Diverse origins and timing of formation of basinal brines in the Gulf of Mexico sedimentary basin

A review of five different field areas in the Gulf of Mexico sedimentary basin (GOM) illustrates some of the potentially diverse chemical and physical processes which have produced basinal brines. The elevated salinities of most of the formation waters in the GOM are ultimately related to the presence of the Middle Jurassic Louann Salt. Some of these brines likely inherited their salinity from evaporated Mesozoic seawater, while other saline fluids have been produced by subsequent dissolution of salt, some of which is occurring today. The timing of the generation of brines has thus not been restricted to the Middle Jurassic. The mechanisms of solute transport that have introduced brines throughout much of the sedimentary section of the GOM are not entirely understood. Free convection driven by spatial variations in formation water temperature and salinity is undoubtedly occurring around some salt structures. However, the driving mechanisms for the broad, diffusive upward solute transport in the northern Gulf rim of Arkansas and northern Louisiana are not known. In the Lower Cretaceous of Texas, fluid flow was much more highly focused, and perhaps episodic. It is clear that many areas of the Gulf basin are hydrologically connected and that large‐scale fluid flow, solute transport, and dispersion have occurred. The Na‐Mg‐Ca‐Cl compositions of brines in the areas of the Gulf Coast sedimentary basin reviewed in this article are products of diagenesis and do not reflect the composition of the evaporated marine waters present at the time of sediment deposition. Large differences in Na, Ca, and Mg trends for waters hosted by Mesozoic versus Cenozoic sediments may reflect differences in: (i) the sources of salinity (evaporated seawater for some of the Mesozoic sediments, dissolution of salt for some of the Cenozoic sediments); (ii) sediment lithology (dominantly carbonates for much of the Mesozoic sediments, and dominantly siliciclastics for the Cenozoic sediments); or (iii) residence times of brines associated with these sediments (tens of millions of years versus perhaps days).     

Salinity structure of the central North Slope foreland basin, Alaska, USA: implications for pathways of past and present topographically driven regional fluid flow

Previous studies of the areal variation in heat flow in the National Petroleum Reserve Alaska (NPRA) support the existence of an active topographically driven regional fluid flow regime in this central part of the North Slope foreland basin. Drilling records and wireline logs for over 30 wells drilled in the NPRA provide additional field information, which can be used to further constrain interpretation of the pattern of regional flow of basinal waters within the NPRA. Hydraulic heads estimated from drilling mud weights show that ground water flow occurs generally from south to north, but with divergence to the north‐east and north‐west away from the central part of the NPRA towards coastal areas of elevated shallow heat flow. Salinities calculated from SP logs range from less than 1 g L^?1, to marine values of 35 g L^?1, to hypersaline values of over 150 g L^?1. The entire upper sedimentary section to a depth of 2 km or more in the eastern part of the NPRA has been preferentially flushed with meteoric water through an area corresponding to the sandiest portion of the Nanushuk group. Deeper areas of low salinity occur within the Sadlerochit and Lisburne sections. The pattern of regional flow in the east is complicated, however, by the presence of a large mass of hypersaline water at depth. It is not known whether these brines are being displaced laterally and upward towards the discharge end of the basin or whether fresher waters are simply riding up over the top. Deep, hypersaline waters also occur in fault slices in the Brooks Range and have survived meteoric flushing. The brines were probably formed at the time of deposition of the Lisburne carbonates. The fluid flow regime to the west is different. Low‐salinity waters may be flowing northward underneath this section through the Ellesmerian section and discharging upward nearer the coast. However, sparse well log control severely limits what can be deduced about the details of flow paths in the central and western parts of the NPRA.     

Topography‐driven flow versus buoyancy‐driven flow in the U.S. midcontinent: implications for the residence time of brines

Topography‐driven flow is normally considered to be the dominant groundwater flow system in uplifted sedimentary basins. In the U.S. midcontinent region east of the Rocky Mountains, the presence of brines derived from dissolution of halite suggests that significant topography‐driven flushing has occurred to remove older brines that presumably formed concurrently with Permian evaporites in the basin. However, the presence of evaporites and brines in the modern basin suggests that buoyancy‐driven flow could limit topography‐driven flushing significantly. Here we used numerical models of variable‐density fluid flow, halite dissolution, solute transport, and heat transport to quantify flow patterns and brine migration. Results indicate the coexistence of large‐scale topography‐ and buoyancy‐driven flow. Buoyancy‐driven flow and low permeability evaporites act to isolate brines, and the residence time of the brines was found to be quite long, at least 50 Myr. The modern distribution of salinity appears to reflect near‐steady‐state conditions. Results suggest that flushing of original evaporatively‐concentrated brines occurred tens of millions of years ago, possibly concurrent with maximum uplift ca. 60 Ma. Simulations also suggest that buoyancy‐driven convection could drive chemical exchange with crystalline basement rocks, which could supply significant Ca²⁺, Sr²⁺, and metals to brines.     

Infiltration of basinal fluids into high-grade basement, South Norway: sources and behaviour of waters and brines

Quartz veins hosted by the high‐grade crystalline rocks of the Modum complex, Southern Norway, formed when basinal fluids from an overlying Palaeozoic foreland basin infiltrated the basement at temperatures of c. 220°C (higher in the southernmost part of the area). This infiltration resulted in the formation of veins containing both two‐phase and halite‐bearing aqueous fluid inclusions, sometimes with bitumen and hydrocarbon inclusions. Microthermometric results demonstrate a very wide range of salinities of aqueous fluids preserved in these veins, ranging from c. 0 to 40 wt% NaCl equivalent. The range in homogenization temperatures is also very large (99–322°C for the entire dataset) and shows little or no correlation with salinity. A combination of aqueous fluid microthermometry, halogen geochemistry and oxygen isotope studies suggest that fluids from a range of separate aquifers were responsible for the quartz growth, but all have chemistries comparable to sedimentary formation waters. The bulk of the quartz grew from relatively low δ¹⁸O fluids derived directly from the basin or equilibrated in the upper part of the basement (T < 200°C). Nevertheless, some fluids acquired higher salinities due to deep wall‐rock hydration reactions leading to salt saturation at high temperatures (>300°C). The range in fluid inclusion homogenization temperatures and densities, combined with estimates of the ambient temperature of the basement rocks suggests that at different times veins acted as conduits for influx of both hotter and colder fluids, as well as experiencing fluctuations in fluid pressure. This is interpreted to reflect episodic flow linked to seismicity, with hotter dry basement rocks acting as a sink for cooler fluids from the overlying basin, while detailed flow paths reflected local effects of opening and closing of individual fractures as well as reaction with wall rocks. Thermal considerations suggest that the duration of some flow events was very short, possibly in the order of days. As a result of the complex pattern of fracturing and flow in the Modum basement, it was possible for shallow fluids to penetrate basement rocks at significantly higher temperatures, and this demonstrates the potential for hydrolytic weakening of continental crust by sedimentary fluids.     

Quantitative basin modeling: present state and future developments towards predictability

A critique review of the state of quantitative basin modeling is presented. Over the last 15 years, a number of models are proposed to advance our understanding of basin evolution. However, as of present, most basin models are two dimensional (2‐D) and subject to significant simplifications such as depth‐ or effective stress‐dependent porosity, no stress calculations, isotropic fracture permeability, etc. In this paper, promising areas for future development are identified. The use of extensive data sets to calibrate basin models requires a comprehensive reaction, transport, mechanical (RTM) model in order to generate the synthetic response. An automated approach to integrate comprehensive basin modeling and seismic, well‐log and other type of data is suggested. The approach takes advantage of comprehensive RTM basin modeling to complete an algorithm based on information theory that places basin modeling on a rigorous foundation. Incompleteness in a model can self‐consistently be compensated for by an increase in the amount of observed data used. The method can be used to calibrate the transport, mechanical, or other laws underlying the model. As the procedure is fully automated, the predictions can be continuously updated as new observed data become available. Finally, the procedure makes it possible to augment the model itself as new processes are added in a way that is dictated by the available data. In summary, the automated data/model integration places basin simulation in a novel context of informatics that allows for data to be used to minimize and assess risk in the prediction of reservoir location and characteristics.     

Fluid inclusion constraints on the origin of the brines responsible for Pb–Zn mineralization at Pine Point and coarse non‐saddle and saddle dolomite formation in southern Northwest Territories

The Pine Point region is a classic metallogenic mining camp that produced over 58 million short tons of Zn–Pb ore from approximately 40 base‐metal mineralized deposits hosted by Middle Devonian carbonates. The ore deposits are localized in paleokarstic features found in the epigenetic ‘Presqu'ile’ dolomite that preferentially replaced some of the upper barrier limestones. The main ore‐stage sulfides include galena, sphalerite, marcasite, and pyrite. A bulk fluid inclusion chemistry study was carried out on sulfide, coarse non‐saddle and saddle dolomite and calcite samples from the Pine Point and Great Slave Reef deposits, and unmineralized coarse non‐saddle and saddle dolomite samples from Hay West, Windy Point and Qito areas. Molar Cl/Br ratio data from Pine Point indicate the presence of four fluids at different stages of the paragenesis. The fluids trapped in sulfides and ore‐stage dolomites predominately consist of a Br‐rich fluid with a composition similar to that of evaporated seawater (fluid A), and a very Br‐enriched fluid of unknown origin (fluid B). Both these fluids are CaCl₂–NaCl (Na to Ca ratios of 1:10)‐rich brines and have compositions unlike the modern formation waters in the Devonian aquifers in the basin today. A third, relatively Cl‐rich (or Br‐poor), fluid (fluid C) was identified in two samples and may have acquired some chlorinity by dissolving halide minerals. Mixing between the Br‐rich fluid A and a dilute fluid also occurred in the later stages of the paragenesis, resulting in the formation of calcite and native sulfur. Saddle and coarse dolomites not associated with significant sulfide mineralization have a narrow range of halogen compositions similar to fluid A. There is no evidence of fluid B or C in the unmineralized samples. Relative to a modern‐day seawater compositions all the fluids have had some modification of their cation compositions. There is some weak evidence for interactions with clastic units or crystalline basement rocks. It is also possible however, that the evaporative brines could have formed from a relatively CaCl₂‐rich, NaCl‐depleted Devonian seawater, unlike the composition of modern‐day seawater.     

Reasoned use of chemical parameters for the diagnostic evaluation of the state of preservation of waterlogged archaeological wood

Waterlogged archaeological wood undergoes decay processes that depend on both the burial conditions and the constituting species, and which cause the depletion of the structural components of wood cells. To quantitatively assess the state of preservation of the decayed material, specific parameters are usually measured by means of both chemical and physical analyses. In this paper an innovative approach in the use of the data obtained from these kinds of measurements is developed. A series of 132 archaeological wood samples of different wood species, burial times and states of preservation, and coming from different sites in Italy, was analysed. Their residual chemical composition, maximum water content and basic density were measured, and a reasoned use of these parameters was carried out through their elaboration, with the aim of both evaluating eventual incongruence or anomalies in the raw physical and chemical data (which has never been accomplished so far) and directly comparing in a reliable way the analytical results obtained from archaeological samples with very different states of preservation. This approach allowed defining the effective values of chemical parameters related to wood decay according to a same reference basis of calculation among the various data. By this way, it was possible to state that lignin can be also attacked by the agents causing biotic decay, and that in hardwoods its decay is more related to the burial conditions than to the wood species. Instead, the mechanism of polysaccharide depletion is diversified: conifers showed a uniform behaviour whereas hardwoods were more species-dependent. Moreover, in addition to the chemical composition, also anatomical factors influence the carbohydrate rate of decay in waterlogged wood.     

Historians, prehistorians, and the tyranny of the historical record: Danish state formation through documents and archaeological data

Historians traditionally have viewed the emergence of Denmark as a nation-state through western European primary sources, inferring a fragmented, politically divided region between AD 800 and AD 1050. Conversely, archaeologists using local-scale, single-site data argue for unification by ca. AD 800. An alternative is offered, combiningregional-scale archaeological methods (rank-size analyses) and consideration of westernand northern European texts. This approach reveals that as disparate polities unified, the “homelands” of ruling dynasties came under control quickly, while peripheral areas remained largely autonomous. To incorporate peripheral areas, rulers manipulated the location and function of political and economic centers. Local resistance to change is reflected in slow, uneven unification, interregional elite competition, and eventually, armed rebellion. The apparent discrepancies between historic and prehistoric data are no error; in fact, they mirror the inherent conflicts of this profound social transformation.     

Package FLUIDS. Part 3: correlations between equations of state, thermodynamics and fluid inclusions

The computer package FLUIDS ( Bakker 2003 ) has been revised to calculate fluid properties in pores and inclusions. The programs are provided with a Graphical User Interface (GUI) and are adapted to new operating systems, including MacOS, Windows and Linux. The van der Waals equation of state has been added to the group Loners and is used to illustrate a large variety of calculation procedures for many thermodynamic parameters and properties. The mathematical transformations can be applied to any equation of state with the form p ( V , T , n ), i.e. the pressure of a multi-component fluid is expressed as a function of volume, temperature and amount of substance. The fluid properties that are usually observed in microthermometric analyses of fluid inclusions, such as phase separation, phase coexistence and stability, can be predicted with these equations of state by using its spinodal and critical point calculations, in addition to fugacity calculations of liquid and vapour phases. The computer program LonerW can be freely downloaded from the website: http://fluids.unileoben.ac.at/Computer.html .     

Selected physical parameters to characterize the state of preservation of waterlogged archaeological wood: a practical guide for their determination

Non-destructive and destructive methods for determining the physical parameters of waterlogged wood such as the porosity, the water content, the wet and dry bulk densities plus the density of the cell wall material are presented. Considerations in respect to determination of masses, volumes and sampling size are discussed.     

Origin of palaeo‐waters in the Ordovician carbonates in Tahe oilfield,Tarim Basin: constraints from fluid inclusions and Sr,C and O isotopes

Petrographic features, isotopes, and trace elements were determined, and fluid inclusions were analyzed on fracture‐filling, karst‐filling and interparticle calcite cement from the Ordovician carbonates in Tahe oilfield, Tarim basin, NW China. The aim was to assess the origin and evolution of palaeo‐waters in the carbonates. The initial water was seawater diluted by meteoric water, as indicated by bright cathodoluminescence (CL) in low‐temperature calcite. The palaeoseawater was further buried to temperatures from 57 to 110°C, nonluminescent calcite precipitated during the Silurian to middle Devonian. Infiltration of meteoric water of late Devonian age into the carbonate rocks was recorded in the first generation of fracture‐ and karst‐filling dull red CL calcite with temperatures from <50°C to 83°C, low salinities (<9.0 wt%), high Mn contents and high ⁸⁶Sr/⁸⁷Sr ratios from 0.7090 to 0.7099. During the early Permian, ⁸⁷Sr‐rich hydrothermal water may have entered the carbonate rocks, from which precipitated a second generation of fracture‐filling and interparticle calcite and barite cements with salinities greater than 22.4 wt%, and temperatures from 120°C to 180°C. The hydrothermal water may have collected isotopically light CO₂ (possibly of TSR‐origin) during upward migration, resulting in hydrothermal calcite and the present‐day oilfield water having δ¹³C values from ?4.3 to ?13.8‰ and showing negative relationships of ⁸⁷Sr/⁸⁶Sr ratios to δ¹³C and δ¹⁸O values. However, higher temperatures (up to 187°C) and much lower salinities (down to 0.5 wt%) measured from some karst‐filling, giant, nonluminescent calcite crystals may suggest that hydrothermal water was deeply recycled, reduced (Fe‐bearing) meteoric water heated in deeper strata, or water generated from TSR during hydrothermal water activity. Mixing of hydrothermal and local basinal water (or diagenetically altered connate water) with meteoric waters of late Permian age and/or later may have resulted in large variations in salinity of the present oilfield waters with the lowest salinity formation waters in the palaeohighs.     

科学发展观的形成背景与历史地位--兼与赵凌云、张连辉先生商榷

科学发展观是当代中国富有创造性的发展理论,是新中国成立以来的第四代发展观.马克思主义发展观、苏联发展观和当代国外发展观,是新中国成立以来的发展观演变特别是科学发展观提出的理论背景.科学发展观在发展目标上具有全面性,在发展方式上具有统筹性,在发展目的上具有人本性.     

Using airborne small-footprint laser scanner data for detection of cultural remains in forests: an experimental study of the effects of pulse density and DTM smoothing

Cultural remains are laborious to register by means of field surveys. Thus, in recent years several trials using remote sensing data to detect cultural remains have been carried out. The most promising remote sensing technique for such purposes is airborne laser scanning (ALS) from which digital terrain models (DTM) that enable visual interpretations of anomalies on the ground are generated. Although it has been documented previously that ALS is a powerful data source for detection of cultural remains, it has not yet been carried out studies that focus on the effects of the point density of the ALS data and properties of the subsequent generation of the DTM on the detection success of cultural remains. Thus, this study aimed at analyzing these effects by letting four experienced archeologists interpret DTMs generated from ALS data with point densities of 1 p m⁻², 5 p m⁻², and 10 p m⁻², each with three different levels of DTM smoothing. The experiment was conducted according to a randomized complete block design and the analyses were carried out using analysis of variance. The results showed that there was a significant improvement in the detection success when the point density was increased from 1 p m⁻² to 5 p m⁻². There were also some improvements when increasing the point density further to 10 p m⁻², but they were less pronounced. Furthermore, the results showed that the DTM smoothing did not have any significant effect on the detection success.     

Hydrology of the Western Arkoma basin and Ozark platform during the Ouachita orogeny: implications for Mississippi Valley-type ore formation in the Tri-State Zn–Pb district

Numerical groundwater modeling was used to investigate the role of fluid flow associated with uplift of the Arkoma basin during the closing stages of the Ouachita orogeny in forming the Mississippi Valley‐type Zn–Pb ores of the Tri‐State district. The model hydrostratigraphy was flexurally compensated to account for the restoration of Pennsylvanian–Permian sediments removed since the close of the orogeny in estimating the regional paleotopographic gradient. Estimates of the amount of Pennsylvanian–Permian sediment that has been removed by erosion vary widely. A thick and a thin endmember case were considered, and in both cases topographydriven fluid flow was shown to have been an important mechanism for groundwater motion, with a lesser component contributed during the early stages of uplift by overpressuring created by compaction in the deep portion of the Arkoma basin. The Pennsylvanian–Permian sediments and underlying Western Interior Plains confining system acted as thick capping aquitards that caused slow rates of groundwater flow over much of the profile. As a result, meteoric water infiltration initiated during uplift was slow to flush saline formation waters, allowing MVT ore‐forming salinities to persist at Tri‐State on the order of at least 10⁰ Myr. The slow groundwater flow rates also caused heat transport to occur primarily by conduction rather than advection. Despite this, MVT ore‐forming temperatures were still reached at Tri‐State for both endmember cases of Pennsylvanian–Permian aquitard thickness, though much more readily in the thick aquitard case. Faults within the Tri‐State district served as a regional fluid focusing mechanism and probably played a more important role in localizing mineralization than the window in the Ozark confining unit that occurs in the district. Fluids rising along these faults could have cooled by about 8–10°C and as much as another 0.3°C km^?1 as they flowed laterally northward. This temperature change alone however would not have been sufficient to precipitate the total mass of metal sulfide ore occurring at Tri‐State.     

Cultures of the eighth and seventh millennia BP in the southern Levant: A review for the 1990s

The Pottery Neolithic of the southern Levant (the eighth and seventh millennia BP) was a crucial period in which the foundations were laid for the development of complex societies and urban civilization. This article summarizes the current state of research in this area during this period. Past and present research in Israel and Jordan is reviewed, and methodological problems in fieldwork and analysis are discussed. We attempt a systematic definition of the archaeological entities. For each such entity, we present the available data on chronostratigraphy, characteristics of the material culture (including lithics, ceramics and architecture), burial customs, figurines and images, economy, and site-distribution. While the Yarmukian and Jericho IX occupied territories of similar size and seem to represent entities on the scale of a culture, the later Wadi Raba entity extended over a larger area and was of longer duration. A chronostratigraphic summary is presented, and the major entities are compared in terms of site-types, economy, burials, and geographical distribution.     

Entrepreneurial industry structures and financial institutions as agents for path dependence in Southwest Norway: the role of the macroeconomic environment

ABSTRACT

Guided by an evolutionary perspective, we study how macroeconomic shifts as an exogenous factor contribute to the endogenous roles of financial institutions and the entrepreneurial industry structure as indicators for path extension or diversification in Southwest Norway. Path extension implies that new firm formation reproduces itself with limited variation. Path diversification implies a departure from existing paths, in that entrepreneurial activities expand into unrelated or related industries. Between 1992 and 1998, we observe a departure from path extension and an increase in entrepreneurial path diversification into unrelated industries, but this trend declines in the following years. The increase and decline are stronger for Southwest Norway than for the rest of the country. Throughout the whole period of observation (1992–2011), we observe a steady decline in path diversification into related industries. Thus, Southwest Norway, and the country as a whole, experiences an extension of an industry structure that increasingly reproduces itself, which implies stronger path dependence and decreasing diversification of related and unrelated entrepreneurial activity. Financial institutions mostly reinforce path extension, even in periods when abundant capital is available, but to some degree, they also induce related path diversification.     

Computing geochemical mass transfer and water/rock ratios in submarine hydrothermal systems: implications for estimating the vigour of convection

A method of calculating chemical water/rock ratios is presented that enables the estimation of fluid velocities in open, flow‐through hydrologic systems. The approach is based on relating the gain/loss of a chemical species per kilogram of solid phase to the loss/gain of that species in the fluid phase, integrated across a specified length of the flowpath. After examining the underlying approximations of the approach using a one‐dimensional model of seawater moving through a basalt under nonisothermal conditions, the method is applied to representative zones within a two‐dimensional hydrothermal convective system. The method requires that regions within the flow system can be identified in which the direction of flow is steady for an extended period of time. Estimates of fluid velocity are spatial and temporal averages for the length of the flowpath used in the calculation. The location within the flow system and the nature of the alteration reactions determine which species can provide reliable values of the chemical water/rock ratio and useful estimates of fluid velocities. Over the length of the flowpath considered, the calculation of water/rock ratios works best when a species is controlled by a single reaction. Accurate estimates are favoured if the concentration profile of a species along the flowpath increases or decreases monotonically. If the length of the flowpath extends over more than one reaction zone, then erroneous estimates of the water/rock ratio and fluid velocity are more likely. Model calculations suggest that the quartz/silica system should provide reliable estimates for fluid velocity under a wide range of temperature and flow conditions, in particular in those regions of a system at or near quartz equilibrium, so that the aqueous silica concentration is buffered by quartz and correlated with the temperature distribution.