Search

This study investigates the depositional environments and soft sediment deformation within the Early Jurassic Ammonitico Rosso Formation in the External Ionian Basin (Western Greece), focusing on its biostratigraphy, sedimentology, and tectonic activity. This research provides new insights into the depositional environment of the Ammonitico Rosso Formation and its transitions with the underlying and overlying formations. Syn-rift tectonics at the time of deposition formed half-grabens, which influenced sedimentary processes and created conditions for seabed slumping. Detailed field mapping and microfacies analysis revealed two distinct depositional environments: deep-water to open-shelf settings and platform-margin reefs. The entire Ammonitico Rosso Formation is allochthonous, deposited as repetitive slices of little-disturbed stratified sediments capped by debrites near the toe of a complex submarine landslide. The presence of well-preserved fossils, such as planktonic and benthic foraminifera, Radiolaria (both Spumellaria and Nassellaria), and ammonites, allowed precise age determinations, suggesting that the first appearance of Globuligerina might predate previous records, occurring first in the Pliensbachian rather than the Toarcian. These findings contribute to the ongoing debate on the depth and conditions of Ammonitico Rosso deposition, supporting the hypothesis of a relatively deep, open-shelf environment influenced by slope instability. [ABSTRACT FROM AUTHOR]

Upper Miocene volcanic and plutonic rocks on Kos island preserve a record of magmatic and tectonic events in the transition zone between the Aegean and Anatolian microplates. Their field setting, syn-intrusion deformation, mineralogy, and geochemistry were investigated. Volcanic rocks, including trachyandesite flows and trachyandesite to rhyolite domes, were extruded on a central E–W horst and directly overlie Alpine basement. Thick successions of trachytic flow tuffs are interbedded with fluvial and lacustrine basinal sediments to the south of this horst. Volcanism was synchronous with the emplacement of the Dikeos monzonite pluton, which is geochemically similar to some lithic clasts in the thick flow tuffs and is cut by mafic dykes including lamprophyres. Two main types of mafic magma were present: a K-rich lamprophyric magma that evolved to trachyandesite and more calc-alkaline magma similar to mafic enclaves in the monzonite. Syn-intrusion structures in the monzonite indicate emplacement during E–W sinistral strike-slip faulting that created local transtensional deformation, providing accommodation for a Dikeos magma reservoir. A change in the style of deformation in the Late Miocene led to NW-striking extension in the footwall, occupied by mafic dykes and mineralized veins, and extensional detachment of the hanging wall, resulting in unroofing of the monzonite. [ABSTRACT FROM AUTHOR]

The Naskapi Member of the Logan Canyon Formation, a 150 m thick shale-dominated unit, lies in between sand-dominated units of Upper Missisauga Formation below and the Cree Member above. The great decrease in sediment supply has been suggested as due to tectonic and (or) eustatic sea-level changes. Wireline logs and recent biostratigraphy of 30 wells from the Scotian Shelf and Georges Bank, mudstone geochemistry from the Naskapi and Cree Members, and modal composition and chemical variation of detrital heavy minerals in sandstones were examined to better understand the deposition of the Naskapi Member and its regional implications. Minor sandy intervals at the base of the Naskapi Member were correlated based on gamma and sonic log signatures from the type section in the Cree E-35 well to progressively more distant wells, on the assumption that the sands represent periods of lowered eustatic sea level. Correlation was confirmed by the distribution of highstand black shales in washed cuttings and biostratigraphic markers identified in some wells. The geochemistry of mudstones from the Naskapi Member resembles mudstones sourced from the Meguma Terrane, except for a higher abundance of elements likely reworked in smaller amounts from the Upper Missisauga Formation. Based on the correlation and geochemistry of mudstones and detrital minerals, we suggest the diversion of Sable River through the Gulf of St. Lawrence to either the Orphan Basin or towards western Canada was responsible for the decrease of sediment supply in the Scotian Basin during the deposition of the Naskapi Member shales. Le membre de Naskapi de la Formation de Logan Canyon, une unité de 150 m d'épaisseur dans laquelle les shales sont prédominants, se trouve entre des unités à prédominance de sable de la Formation de Missisauga supérieure en dessous et le membre de Cree au-dessus. Il a été proposé que l'importante baisse de l'apport de sédiments serait due à des changements tectoniques ou eustatiques du niveau de la mer. Des diagraphies et la biostratigraphie récente de 30 puits du plateau néoécossais et du banc de Georges, la géochimie de mudstones des membres de Naskapi et Cree et la composition modale et les variations chimiques des minéraux lourds détritiques dans les grès ont été examinées pour mieux comprendre le dépôt du membre de Naskapi et sa signification à l'échelle régionale. Des intervalles sableux mineurs à la base du membre de Naskapi ont été corrélés à la lumière des signatures de diagraphies soniques et de rayons gamma de la coupe type dans le puits Cree E-35 à des puits de plus en plus éloignés, en partant de l'hypothèse que les sables représentent des périodes de niveau eustatique de la mer abaissé. Les corrélations ont été confirmées par la répartition des schistes noirs de haut niveau dans des déblais lavés et de marqueurs biostratigraphiques identifiés dans certains puits. La géochimie des mudstones du membre de Naskapi ressemble à celle de mudstones provenant du terrane de Meguma, sauf en ce qui concerne leur plus forte abondance d'éléments vraisemblablement mobilisés en petites quantités à partir de la formation de Missisauga supérieure. À la lumière des corrélations et de la géochimie des mudstones et des minéraux détritiques, nous proposons que le détournement de la rivière Sable par le golfe du Saint-Laurent, soit vers le bassin Orphan ou vers l'ouest canadien, expliquerait la diminution de l'apport de sédiments dans le plateau néoécossais durant le dépôt des shales du membre de Naskapi. [Traduit par la Rédaction], 1. Introduction The Aptian Naskapi Member of the Logan Canyon Formation (McIver 1972; Wade and MacLean 1990) is a shale-dominated unit overlying the sandy Upper Missisauga Formation (Late Hauterivian-Barremian) and [...]

Upper Palaeozoic lacustrine basin deposits not only record local tectonism but are also an archive to evaluate global palaeoclimate changes linked to the Late Palaeozoic Gondwanan ice age. The Tournaisian Horton Group of Nova Scotia, south‐east Canada, accumulated in rift basins following the final accretion of peri‐Gondwanan terranes to the Appalachians. Sedimentology, mineralogy and geochemistry of the well‐exposed sandstones and shales at the classic Blue Beach section (ca 353.5 to 352 Ma) reveal the interplay of local tectonism and global climatic controls on lacustrine sedimentation. The lacustrine depositional environment gradually transitioned from deep water offshore at the base of the section to wave‐dominated and fluvial‐dominated nearshore at the top. Multiple small transgressive–regressive sedimentation cycles have an average 21 ka duration, likely related to Milankovitch cyclicity. Unusually abundant soft‐sediment deformation structures and landslides are the sedimentary responses to frequent earthquakes during the most active phase of rift subsidence. The overall succession shows changes from a shallowing‐up balanced‐filled to an overfilled lacustrine basin. The chemical weathering intensity index and the Th/K ratio show a longer‐term trend from dry and cool conditions low in the section to humid and warm conditions near the top, with rapid change in the transition period. The section records the peak of the global mid‐Tournaisian carbon isotope excursion and the corresponding cooling event (354 Ma to approximately 351 Ma). The sedimentary succession is a response to long‐term and short‐term climatic cycles influencing lake level and sediment supply during the time of maximum rift basin subsidence recorded by the soft‐sediment deformation structures. [ABSTRACT FROM AUTHOR]

The Steel Mountain complex in western Newfoundland is one of several possible peri-Gondwanan basement slivers that have been emplaced along the northwestern margin of the Appalachian Orogen. The complex includes feldspathic anorthosite, gabbronorite, and magnetite-ilmenite ore. Megacrysts of plagioclase (andesine), orthopyroxene (hypersthene) and amphibole (hornblende) were analyzed by electron microprobe and they are of similar composition to the groundmass minerals. The ferromagnesian megacrysts have exsolution lamellae of Fe-Ti oxides, magnesio–hornblende, and clinopyroxene. The hornblende megacrysts and the lack of plagioclase in the exsolution lamellae are unusual for Proterozoic anorthosites and result from unusual abundance of water in the parental magma. Whole-rock Nd-Sm isotope determinations give an isochron age of ~1.2 Ga. Ar-Ar dating of biotite rims on hornblende shows an early Ordovician plateau age and the final heating step suggests a ~0.8 Ga age for the amphibole itself. Taken together with published zircon geochronology, these data suggest a provenance in the southern peri-Gondwanan Appalachians. [ABSTRACT FROM AUTHOR]

The Junggar Basin is located on the southwestern margin of the Central Asian Orogenic Belt (CAOB). Whether the Late Permian-Early Triassic tectonic inversion there recorded the final closure of the North Tianshan Ocean or postaccretionary intracontinental deformation remains controversial. Linking the structural style and provenance analysis of the western and northern margins of the Junggar Basin can provide a better understanding of this tectonic event and its geodynamic mechanisms. Seismic reflection profiles show that Early Permian syn-rift half-grabens were followed by the Middle Permian thermal sag, which is characterized by regional onlap and the migration of the depocentre to the centre of the basin. Together with the published isopach and palaeogeography maps in the western margin of the Junggar Basin, the seismic profiles demonstrate that the reactivation of the Ke-Bai and Wu-Xia dextral transpressive fault zones between the West Junggar terrane and the Mahu sag controlled the tilting and deformation of pre-Permian strata and the distribution of Late Permian-Early Triassic fan deltas. The reported igneous and sedimentological evidence indicates that the southern margin of the Junggar Basin was a rift basin controlled by transtensional strike-slip faults in the Early Permian, and also was followed by a Middle Permian thermal sag. Quantitative provenance analysis using detrital zircon geochronology and the DZmix program shows that the West Junggar terrane and Tianshan orogenic belts experienced varied uplift, indicative of a transition from the Middle Permian thermal sag peneplanation to the Late Permian-Early Triassic tectonic inversion involving reactivation of Early Permian normal faults. This intracontinental deformation event in the Junggar Basin was taken up by block counterclockwise rotation during the final amalgamation of the Pangea, which may be the long-range effect of the final closure of Paleo-Asia Ocean in the eastern part of the CAOB. [ABSTRACT FROM AUTHOR]

Abstract: Latest Devonian (~365-358 Ma) A-type granites in the Cobequid Highlands host complex sequences of rare-earth element (REE) and other hydrothermal minerals. The West Moose River pluton is the only [...]

Abstract: Jurassic and Cretaceous sandstones in the Shelburne subbasin and Fundy Basin offshore Nova Scotia, are poorly known but are of current interest for petroleum exploration. The goal of this [...]

Paleocene to Oligocene tectonic processes in northwest Iran resulted in extensive I-type calc-alkaline and alkaline magmatic activity in the Ahar region. Numerous skarn deposits formed in the contact between Upper Cretaceous impure carbonate rocks and Oligocene-Miocene plutonic rocks. This study presents new field observations of skarns in the western Alborz range and is based on geochemistry of igneous rocks, mineralogy of the important skarn deposits, and electron microprobe analyses of skarn minerals. These data are used to interpret the metasomatism during sequential skarn formation and the geotectonic setting of the skarn ore deposit related igneous rocks. The skarns were classified into exoskarn, endoskarn and ore skarn. Andraditic garnet is the main skarn mineral; the pyroxene belongs to the diopside-hedenbergite series. The skarnification started with pluton emplacement and metamorphism of carbonate rocks followed by prograde metasomatism and the formation of anhydrous minerals like garnet and pyroxene. The next stage resulted in retro gradation of anhydrous minerals along with the formation of oxide minerals (magnetite and hematite) followed by the formation of hydrosilicate minerals like epidote, actinolite, chlorite, quartz, sericite and sulfide mineralization. In addition to Fe, Si and Mg, substantial amounts of Cu, along with volatile components such as H2S and CO2 were added to the skarn system. Skarn mineralogy and geochemistry of the igneous rocks indicate an island arc or subduction-related origin of the Fe-Cu skarn deposit.