Major Tectonic Elements Research Articles

The Neogene evolution of the Outer Latakia Basin and its extension into the Eastern Mesaoria Basin (Cyprus), Eastern Mediterranean

The Neogene stratigraphic and structural evolution of the eastern Mesaoria Basin is studied using multi-channel seismic reflection profiles from the eastern marine extension of the basin into the Outer Latakia Basin. The region includes three major tectonic elements: Troodos Larnaka culmination, Kyrenia fold/thrust belt and the intervening Mesaoria and Outer Latakia Basins. The Troodos Larnaka culmination is a large ophiolite-cored ramp anticline developed above a deep-seated S-verging thrust, complemented by a footwall imbricate thrust fan system extending into the Cyprus Basin. The Outer Latakia Basin is a large piggy-back basin, carried on the northern flank of the Troodos Larnaka culmination. The Kyrenia fold/thrust belt is developed as a S-verging trailing imbricate fan system. These three tectonic elements form part of a crustal-scale, S-directed, linked thrust system, which has a protracted tectonic history with major pulses of contraction in the Eo-Oligocene, the late Miocene and the middle Plio-Quaternary. This system extends southward well into the Cyprus Basin and probably links with the subduction zone between the African plate and the Anatolian microplate. Patterns of thrust activity in this linked thrust system exclude models of S-migration of the plate boundary from mid Tertiary to Recent. Instead, the upper plate is viewed as a broad zone of diffuse convergence, distributed across a number of active fold/thrust zones.

Geological development of the Northeast Greenland Shelf

Seismic data from the East Greenland shelf show that the northern part of the shelf, north of 75°N, can be subdivided into five, roughly northeast-trending, major tectonic elements. From west to east they are: the Koldewey Platform, the Danmarkshavn Basin, the Danmarkshavn Ridge, the Thetis Basin and the Marginal High. A sixth tectonic element, the Shannon High, has been defined in the southern part of this area. The offshore areas between 72°30′N and 75°N are dominated by Tertiary plateau basalts, which obscure the acoustic signals from the deeper sedimentary succession. Seismic data from the area north of 75°N indicate the presence of a fairly complete succession of ? Devonian to Neogene age, exceeding the recorded interval (8 sec TWT – 13 km) in thickness in the deeper parts of the Danmarkshavn Basin. The succession has been subdivided into 15 seismic mega-sequences. In absence of well control, they have been dated by comparison to the onshore successions of East Greenland and eastern North Greenland, and the offshore successions in the southern Barents Sea and on the mid-Norwegian shelf. The Upper Palaeozoic succession is broadly similar to that of the southern Barents Sea, i.e. marine-dominated, with thick Upper Carboniferous–Lower Permian halite deposits in the northern Danmarkshavn Basin. The Mesozoic succession seems to show greater similarities to the onshore basins of East Greenland: rifting started during the mid-Jurassic and peaked near the Jurassic–Cretaceous boundary. The post-volcanic succession reflects deposition on a passive margin subjected to temporary uplift during the early Miocene and the latest Miocene to earliest Pliocene.

Plate tectonic evolution of the southern margin of Eurasia in the Mesozoic and Cenozoic

Thirteen time interval maps were constructed, which depict the Triassic to Neogene plate tectonic configuration, paleogeography and general lithofacies of the southern margin of Eurasia. The aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework. The Hercynian Orogeny was completed by the collision of Gondwana and Laurussia, whereas the Tethys Ocean formed the embayment between the Eurasian and Gondwanian branches of Pangea. During Late Triassic–Early Jurassic times, several microplates were sutured to the Eurasian margin, closing the Paleotethys Ocean. A Jurassic–Cretaceous north-dipping subduction boundary was developed along this new continental margin south of the Pontides, Transcaucasus and Iranian plates. The subduction zone trench-pulling effect caused rifting, creating the back-arc basin of the Greater Caucasus–proto South Caspian Sea, which achieved its maximum width during the Late Cretaceous. In the western Tethys, separation of Eurasia from Gondwana resulted in the formation of the Ligurian–Penninic–Pieniny–Magura Ocean (Alpine Tethys) as an extension of Middle Atlantic system and a part of the Pangean breakup tectonic system. During Late Jurassic–Early Cretaceous times, the Outer Carpathian rift developed. The opening of the western Black Sea occurred by rifting and drifting of the western–central Pontides away from the Moesian and Scythian platforms of Eurasia during the Early Cretaceous–Cenomanian. The latest Cretaceous–Paleogene was the time of the closure of the Ligurian–Pieniny Ocean. Adria–Alcapa terranes continued their northward movement during Eocene–Early Miocene times. Their oblique collision with the North European plate led to the development of the accretionary wedge of the Outer Carpathians and its foreland basin. The formation of the West Carpathian thrusts was completed by the Miocene. The thrust front was still propagating eastwards in the eastern Carpathians. During the Late Cretaceous, the Lesser Caucasus, Sanandaj–Sirjan and Makran plates were sutured to the Iranian–Afghanistan plates in the Caucasus–Caspian Sea area. A north-dipping subduction zone jumped during Paleogene to the Scythian–Turan Platform. The Shatski terrane moved northward, closing the Greater Caucasus Basin and opening the eastern Black Sea. The South Caspian underwent reorganization during Oligocene–Neogene times. The southwestern part of the South Caspian Basin was reopened, while the northwestern part was gradually reduced in size. The collision of India and the Lut plate with Eurasia caused the deformation of Central Asia and created a system of NW–SE wrench faults. The remnants of Jurassic–Cretaceous back-arc systems, oceanic and attenuated crust, as well as Tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems.

New Kimberlite Discoveries in Kansas: Magnetic Expression and Structural Setting

A total of 13 kimberlites have been located in a two-county area in northeastern Kansas along the NNE-trending trace of the Proterozoic Midcontinent Rift System, an aborted rift extending from the Lake Superior region southwestward into Oklahoma.The Kansas Geological Survey drilled three new kimberlites in 1999. They are the Baldwin Creek and Tuttle kimberlites located in Riley County and the Antioch kimberlite in Marshall County. They were discovered as part of a systematic ground follow-up of private aeromagnetic data (200–400-m-line spacing) collected by Cominco American Inc. in the early 1980's and donated to the Kansas Geological Survey in 1999. Six exposed kimberlites were discovered prior to 1970 and another four in the early 1980's, one of which is exposed at the surface.Cross-cutting major tectonic elements in NE Kansas are ideal for accommodating the intrusion of kimberlites. The major structural elements are regional NNE-trending, high-angle normal and reverse faults associated with the 1.10 Ga Midcontinent Rift System, and regional, older, high-angle normal and reverse, NW-SE striking, cross-cutting faults which offset portions of the rift. The presence of the rift is identified in regional gravity and magnetic data sets and evidenced in core and cuttings recovered from drill holes that penetrate Precambrian basement. Sedimentary rocks up to about 800 m (3,040 ft) thick and ranging in age from Ordovician to Permian overlie the Proterozoic basement.Ground magnetic surveys were conducted to model the kimberlites and to define targets for drilling and core recovery. These detailed ground magnetic data show that final emplacement of the kimberlite bodies is controlled by N40°W-striking structures, rather than the NNE-trending structures. Modeling of the magnetic anomalies shows that the contacts between the kimberlite bodies and the country rock are steeply dipping.The kimberlites are believed to be Late Cretaceous in age (about 90 my) and range in character from crater and diatreme facies in Riley County to possible hypabyssal facies in Marshall County. The three new kimberlites are buried under a shallow soil cover ranging in thickness up to 8 m (26 ft).

GPS study of active tectonics in Bulgaria: results from 1996 to 1998

To determine the present day kinematics of the major tectonic elements in Bulgaria, part of the northern extent of the Aegean extensional system, we established and surveyed a regional GPS network in 1996, 1997 and 1998. Based on our estimates of the velocities of 17 stations surveyed at least twice, we identify two areas of significant deformation. Between the central Danubian Plain and a 200-km-wide area adjacent to Black Sea, we find 3±1 mm/year of shortening, consistent with compressional focal mechanisms for the Gorna Oriahovitsa fault zone and a NW-trending flexure between higher topography in northeast Bulgaria and the area to the west. South of the Danubian Plain, there is a broad zone of N-S to NNE-SSW extension encompassing the E-W trending Sub-Balkan graben system and Thracian basin of central Bulgaria and with a total differential motion of 3–5 mm/year. The zone of extension appears to continue into the Sofia graben and through a topographically low part of the Stara Planina mountains. This zone of extension marks the northern boundary of the Aegean extensional region, but its western continuation remains unclear. Velocities of 3–4 mm/year to the south and 3 mm/year to the ESE in south central Bulgaria express a clear transition to the Aegean extensional region farther south.

Heat flow, deep temperature and thermal structure across the orogenic belts in Southeast China

The pattern of heat flow density in Southeast China is presented in the form of heat flow map based on 150 values of heat flow measured in recent years. A two-dimensional numerical solution of the heat conduction equation was used to calculate the temperature field to a depth of 60 km along two geotraverses: the 360 km long Wenzhou-Tunxi (WT) and the 1000 km long eastern segment of the Quanzhou-Heishui (QH). They cross all the major tectonic elements of orogenic belts in Southeast China. The steady-state model was solved using the finite element method. The distribution of heat production was derived from seismic refraction results applying the experimental relationship between seismic velocity ( v p ) and radiogenic heat production ( A) incorporated with the observed surface heat generation data in the near-surface crust. The thermal conductivity was assigned to be temperature dependent and related to crustal composition. In the upper crust, the temperature field is found to correspond to the regional variation of the surface heat flow, whereas the mantle heat flow is decisive for the temperature field in the lower crust. Low temperatures are typical of the Later Proterozoic orogenic belt and the Early Paleozoic Foreland Fold-Thrust Belt (FTB) (Moho temperature 415–575°C at a depth of 29–37 km). Temperatures increase toward the Triassic orogenic belt, and the maximum increase in Moho temperature and mantle heat flow occurs in the Triassic orogenic belt and its FTB (550–780°C). Low temperatures (400–500°C at Moho) are also calculated in the Coastal Min-Yue Belt supposed to be a Cretaceous orogenic belt. The “thermal” lithospheric thickness varies between 70 and 190 km, decreasing eastward from the Later Proterozoic Jiangnan in the west to the Triassic Zhe-Min orogenic belts. The mantle heat flow values across the orogenic belts in Southeast China range from 24 to 48 mW m −2 accounting for 51–63% of the surface heat flow.

Tectonics of the Longmen Shan and Adjacent Regions, Central China

The Longmen Shan region includes, from west to east, the northeastern part of the Tibetan Plateau, the Sichuan Basin, and the eastern part of the eastern Sichuan fold-and-thrust belt. In the northeast, it merges with the Micang Shan, a part of the Qinling Mountains. The Longmen Shan region can be divided into two major tectonic elements: (1) an autochthon/parautochthon, which underlies the easternmost part of the Tibetan Plateau, the Sichuan Basin, and the eastern Sichuan fold-and-thrust belt; and (2) a complex allochthon, which underlies the eastern part of the Tibetan Plateau. The allochthon was emplaced toward the southeast during Late Triassic time, and it and the western part of the autochthon/parautochthon were modified by Cenozoic deformation. The autochthon/parautochthon was formed from the western part of the Yangtze platform and consists of a Proterozoic basement covered by a thin, incomplete succession of Late Proterozoic to Middle Triassic shallow-marine and nonmarine sedimentary rocks interru...

An evolutionary model based on geomorphologic and tectonic characteristics of the Maharashtra Coast, India

Abstract The Maharashtra Coast is part of the central west coast of the tectonically ‘passive’ and ‘divergent’ Western Continental Margin of India. Major tectonic elements that characterize the region are the West Coast Fault and the Panvel Flexure. These features have played a major role in the development of coastal geomorphic features, which have been further modified by marine and fluvial processes. Neotectonism is expressed in associated raised marine terraces. The coastal tract of Maharashtra has been divided in three geomorphic blocks on the basis of the role of tectonic elements and spatial distribution of various geomorphic features.

Thermal comparison of mississippi valley-type lead-zinc deposits and their host rocks using fluid inclusion and conodont color alteration index data

Fifteen North American Mississippi Valley-type districts, distributed from the Arctic archipelago to Arkansas and in host rocks ranging in age from Late Cambrian to early Carboniferous, were selected for abroad test survey of Mississippi Valley-type district thermal histories. For each district in which data were collected, histograms of homogenization temperatures for the ore minerals were compared with the temperature range of the corresponding host rocks, as indicated by color alteration index (CAI) determinations on conodonts in the host-rock carbonates. Although a special effort was made to collect conodonts from the Upper Cambrian Bonneterre Formation, host rock to the Southeast Missouri district, all samples were devoid of conodonts. Thus only 14 districts were used in the final analysis.Comparison of fluid inclusion homogenization temperatures in main-stage ore minerals with color alteration index-determined host-rock temperatures reveals that a majority of Mississippi Valley-type districts (Pine Point, Newfoundland Zinc, Mascot-Jefferson City, Copper Ridge, Sweetwater, Central Missouri, Northern Arkansas, and Tri-State) are representative of group 1 (i.e., they are in thermal equilibrium with their host rocks insofar as could be determined by the color alteration index method). Ore minerals in group 2 districts (Upper Mississippi Valley, Polaris, and central Tennessee) are significantly hotter than surrounding host rocks and, as such, define a positive thermal anomaly. Host rocks to the Austinville-Ivanhoe, northern Newfoundland, and Robb Lake deposits (group 3) revealed the highest color alteration index values of North American Mississippi Valley-type districts, with host-rock temperatures greatly exceeding ore mineral fluid inclusion temperatures (negative thermal anomaly).With respect to major tectonic elements of North America, group 3 deposits (cool ore in hot rocks) are positioned within orogenic belts but on the continental side. Some group 1 deposits (ore temperature = host-rock temperature) are well within the continental interior but others are adjacent to orogenic belts on the continental side. Group 2 deposits (hot ore in cool rocks) are all within the continental interior.Current hypotheses regarding the formation of Mississippi Valley-type deposits and simultaneous heating of their host rocks invoke the migration of hot brines set into motion craton-ward by the hydraulic gradient produced by orogenic uplift at the craton edge. Once the ore-bearing fluids entered the foreland carbonate platforms, they traveled through sedimentary aquifers of the continental interior raising the temperature of the thinly covered carbonate rocks. The fluids left, as evidence of their passage, elevated color alteration index values and group 1 Mississippi Valley-type deposits distributed with decreasing homogenization temperatures away from the orogenic front. The correspondence between host-rock and ore temperatures suggests that group 1 deposits were deposited essentially within their own aquifers.Group 2 deposits were formed when the same, or genetically similar, fluids rose from the regional aquifer(s) into structurally controlled conduits in the continental interior, possibly developed as a result of synorogenic doming and arching. This upward channeling of the fluids resulted in rapid and localized fluid flow which precluded or at least inhibited wide-spread heating of the host rocks by ore fluids; consequently, color alteration index values in group 2 districts record only maximum burial depths of the host rocks and bear little relation to temperatures of the ore fluids. Although the cause of the unusually high color alteration index values (4-5) of group 3 districts is not fully understood, it is noted that these districts occur near the extreme outward edge of foreland platforms, near or within the leading margins of orogenic belts. Whether these group 3 host rocks were heated by simple tectonic burial or by passage of heated fluids under shallower conditions is not known.

Superposition of Basement Involved Structures and a Detached Thrust System: A Model for Existing and Potential Production in the San Emigdio Mountains, San Joaquin Valley, California

Seven balanced cross sections document the structural fabric of the San Emigdio Mountains and the adjacent San Joaquin Valley. Major tectonic elements are (1) the Los Lobos normal fault (LLF), (2) the White Wolf reverse fault (WWF), and (3) the Pleito fold-and-thrust belt (PTFB). The Oligo-Miocene LLF system created the distinction between the San Joaquin basin to the north and the Tejon platform to the south. Superposed on the LLF is the younger WWF which has further uplifted the Tejon platform. Along strike, the WWF alternately rotates, truncates, and overrides the LU. The even younger low-angle PTFB is primarily developed on the Tejon platform, but locally interferes both the LLF and WWf. Super position of these structures control the hydrocarbon traps. Wheeler Ridge field (73+MMBOE) is created by the superposition of the PFTB atop of pre-existing basement structures. The field produces from Eocene to late Miocene sands. Some sands are structurally controlled. Due to the complex structural setting, this 1922 field has been extended by discovery of additional reservoirs including a 1989 gas and condensate find in the Oligocene section. This success triggered our comprehensive structural reevaluation. Other fields along and south of the WWF trend are North Tejon (basementmore » involved anticline; 56 MMBOE), Tejon (stratigraphic trap; 36 MMBOE) and Pleito (fault trap; 12 MMBOE) fields. The new structural model suggests two play types for exploration potential: (1) additional fault traps along the WWF trend; and (2) subthrust plays beneath the Pleito thrust. The prolific production history of the WWF trend and large structures mapped beneath the Pleito thrust bode well for future exploration in the San Emigdio Mountains area.« less

Tectonic Evolution and Hydrocarbon Potential of the Southern Moesian Platform and Balkan-Forebalkan Regions of Northern Bulgaria

The major tectonic elements of northern Bulgaria are the east-west-trending Balkan-Forebalkan fold belt and the Moesian platform. Moderate hydrocarbon exploration potential exists in trapping geometries generated during the tectonic evolution of the region coupled with reservoir/seal pairs and source rocks within Mesozoic strata. The tectonic evolution of the region includes Early Triassic to Early Jurassic intracratonic rifting followed by multiphase compression that contracted the rift basin and produced a north vergent fold and thrust belt along the southern margin of the stable Moesian platform. Compression began during the Early Cretaceous, continued during the Paleocene, and concluded during the middle Eocene. Trap types generated during the tectonic evolution include normal fault-bounded rotated blocks in the autochthonous section and elongate, asymmetric anticlines in the allochthonous section. Triassic to Upper Jurassic Marine facies were deposited in an east-west-trending rift. Sediments deposited in a shallow foredeep, which evolved during Lower cretaceous compression, overlay the rift sequence. The Early Mesozoic rift sequence provides the depositional settings for Middle Triassic and lower Middle Jurassic source rock shales and sandstone/carbonate reservoirs ranging from Middle Triassic to Lower Cretaceous. Carbonate reservoirs generally are porous dolomites with intercrystalline, moldic, and vugular pore types interbedded with nonporous limestones. Clastic reservoirsmore » are quartz-rich sandstones with pore types that are reduced intergranular, dissolution, and microporosity. These heterogeneous reservoir targets exhibit poor to good reservoir characteristics and are overlain with sealing lithologies of variable thicknesses.« less

Aptian-Albian palaeogeography of Neo-Tethyan domain

The Aptian-Albian interval (124.5-97.0 Ma) was a critical time both globally and for the Tethyan domain. In the Tethyan domain it was the time when a united Neo-Tethyan subduction zone became established between the future site of the Alps and Southeast Asia and greatly accelerated the rate of north-south convergence throughout the Tethyan region. A consequent widespread transgression on both Laurasian and Gondwanian margins deposited Orbitolina limestones and associated clastics on wide continental shelf areas. On the sea-floor of the Neo-Tethys ocean, organic-rich siliceous black shales, radiolarites, and turbidites with minor amounts of carbonates were deposited. Siliceous black shales accumulated under euxinic conditions of restricted small ocean basins of the Neo-Tethyan realm and along their margins. These areas received large amounts of organic debris from deltaic areas and coastal plains of the neighbouring continental shelves. Following the establishment of the north-dipping subduction zone, the Laurasian passive margin was largely converted to an active one, fringed by a large number of magmatic arcs that greatly influenced the sedimentation on the margin. Land areas and continental basins were widespread on this margin in northern Tibet, China and Indo-China. This was a consequence of the Late Triassic to Early Jurassic continental collissions and accompanied intracontinental convergence that lasted well into the Cretaceous. A detailed Aptian-Albian facies map and a crude palinspastic palaeogeographic map of the entire Tethyan realm are prepared in order to express the contrasts in sedimentation on Laurasian and gondwanian margins and to show the compatibility of the presented data with the most recent and reliable reconstructions of the major tectonic elements in Tethysides.

Vulcan Graben, Timor Sea; Regional Structure From a Magnetic Survey

In late 1989 the Australian Bureau of Mineral Resources (BMR) carried out a regional aeromagnetic survey by contract over the Vulcan Graben region. Elongate short-wavelength anomalies, with wavelengths of 3 to 12 km, amplitudes of 0.2 to 2.0 nT, and with generally northeast strikes, can be correlated for distances of up to 100 km on the basis of their shape and amplitude. Their source appears to be principally at depths of between 0.7 and 3.0 km. Some of the relatively larger amplitude and wavelength anomalies overlie major northwest-dipping normal faults which have been mapped by seismic. All of the elongate anomalies are thought to be due to structures or magnetic deposits associated either directly with NE-trending normal rift faults, or with faults in the post-rift sediments which are related to rift fault reactivation. ENE fault trends, which developed in the Neogene as a result of the collision with Timor, do not appear on the aeromagnetic data. We have mapped numerous northwest-trending faults. These have a spacing of approximately 10 to 25 km. They are thought to be strike-slip because some offset the major northeast-trending normal faults. The northwest trending faults may be due to the reactivation of Palaeozoic trends, the reactivation of Mesozoic transfer faults, or possibly some may be younger and independent of the earlier faults. Some of these faults have previously been mapped on seismic and correspond to seismic 'bad data' areas. These faults may have a major role in the entrapment of hydrocarbon accumulations in the Timor Sea, with most of the significant fields being close to a northwest-trending fault or its extension. In the Timor Sea, high resolution aeromagnetics have proven to be a relatively cheap and cost-effective tool which both complements and supplements the existing seismic data. It should prove equally useful in other areas with extensive seismic coverage. In frontier areas, it should rapidly define the geometry of the major tectonic elements of the basin, allowing for better positioning of seismic programs.

Holocene Displacement of the Malibu Coast Fault Zone, Winter Mesa, Malibu, California: Engineering Geologic Implications

The Malibu Coast Fault Zone (MCFZ) is a major tectonic element in southern California that was heretofore considered to be “nonactive” according to State of California criteria. However, our recent investigations indicate that at least some splays are “active,” for they show tectonic displacement in Holocene time. Accordingly, because the MCFZ crosses rapidly-urbanizing portions of the Los Angeles metropolitan area, it is becoming an increasing geotechnical, as well as a geopolitical, concern for developers and for County and City planners.

The British Siluro-Devonian palaeofield, the Great Glen Fault and analytical methods in palaeomagnetism: comments on paper by K. M. Storetvedtet al.

SUMMARY Late Silurian-early Devonian palaeomagnetic poles throughout the British Isles lie in a coherent group about 1°S and 314°E (A95= 9.6°). The clustering of these poles, which are derived from 11 individual studies of Siluro-Devonian rocks of all the major tectonic elements of Britain, carries two important tectonic implications: 1 the British sector of the Iapetus Ocean, recognizable from Ordovician poles, had closed by late Silurian times; and 2 any postulated mega-shear, whether related to Acadian or Hercynian deformation, is below the limit of palaeomagnetic resolution. The collective rejection of all Siluro-Devonian results by Storetvedt et al. (1990a, b) is demonstrated to be unfounded.

Crustal reflectivity in the Skagerrak area

Reflectors within the crystalline crust are often observed in deep seismic reflection profiling surveys. The lower crust in extensional areas is generally credited with an abundance of reflectors. The deep seismic reflection data (16 s TWT) from the M.V. Mobil Search cruise in Skagerrak show a reflective lower crust and a relatively transparent upper crust in most of the area. Reflectivity seems to be less inside the Oslo Rift, and also beneath the sediment-covered areas. Reflectivity maxima are found near the Moho and at depths of 10–20 km. The latter is taken to coincide with the transition between the brittle upper and ductile lower crust. The distribution of crustal reflectors in Skagerrak and their possible relationships with seismic velocities, earthquake depth distribution and major tectonic elements such as the Fennoscandian Border Zone, the Oslo Rift system and the shield environment are discussed. Hypotheses on the formation of the crustal reflectors are also briefly reviewed.

Anatomy of North America: thematic geologic portrayals of the continent

Six thematic tectonic maps are used to analyse the makeup of the North American continent. Themes are: 1. (1) major tectonic elements of the continent 2. (2) time of last major deformation 3. (3) time of first major deformation 4. (4) miogeoclines and terranes by kindred 5. (5) suture zones and terrane boundaries by age, and 6. (6) time of accretion. Features illustrated include distribution of orogenic belts and their extensions beneath cover sequences to the continental edge, contrast between juvenile and reworked crust in orogenic belts, geometry of ancient continental margins, distribution and classification of accreted terranes, geometry of suture zones and courses of ancient oceans, and how the continent evolved from an assemblage of Archean minicontinents to its present configuration. It is suggested that essentially similar plate tectonic processes controlled continental breakup and assembly from the Archean onwards, albeit with gradual increase in size of continental lithospheric plates and quantitative change in other parameters such as heatflow and character of the mantle.

Influence of Regional Tectonic Framework on Northern Gulf of Mexico Petroleum Maturation and Accumulation

The geographic distribution of biomarker-determined genetic oil types and their spatial pattern of thermal alteration closely follow the regional strike, reflecting the influence of the northern Gulf of Mexico tectonic framework. Oils and source rocks are often in close geographic proximity. The regional distribution of oils reflects the following tectonic features: the Ouachita orogenic belt and thrust zone (onshore area) and the Louann Salt (salt tectonics) in controlling the offshore migrating depocenter. Additionally, great rivers such as the Rio Grande and Mississippi influenced basin formation by contributing large offshore sediment loads. Thermal isolines based on the C{sub 10+} fraction were used to connect many of the fields, but they often crosscut oil type. The pattern of thermal isolines was obtained by regional contouring of (1) methylphenanthrene indices; (2) 5{alpha}C{sub 29} 20R/S sterane ratio; (3) C{sub 20}/C{sub 20}-C{sub 27}, triaromatic steranes; and (4) moretane/hopane ratio. The derived isolines revealed, with differing sensitivity, the major tectonic elements. In particular, the Ouachita thrust zone appears to be a major control on the maturity of onshore oils. By contrast, the maturity of offshore oils is partly controlled by the subsidence history of the migrating depocenter. The Curtis multisource model is supported by the spatialmore » distribution of genetic oil types but complicated by the discovery of differing maturities of oil and gas in the same reservoir. Possibly larger tectonically induced late gas expulsion from mature source rocks may have enhanced oil migration out of immature Tertiary lignites and shales.« less

New Prospective Areas for Geological Exploration in Eastern Europe

Eastern Europe is a highly complex geological region. The region comprises platforms of various ages, each exhibiting a variety of structural styles. The major tectonic elements often straddle more than one country, with each country usually interpreting the geological features differently. This complicates the study of both geology and petroleum occurrence. This study of the geological structure and petroleum occurrence was done for the territory as a whole, notwithstanding national boundaries. Based on a series of structural-geological features, these basins are grouped into three categories: (1) platformal, (2) fold (in fold-nappe belts and intermontane depressions), and (3) combined (at the junctions of platformal and fold areas, i.e., foredeeps). The basins are divided into petroleum subbasins. To scientifically estimate the petroleum prospectivity, VNI-Izarubezhgeologia has recently analyzed the lithofacies characteristics of the sedimentary sequences occurring in Eastern Europe; the palaegeographical environments of sedimentation, organic matter and its maturity,a nd the distribution of reservoirs and seals. As a result of these studies a series of lithofacies maps (18 maps at 1:1,000,000 scale), a tectonic map (1:1,00,000), a petroleum distribution map, a prospectivity map (1:2,500,000), and a series of geodynamic reconstructions have been produced. As the result of this analysis, new petroleum exploration targetsmore » have been outlined. These new targets are in stratigraphic trap zones, in deep horizons (deeper than 3-3.5 km) and in areas defined as a result of geodynamic analysis.« less

The Guayape fault system, Honduras, Central America

The Guayape fault system (GFS) is the longest continuous structural feature in Honduras and a major tectonic element within the Chortis block of the Caribbean Plate. Nevertheless, it has been largely ignored in most tectonic studies of this region, apparently due to lack of detailed information concerning the location, extent, and nature of the system. This paper attempts to fill this gap. The GFS is defined as a complex band of faults, from 2 to 25 km in width, which trends N30°–35°E for 290 km from the Honduras-Nicaragua border near El Paraíso to the Caribbean coast near the mouth of the Río Sico. A probable offshore continuation can be seen in seismic reflection profiles. Field mapping and aerial photograph interpretation indicate that the GFS proper terminates in a series of splay and cross faults in the Jamastrán Valley-El Paraíso area and does not make an en echelon transfer to connect with the Choluteca lineament to the southwest. The most obvious manifestation of the GFS is the fault-controlled alignment of major segments of the Guayambre, Guayape, Tinto, Paulaya, and Sico Rivers. The great length and rectilinearity of the GFS indicate that it is a strike-slip fault, which is confirmed by abundant horizontal and sub-horizontal slickensides, vertical drag-folds, shutterridges, and extensional basins generated by strike-slip displacement. Subsidiary dip-slip faults, expected in a major transcurrent fault system, are common, especially where extensional basins have developed. Stream offsets of about 50 km, some mesoscopic slip indicators, the regional distribution of a shaly member of the Honduras Group, and regional tectonic considerations suggest sinistral displacement on the GFS. On the other hand, three, possibly four, modern topographic depressions along the GFS are dextral strike-slip extensional basins, and dextral mesoscopic slip indicators outnumber sinistral indicators. A two-stage slip history is thereby inferred, with a sinistral-slip phase of more than 50 km displacement followed by a dextral-slip phase of smaller displacement. The GFS truncates units ss young tuffs of the predominantly Miocene Padre Piguel Group as well as younger Tertiary(?) gravels. The extreme topographic crispness of the GFS at many localities and the youthfulness of the strike-slip basins show that the GFS is a young feature; hot springs in four localities and scattered seismic data suggest continued activity, but there is no convincing evidence of significant modern motion on the system. The age for inception of motion is unknown, but the sinistral phase probably sympathetic to Tertiary movement of the Chortis block along the sinistral Motagua-Swan transform (NOAM-CARIB plate boundary). Continued movement of the Chortis along the arcuate plate boundary may have rotated the block into a position favorable for the initiation of dextral slip.