Triassic Sequence Research Articles

Using neutron-compressional to shear sonic porosity logs for electrofacies-based permeability prediction: Permian–Triassic sequence of the central Persian Gulf

In subsurface reservoir studies, permeability is an unpredictable parameter, and the main challenge is identifying a parameter that strongly correlates with it. To address this, analyses were conducted using a comprehensive dataset. The study is based on 1575 thin sections obtained from approximately 402.63 meters of cores, along with 1445 porosity and 1390 permeability data points. Additionally, wireline log data covering 462.63 meters from the Dalan and Kangan formations in a key well located in the central Persian Gulf is included. Based on the available logs, artificial effective porosity logs were obtained through the deterministic petrophysical evaluation methods, using sonic, density, density/neutron, and neutron/sonic. The flow zone indicator, Winland’s R35 and electrofacies were used to manage the heterogeneity. It was concluded that the effective porosity log employed the ratio of compressional to shear wave velocity instead of the sonic log in the neutron/sonic method, demonstrate a strong correlation with permeability. Therefore, it can be used for predicting this variable parameter in heterogenous reservoirs. In this study, a new, repeatable, data-driven approach is introduced that uses wireline log-derived porosity logs. The unique use of Vp/Vs ratios in constructing effective porosity logs offers a novel, highly correlated predictor of permeability.

Lithostratigraphy of the Lower Triassic Formations of the Western Carpathians

The nomenclature of Lower Triassic lithostratigraphic units in the Western Carpathians has not been standardized to date. Reference profiles and stratotypes have not yet been established for all Lower Triassic sedimentary sequences. Lithostratigraphic names of Lower Triassic sedimentary sequences are also not consistent in the edition of Regional Geological Maps of Slovakia 1 : 50,000 published by the Dionýz Štúr State Geological Institute. For a better understanding of lithology, facies changes, paleogeography, etc., it is necessary to re-evaluate the knowledge of Lower Triassic sedimentary sequences and their internal content. This paper presents a view of the lithostratigraphic division of the Lower Triassic in the Western Carpathians. It consists of two parts. The first part contains historical contexts of lithostratigraphic divisions used from the beginning of research to the creation of regional geological maps. The second part presents examples of the division of lithostratigraphic units at documented localities, from some tectonic units of the Western Carpathians, prepared on the basis of field geological mapping. The Triassic sedimentary sequence of the Central / Internal Western Carpathians is composed of 3 distinctive formations: Lower Triassic quartzites, Lunz sandstones (Carnian) and Keuper sandstones (Norian). The Lower Triassic sedimentary sequences are due to their extent and lithology, the most significant element among them. Since the 1980s, the name Lúžňa Formation has been used for the Lower Triassic sequence in the Tatricum, Fatricum and Veporicum. However, its lithostratigraphic division is still affected by the use of the older term Werfen Beds / Formation adopted from the Alpine area to the Carpathians, which should not be used. The overlying part of the Lúžňa Formation with a transition to the Middle Triassic carbonate platform, as well as the transitions from Permian sedimentary sequences to the Lúžňa Formation, have not been systematically subjected to detailed study. In the Hronicum unit, the lithostratigraphic division applies a two-part development, as the lower part is siliciclastic with a presumed partly continental development, while the upper siliciclastic-carbonate part has features of marine environments. However, only the informal lithostratigraphic units of the Benkovo and Šuňava Formations have been established to date. The Hronsek Beds have recently been defined between the two formations, which have a much greater thickness in the southern tectonic units (Silicicum). In these southern units, the continental character at the base of the Lower Triassic strata completely disappears, and it even seems that the Triassic sedimentary record has a fully marine character from the beginning. The sedimentary development is more diverse here, and the Lower Triassic has several specific lithological members. Unfortunately, the applied terminology was not adopted from the Hungarian territory completely correctly, and thus it still provides reserves in the interpretation and understanding of its division. The issue of lithostratigraphic division of Lower Triassic sedimentary sequences in the Western Carpathians is still an open topic.

Evidence of detrital spinel geochemistry for depositional response to the Paleo-Tethyan closure recorded in the Songpan-Ganzi Terrane, eastern Tibetan Plateau

Evidence of detrital spinel geochemistry for depositional response to the Paleo-Tethyan closure recorded in the Songpan-Ganzi Terrane, eastern Tibetan Plateau

Investigating the reservoir quality of the Early Triassic succession with a new perspective on diagenesis and sequence stratigraphy in the center of the Persian Gulf, South Pars

Investigating the reservoir quality of the Early Triassic succession with a new perspective on diagenesis and sequence stratigraphy in the center of the Persian Gulf, South Pars

Stratigraphy of the middle Triassic-lower Cretaceous succession in the Paraná and Uruguayan Chaco-Paraná Basins – An overview based on subsurface data

Stratigraphy of the middle Triassic-lower Cretaceous succession in the Paraná and Uruguayan Chaco-Paraná Basins – An overview based on subsurface data

Evaluation of Maturity (Late Diagenesis) in Source Rocks of Jaisalmer Basin in Rajasthan, India using 57Fe Mössbauer Spectroscopy

Abstract The potential of a source rock for hydrocarbon generation depends on several factors such as the amount, type and maturity level of the organic matter present in it as well as the redox conditions in which the sediments containing the source rocks were deposited. Organic-rich sediments deposited in reducing environment have better prospects for a good quality source rock as compared to those deposited in oxidizing environments. The information about the oxidizing/reducing environment at the time of deposition can be obtained from the presence or absence of certain iron-bearing minerals in sediments. The presence of oxide minerals goethite (α-FeOOH) and/or hematite (α-Fe2O3) indicates that sediments were deposited in an oxidizing environment. Therefore the study of iron-bearing minerals in sediments can be used to understand the qualities of the source rocks. Sedimentary samples were collected from different depths of three wells BT-3, DND-1 and LNR-1 located in different structures of the Jaisalmer basin were investigated to understand the chemical state of iron by using Mössbauer spectroscopy. In most of the samples, iron was found mainly in the form of pyrite (FeS2), siderite (Fe, Mg) CO3, 2:1 layer silicates in high spin Fe3+ and high spin Fe2+ state and (Ca, Fe, Mg) carbonates. In the samples from Lathi and Shumarwali formations that belong to the lower Jurassic and Triassic sequences, α-Fe2O3 (hematite) was indeed observed. It was present in a narrow sedimentary depth interval in the wells BT-3 and DND-1 and in a much broader thickness in well LNR-1. The other sedimentary sequences younger than the Lower Jurassic sediments have not shown the presence of any oxide mineral. The present study indicates that oxidizing environment was present in the entire basin in the Lower Jurassic era at least for some duration. However, the degree of oxidation was not uniform as evident from the distribution pattern of iron oxide mineral (α-Fe2O3). Mössbauer studies of source rocks can also be used as a fingerprint to get information about the thermal history (Palaeo-temperature) of sedimentary sequence which is crucial in hydrocarbon prospecting.

The Nature of the Puchezh-Katunki Impact Structure (the Central Part of the East European Platform): Results of the U‒Th‒Pb Isotope System Study of Detrital Zircons from Explosive Breccias

The Puchezh-Katunki crater is located in the central part of the East European Platform in the area of the Gorky Reservoir, has a diameter of ~80 km and is morphologically expressed by the central uplift of the basement (Vorotilov knoll) and the ring depression surrounding it, on the periphery of which there is a ring terrace. The crater is filled with various coptogenic (explosive (?)) formations – breccias of various types, bodies of suvites and tagamites. The results of studying the U‒Th‒Pb isotopic system of detrital zircon grains from variegated explosive Puchezh breccias in the northwestern part of the ring terrace (three samples) are presented. The weighted average of the three youngest U‒Pb datings of detrital zircon from all studied samples is 258 ± 7 Ma, which corresponds to the Late Permian. We took this dating as the lower age limit of the Puchezh breccias. A comparison of the age sets of detrital zircon grains from the samples studied by us and from (i) crystalline rocks of the Vorotilov knoll and ring depression suvites and (ii) Upper Permian–Lower Triassic sandstones of the Zhukov ravine reference section (Moscow syneclise) was carried out. The absence among the detrital zircon from the Puchezh breccia grains, whose U‒Th‒Pb isotopic system is comparable with the parameters of zircon from the rocks of the Vorotilov knoll and suvites, indicates the local nature of the Puchezh-Katunki explosion, in which the impact-thermal impact did not affect the detrital zircons in rocks of the marginal part of the annular terrace of the crater. The high similarity of the sets of ages of detrital zircon grains from the lens of redeposited sandstones of the Puchezh breccias and Upper Permian rocks of the Zhukov ravine section indicates that the Puchezh breccias were formed mainly due to the recycling of the Upper Permian–Lower Triassic sequences underlying the explosive formations. We consider the Uralides paleoorogen as the main source for the deposits of the central regions of the East European Platform in the stratigraphic interval close to the Permian–Triassic boundary. The deposits were formed as a result of a high degree of mixing and averaging of clastic material of sedimentary flows containing the Uralian and Asha provenance signals.

Permo-Triassic cyclicity on the western shoulder of Muzaffarabad-Hazara paleo-high, during the oceanisation of Neo-Tethys

Permo-Triassic cyclicity on the western shoulder of Muzaffarabad-Hazara paleo-high, during the oceanisation of Neo-Tethys

Palynological investigation of an Upper Triassic sequence in Nanjing area, eastern China, with paleoecological implications

Palynological investigation of an Upper Triassic sequence in Nanjing area, eastern China, with paleoecological implications

Provenance changes for mineral matter in the latest Permian coals from western Guizhou, southwestern China, relative to tectonic and volcanic activity in the Emeishan Large Igneous Province and Paleo-Tethys region

Recent studies have found that the provenance for water-transported sediments in some coal seams in the Late Permian and Early Triassic sequences from SW China have changed from mafic rocks of Emeishan Large Igneous Province (ELIP) to intermediate-felsic and alkaline igneous rocks from the ELIP and Paleo-Tethys convergent margins. However, the mechanism of provenance changes for mineral matter in the late Permian coals from SW China remains unclear. This paper uses the detailed mineralogical and geochemical characteristics of the latest Permian coal-bearing strata from the Huopu coal deposit in SW China to identify the potential detrital provenances of mineral matter.The mineralogy of the Huopu coals is dominated by kaolinite, quartz, and calcite. Fracture-filling kaolinite, calcite, quartz, anatase, as well as closely coexisting fracture-filling kaolinite, quartz, and chamosite, were possibly formed by multiple-stage solution injections. The Al2O3/TiO2 values, REY distribution patterns (REY, rare earth elements and Y), as well as Nb/Yb vs. Al2O3/TiO2 and Zr/TiO2 vs. Al2O3/TiO2 diagrams all indicate that the roof and floor sediments of the coal seam were sourced mostly from the ELIP high-Ti basalts. In contrast, the inorganic matter of the coals was derived from the Kangdian tops exposing (1) the Proterozoic meta-granitic complex; (2) the ELIP’s volcanic complex including, in addition to basalts, alkaline and intermediate-felsic lavas and small intrusions; and (3) volcanic ashes from the Paleo-Tethys convergent margins. The latest Permian sedimentation in the Huopu coal deposit is suggested to have been controlled by tectonic activity along the Xiaojiang Fault that separates the inner ELIP from the Western Yangtze Cratonic Basin (WYCB). This activity is characterized by repeated uplifts of the inner ELIP associated with some downward movements in the WYCB and vice versa. The ELIP uplift and WYCB subsidence may have led to intensive erosion of the ELIP basalts and marine transgression producing the clastic sediments, while the ELIP’s downward movement associated with some WYCB uplift may have promoted peat deposition and erosion of the Kangdian tops exposing both the ELIP intermediate-felsic volcanic rocks and the older meta-granitic complexes. Both sedimentation regimes were evidently accompanied by volcanic activity on the Paleo-Tethys convergent margins, but preservation of the volcanic ash layers was possible only during more quiescent peat-accumulation periods. The reduced detrital supply in these periods would result in a higher proportion of the intermediate-felsic pyroclastic debris disseminated in the coals.

Heterogeneity evaluation of pore types based on dipole shear sonic imager logs by means of statistical parameters, the central Persian Gulf

AbstractHeterogeneity analysis in carbonate reservoirs is of great importance for the interpretation of their characteristics. This study focuses on the evaluation of pore‐type heterogeneity by means of the sonic wave velocities in the carbonate–evaporite series of Permian–Triassic sequences in the Persian Gulf. Thin section petrography and laboratory measured the porosity and permeability of 1576 samples, as well as routine wire‐line logs, were employed. To manage heterogeneity, six electrofacies (EF) were determined based on an integrated analysis of compressional, shear and Stoneley waves as well as three routine logs (gamma, neutron and density). The frequency of pore types in each electrofacies was calculated. Then, the heterogeneity of pore‐type distribution in each electrofacies was measured by standard error and coefficient of variation. Sonic velocity has been compared with the geological properties of electrofacies. Results indicated that velocity is affected by factors other than the amount of porosity, facies or lithology. The standard error values in all electrofacies were close to zero. The coefficient of variation values ranges from 1.08 to 4.60. The lowest amount of coefficient of variation was observed in EF6 in the Khuff (K) 4 zone for moldic porosity. This value for intercrystalline porosity distribution in EF1 in the K1 zone was low, too. These results indicate the lowest standard deviation and the highest homogeneity in the distribution of intercrystalline and moldic porosities in K1 and K4. Also, comparing the mean values of sonic logs in each electrofacies with the total mean value in the whole sequence indicated that there is a relationship between sonic velocity logs and the type of porosity. High values of sonic velocity correspond to intercrystalline porosity in K1 and low values of velocity correspond to moldic porosity in K4. Results show that integrated pore‐type studies should be carried out to understand the sonic velocities in carbonate reservoir rocks.

Unraveling overprinted formation mechanisms of massive dolostone in the Lower Triassic sequence of an isolated carbonate platform in Nanpanjiang Basin, south China

Unraveling overprinted formation mechanisms of massive dolostone in the Lower Triassic sequence of an isolated carbonate platform in Nanpanjiang Basin, south China

Missing link on the western Paleotethys configuration: Stratigraphic constraints on the truncated Triassic “Gornjak” sequence (eastern Serbia, Balkan/Carpathian hinterland)

There is a major overlap of the two lithospheric-scale early Alpine (post-Variscan) extensional geodynamic drivers which contributed to the crustal thinning of the north Mediterranean margin/south European foreland/ Dinaride-Hellenide-Carpathian/Balkan/Rhodope continental amalgamation. A widespread late Permian-Triassic Alpine extension interacted with the coeval Paleotethyan rollback, producing a number of intraplate and marginal basins, later coalesced to form the Neotethys Vardar Ocean. However, some of these externally-positioned, north-south striking elongated basins (eastern Serbia), were abruptly interrupted by an unreported Triassic event. This event truncated the latest Permian to Lower – Middle Triassic sequence of the Getic unit, best exposed near the Gornjak area (Balkan-Carpathian hinterland, “Carpatho-Balkanides”, western Moesian foreland). At Carpathian-Balkan scale, this rather undocumented geodynamic episode is consistent with the “early Cimmerian” “docking” event (recorded within the Moesian platform, and the North Dobrogea Orogen). Based on the surface/ subsurface geological and available scarce literature data, the truncated Lower- and Middle Triassic sedimentary successions of the “Gornjak basin” (eastern Serbia), provide new constraints on the timing of the Triassic western Paleotethyan closure. The study emphasizes a far-field effect of the Upper Triassic Paleotethyan demise and Cimmerian “docking”, largely obscured by the late Alpine shortening and the formation of the Carpathian/Balkan fold-and-thrust belt.

Paleozoic basin indication at south of Papua, Indonesia

Eastern Indonesia Paleozoic basin to recent is still an under-explored basin. The study about this oldest sediment sequence is needed to be done because, in Australia, this sequence is already producing hydrocarbon in several basins, known as the Larapintine petroleum system. This paper is subjected to present Paleozoic sediment occurrence in the south of the Papua area, from outcrop, several wells penetrated this unit and from seismic data. Furthermore, this paper aims to construct a geological schematic diagram in the south of the Papua area. Identified Paleozoic rocks in the southern Papua area are Pre-Permian sequence, consist of Otomona Formation (Late Proterozoic–Cambrian), Tuaba Formation (Ordovician) and Modio Formation (Silurian–Devonian), and Aiduna Formation (Late Carboniferous–Permian) from the Permian–Triassic sequence. Otomona Formation was deposited at the submarine fan environment while the Tuaba Formation was deposited in a shallow marine shelf setting. Modio Formation was deposited at shallow marine to shelf environment, and Aiduna Formation was accumulated at deltaic setting. Paleozoic basin occurred from Arafura sea to onshore of southern Papua with a thickness of up to 5 seconds. This unit’s potential trap is the gentle anticline with geometry up to 8 km long and stratigraphic trap top lap with the unit above it.

Epigenetic-Hydrothermal Fluorite Veins in a Phosphorite Deposit from Balaton Highland (Pannonian Basin, Hungary): Signatures of a Regional Fluid Flow System in an Alpine Triassic Platform

The middle Anisian extensional tectonics of the Neotethyan realm developed a small, isolated carbonate platform in the middle part of the Balaton Highland (western Hungary), resulted in the deposition of uranium-bearing seamount phosphorite on the top of the drowned platform and produced some epigenetic fluorite veins in the Middle Triassic sequence. The stable C-O isotope data of carbonates are shifted from the typical Triassic carbonate ranges, confirming the epigenetic-hydrothermal origin of veining. Primary fluid inclusions in fluorite indicate that these veins were formed from low temperature (85–169 °C) and high salinity NaCl + CaCl2 + H2O type (apparent total salinity: 15.91–22.46 NaCl wt%) hydrothermal fluids, similar to parent fluids of the Alpine-type Pb-Zn deposits. These findings indicate that the Triassic regional fluid circulation systems in the Alpine platform carbonates also affected the area of the Balaton Highland. This is also in agreement with the previously established palinspatic tectonic reconstructions indicating that the Triassic carbonate and basement units in the Balaton Highland area were a part of the Southern Alpine. Similar fluorite veining in phosphorite deposits is also known in the Southern Alpine areas (e.g., Monte San Giorgi, Italy). Raman spectroscopic analyses detected H2 gas in the vapor phase of the fluid inclusions and a defect-rich fluorite structure in violet to black colored growth zones. This unique phenomenon is assumed to be the result of interaction between the uranium-rich phosphorite and the parent fluids of the epigenetic fluorite veins.

Fossil woods from the Olenekian (late Early Triassic) Shaofanggou Formation in the Junggar Basin, Northern Xinjiang, North‐west China

A large number of fossil woods were preserved in the Permian–Triassic sequences in the Junggar Basin of Xinjiang Uygur Autonomous Region. These wood fossils provide a lot of palaeoenvironmental information of the Junggar Basin during the Permian–Triassic transition. Here, we describe the fossil woods collected from the base of the Olenekian Shaofanggou Formation in Dalongkou Anticline. Anatomically, these wood remains closely resemble Junggaropitys dalongkouensis, but they lack growth rings and rays are higher. Thus, we suggest identifying them as J. cf. dalongkouensis. The growth pattern shows that J. cf. dalongkouensis is evergreen and developed under warm and humid environments. However, the data of geochemistry, palaeosol and certain sedimentary features reveal a dry climate. Thus, we speculate that the Olenekian Junggar Basin contained gallery forests in the arid environment.

Increased aridity across the Permian–Triassic transition in the mid‐latitude NE Pangea

The Dalongkou section in Xinjiang, Northwest China has preserved a continuous terrestrial Late Permian–Early Triassic sequence with well‐studied information of biota evolution and isotopic excursion. In order to know the corresponding palaeoclimatic and palaeoenvironmental evolution in this critical transition, chemical weathering indexes (chemical index of alteration [CIA], plagioclase index of alteration [PIA], and chemical index of weathering (CIW)) are analysed in high resolution across the Permian–Triassic Boundary. Results show that the declining trend of the CIA, PIA, and CIW was related to the continuous decrease of the chemical weathering in the latest Permian. The climate in the mid‐latitude NE Pangea was becoming increasingly arid in a generally greenhouse warm climate, causing widespread wildfire and turnover of the fauna and biota, coupled with the environmental deterioration expressed by the anomalies of carbon and mercury. Climatic conditions oscillated in the Early Triassic with possible intermittent rainfall and was likely affected by the strengthening of the megamonsoon. In the latest Permian–earliest Triassic, whether chemical weathering strengthened or weakened, as well as whether the climate was increasingly arid or humid, varied in the different places. The possible reasons inducing this need to be further explored.

Source-to-sink system of Late Permian post-collisional stream-dominated alluvial fans under humid paleoclimate along the Irtysh-Zaisan suture zone, Central Asian Orogenic Belt

Source-to-sink system of Late Permian post-collisional stream-dominated alluvial fans under humid paleoclimate along the Irtysh-Zaisan suture zone, Central Asian Orogenic Belt

A new acritarch spike of Leiosphaeridia dessicata comb. nov. emend. from the Upper Permian and Lower Triassic sequence of India (Pranhita-Godavari Basin): Its origin and palaeoecological significance

A new acritarch spike of Leiosphaeridia dessicata comb. nov. emend. from the Upper Permian and Lower Triassic sequence of India (Pranhita-Godavari Basin): Its origin and palaeoecological significance

Quantitative analysis of geological attributes for reservoir heterogeneity assessment in carbonate sequences; a case from Permian–Triassic reservoirs of the Persian Gulf

Quantitative analysis of geological attributes for reservoir heterogeneity assessment in carbonate sequences; a case from Permian–Triassic reservoirs of the Persian Gulf