On the origin of saline fluids in the KTB (continental deep drilling project of Germany)

Highly saline fluids were encountered during the German Continental Deep Drilling Project (KTB) from depths ranging between 2 and 3 km to about 9 km. The most reliable data were obtained from samples extracted during a long-term pumping test in the 4000-m deep KTB pilot hole. Some 460 m³ CaNaCl brines with about 68 g l⁻¹ total dissolved solids (TDS) and some 270 m³ associated gases, mainly N₂ and CH₄ were pumped to the surface from the main fracture system situated near the bottom of the pilot hole. Geochemical and isotopic data support the hydraulic tests which suggest the presence of an open and large fluid reservoir at depth. The pumped fluids from this main fracture system were released from a deep reservoir situated at more than 5500 m depth which is hydraulically connected with the 9101 m deep KTB main hole, drilled some 250 m to the northeast of the pilot hole.While Ca and Sr contents of the extracted brines may be the result of water-rock interaction, Cl is most likely of external origin. The Cl is hypothesized to derive from geotectonic processes rather than to descending infiltration of paleo-seawater (evaporitic brines). The sampled fluids have probably migrated from a deeper reservoir to their present position since the Cretaceous-Tertiary period due to tectonic activity. However, several isotopic studies have identified an admixture of descending paleowaters down to more than 4000 m depth. The high ³⁶ClCl ratio of the fluids sampled during the long-term pumping test point to a host rock highly enriched in UTh, unlike the sampled KTB country rocks. The fluid reservoir is believed to be in contact with the Falkenberg granite massif situated about 2 km to the E of the KTB holes capable of supplying sufficient neutron flux for considerable subsurface production of 36C1. The NaCl(K, SO₄) precursor fluids of the CaNaCI brines were produced in the course of extensive tectonic processes since the Late Caledonian within the Bohemian Massif.     

Late Cretaceous exhumation history of an extensional extruding wedge (Graz Paleozoic Nappe Complex, Austria)

Late Cretaceous structures within the eastern Graz Paleozoic Nappe Complex define an extruding wedge with north-eastward directed thrusting in eastern portions and strike-slip shear along the margins. Stacking structures are overprinted by south-westward directed extension with low-grade metamorphic rocks in the hangingwall and high-grade basement rocks in the footwall. Pressure–temperature and structural data are obtained from successively opening quartz veins that record various stages of progressive deformation and metamorphism. Fluid inclusion data and related structures show that during extension isothermal decompression from ca. 550°C and 8 kbar down to ca. 450°C and 2 kbar was related to exhumation of rocks from deep crustal levels. The data point to a high geothermal gradient and explain condensed paleo-isotherms due to ductile normal faulting in the eastern areas of the Graz Paleozoic Nappe Complex. The investigated Late Cretaceous structural elements suggest that the Graz Paleozoic Nappe Complex decoupled from the surrounding basement units and operated as a large-scale extension–extrusion corridor that evolved prior to Miocene extrusion tectonics in the Eastern Alps.     

Limitations of Majority Agreement in Crowdsourced Image Interpretation

Crowdsourcing can efficiently complete tasks that are difficult to automate, but the quality of crowdsourced data is tricky to evaluate. Algorithms to grade volunteer work often assume that all tasks are similarly difficult, an assumption that is frequently false. We use a cropland identification game with over 2,600 participants and 165,000 unique tasks to investigate how best to evaluate the difficulty of crowdsourced tasks and to what extent this is possible based on volunteer responses alone. Inter‐volunteer agreement exceeded 90% for about 80% of the images and was negatively correlated with volunteer‐expressed uncertainty about image classification. A total of 343 relatively difficult images were independently classified as cropland, non‐cropland or impossible by two experts. The experts disagreed weakly (one said impossible while the other rated as cropland or non‐cropland) on 27% of the images, but disagreed strongly (cropland vs. non‐cropland) on only 7%. Inter‐volunteer disagreement increased significantly with inter‐expert disagreement. While volunteers agreed with expert classifications for most images, over 20% would have been mis‐categorized if only the volunteers’ majority vote was used. We end with a series of recommendations for managing the challenges posed by heterogeneous tasks in crowdsourcing campaigns.     

Erosion and Flooding—Threats to Coastal Infrastructure in the Arctic: A Case Study from Herschel Island,Yukon Territory,Canada

Arctic coastal infrastructure and cultural and archeological sites are increasingly vulnerable to erosion and flooding due to amplified warming of the Arctic, sea level rise, lengthening of open water periods, and a predicted increase in frequency of major storms. Mitigating these hazards necessitates decision-making tools at an appropriate scale. The objectives of this paper are to provide such a tool by assessing potential erosion and flood hazards at Herschel Island, a UNESCO World Heritage candidate site. This study focused on Simpson Point and the adjacent coastal sections because of their archeological, historical, and cultural significance. Shoreline movement was analyzed using the Digital Shoreline Analysis System (DSAS) after digitizing shorelines from 1952, 1970, 2000, and 2011. For purposes of this analysis, the coast was divided in seven coastal reaches (CRs) reflecting different morphologies and/or exposures. Using linear regression rates obtained from these data, projections of shoreline position were made for 20 and 50 years into the future. Flood hazard was assessed using a least cost path analysis based on a high-resolution light detection and ranging (LiDAR) dataset and current Intergovernmental Panel on Climate Change sea level estimates. Widespread erosion characterizes the study area. The rate of shoreline movement in different periods of the study ranges from ?5.5 to 2.7 m·a^?1 (mean ?0.6 m·a^?1). Mean coastal retreat decreased from ?0.6 m·a^?1 to ?0.5 m·a^?1, for 1952–1970 and 1970–2000, respectively, and increased to ?1.3 m·a^?1 in the period 2000–2011. Ice-rich coastal sections most exposed to wave attack exhibited the highest rates of coastal retreat. The geohazard map combines shoreline projections and flood hazard analyses to show that most of the spit area has extreme or very high flood hazard potential, and some buildings are vulnerable to coastal erosion. This study demonstrates that transgressive forcing may provide ample sediment for the expansion of depositional landforms, while growing more susceptible to overwash and flooding.     

Experimental observations on carbon isotope exchange in carbonate-water systems

This study presents data from experiments investigating carbon isotope exchange between carbonate solution and solid calcite using carbon-13 as a tracer. All experiments were done with calcite saturated solutions and results show that a two-step adsorption-recrystallization reaction takes place. Isotope effects are caused by exchange by carbonate on the solid surface with carbon in the aqueous phase. Adsorption reactions are characterized by a maximum isotopic exchange capacity (IEC) on crystal surfaces of about 10¹¹ reaction sites per cm², following a second order rate law with respect to ¹³C concentration in solution ($\text{constant}\text{kex ? 10}{}^6\text{cm}{}^5\text{mole}{}^{\mathrm{?1}}\text{s}{}^{\mathrm{?1}}$ and $\text{half-life}\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 700}\text{s}$). The adsorption reaction was followed by a first order recrystallization which is characterized by a rate constant of the order of 10^?8 s^?1 and a $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of 10⁷ s. Negative isotopic gradient experiments and runs with calcite crystals in Mg²⁺ spiked solutions provided the preliminary basis for the characterization of the mechanisms of both proposed reactions.     

Upper Ordovician chitinozoans from the Cedarberg Formation of South Africa. Preliminary note

Chitinozoans bracket the geological age of the Soom Shale at the base of the Cedarberg Formation of South Africa as Lower Silurian to Upper Ordovician whereby the oldest age is the more probable. On account of the organic eometamorphism the most likely maximum depth of burial of the Soom Shale was slightly in excess of 5000 meters.