Stratigraphic and Microfacies Study of Kometan Formation (Upper Turonian-Lower Campanian), in the Dokan area, Northern Iraq

The Kometan Formation is widely distributed in the northern (Kurdistan region) and central Iraq. The studied area is located near the Dokan Dam, about 58 km., to the Northwest of the Sulaymaniyah city, Northeastern Iraq. The Kometan Formation is exposed on the southwest flank of the Sarah anticline. The formation consists of limestone and dolomitic limestone, which have cherts nodules throughout the formation. The Gulneri Formation is recorded below the Kometan Formation with unconformable contact, while at the top is bounded by the Shiranish Formation unconformably too. Three microfacies are identified, these are lime mudstone, planktic foraminiferal lime wackestone-packstone, keeld planktonic foraminiferal lime wackestone-packstone microfacies. All the sedimentary and fossil evidence refer that the sedimentary environment of the formation is the outer shelf to upper bathyal at the lower and upper parts of formation and its extension to the middle bathyal in the middle part of the formation. Based on the stratigraphic ranges of the recorded Calcareous nannofossils biozones, the age of the Kometan Formation at Dokan area is Late Turonian-Early Campanian.

Pre-Alpine Tectono-Stratigraphic Reconstruction of the Jurassic Tethys in the High-Pressure Internal Piedmont Zone (Stura di Viù Valley, Western Alps)

We present a detailed description of the tectono-stratigraphic architecture of the eclogite-facies Internal Piedmont Zone (IPZ) metaophiolite, exposed in the Lanzo Valleys (Western Alps), which represents the remnant of the Jurassic Alpine Tethys. Seafloor spreading and mantle exhumation processes related to the Alpine Tethys evolution strongly conditioned the intra-oceanic depositional setting, which resulted in an articulated physiography and a heterogeneous stratigraphic succession above the exhumed serpentinized mantle. “Complete” and “reduced” successions were recognized, reflecting deposition in morphological or structural lows and highs, respectively. The “complete” succession consists of quartzite, followed by marble and calcschist. The “reduced” succession differs for the unconformable contact of the calcschist directly above mantle rocks, lacking quartzite and gray marble. The serpentinite at the base of this succession is intruded by metagabbro and characterized at its top by ophicalcite horizons. Mafic metabreccia grading to metasandstone mark the transition between the “complete” and “reduced” successions. The character of the reconstructed succession and basin floor physiography of the IPZ metaophiolite is well comparable with the Middle Jurassic–Late Cretaceous succession of both the Queyras Complex (External Piedmont Zone) and the Internal Ligurian Units (Northern Apennines) and with modern slow-spreading mid-ocean ridges.

The Beni Bousera marbles, record of a Triassic-Early Jurassic hyperextended margin in the Alpujarrides-Sebtides units (Rif belt, Morocco)?

The timing and process of exhumation of the subcontinental peridotites of the Gibraltar Arc (Ronda, Beni Bousera) have been repeatedly discussed in the last decades. Here we report on high-grade marbles that crop out around the central and southeastern parts of the Beni Bousera antiform of northern Rif. Instead of being mere intercalations in the granulitic envelope (kinzigites) of the peridotites, as currently admitted, they are localized between the kinzigites and the gneisses of the overlying Filali Unit. The marbles occur in the form of minor, dismembered units in a ~30 to 300 m-thick Filali-Beni Bousera ductile shear zone (FBBSZ). They display silicate-rich dolomitic marbles, sandy-conglomeratic calcareous marbles and thinly bedded marble with interleaved phyllites, which demonstrates their sedimentary origin. A stratigraphic or tectonic unconformable contact onto the kinzigites can be locally observed. Pebbles or detrital grains include K-feldspar, quartz, and zircon. Prograde metamorphic minerals are forsterite, Mg-Al-spinel, geikielite, phlogopite, scapolite, diopside, and titanite, which characterize a peak HT-LP metamorphism close to 700-750°C, 4-7 kbar, comparable to that of the overlying Filali gneisses and of the late migmatitic stage of the kinzigites. Second-order structures within the FBBSZ are northwestward ductile thrusts, which determine kinzigite horses thrust over the marbles. Within the latter, NNE-trending folds are conspicuous. The mylonitic structures are crosscut by late, northward dipping normal faults. Varied correlations with comparable settings in the other West Mediterranean Alpine belts are discussed. We propose to correlate the Beni Bousera marbles with the Triassic carbonates deposited over the crustal units of the Alpujarrides-Sebtides. The Triassic protoliths may have been deposited onto the kinzigites or carried as allochthons over a detachment during the Early Jurassic in the frame of the hyper-extension of the Alboran Domain continental crust, as observed in the Adria and Europe inverted margins of the Western Alps. In either of these hypotheses, the currently prevailing paradigm of “hot” exhumation of the Rif–Betic peridotites during the Alpine orogeny would be reconsidered.

Early exhumation of the Beni Bousera granulites and peridotites at the northern margin of the westernmost Tethys (Rif belt, Morocco); new constraints from overlying marbles

<p>The West Mediterranean Alpine belts of the Rif and its northern counterpart, the Betics, are famous for the subcontinental peridotites exposed in their Internal zones (Alboran Domain), the Beni Bousera (BB) and Ronda massifs, respectively. The Beni Bousera Marbles (BBMs) here described are known for long in the northern Rif, but remained overlooked so far. Since <em>Kornprobst (1974)</em>, these marbles have been considered as simple intercalations within the kinzigites (migmatitic granulites) envelope of the BB peridotite. Based on the integration of field mapping, structural and petrology investigations and supported by SHRIMP U-Th-Pb geochronology, we present a new interpretation of these marbles and infer geodynamic implications at the local and regional scale. The field data show that the BBMs form minor, dismembered units within a ~30 to 300 m-thick mylonitic contact zone between the kinzigites and the overlying gneisses of the Filali Unit (Filali-Beni Bousera Shear Zone, FBBSZ). They display bedding structures marked by more or less siliceous marbles and some mica-rich or conglomeratic beds. The FBBSZ includes secondary ductile thrusts that determine kinzigite horses carried NW-ward over the marbles. Within the latter, NNE-trending folds are conspicuous. Brittle, northward-dipping normal faults crosscut the FBBSZ ductile structures. An unconformable contact, either of stratigraphic or tectonic origin, onto the kinzigites can be locally observed. The petrological investigation allows us to define pebbles and/or detrital grains, including K-feldspar, quartz, garnet, and zircon in these high-grade marbles. Peak mineral assemblage consists of forsterite, Mg-Al-spinel, phlogopite, and geikielite (MgTiO3) in dolomite marbles, phlogopite, scapolite, diopside, and titanite in calcite marbles. This characterizes a peak HT-LP metamorphism at ~700-750°C, 4-8 kbar. The BBMs compare with the Triassic carbonates deposited over the crustal units of the Alpujarrides-Sebtides. The detrital cores of the zircon grains from the BBMs yield two U-Th-Pb age clusters of ~270 Ma and ~340 Ma, distinct from the 290-300 Ma age of the zircon grains from the kinzigites (<em>Rossetti et al., 2020</em>), and supporting a Triassic age of the protoliths; the zircon rims yield ~21 Ma ages. The BBMs protoliths may have been deposited onto the kinzigites or carried later as extensional allochthons over a detachment in the frame of the incipient formation of the Alboran Domain continental margin, which is dated from the late Liassic-Dogger in the “Dorsale calcaire” detached units (<em>Chalouan et al., 2008</em>). Thus, the Beni Bousera mantle rocks would have been exhumed at shallow depth during the early rifting events responsible for the birth of the Maghrebian Tethys, i.e., as early as the Triassic-late Liassic.</p><p><strong>Keywords:</strong> BBMs/ FFBSZ/ HT-LP metamorphism/ SHRIMP U-Th-Pb geochronology / hyperextended margin/ mantle rocks exhumation / Gibraltar Arc</p><p><strong>References </strong>:</p><p>Please use this link for access to the cited references:  https://www.docdroid.net/hPSheTG/references-farah-et-al-2021-vegu-pdf </p><p> </p><p> </p><p> </p>

A revision of the stratigraphic nomenclature of the Cambrian–Ordovician strata of the Philipsburg tectonic slice, southern Quebec

The Philipsburg tectonic slice is bounded to the west by a northeast–southwest-trending thrust fault (Logan’s Line) and preserves 10 formations of Middle (?) to Late Cambrian (Milton, Rock River, and Strites Pond formations), Early Ordovician (Wallace Creek, Morgan Corner, Hastings Creek, and Naylor Ledge formations), and early Middle Ordovician (Luke Hill, Solomons Corner, and Corey formations) age. The strata were previously assigned to the Philipsburg Group. Early correlations between the Philipsburg succession and coeval strata of the St. Lawrence Platform were mainly based on sparse macrofauna and inferred stratigraphic position. Unconformities at the Cambrian–Ordovician and Early Ordovician – Middle Ordovician boundaries occurring in autochthonous St. Lawrence Platform and the allochthonous Philipsburg succession (Philipsburg tectonic slice) highlight new stratigraphic interpretations between the inner-shelf (St. Lawrence Platform) and the outer-shelf (Philipsburg) successions. The succession in the Philipsburg tectonic slice is divided into three new groups. The Middle (?) to Upper Cambrian Missisquoi Group (new) includes the Milton, Rock River, and Strites Pond formations. The upper boundary of the Missisquoi Group is defined by the upper unconformable contact between the Upper Cambrian Strites Pond Formation and overlying Lower Ordovician Wallace Creek Formation. The Missisquoi Group correlates with the Potsdam Group of the St. Lawrence Platform. The Lower Ordovician School House Hill Group (new) includes the Wallace Creek, Morgan Corner, Hastings Creek, and Naylor Ledge formations. The upper boundary of this group is marked by a regionally extensive unconformity at the top of the Naylor Ledge Formation and correlates with the younger Beekmantown-topping unconformity. The School House Hill Group is correlative with the lower to upper part of the Beekmantown Group (Theresa Formation and the Ogdensburg Member of the Beauharnois Formation) of the St. Lawrence Platform. The Middle Ordovician Fox Hill Group (new) consists of the Luke Hill, Solomons Corner, and Corey formations. This group correlates with the uppermost part of the Beekmantown Group (Huntingdon Member of the Beauharnois Formation and the Carillon Formation).

U–Pb geochronologic constraints on the cover sequence of the Monashee complex, Canadian Cordillera: Paleoproterozoic deposition on basement

The cover sequence in the Monashee complex is a platformal metasedimentary succession that occupies a nearly unique position in the Canadian Cordillera due to its unconformable contact with exposed crystalline basement. Zircon U–Pb data and field observations show that the lower part of the sequence contains Paleoproterozoic rocks, the oldest known metasedimentary rocks in the Cordilleran miogeocline, and the upper part of the sequence is Mesoproterozoic or younger. Maximum age constraints on the lower part are provided by 1.99 Ga detrital zircons from the basal unit and a 1862 ± 1 Ma orthogneiss upon which it was presumably deposited. Minimum age constraints are provided by rocks that intruded into the lower part: 1852 ± 4 Ma pegmatite, 1762 ± 6 Ma leucogranite, and 724 ± 5 Ma syenitic gneiss. The upper part of the sequence must be considerably younger than the lower part because it contains a detrital zircon dated at ~1.21 Ga. Other detrital zircons, dated at Neoarchean (2.95–2.86 Ga) and Paleoproterozoic (1.85–1.81, 1.75 Ga), suggest a source in the western Canadian Shield. These ages constrain the thickness of Mesoproterozoic and Neoproterozoic metasedimentary rocks in the cover sequence to be < 2 km. Combining these ages with previously interpreted Paleozoic deposition ages for the middle and upper parts of the sequence constrains the thickness to be <0.2 km, considerably less than that of coeval rocks above the Monashee complex in the hanging wall of the Monashee décollement. Such a contrast suggests that deposition above and below the décollement occurred in different parts of the Cordilleran miogeocline.

Cambrian and early Tremadoc rocks of the Llangynog Inlier, Dyfed, South Wales

Until recently no Cambrian rocks were known in the Llangynog area. Detailed mapping has now revealed a succession of ?Lower and Upper Cambrian rocks overlain by Tremadoc rocks. The Allt y Shed Sandstones (new) rest unconformably on the Precambrian, but have yielded no diagnostic fossils and are tentatively assigned to the Comley Series. Succeeding with faulted or unconformable contact is an Upper Cambrian Merioneth Series succession which includes in ascending order: conglomerates, sandstones and siltstones with olenid trilobites and resembling the Treffgarne Bridge Beds of the Haverfordwest area; micaceous shales and siltstones referred to the Ffestiniog Flags Formation; and black mudstones with calcareous concretions and a rich olenid fauna referred to the Dolgellau Formation. Succeeding the latter with possible disconformity is a succession belonging to the lower part of the Tremadoc Series and earlier than any rocks of that series hitherto recorded from the area.

The Malene metasedimentary rocks on Rypeø, and their relationship to Amîtsoq gneisses

Two groups of Malene metasedimentary rocks on Rypeø, a small island south of Godthåb, have been studied in detail in order to evaluate their origin and relationship to older, adjacent Amîtsoq gneiss. Field observation shows that the metasediments range from massive to finely layered, and include an unusual pod-rock ('pseudoconglomerate'), which probably represents a series of deformed sedimentary layers (or lenses) of contrasting competence. Petrographic study indicates that the metasediments are quartz-rich, contain abundant plagioclase and biotite, and small but variable amounts ofsillimanite, muscovite, microcline and garnet. Rare earth elements (REE) in samples of four metasedimentary lithologies are similar to some published analyses of 'tonalitic' Amîtsoq gneiss. These observations suggest that the protolith of the Malene metasediments on Rypeø was dominated by sandstone type lithologies which evolved in a near-shore tidal to fiuviatile environment. These sediments were probably derived by weathering and erosion of Amitsoq gneiss and deposited unconformably on such a gneissic basement. Petrological study indicates that the Rypeø metasediments were metamorphosed to the beginning of Muse + Qtz breakdown (Musc-Sill-Kfsp transition zone), and locally underwent minor amounts of melting. The proposed original unconformable contact relationships, coupled with high-grade polymetamorphism - not only of the supracrustal rocks but also of Amitsoq gneiss - indicates substantial vertical crustal movement, perhaps as much as 75 km since the time of formation of Amitsoq gneiss at - 3750 Ma.

Etude de quelques affleurements jurassiques de la region d'Alcala de los Gazules (prov. de Cadix, Espagne)

Jurassic outcrops in the Subbetic zone of the Alcala de los Gazules region, northern Cadiz, Spain, are nearly always in unconformable contact with Triassic formations and are often extensively dislocated. A complete sequence from Liassic to Cretaceous has been established, nevertheless.

Basement Carboniferous in Upper Teesdale, N. Yorks.

Excavations in Upper Teesdale, N. Yorks, exposed basement Carboniferous at its unconformable contact with underlying shales of probable Silurian age. The lowest basement beds are tough conglomerates cut by compression joints. The constituent pebbles are unsorted, locally derived, and mainly andesites and rhyolites, with vein quartz and shale pebbles. A dreikanter outline is common. The conglomerate is contrasted with others also between the Carboniferous and Lower Palaeozoic in England.