南黄海辐射沙脊群苦水洋DT05钻孔沉积相及环境演化

发布时间：2018-07-11 21:35

本文选题：沉积相 + 沉积环境演化　；参考：《南京大学》2014年硕士论文

【摘要】：南黄海江苏岸外海底,分布着巨大的辐射沙脊群,是中国大陆架浅海所特有的大型沙体组合,内部储存着丰富的海岸演变、河口环境、海面变化、气候变化以及海洋环境的各种环境信息,是研究陆海相互作用及全球环境变化的最理想载体。苦水洋内水下沙脊是南黄海辐射沙脊群东北部潮流堆积沙脊,属于开阔陆架潮流沙脊范畴,研究其全新世以来的沉积环境演变、成因机制,对了解整个辐射沙脊群的动态变化具有深远意义。 2011年11月,在南黄海辐射沙脊群苦水洋海域钻探了6根20-60m长柱样,4根1-1.5m长的短柱样,其中4孔在沙脊上,6孔在潮流通道中。本文选取位于苦水洋南部的柱状样11DT05孔(33°04.475'N,121°48.298'E)作为材料,该孔进尺深度36.97m,实际芯长22.20m,取芯率为60.05%,兼以浅柱样11DT(sc)02柱、11DT(sc)04柱、11DT(sc)05柱、11DT(sc)06柱为辅助,通过室内钻孔描述和岩性编录工作,对样品进行了粒度、210Pb、XRF岩芯扫描的测试和分析,结合14C测年、光释光测年,对苦水洋内水下沙脊的沉积相和长周期演变进行了综合分析,为港口建设提供重要参考资料。根据沉积物岩性、粒度、沉积结构和构造,以及所含生物化石进行沉积相分析,在11DT05孔共识别出4种沉积相类型： (1)潮流沙脊相：位于钻孔最顶部0-5.69m。主要由橄榄灰棕灰色细砂、青灰色粉砂质细砂、橄榄绿色粉砂质细砂以及粉砂组成,夹有棕灰色粉砂质黏土和青灰色黏土质粉砂。常见块状层理、压扁层理(或称脉状层理),以及波状层理,局部发育变形构造。含较多贝壳碎片、云母片,局部有炭屑富集。 (2)陆相硬黏土：该沉积相出现在11DT05孔的中偏上部5.69-6.49m,以杂斑状、花斑状黄棕色黏土、粉砂质黏土为主(质地细腻、致密、粘手)。发育极细的水平—微波状纹层(厚度lmm)。可见大量铁锈斑(大小1-5mmm)、细小植物根茎、以及分散状有机质条斑、铁质、钙质结核。 (3)高潮滩相：该沉积相出现在11DT05孔6.49-13.51m处,平均粒径6.21φ,砂平均含量为7.3%,粉砂平均含量约为75%,黏土平均含量为17.7%。由橄榄灰色深灰色黏土质粉砂、含黏土粉砂或黏土组成,夹薄层粉砂或透镜体状、斑状粉砂体,发育水平纹层(纹层厚度1mm)。 (4)中低潮滩相：该沉积相出现在11DT05孔下部13.51-22.20m,由青灰色粉砂、橄榄灰色粉砂质粗砂、暗黄棕色黏土质粉砂和少量细砂组成。普遍发育透镜状层理、脉状层理(或称压扁层理)和波状层理(砂/泥互层)构成的潮汐韵律层理。按照沉积特征,又可进一步分为中潮滩和低潮滩亚相。 11DT05钻孔沉积物主要由黏土、粉砂质黏土、黏土质粉砂、细砂质粉砂和少量细砂组成。粒度组成上,粉砂的含量最大,占76.13%；其次是砂,含量占19.82%；黏土含量最少,占3.6%。整个钻孔平均粒径在1.78～8.6φ之间波动,平均值为5.68φ；分选系数介于0.51～3.72之间,平均值为1.75,分选较差；偏态范围在-0.46～0.89之间,平均值为0.58；峰态在0.56～5.2之间波动,平均值1.21。4个浅柱样的沉积物全部为极细砂。平均粒径的平均值分布在3.22～3.56φ之间,颗粒较细；分选系数的平均值在0.57～1.41之间,分选较好；偏态平均值在0.02～0.06,近对称；峰态平均值在0.95～1.06,为中等峰态类型。11DT(sc)04柱和11DT(sc)06柱的粒度分布呈现一个上粗下细的沉积序列,反映出近期冲刷作用加剧。柱状样的210pb测试结果表明,潮滩上部的沉积速率介于0.47～3.42cm/a,中部沉积速率为0.16cm/a,下部无法获得沉积速率,反映了近30a来潮滩侵蚀加剧。苦水洋内水下沙脊钻孔长周期演化显示,从晚更新世以来从老到新依次经历了中低潮滩相→高潮滩相→陆相暴露(硬黏土)→潮流沙脊相。在约60-25KaBP晚更新世时期(氧同位素3.0期),进入玉木冰期,全球气候变冷,研究区经历了一个海平面下降过程,发育潮滩环境。在约25-2KaBP晚更新世晚期(氧同位素2.0期),进入晚玉木冰期,此时全球气候再次变冷,海平面又经历了一个下降过程,研究区完全暴露形成标志性的“硬黏土”层。全新世初期经历海侵,研究区复又开始潮滩沉积,随后被海水完全淹没,潮流作用渐强,改造下伏潮滩和“硬黏土”,塑造潮流沙脊地形。沙脊的形成年代可能在距今1-2KaBP左右。14C测年数据、光释光测年数据、210pb、XRF岩芯扫描测试和分析、粒度分析以及与浅柱样的分析对比为上述沉积环境的判别提供了证据。
[Abstract]:The outer seabed of the South Huangjiang river is a large group of radiant sand ridges, which is a large combination of large sand bodies in the shallow sea of China's continental shelf. It is the most ideal carrier for studying the interaction of land, sea and the global environment with abundant coastal evolution, estuarine environment, sea surface change, climate change and various environmental information of the marine environment. The sediment ridge in the bitter water ocean is a tidal sediment ridge in the northeast of the South Yellow Sea, which belongs to the category of tidal sand ridges in the open shelf. It is of profound significance to study the sedimentary environment evolution and the genetic mechanism since the Holocene, and to understand the dynamic changes of the whole radiation sand ridges.
In November 2011, 6 20-60m long columns and 4 1-1.5m long short columns were drilled in the sands of the Southern Yellow Sea, with 4 holes on the sand ridges and 6 holes in the tidal channel. This paper selects a column like 11DT05 hole (33 04.475'N, 121 48.298'E) located in the southern bitterwater ocean as a material. The depth of the hole is 36.97m, the actual core 22.20m, 22.20m, 22.20m core, 22.20m, actual core 22.20m, taken from the actual core 22.20m, taken from the actual core. The core rate is 60.05%, with a shallow column like 11DT (SC) 02 column, 11DT (SC) 04 column, 11DT (SC) 05 column and 11DT (SC) 06 column as auxiliary. Through the indoor borehole description and lithologic cataloging work, the samples are tested and analyzed for the grain size, 210Pb, XRF core scanning and the sedimentary facies and long period evolution of the underwater sand ridges in the bitter water ocean. A comprehensive analysis is made to provide important reference materials for port construction.
Based on sedimentary lithology, grain size, sedimentary structure and structure, and sedimentary facies analysis of the biologic fossils, 4 sedimentary facies types were identified in 11DT05 hole.
(1) tidal sand ridge facies: at the top of the borehole, 0-5.69m. is mainly composed of olive grey brown gray fine sand, green grey silty fine sand, olive green powder sand and silty sand, with brown grey silty clay and green grey clay silt. The structure consists of more shell fragments, mica sheets, and locally enriched with carbon dust.
(2) terrestrial hard clay: the sedimentary facies appeared in the upper middle partial 5.69-6.49m of the 11DT05 hole, with variegated porphyry, variegated yellow brown clay and silty clay (fine texture, dense, sticky). A very thin level of microwave like layer (thickness LMM). A large number of iron rust spots (size 1-5mmm), fine plant rhizomes, and dispersed organic strips were found. Spot, iron, calcareous tuberculosis.
(3) high tidal flat facies: the sedimentary facies appeared at 11DT05 hole 6.49-13.51m, with an average particle size of 6.21 phi, the average content of sand was 7.3%, the average content of silt was about 75%. The average content of clay was 17.7%. from olive gray dark grey clay silt, clay silt or clay, and thin layer silt or lens, porphyritic sandbody, and developed horizontal layer. Lamellar thickness 1mm).
(4) middle and low tidal flat facies: the sedimentary facies appeared in the lower part of the 11DT05 hole 13.51-22.20m, composed of green gray silt, olive grey powder sand, dark yellow brown clay silt and a small amount of fine sand. It can be further divided into middle tidal flat and low tide subfacies.
11DT05 drilling sediments are mainly composed of clay, silty clay, clay silt, fine sand silt and a small amount of fine sand. On the size composition, the content of silt is the largest, which is 76.13%, followed by sand, the content is 19.82%, the clay content is least, and the average diameter of the whole drill hole is between 1.78 and 8.6 phi, the average value is 5.68 phi, and the separation coefficient is 5.68. The average value is between 0.51 and 3.72, the average value is 1.75, the separation is poor, the partial range is between -0.46 and 0.89, the average value is 0.58, the peak state fluctuates between 0.56 and 5.2, and the average value of the 1.21.4 shallow column samples is all fine sand. The average particle size distribution is between 3.22 and 3.56 phi, the particle is fine, the average value of the separation coefficient is 0.57 The separation between 1.41 and 1.41 is better; the mean values are 0.02 ~ 0.06, near symmetry, the average of the peak state is 0.95 ~ 1.06, and the size distribution of the medium peak type.11DT (SC) 04 column and the 11DT (SC) 06 column shows a thick and thin sedimentary sequence, reflecting the recent scour effect plus the play. The 210Pb test results of the columnar sample show that the upper part of the tidal flat is deposited. The rate is between 0.47 and 3.42cm/a, the middle deposition rate is 0.16cm/a, and the lower part is unable to get the deposition rate, which reflects the erosion of the 30A tidal flat.
The long period evolution of the drilling hole length of the sand ridges in the bitter water ocean shows that from the late Pleistocene to the new period, the middle and low tidal flat, the high tide beach phase, the terrestrial exposure (hard clay) and the tidal sand ridge facies were experienced from the late Pleistocene to the late Pleistocene (3 phase of oxygen isotope), and the global climate became cold, and the study area experienced a sea level. In the late Pleistocene (2 phase of oxygen isotopes) in the late Pleistocene (2 stage of oxygen isotope), the global climate was again cooled, and the sea level experienced a decline process, and the study area was completely exposed to a marked "hard clay" layer. The early Holocene experienced transgression in the early Holocene, and the research area began to sink into the tidal flat again. The formation age of the tidal tidal flats and the "hard clay" and shaping the tidal sand ridge are likely to be formed at the date of 1-2KaBP.14C dating from the date, the 210Pb, the XRF core scanning and analysis, the grain size analysis and the analysis of the shallow column samples for the above deposition. The discrimination of the environment provides evidence.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P736.2

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