Paleocurrent Analysis on the Basal Conglomerate of the Model Changzhougou Formation in Qian＇an
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The paleoflow direction of the basal conglomerate of the Changzhougou formation is obtained by the paleocurrent analysis of certain sedimentary structures, and the ancient sedimentary environment of the Qian’an Region is determined by observing the psephicity and gradation of gravel in conglomerate. The results show that the paleoflow direction is from northwest to southwest, and the paleocurrent data manifest a single-peak style in a rose diagram. The average paleoflow direction in the Qian’an region is 265°. The basal conglomerate is of littoral facies, and the sediments of conglomerates are mainly sourced from Shanhaiguan.Keywords:
Paleocurrent
Conglomerate
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به منظور شناخت محیط رسوبی و بررسی تغییرات سطح آب، سازند لالون به سن کامبرین پیشین در برش باهمو به ستبرای 550 متر واقع در بلوک پشت بادام، مورد مطالعه قرار گرفت. مطالعات صحرایی، برداشت 110 دادة جریان دیرینه و بررسی سنگ‌شناسی، بررسی توسط میکروسکوپ الکترونی و تجزیه پراش اشعه ایکس نمونه‌های شیلی، منجر به تحلیل رخساره‌ای، تعیین جهت جریان دیرینه و تفسیر محیط رسوبی دیرینه در این سازند شد. تحلیل رخساره‌های سنگی حاکی از وجود 5 رخسارة سنگی سیلیسی آواری دانه درشت (Gm)، دانه متوسط (Sp, St, Sh) و دانه ریز (Fl) و یک رخسارة کربناتی (دولومیتی) در این نهشته‌ها می‌باشد. رخساره‌های به دست آمده به همراه الگوی بایمدال دو قطبی و شواهد سنگ‌شناسی مانند وجود ماسه‌سنگ‌های گلوکونیت‌دار با بلوغ بافتی و ترکیبی بالا، نشان دهندة رسوبگذاری این نهشته‌ها در محیط پهنه کشندی است. بررسی تغییرات نسبی سطح آب دریا در برش مورد مطالعه، حاکی از وجود دو توالی متمایز می‌باشد که با ناپیوستگی نوع اول (SB1) محصور شده‌اند.
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Conglomerates, the lithified equivalent of gravels alternate with sandstones and mudstones in the upper parts of the Aghajari Formation in the Zagros Basin, southwestern Iran. The thickness of the Aghajari Formation in this studied area is 2221 meters. Polymictic conglomerates form excellent outcrops in the central parts of the study area. From the view of its (coarse) clast composition, the Aghajari Formation consists of two types of conglomerates: 1) limestone-chert clast-supported conglomerate (LCCSC) and 2) limestone clast-supported conglomerate (LCSC). The chronological and spatial relationships between these conglomerates are not easily determined caused by existence some thrust faults at their approximate boundaries. In the vertical succession, various lithofacies were recognized; their textural characteristics and sedimentary structures suggest a non-marine depositional system as they match with standard lithofacies of meandering rivers. Epirogenic movements in the region started in the Oligocene, showed by a polymictic conglomerate beds at the Jahrum-Asmari Formation boundary. These movements then changed to orogenic ones with the depositioning gravelly alluvium now known as Aghajari (upper parts) Formation.
Conglomerate
Outcrop
Palaeogeography
Lithification
Alluvial fan
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The sedimentary succession ranging in age from Permian to Early Triassic in Ruhuhu basin was subdivided into eight informal lithostratigraphic units, identified by the symbols from K1 to K8. Manda Formation (K8) belongs to Early Triassic age and comprises two Members, i.e., Lower Kingori Member and Upper Lifua Member (150-200 m thickness). The implications of present study relate to inter and intra basinal correlations which may provide regional depositional framework from a mass of local details. Present investigation connoting the lithofacies studies in conjunction with palaeocurrent and grain size analysis of the early Triassic strata aims at interpreting the depositional environment of Lifua Member. Based on the present study, five lithofacies have been identified, namely (i) Massive matrix supported paraconglomerate (Gmm), (ii) Massive sandstone (Sm), (iii) Parallel-horizontal laminated sandstone (Sh), (iv) Planar cross-bedded sandstone (Sp) and (v) Fine silt, mud and clay (Fl). Sandstone facies (Sm, Sh, and Sp) exhibit normal grading and unimodal palaeocurrent direction. Grain size analysis indicated that the sandstones were moderately sorted, finely skewed, mesokurtic and most of the grains were silty-sand. Bivariate scatter plots suggest that the Lifua Member sandstone is of riverine environment. Lithofacies, palaeocurrent and grain size studies suggest fluvial environment dominated by sand channel deposits.
Keywords: Lifua Member; Early Triassic; Lithofacies, Paleocurrent; Channel deposits; Ruhuhu basin
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Siltstone
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Paleocurrent
Conglomerate
Siliciclastic
Alluvial fan
Pebble
Lithology
Outcrop
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Grainstone
Bedding
Conglomerate
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The determination of the provenance of sedimentary material is an important step in determining the paleogeography of sedimentary basin;this article presents new data for Late Triassic sedimentation associated with the Yanchang formation in the giant inland Ordos basin catchment.Analysis of paleocurrent directions,composite characteristics,and the spatial distribution of heavy and light minerals within the Chang 101 and Chang 9 depositional stages of the Yanchang formation indicates that sediments within the basin have four distinct provenances,being derived from the northeast,east,south and northwest.Of these 4 provenance directions,the majority of sediment was derived from the northeast and northwest,with sediments derived from the east and south only present in localised areas of the basin.In terms of temporal changes between the Chang 101 and Chang 9 depositional stages,an increase in material with an eastern provenance is coincident with a decrease in material derived from the west,in addition to a change in provenance direction from southwest to more directly south.
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Sedimentation
Palaeogeography
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Conglomerate
Debris flow
Paleogene
Lithology
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Shuanghu Tuonamu region is situated between the Central Uplift Zone and the Northern Qiangtang depression, where the Late Jurassic Xueshan Formation develops extensively with a thickness amounting to 1500m.This paper aims to analyze the stratigraphic and petrological characteristics, the palaeocurrent, and the clastic compositions of Xueshan Formation. The vertical structure of Xueshan Formation is comprised of three sedimentary assemblages. As both delta and alluvial fan sedimentary facies are developed in Xueshan Formation, we can see that the prodelta subfacies is developed in the first member, the delta front and delta plain subfacies are developed in the second member, and the alluvial fan facies is developed within the third member. The results concerning the paleocurrent's complex plane direction style suggests that the provenance of Xueshan Formation comes from the southwest side, and that the lithologic characteristics of the source rocks for Xueshan Formation vary greatly. A quantitative analysis of the clastic compositions of sandstone by using the Dikinson triplot displays that the tectonic background for Xueshan Formation is derived from a parent source controlled by recycled orogen and characterized by recycled quartz, which helps explain that the provenance of Xueshan Formation comes from the southwest of the Central Uplifting Zone.
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Alluvial fan
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Typical Prc- Cretaceous flysch type sediments, called Yubetsu Group, are exposed on northea stern part of Hidaka Belt. The authors have done a three dimensional analysis of internal sedimentary structures utilizing the soft X-ray technique for paleocurrent study of group. From data obtained in this study prevailing current dire ct ion in turbidite of study area is a lateral cu rrent from east to west with minor occurrence of axial current along north-south direction_ Therefore, th e provenance o f middle to upper Yubetsu Group of present study is located to east. To full understanding of geologic development of a geosyncline it is essential to explain paleogeography and nature of hinterland. The direction from which geosynclinal sediments have been transported and mechanism of deposition fo: such materials as well as their nature of provenance must be solve d. In Hid aka Belt, Hokkaido, an enormous volume of Pre·Cretaceous geosynclinal sandstones and shales (Hidaka Supergroup of Hasegawa el aI. , 196 I) occur. Although knowledge of these rocks has been advanced recently through I :50 ,000 geologic mapping of area sin ce 1960s, no reports have yet been available for paleocurrent directions. Also only scanty data are available for compositions of sandstones. To fill this gap of knowledge, we have done a sedimentological study of fl ysch type sediments of Yubetsu Group exposed on northeastern margin of Hidaka Belt (Fig. I). As fly sc h type sediments are well developed with comparatively uncompli cated structure in Yubetsu Group as compared with rocks of Hid aka Supergroup distributed elswhere, study area gave us an unique opportunity for an analysis of paleocurrent directions. For paleocurrent analysis two major lin es of study have been commonly employed; i.e. , study of sole markings which are one of external sedimentary structures, and study of cross lamination and grain orie ntatio n, both of which are one of internal sedimentary structures. Since fly sc h type sediments of Yubetsu Group were normally brittle due to well developed joints, it was difficult 10 observe wide enough bedding plains for external sedimentary structures in field. Also bedding plain shea r has obscured sole markings in most cases. Therefore, we had to emp loy a three dimensional analysis of internal sedimentary structures utilizing soft X-ray technique for our paleocurrent study. The potential of X-ray technique for this sort of study has been established through works of Hamblin( 1962, 1965), Bouma(1969), Picha and Clin e( 1973) and Kiminami(I975a,
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Geosyncline
Flysch
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