Determination of flow exits in the Soultz borehole GPK2 by using the brine displacement method

The article presents a method to derive synthetic flow logs from low rate injection tests in wells, which are otherwise not accessible for logging. The tests were carried out in the 5 km deep geothermal well GPK2 in the Enhanced Geothermal System (EGS) project of Soultz-sous-Forêts (France) and were aimed at characterizing the status of the well before chemical treatments. The method consists of injecting water at constant flow rates into the well initially filled with brine. The wellhead pressure record of this test is transformed into log of the flow velocity versus depth by a technique described in the paper. Applying this method to borehole GPK2, three outlets could be detected and quantified within the cased and uncased section of this borehole. The outlet in the cased section at 3860 m absorbed 15% of the total flow. This depth corresponds to a known casing restriction, which makes the borehole inaccessible for logging operations. The two other outlets are at the casing shoe at 4420 m (15%) and at 4670 m (70%).     

Late Pleistocene dust deposition in the Patagonian steppe - extending and refining the paleoenvironmental and tephrochronological record from Laguna Potrok Aike back to 55 ka

Paleoenvironmental records extending well into the last glacial period are scarce in the steppe regions of southern South America. Here, we present a continuous record for the past 55 ka from the maar lake Laguna Potrok Aike (51°58′ S, 70°23′ W, southern Patagonia, Argentina). Previous studies on a sedimentary core from a lake level terrace near the northern margin of the lake covered parts of Oxygen Isotope Stage (OIS) 3 (59–29 ka) whereas a second core from the centre of the basin comprised the last 16 ka. Tephrostratigraphical constraints and OSL ages from a third core located below the lake level terrace provide the crucial piece to close the gap between the previous coring sites. High-resolution XRF and magnetic susceptibility as well as grain size data indicate a positive hydrological balance alongside with relatively high aeolian activity during the glacial which is contemporaneous with increased dust fluxes in Antarctica. This is therefore the first evidence for contemporaneity of aeolian deposition in both the target area (Antarctica) and in the major source area of Patagonia. During the Holocene climatic conditions driving sediment deposition seem to have been more variable and less dominated by wind compared to glacial times. The identification of a minor lake level lowering at approximately 4 cal ka BP allows to refine earlier paleoenvironmental reconstructions for the Holocene. Within error margins the OSL ages are consistent with published radiocarbon-dated records offering hence a valuable tool for further studies of the sediments from Laguna Potrok Aike. The new chronology confirms the age of three tephra layers up to now only found in Laguna Potrok Aike sediments and ascribed to OIS 3.     

Magmatic-dominated fluid evolution in the Jurassic Nambija gold skarn deposits (southeastern Ecuador)

The Jurassic (approximately 145 Ma) Nambija oxidized gold skarns are hosted by the Triassic volcanosedimentary Piuntza unit in the sub-Andean zone of southeastern Ecuador. The skarns consist dominantly of granditic garnet (Ad_20–98) with subordinate pyroxene (Di_46–92Hd_17–42Jo_0–19) and epidote and are spatially associated with porphyritic quartz-diorite to granodiorite intrusions. Endoskarn is developed at the intrusion margins and grades inwards into a potassic alteration zone. Exoskarn has an outer K- and Na-enriched zone in the volcanosedimentary unit. Gold mineralization is associated with the weakly developed retrograde alteration of the exoskarn and occurs mainly in sulfide-poor vugs and milky quartz veins and veinlets in association with hematite. Fluid inclusion data for the main part of the prograde stage indicate the coexistence of high-temperature (500°C to >600°C), high-salinity (up to 65 wt.% eq. NaCl), and moderate- to low-salinity aqueous-carbonic fluids interpreted to have been trapped at pressures around 100–120 MPa, corresponding to about 4-km depth. Lower-temperature (510–300°C) and moderate- to low-salinity (23–2 wt.% eq. NaCl) aqueous fluids are recorded in garnet and epidote of the end of the prograde stage. The microthermometric data (Th from 513°C to 318°C and salinity from 1.0 to 23 wt.% eq. NaCl) and δ¹⁸O values between 6.2‰ and 11.5‰ for gold-bearing milky quartz from the retrograde stage suggest that the ore-forming fluid was dominantly magmatic. Pressures during the early retrograde stage were in the range of 50–100 MPa, in line with the evidence for CO₂ effervescence and probable local boiling. The dominance of magmatic low-saline to moderately saline oxidizing fluids during the retrograde stage is consistent with the depth of the skarn system, which could have delayed the ingression of external fluids until relatively low temperatures were reached. The resulting low water-to-rock ratios explain the weak retrograde alteration and the compositional variability of chlorite, essentially controlled by host rock compositions. Gold was precipitated at this stage as a result of cooling and pH increase related to CO₂ effervescence, which both result in destabilization of gold-bearing chloride complexes. Significant ingression of external fluids took place after gold deposition only, as recorded by δ¹⁸O values of 0.4‰ to 6.2‰ for fluids depositing quartz (below 350°C) in sulfide-rich barren veins. Low-temperature (<300°C) meteoric fluids (δ¹⁸O_water between −10.0‰ and −2.0‰) are responsible for the precipitation of late comb quartz and calcite in cavities and veins and indicate mixing with cooler fluids of higher salinities (about 100°C and 25 wt.% eq. NaCl). The latter are similar to low-temperature fluids (202–74.5°C) with δ¹⁸O values of −0.5‰ to 3.1‰ and salinities in the range of 21.1 to 17.3 wt.% eq. CaCl₂, trapped in calcite of late veins and interpreted as basinal brines. Nambija represents a deep equivalent of the oxidized gold skarn class, the presence of CO₂ in the fluids being partly a consequence of the relatively deep setting at about 4-km depth. As in other Au-bearing skarn deposits, not only the prograde stage but also the gold-precipitating retrograde stage is dominated by fluids of magmatic origin.     

Regional gravity modeling in terms of spherical base functions

This article provides a survey on modern methods of regional gravity field modeling on the sphere. Starting with the classical theory of spherical harmonics, we outline the transition towards space-localizing methods such as spherical splines and wavelets. Special emphasis is given to the relations among these methods, which all involve radial base functions. Moreover, we provide extensive applications of these methods and numerical results from real space-borne data of recent satellite gravity missions, namely the Challenging Minisatellite Payload (CHAMP) and the Gravity Recovery and Climate Experiment (GRACE). We also derive high-resolution gravity field models by effectively combining space-borne and surface measurements using a new weighted level-combination concept. In addition, we outline and apply a strategy for constructing spatio-temporal fields from regional data sets spanning different observation periods.     

On the automatic parameter calibration of a hypoplastic soil model

Acta Geotechnica - This paper presents an approach for the automatic parameter calibration (AC) of a hypoplastic constitutive soil model. The calibration software developed in this work simplifies...     

A state-dependent hyperelastic-plastic constitutive model considering shear-induced particle breakage in granular soils

Acta Geotechnica - An elastic–plastic constitutive model considering particle breakage for simulation of crushable granular soils behavior is proposed. In the model, elastic strain rates are...     

Decision bias in marine spatial planning of offshore wind farms: Problems of singular versus cumulative assessments of economic impacts on fisheries

The current approval procedure for wind farm proposals in the German EEZ only considers site specific conflict analysis between the wind farm and fisheries. Due to the relatively small spatial coverage of the sites potential opportunity losses to the fisheries are always considered as low or negligible. Cumulative effects on fisheries that will occur once all proposed wind farms are in place are not yet considered adequately. However, those cumulative effects will be quite substantial because, in particular, opportunities to catch such valuable species as flatfish will be considerably reduced.     

Isotopic fingerprints on lacustrine organic matter from Laguna Potrok Aike (southern Patagonia, Argentina) reflect environmental changes during the last 16,000 years

A combination of carbon-to-nitrogen ratios (TOC/TN), Rock Eval-analyses, and stable isotope values of bulk nitrogen (δ¹⁵N) and organic carbon (δ¹³C_org) was used to characterize bulk organic matter (OM) of a piston core from the Patagonian maar lake Laguna Potrok Aike (Argentina) for the purpose of palaeoenvironmental reconstruction. Sedimentary data were compared with geochemical signatures of potential OM sources from Laguna Potrok Aike and its catchment area to identify the sources of sedimentary OM. Correlation patterns between isotopic data and TOC/TN ratios allowed differentiation of five distinct phases with different OM composition. Before 8470 calibrated ¹⁴C years before present (cal. yrs BP) and after 7400 cal. yrs BP, isotopic and organo-geochemical fingerprints indicate that the sediments of Laguna Potrok Aike consist predominantly of soil and diatom OM with varying admixtures of cyanobacterial and aquatic macrophyte OM. For a short phase of the early Holocene (ca. 8470–7400 cal. yrs BP), however, extremely high input of soil OM is implied by isotopic fingerprints. Previous seismic and geochronological results indicate a severe lake-level drop of 33 m below present-day shortly before 6590 cal. yrs BP. It is suggested that this lake level drop was accompanied by increased erosion of shore banks and channel incision enhancing soil OM deposition in the lake basin. Thus, isotopic data can be linked to hydrological variations at Laguna Potrok Aike and allow a more precise dating of this extremely low lake level. An isotopic mixing model was used including four different sources (soil, cyanobacteria, diatom and aquatic macrophyte OM) to model OM variations and the model results were compared with quantitative microfossil data.     

New constraints on carbonation associated with brecciation in hyperextended margins (example of Iberia and Newfoundland margins)

The sequestration of CO₂ occurs naturally in (ultra)‐mafic rocks by carbonation processes and is commonly noted in areas of the seafloor where mantle lithologies are exhumed. As well as carbonation, mantle exhumation is also responsible for rock brecciation. The relationship between carbonation and brecciation is not well constrained. A temporal evolution from syn‐ to post‐tectonic carbonation and brecciation is proposed in line with progressive mantle exhumation. Using a petrological study of brecciated material from IODP drill cores of the Iberia–Newfoundland conjugated margins, we relate crack–seal veins to tectonic brecciation, authigenic calcite with scalenohedral structure to hydraulic brecciation and reworked clasts within cement to (tectono)‐sedimentary processes. Oxygen isotope compositions reveal late‐staged < 50°C carbonate generation in the proximal part of the ocean–continent transition, which have followed an earlier phase of sub‐seafloor carbonate generation. The results are crucial to understand CO₂ exchange within the reworked sub‐seafloor in passive margins and oceanic systems.     

Luminescence dating of lacustrine sediments from Tangra Yumco (southern Tibetan Plateau) using post‐IR IRSL signals from polymineral grains

Radiocarbon dating of bulk organic matter is the most commonly used method for establishing chronologies of lake sediments for palaeoclimate reconstructions on the Tibetan Plateau. However, this method is likely to be problematic because the dated material often suffers from old carbon contamination. Recently, advances in luminescence‐based chronological techniques have provided new options for dating lacustrine sediments. In the current study, we tested for the first time the applicability of a new post‐IR IRSL (pIRIR) measurement protocol for dating fine‐grained polymineral material from a deep‐lake sediment core from the central part of Tangra Yumco, on the southern Tibetan Plateau. Our results show that: (i) radioactive disequilibria in the uranium decay chain were observed in the studied lake sediments, and thus taken into account for dose rate calculation by using a dynamic modelling approach; (ii) the suitability and robustness of the pIRIR protocol measured at 150°C (pIRIR₁₅₀) for our samples are confirmed by a set of luminescence characteristic tests as well as the agreement with an independent age control; (iii) turbidite deposition partly caused an insufficient resetting of luminescence signals and thus apparent overestimation in luminescence dating; (iv) compared with the luminescence‐based age‐depth model, the ¹⁴C ages of bulk organic matter from the studied core generally yielded an age difference of ～2 ka, which is attributed to hardwater reservoir effects in Tangra Yumco. This study highlights the need for multi‐dating approaches of lake sedimentary archives on the Tibetan Plateau.