Seismic stratigraphy and paleogeographic evolution of Fairway Basin,Northern Zealandia,Southwest Pacific: from Cretaceous Gondwana breakup to Cenozoic Tonga–Kermadec subduction

We present the first comprehensive seismic‐stratigraphic analysis of Fairway Basin, which is situated on the rifted continent of Zealandia in the Tasman Sea, southwest Pacific, between Australia and New Caledonia. The basin is 700 km long, 150 km wide, and has water depths of 500–3000 m. We describe depositional architecture and paleogeographic evolution of this basin. Basin formation was concurrent with two tectonic events: (i) Cretaceous rifting during eastern Gondwana breakup and (ii) initiation and Cenozoic evolution of Tonga–Kermadec subduction system to the east of the basin. To interpret the basin history we compiled and interpreted 2D seismic‐reflection profiles and make correlations with DSDP boreholes and the geology of New Caledonia. Five seismic‐stratigraphic units were defined. The deepest and oldest unit, FW3, folded and faulted can be correlated with volcaniclastic sediments and magmatic rocks in New Caledonia that are associated with Mesozoic Gondwana margin subduction. Alternatively, given the basin location 200–300 km west of New Caledonia and inboard of the ancient plate boundary, the unit could have formed as Gondwana intra‐continental basin with no known correlative. The overlying unit FW2b records syn‐rift deposition, probably associated with Cretaceous Gondwana breakup. Subaerial erosion supplied terrigenous sediment into the deltas in the northern part of the basin, as suggested by the truncation surfaces on the basement highs and sigmoid reflector geometries within unit FW2b respectively. Above, unit FW2a records post‐rift sedimentation and passive subsidence as the Tasman Sea opened and the Fairway Basin drifted away from Australia. Subsidence led to the flooding of the basement highs and burial of wave‐cut surfaces. Eocene compressive deformation resulted in minor folding and tilting within the Fairway Basin and was associated with the formation of many diapiric structures. The top of unit FW2 is an extensive unconformity that is associated with erosion and truncation on surrounding ridges. Above this unconformity, unit FW1b is interpreted as a turbidite system sourced from topography created during the Eocene tectonic event, which we interpret as being related to Tonga–Kermadec subduction initiation. Pelagic carbonate sedimentation is now prevalent. Unit FW1a has progressively draped the basin during Oligocene to Pleistocene subsidence. Many small volcanic cones were erupted during this final phase of subsidence, either as a delayed consequence of subduction initiation, or related to Tasmantid and Lord Howe hotspot trails. The northern Fairway Ridge remains close to sea level and its reef system continues to supply carbonate detrital sediments into the basin, most likely during sea‐level lowstands. Fairway Basin contains a nearly continuous record of tectonic and paleoclimatic events in the southwest Pacific since Cretaceous time. Its paleogeographic history is a key piece in the puzzle for understanding patterns of regional biodiversity in the southwest Pacific.     

Tectonics of the Xining Basin in NW China and its implications for the evolution of the NE Qinghai‐Tibetan Plateau

The continuous Cenozoic strata in the Xining Basin record the growth and evolution of the northeastern Qinghai–Tibetan Plateau. Here, the mechanisms and evolution of the Xining Basin during the Cenozoic were investigated by studying the sedimentary facies of 22 Cenozoic sections across the basin and detrital zircon U‐Pb ages of three Cenozoic sections located in the eastern, central and western basin, respectively. In the Eocene (ca. 50–44 Ma), the India‐Eurasia Collision affected the northeastern Qinghai–Tibetan Plateau. The Central Qilian Block rotated clockwise by ca. 24° to form the Xining Basin. The Triassic flysch sediments surrounding the basin were the primary sources of sediment. Between ca. 44–40 Ma, the basin enlarged and deepened, and sedimentation was dominated by saline lake sediments. Between ca. 40–25.5 Ma, the Xining Basin began to shrink and dry, resulting in the deposition of saline pan and saline mudflat sediments in the basin. After ca. 20 Ma, the Laji Shan to the south of the Xining Basin was uplifted due to the northward compression of the Guide Basin to the south. Clasts that eroded from this range dominated the sediments as the basin evolved from a lacustrine environment into a fluvial system. The Xining Basin was an extensional basin in the Early Cenozoic, but changed into a compressive one during the Late Cenozoic, it was not a foreland basin either to the Kunlun Shan or to the western Qinling Shan in the whole Cenozoic. The formation and deformation of the Xining Basin are the direct responses of the India‐Eurasia Collision and the growth of the Qinghai‐Tibetan Plateau.     

普里兹湾陆架表层沉积物粒度特征及其环境指示意义

基于对普里兹湾陆架表层沉积物粒度分析,结合海区动力环境特点,初步探讨了考察区类型、组成及冰海沉积作用特点。研究区表层沉积物大体可分为:砾(G)、泥质砂质砾(ms G)、砾质泥(g M)、砾质泥质砂(gm S)、含砾泥((g)M)、含砾泥质砂((g)m S)、砂(S)、砂质粉砂(s Z)和粉砂(Z)九种类型。依据沉积物粒度特征与地形变化,可将研究区划分为东部含砾泥质区和西部含砾砂质区。在东部含砾泥质区,包括四夫人浅滩、Svenner水道区、普里兹水道区和埃默里海盆区,沉积作用主要受海流影响,冰筏碎屑的影响有限,沉积物总体较细,粘土和细粉砂含量较高,粗粉砂和砂含量较低。在西部含砾砂质区,包括弗拉姆浅滩和埃默里冰架前缘,沉积作用受冰山、埃默里冰架和海流的共同影响,沉积物中粘土含量较低,砂和砾石含量较高,但也有个别站位可能受冰间湖的影响,沉积物粒度偏细。     

Relationships between shelf‐edge trajectories and sediment dispersal along depositional dip and strike: a different approach to sequence stratigraphy

Analysis of shelf‐edge trajectories in prograding successions from offshore Norway, Brazil, Venezuela and West Africa reveals systematic changes in facies associations along the depositional dip. These changes occur in conjunction with the relative sea‐level change, sediment supply, inclination of the substratum and the relief of the margin. Flat and ascending trajectories generally result in an accumulation of fluvial and shallow marine sediments in the topset segment. Descending trajectories will generally result in erosion and bypass of the topset segment and deposition of basin floor fans. An investigation of incised valley fills reveals multiple stages of filling that can be linked to distinct phases of deepwater fan deposition and to the overall evolution of the margin. In the case of high sediment supply, like the Neogene Niger and Orinoco deltas, basin floor fans may develop systematically even under ascending trajectory styles. In traditional sequence stratigraphic thinking, this would imply the deposition of basin floor fans during a period of relative sea‐level highstand. Facies associations and sequence development also vary along the depositional strike. The width and gradient of the shelf and slope show considerable variations from south to north along the Brazilian continental margin during the Cenozoic. During the same time interval, the continental shelf may display high or low accommodation conditions, and the resulting stacking patterns and facies associations may be utilized to reconstruct palaeogeography and for prediction of lithology. Application of the trajectory concept thus reveals nuances in the rock record that would be lost by the application of traditional sequence stratigraphic work procedures. At the same time, the methodology simplifies the interpretation in that less importance is placed on interpretation and labelling of surface boundaries and systems tracts.     

What feeds shelf-edge clinoforms over margins deprived of adjacent land sources? An example from southeastern Brazil

In southeastern Brazil, the Serra do Mar coastal mountain range blocks the sediment influx from arriving at a ca. 1,500 km long continental margin comprising Santos and Pelotas basins. Despite this deprivation, the margin accumulated a ca. 1 km thick sedimentary succession since the Mid-Miocene. Examination of seismic reflection and oceanographic data indicates that shelf-margin clinoform formation exhibits a regional variability, with major sigmoidal clinoforms developed in the transitional area between both basins. Laterally, poorly developed oblique clinoforms constitute isolated depocenters along the shelf margin. The continuous clinoform development in the transitional area is attributed to the major influence on sediment transport patterns of several ocean bottom currents flowing along the margin, such as the Brazil Coastal Current, the Brazil Current and the Intermediate Water Brazil Current. These currents erode, transport and distribute sediments across the shelf break and upper slope from distant sediment sources located either north or south of the study area. The progressive southward strengthening of the Brazil Current could be responsible for a major southward sediment redistribution from the northern Campos Basin, and/or for sediment entrainment from northward-induced transport by the Brazil Coastal Current, originally derived from the De la Plata Estuary. In the transition between Santos and Pelotas basins, the Intermediate Water Brazil Current splits forming the Santos Bifurcation, allowing for a continuous depositional process and clinoform generation. We suggest that ocean bottom currents may shape other shelf-edge ‘contouritic clinoforms’ in continental margins mainly constructed by along-strike sediment transport largely driven by long-term geostrophic currents.     

南沙群岛区域地质地貌与古海洋

本文论述了南沙群岛海底地形、海底沉积物、区域地质、珊瑚礁地质地貌和区域古海洋。     

楚科奇海和加拿大海盆表层沉积物中好气异养细菌的地理分布

本文用MPN法测定楚科奇海和加拿大海盆表层沉积物中好气异养细菌(GAB)的含量,并对其地理学分布进行分析。结果表明,研究区GAB的检出率高达100%。4℃时GAB的含量范围、平均含量为4.00×102-2.40×106个.g-1、1.71×106个.g-1。25℃时GAB的含量范围、平均含量为2.40×105-2.40×107个.g-1、1.10×107个.g-1。无论是含量范围,还是平均含量,均是25℃时的培养结果大于4℃时的培养结果。GAB含量的地理分布趋势是随纬度增高,含量呈降低趋势。在经度变化上则为由东向西,含量呈降低趋势。对沉积物所处水深的分析,表明其在4℃培养得出来的GAB含量随水深增加有下降的趋势,25℃培养出来的GAB含量受环境影响较小,与水深变化关系不明显。     

Testing long-term patterns of basin sedimentation by detrital zircon geochronology, Centralian Superbasin, Australia

Detrital zircon geochronology of Neoproterozoic to Devonian sedimentary rocks from the Georgina and Amadeus basins has been used to track changes in provenance that reflect the development and inversion of the former Australian Superbasin. Through much of the Neoproterozoic, sediments appear to have been predominantly derived from local sources in the Arunta and Musgrave inliers. Close similarities between the detrital age signatures of late Neoproterozoic sedimentary rocks in the two basins suggests that they were contiguous at this time. A dominant population of 1.2–1.0 Ga zircon in Early Cambrian sediments of the Amadeus Basin reflects the uplift of the Musgrave Inlier during the Petermann Orogeny between 560 and 520 Ma, which shed a large volume of detritus northwards into the Amadeus Basin. Early Cambrian sedimentary rocks in the Georgina Basin have a much smaller proportion of 1.2–1.0 Ga detritus, possibly due to the formation of sub‐basins along the northern margin of the Amadeus Basin which might have acted as a barrier to sediment transfer. An influx of 0.6–0.5 Ga zircon towards the end of the Cambrian coincides with the transgression of the Larapintine Sea across central Australia, possibly as a result of intracratonic rifting. Detrital zircon age spectra of sedimentary rocks deposited within this epicontinental sea are very similar to those of coeval sedimentary rocks from the Pacific Gondwana margin, implying that sediment was transported into central Australia from the eastern continental margin. The remarkably consistent ‘Pacific Gondwana’ signature of Cambro‐Ordovician sediments in central and eastern Australia reflects a distal source, possibly from east Antarctica or the East African Orogen. The peak of the marine incursion into central Australia in the early to mid Ordovician coincides with granulite‐facies metamorphism at mid‐crustal depths between the Amadeus and Georgina basins (the Larapinta Event). The presence of the epicontinental sea, the relative lack of a local basement zircon component in Cambro‐Ordovician sedimentary rocks and their maturity suggest that metamorphism was not accompanied by mountain building, consistent with an extensional or transtensional setting for this tectonism. Sediments deposited at ～435–405 and ～365 Ma during the Alice Springs Orogeny have detrital age signatures similar to those of Cambro‐Ordovician sedimentary rocks, reflecting uplift and reworking of the older succession into narrow foreland basins adjacent to the orogen.     

从南极冰盖和气候演化研究历史的回顾看格罗夫山地区新生代沉积岩发现的意义

南极冰盖自形成以来就一直是全球环境体系最重要的组成部分 ,其扩展和消融的动态演化过程不仅是南极大陆最重要的地质过程 ,而且也是全球气候和环境变化最直接的反映和体现。因此 ,有关这一课题的研究一直是国际地质学界所关注的热点。本文回顾了南极冰川和气候演化研究的历史 ,总结了当前这方面研究的成果以及所存在的问题 ,探讨了其未来的发展趋势 ,在此基础上 ,对我国南极考察队发现格罗夫山 (GroveMountains)地区新生代沉积岩的意义进行了阐述     

白令海表层沉积物中的放射虫与海洋环境

通过对白令海 1 2个表层沉积物中微体生物化石放射虫的分析 ,共鉴别放射虫 2 4 72枚 ,计36属、45种。表层沉积物中放射虫的分布特点为 :1 .浅水陆架 -陆坡上部区的粉砂、细砂沉积物中放射虫化石数量少且属种单调。2 .陆坡下部区的火山碎屑及浊流沉积物中放射虫化石亦不丰富。3.海盆区粘土沉积物中的放射虫化石丰度高且分异度高。本区陆架放射虫化石的优势种为Spongotrochus glacialis.影响放射虫分布的主要因素为海流、地形、水深、水温等。另外 ,该区沉积物的物源主要为陆源沉积物、生物源沉积物和火山源沉积物 ,它们主要来源于俄罗斯东部的勘察加半岛、美国的阿拉斯加半岛及阿留申群岛     

长江河口河槽近期沉积特征及影响因子分析

随着流域和河口水利工程建设,长江河槽沉积环境发生了巨大改变,对河势演变和河槽冲淤均产生重要影响。依据长江河口河槽大面积表层沉积物采样和各河槽定点水文观测资料,分析各河槽沉积特征,探讨其影响因子及作用机制。结果表明:河槽沉积物类型以砂质粉砂和粉砂质砂分布最广,粒径分布纵向上呈自西向东减小、横向上自北向南减小趋势,河槽总体主槽粗、边滩细。涨落潮泥沙输运和沉降过程影响河槽纵向沉积分布特征,风浪作用强化了口门段河槽南北沉积环境的差异,北支、北港口门段河槽受到偏北方向风浪作用强烈,沉积物粗化明显。不同泥沙来源是造成河槽整体沉积环境差异的主导因素,南支、南港上段表现为流域来沙的沉积特征,北港、南槽、北槽则表现为流域与海域来沙的混合沉积特征,口外沉积物对口内河槽的影响主要是为口内河槽提供细颗粒物质来源。     

香港地区港湾沙坝的沉积物来源--以香港大屿山岛贝澳湾为例

香港港湾沙坝海滩的沉积物主要来源于河流带来的物质,其他来源是海湾内的残余沉积物和沿岸岩石的侵蚀带来的物质,沙坝的形成与第四纪冰后期海侵无关.由于香港地区河流短小,沉积物数量有限,故香港港湾砂坝坝体小,仅位于湾顶附近,向海推进年代较晚,对海岸环境变化反应甚为敏感.     

长江河口悬浮泥沙的混合过程

根据准同步观测的悬浮泥沙及表层沉积物粒度、流速、含沙量资料, 分析了长江口及临近海域悬浮泥沙在河口的混合过程。长江河口-陆架系统悬浮泥沙中值粒径呈现“细-粗-细”的变化规律, 河口上段悬浮泥沙中值粒径为8.9 μm, 拦门沙海域为10.5 μm, 陆架区为4.5 μm, 北支为9.9 μm, 杭州湾口为5.6 μm, 泥沙类型为粘土质粉砂。河口上段和陆架区悬浮泥沙与表层沉积物的垂向混合作用较弱, 拦门沙区域二者发生强烈的混合和交换, 悬浮泥沙在由长江河口向陆架系统输移过程中仅有表层泥沙保留了流域输入的泥沙粒度特征。长江口悬浮泥沙中值粒径与含沙量呈良好的正相关关系, 水流的剪切作用是引起拦门沙海域泥沙再悬浮、近底高含沙量和悬浮泥沙粒径增加的主要原因, 悬浮泥沙粒径和含沙量的增加主要由粉砂组分的增加引起。2007 年长江河口区范围内悬浮泥沙中值粒径比2003 年普遍减小11％, 含沙量比2003 年减小22%, 河口上段含沙量对流域来沙减少的响应最为敏感, 而拦门沙区的泥沙粒径对流域来沙减少的响应最敏感。在长江流域来沙量减少的背景下, 河口拦门沙区域仍能维持较高的含沙量, 主要缘于河口系统内部的供沙     

The stratigraphic and structural evolution of the Dzereg Basin, western Mongolia: clastic sedimentation, transpressional faulting and basin destruction in an intraplate, intracontinental setting

The Dzereg Basin is an actively evolving intracontinental basin in the Altai region of western Mongolia. The basin is sandwiched between two transpressional ranges, which occur at the termination zones of two regional‐scale dextral strike‐slip fault systems. The basin contains distinct Upper Mesozoic and Cenozoic stratigraphic sequences that are separated by an angular unconformity, which represents a regionally correlative peneplanation surface. Mesozoic strata are characterized by northwest and south–southeast‐derived thick clast‐supported conglomerates (Jurassic) overlain by fine‐grained lacustrine and alluvial deposits containing few fluvial channels (Cretaceous). Cenozoic deposits consist of dominantly alluvial fan and fluvial sediments shed from adjacent mountain ranges during the Oligocene–Holocene. The basin is still receiving sediment today, but is actively deforming and closing. Outwardly propagating thrust faults bound the ranges, whereas within the basin, active folding and thrusting occurs within two marginal deforming belts. Consequently, active fan deposition has shifted towards the basin centre with time, and previously deposited sediment has been uplifted, eroded and redeposited, leading to complex facies architecture. The geometry of folds and faults within the basin and the distribution of Mesozoic sediments suggest that the basin formed as a series of extensional half‐grabens in the Jurassic–Cretaceous which have been transpressionally reactivated by normal fault inversion in the Tertiary. Other clastic basins in the region may therefore also be inherited Mesozoic depocentres. The Dzereg Basin is a world class laboratory for studying competing processes of uplift, deformation, erosion, sedimentation and depocentre migration in an actively forming intracontinental transpressional basin.     

加拿大海盆与楚科奇海沉积物岩芯中好气异养细菌的分布

本文用MPN法测定了两种培养温度下加拿大海盆与楚科奇海10根沉积物岩芯中182份样品的好气异养细菌(GAB)的检出率和含量。结果发现沉积物中GAB检出率高,GAB平均值为4.46×107个·g-1(4℃)和5.47×107个·g-1(25℃)。最高GAB含量出现于20-22cm层,GAB含量在沉积物各层位间波动,总体上呈现中下层沉积物GAB含量低于表层之势。25℃培养时能提高GAB检出率和含量。温度的提高将可能改变测区沉积物GAB的生存环境和生存状况。纬度区间的差异似显出测区中部GAB检出率和含量高于高、低纬度区间之状(4℃培养明显于25℃)。浅水区沉积物中的GAB含量较低,而水越深则GAB含量似越高,以25℃为明显。     

Changing of the guards: Detrital zircon provenance tracking sedimentological reorganization of a post-Gondwanan rift margin

Understanding the development of sedimentary systems during continental rifting is important for tracking environmental change and lithospheric processes. Conceptual models have been developed for the sourcing, routing and facies architecture of sediments in rift-settings, driven in part by quantitative sediment tracking. Here, we present laser ablation split-stream detrital zircon U/Pb geochronology and Hf-isotopes for post-rift (Cretaceous-Paleogene) clastic sediments from Ocean Drilling Program (ODP) wells and Plio-Pleistocene palaeoshoreline material, from the southern margin of Australia. Provenance results are contextualized through comparison with well-characterized source regions and regional pre- and syn-rift sediment reservoirs to track changes associated with Australia-Antarctica separation during East Gondwana break-up. The provenance character of the post-rift sediments studied are distinct from pre-existing sediment reservoirs and demonstrate termination of previously stable sediment routing systems and a dominance of local basement of the Proterozoic Madura and Coompana provinces (~1.2 Ga and CHUR-like Hf-signatures; Moodini Supersuite) in offshore ODP wells. A composite post-rift Cretaceous?-Eocene sample in the easternmost well expresses characteristic Phanerozoic zircon age signatures associated with source regions in eastern Australia that are interpreted to reflect inversion in the Ceduna Sub-basin to the east. Detrital zircon signatures in Plio-Pleistocene palaeoshoreline sediment are also relatively distinct, indicating derivation from coastal erosion in the Leeuwin Complex (~0.5 and 0.7 Ga subchondritic grains) and Albany–Fraser Orogen (~1.2 Ga subchondritic grains) several hundred, to over a thousand kilometers to the west. Collectively, results highlight the fundamental geological processes associated with rifting that dramatically change the character of sediment provenance via (a) isolation of pre-existing primary and secondary sources of detritus, (b) development of new source regions in basin compartmentalized highs and localized fault scarps, and (c) establishment of marine and coastal currents that redefine clastic sediment transport.     

A seismic study along the East Greenland margin from 72°N to 77°N

Around 4370 km of new seismic reflection data, collected along the East Greenland margin between 71°30'N and 77°N in 2003, provide a first detailed view of the sediment distribution and tectonic features along the East Greenland margin. After processing and converting the data to depth, we correlated ODP-Site 913 stratigraphy into the new seismic network. Unit GB-2 shows the greatest glacial sediment deposits beneath the East Greenland continental shelf. This unit is characterized by the beginning of prograding sequences and has, according to our stratigraphic correlation, a Middle Miocene age. It might have been caused by rapid changes in sea level and/or glacial erosion by an early ice sheet or glaciers along the coast. A basement high, presumably a 360 km long basement structure at 77°N–74°54'N, prevents continuous sediment transport from the shelf into the deep sea area in times before 15 Myr. The origin of this prominent structure remains speculative since no rock sample from this structure is available. Seaward dipping reflectors at the eastern flank of this structure strongly support that it is a volcanic construction and is most likely emplaced on continental or transitional crust. The compilation of sediment thickness provide an insight into the regional sediment distribution in the Greenland Basin. An average sediment thickness of 1 km is observed. The north bordering Boreas Basin has a sediment thickness of 1.8 km close to the Greenland fracture zone (GFZ).     

Clinoform growth and sediment flux into late Cenozoic Qiongdongnan shelf margin,South China Sea

The South China Sea continental margin in the Qiongdongnan Basin (QDNB) area has incrementally prograded since 10.5 Ma generating a margin sediment prism more than 4km-thick and 150–200 km wide above the well-dated T40 stratigraphic surface. Core and well log data, as well as clinoform morphology and growth patterns along 28 2D seismic reflection lines, illustrate the evolving architecture and margin morphology; through five main seismic-stratigraphic surfaces (T40, T30, T27, T20 and T0) frame 15 clinothems in the southwest that reduce over some 200 km to 8 clinoforms in the northeast. The overall margin geometry shows a remarkable change from sigmoidal, strongly progradational and aggradational in the west to weakly progradational in the east. Vertical sediment accumulation rate increased significantly across the entire margin after 2.4 Ma, with a marked increase in mud content in the succession. Furthermore, an estimate of sediment flux across successive clinoforms on each of the three selected seismic cross sections indicate an overall decrease in sediment discharge west to east, away from the Red River depocenter, as well as a decrease in the percentage of total discharge crossing the shelf break in this same direction. The QDNB Late Cenozoic continental margin growth, with its overall increased sediment flux, responded to the climate-induced, gradual cooling and falling global sea level during this icehouse period.     

Structural evolution and the partitioning of deformation during basin growth and inversion: A case study from the Mizen Basin Celtic Sea,offshore Ireland

The Celtic Sea basins lie on the continental shelf between Ireland and northwest France and consist of a series of ENE–WSW trending elongate basins that extend from St George’s Channel Basin in the east to the Fastnet Basin in the west. The basins, which contain Triassic to Neogene stratigraphic sequences, evolved through a complex geological history that includes multiple Mesozoic rift stages and later Cenozoic inversion. The Mizen Basin represents the NW termination of the Celtic Sea basins and consists of two NE–SW-trending half-grabens developed as a result of the reactivation of Palaeozoic (Caledonian, Lower Carboniferous and Variscan) faults. The faults bounding the Mizen Basin were active as normal faults from Early Triassic to Late Cretaceous times. Most of the fault displacement took place during Berriasian to Hauterivian (Early Cretaceous) times, with a NW–SE direction of extension. A later phase of Aptian to Cenomanian (Early to Late Cretaceous) N–S-oriented extension gave rise to E–W-striking minor normal faults and reactivation of the pre-existing basin bounding faults that propagated upwards as left-stepping arrays of segmented normal faults. In common with most of the Celtic Sea basins, the Mizen Basin experienced a period of major erosion, attributed to tectonic uplift, during the Paleocene. Approximately N–S Alpine regional compression-causing basin inversion is dated as Middle Eocene to Miocene by a well-preserved syn-inversion stratigraphy. Reverse reactivation of the basin bounding faults was broadly synchronous with the formation of a set of near-orthogonal NW–SE dextral strike-slip faults so that compression was partitioned onto two fault sets, the geometrical configuration of which is partly inherited from Palaeozoic basement structure. The segmented character of the fault forming the southern boundary of the Mizen Basin was preserved during Alpine inversion so that Cenozoic reverse displacement distribution on syn-inversion horizons mirrors the earlier extensional displacements. Segmentation of normal faults therefore controls the geometry and location of inversion structures, including inversion anticlines and the back rotation of earlier relay ramps.     

白令海和楚科奇海总好气异养细菌丰度和对温度的适应性

用平皿培养计数法测定了白令海和楚科奇海测区水和沉积物中的总好气异养细菌(GAB)的丰度 ,并进行了比较。分析了不同海区、测点、不同层次沉积物中GAB丰度及在不同温度中的适应性。结果表明 ,水中GAB检出率大于沉积物 ,但丰度仅为后者的 0 .0 7% ;表层沉积物中GAB检出率高于其它层次 ;白令海GAB检出率、丰度及变幅均高于楚科奇海。所有站点沉积物中GAB含量平均约为 31 66.3× 1 0 2 CFU·g- 1 (湿 ) ;沉积物GAB丰度大致显出低纬度区大于高纬度区之势。温度试验结果表明所试GAB中多数为适冷菌 ,少数可能为中温菌 ,显示出北极海洋细菌对温度有较强的适应性