Geological and structural characteristics of deep-level rock mass of the Udachnaya pipe deposit

For hard rock massifs, structural disturbance is a key indicator of mining structure stability. The presence of intersecting structural elements in the massif reduces rock strength and leads to formation of potential collapse structures. In addition to that, disjunctive deformations that penetrate rock strata serve as channels for fluid migration and connect aquifers into a single system. It was established that the largest of them –faults of east-northeastern, northeastern and northwestern directions – form the kimberlite-bearing junction of the Udachnaya pipe. These faults represent zones of increased fracturing, brecciation and tectonic foliation, distinguished from adjacent areas by increased destruction of the rock mass. Specifics of tectonic fracture distribution within structural and lithological domains are determined by the presence of multidirectional prevailing systems of tectonic fracturing, as well as by differences in their quantitative characteristics. With some exceptions, the main systems form a diagonal network of fractures (northeastern – northwestern orientation), which is typical for larger structural forms – faults. Despite the differences in dip orientation of the systems, most of them correspond to identified directions, which is typical for both kimberlites and sedimentary strata. Overall disturbance of the massif, expressed in terms of elementary block volume, reaches its peak in the western ore body. For such type of deposits, friction properties of fracture structures have average values. Consideration of geological and structural data in the design and development of new levels of the deposit will allow to maintain the necessary balance between efficiency and safety of performed operations.

Lithostratigraphic definition of the Anisian carbonate-ramp deposit of the Annaberg Formation (Middle Triassic, Northern Calcareous Alps, Austria)

Concerning the Middle Triassic stratigraphic succession of the Northern Calcareous Alps (NCA), a modern, litho- and biostratigraphic oriented evaluation of the early- and middle Anisian Annaberg Formation is presented. Due to the fact, that Middle Triassic formations are characterized by a wide distribution within the NCA, any lithostratigraphic definitions of these formations would be of great benefit for mapping geologists, engineers and hydrogeologists. The lithostratigraphic term Annaberg Formation may substitute former designations like “Alpiner Muschelkalk”, “Anisian Limestone and Dolomite” or, partly, “Gutenstein Limestone”. It is exclusively of Anisian age and earlier then the Steinalm and Reifling Formation. Mainly based on microfacies data and lithological data, we define the Annaberg Formation (former: Annaberg Limestone) as one of the most significant Middle Triassic lithostratigraphic units within the NCA. After a detailed description of the type area, findings gained in other areas of the NCA are incorporated to obtain the largest possible overview about the lithological variability and constituents of the Annaberg Formation. As a result, we can describe the Annaberg Formation as mainly organic-rich, medium bedded wackestone, containing remnants of crinoids, little bivalves and gastropods. Typically, fossil-rich layers with accumulations of bivalves and crinoids can often be observed within the Annaberg Formation. In contrast to the Gutenstein Formation no siliceous concretions or fossils (like radiolarians) appear and the fauna is in the main shallow marine. The rock-colour varies from dark- to medium-grey and the bench thicknesses are greater than within the Gutenstein Formation sensu stricto. The fossil content is also larger than in the essentially anaerobe Gutenstein Formation. With respect to the Virgloria Formation the Annaberg Formation is rather planar bedded, not so rich in bioturbation-structures and poor in silica and clay. Hence, the depositional environment of the Annaberg Formation can be described as a restricted carbonate ramp succession, with only minor water movement and separated from the open sea by a shoal with crinoid and brachiopod meadows. Breccias may be an indication for collapse-structures and slumping. In addition, knife-cavity structures (“Messerstichkalke”) indicate an occasional hypersaline environment with precipitation of evaporite-minerals like gypsum. Fossil-rich layers with accumulations of molluscs and crinoids may indicate short-term storm affected sedimentation.

Magmatic activity and hydrocarbon potential revealed by Paleozoic collapse structures in the Hangjinqi area, northern Ordos Basin, China

Collapsed reflections of lower Ordovician carbonates and upper Carboniferous-lower Permian coal-bearing strata occur below the middle Permian lower Shihezi Formation in the Hangjinqi area, northern Ordos Basin. This study takes advantage of three-dimensional seismic data, logging data, core data and well-testing data to investigate the genesis of the collapsed reflections and their implications for hydrocarbon potential. These collapse structures have a subcircular appearance in map view. The columnar reflections in the basement and the volcanic tuff in the lower Shihezi Formation around collapse structures indicate that the formation of these structures are related to magmatic activity. Most of the collapse structures terminate upward in the H1 member of the lower Shihezi Formation, which explains its greater thickness and supports the hypothesis that magmatic activity occurred during the depositional stage of the lower Shihezi Formation in the early middle Permian. The collapse structures can increase the thickness and space of the reservoirs, and the collapse of magma conduit can also increase the thickness of the regional sedimentary cap rock above the collapse structures and improve the sealing capacity of the cap rock. These results provide insights into the magmatic activity and hydrocarbon potential of Paleozoic rocks in the Ordos Basin.

The volcanic geology of Morella Crater, Ganges Cavus and Elaver Vallis, Mars

Mars contains a large number of yet unexplained collapse features, sometimes spatially linked to large outflow channels. These pits and cavi are often taken as evidence for collapse due to the release of large volumes of pressurized groundwater. One such feature, Ganges Cavus, is an extremely deep (~ 6 km) collapse structure nested on the southern rim of Morella Crater, a 78-km-diameter impact structure breached on its east side by the Elaver Vallis outflow channel. Previous workers have concluded that Ganges Cavus, and other similar collapse features in the Valles Mariners area formed due to catastrophic release of pressurized groundwater that ponded and ultimately flowed over the surface. However, in the case of Ganges Cavus and Morella Crater, I show that the groundwater hypothesis cannot adequately explain the geology. The geology of Morella Crater, Ganges Cavus and the surrounding plains including Elaver Vallis is dominantly volcanic. Morella Crater contained a large picritic to komatiitic lava lake (> 3400 km3), which may have spilled through the eastern wall of the basin. Ganges Cavus is a voluminous (> 2100 km3) collapsed caldera. Morella Crater, Ganges Cavus and Elaver Vallis illustrate a volcanic link between structural collapse, formation and potential spillover of a large lake, and erosion and transport, but in this case, the geology is volcanic from source to sink. The geologic puzzle of Morella Crater and Ganges Cavus has important implications for the origins of other collapse structures on Mars and challenges the idea of pressurized groundwater release on Mars.

Seismic stratigraphy of the Klints Bank east of Gotland (Baltic Sea): a giant drumlin sealing thermogenic hydrocarbons

This work analyses six high-resolution multi-channel seismic profiles across the Klints Bank east of Gotland. The Klints Bank consists of a drop-shaped increase of the Quaternary thickness and is oriented in an approximately north-southern direction with a length of over 50 km, a width of about 15 km and a maximum thickness of 150 m. The glacial origin of the Klints Bank can be verified with the dataset presented in this study. We classify the feature as a (giant) drumlin due to its steep up-ice and tapered down-ice face in combination with an orientation parallel to the ice-flow direction of the Weichselian glaciation. The seismic image of the internal structure of the Quaternary unit shows no uniform stratification or deformation patterns; instead, local sub-parallel reflection patterns interlayered with transparent units are observed. The averaged seismic velocity of this unit is about 2000 m/s, which is interpreted as an autochthonous deposition of glaciogenic sediments. Signs of overprinting are interpreted based on the geometry of the flanks of the structure, which appear mostly in the form of collapse structures and lifted blocks due to compressional thrust faulting. Phase-reversed events within and beneath the Quaternary are perceived as strong evidence of fluid (hydrocarbon) presence within the Klints Bank. Organically enriched Palaeozoic shales in south-easterly direction of the Klints Bank presumably give the origin of these thermogenic hydrocarbons.

From orogeny to rifting: insights from the Norwegian ‘reactivation phase’

Based on observations from the Mid-Norwegian extensional system, we describe how, when and where the post-Caledonian continental crust evolved from a context of orogenic disintegration to one of continental rifting. We highlight the importance of a deformation stage that occurred between the collapse mode and the high-angle faulting mode often associated with early rifting of continental crust. This transitional stage, which we interpret to represent the earliest stage of rifting, includes unexpected large magnitudes of crustal thinning facilitated through the reactivation and further development of inherited collapse structures, including detachment faults, shear zones and metamorphic core complexes. The reduction of the already re-equilibrated post-orogenic crust to only ~ 50% of normal thickness over large areas, and considerably less locally, during this stage shows that the common assumption of very moderate extension in the proximal margin domain may not conform to margins that developed on collapsed orogens.

A reanalysis of the collapse of the Heidegroeve: subsidence over an abandoned room and pillar mine due to previously unknown mine workings underneath

In the region of Maastricht, both in the Netherlands and in Belgium, about 400 room and pillar mines have been excavated in weak Upper-Cretaceous limestones. Pillar instability has resulted in a number of large-scale collapses and serious surface subsidence with faulting and sinkhole formation. The Heidegroeve used to be a very stable mine for more than 50 years, until pillars started to fracture and spall unexpectedly in the summer of 1987. The collapse of the abandoned mine occurred in June 1988, and was initially detected when faults and sinkholes had formed at the surface. Originally it was postulated that just creep deformation inside this mine was the main cause. However, a stability analysis revealed that all pillars inside the collapse area showed sufficient safety factors and should still be intact, while the weakest part, with several pillars of insufficient strength, had been fractured but is still standing. In the vicinity of the collapse area mines have been excavated at a lower level. Therefore it was postulated that the collapse of the Heidegroeve was related to an unknown and inaccessible continuation of these mine workings underneath. Indeed, recent, rather adventurous fieldwork revealed a downward collapse-induced fault giving access to open galleries and collapse structures about 3.5 m below the Heidegroeve. Inside the collapse area of the Heidegroeve itself, accessible through openings between the debris fragments, severe tilting of gallery floors was observed, which was probably brought about by punching of pillars of the lower mine. This case study with an unusual result shows that great care must always be taken in the analysis of the stability of mines and the assessment of the risk of surface subsidence.

A new hypothesis that contributes to the formation of cold sludge volcanoes and fluid outlets in tectonic seabed & terrestrial regions; with its helpful interpretation for time fracture sequence of fault segments.

<p>During the co-seismic development of a fault in lithological environments, regions containing cavities may form momentarily or permanently. In the tectonic shift zones, these pressure gaps lead to the formation of irregular new intermediate sediment zones, as infiltrate in to the gap, if the pressure perturbations are large. The semi-fluid sediment material and sea water enter through opening fault sector's surrounding sediments at the far place from dispersing fault energy burst. But pore water infiltration is independent about place of vomited energy burst. In some cases hard material which detached from fault wall or top sediment material, provide isolation lids, as obstacling on 'cell type empty interlaying gaps' at tectonic line. They can collapse again or stay as gap form for a long time with suction force after seismic activities by effects of gravitation or pressure perturbations. For durable gaps, pore water is capable to infiltrate in to the gap with long lasting suction forces.  In these regions, in contrast to gravitational folding or collapse structures, the partial sediment sequence may be drawn and folded into the area of the material with different or close lithological density value. Deformational variety of the displaced materials are related with physical properties of seismic event at opening sector such as friction, displacement parameters (velocity, time), dimensional parameters of gap, and water depth.  The main objective of the paper is to figure out all interference mechanisms about these zones (created by pressure perturbations), which develop rapidly during earthquake fractures (or in some cases fractures generated by impulsive pressure changes such as those created by volcanoes). Fracture of fault segments forms a complex mechanical system associated with bedrock, upper sedimentary sequence, and aquatic environment, depending on the location where they occur, even the atmosphere. Therefore, the displacement may be bi-directional to the lower slit or upward from the seabed during the opening or closing stages of the cavity, depending on the nature with variations of the atmosphere & water-sediment mixture. The strong (pulling or impulsive) pressure perturbation effect associated with permanent cavities caused by rapid breakage pulls the material that may form a sludge volcano or water outlet under deformation and brings the environment to near pressure equilibrium. This simple explanation can help to find real additional effective reason for the different formations of assumed collapse or folding structures created by gravitational movements in geology. The hypothesis after main objective at above mentioned in this article is based on the fact that the emergence of  escapes as squeezed fluid form  of water & sediment from compacted secondary irregularities in the previously broken fault segment will help to understand the next seismic mobility in other tectonic segments by identifying source depth cues through physical and chemical analysis. Geophysical instrumentation and applications are still need further developments of compact reflection line information, because the vertical thin anomalies mentioned in this paper are the most difficult structures for detection.</p>