Matrix-supported Conglomerate Research Articles

Lower Permian Košna conglomerates of the Velebit Mt. (Croatia): modal composition, provenance and depositional environment

The multicoloured ‘Košna’ conglomerates are investigated in the area of the Košna Voda spring, in the Brušane area of Velebit Mt., Croatia. The studied conglomerates consist of red-coloured matrix and clasts of various lithologies (sandstones, limestones, chert and quartz pebbles) and sizes, suggesting provenance from different areas. Average clast size and their percentage was determined by the Udden-Wentworth classification with estimation of the matrix content. Clasts and matrix lithological and mineralogical characteristics were determined using petrographic, ore microscopy, and X-ray diffraction analysis. Sandstone clasts in the studied conglomerates are classified as lithic arenites, subarkoses and arkoses. Limestone clasts are mostly wackestones to packstones with foraminifera, ostracods, echinoid and bryozoan fragments that derive from late Carboniferous/early Permian shallow-marine limestones. Calcispheres and incipient growth forms of Microcodium are also present, suggesting different sediment sources and resedimentation processes. Fragments of fusulinid foraminifera were identified in the matrix of the ‘Košna’ conglomerates. Based on the analyses performed, and field observations, the ‘Košna’ conglomerates are described as early Permian (Cisuralian) polymictic clast-supported to matrix-supported conglomerates and breccia-conglomerates that share structural and textural similarities with conglomerates from other areas in the Dinarides, as well as in the Eastern and Southern Alps. The ‘Košna’ conglomerates are younger than the Sakmarian and are comparable with the Trogkofel limestones of the Carnic Alps and the Karavanke Mts. in Slovenia. We suggest that the studied deposits originated from the uplifted Variscan Mountains during the Variscan and Saalian orogenic movements, and were finally deposited from tractive flows and occasional debris flows in a shallow marine environment of the Palaeo-Tethys, possibly in fan deltas.

Lithofacies Study of Bai Hassan Formation Sequence (Upper Pliocene) in Bekheir Anticline, Zakho Area Northern Iraq

The current study included the Bai Hassan Formation (Upper Bakhtiari) in the Zakho area of northern Iraq. Depending on the grain size class, structures, degree of rounding, sorting, and some other detailed field observations. This formation was divided into eleven lithofacies which are matrix-supported conglomerate, clast-supported conglomerate, laminated sandstone, sandy gravel, planar cross-bedded conglomerate, interbedded siltstone-mudstone, gravely sandstone, interbedded sandstone-conglomerate, lime matrix-supported conglomerate, and caliche lithofacies. These lithofacies are distributed into six coarsening-upward cycles consisting of complete and incomplete cycles, and these lithofacies include sedimentary structures such as imbrication pebbles, bedding plain, load cast, and gravely cross-bedding. The environment of the Bai Hassan Formation represents conjunctive alluvial fan with possible internal lake environments. The study includes the determination of source areas such as sedimentary, igneous, and metamorphic rocks.

The Portofino Conglomerate (Eastern Liguria, Northern Italy): Provenance, Age and Geodynamic Implications

The Portofino Conglomerate (PC) cropping out in the Eastern Liguria is an approximately 500 m thick, very gently folded succession mainly composed of poorly bedded and mostly matrix-supported conglomerates. It stratigraphically rests on the Helminthoid Flysch (UA3) thrusted onto the Antola Unit. We vertically distinguished three mostly ruditic litho/petrofacies: (i) Paraggi (fP) with carbonate clasts from an Helminthoid Flysch succession; (ii) Monte Pallone (fMP) with prevailing carbonate and meta-carbonate clasts and minor quartz-rich (meta)siliciclastic and high-pressure–low-pressure (HP-LP) metabasite clasts; and (iii) Monte Bocche (fMB) with dominant quartz-rich (meta)siliciclastic, meta-carbonate clasts, and minor granitoid elements and medium-temperature–high-temperature (MT-HT) regional metamorphic rocks. The middle-upper Eocen age of Paraggi litho/petrofacies is constrained by well-preserved microforaminifers (e.g., Globigerinatheka) recovered in the matrix. During its sedimentation, the directions of the paleocurrents would indicate that the PC underwent a counterclockwise rotation coeval with the first Cenozoic rotational phase of the Sardinia–Corsica system (50–30 Ma) and then stopped before the sedimentation of the Monte Pallone and Monte Bocche litho/petrofacies. The vertical compositional variation in the sedimentary inputs suggested that the PC is the result of a progressive deepening of the erosional level of a tectonic pile that can be located in the Ligurian Alps Chain. We considered the PC as the likely apical part of a submarine fan deposited in a piggy-back/thrust-top basin within the Alpine nappe stack. This sedimentary body was later tectonically transported eastward with its UA3 Helminthoid Flysch substrate (similarly to Epiligurian Units of the Northern Apennines) onto the Apenninic orogenic system (i.e., the Antola Unit).

Facies analysis, petrography and textural characteristics of the onshore Paleogene-Neogene Lawin Basin, Perak, Peninsular Malaysia: Insights into palaeodepositional environment and provenance

Sedimentological features of the onshore Paleogene-Neogene Lawin Basin are of importance in better understanding the basin evolution and geodynamics. The N-S trending Lawin Basin, which is situated within the Western Belt of Peninsular Malaysia, is an extensional basin that formed during the sinistral movement of the Bok Bak Fault zone. This study evaluates the palaeodepositional environment, reveals the provenance, and interprets the transport dynamics of the mini-basin by integrating facies, petrographic, and grain size analyses. The basin lithologies can be broadly divided into conglomerate and sandy facies, with the former consisting of clast-supported conglomerate, matrix-supported conglomerate, cross-stratified pebble conglomerate, and bedded pebbly conglomerate, whereas the latter comprises massive pebbly sandstone, horizontally bedded sandstone, planar cross-bedded sandstone, and ripple laminated sandstone. The lithologies can be grouped into three main facies associations, including massive conglomerate, stratified conglomerate, and fluvial sandstone deposits, which reflect alluvial fan (debris/gravity flow deposits), braided gravel bar, and channel bar elements, respectively. Petrographic data indicate that the conglomerates are clast- and matrix-supported and were derived from a proximal source. The QFL range of detrital framework grains reveals that sandstones are composed of quartz (43–80 vol%), feldspar (9–54 vol%), and lithic fragments (2–16 vol%). The sandstones are coarse-grained, poorly-sorted, and sub-rounded to sub-angular in texture. They are arkose, sublitharenite, and lithic arkose in composition. QtFL/QmFLt ternary diagrams show that the sandstones are primarily derived from a provenance area comprising continental block material, including uplifted basement rocks and transitional continental deposits. This study proposes that the sandstones had a nearby granitic source (Bintang) and a debris source derived from recycled sedimentary rocks (the Baling Group sediments). Grain size parameters ranges (mean, −2.37 to 0.74 Φ; sorting, 1.22 to 2.07 Φ; skewness −0.21 to 0.91 Φ, kurtosis, 0.66 to 1.98 Φ, and average mean-sorting index of −0.24) are consistent with immature to sub-mature sedimentation deposited within a high-energy fluvial environment.

Provenance, depositional process, and tectonic setting of gold placer from the Bétaré-Oya Gold District (East-Cameroon, Central Africa) along the Precambrian Sanaga fault

The Bétaré-Oya Gold District is one of the three gold districts in East Cameroon with varied types of mining. The study site is an open-cast mine located in an alluvial plain. The strata succession globally consists of two positive sequences represented by three facies associations and seven lithofacies: massive clast-supported (Gcm), massive trough-cross bedded (Gtm), and massive matrix-supported (Gmm) conglomerates; massive sands (Sm); and massive (Fm), heterolothic (Fhl), and convolute and heterolithic (Fhlc) clays. The facies analysis indicates deposition after a recent tectonic event creating a depression, followed by a rapid deposition of varied facies and energies of sedimentation with fluvial and gravity inputs. The deposits come from proximal to distal sources but more proximal. The identified heavy mineral or accompanying minerals reveal a plutonic source (tourmaline sometimes folded), a volcanic source (olivine or clino-pyroxene with cracks), and a metamorphic source (sillimanite, andalusite, and staurolite). In the pan concentrates of placer with high silver (Ag) concentration (100 ppm) are also associated with relative abundance of lead (Pb) (17.8 ppm), zinc (Zn) (27 ppm), and low levels of copper (Cu) (3.1 ppm). The concentration and distribution of some element ratios, such as thorium/scandium (Th/Sc), chromium/thorium (Cr/Th), and europium anomaly (Eu/Eu∗), rare earth elements (REEs) and aluminum oxide/titanium dioxide (Al2O3/TiO2) vs. silicon dioxide (SiO2) plots for the studied sediment indicate heterogeneous sources of rocks with dominance of felsic sources. The discriminant diagram reveals a recycled or sedimentary provenance of the deposited sediments. The tectonic setting plot indicates a collision tectonic setting which is consistent with the Precambrian history of the study area which belongs to the Pan-African North-Equatorial fold Belt. The gold deposits in the Bétaré-Oya area probably derive from several sources, such as a vein source (from magmatic and metamorphic processes of the Neoproterozoic age) and a sedimentary source (from remobilization of ante-Neoproterozoic rocks of Archean and Paleoproterozoic age), deposited during the Cenozoic period linked to the reactivation of the Precambrian Sanaga fault. These are likely associated with a supergene source as indicated by the presence of dissolution microstructures. The cases of detrital gold deposits from several sources has been reported for the Serpont gold deposits in South-East Belgium, and those associated with authigenic forms are known in Poland, New Zealand, and Tanzania.

Lateral and temporal variations of a multi-phase coarse-grained submarine slope channel system, Upper Cretaceous Cerro Toro Formation, southern Chile

ABSTRACTUnderstanding variations in the sedimentary processes and resulting stratigraphic architecture in submarine channel systems is essential for characterizing sediment bypass and sedimentary facies distribution on submarine slopes. In the Santonian to Campanian Cerro Toro Formation, southern Chile, a coarse-grained slope system, informally known as the Lago Sofia Member, developed in a structurally controlled environment, with complex and poorly established relationships with the surrounding mud-rich heterolithic deposits.A detailed architectural analysis of the most continuous and best-exposed channel system in the Lago Sofia Member, the Paine C channel system, provides insights on lateral facies transitions from channel axis to margin, stacked in a multi-phase sequence of events marked by abrupt changes in facies, facies associations, and architecture.The Paine C channel system is incised into siltstones and claystones interbedded with thin-bedded very fine sandstones, interpreted to be either channel-related overbank or unrelated background deposits. The coarse-grained deposits are divided into a lower conglomeratic unit and an upper sand-rich unit. The lower conglomeratic unit can be further subdivided into three phases: 1) highly depositional and/or aggradational, dominated by thick and laterally continuous beds of clast- to matrix-supported conglomerate, herein named transitional event deposits; 2) an intermediate phase, including deposits similar to those dominant in phase 1 but also containing abundant clast-supported conglomerates and lenticular sandstones; and 3) a bypass-dominated phase, which records an architectural change into a highly amalgamated ca. 45-m-thick package composed purely of lenticular clast-supported conglomerates with local lenticular sandstones. Between the conglomeratic phases, a meter-scale package composed of interbedded thin- to medium-bedded sandstone and mudstone deposits is interpreted to drape the entire channel, indicating periods of weaker gravity flows running down the channel, with no evidence of bedload transport.The upper sand-rich unit is divided into lower amalgamated and upper non-amalgamated phases, and represents a rapid architectural change interpreted to record an overall waning of the system. The sandstone unit laps out onto a mass-transport complex which is interpreted to have been triggered initially at the same time as major architectural change from conglomerates to sandstones.While mindful of the fact that each system is a complete analogue only for itself, we propose a new depositional model for coarse-grained submarine channel systems, in which particular characteristics can provide significant insights into architectural heterogeneity and facies transitions in channelized systems, allowing substantial improvement in subsurface facies prediction for fluid reservoirs.

Depositional Facies and Palynofacies Provenance of Clastic Deposits: Insight from Paleocene Strata in Southeast Region, Nigeria

Detailed sedimentary facies and palynofacies provenance studies were carried out on clastic deposits outcropping around the Awka area within the Imo Formation (Paleocene) of the Niger Delta Basin. Seven facies were systematically recognized based on the textural parameters, sedimentary structures and palynological constituents. Interpretation of the prevailing paleoenvironments, palynofacies provenance and depositional mechanisms were derived from the hydrodynamic controls. The sedimentary facies include shales, mudstones, siltstones, heteroliths, cross-bedded sandstones and matrix-supported conglomerates. The palynofacies showed preponderance of amorphous organic matter, marine taxa, opaque particles, with few structured phytoclasts and terrestrial microflora. These palynological microflora constituents are grouped into palynofacies association A and B based on the composition and proportion of the organic particles, stratigraphic position and paleoenvironments of the strata. Facies analysis indicates that the mudrock facies (e.g. shale, mudstone and siltstone) are deposits of deep marine depositional settings with terrestrial input while the sandstones mimic deposits associated with tidal sand waves in shallow sandy seas, braided river and tidally influenced distributary channels. The facies and palynofacies provenance model suggest dominance of terrestrially influenced shallow to deep marine environment evidenced from the abundance of amorphous organic matter and presence of gonyaulacacean dinoflagellate species, Glaphyrocysta ordinata, G. exuberans, and pollen of Proxapertites operculatus, Retitricolporites irregularis with other accompanying marine forms. In addition, the presence of texturally mature coarse- to fine-grained sandstones, variable sedimentary structures, internal bed geometries and nature of bedding are suggestive of tidally dominated shallow marine settings including distributaries channel network deposits.

Study on Microscopic Pore Structure Classification for EOR of Low Permeability Conglomerate Reservoirs in Mahu Sag

The microscopic pore structure controls the fluid seepage characteristics, which in turn affect the final recovery of the reservoir. The pore structures of different reservoirs vary greatly; therefore, the scientific classification of microscopic pore structures is the prerequisite for enhancing the overall oil recovery. For the low permeability conglomerate reservoir in Mahu Sag, due to the differences in the sedimentary environment and late diagenesis, various reservoir types have developed in different regions, so it is very difficult to develop the reservoir using an integrated method. To effectively solve the problem of microscopic pore structure classification, the low permeability conglomerate of the Baikouquan Formation in Well Block Ma18, Well Block Ma131, and Well Block Aihu2 are selected as the research objects. The CTS, HPMI, CMI, NMR, and digital cores are used to systematically analyze the reservoir micro pore structure characteristics, identify the differences between different reservoir types, and optimize the corresponding micro pore structure characteristic parameters for reservoir classification. The results show that the pore types of the low permeability conglomerate reservoir in the Baikouquan Formation of the Mahu Sag are mainly intragranular dissolved pores and residual intergranular pores, accounting for 93.54%, microfractures and shrinkage pores that are locally developed, accounting for 5.63%, and other pore types that are less developed, accounting for only 0.83%. On the basis of clear pore types, the conglomerate reservoir of the Baikouquan Formation is divided into four types based on the physical properties and microscopic pore structure parameters. Different reservoir types have good matching relationships with lithologies. Sandy-grain-supported conglomerate, gravelly coarse sandstone, sandy-gravelly matrix-supported conglomerate, and argillaceous-supported conglomerate correspond to type I, II, III, and IV reservoirs, respectively. From type I to type IV, the corresponding microscopic pore structure parameters show regular change characteristics, among which, porosity and permeability gradually decrease, displacement pressure and median pressure increase, maximum pore throat radius, median radius, and average capillary radius decrease, and pore structure becomes worse overall. Apparently, determining the reservoir type, clarifying its fluid migration rule, and formulating a reasonable development plan can substantially enhance the oil recovery rate of low permeability conglomerate reservoirs.

Migration Rule of Crude Oil in Microscopic Pore Throat of the Low-Permeability Conglomerate Reservoir in Mahu Sag, Junggar Basin

The low-permeability conglomerate reservoir in the Mahu Sag has great resource potential, but its strong heterogeneity and complex microscopic pore structure lead to a high oil-gas decline ratio and low recovery ratio. Clarifying the migration rule of crude oil in microscopic pore throat of different scales is the premise of efficient reservoir development. The low-permeability conglomerate reservoir of the Baikouquan Formation in the Mahu Sag is selected as the research object, and two NMR experimental methods of centrifugal displacement and imbibition replacement are designed to reveal the differences in the migration rule of crude oil in different pore throats. According to the lithology and physical properties, the reservoirs in the study area can be divided into four categories: sandy grain-supported conglomerates, gravelly coarse sandstones, sandy-gravelly matrix-supported conglomerates and argillaceous-supported conglomerates. From type I to type IV, the shale content of the reservoir increases, and the physical property parameters worsen. Centrifugal displacement mainly produces crude oil in large pore throats, while imbibition replacement mainly produces crude oil in small pores. In the process of centrifugal displacement, for type I reservoirs, the crude oil in the pore throats with radii greater than 0.5 μm is mainly displaced, and for the other three types, it is greater than 0.1 μm. The crude oil in the pore throats with radii of 0.02–0.1 μm, which is the main storage space for the remaining oil, is difficult to effectively displace. The crude oil in the pore throats with radii less than 0.02 μm cannot be displaced. The two experimental methods of centrifugation and imbibition correspond to the two development methods of displacement and soaking in field development, respectively. The combination of displacement and soaking can effectively use crude oil in the full-scale pore throat space to greatly improve the recovery of low-permeability conglomerate reservoirs.

Characteristics of Mengger Formation’s volcaniclastic in Cisaat River, Brebes, Central Java, Indonesia

The Cisaat River in Brebes Regency, Central Java, is one of the sites on Java Island where vertebrate fossils were found. Mengger Formation, composed of volcaniclastics material such as tuff and pumice fragments, contains these fossils. The presence of vertebrate fossils along with volcanic deposits has remained unclear of its deposition history. This research characterizes the volcaniclastic rocks in Mengger Formation based on geological field observation and petrography analysis. The study aims to identify and distinguish its primary and secondary volcaniclastic depositional processes. The measured stratigraphic sections reveal that the formation has 7 lithofacies from older to younger, namely grain-supported conglomerate, sandstone, siltstone, sandy mudstone, matrix-supported conglomerate, tuffaceous sandstone, and tuffaceous conglomerate. The primary volcaniclastic materials comprise pumice clast, plagioclase, pyroxene, hornblende, quartz, biotite, lithic fragments, and volcanic glass. In contrast, secondary volcaniclastic or epiclastic-sedimentary materials contain lithic fragments, quartz, plagioclase, pumice clast, and clay matrix. The origin of the resedimented volcaniclastic material was probably derived from a large volume of ignimbrite near the volcano. From the deposit and measurement section, it can be concluded that the type of the Mengger volcaniclastic.

The late Miocene eolian record at the eastern margin of the Puna Plateau, NW Argentina: Evidence of upper-tropospheric paleocirculation

ABSTRACT The Puna–Altiplano Plateau of the Central Andes is the second-highest plateau in the world (after Tibet), with a mean elevation of 4000 m.a.s.l. and an arid to hyperarid climate. Uplift of the Puna–Altiplano Plateau has affected lower-level atmospheric circulation, acting as a barrier to humid easterly winds from the Amazon basin and favoring an across-strike precipitation gradient resulting in a humid climate towards the east of the plateau and an arid to hyperarid climate in the orogen's interior. In the modern climate, the Bolivian High anticyclone regulates upper troposphere circulation, but little is known about the high-altitude tropospheric circulation of the past. This work focuses on the eolian record of the San Antonio de los Cobres basin along the eastern border of the Puna Plateau, NW Argentina, with the aim of analyzing its origin and thus elucidating the late Miocene winds. The eolian deposits are constrained by 7.8 Ma (K/Ar and U/Pb) and 6.4 Ma (U/Pb) ignimbrites at the nearly basal and upper contacts, respectively. Based on stratigraphic, sedimentological, and provenance analysis of the eolian units, we have identified three main facies associations (FAs): FA1) cross-stratified sandstones with large- to small-scale tabular, planar cross-bedding and with trough cross-stratification; FA2) sandstones with planar to low-angle stratification associated with thinly laminated ripple sandstone strata; FA3) medium- to coarse-grained massive sandstones associated with pebbly to bouldery, matrix-supported conglomerates and clast-supported conglomerates. The lateral and vertical facies assemblages indicate a dune field confined to topographic depressions dominated by transverse dunes with straight and sinuous crestlines that laterally grade into sandsheets associated with ephemeral streams. Paleoflows, lithotypes, and grain-size determinations indicate a persistent north-northwest provenance and wind velocities of 24–38 km/h (with maximum velocities of 55–75 km/h). The results of our analysis coupled with data from previous studies indicates that, for at least the last ca. 8 Myr, the winds have been blowing constantly from the north-northwest with an intensity similar to the present. This implies that the paleo-atmospheric circulation had a similar pattern to the present-day one. Therefore, we conclude that the upper-troposphere circulation in the Puna Plateau of NW Argentina was already regulated by the Bolivian High anticyclone during the Miocene, generating constant north-northwesterly winds.

Mafic-ultramafic rocks in the Buqingshan Complex of the East Kunlun Orogen, northern Tibetan Plateau: remnants of the Paleo-Tethys Ocean

ABSTRACT The Buqingshan Complex, the eastern part of the Muztagh–Buqingshan–Anemaqen ophiolitic mélange zone (MBAM), contains a series of oceanic rocks that represent the remnants of the Paleo-Tethys Ocean. Field investigations reveal that the mafic-ultramafic rocks consist mainly of serpentinite, diabase, massive basalt, and pillow basalt. The serpentinites show similar geochemical characteristics to abyssal peridotites, which is probably the residual part of the depleted upper mantle after 17–20% melt extraction. The mafic rocks have geochemical affinities similar to both normal mid-ocean ridge basalt (N-MORB) and oceanic island basalt (OIB). The rocks with N-MORB features (diabases, massive basalts, and pillow basalts) are associated with serpentinites and cherts, characterizing the sequence of MOR-type ophiolites. The OIB-type pillow basalts are characterized by enrichment of Nb, Ti, and LREEs. They are associated with massive bioclastic limestones, limestone breccias, basalt breccias, and matrix-supported conglomerates, resembling a typical seamount sequence of bottom pillow lavas–cap carbonate–slope facies deposits. Zircon U–Pb dating of the diabases yields a Late Carboniferous age at 303 ± 3 Ma. The reported biostratigraphic age data from the overlying limestone suggest the formation age of the basalt basement to be the Early Permian. Linking all the geological, geochemical, and geochronological data together, these pieces of evidence suggest that the Late Palaeozoic N-MORB- and OIB-type rock assemblages in the MBAM are most likely to be fragments of mid-ocean ridge oceanic lithosphere and seamount, respectively. Such new observations also represent the two main stages of the evolution of the Paleo-Tethys Ocean: the spreading of the Carboniferous mid-ocean ridge and the Early Permian plume magmatism.

Lithofacies Analysis of the Tista River Deposits, Rangpur, Bangladesh

Eight (8) distinct lithofacies within the fluviatile reach of the Tista River have been recognized by the detailed study of the sediments as exposed along the river bank and river bars. Genetically, the matrix-supported conglomerate (Gms), massive sand (Sm), Trough cross stratified sand (St), planar cross stratified sand (Sp), ripple laminated sand (Sr) comprise the channel deposits whereas, the ripple laminated sand (Sr), parallel laminated sand (Sh), clay with silt (Fl) and massive Clay (Fm) represent overbank fine deposits. The channel deposits were laid down under relatively high energy conditions compared to the sediments of overbank fines. The stratigraphic succession is indicative of fining upward sequence. The dominance of coarser-grained sediments at the base of the lithostratigraphic unit, especially the matrix supported conglomerate (Gms) suggests that the deposition took place in the proximal part of the Tista Fan, which might be of glacial origin. Massive clay (Fm) is the final stage of vertical aggradations in the overbanks, possibly in the floodplains, flood basins, and back swamps when the velocity of the transporting medium was virtually lean that promotes the deposition of clay materials from suspension. The growth of cracks in the sedimentary succession is resulting from the compaction of the sediments and/or instant change in the paleoslope direction. The unimodal distribution of paleocurrent data with high mode value indicates mainly unidirectional sediment transport. The study of the lithofacies manifests that the deposits are produced by the braided river and debris flows. The modification of the depositional pattern from debris flow to overbank fines discloses the change of climatic condition in the Quaternary period.

The pore structures of different lithofacies in low-permeability sandy conglomerate reservoirs and their diagenetic impacts: A case study from the Es4 member of the northern steep slope in Dongying Depression, Bohai Bay Basin, NE China

Sandy conglomerates are an important reservoir type in the Bohai Bay Basin, China. These reservoirs are characterized by complex lithofacies distribution, low permeability and heterogeneous pore structures that significantly impact reservoir quality and field development strategies. This study evaluated the Es4 member of the Eocene Shahejie Formation based on cores from three wells in the Dongying Depression. The analytical methods include thin section analyses, scanning electron microscopy (SEM), pressure-controlled mercury injection (PMI), rate-controlled mercury injection (RMI) and X-ray computed tomography (CT). The results show that the microscopic pore structures among various lithofacies of the Es4 sandy conglomerate reservoirs are controlled by different levels of diagenetic alteration, resulting in the heterogeneity of macroscopic reservoir quality. The high content of matrix in Mc (matrix-supported conglomerate) reservoirs leads to low primary porosity. Due to the poor grain sorting, Gc (grain-supported fine conglomerate) and Ps (pebbly sandstone) reservoirs lose a great number of primary pores during mechanical compaction process, whereas Ms (massive medium sandstone) reservoirs preserves abundant intergranular pores. Highly mineralized pore fluids, resulting from massive dissolution of volcanic rock fragments and carbonate fragments, contributes to extensive ferroan carbonate cementation during the late diagenetic stage. Powder crystal ankerite, with a grain radius of about 0.02 mm, blocks most pore throats within Gc reservoirs. Authigenic illite and mixed-layer illite/smectite bridges the throats and reduces the pore throat radius exponentially. Moderate dissolution of rock fragments and feldspars generates a number of secondary pores in Gc, Ps and Ms reservoirs, slightly enhancing permeability. With greater residual primary intergranular porosity and more large-size throats, Ms reservoirs possess the best reservoir quality, followed by Ps reservoirs. These research results are crucial to reservoir evaluation and predication in similar sandy conglomerate reservoirs.

Coarse-grained meandering distributive fluvial system of the basal Cedar Mountain Formation, U.S.A.

ABSTRACT The analysis of downstream changes in ancient fluvial systems can better inform depositional models for foreland-basin systems. Herein we analyze the basal deposits of the Early Cretaceous Cedar Mountain Formation of Utah to better understand the variety of fluvial deposits present and to develop a depositional model for the Sevier foreland basin. We also evaluate the long-held interpretation of a braided origin for these deposits and document numerous examples of point-bar deposition in highly sinuous meandering rivers by analysis of large (20 to 60 km2) plan-view exposures. These plan-view exposures allow comparisons between planform and cross-sectional geometries. The study utilizes outcrop data, virtual outcrop models, and satellite imagery to develop a facies model and analyze the architecture of channel bodies in the Buckhorn Conglomerate and Poison Strip Sandstone of the Cedar Mountain Formation. We document downstream (west to east) decreases in lateral channel migration, sinuosity, channel amalgamation, grain size, and percent of fluvial channel facies (conglomerate and sandstone). Fluvial channel deposits occur arranged into larger stratal bodies: multistory–multilateral channel bodies that are dominantly composed of clast-supported conglomerate in the west to a mix of multistory, multilateral, and isolated channel bodies composed of matrix-supported conglomerate in the east. The median width of highly sinuous point bars is similar across the field area (344 m to 477 m), but the inclusion of narrower (median = 174 m), low-sinuosity bar elements in the east indicates an overall reduction in lateral channel migration and sinuosity downstream. Net-to-gross values range from 100% in much of the western outcrops to as low as 38% in the east. Paleocurrent analysis reveals a transverse (west to east) paleoflow for the study interval that merges with axial (south–north) paleoflow near the Utah–Colorado state line. We estimate 104 m3/s-scale discharge and 106 kilometer-scale drainage area for axial rivers based on paleohydraulic analysis which represents a significant part of the Early Cretaceous continental-scale drainage. The observed downstream trends in lateral channel migration, sinuosity, channel amalgamation, grain size, and net-to-gross for the basal Cedar Mountain Formation are consistent with expected trends for sinuous single-thread distributive fluvial systems and are similar to observed trends in the Jurassic Morrison Formation. Medial (Buckhorn Conglomerate) to distal (Poison Strip Sandstone) zones are preserved and span the forebulge to backbulge depozones of a foreland-basin system. Postulated deposits of the proximal distributive fluvial system have been removed during erosion of the foredeep depozone. The easternmost Poison Strip Sandstone and coeval Burro Canyon Formation represent deposits of an axial system at which western-sourced distributive fluvial systems end. Distributive fluvial systems dominate modern foreland basins, and this study suggests that they may constitute a significant proportion of ancient successions.

Characterizing locality- and scale-dependent heterogeneity in conglomerate core and associated fluid flow using X-ray CT imaging

Heterogeneous conglomerates preserving matrix and clasts caused the complex distribution of pore spaces and can eventually influence fluid flow. To evaluate the influence of complex heterogeneous features in conglomerate rock on both pore distribution and fluid flow, two conglomerate cores were analyzed using X-ray computed tomography (X-ray CT). Conglomerate cores (Core I and Core II) characterized by different distributions of matrix and clasts represented highly heterogeneous features; in Core I (clast-supported conglomerate), clasts were evenly distributed through the entire core, but in Core II (matrix-supported conglomerate), large-sized clasts were dominantly positioned at the bottom of core. Such heterogeneous features caused differences in volume of pores (Core I: 7,409.54 mm3 and Core II: 17,525.83 mm3). Based on X-ray CT image analysis, the numerical model (single-phase fluid simulation) was implemented to evaluate the permeability of conglomerate at different scales. Especially, due to inner heterogeneous features (e.g., matrix, clasts, and cracks) in conglomerate cores, permeabilities were changed significantly dependent on the selected location and size of sub-domains representing a few centimeters (kh and kv: 1.18×10-12 to 1.01×10-10m2). This suggests that the effect of small-scale heterogeneity should be evaluated carefully when heterogeneous conglomerate cores were analyzed. Additionally, the measurement scale for X-ray CT analysis should be large enough to capture such heterogeneous features (e.g., the size of clasts).

A late Paleozoic extension basin constrained by sedimentology and geochronology in eastern Central Asia Orogenic Belt

According to sedimentary structure, petrology and sequence analysis from seven sections (S1–S7) across the West Ujimqin basin, the late Carboniferous to Permian sedimentary facies have been recognized and summarized as four sedimentary systems, i.e. the late Carboniferous-early Permian sedimentary system (SA) comprising the alluvial fan–delta–littoral facies, the late Carboniferous sedimentary system (SB) including the littoral facies–delta facies–platform margin facies, the early Permian sedimentary system (SC) characterized by delta front and prodelta facies, and the middle Permian sedimentary system (SD) with alternations of littoral and delta facies. According to the spatial and temporal distribution of the four sedimentary systems, the basin filling process can be divided into three stages. The first stage (324–290 Ma) is dominated by bidirectional terrigenous sediments containing the SA from alluvial fan to delta and littoral facies in the northwestern and the SB from littoral–delta to platform margin facies in the southern, respectively. The second stage (290–270 Ma) is characterized by delta front and prodelta facies of the SC marked by thick-bedded matrix-supported conglomerate, rapid accumulation of terrigenous sediments and volcanic debris, syn-sedimentary deformation and slump. The third stage (270–255 Ma) formed the SD with the alternations of littoral and delta facies, which is represented by complex terrigenous clasts and intra-basin carbonate. These shallow and proximal sedimentary systems from fan delta to littoral facies indicate that there was not oceanic sedimentary system in the eastern CAOB during the late Carboniferous to Permian except for some small red sea basins, which provides convictive evidence that the Paleo-Asian Ocean (PAO) had closed before the late Carboniferous. Detrital zircon dating reveals bidirectional provenances of the West Ujimqin basin, indicating that it was a limited basin between two uplifts, which implies presence of the late Paleozoic “basin and uplift” tectonic framework that developed on the eastern CAOB during the late Paleozoic.

Subaqueous debrites of the Grand ConglomÉrat Formation, Democratic Republic of Congo: A model for anomalously thick Neoproterozoic: “Glacial” diamictites

ABSTRACTVery thick (> 1 km) successions of matrix-supported conglomerates (diamictites) are a very distinctive component of many Neoproterozoic basins. Classically interpreted as glacially deposited sedimentary rocks, their thickness has been seen as requiring exceptional depositional conditions such as world-wide “panglacial” climates. The Neoproterozoic Grand Conglomérat Formation (GC) of Katanga Province, southeastern Democratic Republic of Congo, is a 1.8-km-thick diamictite succession hosting one of the world's largest stratiform copper deposits. Examination of more than 300 km of recently acquired large diameter (up to 4 inches, 10.2 cm) core identifies the diamictites of the GC as debrites that accumulated as part of a deep-water “mass-transport complex” in a tectonically active and volcanically influenced anoxic rift basin. Detailed sedimentological descriptions of debrite facies and their lateral and vertical variability permits new insights into processes of debris-flow formation and transport, and their wider paleoenvironmental and paleotectonic significance. A genetic model is herein presented that highlights the importance of slumping and subaqueous downslope mixing of basin-margin fan-delta gravels, fault breccias, volcanic debris from contemporaneous basaltic fissure eruptions with basinal muds, and the downslope ponding of flows in narrow fault-bounded depocenters. Preservation of such an exceptionally thick subaqueously deposited debrite-dominated mass transport complex lacking any evidence of shallow-water deposition, requires rapid subsidence. Any direct sedimentary evidence of a glacial influence on sedimentation in the wider basin hinterland (if present) has been destroyed and homogenized by mass flow. Indirect evidence of a cold-climate setting is possibly expressed as lonestones in laminated turbidite facies dropped by either glacial or seasonal ice, and by exceptionally rare scratched clasts that may have been striated subglacially. Descriptions and interpretations presented here provide clues to the origin of other unusually thick debrite and turbidite successions elsewhere in other Neoproterozoic basins; their primary paleoenvironmental significance is that they appear to record ponding and focusing of mass flows in narrow, rapidly subsiding fault-bounded depocenters, rather than any unique glacial paleoclimate.

Raised braided stream gravels on Mount Keldağ, Hatay (Eastern Mediterranean coast, Turkey): implications of transformation to beachrock and ensuing tectonic uplift

On the seaward northwest slopes of Mount Keldag, Hatay, the combination of an unconformably overlapping sequence of cemented gravels on a wave-cut platform, and a raised notch and irregular pits left by grazing molluscs on the walls of this notch, carved in an NE-trending high-angle fault plane, retain the record of raised braided stream gravels transformed into beachrock. From the OSL ages, this study reveals that deposition of this sequence occurred between 232.30 ± 31.62 and 214.01 ± 27.42 ka during the penultimate interglacial. The four distinct facies identified are massive matrix-supported conglomerate, massive to crudely stratified gravel, cross-stratified gravel, and clast-supported open-work gravel. Extending to the paleo-coastline during the MIS7 highstand, this sequence was cemented by carbonate and iron-oxide cements and records an uplift of around 0.1 mm/year up to the present.

New insights from the Neocomian basins in the West of Chubut and Santa Cruz provinces, Argentina

This paper presents a regional overview of the Neocomian basins developed in the provinces of Chubut and Santa Cruz, in Argentina, on the light of an extensive compilation of 2D and 3D seismic and borehole data. Neocomian deposits lie, mainly, on the western subsurface sector of both provinces. They are correlated with the Tres Lagunas Formation, Katterfeld and Apeleg formations, or Coyhaique Group, which crop out in Argentina and Chile.The Neocomian Cycle sensu lato was deposited during the Berriasian up to Barremian in a NW trending rift system. The base of the Neocomian fill lies either on top of the Sedimentary Volcanic Complex, (which is correlated with the Lago La Plata Formation), the Early-Middle Jurassic shales and sandstones deposits or Paleozoic metasedimentary deposits.The synrift sequence, regarded as Anticlinal Aguada Bandera Subcycle, is composed of matrix-supported conglomerates, interbedded with volcanic ashes at the base and covered by dark brown shales. The sag or postrift sequence, known as Cerro Guadal Subcycle, filled up the depocenters with sandstones and shales.This paper describes the main morphotectonic features of the area and the stratigraphic architecture of the Cycle. A marine basin is identified in the NW sector of the studied area, where an extended NE paleo-high is recognized. Toward the SE, long narrow NW-trending extensional depressions have developed. The rift infill of these depressions is lacustrine in the Southeast, changing to marine-deltaic toward the North and West.The rift infill is unconformably covered by the Chubut Group volcaniclastic and clastic sediments indicating the early inversion of these depocenters.