Quartzite Member Research Articles

Ichnological analysis of the Kheneg el Aatène Formation (Floian-Dapingian) at its type locality (Saoura Valley, Ougarta Range, southwestern Algeria)

ABSTRACT The Early-Mid Ordovician Kheneg el Aatène Formation of the Ougarta Range is here divided into two members: (i) the Aatène Micaceous Sandstone Member and (ii) the Aatène Quartzite Member. A low diversity trace fossil assemblage is present in the upper part of the second member with abundant Skolithos linearis, Skolithos isp. and Rosselia erecta, common Arenicolites isp. and Diplocraterion isp. and rare Palaeophycus isp. and ?Rusophycus isp. This association is characteristic to the Skolithos ichnofacies and indicates high-energy conditions and opportunistic colonisation within a siliciclastic shallow marine environment. The ichnoassemblage is dominated by vertical traces which occur in great densities forming typical Skolithos pipe-rocks. The pipe-rock ichnofabric is characterised by burrows that are closely spaced and occur at 20 distinct levels. Possible predation has been detected in the same Member due to the presence of ?Rusophycus intersecting worm burrows. High densities of Trypanites are present in two hardgrounds composed of calcareous lithified sandstones developed during transgressive pulses that can be related to the brevis event. Trypanites borings are evidenced for the first time from inorganic hard substrates of the Gondwanan Ordovician. These borings can be related to beginning of the Ordovician Bioerosion Revolution in Gondwana.

Provenance, tectonics and palaeo environment of Mesoproterozoic Saundatti Quartzite Member of Kaladgi Basin, India: A petrographic view.

The Kaladgi Basin, one of the important Proterozoic Sedimentary basins of Peninsular India, exposes a thick sequence of Proterozoic succession composed of a variety of lithologies with predominance of arenaceous rocks interrupted with Carbonate sediments at different stratigraphic levels. The present work focuses mainly on understanding the Sedimentological nature and diagenetic character of the Lower part of the Lokapur sub-group rocks that are exposed in and around Savadatti Town, Belagavi District of Karnataka. These rocks are mainly composed of Arenite sequences of varying grain size. The clastic succession comprises lithologies Sandstones with minor conglomeratic facies at the lower regimes. An attempt is made to identify the detailed petrographic character of the sandstones to understand the provenance and depositional environments based on the detailed petrographic observation. The study suggests that the coarse clastic conglomerates are essentially polymictic types and the sandstones are sub-mature to mature (mineralogically), medium to coarse grained and can be categorized mainly into lithic/feldspathic and quartz arenites. Minor occurance of feldspars as the framework constituent also suggests that the rock have undergone considerable transport. However with their variable degree of alteration (from fresh to partially alter to completely altered grains) associated with textural maturity and nature of Quartz point towards the possibility of derivation of these sediments from two different sources. Palaeocurrent data that indicate a NW palaeoslope suggest the derivation of sediments from a variety of granitic and gnesssic crystalline complexes occurring along the basin margin. The maturity of the sandstones (Quartz Arenites) is attributed to the recycling and re-working of the older sediments. Analysis of Textural parameters of these rocks pointed towards deposition under beach environments. The lack in preservation of much amount of feldspar in these sandstones is indicates a remote source and relatively dry-arid climate of the source area.

Trace fossils, depositional context, and paleogeography of the upper Tal Group (upper lower Cambrian), Lesser Himalaya, India: a Gondwanan succession with no affinities to the Avalonia microcontinent – discussion of paper by Singh et al. (2019)

Terminal Ediacaran–late early Cambrian deposition, faunas and passive margin evolution of the north Indian margin are recorded in the Nigali Dhar syncline succession. Restudy of the upper Tal Group (upper lower Cambrian Koti Dhaman Formation, KDF) ichnofauna from the Khud-Drabil section reduces it to 18 confidently named forms. The lower KDF (Lower Quartzite Member) Cruziana-Rusophycus assemblage is in subtidal (not intertidal) sandsheet facies. The overlying black Shale Member (SM) records trans-East Gondwanan deepening, not intertidal facies, in the Palaeolenus Zone. The SM, with low diversity Planolites-Palaeophycus assemblage, is overlain by subtidal (not intertidal) sandsheet facies of the middle KDF (Arkosic Sandstone Member, ASM) with shallow burrowers and furrowers (Gordia marina assemblage, new; Cruziana ichnofacies). KDF faunas with Cruziana and Rusophycus are similar to coeval, shallow marine associations elsewhere in Gondwana and NW Laurentia. Interpretation of a second KDF section 20 km from Khud-Drabil has confused an understanding of Lesser Himalaya geologic evolution as it claims Ordovician Cruziana species in the ASM and an angular SM–ASM unconformity caused by the Cambrian–Ordovician boundary Kurgiakh orogeny. However, upper lower Cambrian microfaunas occur in and above the ASM, while the angular SM–ASM unconformity is consistent with submarine sliding. KDF-type ichnofaunas do not show a tropical location of Avalonia, which has the distinctive lithofacies and biotas of a high-latitude continent unrelated to Gondwana.

La transición ediacárico-cámbrica: facies sedimentarias versus extinción

Un estudio reciente de la Cuarcita de Rawnsley, en el Ediacárico terminal Ediacaran de la Cordillera de Flinders, Australia meridional, demuestra cómo algunos taxones clave de la biota de Ediacara están restringidos a ciertas facies sedimentarias y determinados niveles estratigráficos. La Cuarcita de Rawnsleycomprende tres miembros separados por discotinuidades: (i) el Miembro basal de la Arenisca de Chace es somera y azoica, aunque destacan las superficies con texturas orgánicas; (ii) el Miemrbo de la Arenisca de Ediacara rellena un Sistema de incisiones submarinas que recortan el miembro inferior de Chace y la Arenisca parálica de Bonney, infrayacente a la Cuarcita de Rawnsley; y (iii) el Miembro de la Arenisca de Ediacara es asimismo recortada de forma erosiva por el Miembro de la Arenisca de Nilpena, menos fosilífera.

Origin and sequence stratigraphic implications of high-alumina glauconite within the Lower Quartzite, Vindhyan Supergroup

Abstract An integrated field, petrographical and geochemical investigation reveals a shallow marine dys-oxic depositional setting for the glauconite at the top of the Mesoproterozoic Lower Quartzite Member of the Vindhyan Supergroup. A thorough facies and paleogeographic analysis indicates a storm-influenced, shallow subtidal depositional condition for the glauconitic sandstone, occupying the mid-level of a transgressive systems tract (TST) deposit, which is capped by the maximum flooding zone (MFZ). The X-ray diffractional parameters confirm the evolved character of the glauconite. The mineral chemical analysis indicates the glauconite is enriched in K2O, MgO and Al2O3 and depleted in Fe2O3(total), compared to the Phanerozoic variety. It formed by the pseudomorphic replacement of the K-feldspar, by the addition of Fe2O3 at consistently high content of K2O, unlike most Phanerozoic examples. The elevated level of H3SiO4, Cl, K, Na, Mg and Fe, possibly derived by the continental weathering and/or contemporary volcanism, facilitated the glauconitization process. The high content of Mg in the glauconite corresponds to the Mg-rich, Mesoproterozoic seawater. A dys-oxic depositional condition, associated with a major marine flooding surface, favoured the formation of glauconite. While the onset of anoxic regime caused the disappearance of glauconite and the deposition of pyritiferous and carbonaceous shale in the overlying condensed zone deposits.

Integrated sedimentological, ichnological and sequence stratigraphical studies of the Koti Dhaman Formation (Tal Group), Nigali Dhar Syncline, Lesser Himalaya, India: paleoenvironmental, paleoecological, paleogeographic significance

Integrated ichnology, sedimentology and sequence stratigraphy of the Lower Quartzite Member to the Arkosic Sandstone Member of the Koti Dhaman Formation (Cambrian Series 2, Stage 4), Tal Group, Nigali Dhar Syncline, Lesser Himalayan lithotectonic zone are presented. Trilobite traces of Gondwanan affinity i.e., Cruziana salomonis, Cruziana fasciculata, Rusophycus dispar and Rusophycus burjensis are recorded along with Arenicolites isp. and Skolithos isp. from the Lower Quartzite Member. A rich and diverse ichnoassemblage attributed to the Cruziana ichnofacies is described for the first time from the Arkosic Sandstone Member of the same formation. Seven ichnofossil assemblages, i.e., Cruziana-Rusophycus, Planolites-Palaeophycus, Cruziana problematica, Diplichnites, Cochlichnus anguineus, Bergaueria perata and Psammichnites gigas have been recognized in the Lower Quartzite to Arkosic Sandstone members of the Koti Dhaman Formation. Seven sedimentary facies i.e., sandstone–shale facies (FT1), cross-bedded (trough and planar) sandstone (FT2), bedded sandstone facies (FT3), shale facies (FT4), shale–sandstone facies (FT5), shale-rippled sandstone facies (FT6) and planar and trough cross-laminated sandstone (FT7) and four facies associations FA1-FA4 are identified in the Koti Dhaman Formation. The formation contains shallowing upward parasequences of a tidal flat complex. Overall, two major events are recognized: i) the break in sedimentation between the Lower Quartzite Member and the overlying Shale Member probably related to forced-regressive event and ii) the facies shift from FT6 to FT7 of the Arkosic Sandstone Member represents an erosive transgressive event; the surface is interpreted as wave ravinement surface, which also serves as a sequence boundary. Integrated ichnology, sedimentology and sequence stratigraphic studies indicate that the Lower Quartzite Member was deposited in a shallow subtidal sand sheet complex and tidal flat complex; the Shale Member was deposited in a mud flat setting of a tidal flat complex, and the Arkosic Sandstone Member in a mixed-flat (tidal flat complex) to sand sheet complex front and margin (subtidal sand sheet complex). Overall, the lower to middle part of the Koti Dhaman Formation represents a tide-dominated shallow subtidal–intertidal to mud-flat subenvironments of the tidal flat complex. A palaeogeographic reconstruction of lower Cambrian (516–514 Ma) is presented based on the distribution of trilobite traces from the Lesser Himalaya and the Bikaner–Nagaur area of Peninsular India (eastern Gondwana), Egypt, Jordan, Turkey (western Gondwana) and Canada (Avalonia).

The Early Ordovician Middle Shale Member (Am3) of the Amdeh Formation and further evidence of conodont faunas from the Sultanate of Oman

AbstractThe Middle Shale Member of the Amdeh Formation is interpreted to be of Early Ordovician age based on its trace fossils, stratigraphic context and a newly discovered fauna of conodonts. The member abruptly overlies the Lower Quartzite Member, which may be Early Cambrian, and passes gradationally-upward into the Upper Quartzite Member, which is probably Early–Middle Ordovician. The 542.5 m thick Middle Shale Member can be divided into two parts: a shaly lower part, and a sandy upper part that contains an influx of heavy minerals. Bioturbation by marine trace fossils is one of the most obvious characteristics of the member. The shales and sandstones are interpreted to be ofCruzianaandSkolithosichnofacies and represent shallow-marine shelf, shoreface, beach and coastal deposits. Sparse shelly fossils occur in the sandy upper part, principally bivalves, inarticulate brachiopods, ostracods and conodonts. The small assemblage of conodonts includes elements interpreted to be Tremadocian (Tetraprioniodus,Drepanoistodus,Drepanodus,Scolopodus, ?Tropodus,SemiacontiodusandTeridontus), and others which may be Floian or ancestral forms of Floian taxa (Balognathidae gen. et sp. indet. A & B and aff.Erraticodon). No acritarchs have been recovered, probably due to high temperatures experienced during burial to >6 km. It is likely that the Middle Shale Member is the seaward equivalent of the Mabrouk and Barakat formations, and an outcrop gamma-ray log supports such a correlation. The trace fossils, sedimentology, conodont fauna and the general lack of macrofossils are in keeping with the regional Tremadocian–Floian of the Arabian margin of Gondwana.

Kiosk domain, Central Gneiss Belt, Grenville Province, Ontario: A Labradorian palimpsest preserved in the ductile deep crust

The Kiosk domain is a thrust sheet within a multi-component Grenvillian thrust stack, the polycyclic (evidence for pre-Grenvillian orogeny present) Bonfield-Kiosk–Algonquin stack. The stack is overlain to east and west by thrust sheets of predominantly monocyclic gneiss and uplifted along a ramp of Archean parautochthonous rocks. Central to the thrust stack, the Kiosk domain contains a homoclinal southeast-inclined core locally preserving granulite facies assemblages. Predominantly amphibolite facies shear zones, bounding and within the stack, and southeast trending folds overprint the margins of the core fabric. Finally, the Kiosk basal shear zone is locally reworked by extension. Monzonitic orthogneiss in Kiosk domain contain zircon with cores indicating protolith ages of ca. 1640Ma, and dark mantles yield an age of migmatization (and possibly of granulite facies) of ca. 1450Ma. However, metadiabase dykes containing granulite assemblages cut the ca. 1450Ma leucosome and share a southeast trending LS fabric with the country rock of the homoclinal core suggesting the possibility of an early Grenvillian, granulite event. Dating the amphibolite facies overprint is generally challenging, thin zircon rims yielding ages with large errors suggest an Ottawan (ca. 1090–1030Ma) age for stacking, consistent with a 1078±28Ma age for a shear zone which cuts the internal fabric of the stack. The Kiosk domain thus preserves successively younger Grenvillian events from core to rim interpreted to represent early thickening (homoclinal core LS fabric), retrogression-related softening (pegmatites), nappe flow (marginal shears and folds), and post convergence extension (localised shearing).The record of Paleo- early Mesoproterozoic igneous-metamorphic history preserved in the Kiosk core is complemented by detrital zircon data from a quartzite member of a metasedimentary assemblage. The detrital zircon display an age concentration spanning ca. 1500–2000Ma with a Penokean (ca. 1850Ma) maximum. Pre-Labradorian components of the age spectrum are similar to published spectra from the Penokean Upper Animikie sediments from the Lake Superior region and may represent reworking of these during early Pinwarian deposition on the Labradorian basement. We speculate that the Kiosk metasediments, metamorphosed at high grade with their hosts at ca. 1459Ma represent a pre-or early-Pinwarian back-arc (age of youngest detrital grain, ca. 1500Ma) in Labradorian crust inverted in the Pinwarian Orogeny and consistent with A-type plutonism of this age present in the Central Gneiss Belt and interpreted to have been emplaced in extended back-arc crust. The Kiosk domain is thus established as a Labradorian member of the peri-Laurentian Great Paleoproterozoic Accretionary Orogen (Condie, 2013), having received detritus from other members of the accretionary orogen as well as Laurentia.

Diagenesis of sandstones and carbonates of the Ignacio Quartzite and McCracken Sandstone Member of the Elbert Formation, southwestern Colorado, U.S.A.

Syndepositional events that affected fluvial, estuarine, and shallow-marine sediments of the units studied in southwest Colorado—the McCracken Sandstone Member of the Elbert Formation and the Ignacio Quartzite—included bioturbation, local formation of glaucony grains and phosphate crusts, local carbonate pedogenesis, and possibly silcrete pedogenesis. Although the sediments were ultimately buried up to approximately 4 km, shallow burial was the site of: (1) reddening of feldspathic sand and shale of the Ignacio Quartzite; (2) initial loss of porosity in both units by compaction of locally abundant clay clasts and clay drapes; and (3) initial partial cementation by overgrowths of feldspar and microquartz crystals. During deeper burial, the quartzarenite sands of the McCracken Sandstone Member of the Elbert Formation underwent compaction to porosity values below that typical of stable packing patterns of rigid grains followed by complete cementation by megaquartz overgrowths to produce highly indurated sandstones. Silica derived from intergranular pressure dissolution in local sandstone beds and during stylolite formation was inadequate to provide the amount of silica present in the cement. Much silica apparently was imported in fluids expelled from adjacent sedimentary basins. Such fluids were also responsible for bleaching red beds in the Ignacio Quartzite, dolomitizing limestone in the McCracken Member, and introducing small amounts of oil, some of which survives as pyrobitumen. Values of stable carbon and oxygen isotopes in dolostones in the McCracken indicate that dolomitization was accomplished by hot fluids. Kaolinite—an alteration product of K-feldspar, illite, and trace amounts of barite and sphene—formed during intermediate to deep burial.

Detrital zircon evidence for non-Laurentian provenance, Mesoproterozoic (ca. 1490-1450 Ma) deposition and orogenesis in a reconstructed orogenic belt, northern New Mexico, USA: Defining the Picuris orogeny

Detrital zircon and igneous zircon U-Pb ages are reported from Proterozoic metamorphic rocks in northern New Mexico. These data give new insight into the provenance and depositional age of a >3-km-thick metasedimentary succession and help resolve the timing of orogenesis within an area of overlapping accretionary orogens and thermal events related to the Proterozoic tectonic evolution of southwest Laurentia. Three samples from the Paleoproterozoic Vadito Group yield narrow, unimodal detrital zircon age spectra with peak ages near 1710 Ma. Igneous rocks that intrude the Vadito Group include the Cerro Alto metadacite, the Picuris Pueblo granite, and the Penasco quartz monzonite and yield crystallization ages of 1710 ± 10 Ma, 1699 ± 3 Ma, and 1450 ± 10 Ma, respectively. Within the overlying Hondo Group, a metamorphosed tuff layer from the Pilar Formation yields an age of 1488 ± 6 Ma and represents the first direct depositional age constraint on any part of the Proterozoic metasedimentary succession in northern New Mexico. Detrital zircon from the overlying Piedra Lumbre Formation yield a minimum age peak of 1475 Ma, and ~60 grains (~25%) yield ages between 1500 Ma and 1600 Ma, possibly representing non-Laurentian detritus originating from Australia and/or Antarctica. Detrital zircons from the basal metaconglomerate and the middle quartzite member of the Marquenas Formation yield minimum age peaks of 1472 Ma and 1471 Ma, consistent with earlier results. We interpret the onset of ca. 1490–1450 Ma deposition followed by tectonic burial, regional Al 2 SiO 5 triple-point metamorphism, and ductile deformation at depths of 12–18 km to reflect a Mesoproterozoic contractional orogenic event, possibly related to the final suturing of the Mazatzal crustal province to the southern margin of Laurentia. We propose to call this event the Picuris orogeny.

Chapter 15 The Witvlei Group of East-Central Namibia

Abstract The Witvlei Group is preserved in two regional synclinoria in the Gobabis-Witvlei area of east-central Namibia and as isolated outcrops 90 km SW of Rehoboth, itself some 200 km south of that area. It consists of mixed, coarse- to fine-grained siliciclastic and carbonate strata deposited in deep- to shallow-marine, and locally non-marine, settings along the post-rift continental margin of the Kalahari Craton prior to the onset of foreland basin sedimentation recorded by the overlying terminal Neoproterozoic–Cambrian Nama Group. No direct age constrains exist for the Witvlei Group, but it post-dates c. 800 Ma rift-related rocks and pre-dates the c . 548 Ma base of the Nama Group, thereby placing it as Cryogenian to Ediacaran in age. The Witvlei Group consists of three main units, from oldest to youngest, the Blaubeker, Court and Buschmannsklippe Formations. The Blaubeker Formation is highly variable in thickness and can be as much as 1000 m thick. It consists mostly of massive, polymict diamictite and, in the area of the type locality, contains conglomerate and pebbly sandstone beds. The diamictic strata combined with the presence of numerous faceted and striated clasts provide the evidence for glaciogenic influences on sedimentation. The highly variable thickness pattern likely reflects the infill of palaeo-valleys formed by the deep erosion and scouring of bedrock by ice, and the conglomerates and pebbly sandstones record glacial outwash processes. The Tahiti Formation is a locally developed, fine-grained sandstone above the Blaubeker Formation. It is poorly exposed and its exact stratigraphic relationship to the Blaubeker rocks and overlying Court Formation remains to be determined. The Blaubeker rocks are overlain sharply by the basal unit of the Court Formation, the Gobabis Member. This Member is from 20 to 60 m thick and consists mostly of dark and light grey laminated dolostones that display a δ 13 C carbonate profile that rises from values of −4‰ in the lowermost beds to values of 5‰ in the topmost. The Gobabis Member is conformably overlain by the shales, marls and thin limestones of the Constance Member followed by quartzites of the uppermost unit of the Court Formation, the Simmenau Member. The basal unit of the Buschmannsklippe Formation is the light to tan and pink grey dolostone of the Bildah Member. Its basal contact is sharp everywhere, and it is gradationally overlain by a coarsening (shoaling) upward succession from shales, thin limestones (some exhibiting formerly aragonitic fans) and fine sandstones of the La Fraque Member, to interbedded quartzites and stromatolitic and cherty dolostones of the Okambara Member. The δ 13 C carbonate profile for the Buschmannsklippe rocks shows that the basal beds of the Bildah Member begin at –4‰, followed by a decline to –6‰ in the lower La Fraque limestones and then a rise to –3‰ in the dolostones of the Okambara Member before being truncated by the base of the regionally unconformably overlying basal Weissberg Quartzite Member of the lower Nama Group. Although no glacial sediments have been recognized below the Bildah Member, its lithofacies character, stratigraphic position and C-isotopic profile are compatible with and strikingly similar to younger Cryogenian cap carbonates. Thus, the Witvlei Group arguably contains both the older and younger cap carbonates of Neoproterozoic time, but only the older Cryogenian glacial deposit.

Palaeoweathering, composition and tectonics of provenance of the Proterozoic intracratonic Kaladgi–Badami basin, Karnataka, southern India: Evidence from sandstone petrography and geochemistry

Petrographic and geochemical data on the sandstones of the Proterozoic intracratonic Kaladgi–Badami basin, southern India are presented to elucidate the palaeoweathering pattern, and composition and tectonics of their provenance. The Kaladgi–Badami basin, hosting the Kaladgi Supergroup, occupies an E–W trending area. The Supergroup unconformably overlies Archaean basement TTG gneisses, granites and greenstones, comprises a cyclic arenite–pelite–carbonate association and is divided into the Bagalkot and Badami Groups. The immature arkosic character of the basal Saundatti Quartzite Member (Bagalkot Group) containing fresh and angular feldspars, along the northern margin of the basin, suggests that during the initial stage of deposition, this part of the basin received sediments from a restricted, uplifted and less weathered source dominated by K-rich granites occurring to the north. In contrast, the Saundatti Quartzite along the southern margin displays a mostly mature, quartz-rich character with less abundant but severely weathered feldspars, and higher SiO 2 and CIA but lower Al 2O 3, TiO 2, Rb, Sr, Ba, K 2O, K 2O/Na 2O, Zr/Ni and Zr/Cr. This is interpreted in terms of a tectonically stable, considerably weathered mixed source (Archaean gneisses, granites and greenstones) along the southern fringe of the basin. The highly mature (quartz arenite) Muchkundi Quartzite Member (also of the Bagalkot Group), occurring higher up in the succession, exhibits minor but severely altered feldspars, and higher SiO 2, Na 2O, CIA, Cr and Ni with lower K 2O, Al 2O 3, TiO 2 and K 2O/Na 2O. This reflects that with the passage of time the source evolved to a uniform, extensively weathered, tectonically stable peneplained provenance which consisted of less evolved TTG gneisses and greenstones. This was followed by closure, deformation and upliftment of the basin hosting the Bagalkot Group and subsequent deposition of the Badami Group. Sandstone Members of this younger Group (Cave-Temple Arenite and Belikhindi Arenite) range widely in mineralogy (quartz arenite to arkose) and chemistry (including CIA), and point to a source that varied from uplifted, less weathered K-rich granites to less evolved, peneplained TTG gneisses and greenstones or even Bagalkot sediments. Variable alteration of feldspars in the Kaladgi sandstones and severe depletion of Ca, Na and Sr in the associated shales indicate a humid tropical (tropical and subtropical) climate facilitating chemical weathering.

Controls to hydrothermal gold mineralization in the Witwatersberg Goldfield; situated in the floor to the south of the Bushveld Complex, South Africa

An exploration programme over the Blaauwbank group of gold deposits in the Witwatersberg Goldfield, which lies to the south and in the footwall of the Bushveld Complex, South Africa, has shown that these deposits possess many similarities and some differences to turbidite-hosted gold deposits. The dominant control to this hydrothermal mineralization is structural, with the associated quartz veins being localized along bedding planes, fold axes and a variety of semi-ductile to brittle faults. The deposits of the Witwatersberg Goldfield are also preferentially located in the Klapperkop Quartzite Member and overlying shales of the Timeball Hill Formation, Transvaal Supergroup. The rocks do not appear to form a particularly favourable protore but rather represent a favourable depositional site. The competency contrast of the shales, siltstones and sandstones in this stratigraphic interval is regarded as being important in facilitating vein formation, and the zone is also characterized by a high Fe 2+/Fe 3+ ratio and high C content, which may have reduced the mineralizing fluids and caused gold to precipitate. Fluid inclusion data show the quartz veins formed at 250–330 °C and pressures of 1.3–1.75 kb, from CaCl 2-rich brines. Comparison with structural studies to the north and with the Sabie-Pilgrim’s Rest Goldfield to the east suggest that the mineralization probably predates the peak of metamorphism related to the intrusion of the Bushveld Complex.

Abstracts of The Paper Published only In The Turkish Edition of This Bulletin The Geology and Petrography of The Late Neoproterozoic-Early Paleozoic Units of Western Taurides (SW Of Sandıklı, Afyon)

S OF THE PAPER PUBLISHED ONLY IN THE TURKISH EDITION OF THIS BULLETIN THE GEOLOGY AND PETROGRAPHY OF THE LATE NEOPROTEROZOIC EARLY PALEOZOIC UNITS OF WESTERN TAURIDES (SW OF SANDIKLI, AFYON) Semih GURSU* and M. Cemal GONCUOĞLU** Abstract.The investigated area including the region of the junction of the Middle and Western Taurides, comprise distinctive Middle Taurides stratigraphy and tectonic features. The units, cropped out in Sandikli, Karadirek, Basagac, Akharim, Tasoluk and surrounding areas are divided into three parts as Sandikli Basement Complex, Early Paleozoic Cover Units and Mesozoic Cover Units. Sandikli Basement Complex is composed of Guvercinoluk formation and Kestel Cayi Porphyroid Suite from bottom to top; Early Paleozoic cover units consist of Gogebakan, Hudai, Caltepe and Seydisehir formations respectively; Ilyasli and Derealani formations represent Mesozoic cover units. Mesozoic Cover Units is technically overlain by Sandikli Basement Complex in the western part of the Sandikli. Sandikli Basement Complex is formed an overturned antiformal structure within NNW SSW direction. Meta-sedimentary and meta-magmatic rocks of Sandikli Basement Complex are described as Guvercinoluk formation and Kestel Cayi Porfiroid Suite. Kestel Cayi Porphyroid Suite is composed of meta-rhyolite/meta-dacite and meta-quartz porphyry dikes. Meta-quartz porphyry dikes of Kestel Cayi Porphyroid Suite intrude the meta-sedimentary rocks of SBC (Guvercinoluk formation) and meta-rhyolite/meta-dacite rocks which formed rhyolitic composition carapace. Sandikli Basement Complex are cut by green-dark green colored continental tholeiitic basalt compositions dikes. Sandikli Basement Complex rocks are unconformably overlain by Early Cambrian Gogebakan formation. Upward, the formation is transitional to Celiloglu member of Hudai forma tion. The unit's age indicate Tommotian (Early Cambrian) age according to trace fossils at the transition between Celiloglu member of Hudai formation and Gogebakan formation. Celiloglu member is made up of alternation of green colored meta-mudstone/meta-siltstone and green-beige colored meta-sandstone and is transitional to Orenkaya quartzite member with slate bearing meta-sandstone (quartzite). Hudai formation is conformably overlain by Lower-Middle Cambrian Caltepe formation, which is made up of reddish-brown colored recrystalized dolomite and pink colored nodular limestones. The unit continues Middle Cambrian Early Ordovician Seydisehir formation including anchi-metamorphic milstone, nodular limestones, shales and sandstones, which have a narrow contact in the investigated area. Mesozoic cover units are represented by Early Liassic Ilyasli formation with Early Liassic-Early Malm Derealani formation. It is considered that the unconformity of Sandikli Basement Complex and Early Cambrian cover units correspond to Main Pan-African unconformity in Menderes Massif (Sengor et. al., 1984) and Menderes Massif, Eastern Taurides and similar units are pertaining to parts of PanAfrican basement.The investigated area including the region of the junction of the Middle and Western Taurides, comprise distinctive Middle Taurides stratigraphy and tectonic features. The units, cropped out in Sandikli, Karadirek, Basagac, Akharim, Tasoluk and surrounding areas are divided into three parts as Sandikli Basement Complex, Early Paleozoic Cover Units and Mesozoic Cover Units. Sandikli Basement Complex is composed of Guvercinoluk formation and Kestel Cayi Porphyroid Suite from bottom to top; Early Paleozoic cover units consist of Gogebakan, Hudai, Caltepe and Seydisehir formations respectively; Ilyasli and Derealani formations represent Mesozoic cover units. Mesozoic Cover Units is technically overlain by Sandikli Basement Complex in the western part of the Sandikli. Sandikli Basement Complex is formed an overturned antiformal structure within NNW SSW direction. Meta-sedimentary and meta-magmatic rocks of Sandikli Basement Complex are described as Guvercinoluk formation and Kestel Cayi Porfiroid Suite. Kestel Cayi Porphyroid Suite is composed of meta-rhyolite/meta-dacite and meta-quartz porphyry dikes. Meta-quartz porphyry dikes of Kestel Cayi Porphyroid Suite intrude the meta-sedimentary rocks of SBC (Guvercinoluk formation) and meta-rhyolite/meta-dacite rocks which formed rhyolitic composition carapace. Sandikli Basement Complex are cut by green-dark green colored continental tholeiitic basalt compositions dikes. Sandikli Basement Complex rocks are unconformably overlain by Early Cambrian Gogebakan formation. Upward, the formation is transitional to Celiloglu member of Hudai forma tion. The unit's age indicate Tommotian (Early Cambrian) age according to trace fossils at the transition between Celiloglu member of Hudai formation and Gogebakan formation. Celiloglu member is made up of alternation of green colored meta-mudstone/meta-siltstone and green-beige colored meta-sandstone and is transitional to Orenkaya quartzite member with slate bearing meta-sandstone (quartzite). Hudai formation is conformably overlain by Lower-Middle Cambrian Caltepe formation, which is made up of reddish-brown colored recrystalized dolomite and pink colored nodular limestones. The unit continues Middle Cambrian Early Ordovician Seydisehir formation including anchi-metamorphic milstone, nodular limestones, shales and sandstones, which have a narrow contact in the investigated area. Mesozoic cover units are represented by Early Liassic Ilyasli formation with Early Liassic-Early Malm Derealani formation. It is considered that the unconformity of Sandikli Basement Complex and Early Cambrian cover units correspond to Main Pan-African unconformity in Menderes Massif (Sengor et. al., 1984) and Menderes Massif, Eastern Taurides and similar units are pertaining to parts of PanAfrican basement.

Multiple pyroxene and amphibole assemblages in the amphibolite facies: Bulk compositional controls

This paper presents studies of samples from different localities of the Garnet-Amphibole-Magnetite (GAM)-Quartzite Member of the Ammonoosuc Volcanics from southern New England, USA. Based on stratigraphic and geochemical evidence, earlier workers interpreted the Ammonoosuc Volcanics as part of a volcanic island-arc complex. As such, these rocks have a highly varied stratigraphy with a wide spectrum of chemical compositions. During subsequent metamorphism, these rocks reached amphibolite-facies conditions (6 kbar and 580–640 °C). Within the Ammonoosuc Volcanics, a fine-grained, garnet-, magnetite-, and amphibole-bearing quartzite forms a distinct stratigraphic horizon. The quartzite commonly shows delicate millimeter- to centimeter-thick layering, which is interpreted as an original depositional feature that could have formed by precipitation from solutions enriched in silica, iron, and manganese. Volcanic detritus that was rich in Al, Ca, Mg, and Na could account for the variation in concentration of these elements, which are present along with Fe, Mn, and Si in some laminae of these quartzites. The mineralogy of layers within these quartzites can vary greatly on the scale of several centimeter. The most mineralogically complex layers contain, in addition to quartz, garnet, and magnetite, and one or more of the amphiboles cummingtonite, anthophyllite, or hornblende. In the most recent investigations of these rocks, both orthopyroxene and clinopyroxene have been identified in a few samples. A comparison of Mn contents of minerals that are common to different assemblages indicates that the pyroxenes are present in bulk compositions rich in Mn. The Mn content of the bulk composition is the most important factor controlling the mineralogy, and increasing the Mn content causes changes in the mineralogy that mimic the same progression of assemblages that is seen in mafic rocks undergoing the amphibolite- to granulite-facies transition.

Environmental interpretation and a sequence stratigraphic framework for the terminal Proterozoic Ediacara Member within the Rawnsley Quartzite, South Australia

Fossils of the Ediacara biota are confined to preservational windows in the Ediacara Member of the Rawnsley Quartzite (Pound Subgroup), from the Flinders Ranges, South Australia. The base of the Ediacara Member is a type 1 sequence boundary incised into the partly lithified Chace Quartzite Member of the Rawnsley Quartzite. The Ediacara Member and the upper half of the Rawnsley Quartzite comprise the Rawnsley depositional sequence, bounded above by the Early Cambrian Uratanna depositional sequence. The Rawnsley sequence developed over an erosional surface cut into the Chace Quartzite Member, with some 250 m of relief. Southeasterly directed palaeovalleys are filled with a sequence of massive sandstone and laminated siltstone passing up into well bedded sandstone. At lowstand, local channels were filled by massive sand. The highstand systems tract consists of several parasequence sets of laminated siltstone and channelized, amalgamated massive sandstone overlain by interbedded siltstone and sandstone grading up into well-bedded, clean sandstone. Impressions of soft-bodied Ediacaran organisms are preserved above the valley fill facies on sandstone partings within upward-shoaling, delta-front environments between storm- and fairweather wavebase. The Ediacara Member is, in places, conformably overlain by up to 500 m of sandstone of the same lithofacies as those underlying the member. Distinctive microbial-mat-bound sand laminae, described as petee structures, are characteristic of the Rawnsley Quartzite above and below the Ediacara Member. During deposition of the Ediacara Member, colonization of the deeper substrates by microbial mat communities enabled preservation of the Ediacara biota. The erosional surface at the base of the Ediacara Member is one of at least four incision events recorded in the terminal Proterozoic and Early Cambrian succession of the Adelaide Geosyncline. The similarity of incision-filling lithofacies of the Rawnsley and Uratanna sequences has, in condensed sections, led to confusion between the depositional sequences. Characteristic trace and body fossil assemblages provide the only clear distinction between depositional cycles spanning the Proterozoic–Cambrian boundary.

Analysis of the Skolithos Ichnofacies from the Cambrian Mont Alto Quartzite Member of the Harpers Formation in South Central Pennsylvania

Analysis of the <i>Skolithos</i> Ichnofacies from the Cambrian Mont Alto Quartzite Member of the Harpers Formation in South Central Pennsylvania

The tin zone: sediment-hosted hydrothermal tin mineralization at Rooiberg, South Africa

The Rooiberg tin field, also known as the Rooiberg Fragment, is located within the western lobe of the Bushveld Complex. The fragment is triangular-shaped, consists of early Proterozoic Transvaal Sequence volcano-sedimentary rocks, and is surrounded by granitoid intrusives of the Lebowa Granite Suite. Practically all the significant tin deposits are hosted by arkoses, located towards the transition with shaly arkoses at the stratigraphic top of the Boschoffsberg Quartzite Member. This stratabound distribution of individual deposits gave rise to the concept of a regionally developed continuous stanniferous zone. On regional scale, the individual deposits are broadly similar and are collectively classified as replacement and open space-filling type. Particular styles of mineralization such as tourmaline pockets/orbicules, disseminated cassiterite, steep and flat dipping sulphidic fractures and hydrothermal carbonate breccias appear to dominate each mine. Petrological and geochemical investigations of four mineralized centres, indicated the presence of a 500–600 m thick stratified zone of pervasively altered clastic sedimentary rocks of possible arkosic precursor composition. Alteration displays a distinct zonal distribution consisting of a grey-green sodic (albitized) foot wall, an approximately 80 m transitional sericitized-tourmalinized sulphidic tin zone and red hematitic potassic hanging wall. The observed zonal pattern and localization of economically significant cassiterite, is explained by the evolutionary path of magmatic stanniferous hydrothermal fluids genetically related to the surrounding acid phase of the Bushveld Complex. Areas of high fracture density, the tectonic focal points, acted as conduits for the ascending reactive fluids. Factors such as fluid-lithostatic pressure equilibration, limited fracture evolution and/or impermeable shaly arkose retarded this ascent. As a result accumulation, lateral spreading of fluid and pervasive alteration occurred over a broad stratified front. Lateral overlapping of these fronts creates the impression of a continuous tin zone. Abundance of geochemical common denominators between the various focal points (mines) supports a shared composition and source for these contemporaneous fluids.

The geology and genesis of the Tarcoola gold deposits, South Australia

The Tarcoola goldfield is located in the Gawler Craton in northwestern Eyre Peninsula, South Australia. The gold deposits are hosted in the Middle Proterozoic Tarcoola Formation, comprised of the fluviatile Peela Coglomerate Member, the shallow marine Fabian Quartzite Member, and the marine Sullivan Shale Member. Mineralization in the goldfield consists of north-northeast to north-northwest trending gold-bearing quartz veins with associated hematite, pyrite, arsenopyrite, sphalerite, chalcopyrite, galena, electrum and gold. Adamellite in contact with the Tarcoola Formation has previously been included in the Middle Proterozoic Hiltaba Suite granitoids, on the basis of an apparent intrusive relationship with the Tarcoola Formation, and the gold-quartz veins were interpreted as being genetically related to the cooling pluton. However, detailed field and petrographic studies have demonstrated that the contact between the Tarcoola Formation and adamellite is a nonconformity. Hence, there is no genetic relationship between the mineralization and the adamellite. Oxygen isotope data indicate that an oreforming fluid, derived from convective circulation of meteoric or seawater, or from formation water, underwent isotope exchange with sediments of the Tarcoola Formation. A magmatic heat source for the hydrothermal system is suggested by the presence of intrusive igneous rocks, including dykes of aplite, quartz monzonite and microdiorite. Sulphur isotope characteristics of the mineralization can be explained by reduction of seawater sulphate or dissolution of disseminated sulphides in the sedimentary sequence. Metals were probably derived from rocks of the Tarcoola Formation. A complex paragenetic sequence involved deposition of minerals in several stages separated by episodes of fracturing. Fluid inclusions in quartz and fluorite show that deposition took place over a temperature range of about 340° to 110°C from a low salinity fluid. Analyses of chlorite coexisting with sulphide minerals suggest deposition of sulphides from about 300° to 170°C. Gold was transported as Au(HS) 2 − and deposition appears to have coincided with a sudden decrease in fO2 at around 260° to 250 °C.

Contents volume 63, 1993

The Kiosk domain is a thrust sheet within a multi-component Grenvillian thrust stack, the polycyclic (evidence for pre-Grenvillian orogeny present) Bonfield-Kiosk–Algonquin stack. The stack is overlain to east and west by thrust sheets of predominantly monocyclic gneiss and uplifted along a ramp of Archean parautochthonous rocks. Central to the thrust stack, the Kiosk domain contains a homoclinal southeast-inclined core locally preserving granulite facies assemblages. Predominantly amphibolite facies shear zones, bounding and within the stack, and southeast trending folds overprint the margins of the core fabric. Finally, the Kiosk basal shear zone is locally reworked by extension. Monzonitic orthogneiss in Kiosk domain contain zircon with cores indicating protolith ages of ca. 1640 Ma, and dark mantles yield an age of migmatization (and possibly of granulite facies) of ca. 1450 Ma. However, metadiabase dykes containing granulite assemblages cut the ca. 1450 Ma leucosome and share a southeast trending LS fabric with the country rock of the homoclinal core suggesting the possibility of an early Grenvillian, granulite event. Dating the amphibolite facies overprint is generally challenging, thin zircon rims yielding ages with large errors suggest an Ottawan (ca. 1090–1030 Ma) age for stacking, consistent with a 1078 ± 28 Ma age for a shear zone which cuts the internal fabric of the stack. The Kiosk domain thus preserves successively younger Grenvillian events from core to rim interpreted to represent early thickening (homoclinal core LS fabric), retrogression-related softening (pegmatites), nappe flow (marginal shears and folds), and post convergence extension (localised shearing).The record of Paleo- early Mesoproterozoic igneous-metamorphic history preserved in the Kiosk core is complemented by detrital zircon data from a quartzite member of a metasedimentary assemblage. The detrital zircon display an age concentration spanning ca. 1500–2000 Ma with a Penokean (ca. 1850 Ma) maximum. Pre-Labradorian components of the age spectrum are similar to published spectra from the Penokean Upper Animikie sediments from the Lake Superior region and may represent reworking of these during early Pinwarian deposition on the Labradorian basement. We speculate that the Kiosk metasediments, metamorphosed at high grade with their hosts at ca. 1459 Ma represent a pre-or early-Pinwarian back-arc (age of youngest detrital grain, ca. 1500 Ma) in Labradorian crust inverted in the Pinwarian Orogeny and consistent with A-type plutonism of this age present in the Central Gneiss Belt and interpreted to have been emplaced in extended back-arc crust. The Kiosk domain is thus established as a Labradorian member of the peri-Laurentian Great Paleoproterozoic Accretionary Orogen (Condie, 2013), having received detritus from other members of the accretionary orogen as well as Laurentia.