东海陆架全新统高分辨率层序地层学研究

在高分辨率１４Ｃ测年、岩石、生物、化学、同位素、气候及磁性地层学研究成果基础上,通过不同沉积背景典型钻孔的沉积学分析,运用层序地层学理论,对东海陆架全新统进行了高分辨率层序划分及对比;建立了全新世层序地层格架及海平面变化过程;提出了相应的层序成因模式。研究结果表明,东海陆架全新统相当于一个发育中的六级（１～１０ｋａ）层序,可进一步划分为３个七级（０．１～１ｋａ）层序和若干个更次级层序。代表１个六级或３个七级周期相对海平面变化过程中叠加有若干更次级的海平面波动,它们与地球旋回谱系中的太阳带、历法带密切相关。七级层序具有与三级层序相近的内部构型和成因格架。在东海陆架全新世沉积演化过程中,长江三角州至少有３次不同程度地越过东海陆架进入冲绳海槽,并滞留有至少３层海侵改造“残积砂”沉积。在东海陆架全新世海平面变化期间,最大海平面时期为约距今６～５ｋａ,大致高于现今海平面２～４ｍ,最低海平面在距今１０ｋａ左右,大约低于现今海平面１３０ｍ。目前,由于温室效应的影响,海平面仍呈小幅度波浪式上升。事实证明,层序地层学不仅丰富了现代海洋沉积学的内容,而且解决了许多海洋沉积学未能解决的问题。     

相对海平面变化与南海珠江深水扇系统的响应

根据微体古生物分析建立起来的珠江口盆地第三系相对海平面曲线,具有与全球海平面变化相一致的三级旋回和不一致的二级旋回。三级海平面升降导致了各沉积层序体系域在宽广陆架和陆坡之间的迁移,研究证实,位于南中国海北缘、珠江口外的陆坡深水区广泛发育第三系多层序叠置的南海珠江深水扇系统。区域性构造作用使得珠江口盆地二级海平面变化与全球海平面变化具有不一致性,并形成与全球海退趋势相反的海侵型海平面曲线。受相对海平面变化的控制,现今处于陆坡深水区的白云凹陷自32Ma南海扩张以来经历了三台阶式的海侵事件,形成了台阶式退积层序组合,具有下粗上细的沉积序列;造就了23.8Ma以前的浅水三角洲-滨岸砂泥岩沉积组合;23.8~10.5Ma的深水扇砂泥岩为主的沉积组合;以及10.5Ma以来主要为远端的细粒沉积为主。     

Oxygen Isotope Records of Core 8KL of the South China Sea and Sea-level Change1

Abstract Based on a comparison between the oxygen isotope records of benthic and planktonic foraminifers from core 8KL of the South China Sea and sea-level change records derived from the Huon Peninsula, New Guinea, it is found that both records are very similar from 72 Ka B.P. to the present, especially for the benthic oxygen isotope record. The linear regression shows that δ¹⁸O changes (0.9995‰ for benthic foraminifers and 1.022‰ for planktonic foraminifers) are equal to 100 m in sea-level fluctuation. After making temperature correction in the δ¹⁸O record of benthic foraminifers from 72 to 120 Ka B.P., the curve of sea-level oscillation of the South China Sea since 186 Ka B.P. has been reconstructed. The lowermost sea-level that occurred in the last glacial maximum and oxygen isotope stage 6 is approximately - 130 m.     

渤海南部莱州湾晚更新世以来沉积演化特征

晚更新世以来渤海南部莱州湾发生了3次重要海侵-海退事件及沉积演化过程,渤海南部多源河流三角洲对莱州湾沉积环境改变作用明显。本文选择莱州湾剖面进行沉积地层对比,结合调查资料和测试数据,初步建立莱州湾沉积地层格架,分析晚更新世以来莱州湾沉积演化过程。研究发现,渤海南部中小河流与黄河泥沙为莱州湾沉积物的共同物质来源,二者在不同阶段分别对莱州湾沉积演化起主导作用。提出本区沉积地层具有分期性、分段性和相关性规律。在124.6~72.0 ka B.P.,60.0~24.4 ka B.P.和10.2~4.0 ka B.P.出现过3次暖湿期,分别对应沧州海侵、献县海侵和黄骅海侵,主要发育滨浅海相沉积,向南退积为三角洲/潮坪—河流沉积;由陆向海,短源河流沉积贡献降低,黄河沉积贡献增加。在72.0~60.0 ka B.P.和24.4~10.2 ka B.P.出现2次冷干期,分别对应玉木早冰期和玉木晚冰期,河流相发育,三角洲进积。受海陆交互作用影响,晚更新世以来渤海南部莱州湾大致经历了浅海相—三角洲—潮坪—浅海相—三角洲—陆相的沉积演化。     

晚松山时南黄海的古长江三角洲

早更新世晚期(加拉米洛亚时开始到松山时结束)，中国东部陆架发生海侵。随着海侵的推进，在南黄海中部出现了较厚的三角洲沉积。在沉积层的垂直序列上，发现了分流河口沙坝、分流河道和分流河口间湾等三角洲前缘沉积亚相的交替。这是一个海侵序列的三角洲层序。在海侵进程中三角洲的进积速率与海水进侵速率基本平衡。南黄海晚松山时古长江三角洲的发现，从一个侧面证明了浙闽隆起带在早期第四纪仍然是继承晚第三纪的一个构造上的隆起及地貌上的屏障，它制约着古长江流向东北方向。     

Sediment distribution and provenance since Late Pleistocene in Laizhou Bay,Bohai Sea,China

There are three transgression-regression events and evolutions of the sedimentary environment by sea level changes since the Pleistocene in the southern section of the Bohai Sea, China. It is obvious that a multi-source fluvial delta sedimentary system may be more dominant in a sedimentary environment. Based on previous research and survey or historical data, we carried out studies on the division of sedimentary units, sedimentary facies analysis and strata division and comparison, which aim to establish the sedimentary stratigraph of Laizhou Bay. We focus on the sedimentary procession of the Laizhou Bay since the early Late Pleistocene. It can be divided into two glacial periods and three interglacial periods, corresponding to two regression and three transgression events in Laizhou Bay since Late Pleistocene. In 124.6–72.0 ka BP, 60.0–24.4 ka BP and 10.2–4.0 ka BP, three times warm-wet periods occurred, respectively corresponding to the Cangzhou transgression, Xianxian transgression, and Huanghua transgression. In 72.0–60.0 ka BP and 24.4–10.2 ka BP, two dry and cold periods, it was the continental sedimentary environment, corresponding to Wurm early glacier and Wurm late glacier. The results show: (1) Sediments have the characteristics of phase and stage under the terrestrial input of the Yellow River and middle-small rivers in the southern section of the Bohai Sea. (2) PI moved towards coastal in Cangzhou transgression strata in early Late Pleistocene. PI moved northward from land in Xianxian transgression strata in the late Pleistocene. PI moved further north in the Huanghua transgression strata in Holocene. (3) During the regressive period, the land source input increased and the estuarine or lagoon sedimentation developed, which manifested as progradational superposition. (4) During the transgressive period, it mainly developed shallow coastal sediment and transitionally formed regressive deposition to the south in delta/tidal flat deposition.©2019 China Geology Editorial Office.     

冰后期以来长江水下三角洲层序地层特征及沉积环境演化*

长江水下三角洲层序地层学研究有助于全面了解长江三角洲地层特征和沉积环境演化模式。通过对长江水下三角洲下切河谷区YD0901和YD0903孔岩心的详细沉积物粒度、特征元素比值(Cl/Ti和Zr/Rb)、沉积相对比分析,恢复了冰后期以来长江水下三角洲层序地层格架。研究区冰后期以来自下而上依次出现河流相、潮汐河流相、河口湾相、浅海相和三角洲相的沉积相序。末次冰期海平面下降,古长江形成下切河谷,古河间地发育硬黏土层,构成五级Ⅰ型层序界面。之后海平面回升,分别于15 cal ka BP和8.0 cal ka BP形成最大海退和最大海侵界面,水下三角洲区域最大海侵发生时间略滞后于平原区,约为7.5 cal ka BP。据此3个层序界面将冰后期地层划分为低位体系域、海侵体系域和高位体系域。钻孔岩心记录揭示了14.8 cal ka BP海侵到达研究区;14.8~13 cal ka BP期间,受MWP-1A冰融水事件影响海平面快速上升,海岸线向陆推进速率可达71.9,km/ka;海退期间各钻孔沉积速率较低,直至2 cal ka BP开始,沉积速率明显增加。     

晚更新世江苏海岸带沉积分布模拟研究

中国边缘海大陆架在晚更新世时期曾是海岸平原,在古长江、古黄河泥沙填充下形成了陆架堆积体,并在全新世发育了南黄海辐射沙脊群、废黄河三角洲和长江三角洲。根据点状的地质钻孔分析和重建,对南黄海-江苏海岸的沉积体系的分布和变化机制尚不明了。作为动力机制探讨,基于气候-海面-沉积系统,根据气候水文学、沉积学原理以及泥沙沉积面的动态高程计算,构建了气候冰川驱动-东黄海地海系统响应-河流沉积建造的数值模式,模拟了14万年、4万年和1万年不同时间尺度江苏海岸线和长江三角洲沉积的变化过程和分布,进而对冰川气候、构造沉降、沉积压实等复杂效应下的海面特征、陆源泥沙沉积和海岸线进行分析。模拟结果与地质钻孔资料揭示的层序和埋深能够进行对比。     

Sedimentary responses to the Pleistocene climatic variations recorded in the South China Sea

Grain-size analyses, coupled with end-member modelling, have been performed on the terrigenous fraction of two Leg 184 Ocean Drilling Program sites (1144 and 1146) from the South China Sea. The grain-size distributions over the last 1.8 Ma enable a new interpretation of their connections to sea-level variations and East Asian monsoon strength. Previous investigations in this area have associated grain-size variability with enhanced eolian input during glacial stages. End-member modelling downgrades the importance of this eolian contribution and indicates that the sediments can be described as a mixture of three end-members: fluvial mud inputs, shelf reworking and river mouth migration. Grain-size variations in the Pleistocene section of the cores indicate a multiple-stage evolution: (i) from 1.8 to 1.25 Ma, the downcore grain-size variations are low but show a correspondence between monsoon rainfall intensity and the fine grain-sized fluvial inputs; no link with sea-level variations is noticeable; (ii) from 1.25 to 0.9 Ma, there is an increase (decrease) in the intermediate (fine) end-member (∼ 100 kyr cycle) that is associated with the onset of a stronger summer monsoon and modest shelf reworking; (iii) from 0.9 to 0 Ma the grain-size record is dominated by global sea-level variations; each glacial stage is associated with extensive shelf reworking and conveyance of coarse particles to the basin.     

晚更新世末期东海北部古冬季风盛衰变更的地质记录

末次冰期最盛时期,干、冷气候盛行,渤海、黄海的大部分地区出现沙漠化,形成众多的沙丘。随着干冷气候的减弱,长江三角洲一带出现硬粘土沉积。冰消期的到来,古季风活动的进一步衰退和海面的不断升高,来自陆架区的东北风不再是干冷的气流,而是湿度逐渐增大的冷湿气流,出现了有利于沼泽发育的环境,以致全新世海侵前夕往往形成薄层泥炭沉积。晚更新世末期以来古冬季风发生、发展和衰退过程与沙漠、硬粘土和泥炭层形成过程相对应。      

黄河源区第四纪地质研究的新进展

通过对黄河源区的钻孔、自然露头的研究, 建立了黄河源区的第四纪地层层序。第四纪地层可划分为下更新统、中更新统、上更新统和全新统。下更新统为河湖相沉积; 中更新统主要有湖积物、冰碛物和冰水沉积物; 上更新统主要有湖积物、冰碛物、冰水沉积物、洪积物和河流沉积物; 全新统主要由河流沉积物、洪积物和湖积物构成。黄河源区的冰期可划分为3期, 即末次冰期、倒数第二次冰期、倒数第三次冰期, 末次冰期又可分为2个冰阶。黄河源区的湖泊演化可划分为早更新世、中更新世和晚更新世—全新世3个阶段: 早更新世的湖泊范围小; 中更新世的湖泊范围明显扩大, 在位置上也较早更新世的湖泊南移; 晚更新世的湖泊经历了两次的扩张—收缩变化, 到了全新世, 除现今还发育的几个湖泊外, 大多数地区的湖水已退出, 基本上转变为河流环境。在晚更新世末期到全新世初期, 封闭黄河源区的多石峡被切开, 湖水外泄, 现今的黄河形成了, 同时发生了袭夺长江水系的水流。     

长江三角洲第四纪海相介形虫的古环境意义

本文根据长江三角洲地区7个钻孔的介形虫化石群古生态的研究成果,并参考有关资料,讨论了该区第四纪海相介形虫的时、空分布及其古环境。文中指出,海相介形虫的分布与该区第四纪海侵层有关,它在距今约0.30Ma形成的海侵层中富集,上述结论与对中国东部沿海平原海平面研究所取得的认识(第四纪高海面仅在0.30Ma以来才表现明显)相一致。该区介形虫化石群的成分较渤海西岸稍多,可能与该地区易受外海影响有关;而它又比广东、福建、香港的化石群简单,这可能是气候、水温差异的表现。     

晚更新世末期北方陆架区沙漠-黄土堆积群的初步研究

晚更新世末期,强劲古季风活动的结果,在中国西部形成沙漠-黄土堆积群(黄土高原及其以西或西北的沙漠区),当它到达陆架区以后,风蚀作用继续存在,会产生同样的地质效果,因而在中国东部陆架区,形成两个新的沙漠-黄土堆积群。其一为渤海沙漠-黄土堆积群,包括渤海海底、渤海海岸一带的古沙漠活动区和辽东半岛西岸、庙岛群岛以及山东蓬莱以西的含有孔虫的黄土沉积。其二为黄海沙漠-黄土堆积群,包括苏北浅滩和长江三角洲地区全新世以前的沙漠活动区和南京一带的下蜀黄土。      

江苏沿岸辐射沙脊物源分析——来自碎屑重矿物与锆石年代学的证据

辐射沙脊是分布在我国江苏沿岸南黄海浅海内陆架上的一种特殊地貌,其沉积物质来源一直广受关注。通过原位微区X荧光光谱分析、重矿物统计学以及碎屑锆石年代学等方法,对江苏沿岸辐射沙脊开展物源分析。结果表明辐射沙脊的重矿物组合为角闪石—绿帘石—铁氧化物,并且角闪石为绝对优势矿物（平均含量55.06%）,其含量远大于绿帘石（平均含量20.71%）。这与长江中重矿物特征相似（角闪石平均含量46.05%,绿帘石平均含量24.69%）。碎屑锆石U-Pb年龄显示出了5个主要的年龄区间及峰值,依次为160~330 Ma（占22.89%,峰值为~200 Ma）;350~550 Ma（占18.61%,峰值为~430 Ma）;650~1 200 Ma（占29.32%,峰值为~750 Ma）;1 700~2 000 Ma（占10.58%,峰值为~1 850 Ma）和2 400~2 600 Ma（占5.09%,峰值为~2 500 Ma）。结合重矿物组分数据和锆石年龄谱分析,并与各潜在源区进行对比,认为辐射沙脊的碎屑重矿物特征以及锆石年龄与长江最为相近,指示长江作为辐射沙脊最主要的物质源区。此外,古黄河三角洲的沉积物显示出对江苏沿岸北部沙脊沉积具有一定的影响,而现代黄河可能对辐射沙脊最北缘提供了沉积物质,该物源分析结果反映了南黄海的海流系统在辐射沙脊搬运沉积体系中起到重要作用。     

南黄海沉积物磁性特征及其对物源变化的指示 ——以南黄海中部泥质区YSC-10孔为例

南黄海中部泥质区是东亚大陆沉积物巨大的汇,识别这一地区的物源变化对理解古气候和古海洋变化有重要作用.基于黄河和长江携带的碎屑物质在磁性特征上的差异,环境磁学参数、磁化率—中值粒径的相关性可用于指示南黄海中部泥质区物源的可能变化.根据YSC?10孔环境磁学参数变化和磁化率—中值粒径的相关关系,推测4.8 cal ka B...     

鲁北平原晚第四纪地层结构及沉积演化

以54个浅层新钻孔和多个野外露头为研究对象,综合沉积物粒度、薄片、微体古生物、孢粉、14C测年及静力触探等资料,分析了鲁北平原晚第四纪的地层结构和沉积类型,总结了晚更新世晚期以来的沉积演化。研究表明,末次冰期盛冰期到冰后期,受地势、气候条件控制的黄河河道迁移和海水进退是影响地层结构和沉积特征的主要因素,南北地层结构差异明显,发育古河道、湖沼、黄土、三角洲、潮坪和滨浅海等沉积类型,其中古河道分布面积最广,自下而上可划分为三期。晚更新世晚期至早全新世早期,受干冷气候影响,发育第Ⅰ期古河道,小清河以南沉积黄土层;早全新世晚期至中全新世,气候转暖导致海平面升高,沿海地区形成海侵层和三角洲,内陆地区继承性发育第Ⅱ期古河道和湖沼沉积;中全新世末期或晚全新世以来,受黄河泛滥影响,沉积第Ⅲ期古河道和现代黄河三角洲。地层结构和沉积物分布的研究对于分析地下水位的变化规律,以及选择合适的地震激发层等均有重要的指导意义。     

辽宁省海岸带主要河口区一万年来沉积速率及海平面波动情况

采用钻探手段,通过14C、OSL测年,利用4孔岩心,计算了辽宁省海岸带主要河口区一万年来沉积速率,并分析了海平面波动情况.研究表明,辽宁海岸带长期平均的河口海岸区的沉积速率较低.其中,辽东半岛东北部黄海海岸带鸭绿江平原全新世早期处于剥蚀环境,大洋河平原全新世平均沉积速率为1.4 mm/a,辽东湾北部下辽河平原全新世平均沉积速率为1.52 mm/a,辽西海岸带大凌河冲积扇全新世平均沉积速率为1.87mm/a.全新世Ⅰ海相层或海陆过渡相层总体上表现为一次海侵,与下辽河平原区盘山海侵相对应,但各地段海平面波动情况不尽一致.     

reconstruction of the holocene coastline of mesopotamia

At the end of the last glacial period, a major marine transgression inundated the head of the Persian Gulf to a position as much as 400 km inland from the present shoreline. After 6000 B.P., the Shatt al-Arab delta prograded southward to its current position. These events had a profound impact on our knowledge of early human occupation and the development of civilization in the Tigris-Euphrates valley. The former settlements of people living on the pre-6000 B.P. coastal plains are today either under the waters of the Gulf or under sediments of the lower alluvial plain.     

Quaternary sedimentation of the Alaskan Beaufort shelf: Influence of regional tectonics, fluctuating sea levels, and glacial sediment sources

The offshore stratigraphy of the Quaternary Gubik Formation of Arctic Alaska has been studied on high-resolution seismic profiles with a maximum sub-seafloor penetration of about 100 m. In general, marine transgressive subunits of the Gubik Formation are wedge-shaped on the shelf, thickening slightly seaward to the shelf break, beyond which they are offset by landslides and slumps. Beneath the eastern third of the Alaskan Beaufort shelf, active folding has created two persistent structural depressions, the Eastern and Western Wedge Terranes, in which the wedge morphology is especially well developed. The youngest transgressive marine wedge, which was deposited in such a way as to fill these depressions, leaving a generally flat present-day shelf surface, is inferred to be late Wisconsin or younger in age because it overlies a prominent disconformity interpreted to have been formed during the late Wisconsin glacial sea-level minimum. The thickness of this youngest wedge, Unit A, locally exceeds 40 m on the outer shelf, yet apparently relict gravel deposits collected from its seabed surface indicate that the depositional rate is presently quite low on the middle and outer shelf. Lithologies of the gravels are exotic to Alaska, but similar to suites exposed in the Canadian Arctic Islands. These observations suggest a depositional scenario in which the retreating Laurentide Ice Sheet shed sediment-laden icebergs from the Canadian Arctic Islands into the Arctic Ocean following the late Wisconsin glacial maximum. These bergs were then rafted westward by the Beaufort Gyre and grounded on the Alaskan shelf by northeasterly prevailing winds. Especially large numbers of bergs accumulated in the wedge terrane embayments—created as sea level rose—and melted there, filling the embayments with their sedimentary cargo. As glacial retreat slowed, depositional rates on the shelf dwindled.This mode of deposition in the Alaskan Beaufort wedge terranes may be typical of early post-glacial transgressive phases throughout Quaternary time. It has resulted in the preservation of disconformities that apparently formed during glacioeustatic lowstands, and whose seaward termination depths, appropriately corrected, may yield estimates of lowstand magnitudes. Knowledge of global sea-level fluctuations back through the Sangamon Interglacial (oxygen isotope stage 5e) and possible correlations with dated onshore deposits have facilitated a tentative correlation of major disconformities in the Beaufort Sea record with major ¹⁸O enrichment maxima in the oxygen isotope curve back through stage 8. In this tentative scheme, close similarities between the two data sets occur both in magnitudes and in numbers of fluctuations intervening between major correlation points. Further testing of the Quaternary depositional model suggested here and of the resulting sea level curve awaits the collection and dating of core samples from the Beaufort wedge terranes.     

渤海西部晚第四纪地层层序特征及沉积响应

渤海是一个仅通过渤海海峡与北黄海相接的半封闭陆架浅海,晚第四纪以来的地层演化过程复杂,目前尚不清楚,且海相地层的形成时代存在争议.为了研究渤海西部晚第四纪以来的地层层序,对高分辨率浅地层剖面声学地层与典型钻孔沉积地层的进行对比分析.研究表明:高分辨率浅地层剖面自下而上划定的7个声学地层单元（U5、U4-2、U4-1、U3、U2、U1-2、U1-1）与钻孔岩心划分的沉积地层单元具有良好的对应关系.与MIS4期、MIS2期低海面时期的沉积间断密切相关的两个层序界面R5、R3,将渤海西部晚第四纪（MIS5期）以来的地层层序自下而上划分为3个层序（SQ3、SQ2、SQ1）:SQ3识别出下部海侵体系域与高水位体系域、上部海退体系域,分别对应MIS5期海平面相对较高时期的滨-浅海相交替沉积（U5）、MIS4期早期滨海相沉积（U4-2）;SQ2自下而上由低水位体系域[MIS4期中晚期与黄河、滦河相关的河湖相沉积（U4-1）]与海侵体系域[MIS3期早中期滨海相沉积（U3）]组成;SQ1自下而上包括低水位体系域[末次冰盛期与滦河相关的河湖相沉积（U2）]、海侵体系域[全新世早中期滨海相沉积（U1-2）]高水位体系域[全新世高海面以来的浅海相沉积（U1-1）].研究区的地层发育受控于海平面变化、沉积物供应、渤海海峡地形及活动构造的共同作用.