constrictional and characterized by subhorizontal shortening in all d...
Abstract The formally named SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt flow ... more Abstract The formally named SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt flow that is preserved in the desert climate of northern Arizona, USA. The flow is independently dated with an 40Ar/39Ar age of 72 ± 4 ka (2σ) and has undergone negligible erosion and/or burial, making its surface an ideal site for direct calibration of cosmogenic nuclide production rates. Production rates for cosmogenic 26Al have been determined from SP flow quartz in this study and are combined with production rates for 10Be, 14C, and 21Ne (Fenton et al., 2019) to yield a suite of production rate ratios. The error-weighted mean, sea-level, high latitude (SLHL) total reference production rate of 26Al is 25.8 ± 2.5 at/g/yr (2 σ x ‾ ; standard error) using time-independent Lal (1991)/Stone (2000) (St) scaling factors. The St scaled spallogenic 26Al rate is 25.0 ± 2.4 at/g/yr integrated over the past 72 ka. This rate overlaps within 2σ uncertainty with other St-scaled production rates in the literature. SLHL spallogenic 26Al production rates in SPICE quartz (SP Flow Production-Rate Inter-Calibration Site for Cosmogenic-Nuclide Evaluations) are nominally lower if time- dependent Sf, Sa, and Lm scaling factors are used, yielding values of 22.9 ± 2.2 at/g/yr, 22.6 ± 2.2 at/g/yr, and 24.1 ± 2.2 at/g/yr (2 σ x ‾ ), respectively. All 26Al production rates in SP flow quartz overlap within 2σ uncertainty, regardless of time independent or time dependent scaling. Production rate ratios for cosmogenic 26Al/10Be, 26Al/14C, and 26Al/21Ne are based on the total, local production rates of each cosmogenic nuclide, independent of scaling models, and have error-weighted means (±2 σ x ‾ ; standard error) of 6.7 ± 0.6, 2.23 ± 0.20, and 1.51 ± 0.13, respectively. This study suggests that, similar to cosmogenic 21Ne and 10Be production rates in SP flow quartz, production rates of cosmogenic 26Al in quartz do not significantly increase when integrated over 72 ka, a time span which includes the period of decreased magnetic strength from 20 to 50 ka.
Abstract Unicellular eukaryotes, also called protists, are potentially fast evolving organisms. T... more Abstract Unicellular eukaryotes, also called protists, are potentially fast evolving organisms. The small size of protists, their fast reproduction rate and ability to form cysts as well as their adaptability to extreme conditions allow them to associate to endemic animals, plants, saline lakes and soil even in extremely arid systems. These properties make unicellular eukaryotes ideal model organisms to combine studies on evolutionary processes of very different groups of organisms and across very different time scales comprising even geological ones. The hyperarid Atacama Desert offers a study area unique on Earth, where a predominantly arid climate was present for millions of years. A comprehensive analysis of the diversity of unicellular eukaryotes in different habitats (endemic desert plant phyllosphere, the gut of endemic darkling beetles, isolated hypersaline waters) revealed a dataset distinct and divergent from other regions on Earth. We used standard isolation and cultivation protocols to elucidate divergence patterns for a variety of very different and independent taxonomic groups of protists such as gregarines and ciliates among alveolates, placidids among stramenopiles and choanoflagellates among opisthokonts. The ability to rapidly adapt to extreme environments, which enhance a fast divergence rate at high UV radiation, has only been reported for prokaryotes up to now. The establishment of arid to hyperarid conditions in the Atacama Desert about 20 Ma ago has obviously led to an isolation of protist populations followed by a radiation of species. There are only a few regions on Earth with similar extreme salinity conditions reducing the chance of an exchange between protist populations. Divergence patterns in unicellular eukaryotes in very different phylogenetic groups independently mirror the effect of geological evolution and climate variability during the Neogene.
Abstract The Atacama Desert frequently serves as model system for tracing life under extremely dr... more Abstract The Atacama Desert frequently serves as model system for tracing life under extremely dry conditions. We hypothesized that traces of life in the Atacama Desert follow distinct micro- and macro-scale gradients such as soil depth and elevation, respectively. Different depth intervals of surface soils (0–1, 1–5, and 5–10 cm) were sampled at five sites along an elevational transect near the Quebrada Aroma, spanning from the hyperarid core of the desert towards the arid Western Andean Precordillera (1300 to 2700 m a.s.l.), and from one additional site in the hyperarid core near Yungay. We determined the contents of major elements, pedogenic minerals and oxides, organic carbon (OC), and its δ13C and δ15N isotopic composition. The presence of living microorganisms was assessed by cultivation, and bacterial community composition was analyzed based on 16S rRNA gene sequencing. Additional information about past and present plant and microbial life was obtained from lipid biomarker analysis. We did not detect consistent micro-scale distributions for most of these proxies within the soils. However, concentrations of OC and of long-chain, plant wax-derived n-alkanes increased in soils along the aridity gradient towards the wetter sites, indicating the presence of past life at places presently not covered by vegetation. Likewise, bacterial abundance and diversity decreased as hyperaridity increased and the microbial community composition changed along the transect, becoming enriched in Actinobacteria. The distributional patterns of phospholipid fatty acids (PLFAs) confirmed the larger bacterial diversity at the higher, more humid sites compared to the drier ones. Archaeal isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) and bacterial branched (br)GDGTs, which can also indicate past life, did not follow a clear elevational trend and were absent at the driest site. Taken together, plant-derived and microbiological markers follow primarily the macro-scaled elevation and aridity gradient. Viable bacteria are present even at the driest sites, while detected biomolecules also indicate past life. The detection of past plant life in nowadays apparently lifeless regions suggests that conditions for life were less hostile in former times.
Abstract The SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt with an 40Ar/39Ar ag... more Abstract The SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt with an 40Ar/39Ar age of 72 ± 4 ka (2σ). The flow is preserved in the desert climate of northern Arizona, USA. Its unweathered appearance and the lack of soil development indicate it has undergone negligible erosion and/or burial, making it an ideal site for direct calibration of cosmogenic nuclide production rates. Cross-calibrated production rates and production rate ratios for cosmogenic 21Ne, 10Be, and 14C have been determined from SP flow quartz. Production rate ratios for 21Ne/10Be, 21Ne/14C, and 14C/10Be are based on the total, local production rates of each cosmogenic nuclide, independent of scaling models, and have error-weighted means (±2σ uncertainty) of 4.44 ± 0.32, 1.43 ± 0.10, and 2.85 ± 0.21, respectively. Error-weighted mean, sea-level, high latitude (SLHL) total reference production rates of 21Ne, 10Be, and 14C are 17.0 ± 1.1, 3.84 ± 0.27, and 11.2 ± 0.6 at/g/yr (2σ), respectively, using time-independent Lal (1991)/Stone (2000) (St) scaling factors. St scaled spallogenic 10Be and 14C rates are 3.73 ± 0.26 and 9.2 ± 0.6 at/g/yr, respectively. 21Ne and 10Be production rates are integrated over the past 72 ka, whereas 14C production rates are integrated over 25 ka, the time at which SP flow quartz has reached saturation with respect to 14C. These rates overlap within 2σ uncertainty with other St-scaled production rates in the literature, including the total reference SLHL 21Ne production rate of Niedermann (2000), which is revised in this paper to 16.8 ± 3.3 at/g/yr (2σ; St scaling) to reflect a recent change in age control at the Sierra Nevada sites. All SLHL production rates are lower if time- dependent Sf, Sa, and Lm scaling factors are used. For example, error-weighted mean, sea-level, high latitude (SLHL) total reference production rates for 10Be as calculated in the CREp online calculator range from 3.49 ± 0.23 to 3.74 ± 0.25 at/g/yr (2σ), using time-dependent Lm scaling factors. Commonly used SLHL 10Be and 14C production rates in the literature were calibrated on surfaces that have been exposed to cosmic rays for less than 20 ka. Between 20 and 50 ka, the geomagnetic field is proposed to have been weaker than it is today. Production rates of cosmogenic nuclides increase during periods of weaker geomagnetic field strength. However, our study finds no measureable difference between St-scaled production rates of cosmogenic 21Ne and 10Be over the past 20 ka and St-scaled 21Ne and 10Be production rates over the past 72 ka. As such, the study suggests that 21Ne and 10Be production rates in quartz were not significantly greater during the proposed period of decreased magnetic strength from 20 to 50 ka.
Abstract Crustal movement along the coastline of the Arabian Sea in Oman is quantified along a 72... more Abstract Crustal movement along the coastline of the Arabian Sea in Oman is quantified along a 72 km long coastal section characterised by staircases of marine terraces. An extensive topographic, geomorphological and geological survey was conducted on these terraces and an age model based on cosmogenic nuclide (10Be, 36Cl) and optically stimulated luminescence dating is presented, together with a new approach to extract palaeo-shorelines from a high-resolution digital elevation model. The uplifting crustal block is fault bounded and is composed of obduction related peridotites overlain by shallow marine limestone. Nine distinct terrace levels are identified and the results indicate continuous uplift between Marine Isotope Stage (MIS) 5a and MIS 19. The calculated uplift rates vary along the coastline and a northward tilting of the uplifted coastal block is interpreted as evidence for differential uplift. The geomorphology of the terraces proves that the tilting must have taken place after the last interglacial. Tectonic forcing of the uplift by a crustal forebulge associated with the Makran Subduction Zone is discussed. It is also concluded that the uplift involves processes of serpentinisation of the peridotites in combination with karstification of the overlying limestone formations. As water is essential for both processes, climate change during the Quaternary apparently played a significant role in the uplift process as well as hydro-isostasy.
Two natural mineral separates, labeled CoCal-N and CoFsp-N, have been prepared to serve as interc... more Two natural mineral separates, labeled CoCal-N and CoFsp-N, have been prepared to serve as intercomparisonmaterial (ICM) for in situ-produced cosmogenic 36Cl and natural chlorine (Clnat) analysis. The sample CoCal-N isderived from calcite crystals in a Namibian lag deposit, while the sample CoFsp-N is derived from a single crystalof alkali-feldspar from a Namibian pegmatite. The sample preparation took place at the University of Cologneand a rotating splitter was used to obtain homogeneous splits of both ICMs. Forty-five measurements of CoCal-N(between 1 and 16 per facility) and forty-four measurements of CoFsp-N (between 2 and 20 per facility) havebeen undertaken by ten target preparation laboratories measured by seven different AMS facilities. The internallaboratory scatter of the 36Cl concentrations indicates no overdispersion for half of the laboratories and 3.9 to7.3% (1σ) overdispersion for the others. We show that the CoCal-N and CoFsp-N splits are homogeneous regardingtheir ...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Abstract A new multi-isotope plutonium standard for isotopic ratio measurements with Accelerator ... more Abstract A new multi-isotope plutonium standard for isotopic ratio measurements with Accelerator Mass Spectrometry (AMS) was created by gravimetric mixing of different single-isotope standards provided by IRMM (Pu-239, Pu-240, Pu-242, Pu-244). This standard material has been measured at the AMS facilities at Canberra (Australia), Cologne (Germany), Caserta (Italy), Sevilla (Spain) and Zurich (Switzerland). Additionally, the material was characterized using a Neptune MC-ICPMS (multi-collector inductively coupled plasma mass spectrometry) at the joint Cologne-Bonn isotope facility. The results of this laboratory intercomparison are presented and consensus values for the isotope compositions of the standard material are proposed.
Abstract Dating the transport/deposition time of supratidal coarse-clast deposits is difficult, l... more Abstract Dating the transport/deposition time of supratidal coarse-clast deposits is difficult, limiting their value for inferring frequency-magnitude patterns of high-energy wave events. On Bonaire (Leeward Antilles, Caribbean), these deposits form prominent landforms, and transport by one or several Holocene tsunamis is assumed at least for the largest clasts. Although a large dataset of 14C and electron spin resonance (ESR) ages is available for major coral rubble ridges and ramparts, it is still debated whether these data reflect the timing of major events, and how these datasets are biased by the reworking of coral fragments. As an attempt to overcome the current challenges for dating the dislocation of singular boulders, three distinct dating methods are implemented and compared: (i) 14C dating of boring bivalves attached to the boulders; (ii) 230Th/U dating of post-depositional, secondary calcite flowstone and subaerial microbialites at the underside of the boulders; and (iii) surface exposure dating of overturned boulders via 36Cl concentration measurements in corals. Approaches (ii) and (iii) have never been applied to coastal boulder deposits so far. The three 14C age estimates are older than 40 ka, i.e. most probably beyond the applicability of the method, which is attributed to post-depositional diagenetic processes, shedding doubt on the usefulness of this method in the local context. The remarkably convergent 230Th/U ages, all pointing to the Late Holocene period (1.0–1.6 ka), are minimum ages for the transport event(s). The microbialite sample yields an age of 1.23 ± 0.23 ka and both flowstone samples are in stratigraphic order: the older (onset of carbonate precipitation) and younger flowstone layers yield ages of 1.59 ± 0.03 and 1.23 ± 0.03 ka, respectively. Four coral samples collected from the topside of overturned boulders yielded similar 36Cl concentration measurements. However, the computed ages are affected by large uncertainties, mostly due to the high natural chlorine concentration. After correction for the inherited component and chemical denudation since platform emergence (inducing additional uncertainty), the calculated 36Cl ages cluster between 2.5 ± 1.3 and 3.0 ± 1.4 ka for three of four boulders whilst the fourth one yields an age of 6.1 ± 1.8 ka, probably related to a higher inheritance. These 230Th/U and 36Cl age estimates are coherent with a suggested tsunami age of
Cosmogenic surface exposure dating is a powerful tool for reconstructing long term slip rates on ... more Cosmogenic surface exposure dating is a powerful tool for reconstructing long term slip rates on active faults and may provide evidence for temporal earthquake clustering (e.g. Benedetti et al., GRL, v.29, 2002). Extensional faults in limestone are particularly amenable to this type of study because they commonly produce a striated bedrock scarp, exhumed by faulting, that can be sampled to
<p>The shape of soil-mantled hillslopes is typically attributed to erosion rate and... more <p>The shape of soil-mantled hillslopes is typically attributed to erosion rate and the transport efficiency of the various processes that contribute to soil creep. While climate is generally hypothesized to have an important influence on soil creep rates, a lack of uniformity in the measurement of transport efficiency has been an obstacle to evaluating the controls on this important landscape parameter. We addressed this problem by compiling a data set in which the transport efficiency has been calculated using a single method, the analysis of hilltop curvatures using 1-m LiDAR data, and the erosion rates have also been determined via a single method, in-situ  <sup>­</sup>cosmogenic <sup>10</sup>Be concentrations. Moreover, to control for lithology, we chose sites that are only underlain by resistant bedrock. The sites span a range of erosion rates (6 – 1373 mm/kyr), annual precipitation (31 – 320 cm/yr), and aridity index (0.08 – 1.38). Surprisingly, we find that hilltop curvature varies with the square root of erosion rate, whereas previous studies predict a linear relationship. In addition, we find that the inferred transport coefficient also varies with the square root of erosion rate but is insensitive to climate. We explore various mechanisms that might link the transport coefficient to the erosion rate and conclude that present theory regarding soil-mantled hillslopes is unable to explain our results and is, therefore, incomplete. Finally, we tentatively suggest that bedrock processes may be responsible for the shape of hillslope profiles at our sites.</p>
Polygonal patterned grounds are common surface expressions of subsurface dynamics in periglacial ... more Polygonal patterned grounds are common surface expressions of subsurface dynamics in periglacial and Martian environments. In the Periglacial these structures are typically associated with vertically laminated wedges in the subsurface being the product of cryogenic processes. These landscape features similarly occur in arid to hyperarid environments, such as in the Atacama Desert. Due to the salt-dominated soil of the Atacama Desert, haloturbation and salt heave mechanisms control the formation of wedges and polygons under arid conditions. We present x-ray diffraction and x-ray fluorescence analyses of wedges from the central Atacama Desert that contain various calcium-sulfate phases as potential drivers for the wedge-growth activity. The formation of these wedges is connected to varying water activity. Hydration-and dehydration-induced phase transitions of calcium-sulfate phases result in significant volumetric changes in the soils. In combination with crystallisation pressure of (re-)precipitated salts from infiltrated solutions, these processes significantly contribute to the subsurface stress field. The upward stress release is assumed to express in a microtopographic signature of the surface, such as the polygonal patterned ground. In order to investigate the polygon-wedge system under arid conditions, we will present a combination of sedimentological, mineralogical, and geochemical analyses of subsurface wedges from the central Atacama Desert. We also present data constraining the formation age of calcium sulfate-dominated wedges that formed within the El Diablo Formation of Miocene age.
Polygonal patterned grounds are common surface expressions of subsurface dynamics in periglacial ... more Polygonal patterned grounds are common surface expressions of subsurface dynamics in periglacial and Martian environments. In the Periglacial these structures are typically associated with vertically laminated wedges in the subsurface being the product of cryogenic processes. These landscape features similarly occur in arid to hyperarid environments, such as in the Atacama Desert. Due to the salt-dominated soil of the Atacama Desert, haloturbation and salt heave mechanisms control the formation of wedges and polygons under arid conditions. We present x-ray diffraction and x-ray fluorescence analyses of wedges from the central Atacama Desert that contain various calcium-sulfate phases as potential drivers for the wedge-growth activity. The formation of these wedges is connected to varying water activity. Hydrationand dehydration-induced phase transitions of calcium-sulfate phases result in significant volumetric changes in the soils. In combination with crystallisation pressure of (r...
We established a new laboratory for noble gas mass spectrometry that is dedicated to the developm... more We established a new laboratory for noble gas mass spectrometry that is dedicated to the development and application to cosmogenic nuclides at the University of Cologne (Germany). At the core of the laboratory are a state-of-the-art high-mass-resolution multicollector Helix MC Plus (Thermo Fisher Scientific) noble gas mass spectrometer and a novel custom-designed automated extraction line. The mass spectrometer is equipped with five combined Faraday multiplier collectors, with 10 12 and 10 13 preamplifiers for faraday collectors. We describe the extraction line and the automated procedure for cosmogenic neon and the current performance of the experimental setup. Performance tests were conducted using gas of atmospheric isotopic composition (our primary standard gas), as well as CREU-1 intercomparison material, containing a mixture of neon of atmospheric and cosmogenic composition. We use the results from repeated analysis of CREU-1 to assess the performance of the current experimental setup at Cologne. The precision in determining the abundance of cosmogenic 21 Ne is equal to or better than those reported for other laboratories. The absolute value we obtain for the concentration of cosmogenic 21 Ne in CREU is indistinguishable from the published value.
Water is the defining feature of the habitable Earth; it is essential for all life as we know it.... more Water is the defining feature of the habitable Earth; it is essential for all life as we know it. Evolution of life in extremely water limited environments, which cover significant portions on of the Earth, is not well understood. Akin to life, water-driven processes leave unique marks on the Earth's surface. Mars is the only other planet known to bear the marks of water-driven surface processes, albeit fossil and of great age. The slow surface processes that may operate even in the virtual absence of liquid water are essentially unknown. What is evident is that transient episodes of increased water availability leave long lasting traces in extremely water limited environments. Intriguingly those traces of bursts in Earth surface evolution have rarely been related to bursts in biological colonization/evolution, and vice versa, although both relate to the same trigger: water. The objective of the presented Coordinated Research Centre (CRC 1211; http://sfb1211.uni-koeln.de/), involving twenty projects conducted at the Universities of Cologne, Bonn and Aachen, the Research Centre Jülich, and partner institutions in Chile (UCN Antofagasta; Univ. Antofagasta; CEAZA, La Serena; PUC Santiago), is to investigate the mutual evolutionary relationships between Earth surface processes and biota. The target areas are arid to hyper-arid systems, where both biota and Earth surface process are severely and predominantly limited by the availability of water. The initial target is the Atacama Desert (7/2016-6/2020), in a possible second phase (7/2020-6/2024) research in the Atacama would be joined by comparative research the Namib Desert. Primary research aims are to isolate the key fingerprints of biological activity at the (water) limit of the habitable Earth, and to characterize the Earth surface processes operating in the (virtual) absence of liquid water. We aim to characterize thresholds for biological colonization and concurrent fluvial transformation of landscapes, the tipping point(s) of biotically and abiotically controlled Earth surface systems, and establish detailed long-term terrestrial climatic records of the oldest and most arid zones on Earth. Chronometric and spatial information on the colonization and radiation of biota will be related to the landscape evolution and their common driver; climate.
The Mejillones Peninsula is a promontory extending spectacularly from the northern Chilean coastl... more The Mejillones Peninsula is a promontory extending spectacularly from the northern Chilean coastline. The peninsula is marked by well preserved marine terraces extending from just above sea-level to greater than 400 m. These staircased planar expressions result from a combination of glacioeustatic sea-level fluctuation and tectonic uplift. It has been shown by several studies that such terraces are formed during interglacial marine high-stands and are preserved because of abandonment in intervening sea-level low-stands. Post Mid Pleistocene transition high-stands (MIS 1 to 19) were within 10 m of the current sea-level (Siddall et al. 2006). We present cosmogenic Be exposure ages from marine pebbles deposited on the surface of the terraces when they were at sea-level in order to constrain the uplift history of the northwestern highland part of the peninsula. Based on the mean age (n=10) of the oldest terrace measured (∼140 m) we obtain an average uplift rate of ∼0.3 m/ka for the last...
Abstract. We established a new laboratory for noble gas mass spectrometry that is dedicated to th... more Abstract. We established a new laboratory for noble gas mass spectrometry that is dedicated to the development and application to cosmogenic nuclides at the University of Cologne (Germany). At the core of the laboratory are a state-of-the-art high-mass-resolution multicollector Helix MC Plus (Thermo Fisher Scientific) noble gas mass spectrometer and a novel custom-designed automated extraction line. The mass spectrometer is equipped with five combined Faraday multiplier collectors, with 1012 and 1013 Ω pre-amplifiers for faraday collectors. We describe the extraction line and the automated procedure for cosmogenic neon and the current performance of the experimental set-up. Performance tests were conducted using gas of atmospheric isotopic composition (our primary standard gas), as well as CREU-1 intercomparison material, containing a mixture of neon of atmospheric and cosmogenic composition. We use the results from repeated analysis of CREU-1 to assess the performance of the curren...
Neogene constriction in the northern chilean Coastal Cordillera: Neotectonics and surface dating ... more Neogene constriction in the northern chilean Coastal Cordillera: Neotectonics and surface dating using cosmogenic 21Ne. This work documents fault activity and the Neogene’s strain fi eld in northern Chilean Coastal Cordillera. Fault activity is expressed as a group of fault scarps and fault-bend fold scarps whose orientation defi nes three main domains WNW-ESE, N-S and NNW-SSE. The WNW-ESE and N-S faults show reverse kinematics, and NNW-SSE faults shows dextral-reverse kinematics. Exposure ages using cosmogenic Ne show that the faults disrupt an Oligocene-Miocene landscape preserved at the Coastal Cordillera. Inactive valleys incised in this landscape are offset by the faults showing that faults were active after 4 and 2 Ma. Ar/Ar chronology of displaced volcanic tuffs and the deformation of Late Pleistocene sediments indicate that fault activity remain still active during the Quaternary. The deformation regime is constrictional and characterized by subhorizontal shortening in all d...
Abstract The formally named SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt flow ... more Abstract The formally named SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt flow that is preserved in the desert climate of northern Arizona, USA. The flow is independently dated with an 40Ar/39Ar age of 72 ± 4 ka (2σ) and has undergone negligible erosion and/or burial, making its surface an ideal site for direct calibration of cosmogenic nuclide production rates. Production rates for cosmogenic 26Al have been determined from SP flow quartz in this study and are combined with production rates for 10Be, 14C, and 21Ne (Fenton et al., 2019) to yield a suite of production rate ratios. The error-weighted mean, sea-level, high latitude (SLHL) total reference production rate of 26Al is 25.8 ± 2.5 at/g/yr (2 σ x ‾ ; standard error) using time-independent Lal (1991)/Stone (2000) (St) scaling factors. The St scaled spallogenic 26Al rate is 25.0 ± 2.4 at/g/yr integrated over the past 72 ka. This rate overlaps within 2σ uncertainty with other St-scaled production rates in the literature. SLHL spallogenic 26Al production rates in SPICE quartz (SP Flow Production-Rate Inter-Calibration Site for Cosmogenic-Nuclide Evaluations) are nominally lower if time- dependent Sf, Sa, and Lm scaling factors are used, yielding values of 22.9 ± 2.2 at/g/yr, 22.6 ± 2.2 at/g/yr, and 24.1 ± 2.2 at/g/yr (2 σ x ‾ ), respectively. All 26Al production rates in SP flow quartz overlap within 2σ uncertainty, regardless of time independent or time dependent scaling. Production rate ratios for cosmogenic 26Al/10Be, 26Al/14C, and 26Al/21Ne are based on the total, local production rates of each cosmogenic nuclide, independent of scaling models, and have error-weighted means (±2 σ x ‾ ; standard error) of 6.7 ± 0.6, 2.23 ± 0.20, and 1.51 ± 0.13, respectively. This study suggests that, similar to cosmogenic 21Ne and 10Be production rates in SP flow quartz, production rates of cosmogenic 26Al in quartz do not significantly increase when integrated over 72 ka, a time span which includes the period of decreased magnetic strength from 20 to 50 ka.
Abstract Unicellular eukaryotes, also called protists, are potentially fast evolving organisms. T... more Abstract Unicellular eukaryotes, also called protists, are potentially fast evolving organisms. The small size of protists, their fast reproduction rate and ability to form cysts as well as their adaptability to extreme conditions allow them to associate to endemic animals, plants, saline lakes and soil even in extremely arid systems. These properties make unicellular eukaryotes ideal model organisms to combine studies on evolutionary processes of very different groups of organisms and across very different time scales comprising even geological ones. The hyperarid Atacama Desert offers a study area unique on Earth, where a predominantly arid climate was present for millions of years. A comprehensive analysis of the diversity of unicellular eukaryotes in different habitats (endemic desert plant phyllosphere, the gut of endemic darkling beetles, isolated hypersaline waters) revealed a dataset distinct and divergent from other regions on Earth. We used standard isolation and cultivation protocols to elucidate divergence patterns for a variety of very different and independent taxonomic groups of protists such as gregarines and ciliates among alveolates, placidids among stramenopiles and choanoflagellates among opisthokonts. The ability to rapidly adapt to extreme environments, which enhance a fast divergence rate at high UV radiation, has only been reported for prokaryotes up to now. The establishment of arid to hyperarid conditions in the Atacama Desert about 20 Ma ago has obviously led to an isolation of protist populations followed by a radiation of species. There are only a few regions on Earth with similar extreme salinity conditions reducing the chance of an exchange between protist populations. Divergence patterns in unicellular eukaryotes in very different phylogenetic groups independently mirror the effect of geological evolution and climate variability during the Neogene.
Abstract The Atacama Desert frequently serves as model system for tracing life under extremely dr... more Abstract The Atacama Desert frequently serves as model system for tracing life under extremely dry conditions. We hypothesized that traces of life in the Atacama Desert follow distinct micro- and macro-scale gradients such as soil depth and elevation, respectively. Different depth intervals of surface soils (0–1, 1–5, and 5–10 cm) were sampled at five sites along an elevational transect near the Quebrada Aroma, spanning from the hyperarid core of the desert towards the arid Western Andean Precordillera (1300 to 2700 m a.s.l.), and from one additional site in the hyperarid core near Yungay. We determined the contents of major elements, pedogenic minerals and oxides, organic carbon (OC), and its δ13C and δ15N isotopic composition. The presence of living microorganisms was assessed by cultivation, and bacterial community composition was analyzed based on 16S rRNA gene sequencing. Additional information about past and present plant and microbial life was obtained from lipid biomarker analysis. We did not detect consistent micro-scale distributions for most of these proxies within the soils. However, concentrations of OC and of long-chain, plant wax-derived n-alkanes increased in soils along the aridity gradient towards the wetter sites, indicating the presence of past life at places presently not covered by vegetation. Likewise, bacterial abundance and diversity decreased as hyperaridity increased and the microbial community composition changed along the transect, becoming enriched in Actinobacteria. The distributional patterns of phospholipid fatty acids (PLFAs) confirmed the larger bacterial diversity at the higher, more humid sites compared to the drier ones. Archaeal isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) and bacterial branched (br)GDGTs, which can also indicate past life, did not follow a clear elevational trend and were absent at the driest site. Taken together, plant-derived and microbiological markers follow primarily the macro-scaled elevation and aridity gradient. Viable bacteria are present even at the driest sites, while detected biomolecules also indicate past life. The detection of past plant life in nowadays apparently lifeless regions suggests that conditions for life were less hostile in former times.
Abstract The SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt with an 40Ar/39Ar ag... more Abstract The SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt with an 40Ar/39Ar age of 72 ± 4 ka (2σ). The flow is preserved in the desert climate of northern Arizona, USA. Its unweathered appearance and the lack of soil development indicate it has undergone negligible erosion and/or burial, making it an ideal site for direct calibration of cosmogenic nuclide production rates. Cross-calibrated production rates and production rate ratios for cosmogenic 21Ne, 10Be, and 14C have been determined from SP flow quartz. Production rate ratios for 21Ne/10Be, 21Ne/14C, and 14C/10Be are based on the total, local production rates of each cosmogenic nuclide, independent of scaling models, and have error-weighted means (±2σ uncertainty) of 4.44 ± 0.32, 1.43 ± 0.10, and 2.85 ± 0.21, respectively. Error-weighted mean, sea-level, high latitude (SLHL) total reference production rates of 21Ne, 10Be, and 14C are 17.0 ± 1.1, 3.84 ± 0.27, and 11.2 ± 0.6 at/g/yr (2σ), respectively, using time-independent Lal (1991)/Stone (2000) (St) scaling factors. St scaled spallogenic 10Be and 14C rates are 3.73 ± 0.26 and 9.2 ± 0.6 at/g/yr, respectively. 21Ne and 10Be production rates are integrated over the past 72 ka, whereas 14C production rates are integrated over 25 ka, the time at which SP flow quartz has reached saturation with respect to 14C. These rates overlap within 2σ uncertainty with other St-scaled production rates in the literature, including the total reference SLHL 21Ne production rate of Niedermann (2000), which is revised in this paper to 16.8 ± 3.3 at/g/yr (2σ; St scaling) to reflect a recent change in age control at the Sierra Nevada sites. All SLHL production rates are lower if time- dependent Sf, Sa, and Lm scaling factors are used. For example, error-weighted mean, sea-level, high latitude (SLHL) total reference production rates for 10Be as calculated in the CREp online calculator range from 3.49 ± 0.23 to 3.74 ± 0.25 at/g/yr (2σ), using time-dependent Lm scaling factors. Commonly used SLHL 10Be and 14C production rates in the literature were calibrated on surfaces that have been exposed to cosmic rays for less than 20 ka. Between 20 and 50 ka, the geomagnetic field is proposed to have been weaker than it is today. Production rates of cosmogenic nuclides increase during periods of weaker geomagnetic field strength. However, our study finds no measureable difference between St-scaled production rates of cosmogenic 21Ne and 10Be over the past 20 ka and St-scaled 21Ne and 10Be production rates over the past 72 ka. As such, the study suggests that 21Ne and 10Be production rates in quartz were not significantly greater during the proposed period of decreased magnetic strength from 20 to 50 ka.
Abstract Crustal movement along the coastline of the Arabian Sea in Oman is quantified along a 72... more Abstract Crustal movement along the coastline of the Arabian Sea in Oman is quantified along a 72 km long coastal section characterised by staircases of marine terraces. An extensive topographic, geomorphological and geological survey was conducted on these terraces and an age model based on cosmogenic nuclide (10Be, 36Cl) and optically stimulated luminescence dating is presented, together with a new approach to extract palaeo-shorelines from a high-resolution digital elevation model. The uplifting crustal block is fault bounded and is composed of obduction related peridotites overlain by shallow marine limestone. Nine distinct terrace levels are identified and the results indicate continuous uplift between Marine Isotope Stage (MIS) 5a and MIS 19. The calculated uplift rates vary along the coastline and a northward tilting of the uplifted coastal block is interpreted as evidence for differential uplift. The geomorphology of the terraces proves that the tilting must have taken place after the last interglacial. Tectonic forcing of the uplift by a crustal forebulge associated with the Makran Subduction Zone is discussed. It is also concluded that the uplift involves processes of serpentinisation of the peridotites in combination with karstification of the overlying limestone formations. As water is essential for both processes, climate change during the Quaternary apparently played a significant role in the uplift process as well as hydro-isostasy.
Two natural mineral separates, labeled CoCal-N and CoFsp-N, have been prepared to serve as interc... more Two natural mineral separates, labeled CoCal-N and CoFsp-N, have been prepared to serve as intercomparisonmaterial (ICM) for in situ-produced cosmogenic 36Cl and natural chlorine (Clnat) analysis. The sample CoCal-N isderived from calcite crystals in a Namibian lag deposit, while the sample CoFsp-N is derived from a single crystalof alkali-feldspar from a Namibian pegmatite. The sample preparation took place at the University of Cologneand a rotating splitter was used to obtain homogeneous splits of both ICMs. Forty-five measurements of CoCal-N(between 1 and 16 per facility) and forty-four measurements of CoFsp-N (between 2 and 20 per facility) havebeen undertaken by ten target preparation laboratories measured by seven different AMS facilities. The internallaboratory scatter of the 36Cl concentrations indicates no overdispersion for half of the laboratories and 3.9 to7.3% (1σ) overdispersion for the others. We show that the CoCal-N and CoFsp-N splits are homogeneous regardingtheir ...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Abstract A new multi-isotope plutonium standard for isotopic ratio measurements with Accelerator ... more Abstract A new multi-isotope plutonium standard for isotopic ratio measurements with Accelerator Mass Spectrometry (AMS) was created by gravimetric mixing of different single-isotope standards provided by IRMM (Pu-239, Pu-240, Pu-242, Pu-244). This standard material has been measured at the AMS facilities at Canberra (Australia), Cologne (Germany), Caserta (Italy), Sevilla (Spain) and Zurich (Switzerland). Additionally, the material was characterized using a Neptune MC-ICPMS (multi-collector inductively coupled plasma mass spectrometry) at the joint Cologne-Bonn isotope facility. The results of this laboratory intercomparison are presented and consensus values for the isotope compositions of the standard material are proposed.
Abstract Dating the transport/deposition time of supratidal coarse-clast deposits is difficult, l... more Abstract Dating the transport/deposition time of supratidal coarse-clast deposits is difficult, limiting their value for inferring frequency-magnitude patterns of high-energy wave events. On Bonaire (Leeward Antilles, Caribbean), these deposits form prominent landforms, and transport by one or several Holocene tsunamis is assumed at least for the largest clasts. Although a large dataset of 14C and electron spin resonance (ESR) ages is available for major coral rubble ridges and ramparts, it is still debated whether these data reflect the timing of major events, and how these datasets are biased by the reworking of coral fragments. As an attempt to overcome the current challenges for dating the dislocation of singular boulders, three distinct dating methods are implemented and compared: (i) 14C dating of boring bivalves attached to the boulders; (ii) 230Th/U dating of post-depositional, secondary calcite flowstone and subaerial microbialites at the underside of the boulders; and (iii) surface exposure dating of overturned boulders via 36Cl concentration measurements in corals. Approaches (ii) and (iii) have never been applied to coastal boulder deposits so far. The three 14C age estimates are older than 40 ka, i.e. most probably beyond the applicability of the method, which is attributed to post-depositional diagenetic processes, shedding doubt on the usefulness of this method in the local context. The remarkably convergent 230Th/U ages, all pointing to the Late Holocene period (1.0–1.6 ka), are minimum ages for the transport event(s). The microbialite sample yields an age of 1.23 ± 0.23 ka and both flowstone samples are in stratigraphic order: the older (onset of carbonate precipitation) and younger flowstone layers yield ages of 1.59 ± 0.03 and 1.23 ± 0.03 ka, respectively. Four coral samples collected from the topside of overturned boulders yielded similar 36Cl concentration measurements. However, the computed ages are affected by large uncertainties, mostly due to the high natural chlorine concentration. After correction for the inherited component and chemical denudation since platform emergence (inducing additional uncertainty), the calculated 36Cl ages cluster between 2.5 ± 1.3 and 3.0 ± 1.4 ka for three of four boulders whilst the fourth one yields an age of 6.1 ± 1.8 ka, probably related to a higher inheritance. These 230Th/U and 36Cl age estimates are coherent with a suggested tsunami age of
Cosmogenic surface exposure dating is a powerful tool for reconstructing long term slip rates on ... more Cosmogenic surface exposure dating is a powerful tool for reconstructing long term slip rates on active faults and may provide evidence for temporal earthquake clustering (e.g. Benedetti et al., GRL, v.29, 2002). Extensional faults in limestone are particularly amenable to this type of study because they commonly produce a striated bedrock scarp, exhumed by faulting, that can be sampled to
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