Sandstone Intercalations Research Articles

Anisotropy in Stratified and Equivalent Media: Kinematic and Amplitude Analysis

We implemented an elastic-anisotropic seismic modeling algorithm via synthetic models to evaluate different geological scenarios, where intercalations of sandstones and shales, carbonates and shales and halite and high-speed salt were simulated. These lithologies were selected based on their abundance in the sedimentary record and the importance they have in the composition of petroleum systems. We analyzed the results relative to kinematic and dynamic aspects to broaden the understanding of how these elements act in the presence of anisotropy. Additionally, the elastic and anisotropic parameters of intercalations composed by the referred lithologies were analytically estimated, thus obtaining the characteristics of several equivalent media. The results confirm previous postulations that the intercalation of layers with different properties can generate extrinsic anisotropy, contributing to the perspective of different wavelength(λ)/thickness ratios favorable to such effects. The results indicate that λ/thickness ratios greater than 6 are propitious for extrinsic anisotropy generation and the use of equivalent media as substitutes for stratified layers are ratified for thicknesses lower than 10 meters. Also, it was observed that in most cases, intrinsic anisotropy has a main role over extrinsic anisotropy.

Palynological Studies of Some Coaly Shales around Gamawa Kumo area, Gongola Basin, Northern Benue Trough, Nigeria

Thirty (30) outcrop samples from a section at Gamawa area, Gongola basin, Northern Benue trough were palynologically analyzed to determine age, and paleo-depositional conditions of the strata. Lithological the section is composed of silts, clays and sandstone intercalations at the base followed by coaly shales and bioturbated silty to fine-grained sandstones at the top. Samples were treated with Hydrochloric and Hydrofluoric acids to remove carbonates and silicates respectively and slides were prepared using standard techniques. A total of 1250 palynomorph specimens were recovered. A palynological age of Upper Maastrichtian was assigned to this interval best on the assemblage of Maastrichtian diagnostic marker species of Longapertites marginatus, Proxaperties operculatus, Spinizonocolpites Baculatus, Monocolpites marginatus especially by the abundance of Pollen Spinizonocolpites Baculatus. Based on the low palynomorph marine index and dominating presence of Palme group species, especially the Spinizonocolpites Species the study suggested a paleodepositional condition of a mangrove forest with evidence of tidal dominated estuarine conditions in mostly brackishwater and a temperate climate.

An empirical assessment of selection excavation methods and support system in Budong-Budong Dam diversion tunnel, Central Mamuju, West Sulawesi Province

Budong-Budong Dam is located on Salulebo River, West Sulawesi Province, and has a diversion tunnel to divert river flow so as not to interfere with construction at the main dam. This diversion tunnel has a D shape which is dimensions 5 m. The Method used in empirically assessing rock mass quality is Rock Mass Rating (RMR) and Japan Society of Civil Engineers (JSCE). The data used are RMR values and rock-type categories. The results show that the diversion tunnel is in lithology tuffaceous sandstone intercalation tuffaceous siltstone and tuffaceous breccias. Weathering degree from slightly-weathered to highly-weathered. The dominance RMR value is 27-53 and rock-category is CII with L massif rock type. The excavation method based on RMR is top-heading and bench and the excavation method based on JSCE is a full-face method with an auxiliary bench cut. Support systems proposed by RMR and JSCE are rock-bolts, shotcrete, and steel sets (steel support). Even though it has been done empirically, it needs to be considered for modeling to be effective and efficient.

Microfacies Analysis and Depositional Environment of the Middle Eocene Avanah Formation in Haibat Sultan Area, Iraqi Kurdistan Region

The Avanah Formation (Middle Eocene) was studied in the Haibat sultan section at Bina Bawi Anticline, Northeast of Erbil city within the Iraqi Kurdistan region. The field observation indicated that the formation occurs as Carbonate interbeds within the lower and middle parts of the Gercus Formation, which consists mainly of light yellowish to creamy color, well-bedded, marly, and dolomitic limestone with some intercalations of sandstones and marls reaching about 32 m thick characterized by lateral variations in facies and thicknesses. A petrographic study of 16 thin slices of carbonate rocks indicated that most of the matrix is composed of micrite, with a few microspars. Foraminifers, dasycladacean green alge, and Ostracods make up the skeleton grains. Non-skeletal grains mainly include peloids, intraclasts, and extraclasts. Depending on detailed microfacies analysis in the current study, five main microfacies and fourteen submicrofacies were discovered. The total of all petrographic, facies and textural investigations indicates that the Avanah Formation in the Haibat Sultan area was deposited in the shallow marine inner platform within subtidal, intertidal, and supratidal environments

Biostratigraphy of Yazdanshahr No.2 section in Kerman area, Central Iran, based on conodont communities

Yazdanshahr No.2 section, which consists mostly of Bahram and Sibzar formations is located in the Zarand city, northern Kerman province (Central Iran). Five biozones have been identified based on the conodont community. The first biozone, which includes Padehat (15 meter) and Sibzar formations (75 meter), was distinguished based on genera Bipennatus and Icriodus and the probable corresponding age was considered to span Emsian to Eifelian. The second biozone is recognized by the first appearance of index taxon Polygnathus varcus (varcus Zone: early to middle Givetian). The third biozone starts with the firth appearance of the index genus Icriodus expansus (expansus zone: middle Givetian). The base of the Fourth biozone is recognized by the first appearance of the genus I. subterminus (subterminus Zone: middle to late Givetian) and the last biozone was distinguished with the first appearance of genera Ancyrodella and Polygnathus incompletes in the Givetain-Frasnian boundary (falsiovalis to crepida Zone?: Frasnian to Famenian?). Bahram Formation (94 meter) consists of Fossiliferous limestone (varcus to subterminus Zone) at the lower part, and alternation of dolomite and sandstone (falsiovalis to crepida Zone?) at the upper part. Sibzar Formation consists of Middle Devonian dolomite and limy dolomite containing intercalation of sandstone and limestone layers.

Latest Oligocene to middle Miocene low-latitude calcareous nannofossil biostratigraphy and paleoenvironmental interpretations of stratigraphic well 4, Sinú-San Jacinto onshore basin, northwest Colombia

Calcareous nannofossils are one of the main fossil groups used in the petroleum industry to determine the relative age and correlation of lithofacies identified in gas and oil wells. A limited number of biostratigraphic zonation schemes based on nanoplankton and paleoceanographic reconstructions have been suggested to onshore Colombian Caribbean. Most of them are compiled in several publications for the northern Colombian units (Mejía-Molina et al., 2008, 2010). In this study, a medium to high-resolution biostratigraphy study was carried out on one of the best-known Neogene sedimentary successions in the Sinú-San Jacinto onshore Basin, where the Stratigraphic Well 4 (SW4) was drilled by Ecopetrol, the Colombian state-run oil company. The nannoplankton biostratigraphic zonation proposed here constitutes the first calcareous nanoplankton research to construct a biochronologic scheme for the Neogene of northern Colombia, which has direct applications for oil exploration, global energy matrix and the transition to clean energy in the onshore areas of the Sinú-San Jacinto domain. The section studied has a thickness of ∼269 m and comprises mainly a very thick succession of claystone and mudstone with occasional intercalations of silty sandstones corresponding to the El Carmen Formation. The studied interval is assigned to the nannofossils Zones NP25 (CP19) to NN4 (CN3) of Martini (1971) and Okada and Bukry (1980), spanning from the latest Oligocene (latest Chattian) to middle Miocene (early Langhian), approximately 24 Ma to 15 Ma. Intervals without fossil content were identified in the record and could constitute hiatuses, but the nannofloral events, which define the limits of the biozones, can be identified. Global and regional climatic changes which occurred in the Caribbean region at those times are reflected in important changes in the fossil assemblages and abundance pattern of nanoplankton. These could indicate variability in environmental conditions linked to temperature and increased nutrients within the nannofossil communities in this part of the San Jacinto folded belt (SJFB), northwest Colombia. Middle Miocene Climate Optimum (MMCO) episodes of “blooming” intervals of Sphenolithus were identified, accompanied with a drastic reduction in total nannofossil abundance and CaCO3 content. Since the Caribbean geology is framed in a very complex scenario, the data acquired and presented in this research has a potential application to improve the current stratigraphy in the area, targeted to hydrocarbon exploration and studies related to the global energy matrix and the transition to clean energy. It also strengthens the paleoceanographic reconstructions based on these organisms at low latitudes.

The First Side-Necked Turtle (Pleurodira, Bothremydidae) from the Campanian (Late Cretaceous) of Egypt

The Quseir Formation is an Upper Cretaceous (Campanian) deposit in the Kharga oasis of the Southwestern Desert (Egypt). This formation comprises a clastic sequence of bioturbated mudstone and sandstone intercalations, including rare scattered and fragmented vertebrate remains such as shark teeth, dinosaur remains, and turtle plates. These deposits indicate a supratidal marsh environment. A complete shell of a turtle discovered from the Quseir Formation, at the Kharga oasis, is attributed here to Bothremydini (Pleurodira, Bothremydidae), and determined as a new taxon: Khargachelys caironensis gen. et sp. nov. This form represents the only Bothremydini member currently identified in the Campanian record not only of Egypt but also of North Africa. Therefore, it helps fill the missing evolutionary gap from the Late Cretaceous pleurodires in Egypt and in North Africa.

Detrital zircon U–Pb geochronology and fluvial basin evolution of the Liuqu Conglomerate within the Yarlung Zangbo Suture Zone: A critical geochronometer for the collision tectonics of the Tibetan-Himalayan Orogenic Belt

We present new U-Pb detrital zircon ages, depositional history and tectonic model for the Liuqu Conglomerate (LQC) in southern Tibet that represents a critical geochronometer for the collision history of the Tibetan-Himalayan Orogenic Belt. LQC is a ∼5 km–thick, late Mesozoic–Cenozoic molasse deposit occurring strictly within the Yarlung Zangbo Suture Zone (YZSZ) and is tectonically overlain to the north by the Cretaceous Xigaze ophiolite and to the south by the Mesozoic Tethyan Himalaya sequence. It consists of matrix- and clast-supported conglomerates with sandstone intercalations, and its matrix includes poorly to moderately sorted sandstone and mudstone. New U–Pb detrital zircon dating of LQC sandstones has revealed a youngest zircon age of 307 ± 13 Ma and an oldest zircon age of 3362 ± 51 Ma. The age spectrum of zircons displays a prominent peak of ∼935 Ma, two large peaks at ∼516 Ma and 1474 Ma, and two small clusters of ∼2429 Ma and ∼2772 Ma that point to East Gondwana as the likely provenance for the LQC depocenter. The LQC represents fluvial deposits of an axial river system, which developed in an orogen-parallel, transtensional accommodation space within the YZSZ, after the collision of the Late Jurassic-Early Cretaceous Trans–Tethyan arc–trench system with the northern edge of India in the latest Cretaceous. The Indian subcontinent with the accreted Tethyan ophiolites and the intra–suture LQC depocenter arrived at and collided with the active margin of Eurasia during the latest Oligocene (∼23 Ma). The LQC depocenter started receiving clastic material and zircons for the first time from the Gangdese Magmatic Belt and the Xigaze forearc basin to the north by ∼20 Ma. The ensuing continent–continent collision resulted in significant crustal uplift across the collision zone, and in the inversion and rapid exhumation of the LQC strata by the early–Middle Miocene. The depositional and exhumation history of the fluvial LQC formation within the YZSZ involved two discrete collision events during the evolution of the Tibetan-Himalayan Orogenic system.

Systematics, ecology, and biochronology of blancan horses from Sonora, northwestern Mexico

We describe a set of dental and postcranial horse material recovered from the locality Los Hornitos, northeastern Sonora, northwestern Mexico. The fossil-bearing unit consists of brown silt with intercalation of fine-grained sandstone and bioturbated incipient soils, set in an alluvial environment and considered Pliocene in age. The comparative study of the available sample indicates the presence of two species: the small-sized hipparionine Nannippus peninsulatus and the medium-sized and primitive equine Equus simplicidens. The isotope composition of δ13C and δ18O in dental enamel tooth indicates a C3–C4 mixed diet for these species and suggests the presence of woodland and open areas in Los Hornitos during the Pliocene. The less negative δ13C values observed in E. simplicidens are related to a more C4 diet, preferring to roam open habitats. The coexistence and optimal resource partitioning between these species are explained, considering their differences in dietary behavior, body size, home range, and/or vagility. The recognized horse species are typical of the Blancan North American Land Mammal Age, and their biochronological information from the southwestern United States and central Mexico establishes the probable age of the Los Hornitos at about 3.9–2.6 Ma, corresponding to the Blancan III or late early Blancan – early late Blancan.

Textural and Paleoenvironmental Characterization of the Campano-Maastrichtian Patti Sandstone, Southern Bida Basin, Northcentral Nigeria

Field and granulometric investigation of Patti Sandstone were carried out with a view towards establishing the lithological sequence, geological processes, textural characteristics and paleoenvironment of deposition of the sediments. Field study entailed basic field procedures and sedimentological descriptions which encompass physical factors such as textural parameter, composition, colour and structures; biological inference in terms of fossil content and chemical character in terms of chemical composition and post depositional diagenesis effect. Granulometric laboratory procedure includes weighing and sieving of samples with set of sieves; calculated cumulative percentages, software input of data to generate statistical parameters such as mean, standard deviation (sorting), skewness, kurtosis and ternary diagrams. Field observations show that the lower part of the outcrop section has alternation of claystone and shale; the mid-section shows coarsening-up sequence of shale, clay and sandstone facies of a retrogradational system, while the upper part is composed of intercalation of claystone and sandstone in repetitive pattern, various thicknesses and colours. The textural characteristics of the sandstone are generally coarse-fine grains, reddish to greyish in colour, rounded to subrounded and moderately to well sorted. Structurally, the outcrops are planar cross bedded, wavy laminated and concretional. Granulometric result categorized the sandstones into fine, medium and coarse grained particles; well sorted to moderately well sorted, characterized by lateral retrogradational sequence from the shoreline. The skewness varies from fine skewed, very fine skewed and symmetrical. Kurtosis values suggest multi-sourced particles deposited in marine and fluviatile paleoenvironments.

An integrated approach of reservoir characterization of Y gas field in Central Bredasdorp Basin, South Africa

The study attempts to address the knowledge gap in the Bredasdorp Basin Offshore South Africa by using newly acquired seismic data with an enhanced resolution, integrating core and well log to provide a solution. The main objective of this study was a volumetric sandstone reservoir characterization of the 13At1 and 10At1 sandstones deposited in the upper shallow marine environment. The results reveal four facies grouped as facies 1(claystone), facies 2(intercalation of claystone and sandstone, facies 3(medium sandstone), and facies 4 fine-medium sandstone grain deposited in a deep marine environment. Facies 3, the medium-grained sandstone, has the best reservoir quality rock, while facies 1, which is predominantly claystone, has the least rock quality. The study has produced a calculated volume of gas in the 10At1 sand (upper and lower sand is 30.01 billion cubic feet (bcf)) higher than that of the 13At1 sand (27.22 bcf of gas). Improved seismic resolution enhanced the accuracy of results. It is advisable to focus further field development in the eastern part of the Y gas field because of good reservoir quality and production developed due to the sand in the 10At1 sequence.

Disentangling climate signal from tectonic forcing: The Triassic Aghdarband Basin (Turan Domain, Iran)

The Middle–Upper Triassic Aghdarband Basin, NE Iran, consists of a strongly deformed marine and non-marine stratigraphic succession, deposited along the southern margin of Asia in a highly complex tectonic context related to a back-arc setting. The youngest deformed units of the Aghdarband area consist of a rather monotonous sequence of brown-colored shales, with intercalations of siltstones and fine-grained sandstones forming the Miankuhi Formation. The shale-dominated Miankuhi Formation rests on an unconformity surface, separating it from the underlying Sina Formation. A multidisciplinary study based on sedimentological, palynological, and paleobotanical data permits to reconstruct the depositional environments, sedimentary evolution, and paleoclimate conditions of the upper Sina and the lowermost Miankuhi formations. The palynological association of the lowermost part of the Miankuhi Formation yielded sporomorphs of the latest early Carnian to early late Carnian age. Qualitative and quantitative analyses document a shift from xerophytic associations in the upper Ladinian (upper Sina Formation) to hygrophytic assemblages in the Carnian (lower Miankuhi Formation). This increase in hygrophytic elements is also observed in coeval Tethyan outcrops at the same latitudinal belt, suggests a more humid climate in the lower part of the Miankuhi Formation, and correlates this part of the succession with a record of the Carnian Pluvial Episode. The sedimentological and stratigraphical analyses show an evolution from prodelta to delta setting in the upper Sina Formation, then an unconformity enhanced by an interval of fluvial deposits with histosol levels in the basal Miankuhi Formation, in correspondence with the hygrophytic assemblages. The unconformable boundary between the Miankuhi and the Sina formations is, consequently, interpreted as a result of the sea-level fall associated with the humid climate shift, occurring in close association with the first effects of the Eo-Cimmerian Orogeny along the suture zone, taking to a regional reorganization of the basins architecture and the end of volcanic activity in the back-arc region. The main deformations related to the Eo-Cimmerian event thus, correspond in the Aghdarband Basin to the tectonic event that deformed the Miankuhi Formation. This event is probably older than the middle Norian (217.1 ± 1.7 Ma) but younger than the late Carnian, testifying to a diachronicity in the record of collision along the Iranian Cimmerian blocks and Southern Laurasia according to the different considered structural positions. • Stratigraphical and sedimentological revision of Upper Triassic strata from NE Iran • Palynological studies assignm the basal Miankuhi Formation to the Carnian age • Paleobotanical data show clear evidence of the Carnian Pluvial Episode in Iran • The best available estimation of the onset of Eo-Cimmerian event in NE Iran

Depositional Environment of Nampol Formation and Its Implications as Potential Source Rocks in the Sumbermanjing Area, South Malang

The decline in oil and gas production inevitably forces explorationists to be more creative in finding new potential reserves. Nampol Formation is expected to have the potential to become hydrocarbon source rocks due to their organic matter content. However, the depositional environment of Nampol Formation has not been thoroughly researched. The focus of this research is to reveal the depositional environment of Nampol Formation that may lead to a suitable condition for the deposition of potential source rocks layers. Detailed geological mapping in several selected traverses and micropaleontological analysis was carried out to determine lithological characteristics and depositional environment of Nampol Formation. The microfacies approach was also used to determine the carbonate facies zone of this unit. Source rock samples taken from outcrops on the surface then were analysed to evaluate organic matter content, type of kerogen thermal maturity, and its potential to produce hydrocarbons. The Nampol clastic limestone unit in the study area is composed of clastic limestone with intercalation of black shale, claystone, siltstone, sandstone and calcareous claystone. The microfacies approach shows that the wackestone and mudstone belong to the SMF 15-M (Ooid wackestone) and SMF 23 (Non-fossiliferous mudstone) which can be interpreted belong to Facies Zone (FZ) 8 in the Flügel carbonate facies model (2004). This zone is located in the Restricted interior platform or platform environment with closed water circulation which is situated behind the barrier reef (back reef). Based on the results of geochemical analysis, source rock samples from Nampol Formation can be considered as a gas prone source rock, with type III kerogen, total organic content ranging from 3.48 – 26.18 wt%, po-sess the potential to produce

Potential of Shallow Groundwater for Household Level Irrigation Practices in Tahtay Koraro Woreda, Tigray, Northern Ethiopia

This paper deals with the results of a pilot study conducted to estimate the shallow groundwater resource potential and irrigation capacity at the household level in Tahtay Koraro Woreda, northwestern zone of Tigray, Ethiopia. The potential evapotranspiration and actual evapotranspiration of the study area are estimated to be 1484 mm/year and 814 mm/year respectively. The runoff is approximately calculated to be 280 mm/year and the annual groundwater recharge is estimated to be 29 mm/year. The total annual groundwater abstraction for human, livestock, and irrigation is estimated to be 25 mm/year. It should be noted that the groundwater recharge rate is expected to remain constant while the total annual groundwater discharge is expected to increase from year to year. This relation when projected over a long period may result in a negative groundwater budget which can result in depletion of groundwater (lowering of groundwater levels), reduced baseflow to streams, and deterioration of water quality. The computed values for hydraulic conductivity of the aquifers range from 1.63 m/day to 7.27 m/day with an average value of 4.9 m/day and transmissivity from 48.9 m2/day to 218.1 m2/day with an average value of 147.14 m2/day. The aquifers in the highly weathered basalt and highly weathered siltstone – sandstone intercalation have transmissivity values ranging from 99 m2/day to 218.1 m2/day with an average value of 157 m2/day and are grouped into the moderate potentiality aquifers category. The aquifers in the slightly weathered and fractured metavolcanics grouped under low potentiality based on the lower transmissivity values (<50 m2/day). The study area has low to moderate groundwater potentiality, hence, large-scale groundwater pumping is not possible. Therefore, the current activity of using hand dug wells for household-level irrigation is the best way of using groundwater for irrigation and other uses as well. Increasing the depth of the existing hand dug wells that are constructed in highly weathered basalt and highly weathered siltstone – sandstone intercalation can also enhance the yield of the hand dug wells. It is recommended to use water-saving irrigation technologies rather than increasing the number of wells. This will also help in increasing the irrigation area. Groundwater recharge enhancement structures such as trenches, percolation ponds, and check dams be constructed in scientifically selected localities to further enhance the groundwater potential.

Sedimentary facies, stratigraphy, and depositional environments of the Ecca Group, Karoo Supergroup in the Eastern Cape Province of South Africa

Abstract The stratigraphy of the Ecca Group has been subdivided into the Prince Albert, Whitehill, Collingham, Ripon, and Fort Brown Formations in the Eastern Cape Province, South Africa. In this article, we present detailed stratigraphic and facies analyses of borehole data and road-cut exposures of the Ecca Group along regional roads R67 (Ecca Pass), R344 (Grahamstown-Adelaide), R350 (Kirkwood-Somerset East), and national roads N2 (Grahamstown-Peddie) and N10 (Paterson-Cookhouse). Facies analysis of the Ecca Group in the study area was performed to deduce their depositional environments. Based on the lithological and facies characteristics, the stratigraphy of the Prince Albert, Whitehill, Collingham, and Fort Brown Formations is now subdivided into two informal members each, while the Ripon Formation is subdivided into three members. A total of twelve lithofacies were identified in the Ecca Group and were further grouped into seven distinct facies associations (FAs), namely: Laminated to thin-bedded black-greyish shale and mudstones (FA 1); Laminated black-greyish shale and interbedded chert (FA 2); Mudstone rhythmite and thin beds of tuff alternation (FA 3); Thin to thick-bedded sandstone and mudstone intercalation (FA 4); Medium to thick-bedded dark-grey shale (FA 5); Alternated thin to medium-bedded sandstone and mudstone (FA 6); and Varved mudstone rhythmite and sandstone intercalation (FA 7). The FAs revealed gradually change of sea-level from deep marine (FA 1, FA 2, FA 3 and FA 4, FA 5, and FA 6) to prodelta environment (FA 7). This implies that the main Karoo Basin was gradually filling up with Ecca sediments, resulting in the gradual shallowing up of the water depth of the depositional basin.

The Numidian Sandstones in northern Morocco: Evidence for early Burdigalian autochthonous deposition on top of the Tanger Unit

The Numidian Sandstones are widespread throughout the western Mediterranean, from Spain and North Africa to southern Italy. They consist of intercalations of thick ultra-mature sandstones within brownish shale deposits. Crucial issues about the Numidian Sandstones are still under debate, such as their pertinence to an undisputed paleogeographic domain and their age. In addition, in the Moroccan Rif, detailed sedimentological studies are still lacking, preventing the understanding of the main features of the sedimentary basin in which the Numidian Sandstones were deposited. This paper aims to reconstruct the Numidian Sandstone depositional environment via a detailed sedimentological study and provides new time constraints through quantitative analyses of calcareous nannofossil assemblages. The Numidian Sandstone sedimentary features suggest a depositional environment located in the transition between a lower muddy slope and a deeper basin plain. Quartz-rich sandy turbidites supplied sediments to this basin during a tectono-sedimentary event lasting ca. 1 Myr in the early Burdigalian. A key section from the Tanger Unit shows the Numidian Sandstones in stratigraphic continuity with the pre-Numidian deposits of the External Tanger Unit (Intrarif sub-domain). This evidence allows us to reject the notion of the Numidian Sandstones as a nappe, detached at their base from the pre-Oligocene deposits of the more internal units of the Flysch Basin. The new biostratigraphic analyses performed on the Numidian Sandstones from northern Morocco mostly correlate with the depositional age of the Numidian Sandstones outcropping in the rest of the Maghrebian Chain. The Numidian sand event, which affected the SW sector of the Mediterranean Basin from the Betics to the southern Apennines, was a unique and extensive event that was possibly triggered by the interplay among the uplift of the Atlas Chain, the sea-level drop at 20.4 Ma, and the establishment of a humid climate in North Africa at the beginning of the Miocene.

Micro biostratigraphy and paleo environment of Oligo-Miocene deposits in north of central Iran

Oligo-Miocene rocks are deposited between Pyrenean and Pasadenian orogenic phases. This rocks in central Iran back arc deposits are named Qom formation. There are well developed outcrops of Qom formation at the North of Central Iran zone. In order to study microbiostratigraphy of the formation, Three sections, north west of Darjazin town , Bonak mount and Arvaneh were selected. In these sections Qom formation with discontinuity overlays the Lower Red formation and with the same quality under the Late Miocene Conglomerate with intercalations of Sandstone, which is equivalent to the Upper Red Formation is placed. The main lithological composition of the Qom Formation in the study area alternates between layers of limestone and Marl with intercalations of siliciclastic rocks. Members and submembers of the Qom formation type area are not visible in this area and can only based on the lithological characteristics divide to local units. Based on bentic foraminifera and other microbiostratigraphical data, Qom Formation age in north west-west of Semnan (Darjazin-After zone), which is located in the Central Alborz structural- sedimentary zone, is early Miocene epoch and Burdigalian stage, which is the equivalent of Borelis melo curdica-Borelis melo biozone.

MORPHOMETRIC ANALYSIS OF BAUR CATCHMENT IN LESSER HIMALAYA: USING GEO-SPATIALTECHNIQUES

The current assessment is an undertaking to evaluateand compare variousmorphometric parameters of the Baur catchment. Morphometric analysis of the river basin provides a quantitative description of the drainage system, which is an important aspect of the categorization of the basin (Strahler, 1964).The Baur catchment is located in the outer part of the Lesser Himalaya in the Kumaun region, which is a major part of Western Himalaya.The geographical area of Baur Catchment is 106.233Km2.Morphometric analysis of Baur Catchment includes linear, areal, and relief aspects.The calculation of the morphometric parameter, along with map preparation, was performed with the help of GIS techniques and ancillary material.Most of the area of Baur Catchment is occupied by Siwalik Group (sandstone and clay intercalation with pseudo-conglomerate) of rocks.The entire Baur Catchment has found 6th order drainage, which reveals sub-dendritic to a dendritic type of drainage pattern. It is observed that the drainage density of the Baur Catchment is 3.525 km/halfkm2.

The geometry, sedimentary filling and depth estimate of the Mirandiba Basin, Pernambuco, Brazil: new insights about the depositional regional gap of rift phases in the interior basins

The Mirandiba Basin has a well-defined stratigraphic sequence and its sedimentation may be directly correlated with the Jatoba Basin and some other interior basins. The sedimentation began in intracratonic conditions with a Paleozoic sequence (Tacaratu/Inaja Formations), which acted as a substrate without any genetic relationship with the basin. The fluvial Tacaratu Formation emerges beyond the limits of this basin, where a remnant core named here as Poco do Ico was found wrapped around the basement to the west of the basin. Subsequently, there was a deposition in a shallow marine environment of the Inaja Formation (Devonian) formed by the intercalation of clay/siltstones and sandstones with ichnofossils. Pre-rift sedimentation occurs over the Paleozoic sequence, characterized in the basin by the lacustrine sediments of the Alianca Formation, represented by the intercalation of shales and calcarenites with desiccation cracks and fossil fragments. In spite of depositional gap described between the local Aratu and Alagoas Stages, the presence of Salvador Formation close to the north border fault may represent a rare rift phase record in the interior basins. The post-rift sequence is represented by the Marizal Formation, deposited during the Aptian. This formation is distinguished by the intercalation of fine sandstone, siltstone and conglomerate deposited in an alluvial fan environment. The pre-rift, rift and post-rift sedimentation are embedded in the depocenter of the basin, where the main NE-SWgraben stands out. A gravity survey was carried out, which obtained a negative, asymmetric Bouguer anomaly, with gradients added to the northwest, suggesting the existence of a half-graben. The result of the gravity 3D model indicates the existence of a main depocenter in the NE-SW direction with depths of up to 400 meters. These geophysical results support the tubular well location drilled 410 m in depth that was used in this work to better characterize the basin. The joint interpretation of gravity, aeromagnetic and structural data suggest that the half-graben framework of the basin developed by the evolution of a pull-apart extension system. The structural system that gave rise to the Mirandiba Basin has the maximum compression tensioner oriented to NE-SW and the distention to NW-SE. It has a depth of around 400 meters and the depressions formed by tectonic events were filled by Post-Tacaratu sedimentation.

Benthic microbial mats from deep-marine flysch deposits (Oligocene Menilite Formation from S Poland): Palaeoenvironmental controls on the MISS types

Sedimentary structures produced by benthic microbial mats have been reported from various ancient shallow-marine deposits, but examples from deep-marine settings are rare. This study focusses on the microbially induced sedimentary structures (MISS) from fine-grained clastic deposits and carbonates of the Oligocene Menilite Formation that were deposited in a deep-marine environment periodically affected by distal turbidity currents. At the study location, the MISS-bearing deposits are represented by grey to black shales with intercalations of fine-grained sandstones, siltstones and limestones. The MISS were documented in thin sections and using scanning electron microscopy with elemental mapping. Four of the recognised MISS record periods of in-situ formation, which are attributed to a significant sedimentation slowdown, ranging approximately from a few weeks to more than a year. These four MISS include laterally continuous irregularly laminated layers, carbonaceous laminae regularly alternating with calcareous laminae, networks of thin carbonaceous laminae anastomosing between peloids, and irregularly laminated lenses occurring within siltstone-sandstone layers. The other MISS reveal signatures of erosion and redeposition by turbidity currents. They include small lenses representing mat chips and irregularly laminated lenses interfingering with the surrounding mudstone, which represent torn and re-established fragments of mats. The exceptional preservation of articulated fish skeletons that form Konservat-Lagerstätten within the studied succession is explained by the presence of epibenthic mats, which covered the fossil remnants. Microbial overgrowths protected fish carcasses against decay and floating, and facilitated precipitation of early diagenetic carbonates, which enabled fast fossilisation of the remnants.This study indicates that the interpretation of depositional conditions prevailing in a deep-marine setting may benefit considerably from the analysis of MISS. It also shows that the sedimentation rate of flysch deposits may be more variable than commonly assumed, as hiatus intervals are hidden within both hemipelagic deposits and amalgamated turbidite beds. The identification of various MISS types may be significant in distinguishing turbidites from hemipelagic deposits within homogenous muddy successions.