Intraformational Conglomerates Research Articles

Stratigraphy and microfacies analysis of the Lower–Middle Jurassic platform carbonate succession in the Yeşilovacık (Mersin) area (Central Taurides, S Turkiye)

This study covers the detailed analyses of stratigraphy, microfacies and depositional environments of the Lower-Middle Jurassic carbonate succession in the southern part of Anatolide-Tauride Carbonate Platform in southern Türkiye (south of Central Taurides, around Yeşilovacık). The carbonate succession is composed of the Dibekli and Tokmar formations, and the Işıklıkızıtepe Member which forms the base of the Tokmar Formation. The Dibekli Formation (Upper Sinemurian-Lower Bajocian) is composed of limestones intercalated with intraformational conglomerates in the lower parts, with dolostones in the lower to middle parts and with oncoidal limestones in middle to upper parts. The Işıklıkızıtepe Member (Upper Bajocian) starts with basal conglomerates containing brown-red- iron nodules and consists of sandstone and sandy-clayey limestone alternations. These are overlain by thin limestone layers passing upward to thick-bedded dolostones of the Tokmar Formation (Upper Bajocian–Bathonian). The middle to upper parts of the formation are composed of sandy, oncoidal limestones rich in bivalve shells and end with dolostones-limestone alternations in the upper part. According to microfacies analyzes and litho-bio content; Late Sinemurian-Plesbachian is a period that low-to moderate-energy, restricted inner platform conditions dominated the depositional environments. The presence of comman intraformational conglomerates shows tectonic activity from time to time in this period. The Toarcian to the earliest Bajocian, low-energy intertidal and shallow lagoon conditions dominated the depositional environments, and in the Early Bajocian, the depositional environment changed to a high-energy sand shoal and above wave base environment. The basal conglomerate consisting of brown-red, iron-noduler and bauxite grains at the base of the earliest Late Bajocian indicates a short-term emersion and continued under low energy shallow lagoonal conditions during the Late Bajocian–Bathonian. Environmental changes during the Toarcian to Early Bajocian, and the earliest Late Bajocian short-term emersion, and the environmental changes during the Late Bajocian-Bathonian are interpreted to short-term sea level changes. Yeşilovacık Lower-Middle Jurassic carbonate sequences are correlated with those in peri-Mediterranean platforms. They show close similarities to the other Tauride carbonate sequences in terms of stratigraphy and facies. Paleontological and sedimentological analyses enable us to reconstruct a detailed dating and paleoenvironmental evolution for the Yeşilovacık carbonate deposits during the Lower-Middle Jurassic period.

Sandstones and red beds in the Lower Cretaceous Sidi Aich Formation, Chotts Basin (Southern Tunisia): facies, architecture and depositional environments

Abstract The Lower Cretaceous deposits of North Africa represent a terrestrial to shallow-marine sandstone-dominated succession often referred to as the ‘Continental Intercalaire’ and Nubian Sandstone informal groups. The upper Barremian Sidi Aich Formation of the Continental Intercalaire is distinguished throughout the Chotts basin of southern Tunisia by sandstone-dominated sequences within conglomerate, calcareous siltstone and palaeosol red bed occurrences. This paper aims to highlight: (1) the facies distribution, internal architecture and depositional environment of the sandbodies; and (2) the origin, spatial distribution and architecture of the red beds that underlined and topped sandbodies. Strata in the Zimlet El Beida anticlinal structure, Chotts basin, offer a good opportunity for detailed field observations and bed-by-bed logging of three representative lithostratigraphic sections. Detailed sedimentological investigation allows the recognition of several lithofacies grouped into three facies associations indicating tidal flat, tidal channel and tidal bar depositional settings characterizing a transgressive tide-dominated estuarine system that developed during an episode of relative sea-level fluctuations in the Early Cretaceous. The high-resolution petrographic, mineralogical and geochemical analyses of the red beds allow the differentiation of three distinct lithofacies sets including: (1) intraformational conglomerates; (2) calcareous siltstones; and (3) palaeosol. Major red beds comprise detrital grains inherited from the host or parent sediment and authigenic minerals (dolomite, calcite and hematite) precipitated during the diagenetic processes. Grain components have been partially or completely cemented and/or replaced by terrestrial phreatic dolomite. The negative δ 13 C and δ 18 O signatures of the dolomite analyses indicate that the dolomitization processes have been influenced by fluctuations of the groundwater table or climate change from semi-arid to semi-humid conditions. This study, therefore, may provide useful data for the better understanding of the internal architecture of the red beds associated with sandbodies that represent the main and significant potential reservoir within the Lower Cretaceous Continental Intercalaire sandstone-dominated groundwater aquifers of the Chotts basin.

Tracking Rodinia Into the Neoproterozoic: New Paleomagnetic Constraints From the Jacobsville Formation

AbstractThe paleogeography of Laurentia throughout the Neoproterozoic is critical for reconstructing global paleogeography due to its central position in the supercontinent Rodinia. We develop a new paleomagnetic pole from red siltstones and fine‐grained sandstones of the early Neoproterozoic Jacobsville Formation which is now constrained to be ca. 990 Ma in age. High‐resolution thermal demagnetization experiments resolve detrital remanent magnetizations held by hematite. These directions were reoriented within siltstone intraclasts and pass intraformational conglomerate tests—giving confidence that the magnetization is detrital and primary. An inclination‐corrected mean paleomagnetic pole position for the Jacobsville Formation indicates that Laurentia's motion slowed down significantly following the onset of the Grenvillian orogeny. Prior rapid plate motion associated with closure of the Unimos Ocean between 1,110 and 1,090 Ma transitioned to slow drift of Laurentia across the equator in the late Mesoproterozoic to early Neoproterozoic. We interpret the distinct position of this well‐dated pole from those in the Grenville orogen that have been assigned a similar age to indicate that the ages of the poles associated with the Grenville Loop likely need to be revised to be younger due to prolonged exhumation.

First Results of the Intraformational Conglomerate Test of the Late Riphean Katav Formation (Southern Urals)

Detailed petrographic, electron-microscopic, and paleomagnetic studies were conducted on flatbedded synsedimentary carbonate breccias from three blocks of rocks (one block from Minyar, two blocks from Katav-Ivanovsk) to verify the ideas about the time of formation of the high-temperature component (HTC) of natural remanent magnetization (Jn) of limestones from the Upper Riphean Katav Formation, Southern Urals. Petrographic and electron-microscopic observations revealed that the composition of pebbles corresponds to that of the host matrix rocks, thus enabling the use of an intraformational conglomerate test. In all the studied blocks, the distribution of paleomagnetic directions for pebbles is generally chaotic, with the concentration parameter not exceeding 3. These test results meet the Graham criterion. The pebbles’ average Jn have a larger confidence oval and differ significantly from the matrix’s directions with a much smaller confidence oval. The Hodges-Ajne test was applied to the blocks from Katav-Ivanovsk. The Rayleigh test was used for the block from Minyar. The results obtained at this stage indicate that the HTC of magnetization of the Katav limestones may have a primary origin. If this is confirmed, the Katav Formation would be a good paleomagnetic record of the Earth’s Neoproterozoic history and provide valuable insights into the geomagnetic field behavior in the Late Precambrian.

Depositional Setting of Khurmala Formation (Paleocene-Early Eocene) in Nerwa section, Berat Anticline, Kurdistan Region, Northern Iraq

The depositional environment of the Khurmala Formation (Paleocene-Early Eocene) has been investigated in the Nerwa section, the southern limb of the Berat anticline in the High Folded Zone of Iraq. The thickness of the formation in the studied section was about 113m and can be divided into three units; fossiliferous bedded limestone unit (Unit A), massive dolomitic limestone unit (Unit B) and bedded marly dolomitic limestone unit (Unit C). The petrographic study of the 81 thin sections of the Khurmala carbonates revealed that the majority of skeletal grains are shallow marine derivative faunas and non-skeletal grains include peloids, cortoids and intraclasts. Depending on detailed field observations and petrographic study of the carbonate rocks, five main microfacies were recorded, these are; lime mudstone, lime wackestone, lime packstone, grainstone and boundstone in addition to one lithofacies which is an intraformational conglomerate. Based on the integration of the recognized microfacies and the field criteria of the Khurmala Formation, two facies associations were identified which elucidate deposition in a lagoonal environment including reef patches. Accompanying facies indicate that the formation's sedimentary model is a ramp carbonate platform.

Geochemistry, ichnology, and sedimentology of omission levels in Middle Triassic (Muschelkalk) platform carbonates of the Germanic Basin (southern Poland)

Sedimentology and paleoecology of omission or discontinuity surfaces in carbonate strata is well documented, but the geochemistry of such surfaces is poorly recognized. This work describes morphology, fabrics, geochemistry, and biota succession in omission levels from Middle Triassic (Muschelkalk) platformal carbonates in Upper Silesia, southern Poland. Three types of omission levels are distinguished: firmgrounds, hardgrounds, and intraformational conglomerates. (1) Firmgrounds are characterized by burrows of Balanoglossites triadicus . Some burrows are enclosed by a dark and/or (minor) bright diagenetic halo. The prevailing dark color, lower δ 13 C and δ 18 O ratios, and increased concentration of redox-sensitive elements (U, As, Mo, Cu, Zn, Pb, Ni) in the halos compared to the host micrite indicate a significant enrichment in organic matter, which most likely resulted from impregnation of the burrow walls with organic mucus from the burrowing organism, a process observed in modern burrows. The burrow walls were in contact with stagnant saline water (recorded by elevated 87 Sr/ 86 Sr), but were locally bleached by oxygenated fresh seawater pumped by the burrow producer. (2) Hardgrounds show encrustations of the bivalve Placunopsis ostracina and borings Trypanites weisei . In many hardgrounds, the uppermost 5-mm-thick layer has a different color and higher δ 18 O values than the underlying micrite. This heavier δ 18 O signal reflects a higher content of 18 O-enriched early-marine microcrystalline cement precipitated from colder bottom seawater. (3) Intraformational conglomerates consist of flat pebbles derived from reworked firmgrounds and hardgrounds. Many pebbles contain the same encrustations and borings as observed in the hardgrounds, which occur on both sides of the clasts and mimic their shape, indicating that they were developed after pebble formation. All studied types of omission level are laterally discontinuous at some scale and are thus unsuitable for regional correlation. • Firmground burrows are surrounded by dark and/or minor bright early diagenetic haloes. • Dark haloes are enriched in redox-sensitive elements and 12 C and 87 Sr stable isotopes. • These proxies suggest organic matter in burrow walls and stagnant water in burrows. • Hardground top surfaces show discoloration, bedding-parallel halo, and elevated δ 18 O. • This elevated δ 18 O implies early cementation by cold bottom seawater.

Synsedimentary deformation structures within the Paleoproterozoic Espanola Formation, Huronian Supergroup, Canada: Implications for basin tectonism and paleodepositional conditions

The Espanola Formation represents part of the lower Huronian Supergroup (2.45–2.2 Ga), which is interpreted to have been deposited in a restricted, fault-bound, intracontinental rift basin during Early Proterozoic episodes of crustal stretching and contemporaneous faulting along the southern margin of the Archean Superior Province. Field examination of Espanola Formation outcrops exposed north of Elliot Lake, Ontario, Canada, revealed widespread synsedimentary deformation structures, which can be broadly grouped into three main categories: (1) forceful-injection structures, (2) slump structures, and (3) soft-sediment deformation structures. Examples of these structures include clastic dykes, large-scale slump structures, intraformational conglomerate, load casts, ball-and-pillow structures, convolute laminae, and dish-and-pillar structures. Most of the reported deformation structures are restricted to discrete stratigraphic horizons, are laterally continuous on an outcrop scale, are abundant and widespread across the studied region and are confined between undisturbed strata of similar lithology. These characteristics strongly indicate an origin by liquefaction and fluidization mechanisms that were triggered by syndepositional rift-related seismic activity, inferred to have been induced by movement along bounding normal faults during subsidence of the lower Huronian basin. Autogenic triggers such as overloading by rapid sedimentation, slump emplacement, inverse density gradient, gravity-driven sediment transport and mobilization, and storm waves may have also locally contributed to the development of the reported soft-sediment deformation structures.

Sedimentary facies analysis of the fluvial environment in the Siwalik Group of eastern Nepal: deciphering its relation to contemporary Himalayan tectonics, climate and sea-level change

The Siwalik Group, ranging from the Early Miocene to Pleistocene, is believed to be deposited in the fluvial environment and controlled by contemporary Himalayan tectonics and climate. In this study, we established the fluvial environment and its controlling factors responsible for the deposition of the Siwalik succession along the Muksar Khola section in the eastern Nepal Himalaya. Five sedimentary facies associations are identified; these are interpreted as the deposits of flood plain-dominated fine-grained meandering river (FA1), flood-dominated overbank environment (FA2), sandy meandering river (FA3), anastomosing river (FA4), and debris flow-dominated gravelly braided river (FA5). These changes in the fluvial system occurred around 10.5 Ma, 10.0 Ma, 5.9 Ma and 3.5 Ma, defined by existing magnetostratigraphy constraints, due to the effects of hinterland tectonics, climate and sea-level change and continuous drifting of the foreland basin towards the hinterland concerning depositional age. The thick succession of an intraformational conglomerate reveals intensification of the monsoon started around 10.5 Ma in the eastern Nepal Himalaya. The present study also shows asynchronous exhumation of the Himalaya from east to west brought a significant difference in the fluvial environment of the Neogene foreland basin.

New Paleointensities From the Skinner Cove Formation, Newfoundland, Suggest a Changing State of the Geomagnetic Field at the Ediacaran‐Cambrian Transition

AbstractThe geomagnetic field in the Ediacaran period appears to be characterized by anomalous directions, high reversal frequencies, and ultra‐low field strength. At the Ediacaran‐Cambrian transition, apparent polar wander paths become less controversial, but hyper‐reversing fields with reversal frequencies similar to earlier in the Ediacaran have been reported until the mid‐Cambrian. To understand the long‐term behavior of the magnetic field during this transitional interval, information about the field strength is vital but currently lacking. To improve the intensity record at that time, samples of volcanic rocks from the 550 Ma Skinner Cove Formation, western Newfoundland, have been used for paleointensity determination. This multi‐method paleointensity study, utilizing thermal and microwave Thellier as well as double‐heating Shaw and pseudo‐Thellier experiments produces paleointensity estimates of 2.6–10.3 μT, corresponding to virtual dipole moments of 0.65–2.25 × 1022 Am2. Analyses using scanning electron microscopy and rock magnetic measurements, as well as a positive intraformational conglomerate test, suggest that the remanence is primary. These intensity estimates are higher than earlier Ediacaran intensities and could point to the geomagnetic field entering into a stronger, more dipole‐dominated state at the Ediacaran‐Cambrian boundary.

An Initial Collision of India and Asia in the Equatorial Humid Belt

AbstractPaleocene lavas of the Dianzhong Formation preserved in the Linzhou Basin of South Tibet provide a unique opportunity to constrain the initial geometry of the India‐Asia collision; however, earlier studies argued a complex magnetic signature resulting from thermal and/or chemical remagnetizations. To better characterize the remanences obtained from the Dianzhong lavas, we carried out an intraformational conglomerate test on a previously‐studied section in the Linzhou Basin. The positive conglomerate test suggests that the characteristic remanences reported from the Dianzhong Formation are primary. The updated Paleocene pole confirms a paleolatitude of 6.7° ± 4.4°N for the Lhasa terrane and positions the southern margin of Asia in the equatorial humid belt. An initial collision, between India, Asia and an intra‐oceanic arc in the equatorial humid belt, may have intensified silicate weathering and resulted in an extra consummation of carbon dioxide, which contributes to a long‐term cooling of the Earth during the Cenozoic.

Neoproterozoic sedimentation and depositional environment: an example from Narji Formation, Cuddapah Basin, India

In the west-central part of Kurnool sub-basin of Cuddapah Basin, around Betamcherla–Bagannapali area, the Neoproterozoic Narji Formation rocks (Kurnool Group) of Cuddapah Supergroup are deposited. Sedimentary facies analysis including sedimentary structures and petrographic analysis of the studied samples have been carried out for understanding the depositional environment of the studied formation during Neoproterozoic time period. Sedimentological investigation of the studied formation rocks reveals intertidal-to-subtidal facies associations consisting of six lithofacies such as quartzite bearing massive purple limestone, laminated limestone, calcareous shale, heterolithic, massive whitish grey limestone and intra-formational conglomerate. Sedimentary deformation structures such as load structures and slump structures (micro-faults and folds) indicate perturbation and basin subsidence. Presence of pyrite (reducing condition) and glauconite also indicates shallow marine sediments (at depths of 50–300 m). Overall, the entire basin-fills are inferred to be deposited in shallow marine tidal flat area with occasional deep burial condition in an isolated basin with little clastic influx. Comparing with other coeval successions of Narji Formation lithology, it can be concluded that similar type of depositional milieu prevailed over the globe at early Neo-Proterozoic time during the formation of Rodinia.

The first upper Silurian land-derived palynological assemblage from South America: Depositional environment and stratigraphic significance

A thick succession of quartz-rich sandstones cropping out in the middle part of the Villacorta Creek, on the western slope of the Sierra del Famatina (Valle Hermoso, La Rioja Province, northwestern Argentina) was recently recognized as the Villacorta Formation. The sandstone package rests disconformably on greenish sandstones of the Ordovician Suri Formation and is overlain along a marked angular unconformity by rocks of the upper Carboniferous Agua Colorada Formation (Paganzo Group). The Villacorta Formation is divided into four intervals, the lower one is formed by quartz-rich sandstones showing large-scale cross-stratification; the second part is similar but includes some levels of intraformational conglomerates and shows a decrease in both grain-size and the scale of the cross-bedding sets. The third section comprises medium- and coarse-grained sandstone with intercalation of fine-grained sandstones. The upper interval corresponds to two thickening and coarsening upwards successions. This last section was deposited in a deltaic environment where the top of mouth bars and lagoon deposits preserved palynological assemblages and phytodebris. A low-diversity palynological assemblage recovered from these mudstone levels includes abundant nematophyte cuticular-like fragments, cryptospores (monads, dyads, tetrads) and trilete spores (e.g., Scylaspora scripta, Emphanisporites protophanus). The stratigraphic relationships of the succession and the palynological assemblage suggest a late Silurian age for the Villacorta Formation. The exclusive presence of land-derived components in the organic residue allows to capture a snapshot of the terrestrial vegetation and constitutes the first record of this type of palynological association and nematophyte remains in this southern region. This assemblage improves previous paleogeographic reconstruction enlarging the extent of Silurian basins in Argentina. The shallowing successions of the Famatina region pass to marine deposits in the Precordillera area, indicating a westward transition to offshore environments.

A Middle Pennsylvanian (early Asturian) tropical dry forest, Atokan-Desmoinesian boundary, Illinois Basin, USA

Six late Atokan (early Asturian) floras from seasonally dry environments are described and quantitatively analysed from adpressions and palynomorphs. Collections are from the eastern margin of the Illinois Basin, USA, in an 80 km N-S transect. Plant fossils occur in sedimentary rocks below the underclay (paleosol) of the Minshall-Buffaloville Coal Member (thus, not “roof-shale” assemblages), uppermost Brazil Formation. Growth of floras under season dryness is indicated by outcrop and lithological features that suggest deposition in flashy discharge streams, including intraformational conglomerates, plant fossils that cross bedding planes indicating rapid, episodic burial, and local rhythmically laminated sediments. Common charcoal clasts are consistent with seasonal climate. Cordaitalean foliage dominates the macroflora, accompanied by the dryland elements Lesleya sp., Taeniopteris sp. cf. T. multinervia, and Sphenopteridium sp. Two unusual forms of foliage are presumed to be rare or novel dryland species. Small numbers of wetland/periwetland taxa include calamitaleans, Linopteris neuropteroides, Karinopteris/Eusphenopteris sp., marattialean fern foliage, Senftenbergia plumosa, cf. Zeilleria avoldensis and Sphenopteris sp. The palynoflora is dominated by marattialean tree ferns, wetland plants with broad dispersal capacities and environmental tolerances. Subdominant elements also have strong wetland affinities. Palynoflora-macroflora mismatches may reflect primary ecology, palynomorph reworking, or both. The occurrence of these floras near the Atokan-Desmoinesian (~ Bolsovian-Asturian) boundary coincides with an array of physical and geochemical data that indicate change from weak rainfall seasonality to marked seasonality at all phases of glacial-interglacial cycles, reflected prominently in the stratigraphic record from the localities studied.

Barren Meandering Streams in the Modern Toiyabe Basin of Nevada, U.S.A., and Their Relevance To the Study of the Pre-vegetation Rock Record

Abstract Modern meandering streams devoid of plant life have long been ignored despite their relevance to the study of sedimentary landscapes in the long span of Earth's history that preceded the greening of continents. We present a sedimentologic and remote-sensing analysis of the McLeod Springs Wash, a small-scale, endorheic, and barren fluvial fan in the Toiyabe Basin of Nevada, USA. Fluvial channels therein undergo avulsion at the sub-decadal scale, and follow a morphodynamic cycle from low-sinuosity, higher-gradient, and sediment-starved streams into meandering, lower-gradient channels prone to overspilling. Sedimentation is purely clastic and, unlike in other arid-climate endorheic basins, water recharge maintains positive hydrologic budgets year-round such that any contribution to bank strength due to precipitation of evaporites is ruled out. Likewise, the unvegetated nature of the meandering channels excludes any direct biotic forcing on sedimentation, leaving an equilibrium between discharge, gradient, and bank strength aided by cohesive mud fractions as the main mechanism responsible for channel meandering. Point bars compose a volumetrically significant fraction of the McLeod Springs Wash's stratigraphic record, and consist of sub-meter-thick, fining-upward inclined ripple strata floored by intra-formational conglomerate. Their sedimentary record remains non-diagnostic unless morphodynamic analyses based on accretion and paleoflow vectors are integrated. Interpreting river planform from these deposits is complicated by swift channel avulsion and migration relative to alluvial aggradation, which make the preservation of entire channel-bar complexes exceptional. We conclude that a significant bias may exist against the interpretation and volumetric estimation of the pre-vegetation meandering-fluvial rock record, and that the application of classic point-bar models based on inclined heterolithic stratification to Ordovician and older rocks is intrinsically flawed.

A FACIOLOGIA DO GRUPO PASSA DOIS NO RIO GRANDE DO SUL

The study of geological sections in the outcropping area of the Passa Dois Group in Rio Grande do Sul, complemented with the study of cores from drillings for coal, showed the relations in the State, which are related bellow. 1) The Passa Dois Group is constituted by the Irati and Estrada Nova Formations; the Rio do Rasto Formations is lacking. 2) The thickness of the group is about 100 m. 3) The contact with the subjacent formation is characterized by the occurrence of limestone concretions immersed in a grey silty shale, very similar to the Palermo Formation. 4) The Irati Formation has two facies. One characterized by the occurrence of two beds of pyrobituminous shale associated with fossiliferous limestone lenses. These two beds are intercalated with a grey silty shale with concoidal fracture, and with yellowish limestone concretions immersed in it. This facies, when present, occupies the lower part of the formation and was called Tiaraju facies. The second facies, partially synchronous with the first one, is constituted by grey silty shales with limestone concretions and West of Pantano Grande, is cut by oblique veins of silica. Toward the east it is predominantly siltic, showing cross-lamination. This facies ends the Irati deposition in the State and was called Valente facies. 5) The Estrada Nova Formation also has two lithologic facies, one being pellitic; the other, sandy, which, when present, occupies the top. The pellitic facies was called Caveiras facies and is characterized by the development of pink and red colours alternating with grey. The sandy facies, also reddish, is characterized by lenticular bodies of very fine sandstone, by occurrences of limestone lenses with irregular shapes, and also by large limestone concretions. This facies was called Armada facies. 6) The upper limit of the group was set on the contact of the above mentioned lithologies with a pink medium sanstone, with planar and channal cross stratifications, and with intraformational conglomerates.

Depositional history of the Late Barremian deposits (Sidi Aïch Formation) in central Tunisia and adjacent parts of Algeria: A geostatistical revelation

The lithofacies analysis of the Sidi Aïch Formation and equivalents in Tunisia and adjacent parts of Algeria was carried out using probabilistic and quantitative approach as Discrete Time Markov Chain (DTMC) and entropy functions coupled with detailed sedimentary analyses with a view to decipher the Late Barremian depositional history. The Late Barremian successions exhibit asymmetric, fining-upward and retrograding to aggrading cycles in both outcrop and borehole data. Complete cycles typically start with intraformational conglomerates or trough and planar cross-stratified coarse sands, overlain by fine-grained sands, which are succeeded, in turn, by laminated sands, silts, clays and carbonates, and ends with paleosoils. Such ideal succession of lithofacies is observed at Zemlet el Baidha Hill in Tunisia and OuM.1 borehole in northeast Algeria marked by high values of entropy. The entropy analysis indicates deposition in a neritic environment with interplay of fluvial (and rarely alluvial) processes. The facies associations observed at Zemlet el Baidha Hill document evidences of wave and tide dominated coast with complex-gradient of environments that graded from neritic (upper to lower shoreface) to coastal settings (lagoons, embayments, restricted bays, mires, swamps etc.). The architecture of lithofacies appears to have been controlled by autocyclic processes (effects of local tectonics, basin bathymetry, lateral redistribution of deposits by longshore waves and tide currents) and allocyclic processes (global decrease of relative sea-level and sediments supply). Due to large salinity variations, wave action, ephemeral and local aspects of these marginal environments, the ichnodiversity was often limited in time and space, and inhibited the development of fossils during the onset of deposition of Sidi Aïch Formation and its equivalents.

Interpretation of massive sandstones in ephemeral fluvial settings: A case study from the Upper Candelária Sequence (Upper Triassic, Paraná Basin, Brazil)

Ephemeral rivers display a wide range of upper- and lower-flow regime structures due to great flow-velocity changes during the floods. The development of flow structures in these setting is yet to be understood, especially in the formation of thick, massive sandstones. The Upper Triassic of Southern Gondwana was marked by a climate with great seasonal changes, yet there is no description of river systems with seasonal characteristics in Southern Gondwana. This work aims to characterize a ephemeral alluvial system of the Upper Triassic of the Paraná Basin. The characteristics of the deposits are discussed in terms of depositional processes through comparison with similar deposits from literature, flow characteristics and depositional signatures compared to flume experiments. The alluvial system is divided in four facies associations: (1) channels with wanning fill, characterized by low width/thickness ratio, tabular bodies, scour-and-fill structures with upper- and lower-flow regime bedforms; (2) channels with massive fill, characterized by low w/t ratio, sheet-like bodies, scour-and-fill structures with massive sandstones; (3) proximal sheetfloods, characterized by moderate w/t ratio, sheet-like bodies with upper- and lower-flow regime bedforms and (4) distal sheetfloods, characterized by high w/t ratio, sheet-like bodies with lower-flow regime bedforms. Evidence for the seasonal reactivation of the riverine system includes the scarcity of well-developed macroforms and presence of in-channel mudstones, thick intraformational conglomerates, and the occurrence of well- and poorly-preserved vertebrate bones in the same beds. The predominantly massive sandstones indicate deposition from a hyperconcentrated flow during abrupt changes in flow speed, caused by de-confinement or channel avulsion, whereas turbulent portions of the flow formed the upper- and lower-flow regime bedforms after the deposition of the massive layers. The upper portion of the Candelária Sequence records a good example of strongly ephemeral alluvial systems, where the predominance of massive sandstones is a particular characteristic.

The provenance, petrology and sedimentology of building stone in Bromyard, Herefordshire, UK

A multi-disciplinary study was undertaken of the Lower Old Red Sandstone building stones of Bromyard, Bromyard Downs and Bringsty Common, Herefordshire, UK, to trace their original quarry sources. 196 stone structures were recorded in detail and 3 broad lithological groups recognised. Combining old maps, archival sources, Light Detection and Ranging (LiDAR) data and testimony of local residents, the historic quarries in the area have been mapped. Field studies of the geology of quarries and outcrops have established the area of origin of two distinctive coarse grained lithologies. Intraformational conglomerates have been demonstrated, with some confidence, to be derived from Bromyard itself. Coarse, pebbly, quartzose sandstones have been traced to Bringsty Common and shown to be used only in the church in Bromyard before the 20th century. The origins of fine grained sandstone are found to be more complex. Through a combination of fieldwork and archival research, Clater Park Quarry is indicated as the origin of high quality green sandstones in Bromyard. 15 samples of sandstone from the Bromyard Downs, have been petrographically analysed by point counting to determine their clastic and mineralogical proportions. Early results of this analysis are presented which show modal variation in lithics, feldspars and cements that may serve to link quarries to buildings. Finally, it is suggested that at least some of the diversity of stone present in Bromyard is the result of slight variation in depositional processes in the immediately underlying bedrock.

Facies Changes Between Kolosh and Sinjar Formations Along Zagros Fold–Thrust Belt in Iraqi Kurdistan Region

The present study is concerned with lateral and vertical facies changes between Kolosh (Paleocene) and Sinjar (or Khurmala) (Paleocene-Early Eocene) Formations in Sulaimani and Duhok area, Kurdistan Region, NE-Iraq. The latter and former formations are belonging to basinal clastic (turbidite) and reefal carbonate facies respectively. The facies changes are documented in six sections by field studies and evaluation of previous ideas and data which are critically discussed and compared to the result of the present study. The special attention is directed towards the contact between the two Formations in relation to conformity. All the studies achieved before 2002 showed conformable contact between the two formations while the most recent study found large a gap (erosional unconformity) between the two formations which persisted for 5million years. According to latter study, the sea level fall associated with this unconformity assigned to be type one and type two sequence boundaries in the east of Darbandikhan, north of Koya towns and the Bekhme gorge.Conversely, the present study has not recorded gaps in the sedimentation in the studied sections either in Sulaimani or Dohuk area. The contact can be regarded as transgressive system tract which represented by green marl or sandstone, which changes to limestone of Sinjar or Khurmala Formation (HST).The conglomerate beds that are recorded in the previous studies at the contact of the two formations are not proved in the present study. The previously recorded conglomerate is located inside the upper part of the Kolosh Formation not in the contact and it represents submarine fan feeder channel. In contrast to previous studies, neither incised valleys nor erosional unconformity are found at the contact between the two formations in the studied area. The one meter intraformational conglomerate that are found (in some previous studies) in the Bekhme gore is not found in the present study. It is observed that the Kolosh Formation, at Bekhme Gore consists of green marl and sandstone with one bed of Khurmala Formation. The green marl is changes totally to dolomitic limestone of the latter Formation toward northwest at the north of Saru Kani village near Bujeel town. This proves that both formations are deposited in one basin and Khurmala formation has the age of Lower Paleocene to Lower Eocene.

Palaeomagnetic and geochronological data from Late Mesoproterozoic redbed sedimentary rocks on the western margin of Kalahari craton

Abstract Redbeds of the Aubures Formation constitute the uppermost stratigraphic unit in the Mesoproterozoic Sinclair succession of southern Namibia. Aubures palaeomagnetic remanence vectors, held almost exclusively by hematite, document at least one geomagnetic polarity reversal in the stratigraphy, a positive intraformational conglomerate test indicating primary magnetization and greatest concentration of characteristic directions at 50–60% untilting, indicating that deformation was coincident with sedimentation. The new Aubures palaeomagnetic pole, at 56.4°N and 018.0°E with A 95 =11.3°, is located on the apparent polar wander path of the Kalahari craton, between poles of the 1110 Ma Umkondo igneous event and the c. 1090 Ma Kalkpunt redbeds of the Koras Group near Upington, South Africa. This distinctive concordance suggests that Aubures sediments have an age of approximately 1100 Ma, that the Sinclair region was probably part of Kalahari at that time and that the Aubures and Kalkpunt redbeds are broadly correlative. New laser-ablation inductively coupled plasma mass spectrometry detrital zircon results from the Aubures Formation, including a youngest age component (1108±9 Ma) that is coincident with the Kalahari-wide Umkondo large igneous province, conform to this interpretation. Palaeomagnetism and geochronology of the Sinclair succession can provide kinematic constraints on the tectonic evolution of Kalahari as it approached other cratons in the growing Rodinia supercontinent.