Shallow Drill Holes Research Articles

Heat flow of northern Norway, new data and geodynamic implications

The present contribution introduces new heat flow data from northern Norway, a region of the Baltic Shied and Scandinavian Caledonides that has been poorly covered until now. We computed heat flow values based on data gathered in ten boreholes reaching total depths ranging between ∼390 m and 960 m below ground level. Abundant core material for five of the studied boreholes allowed for precise determination of thermal conductivity profiles. The new determinations represent significant improvement with respect to the few pre-existing heat flow values that were based on shallow drillholes and lake measurements. The obtained heat flow values range between ∼40 and 70 mW/m2, after corrections, and suggest significant heat flow decrease (i.e. ∼10–20 mW/m2) from chiefly Proterozoic terrains to the Archean nucleus in NE Norway. The results suggest also sharp decrease in heat flow from the NE Atlantic to the Lofoten-Vesterålen margin but rather smooth gradients from the Barents Shelf to the continent. The former may be associated with abrupt deepening of the base of the lithosphere below the Lofoten-Vesterålen margin, as already suggested by previous seismic tomography studies and consistent with drastic strain focusing and the formation of a narrow margin. In contrast, gradual deepening of the base lithosphere towards the continent appears to be in agreement with the observed diffuse deformation that took place in the comparatively wide Western Barents Shelf.

The genesis of acid alteration in the Luohe IOA-type deposit, Eastern China and its constraints on mineralization

Luohe is the largest IOA-type deposit in the Middle and Lower reaches of the Yangtze Metallogenic belt. The iron ore body is hosted in thick volcanic rocks, and widespread acidic alteration (secondary quartzite) developed at shallow depths, providing an excellent opportunity to study the genesis of acidic alteration rocks and the genetic links with the IOA mineralization. In this study, detailed mineralogy, in situ sulfur isotopes, and trace element analyses were performed on pyrite from a shallow drill hole in the Luohe deposit. The results indicate that the formation time of acidic alteration is between magnetite (stage II) and anhydrite-pyrite (stage IV), with pyrite sulfur isotopes ranging from −14 to 4‰, which is significantly different from those in stage IV (7-9‰). The anomaly negative sulfur isotope suggests the existence of SO2 disproportionation reaction, and the δ34S of pyrite increases with depth decrease, ultimately falling within the mantle sulfur range. This indicates that the sulfur origin of acidic alteration pyrite is a single magma sulfur source, which is significantly different from the deep iron mineralization system (magmatic + evaporite). The trace elements Co, Ni, As, Ti, Cu, Sb, Tl in pyrite indicate that the acidic alteration fluid has the characteristics of low temperature, low pH, and is rich in F and Cl. Combined with the sulfur isotope results, it is believed that pyrite in the acidic alteration rock of the Luohe was formed by the mixing of gaseous SO2 and shallow groundwater, which is a part of the Luohe magmatic-hydrothermal mineralization system and an important indication for regional exploration of similar deposits.

Application of Treatment for Deep Hole Drilling Debris in Gas-Rich Soft Coal Seams

Hole accidents occurring in the drilling process and borehole collapse encountered in gas production are obstacles standing in the way of high efficiency of gas drainage through the outburst-prone soft coal seams in China. The fundamental testing data from existing suspending agents were combined to prepare a suspension in a specific density for testing debris disposal technology considering several adverse effects. Those effects include the sizeable residual volume of drilling debris, difficult debris disposal, the low effective utilization rate of drill holes, and the unideal extraction effect in drill holes with long-distance downward drill holes. The testing outcomes indicated that the suspension-aided debris disposal could contribute to the following aspects: discharging residual drilling debris out of the drill hole, rinsing the drill hole, preventing drilling debris from filling the coal seam, providing the adequate drill hole depth, and improving the effects of gas extraction. As a result, the gas production in shallow drill holes was increased by 40%, with gas concentration elevated by 21%. In addition, the scalar quantity and extraction concentration in the gas concentration of deep drill holes were increased by 84% and 260%, respectively. This study was undertaken to provide a specific reference for debris disposal work of deep drill holes for gas-rich soft coal seams.

Detection of Near-Surface Permeable Zones Based on Spatial Correlation Between Radon Gas Concentration and DTM-Derived Lineament Density

Radon-222 (Rn) concentrations in soil gas have been used to locate near-surface permeable zones (e.g., fractures, faults) along which hydrothermal fluids ascend in geothermal fields. However, permeable zone detection over a field is often difficult owing to limited numbers and locations of Rn data points. This study aims to develop methodology to enable the regional detection of permeable zones by multivariate geostatistical modeling of Rn concentrations using the Wayang Windu geothermal field (WWGF) in West Java, Indonesia as a model case. Rn concentrations were measured using sampled gases from 17 shallow drill holes with 3–5 m depth over a 5.30 × 9.20 km area. The measurements were repeated over five periods in 2016–2017. To supplement the Rn point data, we produced a digital terrain model with 20-m resolution using an unmanned aerial vehicle and extracted lineaments using the modified segment tracing algorithm (m-STA). Three types of lineament density maps with a grid-cell size of 0.25 × 0.25 km were prepared for the densities of lineament frequency (number), total length and number of intersections in a unit cell. The Rn concentrations measured during the five periods were mapped over the WWGF by the collocated cokriging method using Rn concentrations as the primary variable (point data) and lineament density as the secondary variable (within the grid-cell data). A fuzzy logic approach was then applied to assess permeability as an index of 0–1 by overlaying the estimated Rn concentrations and three types of lineament density. The detected permeable zones mainly overlap with the geothermal manifestations and regional faults, and the permeable indexes generally correspond with Rn concentrations from eight new drill holes, which verify the effectiveness of the proposed method.

Seismic imaging in the eastern Scandinavian Caledonides: siting the 2.5 km deep COSC-2 borehole, central Sweden

Abstract. The Collisional Orogeny in the Scandinavian Caledonides (COSC) project, a contribution to the International Continental Scientific Drilling Program (ICDP), aims to provide a deeper understanding of mountain belt dynamics. Scientific investigations include a range of topics, from subduction-related tectonics to the present-day hydrological cycle. COSC investigations and drilling activities are focused in central Scandinavia, where rocks from the middle to lower crust of the orogen are exposed near the Swedish–Norwegian border. Here, rock units of particular interest occur in the Seve Nappe Complex (SNC) of the so-called Middle Allochthon and include granulite facies migmatites (locally with evidence of ultra-high pressures) and amphibolite facies gneisses and mafic rocks. This complex overlies greenschist facies metasedimentary rocks of the dolerite-intruded Särv Nappes and underlying, lower grade Jämtlandian Nappes (Lower Allochthon). Reflection seismic profiles have been an important component in the activities to image the subsurface structure in the area. Subhorizontal reflections in the upper 1–2 km are underlain and interlayered with strong west- to northwest-dipping reflections, suggesting significant east-vergent thrusting. Two 2.5 km deep fully cored boreholes are a major component of the project, which will improve our understanding of the subsurface structure and tectonic history of the area. Borehole COSC-1 (IGSN: http://hdl.handle.net/10273/ICDP5054EEW1001), drilled in the summer of 2014, targeted the subduction-related Seve Nappe Complex and the contact with the underlying allochthon. The COSC-2 borehole will be located further east and will investigate the lower grade, mainly Cambro-Silurian rocks of the Lower Allochthon, the Jämtlandian décollement, and penetrate into the crystalline basement rocks to identify the source of some of the northwest-dipping reflections. A series of high-resolution seismic profiles have been acquired along a composite ca. 55 km long profile to help locate the COSC drill holes. We present here the results from this COSC-related composite seismic profile (CSP), including new interpretations based on previously unpublished data acquired between 2011 and 2014. These seismic data, along with shallow drill holes in the Caledonian thrust front and previously acquired seismic, magnetotelluric, and magnetic data, are used to identify two potential drill sites for the COSC-2 borehole.

Platinum mineralization in the Kapalagulu Intrusion, western Tanzania

Low-grade copper and nickel mineralization was found near the eastern shore of Lake Tanganyika at Kungwe Bay in the early part of the twentieth century. The mineralization occurs in harzburgite at the base of a layered gabbro complex known as the Kapalagulu Intrusion, emplaced between the Paleoproterozoic Ubendian basement and overlying Neoproterozoic Itiaso Group metasediments. Several mining and exploration companies continued the geophysical and drilling exploration for base metals throughout the last century culminating in the discovery of high-grade platinum-group element (PGE) mineralization associated with chromitite and sulfide-bearing harzburgite within the southeastern extension of the Kapalagulu Intrusion (known as the Lubalisi Zone) that is covered by a layer of nickel-rich laterite regolith. The poorly layered southeastern harzburgite forms part of the >1500 m-thick Lower Ultramafic Sequence and resembles a dike-like body that flares upwards into a succession of well-layered gabbroic rocks of the Upper Mafic Sequence. No PGE mineralization has been found in the layered gabbro; all the mineralization is associated with the chromite- and sulfide-rich harzburgite of the Lower Ultramafic Sequence and the laterite regolith overlying the mineralized harzburgite. The Lubalisi Zone harzburgite is underlain by basal dunite and overlain by an interval of layered harzburgite and troctolite and this ultramafic sequence is folded into a syncline that plunges towards the northwest that has been modified by major dolerite-filled faults orientated subparallel to the fold axial surface. Extensive deep drilling in the Lubalisi Zone of the Kapalagulu Intrusion shows that the folded harzburgite can be subdivided into a lower feldspathic harzburgite, a harzburgite containing chromitite seams and intervals of sulfide and chromite mineralization known as the Main Chromite Sulfide Succession (MCSS), an overlying sulfide-rich harzburgite, and an upper feldspathic harzburgite. Impersistent, stratiform PGE mineralized horizons occur within the MCSS harzburgite from which drill core samples were taken for platinum-group mineral (PGM) characterization from two drill holes. Where the PGE reefs reach the surface there is residual PGE mineralization within the laterite regolith from which drill core samples were taken from various laterite lithological units for PGM characterization. As the harzburgite PGE reefs contain significant concentrations of both sulfide and chromite (including chromitite seams) they resemble the PGE-rich chromitite seams of the Bushveld Complex rather than the PGE-bearing Main Sulfide Zone of the Great Dyke and Main Sulfide Layer of the Munni Munni Complex. The dominant Pd PGM in three PGE reef samples varies, ranging (n = 164, relative wt%) from bismuthides (63 %), bismuthtellurides (19 %), and tellurides (6 %), to tellurides (39 %), bismuthtellurides (24 %), stannides (14 %), and alloys (13 %), and to antimon-arsenides (33 %), stannides (21 %), bismuthides (17 %), tellurides (13 %), and alloys (10 %). From 13.5 % to 21.0 % of the total Pd occurs as a solid solution in pentlandite. The three samples have similar Pt PGM modal distributions (n = 172, relative wt%); the dominant Pt mineral is sperrylite (79, 58, and 47 %) followed by tellurides (15, 17, 21 %), alloys (2, 1, 1 %), and sulfides (2, 1, 0 %). Comparison of Pd/Pt ratios from assays to those calculated from minerals show that the data for the Pt and Pd PGM are very robust, confirming the concentration methodology and characterization. Study of samples from a shallow drill hole penetrating the laterite regolith shows that the primary Pd mineralization has not survived oxidation, is mainly dispersed, but some was reconstituted to form secondary minerals: cabriite, unnamed tellurides, a selenide, a Pd-Te-Hg mineral, alloys and Pd-bearing secondary sulfides (millerite and heazlewoodite). The primary Pt minerals are more resistant to oxidation and dissolution, especially sperrylite and isoferroplatinum, but it is likely that other Pt alloys (tetraferroplatinum and tulameenite) are of secondary origin after dissolution of Pt tellurides.

A Web-Based Resource for Investigating Environmental Change: The Emigrant Pass Observatory

ABSTRACT We present a user-friendly, data-driven Web site (http://thermal.gg.utah.edu/facilities/epo/) for a geothermal, climate change observatory that is educational for the general public, students, and researchers alike. The Emigrant Pass Observatory (EPO), located in the Grouse Creek Mountains in northwestern Utah, gathers both meteorological data (solar radiation, air temperature, rainfall, wind speed and direction, and snow depth) and subsurface temperatures in shallow drillholes. Our website has three main functions: (1) it provides a tutorial for understanding both local climate and climate change, and their relation to diffusion of temperatures into the Earth's subsurface; (2) it facilitates user-defined accessibility to download available climate data; and (3) it contains lesson ideas for using real data to understand local climate. EPO data and resources are ideal for active learning projects. Additionally, our collaboration with ongoing outreach projects (e.g., NSF-sponsored GK–12) in Utah promote the use and understanding of climate change data among students and educators, thus filling a valuable niche in local education.

Geochemistry, isotopic composition (δ 18O, δ 2H, 87Sr/ 86Sr, 143Nd/ 144Nd) in the groundwater of French Guiana as indicators of their origin, interrelations

The current use of untreated river water for drinking purposes by the population of French Guiana has important impacts on public health. Consequently, groundwater is of major importance as a possible alternative drinking water supply to reduce these impacts. Since French Guiana belongs to the Guyana Shield, sustainable water management can be expected to depend increasingly on water from fissured aquifers in hard rocks. Groundwater samples were collected from shallow drill holes in the densely populated coastal area, and deeper wells in the basement (around Cayenne and along the Maroni and Oyapock rivers). This study reports on major and trace elements for which Na + and Ca 2+ excess with regard to Cl reflect the role of water-rock interaction, as well as Sr and Nd isotopes that reflect the role of the different lithologies. δ 18O and δD in waters give constraints on the water cycle (recharge and evaporation processes).

The role of deep seismic reflection data in understanding the architecture and petroleum potential of Australia's onshore sedimentary basins

The onshore energy security program, funded by the Australian Government and conducted by Geoscience Australia, has acquired deep seismic reflection data across several frontier sedimentary basins to stimulate petroleum exploration in onshore Australia. Detailed interpretation of deep seismic reflection profiles from four onshore basins, focussing on overall basin geometry and internal sequence stratigraphy, will be presented here, with the aim of assessing the petroleum potential of the basins. At the southern end of the exposed part of the Mt Isa Province, northwest Queensland, a deep seismic line (06GA–M6) crosses the Burke River structural zone of the Georgina Basin. The basin here is >50 km wide, with a half graben geometry, and bounded in the west by a rift border fault. Given the overall architecture, this basin will be of interest for petroleum exploration. The Millungera Basin in northwest Queensland is completely covered by the thin Eromanga Basin and was unknown prior to being detected on two seismic lines (06GA–M4 and 06GA–M5) acquired in 2006. Following this, seismic line 07GA–IG1 imaged a 65 km wide section of the basin. The geometry of internal stratigraphic sequences and a post-depositional thrust margin indicate that the original succession was much thicker than preserved today and may have potential for a petroleum system. The Yathong Trough, in the southeast part of the Darling Basin in NSW, has been imaged in seismic line 08GA–RS2 and interpreted in detail using sequence stratigraphic principles, with several sequences being mapped. Previous studies indicate that the upper part of this basin consists of Devonian sedimentary rocks, with potential source rocks at depth. In eastern South Australia, seismic line 08GA–A1 crossed the Cambrian Arrowie Basin, which is underlain by a Neoproterozoic succession of the Adelaide Rift System. Stratigraphic sequences have been mapped and can be tied to recent drilling for mineral and geothermal exploration. Shallow drill holes from past petroleum exploration have aided the assessment of the petroleum potential of the Cambrian Hawker Group, which contains bitumen in the core, indicating the presence of source rocks in the basin system.

Boron isotope geochemistry and U–Pb systematics of altered MORB from the Australian Antarctic Discordance (ODP Leg 187)

Boron and Pb isotopic compositions together with B–U–Th–Pb concentrations were determined for Pacific and Indian mantle-type mid-ocean ridge basalts (MORB) obtained from shallow drill holes near the Australian Antarctic Discordance (AAD). Boron contents in the altered samples range from 29.7 to 69.6 ppm and are extremely enriched relative to fresh MORB glass with 0.4–0.6 ppm B. Similarly the δ 11B values range from 5.5‰ to 15.9‰ in the altered basalts and require interaction with a δ 11B enriched fluid similar to seawater ∼ 39.5‰ and/or boron isotope fractionation during the formation of secondary clays. Positive correlations between B concentrations and other chemical indices of alteration such as H 2O CO 2, K 2O, P 2O 5, U and 87Sr/ 86Sr indicate that B is progressively enriched in the basalts as they become more altered. Interestingly, δ 11B shows the largest isotopic shift to + 16‰ in the least altered basalts, followed by a continual decrease to + 5–6‰ in the most altered basalts. These observations may indicate a change from an early seawater dominated fluid towards a sediment-dominated fluid as a result of an increase in sediment cover with increasing age of the seafloor. The progression from heavy δ 11B towards lighter values with increasing degrees of alteration may also reflect increased formation of clay minerals (e.g., saponite). A comparison of 238U/ 204Pb and 206Pb/ 204Pb in fresh glass and variably altered basalt from Site 1160B shows extreme variations that are caused by secondary U enrichment during low temperature alteration. Modeling of the U–Pb isotope system confirms that some alteration events occurred early in the 21.5 m.y. history of these rocks, even though a significant second pulse of alteration happened at ∼ 12 Ma after formation of the crust. The U–Pb systematics of co-genetic basaltic glass and variably low temperature altered basaltic whole rocks are thus a potential tool to place age constraints on the timing of alteration and fluid flow in the ocean crust.

Ultrahigh pressure metamorphic rocks from the Chinese Continental Scientific Drilling Project: I. Petrology and geochemistry of the main hole (0–2,050 m)

The main hole (MH) of the Chinese Continental Scientific Drilling Project (CCSD) in southern Sulu has penetrated into an ultrahigh-pressure (UHP) metamorphic rock slice which consists of orthogneiss, paragneiss, eclogite, ultramafic rock and minor schist. Recovered eclogites have a UHP metamorphic mineral assemblage of garnet + omphacite + rutile ± phengite ± kyanite ± coesite ± epidote. Ultramafic rocks contain garnet + olivine + clinopyroxene + orthopyroxene ± Ti-clinohumite ± phlogopite. Gneisses and schists contain an amphibolite-facies paragenesis, but their zircons have coesite, garnet, omphacite (or jadeite) and phengite inclusions, indicating that eclogites and gneisses have been subjected to in situ UHP metamorphism. Using available geothermobarometers, P–T estimates of 3.1–4.4 GPa and 678–816°C for eclogites were obtained. If surface outcrops and neighboring shallow drill holes are considered together, we suggest that a huge supracrustal rock slab (> 50 km long × 100 km wide × 5 km deep) was subducted to a depth > 100 km and then exhumed to the surface. The depth interval (0–2,050 m) of the CCSD-MH can be divided into six lithological units. Unit 1 consists of alternating layers of quartz-rich and rutile-rich eclogites, with thin interlayers of gneiss and schist. Eclogites of unit 1 are characterized by Nb, Ta, Sr and Ti depletions, low Mg number and general LREE enrichment. Unit 2 comprises rutile- and ilmenite-rich eclogite and minor “normal” eclogite and is characterized by high TiO2, total Fe, V, Co and Sr, and very low SiO2, alkali, Zr, Ba, Nb, Ta and total REE contents, and LREE-depleted REE patterns with slightly positive Eu anomalies. Unit 3 contains ultramafic rock and minor MgO-rich eclogite. Protoliths of UHP rocks from units 1, 2 and 3 represent a layered mafic to ultramafic intrusion at crustal depth. Units 4 and 6 consist of interlayered eclogite and paragneiss; the eclogites are characterized by Th, U, Nb, Ta and Ti depletion and K enrichment and LREE-enriched REE patterns. Paragneisses show Nb, Ta, Sr and Ti depletions and LREE-enriched REE patterns occasionally with slightly negative Eu anomalies, indicating that their protoliths represent metamorphic supracrustal series. Unit 5 consists mainly of orthogneisses, showing distinct Nb, Ta, Sr and Ti depletions, and LREE-enriched REE patterns with pronounced negative Eu anomalies, suggesting granitic protoliths. In conclusion it is proposed that the southern Sulu UHP belt consists of a series of meta-supracrustal rocks, a layered mafic–ultramafic complex and granites.

RESERVOIR QUALITY, DIAGENESIS AND SEDIMENTOLOGY OF THE PALE AND SUBU SANDSTONES: RE-VISITING THE EASTERN PAPUAN BASIN, PAPUA NEW GUINEA

Two shallow diamond drill holes (Subu–1 and Subu–2) continuously cored in August and September 2001 by InterOil Australia represent the first sub-surface penetrations of reservoir quality sandstones in the Eastern Papuan Basin of Papua New Guinea. These wells intersected two sedimentologically distinct thick quartz sandstones (>100 m). The upper sandstone unit is Campanian in age and is correlated with the Pale Sandstone, whereas the lower sandstone is of Turonian age and has not been reported previously, and is tentatively named as the Subu Sandstone in this paper.The core has been the subject of detailed reservoir quality and diagenetic study as part of a multi-disciplinary study conducted by CSIRO Petroleum. The results of the reservoir quality portion of this study form the basis of this report and demonstrate the following:There are two distinct depositional systems present with a lower sandy slope apron and basin floor fan system (Subu Sandstone) and a younger upper shoreface-shallow marine depositional system (Pale Sandstone).While the porosity and permeability data for subsurface samples (5 to 16% and 0.1 to 1000mD) are lower than previously reported by Boult and Carman (1990) for surface samples both the sandstone units demonstrate thick, good reservoir quality reservoir capable of holding significant volumes of hydrocarbons.Bitumen is present in the pore space through out the sandstones in both wells. The presence of biodegraded hydrocarbons demonstrates that liquid hydrocarbons have been generated in the basin and have either migrated through the Subu and Pale sandstone or have been reservoired in them.Associated with the bitumen is pyrite precipitated as an in-situ by-product of shallow biodegradation of the parent liquid hydrocarbon as indicated by sulphur isotope analysis.Diagenetic effects include compaction (the dominant control on reservoir quality), minor quartz cementation, minor secondary porosity generation, and in thin zones localised carbonate cementation.Despite their very different depositional settings and age difference the thin section petrology of the Pale and Subu sandstones are very similar. The subtle difference between them is textural (grain size, sorting) and detrital clay content. The Subu Sandstone is typically finer grained, displays a higher degree of sorting and has a higher detrital clay content than the Pale Sandstone.The character of these sandstones may have as much to do with provenance as with depositional environment and may indicate a separate quartz-rich depositional system sourcing sediment from the Australian craton independent of the Fly Platform Toro/Imburu systems.

Constraints on the thermal and tectonic evolution of Greymouth coalfield

The southern end of the Paparoa Range in Westland, South Island, New Zealand, comprises an asymmetrical, southward plunging, faulted (Brunner‐Mt Davy) anticline, the eastern limb of which is common with the western limb of an asymmetrical (Grey Valley) syncline forming a Neogene foreland basin (Grey Valley Trough). The faulted anticline is a classic inversion structure: compression during the Neogene, associated with the development of the modern Australia‐Pacific plate boundary, caused a pre‐existing normal fault zone, about which a late Cretaceous‐Oligocene extensional half graben had formed (Paparoa Trough), to change its sense of displacement. The resulting basement loading formed the foreland basin, containing up to 3 km of mainly marine sedimentary section. Fission track results for apatite concentrates from 41 shallow drillhole and outcrop samples from the Greymouth Coalfield part of the Brunner‐Mt Davy Anticline are reported and interpreted, to better establish the timing and amount of inversion, and hence the mechanism of inversion. The fission track results integrated with modelling of vitrinite reflectance data, show that the maximum paleotemperatures experienced during burial of the Late Cretaceous and mid‐Eocene coal‐bearing succession everywhere exceeded 85°C, and reached a peak of 180°C along the axis of the former basin. Cooling from maximum temperatures occurred during three discrete phases: 20–15 Ma, 12–7 Ma, and c. 2 Ma to the present. The amount of denudation has been variable across the inverted basin, decreasing westward from a maximum of c. 2.5 km during the first deformation phase, c. 1.2 km during the second phase, and 1.4 km during the third phase. It appears that exhumation over the coalfield continued for about 2 m.y. beyond the biostratigraphically determined time ranges of each of two synorogenic unconformities along the western limb of the Grey Valley Syncline. Stick‐slip behaviour on the range front fault that localised the inversion is inferred. The tectonic evolution of the anticline‐syncline pair at the southern end of the Paparoa Range, is therefore identical in style, and similar in timing, to the development of the Papahaua Range‐Westport Trough across the Kongahu Fault Zone, in the vicinity of Buller Coalfield.

Electrical resistivity surveys, ascension Island, South Atlantic Ocean

Reconnaissance electrical resistivity surveys, completed on Ascension Island as one part of an integrated geothermal exploration program, define a 5 km 2 area of low resistivity within the central part of the island. Dipole-dipole lines help to define the vertical resistivity structure and suggest the incursion of seawater beneath much of the area surveyed. A zone of 5–10 Ωm indicated by numerical modeling suggests possible alteration and geothermal brines that may have mixed with seawater, above a geothermal reservoir. Temperature gradients in shallow drillholes and a deep exploration well indicate the presence of a deep geothermal system in this area.

High-resolution temperature logging in shallow drillholes for the determination of terrestrial heat flow: field examples and analysis

The first 200 m of the Earth's crust is the depth range most investigated by drilling. Temperature profiles in such shallow drillholes generally show severe influences of groundwater flow; therefore they are rarely used for heat flow determinations. But regardless how severely the temperature logs are influenced by advective heat transfer the “background” conductive heat flow signal is still present in the data. It is shown how to handle distorted temperature profiles by means of simple one-dimensional, steady-state models. The undisturbed (“background”) heat flow is estimated by model calculations; the comparison of the modelled temperature profiles with the measured logs is a test for the credibility of the modelling approach. Examples from northwestern Switzerland and northwestern Turkey with irregular temperature profiles are given for the following situations: conductive-convective regime with vertical groundwater movement over the entire observation depth; vertical flow in a certain layer located between purely conductive layers; and water flow inside of the drillhole. Measured temperature profiles can be approximated by modelling within ±0.2°C. Repeated, high-precision digital temperature logging is needed to prove the temporal stability of the convective disturbances in order to use steady-state models.

Petrography, geochemistry, and depositional setting of the San Pedro and Santo Tomas coal zones: Anomalous algae-rich coals in the middle part of the Claiborne Group (Eocene) of Webb County, Texas

Two coal zones, the San Pedro and the overlying Santo Tomas, are present for nearly 35 km in outcrop, surface and underground mines, and shallow drill holes along the strike of the middle part of the Claiborne Group (Eocene) in Webb County, Texas. A sandstone-dominated interval of 25 to 35 m separates the two coal zones, which range up to 3 m in thickness. Each coal zone contains carbonaceous shales, thin (<0.75 m) impure coal beds, and thin (<0.85 m) but commercially significant nonbanded coal beds. The nonbanded coals are different from other Tertiary coals of the Gulf of Mexico Coastal Plain: unlike lignites that are typical of the older Wilcox Group (Paleocene-Eocene) and younger Jackson Group (Eocene), nonbanded coals of the Claiborne Group have high vitrinite-reflectance values (0.53 R max) and high calorific yields (average 6670 kcal/kg or 12,000 Btu, dry basis). The coals are weakly agglomerating (free-swelling index is 1.5–2.0) and have an apparent rank of high-volatile bituminous. The coal-bearing portion of the middle Claiborne Group in the Rio Grande area represents a fining-upward transition from sandstone-dominated, marine-influenced, lower delta plain depositional environments to more inland, mudstone-rich, predominantly freshwater deltaic settings. Discontinuities within the San Pedro coal zone are attributed mainly to the influence of contemporaneous deposition of distributary mouth-bar sand bodies. The less variable nature of the Santo Tomas coal zone reflects its origin in the upper part of an interlobe basin that received only minor clastic influx. Petrographic attributes of the nonbanded coals indicate that they formed subaqueously in fresh to possibly brackish waters. A highly degraded groundmass composed of eugelinite is the main petrographic component (approximately 71%, mineral-matter-free basis). An enriched liptinite fraction (approximately 23%) probably accounts for unusually high calorific values. There is negligible inertinite. Petrographic study of polished blocks indicates that approximately 10 percent of the nonbanded coal from both coal zones is composed of green algae fructifications, which also occur in clastic rocks of the coal-bearing interval. Such algal material cannot be identified or quantified by conventional coal petrographic techniques that utilize particle pellets or by palynological analyses that include acid preparation.

Supplementary ground Geophysics for Airborne Electromagnetic Salinity Survey over Jemalong-Wyldes Plains Area

Airborne transient electromagnetic (TEM) methods initially developed for the detection of deep conductive targets are continuously being upgraded to improve near-surface resolution of both vertical and lateral conductivity distributions suitable for salinity mapping. However, since it is a combination of location, proximity to the surface, as well as the mobility of saline groundwater that constitutes the problem, it is important to the hydrogeologist to map the complete subsurface structure responsible for the aquifer framework. A QUESTEM survey was flown over the Jemalong-Wyldes Plains area, New South Wales, by World Geoscience Corporation with the help of funding by the National Soil Conservation Program. The data have been re-evaluated with respect to ground TEM, DC resistivity, GEONICS EM 34-3, shallow drill hole sampling and a comprehensive hydrogeological investigation. Apparent conductance maps were used to guide the location of specific ground surveys, and conductivity-depth sections calculated from the airborne data were used for semi-quantitative comparison with the ground methods. Comparison with TEM and DC resistivity results showed correlation with true conductivity trends down to ~140 m. Comparison with GEONICS EM 34-3 data and electrical conductivity (EC) measurements on drill cutting samples to a depth of 10 m also showed good correlation with the near-surface features of the airborne TEM conductivity-depth section. The significant correlation with both shallow and deep conductivity trends observed in ground surveys suggests that the presentation of complete conductivity-depth sections calculated from airborne TEM, should become routine procedure in hydrogeological investigation.

Integration of Geology, Non-Seismic Geophysics and Seismic Data in a Structurally Complex, Frontier Oil Play: Northern Sangre de Cristo Mountains/Northeast San Luis Basin, Colorado: ABSTRACT

The discovery of live Cretaceous oil in mineral exploration drill holes, followed by the identification of Mesozoic sediments in outcrop and in shallow drill holes, has lead to an integrated approach to exploration of a structurally complex, frontier oil play in south-central Colorado. Gravity, aeromagnetic, magnetotelluric (MT), and time domain electromagnetic (TDEM) data were acquired and interpreted in the initial stages of the project. Models derived from the geophysical data were augmented with geologic field work to explain specific anomalies. Interpretation of the gravity data was constrained by density measurements on representative rock samples collected in the field. Seismic data, acquired in the most recent exploration stage, provided confirmation and modification of the basin margin geometry. Velocity data from the seismic was integrated with resistivity, density, magnetic and geologic data to predict lithologies on an intermediate fault block located between the Sangre de Cristo Mountains and the San Luis Basin.

Evidence for a cyclic variation of permafrost temperatures in northern alaska

AbstractObservations of permafrost temperatures in shallow drill holes in northern Alaska near the Beaufort Sea coast show that these temperatures have cycled during the decade from 1983 to 1993. The two sites nearest the coast indicate a period of about 10 years and an amplitude at the permafrost surface of about 2°C. The two sites farthest from the coast have similar periods but reduced amplitudes of about 0.6°C. Changes in air temperatures, snowfall, length of sea ice season, solar effects, and other factors could, in principle, produce the observed temperature changes. Barrow air temperatures have a periodicity of 10.1 years but currently lead the sunspot cycle. Snowfall also shows evidence for a periodicity near 10 years. Near Prudhoe Bay, the length of the sea ice season increased about one week from 1979 to 1986 which could have caused a decrease in coastal air temperatures. The sunspot cycle (10–11 year period) leads temperatures at the 30 m depth by two to three years which is about the expected lead. During the descending part of the last solar cycle, satellite measurements of the solar total irradiance showed a decrease of about 3W m−2, which is about four times the calculated mean energy flux at the permafrost table (0.6 to 0.7 W m−2) required to produce the observed temperature changes.

The thermal regime of intertidal permafrost, George River estuary, Ungava Bay, Quebec

Permafrost in tidal-marsh sediments was studied along the estuary of George River, Ungava Bay, northern Quebec. In this macrotidal environment, wide tidal flats and marshes lie in bays along the shoreline. Discontinuous permafrost bodies occur in the silty sediments underlying the marshes in the upper part of the intertidal zone, where submersions by large tides and storm surges are rare and where the icefoot freezes to the ground in winter. The permafrost is about 5 m thick, saline, and ice poor. According to logged thermal data, a freezing-point depression of 0.9 °C is estimated for the intertidal sediments. Tidal submersions during the ice-free season have a transient warming effect on the soil profile due to water percolation in the active layer and delay freeze back at the beginning of winter. Observations in shallow drill holes and along a thermistor cable indicate that the intertidal permafrost degraded at the Kangiqsualujjuaq observation site from 1984 to 1987. From 1987 to 1990, observations and logged data clearly show aggradation and cooling of the permafrost. Those changes in ground thermal regime are the result of recent climatic variations.