Estimation of hydraulic permeability considering the micro morphology of rocks of the borehole YAXCOPOIL-1 (Impact crater Chicxulub,Mexico)

Internal surface, formation factor, Nuclear Magnetic Resonance (NMR)-T2 relaxation times and pore radius distributions were measured on representative core samples for the estimation of hydraulic permeability. Permeability is estimated using various versions of the classic Kozeny–Carman-equation (K–C) and a further development of K–C, the fractal PaRiS-model, taking into account the internal surface. In addition to grain and pore size distribution, directly connected to permeability, internal surface reflects the internal structure (“micro morphology”). Lithologies could be grouped with respect to differences in internal surface. Most melt rich impact breccia lithologies exhibit large internal surfaces, while Tertiary post-impact sediments and Cretaceous lithologies in displaced megablocks display smaller internal surfaces. Investigations with scanning electron microscopy confirm the correlation between internal surface and micro morphology. In addition to different versions of K–C, estimations by means of NMR, pore radius distributions and some gas permeability measurements serve for cross-checking and calibration. In general, the different estimations from the independent methods and the measurements are in satisfactory accordance. For Tertiary limestones and Suevites bulk with very high porosities (up to 35%) permeabilites between 10⁻¹⁴ and 10⁻¹⁶ m² are found, whereas in lower Suevite, Cretaceous anhydrites and dolomites, bulk permeabilites are between 10⁻¹⁵ and 10⁻²³ m².     

Differential rotation in a solar-driven quasi-axisymmetric circulation

We consider the concept of a quasi-axisymmetric circulation to explore the global scale dynamics of planetary atmospheres. The momentum and energy transport processes in the smaller scales are formulated in terms of anisotropic eddy diffusion. In the early work of Williams and Robinson (1973) these concepts have been introduced to describe the Jovian circulation. Our study differs in that we adopt a spectral model (with vector spherical harmonics) and consider a linear system; we are also examining a different parameter regime. The troposphere of Jupiter is assumed to be weakly convectively unstable, and the circulation is driven by the fundamental component of solar differential heating with a broad maximum at the equator. Mode coupling arising from the Coriolis action is considered in self consistent form, and momentum and energy are allowed to cascade from lower to higher order modes. With a limited number of spherical harmonics, up to order 40, and with homogeneous boundary conditions, the conservation equations are integrated between the 25 and 10^–5 bar pressure levels. In addition, a simplified single layer model is discussed which, even though heuristic in nature, elucidates and complements the numerical results. Our analysis leads to the following conclusions: (a) For a negative stability, S ₀ = T ₀/r + , the energy transports arising from large scale advection by the meridional circulation can amplify the response to the external heating. This crucially depends on the latitudinal structure of the circulation, so that banded wind fields with equatorial zonal jets are preferentially excited. (b) With a negative stability of order S ₀ ~ – 10^–6 K cm^–1, the computed number of positive (and negative) zonal jets is similar to that observed on Jupiter. (c) The observed magnitudes in the zonal wind velocities require that the vertical eddy diffusion coefficient is of the order K _r ~ 3 × 10⁵ cm² s^–1, which in turn is consistent with the observed outward flux of energy from the planetary interior (F K _r S ₀ ); this diffusion rate is also of the right order of magnitude to obey mixing length theory. (d) The ratio between the horizontal and vertical eddy diffusion coefficients (relative mixing factor) is of critical importance. If it is too large ( 10⁵), differential rotation or alternating zonal jets cannot be maintained; if it is too small ( 10⁴), the equator tends to corotate. The intermediate value of order R ~ 5 × 10⁴ is again consistent with mixing length theory. (e) With the above constraints on the transport coefficients, the flow is quasigeostrophic. (f) The meridional circulation is multicellular and of the Ferrel-Thomson type. It is consistent with the observed cloud striations in the Jovian atmosphere. (g) In the stable stratosphere at higher altitudes the fundamental component, directly driven by the Sun, dominates. The circulation degenerates, and broad, positive zonal jets develop at middle latitudes, resembling the observed wind field in the visible cloud cover of the Venus atmosphere.Applied Research Corporation, Landover, Maryland, U.S.A.     

Structure of Palaeogene sediments in east Ellesmere Island: Constraints on Eurekan tectonic evolution and implications for the Nares Strait problem

The “Nares Strait problem” represents a debate about the existence and magnitude of left-lateral movements along the proposed Wegener Fault within this seaway. Study of Palaeogene Eurekan tectonics at its shorelines could shed light on the kinematics of this fault. Palaeogene (Late Paleocene to Early Eocene) sediments are exposed at the northeastern coast of Ellesmere Island in the Judge Daly Promontory. They are preserved as elongate SW–NE striking fault-bounded basins cutting folded Early Paleozoic strata. The structures of the Palaeogene exposures are characterized by broad open synclines cut and displaced by steeply dipping strike-slip faults. Their fold axes strike NE–SW at an acute angle to the border faults indicating left-lateral transpression. Weak deformation in the interior of the outliers contrasts with intense shearing and fracturing adjacent to border faults. The degree of deformation of the Palaeogene strata varies markedly between the northwestern and southeastern border faults with the first being more intense. Structural geometry, orientation of subordinate folds and faults, the kinematics of faults, and fault-slip data suggest a multiple stage structural evolution during the Palaeogene Eurekan deformation: (1) The fault pattern on Judge Daly Promontory is result of left-lateral strike-slip faulting starting in Mid to Late Paleocene times. The Palaeogene Judge Daly basin formed in transtensional segments by pull-apart mechanism. Transpression during progressive strike-slip shearing gave rise to open folding of the Palaeogene deposits. (2) The faults were reactivated during SE-directed thrust tectonics in Mid Eocene times (chron 21). A strike-slip component during thrusting on the reactivated faults depends on the steepness of the fault segments and on their obliquity to the regional stress axes.Strike-slip displacement was partitioned to a number of sub-parallel faults on-shore and off-shore. Hence, large-scale lateral movements in the sum of 80–100 km or more could have been accommodated by a set of faults, each with displacements in the order of 10–30 km. The Wegener Fault as discrete plate boundary in Nares Strait is replaced by a bundle of faults located mainly onshore on the Judge Daly Promontory.     

Gap flow measurements during the Mesoscale Alpine Programme

Summary The lowest pass through the Alpine crest, the Brenner Pass, was heavily instrumented with ground-based and air-borne in-situ and remote sensors during the Special Observation Period (SOP) of the Mesoscale Alpine Programme (MAP) in the fall of 1999 to study gap flow. The main objectives were to study the combined effects of changes of terrain height and changes of width in altering the flow characteristics, to investigate the coupling of the gap flow to the flow aloft, and to provide high-density measurements in the along- and cross-gap directions.Gap flows occurred during one third of the 70-day SOP, a frequency above the long term average. Gap flows took place with and without accompanying cross-barrier flow and with and without a capping inversion. A case study demonstrates the hydraulic jump-like features that occurred in gap flow on 30 October 1999 and illustrates the types of data available for further analyses.     

Environmental changes in northern New Zealand since the Middle Holocene inferred from stable isotope records (δ15N, δ13C) of Lake Pupuke

Maar lakes in the Auckland Volcanic Field are important high-resolution archives of Holocene environmental change in the Southern Hemisphere mid-latitudes. Stable carbon and nitrogen isotope analyses were applied on bulk organic matter and the green alga Botryococcus from a sediment core from Lake Pupuke (Auckland, North Island, New Zealand) spanning the period since 7,165?cal.?year BP. The origin of organic matter was established using total-organic?Ccarbon-to-nitrogen ratios (TOC/TN) as well as organic carbon (??¹³C_OM) and nitrogen (??¹⁵N) isotope composition of potential modern sources. This approach demonstrated that the contribution of allochthonous organic matter to the lake sediment was negligible for most of the record. The sedimentary TOC/TN ratios that are higher than Redfield ratio (i.e. >7) are attributed to N-limiting conditions throughout the record. Variations of nitrogen and carbon isotopes during the last 7,165?years are interpreted as changes in the dominant processes in the lake. While epilimnetic primary productivity controlled isotope composition before 6,600?cal.?year BP, microbial processes, especially denitrification and methane oxidation, caused overall shifts of the ??¹⁵N and ??¹³C values since the Mid-Holocene. Comparisons with climate reconstructions from the Northern Island suggest that changes in the wind-induced lake overturn and a shift to more pronounced seasonality were the most likely causes for lake-internal changes since 6,600?cal.?year BP.     

Holocene environmental dynamics of south-eastern Brazil recorded in laminated sediments of Lago Aleixo

Environmental changes of the last 9,300 years were reconstructed by geochemical and pollen analyses of a 14-m-long, laminated sediment core from Lago Aleixo, south-eastern Brazil. Fossil pollen assemblages indicate open savannah vegetation (campo cerrado) and gallery forests until approximately 6,900 cal. BP. During that time, siderite laminae were deposited under anoxic conditions at the lake bottom. Then, increased rainfall and a shorter annual dry period allowed gallery forests and semi-deciduous forests to expand, leading to more closed cerrado vegetation. High-intensity rainfall events during this period are recorded as peaks in K and Ti concentrations. The sediment facies during this period consists of alternating layers of diatoms and minerogenic matter. C/N ratios imply that algae and perhaps soils, too, were the main contributors to sediment organic matter. Biogenic silica and δ¹³C_org variations indicate increasing primary productivity, which was related to higher nutrient flux from intensified leaching of soils, as shown by rising K/Al ratios. Around 800 cal. BP, a closed, semi-deciduous forest developed under present-day climate conditions. Slope stabilization diminished erosion processes in the catchment and caused reduced input of minerogenic matter into the basin. Human impact is evident in the topmost homogeneous sediments, as removal of the stabilizing forest cover amplified soil erosion. The continuous trend to more humid conditions during the Holocene probably reflects increased influence of the Amazon Basin as a moisture source. We conclude that the Lago Aleixo sediment archive was a sensitive recorder of environmental dynamics in tropical South America, which were mainly controlled by changes in precipitation patterns.     

Modeling the temperature of the polar mesopause region: Part II—Intra-seasonal monthly oscillations

Measurements show that the polar mesospheric clouds (PMC) can vary, in the zonal mean, with periods around 1 month [Bailey et al., 2005. Observations of polar mesospheric clouds by the Student Nitric Oxide Explorer. J. Geophys. Res. 110, D13203, doi:10.1029/2004JD005422]. This observation has been the impetus for the present paper, where we describe corresponding temperature oscillations generated by the Numerical Spectral Model (NSM). Our numerical results are taken from the 3D and 2D versions of the NSM, which produce inter-annual and long-term variations in the polar mesopause region, as discussed in the accompanying paper (Part I). In the NSM, the intra-seasonal temperature variations with periods around 2 months are generated by the meridional winds that in turn are accelerated by the momentum deposition from small-scale gravity waves (GW) propagating north/south. The wave-driven dynamical process underlying the oscillations is intrinsically non-linear like that generating the quasi-biennial oscillation (QBO). Our analysis demonstrates that the seasonal annual and semi-annual variations excite the oscillation frequencies through non-linear cascading.     

2D Airflow over a Double Bell-Shaped Mountain

Summary. ?The airflow over an idealized orography with two mountain peaks and a valley between is investigated using a non-linear numerical model. The flow is assumed to be two-dimensional and nonrotational. Surface friction is neglected. This setup is a first step in studying the modifications a finely structured “real” topography introduces to the well-studied flow over one isolated obstacle. The sensitivity of the flow behavior to the valley width is examined for the case of specified mountain volume as well as constant non-dimensional mountain height. Flow patterns for linear, weakly nonlinear, wave breaking and upstream blocking cases are examined. Whereas the nondimensional mountain height is still the main measure of the nonlinearity of the flow, the differing steepness of upslope and downslope caused by the separating valley, strengthens nonlinear effects. It also modifies wave breaking and upstream blocking. For wide enough valleys wave breaking regions can form above both peaks. Received January 20, 1999/Revised June 28, 1999     

Conjecture about a hurricane system in the Jovian atmosphere

Kuiper (1972) had suggested that the Great Red Spot (GRS) of Jupiter is a giant hurricane. We present further arguments in support of this idea and propose that it may also apply to the smaller vortices such as the white and brown ovals (barges). Our estimates indicate that the spin-down time-constants for these Jovian vortices are significantly shorter than the observed lifetimes. Thus, the motions must be sustained through the continued release of internal energy. In analogy with the CISK mechanism for the terrestrial hurricane, transport of water vapor, which is observed on Jupiter, may provide the latent energy to fuel the motions. The energy the planet emits must be transported upwards; therefore its troposphere should be convectively unstable. In such an atmosphere, the proposed solar driven meridional circulation is multicellular, of the Ferrel-Thomson type. If the energy transport from the planetary interior is accelerated by the upward motions in the circulation, eastward zonal jets develop such as observed in the equatorial region. But if the upward flow of energy is impeded by the prevailing downward motions in the meridional circulation (which occur, for example, near 20 latitude), we propose that the convective instability is amplified. The conditions then are more favorable for the development of hurricanes which may appear in the form of the GRS and the white and brown ovals. The GRS with its large size and long life time (indicating that it is very deep) is unique, and we suggest that it may have been induced by meteor impact.     

Rock elasticity as a function of the uniaxial stress: laboratory measurements and theoretical modelling of vertical transversely isotropic and orthorhombic shales

We apply a rock-physics model that describes the relationship between the effective stress and rock elasticity. We experimentally obtain and analyse a data set containing one vertical transversely isotropic and one orthorhombic shale sample. The vertical transversely isotropic symmetry of the first sample is caused by the layered structure of the rock. The seismic orthorhombicity of the second sample could be explained after microscopic analysis of thin section, which demonstrates an imperfect disorder of inhomogeneities. Both samples were loaded uniaxially in a quasi-static regime. During the loading, we measured stress-dependent seismic velocities and sample deformations. For the analysis of the stress-dependent velocities and stiffnesses, we modelled the measured data set using a recent generalization of the porosity deformation approach. Comparison of the experimentally determined and numerically modelled data supports the applicability of the theory and helps in the interpretation of experimentally obtained data. In agreement with the theory, uniaxial stress increases the elliptic component of the seismic anisotropy and does not impact the anellipticity parameter. We demonstrate the distinct influence of the stiff and compliant porosities on the stress sensitivity of the elastic properties.