Deep-seated Fault System Research Articles

Source rock potential, main depocenters, and CO2 occurrence in the pre-salt section of Santos Basin, southeast Brazil

The absence of expressive hydrocarbon columns and high CO2 content observed in the pre-salt of Santos Basin reservoirs over the last decade reveal the risk of hydrocarbon charge and contamination to be a relevant concern in exploration activities in the basin. Therefore, this study was focused on elucidation of the source potential, basin depocenters, and CO2 occurrence in the pre-salt of the Santos Basin, aimed at reducing risk of upcoming exploration activities. Based on geochemical analysis, our study revealed that Late Barremian-Early Aptian fine-grained rock intervals, rich in organic matter, from the Itapema Formation and secondarily, from the Piçarras Formation, are likely the main source rocks of the Santos Basin. Seismic interpretation revealed five wide pre-salt depocenters. The Main Depocenter, followed by the Central and North depocenters, could be the major hydrocarbon sources for pre-salt reservoirs. Based on the CO2 distribution data, low amounts of the contaminant (under 5%) were detected in the post-salt and proximal pre-salt reservoirs, with intermediate values (from 10 to 50%) in the main pre-salt accumulations. High CO2 amounts (over 50%) were encountered mainly in a northeast to southwest trend, linking Peroba-Júpiter-Libra areas, and could be related to a deep-seated fault system associated with mantle contamination.Accordingly, the northern and central parts of the Central Santos sub-basin have a low risk of hydrocarbon charge and contamination, whereas its eastern portion has a high risk because of the absence of an expressive hydrocarbon column and elevated CO2 content. The Southwest Santos sub-basin presented a high risk for pre-salt discoveries because of salt windows which limit the top seal for pre-salt-sourced hydrocarbons. In the Southeast Santos sub-basin, the risk of hydrocarbon charge and contamination is significant because of the absence of mapped depocenters and its location on a crustal domain favorable to mantle CO2 access.

From hot to cold? – Hydrothermal activities as a source for icy-debris flows on Dryas Mons, Terra Sirenum, Mars

During an extensive grid-mapping campaign on Mars' southern hemisphere, we have detected so-called sheet flow deposits, which are defined by distinctive lobate fronts, thin and mostly planar layers, and faint sub-parallel surface lineations. They originate from the high plains of Dryas Mons, a large massif of impact and tectonic origin, and follow the topographic gradient down into the adjacent basins. Their sources often coincide with steep and multi-layered outcrops. This work addresses the formation of these deposits, and if they are related to the unique tectonic and endogenic environment of Dryas Mons. We applied photogeological mapping, age determinations by crater counts, as well as topographic and heat flow measurements in order to reconstruct the evolution of these landforms. The calculated ages (mid to late Amazonian), their location in the mid-latitudes, as well as some specific morphologies like lobate flow fronts are typical for standard viscous-flow features on Mars. In contrast to such viscous-flow features, the sheet flow deposits occur isolated in the Dryas Mons region. Aside from that, major other landforms, typical for viscous-flow features are lacking, like sublimation pits, brain terrain or arcuate deformations. Considering these similarities and differences, we suggest that both landforms viscous-flow features and the sheet flow deposits of Dryas Mons were formed by the involvement of volatiles; however, at varying amounts and by different emplacement processes. As the formation of the sheet flow deposits is located in an area with one of the highest heat flow values planet-wide, we calculated if the heat flow could be a potential trigger for the release of outcropping volatile-rich layers. However, our calculations have shown that the heat flow is still insufficient to enable near-surface melting. Instead, we suggest that the volatiles originate from deep layers affected by magmatic and/or intrusive activities in a tectonically active environment. These conditions led to melting and mobilisation of the volatiles by advective hydrothermal processes. Thus, the volatiles migrated upward along hypothesized deep-seated fault systems, formed by Noachian/Hesperian impacts and tectonic activities, until they reached conductive layers outcropping at Dryas Mons, enabling them to drain. After their release to the cold Amazonian atmosphere, this mixture of volatiles and solids partially froze, resulting in a comparatively high viscosity, and hence, a slow and laminar (non-turbulent) movement. This flow behaviour might have led to the formation of the lineations at their surface along shear zones. Hence, we suggest that the sheet flow deposits may have originally formed as slowly moving icy debris flows during the mid- to late Amazonian.

A geochemical comparison between volcanic and non-volcanic hot springs from East Malaysia: Implications for their origin and geothermometry

• Non-volcanic hot springs are K-Na-bicarbonate rich waters with low SO 4 contents. • Volcanic hot springs are neutral chloride waters with high SO 4 contents. • Radioactivity of granites is the main heat source for non-volcanic hot springs. • Volcanic activity is the main heat source for volcanic hot springs. • Hot springs show intermediate to high enthalpy with potential energy generation. Sources of volcanic and non-volcanic thermal sources have been studied in East Malaysia to differentiate their geothermal reservoir temperatures and first-ever reports on its geochemical processes that affect the evolution of the constituents of thermal groundwater subsurface circulation. The study of geothermal potentials includes indices of geochemistry, geothermometry, and mineral saturation. The surface temperatures of thermal springs range from 27 to 56 °C, and the pH values range from 5.6 to 9.0. The geochemical characteristic distinguishes non-volcanic thermal sources as K-Na-HCO 3 , while volcanic thermal sources present the Cl-HCO 3 -SO 4 -Na type. The quartz geothermometer showed that the reservoir temperatures of non-volcanic hot springs range between 61 and 135 °C. In comparison, the volcanic thermal sources range from 55 to 185 °C requiring 257 to 565 kJ/kg and energy from 231 to 786 respectively to heat water. Subsequently, it is defined as intermediate to slightly high enthalpy for most thermal springs, especially volcanic springs. The mixing of hot water with sources close to the surface can be seen by the disagreement between the silica and cation geothermometers and the disequilibrium with their associated host rocks as indicated from the plot of studied hot springs in the Na-K-Mg ternary diagram and saturation indices calculations. Radiogenic granitic host rock represents the main heat source for non-volcanic hot springs govern by meteoric water generated in deep-seated fault systems. Meanwhile, in volcanic areas with high secondary permeability caused by faults, fractures and fractures, meteorological waters can descend to a considerable depth and heat up. In a favourable situation, thermal waters return to the surface by faults and fracture zones.

Deep hydrothermal activity in hydrocarbon reservoirs, South Kuwait

Fluid inclusion (FI) data provide insights into the origin of hot fluids in Cretaceous and Jurassic reservoirs in south Kuwait. FI data for Cretaceous reservoirs show anomalously high temperatures exceeding 200 °C compared to samples from the Jurassic. In addition, formation water chemical geothermometry data also show anomalous water-rock equilibration temperatures. The preservation of high temperatures indicates rapid migration from depth through deep-seated fault systems. This implies that very hot fluids probably migrated up-fault from near basement to the Cretaceous section. This approach helps to understand the role of hydrothermal activity associated with basement faults in south Kuwait.

Reactivity of Geothermal Reservoir Rocks under Temperature Conditions Found in the Upper Rhine Graben (Germany)

Deep seated fault systems play an important role for deep geothermal applications, particularly in volcanic inactive regions with low natural matrix permeability, such as the Upper Rhine Graben (URG, SW Germany). Fluid migration and heat transport occur through a network of connected fissures and faults, which generally are saturated with highly saline fluids. Alteration processes of primary mineral phases are a crucial for the evolution of the fissure permeability and thus, the lifetime of the geothermal reservoir. The aim of this experimental research is to investigate the interaction between reservoir rocks and synthetic close-to-nature brines to comprehend the alteration path from primary minerals to an alteration mineral assemblage. Primary reactions are intense quartz dissolution, chloritization of biotites in the granite samples, albitization of K-feldspar (granite and sandstones) and an extensive precipitation of highly euhedral analcime crystals on the surface of sandstone samples.

Toward understanding the post‐collisional evolution of an orogen influenced by convergence at adjacent plate margins: Late Cretaceous–Tertiary thermotectonic history of the Apuseni Mountains

The relationship between syn‐ to post‐collisional orogenic shortening and stresses transmitted from other neighboring plate boundaries is important for understanding the kinematics of mountain belts, but has received little attention so far. The Apuseni Mountains are an example of an orogen in the interference zone between two other subduction systems located in the external Carpathians and Dinarides. This interference is demonstrated by the results of a combined thermochronological and structural field study that quantifies the post‐collisional latest Cretaceous–Tertiary evolution. The exhumation history derived from apatite fission track and (U‐Th)/He thermochronology indicates that the present‐day topography of the Apuseni Mountains originates mainly from latest Cretaceous times, modified by two tectonic pulses during the Paleogene. The latter are suggested by cooling ages clustering around ∼45 Ma and ∼30 Ma and the associated shortening recorded along deep‐seated fault systems. Paleogene exhumation pulses are similar in magnitude (∼3.5 km) and are coeval with the final collisional phases recorded in the Dinarides and with part of the Carpathian rotation around the Moesian promontory. These newly quantified Paleogene exhumation and shortening pulses contradict the general view of tectonic quiescence, subsidence and overall sedimentation for this time interval. The Miocene collapse of the Pannonian Basin did not induce significant regional exhumation along the western Apuseni flank, nor did the subsequent Carpathian collision. This is surprising in the overall context of Pannonian Basin formation and its subsequent inversion, in which the Apuseni Mountains were previously interpreted as being significantly uplifted in both deformation stages.

Composition and origin of natural gases accumulated in the Polish and Ukrainian parts of the Carpathian region: Gaseous hydrocarbons, noble gases, carbon dioxide and nitrogen

Ten natural gas samples associated and non-associated with oil in the Polish and Ukrainian Flysch Carpathians and Mesozoic Basement of the Carpathian Foredeep were analysed for molecular and stable isotope compositions as follows: 12, 13C in CH 4, C 2H 6, C 3H 8, and CO 2, 1, 2H in CH 4, 14, 15N in N 2, and 3, 4He, 20, 21, 22Ne, 36, 38, 40Ar, 84Kr and 132Xe in noble gases. The gaseous hydrocarbons both in the Silesian Unit of the Outer Flysch Carpathians and Mesozoic Basement are generally genetically related to thermogenic processes and occasionally to microbial carbon dioxide reduction. These gases were mainly generated from mixed type II/III kerogen during middle stage of the low-temperature thermogenic processes. Gaseous hydrocarbons from Starunia in the Boryslav-Pokuttya Unit were generated from type II kerogen during middle stage of the low-temperature thermogenic processes. He is generally of crustal origin with more than 99.2% of radiogenic 4He, but appreciable amount of 3He is probably derived from the upper mantle. The 3He might have been derived from the Pieniny Klippen Belt deep-seated fault system or Neogene and Pleistocene andesitic and basaltic volcanism occurred in the eastern Carpathian area. Nucleogenic 21Ne and 22Ne were analysed in all the samples. The nucleogenic 21Ne shows good correlation with radiogenic 4He with the production ratio of 4He/ 21Ne = (1–3) × 10 7 in the crust. These isotopic values indicate a common source for these gases, where both the nuclear reactions of α-decay and ( α, n) are occurring. Concentrations of radiogenic 4He and 40Ar and excess 21Ne in the samples from the Mesozoic Basement are generally higher and more scattered compared with those in the Silesian Unit. The larger concentrations of radiogenic and nucleogenic isotopes in the natural gases from the Mesozoic Basement is probably related to older geological formations than younger formations of the Silesian Unit. Carbon dioxide was generally generated during the thermal transformation of organic matter, and occasionally during microbial processes. Nitrogen was mainly generated during thermal transformation of organic matter and also originated from atmosphere. A least part of carbon dioxide and nitrogen may have been produced in crust.

Natural discharge: A key to sustainable utilization of fossil groundwater

Summary Rising demands for fresh water supplies in arid lands are leading to excessive exploitation and unsustainable mining of non-renewable fossil groundwater. Using the Nubian Aquifer of Saharan Africa as a test site, we demonstrate an integrated approach to identify areas of discharge that could have gone undetected, and to model extraction that is sustained by natural discharge. Using isotopic and geochemical analyses along with field and remote sensing data we show that discharge of the Nubian Aquifer is occurring on a larger scale, primarily through deep-seated fault systems, and that ascending groundwater discharges into relatively thick alluvial aquifers proximal to the fault complex that defines the River Nile and the Gulf of Suez. We develop a hydrologic model to assess the discharge and to constrain sustainable extraction in the Asyuti area along the River Nile and to demonstrate a replicable model for similar reservoirs. A two-dimensional groundwater flow model was constructed and calibrated against head data from 19 wells. Results point to a significant contribution to the Asyuti groundwater system from rising Nubian groundwater (3.19 × 10 7 m 3 /yr: 75% of incoming flow) and a modest contribution (1.08 × 10 7 m 3 /yr: 25% of incoming flow) from surface runoff. Approximately 2.5 × 10 7 m 3 /yr of groundwater could be used in a sustainable manner in Asyuti. Assuming geologic settings and discharge rates similar to those at Asyuti, we estimate that 70 × 10 7 m 3 /yr of groundwater may be available for sustainable development in similar settings around the River Nile and the Gulf of Suez.

Regional structures related to mineral deposit clusters in western United States, based on magnetic and gravity interpretations

We explore the utility of regional gravity and magnetic data as an aid in understanding the distribution of large Mesozoic and Cenozoic ore deposits (primarily epithermal and pluton-related precious- and base-metal deposits and sediment-hosted gold deposits) in the western United States Cordillera (Fig. 1). To investigate the regional controls on mineral deposits, broad relationships between geophysical features and the structural geology important to the localization of deposits are discussed first. Then specific deposit clusters are considered by addressing possible deep-seated, regional controls on ore deposition. In order to investigate the usefulness of geophysical data to determine regional structures and their relationship to the distribution of ore deposits in the western United States, we adopt several working hypotheses that have appeared frequently in the literature. Implicit throughout this study are the following: (1 ) regional deep-seated fault systems can localize igneous activity, major ore deposits and ore districts; (2) these fault systems are susceptible to repeated reactivation through geologic time; and (3) intersecting fault systems are especially favorable for ore deposits.

Application of ground geophysical data to the uranium occurrences of El-Erediya area, Central Eastern Desert, Egypt

Ground geophysical surveys were conducted in l-Erediya prospect area, located in the Central Eastern Desert, Egypt. These surveys include ground magnetic and spectrometric. The integration of the results obtained from the magnetic data, aided by geological information, led to the construction of basement tectonic map for the area under consideration. Gamma-ray spectrometric data revealed that the jasperoid veins, faults zones and fracture zones in the El-Erediya area are reflected by the highest spectrometric concentration, whereas granites are reflected by the highest radioactivity rock unit in the area; the amphibolites show up with the lowest radiometric level. The qualitative and quantitaive analysis of the observed magnetic anomalies in relation to the main structural and lithologic manifestations reveals that the average depth to the causative magnetic bodies lies within the basement complex, at two disturbing interfaces 80 and 250 m. From the application of the autocovariance function to the different magnetic and spectrometric data of the studied area, one can state that: there might by radioelement mineralization (U) controlled by WNW structural and having a deep seated fault system; there might be radioelement mineralization (K, eTh) controlled by NW structural and having a deep seated fault system; the EW near surface structure is of shallow origin.

Facies differentiation caused by wrench deformation along a deep-seated fault system (Léon line, Cantabrian Mountains, North Spain)—reply

Abstract The “Leon line” is a deep-seated fault system in the Variscan orogen of the Canta-brian Mountains. This fault system appears to have been active at least from the early Devonian to the end of the Carboniferous. Vertical as well as horizontal movements resulted in a strikingly different development of facies conditions to the north and south of the Leon line.

Facies differentiation caused by wrench deformation along a deep-seated fault system (León line, Cantabrian Mountains, North Spain)—discussion

Facies differentiation caused by wrench deformation along a deep-seated fault system (León line, Cantabrian Mountains, North Spain)—discussion

The neocene—quaternary tectonics and regularities of the mineral-water springs arrangement in Afghanistan

There are more than 150 carbonated and nitrous thermal-water springs in Afghanistan, restricted to the major faults and confined to those areas where deep-focus earthquakes are quite common. There are belts and zones with the mineral-water springs coinciding with the major fault zones. The major structures of Afghanistan, and consequently the major belts with the mineral-water springs, converge in the Shekary—Ghorband area. There is a single intercommunicated system of mineral-water springs discharge, due to the present-day movements in deep-seated and open fault zones. The distribution of the carbonated and nitrous thermal-water types in this system is predetermined by the depth of these open faults, by the presence of heat hearths, as well as by neotectonic movements which form the discharge channelways. The deepest portion of this system, restricted to its major carbonated water resources, is located in the knot area of the HariRod, Qarghanaw, Chaman-Moqur, Central Badakhshan, and Helmand major faults. This area is currently the most seismic in the country and the composition of the carbonated-water springs is unique, having very high content of Li, Rb, Cs, B, Ge, Be, As, Ba and Sr. The high content of Li, Rb, Cs and B in this water classifies it as an industrial-type water. The isotopic composition (and in particular the O 18 isotope content of −10.9–11.9%) points to a meteoric origin of the water. The functioning of this artesian-water system suggests present-day tectonic activity in the area. The main orographie point where the major three watersheds of the AmuDarya, Indus and Seistan drainage areas intersect is located in this area. Away from the center of this deep-seated fault system, the carbonic acid content and the total mineralization of the groundwater are diminished with the increased temperature and discharge of the water springs; there are nitrous thermal-water springs some distance from the center of the system, emphasizing the presence of the currently active movements along the faults.

Facies differentiation caused by wrench deformation along a deep-seated fault system (León line, Cantabrian Mountains, North Spain)

The “León line” is a deep-seated fault system in the Variscan orogen of the Canta-brian Mountains. This fault system appears to have been active at least from the early Devonian to the end of the Carboniferous. Vertical as well as horizontal movements resulted in a strikingly different development of facies conditions to the north and south of the Leon line.

Flux of CO2 from the Lithosphere in the Bohemian Massif

THE important feature of the NW part of the Variscan Bohemian Massif in Czechoslovakia1,2 is a 140 km long graben structure that was tectonically active in the Oligocene and Miocene. Tertiary and early Quaternary volcanic activity and present day hot and cold mineral springs, of maximum temperature 72° C, spatially coincide with the structure. Some of the springs produce gaseous CO2. The rocks yielding the water are felsic igneous or felsic metamorphic rocks. The recent study of natural equilibration between meteoric water and felsic rocks in the area3 indicates that the hydrolysis of primary aluminium silicates and the formation of clay minerals and calcite are the chief processes which control the chemistry of the subsurface waters. Because limestones and dolostones which can release enormous quantities of CO2 by natural thermal decomposition4 are scarce in the region and abundant amounts of organic matter are not likely to be present in the felsic rocks the large amount of CO2 in the subsurface waters must be derived from other sources. It has been widely assumed that the gaseous CO2 in the springs represents a final stage of the Tertiary and early Quaternary volcanic activity5. According to the available geological evidence6 it may be concluded that both the CO2 and the basaltic volcanism are manifestations of deep seated fault systems along which CO2 of a deep, not well understood, origin escapes from or through the lithosphere. If this is true, higher partial pressures of CO2 should be encountered in the subsurface waters of the NW part of the Bohemian Massif, as compared to localities where no excessive flux of CO2 is reported.

Geology and Petroleum Potentials of Central and South Afghanistan

Afghanistan is in a broad mobile belt extending mainly east-west between the old shield of Fennosarmatia in the north and Gondwana in the south. Four major geotectonic units separated by deep-seated fault systems can be recognized. These units are: (1) North Afghan-Tadjik unit, (2) East Iran-Central Afghan unit, (3) East Afghanistan-West Pakistan unit, and (4) marginal region of the Indian shield. In central and south Afghanistan the following blocks can be distinguished: in the East Iran-Central Afghan unit, the Farah, Helmand, and Seistan fault blocks; in the East Afghanistan-West Pakistan unit, the Nooristan fault block, and in the marginal region of the Indian shield, the Katawaz fault block. No prospects, or at best poor prospects, exist for the discovery of economically exploitable petroleum in the Farah, Helmand, Seistan, and Nooristan fault blocks. Petroleum possibilities are assumed to exist in the Katawaz fault block of southeastern Afghanistan. The Katawaz fault block is the only one in southern Afghanistan in which a maximum of 9,000 m (30,000 ft) of late Paleozoic, Mesozoic, and Paleogene sediments have been deposited on the basement. The facies are predominantly marine. Potential reservoir rocks probably are represented by clastic strata deposited at the Cretaceous-Tertiary transition and by sandstone intercalated in the Paleogene sequence. Good to excellent trapping conditions could exist in regularly folded anticlines of Oligocene age as much as 50 km (30 mi) long. Depositional wedges within the subsurface Mesozoic and Paleogene formations could be present. Seismic reconnaissance surveys would provide more precise data pertinent to the existence of favorable structures.

Petroleum Possibilities of Central and South Afghanistan: ABSTRACT

Afghanistan is situated within a broad mobile belt extending mainly east-west between the old shield of Fennosarmatia in the north and Gondwanaland in the south. Four major geotectonic units separated by deep-seated fault systems can be recognized. These units are: (1) North Afghan-Tadjikian unit, (2) East Iran-Central Afghan unit, (3) East Afghan-West Pakistan unit, and (4) marginal region of the Indian shield. In central and south Afghanistan the following blocks can be distinguished: East Iran-Central Afghan unit with the Farah block, Helmand block, and Seistan block; East Afghan-West Pakistan unit with Nooristan block; and marginal region of the Indian shield with Katawaz block. None or only poor prospects exist for the discovery of economically exploitable occurrences of petroleum in the Farah, Helmand, Seistan, and Nooristan blocks. Petroleum possibilities are assumed to exist in the Katawaz block of southeastern Afghanistan. The Katawaz block is the only one of southern Afghanistan in which a maximum of 9,000 m of Paleozoic, Mesozoic, and Paleogene sediments have been deposited on the basement. The facies are predominantly marine. Potential reservoir rocks are probably represented by clastic strata deposited at the Cretaceous-Tertiary transition and by sandstones intercalated in the Paleogene sequence. Good to excellent trapping conditions could exist in regularly folded Oligocene anticlines as much as 50 km long. Depositional wedges within the subsurface Mesozoic and Paleogene formations could be present. Seismic reconnaissance surveys would provide more End_Page 363------------------------------ precise data pertinent to the existence of favorable structures. End_of_Article - Last_Page 364------------

Three Ozark earthquakes*

Abstract This paper continues the discussion of the seismicity of the Middle Mississippi Basin. Seismographic and macroseismic data are presented on three Missouri earthquakes: (1) the Little Saline Creek earthquake, January 15, 1945; (2) the Doniphan, Missouri, earthquake, May 15, 1946; and (3) the Little Black River earthquake, December 1, 1947. Many geological studies have established the existence of three major fault zones in the basement; the Mississippi embayment zone, the Shawneetown-Rough Creek zone, and the Ste. Genevieve zone. The earthquake of January 15, 1945, is additional evidence that the Ste. Genevieve fault zone is seismically active. The other two shocks are not directly associated with the major fault zones. They, together with previous similar minor activity, may be associated with a deep-seated fault system near the physiographic margin of the Ozarks or with deep-seated fractures on the southeastern flank of the uplift.