High-resolution seismic analysis of the coastal Mecklenburg Bay (North German Basin): the pre-Alpine evolution

The pre-Alpine structural and geological evolution in the northern part of the North German Basin have been revealed on the basis of a very dense reflection seismic profile grid. The study area is situated in the coastal Mecklenburg Bay (Germany), part of the southwestern Baltic Sea. From the central part of the North German Basin to the northern basin margin in the Grimmen High area a series of high-resolution maps show the evolution from the base Zechstein to the Lower Jurassic. We present a map of basement faults affecting the pre-Zechstein. The pre-Alpine structural evolution of the region has been determined from digital mapping of post-Permian key horizons traced on the processed seismic time sections. The geological evolution of the North German Basin can be separated into four distinct periods in the Rerik study area. During Late Permian and Early Triassic evaporites and clastics were deposited. Salt movement was initiated after the deposition of the Middle Triassic Muschelkalk. Salt pillows, which were previously unmapped in the study area, are responsible for the creation of smaller subsidence centers and angular unconformities in the Late Triassic Keuper, especially in the vicinity of the fault-bounded Grimmen High. In this area, partly Lower Jurassic sediments overlie the Keuper unconformably. The change from extension to compression in the regional stress field remobilized the salt, leading to a major unconformity marked at the base of the Late Cretaceous.     

柴达木盆地东北缘中新统遗迹化石组合及其沉积环境

研究遗迹化石对于恢复古生物活动方式、习性和古环境具有重要意义。在柴达木盆地东北缘双湖地区中新统发现了遗迹化石。经鉴定,研究区的遗迹化石主要包括2大类4属4种:居住迹Palaeopycus heberti（赫伯特古藻迹）,Skolithos verticalis（垂直石针迹）;进食迹Scoyenia gracilis（纤细斯柯茵迹）和Taenidium satanassi（箱形条带迹）。根据研究区的遗迹化石分布及沉积环境分析,该地可划分出一个遗迹组合:Scoyenia-Taenidium-Skolithos遗迹组合, 代表了潮湿气候条件下的浅湖环境。当前化石的发现填补了柴达木盆地东北缘双湖地区中新世遗迹化石研究的空白。     

塔里木盆地下奥陶统蓬莱坝组白云岩成因及储层主控因素分析——以巴楚大班塔格剖面为例

寒武系-下奥陶统白云岩是塔里木盆地非常重要的勘探接替领域,但由于白云岩埋藏深度大,勘探和研究程度低,目前的认识程度无法满足勘探的需求,尤其是白云岩储层成因和分布的认识。本文以巴楚地区大班塔格剖面蓬莱组白云岩的精细解剖为例,测制解剖剖面9条,采集样品195块,系统的开展了岩石薄片、物性及地球化学特征分析,取得了两个方面的新的认识。1)是塔里木盆地蓬莱坝组发育粉晶、细晶、中晶和粗晶四种白云岩,主要形成于早-中埋藏期与海源流体有关的白云石化作用中,局部受到热液改造,其晶粒大小与原岩结构的粗细及孔隙空间的大小有关,原岩结构粗,形成的白云石晶粒就粗,原岩孔隙空间大,白云石晶粒就大。2)是白云岩储层的分布具成层性和旋回性,孔隙发育段总体位于向上变浅旋回的顶部,与高频旋回的暴露面有关,其载体以细-粗晶白云岩为主,孔隙主体来自原岩孔隙的继承和再调整,少量来自埋藏(热液)溶蚀作用,而并不是传统观点所认为的白云石化作用建造孔隙,这一认识对塔里木盆地深层白云岩有效储层预测具重要的指导意义。     

新疆阿克苏地区城市自然灾害脆弱性评价研究

塔里木盆地是我国最大的半封闭型内陆盆地, 干旱、大风、沙尘暴、洪水以及地震、雪灾等自然灾害频繁.为了提高塔里木盆地城市应对自然灾害的能力, 以阿克苏地区为例, 在广泛借鉴国内外灾害脆弱性评价的指标体系与评价模型的基础上, 以多灾种复合情况为背景, 构建塔里木盆地自然灾害脆弱性评价指标体系, 运用模糊综合评价法进行脆弱性评价, 并对各指标进行对比分析.结果表明: 阿克苏市、新和县、阿瓦提县的高脆弱度值最高, 分别为0.48、0.36及0.40, 属于高脆弱度; 温宿县、沙雅县的中脆弱度值较高, 分别0.24和0.26, 属于中脆弱度; 库车县、拜城县、乌什县、柯坪县的低脆弱度值较高, 分别为0.48、0.45、0.36及0.35, 属于低脆弱度.根据各县市自然灾害脆弱性评价结果, 结合区域特点, 提出了防灾抗灾的对策建议, 对塔里木盆地城市降低脆弱性、减轻自然灾害影响有一定借鉴意义.     

Early Devonian synorogenic alluvial-fan deposits of the Maccullochs Range,western New South Wales

The Early Devonian, Maccullochs Range beds (new) of the Winduck Interval largely comprise non-marine fine-grained sheet-flood-deposited sandstones which lie in the southeast sector of the Darling Basin Conjugate Fault System. Deposition of the >2.5 km-thick sequence occurred on the Wilcannia, Towers and Coolabah Bore alluvial fans, that were sourced largely from lightly indurated sandstone caps overlying a large basement high lying north of the Darling River Lineament, and also from west of Maccullochs Range (Coolabah Bore Fan). Four lithofacies are recognised. Lithofacies 1, massive sandstone, is proximal and was deposited from hyperconcentrated sheet floods. The more distal lithofacies 2 is partly massive, partly laminated and partly affected by soft sediment slumping during its deposition. It contains 1.3 – 3.5 m-thick sheet-flood successions that rarely show cross-bedding. Lithofacies 3 and 4 are minor: lithofacies 3, stream-flood deposited, comprises coarse-grained, pebbly sandstone and lithofacies 4, transient playa lake deposits that are locally intercalated with lithofacies 2. In lithofacies 2, thick massive fine-grained sandstone is commonly overlain by laminated sandstone that was deformed when soft. Incised channel deposits in lithofacies 2 deposits are rare and palaeosols were not discovered. Permanency of the positions of two of the alluvial fans, and by inference their feeder streams, remained unchanged for ～9 million years. The fans overlie probable floodplain deposits observed in a quarry in the easternmost part of the study area. Marine fossils are very minor in the range—the brachiopod Howellella jaqueti at one locality indicates an Early Devonian age for one of the brief marine incursions into what was normally an alluvial-fan environment. Very brief marine incursions elsewhere in the group are deduced from the presence of very rare fossil gastropods.     

Characterising the distribution of near-shore submarine groundwater discharge along a coastline using 222Rn and electrical conductivity

The spatial and temporal distribution of near-shore fresh submarine groundwater discharge (SGD) was characterised from the coastal aquifers of the Willunga Basin, South Australia, an extensive aquifer system that supports an important viticultural region. Measurements of electrical conductivity (EC) and ²²²Rn (radon) activity were collected at 19 sites along the coastline during the Southern Hemisphere spring (2011) and summer (2013). At each site, samples were collected from the surf zone as well asporewater from beach sediment in the intertidal zone. Surf-zone radon activity ranged from <5 to 70mBq L^–1, and intertidal porewater radon ranged over two orders of magnitude (220–36 940 mBq L^–1) along the Willunga Basin coastline during both surveys. Overall, surf-zone and porewater EC was lower in the spring 2011 survey than in the summer 2013 survey. Porewater EC was similar to that of coastal water at most sites along the coastline, except at three sites where porewater EC was found to be lower than coastal water during both surveys, and three sites where evaporated seawater was observed in the summer survey. Based on the patterns in radon and EC along the coastline, two sites of localised fresh SGD were identified, in addition to a groundwater spring that is known to discharge to the coast. The results indicate that near-shore fresh SGD occurs as localised seeps rather than diffuse seepage along the entire coastline. The apparent absence of groundwater discharge at most locations is also consistent with current evidence suggesting that extensive groundwater pumping within the basin has resulted in seawater intrusion across much of the coastline. These observations also suggest that previous studies are likely to have over-estimated SGD rates from the Willunga Basin because they assumed that SGD occurred along the entire coastline.     

Lithostratigraphy and depositional environment of the Permian Nowra Sandstone in the southwestern Sydney Basin,Australia

Lithofacies in the mid‐Permian Nowra Sandstone indicate a middle/upper shoreface to foreshore environment of deposition under the influence of storm‐generated waves and north‐northeasterly directed longshore currents. Palaeogeographic reconstruction for the Nowra Sandstone portrays a sand‐dominated high energy shelf and offshore shoal forming a sequence thickening seaward away from the western shore of the Sydney Basin. The shoal‐crest at the outer edge of the shelf trends north‐northeast. It is characterized by fine‐ to medium‐grained sandstone with upper flow regime structures and a high proportion of conglomerate, whereas coarser sandstone with lower energy bedforms occurs along the seaward side of the shoal. In the deeper water to the east, the lower Nowra Sandstone becomes rapidly thinner as it passes seaward, via bioturbated storm redeposited sandstone beds, into the shelf deposits of the Wandrawandian Siltstone. This sequence accumulated during a regressive event and the base of the formation becomes progressively younger eastward. The sand may have been supplied by rivers along the western coast but the major source was south of the study area. The lower Nowra Sandstone is separated from the upper part of the formation by an extensive ravinement surface overlain by the Purnoo Conglomerate Member. In contrast to the lower unit, the upper Nowra Sandstone forms a westward thickening wedge that represents a backstepping nearshore sand facies that accumulated during a transgression. The upper Nowra Sandstone passes vertically and laterally eastward into the Berry Siltstone. Thus both boundaries of the Nowra Sandstone are diachronous, first younging eastward and then westward as a response to a regressive‐transgressive episode.     

Heavitree Quartzite,a Neoproterozoic (ca 800–760 Ma), high‐energy,tidally influenced,ramp association,Amadeus Basin,central Australia

The Neoproterozoic Heavitree Quartzite is widespread in the Amadeus Basin and has correlatives in all of the major central Australian intracratonic basins. The origin of the formation is enigmatic, not only because of its widespread sheet‐like distribution and uniformity of composition, but also because intense silicification makes facies studies difficult. Recently discovered exposures at the eastern end of the basin are relatively free of diagenetic quartz allowing a detailed study of sedimentary structures and an understanding of the depositional architecture of the formation. The formation, which consists largely of pale‐tan or white quartzose sandstone interbedded with rare laminated mudstone and conglomerate intervals, was deposited in at least four depositional sequences. The sheet‐like nature of the sandstone results from an abundant supply of sediments deposited in a high‐energy, open, shelf‐like environment on a regionally subsiding, low‐gradient ramp. Environmental settings switched both laterally and temporally between sand waves deposited by reversing tidal flow and higher velocity unidirectional currents involving dunes and plane beds. In the early stages of deposition, mud‐dominated, tidal‐flat environments alternated with higher energy, sand‐dominated, tidally influenced settings. However, in the later stages of deposition a major eustatic sea‐level fall moved base‐level basinwards, earlier sediments were reworked by streams to form a ravinement surface, gravel was carried well into the basin and fines largely disappeared from the environment. Gravel deposition was followed by a return to high‐energy, tidally influenced deposits involving large sand waves or dunes. Towards the top of the formation sand waves deposited by reversing tidal currents gradually decline and are eventually replaced by dunes deposited by unidirectional current flow. The transition to the shallow‐marine, anoxic rocks of the Bitter Springs Formation is gradational in response to increased accommodation in a ramp setting which lacked a clearly defined shelf break. The Heavitree Quartzite was probably deposited as a direct response to the events surrounding the assembly and breakup of Rodinia, in particular peneplanation during regional uplift in response to a rising mantle plume followed by broad regional subsidence as the plume decayed prior to the breakup of the supercontinent. The large supply of quartz sand resulted from peneplanation associated with the rising plume and the lack of soil‐stabilising vascular plants, an environmental setting with no modern analogue. The ultimate disposition of fines is not known but, given the environment of deposition, it is likely that they were removed during peneplanation and bypassed the sag basin completely.     

Geochemistry of Brines from Salt Ore Deposits in Western Tarim Basin

In the geological evolution of the Tarim Basin, many transgressions and relictions happened. So there have been plentiful sources of salt. Moreover, because of uttermost drought, a lot of salt has been deposited. It is possible to find potash salt in this area. In our fieldwork, we have found salt and brine in western Tarim Basin. Based on a geological survey and the characteristics of sedimentary facies and paleogeography, this paper deals with the geochemical parameters and discusses the possibility of formation of potash salt in terms of the chemical analyses of samples collected from western Tarim Basin. Results of brine analysis lead to some conclusions: most of these salt brines have eluviated from very thick halite beds, mainly chloridetype salt and this kind of halite does not reach the stage of potash deposition in all aspects; WKSL (Wukeshalu) occupies a noticeable place, and we should attach importance to this district because there have been some indicators of the occurrence of potash deposits as viewed from the contents of Br and K. Finally, low Br contents are recognized in the Tarim Basin as a result of salt aggradation, and this point of view has been proved by the results of this experiment and the data available. It cannot depend upon the index of Br to judge the evolution stage of halite. We must look for other facies of potash except marine facies.     

塔里木盆地库车坳陷白垩纪层序地层格架及古地理演化

白垩纪的库车坳陷是一个干旱气候条件下的内陆坳陷,其中只发育下白垩统,为一套干旱红层地层,进一步划分为亚格列木组、舒善河组、巴西盖组和巴什基奇克组。该套干旱红层,包括洪积扇砾岩、间歇性河流砂砾岩、风成砂岩和沙漠湖紫红色泥岩等沉积。这些沉积在地层记录中常以一种特别的旋回性形式产出,在不整合面及其相关面之上首先沉积的是洪积扇砾岩和间歇性河流砂砾岩所构成的冲积沉积物,向上逐渐演变为沙漠湖红色泥岩,在成湖初期或湖退期发育了滨湖相风成砂岩,它们构成了一个较为典型的沙漠沉积体系。从冲积沉积到湖泊沉积构成总体向上变细的沉积相序组合。按照地层记录的旋回性进行三级沉积层序划分,将库车坳陷下白垩统划分为5个三级沉积层序即SQ1至SQ5。下白垩统的顶和底界面均为间断时间很长的区域不整合面,由它们所限定的下白垩统本身则构成一个二级构造层序,在二级构造层序内三级沉积层序常常形成有规律的叠加形式,下部的SQ1和上部的SQ5发育较多的冲积粗碎屑物,中部SQ2至SQ4则以湖泊相沉积为主。与海相地层不同,库车坳陷白垩系中由三级层序和二级层序所代表的地层记录中的中周期和长周期旋回的主要控制因素是幕式构造沉降,沉降初期由于地形高差大而以发育冲积粗碎屑物为主,均衡沉降期则与成湖期相对应从而发育较多的细粒沙漠湖沉积。以沉积物的时间演化序列和沉积相的空间展布形式所代表的规律性入手,建立库车坳陷下白垩统的层序地层格架,在层序地层框架内,系列层序地层格架栅状图和相应的古地理图较为清晰地反映出早白垩世库车坳陷的古地理面貌,以及相应的沉积岩相古地理演变过程。