The offshore Sierra Leone basin is an exploration frontier area with commercial hydrocarbon potential. The basin is located at the northernmost end of the equatorial Atlantic margin in the South Atlantic; it is bound to the South by the Gulf of Guinea Petroleum province. The Sierra Leone margin has not had the exploration attention like most basins in the equatorial Atlantic, such lack of attention may be explained by the structural complexity of the basin. Despite the recent successful petroleum activities in the basin, very little geological information have been placed in the public domain by the operators. This research will be the first published detailed analysis of the offshore Sierra Leone basin. This work focuses on the broader aspects of basin structural evolution, seismic stratigraphy and reservoir development. The basin analysis is based on 2D seismic dataset, acquired in 2002 by TGS-NPEC. Seven megasequence boundaries have been identified in the offshore Sierra Leone basin. There is one megasequence boundary each in the pre-transform and syn-transform phases. The post-transform phase is composed of five megasequences. They have been dated using well data information and through correlation with the seismic surfaces of adjacent basins in the region. The Sierra Leone margin is structurally divided into three segments, which evolved through transtensional and/or extensional rifting. From a geological perspective, this basin straddles a major tectonic transition zone (the Sierra Leone Transform). The Mesozoic-Cenozoic tectonic evolution of the basin was partly controlled by basement heterogeneity and plate kinematics. This study also highlights the importance of N-S and ENE-WSW trending Archaean structural lineaments, which were vectors for the Sierra Leone margin segmentation. The structural division of the Sierra Leone margin into the Northern, Central andSouthern segments is based on varying structural geometries. The Northern and Central segments developed as rift-transform margins, while the Southern segment developed as a volcanic rifted margin. Syn-transform sequences (late Early Cretaceous) show the influence of normal fault related subsidence and uplift, modified by localised transpressional deformation. The basin bounding faults and half grabens are oriented at high angles to the ensuing passive margin slope strike. Post-transform sequences (Late Cretaceous to Present) are dominated by major phases of slope failure and the development of extensive lowstand submarine fan systems. Some models of slope failure and synchronous development of submarine channel and canyon systems have been developed for this basin. Extensional slope failure is controlled by pre-existing structural trends. Submarine canyons which developed in the hanging-walls of these fault-blocks, became the site of rapid head-ward expansion of turbidite filled channels. The temporal development of these systems are expected to have profoundly affected the distribution and quality of key play elements, such as reservoirs and stratigraphic traps in slope settings, and the distribution of sands in deeper water and base of slope plays.

The Pliocene world c.5.3 Ma to c.2.58 Ma exhibited a relatively stable climate with a warmer global mean surface temperature than present-day by ~2 °C to 3 °C, and palaeoclimate analysis from this interval is used to understand climate drivers in ‘warmer world’. Previous oxygen isotope thermometry investigations of Pliocene southern North Sea Basin (SNSB) Aequipecten opercularis from the Coralline Crag Formation in Suffolk, UK repeatedly reveal evidence of a cold-temperate climate regime. Contrastingly, other biological proxies record a warm-temperate/sub-tropical regime. This investigation concentrated on oxygen, carbon and microgrowth increment widths (MIWS) of fossil shell material from Pliocene SNSB spanning an interval of~4.4 Ma to ~2.5 Ma. The study sites included shallow marine Pliocene formations from the western and eastern SNSB, the Ramsholt Member of the Coralline Crag Formation, Suffolk UK, and the Luchtbal Sands and Oorderen Sands Members of the Lillo Formation, Belgium, and the Oosterhout Formation in the Netherlands. Oxygen isotopic palaeotemperature results showed cooler summer temperatures than presently in the SNSB, which were reflective of a cool-temperate regime. There was no evidence of warm-temperate or sub-tropical summer palaeotemperatures in the Pliocene SNSB as suggested by other planktonic proxies. This investigation discussed the possible causal factors for the cooler – than- expected winter and summer palaeotemperatures in the ‘warmer’ Pliocene world as recorded by this proxy. Discrepancies between the cool summer benthic palaeotemperatures from the bivalves and the warmer sub-tropical or warm-temperate summer palaeotemperature estimations from planktonic biological proxies was rectified by the application of a theoretical summer stratification factor (SSF). However, rectifying the discrepancies between cooler (cold-temperate) benthic winter palaeotemperatures and the warmer winter palaeotemperatures from other proxies was difficult because stratification does not occur during the winter. Dormancy behaviours in the warm- temperate –sub-tropical organisms was proposed as a suitable mechanism to allow their coexistence with the cool-tolerant bivalves, which were able to grow and feed underneath the thermocline during the summer months. Therefore, the investigation showed how the Pliocene SNSB exhibited a greater seasonality than occurs presently in the SNSB. The driver for the cooler winter temperatures in the Pliocene SNSB was not identified. Localised explanations including continental wind effects, interannual variations in MOC strength, and increased storm activity in the winter bringing cooler water into the SNSB were all suggested as potential drivers. Global features of climate including interglacial/glacial cycles and orbital forcing effects were factors also proposed for the overall mixed palaeotemperature signal in the Pliocene SNSB.

No description available.

The study uses subsidence analysis of three deep wells to basement combined with sequence stratigraphic mapping to show that a 85,000 km² area of the Eastern Venezuelan foreland basin in the region of the Orinoco Delta underwent three main stages of foreland-related subsidence that followed a protracted Cretaceous - late Oligocene period of precollisional, passive margin formation. Phase 1 consists of increased foreland basin subsidence in the late Oligocene to middle Miocene (23 - 13 Ma) at average sedimentation rates of 0.14 mm/yr. Clastic rocks of Phase 1 include the Freites Formation, a 1.2 km-thick section of greenish-gray fissile shale and shaly sandstone deposited in shallow marine- neritic environments. Seismic facies show progradation of Phase 1 clastic rocks as a wedge from the NE and NNE. Clastic rocks deposited during the accelerated Phase 2 in the middle to late Miocene (13 -11 Ma at sedimentation rates of 1.45 mm/yr) include the La Pica Formation, a 2.7 km-thick section of gray silt and fine-grained sandstone deposited in shallow marine/coastal proximal environments. Seismic facies show progradation of Phase 2 clastic rocks as a wedge to the northeast. Phase 3 consists of decelerating foreland basin subsidence in the period of late Miocene-mid Pliocene (11-6 Ma at average sedimentation rates of 0.86 mm/yr). Sedimentary rocks deposited during this period include the Las Piedras Formation, a 1.45 km-thick section of sandstone, carbonaceous siltstone and shale deposited in deltaic environments. Seismic facies show a progradation of Phase 3 clastic rocks as a wedge to the northeast and east-northeast. Deeper marine environments and more rapid subsidence rates of Phases 1 and 2 are interpreted as an underfilled foreland basin controlled by active thrusting along the Serrania del Interior at the northern flank of the basin. Deltaic environments and slower rates of Phase 3 are interpreted as an overfilled foreland related to rapid seaward progradation of the Orinoco Delta and its filling of the former, dynamically- maintained interior seaway. Paleogeographic maps constrained by wells and seismic lines show a large regression of the Orinoco River towards the west across the Columbus basin and Eastern Venezuelan basin during the late Miocene and the Paleocene. In this foreland basin setting, the effects of thrust-related tectonic subsidence and early deposition of the Orinoco Delta play a larger role in the early Miocene-Pleistocene sequences than eustatic effects. / text

Cheap water, massive federal subsidies and political clout have sustained rice farming in the lower Colorado River basin for decades, but now the industry is in a precarious situation. Drought, population growth upstream and economic boom in Austin are pushing out the practice because of increasing demand for Texas’ scarce water resources. The tightening supply of water raised questions about the sustainability of producing such a water intensive crop in the state. Drought has cut off the cheap water to farmers for three years, and a mobilized coalition of upper river basin interests is calling for a permanent end to subsidized water. It’s increasingly clear that the politics of water in a drought-prone future is likely to side with cities, where voters are heavily concentrated. Rice farmers have scrambled to adapt. Larger rice farms have switched to groundwater. Some farmers have swapped rice for corn, milo or soybeans to keep their income. Crop insurance, which made up for at least 55 percent of the money lost in drought, softened the blow for rice farmers. But revenues in rice-related industries in Wharton, Matagorda and Colorado counties have dropped sharply and some businesses have already packed it in. These new realities cast uncertainties throughout the lower river basin, where locals fear this way of life is disappearing. / text

The Mississippian Barnett Formation is a prolific shale-gas reservoir that was deposited in the Fort Worth Basin, Texas. Many previous studies of the Barnett Formation have been conducted in the main production area; few studies have been made of the Barnett Formation in the southern part of the basin, which is a less productive area. In the present research, several cores from the Barnett Formation in Hamilton County, southeast Fort Worth Basin, are studied in detail. Two vertical, continuous cores from Hamilton County, Texas, were studied to delineate the depositional setting, lithofacies, pore types, and reservoir quality of the Barnett Formation in the area. Five lithofacies were defined by analysis of the two cores: (1) laminated clay-rich silty and skeletal peloidal siliceous mudstone; 2) laminated skeletal silty peloidal siliceous mudstone; 3) nonlaminated silty peloidal calcareous mudstone; 4) laminated and nonlaminated skeletal calcareous mudstone; and 5) skeletal phosphatic packstone to grainstone. As indicated from this study, the dominant organic matter type is a mixture of Type II (major) and Type III (minor) kerogen having a mean TOC content of approximately 4%. Analysis of Rock Eval data shows that most of the interval is within the oil window; calculated Ro is approximately 0.9%. Organic geochemistry shows that the hydrocarbon generation potential of the abundant oil-prone kerogen was excellent. Mineralogical analysis reveals that the two types of siliceous mudstone, which are similar in composition to the siliceous mudstone in the main producing area in the northern Fort Worth Basin, are good for hydraulic fracturing and production, but they are also limited by their marginal thickness. Organic matter pores, which are the dominant pore types in these two cores, are consistent with pore types found in currently producing wells in the Newark East Field. This research also suggests that the deposition of Barnett Formation was controlled largely by basinal geometry, suspension settling, and slope-originated gravity-flow events. Skeletal deposits and carbonate-silt starved ripples suggest gravity-flow deposits and bottom-current reworking during deposition. Redox-sensitive elements and degree of pyritization both indicate anoxic/euxinic conditions during the deposition of the Barnett Formation. / text

<p>Övergödning utgör ett av de allvarligaste hoten mot Östersjöns miljö. Storleken av näringsbelastningen till havet behöver därför bestämmas med hjälp av tillgängliga matematiska modeller. Modellen ”Generalised Watershed Loading Functions” (GWLF), en ickedistribuerad parametermodell som uppskattar hydrologi och månatlig näringsbelastning, tillämpades på avrinningsområdet till Daugava som mynnar i Östersjön. Syftet med studien var att genom modellering av historisk transport av näringsämnen till Östersjön ta fram parametrar och indata som sedan kan användas vid applicering av GWLF på omkringliggande avrinningsområden. Data från 1990-talet användes för kalibrering av modellen och data från 1980-talet för validering. Årlig kvävebelastning modellerades med R2värdet 0,78 för kalibreringsperioden. Modellerad årlig kvävebelastning för valideringsperioden underskattades med ungefär 30 % vilket troligen beror på att kvävekoncentrationer i grundvatten och ytavrinning minskade mellan 1980- och 1990-talen.</p><p>Fosforbelastningen underskattades jämfört med rapporterade värden vilket troligen beror på att enskilda avlopp inte inkluderades och att rapporterade punktutsläpp är för låga.</p><p>Modifikationer av modellen föreslås för prediktion av näringsbelastningar under lång tid och behovet av harmoniserad, uppdaterad och lättillgänglig data för näringstransportsmodellering diskuteras.</p> / <p>Eutrophication is one of the most serious threats to the Baltic Sea environment. Nutrient loading into the sea therefore needs to be quantified by available mathematical models. The Generalised Watershed Loading Functions (GWLF), a lumpedparameter model that predicts hydrology and monthly nutrient loads, was applied to the Daugava River Basin, discharging into the Baltic Sea. The aim of the study was to model historic transport of nutrients into the Baltic Sea and thereby produce estimates of parameters and input data needed for a spatial extension of the GWLF to surrounding river basins.</p><p>Calibration data were taken from the 1990’s and validation data from the 1980’s. Yearly nitrogen loads were modelled with an R2 value of 0.78 for the calibration period. Predicted yearly nitrogen loads for the validation period were about 30 % lower than reported values, probably depending on decreasing groundwater and runoff concentrations between the 1980’s and 1990’s. Phosphorus loads were underestimated compared to reported values, the main reason probably being the exclusion of septic systems and too low reported point sources.</p><p>Modifications of the model are suggested for longterm predictions of nutrient loads and the need for harmonised, uptodate and generally accessible data for nutrient transport modelling discussed.</p>

Topography growth and sediment fluxes in active subduction margin settings are poorly understood. Geological record is often scarce or hardly accessible as a result of intensive deformation. The Hawke Bay forearc basin of the Hikurangi margin in New Zealand is well suited for studying morphstructural evolution. It is well preserved, partly emerged and affected by active tectonic deformation during Pleistocene stage for which we have well dated series and well-known climate and eustasy. The multidisciplinary approach, integrating offshore and onshore seismic interpretations, well and core data, geological mapping and sedimentological sections, results in the establishment of a detailed stratigraphic scheme for the last 1.1 Ma forearc basin fill. The stratigraphy shows a complex stack of 11 eustasy-driven depositional sequences of 20, 40 and 100 ka periodicity. These sequences are preserved in sub-basins that are bounded by active thrust structures. Each sequence is characterized by important changes of the paleoenvironment that evolves between the two extremes of the glacial maximum and the interglacial optimum. Thus, the Hawke Bay forearc domain shows segmentation in sub-basins separated by tectonic ridges during sea level lows that become submerged during sea level highs. Over 100 ka timescale, deformation along active structures together with isostasy are responsible of a progressive migration of sequence depocenters towards the arc within the sub-basins. Calculation of sediment volumes preserved for each of the 11 sequences allows the estimation of the sediment fluxes that transit throughout the forearc domain during the last 1.1 Ma. Fluxes vary from c. 3 to c. 6 Mt.a⁻¹. These long-term variations with 100 ka to 1 Ma timescale ranges are attributed to changes in the forearc domain tectonic configuration (strain rates and active structure distribution). They reflect the ability of sub-basin to retain sediments. Short-term variations of fluxes (<100 ka) observed within the last 150 ka are correlated to drastic Pleistocene climate changes that modified erosion rates in the drainage area. This implies a high sensitiveness and reactivity of the upstream area to environmental changes in terms of erosion and sediment transport. Such behaviour of the drainage basin is also illustrated by the important increase of sediment fluxes since the European settlement during the 18th century and the following deforestation.

A basin analysis of the Oligocene Porter Group rocks in Castle Hill Basin, Canterbury, was completed. The Porter Group contains the Coleridge Formation which comprises a lower sandstone unit and an upper micritic limestone unit, and the Thomas Formation which consists of biosparite limestone and interbedded tuffs. Basin analysis provided evidence that the Coleridge Formation lower sandstone unit was deposited in an inner shelf setting based upon its moderate sorting, large grain size range, laterally continuous geometry and lack of bedforms due to intense bioturbation. The upper micritic limestone is a mid shelf deposit composed of micrite and minor clastic grains. Provenance analysis has classified the lower sandstone unit as a quartz arenite. Both metamorphic and plutonic source areas are likely for the sandstone, along with reworked grains from underlying Formations based on QFL, SEM-CL, heavy mineral and glauconite analysis. The Thomas Formation limestone is a typical New Zealand cool water biosparite deposited on the inner shelf as a result of storms and debris flows, with the upper cross-bedded limestone lithofacies being reworked by currents in shallow water. Petrographic data showing multiple stages of diagenesis at the upper contact of the Thomas Formation provides evidence for a major tectonic event. The interbedded tuffs are a result of basaltic marine volcanism on the inner to mid shelf. The tuffs are reworked and deposited by turbidity current, debris flow and storms. Analysis of a dike within the Thomas Formation volcanics showed a weakly alkaline geochemical signature that is indicative of volcanism related to extension. A regional synthesis compared the Porter Group rocks in Castle Hill Basin with Oligocene rocks in North Canterbury, West Coast and North Otago. Oligocene quartz-rich sandstones are found in Castle Hill Basin, Harper Valley, Avoca and Culverden while micritic limestone is found on the East Coast from Marlborough to Otago. Oligocene basaltic volcanics interbedded with limestone and karst unconformities are found in Castle Hill Basin, Culverden and Otago. Normal faulting may be responsible for thickness variations and several regional karst unconformities in the eastern South Island. Plate reconstructions based on sea floor magnetic anomalies also suggests the New Zealand region was tectonically active during the Oligocene. Mounting evidence, including Eocene-Oligocene faulting and volcanism in the South Island, suggests that New Zealand may not be best described as a passive margin during the Early-Mid Tertiary.

wo digital-computer models of the ground-water reservoir of the Tucson basin, in south-central Arizona, were constructed to study errors in digital models and to evaluate the worth of additional basic data to models. The two models differ primarily in degree of detail -- the large-scale model consists of 1,890 nodes, at a 1/2-mile spacing; and the small-scale model consists of 509 nodes, at a 1-mile spacing. Potential errors in the Tucson basin models were classified as errors associated with computation, errors associated with mathematical assumptions, and errors in basic data: the model parameters of coefficient of storage and transmissivity, initial water levels, and discharge and recharge. The study focused on evaluating the worth of additional basic data to the small-scale model. A, basic form of statistical decision theory was used to compute expected error in predicted water levels and expected worth of sample data (expected reduction in error) over the whole model associated with uncertainty in a model variable at one given node. Discrete frequency distributions with largely subjectively-determined parameters were used to characterize tested variables. Ninety-one variables at sixtyone different locations in the model were tested, using six separate error criteria. Of the tested variables, 67 were chosen because their expected errors were likely to be large and, for the purpose of comparison, 24 were Chosen because their expected errors were not likely to be particularly large. Of the uncertain variables, discharge/recharge and transmissivity have the largest expected errors (averaging 155 and 115 feet, respectively, per 509 nodes for the criterion of absolute value of error) and expected sample worths (averaging 29 and 14 feet, respectively, per 509 nodes). In contrast, initial water level and storage coefficient have lesser values. Of the more certain variables, transmissivity and initial water level generally have the largest expected errors (a maximum of 73 per feet per 509 nodes) and expected sample worths (a maximum of 12 feet per 509 nodes); whereas storage coefficient and discharge/ recharge have smaller values. These results likely are not typical of those from many ground-water basins, and may apply only to the Tucson basin. The largest expected errors are associated with nodes at which values of discharge/recharge are large or at which prior estimates of transudssivity are very uncertain. Large expected sample worths are associated with variables which have large expected errors or which could be sampled with relatively little uncertainty. Results are similar for all six of the error criteria used. Tests were made of the sensitivity of the method to such simplifications and assumptions as the type of distribution function assumed for a variable, the values of the estimated standard deviations of the distributions, and the number and spacing of the elements of each distribution. The results are sensitive to all of the assumptions and therefore likely are correct only in order of magnitude. However, the ranking of the types of variables in terms of magnitude of expected error and expected sample worth is not sensitive to the assumptions, and thus the general conclusions on relative effects of errors in different variables likely are valid. Limited studies of error propagation indicated that errors in predicted water levels associated with extreme erroneous values of a variable commonly are less than 4 feet per node at a distance of 1 mile from the tested node. This suggests that in many cases, prediction errors associated with errors in basic data are not a major problem in digital modeling.