Sedimentary Depositional Environments Research Articles

Stratigraphy and geochronological constraints of the Serra Sul Formation (Carajás Basin, Amazonian Craton, Brazil)

The Carajás Basin, Amazonian Craton, hosts extensive Neoarchean to Paleoproterozoic sedimentary archives, which are still poorly constrained regarding their depositional settings, ages, and type of basin in which they have been deposited. In this study, we performed detailed sedimentological investigations and U-Pb dating of detrital zircon in four drill cores intercepting the recently defined Serra Sul Formation. Our data show that this formation corresponds to various shallow to deep subaqueous environments. Shallow water environments are characterized by local occurrences of microbially-mediated structures, while deep water environments are characterized by polymictic conglomerates resulting from the mixing of materials of different origins during downslope debris flow. Both sedimentary facies and common occurrence of syn-sedimentary deformations attest for recurrent slope instabilities. Geochronological investigations allow to define a maximum depositional age of 2684 ± 10 Ma, that is several tens million years younger than other Neoarchean sedimentary units of the Carajás Basin. Major peaks in age distribution indicate that the Serra Sul Formation derives from local sources that constitute the basement of the Carajás Basin. The infilling of the Carajás Basin by local sources, together with sedimentary facies and depositional environments attesting for slope instabilities, suggest that the Serra Sul Formation was deposited during an active extensional tectonic phase. Such Neoarchean to early Paleoproterozoic tectonic setting compares with those documented in many other cratons worldwide and suggests that it could correspond to the break-up of one of the first documented supercontinent.

Characterization of sedimentary environment, provenance and distribution of heavy minerals along the Tamil Nadu shoreline, East coast of India

Placer mineral deposits and their limited occurrence have gathered worldwide attention for researchers and geologists to exploit new areas of deposition. This research aims to know the transportation and depositional environment of sediments, provenance and distribution of heavy minerals between Besant Nagar and Sathurangapattinam in the coastal region of Tamil Nadu (India). The sediment samples are collected for textural analysis, magnetic susceptibility (MS), petrographical and mineralogical (XRD) studies of sediment samples, including the heavy minerals studies. Grain size analysis showed fine to medium-grained sandy sediment with very well to moderately sorting indicate reworking of beach edges accompanied by unimodal to the trimodal distribution of sediment from the riverine and marine environment. Grains are mostly symmetrically skewed with platykurtic to leptokurtic nature, indicating low- to high-energy environment prevailing in the region where the deposition and erosion are equally balanced in the area. Bivariate and one percentile–median (CM) pattern plots indicated that most of the sediment is deposited by beach processes transporting sediment by bottom suspension and rolling. The amounts of magnetic or iron-bearing minerals are high in locations no. 1 (Besant Nagar beach), 5 (Injambakkam beach) and 12 (Tiger cave beach) interpreted using MS studies, whereas the heavy mineral weight percentage is higher in locations no. 11 (Pattipulam beach) and 12 (Tiger cave beach). The correlation plot of Heavy wt% vs MS showed positive correlation and in general plots deciphered that the locations with high wt% (Besant Nagar, Injambakkam and Tiger cave beach) showed higher MS indicating the presence of magnetic minerals and the correlation plot between individual mineral grain count% vs MS explicated that the locations were rich in magnetic minerals like ilmenite, magnetite (opaques) and epidote (medium magnetic). The petrographical study of heavy mineral and XRD analysis revealed that the study area contained a high percentage of opaques, garnet, zircon, rutile, chlorite, sillimanite, hypersthene, hornblende, tourmaline, possibly derived from charnockites, granulite gneiss, migmatites and basic dykes. The overall investigation concludes that the sediments are distributed at various locations by marine processes depositing sediment rich in magnetic and heavy minerals derived from various rock type sources transported by rivers and later driven by longshore currents of oceans flowing from S to N, N to S during different months and SW–NE monsoon play a vital role in the distribution of beach placers.

Hydrogeochemical characterization and quality evaluation of groundwater suitability for domestic and agricultural uses in the state of Qatar

This study aims to investigate the groundwater (GW) quality in Qatar to be utilized in domestic and agricultural uses. The integrated physiochemical analysis along with hydrochemical faces analysis, geochemical modeling, statistical and geostatistical analysis was conducted. The results showed that the GW samples mainly have the following cations Na+ > Ca2+ > Mg2+ >K+ abundantly, while Cl− > SO42− > HCO3− > NO3− were the main anions. The obtained analytical values of the GW samples were plotted on Piper, Schoeller, Ternary, Ludwig Langelier, Giggenbach Triangle, Durov, and stiff graphs. The hydrogeochemical facies and the obtained graphs confirmed that most of the analyzed GW samples fall into two types of water namely calcium-chloride-type (SO4–Cl and Ca–Mg) and sodium-chloride-type (SO4–Cl and Na–K). Three principal components were yielded from the principal component analysis (PCA), which are the first principal component (PC1), second principal component (PC2), and third principal component (PC3) with ≥1 Eigenvalues, and total variance of 49, 31, and 19.9%, respectively. A positive loading of Mg, Th, Sr, Ca, TDS, SO4, Li, Cl, F, Br, Cd, K, Ba, and Na has been shown by the PC1; representing the factors which are contributing to the high salinity of the GW due to the salt water intrusion and the mineralization of rocks and soil which is supported by the water type classification and saturation indices. The PC2 showed a negative loading of U, Al, Se, Mo, Mg, and temperature, which could be associated with a localized sedimentary depositional or hydrogeochemical environment. The PC3 showed a positive loading of Ni, Zn, Be, pH, Cu, Co, Fe, B, V, and TOC, which indicates the dissolution and precipitation (reducing and oxidizing factor) such as iron which is a redox-sensitive variable.

Reconstruction of the depositional sedimentary environment of Oligocene deposits (Qom Formation) in the Qom Basin (northern Tethyan seaway), Iran

Abstract During the Rupelian–Chattian, the Qom Basin (northern seaway basin) was located between the Paratethys in the north and the southern Tethyan seaway in the south. The Oligocene deposits (Qom Formation) in the Qom Basin have been interpreted for a reconstruction of environmental conditions during deposition, as well as of the influence of local fault activities and global sea level changes expressed within the basin. We have also investigated connections between the Qom Basin and adjacent basins. Seven microfacies types have been distinguished in the former. These microfacies formed within three major depositional environments, i.e., restricted lagoon, open lagoon and open marine. Strata of the Qom Formation are suggested to have been formed in an open-shelf system. In addition, the deepening and shallowing patterns noted within the microfacies suggest the presence of three third-order sequences in the Bijegan area and two third-order depositional sequences and an incomplete depositional sequence in the Naragh area. Our analysis suggests that, during the Rupelian and Chattian stages, the depositional sequences of the Qom Basin were influenced primarily by local tectonics, while global sea level changes had a greater impact on the southern Tethyan seaway and Paratethys basins. The depositional basins of the Tethyan seaway (southern Tethyan seaway, Paratethys Basin and Qom Basin) were probably related during the Burdigalian to Langhian and early Serravallian.

Sedimentary Facies and Depositional Environment of Long Sediment Cores from the Nakdong Incised-valley Fills, Southeastern Korea

Hong, S.-H.; Chun, S.S.; Kim, J.-C.; Lee, G.-S.; Yoon, H.-H., and Yoo, D.-G., 2020. Sedimentary facies and depositional environment of long sediment cores from the Nakdong incised valley fills, southeastern Korea. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 511–515. Coconut Creek (Florida), ISSN 0749-0208.Two deep-drilled cores were obtained from the Nakdong River delta in 2016. Based on the sediment structure, composition and texture, the deposits can be divided into four depositional units: I) fluvial sediments, II) estuarine sediments, III) coastal sediments, and IV) delta sediments. The lowermost Unit I is about 25 m thick and comprised clast-supported gravel and massive sand. The age dates of the upper part of Unit 1 is 49.7 ± 5.3 ka. Unit II consists of thin silt laminations that vary rhythmically in thickness, suggesting tidal influences in the estuarine environment. The age dates of this unit range from 10.9 ± 0.18 to 9.6 ± 0.11. Unit III is composed of cross-bedded sand, which contains peat materials and shell fragments and is interpreted to rapidly deposited sand bars in coastal environment. The age of Unit III had 9.7 ± 0.18 ka. Unit IV is composed of extremely bioturbated sandy mud and cross-laminated sand. The age dates of Unit IV ranges from 7.4 ± 0.5 to 0.8 ± 0.09 ka, the deposits belonging to the Holocene. These results indicate that depositional units in the study area consists of fluvial deposits of forced regression formed during the MIS 3, estuarine to tidal flat deposits during deglacial transgression, prograding delta deposits during postglacial periods.

Vertical distribution of radionuclides in Lake Qinghai, Qinghai-Tibet Plateau, and its environmental implications

Radionuclides are widely used to perform geochronologic investigations of the trace sediment deposition process in aquatic environments on different temporal scales. This study presents the activities of radionuclides to select a reasonable geochronologic dating method and study the sediment depositional environment in Lake Qinghai on the Qinghai-Tibet Plateau. The range of activities (Bq.kg−1) of 137Cs, 226Ra, 238U, 228Ra, 228Th, and 40K were 2–103, 24–49, 33–156, 20–49, 30–50, and 403–664, respectively. The sedimentation flux was calculated as 1.66 × 106 ton.a−1 based on the summary sedimentation rate in Lake Qinghai, and the sediment contributions from rivers, authigenic carbonates, lacustrine organisms, and atmospheric deposition were 45.18%, 22.44%, 3.02%, and 29.36%, respectively. The decreased 226Ra/238U radioactivity ratios from the catchment to the lake centre indicated that the removal of uranium relative to its daughter products occurs during erosion processes. The positive 228Thex (excess 228Th) values in the upper 1 cm of the sediment suggested that the sediment in the top 1 cm have been resuspended, mixed and/or transported. The distribution of 137Cs in the sediments indicated that the maximum activity of 137Cs in the sediments corresponds to the 1963 peak in the global fallout from atmospheric nuclear weapons testing; moreover, the 1986 Chernobyl accident signal was difficult to identify. The use of 137Cs as a chronologic tool must be performed carefully due to its migration process in sediments.

Evolution from estuary to delta: Alluvial plain morphology and sedimentary characteristics of the Shoalhaven River mouth, southeastern Australia

The Shoalhaven River in southern New South Wales (NSW) drains a catchment of ~7000 km2, forming a barrier estuary at its mouth with a prograded strandplain to its north. Previous coring and dating across the floodplain and adjacent strandplain indicate progressive infill of the estuarine basin over the past 7000 years. Over this time the system transitioned from a wave-dominated estuary to a wave-dominated delta. The Shoalhaven River appears to have initially discharged to the sea at Crookhaven Heads, until it adopted a more direct route through an intermittently open mouth at Shoalhaven Heads; construction of Berrys Canal in 1822 now permanently links the Shoalhaven River to the adjacent smaller Crookhaven River. Airborne LiDAR reveals details of topography of prominent levees and meander scroll bars that flank the lower reaches of the river and beach/foredune ridges to the north. Sedimentological and mineralogical characteristics of modern sediment samples collected from the river channel, the beach, and the barrier reveal that the Shoalhaven River is dominated by quartz sand along its predominantly straight course through the infilled estuarine plains. This is in contrast to the tripartite classification of sedimentary depositional environments, comprising sandy fluvial delta, central mud basin, and sandy marine barrier, that characterised the initial wave-dominated estuary 7000 years ago, and is typical of most barrier estuaries in NSW. Grain size decreases downstream and sands have a higher feldspar content, and angularity, than is typical of marine sand that has been reworked in the nearshore. This fluvially-derived component is delivered to the coast intermittently by floods that re-open Shoalhaven Heads, as shown by retrospective analysis of aerial photography and satellite imagery. Grain size decreases with distance alongshore from the river mouth indicating that these sands are transported north by longshore drift to augment a gradual onshore delivery of sand within this coastal compartment. Scanning electron microscopy of selected grains implies that this fluvial sand has been contributing to incremental formation of beach ridges for much of the past 3000 years since the estuarine basin has been largely infilled, with a slight detectable acceleration in the rate of progradation.

REDE GEODÉSICA PARA MONITORAMENTO DE PROCESSOS DE SUBSIDÊNCIA NA PLANÍCIE DELTAICA DO RIO SÃO FRANCISCO

Processos de subsidência são caracterizados pelo movimento de uma porção da superfície da Terra na qual resulta no rebaixamento do terreno. Os ambientes sedimentares deposicionais, como é o caso dos deltas, são propensos à subsidência devido à compactação de sedimentos. O objetivo principal deste trabalho é o desenvolvimento de um projeto geométrico e implantação de uma rede geodésica para o acompanhamento periódico da subsidência na planície deltaica do Rio São Francisco. Cordões litorâneos holocênicos presentes na planície tiveram suas altitudes avaliadas a partir de perfis topográficos longitudinais obtidos por levantamentos GNSS (Global Navigation Satellite System). Em alguns cordões, desníveis médios na ordem de 3,2 m e 5,5 m foram detectados na porções sul e norte da planície, respectivamente, sendo um indicativo de rebaixamento da superfície devido a acentuados processos de subsidência que ocorreram desde o holoceno. As informações de rebaixamento dos cordões permitiram identificar áreas vulneráveis aos processos de subsidência, dando suporte ao projeto de uma rede geodésica composta por 26 vértices de monitoramento.

Facies Architecture Analysis for Paleo-environment Evaluation in “Tom” Oil Field, Eastern Niger Delta, Nigeria

The cored section of reservoir C, well 4 of the drilled five wells that penetrated three reservoirs A, B and C in “TOM” oil field, Eastern Niger Delta was analysed and described on the basis of lithofacies, sedimentary structures and trace fossil records by using core data and wireline log motifs, with the aim of carrying out thorough geological core analysis to interpret the depositional environment of the oil field. The lithofacies are sandstones with interbedded mudstones and siltstones, the dominant sedimentary structures are parallel to ripple cross laminations, hummocky and swaley cross stratifications, sandy hetherolitics, planar to low angle cross bedding with traces of Teichichnus and Ophiomorpha burrows. The gamma-ray log motifs were noted and used to further constrain the character of the sedimentary facies and depositional environment of the field. A tidal incised – fluvial dominated shallow marine (lower, middle, upper shoreface) comprises of tidal channel sands and tidal flat of the coastal shelf depositional setting in the marginal marine mega depositional environment had been inferred for the “TOM” field.
 Keywords: Shoreface, Reservoir, Lithofacies, Structures

Palaeoenvironments of northwestern Bulgaria and northeastern Serbia during the Jurassic

Jurassic rocks in the Danube Region of northwestern Bulgaria and northeastern Serbia have been the subject of numerous earlier studies that have shown notable similarities between their sedimentary facies and depositional environments. In terms of regional palaeotectonic zonation, this area represents the westernmost parts of the Vidin Early–Middle Jurassic Complex Horst and the Mihaylovgrad Early–Middle Jurassic Graben in NW Bulgaria, as well as the easternmost part of the Lower Danubicum in NE Serbia, which collectively take part of the Jurassic Moesian Platform. For compiling an overall conception of the palaeoenvironments that existed during the Jurassic, nine palaeoenvironmental sketch maps, from the Aalenian to the late Tithonian, have been composed in this study, based on reinterpretation of the data borrowed from previous literature. It became evident that the Middle Jurassic sedimentary successions of the Danube Region record an evolution from an initially isolated lacustrine-palustrine depositional setting (Aalenian) to rapidly expanding shallow to moderately deeper-marine sandy-calcareous setting (late Bajocian–early Callovian). From the middle Callovian and onwards, during the Late Jurassic, the region became an area of laterally extensive pelagic and platform carbonate deposition. This interpretation is consistent with the available earlier data, but it links the facies and their respective settings from NW Bulgaria to NE Serbia, which has not been made to date and will be of benefit for future regional correlations.

Sedimentary facies and depositional environments of the Oligocene–early Miocene marine Qom Formation, Central Iran Back-Arc Basin, Iran (northeastern margin of the Tethyan Seaway)

The Qom Formation was deposited at the northeastern margin of the Tethyan Seaway. To analyze the sedimentary facies and depositional environments, the marine Qom Formation deposits in the Qom-Natanz region (Central Iran Back-Arc Basin) were studied. The Qom Formation is the main reservoir and source rock of hydrocarbons in central Iran. Studying the Qom Formation in Khurabad (SE Qom) and Natanz sections revealed that the study sections are dominated mainly by larger benthic foraminifera, coralline red algae, and corals. The Qom Formation is “Rupelian–Burdigalian” and “Rupelian?–Aquitanian” in age in the Khurabad and Natanz sections, respectively. Based on component distributions, texture, and field investigations, 14 different facies were identified and interpreted. A homoclinal ramp is the suggested model for the deposition of the Qom Formation in the study sections. Accordingly, open marine (middle ramp), lagoon (inner ramp), and peritidal flat/beach as major depositional environments were identified. The middle ramp was characterized by the association of perforate foraminifera, coralline red algae, bryozoans, echinoids, as well as planktonic foraminifera. The distal part of the inner ramp was characterized mainly by the co-occurrence of perforate and imperforate foraminifera. Coral patch reefs were also present, but there is no reef complex with sigmoidal geometries. The proximal part of the inner ramp was characterized mainly by imperforate foraminifera with low diversity. The terrigenous facies were more probably deposited in the high-stressed shoreface to the shallow inner ramp. However, the evaporative facies were deposited in a saltern environment. The abundant presence of larger benthic foraminifera (perforate and imperforate) and coralline red algae, as well as the presence of z-corals, emphasize a tropical–subtropical palaeoenvironment.

Illite distribution and morphology explaining basinal variations in reservoir properties of Upper Jurassic sandstones, Danish North Sea

Abstract Growth of fibrous illite may destroy an otherwise promising sandstone reservoir, even sandstones characterized by microquartz coatings. Therefore detailed petrographical and diagenetic investigations were performed in order to understand the factors that control illite precipitation and other factors affecting the reservoir properties in the Upper Jurassic Heno Formation. The Heno Formation is encountered in large parts of the Danish Central Graben, where its lower part – the Gert Member – was mainly deposited in back-barrier environments and its upper part – the Ravn Member – was deposited in a shoreface environment. In total, 215 core samples from 15 wells were investigated petrographically by optical and scanning electron microscopy. This was supplemented by plug porosity and permeability measurements and X-ray diffraction of bulk and clay fraction. The investigations show, among other things, that microquartz coatings may help to preserve porosity and permeability, whereas the permeability is reduced when microquartz occurs combined with fibrous illite. Illite precipitation is largely governed by the amounts of K-feldspar present during burial. Consequently, the initial abundance of K-feldspar (in the sediment source area) and its alteration during and immediately after deposition, in particular during subaerial exposure (at sequence boundaries), has a major influence on the final reservoir properties of the sandstones. The risk of illite precipitation can largely be predicted from the available sediment source material, depositional environment and burial depth.

Discussion of the paper by Imad M. Ghafor and Ibrahim M.J. Mohialdeen, 2018, entitled “Early cretaceous microfossils associations (foraminifera, ostracoda, calcareous algae, and coral) from the Garagu formation, Duhok area, Kurdistan region, northern Iraq” (Arabian Journal of Geosciences, 11:407)

A recent “micropaleontological” publication on a Lower Cretaceous classical lithostratigraphic unit at its type locality in N Iraq, the Garagu Formation, suggested that, at this exact location, this facies-driven unit could span a “late Valanginian-Barremian” time interval and that its facies were indicative of “shallow marine with normal to hypersaline conditions, shelf lagoonal environment, and open platform” environment. Of the twenty samples originally collected by the authors, eleven thin sections were reexamined. On the basis of this limited material, a second assessment is presented here. Most micropaleontological identifications prove wrong, and they cannot “support an age determination of the late Valanginian-Barremian”. Similarly, contrary to the authors’ opinion and except for one sample, all microfacies suggest that the sedimentary depositional environments were representative of a lower shoreface to an offshore shelf setting depending on relative sea level changes. More than half a century after the publication of the “Lexique International de Stratigraphie”, the Garagu Formation, as do most lithostratigraphic units defined in the Middle East, requires a full reassessment with the support of genuine experts.

DETERMINING TEXTURAL AND GEOCHEMICAL ELEMENT CHARACTERISTICS OF SEAFLOOR SEDIMENT USING MULTIVARIATE ANALYSIS ALONG THE SIMEULUE SUB-BASIN, INDONESIA

The Simeulue sub-basin is situated off north-western Sumatra between the outer arc and the mainlands. The sediment and geochemical element characteristics of basins are the important sedimentology variables to recognize the process of sediment deposition. However, the characteristics of the sediment and the geochemical elements in the Simeulue subbasin have not been well explained. This study aims to investigate the textural and geochemical elements characteristics of marine sediments and the distribution of these two variables to determine the sedimentary facies in the Simeulue sub-basin. Samples were taken from various depths in the sub-basin and collected during the 2017 Expedition of “Widya Nusantara” by using the “Baruna Jaya VIII” Research Vessel. The grain size trend analysis showed that the middle part of the basin was dominated by mud, while the edge of the basin near the island (mainland) was mostly dominated by coarser sediments. A geochemical element analysis was performed on each sample to observe the origin of the sediments. The results of these two analyses were subjected to multivariate statistics. This approach was selected because it is appropriate for determining the sedimentary facies and the depositional environments. Based on the multivariate analysis, the sedimentary facies in the Simeulue sub-basin was divided into five facies with similar sediment characteristics and depositional environments. These facies were deposited in the environment with low to medium energy.

Investigation of factors influencing geological heterogeneity in tight gas carbonates, Permian reservoir of the Persian Gulf

Understanding the spatial distribution of petrophysical properties in carbonate reservoirs is complicated due to their heterogeneity and sensitivity to diagenesis along with important facies variations. The reservoir evaluation in tight carbonates is even more complicated. The Permian Dalan Formation in the central part of Persian Gulf is generally considered as conventional carbonate reservoir. However, in this study, a part of K3 unit of this formation is introduced as a tight carbonate reservoir. To identify the factors influencing the quality of this unit, the sedimentary facies, depositional environments, diagenetic processes, and pore-type distribution were studied in details on 402 thin sections. Porosity and permeability of K3 are mainly controlled by dolomitization, dissolution, compaction, and cementation. MICP-based (mercury injection capillary pressure) methods, FZI*(FZI-star), and rock fabric numbers were considered to recognize the factors controlling heterogeneity of this unit. The MICP-based methods of Winland, Pittman, and Rezaee were combined with 3 porosity cutoffs to detect the heterogeneities of tight carbonates. None of these methods provided a high degree of correlation between porosity and permeability of the samples. The results of rock fabric number showed that samples with similar reservoir quality are the product of different diagenetic processes. Results obtained in this study demonstrate that the FZI*(FZI-star) and rock fabric number classifications are the most suitable methods for differentiating the tight zone and non-reservoir/reservoir parts in carbonates of K3 unit.

Extension Related Magmatism and Basin Evolution in Northwestern Part of the Cuddapah Rift, India

Spatial distribution and field relationship of igneous intrusives viz. basic dykes, pink granite-leucogranite-tourmaline pegmatites and quartz reefs across interface between the Neoarchean Gadwal schist belt (Basement) and the Proterozoic Cuddapah basin have been documented. The Cuddapah basin is a half graben (rift) developed at right angle to the basement and displays two sets of faults: (1) NE-SW longitudinal and (2) NW-SE transverse. The longitudinal faults oriented parallel to basin margin have controlled sedimentation, subsidence and uplift. The transverse faults extending from rift shoulder (basement) right into central part of the basin are post depositional faults and imparted en-echelon pattern to the basement-basin interface. Sedimentary facies, depositional environments and basin setting indicate that the basin fill was deposited in a rift setting over the northwestern part of the epeiric sea embayment that flooded on to the Dharwar batholith of the Eastern Dharwar craton. Basin evolution stages have been outlined. Basin uplift/inversion is controlled by reverse faults and is viewed as a cause and effect to the post Cuddapah extension related magmatism which is attributed to magma underplating in the environs of the northwestern part of the Cuddapah rift at crustal levels.

Grain-size characteristics and net transport patterns of surficial sediments in the Zhejiang nearshore area, East China Sea

Summary Spatial variations in grain-size parameters can reflect sediment transport patterns and depositional dynamic environments. Therefore, 616 surficial sediment samples taken from the Zhejiang nearshore area in the East China Sea were analyzed to better understand the net sediment transport pattern in this region. The study area is generally dominated by clayey silt and has relatively coarse mud sediment in the southeast. The sorting coefficient of surface sediment is higher than 1.4, and sediment is poorly sorted throughout the study area. The skewness has a strong correlation with the mean grain-size diameter. The net sediment transport pathways obtained by the grain-size trend analysis indicate several distinct characteristics of the surficial sediment transport. The sediment is transported southward under the action of the stronger southward Zhejiang–Fujian Coastal Current (ZMCC) in winter in the upper part of the nearshore area. Influenced by the obstruction of the Taiwan Warm Current (TWC) and the tidal current, surficial sediment transport vectors display two areas of grain-size trend convergence and indicate the net deposition environment has a high sedimentation rate. However, the transport is mainly toward the north under the control of the prevailing northward ZMCC and the strong TWC in the summer. The sedimentary rate is closely related to the processes of the sediment transport. On the one hand, sediment transportation affects the depositional rate in a different environment. On the other hand, the modern sedimentary rate can reflect indirectly the sediment source and sediment transportation.

Sources of Sediment Clasts and Depositional Environment of the Upper Paleozoic Shazagaitui and Zhipkhoshi Formations of the Chiron Basin, Eastern Transbaikalia

The article presents the results of comprehensive geological and geochemical study of the sedimentary rocks of the Upper Paleozoic Shazagaitui and Zhipkhoshi formations filling the upper part of the Chiron Basin, as well as U–Pb geochronological and Lu–Hf isotopic studies of zircons from these formations. The geochemical features of the terrigenous rocks of the Shazagaitui and Zhipkhoshi formations indicate that they were formed in a subduction zone environment. The presence of conglomerates and gravelstones and the predominance of unrounded and subrounded fragments in the rocks of the Shazagaitui and Zhipkhoshi formations also indicate their sedimentation in tectonically active zones. The abundant detrital zircons of Paleoproterozoic age, as well as the Paleoproterozoic and Archean Hf model ages of most of the zircons in the sandstones of the Shazagaitui and Zhipkhoshi formations, suggest that the main source of sediment clasts for these formations are the magmatic and metamorphic rocks of the southern surrounding of the North Asian Craton. However, the presence of Devonian–Carboniferous zircons with relatively young (mostly Neoproterozoic) Hf model ages is evidence that these zircons in the sedimentation basin were derived through erosion of mature (?) island arcs, but the contribution of this source is minor. The obtained results in combination with our regional geological data from previous studies suggest that the sediments of the Shazagaitui and Zhipkhoshi formations were accumulated in a basin setting on the southern framing of the North Asian Craton facing the Paleozoic Ocean.

캐나다 앨버타주 몬트니층의 퇴적상과 퇴적환경: 가스함유 셰일층의 파쇄효율 향상을 위한 퇴적학적 특성화

캐나다 앨버타주에 분포하는 몬트니층은 중생대 트라이아스기 초기에 형성된 가스함유 셰일층으로서, 이 연구에서는 셰일가스층 개발 시 파쇄특성을 결정하는 근원암저류층의 퇴적학적 다양성을 이해하기 위하여 Kakwa 시추공 코어(총연장 약 200 m)에서 퇴적상 분석을 통해 퇴적작용과 형성환경을 해석하였다. 연구지역의 몬트니층은 전 구간에 걸쳐 60% 내외의 석영과 장석을 함유하는 실트암과 실트질 이암으로 이루어져 있으며, 암석코어의 조직과 퇴적구조에 따라 균질상(HM), 평행엽층리상(PL), 사엽층리상(XL), 희미한 엽층리상(IL), 생교란상(BT), 변형상(DF) 등 6개의 퇴적상이 구분된다. 몬트니층의 전반적인 퇴적상의 구성은 상부와 하부 구간에서 대조적으로 나타나는데, 하부 몬트니층에서는 점토광물과 유기물의 함량이 상부 몬트니층에 비해 다소 높게 나타나며, 안정적이고 지속적인 저에너지 환경을 지시하는 퇴적상이 우세하다. 반면에 상부 몬트니층의 퇴적상은 고에너지 수층운동(파도, 폭풍)에 의한 퇴적, 침식, 변형 구조, 그리고 퇴적 후의 생물교란에 의한 구조 등을 특징으로 하고 있다. 따라서 몬트니층이 형성되는 동안, 퇴적환경은 상대적 해수면의 하강으로 인해 폭풍파 기저면 하부의 외해 혹은 심해에서 파도와 폭풍의 영향이 우세한 폭풍파 기저면 상부의 대륙붕 연안 환경으로 점차 변화된 것으로 해석된다.

Biostratigraphy and Depositional Environment of Cenozoic Sediments in Deep Water Block, Krishna-Godavari Basin

Biostratigraphy and Depositional Environment of Cenozoic Sediments in Deep Water Block, Krishna-Godavari Basin