Search

ABSTRACTA detailed geological map of the Les Avellanes salt Diapir (South-Central Pyrenees, Spain) that includes both the diapir body and adjacent areas is presented to understand the diapir evolution and geometry. Structural, stratigraphical, and sedimentary data north and south of the diapir is used to infer the timing of its emplacement. The northern diapir boundary is characterized by a set of extensional faults oblique to the main Pyrenean trend, while the southern boundary is an extrusive salt sheet that overlays the late Eocene-early Oligocene sequence in three adjacent sub-basins. Salt extrusion occurred due to synorogenic folding. The topography created as salt extruded trapped the arrival of external sediments from the north, blocking the transport pathways southward. Low sedimentation rates southwards allowed for the lateral salt extrusion, advancing southwards from the feeder. The salt sheet emplacement was postdated by Oligocene conglomerates, indicating that the salt extrusion was a relatively quick event.

The South China Sea is one of the four major offshore oil and gas accumulation centers in the world. Many oil and gas fields and hydrate deposits have been found on the northern slope of the South China Sea. The amount of hydrate resources is huge. Relying on high-precision seismic exploration technology, the exploration of hydrate deposits in the South China Sea has progressed greatly in recent years, but the success rate of seismic detection technology needs to be improved. Scientific drillings have proved that there are multiple solutions to find hydrate only by identifying BSR in the stable zone, while the research on hydrate accumulation system is not deep enough, especially the migration, accumulation and dispersion system. Fractures are the main systems of hydrate accumulation and mineralization in the north of the South China Sea. In order to effectively characterize the fracture system of hydrate, this paper, combined with the successful experience of oil and gas reservoir migration and accumulation system research, applied the fracture identification technology used to study fracture channels to discover the diapir gas field to the BSR area of Qiongdongnan Basin, and successfully identified the hydrate fracture transport system. Based on the results, the migration efficiency was discussed. In the study of gas hydrate accumulation systems, the seismic characterization of fractures can be used as a means to study the transport system.

From the 1970s, the Dead Sea experienced severe halo-karstification and anthropogenic modifications. Progressively, but at an accelerating rate, subsidence, landslides, and sinkholes have increased in number and magnitude. The hazards’ triggering factors are the terminal lake level lowering at more than one meter per year and the dynamic equilibrium of the hydrogeological system. Over the Lisan peninsula, archived satellite images revealed the extent of the damaged areas. On 22 March 2000, the destruction of dike 19 represented a loss of 38 M USD. This is the most important event recorded since the beginning of the Dead Sea recession some 50 years ago. In 2018, a rehabilitation project of that dike started. This research analyses the viability of the reinstatement works. The advanced space borne radar interferometry technique is applied to map ground deformations before and during the project. This article reveals that the ongoing rehabilitation and reinstatement works of dike 19 are threatened by ongoing halo-karstification processes. Field observations and subsidence/uplift dynamics support this statement. The past experiences are taken into consideration to adapt industrial expansion strategies. However, the permeability of the salt pan floor could trigger a fast development of a karst system able to destroy the rehabilitated dike 19.

Southern Iran hosts abundant salt karst phenomena in numerous salt diapirs. This paper provides a new insight into the relationships among climate, cap soil and salt karst hydrogeology. Cave systems were documented and mapped. Soil, drip, stream, and flood waters from different environments were studied at several diapirs. It was revealed that the soil water chemistry depends on both the climate and cap soil thickness. In semi-arid climates, a thick cap soil forms (>3 m) and water has very low TDS values (0.15 g/l). In arid climates, a shallow cap soil forms, and soil water is gypsum-saturated with low dissolved halite contents. In both environments, drip waters from salt caves and springs displayed high TDS values (255 to 347 g/l). This is explained by the dissolution of halite and minor anhydrite/gypsum, a K-Mg sulfate and sylvite. Spring water plots on a local meteoric water line, whereas drips in caves have an evaporative signature. The flash flood runoff is dominated by event rain water based on isotopic data, while springs are dominantly supplied by a base flow component. The mean residence time of water on the diapirs is controlled by the cap soil thickness. Water residence times may reach several hundreds of years on a thick cap soil based on an exponential model butsoil.

The structure of the southwestern branch of the Alpine orogen is affected by the extensive Late Triassic evaporites. These evaporites have been involved in polyphased salt tectonics since the early Liassic, coeval with the Tethyan rifting, and are the décollement level for thrusts in the external parts during Alpine orogeny. The role of salt tectonics in this branch of the Alpine arc is re-evaluated in order to determine the relative importance of early deformation related to salt motion with respect to deformation related to main Alpine compressional events. This paper focuses on one structure identified as diapiric since the 1930’s: the Astoin diapir (Goguel, 1939). Analysis of geological maps together with new field work have allowed to better define diapirism in the Upper Triassic evaporites outcrops around Astoin. Study of the diapir and the surrounding depocenters reveals a major involvement of salt in the structuration of the area, since the Liassic. Several salt ridges are linked to a main diapiric structure, explaining why we call it the “diapiric complex” of Astoin. Salt tectonics was initiated during the Liassic rifting, and a few locations show evidence of reactive diapirism whereas in others evidence of passive diapirism as early as the Liassic is seen. Passive diapirism continued during the post-rift stage of Alpine margin history in the Late Jurassic and Cretaceous when an allochthonous salt sheet was emplaced. Diapirism also occurred during the Oligocene while the Alpine foreland basin was developing in this part of the European margin of the Alps. Serial interpretative cross-sections have been drawn in order to illustrate the lateral variations of diapirism and structural style. Sequential evolutions for each cross-section are proposed to reconstruct the diapiric complex evolution through time. The Astoin diapir shows a complex structural framework with an important along-strike variation of diapiric activity. Most of the geometries are inherited from salt tectonics that occurred during extension, and in some places these early structures are overprinted by Alpine compressional structures.

The diapir anticline microdepression of Ocna Şugatag underwent an accelerated transformation immediately after the end of salt mining (at the beginning of the 1960s). During this period of over 50 years of evolution, lake basins formed and disappeared, either naturally, in small sinkholes, or mostly due to the collapse of salt mine adits or chambers, which led to the creation of large-sized lake basins. There is an accelerated dynamics of these basins, as indicated by the sliding of part of the banks at a pace of 0.5-1.5 meters/year. The collapse of the mines is far from over, because the largest mines (Mihai and Dragoş) are partly affected and the pillars supporting the ceiling of the adits have a small diameter. Given the present conditions, when the underground brine is used for bathing and treatment purposes, in short time it is possible that new lakes emerge, even larger than the already existing ones. From the point of view of the lake potential, there are important differences, according to the degree of salinity of the water and the more or less accelerated dynamics of the lake basins. The latest two years witnessed an important development of the tourism infrastructure in the analysed area, as well as arrangements of the lakes, which determined a significant increase in the number of tourists searching for outdoor bathing, especially during week-ends.

Numerical solution of the Navier-Stokes equations for free and forced convection in solid and porous media is challenging as an evolution equation for pressure is lacking. An information technology is proposed on the basis of a new system of hydrodynamic equations. It provides for distinguishing between free and forced convection components and allows estimation of parameters of the cumulative convective flow by calculating values of its two components. A classical system of equations of the ellipticparabolic type is developed for solving the problems of heat and mass transfer. The system describes vortex structures which occur in the gravitational field in all media in case of density stratification. A majority of the available computation methods and schemes can be applied for numerical solutions of the proposed system; therefore modeling can be simplified, while the scope of the system’s application can be expanded. Possible applications of the proposed information technology are demonstrated by examples showing how problems of low-mantle plume and diapir formation and rifting in the lithosphere-crust system can be solved.

An integrated geologic study was performed in the Baiyun–Liwan deep water areas, Pearl River Mouth Basin, based on the achievements obtained during the past five exploration stages. The following understandings were obtained. (1) The Baiyun Sag has superior source rock conditions and has experienced three tectonic evaluation stages like rifting, rifting-depression and depression. The Wenchang–Enping Fms deposited during the rifting stage have large hydrocarbon generation potentials. During the rifting-depression and depression stages, the deposition in the study area was controlled by the Oligocene and Miocene shelf slope break zones. The Oligocene Zhuhai Fm shallow marine delta-longshore depositional system and the Miocene Zhujiang–Hanjiang Fms deep fan depositional system were formed, and they are the most favorable reservoir-caprock assemblages in the study area. (2) The Hydrocarbon accumulation pattern in the deep waters is different from that in the northern shallow waters. Shelf slope break zone, composite conduction system consisting of structural ridge, fault, sandbody, unconformity and fluid diapir as well as late tectonic movement are the three major factors controlling hydrocarbon migration and accumulation in the study area. (3) The Liwan 3-1 gas field is a typical example. The superior trapping conditions, high-quality reservoirs of delta distributary channel controlled by shelf slope break zone, vertical conduction system consisting of fault and diapir, as well as the overlying massive marine mudstone caprock provide favorable geologic conditions for the formation of large gas fields. Four areas were identified as the targets of gas exploration in the near future: the deep water fan system in the central sag, the structural-stratigraphic traps in the uplifted areas on both sides of the main sag of Baiyun, a series of large structural traps on the fault terrace to the southwest of the main sag, and the ultra-deep frontiers in sags such as Liwan to the south of the main sag.

The distribution, structure and origin of the hill range of Vaivara Sinimäed and bedrock folds are discussed. Many narrow (150–500 m), east- to northeast-trending folds with 1–10 km long axes are found in the studied area. Anticlines resulting from diapiric processes are prevailing. Cambrian clay-, silt- or sandstones are cropping out in the centre of the anticlines. Terrigenous outcrop zones are surrounded by Middle Ordovician carbonate rocks, which enabled us to use low-resistivity anomalies for tracing the distribution of the proven anticlines. The Vaivara Sinimäed, a 3.3 km long and 200–300 m wide range of three elongated hills, rise 20–50 m above the surrounding land. The tops of Tornimägi, Põrguhauamägi and Pargimägi hills are 69, 83 and 85 m a.s.l., respectively. Two saddles between the hills are on the level of 50–55 m a.s.l. Uplift of Middle Ordovician carbonate rocks at Pargimägi Hill is mostly due to the thickening of Cambrian claystone. Its core, and most likely also the cores of Tornimägi and Põrguhauamägi hills, consist of squeezed-out and folded sedimentary bedrock, diapirs, which are probably of glaciostatic origin. The dominant glaciotectonic feature is a glacial erratic. The surrounding bedrock and cores of the hills are covered with a thin blanket of Quaternary deposits: till, glaciofluvial gravel and sand, glaciolacustrine silt and clay. The Vaivara Sinimäed as a whole represent a diapir, modified by glaciers.