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1.
Reinhardt L. Kudrass H.-R. Lückge A. Wiedicke M. Wunderlich J. Wendt G. 《Marine Geophysical Researches》2002,23(4):335-351
About 6000 km of both bathymetric and high-resolution acoustic profiles were acquired on the shelf and upper slope offshore Peru between 9° S and 14° S. Two new sediment echosounder systems – SEL-96 and SES-2000DS – provided details of the sedimentary structures of the Quaternary sequences within the Sechura-Salaverry, Huacho and Pisco Basins. To a great extent, the poleward undercurrent determines the distribution of sediments. The undercurrent has generated numerous erosional unconformities, it has winnowed hardgrounds and has created mudwaves common between 250 m and 400 m water depth. Distinct subbottom reflectors within sedimentary units represent hiatuses due to periods of intensified winnowing or non-deposition. Erosional unconformities usually marked by pronounced reflectors suggest shifts of the undercurrent system related to climatic changes and eustatic variations of sea level. On a larger scale, the stacked prograding depositional sequences reflect the sea-level cycles of the Middle Pleistocene to the Holocene. Based on the stratigraphy of our piston cores and that of Ocean Drilling Program (ODP) Site 680, the depositional sequences limited by extended unconformities were assigned to oxygen isotope stages 1 to 7. Other sedimentary structures are small straight channels that were conduits for downslope sediment transport. Deformed sediments associated with synsedimentary normal faults result from creep movements indicating beginning slope failure. 相似文献
2.
论述了福建省莆田县忠门乡苦鹅头村东南海岸一套全新世含生物碎屑的砂、砾岩的沉积特征、沉积环境及其对海平面变化的反映。砂、砾岩层可划分成上、下两段,具有不同的成因。下段（０￣２．６ｍ）为海滩沉积,形成于中全新世高海平面时期。上段（２．６￣８ｍ）是全新世晚期（约３￣２ｋａ ＢＰ）的风沙沉积,内部夹有两个弱土壤化层,表明在风沙沉积作用过程中有过两次短暂的气候波动。 相似文献
3.
长江干流江苏段地处长江下游河口地区,全线位于感潮河段,沿程水位既受上游长江径流、外海潮位、台风的影响,也受到工情变化、支流入汇等影响。长江江苏段现行洪潮设计水位是按《长江流域综合利用规划简要报告》(1990年)中确定的无台风影响水位实施。近年来,由于上游水、沙、工情条件变化,开展上游大通径流、风暴潮、区间入汇等对沿程洪潮水位的影响研究十分必要。建立大通至长江口二维水沙数学模型与外海风暴潮模型,研究不同影响因素作用下长江干流江苏段沿程洪潮设计水位变化。研究成果表明:南京河段水位主要受上游径流影响;江阴以下主要受外海潮汐及风暴潮的影响;南京至江阴段则受上游径流、外海潮汐、风暴潮三者的共同作用影响。外海天文大潮、风暴潮"两碰头"和上游大径流、外海天文大潮与风暴潮"三碰头"引起的沿程增水值呈驼峰分布,最大值分别发生在江阴和天生港附近,最大增幅1.65 m。研究结果已为长江江苏段堤防防洪能力提升工程建设提供技术支撑。 相似文献
4.
William R Dupr 《Marine Geology》1984,60(1-4):435-454
The Santa Cruz coastal terrace fringes much of the northern Monterey Bay region, California. It consists mainly of a regressive sequence of high-energy, barred nearshore marine sediments deposited during the last (Sangamonian) highstand of sea level. This sequence can be sub-divided into several depth-dependent facies on the basis of paleo-current data and vertical sequence of sedimentary structures. These include a lower shoreface facies deposited in 10–16 m water depth, an upper shoreface facies (including both a storm-dominated assemblage and a surf zone assemblage) deposited in 0–10 m water depth, and a foreshore facies deposited in the swash zone, up to 3.5 m above high tide.
The magnitudes of the storm events responsible for depositing these sediments were estimated by calculating paleo-wave heights using a variety of criteria (e.g., critical threshold equations, breaker depths, berm heights). In addition, the climate and paleogeography during the deposition of these sediments were essentially the same as today, allowing the use of present-day wave statistics to estimate the frequency of these storm events. The largest storms formed offshore-flowing currents (e.g., rip, wind-forced, and possibly storm-surge ebb currents) that resulted in the deposition of approximately 30% of the sediments seaward of the surf zone; however, the magnitude and frequency of these events are unknown. The remaining 70% of the sediment beyond the surf zone was deposited in response to smaller storm waves which were, on the average, at least 1.6 m high; such waves presently occur no more than 15% of the time. Sediments deposited during “fairweather” conditions (i.e., the remaining 85% of the time) have a low preservation potential, and are generally not preserved in this facies. In contrast, surf zone sediments were deposited by a variety of processes associated with waves whose maximum offshore heights were probably ≤ 2.2 m; such waves presently occur up to 92% of the time. Sediments within the swash zone were deposited by waves up to 3 m high, the largest of which presently occur approximately 2% of the time.
Most of the sediments were deposited by storms of intermediate magnitude and frequency; different facies, however, appear to preferentially record events of different recurrence intervals. In particular, surf zone sediments were deposited under relatively small storm and post-storm conditions, whereas sediments deposited farther offshore record increasingly larger, less frequent storm events. Relatively rare events (e.g., the 100 or 1000 yr events) do not appear to have significantly affected sedimentation in these nearshore environments. 相似文献
5.
渤海新近纪古湖发育的直接证据 总被引：8，自引：1，他引：7
通过渤海5口钻井的沉积有机质分析,以沉积有机质中浮游藻类丰度和类型、无定形有机质含量变化以及地层序列中富藻沉积层发育程度。作为指示湖相沉积环境发育的标志,确定渤海新近纪湖相沉积层的分布特征及渤海古坳陷湖的发育特征。分析表明,浮游藻类和无定形有机质含量高的层段在馆陶组和明下段都有分布,但发育最好的是在明下段下部。这是渤海新近纪湖相沉积地层存在的直接证据。从湖相沉积发育的差异看,馆陶组和明化镇组时期的古湖有着不同的特征,馆陶组早期渤海的湖泊可能很小,馆陶组中、晚期为湖泊扩张期,从含浮游藻类和无定形有机质沉积层纵向变化频繁出现可以看出浅湖沉积环境的不稳定性。新近纪古湖的盛期是在明下段下部沉积时段,当时渤海淡水湖泊普遍存在。 相似文献
6.
东海陆架中北部沉积物粒度特征及其沉积环境 总被引：4，自引：1，他引：3
通过对东海陆架表层沉积物粒级组成、粒度参数、14C年龄和微体古生物组合的综合分析,绘制了东海陆架的沉积物类型分布图;运用Folk等(1970)沉积物分类方法将东海表层沉积物分成砂、粉砂、粉砂质砂、砂质粉砂、砂质泥5种类型,其中粉砂质砂分布最广,砂质泥分布最少;沉积物由陆向海粒度变粗,反映沉积过程中的物源和沉积动力控制作用。根据沉积环境及成因分析,可将东海陆架沉积分为3类:分别是长江口外席状砂沉积区、现代泥质沉积区和陆架中部砂质沉积区。长江口外砂质沉积是全新世冰消期晚期潮流作用及风暴潮流共同作用的产物,是高海平面以来太平洋潮波系统作用下的潮流沙沉积,沙波地貌仍在发生变化。现代泥质沉积区包括长江前三角洲沉积、浙闽沿岸流沉积和济州岛西南泥质沉积三个区域,不同沉积区的成因机制不同。陆架中部砂质沉积是末次冰盛期之后海侵作用下发育的砂质沉积物,在海侵的不同阶段中沉积物被冲刷改造,具有不等时性特征,沉积环境与现代陆架海洋环流的动力特征不一致,现代沉积作用较弱,仅接受悬浮体细粒沉积。 相似文献
7.
Drilling at the site UBGH1-9, offshore Korea in 2007, revealed varied gas-hydrate saturation with depth and a wide variety of core litholgies, demonstrating how the variations in the lithology are linked with those in gas-hydrate saturation and morphology. Discrete excursions to low chlorinity values from in situ background chlorinity level occur between 63 and 151 mbsf. In this occurrence zone, gas-hydrate saturations estimated from the low chlorinity anomalies range up to 63.5% of pore volume with an average of 9.9% and do not show a clear depth-dependent trend. Sedimentary facies analysis based on grain-size distribution and sedimentary structures revealed nine sediment facies which mainly represent hemipelagic muds and fine- to medium-grained turbidites. According to the sedimentary facies distribution, the core sediments are divided into three facies associations (FA): FA I (0–98 mbsf) consisting mainly of alternating thin- to medium-bedded hemipelagic mud and turbidite sand or mud beds, FA II (98–126 mbsf) dominated by medium- to very thick-bedded turbidite sand or sandy debris flow beds, and FA III (126–178 mbsf) characterized by thick hemipelagic mud without intervening discrete turbidite sand layers. Thermal anomalies from IR scan, mousse-like and soupy structures on split-core surfaces, non-destructive measurements of pressure cores, and comparison of gas-hydrate saturations with sand contents of corresponding pore-water squeeze cakes, collectively suggest that the gas hydrate at the site UBGH1-9 generally occurs in two different types: “pore-filling” type preferentially associated with thin- to medium-turbidite sand beds in the FA I and “fracture-filling” type which occurs as hydrate veins or nodules in hemipelagic mud of the FA III. Gas-hydrate saturation in the FA II is generally anomalously low despite the dominance of turbidite sand or sandy debris flow beds, suggesting insufficient methane supply. 相似文献
8.
Liang Yuanbo Lu Bo Huang Shaojian Li Tinghuan Yang Weiguang Wen Yaolin 《Marine Georesources & Geotechnology》2013,31(3-4):189-201
Abstract The possibility of seafloor failure under external loadings on a gently sloping continental shelf is controlled, to a large extent, by the geotechnical characters of subbottom sediments (e.g., shear strength, compressibility, and liquefaction potential) and structural factors (e.g., sedimentary stratification). By means of undis‐turbing coring, in‐situ acoustic measurement, and subbottom profiling, the authors conducted an investigation into the seafloor instabilities and possibilities of sediment slope failure within the continental shelf off the Pearl River mouth, which is one of the most important areas for offshore development in the northern South China Sea. Based on in‐situ and laboratory measurements and tests for sediment physical properties, static and dynamic behavior, and acoustic characteristics, the analyses indicate: (1) subbottom sediments that originated from terrigenous clay during the Pleistocene are compact and overconsolidated, and the mean sound velocity in such sediments is relatively high; (2) the maximum vertical bearing capacity of subbottom sediments is efficiently conservative on the safe side for dead loads of light structures, and the trench walls are stable enough while trenching to a depth of about 2 m below the seafloor under still water; and (3) it is quite improbable that the subbottom sediments liquefy under earthquake (M ≤ 6) or storm wave loading. 相似文献
9.
10.
南海表层沉积物与水柱中沉降颗粒物对比研究及其古环境再造意义 总被引：1，自引：0，他引：1
分析了南海62个表层沉积物样品中生源(有机质、碳酸钙和蛋白石)和非生源(岩源物质)组分的含量变化和分布特征,并以沉积学分区为基础,结合5个沉积物捕获器站位,将南海划分为N、C-NE、SW和S 4个区域,对比分析了各区表层沉积物和水柱中沉降颗粒物中各组分含量、沉积通量分布特征和变化,探讨了表层沉积物的输出生产力、沉降颗粒物的初级生产力及真光层下100 m输出生产力三者之间的对应关系.结果显示:南海4个海域表层沉积物中各组分平均含量多数低于沉降颗粒物中的平均含量,而碳酸钙、岩源物质的沉积通量却多数高于沉降颗粒物中的沉积通量,分析得出表层沉积物中各组分平均含量和沉积通量不仅受水柱中各组分输出量影响,还受到陆源物质输入、溶解作用和上层水体营养盐影响.南海表层沉积物中生源组分沉积通量大小对应其输出生产力的大小.但是,由于陆源有机质、生源颗粒侧向漂移的影响,表层沉积物的输出生产力大小分布并不完全对应沉降颗粒物的初级生产力大小分布,尽管南海真光层下100 m输出生产力与沉降颗粒物的初级生产力比值与世界大洋"f"比平均值基本一致,但是,明显低于表层沉积物的输出生产力大小,只有在沉降颗粒物的初级生产力较高区域,真光层下100 m输出生产力大小才最接近表层沉积物的输出生产力大小. 相似文献
11.
本文对福清湾北部及其以东近岸海域的地质地貌，潮流和波浪等沉积环境因素，以及对沉积物和悬浮泥沙的粒度，矿物特征进行研究，认为福清湾为溺谷型的半封闭潮汐汊道海湾存在着较大的潮差和潮流流速，沉积物沿潮流方向呈东粗西细和岸边细、向海变粗的潮流分异特征，潮流控制着沉积物的布局，而属于潮控的浅海沉积环境。 相似文献
12.
The depositional sedimentary structures and textures of a single-barred nearshore system on the Atlantic coast of eastern Long Island, New York, were studied along seven shore-normal transects. Data along these transects consisted of textural analysis of 160 sediment samples, temporal bedform observations, and 42 can cores for the analysis of sedimentary structures.
Six sedimentary subenvironments were observed, based on distinct combinations of sediment color and texture, bedforms, physical, and biogenic sedimentary structures, and benthic infaunal communities. The shoreface environment is divided into the upper shoreface, the longshore trough, and the longshore bar. The divisions of the inner shelf environment are the shoreface-inner shelf transition, the offshore, and the coarse-grained deposit. The first five subenvironments are arranged in bands parallel to the shoreline, whereas the coarse-grained deposit occurs in patches across the inner shelf.
The location of fair-weather wave base, coinciding with a reduction in slope (3.0–0.3°) from the shoreface to the inner shelf, is characterized by the cessation of debris surge in the troughs of ripples, the formation of a “rust layer” of microorganisms over the bedform surface, and a sediment color change caused by an increase in organic detritus. The sequence of bedforms and physical sedimentary structures observed in this system fits well with existing wave-generated (oscillatory) flow regime models. These models explain the observed sequences as a response to the degree of asymmetric flow created by shoaling waves. Distribution of biogenic structures and assemblages of infaunal organisms is influenced by the distance landward or seaward of fair-weather wave base.
The overall relationships of this nearshore system can then be summarized as a hypothetical prograding stratigraphic sequence. The entire sequence is underlain by organic-rich, bioturbated, offshore deposits. Overlying the offshore is the planar-laminated sediments of the transition. Grading upward from the transition are the cleaner, planar-laminated, seaward slope deposits of the longshore bar. Above this, is a distinct erosional surface indicating the base of the massive to cross-laminated coarse sediments of the longshore trough. Capping the sequence are the cross- to planar-laminated, clean sands of the upper shoreface and foreshore. 相似文献
13.
Numerous studies have been carried out to identify storm deposits and decipher storm-induced sedimentary processes in coastal and shallow-marine areas. This study aims to provide an in-depth review on the study of coastal storm deposits from the following five aspects. 1) The formation of storm deposits is a function of hydrodynamic and sedimentary processes under the constraints of local geological and ecological factors. Many questions remain to demonstrate the genetic links between storm-related processes and a variety of resulting deposits such as overwash deposits, underwater deposits and hummocky cross-stratification (HCS). Future research into the formation of storm deposits should combine flume experiments, field observations and numerical simulations, and make full use of sediment source tracing methods. 2) Recently there has been rapid growth in the number of studies utilizing sediment provenance analysis to investigate the source of storm deposits. The development of source tracing techniques, such as mineral composition, magnetic susceptibility, microfossil and geochemical property, has allowed for better understanding of the depositional processes and environmental changes associated with coastal storms. 3) The role of extreme storms in the sedimentation of low-lying coastal wetlands with diverse ecosystem services has also drawn a great deal of attention. Many investigations have attempted to quantify widespread land loss, vertical marsh sediment accumulation and wetland elevation change induced by major hurricanes. 4) Paleostorm reconstructions based on storm sedimentary proxies have shown many advantages over the instrumental records and historic documents as they allow for the reconstruction of storm activities on millennial or longer time scales. Storm deposits having been used to establish proxies mainly include beach ridges and shelly cheniers, coral reefs, estuary-deltaic storm sequences and overwash deposits. Particularly over the past few decades, the proxies developed from overwash deposits have successfully retrieved many records of storm activities during the mid to late Holocene worldwide. 5) Distinguishing sediments deposited by storms and tsunamis is one of the most difficult issues among the many aspects of storm deposit studies. Comparative studies have investigated numerous diagnostic evidences including hydrodynamic condition, landward extent, grain property, texture and grading, thickness, microfossil assemblage and landscape conformity. Perhaps integrating physical, biological and geochemical evidences will, in the future, allow unambiguous identification of tsunami deposits and storm deposits. 相似文献
14.
Characterizing the depositional settings for sedimentary organic matter distributions in the Lower Yangtze River-East China Sea Shelf System 总被引：2，自引：0，他引：2
Chun Zhu Zhang-Hua Wang Bin Xue Pei-Song Yu Jian-Ming Pan Thomas Wagner Richard D. Pancost 《Estuarine, Coastal and Shelf Science》2011
Grain-size distributions, total organic carbon (TOC) and total nitrogen (TN) concentrations, and TOC/TN ratios (C/N) were analysed for surface sediments from the Lower Yangtze River-East China Sea (ECS) shelf system. Hierarchical cluster analysis of grain-size parameters (mode, mean, sorting, skewness and kurtosis) has been employed to characterize grain-size compositions. The results suggest there are five grain-size compositional types (type-I–V) that fingerprint distinct depositional conditions. In areas with high sedimentation rates, hydrological sorting preferentially enriches the fraction coarser than 6.4ø (12 μm) in shallow seafloor sediments (water depth<30 m) by transporting the finer fraction to the deeper seafloor (water depth>30 m), and thus forms grain-size compositional type-I (shallow) and type-II (deep). In the open shelf, where modern sediment supply is very limited, grain-size types-III–V are identified according to different winnowing intensity. Overall TOC contents significantly correlate with mud proportions, suggesting muddy sediments are the primary control on OM accumulation. However, de-association of terrestrial OM from fine sediments in the Estuary and the occurrence of presumably relict OM in the open shelf exert additional controls on OM dispersal and carbon cycling in the ECS. By considering geography, oceanography, sediment source, and the relation between sedimentation conditions and sedimentary OM distributions, we define six depositional settings: the lower river, the estuary, the coast, the offshore upwelling area, the erosional area, and the open shelf. These settings describe the sediment dispersal and associated organic matter cycling in the Lower Yangtze River-ECS shelf system. 相似文献
15.
Erosional unconformity surfaces are key indicators for the variations in eustatic sea level, ocean dynamics and climatic conditions which significantly affect depositional environments of sedimentary successions. Using a dense grid of 2D seismic data, we present new evidence from a frontier basin, the offshore Durban Basin, of a mid-Miocene age erosional unconformity that can be correlated with analogous horizons around the entire southern African continental margin.In the Durban Basin, this unconformity is typified by the incision of a mixed carbonate-siliciclastic wedge and ramp margin by a series of submarine canyons. Epeirogenic uplift of southern Africa characterised this period, with erosion and sediment bypass offshore concomitant with increases in offshore sedimentation rates. Although epeirogenic uplift appears to be the dominant mechanism affecting formation of the identified sequence boundary, it is postulated that an interplay between global eustatic sea-level fall, expansion of the east Antarctic ice sheets, and changes in deep oceanic current circulation patterns may have substantially contributed to erosion during this period. 相似文献
16.
The Kachchh sedimentary basin in the western continental margin of India is a peri-cratonic rift basin which preserves a nearly complete rock record from Middle Jurassic to Recent, punctuated by several stratigraphic breaks. The Cenozoic sediments exposed in the western part of the Kachchh mainland extend offshore into the present-day continental shelf. The unique feature of the outcropping area is a nearly complete, richly fossiliferous and easily accessible Cenozoic succession. Detailed field mapping and litho-biostratigraphic studies have made it possible to identify the chronostratigraphic units, map them in the field and extend the correlation into the offshore, aided by the development of continuously recognizable key biostratigraphic horizons and time boundaries. Detailed field mapping of key sections integrated with the litho-biostratigraphic information has helped in working out a sequence stratigraphic framework for the Cenozoic succession in the basin. The succession comprises a first-order passive margin sequence. Excellent biostratigraphic control has enabled identification of unconformities of various magnitudes which in turn have helped in mapping 5 second-order and four third-order sequences. Each sequence is discussed with respect to its extent, nature of sequence boundaries, sedimentary fill, key sequence stratigraphic surfaces and depositional setup, to understand the Cenozoic sequence stratigraphic architecture of the basin. 相似文献
17.
《Marine Geology》2005,214(4):389-409
The innermost shelf of the eastern Korea Strait is a ria-type coastal sea comprising islands, intervening passageways and embayments. A detailed analysis of high-resolution (1−10 kHz) subbottom profiles and core sediments from this area reveals complicated depositional and distributional patterns of the Holocene mud deposits related to complex topography with varying supply of the adjacent Nakdong riverine sediments. Sediments from the Nakdong River were bifurcated around Gadeok Island, forming two proximal systems: Nakdong and western Gadeok systems. These proximal systems prograded offshore (southward) by active sediment supply from the Nakdong River in the early stage. Suspended sediments passing through the Nakdong system formed the distal (Gadeok Waterway and eastern Geoje) systems in the area between the northern Geoje and Gadeok islands. These distal systems show a northwestward (onshore) prograding tendency to Jinhae Bay, the biggest bay in the vicinity of the Nakdong estuary in which the Jinhae Bay system developed. In the late stage, a remarkable decrease of sediment supply from the Nakdong River has caused retrograding geometry of the two proximal systems. However, the most distal (Jinhae Bay) system has continuously prograded bayward due to the persistent supply of sediments resuspended by strong tidal currents from nearby distal (Gadeok Waterway and eastern Geoje) systems. These complex depositional features indicate that topography has an important influence on depositional developments of the Holocene mud deposits by controlling path and intensity of sediment dispersal and resuspension processes. 相似文献
18.
近百年来黄河改道及输沙量变化对山东半岛泥质楔沉积物粒度特征的影响 总被引：1，自引：1，他引：0
对山东半岛泥质楔柱状样进行沉积物粒度分析，并在210Pb测年基础上结合黄河年输沙量、悬浮泥沙粒径、河口位置及沿岸流强弱替代指标等数据研究近百年来黄河改道及输沙量变化对远端沉积区沉积特征的影响。研究结果显示，研究区沉积物粒度的变化是黄河入海泥沙特征和沿岸流等水动力作用共同影响的结果。1884–1939年及1947–1999年，研究区沉积物粒度特征的变化主要受到沿岸流强弱的影响；1939–1947年及1999–2012年，受1938–1947年花园口决堤以及20世纪90年代末以来黄河年输沙量持续偏低致使源区泥沙不足的影响，沉积物粒度相对粗化，与沿岸流强度的相关性减弱。与黄河入海泥沙近端沉积区不同，研究区粒度特征对黄河尾闾改道事件不敏感，且对花园口决堤及年输沙量低于临界值的响应有一定程度的延迟，这与该区沉积物经历了再悬浮过程及中间复杂的物质混合有关。黄河改道及输沙量变化仍然是远端沉积区沉积特征演化不可忽视的因素。 相似文献
19.
中国东南近海海底沉积物声学物理性质及其相关关系 总被引：17，自引：3，他引：17
在获得的数据资料基础上,发现了中国东南近海海底沉积物声学物理参数的平面分布规律,通过对这些参数的回归分析以及对声速和沉积物密度的估计,建立了经验公式。结果显示,中国东南近海海底沉积物的基本声学物理特性如下:沉积物类型多样而且复杂,从黏土到砂砾有13个颗粒组分组合;沉积物物理力学参数变化范围较大;沉积物声学性质相对于附近海域的数据变化范围更大。这些都与海底沉积环境、沉积物来源、沉积条件和沉积作用过程有关。该项研究有助于建立海底地声模型及开展应用。 相似文献
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本文着重讨论了长城湾现代滨岸砾石沉积的形态、规模、粒度和组构特征及滨岸带沉积动力环境。认为砾石堆积体系中高纬滨岸风暴沉积的产物。堆积体规模较小，形似堤坝，走向与海岸线大体平行。砾石主要由玄武质火山熔岩的岩屑组成，颗粒表面新鲜，多为扁度差的多角体，保留着冰碛砾石的粒态特征。粒度组成和粒级分配上具有冰川－海洋作用双重性质。砾石堤中砾石排列杂乱，层序不清，层理构造不发育，形态分带不显著，仅在堤的向海侧稍显粒度分带现象，由堤的顶部到上中部至基部，分别为砾石带、粗细砾带和砂砾带。滨岸带不同地貌部位，沉积动力环境存在一些差异。从风暴高潮位至大潮低潮位，水动力的簸选作用具有好→差→较好→较差的规律性变化，沉积物随之出现：较粗较匀→粗细混杂→较细较匀→粗细颗粒较混杂的韵律式波动。并指出这些特征与极区独特的自然地理条件有关。 相似文献