Frost risk mapping for landscape planning: A methodology

Summary Minimum air temperatures were measured during three winters with a network of stations in open, undulating terrain. It was observed that the change in minimum air temperature with elevation could be predicted from mean nighttime windspeed, total nighttime net radiation loss and a hill-top reference minimum temperature. It was also found that the deviation of temperatures at individual sites could be predicted from a local terrain parameter which reflects the extent of cold air accumulations. Thus a methodology for frost risk mapping has been developed which is based on regional weather dataand local terrain analysis. This paper describes the model and illustrates the regional weather and terrain effects with three-dimensional block diagrams.With 8 Figures     

Magnetic Anisotropy as an Aid to Identifying CRM and DRM in Red Sedimentary Rocks

To further evaluate the potential of magnetic anisotropy techniques for determining the origin of the natural remanent magnetization (NRM) in sedimentary rocks, several new remanence anisotropy measurement techniques were explored. An accurate separation of the remanence anisotropy of magnetite and hematite in the same sedimentary rock sample was the goal.In one technique, Tertiary red and grey sedimentary rock samples from the Orera section (Spain) were exposed to 13 T fields in 9 different orientations. In each orientation, alternating field (af) demagnetization was used to separate the magnetite and hematite contributions of the high field isothermal remanent magnetization (IRM). Tensor subtraction was used to calculate the magnetite and hematite anisotropy tensors. Geologically interpretable fabrics did not result, probably because of the presence of goethite which contributes to the IRM. In the second technique, also applied to samples from Orera, an anisotropy of anhysteretic remanence (AAR) was applied in af fields up to 240 mT to directly measure the fabric of the magnetite in the sample. IRMs applied in 2 T fields followed by 240 mT af demagnetization, and thermal demagnetization at 90°C to remove the goethite contribution, were used to independently measure the hematite fabric in the same samples. This approach gave geologically interpretable results with minimum principal axes perpendicular to bedding, suggesting that the hematite and magnetite grains in the Orera samples both carry a depositional remanent magnetization (DRM). In a third experiment, IRMs applied in 13 T fields were used to measure the magnetic fabric of samples from the Dome de Barrot area (France). These samples had been demonstrated to have hematite as their only magnetic mineral. The fabrics that resulted were geologically interpretable, showing a strong NW-SE horizontal lineation consistent with AMS fabrics measured in the same samples. These fabrics suggest that the rock's remanence may have been affected by strain and could have originated as a DRM or a CRM.Our work shows that it is important to account for the presence of goethite when using high field IRMs to measure the remanence anisotropy of hematite-bearing sedimentary rocks. It also shows that very high magnetic fields (>10 T) may be used to measure the magnetic fabric of sedimentary rocks with highly coercive magnetic minerals without complete demagnetization between each position, provided that the field magnetically saturates the rock.     

Haynesville Shale Well Performance and Development Potential

Louisiana’s Haynesville Shale is one of several unconventional gas plays that have been discovered in the U.S. in recent years and promise to dramatically change the course of future domestic energy development. The Haynesville Shale is the deepest, hottest, and highest pressured shale among the big four plays in the U.S. with drilling and completion cost ranging between 7 and7 and 10 million per well. The average Haynesville well has an initial production rate of 10 MMcfd and declines rapidly, producing 80% of its expected recovery during the first 2 years of production. The purpose of this article is to describe the productivity characteristics of Haynesville wells, project future production from the inventory of active wells, and assess production potential based on drilling scenarios. We offer statistical analysis of the wells drilled to date and construct type profiles to characterize the play. We estimate that the current inventory of Haynesville wells will produce 3 Tcf over their lifecycles, and within the next 3 years, cumulative build-out in the region will range between 3 and 9 Tcf. To maintain current gas production levels in the state, we estimate that about 550 shale gas wells per year will need to be brought online over the next 3 years.     

Estimating water balance components of tropical wetland lakes in the Pantanal dry season,Brazil

Abstract

Water balance studies with stable water isotopes have rarely been conducted in remote and tropical wetland areas. As such, little is known regarding the water balance and groundwater–surface water interaction in the Pantanal, one of the largest and most pristine wetlands in the world. We applied MINA TrêS, a water balance model utilizing stable water isotopes (δ¹⁸O, δ²H) and chloride (Cl^-) to assess the dry-season hydrological processes controlling groundwater–surface water interactions and the water balance of six floodplain lakes in the northern Pantanal, Brazil. Qualitatively, all lakes exhibited similarity in hydrological controls. Quantitatively, they differed significantly due to morphological differences in controlling groundwater inflow and lake volume. Our approach is readily transferable to other remote and tropical wetland systems with minimal data input requirements, which is useful in regions with sparse hydrometric monitoring.

Editor Z.W. Kundzewicz     

Structural and stratigraphical constraints on the kinematics history of the Southern Tan–Lu Fault Zone during the Mesozoic Anhui Province, China

The Tan–Lu Fault Zone (TLFZ) extends in a NNE–SSW direction for more than 2000 km in Eastern China. It has been considered either as a major sinistral strike-slip fault, as a suture zone or as a normal fault. We have conducted a structural analysis of the southern segment of this fault zone (STLFZ) in the Anhui Province. The ages (Triassic to Palaeocene) of the formations affected by the faults have been re-appraised taking into account recent stratigraphical studies to better constraint the ages of the successive stages of the kinematics of the STLFZ. Subsequently, the kinematics of the faults is presented in terms of strain/stress fields by inversion of the striated fault set data. Finally, the data are discussed in the light of the results obtained by previous workers.We propose the following history of the STLFZ kinematics during the Mesozoic. At the time of collision, a  NNE orientated Tan–Lu margin probably connected two margins located north of the Dabie and Sulu collision belts. During the Middle–Late Triassic, the SCB has been obliquely subducted below the NCB along this margin which has acted as a compressional transfer zone between the Dabie and Sulu continental subduction zones. The STLFZ has been initiated during the Early Jurassic and has acted as a sinistral transform fault during the Jurassic, following which the NCB/SCB collision stopped. A  NW-trending extension related to metamorphic domes was active during the basal Early Cretaceous ( 135–130 Ma); it has been followed by a NW–SE compression and a NE–SW tension during the middle–late Early Cretaceous ( 127 to  105 Ma, possibly  95 Ma); at that time the TLFZ was a sinistral transcurrent fault within the eastern part of the Asian continent. During the Late Cretaceous–Palaeocene, the STLFZ was a normal fault zone under a WNW–ESE tension.     

The problem of inherited Ar* in dating impact glass by the Ar/Ar method: Evidence from the Tswaing impact crater (South Africa)

The Tswaing meteorite impact crater is a 1.13 km diameter structure located in the 2.05 Ga Nebo granite of the Bushveld Complex. The impact age had previously been determined by fission track dating to 220 ± 104 ka. ⁴⁰Ar/³⁹Ar step-heating and total fusion experiments performed on single- and multi-grain impact glass aliquots gave apparent ages ranging from 1.0 ± 0.3 Ma to 204 ± 6 Ma. These “ages” indicate that the radiogenic Ar derived from the target rocks has not been completely degassed as a result of the impact process, despite fusion of the target material. Results of step-heating experiments imply that the trapped within the glass is located in two distinct reservoirs thought to be the glass matrix and fluid/vapor inclusions (or un-melted residual clasts). Calculations assuming an age of 0.2 ± 0.1 Ma for Tswaing (fission track data) reveal that the amount of inherited ⁴⁰Ar*() relative to the pre-impact concentration varies from 0.015% to 4.15%. The spread defined by likely reflects the various quench rates experienced by the glass, most certainly due to the pre-impact position of the sample relative to the center of the crater. We compare the influence of on the apparent ⁴⁰Ar/³⁹Ar age determination of five impact structures. Our calculations show that the main characteristic controlling the age offset (for a given proportion of ) is the age difference between the impact and the target rocks (i.e., the ⁴⁰Ar* concentration in the target rock). The buffer effect for a given crater structure can be predicted knowing the age of the basement and having a rough estimation of the age of the crater structure itself. The occurrence of is likely influenced by (1) the degree of polymerization (i.e., silicate structure complexity) of the target rock and presumably related to the diffusivity of Ar in the melt and glass, (2) the Ar partial pressure at the grain boundary, (3) the quantity of energy involved in the impact, and (4) the porosity of the target rocks. For glass that inevitably suffers inherited and/or excess ⁴⁰Ar*, the use of the inverse isochron technique can be appropriate but should be applied with careful statistical treatment.     

Longshore variations in nearshore wave processes at magilligan point,northern ireland

Magilligan Point is a recurved cuspate foreland at the mouth of Lough Foyle. Two wave regimes intersect in the estuary mouth and the manner of their interplay controls shoreline changes. Ocean swell waves from the N and NE are refracted around the recurve, losing both height and energy longshore. Width of the surf zone decreases and waves tend to steepen, although both these changes and wave refraction owe something to nearshore geometry. Angle of wave approach becomes more acute and a westerly flowing longshore current moves sand S and SW along the beach. Estuary waves from the S and SW are wind-driven with high-frequencies and steepnesses. They generate a northeasterly current which returns material N, but dies out as the waves become obliterated by nearshore attenuation and breaking of swell. It is possible to identify a time-averaged null-point where shoreline wave power is balanced, although this tends to shift over short periods causing rapid morphological changes. The existence of two independent, but counteractive cells ensures the long-term maintenance of the foreland, without requiring major or continuous supplies of fresh sediment.