HVSR,SSR, and VS30 Values at Three New Zealand Basin Arrays

Microtremors and small earthquakes have been recorded on three small soft-soil basins in New Zealand, and on the surrounding rock, using arrays of up to twenty velocity seismographs. Comparisons of the resultant HVSR (Horizontal to Vertical Spectral Ratio) and SSR (Standard Spectral Ratio) values show that near the centre of the basins HVSR values can constitute good proxies for SSR values, but that near the basin edges this relationship may fail. The failures involve HVSR both under-predicting and over-predicting SSR. The location of effective basin edges may not be immediately obvious. Furthermore, there appears to be no relationship between values of Vs30 and values of HVSR or SSR for the basins, suggesting that Vs30 may be of limited value in distinguishing between soil classes.     

Considering Soil-Nonlinearity Effect on Seismic Performance Evaluation of Structures based on Pushover Analysis

According to the most of current seismic codes, nonlinear soil behavior is commonly ignored in seismic evaluation procedure of the structures. To contribute on this matter, a pushover analysis method incorporating the probabilistic seismic hazard analysis (PSHA) is proposed to evaluate the effect of nonlinear soil response on seismic performance of a structure. The PSHA outcomes considering soil nonlinearity effect is involved in the analysis procedures by modifying the site-specific response spectrum. Results showed that incorporation of nonlinear soil behavior leads to an increase in displacement demand of structures which should accurately be considered in seismic design/assessment procedure. Results of implemented procedure are confirmed with the estimated displacement demand including soil-structure interaction (SSI).     

Macropalaeontology of the Trochocyathus-Trematotrochus band (Paleocene/Eocene boundary), Dilwyn Formation,Otway Basin,Victoria

Two new brachythoracids are described from the Taemas Limestone. Arenipiscis westolli gen. et sp. nov. possesses a skull-roof with deeply embayed posterior and elongate anterolateral margins, a large fused rostropineal plate, and orbits anteriorly placed and deeply notching the skull. The visceral skull-roof surface is developed with strong relief. The trunk-shield is poorly known, but the median dorsal plate probably had a prominent carinal process. Errolosteus goodradigbeensis gen. et sp. nov. is known only by an incomplete skull-roof, and anterior lateral and posterior ventrolateral plates. It has a highly distinctive ridged ornament. The affinities of these forms are considered in a discussion of brachythoracid interrelationships, and it is concluded that they are interchangeable on a cladogram with Buchanosteus. Other brachythoracids from the fauna, recently described by White, are considered, and it is suggested that Goodradigbeeon is phyletically primitive and Taemasosteus phyletically advanced relative to Buchanosteus. Schemes of brachythoracid interrelationships recently proposed by Denison and by Miles &; Dennis are compared, and a new scheme is proposed.     

Record of the deep marine Clinocythereis australis Ayress and Swanson, 1991 (Ostracoda) from the upper Miocene Tambo River Formation,Gippsland Basin,Australia: Palaeo-oceanographic and biostratigraphic implications

A new species of Tertiary lungfish, Neoceratodus djelleh, is based on two well-preserved upper tooth plates, from Duaringa, Queensland. Both specimens are elongate and have curved mediolingual faces and poorly defined ridges, with little trace of crests or clefts on the flat occlusal surface. Each ridge is supported by a bony base which extends into a peak. Enameloid is present, showing growth lines without associated cusps on the labial surface. Another specimen from Billeroo Creek, South Australia, is referred to Neoceratodus cf. N. djelleh.     

Origin of dolomites in the Cambrian (upper 3rd‐Furongian) formation,south‐eastern Sichuan Basin,China

The origin of large‐scale ancient dolomite is one of the most hotly debated topics in sedimentology. The Loushanguan group of the upper 3rd‐Furongian Cambrian series on the south‐eastern margin of the Sichuan Basin consists of numerous dolomites, and the origins of these dolomites have never been reported previously although they are probably good hydrocarbon reservoirs. Based on a systematic analysis of petrology, fluid inclusions, carbon and oxygen isotopes, trace elements and rare earth elements (REEs), this study provides some unique insights into the origins of the dolomites. Four dolomite types have been identified in the study area: dolomicrite, fabric‐retentive oolitic dolomite, fabric‐obliterative dolomite and saddle dolomite cement. In the dolomicrite and fabric‐retentive oolitic dolomite, high Sr contents (with respect to the fabric‐obliterative dolomite) and the lack of two‐phase aqueous inclusions suggest that they formed at shallow‐to‐intermediate burial depths at low temperatures (<50–60°C). Carbon and oxygen isotopes and seawater‐like REE+Y characteristics of the dolomicrite and fabric‐retentive oolitic dolomite indicate that the dolomitizing fluids were evaporated seawater or slightly modified seawater. The obliteration of the original sedimentary fabric and relatively low δ¹⁸O and Sr values compared to the fabric‐retentive dolomite indicate that fabric‐obliterative dolomite formed at intermediate‐to‐deep burial diagenesis. The chemical composition approaches pure dolomite and the REE+Y characteristics are similar to those of the fabric‐retentive dolomite, indicating that the fabric‐obliterative dolomite was formed due to the recrystallization of the previously formed fabric‐retentive dolomite at elevated burial depths and temperatures. High fluid inclusion homogenization temperatures (115–150°C), low δ¹⁸O values, nonplanar‐a crystals and seawater‐like REE+Y characteristics suggest that saddle dolomite cement formed by reprecipitation of dolomite that related to seawater‐driven and deep burial fluid. In the study area, dolomicrite and fabric‐retentive oolitic dolomite may have been formed by penecontemporaneous or seepage‐reflux dolomitization during early‐stage diagenesis. Subsequently, during progressive burial, most of the fabric‐retentive dolomite was converted into fabric‐obliterative dolomite by recrystallization. This study confirms that fabric‐obliterative dolomite was the main dolomite type, and although deeply buried, these Cambrian dolomites most likely have preserved coeval seawater geochemical signals.     

Linked thermal convection of the basement and basinal fluids in formation of the unconformity‐related uranium deposits in the Athabasca Basin,Saskatchewan, Canada

World‐class unconformity‐related U deposits in the Athabasca Basin (Saskatchewan, Canada) are generally located within or near fault zones that intersect the unconformity between the Athabasca Group sedimentary basin rocks and underlying metamorphic basement rocks. Two distinct subtypes of unconformity‐related uranium deposits have been identified: those hosted primarily in the Athabasca Group sandstones (sediment‐hosted) and those hosted primarily in the underlying basement rocks (basement‐hosted). Although significant research on these deposits has been carried out, certain aspects of their formation are still under discussion, one of the main issues being the fluid flow mechanisms responsible for uranium mineralization. The intriguing feature of this problem is that sediment‐hosted and basement‐hosted deposits are characterized by oppositely directed vectors of fluid flow via associated fault zones. Sediment‐hosted deposits formed via upward flow of basement fluids, basement‐hosted deposits via downward flow of basinal fluids. We have hypothesized that such flow patterns are indicative of the fluid flow self‐organization in fault‐bounded thermal convection (Transport in Porous Media, 110, 2015, 25). To explore this hypothesis, we constructed a simplified hydrogeologic model with fault‐bounded thermal convection of fluids in the faulted basement linked with fluid circulation in the overlying fault‐free sandstone horizon. Based on this model, a series of numerical experiments was carried out to simulate the hypothesized fluid flow patterns. The results obtained are in reasonable agreement with the concept of fault‐bounded convection cells as an explanation of focused upflow and downflow across the basement/sandstone unconformity. We then discuss application of the model to another debated problem, the uranium source for the ore‐forming basinal brines.     

The salt chimney effect: delay of thermal evolution of deep hydrocarbon source rocks due to high thermal conductivity of evaporites

Half of the topseals to the world's largest oilfields are evaporites. Rock salt has a thermal conductivity two to four times greater than that of other sedimentary rocks found in oil‐ and gas‐bearing basins. Strong heat conduction through evaporites can increase the geothermal gradient above evaporite deposits, resulting in a positive thermal anomaly and above‐average temperature while simultaneously decreasing the geothermal gradient below evaporites, resulting in a negative thermal anomaly. Most Triassic–Jurassic hydrocarbon source rocks in the Kuqa Basin, western China, are overlain by ~1500‐m‐thick Tertiary evaporites with underlying Cretaceous sandstones and mudstones. Directly measured strata temperatures indicate an obvious break in the steepness of the geothermal gradient above and below Paleogene evaporites, with a significantly steeper geothermal gradient above the evaporites. Simulations of the thermal evolution of source rocks based on data collected from well Kela‐2 indicate that if the thickness of evaporites (mainly rock salt and anhydrite rock) in overlying rocks above source rocks increases compared with the thickness of siliciclastic rocks in the overlying rocks, then strata temperatures and vitrinite reflectance in Jurassic source rocks will decrease accordingly. Our thermal simulations based on the thickness and thermal conductivity of evaporites accurately coincide with previous studies based on homogenization temperatures, hydrocarbon–water contact retrospection, and carbon isotope results from natural gases. The gas generation center located in the Kalasu Tectonic Belt today is also sealed in an evaporite‐related structural trap that formed at this time. Therefore, the speculated natural gas generation times not only correlate with the evaporite‐related structural trap formation, but the calculated maturity of deep source rocks below the evaporites also coincides with current gas reserves. And our studies can help to find the deep oils and gases under thick evaporites.     

Hunting and Foraging in the Eyasi Basin, Northern Tanzania: Past, Present and Future Prospects

In this paper I document the history of hunting and foraging in the Eyasi Basin, northern Tanzania, from about 130,000 bp to contemporary times, by reviewing the available archaeological, palaeontological, historical and ethnographic data. The review reveals a complex co-existence and interactions between hunter-foragers and herders and farmers from about 3,000 bp until the present. In addition, the review exposes intricate opportunities and at the same time risks/constraints that face extant Hadzabe hunter-foragers in the 21st century. The Hadzabe are a group of about 800–1,000 people who live in the Eyasi Basin. Traditionally, they are viewed as hunter-foragers—people who acquire nearly all of their food by hunting wild animals and foraging wild plant foods and honey. Although Hadzabe have been closely surrounded by other ethnic and cultural groups with whom they have interacted, for at least the last 100 years, their existence as a cultural group in the 21st century is in doubt. Mitigation measures are required in order to enhance the existence of this important cultural group.

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Résumé Cet article est une présentation de l’histoire de chasse et d’affourragement au Bassin Eyasi dans le nord de la Tanzanie, dès les environs de 130.000 ans avant présent, aux périodes contemporaines. On fait une revue des données archéologiques, anthropologiques, paléonthologiques, historiques ainsi que éthnographiques disponibles. La revue indique qu’il y a une coexistence et interaction complexes entre les chasseurs-fourrageurs, bouviers, et cultivateurs il y a 3.000 ans jusqu’au présent. En outre, la revue présente des occasions et en même temps des risques et contraintes complexes qui se posent aux Hadzabé: un groupe d’environ 800–1000 personnes (chasseurs-fourrageurs) qui vivent dans le bassin Eyassi. Traditionnellement, les Hadzabé sont regardés comme, les personnes qui obtiennent présque toutes leurs nourritures de la chair des animaux sauvages, des aliments végétaux sauvage et du miel. Bien que les Hadzabé aient été étroitement environnés et qu’ils aient interagis avec d’autres groupes éthniques et culturels au cours de 100 années passées leur existence au 20ème siècle en tant que groupe culturel est incertaine. Donc, des mesures sont exigées pour soutenir l’existence de ce groupe culturel important.

     

良渚文化神徽解析

良渚文化的中心在太湖流域,太湖流域的原始文化从早期发展到良渚文化时期,是良渚文化神徽产生的时间条件;太湖流域特殊的地理环境和气候条件,是良渚文化神徽产生的空间条件。由于这一地区的人对频繁发生的洪水的恐惧,从而把雷神作为天神来敬仰,这正是良渚文化神徽的真正内涵,这种信仰在某些少数民族地区流传至今。     

Overpressure and petroleum generation and accumulation in the Dongying Depression of the Bohaiwan Basin, China

The occurrence of abnormally high formation pressures in the Dongying Depression of the Bohaiwan Basin, a prolific oil‐producing province in China, is controlled by rapid sedimentation and the distribution of centres of active petroleum generation. Abnormally high pressures, demonstrated by drill stem test (DST) and well log data, occur in the third and fourth members (Es3 and Es4) of the Eocene Shahejie Formation. Pressure gradients in these members commonly fall in the range 0.012–0.016 MPa m^?1, although gradients as high as 0.018 MPa m^?1 have been encountered. The zone of strongest overpressuring coincides with the areas in the central basin where the principal lacustrine source rocks, which comprise types I and II kerogen and have a high organic carbon content (>2%, ranging to 7.3%), are actively generating petroleum at the present day. The magnitude of overpressuring is related not only to the burial depth of the source rocks, but to the types of kerogen they contain. In the central basin, the pressure gradient within submember Es32, which contains predominantly type II kerogen, falls in the range 0.013–0.014 MPa m^?1. Larger gradients of 0.014–0.016 MPa m^?1 occur in submember Es33 and member Es4, which contain mixed type I and II kerogen. Numerical modelling indicates that, although overpressures are influenced by hydrocarbon generation, the primary control on overpressure in the basin comes from the effects of sediment compaction disequilibrium. A large number of oil pools have been discovered in the domes and faulted anticlines of the normally pressured strata overlying the overpressured sediments; the results of this study suggest that isolated sandstone reservoirs within the overpressured zone itself offer significant hydrocarbon potential.