bluuebunny/crossref_metadata_2025 huggingface dataset:
Episodic growth of a Waulsortian buildup: the Lower Carboniferous Muleshoe Mound, Sacramento Mountains, New Mexico, USA
Authors: Kirkby Kent C. , Hunt Dave
Published: April 2008

Muleshoe Mound is a composite Waulsortian buildup that crops out along the western escarpment of the Sacramento Mountains, New Mexico. Exceptional exposures of Muleshoe Mound have enabled a detailed stratigraphic model to be developed, subdividing the buildup into five separate stratal units. Each stratal unit differs in facies, geometry and symmetry, reflecting changes in the character and intensity of different environmental conditions (energy, carbonate production, oxygenation and accommodation space). Hiatal surfaces mark periods of mound crisis and/or sea-level fluctuations. These hiatal surfaces highlight the episodic nature of the mound’s growth. Episodic growth acted as an important control on this buildup’s development, facies and early diagenesis. Features and patterns of the Muleshoe Mound conflict with the traditional interpretation of the Waulsortian as quiet, stable, deep-water buildups. Muleshoe Mound appears to have grown in appreciable currents where accommodation space was a crucial control on growth.
Dinantian depositional environments along the northern margin of the Solway Basin, UK
Authors: Maguire Kelly , Thompson Jillian , Gowland Stuart
Published: April 2008

A sedimentological study has been conducted on the Dinantian strata of the tectonically separated Rerrick and Kirkbean Outliers on the northern margin of the Solway Basin. The Rerrick succession, comprising a sequence of largely non-marine alluvial fan, fluvial and coastal plain clastic rocks, represents a tectonically influenced lateral dispersal system sourced from the northern margin of the Solway Basin. In contrast, the Kirkbean succession is considered to represent the deposits of a tectonically stable shallow-marine shelf subject to both limestone and clastic deposition. Periodically, axial fluvial systems draining westward established delta front conditions on the shelf. The depositional model presented here suggests both lateral and axial dispersal systems were active within the Solway Basin during the Dinantian.
A palynofacies analysis of the Dinantian (Asbian) Glenade Sandstone Formation of the Leitrim Group, northwest Ireland
Authors: Smith Jim
Published: April 2008

A quantitative palynofacies analysis of the Dinantian (Asbian) Glenade Sandstone Formation in two boreholes from the Glangevlin area, northwest Ireland, was carried out. It was found that the sands of the Glenade Sandstone Formation prograded rapidly over an arid lagoonal environment in the area of the more proximal northern borehole, but were deposited directly on top of the laminated dolomites of the underlying Meenymore Formation in the area of the southern borehole. Fluvial conditions predominated in the northern area, while lagoonal conditions were established in the southern area, before a major anoxic marine transgression, 12.7 m above the base of the Glenade Sandstone Formation in both areas, submerged the flat landscape. In both areas the dominantly fluvial environment above the marine transgression was periodically replaced by more lagoonal environments.

The flora at the time of deposition of the Glenade Sandstone Formation may have been dominated by ferns, tree-ferns and small seed-ferns, while herbaceous and arborescent lycopods, typically present in Carboniferous coal swamps, may have been absent.
Tsunami waves generated by volcanic landslides: an assessment of the hazard associated with Kick ’em Jenny
Authors: Smith M. S. , Shepherd J. B.
Published: April 2008

Landslides and rock falls generating tsunamis constitute a serious element of risk at steep-sided volcanoes located in close proximity to water, especially when the volcano’s structure is cut by faults or altered by fumaroles and where there has been a history of subsidence or signs of incipient caldera formation. Approximately 5% of known tsunami events have been generated by volcanoes, producing some of the most destructive tsunamis on record. A preliminary study suggests that Kick ’em Jenny is a prime candidate for tsunamigenic events on a potentially hazardous scale, possibly affecting the whole of the eastern Caribbean region. An estimate of the potential height of tsunami waves generated following slope failure on the flanks of Kick ’em Jenny has been found using the basic solitary wave theory combined with equations of energy conservation. Generally, landslide-generated tsunamis possess little energy and, unless they are confined in a bay or channel, are only hazardous close to the source. However, the results show that with the low-lying Grenadine Islands situated a few kilometres to the east, even a relatively small landslide event at Kick ’em Jenny has the potential to produce waves that would prove hazardous to both coastal populations and ships.
Recurrent landslides events on the submarine flank of Piton de la Fournaise volcano (Reunion Island)
Authors: Labazuy Philippe
Published: April 2008

New studies confirm the existence of large landslide events related to both the Piton des Neiges and the Piton de la Fournaise volcanic systems. Like many other island basaltic shield volcanoes, Réunion Island has had a complex evolution combining construction processes and recurrent destructive events. Landslide deposits probably form an important part of its internal structure. Sliding events and related tsunamis are one of the major hazards of this kind of volcanic activity, in an intraplate oceanic context.

The submarine flank of Piton de la Fournaise has been extensively studied using Seabeam bathymetry and high resolution side-scan sonar images. The eastern submarine flank is entirely covered by 550 km
3
of landslide deposits, which are mainly subaerially erupted basaltic lavas, transported and fractured in large-scale mass wasting. Volumetric considerations imply recurrent partial destruction of the edifice, by landsliding, during its construction. For each sector collapse the fundamental process is the sliding of large blocks, up to several kilometres in length. Fractions of the slide blocks break up and evolve into debris avalanches.

Analogue experiments have been carried out to tentatively explain the geometry of these periodic large landslides of the unbuttressed flank. The morphology and the deformation in the landslides of the model are compared to the natural system of Piton de la Fournaise.
Effects of botanical composition, soil origin and composition on mineral concentrations in dry season pastures in western Kenya
Authors: Jumba I. O. , Suttle N. F. , Hunter E. A. , Wandiga S. O.
Published: April 2008

The influence of botanical (pasture species), geographical (altitude) and pedological (bedrock type, soil pH and extractable mineral concentration) factors on mineral concentrations in dry season pasture was studied in samples of topsoil and herbage from 135 sites on 84 farms in the Mt Elgon region of western Kenya. Of the four major elements measured in herbage, only S was affected by geology, low values being found above Tertiary volcanic (TV) and metamorphic gneiss (MG) bedrocks. By contrast, only P was not affected by species, Setaria being low and Kikuyu grass usually high in macro minerals. Of the seven trace elements analysed in herbage, geology influenced only one: Cu; low values were again found above TV and MG but Cu availability to grazing ruminants would be relatively high because of the associated low S values. By contrast, only Se was unaffected by species, Kikuyu grass being high in all but Mn. Soil bedrock had a greater influence on soil composition but correlations between extractable soil and herbage mineral concentrations were poor for all elements, even within botanical species after correction for soil pH and soil contamination. Concentrations of Ca, P, Mg, S, Cu and Zu were often less than tabulated requirements for grazing livestock. However, risks of deficiency could not be predicted from the pedological factors measured.
The distribution of trace and major elements in Kenyan soil profiles and implications for wildlife nutrition
Authors: Maskall John , Thornton Iain
Published: April 2008

Concentrations of trace and major elements are examined in several soil profiles from national parks and wildlife reserves in Kenya. Broad variations in soil trace element concentrations between locations are largely attributable to differences in parent material and variations in soil pH are related to sodium and calcium concentrations. However, element concentrations and distributions are also influenced by soil forming processes. The process of sodication in alkaline solonetz soils in Lake Nakuru National Park appears to have lowered the concentrations of copper, cobalt and nickel in the surface horizon. At Amboseli National Park, a marked accumulation of molybdenum, sodium, potassium, calcium and magnesium in the surface horizon of an alkaline solonchak is probably due to salinization processes. Apparent mobilization of copper, cobalt and nickel down the profile of a humic nitisol in the Aberdares Salient is associated with eluviation and leaching processes. In two andosols and an ando-humic nitisol, copper, cobalt and nickel tend to accumulate in the surface horizon in association with organic matter. In vertisols from Amboseli National Park and Lewa Downs Wildlife Reserve, the relatively constant trace element concentrations in the A and B horizons are linked to the self-swallowing processes that characterize this soil type. The elevated pH in the solonetz and solonchak soils at Lake Nakuru and Amboseli National Parks results in enhanced uptake of molybdenum in the grass species
Sporobulus spicatus
. At Lake Nakuru National Park, high molybdenum concentrations in this and other plant species are associated with low copper status of impala. The implications of soil geochemistry for the trace element nutrition of wild animals in small conservation areas are discussed.
Biogeochemistry and metal biology
Authors: Selinus O. , Frank A. , Galgan V.
Published: April 2008

Environmental monitoring of metals on two trophic levels is presented: a biogeochemical technique developed at the Geological Survey of Sweden, using aquatic mosses and roots of aquatic plants, and a bioanalytical-chemical technique developed at the National Veterinary Institute based on organ tissues from the moose (
Alces alces
L.), a wild ruminant living in the Swedish forests.

The usefulness of the techniques is exemplified by monitoring of Cd in southern Sweden. The results of both monitoring systems are in close agreement. Together with analysis of crops and drinking water the results indicate a region with elevated Cd burden. Also the changing environment is monitored by the moose. Decreasing concentrations of essential and toxic metals (cations) and increasing molybdenum concentration (anion) were found in a strongly acidified region of Sweden by comparison with a reference material from 1982. pH increase of the environment of the moose is indicated, probably by liming. It resulted in severe copper and chromium deficiency of the moose and was suggested as the cause of a ‘mysterious’ disease in the moose.

Comparison of the techniques confirms the advantage of using metal-monitoring maps in interpreting biological data and also the predictive value of the monitoring maps in biological contexts.
Biogeochemical factors affecting groundwater quality in central Tanzania
Authors: Bowell R. J. , McEldowney S. , Warren A. , Mathew B. , Bwankuzo M.
Published: April 2008

Analysis of groundwaters from the Makutuapora aquifer in the Dodoma region of central Tanzania has revealed a relationship between mineral-water interactions, water chemistry, bedrock geology, and microbiology. Groundwaters were slightly alkaline (pH 6–7.8) and essentially Na-Ca-HCO
3
-Cl, with minor K, Mg, F, and SO
2−
4
. Variations in water chemistry, particularly Ca/Na and Mg/Ca, ratios are related to the progressive alteration of feldspars and ferromagnesium minerals. The constant Na/Ca and Mg/Ca ratios noticed over mature aquifers and wells indicates that a steady-state is attained between aluminosilicates and groundwater. While erratic Fe/Mg and Na/K ratios denote a more open system or rather a greater diversity in minerals hosting these elements participating in mineral-water reactions. In places total concentrations of Fe, Mn, and Al can each exceed 1 mg l
−1
with most of the metal held in particulate form (> 0.45 μm). The increase in metals suggests an imbalance in the steady-state reactions between magmatic minerals and leachate, possibly related to microbial activity. Fifty percent of the groundwaters were contaminated by significant numbers of thermotolerant coliforms indicating considerable risk of contamination by faecal pathogens. Numbers of faecal coliforms were positively correlated with K, Na, NO
3
−
, PO
4
3−
and BOD. Groundwater chemistry also affected the activity of the indigenous microbial community. Microbial biomass appeared to be unaffected by differences in groundwater chemistry. The numbers of selected physiological bacterial types (e.g. organisms contributing to the nitrogen and sulphur cycles) and the range of protist morphotypes, isolated from the tropical groundwater systems, were broadly similar to those found in temperate groundwater. Total concentration of metals such as Al, Fe, Co and Mn certainly exceed levels at which these metals could be considered toxic although if these metals are present in non-labile forms (as suggested by other studies) then the potential toxicity would be negligible. At present the major concerns for health are high seasonal salinities in the groundwaters and high faecal contamination.
Kriging: a method of estimation for environmental and rare disease data
Authors: Oliver M. A.
Published: April 2008

Most properties that are distributed in geographical space vary, and often in a complex way. The information available is usually fragmentary, but we often want to know the values at intermediate locations. This is the case for both environmental and disease data. However, the nature of the data and the information that we require from them ultimately can be quite different. For rare disease knowing its spatial distribution is often not enough, we also want to know the variation in the underlying risk. At present direct links between disease and factors in the environment are tenuous; however, there is increasing interest in obtaining more precise evidence. Geostatistics provides us with a means of analysing both kinds of data underpinned by the same body of theory, the Theory of Regionalized Variables. Two types of geostatistical estimation are described here. Disjunctive kriging for estimating the probabilities of exceeding particular threshold values in the environment: it is illustrated with an example of soil salinity in Israel. Standard geostatistical technique has been adapted to analyse the spatial distribution of a rare disease, and to estimate the risk of developing it: this is illustrated with an analysis of childhood cancer in the West Midlands Health Authority Region where the risk appears largest in rural areas. The aim in the future is to use the information from both approaches to identify areas for further investigation concerning the aetiology of certain diseases.
Origins and palaeoceangraphic significance of laminated daitom ooze from the Eastern Equatorial Pacific Ocean
Authors: Kemp Alan E. S. , Baldauf Jack G. , Pearce Richard B.
Published: April 2008

Laminated diatom ooze (LDO) has been recovered from several ODP Leg 138 sites and now is also recognized from several DSDP Leg 85 sites. These remarkable sediments are the result of massive and episodic flux of mats of the diatom
Thalassiothrix longissima
. By analogy with the
Rhizosolenia
diatom mat-forming events monitored by JGOFS (Joint Global Ocean Flux Study) in the equatorial Pacific Ocean during cooling conditions in late 1992, these episodes of massive flux of
T. Iongissima
mats may represent the ‘fall out’ from major frontal systems generated during La Niña (anti-El Niño) events. Laminations were preserved in the mat deposits because of the rapid mat deposition and high strength of the diatom mat meshwork, that subjugated benthic activity. This new mechanism of preservation of lamination in marine sediments has wide implications for other laminated sequences. The sustained periods of mat deposition documented in Neogene sediments of the eastern equatorial Pacific Ocean are part of the major cycles in the relative abundance of carbonate and silica in the region and, possibly, in the case of some intervals, also in the Atlantic Ocean.
Magmatic segmentation of mid-ocean ridges: a review
Authors: Batiza Rodey
Published: April 2008

Tectonic and magmatic segmentation of ridges occurs at several scales that overlap or form a continuum. A good working hypothesis is that segmentation is hierarchical and that magmatic and tectonic segmentation are linked and related by mantle flow and upwelling patterns. The largest scale of magmatic segmentation is isotopic, reflecting differences in mantle history and composition spanning a range of scales as large as individual ocean basins or larger. Superimposed, is the most conspicuous scale of segmentation, defined by large transforms and/or non-transform offsets. Magmatically, this scale of segmentation seems to reflect differences in the melting process together with the effects of smaller scale mantle heterogeneity. There appear to be differences between slow- and fast-spreading magmatic segments, although other factors such as magma supply, plume influence and ridge obliquity may also have important effects. Recurring patterns at individual segments, at least partly independent of spreading rate, include: constancy v. variability in inferred melting parameters, regular v. irregular spatial distribution of enriched basalts, MgO values, and other parameters, and correlation vs. no correlation of chemistry with axial depth.

The smallest scales of magmatic segmentation require the most closely spaced and detailed sampling. Since there have been relatively few studies of this type, there are many questions remaining. It is likely that this scale of segmentation is controlled by deep crustal and shallow upper mantle processes. However, the superimposed effects of mantle heterogeneity and time-dependent processes such as volcanic-magmatic cycles complicate the picture.
Restricted melting under the very slow-spreading Southwest Indian ridge
Authors: Robinson C. J. , White R. S. , Bickle M. J. , Minshull T. A.
Published: April 2008

The major element chemistry of basaltic glass from two localities on the Southwest Indian Ridge is consistent with the occurrence of reduced melting under this very slow spreading ridge compared with that under ‘normal’ oceanic spreading centres. This agrees with theoretical models for mantle melting which include the influence of conductive heat loss from the mantle as it wells up beneath very slowly separating plates. There are distinct chemical differences between the two areas of study. Basaltic samples from the segment at 57°E have consistently lower Na
2
O, Al
2
O
3
and SiO
2
and higher FeO, CaO/Al
2
O
3
, K
2
O and TiO
2
than those from 66°E. The 57°E lavas have an MgO range of 5.9–7.5 wt% and define approximately linear oxide trends versus MgO, while the 66°E lavas have too small a range of MgO values (6.8–7.8 wt%) to define any trends. The chemical data can be interpreted in terms of different extents of melting at different mean pressures.
Characterization and interpretation of
P-T
paths with multiple thermal peaks
Authors: Whitney Donna L. , Dilek Yildirim
Published: April 2008

Using pressure-temperature (
P-T
) paths to decipher sequences of tectonic events in the evolution of contractional orogens is difficult because in most metamorphic terrains only a limited part of the path can be inferred from petrologic evidence. Perturbations such as thermal pulses may not be recorded if they occurred over very short geological time scales. Deviations from standard
P-T
path shapes (e.g. pressure and temperature increase followed by decompression and cooling) are seldom recognized although they may reflect major crustal processes that affect the thermal structure of continents during active tectonism. In particular, recognition of complex
P-T
trajectories with multiple thermal peaks is essential for understanding tectonic, metamorphic and magmatic processes that occur during unroofing of metamorphic terrains. Using the example of the Niğde metamorphic core complex (Turkey) and other similar terrains, we propose that
P-T
paths with initial Barrovian trajectories followed by one or more low-pressure-high-temperature thermal spikes (increase in temperature at nearly constant pressure) may be characteristic of metamorphic core complexes. These temperature spikes are commonly associated with granitic magmatism that results when metasedimentary rocks are buried and heated during regional metamorphism. Additional thermal contributions such as enhanced mantle heat flow or mafic magmatism are not required to explain the thermal spikes.
On the occurrence and characterization of ultrahigh-temperature crustal metamorphism
Authors: Harley Simon L.
Published: April 2008

Ultrahigh-temperature (UHT) crustal metamorphism is a division of medium-pressure granulite facies metamorphism where peak temperatures of 900–1100°C have been attained at pressures in the range 7–13 kbar. The key indicators of UHT conditions are mineral assemblages involving combinations of sapphirine, garnet, aluminous orthopyroxene, cordierite, sillimanite, spinel and quartz in pelites and quartzites. Experimentally constrained and calculated FMAS and KFMASH petrogenetic grids involving these phases and additional osumilite and melt indicate that sapphirine + quartz is stable only at >1040°C in reduced rocks, that osumilite is restricted to >900°C for pressures greater than 6 kbar and has an ultimate stability limit of 9 kbar in FMAS, and that the orthopyroxene + sillimanite + quartz assemblage is restricted to pressures greater than 8 kbar in KFMASH. These criteria, coupled with the grids isoplethed for the Mg/(Mg + Fe) of garnet and Al-content of orthopyroxene allow the peak pressure-temperature (P-T) conditions of several UHT occurrences to be defined and the post-peakP-Tpaths delineated.

UHT conditions are seldom determined from slowly cooled granulites using conventional geothermometry principally because of the propensity of Fe-Mg exchange thermometry to only record closure temperatures of 700–850°C. However, pressure-convergence calculations for several granulites with UHT mineral assemblages yield back-calculated mineral compositions that are consistent with temperatures of 950–1000°C prior to post-peak Fe-Mg re-equilibration. The best compositional indicator of UHT conditions remains the preservation of high Al2O3contents (8–12 wt%) in orthopyroxene coexisting with garnet, sillimanite or sapphirine.

TheP-Tconditions and records preserved in the currently documented UHT localities and terranes are varied. Both types of post-peakP-Tpath isobaric cooling and isothermal decompression (ITD) are recorded from reaction textures in different UHT terranes, and several preserve very similar ITD histories that may reflect the final stage of collisional orogenesis. Although counter-clockwise and clockwiseP-Tpaths have been proposed on the basis of textural observation for some terranes, the progradeP-Thistories of most UHT areas are not known. Such information, and further experimental constraints on quartz-absent assemblages at UHT conditions, are of prime importance to interpret further this extreme form of crustal metamorphism.
Making movies: phase diagrams changing in pressure, temperature, composition and time
Authors: Worley Brenton , Powell Roger
Published: April 2008

Quantitative phase diagrams, and in particular phase diagram movies, offer a powerful and versatile forward approach to modelling the
P-T-x-t
relationships of natural mineral assemblages. Phase diagram movies are ideal for illustrating the continuous way in which mineral compositions and assemblages evolve with changing
P-T-x
conditions. A feature of the animation process, is that it also enables an extra variable to be represented by the running time of the movie. A methodology for producing quantitative phase diagram movies is illustrated using the example of the AFM compatibility diagram. This approach involves the calculation of phase equilibria at critical values of the animating variable (in this case temperature), with interpolation of the data between these values. Phase equilibria calculations were performed using Thermocalc v2.5, and data interpolation and construction of the individual phase diagrams (or movie frames) was achieved in
Mathematica
® v2.2.2 using purpose-written code. Although the details of the technique, and the code, have been designed for use with this particular application, the approach is quite general.
Tephra dispersal
Authors: Bursik M.
Published: April 2008

Our understanding of the spread of volcanic ejecta from eruption columns has evolved significantly since the first quantitative studies. Given recent advances, it is possible to describe much of the physics of tephra dispersal, and to construct a relatively robust model for the spread of tephra in the proximal region of a volcanic eruption plume. Results from such modelling compare well with data on tephra fall deposits. More distal dispersal, driven as it is by atmospheric motions, has also been treated extensively, by atmospheric scientists as well as by volcanologists. Results from these studies have been compared with satellite data and have been found to be accurate in terms of predicting ash cloud trajectories. Comparisons of the various models with data point out several areas where research could be productively directed in future. The transition from tephra transport by the plume to that by the atmosphere is poorly understood: processes related to transport between plume and ground are poorly known: the layering of the stratosphere needs to be considered more thoroughly to understand transport processes over periods of days to months; and the total grain size distributions of fall deposits and eruption plumes have probably been incompletely characterized in the past.
Geochemical trends in Early Tertiary palaeosols from northeast Ireland: a statistical approach to assess element behaviour during weathering
Authors: McAlister John J. , Smith Bernard J.
Published: April 2008

Geochemical and statistical analyses (principle components and Cluster analysis) are used to study changes in element concentration in a range of chemically complex palaeosols from northeast Ireland produced under humid tropical conditions. Chemical analyses characterize the samples and statistical techniques show trends in elemental concentration due to chemical weathering processes. Simple ratios allow the concentration of each element to be examined in individual samples and a ternary diagram classifies these palaeosols with respect to their degree of lateritization. Results demonstrate the general value of statistical analyses in grouping chemically complex palaeosols in terms of element enrichment and depletion as a result of chemical weathering. This approach is independent of any preferred mechanism in the process of rock weathering. It also points out that the theoretical behaviour of elements does not follow those determined by statistical analysis. This technique could also be applied to the classification of present-day lateritic soils.
Environmental interpretation and evolution of the Tertiary erosion surfaces in the Iberian Range (Spain)
Authors: Gutiérrez-Elorza M. , Gracia F. J.
Published: April 2008

The geomorphological analysis of regional Neogene erosion surfaces is of great geological interest as it helps in the reconstruction of the environmental evolution of continental areas. Moreover, the structural analysis of their deformation is a good approach to the identification of the main neotectonic trends at a regional scale. The Iberian Range is an excellent example of the application of this kind of study. It shows four stepped Neogene erosion surfaces, well preserved in general and whose ages range from the middle Miocene to the Villafranchian. Their formation is related to planation processes in semi-arid conditions. The stepping of surfaces is related to distensive Neogene tectonic pulses of sufficient magnitude for the planation processes to be interrupted.
Neogene palaeosurfaces in the volcanic area of Central Slovakia
Authors: Lacika Ján
Published: April 2008

Two types of Neogene palaeosurfaces occur in the Central Slovakia Volcanic Area, these being volcanic and planational in origin. The volcanic palaeosurfaces are currently represented as topographic remnants which were originally created as a result of Neogene-Pleistocene andesite-rhyolite (Badenian-Panonian) and basaltic (Pontian-Upper Pleistocene) volcanic activity in the region. During the intervening and subsequent periods of relative volcanic and tectonic quiescence, geomorphological processes of landform evolution became dominant and, consequently, a total of four generations of Neogene planation surfaces may be identified in the study area. From the topmost, or oldest surface, these are: a high-level Middle Miocene surface; an Upper Miocene middle or intramontane level; an intermediate level of Pontian age; and lowermost, a sub-montane level dated as Upper Pliocene-Lower Pleistocene, found at the present river level. All of the Neogene palaeosurfaces in the Central Slovakia Volcania Area, of both volcanic and erosional origins, currently display an advanced state of erosion and dissection as a result of Alpine uplift effects: a total of six main types of relief may be recognized.
High-altitude palaeosurfaces in the Bolivian Andes: evidence for late Cenozoic surface uplift
Authors: Kennan L. , Lamb S. H. , Hoke L.
Published: April 2008

Low relief palaeosurfaces are widely preserved in the Cordillera Oríental of the Bolivian Andes at altitudes between 2000 m and 4000 m in a region up to 100 km wide and 600 km long. Remnants of these nearly horizontal or gently undulating erosion surfaces, from 5 to 2000 km
2
in area, cut across folded Palaeozoic to Cenozoic bedrock. They appear to be erosional pediments formed between 12 and 3 Ma along broad, low gradient, valleys, which are generally undeformed. In detail, the morphology of surface remnants can be used to construct two distinct palaeodrainage basins. Very little of the material eroded during surface cutting appears to have remained within the Cordillera Oriental and must have been carried into a foreland basin, now preserved in the Subandean fold and thrust belt. The palaeovalleys are generally parallel to the dominant north-south structural grain, forming a tortuous low gradient drainage system which flowed into the foreland basin in an east-west distance of < 150 km. Reconstructions of the drainage systems suggest that they have been uplifted
c.
2 km since their formation. These estimates are consistent with plausible models of uplift of the Cordillera Oriental as a consequence of intense deformation in the Subandean fold and thrust belt since
c.
10 Ma. However, only since 3 Ma have the surfaces been deeply dissected by drainage cutting more directly across the structural grain. The timing of deep dissection may be partly related to a climate change to wetter and colder conditions.
Variation in thermal history styles around the Irish Sea and adjacent areas: implications for hydrocarbon occurrence and tectonic evolution
Authors: Green Paul F. , Duddy Ian R. , Bray Richard J.
Published: April 2008

Thermal history is a major factor in determining hydrocarbon prospectivity in the Irish Sea region. Early application of Apatite Fission Track Analysis (AFTA®) to exploration wells revealed early Tertiary palaeotemperatures around 110°C or more. More recent studies in the Irish Sea and adjacent areas, using a combination of AFTA and vitrinite reflectance (VR), have revealed at least three additional palaeo-thermal episodes: pre-Permian (>290 Ma), late Permian to mid-Triassic (260 to 220 Ma) and Early Cretaceous (140 to 110 Ma). Other evidence of early paleo-thermal effects, for which timing is only constrained to the interval 300 to 150 Ma, may reflect these or additional episodes.

In some areas, early effects involved extremely high palaeogeothermal gradients. Early Cretaceous gradients are unconstrained due to a lack of wells in which palaeotemperatures reflect this episode. Early Tertiary palaeotemperatures derived from AFTA and VR in wells from the southern part of the East Irish Sea Basin define a consistent linear depth profile with a gradient of only 10°C km
−1
. Wells from the north of the region also define a broadly consistent profile but with a much higher gradient. The low gradients are thought to reflect flow of hot fluids while the high gradients to the north may be associated with igneous activity in that region.

Our preferred interpretation of the early Tertiary palaeo-thermal effects involves a combination of burial by around 1.5 to 2 km of post-Triassic sediment and the thermal effects of hot fluid flow, probably from north to south and associated with igneous activity. This interpretation is consistent with geological evidence and is supported by structural data, sonic velocity data and geochemical observations.

Different combinations of these episodes lead to a wide variety of thermal history styles across the region. The southern part of the East Irish Sea Basin, containing major accumulations of oil and gas, is characterized by the most suitable thermal history conditions for generation and preservation of hydrocarbons to the present day. In adjacent regions, thermal histories are more complex, and those identified to date are generally less suitable particularly for preservation of hydrocarbons to the present day. Future exploration in these areas will require a thorough understanding of the thermal history of Carboniferous source rocks in order to define the most prospective regions.
Real and relict direct hydrocarbon indicators in the East Irish Sea Basin
Authors: Francis A. , Millwood Hargrave M. , Mulholland P. , Williams D.
Published: April 2008

Seismic amplitude anomalies associated with the presence of hydrocarbon gas now play an important role in the exploration of the East Irish Sea Basin. Tilted flat spots were first observed on data acquired by JEBCO Seismic Ltd. in 1986 within the productive Triassic reservoir of the Sherwood Sandstone Group located in Quadrant 110 (offshore North Wales). With hindsight Direct Hydrocarbon Indicators (DHIs) can now be identified on seismic data acquired in earlier phases of the exploration of the East Irish Sea Basin, although many anomalies were not always identified as such at that time.

This study determines the geophysical parameters by which amplitude anomalies associated with diagenetic variations could be separated from anomalies associated with the presence of gas in the reservoir. The predicted model results are compared with the seismic response of proven fields, discoveries and relict or palaeo-DHIs around the basin. Practical implications for effective exploration, development and production methods in the Sherwood Sandstone are suggested.
Bulgarian low rank coals: geology and petrology
Authors: Šiškov George D.
Published: April 2008

The largest coal-forming maximum in Bulgaria took place during the Neogene. Fifteen coal deposits are located in four coal-bearing provinces. The coal deposits south of the Balkan Mountains were formed in small grabens and depressions filled with molasse. Only the coals in Northern Bulgaria were formed in a small palaeodelta. The coal measures are of varying thickness and contain a few coal seams, with compact to complex structure and a range of thickness. Three groups are defined on the basis of maceral composition, allowing a reconstruction of the coal-forming ecosystems and the genesis of the genotypes during biochemical coalification. According to Alpern’s classification the coals have middle to high ash content (ashy to coaly facies). They are of huminite type with low liptinite and inertinite content, and of low rank — lignite and mat brown coals.
The distribution of sulphur in the Palaeocene coals of the Sindh Province of Pakistan
Authors: Baqri S. R. H.
Published: April 2008

46 samples of coals were collected, representing eastern and western coalfields of the Sindh Province of Pakistan to investigate any systematic quantitative changes in total sulphur. The coal is Palaeocene in age and the number and thickness of coal seams decreases from east to west. The sulphur content was determined as total sulphur on an elemental analyser Carlo Erba model EA 1108 on a dry basis. The sulphur content displays systematic variations and increases gradually from east to west. It is about 1.44% in the eastern coalfields at Tharparkar, 2.55% in the central coalfields at Badin and 4.95% in the western coalfields at Lakhra. The Palaeocene coalfields of the Sindh Province were deposited in shallow continental lagoonal areas towards Tharparkar in the east and comparatively down dip deeper areas with brackish waters (deltas, estuaries) towards the Lakhra in the west. The distribution of sulphur displays a good theoretical example in the change of depositional environment from fresh water to brackish waters environments. It is concluded that the coalfields with low sulphur occur in the east as compared to the coalfields with high sulphur in the west.
Geological research into gas sorbed in the coal seams of the Carboniferous in the Mšeno-Roudnice Basin, Czech Republic
Authors: Holub V. , Eliáš M. , Hrazdíra P. , Franců J.
Published: April 2008

In 1994 research in the Czech Republic began into coalbed methane (CBM). The target of this research is the coal seams of the Mšeno-Roudnice Basin, in the region between Mělník and Benátky nad Jizerou. This region was chosen as a model area for evaluating the CBM potential in the Permo-Carboniferous continental basins in the Bohemian Massif. The first stage of the work was directed towards obtaining data for basin analysis, the completion of lithological, stratigraphic and structural surveys particularly concentrated on fault deformation of the basin filling. A general study was conducted into the problem of the sorbed gases with respect to the occurrence of CBM. The latest interpretation of laboratory analysis of the Mělník Main coal seam shows a methane content of 4–10 m
3
/t in the coal at a depth of 250 to 800 m.
Structure, stratigraphy and petroleum geology of the SE Nam Con Son Basin, offshore Vietnam
Authors: Matthews S. J. , Fraser A. J. , Lowe S. , Todd S. P. , Peel F. J.
Published: April 2008

New well and seismic data acquired during recent exploration of the SE Nam Con Son Basin, offshore Vietnam, have been evaluated to assess the tectonostratigraphic evolution.

The offshore Vietnamese region has evolved in response to the complex relative motions of Indochina, Peninsular Malaysia, Borneo and the East Vietnam/South China Sea during the Cenozoic. On a regional scale these motions have been accommodated by strike-slip fault development, crustal extension and contraction. Rift pulses occurred in the SE Nam Con Son Basin from the Palaeogene to the earliest Late Miocene in response to the interaction of East Vietnam/South China Sea rift propagation and regional transtensional shear to the west of the evolving ocean basin. The structural evolution was complicated by mild contractional deformation during the Middle Miocene which was broadly synchronous with development of the largest inversion structures in the nearby West Natuna Basin.

The oldest dated Tertiary rocks in the SE Nam Con Son Basin are fluvio-deltaic sediments of Late Oligocene age which have been penetrated by several wells. Early to Mid-Miocene depositional environments ranged from non-marine to outer shelf, with a predominantly clastic basin-fill. The thickest Lower to Middle Miocene occurs in N-S- to NE-SW-trending half grabens.

A regionally recognized truncational unconformity of late Mid-Miocene age has resulted partly from the combined effects of the mild inversion and by the erosion of uplifted footwalls. During the Late Miocene there was rapid and widespread deepening of depositional environments, synchronous with net-extensional fault reactivation on many previously developed rift structures. The stratigraphic response to this increased bathymetry was the growth of isolated carbonate build-ups on pre-existing structural highs, progradation of the palaeo-Mekong delta system and associated deep-marine submarine channel development and erosion.

This pulsed structural and stratigraphic evolution has resulted in deposition of source, reservoir and seals, and produced a variety of potential trapping styles.
Predicting reservoir quality during exploration: lithic grains, porosity and permeability in Tertiary clastic rocks of the South China Sea basin
Authors: Worden R. H. , Mayall M. J. , Evans I. J.
Published: April 2008

Tertiary sandstones in the Gulf of Thailand, Malay and South China Sea basins have been supplied with sediment rich in pelitic metamorphic rock fragments, weathered basic igneous rock fragments and micaceous rock fragments by similar drainage systems. We have analysed data from the Gulf of Thailand and Malay basins to predict reservoir quality in the South China Sea basin. These Tertiary sandstones contain 20–40% lithic rock fragments that are rich in clay minerals. There are good correlations between both porosity and permeability and the total clay mineral content. They undergo rapid loss of porosity with depth at a rate commensurate with sandstones bearing 20–40% ductile grains. The relationship between porosity and permeability is also strongly influenced by the presence of ductile grains. The rapid loss of permeability with porosity is a result of ductile grains being squeezed between the rigid grains, blocking pore-throats and leaving isolated, ineffective porosity. Mineral cements seem to be unimportant modifiers of porosity or permeability. The rapid loss of porosity with depth and the decrease in permeability with porosity leads to low permeabilities at shallow depths relative to many other hydrocarbon provinces (e.g. North Sea, Gulf of Mexico, etc.) which have lower ductile grain contents. We have used modelled compaction curves for sandstones with 20 and 40% ductile grains to predict a porosity value for any given depth. We have also used sandstones of 100 and 300 μm grain size to predict permeability for a given porosity. The combination of these predictions can be used to predict permeability as a function of depth of burial. The choice of ductile content and grain size will depend upon the conditions of deposition. The main positive reservoir quality anomaly may result from overpressure generation before or during the final phase of burial.
Fault seal analysis of SE Asian basins with examples from West Java
Authors: Beach Alastair , Lawson Brown J. , Brockbank Paul J. , Knott Steven D. , McCallum Jean E. , Welbon Alastair I.
Published: April 2008

A regional fault seal analysis study of SE Asian basins was carried out in order to define trends for predicting sealing faults. Map and well data were analysed and relationships were obtained between fault and reservoir parameters and fault seal. The parameters found to be most useful for discriminating between sealing and non-sealing faults in the region were fault strike, fault mode (oblique slip faults are most likely to be sealing), fault throw (faults with high throws are most likely to be sealing), depth (shallow faults are most likely to be sealing) and thickness-throw. Other parameters measured, some of which are useful for fault seal prediction in some basins, are: fault type (bounding faults, within-field faults, across-field faults), net-to-gross ratio, average reservoir porosity, average reservoir permeability, differences in hydrocarbon contact elevation across faults, hydrocarbon column height held back by sealing faults, and reservoir pressure and temperature. Data from over 150 faults from fields within West Java are presented to illustrate the main results of the analysis.
Constraints on strike-slip motion from seismic and gravity data along the Vietnam margin offshore Da Nang: implications for hydrocarbon prospectivity and opening of the East Vietnam Sea
Authors: Roques D. , Matthews S. J. , Rangin C.
Published: April 2008

The Vietnamese continental margin records the tectonic processes which have controlled opening of the East Vietnam Sea basin. The geometry and chronology of Cenozoic structures linked to the opening of this marginal basin have been studied offshore Da Nang (central Vietnam), based on unpublished data acquired by BP Exploration from 1989 to 1991. These data demonstrate that a N160° E fault trend is the main structural orientation recognised on both gravity and seismic data. Important crustal extension on shallow-dipping fault planes striking N060° E and connected to the N160° E faults is observed also. This horse-tail map-pattern is compatible with transtensional dextral motion along the N160° E faults. The discrepancy between the amount of motion observed onshore and offshore suggests the presence of a major shear zone which trends subparallel to the east Vietnam margin. This shear zone is located in the region of the offshore Qui Nhon ridge, which is blanketed by carbonate sediments. These carbonates have been drilled and dated as Middle Miocene. Dextral motion along this shear zone diminished during the late Early Miocene (around 20 Ma.), as evidenced by the onset of carbonate deposition on top of the ridge. This is broadly synchronous with propagation of the East Vietnam Sea basin towards the southwest. This major shear zone has been a fundamental part of the fault network which developed during opening of the East Vietnam Sea.

The structural development of the offshore Da Nang region has resulted in the development of contrasting sub-basin geometries; those within the major shear zone appear to be relatively restricted laterally whereas those to the east display geometries more typical of extensional sub-basins. Both sub-basins show a variety of potential hydrocarbon trapping styles and by analogy with comparable areas in SE Asia have the potential to contain important oil reserves, in addition to the considerable volume of gas already proven by recent drilling.