Tuffaceous Sand Research Articles

Landslide Potential in Cihanjuang, Cimanggung, Sumedang, West Java Province

Landslides occurred in the Cihanjuang area, Cimanggung, Sumedang Regency, West Java on January, 9th 2021 with 40 fatalities and several buildings severely damaged. This area is in the form of hills with a fairly steep slope and housing is built on it. Geologically, the research area is composed of Undecomposed Young Volcanoes (Qyu) in the form of tuffaceous sand, lapilli, breccias, lava, and agglomerates. The research aims to determine the potential and volume of landslides. The research method used is conducting geotechnical testing and carrying out topographical mapping. Geotechnical tests carried out were water content, specific gravity, sieve analysis, hydrometer, and direct shear strength. The geotechnical test results showed that water content: 16.37% – 31.26%, cohesion: 59.2 kPa – 112.7 kPa, and internal friction angle: 6.30° – 30.50°, percentage of gravel and sand 11.10 % – 34.90 %, percentage of silt and clay 65.10 % – 88.90 %. According to USCS, this soil sample includes the MH-CH-OH classification Topographical mapping was carried out covering an area of 7.006 hectares. The internal friction angle is relatively steep, and the percentage of gravel and sand is quite high, so water infiltration becomes easy, so the Cimanggung area has a high potential for landslides. From the topographic mapping, the volume of the landslide was around 161.981 m³. To maintain slope stability and avoid landslides, apart from planting strong-rooted plants in areas with high elevations, they also manage the drainage by making waterways on the northwest and southeast sides of the steep slopes to the main road.

A COMBINED METHOD OF 1D AND 2D RESISTIVITY FOR GROUNDWATER LAYER ESTIMATION AT A FARMING AREA IN REJOMULYO VILLAGE

The groundwater depends on when it is available, more in the rainy and less in the dry seasons. Fluctuation in water availability is a significant problem in activities continuously requiring large amounts of water, such as agriculture. Hence, it is necessary to increase the number of water resources to meet the community's needs. Therefore, the groundwater layer zone was estimated as an initial study at the dry farmland in Rejomulyo village, Jati Agung district, South Lampung, using a combined method between the 1D resistivity method of the Schlumberger array and the 2D form of the Wenner configuration. Each sounding point and the 2D line have a maximum stretch length of 300 m. The 1D outcome correlates to the 2D data processing result to produce a subsurface lithology model. As a result, the research area has three primary layers with three rock types. The first layer has a resistivity value of less than 20 Ωm and is identified as tuffaceous clay. Then the second layer with a resistivity range of 60–66 Ωm is tuffaceous sand, this rock which is referred to as the groundwater layer with a depth of 11-40 m. The last layer has a high resistivity value of 120–141 Ωm as tuff. Based on the results of 3D visualization, the groundwater layer in the study area spreads to the southeast with a confined aquifer type. This targeted rock layer can be utilized for groundwater production.

Identification of the Aquifer Layer using the Geoelectric Method in Teupin Batee Village, Aceh Besar

The need for clean water around the world is related to the increasing population, especially in Teupin Batee Village, Aceh Besar District. In addition to surface water, groundwater is one of the potentials that can be utilized by the community, particularly for household needs. The purpose of this study is to identify the aquifer layer using the geoelectric method. One of the geophysical methods that can be used to map groundwater potential is the geoelectrical method based on the resistivity value of subsurface rocks. This study uses the Wenner-Schlumberger array because it can map subsurface structures both vertically and horizontally. From the results of the study, it was found that there are four different layers in this research area including, the top soil layer, hard rock, tuffaceous sand and sand layer as aquifer layer. The top soil layer is mixed with tuff, sand and volcanic breccia to a depth of 8 m with a resistivity value of 5-25 ?m. The Hard rock layer is at a depth of 8 m – 30 m with a resistivity value of 45-220 ?m. The tuffaceous sand layer has a resistivity value ranging from 25-55 ?m. While the sand layer or aquifer is at a depth of 10 m – 60 m with a resistivity value of <10 ?m which is separated by a layer of tuffaceous sand between the two aquifer layers.

Provenance and compositional variations of intra-caldera lake sediments at La Primavera, Jalisco, Western Mexico

The multi-proxy provenance analyses carried out in the Upper Pleistocene sediments of the La Primavera intra-caldera paleolake in western Mexico document the evolution of source areas. This lake formed a few thousand years after the caldera collapse (~95 ka) and lasted until the intra-caldera resurgence process that ended 75 ka ago. Between 93.8 and 71 ka the sedimentary succession that filled the lake was affected by the extrusion of domes at its central part and the constant influx of volcaniclastic debris. Ring-fault domes and extra-caldera activity sourced at San Miguel volcano provided additional volcanic debris into the lake. Based on our multi-proxy studies and recent age determinations of the post-caldera activity is likely that the paleolake was coggled at 78 ka in the central sector of the caldera, synchronously with the caldera resurgence. The resulting deposits (volcaniclastic debris) are tuffaceous sands characterized by lithoarenites rich in neo-volcanic grains, mainly vitrophyric and felsitic volcanic fragments with similar characteristics to the rocks of the Ixtahuantonte, El Nejahuete composite dome, Cerro Alto, Las Pilas, and Dos Coyotes domes. Geochemically, the sediments of the La Primavera caldera exhibit concentrations and elemental relationships of major and trace elements similar to the average of the upper continental crust. However, the high concentrations of some elements, such as La, Th, Ti, and Zr are related to the hyperalkaline nature of the magmatism that originated this volcanic caldera. The concentrations of SiO2/Al2O3, Na2O/K2O, Th, Sc, and Zr/10 indicate a passive margin tectonic setting deposition under low weathering conditions.

Fossil fish otoliths from the Chibanian Miyata Formation, Kanagawa Prefecture, Japan, with comments on the paleoenvironment

The Paleo-Tokyo Bay (Kanto Plateau) that persisted during the transgression periods in the Middle-Late Pleistocene is known for its rich marine fauna that accommodated both the warm and cold water taxa brought by the Kuroshio and Oyashio Currents, respectively. However, little is known on the paleoichthyofauna in this area and the processes shaping the marine ichthyofauna of modern southern Kanto. We used fossil fish otoliths and teeth discovered in the Sha’ana Tuffaceous Sand Member belonging to the Chibanian Miyata Formation, exposed at Sha’ana-dai, Miura City, Kanagawa Prefecture, Japan, to reconstruct the paleoichthyofauna and its associated paleoenvironment and explore the content of fish assemblages during this period. The Sha’ana Tuffaceous Sand Member was composed of upper sandy mud and lower muddy sand horizons at the exposure. A total of 1,675 fish remains were collected from this site, of which 1,389 were assigned to 62 distinct taxa (20 orders, 31 families). The taxonomic composition revealed taxa from various environments, including shallow continental shelf, epi- to meso-pelagic settings, and the majority were from a generally temperate climatic zone. Paleoenvironmental analyses suggested that the fish assemblages were from the continental shelf (approximate depth of 100–200 m) in a temperate sea where both warm Kuroshio and cold Oyashio Currents had an influence on the biota. The analysis also showed that two boreal fishes, namely Clupea pallasii and Theragra chalcogramma, once had a wider distribution that extended to the southwestern areas of the Paleo-Tokyo Bay. This study provides a more complete view of the related paleobiogeography of marine fishes during the Chibanian and is essential for reconstructing the evolutionary processes of the rich ichthyofauna in the southern Kanto.

Geochemical Evolution and Groundwater Flow System in Batujajar Groundwater Basin Area, West Java, Indonesia

DOI:10.17014/ijog.7.1.87-104Batujajar and its surrounding areas, situated in the west of the Bandung Basin, are geologically composed of various Tertiary rock formations with complex fold and fault systems. Springs and drilled wells in sandstone aquifers, tuffaceous sand, and tuffaceous breccias mark the development of their aquifer systems. This study aimed to determine the characteristics of the hydrogeochemistry by analyzing major ions and stable isotopes (18O and 2H) of thirty-four hydrogeological objects. The groundwater flow pattern in this area is controlled by northwest-southeast lineament, as indicated by the emergence of springs along the transition zone between areas with high and low lineament density. In order of dominance, the groundwater facies are as follows:Ca-Mg-HCO3>Ca-HCO3>Ca-Na-Mg-HCO3>Na-Ca-HCO3. Hydrochemical evolutions were detected from the change of cations from Ca2+ to Mg2+ and then Na+, and this is believed to be the product of cation exchange and dissolution of silicate minerals. However, evolutions toward anion changes were not apparent yet, meaning that HCO3- ions still prevail, or in other words the groundwater flow system is local. Nevertheless, the geological and hydrogeochemical analyses, along with the relative compositions of stable isotopes, revealed that the groundwater had three systems, namely shallow, intermediate, and deep groundwater flows; all of which were segmented in three subgroundwater basins (Sub-GWB). Aquifer systems with shallow to intermediate groundwater flow were found in Sub-GWB-A, Sub-GWB-B, and Sub-GWB-C, while the other ones with deep groundwater flow system were identified in Sub-GWB-B and Sub-GWB-C.Fracture system has an important role as a connector between recharge system in hilly areas and discharge system in plain areas.

Erodibility Factor in Weathered Volcanic Rock in Jatinangor, West Java, Indonesia

A regional development will decrease the open green space that will affect the less water infiltration during the rainy season and causing the high intensity of the erosion rate. Jatinangor is a well-known new satellite city that located in undulating volcanic hills as the part of the Southeast Mt Manglayang. This area has been degraded from agricultural land into the residential and educational area. This study aims to determine the erodibility factor potential as one of the important factors to an erosion prediction. The data were obtained by collecting several undisturbed samples and tested the grain size and hydrometer analysis, atteberg limit test to know the grain size distribution. This result showed that Jatinangor Area has a high potential value of erodibility that caused by the silt domination and Ilite clay mineral that potential to swelling. The high erodibility values are affected by volcanic material as the parent rock that consists of Tuff, Lapilli Tuff, Grain supported and matrix supported Breccia with Plagioclase and K-Feldspar percentage 15-35%. Whereas the low erodibility value in the higher clay soil percentage is affected by the less percentage of plagioclase and K-fledspar, and the Tuffaceous sand matrix that difficult to erodible. The conservations are needed to decrease the erodibility effect and minimize the erosion rate annual.

Geoelectricity Data Analysis For Identification The Aquifer Configuration In Bandorasawetan, Cilimus, Kuningan, West Java Province

Indonesian water consumption is influenced by the people growth. One of Water consumption fulfilment by groundwater aquifer. Bandorasawetan is one of the areas which predicted have proper potential due to located in East of Mt. Ceremai that predicted recharge area. Based on regional geological data, Bandorasawetan is an undifferentiated young volcanic product which consists of lava, breccia, lapilli, and tuffaceous sand. Geophysics method for groundwater prediction is 2-D geoelectrical with Wenner – Schlumberger configuration. The result of acquisition is obtained resistivity value from 0 - >1000 Ohm. m. Interpretation from data distribution is consist of two resistivity range that describes lithology on the research area, such as: 0 – 150 Ohm.m contributed as aquiqlud with tuffaceous sand lithology and > 150 Ohm.m interpreted as volcanic breccia lithology. Volcanic breccia has a role as aquifer in study area, the conclusion is distribution of resistivity value with range > 150 Ohm.m be the reference to developing groundwater resource in study area. Depth of aquifer is varying, deeper to the east. In Line – 1, depth of the aquifer is 48 meters and in Line – 2, depth of aquifer be 60 meters.

Surface Rupture and Geotechnical Features of The July 2, 2013 Tanah Gayo Earthquake

DOI:10.17014/ijog.3.2.95-105An assessment of surface rupture and collateral ground failures can help to evaluate the impact of future earthquakes. This paper presents the results of a field survey conducted to map the surface rupture and geotechnical phenomena associated with the ground shaking during the July 2, 2013 earthquakes in Tanah Gayo Highland. The objectives of this survey are to document and to characterize the surface ruptures as well as to identify types of earthquake-induced ground failures. Results of the survey identified four best sites of possible surface rupture. Two locations are obvious surface ruptures that can be traced on primary topographic feature of the active fault segment from the north to the south, crossing Pantan Terong Hill. The fault segment has a total mapped length of 19 km, with WNW trending zone and a dextral rupture offset. The ground shaking also resulted in landslides and liquefaction in areas underlain by very fine-grained tuffaceous sands. Based on the field survey, it can be concluded that the newly defined active fault segment, the Pantan Terong segment, is likely the segment that ruptured at the July 2, 2013 Tanah Gayo earthquake. Due to the soil types and unstable rocky slopes in the hilly Central Aceh region, large-scale landslides are primary risks during an earthquake event in this region.

TECHNOLOGY AND THE PROPERTIES OF THE FIRE-RETARDANT FIBROGIPSOVERMIKULITOBETONNYKH COMPOSITES WITH THE APPLICATION OF THE VOLCANIC ROCKS

Fire-retardant composites with the application of gypsum, unslaked lime, distended vermiculite, tuffaceous sand, basaltic fibers and resin of wood of that saponified are developed. The methods of the preparation of fire-retardant mixture and molding of articles made of the composites are investigated. Are given the results of experimental and theoretical studies of the fire resistance of armotsementnykh elements with the fire-retardant layer from the gipsovermikulitotufobetonnykh and fibrogipsovermikulitotufobetonnykh composites.

Pliocene sinistral slip across the Adobe Hills, eastern California–western Nevada: Kinematics of fault slip transfer across the Mina deflection

The Adobe Hills region (California and Nevada, USA) is a faulted volcanic field located within the western Mina deflection, a right-stepping zone of faults that connects the northern Eastern California shear zone (ECSZ) to the south with the Walker Lane belt (WLB) to the north. New detailed geologic mapping, structural studies, and 40 Ar/ 39 Ar geochronology in the Adobe Hills allow us to calculate fault slip rates and test predictions for the kinematics of fault slip transfer into the Mina deflection. The Adobe Hills are dominated by Pliocene tuffaceous sandstone, basaltic lavas that yield 40 Ar/ 39 Ar ages between 3.13 ± 0.02 and 3.43 ± 0.01 Ma, and basaltic cinder cones. These Pliocene units unconformably overlie Middle Miocene latite ignimbrite that yields an 40 Ar/ 39 Ar age of 11.17 ± 0.04 Ma, and Quaternary tuffaceous sands, alluvium, and lacustrine deposits cap the sequence. Northwest-striking normal faults, west-northwest–striking dextral faults, and northeast-striking sinistral faults cut all units; the northeast-striking sinistral faults are the youngest and most well developed fault set. We calculate ∼0.1 mm/yr of approximately east-west horizontal extension and northwest dextral shear since the Pliocene. The prominent northeast-striking sinistral faults offset basalt ridgelines, normal fault–hanging-wall intersections, a channelized basalt flow, a basalt flow edge, and a basalt flow contact a net minimum of 921 ± 184 to 1318 ± 264 m across the Adobe Hills. These measured sinistral offsets yield a minimum Pliocene sinistral fault slip rate of 0.2–0.5 mm/yr; our preferred minimum slip rate is 0.4–0.5 mm/yr. The geometry and orientation of the prominent sinistral faults are consistent with simple shear/couple clockwise block rotation within a broad dextral shear zone. Vertical axis block rotation data are needed to test this interpretation. We propose that a set of faults subparallel to Sierra Nevada–North America motion and associated releasing steps, located west of the White Mountains fault zone and east of the Long Valley Caldera, transfer a portion of dextral Owens Valley fault slip northwestward onto the sinistral faults in the Adobe Hills. Dextral slip distributed across faults between the White Mountains fault zone and the Sierra Nevada and east of the Fish Lake Valley fault zone may account for the apparent discrepancy between summed long-term geologic slip rates and present-day geodetic rates across the northern ECSZ. Fault slip in the Adobe Hills is part of a regional pattern of initiation and renewal of dextral, sinistral, and normal fault slip during the Pliocene that extends from lat ∼40°N to ∼36°N within the ECSZ-WLB and along the western margin of the Basin and Range Province. This regional deformation episode may be related to changes in gravitational potential energy.

The Baer Depression Tuffaceous Sandstone Reservoir Characteristics and Logging Response Research Status, Problems

In logging field, saturation evaluation in tuffaceous sandstone reservoirs has been a difficult issue to be solved urgently. It is mainly due to the effect of complex pore structures in tuffaceous sandstone reservoirs. Compared with the normal sandstones, the tuffaceous sands have the properties of diversity origination, complex mineral components, easily transformed mineral, complex digenesis and porosity evolution .The comprehensive analyses of cores, thin slices, SEM, mercury-injection data and former research outcome of Beier oilfield on the porous structure and reservoir physical property of sandstones. The tuffaceous alteration is different under different burial phase and diagenetic environment and has different effects on the porosity of coarse grain have a constructive affection to the secondary porosity.

Fossilization Type of Elephas hysudrindicus from Blora on the Basis of Petrographic and Scanning Electron Microscopic Analyses

DOI: 10.17014/ijog.v6i2.117Either fossils of the hominid or vertebrate have long been known from terraces along the Solo River in Central and East Java. Most terraces consist of andesitic sand to andesitic tuffaceous sand with either gravelpebble or conglomerate and some of them contain vertebrate fossils. It is in this place, an ancient elephant fossil named Elephas hysudrindicus was discovered in 2009. This fossil was discovered at an abandoned sand quarry of Sunggun area, Medalem Village, Kradenan Subregency, Blora Regency which and can be mentioned as a great event for the Geological Museum. It was said as a phenomenal discovery, because the fossil was found within the terrace with condition of nearly complete skeleton of an individual elephant. Some bone fragments of Elephas hysudrindicus fossil is treated as rock specimens because a number of minerals fill in either pore spaces or cavities or cracks within bones, and such infilling minerals can be observed in cut sections of the bones. Main goals of the study are to determine the distribution and type of minerals within the bones, interpret environment of deposition, and identify fossilization type. The methodology used in this study consists of petrographic and Scanning Electron Microscopic (SEM) analyses. Based on the petrographical observation, some bone specimens of Elephas hysudrindicus fossil are characterized by fibrous and porous feature with cracks occuring locally. Whilst, examination with SEM shows that the bone specimens are apparently composed of collophane or massive cryptocrystalline variety of apatite as the principal component of fossil bone, having physical characteristic of spheroidal structure and cavities of 100 to 1500 micron (μ) in diameter. Most cavities and pore spaces are predominantly filled in by either authigenic crystals of rhombohedral calcite and lesser pseudohexagonal kaolinite with either slightly minerals of manganese oxide or iron oxide or ilmenite, including oxidized kaolinite and calcium iron silicate. Impregnation during diagenesis may be the most appropriate expression for fossilization process of the Elephas hysudrindicus. It is indicated by the existing authigenic minerals within the bones cavities, pore spaces, and cracks which are possibly due to precipitation of mineralized fluids originated from groundwater within the terrace.

坑井データを用いたアスファルテン析出挙動の推定

The Minami Kuwayama oil field is located 2 km to the northwest of Gosen city, Niigata prefecture. The reservoir depth is at 3,000-3,500m, formed out of tuffaceous sands. Soon after the field discovery in 2003, early commercial production was started. In this field, it is thought that asphaltenes have been deposited in the reservoir since the early production period, while asphaltane deposition trouble arises generally in surface facilities or wellbore tubing. Costly chemical treatments, such as solvent injection into the reservoir, have been applied several times. However, it is found that effects of the treatment do not last long, i.e. any permanent solutions are necessary to develop this field efficiently.In the first step for the solution, laboratory experiments and reservoir simulations were carried out. In the laboratory experiments, it was found that asphaltenes were precipitated in the reservoir condition and its size was large enough to plug the pore space. Reservoir simulations suggested that the decline of production was due to the asphaltene deposition by taking into account the asphaltene precipitation and deposition process.

Mineralisasi pada batuan induk batugamping di daerah Lepadi, Dompu, Nusa Tenggara Barat

http://dx.doi.org/10.17014/ijog.vol3no3.20086Lepadi area situated in the Regency of Dompu, West Nusa Tenggara, is occupied by limestone unit comprising limestone and sandy limestones; and sandstones which are occasionally found as lenses within units of tuffaceous sand and tuff breccia. Indication of metallic mineralization is shown by the occurrence of the base metal-bearing quartz veins penetrating a host rock of limestone. A pervasive hydrothermal alteration was formed as chlorite-calcite- muskovite/sericite-quartz and kaolinite/haloysite series with veins consisting of massive quartz veinlets (millimeter to 2.0 cm maximum width) and very thick vuggy quartz veins (± 3.2 m width). The first quartz type contains ore minerals such as galena, sphalerite, chalcopyrite, pyrite and iron oxide; whilst the second type has a predominant galena content with an association of, chalcopyrite, covelite, pyrite and iron oxide which occurred as tiny vugs filling and distributed sporadically within the quartz body. The result of studies by using microscope (petrography and mineragraphy), infra-red analysis (PIMA), chemical analysis and fluid inclusion on entirely altered rock/ore mineral/quartz vein samples reveals that the alteration and mineralization processes might occur in a mineralization system involving hydrothermal fluid of near neutral at the temperature ranging from 275º - 200oC. It brings to a suggestion that deposition of quartz veins and associated ore minerals has taken place in a depth ranging from 620 – 150 m beneath paleosurface. It is based on hydrothermal fluid’s salinity ranging from 1.2 – 2.2 equivalent wt.% NaCl de- tected from fluid inclusion within quartz crystal samples.

Taphonomy of the fossil hominid bones from the Acheulean site of Castel di Guido near Rome, Italy

Castel di Guido near Rome is one of the few open air Middle Pleistocene European sites that has yielded hominid skeletal remains associated with fossil fauna and Acheulean implements. The fossil hominid bones include two femoral shafts, respectively designated Castel di Guido-1 (CdG-1) and CdG-2, an occipital fragment (CdG-3), a right maxilla lacking teeth (CdG-4), a portion of right parietal (CdG-5), a right temporal (CdG-6), and a fragment of left parietal vault (CdG-7). CdG-1 through CdG-4 were collected in 1979–1982 on the surface, together with fossil fauna, where ploughing incised fossiliferous tuffaceous sands. Excavations conducted in the same area from 1980 to 1990 led to the discovery of CdG-5, CdG-6 and CdG-7 within the tuffaceous sands, which were shown to overlay a bone-bearing paleosurface, with abundant evidence of hominid activities. The Castel di Guido hominid assemblage poses intriguing taphonomic questions. The analysis of the physical evidence offered by the bone surfaces, reported in the present study, indicates that the hominid skeletal remains were heavily fragmented before fossilization and exposed to carnivores and rodents, as well as to trampling and/or friction in abrasive sediment. Although definitive conclusions cannot be reached on the basis of the available evidene, it is possible that clusters of incisions localized on specific regions of the Castel di Guido fossil hominid bones might reflect deliberate human manipulations.

Quaternary faulting history along the Deep Springs fault, California

New geologic mapping, structural studies, geochronology, and diffusion erosion modeling along the Deep Springs fault, California, shed light on its Quaternary faulting history. The Deep Springs fault, a 26km-long, predominantly north-northeaststriking, west-northwestdipping normal fault bounding the eastern side of Deep Springs Valley, cuts Jurassic batholithic rocks nonconformably overlain by middle Miocene to Pleistocene stream gravels, coarse-grained sand, tuffaceous sand, unwelded to partially welded tuff, and Bishop ash, as well as Quaternary coarse- to finegrained alluvial fan deposits. The 40 Ar/ 39 Ar geochronology yields ages of 3.09 0.08 Ma for the unwelded tuff and 753 4k a for the Bishop ash. Holocene debris flows, a landslide, and recent alluvium bury the youngest fault scarp. The Deep Springs fault is characterized by multiple fault planes and fault scarps that become progressively younger toward the basin. The dip of the fault plane varies from 20 to 87 and fault-plane and striation measurements indicate an average orientation of N23E, 47NW, and N77E, 49SW, respectively. The offset of Bishop ash and underlying tuff across the Deep Springs fault indicates horizontal extension and vertical slip rates of 0.7 and 0.9 mm/yr, respectively, since the eruption of the Bishop Tuff, and 0.2 and 0.2 mm/yr, respectively, since the eruption of the unwelded tuff. If the vertical slip rate since the eruption of the Bishop Tuff has remained constant through time, then slip along the Deep Springs fault began ca. 1.7 Ma. Younger fault scarps to the west of the bedrock fault cut Quaternary deposits; scarp offset ranges from 0.8 to 17.5 m and scarp slope angle ranges from 8 to 37. Topographic profiling of the smallest, least eroded fault scarps, with an average surface offset of 2.7 m, indicates that these scarps developed as the result of a single earthquake and ruptured an 20km-long segment of the fault. Radiocarbon analyses on detrital charcoal, located in the footwall block of one of these scarps, yield an age of 1.960 0.055 ka. Diffusion erosion modeling of these fault scarps yields an elapsed time of 1.7 0.5 k.y. since these fault scarps formed. Making reasonable assumptions about the depth of this earthquake and shear modulus, we estimate a moment magnitude, MW 7.0, for this earthquake. The Deep Springs fault is one of several displacement-transfer normal faults that define a zone of distributed deformation between subparallel right-lateral strike-slip faults east of the Sierra Nevada that make up the northern part of the eastern California shear zone. The young age and recent earthquake activity along the Deep Springs fault are consistent with a model proposed for the kinematic evolution of this part of the eastern California shear zone.

NMR as Standard Porosity Tool in the San Jorge Basin: Log Responses and Applications

Summary This paper describes our experience with nuclear magnetic resonance (NMR) logs since their introduction in the San Jorge basin in June 1995. To date, more than 400 logs have been run by Western Atlas and Schlumberger using Numar's magnetic resonance imaging tool (MRIL) and combinable magnetic resonance (CMR) tools, respectively, and more than 2,000 zones have been perforated and tested. This has allowed us to characterize the response of the tools in shaly and tuffaceous sands, compare the response of the Numar and Schlumberger tools with each other and with cores, detect the limitations of present tool designs, and relate NMR pore-size distribution and permeability to oil production.

Sedimentation and basin evolution in the Paleogene of the Northern North Sea and Faeroe–Shetland basins

Thermal uplift of northern Britain during the Paleogene converted the Northern North Sea and Faeroe-Shetland areas from deep, sediment-starved basins into areas dominated by coarse clastic submarine fan and deltaic sedimentation. The uplift resulted from the initiation of a thermal plume which affected much of Greenland, western Norway and northern Britain in the Paleogene and which continues today, its axis lying under Iceland. The volume and grain size of the clastic input increased during the Paleocene as the source area was uplifted. This uplift reached a peak in the mid-Thanetian (late Paleocene) when large volumes of coarse clastic sediment poured east into the Northern North Sea Basin and northwest into the Faeroe–Shetland basin to accumulate as basin floor fans. Hebridean volcanism also peaked at this time, supplying tuffaceous sands which are found in both basins, as well as lavas which erupted over much of the area between the Hebrides and the Faeroes. The basin edges acted as bypass zones, sediments being only temporarily dumped on delta slopes before failure transported them basinward in turbidity currents. Thus the fluvial input was not significantly reworked and the fans developed as mixed sand–mud systems. By the late Thanetian, fan sedimentation had shallowed the basins sufficiently for deltas to prograde seawards. Small fans lay at the foot of these deltas and coal swamps developed on the delta plains. Sedimentation almost completely filled the relatively small Faeroe–Shetland Basin. In the early Ypresian (earliest Eocene) volcanism became concentrated along the rift northwest of . . .

Palynological and petrological characterization of a North Sea Palaeocene volcaniclastic sequence

A short cored borehole (82/15) drilled by the British Geological Survey in the Inner Moray Firth Basin, North Sea, penetrated a thin lignite overlain by a volcaniclastic unit. The terrestrially sourced Late Palaeocene palynoflora of the lignite is comparable to those recovered from the Thanet Beds of southern England and to the intrabasaltic sediments of Ardnamurchan, Scotland. Petrological analysis of the volcanics enables a close comparison to be made to the MORB-type Preshal Mhor basalts of Skye and the tuffaceous sands of the uppermost Andrew Formation of the Outer Moray Firth Basin. Palynological analysis of samples from the uppermost Andrew Formation of the Outer Moray Firth Basin and Viking Graben confirms the comparison.