Conglomerate Facies Research Articles

Facies of Quaternary Sediments In Bunga Village, North Luwuk District, Banggai Regency, Central Sulawesi

Abstract The distribution of Quaternary sedimentary rock deposits in Indonesia is quite extensive, and one of them is in the Quaternary coral reef units, which are evenly distributed along the eastern arm of Sulawesi. The research was conducted in Bunga Village, North Luwuk District, Banggai Regency, Central Sulawesi Province. This research was motivated by the lack of geological data, so the topic of developed facies became an interesting topic to be researched. Data was collected from a cliff at the coordinates 0053′57,57.1″N-122054′43′6″E. Stratigraphic measurements aim to determine the facies, depositional environment, and sedimentation mechanisms developed in the study area. The research was conducted using the method of field data collection and laboratory analysis. Collecting field data was carried out with measured stratigraphic with a 1:100 scale and taking several rock samples. Laboratory analysis was carried out in paleontological and petrographic analysis, which was carried out to determine the composition of the constituent rock and fossil identification, especially foraminifera in thin sections of rock that were selected. Based on the study’s results, the total rock layers measured in the study area were 15 m. Facies found in the stratigraphic path of the study area are floatstone facies, rudstone facies, allochemic sandstone facies, polymict conglomerate facies. The type of deposition environment of limestone and allochemic sandstone in the study area is on the foreslope, while the conglomerate facies is included in the fan delta deposition environment. Overall, the sedimentation dynamics in this area are in a high energy environment, indicating that the facies that developed were deposited with a sediment gravity flow mechanism.The results of the analysis of fossils found Cyclammina cancellata sp., Orbulina universa sp., Globigerina bulloides sp., and Trilobatus immaturus sp., which indicates the limestone in the study area was deposited in the Late Pleistocene to early Holocene.

The depositional evolution and associated controls on the reservoir property in the Permian Upper Urho Formation, southern Zhongguai Rise, Junggar Basin, northwest China

The Permian strata in southern Zhongguai Rise are famous for their abundant petroleum reservoirs. The depositional evolution of the Upper Urho Formation has been studied by analyzing the interactions between the sedimentary environments and the diagenetic evolution based on the comprehensive analysis of geologic and geophysical data sets. The obtained results have shown that fan delta deposits, overlain by lacustrine deposits, are deposited. Proceeding upward, the fan delta succession is characterized by retrogradational patterns, such as sandstone facies and conglomeratic facies. These facies have shown different clay mineralogic compositions, porosity, and physical properties. The sandstone facies indicate well-sorted and well-rounded sedimentological textures with good physical properties. In contrast, the conglomeratic facies indicate poorly sorted and poorly rounded sedimentological textures with poor physical properties. All of these characteristics lead to reservoir heterogeneity resulting from sedimentary facies and diagenesis.

Significance of a Mesoproterozoic tide-reworked fan delta – tidal flat transition: A transgressive-regressive model

Records of tide-reworked fan delta facies models are rare in literature, attributed to their lower abundances due to complex sediment distribution pattern by two exclusive end-member flows, viz., a seaward directed subaerial to subaqueous debris flow, and dominant tidal current system interfering with and reworking the debris flow. Lack of appropriate analogues of tide-reworked fan deltas makes the ancient examples more significant. The analysis of such rare tide-reworked fan deltas from deep-time, e.g., Mesoproterozoic, turns out to be unique due to the gap in clear understanding of the alluvial-fluvial vs marine processes in non-vegetated land parts. The lower part of the Mesoproterozoic Rajgarh Formation, Lalsot Basin, North Delhi Fold Belt, Aravalli Craton in NW India, provides a rare record of a tide-reworked fan delta depositional system. Sedimentary facies analysis reveals eleven lithofacies grouped under three major facies associations, viz., (i) gravel-rich conglomerate facies association, characterized by stacked debris flow deposits forming a subaerial alluvial fan, representing the delta topset component, followed downslope by (ii) pebbly, cross-stratifed sandstone facies association, characterized by reworking of the subaqueously emplaced debris flows by ebb-tidal currents, to produce the mouth bar and the delta front depositional systems, and finally, (iii) sandstone-mudstone heterolithic facies association, characterized by abundant tidal signatures in pebble-free thin-bedded sandstone-mudstone heteroliths with tidal bundles, herringbone cross-strata and wave ripples, characterizing a stable platformal subtidal-intertidal flat depositional system. The lower-middle part of the succession records an aggradational stratal stacking pattern of the subaerial alluvial fan changing to progradational stratal stacking of the laterally accreted debris-rich tide-led clinoforms producing the delta topset – mouth bar – delta front transiton of a tide-reworked fan-delta under successive regressive conditions, representing syn-rift deposition near the basin margin. A retrogradational stratal stacking pattern overlies the fan-delta succession, and signifies a transgression by landward encroaching tidal flat system over the fan-delta system during post-rift phase in a stable platformal setup, where debris supply is ceased. A regressive-transgressive model characterizing the transition from a fan-delta to tidal flat depositional systems portrays fluctuations in the accommodation conditons in response to complex interplay of basin tectonics and relative sea level changes in the Mesoproterozoic riftogenic Lalsot Basin.

Investigating the mineralogical and geochemical composition of fluvial sediments of Watari river system, Kano, Nigeria

A key objective of this research is to conduct a mineralogical and geochemical screening of the fluvial sediments in Watari river. Data collected from this study can be used to further enhance scientific understanding of the fluvial processes in the Watari basin as well as the larger Hadejia-Jama' are basin. The geological data can also be used as input information for the prediction of sedimentation rates in the Watari dam, Kano. An intensive field was conducted to explore thebedforms (sand bars, ripples, and sand filled channel or dunes) of the proximal channel environments, platform geometry and sinuosity.X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses were used to study the mineralogy and chemical composition of the collected samples, respectively. The Watari river can be considered as braided due to the presence of smaller multi-threaded channels, braid or channel bars. The lithology of exposures observed at the river bank show a series of depositional cycles that comprise mudrocks (light and dark), sandstone, conglomerate and a basal quartzitic gravel deposit. The wacke and sub-litheranite rocks were sourced from mafic and intermediate igneous rocks. The relatively high La and Ce in the mudrocks can be attributed mainly to the adsorption of Ce onto Fe-oxides which are abundant in the fluvial sediments eroded from lateritic soils. From the bivariate plot of Al2O3/SiO2 against Fe2O3+MgO, the sandstone facies fall under the passive continental margin, while the quartzite and conglomerate facies are grouped under the foreland basin, and the light mudrock facies is classified under the continental island arc. In addition, the plot of Al2O3/(CaO + Na2O) against Fe2O3+MgO shows the sandstone and quartzite facies fall under the foreland basin. The relatively high concentration of feldspar and muscovite mica in the siliciclastic facies is indicative of close proximity to parent material, and low degree of weathering and diagenesis. The variability in the mineral composition points toward different cycles of fluvial sedimentation, diverse provenance, and wide range of source materials.The geochemical data further buttresses the variability in provenance, wider geographic area of the sediments or re-deposition and reworking by fluvial actions.

Along-strike tectonic evolution of the Neogene Bermejo foreland basin and Eastern Precordillera thrust front, Argentina (30-32°S)

The Bermejo retroarc foreland basin system formed in flexural response to Cenozoic crustal thickening in the Andean orogenic system, specifically, the eastward propagation of the Precordillera fold-thrust belt and the basement-involved uplift of the Sierras Pampeanas. Previous work in the region has mainly focused on the mechanisms and expression of flat slab subduction and the structural geometry of the basement-involved Sierras Pampeanas and east-directed Precordillera fold-thrust belt at depth, advancing our understanding of the Bermejo basin history north of 31°S. However, the along strike evolution of the basin system to the south remains unresolved and contrasting tectonic models have proposed the Bermejo basin evolved synchronously versus asynchronously through time. Our study seeks to constrain the along-strike Neogene tectonics of the Bermejo basin via well-exposed Miocene fluvial stratigraphic intervals along the Eastern Precordillera, integrated with detrital zircon U–Pb geochronology provenance and detrital apatite (U–Th)/He thermochronology datasets. New data from two Neogene stratigraphic sections in the southern Bermejo basin constrain deposition between 13 and 6 Ma. Dominant fluvial-lacustrine mudstones, siltstones, and sandstones transition into fluvial-megafan deposits capped by alluvial fan conglomerate facies, tracking the eastward migration of Precordillera deformation. The cessation of sedimentation, and thermal history models of apatite (U–Th-Sm)/He thermochronology ages, indicates basin incorporation into the orogenic wedge by 6 Ma. When we compare our southern datasets with previous constraints from the northern Bermejo basin, we observe, from north to south: (1) a time-transgressive trend in basin initiation, (2) a ∼3 km decrease in stratigraphic thicknesses, and (3) older exhumation along the thrust front. These trends highlight the asynchronous nature of the Bermejo foreland basin system and along-strike variability of Precordillera thrust-front evolution.

Petrographic and Kinematic Analysis of the Itombwe Synclinorium Formations Exposed at Tshondo and Bugoy (South-Kivu region, Democratic Republic of the Congo)

The purpose of this study is to investigate the Itombwe synclinorium formations that were affected by the late Pan-African orogenesis in the nordeastern Congo. A variety of controversies surround Tshondo and Bugoy's tectonic evolution and associated metasedimentary formations. A field-based approach combined with paleostress inversion techniques and petrographic analyses were conducted on 190 structural measurements and 6 rock samples used in this study. The results reveal the presence of four major petrographic facies: conglomeratic facies (conglomerate and diamictite), carbonate facies (travertine), greenschist facies (graphitic black shale and pelite), as well as quatzitic facies (quartzite and sandstone). The mineral assemblages consisting of high contents (>70%) of muscovite/sericite and biotite albite, plagioclase, quartz, and some opaque minerals. With the assistance of Win-Tensor software, the kinematic analysis reveals two major deformation phases, (1) a ductile deformation phase (D1-2), which is associated with isoclinal folds and strike-slip faults, and (2) a submeridian brittle deformation phase (D2), which generated extensive faults trending NNW-SSE to NE-SW directions, while reactivating bedding surfaces (NE-SW) in a series of secondary faults. The findings of this research may assist geologists in conducting core logging operations and provide a baseline for understanding the relationship between rock, minerlization, and tectonics in mineral-rich areas.

Hydroclimatic and geochemical palaeoenvironmental records within tufa: A cool-water fluvio-lacustrine tufa system in the Wadi Dabsa volcanic setting, western Saudi Arabia

A series of uncharacterised tufa deposits within the lowland volcanic provinces of western Saudi Arabia are investigated here in order to account for their presence and to examine their utility as a palaeoenvironmental archive. The Wadi Dabsa basin, in the Harrat Al Birk, is part of the Saharo-Arabian region, where there is increasing evidence for multiple hominin dispersals during windows of reduced aridity during the last ~400 ka of the Late Quaternary. This first and detailed petrological and geochemical characterisation of these tufa carbonates is particularly important for palaeoenvironmental and climatological reconstruction at a site that contains a major concentration of Early and Middle Stone Age artefacts. We aim to determine the nature of deposition, to answer whether these are cool, freshwater tufa or hydrothermal travertine, and to establish what the tufa settings, stratigraphies and facies reveal about the hydroclimatic regime in this semi-arid environment.A widespread lacustrine-paludal and fluvial tufa system is preserved, as well as topographically-controlled tufa barrages and cascades. Observable sections, exposed by incision, reveal a thickness of tufa deposits of 3 to 6 m in places, which contain two packages of tufa-cemented conglomerate facies. This allows us to provide a conceptual model for the deposition of semi-arid tufa, based on existing type sites in the Naukluft Mountains of Namibia and the Ebro Basin of Spain. The varied topography within this volcanic harrat provides a setting at Wadi Dabsa that combines the low-lying lacustrine-paludal model from Spain with the steeper and higher-energy model from Namibia. The two tufa-cemented bedload units and the evidence for post-depositional erosion of other tufa facies indicates a shifting hydroclimatic regime, with episodes during which the basin contained water and there was steady flow in the fluvial channels, alternating with episodes of high-energy flashy flows.Geochemical analysis using 87Sr/86Sr isotopic ratios (0.7049 to 0.7056 with one sample at 0.7062) and stable carbon isotopes (−12.9 to −6.3‰) reveal that these are cool-water tufas were deposited from meteoric water that has interacted with both metamorphosed limestone in the Asir Escarpment and the mafic metavolcanic bedrock of the Wadi Dabsa Basin, without a geothermal influence. These tufa are low-concentration‑magnesium calcite, with traces of quartz (to a maximum of 3%) and other silicates. Some samples have ≤7.5% palygorskite, which along with petrological evidence for microbial filaments suggests the importance of biomineralisation by cyanobacteria within some of these tufa. Petrological analysis shows the fabrics are dominated by micrite cements with some microspar, and very little post-depositional alteration. Where samples are banded, this reflects variation in calcite crystal size as opposed to any striking variations in mineralogical composition. Oxygen stable isotopic composition (−14.6 to −1.9‰) indicates deposition from an isotopically more depleted rainfall source than the modern day, noting additional corrections for unknown past temperature and any other fractionation effects are needed. Depleted rainfall sources in this region may relate to either a far-travelled Atlantic moisture source or a higher-intensity Indian Ocean monsoon source, or some combination.

Studies on lithofacies sequences in the Hoanh Bo basin, Quang Ninh province by using Markov chain model and Entropy function

The succession of lithofacies in the Dong Ho and Tieu Giao formation's Hoanh Bo basin was statistically analyzed using the modified Markov chain model and the function of Entropy. Based on the field definitions, petrographic investigation, and their borehole logs, the lithofacies study was carried out to determine the sediment deposition system and the deposition environment. Seventeen sub - lithofacies organized within the succession are recognized in three lithofacies associations. The analysis result of the Markov chain and chi-square or X2 test indicates that the deposition of the lithofacies is a non - markovian process and represents cyclic deposition of asymmetric fining - upward. To evaluate the randomness of the occurrence of lithofacies in a succession, entropy analysis was performed. Each state is associated with two types of entropy; one is relevant to the Markov matrix expressing upward transitions (entropy after deposition) and the other is relevant to the downward transition matrix (entropy before deposition). The energy regime calculated from the maximum randomness entropy analysis indicates that changing patterns in a deposition has resulted from rapid to steady flow. This results in a change in the depositional pattern from alluvial - fluvial to lacustrine environments, specifically from conglomerate facies (A1) → sandstone facies (A2)→ fine-grained and non - debris facies (A3).

Reservoir characterization of fluvio-deltaic sandstone packages in the framework of depositional environment and diagenesis, the south Caspian Sea basin

The Middle Pliocene Fasila and Balakhany Suites are important petroleum-bearing reservoirs in the South Caspian Basin. There are four lithofacies associated with the interbedded sandprone reservoir intervals. The mineral constituents, sedimentary structures and depositional setting of the productive interval are interpreted as river-dominated depositional setting, including conglomeratic facies relating to a channel floor sub-environment and sandstone facies associated with the upper parts of river channels. The drainage basin of the Volga River is considered as the provenance for these deposits derived from basement rock outcrops to the north, which belongs to the Russian Precambrian semi-oceanic continental platform. Reservoir quality is assessed using the core-based porosity and permeability data in relation to the sedimentary and diagenetic processes influencing each lithofacies. Lithofacies 1 and 2 have good reservoir quality, while lithofacies 3 and 4 have poorer reservoir quality. Reservoir quality is controlled by both depositional setting (grain size and texture) and diagenetic imprints associated mainly with compaction, cementation and neumorphism. The role of clay minerals in the diagenesis of the sandstones with increasing burial depth is revealed by SEM and XRD analysis. Clay minerals progressively alter to illite, smectite and chlorite with increasing burial depth. This alteration leads to the occlusion of pore throats and degrading reservoir permeability.

Depositional process and dispersal pattern of a faulted margin hyperpycnal system: The Eocene Dongying Depression, Bohai Bay Basin, China

There has been an increased attention on hyperpycnal flows due to its importance in delivering large volumes of sediments into deep-water. The process and products of hyperpycnal flow in tectonically-active margins are still poorly understood, and potentially constitute one of the most important deep-water mechanisms in rift basins. This study integrates core data, well-logging and 3D seismic data to investigate the hyperpycnal flow process and dispersal pattern on the Eocene Dongying rift margin. 17 facies, including 5 conglomerate facies, 9 sand facies and 3 mud facies are identified, interpreted as the product of debris flows, traction currents, turbidity currents, transitional flows and lofting plumes, and suggesting the complex blend in flood-triggered hyperpycnal flow on rift margin. Two different hyperpycnal flow types are identified and a related process model is proposed based on facies sequence, distribution, transport mechanism and flood discharge analysis, including seasonal-flood triggered hyperpycnal flow (SHF) and outburst-flood triggered hyperpycnal flow (OHF). The evolution of the hyperpycnal system suggests two dispersal styles, including proximal sublacustrine fan dominated by OHF and distal sublacustrine fan dominated by SHF, respectively. Climate and tectonic movements are suggested to be the main factors controlling hyperpycnal flow generation and deposition on rift margins. The relatively arid climate enhanced seasonal-flood activity and associated sustained and stable SHF, which further prompt distal sublacustrine fan development during a weak rifting period. On the other hand, the generation of outburst-floods can be attributed to the enhanced fault activity, which corresponds to the periodical tectonic movements in the basin. As a result, proximal sublacustrine fans tend to develop in near-shore topographic lows down-dip of syn-depositional faults due to increased tectonic activities, accommodation and enhanced OHF. A deep-water depositional model is proposed for hyperpycnal systems on rift margins by emphasizing the variety in sedimentary process and dispersal patterns controlled by climate and tectonics forces, which may provide new insights into hyperpycnal flow theories and deep-water exploration in world rift basins.

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.

The Neoarchean Conglomerate-Hosted Gold of the West Pilbara Craton, Western Australia

Abstract Recently discovered Au in boulder conglomerate between the Mesoarchean West Pilbara superterrane basement and the overlying volcano-sedimentary stratigraphy of the Neoarchean Fortescue Group in Western Australia has renewed comparisons with the Witwatersrand conglomerate Au deposits in South Africa. As such, this has reignited the question of the Pilbara and Kaapvaal cratons being linked as part of the postulated Vaalbara continent during the Archean. However, little is known about the origin of the Pilbara conglomerate Au and its host conglomerates, as they are hitherto unstudied, and their formation and/or source is uncertain. Here we present a detailed study on the textures, composition, and sedimentology of one newly discovered Pilbara conglomerate Au deposit at the base of the Neoarchean Fortescue Group in the northwestern Pilbara craton. The Pilbara conglomerate Au occurrences are characteristically Ag-bearing but Hg-poor polycrystalline discoid masses that are overgrown by Au-poor chloritic halos, which are further enveloped by a hydrothermal alteration halo of disseminated Au within chlorite. Both the discoids and the auriferous chlorite halo are Ag bearing, with up to ~9 wt % Ag, consistent with a hydrothermal (orogenic) origin. The discoids do not display any physical or chemical evidence for sedimentary transport; thus, their formation (placer versus hydrothermal) remains unclear. However, the position of the Au in the conglomerate, limited to the basal section of the conglomerate, is difficult to account for in a purely hydrothermal deposit model. We argue the Pilbara conglomerate Au represents a modified placer deposit from a primary orogenic Au source, with surface evidence for sedimentation removed by partial dissolution during later hydrothermal alteration in the host conglomerate and the crystalline basement. While the basal Fortescue Group conglomerate Au shares commonalities with the time equivalent (>~2.7 Ga) Venterspost Conglomerate Formation, which overlies the Witwatersrand Supergroup, inconsistencies remain, with different Au chemistries and tectonic, magmatic, sedimentary, and metamorphic-metallogenic histories of the Pilbara and Kaapvaal cratons prior to deposition of the >2.7 Ga conglomerate sequences. This collectively indicates the drivers of Au metallogenesis and ultimate Au deposition in conglomerate facies were fundamentally different in the Pilbara and Kaapvaal cratons.

Glacial origin of the Cryogenian Nantuo Formation in eastern Shennongjia area (South China): Implications for macroalgal survival

The Cryogenian Period was characterized by global glaciations, imposing extreme environmental stresses on early multicellular organisms. Globally distributed diamictite deposits are the major evidence for these glaciation events, but the glacial origin of at least some of these diamictite deposits has been disputed, complicating interpretations of the environmental conditions influencing the evolution of life in the Cryogenian (~720–635 Ma). In this study, we conducted a systematic sedimentological investigation of the Marinoan-age (~650–635 Ma) Nantuo Formation in six sections representing a ~20-km-long, east–west transect in the eastern Shennongjia area of South China. The Nantuo Formation, which ranges in thickness from ~2 m in the east to ~300 m in the west, comprises diamictite, conglomerate, lonestone-bearing sandstone, green siltstone, and black shale facies. The eastern sections (e.g., Longxi and Wushanhu) consist mainly of diamictite facies exhibiting micro-scaled rotation structures, microshear, grain stacking, grain-to-grain contacts and water-escape structures, supporting their deposition in a subglacial setting. In contrast, the western sections (Shijiahe, Liziping and Songluo) consist of massive and graded diamictite and conglomerate facies, consistent with an origin as glacially induced submarine debris flows. Furthermore, the lonestone-bearing sandstone facies in these sections contain abundant dropstones and mud pellets within finely-laminated turbidites, indicating an ice-rafted origin with locally reworking by turbidity currents. The green siltstone and black shale facies lack glacigenic features and may represent late deglacial deposits. Based on thickness and facies variations among the study sections, we infer that the Nantuo Formation records glacial sedimentation on a complex paleotopographic surface that was incised into the underlying bedrock, with subglacial deposits to the east transitioning into glaciomarine deposits to the west of study area. The distal Songluo section likely records three cycles of glacial advance and retreat in the form of a facies alternation between diamictite and black shale, consistent with a dynamically fluctuating ice margin. In summary, our sedimentological investigation supports a glacial origin for the Nantuo Formation in the eastern Shennongjia area. The occurrence of the benthic macroalgal-dominated Songluo Biota in the black shale facies at Songluo suggests that strong glacial retreats provided niches for macroalgal survival in the Cryogenian glacial ocean.

Arquitectura estratigráfica, paleogeografía y proveniencia sedimentaria de las rocas cenozoicas del sur de Perú (Tacna, 18° S)

The Cenozoic rocks lying in the Province of Tacna (18° S), southern Perú, represent approximately 600 m of stratigraphic thickness. This stacking groups the Sotillo (Paleocene), Moquegua Inferior (Eocene), Moquegua Superior (Oligocene), Huaylillas (Miocene) and Millo formations (Pliocene), and these are the sedimentary fill of the Moquegua Basin. The sediments of the three latter formations are organized into nine sedimentary facies and five architectural elements. Their facies associations suggest the existence of an ancient highly channelized multi-lateral fluvial braided system, with upward increase of pyroclastic and conglomeratic depositions. The heavy mineral spectra make each lithostratigraphic unit unique and distinguishable, being the sediments of the Moquegua Superior Formation rich in garnets, titanites and zircons; while the sediments of the Huaylillas and Millo formations in clinopyroxenes. This mineral arrangement becomes an excellent tool for stratigraphic correlations between outcrops and subsurface stratigraphy (by means of well cores studies) and allow to sketch out a new stratigraphic framework and a complex of rocky blocks bounded by normal faults, often tilted. The sediment mineralogy also suggests that the rocks conforming the Western Cordillera were the main source of sediments for the Moquegua Basin in Tacna. In this context, the detritus of the Moquegua Superior Formation derives mainly from the erosion of the rocks forming the Coastal Basal Complex (Proterozoic), the Ambo Group (Carboniferous) and the Junerata/Chocolate Formation (Early Jurassic). The Huaylillas Formation is a pyroclastic and sedimentary unit which components derived mainly from the Huaylillas volcanism (Miocene) and partly from the denudation of the Toquepala Group (Late Cretaceous). The Huaylillas Formation widely contrasts to the underlying Moquegua Superior Formation due its mineralogy and facies. Finally, the detritus of the Millo Formation derived mostly from the rocks forming the Barroso Formation (Pliocene), and their facies represent a higher contrast in relation to the underlying units due its notorious conglomerate facies.

Clasts in Archean conglomerates and implications for uplift: Evidence from the 2.7 Ga Agnew Greenstone Belt (Western Australia)

Archean greenstone belts commonly consist of a stratigraphy that records subaqueous deposition capped by subaerial sedimentation, yet it remains unclear if the controls on this change were driven by horizontal or vertical processes. Clasts in conglomerates can provide important constraints on this question because they inform on the changing nature of sources. The 2.7 Ga Agnew Greenstone Belt, Yilgarn Craton, Australia, provides the ideal opportunity for such a study because it contains abundant and diverse conglomerate facies and its basal stratigraphy is well understood. This study focusses on the texture and composition of lithic clasts derived from three stratigraphic conglomerate units and their host successions. The lowermost conglomerate-bearing unit, hosted in the Vivien Formation, unconformably overlies the mafic-ultramafic lavas and intrusions of the Kalgoorlie Group (ca. 2720–2690 Ma) and is dominated by aphyric to porphyritic mafic and felsic volcanic clasts. The conformably overlying Maria Mine Formation conglomerates contain a higher proportion of felsic clasts with medium- and plutonic groundmass textures. The Vivien and Maria Mine Formations (ca. 2690–2670 Ma) are dominated by cherts, turbidites and conglomerates, and represent subaqueous sediments formed in the ring-plain surrounding an emergent volcanic island. The unconformably overlying Scotty Creek Formation (ca. 2665–2655 Ma) contains conglomerates with many plutonic felsic clasts, and is dominated by bedded and cross-bedded sandstones formed in a subaerial environment. Whole-rock geochemistry of mafic and ultramafic clasts matches the local Kalgoorlie Group rocks and indicates progressive erosion of the underlying supracrustal sequence. Undeformed conglomerates lack clasts with metamorphic foliations, indicating uplift by horizontal compression could not have been significant before ca. 2655 Ma, which is considered as the time of the first major compressional event in many published structural frameworks for the region. The systematic erosion of a felsic stratovolcano, its associated plumbing system, and any resultant upwarping of underlying sequences through vertically-driven diapirism, better explains the progressive changes observed in clast texture and composition, as opposed to horizontally-driven uplift, such as compression associated with subduction.

Facies and architectural variability of sub‐seismic slope‐channel fills in prograding clinoforms, Mid‐Jurassic Neuquén Basin, Argentina

AbstractMost slope‐channel outcrop studies have been conducted at continental margin‐scale on seismic data. However, in foreland and back‐arc deepwater settings, sub‐seismic scale slope channels hold equally important information on deepwater sediment delivery, often in hydrocarbon‐bearing provinces. One such slope‐channel system is examined in Lower Jurassic prograding shelf‐margin clinoforms in Bey Malec Estancia, La Jardinera area, southern Neuquén Basin, Argentina. In a 4 km wide, 300 m tall, slightly oblique‐ to depositional‐dip section of Jurassic Los Molles Formation deepwater slope deposits, seven clinoform timelines were identified by isolated slope‐channel fills with thicknesses less than 50 m. Sedimentary logs, satellite images, a digital elevation model and drone photogrammetry were used to map variations in downslope channel geometry and infill facies. The slope channels are filled with sediment density flow deposits: poorly sorted conglomeratic debrites, structureless sandy high‐density turbidites and well‐sorted, fine‐grained, graded low‐density turbidites. The debrite portion decreases downslope, whereas high‐ and low‐density turbidites increase. A grain‐size analysis reveals a broad downslope fining trend of turbidite and debrite beds within slope channels with increasing water depth, and some notable bypass of conglomeratic facies to the lowermost slope channels and basin floor fans. The architecture of the slope channels changes from lateral to aggradational infill downstream. The Bey Malec clinoforms and its slope channels add new knowledge on downslope changes for sediment delivery in relatively shallow (<500 m water depth), prograding‐dominant deepwater basins. They also highlight one of very few outcropping examples of oblique‐type clinoforms.

Caracterização faciológica e evolução sedimentar da Formação Moeda (Supergrupo Minas) na porção noroeste do Quadrilátero Ferrífero, Minas Gerais

A Formação Moeda, ao longo da região noroeste do Quadrilátero Ferrífero, registra os primeiros estágios da Bacia Minas, desenvolvida no limite Neoarqueano/Paleoproterozoico no sul do Cráton do São Francisco (CSF). Este trabalho analisa essa unidade a partir de seis perfis estratigráficos de detalhe nos quais foram identificadas nove fácies sedimentares: quatro conglomeráticas (Gms, Gm, Gt e Gp), três essencialmente areníticas (St, Sp e Sh) e duas predominantemente pelíticas (Fl e Fsc). As seções estratigráficas foram correlacionadas, possibilitando o agrupamento das fácies em cinco associações geneticamente relacionadas. As associações de fácies AF1 e AF2 representam sistemas de leques aluviais que evoluíram para planícies fluviais entrelaçadas. AF3 está relacionada a um sistema lacustre associado a marinho raso nas porções distais. Por fim, as associações de fácies AF4 e AF5 representam planícies fluviais entrelaçadas encerradas por uma transgressão marinha no estágio final de evolução da bacia. Com o auxílio do mapeamento geológico-estrutural de detalhe dessas associações e da confecção de uma seção restaurada foi possível interpretar que as AF1, AF2, AF3 e a porção basal da AF4 foram depositadas durante os estágios iniciais do rifteamento continental, e as demais associações materializam a transição rifte-margem passiva.

Deepwater to fluvio-deltaic stratigraphic evolution of a deglaciated depocenter: The early Permian Rio do Sul and Rio Bonito formations, southern Brazil

This paper describes facies relationships and stratigraphic architecture of early Permian deglacial deepwater to fluvio-deltaic deposits exposed in the eastern border of the Paraná Basin, southern Brazil. The studied succession is located in the Rio do Sul depocenter and comprises an upward transition between the topmost interval of the Itararé Group (Rio do Sul Formation) and the lowermost unit of the Rio Bonito Formation (Triunfo Member). Geological mapping and facies analysis allowed the recognition of the following facies associations, vertically stacked: thin and thick-bedded turbidites, hyperconcentrated and concentrated density-flow deposits (hyperpycnites), mass-transport deposits, fine-grained heterolithic beds of prodelta, delta-front, shoreface and delta-plain deposits, as well as fluvial beds resting on incised valleys. The stratigraphic analysis through the interpretation of the facies associations, stacking pattern and paleocurrent dispersal trends were enough to define the clinoform stratigraphic architecture, composing a progradational-aggradational pattern. The paleoflows for all facies associations show a main trend towards the south-southwest. In this context, hyperpycnal beds can represent a glacial source from the northeast, because of striated and faceted clasts immersed in the conglomeratic facies, whereas turbidites have been understood as the products of their dilution. Likewise, mass-transport deposits are related to the collapse of the shelf-margin delta, represented by allochthonous blocks composed of deltaic beds within the mass-flow diamictites. Thus, these mass-transport deposits do not evolve downslope to turbidity currents. This configuration was likely for building the relief of the slope system, probably a shelf-edge delta susceptible to mass failure. Paleo-ice flows towards SW recorded in the Rio do Sul Formation, genetic related to fluvio-deltaic deposits of Rio Bonito Formation, highlight the scenario of final stages of the Late Paleozoic Ice Age in the SW of Gondwana and support the previous researches which point to the presence of diachronous ice-spreading centers from paleohighs.

Permo-Triassic Qiseib Formation, Western Side of the Gulf of Suez, Egypt: A Link of Fluvial Facies with Sequence Stratigraphy

Facies analysis of the studied Permo-Triassic Qiseib Formation indicates the presence of five lithofacies. These lithofacies are: matrix-supported conglomerates facies (facies A), coarse-to medium-grained sandstone facies (facies B), heterolithic facies (interbedded sandstone and siltstone) (facies C), interbedded siltstone and claystone facies (facies D), and mixed clastic-carbonate facies (facies E). These facies were deposited in two fluvial environments: low sinuosity braided and high sinuosity meandering. The braided stream deposits dominate the southern portion of the studied area, whereas the meandering stream deposits prevailed in the northern portion. The fine-grained meandering stream deposits grade laterally to the northern part of the study area into tidally-influenced fine-grained meandering strata (estuarine mud). In terms of its sequence stratigraphy, the Qiseib Formation represents a fluvial depositional sequence bounded by two sequence boundaries. This fluvial sequence comprises lowstand-, transgressive- and highstand systems tracts. The Lowstand Systems Tract (LST) is predominantly characterized by braided coarse-grained sandstone deposits (Braided stream facies) with limited fine-grained clastics (floodplain facies). TST includes the coeval tidally-influenced fine-grained meandering strata that occur in the extreme north of the study area. The highstand systems tract (HST) is assigned to the sand bodies of the crevasse splay that encased within the floodplain mudstones, where base level rise slows down. Architectures of deposition of the studied Qisieb Formation were mainly controlled by tectonics and climate change. Influence of sea-level control could be developed during deposition in the northern part of the study area, where the tidally-influenced downstream deposits (estuarine mudsone and siltstone) dominated. Also, the relative proportion of fluvial channel sand bodies and fine over bank deposits of the Qisieb Formation were a result of changes in the balance between accommodation space (A) and sediment supply(S).

Early Mesozoic Detrital and Evaporitic Syn-Rift Series of Mohammedia-Benslimane-ElGara-Berrechid Basin (Meseta, Morocco): Sedimentary and Palaeoenvironmental Evolution and Comparison with Neighboring Basins

The Triassic basin of Mohammedia-Benslimane-ElGara-Berrechid contains a sedimentary series consisting of a sandy-conglomeratic formation (Formation A) at the base, surmounted by an argillaceous-saliferous formation (Formation B), the whole being capped by Late Triassic-Early Jurassic basalts. Formation (A) is formed by conglomeratic facies with alternations of sandstone in the middle and top of the formation. Formation (B) is subdivided into two members: (1) mudstone-siltstone member formed by alternations of mudstone and siltstone facies; and an argillaceous-saliferous member (2) composed by mudstone and evaporite facies. Sedimentary analysis carried out on more than ten outcrops and on four cores sample that have identified fifteen types of facies and seven architectural element and facies associations. It leads to the reconstruction of depositional environments during the Upper Triassic in the basin. Also, this work allowed a comparison of the sedimentary series of this basin with those of the other basins of the Moroccan Atlantic margin on one side and the North-east American margin on the other side.