Central Part Of Basin Research Articles

Effects of Killari earthquake on the paleo-channel of Tirna River Basin from Central India using anisotropy of magnetic susceptibility

The Killari Earthquake (Moment magnitude 6.1) of September 30, 1993, occurred in the state of Maharashtra, India, has an epicenter (18°03′ N, 76°33′ E) located at ~ 40 km SSW of Killari Town. The ~ 125 km long basin of Tirna River, close to the Killari Town, currently occupies the area that has witnessed episodic intra-cratonic earthquakes, including the Killari Earthquake, during last 800 years. The anisotropy of magnetic susceptibility (AMS) study was performed on ~ 233 soft sedimentary core samples from six successions located in the upper to lower stream of the Tirna River basin in the present study in order to evaluate the effects of earthquake on the river flow dynamics and its future consequence. The AMS Kmax orientations of the samples from the upper reach of the river section suggest that the sedimentation in this part of the river was controlled by a N–S to NNW–SSE fluvial regime with a low or medium flow velocity. In the middle reaches of the basin, an abrupt shift in the palaeo-flow direction occurred to W–E with low velocity flow. However, a NW–SE higher palaeo-flow regime is identified in the following central part of the basin in down-stream direction, followed by a low-velocity palaeo-flow regime at the lower reach of the Tirna basin. We attribute the sudden high flow velocity regime in the central part of the river basin to an enhanced gradient of the river that resulted from the reactivation of a NW–SE fault transecting the Tirna River basin at the Killari Town. As the NW–SE faulting in regional scale is attributed as the main cause of Killari Earthquake, the reactivation of this fault, thus, could enhance the further possibility of an earthquake in near future, and hence leading to devastating flood in the almost flat-lying downstream part of the Tirna River.

Depositional environment and reservoir quality of Miocene sediments in the central part of the Nam Con Son Basin, southern Vietnam shelf

Abstract The Nam Con Son Basin is a rift basin that formed offshore southern Vietnam at the time of opening of the East Vietnam Sea (South China Sea). The Cenozoic stratigraphy in the basin is subdivided into four megasequences based on the main tectonic stages of basin evolution: syn-rift 1, inter-rift, syn-rift 2 and post-rift. This study investigates the depositional environment and reservoir quality of the Miocene sediments in the central part of the basin, and thus discusses the later part of the inter-rift, the second syn-rift and the post-rift megasequences. We focus on seismic interpretation, sediment core analysis, biostratigraphy and well-log analysis. The Lower Miocene depositional succession is dominated by stacked, coarsening-upward/progradational packages, possibly related to the interplay between high sediment supply and fluctuating sea-levels. The depositional environment is fluvio-deltaic to paralic. The Middle Miocene depositional succession is characterized by an upward deepening trend which seems related to northeast-southwest rift propagation. During this time, several intra-rift packages demonstrate increasing rift-forming activities that resulted in deposition of footwall-derived turbidite deposits in the central grabens/half grabens and non-deposition/erosion on structural highs. Shallow marine facies dominated in the west while the deep marine settings occurred in most of the eastern part of study area. Carbonate platforms were initiated and widely developed on the structural highs in the southeast and north as a result of overall marine transgression and backstepping of the clastic shoreline toward the west. The upper bounding surface of this succession is a regional unconformity marking the boundary between the syn-rift 2 and the post-rift megasequences. During the Late Miocene, deep marine facies extended across the entire study area with extensive submarine fan deposits and submarine channels downcutting W-E and S-NE, which extended across the shelf and slope. The Miocene sandstones comprise mostly fine to very fine-grained, feldspathic litharenite to lithic arkose. Deep marine turbidite sandstones of the Upper Miocene succession exhibit the best reservoir qualities (both porosity and permeability) of all the sedimentary facies examined. Paralic sandstones of the Lower Miocene succession and footwall-derived turbidite sandstones of the Middle Miocene succession have similar reservoir qualities. Relatively good reservoir quality sandstones of the Middle and Upper Miocene successions were deposited as thick massive turbidites. However, parallel-laminated turbidites and slumps/debris flows often show poor to moderate reservoir qualities. Precipitation of carbonate cement during burial diagenesis has destroyed the reservoir quality of the Miocene sandstones.

Systematic heat flow measurements across the Wagner Basin, northern Gulf of California

A primary control on the geodynamics of rifting is the thermal regime. To better understand the geodynamics of rifting in the northern Gulf of California we systematically measured heat-flow across the Wagner Basin, a tectonically active basin that lies near the southern terminus of the Cerro Prieto fault. The heat flow profile is 40 km long, has a nominal measurement spacing of ∼1 km, and is collocated with a seismic reflection profile. Heat flow measurements were made with a 6.5-m violin-bow probe. Although heat flow data were collected in shallow water, where there are significant temporal variations in bottom water temperature, we use CTD data collected over many years to correct our measurements to yield accurate values of heat flow. After correction for bottom water temperature, the mean and standard deviation of heat flow across the western, central, and eastern parts of the basin are 220 ± 60, 99 ± 14, 889 ± 419 mW m−2, respectively. Corrections for sedimentation would increase measured heat flow across the central part of basin by 40 to 60%. We interpret the relatively high heat flow and large variability on the western and eastern flanks in terms of upward fluid flow at depth below the seafloor, whereas the lower and more consistent values across the central part of the basin are suggestive of conductive heat transfer. Moreover, heat flow across the central basin is consistent with gabbroic underplating at a depth of 15 km and suggests that continental rupture here has not gone to completion.

Geofluid dynamic concept of hydrocarbon accumulation in natural reservoirs

Most modern theories axiomatically assume that hydrocarbons (HCs), which migrate in different ways from the generation zones and sources with high gradients of reduced pressures, concentrate in autochthonous natural reservoirs possessing smaller levels of reservoir energy. Hydraulic drainage of reservoirs is possible in principle through only three mechanisms: (i) horizontally oriented regional elisional water flow upwards, along the plunge of general folding from central parts of basins towards their peripheral frames; (ii) owing to the effect of lateral pressure of groundwater immediately in traps, with subsequent pushing out by high-pressure fluids supplied to the sunken parts of folds; (iii) vertically directed, from bottom to top, overflow injection mechanism. The study of their possible implementations and relative ratios in the outcome comprise the content of the proposed fluid-dynamic concept of HC accumulation.

Distribution of Clay Minerals In the Northern North Sea Basin During the Paleogene and Neogene: A Result of Source-Area Geology and Sorting Processes

Abstract: Clay-mineral compositions have been analyzed in samples from the Danish, Norwegian, British, and Dutch North Sea sectors and from onshore Denmark and Germany, comprising both wells and outcrops (clay pits and cliff sections). The time slices investigated comprise from the Paleogene, the post-Ekofisk Fm. interval of the Paleocene, the entire Eocene, and the entire Oligocene. The Neogene time slices investigated comprise the following Miocene intervals: the Vejle Fjord Fm., the Klintinghoved Fm., the Arnum Fm., and the Gram Fm. There were not enough samples from offshore wells to make a detailed stratigraphic subdivision of the Paleogene. It was, however, possible to refer Miocene samples to specific lithostratigraphic units. The onshore Danish nomenclature was applied, and seismic sections were used to correlate between wells and outcrops. Existing biostratigraphic data were used to control the stratigraphic interpretation. The distribution of the most dominant clay minerals—smectite, chlorite, kaolinite and illite—are shown on maps comprising the Paleocene, Eocene, Oligocene, and the formations Vejle Fjord Fm., Klintinghoved Fm., Arnum Fm., and Gram Fm. from the Miocene. The investigation has shown that the source-rock composition plays an important role in the clay-mineral content of the sediments. For example, smectite makes up a higher proportion in periods with substantial supply of volcanic material, especially in the Paleocene and early Eocene. In source areas, where metamorphic rocks dominate, chlorite is present in the sediment adjacent to these areas. The illite content in sediments increases where the source area is dominated by granites and/or gneisses. Sorting of the supplied suspended material generally controls the depositional area for the minerals. For example, the larger particles of kaolinite are generally more abundant in nearshore areas, whereas the relatively small smectite particles normally dominate in the central parts of the sedimentary basins. Illite and chlorite are relatively abundant in areas between those rich in smectite, present in the central part of the basin, and those rich in kaolinite, present in the marginal parts of the basin. Climatic conditions during erosion and deposition seem to play an important role, especially in the distribution of chlorite, which is rather sensitive to chemical weathering. This means that chlorite makes up a greater proportion of the sediment in periods with colder climate, such as in the Oligocene and late Miocene. The uplift of surrounding areas seems to be an important factor for the amount of detrital material transported to the North Sea. The elevation of marginal areas also played an important role in the reworking of Paleogene sediments during the Neogene. Mass flows, including turbidity currents, have redistributed marginal kaolinite-rich sediments, deposited in marginal areas of the basin, to more basin-central locations, especially in the Paleocene Viking Graben. Diagenetic modification of the originally supplied clay minerals seems to be minor since the highest contents of smectite occur in the oldest and deepest areas with more than 3 km of overburden. The reason for this is believed to be the extremely low permeability of the very fine-grained smectite-dominated clays hindering water from being expelled from the sediments, combined with low contents of K-bearing minerals necessary for the formation of illite from smectite.

Lithofacial complexes of quaternary deposits in the central and southeastern baltic sea

Geological and seismic profiling data (more than 25000 km of seismic profiles and about 1000 sediment sampling stations) collected during the last 30 yr by research vessels of the Shirshov Institute of Oceanology, Russian Academy of Sciences are summarized. Seismic records are directly correlated with sediment cores. The distribution map (scale 1 : 500000) of Quaternary lithofacial complexes corresponding to certain stages of the Baltic Sea evolution is compiled. The following four complexes are distinguished (from the base to the top): (I) moraine, with maximum thicknesses 60 and 170 m in valleys and ridges respectively: (II) varved clay of periglacial basins and from the Baltic Ice Lake (BIL), up to 25 m thick in depressions; (III) lacustrinemarine homogeneous clay with a thickness up to 4–8 m in depressions; (IV) marine sediments (mud, aleurite, coarse-grained deposits) accumulated in environments with intense bottom currents activity (thickness 2–4 m in the Gotland Basin, 4–6 m in the Gdansk Basin, and 10–20 m in fans and prodeltas). The Quaternary sequence is cut through by inherited valleys, where the thickest Holocene sediments are noted. Today, these valleys serve as routes of sediment transport to slope bases and central parts of basins. Outblows of deep gas (through faults and fractures) and diagenetic gas (from sediments) to the bottom surface also occur in the valleys. Sedimentation rates are higher in the Gdansk Basin (up to 100–120 cm/ka). Thick sand, aleurite, and mud bodies are accumulated here (about 15–20 m in the Visla River prodelta). The sedimentation rate is slower in the Gotland Basin (up to 50–60 cm/ka), where thin (2–4 m) sections of more fine-grained mud occur

Petroleum Migration Pathways and Charge Concentration: A Three-Dimensional Model

Petroleum migration pathways through a basin are determined by the three-dimensional distribution of discontinuous sealing surfaces, which are usually parallel to bedding. The petroleum migrates below the sealing surface, taking the structurally most advantageous route. The three-dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper. Application of the model to the Paris and Williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models. Pathways form a dense network overlying generating areas in the central parts of basins. Toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing-surface morphologies. Eventually, these pathways may reach the surface as seepages. It is important to integrate surface outcrops of migration routes (surface seepages) into migration modeling. Deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal, fault juxtaposition, or cross-formational seals such as salt intrusions. Deflection of pathways also occurs where there are hydrodynamic conditions in response to topography-driven groundwater flow. Zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies, or juxtaposition to nonsealing strata by faults. Vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture. Reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool. It assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion.

Iron- and manganese-rich sediments as an indicator of hot spring activities at the bottom of Lake Mashu, Japan.

Ten core samples and 78 dredge samples from Lake Mashu, a remote oligotrophic caldera lake in Hokkaido, Japan, were analyzed to reconstruct the history of hot spring activities on the lake bottom. The sedimentation rate was estimated using common tephra layers found both in Lake Mashu and in adjacent Lake Kussharo. From the depositional age of the upper common tephra (250 B.P.) obtained by 210Pb dating of the Lake Kussharo core, the sedimentation rate of Lake Mashu was calculated to range 6.4 to 7.4 mg/cm2 y. Iron and Mn that originated from hot springs on the lake bottom are oxidized in the oxic lake water to form Fe and Mn-rich layers. Iron is accumulated in the central parts of basins, whereas Mn is accumulated in relatively peripheral areas. The horizontal separation of these elements in the sediment is attributed to the difference in oxidation rate. Manganese content in pore water increases with depth at a site of Mn accumulation. This indicates that Mn is mobilized and deposited forming Mn concentrated layer just above Fe concentrated layer. X-Ray photoelectron spectroscopic examination revealed that Fe was in the form of ferric oxyhydroxide, and that Fe and Mn were concentrated on the surface of sediment particles. Annual depositional rates of Fe and Mn correspond approximately to the reported rates of supply from lake-bottom springs. Therefore Fe and Mn contents in the sediment indicate the variations in hot spring activity at the lake bottom. This activity has fluctuated in intensity over the last 700 years, but now appears to be diminishing.

Geology of the Oil and Gas Bearing Permian Formation in the Polish Lowlands

Permian rocks occur over more than 80% of the Polish territory and, in middle Poland, they occur at considerable depth, from 2 to 6 km. The Early Permian was a period of long-lasting intensive volcanic activity. The Late Permian and Zechstein began with desert deposition which was followed by evaporitic deposition of a shallow epicontinental sea. The middle Polish trough (MPT) constituted the central part of the late Permian basin and was the site of the earliest and longest deposition with the most intensive periodical subsidence not compensated by sedimentation. Subsidence rate and syndepositional faulting substantially controlled the paleogeographic pattern. The final structure of the oil and gas fields was caused by late diagenesis and Upper Cretaceous structural remodeling. The upper Rotliegendes have the biggest natural gas fields. Reservoir rocks are sandstone and sandstones interfingering with conglomerates in tectonically active zones. The most promising areas for hydrocarbon exploration are the marginal parts of the basin (UPL) and the contact zone between MPT and the adjacent platforms. In the central part of the basin, the most promising are sandstone complexes on elevated tectonic blocks. Zechstein hydrocarbon fields occur in carbonate horizons of the first three cycles (PZ1, PZ2, and PZ3). Inmore » some areas, the Zechstein limestones (Cal), constitute the natural gas reservoir. Main dolomite (Ca2), oil, gas, and condensate fields are connected with the carbonate platform or its slope. Source rocks for oil occur in the Ca2 basinal facies or in the deeper parts of the platform-type lagoons. Oil migration is short and lateral, from either the basin or lagoon, toward the carbonate platform. Gas in Ca2 derived from the sub-Zechstein basement and migrated vertically along fault zones. The most prospective areas are reservoir horizons of the carbonate platform occurring in the near source rocks. The play dolomite Ca3 is not very promising.« less

Arsenic in ground-water under oxidizing conditions, south-west United States

Concentrations of dissolved arsenic in ground-water in alluvial basins of Arizona commonly exceed 50 μg L(-1) and reach values as large as 1,300 μg L(-1). Arsenic speciation analyses show that arsenic occurs in the fully oxidized state of plus 5 (As+5), most likely in the form of HAsO4(∼2), under existing oxidizing and pH conditions. Arsenic in source areas presumably is oxidized to soluble As before transport into the basin or, if after transport, before burial. Probable sources of arsenic are the sulphide and arsenide deposits in the mineralized areas of the mountains surrounding the basins. Arsenic content of alluvial material ranged from 2 to 88 ppm. Occurrence and removal of arsenic in ground-water are related to the pH and the redox condition of the ground-water, the oxidation state of arsenic, and sorption or exchange. Within basins, dissolved arsenic correlates (P<0.01) with dissolved molybdenum, selenium, vanadium, and fluoride and with pH, suggesting sorption of negative ions. The sorption hypothesis is further supported by enrichment of teachable arsenic in the basin-fill sediments by about tenfold relative to the crustal abundance and by as much as a thousandfold relative to concentrations found in ground-water. Silicate hydrolysis reactions, as defined within the alluvial basins, under closed conditions cause increases in pH basinward and would promote desorption. Within the region, large concentrations of arsenic are commonly associated with the central parts of basins whose chemistries evolve under closed conditions. Arsenic does not correlate with dissolved iron (r = 0.09) but may be partly controlled by iron in the solid phase. High solid-phase arsenic contents were found in red clay beds. Large concentrations of arsenic also were found in water associated with red clay beds. Basins that contain the larger concentrations are bounded primarily by basalt and andesite, suggesting that the iron content as well as the arsenic content of the basin fill may play a role in the occurrence of arsenic in ground-water. Under oxidizing conditions in Arizona, arsenic in ground-water appears to be controlled in part by sorption or desorption of HAsO4(∼2) on active ferric oxyhydroxide surfaces.

West Siberian Basin: ABSTRACT

The West Siberian basin (~3.4 × 106 sq km) is one of the largest structural-sedimentary basins of the world. The basin was relatively undisturbed by post-Triassic tectonism and erosion and is little changed from its original form when Early Jurassic deposition began about 180 m.y. ago. The large Khanty structural high in the central part of the West Siberian basin is nearly 1,000 km long and 400 km wide. The axis bears five large domes, separated by depressions. The Khanty arch was a structural entity throughout the Mesozoic and is quite clearly the locus of greatest oil occurrence. Although the depositional history of the basin was one of continual incursion and retreat of the sea, three megarhythms are recognized in the sedimentary fill: Triassic-Aptian, Aptian-Oligocene, and Oligocene-Quaternary. Continental sediments predominate at the base of each megarhythm, and largely marine and nearshore sediments are present at the top. Megarhythms are made up of macro-, meso-, and microrhythms, each of which has its transgressive and regressive phases. The search for paleoshorelines and related stratigraphic traps seems to be yet in an early stage. Three major productive areas are recognized in the basin. In the west, near the Ural Mountains, oil and gas are produced from Upper Jurassic sandstones that pinch out against basement blocks. Along the middle End_Page 432------------------------------ course of the Ob River in the central part of the basin, production is largely oil from Lower Cretaceous arkosic sandstones on anticlines. Samotlor, the largest oil field in the USSR, is in this area. In the northern part of the basin, mainly gas is produced from Upper Cretaceous clastic rocks on anticlinal traps. Urengoy, the world's largest gas field, is located in this area. End_of_Article - Last_Page 433------------