Tectonostratigraphic framework and depositional history of the deepwater Ulleung Basin,East Sea/Sea of Japan

The Ulleung Basin, East Sea/Japan Sea, is a Neogene back-arc basin and occupies a tectonically crucial zone under the influence of relative motions between Eurasian, Pacific and Philippine Sea plates. However, the link between tectonics and sedimentation remains poorly understood in the back-arc Ulleung Basin, as it does in many other back-arc basins as well, because of a paucity of seismic data and controversy over the tectonic history of the basin. This paper presents an integrated tectonostratigraphic and sedimentary evolution in the deepwater Ulleung Basin using 2D multichannel seismic reflection data. The sedimentary succession within the deepwater Ulleung Basin is divided into four second-order seismic megasequences (MS1 to MS4). Detailed seismic stratigraphy interpretation of the four megasequences suggests the depositional history of the deepwater Ulleung Basin occurred in four stages, controlled by tectonic movement, volcanism, and sea-level fluctuations. In Stage 1 (late Oligocene through early Miocene), syn-rift sediment supplied to the basin was restricted to the southern base-of-slope, whereas the northern distal part of the basin was dominated by volcanic sills and lava flows derived from initial rifting-related volcanism. In Stage 2 (late early Miocene through middle Miocene), volcanic extrusion occurred through post-rift, chain volcanism in the earliest time, followed by hemipelagic and turbidite sedimentation in a quiescent open marine setting. In Stage 3 (late middle Miocene through late Miocene), compressional activity was predominant throughout the Ulleung Basin, resulting in regional uplift and sub-aerial erosion/denudation of the southern shelf of the basin, which provided enormous volumes of sediment into the basin through mass transport processes. In Stage 4 (early Pliocene through present), although the degree of tectonic stress decreased significantly, mass movement was still generated by sea-level fluctuations as well as compressional tectonic movement, resulting in stacked mass transport deposits along the southern basin margin. We propose a new depositional history model for the deepwater Ulleung Basin and provide a window into understanding how tectonic, volcanic and eustatic interactions control sedimentation in back-arc basins.     

Basin analysis palaeo-landscape modelling: Testing the critical controls using experimental design constrained by a real 3D geological model,Gippsland Basin,Australia

The main controlling variables for palaeo-landscape evolution are investigated to assess their relative importance using the Gippsland Basin geological history. Palaeo-landscape reconstruction is a complicated process controlled and affected by multiple variables, including tectonic, palaeo-environment, sea-level change, rainfall, sediment erosion, transportation, deposition, etc. The Basin and Landscape Dynamics software (Badlands) software was used with an efficient experimental design (ED) to guide the selected scenarios, process the results, and generate the multi-variate equations that define and identify the important controlling variables. The ED was used to test and identify the main uncertainties and their possible ranges, based on actual field data, while at the same time ensuring that the full multi-dimensional space for those variables was covered to enable the computation of multivariate equations from the minimum number of scenario runs. A full suite of 3D forward palaeo-landscape models of the Gippsland Basin was built to reconstruct the basin history from its formation to the present (Early Cretaceous to Holocene, 137-0 Ma). The models are compared to the corresponding full 3D realistic structural and stratigraphic model of the basin that has been built in Petrel (Schlumberger software). This constrains the sedimentary, stratigraphic, burial and thermal histories to the relative subsidence rates and basin-fill for each geological sequence by using the model isopachs input to the Badlands modelling. The ED required only 22 scenarios to fit 12 identified variables and test for possible interactions with each other. The most significant variables are those that control sediment supply including non-marine erodibility, rainfall, (Rainfall × Area) exponent m, Slope and critical slope while maximum % Marine Deposition and marine dispersal are also required to fill the marine accommodation space. Sea Level and subsidence only become significant when rapid enough to outpace sediment supply. The controlling factors change over time with basin development from rift to post-rift phases and interactions are highly significant.     

气候变化和人类活动对鄱阳湖流域入湖输沙量影响的定量估算

采用HydroTrend水文模型,以鄱阳湖流域的赣江、抚河、信江、饶河和修水为研究对象,基于1956-2010年鄱阳湖流域气候数据、水沙数据及其他相关资料,分别模拟了5个子流域的入湖水沙通量变化。在此基础上,探讨了气候变化、植被覆盖变化和水库修建活动对输沙量变化的影响,并定量估算了上述因子对流域输沙量变化的贡献。结果表明：① 1956-2010年,气候、植被和水库三种因子影响下的流域年均输沙量分别为15.5 Mt、20.8 Mt、8.5 Mt,而三种因子共同影响下的流域年均输沙量达到12.6 Mt。② 1956-2010年,植被覆盖变化使流域年均输沙量增加4.2 Mt,而水库拦截造成流域年均输沙量减少8.2 Mt,两者分别占实际年均输沙量的32.4%和63.2%。③ 1956-1989年,植被覆盖变化导致的输沙增加量和水库修建拦截导致的输沙减少量均为5.1 Mt/a,两者对流域输沙量贡献持平;1990-2010年,水土流失加重导致的输沙增加量和水库拦截导致的输沙减少量分别为2.7 Mt/a和13.3 Mt/a,水库对入湖输沙量的影响效应是植被覆盖变化的5倍左右。     

川中丘陵区和三峡地区小流域侵蚀产沙的塘库沉积137Cs断代

选择川中丘陵区和三峡地区四川盐亭、南充和重庆开县的4个小流域,采集塘库沉积泥沙137Cs样品,确定了1963年以来塘库淤沙量,并据此分析了流域输沙模数和侵蚀模数。研究表明,开县春秋沟的淤沙模数最高,为1869t.km-2.a-1;盐亭武家沟和集流沟分别为701t.km-2.a-1和710 t.km-2.a-1;南充天马湾沟为566 t.km-2.a-1。对小流域地貌特征的分析和谷地水田取样结果表明,除塘库淤积区外,各小流域谷地内基本无泥沙淤积。因此,除南充天马湾沟按现有水面面积作为淤积面积求算的淤沙模数明显偏小外,其他小流域的塘库淤沙模数基本可以表征各研究小流域的侵蚀模数。对研究小流域侵蚀产沙影响因素的分析表明,除降雨和土地利用状况外,地形起伏、土壤抗蚀性及岩层产状也是三地侵蚀程度差异的重要原因。