ogs5py: A Python-API for the OpenGeoSys 5 Scientific Modeling Package

High-performance numerical codes are an indispensable tool for hydrogeologists when modeling subsurface flow and transport systems. But as they are written in compiled languages, like C/C++ or Fortran, established software packages are rarely user-friendly, limiting a wider adoption of such tools. OpenGeoSys (OGS), an open-source, finite-element solver for thermo-hydro-mechanical–chemical processes in porous and fractured media, is no exception. Graphical user interfaces may increase usability, but do so at a dramatic reduction of flexibility and are difficult or impossible to integrate into a larger workflow. Python offers an optimal trade-off between these goals by providing a highly flexible, yet comparatively user-friendly environment for software applications. Hence, we introduce ogs5py , a Python-API for the OpenGeoSys 5 scientific modeling package. It provides a fully Python-based representation of an OGS project, a large array of convenience functions for users to interact with OGS and connects OGS to the scientific and computational environment of Python.     

Residual dune ridges: Sedimentary architecture,genesis, and implications for palaeo-climate reconstructions

Sedimentary architecture and genesis of residual dune ridges in a temperate climate are presented and implications for their use as archive of changes in long-term precipitation and wind climate are discussed. Residual dunes are common features of wet aeolian systems, where they form sets of shallow ridges, oriented perpendicular to the prevailing wind direction. Residual dune ridges of the study area are vegetated and typically elevate 0.6 to 2.5 m above the surrounding interdune flats. They develop on the lower stoss side of active transgressive dunes, triggered by periods of elevated groundwater table and hence colonization of the foot of the dune by rapid growing pioneer vegetation. Stabilized by plants, the growing ridge detaches from the active transgressive dune and gets abandoned within years in the course of the downwind-migration of the transgressive dune. Grain-size data suggest a main sediment supply from the transgressive dune and only minor input from other sources. Ground-penetrating radar reveals that the residual dune ridges are composed of windward-dipping as well as leeward-dipping sedimentary beds. Leeward-dipping strata reflect sediment supply from the parental dune, whereas windward-dipping beds are seen to result from sediment redistribution along the ridge and sediment supply from the adjacent swales during the ridge growth period. Multi-annual to multi-decadal variability in precipitation leads to the development of sequences composed of tens of ridges, spanning time periods of several centuries. Spacing of individual ridges in these sequences is controlled not by long-term variability in precipitation alone, but probably also reflects variable wind intensity which affects the migration rate of the parental dune. The important role of vegetation in ridge construction makes these landforms a demonstrative example of landscape development by geo-biosphere interacting processes.     

Mesozoic mafic alkaline magmatism of southern Scandinavia

More than 100 volcanic necks in central Scania (southern Sweden) are the product of Jurassic continental rift-related mafic alkaline magmatism at the southwest margin of the Baltic Shield. They are mainly basanites, with rarer melanephelinites. Both rock groups display overlapping primitive Mg-numbers, Cr and Ni contents, steep chondrite-normalized rare earth element patterns (La_N /Yb_N = 17–27) and an overall enrichment in incompatible elements. However, the melanephelinites are more alkaline and have stronger high field strength element enrichment than the basanites. The existence of distinct primary magmas is also indicated by heterogeneity in highly incompatible element ratios (e.g. Zr/Nb, La/Nb). Trace element modelling indicates that the magmas were generated by comparably low degrees of melting of a heterogeneous mantle source. Such a source can best be explained by a metasomatic overprint of the mantle lithosphere by percolating evolved melts. The former existence of such alkaline trace element-enriched melts can be demonstrated by inversion of the trace element content of green-core clinopyroxenes and anorthoclase which occur as xenocrysts in the melanephelinites and are interpreted as being derived from crystallization of evolved mantle melts. Jurassic magmatic activity in Scania was coeval with the generation of nephelinites in the nearby Egersund Basin (Norwegian North Sea). Both Scanian and North Sea alkaline magmas share similar trace element characteristics. Mantle enrichment processes at the southwest margin of the Baltic Shield and the North Sea Basin generated trace element signatures similar to those of ocean island basalts (e.g. low Zr/Nb and La/Nb) but there are no indications of plume activity during the Mesozoic in this area. On the contrary, the short duration of rifting, absence of extensive lithospheric thinning, and low magma volumes argue against a Mesozoic mantle plume. It seems likely that the metasomatic imprint resulted from the earlier Permo-Carboniferous rifting episode which affected the entire study area and clearly was accompanied by plume activity (Ernst and Buchan in American Geophysical Union, pp 297–337, 1997). Renewed rifting in Jurassic times triggered decompression melting in the volatile-enriched lithospheric mantle and the alkaline melts generated inherited the earlier stored plume signature.This revised version was published online September 2004 with a correction to the footnote of the sample list.     

Characterization of Late Cretaceous to Miocene source rocks in the Eastern Mediterranean Sea: An integrated numerical approach of stratigraphic forward modelling and petroleum system modelling

Stratigraphic forward modelling was used to simulate the deposition of Upper Cretaceous, Eocene and Oligo‐Miocene source rocks in the Eastern Mediterranean Sea and, thus, obtain a process‐based 3D prediction of the quantity and quality distribution of organic matter (OM) in the respective intervals. Upper Cretaceous and Eocene models support the idea of an upwelling‐related source rock formation along the Levant Margin and the Eratosthenes Seamount (ESM). Along the margin, source rock facies form a narrow band of 50 km parallel to the palaeo shelf break, with high total organic carbon (TOC) contents of about 1% to 11%, and HI values of 300–500 mg HC/g TOC. On top of the ESM, TOC contents are mainly between 0.5% and 3% and HI values between 150 and 250 mg HC/g TOC. At both locations, TOC and HI values decrease rapidly towards the deeper parts of the basin. In the Oligo‐Miocene intervals, terrestrial OM makes up the highest contribution to the TOC content, as marine organic matter (OM) is diluted by high‐sedimentation rates. In general, TOC contents are low (<1%), but are distributed relatively homogenously throughout the whole basin, creating poor quality, but very thick source rock intervals of 1–2 km of cumulative thickness. The incorporation of these source rock models into a classic petroleum system model could identify several zones of thermal maturation in the respective source rock intervals. Upper Cretaceous source rocks started petroleum generation in the late Palaeocene/early Eocene with peak generation between 20 and 15 Ma ca. 50 km offshore northern Lebanon. Southeast of the ESM, generation started in the early Eocene with peak generation between 18 and 15 Ma. Eocene source rocks started HC generation ca. 25 Ma ago between 50 and 100 km southeast of the ESM and reached the oil to wet gas window at present day. However, until today they have converted less than 20% of their initial kerogen. Although the Miocene source rocks are mostly immature, Oligocene source rocks lie within the oil window in the southern Levant Basin and reached the onset of the wet gas window in the northern Levant Basin. However, only 10%–20% of their initial kerogen have been transformed to date.     

Late Maastrichtian litho- and ecocycles from hemipelagic deposits of eastern Sinai, Egypt

A biostratigraphical and palaeoecological survey employing calcareous nannofossils and planktonic and benthonic foraminifera has been carried out in four sections of hemipelagic marls and chalks of the Late Maastrichtian Abathomphalus mayaroensis Zone of eastern Sinai, in order to evaluate the mechanisms controlling the composition of the well preserved microfauna and nannoflora.The Abathomphalus mayaroensis Zone in eastern Sinai can be easily identified by the wide occurrence of the index fossil A. mayaroensis and can be further subdivided by the first occurrences of Plummerita reicheli (ex. P. hantkeninoides) and Micula prinsii. Microfossil abundances and lithologies are characterised by pronounced repetitive distribution patterns. These include low and high frequency fluctuations of the planktonic/benthonic (P/B) foraminiferal ratio, repetitive changes in the abundance of calcareous nannofossils and benthonic foraminifera, as well as the development of chalk-marl couplets and thinning upward chalk packets. both microfossil distribution patterns and the occurrence of rhythmites are attributed to changes in primary palaeoproductivity. Semiquantitative investigations of calcareous nannofossils and a few selected benthonic foraminifera yield evidence of the presence of high (HP) and low (LP) productivity assemblages.The interpreted HP assemblage is dominated by Glaukolithus diplogrammus, Manvitella pemmatoidea, Microrhabdulus decoratus and Micula murus and the benthonic foraminifera Neoflabellina jarvisi; the LP assemblage is characterised by Lithraphidites quadratus and Bolivinoides draco. However, further quantitative studies are necessary to reconstruct the exact composition of these assemblages and to explain deviatory developments. The chalk-marl couplets, thinning-upward chalk packets and the high frequency P/B patterns are interpreted to reflect productivity changes related to orbital forcing. These hemipelagites were deposited during the latest phase of the southern Tethyan upwelling system, which was active from the Santonian to the Late Maastrichtian with a peak in the Campanian. Termination of upwelling just before the K/T boundary also provides a good explanation for the change towards a palaeobathymetric control on foraminiferal distribution, as observed for the Palaeocene of central east Sinai.     

Generation of Meteorological Tsunamis (Large Amplitude Seiches) Near the Balearic and Kuril Islands

Extreme atmosphere-induced seiche oscillations occasionally occur in specific inlets and bays of the world ocean causing severe damage to coastal areas, ships and port constructions. Ciutadella inlet (Menorca Island, Western Mediterranean) can be singled out as a place where such large seiches, locally known as rissaga, are quite common. Similar (although weaker) oscillations are also regularly observed in bays of Shikotan Island (South Kuril Islands, northwestern Pacific). Several spectacular events in these regions, identified in the first part of this study (Rabinovich and Monserrat, 1996), are analysed to determine the atmospheric parameters responsible for the generation of large-amplitude seiches. Their generation mechanism was shown to be quite different from that causing ordinary background oscillations. Coincidence of some external factors and certain resonance effects seem to be necessary to produce the destructive waves. In particular, rissaga waves in Ciutadella inlet were found to be related to significant atmospheric disturbances propagating from the southwest, coinciding with the orientation of the inlet, and having a phase speed of about 3 m/s, which is close to the phase speed of long waves offshore from Menorca. Pronounced resonant properties of the inner basin strongly amplify incoming waves in Ciutadella inlet. In contrast, the bays of the northwestern coast of Shikotan Island are protected from normally incident atmosphere-induced waves by the elongated Kunashir Island, hence the whole situation there is not so favorable for the excitation of large seiches.     

Long-wavelength propagation of waves in jointed rocks - study using resonant column experiments and model material

The wave propagation in jointed rock mass depends on many factors, in particular the wave frequency, existing stress conditions and the induced strain levels. When the wavelength of the propagating wave is much longer than the spacing of the joints, it is referred to as long-wavelength condition. This is a dominant condition in seismological studies due to the presence of closely spaced joints in rocks. A comprehensive study on long-wavelength propagation of shear and compression waves in very weak rocks has been carried out with the help of a resonant column apparatus using a model material (plaster of Paris) at various strain levels. The working principle and suitability of the apparatus for testing stiff samples are discussed. The velocity reductions of shear and compression waves across joints are obtained. The influence of frictional and filled joints in attenuating stress waves under various strain levels is analysed. Wave velocities are found to be reduced with increasing strain levels and decreasing joint spacing. The joints with gouge material are more efficient at damping the waves. It is recognised that wave velocity reductions and damping across joints are functions of confining stress and strain levels induced in very weak rocks.