Volcanism Pacing Slumping Gravity Flow Deposits during the Late Carboniferous in the Southern Margin of the Junggar Basin,China

Deep-water gravity depositional processes and evolution in arc systems have become topics of intense research focus in recent years.This study discusses the co-evolution of volcanism and deep-water gravity flow deposits at the southern margin of the Junggar Basin,based on petrology,geochronology and geochemical analyses.The results show that a massive collapse of unstable sediments from the slope was triggered by volcanism,resulting in the formation of slumping gravity flows.The occurrence of volcanic beds in the slump deposits confirm that synchronous volcanism likely affected sediment instability,triggering gravity flows.The Th/Yb,Ta/Yb and Th/Ta elemental ratios,U-Pb ages of detrital zircons and paleocurrent directions indicate that the North Tianshan(NTS)island arc represents the provenance of the Qianxia Formation.Moreover,statistical data on the pyroclastic components in the gravity flow deposits reveal an intensity index of volcanism,indicating that volcanism is strongly related to gravity flow deposits,especially in terms of the type and distribution of the deposits.A model for volcanically-triggered deep-water gravity flow deposits is established,in order to provide a more in-depth understanding of the co-evolution of volcanism and gravity flow deposits within the depositional setting of the late Paleozoic NTS oceanic subduction margin in the Junggar Basin.

Depositional process of hyperpycnal flow deposits:A case study on Lower Cretaceous Sangyuan outcrop in the Luanping Basin,Northeast China

Sedimentary process research is of great significance for understanding the distribution and characteristics of sediments.Through the detailed observation and measurement of the Sangyuan outcrop in Luanping Basin,this paper studies the depositional process of the hyperpycnal flow deposits,and divides their depositional process into three phases,namely,acceleration,erosion and deceleration.In the acceleration phase,hyperpycnal flow begins to enter the basin nearby,and then speeds up gradually.Deposits developed in the acceleration phase are reverse.In addition,the original deposits become unstable and are taken away by hyperpycnal flows under the eroding force.As a result,there are a lot of mixture of red mud pebbles outside the basin and gray mud pebbles within the basin.In the erosion phase,the reverse deposits are eroded and become thinner or even disappear.Therefore,no reverse grading characteristic is found in the proximal major channel that is closer to the source,but it is still preserved in the middle branch channel that is far from the source.After entering the deceleration phase,normally grading deposits appear and cover previous deposits.The final deposits in the basin are special.Some are reverse,and others are normal.They are superimposed with each other under the action of hyperpycnal flow.The analysis of the Sangyuan outcrop demonstrates the sedimentary process and distribution of hyperpycnites,and reasonably explain the sedimentary characteristics of hyperpycnites.It is helpful to the prediction of oil and gas exploration targets in gravity flow deposits.

An Upward Shallowing Succession of Gravity Flow Deposits in the Early Cretaceous Lingshandao Formation,Western Yellow Sea

Objective Several well-exposed gravity flow deposits in the Early Cretaceous Lingshandao Formation provide a rare opportunity to study deep-water processes. The main objective of this work is to establish the spatial and temporal relationships between the various gravity flow deposits, and thus to establish their sequence stratigraphic patterns and depositional conditions.

Evolution and controlling factors of the gravity flow deposits in the Miocene sequence stratigraphic framework,the Lower Congo-Congo Fan Basin,West Africa

To understand the evolution of the Miocene gravity flow deposits in the Lower Congo-Congo Fan Basin,this paper documents the Miocene sequence stratigraphic framework,the depositional characteristics and the controlling factors of the gravity flow system.Based on the establishment of high-resolution sequence stratigraphic framework,lithofacies characteristics and sedimentary units of the gravity flow deposits in the region are identified by using seismic,well logging and core data comprehensively,and the sedimentary evolution process is revealed and the controlling factors are discussed.The Miocene can be divided into four 3 rd-order sequences(SQ1-SQ4).The gravity flow deposits mainly include siliciclastic rock and pelite.The main sedimentary units include slumping deposits,mass transport deposits(MTD),channel fills,levee-overbank deposits,and frontal lobes.In the Early Miocene(SQ1),mainly gull-wing,weakly restricted to unrestricted depositional channel-overbank complexes and lobes were formed.In the early Middle Miocene(SQ2),W-shaped and weakly restricted erosional-depositional channels(multi-phase superposition)were subsequently developed.In the late Middle Miocene(SQ3),primarily U-shaped and restricted erosional channels were developed.In the Late Miocene(SQ4),largely V-shaped and deeply erosional isolated channels were formed in the study area.Climate cooling and continuous fall of the sea level made the study area change from toe of slope-submarine plain to lower continental slope,middle continental slope and finally to upper continental slope,which in turn affected the strength of the gravity flow.The three times of tectonic uplifting and climate cooling in the West African coast provided abundant sediment supply for the development of gravity flow deposits.Multistage activities of salt structures played important roles in redirecting,restricting,blocking and destroying the gravity flow deposits.Clarifying the characteristics,evolution and controlling factors of the Miocene gravity flow deposits in the Lower Congo-Congo Fan Basin can provide reference for deep-water petroleum exploration in this basin.

Sedimentary characteristics and model of gravity flow channel-lobe complex in a depression lake basin:A case study of Chang 7 Member of Triassic Yanchang Formation in southwestern Ordos Basin,NW China

To reveal the development characteristics and distribution of gravity flow sedimentary system under micro-paleogeomorphologic units of the Chang 7 Member of Triassic Yanchang Formation in the southwestern Ordos Basin,on the basis of the restoration of the paleogeomorphological form of the Chang 7 depositional period by the impression method,each micro-paleogeomorphologic unit was depicted in-depth,and the characteristics and development models of gravity flow deposits in the study area were studied in combination with outcrop,core,mud logging and log data.The results show that:(1)The paleogeomorphology in the Chang 7 depositional period was an asymmetrical depression,wide and gentle in the northeast and steep and narrow in the southwest.Three sub-paleogeomorphologic units were developed in the basin,including gentle paleo-slope,paleo-slope and paleo-depression,and they can be further subdivided into eight micro-paleogeomorphologic units:bulge,groove,slope break belt,plain of lake bottom,deep depression of lake bottom,paleo-channel,paleo-ridge of lake bottom,and paleo-uplift of lake bottom.(2)There are 9 types of lithofacies and 4 types of lithofacies assemblages of Chang 7 Member.According to lithofacies composition and lithofacies vertical combination,the gravity flow deposit is further divided into 5 types of microfacies:restricted channel,unrestricted channel,natural levee,inter-channel,lobe.(3)Paleogeomorphology plays an important role in controlling sediment source direction,type and spatial distribution of sedimentary microfacies,genetic types and distribution of sand bodies in Chang 7 Member.

Sedimentary Facies Characteristics of Chang 6 and Chang 7 Members of Yanchang Formation in Heshui Area, China

This paper takes Chang 6 and Chang 7 of Yanchang Formation in Heshui area of China as the research object. This study first divides the strata of Chang 6 and Chang 7. According to the review data, significant geological activities have caused a large settlement of the strata in this area. During the Chang 6 period, a lacustrine basin sedimentary system developed, reaching its peak in the Chang 7 period. The Chang 6 and Chang 7 members primarily feature deep-water gravity flow sedimentary systems, which can be categorized into three subfacies: outer fan, middle fan, and inner fan. These systems also exhibit turbidite fan sedimentary patterns, ranging from deep lake to semi-deep lake facies. By examining these sedimentary models, we can identify different types of turbidite deposits. Understanding the process of gravity flow deposition and the evolution of ancient lakes is crucial for guiding oil and gas exploration and conducting paleogeographic research.

Depositional Characteristics of Lake-Floor Fan of Cretaceous Lower Yaojia Formation in Western Part of Central Depression Region,Songliao Basin

ABSTRACT： Based on the integrated subsurface data, including those of over 600 m drilled cores, more than 30 drilled wells and 600 km^2 three-dimensional （3D） seismic-reflection data of the study area, the characteristics of the lake-floor fan of lower Yaojia （姚家） Formation have been clarified. An evident lacustrine slope break and a steep slope belt developed in the west of Songliao （松辽） basin during depositional period of Qingshankou （青山口）-Yaojia formations （K2）. The slope gradient was about 15 m/kin. During the depositional period of lower Yaojia Formation, the lake shrank and the shore line of the western Songiiao basin shifted to the lacustrine slope-break. The wedge-shaped sediment body, which is interpreted as the lowstand system tract of SQyl （LSTy1）, developed in the area below the slope-break. The LSTy1 is pinched out in the west of the study area. As to the thickness of LSTy1, it is thicker in the east with 50 m in its thickness than in the west. The LSTy1, rich in sandstone, can be divided into lower part LSTy1L and upper part LSTy1u based on two onlap seismic reflection phases, and core and logging data clearly. The various sediments＇ gravity flow deposits developed and the complex of lake-floor fan formed in the LSTy1 under the slope-break in the western part of the central depression region. The lake-floor fan consists of various sediments＇ gravity flow deposits, including： （1） turbidity deposits with characteristics of Bouma sequences; （2） sand-bearing muddy debrite dominated by mud and mixed by sand; （3） mud-bearing sandy debrites characterized by dominated sand and mixed by mud; （4） sandy debris laminar flow deposits with massive or inclined bedding, and （5） sandy slump deposits developed as deformational sedimentary structure. During the lower lake-level period （LSTy1L）, the western clino-form region was erosion or sediment pass-by area; the terrigenous clasttc was directly trans-ported to deep-water area, converted to channelized sandy debris flow, and combined with slump derived gravity flow deposited in the lower part of the slope and the deep depression region, which then formed lake-floor fans. During higher lake-level period （LSTylu）, terrigenous clastic deposited in the upper part of the slope, and formed deltaic depositional system; while in the lower part of the slope, the deep depression area was filled by lake-floor fans which were mainly slump deposits. The sandstone bodies of the lake-floor fan are the favorable targets of subtle oil-bearing traps in the western part of the central depression region.