Stages Of Tectonic Activity Research Articles

Microfacies and Depositional Conditions of Jurassic to Eocene Carbonates: Implication on Ionian Basin Evolution

In order to decipher the paleo-depositional environments, during the Late Jurassic to Early Eocene syn-rift stage, at the margins of the Ionian basin, two different areas with exposed long sequences have been selected, Kastos Island (external margin) and Araxos peninsula (internal margin), and were examined by means of microfacies analysis and biostratigraphy. On Kastos Island, based on lithological and sedimentological features, the following depositional environments have been recognized: an open marine/restricted environment prevailed during the Early Jurassic (“Pantokrator” limestones), changing upwards into deep-sea and slope environments during the Late Jurassic and Early Cretaceous (Vigla limestones). The Upper Cretaceous (Senonian limestones) is characterized by a slope environment, whereas during the Paleogene, deep-sea and toe of slope conditions prevailed. In Araxos peninsula, Lower Cretaceous deposits (“Vigla” limestones) were accumulated in a deep-sea environment; Upper Cretaceous ones (Senonian limestones) were deposited in slope or toe of slope conditions. Paleocene limestones correspond to a deep-sea environment. In Araxos peninsula, changes occurred during the Cretaceous, whereas on Kastos Island, they occurred during the Paleocene/Eocene, related to different stages of tectonic activity in the Ionian basin from east to west.

COMPOSITION AND STRUCTURE OF THE NEPSKY AND TIRSKY FORMATION OF THE PRILENSK-NEPSKY STRUCTURAL-FACIES ZONE OF THE NEPA-BOTUOBA ANTECLISE BY THE RESULTS OF CORE MATERIAL STUDIES

Background. Clarification of the structure of sedimentary formations located on the Siberian Platform by means of lithological and petrographic core studies has a theoretical and practical significance for the creation of geological models for oil and gas prospecting and exploration works. Aim. To characterize and compare the composition of the upper Vendian of the central and southern parts of the Prilensk-Nepsky structural-facies zone. Materials and methods . Core samples for analysis were obtained from boreholes in the Preobrazhenskaya, Verkhnechenskaya, Danilovskaya, Yaraktinskaya and other areas. The article is based on the results of a layered lithological description of the cores from 15 wells with a total core output of 560 m in the interval of the Nepsky and Tirsky formations; the petrographic analysis of 540 thin sections; the determination of grain size distribution of rocks by laser light scattering in 220 samples; and X-ray diffraction analysis of 540 samples. Results . The Nepsky formation is represented by the following lithotypes: conglomerates, gravelites, sandstones, aleurolites and argillites. The section of the southern part of the structural-facies zone, compared to its central part, is characterised by increased claying. This is associated with the location of this zone in transitional coastal-marine environments, where large river systems were discharged carrying sandy-clay material into the basin. The source of the terrigenous rocks was felsic igneous rocks. The section of the Tirsky formation of the central part is represented (from bottom to top) by a transition from argillites and aleurolites to dolomites. In the section of the southern part, basal sandstones lie at the base, alternating upstream with clay-carbonate rocks. Conclusion . The material composition of the studied sediments reflects the specifics of sedimentation during the Nepsky and Tirsky time periods. For the first time, the Tirsky formation of the southern part of the structural-facies zone was divided into four lithological members. The formation of basal sandy rocks at the bottom of the sub-formations is associated with the stages of tectonic activity and positive tectonic movements that initiated relatively rapid weathering and transportation of terrigenous material from adjacent heights to the sedimentation basin.

Carboniferous carbonate rocks of the Chukotka fold belt: Tectonostratigraphy, depositional environments and paleogeography

New faunal data from Carboniferous carbonates on Wrangel Island and Chukotka Peninsula (within Kuul, Alyarmaut and Polyarnyui Uplifts) are used to identify stratigraphic sequences and for regional correlations. The facies and geochemical data indicate that Carboniferous sediments on Wrangel Island, Kibera Cape and the Alyarmaut Uplift were deposited on a carbonate platform that was part of the passive continental margin of Arctida (the Hyperborean platform). Limestone of the Polyarnyui Uplift was formed on an isolated seamount in the oceanic basin. The geochemical and isotopic characteristics of rocks on Wrangel Island and in the Kuul and in the Alyarmaut Uplifts show the alternation of limestone formed in marine environments and limestone with the characteristics of a freshwater basin. Limestones of the Polyarnyui Uplift formed in a seamount of oceanic marine environment. A new paleogeographic model is proposed based on faunal, isotopic and geochemical characteristics of limestone. In the Early Carboniferous, carbonate platform were located in Chukotka and in the Wrangel Island. In the Late Carboniferous, the area of carbonate sedimentation was reduced and deposits accumulated in a shallower setting in Wrangel Island and in Kuul Uplift. Correlation of the Carboniferous sequences, sedimentary environments and geochemical composition of limestones on the carbonate platform showed three stages of tectonic activity: i) the boundary between the Visean and Serpukhovian Stages corresponds to regional uplift of the carbonate platform and termination of carbonate sedimentation in the oceanic basin; Tectonic reorganization within the ii) Bashkirian Stage and at the iii) beginning of the Early Permian is expressed only in the sequences of the Wrangel Island.

Tectonics of the Ninety-East Ridge

New multibeam bathymetry data and multichannel seismic profiles over 7 detailed survey sites collected during cruise no. KNOXRR06 of the R/V Rodger Revelle in 2007 fundamentally expanded the concepts about the structure of the sedimentary cover of the Ninety-East Ridge, which were based on the results of previous studies. They allow making a step forward in interpreting the nature of the unconformities and deformations. The deformation pattern of the sedimentary cover suggests three stages of tectonic activity over the ridge during the Paleocene, Eocene, and Late Miocene. As suggested by the high present-day seismicity, the last stage might continue to the present time. In addition, indirect criteria indicate young intraplate volcanism at the last stage. New data is reviewed in the context of two models of the ridge formation. The first model follows a well-known concept of the ridge representing a trace of the Kerguelen hotspot. The second one relates large outflows of basalts to the development of a giant fracture under conditions of global extension, which continued later during the sedimentary cover formation. Additional integrated geological and geophysical studies are required for understanding the nature of this unique feature.

Pliocene to Quaternary tectonics in the Horná Nitra Depression (Western Carpathians)

Pliocene to Quaternary tectonics in the Horná Nitra Depression (Western Carpathians)The Horná Nitra Depression is an Upper Miocene-Quaternary intramontane sedimentary basin. This N-S elongated half-graben structure is rimmed from the west by the marginal Malá Magura fault which is the most distinctive fault in the Horná Nitra Depression, traditionally considered as an active fault during the neotectonic phase. This dislocation is attended by contrasting landforms and their parameters. The lowS-indexof about 1.10, at least two generations of well-preserved faceted slopes along this fault, and longitudinal river valley profiles point to the presence of a low-destructed actual mountain front line, which is typical for the Quaternary active fault systems. Comparison with known normal fault slip rates in the world makes it possible to set an approximate vertical slip rate between 0.3-1.1 m · kyr-1. The present-day fault activity is considered to be normal, steeply dipping towards the east according to structural and geophysical data. The NNW-SSE present-day tectonic maximum horizontal compressional stressSHand perpendicular minimum horizontal compressional stressShwas estimated in the Horná Nitra region. The Quaternary activity of the Malá Magura fault is characterized by irregular movement. Two stages of important tectonic activity along the fault were distinguished. The first stage was dated to the Early Pleistocene. The second stage of tectonic activity can by dated to the Late Pleistocene and Holocene. The Malá Magura fault is permeable for gases because the soil atmosphere above the ca. 150 meters wide fault zone contains increased contents of methane and radon.

Timing of deformation phases within the South Finland shear zone, SW Finland

The Palaeoproterozoic Svecofennian crust in southern and central Fennoscandia was established about 1.8 Ga ago after a prolonged history of accretion and intrusion. During late stages of the Svecofennian orogeny, deformation was partitioned into several crustal-scale shear zones in present-day Finland, Sweden and Estonia. One such major ductile deformation zone, ‘the South Finland shear zone’ (SFSZ) extends for almost 200 km through the Åland archipelago in southwestern Finland, and further along the southern and southwestern coast of Finland. This more than a kilometer wide transpressional zone appears to have been repeatedly reactivated. The deformation started with a period of regional, ductile dextral shearing of igneous rocks, producing striped granodioritic and tonalitic gneisses. The ductile phases are locally overprinted and followed by ductile to semi-ductile deformation evidenced by mylonite zones of variable width. The last stage of tectonic activity along the shear zone is recorded by pseudotachylites. Within this study, we dated zircons (SIMS U–Pb) and titanites (ID-TIMS U–Pb) from eight rock samples, and two pseudotachylite whole-rock samples ( 40Ar/ 39Ar) in order to reconstruct the deformation and (re)activation history of the shear zone. The results suggest that the medium-grained gneisses underwent three distinct deformation phases separated by time intervals without regional deformation. The ductile deformation within the study area initiated at ∼1.85 Ga. A second, more intensive deformation phase existed around 1.83 Ga, by which the shear zone was already well developed. Finally, the last ductile event is recorded by ∼1.79 Ga metamorphic titanites in relatively granoblastic granitoid gneisses that nevertheless already display protomylonitic textures, suggesting the initiation of large-scale mylonitisation around or soon after this time. The age of a pseudotachylite sample and, hence, the brittle deformation is bracketed between 1.78 and 1.58 Ga based on the age of pegmatites cut by pseudotachylites as well as 40Ar/ 39Ar minimum ages for the pseudotachylite, respectively. The data imply that the rocks within the study area entered the ductile–brittle transition zone due to rapid cooling and exhumation of the crust after ∼1.79 Ga.

Fluid inclusions in high-pressure granulites of the Pan-African belt in Tanzania (Uluguru Mts): a record of prograde to retrograde fluid evolution

The high-pressure granulites of the Uluguru Mountains are part of the Pan-African belt of Tanzania, the metamorphic evolution of which is characterized by an anticlockwise P-T path. Mineral assemblages that represent distinct metamorphic stages are selected for fluid inclusion studies in order to deduce the fluid evolution in metapelites and pyroxene granulites from the prograde to the retrograde stage. Fluid inclusion data improve the petrologically derived P-T path and confirm the anticlockwise evolution. Fluid inclusions in quartz enclosed in garnet porphyroblasts in metapelites preserve prograde fluids of CO2–N2 composition and later-trapped pure CO2. During isochoric heating at temperatures near the peak of metamorphism, deformation and recrystallization led to fluid homogenization yielding N2-poor CO2 composition in the metapelites. Near-peak CO2–N2 fluid inclusions in quartz of metapelites and CO2 inclusions in garnet-pyroxene granulites are characterized by perfect negative crystal shape. Garnet formed in veins and as coronas around orthopyroxene represent the near-isochoric/isobaric cooling stage which is characterized by high-density CO2-rich fluid inclusions. Up to 15 mol% N2 in some primary CO2 inclusions in corona garnet indicate small-scale fluid heterogeneity during the static garnet growth. The fact that high-density fluid inclusions are preserved, suggests a shallow dP/dT slope of the uplift path. Nevertheless, some fluid inclusions decrepitated or re-equilibrated and low-density CO2 inclusions were trapped in the garnet-pyroxene granulite while N2–CH4 inclusions formed in the metapelites. Different fluid compositions in metapelite and metabasite argue for an internal control of the fluid composition by phase equilibria. In shear zones where the pyroxene granulite was transformed into scapolite-biotite schist, CO2–N2 and low-density N2–CH4 fluid inclusions indicate several stages of tectonic activity and suggest fluid influx from the nearby metapelites. High- and low-salinity aqueous inclusions observed beside CO2 inclusions in garnet-pyroxene granulites, in vein quartz and shear zones could be of high-grade origin but are mainly re-equilibrated or re-trapped along healed microfractures during lower-grade stages.

Neogene fault activity and morphogenesis in the basement area north of the KTB drill site (Fichtelgebirge and Steinwald)

The Fichtelgebirge and Steinwald areas are situated at the western end of the Cenozoic Eger graben. Repeated Neogene fault activity and polyphase morphogenesis created a complex morphotectonic structure. Based on morphotectonic criteria three stages of tectonic activity can be determined: (a) late Oligocene to early Miocene; (b) middle-late Miocene; and (c) late Pliocene to early Pleistocene. Due to the Neogene tectonic movements, the pre-basaltic (preOligocene to Miocene) landscape has been differentially uplifted/downthrown and intensely modified by post-basaltic surface planation (HF). Broad paleovalleys (AT) of late Miocene to early Pliocene age and a system of Pliocene and Quaternary fluvial terraces and pediments (BT and ET) have been incised into the widespread HF relief elements. Due to repeated faulting and erosion, the stratigraphic record of Neogene sediments within the studied area is fragmentary.

Peculiarities of Petroleum Formation in Highly Bituminous, Siliceous, Shaly, Carbonaceous Facies, Timan-Pechora Basin, USSR: ABSTRACT

Over 50 oil and gas fields with total reserves of about 6 × 109 BOE have been discovered in the Timan-Pechora basin, one of the most important Russian frontiers. Almost all the sequence is productive, although major reserves are confined to two stratigraphic intervals beneath regional seals. Principal source rocks are the so-called Domanik facies, 25 to 150 m (82 to 492 ft) thick, represented by rapidly alternating black shales, chert, marls, and siliceous and organic limestones. Exclusively sapropelic organic matter averages 5 to 7% and reaches 20% or more. Soluble bitumen is very abundant (1 to 2 wt. %) and contains all the components characteristic of crudes: from light oils to heavy tars and typical high-molecular asphaltenes. These characteristics exi t even on the basin's periphery where Domanik facies are only marginally mature. In other areas, Domanik facies are mature; they are probably overmature in the deepest troughs. Outside the area covered by Domanik facies, pools and even significant shows are absent. Deposition of this prominent facies began during the end of early Frasnian time in a wide stagnant sea that covered the eastern edge of the Russian platform. Beginning in the late Frasnian, shallow-water carbonate sedimentation resumed along the basin's edges and on uplifted blocks. Condensed Domanik deposits continued to form in the gradually deepening sea on the east side of the basin. Barrier reefs and clastic terraces that prograded basinward formed along the northern and western boundaries. The deep-water trough was finally filled by thick clastics at the end of early Tournaisian time. The unusual composition of Domanik facies and their exceptional enrichment by sapropelic organic matter result in their peculiarities as petroleum source rocks. Lithology of the rocks, particularly the abundance of huge carbonate concretions fully or partly replaced by silica, suggests a long delay in lithification and the relative importance of the late diagenetic stage of oil generation. This explains the presence of immature oils in underlying Devonian clastics and their absence elsewhere in the sequence. On the other hand, Domanik facies, owing to significant silicification that trapped giant amounts of bitumen in the rocks, became a natural repository of oil during geologic history. This oil migrated because of fracturing, especially during stages of tectonic activity. Spatial istribution of oil types and deposits of solid bitumen in traps having different ages of formation, clearly shows predominance of pulse-like vertical migration. Migration of oil from the Domanik continued during late stages of geologic history along with block uplifting, cooling of the sedimentary cover, and absence of sedimentation. Thus, methods of applied geochemistry that invoke models of heating should not be applied to Domanik-type rocks and more geologic data are required to assess their role as oil sources. End_of_Article - Last_Page 561------------

Observations sur la ride triasique de Belus (Landes)

Abstract Recent borings along a north-south line in the Belus region, Landes, France, show that a Triassic diapir is wedged into the core of the Belus fold. The upper Cretaceous and Tertiary formations of the Belus-Saint-Lon region were subjected to four stages of tectonic activity. Injection of the diapir structures probably took place during Aquitanian crustal movements (the last of the four stages).