An overview on source rocks and the petroleum system of the central Upper Rhine Graben

International Journal of Earth Sciences - The petroleum system of the Upper Rhine Graben (URG) comprises multiple reservoir rocks and four major oil families, which are represented by four distinct...     

Nitrogen cycling in the German Bight (SE North Sea) — Clues from modelling stable nitrogen isotopes

Nitrogen isotope values (δ¹⁵N) of surface sediments in the German Bight of the North Sea exhibit a significant gradient from values of 5–6‰ of the open shelf sea to values above 11‰ in the German Bight. This signal has been attributed to high reactive N (N_r) loading enriched in ¹⁵N from rivers and the atmosphere. To better understand the processes that determine the intensity and spatial distribution of δ¹⁵N anomalies in surface sediments, and to explore their usefulness for reconstructions of pristine N-input from rivers, we modeled the cycling of the stable isotopes ¹⁴N and ¹⁵N in reactive nitrogen through the ecosystem of the central and southern North Sea (50.9–57.3°N, 3.4°W−9.2°E) for the year 1995. The 3D-ecosystem model ECOHAM amended with an isotope-tracking module was validated by δ¹⁵N data of surface sediments within the model domain. A typical marine value (δ¹⁵N_nitrate=5‰) was prescribed for nitrate advected into the model domain at the seaside boundaries, whereas δ¹⁵N_nitrate of river inputs were those measured bi-monthly over 1 year; δ¹⁵N values of atmospheric deposition were set to 6‰ and 7‰ for NO_x and NH_y, respectively. The simulated δ¹⁵N values of different nitrogen compounds in the German Bight strongly depend on the mass transfers in the ecosystem. These fluxes, summarized in a nitrogen budget for 1995, give an estimate of the impacts of hydrodynamical and hydrological boundary conditions, and internal biogeochemical transformations on the nitrogen budget of the bight.     

Quaternary palaeoenvironments and multi-storey valley fill architecture along the Mezen and Severnaya Dvina river valleys,Arkhangelsk region,NW Russia

The modern Severnaya Dvina and Mezen river systems in the Arkhangelsk region, NW Russia, are located within extensive palaeovalley systems. The palaeovalleys form depressions in bedrock and have controlled the drainage systems in the area at least since the Last Interglacial. Vertically stacked marine to fluvial sediments reflect deposition during fluctuating climate and sea levels.A compilation of lithostratigraphical data collected during the last decade has been coupled with bedrock topography and geomorphology from satellite images in order to describe the valley fill architecture for the two valley systems. Each system has been divided into a number of depositional units (storeys) separated by incision/non-deposition and used to investigate the timing of aggradational versus incisional phases. Time constraints for each phase are provided by optically stimulated luminescence (OSL) ages, and aggradation and incision are linked to independent records of climate and sea level change.The pattern of aggradation and erosion is regional and primarily driven by episodes of increasing and decreasing sediment supply. Aggradation is correlated to times of deglaciation with high sediment supply from the ice margin, release of sediment from ice-dammed lakes and low vegetation and degradation of permafrost on the flood plain. Incision is related to cold intervals with low sediment supply, delayed incision due to isostatic uplift and drainage of ice-dammed lakes. Relative sea level change controls the distribution of marine deposits, which show significant regional variations due to variable isostatic response across the region. Sea level change plays a limited role for fluvial aggradation/incision in the study area.     

Coronal Holes and Solar Wind High-Speed Streams: I. Forecasting the Solar Wind Parameters

We analyze the relationship between the coronal hole (CH) area/position and physical characteristics of the associated corotating high-speed stream (HSS) in the solar wind at 1 AU. For the analysis we utilize the data in the period DOY 25 – 125 of 2005, characterized by a very low coronal mass ejection (CME) activity. Distinct correlations between the daily averaged CH parameters and the solar wind characteristics are found, which allows us to forecast the solar wind velocity v, proton temperature T, proton density n, and magnetic field strength B, several days in advance in periods of low CME activity. The forecast is based on monitoring fractional areas A, covered by CHs in the meridional slices embracing the central meridian distance ranges [−40°,−20°], [−10°,10°], and [20°,40°]. On average, the peaks in the daily values of n, B, T, and v appear delayed by 1, 2, 3, and 4 days, respectively, after the area A attains its maximum in the central-meridian slice. The peak values of the solar wind parameters are correlated to the peak values of A, which provides also forecasting of the peak values of n, B, T, and v. The most accurate prediction can be obtained for the solar wind velocity, for which the average relative difference between the calculated and the observed peak values amounts to %. The forecast reliability is somewhat lower in the case of T, B, and n ( , 30, and 40%, respectively). The space weather implications are discussed, including the perspectives for advancing the real-time calculation of the Sun – Earth transit times of coronal mass ejections and interplanetary shocks, by including more realistic real-time estimates of the solar wind characteristics.     

Variability of extreme events in the Colombian Pacific and Caribbean catchment basins

This paper analyses the behavior of extreme events of surface precipitation and temperature inside the Pacific and Caribbean Catchment Basins in Colombia using several datasets such as observations, reconstructed data, NCEP-NCAR and ERA-40 reanalyses and data from the regional model REMO. We use an extreme value method that selects the time series excesses over a nonstationary threshold and adjusts them to a generalized Pareto distribution. The goodness of fit is evaluated through a test that includes the Cramer–von Mises, Kolmogorov–Smirnov and Anderson–Darling statistics and the p values generated by parametric bootstrap resampling. The test not only evaluates the goodness of fit but also the threshold choice. The parameters are presented in maps that allow recognition of the features of the extreme behaviour inside the catchment basins, and differences and similarities between them. Maps of return periods for the maximum extreme events are also presented. A strong influence of the El Niño–Southern oscillation on the extreme events of both temperature and precipitation is found in the two catchment basins.     

Shrinking and Cooling of Flare Loops in a Two-Ribbon Flare

We analyze the evolution of the flare/postflare-loop system in the two-ribbon flare of November 3, 2003, utilizing multi-wavelength observations that cover the temperature range from several tens of MK down to 10⁴ K. A non-uniform growth of the loop system enables us to identify analogous patterns in the height–time, h(t), curves measured at different temperatures. The “knees,” “plateaus,” and “bends” in a higher-temperature curve appear after a certain time delay at lower heights in a lower-temperature curve. We interpret such a shifted replication as a track of a given set of loops (reconnected field lines) while shrinking and cooling after being released from the reconnection site. Measurements of the height/time shifts between h(t) curves of different temperatures provide a simultaneous estimate of the shrinkage speed and cooling rate in a given temperature domain, for a period of almost ten hours after the flare impulsive phase. From the analysis we find the following: (a) Loop shrinkage is faster at higher temperatures – in the first hour of the loop-system growth, the shrinkage velocity at 5 MK is 20 – 30 km s⁻¹, whereas at 1 MK it amounts to 5 km s⁻¹; (b) Shrinking becomes slower as the flare decays – ten hours after the impulsive phase, the shrinkage velocity at 5 MK becomes 5 km s⁻¹; (c) The cooling rate decreases as the flare decays – in the 5 MK range it is 1 MK min⁻¹ in the first hour of the loop-system growth, whereas ten hours later it decreases to 0.2 MK min⁻¹; (d) During the initial phase of the loop-system growth, the cooling rate is larger at higher temperatures, whereas in the late phases the cooling rate apparently does not depend on the temperature; (e) A more detailed analysis of shrinking/cooling around one hour after the impulsive phase reveals a deceleration of the loop shrinkage, amounting to ā ≈ 10 m s⁻² in the T < 5 MK range; (f) In the same interval, conductive cooling dominates down to T ≈ 3 MK, whereas radiation becomes dominant below T ≈ 2 MK; (g) A few hours after the impulsive phase, radiation becomes dominant across the whole T < 5 MK range. These findings are compared with results of previous studies and discussed in the framework of relevant models.     

The solar soft X-ray background flux and its relation to flare occurrence

Solar Physics - The soft X-ray background flux (XBF) based on GOES 1–8&;nbsp;Å measurements for the period 1975–2003 is studied. There is strong evidence that in the XBF the...     

Comparisons between marine productivity and terrestrial input records in the Gulf of California over the last 28 ka

We study the marine and terrestrial contributions in the Gulf of California (GC) to understand the relationship between continental climate and oceanographic variability over the last 28 ka. In Core AII125-8-JPC-20, we examine aeolian and riverine inputs as nutrients for biological productivity. We use biogenic silica (%opal), total organic carbon (%TOC) and calcium carbonate (%CaCO₃) as proxies for primary productivity, and lithic fraction distributions as proxies for terrigenous transport. At the core site, biogenic and lithic components are in phase at millennial-scale in response to regional climate conditions. During the Late Pleistocene, the GC shelf area was above sea level and the western margin showed transient episodes of increased fluvial inputs. Episodic increases in %opal and reduced %TOC suggest upwelling events but ineffective C-export to the sediment. During stadial events (Heinrich 2, Heinrich 1, Younger Dryas), regional declines in %opal, but increases in %CaCO₃ and TOC, suggest efficient C-export by carbonate organisms. During most of the Holocene, dust inputs are higher. Episodic increases in %TOC suggest higher C-accumulation, although this is not controlled by siliceous or calcareous organisms. In the GC, besides upwelling and current advection, nutrient inputs driven by terrestrial climate have an impact on the biological C-pump. © 2020 John Wiley & Sons, Ltd.     

Structures along the Orobic thrust, Central Orobic Alps, Italy

A series of regional deformation phases is described for the metamorphic basement and the Permian cover in an area in the central Orobic Alps, northern Italy. In the basement deformation under low-grade amphibolite metamorphic conditions is followed by a second phase during retrograde greenschist conditions. These two phases predate the deposition of the Permian cover and are of probable Variscan age. An extensional basin formed on the eroded basement during the Late Carboniferous, filled with fan conglomerates and sandstones, and rhyolitic volcanic rocks. Well-preserved brittle extensional faults bound these basins. Further extension deformed basement and cover before the onset of Alpine compressional tectonics. Cover and basement were deformed together during two phases of compressional deformation of post-Triassic age, the first giving rise to tectonic inversion of the older extensional faults, the second to new thrust faults, both associated with south-directed nappe emplacement and regional folding. Foliations develop in the cover only during the first phase of deformation as part of the activity on “shortening faults”. Main activity on the Orobic thrust actually postdates the first phase of thrusting and foliation development in the cover.