Triassic carbonate submarine fans along the Arabian platform margin, Sumeini Group, Oman

ABSTRACT The Sumeini Group formed along the passive continental margin slope that bounded the northeastern edge of the Arabian carbonate platform. With the initial development of this passive continental margin in Oman during Early to Middle Triassic time (possibly Permian), small carbonate submarine fans of the C Member of the Maqam Formation developed along a distally steepened slope. The fan deposits occur as several discrete lenticular sequences of genetically related beds of coarsegrained redeposited carbonate (calciclastic) sediment within a thick interval of basinal lime mudstone and shale. Repeated pulses of calciclastic sediment were derived from ooid shoals on an adjacent carbonate platform and contain coarser intraclasts eroded from the surrounding slope deposits. Sediment gravity flows, primarily turbidites with lesser debris flows and grain flows, transported the coarse sediments to the relatively deep submarine fans. Channel erosion was a major source of intraformational calcirudite. Two small submarine fan systems were each recurrently supplied with calciclastic sediment derived from point sources, submarine canyons. The northern fan system retrogrades and dies out upsection. The southern fan system was apparently longer-lived; calciclastic sediments in it are more prevalent and occur throughout the section. The proximal portions of this fan system are dominated by channelized beds of calcirudite which represent inner- to mid-fan channel complexes. The distal portions include mostly lenticular, unchannelized beds of calcarenite, apparently mid- to outer-fan lobes. Carbonate submarine fans appear to be rare in the geological record in comparison with more laterally continuous slope aprons of coarse redeposited sediment. The carbonate submarine fans of the C Member apparently formed by the funnelling of coarse calciclastic sediment into small submarine canyons which may have developed due to rift and/or transform tectonics. The alternation of discrete sequences of calciclastic sediment with thick intervals of ‘background’ sediment resulted from either sea-level fluctuations or pulses of tectonic activity.     

A point-sourced calciclastic submarine fan complex (Eocene Anotz Formation, western Pyrenees): facies architecture, evolution and controlling factors

A complete transect of a fossil carbonate ramp slope has been reconstructed using outcrop data from the Lower-Middle Eocene Anotz Formation in the western Pyrenees. The Anotz Formation contains four calciclastic (mostly bioclastic) members encased within hemipelagic marl/limestone alternations, each calciclastic member representing a submarine fan system. Individual fans are composed of a gullied upper slope, a leveed feeder channel, a channelized lobe area, an unconfined lobe zone and a peripheral lobe fringe that grades downcurrent into basinal deposits. Quantitative data on the dimensions and degree of lateral continuity and vertical connectivity of the Anotz calciclastic fan elements are presented. These data provide information for a better understanding of the intrinsic nature of calciclastic submarine fans and to model their reservoir potential. The long-term evolution of the Anotz carbonate slope was generally progradational, as evidenced by the four discrete episodes of calciclastic-fan development. The location of the fans was controlled by the synsedimentary tectonic activity of the Pamplona fault, which created a slope valley along which the reworked shallow-water calciclastic sediments were funnelled. In addition, episodic basinward tilting of the shallow-water carbonate ramp, linked to the development of the South Pyrenean foreland basin, switched on and off the process of calciclastic resedimentation and determined the growth or abandonment of the fan systems.     

Deposition and derivation of clastic carbonates on a Mesozoic continental margin, Othris, Greece

The Othris Mountains of eastern Greece contain a calcareous continental margin/ocean basin sequence exposed in a stack of Cretaceous thrust sheets. Upper Triassic to Lower Cretaceous shelf, submarine fan and basinal successions overlie shallow marine units of Lower Triassic and Permian age. In off-shelf sequences the older sediments are separated from the younger by a horizon of alkaline ‘early-rifting’ basalts. Ophiolites overthrust the marginal sequence. Pre-rifting sediments are represented by a varied suite of limestones and clastics resting on metamorphic basement and include distinctive, green lithic arenites. In the thrust sheet immediately over the para-autochthonous shelf sequence, pre-rifting sediments are separated from the rift basalts by an intermittent horizon of calcareous sandstones and conglomerates reworked from uplifted basement and older sediments. Textural and petrographic immaturity suggests that these are probably deposits derived from fault scarps, produced in an early phase of rifting. Above the basalts in the same sheet is a suite of calciclastic sediment-gravity-flow deposits, apparently sedimented on a submarine fan. Progressive downslope modification of calcirudites suggests deposition from evolving, high concentration flows. Massive calcarenite facies (? grain flows) are unusually abundant; a possible reflection of a shallow palaeo-shelf break since provenance and palaeocurrent evidence proves the clastic carbonates to have been derived from a calcareous shelf. In addition to limestone lithoclasts the calcirudites, but not the massive calcarenites, contain fragments of pre-rifting lithologies including the distinctive arenites. Since the shelf sequence in Othris is totally nondetrital these clasts imply derivation of coarse sediment from an off-shelf position; probably the walls of a submarine canyon. This may have occurred either by direct erosion of wall rock, or by reworking of material from an older clastic sequence. In the latter case the inferred fault-scarp deposits are a likely source.     

湖南道县、宁远一带中泥盆统棋梓桥组中的台地前缘斜坡异地碳酸盐沉积

沿台地边缘斜坡沉积的古代碳酸盐再沉积物是最近十年来才引起沉积学者广泛注意的一种深水碳酸盐类型,包括碳酸盐重力流,重力滑动(滑塌)沉积及塌磊裙。重力流及由于重力作用引起的沉积物与浅水碳酸盐或深水原地碳酸盐沉积相比,有很大的差异。它们的主要岩石类型是异地碳酸盐,为一套在重力作用下顺坡而下流动的碳酸盐沉积物。前礁塌磊是台地边缘礁坠落到陡崖下的礁块堆积,也称为礁崖塌积。     

Anatomy of a modern open-ocean carbonate slope: northern Little Bahama Bank

The open-ocean carbonate slope north of Little Bahama Bank consists of a relatively steep (4°) upper slope between water depths of 200 and 900 m, and a more gentle (1–2°) lower slope between depths of 900 and 1300+ m. The upper slope is dissected by numerous, small, submarine canyons (50–150 m in relief) that act as a line source for the downslope transport of coarse-grained carbonate debris. The lower slope is devoid of any well-defined canyons but does contain numerous, small (1–5 m) hummocks of uncertain origin and numerous, larger (5–40 m), patchily distributed, ahermatypic coral mounds. Sediments along the upper slope have prograded seaward during the Cenozoic as a slope-front-fill seismic facies of fine-grained peri-platform ooze. Surface sediments show lateral gradation of both grain size and carbonate mineralogy, with the fine fraction derived largely from the adjacent shallow-water platform. Near-surface sedimentary facies along the upper slope display a gradual downslope decrease in the degree of submarine cementation from well-lithified hardgrounds to patchily cemented nodular ooze to unlithified peri-platform ooze, controlled by lateral variations in diagenetic potential and/or winnowing by bottom currents. Submarine cementation stabilizes the upper part of the slope, allowing upbuilding of the platform margin, and controls the distribution of submarine slides, as well as the headward extent of submarine canyons. Where unlithified, sediments are heavily bioturbated and are locally undergoing dolomitization. Upper slope sediments are also ‘conditioned’eustatically, resulting in vertical, cyclic sequences of diagenetically unstable (aragonite and magnesian calcite-rich) and stable (calcite-rich) carbonates that may explain the well-bedded nature of ancient peri-platform ooze sequences. Lower slope sediments have prograded seaward during the Cenozoic as a chaotic-fill seismic facies of coarse-grained carbonate turbidites and debris flow deposits with subordinate amounts of peri-platform ooze. Coarse clasts are ‘internally’derived from fine-grained upper slope sediments via incipient cementation, submarine sliding and the generation of sediment gravity flows. Gravity flows bypass the upper slope via a multitude of canyons and are deposited along the lower slope as a wedge-shaped apron of debris, parallel to the adjacent shelf edge, consisting of a complex spatial arrangement of localized turbidites and debris flow deposits. A proximal apron facies of thick, mud-supported debris flow deposits plus thick, coarse-grained, Ta turbidites, grades seaward into a distal apron facies of thinner, grain-supported debris flow deposits and thinner, finer grained Ta-b turbidites with increasing proportions of peri-platform ooze. Both the geomorphology and sedimentary facies relationships of the carbonate apron north of Little Bahama Bank differ significantly from the classic submarine fan model. As such, a carbonate apron model offers an alternative to the fan model for palaeoenvironmental analysis of ancient, open-ocean carbonate slope sequences.     

台湾峡谷HD133和HD77柱状样的沉积构成和发育背景

分别对南海东北部台湾峡谷内水深3 280 m的HD133和峡谷外水深3 378 m的HD77重力活塞柱状样进行了沉积物粒度、古生物和碳酸钙含量分析,利用AMS14C同位素测年和沉积速率初步认定是属于MIS3a以来的沉积。按沉积物粒度和碳酸钙含量可将两支柱状样划分为3套沉积层段:上部层段1和下部层段3均以粉砂质黏土为主,夹薄层粉砂,深水底栖有孔虫含量高,碳酸钙低于10%,代表受重力流作用较弱的正常深海沉积;中部层段2发育一套以中-细粒为主的厚砂层,含大量浅水底栖有孔虫,碳酸钙含量可高达60%,AMS14C测年出现倒置现象,表明主要为浅水重力流沉积。柱状样的沉积构成响应同期海平面变化,特别表现在深水砂层沉积的两大控制因素:在时间上,低海平面时期大量浅水和陆源碎屑物质直接输送到陆坡之下的深水区,形成富砂的层段2;在空间上,峡谷水道是重力流的物质输送通道,地形优势使得重力流携带物优先在水道中发生沉积,造成HD133柱的含砂量明显高于HD77柱状样。     

海底扇沉积相模式、沉积过程及其沉积记录的指示意义

海底扇是由沉积物重力流形成的海底沉积体。其分类学和相模式研究表明,海底扇主要由海底水道、溢岸及朵叶体等沉积单元构成。然而古代和现代海底扇沉积均无法由单一的通用相模式进行解释。以粒度差异所建立的相模式类型涵盖了多方面信息,相对简单实用。海底扇的触发机制主要包括海底沉积物失稳、洪水型异重流、海洋动力过程及复合成因机制等类型。海底扇的主导流体类型（碎屑流与浊流）、海底地貌形态（限制性与非限制性）及海洋动力条件（底流作用）深刻影响了海底扇的沉积作用、平面形态及空间组合特征,整体上分为三类。其中,浊流沉积主导的海底扇在非限制性海底环境中主要表现为扇状或指状形态,在限制性海底环境中则直接受控于盆地的地貌形态;碎屑流沉积主导的海底扇以块体搬运为特征,平面上表现为舌状和叶状展布形态;底流与重力流共同作用形成的混合型海底扇朵叶体沿底流流向侧向偏转,部分受底流改造沉积形成孤立漂积丘状形态。海底扇沉积物记录了环境信号从“源”到“汇”传输效率和保存程度,对构造变形和古气候变化具有重要的指示作用。人类世以来的现代海底扇沉积物同时也是深海微塑料、陆源有机碳的重要储库,定量评估其丰度特征对于环境评价、污染治理与管控及全球碳循环均具有深远的现实意义。     

Glacimarine lithofacies,provenance and depositional processes on a West Greenland trough‐mouth fan

Along the West Greenland continental margin adjoining Baffin Bay, bathymetric data show a series of large submarine fans located at the mouths of cross‐shelf troughs. One of these fans, termed here ‘Uummannaq Fan’, is a trough‐mouth fan built largely by debris delivered from a fast‐flowing outlet of the Greenland Ice Sheet during past glacial maxima. Cores from this fan provide the first information on glacimarine sedimentary facies within a major West Greenland trough‐mouth fan and on the nature of Late Weichselian–Holocene glacigenic sediment delivery to this region of the Baffin Bay margin. Glacigenic debris flows deposited on the upper slope and extending to at least 1800 m water depth in front of the trough‐mouth are related to the remobilization of subglacial debris that was delivered onto the upper slope at times when an ice stream was positioned at the shelf edge. In contrast, sedimentary facies from the northern sector of the fan are characterized by hemipelagic and ice‐rafted sediments and turbidites; glacigenic debris flows are notably absent in cores from this region. Quantitative X‐ray diffraction studies of the <2‐mm sediment fraction indicate that the bulk of the sediment in the fan is derived from Uummannaq Trough but there are distinct intervals when sediment from northern Baffin Bay sources dominates, especially on the northern limit of the fan. These data demonstrate considerable variation in the nature of sediment delivery across the Uummannaq Fan when the Greenland Ice Sheet was at the shelf edge. They highlight the variability of glacimarine depositional processes operating on trough‐mouth fans on high‐latitude continental margins during the last glacial maximum and indicate that glacigenic debris flows are just one of a number of mechanisms by which such large depocentres form. Copyright © 2012 John Wiley & Sons, Ltd.     

Sedimentation of submarine fan deposits in the Pindos foreland basin,from late Eocene to early Oligocene,west Peloponnesus peninsula,SW Greece

Turbidite facies distribution and palaeocurrent analysis of submarine fan evolution in the Pindos foreland basin of west Peloponnesus peninsula (SW Greece) indicate that this part of the foreland was developed during Late Eocene to Early Oligocene in three linear sub‐basins (Tritea, Hrisovitsi and Finikounda). The basin fill conditions, with a multiple feeder system, which is characterized by axial transport of sediments and asymmetric stratigraphic thickness of the studied sediments, indicate that the Pindos Foreland Basin in this area was an underfilled foreland basin. Sediments are dominated by conglomerates, sandstones and mudstones. The flow types that controlled the depositional processes of the submarine fans were grain flows, debris flows and low‐ and high‐density turbidity currents. The sedimentary model that we propose for the depositional mechanisms and geometrical distribution of the turbidite units in the Tritea sub‐basin is a mixed sand‐mud submarine fan with a sequential interaction of progradation and retrogradation for the submarine fan development and shows a WNW main palaeocurrent direction. The Hrisovitsi sub‐basin turbidite system characterized by small‐scale channels was sediment starved, and the erosion during deposition was greater than the two other studied areas, indicating a more restricted basin topography with a NW main palaeocurrent direction. The Finikounda sub‐basin exhibits sand‐rich submarine fans, is characterized by the presence of distinct, small‐scale, thickening‐upward cycles and by the covering of a distal fan by a proximal fan. It was constructed under the simultaneous interaction of progradation and aggradation, where the main palaeocurrent direction was from NNW to SSE. Copyright © 2012 John Wiley & Sons, Ltd.     

华南海相深水重力沉积相模式

通过对华南地区诸多海相盆地深水沉积物的详细解剖,识别出一个由重力搬运沉积形成的完整岩类系列,包括孤立岩块、滑动滑塌和重力流沉积三个基本端元大类。这些重力流沉积以不同的型式组合构成了三大类七亚类各具特征的深水沉积体系。Ⅰ陆源碎屑体系包括(1)海底扇和(2)轴向搬运沉积亚体系。Ⅱ碳酸盐体系包括(1)碳酸盐缓坡,(2)沟槽型碳酸盐斜坡和(3)碳酸盐陡坡。Ⅲ混合物源体系包括(1)碳酸盐斜坡体系与陆屑海底扇组合;(2)碳酸盐斜坡体系与火山碎屑重力流轴向搬运沉积体系。     

Status and Trends in Research on Deep-Water Gravity Flow Deposits

Deep-water gravity flows are one of the most important sediment transport mechanisms on Earth. After 60 years of study,significant achievements have been made in terms of classification schemes,genetic mechanisms,and depositional models of deep-water gravity flows. The research history of deep-water gravity flows can be divided into five stages: incipience of turbidity current theory; formation of turbidity current theory; development of deep-water gravity flow theory; improvement and perfection of deep-water gravity flow theory; and comprehensive development of deep-water gravity flow theory. Currently,three primary classification schemes based on the sediment support mechanism,the rheology and transportation process,and the integration of sediment support mechanisms,rheology,sedimentary characteristics,and flow state are commonly used.Different types of deep-water gravity flow events form different types of gravity flow deposits. Sediment slump retransportation mainly forms muddy debris flows,sandy debris flows,and surge-like turbidity currents. Resuspension of deposits by storms leads to quasi-steady hyperpycnal turbidity currents(hyperpycnal flows). Sustainable sediment supplies mainly generate muddy debris flows,sandy debris flows,and hyperpycnal flows. Deep-water fans,which are commonly controlled by debris flows and hyperpycnal flows,are triggered by sustainable sediment supply; in contrast,deep-water slope sedimentary deposits consist mainly of debris flows that are triggered by the retransportation of sediment slumps and deep-water fine-grained sedimentary deposits are derived primarily from finegrained hyperpycnal flows that are triggered by the resuspension of storm deposits. Harmonization of classification schemes,transformation between different types of gravity flow deposit,and monitoring and reproduction of the sedimentary processes of deep-water gravity flows as well as a source-to-sink approach to document the evolution and deposition of deep-water gravity flows are the most important research aspects for future studies of deep-water gravity flows study in the future.     

Sedimentary processes in a submarine canyon excavated into a temperate‐carbonate ramp (Granada Basin,southern Spain)

During the Late Tortonian, shallow‐water temperate carbonates were deposited in a small bay on a gentle ramp linked to a small island (Alhama de Granada area, Granada Basin, southern Spain). A submarine canyon (the ‘Alhama Submarine Canyon’) developed close to the shoreline, cross‐cutting the temperate‐carbonate ramp. The Alhama Submarine Canyon had an irregular profile and steep slopes (10° to 30°). It was excavated in two phases reflected by two major erosion surfaces, the lowermost of which was incised at least 50 m into the ramp. Wedge‐shaped and trough‐shaped, concave‐up beds of calcareous (terrigenous) deposits overlie these erosional surfaces and filled the canyon. A combination of processes connected to sea‐level changes is proposed to explain the evolution of the Alhama Submarine Canyon. During sea‐level fall, part of the carbonate ramp became exposed and a river valley was excavated. As sea‐level rose, river flows continued along the submerged, former river‐channel, eroding and deepening the valley and creating a submarine canyon. At this stage, only some of the transported conglomerates were deposited locally. As sea‐level continued to rise, the river mouth became detached from the canyon head; littoral sediments, transported by longshore and storm currents, were now captured inside the canyon, generating erosive flows that contributed to its excavation. Most of the canyon infilling took place later, during sea‐level highstand. Longshore‐transported well‐sorted calcarenites/fine‐grained calcirudites derived from longshore‐drift sandwaves poured into and fed the canyon from the south. Coarse‐grained, bioclastic calcirudites derived from a poorly sorted, bioclastic ‘factory facies’ cascaded into the canyon from the north during storms.     

内蒙古固阳渣尔泰山群增隆昌组台前斜坡碳酸盐角砾岩的成因

内蒙古固阳渣尔泰山群增隆昌组晚期沉积环境演化为碳酸盐岩台地。重点研究了台前斜坡碳酸盐角砾岩的岩性、岩相和相序特征 ,识别出重力滑动、浊流和风暴重力流成因的角砾岩 ,探讨了不同成因的角砾岩与海平面变化的响应关系。研究表明 ,角砾岩主要形成于海平面的上升速率减慢或最大静止期 ,此时台地碳酸盐岩产率过剩 ,大量的碳酸盐岩由地震、重力、风暴流带入斜坡和坡底 ,形成异地角砾岩。     

川北下寒武统仙女洞组台缘斜坡碳酸盐岩重力流沉积

基于重力流剖面的野外观察、露头解剖及镜下鉴定等分析手段,对四川盆地北部下寒武统仙女洞组台缘斜坡碳酸盐 岩重力流沉积及发育机制进行了研究。研究区位于仙女洞组,主要沉积粉砂质泥岩、生屑泥晶灰岩、藻灰岩等3种岩石类 型;根据层面上产出形态的不同,将该区碳酸盐岩重力流沉积分为似瘤状碳酸盐岩重力流沉积和角砾型碳酸盐岩重力流沉 积2类。结合露头区重力流沉积物粒度及岩性变化,将碳酸盐岩重力流沉积由下至上划分出5个发育期次,期次内部重力流 沉积物由细变粗,纵向上呈现出明显的叠置关系,与仙女洞组时期所经历的海退环境大致吻合。地震、风暴浪等触发机制 导致台缘斜坡上部松散沉积的灰泥丘块体发生破碎并沿斜坡发生滑塌,伴随水体注入,大块砾石在沉积物-水体混合的环 境中发生破碎搅动,形成大小不等的块体,深水底流等作用对未固结或弱固结的砾屑灰岩进行溶蚀、改造,最终形成了层 面形态特征不同的2类似瘤状碳酸盐岩重力流沉积。角砾型碳酸盐岩重力流沉积则主要是未破碎的巨型灰泥丘块体经搬运 和短距离滑塌,最终与似瘤状砾屑灰岩共同沉积而成。     

黔东湘西寒武纪碳酸盐台地边缘和斜坡沉积特征及大陆边缘构造性质讨论

本文研究了寒武纪台地边缘和斜坡沉积特征、沉积模式演化及与扬子板块东南缘构造演化的关系,认为该区从寒武纪到早奥陶世为长期发育以加积和推进为主的碳酸盐台地;该区长期处于稳定下沉的构造背景,说明扬子板块东南缘已进入成熟被动陆缘阶段。在台地和斜坡上形成向上变浅或向上先变粗后变细的沉积旋回。并着重论述了斜坡碎屑流沉积类型、特征和成因机制;其碳酸盐碎屑流主要为复合支撑机制,其流动过程中普遍存在脉动性或波动性及流动转化现象;系统建立了寒武纪台地边缘模式及演化序列;探讨了板块构造演化与成矿作用关系,指出湘黔汞矿带、铅锌矿带可能与逆冲席有关。     

沾化凹陷孤岛西部斜坡带沙三段重力流沉积特征与源-汇体系

以岩芯观察、粒度分析、薄片鉴定、测井资料和地震资料解释等为主要手段,研究渤海湾盆地沾化凹陷孤岛西部斜坡带沙三段主要沉积物重力流类型及其沉积特征,探讨不同触发机制下的沉积物重力流演化过程和构造活动对重力流沉积过程及砂体展布的控制,总结源-汇耦合体系,建立斜坡带重力流砂体发育模式。结果表明:研究区沙三段沉积时期发育异重流、碎屑流、浊流、液化流和滑动-滑塌五种沉积物重力流,具有洪水型和滑塌型两种触发机制,流体演变总体处于碎屑流向浊流演化的早期阶段,推测研究区以北深水区仍发育碎屑流沉积且开始广泛发育浊流沉积。构造作用对研究区沙三段流体性质与演化、同生变形构造和重力流成因砂体的发育与分布具有明显的控制作用。总体上,研究区具有断槽沟谷、断裂坡折、断裂走向斜坡及缓坡沟谷等4种主要的源-汇耦合体系。纵向上,研究区沙三段自下而上由（半）深湖、近岸水下扇、滑塌扇沉积演变为滨浅湖、辫状河三角洲以及扇三角洲沉积;平面上,研究区东部主要发育来自孤岛凸起的扇三角洲前缘和近岸水下扇,西部主要发育来自陈家庄凸起的辫状河三角洲前缘,中部主要发育串珠状滑塌扇体。     

中建海底峡谷地貌及沉积特征的分段性

中建海底峡谷具有分段性,但分段的关键地貌特征、各段沉积充填及其控制因素缺乏精细描述和系统论证.综合利用高分辨率二维和三维地震资料,结合水深地貌数据,对中建海底峡谷地貌及沉积特征进行了详细分析,总结了其南北段沉积过程的主控因素.中建海底峡谷呈NW向顺直展布于广乐隆起与西沙隆起之间,以华光礁附近的地貌高点为拐点被分为南北两段.中建海底峡谷北段沉积体系包括重力流沉积（水道、席状沉积、滑塌体）和底流沉积（漂积体、环槽、谷槽）,南段以重力流水道和海底扇为主.北段沉积体系受底流和重力流交互作用控制,底流自中中新世开始出现,改造重力流水道,使其出现侧向迁移或翼部不对称现象,上新世以后重力流作用减弱,底流作用增强,沉积物波和漂积体广泛发育;峡谷南段水道表现出侵蚀-沉积-废弃的沉积旋回,未见底流沉积现象.相对海平面变化导致碳酸盐生产率变化影响物源供应,从而控制水道沉积演化,碳酸盐台地的“高位溢流”作用决定水道在高水位时发育.      

Sedimentation during carbonate ramp-to-slope evolution in a tectonically active area: Bowland Basin (Dinantian), northern England

The Bowland Basin (northern England) contains a series of carbonates and terrigenous mudstones deposited during the Ivorian to early Brigantian. Two regional depositional environments are indicated by facies and facies associations. Wackestone/packstone and calcarenite facies indicate deposition in a carbonate ramp environment, while lime mudstone/wackestone, calcarenite and limestone breccia/conglomerate facies, often extensively slumped, represent a carbonate slope environment. Stratigraphic relations suggest that the depositional environment evolved from a ramp into a slope through the Dinantian. Two main sediment sources are indicated by the sequence; an extra-basinal terrigenous mud source and a supply of carbonate from the margins of the basin. Deposition from suspension and from sediment gravity flows, in situ production and remobilization of sediment during sedimentary sliding were important processes operating within the basin. Periods of enhanced tectonic activity in the late Chadian to early Arundian and late Asbian to early Brigantian are indicated by basin-wide horizons of sedimentary slide and mass flow deposits. Both intervals were marked by a decline in carbonate production resulting from inundation and uplift/emergence. The first of these intervals separates deposition on a seafloor with gentle topography (carbonate ramp) from a situation where major lateral thickness and facies variations were present and deposition took place in a carbonate slope environment. The second interval marks the end of major carbonate deposition within the Bowland Basin and the onset of regional terrigenous sedimentation.     

Sediment dispersal and accumulation in tectonic accommodation across the Gaoping Slope,offshore Southwestern Taiwan

Distribution and architecture of slope basins across a continental slope vary as a consequence of accommodation forming, sediment dispersal rates, canyon cutting, sediment filling and different sediment transporting mechanisms. The area offshore Southwestern Taiwan is generally recognized as having active tectonics and high sediment deposition rates. In the Gaoping Slope, slope basins are formed by the developments of folds, faults and diapiric intrusions. Portions of the sediments discharged from the Taiwan mountain belt have been trapped in these basins in the Gaoping Shelf and Gaoping Slope. The rest of the sediments were transported to deep sea areas through submarine canyons. This complex system of folds, faults, diapirs, slope basins, submarine canyons, and sediment deposits has also readjusted the morphology of the Gaoping Slope. This study examines the linkage between accommodation spaces of tectonic and sedimentary processes in the Gaoping Slope through seismic facies analysis. Four seismic facies which include convergent-symmetrical facies, convergent-baselapping facies, chaotic facies, and parallel and drape facies, and different deposition patterns have been recognized in the Gaoping Slope basins. The thick mud layers which are regarded as the source of diapiric intrusions are first observed beneath the basin. Strata records show that the accommodation spaces in various slope basins have increased or decreased during different stages of basin evolution. Because of the competition between regional tectonism (accommodation space variations) and sediment routing distance from provenance to depository (sediment input variations), most under-filled basins lie in the lower slope domain in the Gaoping Slope, but also in the upper slope domain east of the Gaoping Submarine Canyon. This observation suggests that in the inner Gaoping Slope west of the Gaoping Submarine Canyon, sediment deposition rate is higher than the basin subsidence rate, the topography of the upper slope domain there is “healed”, and most sediments are overfilled in the slope basins now. Besides the sequential steps of sedimentary disposal in the filling-and-spilling model, we have also observed evidences which indicate that mass movements and submarine canyons in the area have significantly changed the sediment dispersal patterns in the slope basins of the Gaoping Slope. We suggest that although filling-and-spilling is a key sedimentary process in the Gaoping Slope, tectonic activities, mass wasting events and canyon feeding processes have diversified sediment transporting mechanisms from the inner to outer slopes in the area offshore Southwest Taiwan.