Early Cretaceous Tectonism and Diatoms in Korea

The Early Cretaceous Sindong Group, a non-marine molasse, unconformably overlies the folded earliest Cretaceous Myogok Formation. The tectonism that folded the Jaseong Synthem including the Myogok and other formations is here called the Nakdong-Jaeryeonggang （N-J） tectonism. The Oknyeobong and Dabokni Formations are discussed to show that they belong to the Jaseong Synthem. The Dabokni Formation yielded fossil diatoms whose age has been referred as the ＂earliest Cretaceous＂ based on the geologically constrained age of the fossil-bearing deposit. The age of the N-J tectonism appears Barremian as it is between the Hauterivian Myogok Formation and the Aptian Sindong Group with the TPN （Trigonioides-Plicatounio-Nippononaia） fauna. The N-J tectonism, an orogeny, quite deformed pre-Aptian strata in Korea, but can hardly find its reported equivalent in NE China. A revised correlation table shows that the Jaseong- Sindong sequence corresponds to the Jehol Group of China. The Sindong-Hayang transition was characterized by basin migration and dextral rotation probably caused by the Tan-Lu fault system in a broad sense.

Improvement of reservoir quality of ultra-deep tight sandstones by tectonism and fluid:A case study of Keshen gas field in Tarim Basin,western China

The Keshen gas field is one of the most important natural gas supply sources in the Tarim basin,western China.The main gas producing interval there is the Lower Cretaceous Bashijiqike Formation(K1bs),it is an ultra-deep tight reservoir whose buried depth exceeds 6000 m,and it shows a low matrix porosity(<10%)and extremely low matrix permeability(<0.1mD).However,this reservoir can supply extremely high and stable gas production due to improvement of reservoir quality by tectonism and fluid.Based on tectonic evolution analysis by plenty of lab data of core plugs or thin sections,the enhancement models of tectonism and fluid are built,evidence suggests both tectonism and fluid improve the reservoir quality greatly.Tectonic evolution produces lots of natural fractures in 3stages which promote the ultra-deep tight reservoir permeability 10–200 times,then,testing results of new boreholes without fracturing show reservoir permeability underground can reach 20 mD.Furthermore,fluid dissolution increases reservoir porosity 1–2 times,the main dissolved mineral is feldspar,all fluid dissolution came from the unconformity controlling the dissolution distance.Tectonism and fluid interact on each other:Tectonism controls fracture distribution and types of diagenic fluid in reservoir,but fluids influence fracture cements and dissolution.Both tectonic folding and the fluid flow control the sweet point reservoir located in upper 150 m formation.

Petrological and geochemical characteristics of the Ordovician-Silurian black shale in eastern Sichuan and western Hubei,South China:Differential sedimentary responses to tectonism and glaciation

During the Ordovician-Silurian transition period,the Yangtze area experienced significant environmental changes,which were recorded by the widely distributed black shale of the Upper Ordovician Wufeng and Lower Silurian Longmaxi formations.However,the petrological and geochemical analyses of the Upper Ordovician-Lower Silurian black shale in Well JY1(eastern Sichuan Basin)and Well YY2(western Hubei Province)drill cores show that there are some significant differences with respect to lithology,thickness,and geochemical characteristics despite the long-term similar variation trend in petrology and geochemistry.This may suggest some major environmental changes and their differential influence on black shale deposition in the Yangtze area.Based on the analyses of lithology,total organic carbon(TOC),Mo_(EF),and U_(EF),four long-term sedimentary cycles(one for the Wufeng Formation and three for the Longmaxi Formation)were identified in Well JY1.In Well YY2,only three long-term sedimentary cycles can be recognized(one for the Wufeng Formation and two for the Longmaxi Formation).Different from the gradual increase of the geochemical proxies(such as TOC,MoEF,and NiEF)followed by an abrupt decrease in the Wufeng Formation,these proxies of the Silurian sedimentary cycles in both wells exhibit an abrupt increase at the base followed by a gradual decrease,showing that controlling mechanisms for the Lower Silurian black shale deposition in the study areas were different from those of the Upper Ordovician black shale.However,the black shale of each Silurian cycle in Well JY1 is much thicker than that in Well YY2.Compared with the thick silty mudstone developed in Well JY1 during the Rhuddanian-Aeronian transition,there is a stratigraphic gap in Well YY2 except for a thin calcareous dolostone formed in a strongly restricted environment.These differences indicate that tectonism and glacial eustasy should be the key factors for black shale development,but their influences on the deposition of the Lower Silurian black shale varied between eastern Sichuan Basin and western Hubei province.Since the early Rhuddanian stage,continuous tectonic subsidence in eastern Sichuan Basin promoted the development of thick black shale,while a persistent tectonic uplift in western Hubei Province led to the formation of thin black shale.Meanwhile,the study areas experienced a significant sealevel drop related to intensified glaciation during the Rhuddanian-Aeronian transition,which is recorded by the low chemical index of alteration(CIA)values in both wells.This resulted in the formation of a stratigraphic gap in western Hubei Province and the deposition of thick silty mudstone in eastern Sichuan Basin.Moreover,abrupt increases in CIA,TOC,Mo_(EF),and Ni_(EF) observed in the lower part of the Aeronian black shale in the two wells suggest that eastern Sichuan Basin and western Hubei Province experienced a significant sealevel rise during the early Aeronian stage,which may be related to a global warming event.Subsequently,eastern Sichuan Basin and western Hubei Province both suffered a significant tectonic uplift related to the Kwangsian Movement leading to the termination of the Aeronian black shale formation.However,the thickness variations of the Aeronian black shale in the two study areas indicate that remarkable geomorphological differences persisted in these two areas until the middle Aeronian stage.Thus,this study not only reveals differences of the Upper Ordovician-Lower Silurian black shale in eastern Sichuan Basin and western Hubei Province,but also interprets the causes of these differences,which provide new data and perspectives for the understanding of global paleoclimate and sea-level changes during the Ordovician-Silurian transition.

Quantifying the influence of magmatism and tectonism on ultraslow-spreading-ridge hydrothermal activity:Evidence from the Southwest Indian Ridge

Hydrothermal activity in mid-ocean ridges(MORs)is an important intermediary for the mass and heat exchange between the ocean and lithosphere.The development of hydrothermal activity on MORs is primarily controlled by coupled magmatic and tectonic activities.In ultraslow-spreading ridges,deepdipping low-angle normal faults with large offsets,typically detachment faults in the inside corners of ridge offsets,favor the formation of tectonic-related hydrothermal activities,whereas volcanic-related hydrothermal fields are typically developed in neovolcanic zones in this category of the ridge system.However,whether tectonic or magmatic activity is dominant and to what extent they control the formation of hydrothermal activities on ultraslow-spreading ridges remain unclear.Segments in the west and east of the Gallieni transform fault(TF)located in the ultraslow-spreading Southwest Indian Ridge(SWIR),namely,western area(WA)and eastern area(EA),exhibit distinct magma-supply conditions that provide favorable conditions for examining the influence of magmatic and tectonic activities.We generated prediction models for these areas using the spatial analysis of the water depth,minor faults,large faults,ridge axis,nontransform discontinuity(NTD)inside corners,TF inside corners,Bouguer gravity anomaly,magnetic anomalies,and seismic activities.By employing the weights of evidence method,we reported that the formation of seafloor hydrothermal systems in SWIR was primarily correlated to the NTD inside corner,ridge axis,and minor fault(i.e.,contrast values(C)of 4.186,3.727,and 3.482 in WA and 4.278,3.769,and 3.135 in EA).Furthermore,EA was significantly affected by the TF inside corner(C=3.501),whereas WA was influenced by large faults(C=4.062).Our results demonstrated that tectonism was the primary controlling factor in the development of hydrothermal activities in the study area,and the contribution of magmatism was secondary,even in WA,which has a relatively robust magma supply.We delimited prominent prospecting areas at each side based on posterior probability.Our results provided insights into the formation mechanisms of hydrothermal activities and support prospecting in MORs.

Magmatic-tectonic response of the South China Craton to the Paleo-Pacific subduction during the Triassic:a new viewpoint based on Well NK-1

The Nansha Block(NB)is one of the blocks separated from the southern margin of the South China Craton(SCC)by the western Pacific subduction,which contains rich information of geodynamic and tectonic transformation.To reveal the essence of western Paleo-Pacific subduction during the Triassic period,Well NK-1 in this block was selected for petrographic study,and published research data from other cooperative teams were compared.A double-cycle pattern of basic to neutral magmatic volcanism was established,and 36 lithological rhythmic layers and representative cryptoexplosive breccia facies and welded tuff bands were identified.Combined with a reanalysis of published geochronological data,geochemical elements,and isotope geochemistry,we found that the rock assemblages could be divided into an intermediate-acid dacite(DA)series(SiO_(2)>65%)and basaltic(BA)series(Co<40μg/g),which was formed during the early Late Triassic((218.6±3.2)–(217.9±3.5)Ma).BA exhibits obvious calc-alkaline island-arc magmatic properties:(^(87)Sr/^(86)Sr)_i ratio ranging 0.70377–0.71118(average:0.70645),^(147)Sm/^(144)Nd ratio ranging 0.119–0.193(average:0.168),and chondrite-normalized rare earth element(REE)curves being flat,while DA exhibits remarkable characteristics of subducted island-arc andesitic magma:(^(87)Sr/^(86)Sr)_i ratio(0.70939–0.71129;average:0.71035),εNd(t)value(-6.2–-4.8;average:-5.6)andε_(Hf)(t)value(-2.9–-1.7,average:-2.2)show obvious crust-mantle mixing characteristics.BA and DA reveal typical characteristics of island-arc magma systems and typeⅡenriched mantle(EM-Ⅱ)magma.BA magma was likely resulted from the process whereby the continental crust frontal accretionary wedge was driven by the Paleo-Pacific slab subduction into the deep and began to melt,resulting in a large amount of melt(fluid)joined the asthenosphere on the side of the continental margin.In contrast,DA magma was likely resulted from the process whereby the plate front was forced to bend with increasing subduction distance,which triggered the upwelling of the asthenosphere near the continent and subsequently led to the partial melting of the lithospheric mantle and lower crust due to continuous underplating.The lithospheric thinning environment in the study area at the end of Triassic created suitable conditions for the separation between the NB and SCC,which provided an opportunity for the formation of the early intracontinental rift during the later expansion of the South China Sea(SCS).

Sedimentological evidence of climate-tectonic interaction in the upper Satluj catchment of NW Himalaya

Quaternary valley fill deposits in the Upper Satluj Valley of NW Himalaya act as archives of changing climate-tectonic dynamics in a region.Quaternary landforms help in decoding the relationship between climate and tectonics.Kinnaur region is traversed by several active faults and thrusts such as the Kaurik-Chango Fault(KCF)and Sangla Detachment(SD),thereby making upper Satluj Valley tectonically active.Morphotectonic parameters such as width of valley floor(Vfw),Normalized Steepness Index(KSn)and geomorphological evidences such as the presence of huge strath terraces,narrowing of the river valley and palaeolake deposits point towards the tectonically active nature of the terrain.This arid,high elevation region is also climatically sensitive as it falls in a transient climatic zone which receives rainfall only during abnormal monsoon months.Excessive rainfall causes outburst floods,a common phenomenon in the area due to the blocking of headwater in the upper reaches of the Satluj valley.As a result,the Quaternary sequence is modified from time to time.The transition from hypo concentrated deposits to channel deposits and ponding events are prominent in the depositional sequence,resulting from a response to climate.The studied Quaternary sediments reveal that the Trans-Himalayan region of the upper Satluj valley is affected by tectonic-climate variability,making it vulnerable to geohazards.

Geomorphic signatures and active tectonics in western Saurashtra,Gujarat,India

Active tectonics in an area includes ongoing or recent geologic events.This paper investigates the tectonic influence on the subsidence,uplift and tilt of western Saurashtra through morphotectonic analysis of ten watersheds along with characteristics of relief and drainage orientation.Watersheds 7-9 to the north(N)are tectonically active,which can be linked with the North Kathiawar Fault System(NKFS)and followed by watersheds 6,10,1,4 and 5.Stream-length gradient index and sinuosity index indicate the effect of tectonic events along the master streams in watersheds 6-9.Higher R^(2)values of the linear curve fit for watershed 7 indicate its master stream is much more tectonically active than the others.The R^(2)curve fitting model and earthquake magnitude/depth analysis confirm the region to be active.The reactivation of the NKFS most likely led to the vertical movement of western Saurashtra.

Study on the evolution of solid–liquid–gas in multi-scale pore methane in tectonic coal

The rich accumulation of methane(CH_(4))in tectonic coal layers poses a significant obstacle to the safe and efficient extraction of coal seams and coalbed methane.Tectonic coal samples from three geologically complex regions were selected,and the main results obtained by using a variety of research tools,such as physical tests,theoretical analyses,and numerical simulations,are as follows:22.4–62.5 nm is the joint segment of pore volume,and 26.7–100.7 nm is the joint segment of pore specific surface area.In the dynamic gas production process of tectonic coal pore structure,the adsorption method of methane molecules is“solid–liquid adsorption is the mainstay,and solid–gas adsorption coexists”.Methane stored in micropores with a pore size smaller than the jointed range is defined as solid-state pores.Pores within the jointed range,which transition from micropore filling to surface adsorption,are defined as gaseous pores.Pores outside the jointed range,where solid–liquid adsorption occurs,are defined as liquid pores.The evolution of pore structure affects the methane adsorption mode,which provides basic theoretical guidance for the development of coal seam resources.

U-Pb zircon ages and petrogeochemistry and tectonic implications of gabbro and granite in southwest Lahad Datu area of Sabah, Malaysia

The southwest Lahad Datu felsic rocks were previously thought to have formed in the late Triassic as part of the microcontinental crystalline basement.Based on U-Pb ages,geochemistry,and the Hfisotopes of zircon from the southeastern Sabah gabbro and granite,in this study,the tectonic properties of the Sabah area during the Triassic were investigated.The weighted average U-Pb zircon ages of the gabbro and granite samples were determined to be(230.9±2.5)Ma and(207.1±3.3)Ma,respectively.The granite had SiO_(2) contents of 66.54%-79.47%,low TiO_(2) contents of 0.08%-0.3%,Al_(2)O_(3) contents of 10.97%-16.22%,Na_(2)O contents of 5.91 %-6.39%,and low K_(2)O contents of 0.15%-0.65%.The chondrite-normalized rare earth element(REE) patterns exhibit light REE enrichment,with right-sloping curves.The primitive mantle-normalized trace element spider diagrams exhibit Th,U,La,Sr,and Zr enrichment and Nb,Ta,P and Ti depletions,i.e.,the geochemical characteristics of typical island arc igneous rocks.The tectonic discriminant diagram indicates that the granite is a volcanic arc granite.The Hf isotopic an alysis of gabbro zircon revealed that the zircons have ε_(Hf)(t)values of 12.08-16.24(mean of 14.32) and two-stage model ages(t_(DM2)) of 223-491 Ma(mean of 347 Ma).This indicates that the diagenetic magma of the gabbro was mainly derived from melting of newly formed crustal materials.The ophiolite in southeast Sabah has existed since the early Late Triassic.The crystalline basement granite in southeastern S abah was emplaced lasted from late Triassic to early Cretaceous.Based on previous studies and global plate reconstruction models,it is speculated that the southeastern Sabah granite may have been formed in an island arc setting,i.e.,where the oceanic crust of the Paleo-Tethys Ocean collided with the oceanic crust of the Panthalassa Ocean.

Petrogenesis and tectonic implications of the Silurian adakitic granitoids in the eastern segment of the Qilian Orogenic Belt,Northwest China

Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series.Both are peraluminous in composition and have relatively depleted Nd isotopic [ε_(Nd)(t) =(-3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Postcollisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.

Petrogenesis and Tectonic Implications of the Early Triassic Nianzi Adakitic Granite Unit in the Yanshan Fold and Thrust Belt:New Constraints from U-Pb Geochronology and Sr-Nd-Hf Isotopes

The Nianzi granite unit,which includes the Nianzi,Xiaolianghou and Xiawopu granitic intrusions,is a significant component of the northern part of the North China Craton(NCC)and is situated in the Yanshan fold and thrust belt(YFTB).However,there is still debate regarding the tectonic evolutionary history of the YFTB during the late Permian to Triassic period,specifically regarding the timing of subduction and collision between the NCC and the Paleo-Asian Ocean.The Nianzi granite unit exhibits unique petrological,geochronological and geochemical signatures that shed light on the tectonic evolutionary history of the YFTB.This study presents detailed petrology,whole-rock geochemistry,together with Sr-Nd isotopic,zircon U-Pb dating and Lu-Hf isotopic data of the granites within the Nianzi granite unit.Our findings demonstrate that the granites primarily consist of subhedral K-feldspar,plagioclase,quartz,minor biotite and hornblende,with accessory titanite,apatite,magnetite and zircon.Zircon U-Pb dating indicates that the Xiaolianghou granite was emplaced at 247.5±0.62 Ma.Additionally,the adakitic characteristics of the Nianzi,Xiawopu and Xiaolianghou granitic intrusions,such as high Sr and Ba contents and high ratios of Sr/Y and(La/Yb)N,combined with negative Sr-Nd and Lu-Hf isotopes(87Sr/86Sr)i=0.705681–0.7057433,εNd(t)=−21.98 to−20.97,zirconεHf(t)=−20.26 to−9.92,as well as the I-type granite features of high SiO_(2),Na_(2)O and K_(2)O/Na_(2)O ratios,enriched Rb,K,Sr and Ba,along with depleted Th,U,Nb,Ta,P and Ti,suggest that the Nianzi granitic unit was mainly derived from the partial melting of a thickened lower crust containing hydrous,calc-alkaline to high-K calc-alkaline,mafic to intermediate metamorphic rocks.In light of these parameters,we further integrate our data with previous studies and conclude that the Nianzi granitic unit was generated in a post-collisional extensional environment during the Early Triassic.

Formation mechanism of fault accommodation zones under combined stress in graben basin:Implications from geomechanical modeling

A fault accommodation zone is a type of structure that is defined as regulating displacement and strain between faults structure.Increasing numbers of fault accommodation zones are being identified in graben basins,indicating the potential exploration target and petroleum accumulation areas.This study aims to analyze the formation mechanism and development of fault accommodation zones under combined stress by a numerical simulation method considering geomechanical modeling.Using three-dimensional(3-D)seismic interpretation and fractal dimension method,exampled with the Dongxin fault zone,the fault activity and fault combination pattern were conducted to quantitatively characterize the activity difference in fault accommodation zones.Combined with mechanical experiment test,a geomehcanical model was established for fault accommodation zones in a graben basin.Integrating the paleostress numerical simulations and structural physical simulation experiment,the developmental characteristics and genetic mechanism of fault accommodation zones were summarized.Influenced by multi movements and combined stresses,three significant tectonic evolution stages of the Dongxing Fault Zone(DXFZ)were distinguished:During the E_(s)^(3)sedimentary period,the large difference in the stress,strain,and rupture distribution in various faults were significant,and this stage was the key generation period for the prototype of the DXFZ,including the FAZ between large-scale faults.During the E_(s)^(2)sedimentary period,the EW-trending symmetric with opposite dipping normal faults and the NE-SW trending faults with large scale were furtherly developed.The junction area of two secondary normal faults were prone to be ruptured,performing significant period for inheriting and developing characteristics of fault accommodation zones.During the Es1 sedimentary period,the high-order faults in the DXFZ exhibited the obvious fault depressions and strike-slip activity,and the fault accommodation zones were furtherly inherited and developed.This stage was the molded and formative period of the FAZ,the low-order faults,and the depression in the DXFZ.

An integrated north–south paleo-Dadu-Anning River: New insights from bulk major and trace element analyses of the Xigeda Formation

The Xianshuihe-Anninghe fault extends SE–S and constitutes the southeastern margin of the Tibetan Plateau.However,the Dadu River which is associated with the fault does not flow following the path,but makes a 90ºturn within a distance of 1 km at Shimian,heading east,and joins the Yangtze River,finally flowing into the East China Sea.Adjacent to the abrupt turn,a low and wide pass near the Daqiao reservoir at Mianning separates the N–S course of the Dadu River from the headwater of the Anning River which then flows south into the Yunnan Province along the Anninghe fault.Therefore,many previous studies assumed southward flow of the paleo-Dadu River from the Shimian to the Anning River.However,evidences for the capture of the integrated N–S paleo-Dadu-Anning River,its timing,and causes are still insufficient.This study explored the paleo-drainage pattern of the Dadu and Anning Rivers based on bulk mineral and geochemical analyses of the large quantities of fluvial/lacustrine sediments along the trunk of the Dadu and Anning Rivers.Similar with sands in the modern Dadu River,the Xigeda sediments also exhibit a granitoid affinity with the bulk major mineral compositions of quartz(>50%),anorthite(about 10%),orthoclase(about 5%),muscovite(about 5%),and clinochlore(about 4%).Correspondingly,bulk major elements show high SiO_(2),with all samples>60%,and some of them>70%,low TiO_(2)(≤0.75%),P_(2)O_(5)(≤0.55%),FeO*(≤5%),and relatively high CaO(1.02%–8.51%),Na_(2)O(1.60%–2.52%),and K_(2)O(2.17%–2.71%),with a uniform REE patterns.Therefore,synthesizing all these results indicate that these lacustrine sediments have similar material sources,which are mainly derived from its course in the Songpan-Ganzi flysch block,implying that the paleo-Dadu originally flowed southward into the Anning River and provided materials to the Xigeda ancient lake.The rearrangement of the paleo-Dadu River appears to be closely related to the locally focused uplift driven by strong activities of the XianshuiheXiaojiang fault system.

The Middle and Lower Cambrian salt tectonics in the central Tarim Basin,China:A case study based on strike-slip fault characterization

Due to the considerable depth of the salt layers and the lack of calibration by exploratory drilling,the interpretation of the Middle and Lower Cambrian salt formations in the central Tarim Basin poses a challenge.In this paper,we apply the coupling and decoupling deformation theory in salt tectonics to analyze the No.7 fault mapped in the seismic datasets by the response characteristics of the Middle and Lower Cambrian layers.By quantifying the stratigraphic framework of the Middle and Lower Cambrian strata,we define the position of the salt layer with the seismic data.Structural decoupling is observed in the Middle and Lower Cambrian sequences in the Shuntuoguole Low Uplift,while deformation coupling is observed in these two sequences in the Shaya Uplift.

Tectonic geomorphology of Türkiye and its insights into the neotectonic deformation of the Anatolian Plate

Quantitative geomorphic analyses are usually powerful in identifying active tectonics across global orogenic belts.Our present study will focus on the Anatolian Plate which hosts a lot of recent catastrophic earthquakes in Türkiye.Six geomorphic indices for 100 sub-basins around Türkiye have been computed including local relief,slope,normalized steepness index(k_(Sn)),hypsometric curve and integral(HI),transverse topographic symmetry factor(Tf),and the basin asymmetry factor(Af).The averaged kSnand Af values have shown four high-value anomalous zones,suggesting relatively high uplift rates featured by high river incision and regional tilting.The values of 0.35≤HI<0.6 for basins with S-shaped curves imply intensive tectonic activities along the eastern part of the North Anatolian Fault Zone(NAFZ),the Northeast Anatolian Fault Zone(NEAFZ),the East Anatolian Fault Zone(EAFZ),and the Central Anatolian Fault Zone(CAFZ).All results of the geomorphic indices analysis suggest a relatively high degree of tectonic activity in the following four areas,the Isparta Angle,the Eastern Black Sea Mountains,the South-eastern Anatolia Region,and the Central Anatolian fault zone.We further suggest that the eastern part of the NAFZ,NEAFZ,EAFZ,and CAFZ will be more active in tectonic activities,with a greater potential for strong earthquake occurrence.

Palaeogene Sandstones of the Manika Plateau in Kolwezi (DR Congo): Sedimentological and Geochemical Characterization, Provenance, Palaeoalteration and Tectonic Context

This work presents a study of the Paleogene sandstones of the Manika plateau in Kolwezi, DR Congo. These sandstones belong to the “Grès polymorphes” group, which together with the overlying “Sables ocre” makes up the Kalahari Supergroup. Sedimentological and geochemical analyses have enabled us to characterize these sandstones and determine their origin, the conditions of their formation and the tectonic context in which they were developed. The results show that the sandstones are quartz arenites with a high level of mineralogical, textural and chemical maturity. They are recycled sandstones, formed in an intracratonic sedimentary basin, in the context of a passive continental margin, after a long fluvial transport of sediments. These sandstones initially come from intense alteration of magmatic rocks with felsic composition, mainly tonalite-trondhjemite-granodiorite (TTG) complexes, in hot, humid palaeoclimatic conditions and oxidizing environments.

Formation,evolution,reconstruction of black shales and their influence on shale oil and gas resource

Black shales are important products of material cycling and energy exchange among the lithosphere,atmosphere,hydrosphere,and biosphere.They are widely distributed throughout geological history and provide essential energy and mineral resources for the development of human society.They also record the evolution process of the earth and improve the understanding of the earth.This review focuses on the diagenesis and formation mechanisms of black shales sedimentation,composition,evolution,and reconstruction,which have had a significant impact on the formation and enrichment of shale oil and gas.In terms of sedimentary environment,black shales can be classified into three types:Marine,terrestrial,and marine-terrestrial transitional facies.The formation processes include mechanisms such as eolian input,hypopycnal flow,gravity-driven and offshore bottom currents.From a geological perspective,the formation of black shales is often closely related to global or regional major geological events.The enrichment of organic matter is generally the result of the interaction and coupling of several factors such as primary productivity,water redox condition,and sedimentation rate.In terms of evolution,black shales have undergone diagenetic evolution of inorganic minerals,thermal evolution of organic matter and hydrocarbon generation,interactions between organic matter and inorganic minerals,and pore evolution.In terms of reconstruction,the effects of fold deformation,uplift and erosion,and fracturing have changed the stress state of black shale reservoirs,thereby having a significant impact on the pore structure.Fluid activity promotes the formation of veins,and have changed the material composition,stress structure,and reservoir properties of black shales.Regarding resource effects,the deposition of black shales is fundamental for shale oil and gas resources,the evolution of black shales promotes the shale oil and gas formation and storage,and the reconstruction of black shales would have caused the heterogeneous distribution of oil and gas in shales.Exploring the formation mechanisms and interactions of black shales at different scales is a key to in-depth research on shale formation and evolution,as well as the key to revealing the mechanism controlling shale oil and gas accumulation.The present records can reveal how these processes worked in geological history,and improve our understanding of the coupling mechanisms among regional geological events,black shales evolution,and shale oil and gas formation and enrichment.

Cretaceous Large Igneous Provinces (LIPs) Affect Sedimentary Processing: Jordan, Arabian Plate;NW Germany, Central Europe

Both the NE Gondwana Platform (Jordan) and the Carpathian/NW Europe Seaway towards the N Atlantic expose comparable sequence analytical patterns as i.e. the Maximum Flooding Surface (MSF), relating to the Arabian Shelf, throughout one of the warmest Phanerozoic Epochs. Supervolcanic Large Igneous Provinces (LIPs), (explosive island arc andesitic volcanism), Mid-Oceanic Rift Basalts (MORB), (S/N Atlantic, Arctic) and kimberlitic volcanism (W Gondwana) provided striking conditions for an immense influence (tuff, degassing, T) on the sedimentary processing throughout the Cretaceous, mainly verified by K-montmorillonite , dozens of tuff beds (predominantly in NW Germany), zeolite, cristobalite, extremely high chert occurrences as well as the reconfirming of the global anoxic event around the Cenomanian/Turonian b. (94 Ma) by a positive ∂13C-maximum (~0.5%). Thus the lithofacies spectrum (carbonate rocks, chalk, chert, porcellanite, shale) was affected by pH, Eh, T, photosynthesis, and greenhouse gases—change during varying positive/negative climate forcing. While acid sturzrain events caused the transformation of arkosic/subarkosic sediments of the hinterlands to quartz arenite cycles deposited on the Jordanian Platform during early Cretaceous, the other patterns mentioned, led to a rapid change of lithofacies through Late Cretaceous. The southward directed Neotethys transgression can be reconstructed during the Early Cretaceous by glauconite-aged tidalites that give hint on transpressional tectonics during the Upper Cenomanian east of the Dead Sea. The Cretaceous/Paleogene (K-Pg) transitional zone evidences a zone of several cumulative events (island arc-volcanism) and the Chicxulub impact, indicated by at least two extinctions phases. The southward obduction of the Palmyrides, Syria and related transtensional/transpressional strike slip tectonics (partially pull-apart structures) left a fast facies change on the Jordanian Platform.

Gravity Fault Subsidence and Beach Ridges Progradation in Quinta-Cassino (RS) Coastal Plain, Brazil

Ground penetrating radar (GPR) surveys have being applied to investigate very near-surface stratification of sedimentary units in coastal plains and to define their depositional conditions. This paper presents, however, low-frequency GPR survey to investigate fault-related depositional systems at greater depths. The Quinta-Cassino area in the Rio Grande do Sul Coastal Plain (RGSCP, Brazil) shows a wide strandplain that is made off by very long, continuous, and linear geomorphic features (beach ridges). This strandplain extends for ~70 km southward. The beach ridges show low-angle truncations against the Quinta escarpment, and also truncations in the strandplain. The traditional approach points that RGSCP was developed by juxtaposition of four lagoons/barrier systems as consequence of sea level changes;previous model assumes that no deformational episode occurred in RGSCP. The geophysical and geological surveys carried out in this area showed the existence of listric fault controlling the beach ridges in the escarpments and hanging-wall blocks. The radargrams could distinguish Pleistocene basement unit anticlockwise rotation, thickening of beach ridges radarfacies close to listric normal faults, and horst structures. These deformational features indicate that the extensional zone of a large-scale gravity-driven structure controlled the mechanical subsidence, the Holocene sedimentation and its stratigraphic and geomorphic features in the Quinta-Cassino area to build up an asymmetric delta. The results point to a new approach in dealing with RGSCP Holocene evolution.

Depositional architecture of the Tertiary tectonic sequences and their response to foreland tectonism in the Kuqa depression, the Tarim Basin

The Tertiary Kuqa depression is a foreland basin generated by flexural subsidence resulting from the southward thrusting of the southern Tianshan Mountains. Tertiary basin fills of the depression can be classified into four tectonic sequences bounded by gentle angular unconformities. The sequences are composed of two parts, the lower transgressive and the upper progradational successions, which are separated by a regional maximum transgressive surface. The development of these sequences is attributed to the foreland tectonic process from flexural subsidence caused by thrust loading to rebounded uplift due to the erosion and stress release. The generation of the angular unconformities defining the tectonic sequences has been interpreted as the result of the rebounded uplift and the following thrusting. It has been found that there is a significant difference in depositional pattern between the northeastern and the northwestern margins. The relatively strong thrusting and mountain building occurring along the northwestern margin resulted in the development of thick-bedded alluvial fan and angular unconformities. The northeastern margin, in contract, lacks thick alluvial fan accumulation due to weak thrusting. This difference is likely related to the pre-existing east-west partition of the basin basement.