南海西北次海盆西北陆缘深水沉积体系及其演化研究

发布时间：2018-06-30 02:32

本文选题：深水沉积体系 + 底流　；参考：《中国地质大学》2014年博士论文

【摘要】：深水(水深200m)沉积物中能够记录有关深水动力学、古海洋学、古气候学等方面的丰富信息,“深水沉积体系研究”的相关领域日益受到全世界范围沉积学、海洋学、气候学研究人员的高度关注。目前,中国南海的深水沉积研究是主要集中在古海洋学和古气候学方面的,但是缺乏对深水沉积体系(尤其是等深流沉积体系)发育演化所涉及的地质学、海洋学等信息的系统分析。本文通过高分辨率二维地震、测井等地球物理学资料以及海水电导、温度、盐度等物理海洋学资料,描述南海西北次海盆西北陆缘约700-3500m水深范围的深水沉积体系特征,总结不同类型深水沉积体系内部构成及空间展布规律,并分析、研究其形成发育过程中的控制因素和演化机制。 1.本文研究区地处海南岛以东、西沙群岛以北(东经113°-114。30'；北纬18°-19°30'),海域面积约1×104km2。研究区北部为珠江口盆地南部隆起区,西南部是西沙海槽,东南部属于西北次海盆深海平原。珠江口盆地南部隆起区出露两处海山,名为一统暗沙(水深700-1000m)和神狐南海山(水深1100-1300m)。两处海山相距约50km,出露形态在平面上均为长轴呈WSW-ENE的椭圆形。神狐南海山长轴方向出露山体规模约为26.5km,短轴方向约为6km；一统暗沙长轴方向规模约为16km,短轴方向约为8km。本文所采用的数据包括南海西北次海盆西北陆缘-深海平原结合带的高分辨率二维地震、测井等地球物理学以及海水电导、温度、盐度等物理海洋学资料。 2.描述了在西北次海盆西北陆缘区陆坡上发育的不同类型深水等深流和重力流沉积体系特征。高分辨率二维地震资料显示：(1)一统暗沙和神狐南海山附近的宽缓陆坡上(水深约700-1500m,平均坡度1.2°)发育独具特色的“海山相关等深流沉积体系”,包括环槽(moat)、伸长状-丘状漂积体(elongated-mounded drifts)、黏附型漂积体(plasterd drifts)、等深流沉积水道(contourite channels)、犁沟(furrows)等。(2)珠江口盆地南部隆起区以南水深约1500-2500m陡峭陆坡(平均坡度2°)广泛发育重力流坡移沉积(mass-wasting deposits),频繁见垂直陆坡方向展布的深水“无头型”峡谷,构成重力流“坡移沉积体系”和“峡谷沉积体系”。(3)西北次海盆西北陆缘下陆坡区(水深2500m),坡度稍缓(平均坡度1.5°),坡移现象明显减少,普遍发育等深流沉积席状漂积体(sheeted drift)。该区主要发育“等深流沉积体系”和“峡谷体系”。 3.精细刻画了“海山相关等深流沉积体系”中环槽、伸长状-丘状漂积体、黏附型漂积体、等深流沉积水道、犁沟和无沉积区等沉积／侵蚀单元的外部形态和内部构成。“环槽”指底流侵蚀作用下,沿海山／陆坡坡脚形成的下凹地形；研究区内见环槽沿一统暗沙和神狐南海山北侧坡脚发育,宽度约2-5km,环槽底为光滑而平坦的侵蚀(负)地形,深度变化从约15m至超过100m。“伸长状-丘状漂积体”指与环槽共生的、由底流沉积作用形成的伸展状堆积物；研究区伸长状-丘状漂积体主要发育在环槽北侧的宽缓陆坡上,其沉积厚度的变化范围较大(从100ms TWT至超过500ms TWT);地震相主要表现为极连续、平行-亚平行、中-高振幅的反射特征。“黏附型漂积体”指受低速率水流活动控制的、通常发育在较缓陆坡上的堆积体；研究区内在神狐南海山北壁和一统暗沙南壁上分别发育一套黏附型漂积体,沉积厚度分别为200ms TWT左右和100ms TWT;其地震相表现出低振幅、连续性较弱、平行-亚平行的反射特征。“等深流沉积水道”指由底流侵蚀作用产生的、平行于陆坡方向展布的下凹地形；研究区内所发现的等深流沉积水道主要发育在神狐南海山以北(环槽北侧)的伸长状-丘状漂积体沉积中,以及神狐南海山以东的宽缓陆坡上；水道宽度约2-10km,下切深度变化范围从10m至60m不等。“犁沟”特指由底流侵蚀作用形成的、沿陆坡方向展布的、下切深度小于10m的侵蚀地形；研究区内所见的犁沟主要发育在神狐南海山北侧(环槽北侧)的伸长状-丘状漂积体沉积中。“无沉积区”指在稳定底流活动作用下的“过路不沉积”区域,主要在神狐南海山以东的宽缓陆坡上出现。 4.分析了研究区海山附近等深流沉积/侵蚀单元的形成发育与南海中层水(反气旋式环流,水深范围从约350m至1500m或更深,水温约5℃)底流活动之间的关系。北半球海山地形附近(即本文中水深范围约700-1000m的一统暗沙和约1200-1400m的神狐南海山),自西向东的水流(即南海中层水底流)受科氏力右转作用,在海山北侧受到地形限制,水流速度大幅增加,发生侵蚀作用；海山南侧区域受到山体地形的“遮挡”,水流速度渐渐减小,发生沉积作用。由此可知,海山北侧水流侵蚀能力强,可沿海山北缘山脚形成环槽；环槽北侧的陆坡则接受沉积,发育伸长状-丘状漂积体；环槽中水流随地形变化而速度减缓时,可在环槽南侧(神狐南海山北缘)发育黏附型漂积体；同一侧(海山以北)远离海山的底流活动未受到地形限制,可在环槽北侧的伸长状-丘状漂积体沉积中形成常规的等深流沉积水道或犁沟。海山南侧区域主要接受底流活动的沉积作用,形成沉积区；一统暗沙南壁上可见黏附型漂积体。随着底流经过并离开海山区的隆起地形,底流活动的能量、速度逐渐恢复至常态,环槽逐渐消失；至神狐南海山东侧宽缓陆坡(水深约1100-1300m)处主要发育常规的等深流沉积水道,以及“过路不沉积”的特征。 5.通过海底地形和二维地震测线等资料,在研究区识别出10条陆坡限制型(无头型)峡谷后对其编号,并且详细描述其外观形态和内部结构特征。除下部陆坡(水深约3000m)处的两条峡谷(峡谷9和10)以外,其它峡谷均呈NNW-SSE方向展布,延伸长度超过20km,峡谷宽度约2-30km,最大下切深度变化范围从十几米至超过900m不等。峡谷9和10延伸长度较短(约3km),宽度较窄(6km),但下切深度均超过200m。深水无头型峡谷形成过程中,受到低位体系域和陆架边缘下切谷侵蚀影响的可能性极小；其成因机制更可能受“退后型滑移/滑塌”作用或与断层相关的构造活动所控制。峡谷5在水深约1350坡度约1°处呈NNW-SSE走向,宽度约6.5km,下切形态呈不对称V型,下切深度约140m；在峡谷内部沉积结构中可识别出晚中新世(T4,11.5Ma)以来连续发育的峡谷侵蚀界面,表现为连续、高振幅的地震反射特征；晚中新世以来的峡谷侵蚀界面具有明显向ENE方向的迁移特征,指示该峡谷体系可能受持续的、较强烈的、自西向东的底流活动的改造作用,从而导致峡谷体系强制性向东迁移；上述自西向东的底流活动与附近深度范围内形成“海山相关等深流沉积体系”的水流活动方向一致,很可能同属南海中层水循环。峡谷5以西约15km处的中部陆坡(水深约1500-2500m)上发育峡谷6,该峡谷在水深约1790m、坡度约2°的位置表现出具有平坦峡谷底的U型下切形态(下切深度约135m,峡谷宽度约4km)；峡谷两侧发育丘状天然堤沉积,沉积物表现出高振幅且相当连续的地震反射特征,且晚中新世以来自下而上表现出加积型的沉积序列;峡谷ENE一侧的天然堤沉积表现出平行-亚平行的地震反射特征,而WSW一侧的天然堤沉积中出现明显的波状沉积特征。波状沉积物表现出波状、极连续且相互平行、中-高振幅的地震反射特征；波形完整,具有中等尺度规模(波长小于2km而波高小于60m)；各波形之间具有相似的内部反射特征,整体表现出沿陆坡方向向上(NNW方向)的迁移现象；根据所上述波状沉积物的发育位置和沉积特征,推测其属于浊流沉积物波。 6.揭示了研究区水深约1500-2500m范围内,陡峭陆坡(平均坡度2°)处沉积过程与重力流作用的关系。该范围坡度大,沉积环境不稳定,广泛发育重力流坡移沉积和无头型峡谷沉积。鲜见等深流沉积,一方面可能因底流活动弱,不足以造成沉积／侵蚀记录；另一方面可能因频繁的重力流活动对底流沉积记录反复破坏,以至于无法通过二维地震资料识别。通过地震沉积学记录,在该范围内的坡移沉积区中可识别出连续叠加滑塌体、失稳滑动面、滑移痕和分离滑塌体等沉积单元。而且本区罕有地震活动,未现天燃气水合物或油气强烈富集,故推测“陡峭陆坡”很可能是诱发大规模陆坡失稳,进而发生坡移的决定性因素。 8.查明了西北次海盆西北陆缘研究区深水沉积体系发育演化的重要控制因素。研究区陆坡形态自东向西的明显变化(逐渐变陡),以及不同深度范围南海洋流活动方向、强度的差异,都是控制该区深水沉积体系发育演化的重要因素。研究区东部陆坡形态表现出三级“分阶”的轮廓,上部Ⅰ型阶(水深1500m)和下部Ⅲ型(水深2500m)均为坡度较缓的陆坡(平均坡度小于1.5°),主要发育等深流沉积/侵蚀单元；中部Ⅱ型阶坡度大(平均坡度2°),主要发育峡谷沉积和坡移沉积。三级分阶状的轮廓向西逐渐消失,变为“Ⅰ缓-Ⅱ陡“的二级分阶；上部Ⅰ型阶主要发育等深流沉积水道以及底流“过路不沉积”的无沉积区；下部Ⅱ型阶主要发育坡移沉积和峡谷沉积；不发育Ⅲ型阶及相关等深流席状漂积体沉积。最终在研究区西部陆坡,陆坡轮廓演变为无分阶、整体陡峭的单一Ⅱ型陆坡；水深1500m以上为神狐南海山南壁,水深2500m及以下为西沙海槽北壁),至此深水沉积体系仅发育坡移沉积和峡谷沉积。 9.根据精细的地震沉积学记录,针对本文研究区水深1500m之上陆坡处所发育的等深流沉积／侵蚀特征,提出了“西北次海盆西北陆缘区深水等深流沉积的发育演化最早可追溯至晚中新世早期”。从不整合界面T4(11.5Ma)自下而上至现今海底沉积物中,利用地震相差异特征识别出六个地震沉积单元(沉积单元1-6)。自沉积单元2底界面向上至现今海底,可见持续、稳定发育的等深流沉积／侵蚀特征(加积型序列),暗示南海西北次海盆西北缘陆坡区的稳定底流作用可追溯至晚中新世早期。通过分析、对比神狐南海山附近晚中新世以来沉积物的地震相特征,发现随着海山逐渐被掩埋,海山地形对水流的限制、加速作用也逐渐消失；之后底流活动将呈常规状态持续作用于海底,早期所发育的、极具特色的环槽逐渐被常规的等深流沉积水道取代。海山出露-被掩埋的过程明显控制了其周缘等深流沉积的发育类型；反之,等深流沉积的内部构成也反映了海底地形——特别是海山地貌由出露向被掩埋消失的变化过程。综上,深水沉积体系研究为物理海洋学和海洋沉积学之间的学科交叉研究搭建了新的桥梁,更为南海新生代古海洋学和深海动力学研究提供了新资料。
[Abstract]:Deep water (water depth 200m) deposits can record abundant information about deep water dynamics, paleoceanography, paleoclimatology and so on. The related fields of "deep water depositional system research" are increasingly concerned with the worldwide sedimentology, oceanography and Climatology researchers. At present, the study of deep water deposits in the South China Sea is the main focus. In the field of paleoceanography and paleoclimatology, there is a lack of systematic analysis of geology, oceanography, and other information about the development and evolution of the deep-water depositional system (especially the sedimentary system). In this paper, geophysical data such as high resolution two-dimensional earthquakes, logging, and other physical oceanographic data, such as seawater conductivity, temperature, salinity and so on, are used in this paper. The characteristics of the deep water depositional system of the northwest continental margin of the northwest sub sea basin of the South China Sea are described in the depth of 700-3500m water depth. The internal structure and spatial distribution of different types of deep-water sedimentary systems are summarized, and the control factors and evolution mechanisms in the process of formation and development are analyzed.
1. the study area is located in the east of Hainan Island, north of Paracel Islands (113 degree -114.30'of Dongjing and 18 -19 30' in north latitude), the north of the study area about 1 x 104km2. area is the southern uplift area of the Pearl River Mouth Basin, the southwest is the trough, the southeast belongs to the northwest Basin deep sea plain, and the southern uplift area of the Pearl River Mouth Basin shows two seamounts. It is named as 700-1000m and Shenhu Nanhai mountain (water depth 1100-1300m). The two seamounts are about 50km, and the outcropping form is WSW-ENE oval on the long axis. The long axis of the Shenhu Nanhai mountain is about 26.5km and the short axis is about 6km; the direction of the dark sand long axis is about 16km, and the short axis is about 8km. Ben. The data used in this paper include the high resolution two-dimensional earthquake of the northwest continental margin of the northwest sub sea basin of the South China Sea, the geophysics such as logging, and the physical oceanographic data of sea water conductivity, temperature, salinity and so on.
2. the characteristics of deep and gravity flow depositional systems of different types of deep water developed on the continental slope of the northwest continental margin of the northwest sub sea basin were described. The high resolution two-dimensional seismic data showed that (1) the wide slow continental slope in the vicinity of the unified dark sand and the Shenhu Nanhai mountain (the depth of water depth is about 700-1500m, the average slope 1.2 degrees) developed unique "sea mountain related deep flow". The depositional system includes moat, elongated-mounded drifts, plasterd drifts, contourite channels, furrows, etc. (furrows). (2) the slope of the southern uplift of the Pearl River Mouth Basin is widely developed by the deep slope of a steep slope of 2 degrees in the southern water depth of the Pearl River Mouth Basin (the average slope of the slope). Mass-wasting deposits, frequently seen the deep water "no head" Canyon in the direction of vertical slope, constitutes the gravity flow "slope shifting depositional system" and "Canyon depositional system". (3) the northwestern sub basin northwest continental margin lower continental slope area (water depth 2500m), the slope is slightly slow (flat gradient 1.5 degrees), the slope shift phenomenon is obviously reduced, widespread development and so on deep flow sedimentation Sheeted drift. The area mainly develops "equal deep flow depositional system" and "Canyon system".
3. a fine depiction of the slots, elongate collucreting collucreting bodies, adhesion type drifting bodies, and the external morphology and internal composition of the sedimentary / erosion units such as ploughing and non depositional areas are carefully depicted in the "seamount related equal deep flow depositional system". In the study area, the width of the slots and the north side slope of the South China Sea Mountain of Shenhu is about 2-5km, and the bottom of the ring groove is smooth and flat erosion (negative) topography. The depth changes from about 15m to more than 100m. "extensional collucret", which refers to the extensional deposits formed by the bottom flow deposition with the ring trough, and the extensional hillock in the study area. The drifting bodies are mainly developed on a wide slow continental slope north of the ring trough, with a large range of variation in sedimentary thickness (from 100ms TWT to more than 500ms TWT), and the seismic facies are characterized by very continuous, parallel subparallel, medium to high amplitude reflection characteristics. "Adhesive type drifting" refers to low rate flow activity, usually developed on a slower slope. A set of adherent drifting bodies developed separately in the north wall of the South China Sea and the southern wall of the yunu Sands of Shenhu, respectively. The sedimentary thickness is about 200ms TWT and 100ms TWT, respectively, and the seismic facies show low amplitude, weak continuity and parallel subparallel reflection characteristics. In the study area, the equal deep flow sedimentary waterways found in the study area are mainly developed in the elongate collucret deposits of the north side of the South China Sea (the north side of the ring trough) and on the broad gentle slope east of the South Sea Mountain of Shenhu; the width of the waterway is about 2-10km and the range of the lower cutting depth varies from 10m to 60m. " The gully is mainly formed by the erosion of the bottom flow, along the slope direction, the erosion terrain is less than 10m, and the furrows in the study area are mainly developed in the elongated Qiu Zhuangpiao's deposit on the north side of the South China Sea Mountain (the north side of the ring trough). "No sedimentary area" refers to "no deposition" under the action of stable underflow. The area appears mainly on the wide slope of the east of Shenhu Nanhai mountain.
4. the relationship between the formation and development of the deep stream deposition / erosion unit near the seamount in the study area and the bottom flow of the South China Sea middle layer water (anti cyclonic circulation, water depth range from about 350m to 1500m or deeper, and water temperature about 5 degrees C). Nan Haishan), the flow of water from the west to the East (that is, the middle sea bottom flow in the South China Sea) is affected by the Coriolis force, which is restricted by the terrain on the northern side of the seamount, and the velocity of the flow is greatly increased and the erosion action occurs. The southern region of the seamount is "blocked" by the terrain of the mountain, and the velocity of the flow is gradually diminished and deposited. Thus, the erosion of the north side of the seamount can be seen. With strong force, the ring groove can be formed along the foot of the northern margin of the seamount; the continental slope on the north side of the ring groove is deposited and develops the elongate - collucreting body. When the velocity of the water flow in the ring groove slows down with the terrain, the adhesive type drifting body can be developed on the south side of the ring trough (the northern margin of the South China Sea, the South China Sea), and the undercurrent activity far away from the seamount on the same side (north of the seamount) has not been subjected to the topography. Limiting the formation of conventional equal deep flow sedimentary waterways or ploughs in the elongated collucret deposits on the north side of the ring trough. The southern region of the seamount mainly receives sediment from the undercurrent activity and forms a sedimentary area. The energy is gradually restored to normal, and the ring groove is gradually disappearing, and to the slow continental slope of the Shandong side of the South China Sea in the South China Sea (the depth of water is about 1100-1300m), the conventional equal deep flow sedimentary waterways are mainly developed and the characteristics of "non deposition".
5. through the data of the seabed terrain and the two-dimensional seismic survey lines, the number is numbered after identifying 10 continental slope restricted canyons, and its appearance and internal structure characteristics are described in detail. Except for the two canyons (Canyon 9 and 10) at the lower slope (water depth about 3000m), the other canyons are distributed in the direction of NNW-SSE and extend long. The width of the canyon is about 2-30km, the width of the maximum cutting depth varies from more than 10 meters to more than 900m. The 9 and 10 Canyon length of the canyon is short (about 3km) and the width is narrower (6km), but the depth of the cutting is more than in the formation process of 200m. deep water Canyon, and the possibility is very little by the low body region and the erosion of the grain cutting under the continental shelf. Its genetic mechanism is more likely to be controlled by the "backward slip / slide" or the tectonic activity associated with the fault. The canyon 5 has a NNW-SSE direction at about 1350 slope at about 1 degrees, the width of which is about 6.5km, the undercut form is asymmetrical V, and the lower cutting depth is about 140m; in the inner sedimentary structure of the canyon, the late Miocene (T4,11.5Ma) can be identified. The continuous development of the canyon erosion interface is characterized by continuous and high amplitude seismic reflection, and the erosion interface of the canyon since the late Miocene has a distinct migration characteristic to the ENE direction, indicating that the canyon system may be sustained, stronger, from west to East, thus leading to the mandatory eastward migration of the Canyon system. The movement of the bottom flow from the west to the East is consistent with the flow direction of the "seamount related deep flow depositional system" in the vicinity of the depth range. It is likely to be the same as the middle sea water cycle in the South China Sea. The central slope (about 1500-2500m depth of water depth about 15km) at the 5 West of the canyon is developed in the canyon, and the canyon is about 1790m in depth and about 2 degrees in the slope. U undercut forms with flat Canyon bottom (lower cutting depth is about 135m and Canyon width about 4km); both sides of the canyon are deposited with a hilly natural embankment, and the sediments show high amplitude and quite continuous seismic reflection characteristics, and the late Miocene epoch shows a sedimentary sequence from lower up and up, and a natural dike deposit table on the side of the canyon's ENE side The seismic reflection characteristics of parallel sub parallel are present, and there are obvious wave depositional features in the natural dike deposits on one side of the WSW. The wavy sediments are wavy, very continuous and parallel to each other, with medium and high amplitude seismic reflection characteristics; the wave form is complete, with a medium scale scale (the wave length is less than 2km and the wave height is less than 60m); the waveforms are between the waveforms. With similar internal reflection characteristics, the migration in the direction of the slope upward (NNW direction) is shown as a whole. According to the development position and sedimentary characteristics of the above wavy sediments, it is presumed to belong to the turbidite sediment wave.
6. the relationship between the sedimentation process and the action of gravity flow in the steep slope (average slope 2 degrees) is revealed in the area of the study area. The slope is large, the sedimentary environment is not stable, the gravity flow slope deposit and the no head Canyon deposit are widely developed. There are few deep current deposits. On the one hand, it may be weak and not enough to cause deposition. On the other hand, the sedimentary records of undercurrent deposits may be repeatedly destroyed by frequent gravity flow activities so that it can not be identified by two-dimensional seismic data. Through seismic sedimentology records, continuous superposition slip bodies, unstable sliding surfaces, slip marks and separate slide bodies can be identified in the sedimentary area of this range. In addition, there are few seismic activities in this area, and the gas hydrate or oil and gas enrichment is not very strong in the present day. Therefore, it is presumed that the "steep slope" may be the decisive factor to induce the instability of the large scale slope and then the slope shift.
8. the important control factors for the development and evolution of the deep-water depositional system in the northwest continental margin research area of the northwest sub sea basin are identified. The obvious change (gradually steepening) from east to West in the study area and the direction of the South China Sea flow in different depths and the difference in intensity are important factors for controlling the development and evolution of the deep water depositional system in this area. The eastern slope of the region shows the outline of three grade "sub order". The upper part I (water depth 1500m) and the lower third type (water depth 2500m) are both gentle slope of the slope (the average slope is less than 1.5 degrees), the main development equal deep flow deposition / erosion unit, the middle grade II order slope is large (the average slope 2 degree), the main development Canyon deposition and slope migration deposit. Three grade. The outline of the fractional order gradually vanished westward to the two order of "I slow - II steepness"; the main development of the upper part I was the main development of the deep flow sedimentary waterway and the undeposited undeposited region of the underflow, and the lower stage II type was mainly developed by slope deposits and Canyon deposits; Finally, in the western slope of the study area, the silhouette of the continental slope evolved into an undivided, unitary and steep single type of continental slope; the depth of water was more than 1500m of the south south wall of the Shenhu Nanhai mountain, and the depth of water was 2500m and below the north wall of the Xisha trough. At this point only the sedimentary and Canyon deposits were developed in the deep water system.
9. according to the fine seismic sedimentology records, the deep deep flow sedimentation in the northwest continental margin of the northwest sub basin was put forward in view of the characteristics of the equal deep flow deposition and erosion developed on the slope above the water depth of 1500m in this study area.
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P736.21

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