浙江江郎山丹霞地貌发育的年代与成因

江郎山位于华南褶皱系、江山-绍兴深断裂和保安-峡口-张村断裂带之间.白垩纪早期这两大断裂的拉张断陷导致峡口盆地的形成,随之主要有下白垩统永康群馆头组(K1g)、朝川组(K1c)和方岩组(K1f)在盆地中的沉积.白垩纪晚期上述两大断裂发生强烈挤压活动,峡口盆地逐渐隆升.新生代以来,峡口盆地在构造抬升中,产生大量张断裂和节理,加速了对岩体的切割,以及岩体被切割后的崩塌,导致了丹霞地貌的发育.江郎山丹霞地貌申报世界自然遗产的主要依据是其特有的壮观而独特的老年期孤峰-巷谷以及生动而逼真的象形石丹霞地貌特征、独特的地台活化现象与重要的岩石学科学研究意义以及该区特有的重要事件地层学和古生物学研究的科学意义.本文根据对江郎山亚峰垂直贯穿于丹霞地貌岩层永康群中辉绿岩脉标本K-Ar法的测年,揭示了当地峡口红层盆地抬升的时代为晚白垩世77.89±2.6Ma BP(K2),这也是我国目前丹霞地貌研究中所测得的可靠年代学数据.     

浙江方岩丹霞地貌类型及其空间组合

浙江方岩突出的丹霞地貌类型有围谷、方山、峰丛、石柱和凹槽等,它们的空间组合沿着北西-南东方向有规律的排列:西北部五峰书院一带的凹槽和岩穴发育典型,中部鸡鸣峰、桃花峰等处分布有大量的新鲜崩积石,东南部石鼓寮的石鼓、石柱尤为突出,在峰丛与平原交汇的东、南和西三侧被围谷所环绕.这种组合体现了随着构造隆升,在以外力作用为主的不断"雕塑"下,丹霞地貌的发育一般经历了差异风化、重力崩塌、流水侵蚀搬运,完成地貌循环侵蚀的过程,期间孕育了绚丽多姿的丹霞地貌,它们主要发育于早白垩世晚期的方岩组(K1f)冲积扇-扇前辫状河相岩层中.其中,岩性的差异风化规律和辫状河相沉积的特点,可以通过对三个样点的实验数据分析加以证实.方岩丹霞地貌是在我国申报世界自然遗产丹霞地貌区中"青年期"类型的突出代表,符合申报世界自然遗产中具有突出、普遍的美学和科学价值的理由.     

中国丹霞地貌的面积概算——粤北坪石红层盆地的实证研究

中国丹霞地貌的中生代优势以及陆相沉积特征是中国的特色也具有世界代表性。通过对中生代主要出露红层盆地室内计算机空间叠置分析,利用大量的野外现场调研检验等手段,计算出不同时期不同规模的红层面积。其中,中侏罗世3个红盆面积45.16×10~4km~2,中、晚侏罗世28个红盆面积149.17×10~4,早白垩世17个红盆面积55.97×10~4km~2,晚白垩世24个红盆面积106.9×10~4km~2,早第三纪31个红盆面积135.73×10~4km~2。通过对实地测量及对比分析,发现红层盆地建造发育成丹霞地貌的贡献率为6.5%左右。可计算中、晚侏罗世红层发育的丹霞地貌面积为9.7×10~4km~2,早白垩世红层发育的丹霞地貌面积3.6×10~4km~2,晚白垩世24个红盆面积6.9×10~4km~2,早第三纪31个红盆面积8.8×10~4km~2,这样统计中国丹霞地貌的总面积为29×10~4km~2。这一数字因丹霞地貌自身发育的阶段性会出现偏差,考虑气候-构造-地貌相互耦合作用的结果,典型丹霞地貌随着时间的推移,增加和减少的面积将达到一个平衡,基本稳定在20×10~4km~2左右,这就是中国丹霞地貌的面积数据。     

滇西思茅盆地西缘早白垩世沉积物源分析及盆地形成和演化探讨

滇西思茅盆地位于澜沧江断裂带和金沙江—红河断裂带之间,呈北西—南东向带状展布,在构造上处于冈瓦纳与欧亚两大构造域的过渡地带,其形成发展与古特提斯的演化、印度板块的向北漂移和俯冲消亡关系十分密切。通过对思茅盆地西缘早白垩世的沉积物分析表明,滇西思茅盆地西缘早白垩世的沉积环境主要为河湖相,沉积物源为盆地西侧的澜沧江造山带。结合构造背景,认为盆地的形成经历了碰撞后裂谷阶段、陆内坳陷阶段、复合型前陆盆地阶段和走滑拉分盆地四个阶段。     

陕北丹霞地貌特征及国内外对比研究

通过野外考察,并结合地质资料和样品分析,对陕北丹霞地貌形成的地质构造背景、红层岩性、形态特征、演化过程等进行系统阐述,并与中国东南部湿润区及国外的典型丹霞地貌进行对比,总结其共性和差异。结果表明：陕北丹霞地貌形成的构造环境为大型内陆坳陷盆地——鄂尔多斯盆地,主要成景地层为洛河组紫红色中-细粒长石石英砂岩,形成于早白垩世的干旱沙漠环境,发育大型交错层理,其碎屑颗粒分选性和磨圆度较好,但结构松散,胶结程度较弱,颗粒表面有碟形撞击坑等典型风成砂岩特征。陕北丹霞地貌最显著的特征是顶部有第四纪黄土盖层,形成覆盖型丹霞,地貌发育总体上处于青年期,整体为高原-峡谷景观,发育密集的沟谷群和连续的丹霞崖壁,但孤立的单体地貌较少。陕北丹霞地貌演化过程可划分为早白垩世红层沉积-晚白垩世红层盆地构造抬升和古丹霞发育-古近纪以来间歇式抬升-第四纪黄土覆盖等4个阶段。国内外对比方面,陕北丹霞与中国东南部湿润区的丹霞地貌在构造环境,物质基础,地貌特征等方面差异较显著,但与美国西部的丹霞地貌存在许多相似性。     

广丰盆地丹霞地貌遥感影像特征

江西广丰盆地红层发育于早白垩世晚期至晚白垩世,盆地内发育石寨、石峰、峰林和峰丛等丹霞地貌景观.通过遥感影像目视解译,建立丹霞地貌遥感影像解译标志,解译出8处丹霞地貌区,归纳为5种丹霞地貌遥感影像特征.丹霞地貌区节理构造发育,节理走向受边界断裂控制,揭示了断裂构造对丹霞地貌发育特征和发育类型的控制作用.     

浙江江郎山丹霞地貌区岩性特征

对浙江江郎山丹霞地貌区主要岩层方岩组(K1f)的22块岩石标本进行常量元素、氧化物含量的X荧光和薄片偏光显微镜鉴定,分析了江郎山丹霞地貌发育的岩性特征与地貌成因的关系:(1)方岩组(K1f)砾岩中的火山岩砾石和岩屑含量普遍较高,SiO2含量普遍也很高(在44.90%～75.80%之间),表明岩性总体上抗风化能力强,这使江郎山丹霞地貌最具特色的"三爿石"历经沧桑仍能巍然屹立,江郎山也因此成为丹霞地貌发育晚年时期的典型代表.(2)方岩组(K1f)的砂岩抗风化能力相对较弱,其胶结物的主要成分为方解石,粒间孔隙约占20%～25%,局部可见方解石胶结物的溶蚀现象.岩石薄片鉴定可看出,其粒间孔隙很可能是方解石胶结物被溶蚀后的结果,而且构成砂岩的岩体的流纹岩岩屑等其本身就具有气孔构造,这些岩屑在显微镜下可见已经强烈泥化,岩体抗风化程度较低,这是构成该区地貌岩性之一的砂岩被侵蚀和风化程度较高的主要原因.(3)在江郎山丹霞地貌发育过程中方岩组(K1f)岩性对地貌的形成起了基础和决定性的作用.这种岩性的特征及抗风化能力的不同导致的差异风化现象,对该区丹霞地貌后期的微地貌发育具有重要的影响,岩性差异风化是江郎山山体崩塌、扁平状洞穴的形成的重要因素,这也为研究江郎山等丹霞地貌山区地质灾害的岩性特征奠定了基础.     

江西永丰-崇仁盆地晚白垩世沉积体及其演化模式

华东南地区白垩纪地壳伸展作用形成一系列SW-NE向展布的陆相断陷盆地,一般由粒度较粗的红色碎屑岩地层充填。赣杭构造带西段的江西永丰-崇仁盆地晚白垩世龟峰群角度不整合覆盖于早白垩世鹅湖岭组碎斑熔岩之上,自下而上包括河口组、塘边组和莲荷组。根据野外露头剖面沉积组构特征,可以识别出冲积扇、河流和湖泊等三种沉积体系。对各沉积相沉积物组成、沉积构造、垂向相序进行了探查认为,研究区上白垩统具有粗-细-粗的粒度变化旋回特征,反映了自下而上由冲积扇、河流到河流、湖泊再到冲积扇、河流沉积体系的有序变化。结合区域构造演化资料,初步建立的盆地沉积演化模式表明,河口组和塘边组为连续沉积,代表了断陷盆地开始发育和湖盆扩大阶段,反映了控盆构造由强烈活跃期到间歇宁静期的逐渐过渡。莲荷组再次以冲积扇和辫状河相砾岩为主,其中大量来自下伏红层的砾石成分说明莲荷组沉积时期控盆构造运动加剧。江西永丰-崇仁盆地沉积体系时空上明显的变化过程,可能是赣杭构造带晚白垩世陆相断陷盆地演化主要受区域断裂控制的一个典型代表。     

兰坪-思茅盆地勐野井组钾盐矿床成矿构造背景

兰坪—思茅盆地是国内唯一发现古钾盐沉积的盆地。对云南兰坪—思茅盆地钾盐成矿背景作了总结与分析,指出中生代以来盆地经历了陆内裂谷形成到消亡、侏罗纪箕状断陷盆地发育、早白垩纪双断式断陷盆地发育、早白垩晚期干化成盐和后期挤压走滑几个阶段。在此基础上通过盐系地层沉积特征的分析,得到了盆地在成盐期(早白垩世晚期)构造活动强烈,由统一的湖盆解体为多个次级成盐盆地,盐类资源的沉积应该分属不同的沉积序列的认识。兰坪—思茅盆地成盐期构造背景分析对于了解该区蒸发岩矿床特征和成矿机理具有重要的参考意义。     

内蒙古卓资县厂不浪银多金属矿床地质特征及找矿方向

厂不浪银多金属矿床产于早白垩世明星沟火山断陷盆地北部边缘,出露地层简单,岩浆岩大致可划分两期,其中早白垩世酸性侵入岩与成矿密切相关。北西向大路-厂不浪断裂(F5)为本区导矿构造,其次级断裂带属容矿构造,北西向断裂控制了矿体的形态、规模和产状。矿床成因类型属受北西向断裂构造控制的低温热液脉型矿床。1、4号主矿体沿走向和倾向均具有尖灭再现、膨缩现象。施工的ZK7-1号钻孔见到的4号矿体具厚度增大,品位变富的趋势,因此,深部找矿是本区未来的找矿方向。     

Age and genesis of the Danxia landform on Jianglang Mountain, Zhejiang Province

Jianglang Mountain is situated at the transitional zone of South China fold-system, Jiangshan–Shaoxing deep fracture zone and Baoan–Xiakou–Zhangcun fracture zone. The forming of the Xiakou basin was attributed to the pull-apart fault depression by the above fractures in earlier Cretaceous, afterward, series deposits such as Guantou formation (K1g), Chaochuan formation (K1c) and Fangyan formation (K1f) which belong to Yongkang group, the lower Cretaceous layer accumulated in the Xiakou basin. In late Cretaceous, the above fractures occurred to extrude and the basin began to uplift, meanwhile, amounts of tension fissures and joints were produced since Cenozoic, which accelerated water-dicing into bed-rock. Consequently, landform-building processing: weathering, eroding and collapsing etc. were prevalent as finally to develop the so-called Danxia landform. The Jianglang Mountain landscape zone of the Danxia landform to apply for world natural relics are relying on unique and unparalleled peak, sky-split valley with vivid stones and reviving of platform. What is more, there is significance of study at lithology, stratigraphy and paleo-biology. According to dating for specimen of ophitic vein through-crossing the Yongkang group of Yafeng Peak by K-Ar method, this article revealed the uplift age of red-bed basin to be 77.89±2.6 MaBP (K2) i.e. late Cretaceous, and it is the first chronological datum of Danxia landform research in China.     

Types and spatial combinations of Danxia landform of Fangyan in Zhejiang Province

The prominent types of Danxia landform in Fangyan include enclosed valleys, mesas, peaks, stone columns and grooves etc. Their spatial combinations have regular configurations along the northwest–southeast direction: typical grooves and caves are located in the northwestern Wufengshuyuan mainly; abundant fresh collapsed stones may be observed in central Jimingfeng and Taohuafeng; stone drums and stone columns are in the southeastern Shiguliao particularly; enclosed valleys are encircling joints of peaks and plains from three directions east, west, and south. Their spatial combinations reflect that the developments of Danxia landform have undergone stages of geomorphic cyclical erosion in the form of weathering, collapse, transportation, sedimentation and other processes, together with the “sculpture” of external forces mainly as tectonic uplift. The picturesque Danxia landform began its formation at that point. Danxia landform developed mainly in the strata of Fangyan Formation (K1f) caused by the alluvial fan-braided river phase of anterior fan in the late period of the Early Cretaceous. Regular patterns of weathering of stones and features of braided alluvial phase sediments may be verified by the analysis of three groups of experimental data. Danxia landform of Fangyan is a unique representative of the “adolescent” development type in the application of the World Natural Heritages status in China, by virtue of its outstanding universal aesthetic and scientific value.     

Oligocene to Early Miocene sedimentation and tectonics in the southern part of the Calabrian-Peloritan Arc (Aspromonte, southern Italy): a record of mixed-mode piggy-back basin evolution

The Calabrian-Peloritan Arc (southern Italy) represents a fragment of the European margin, thrusted onto the Apennines and Maghrebides during the Europe-Apulia collision in the late Early Miocene. A reconstruction of the pre-Middle Miocene tectono-sedimentary evolution of the southern part of the Calabrian-Peloritan Arc (CPA) is presented, based on a detailed analysis of the Stilo-Capo ?Orlando Formation (SCO Fm). Deposition of the SCO Fm occurred in a series of mixed-mode piggy-back basins. Basin evolution was controlled by two intersecting fault systems. A NW-SE oriented system delimited a series of sub-basins and fixed the position of feeder channels and submarine canyons, whereas a NE-SW oriented system controlled the axial dispersal of coarse-grained sediments within each of the sub-basins. From base to top, sedimentary environments change from terrestrial and lagoonal to upper bathyal over a timespan of approximately 12 Myr (late Early Oligocene-late Early Miocene). During this interval, extensional tectonic activity alternated with oblique backthrusting events, related to dextral transpression along the NW-SE oriented faults. This produced a characteristic pulsating pattern of basin evolution. Oligocene-Early Miocene evolution of the W. Mediterranean basin was dominated by ‘roll back’ of the Neotethyan oceanic lithosphere. Considerable extension in the overriding European Plate gave rise to the formation of a back arc-thrust system. The initial stages of Calabrian Basin evolution are remarkably similar to the evolution of rift basins in the back arc (Sardinia). The Calabrian basins, which are inferred to have originated as thin-skinned pull-apart basins, were subsequently incorporated into the Apennines-Maghrebides accretionary wedge by out-of-sequence thrusting, and became decoupled from the back arc. Periodic restabilization of the accretionary wedge, resulting in an alternation of backthrusting and listric normal faulting, provides an explanation for the structural evolution of these mixed-mode basins. The basins of the southern part of the CPA may be termed ‘spanner’ or ‘looper’ basins, in view of their characteristic pulsating structural evolution, superimposed upon their migration toward the foreland. This new term adequately accounts for the occurrence of tectonic inversions in long-lived piggy-back basins, as expected in the light of the dynamics of accretionary wedges.     

Types and spatial combinations of Danxia landform of Fangyan in Zhejiang Province

The prominent types of Danxia landform in Fangyan include enclosed valleys, mesas, peaks, stone columns and grooves etc. Their spatial combinations have regular configurations along the northwest-southeast direction: typical grooves and caves are located in the northwestern Wufengshuyuan mainly; abundant fresh collapsed stones may be observed in central Jimingfeng and Taohuafeng; stone drums and stone columns are in the southeastern Shiguliao particularly; enclosed valleys are encircling joints of peaks and plains from three directions east, west, and south. Their spatial combinations reflect that the developments of Danxia landform have undergone stages of geomorphic cyclical erosion in the form of weathering, collapse, transportation, sedimentation and other processes, together with the “sculpture” of external forces mainly as tectonic uplift. The picturesque Danxia landform began its formation at that point. Danxia landform developed mainly in the strata of Fangyan Formation (K₁ f) caused by the alluvial fan-braided river phase of anterior fan in the late period of the Early Cretaceous. Regular patterns of weathering of stones and features of braided alluvial phase sediments may be verified by the analysis of three groups of experimental data. Danxia landform of Fangyan is a unique representative of the “adolescent” development type in the application of the World Natural Heritages status in China, by virtue of its outstanding universal aesthetic and scientific value.     

Mineral-Potential Mapping for MVT Deposits with Limited Data Sets Using Landsat Data and Geological Evidence in the Borden Basin, Northern Baffin Island, Nunavut, Canada

Posterior probabilities of occurrence for Zn-Pb Mississippi Valley Type (MVT) mineralization were calculated based on evidence maps derived from regional geology, Landsat-TM, RADARSAT-1, a digital elevation model and aeromagnetic data sets in the Borden Basin of northern Baffin Island, Canada. The vector representation of geological contacts and fault traces were refined according to their characteristics identified in Landsat-TM, RADARSAT-1, DEM, slope, aspect, and shaded relief data layers. Within the study area, there is an association between the occurrence of MVT mineralization and proximity to the contact of platformal carbonates and shale units of the adjacent geological formation. A spatial association also tends to exist between mineralization and proximity to E-W and NW-SE trending faults. The relationships of known MVT occurrences with the geological features were investigated by spatial statistical techniques to generate evidence maps. Supervised classification and filtering were applied to Landsat-TM data to divide the Society Cliffs Formation into major stratigraphic subunits. Because iron oxides have been observed at some of the MVT occurrences within the Borden Basin, Landsat-TM data band ratio (3/1) was calculated to highlight the potential presence of iron-oxides as another evidence map. Processed Landsat-TM data and other derived geological evidence maps provided useful indicators for identifying areas of potential MVT mineralization. Weights of evidence and logistic regression were used independently to integrate and generate posterior probability maps showing areas of potential mineralization based on all derived evidence maps. Results indicate that in spite of the lack of important data sets such as stream or lake sediment geochemistry, Landsat-TM data and regional geological data can be useful for MVT mineral-potential mapping.     

根据临汾盆地的演化过程分析“丁村组”的年代

自1954年发现“丁村人”化石至今,“丁村组”的年代长期存在很大争论。通过对S₅以来临汾盆地地貌沉积演化过程的研究,揭示出“丁村组”的堆积是在S₁早期的一次区域构造抬升引起盆地湖退后才开始发生的,时间距今大约13万年。结合上覆“丁村组”的黄土古土壤分析,发现其堆积结束于距今约5.2万年。“丁村组”的堆积与气下S₁古土壤的发育和L₁黄土下半段的堆积几乎是同期的,其形成时代横跨了中、晚更新世。     

The interior rifts of the Yemen - analysis of basin structure and stratigraphy in a regional plate tectonic context

The full extent of Mesozoic rift basins within interior Yemen has only recently been established. This work presents a detailed documentation of the stratigraph)., structure and basin development of the Marib-Shabwa and Sirr-Sayun basins, and the Jeza Trough. Yemen is located at the south-western margin of the Arabian Plate, which for most of its early geological history formed part of the northern passive margin of Gondwanaland. Mesozoic break up of the super-continent was associated with major rifting in the Late Jurassic (main phase) and Early Cretaceous. Orientation of the rift basins reflects an inheritance from deep-seated Precambrian structural trends which cross the Arabian Plate. The resultant structure of basement highs, tilted fault blocks, marginal terraces and central graben highs is illustrated in a series of detailed cross-sections. A comprehensive stratigraphic framework has also been established for the Jurassic and Cretaceous basin-fill, enabling thickness and facies variations to be analysed. This reveals a clear shift in the main period of fault-related, high sediment accumulation rates, both within and across the three interior basins of Yemen. In the western Marib-Shabwa Basin, the fill is dominantly Late Jurassic, whilst the eastern Shabwa Basin and Sirr-Sayun Basin exhibit a progressively increased, and younger, Early Cretaceous fill. The main period of fault-related sedimentation in the most easterly basin, the Jeza Trough, is wholly Cretaceous. Plate tectonic reconstructions of the area for this period have documented the separation and subsequent north-eastward movement of the Indian Plate, away- from Africa-Arabia. We believe this may have been the causal mechanism in the progressive eastward migration of rift activity in the Yemen.     

Climatic control on Lower Cretaceous sedimentation in a playa-lake system of a tectonically active basin (Huérteles Alloformation,Eastern Cameros Basin,North-Central Spain)

The Berriasian Huérteles Alloformation is the fourth alloformation in which the Tithonian-Berriasian Depositional Sequence is divided in Eastern Cameros Basin. This depositional sequence can be recognized in several basins East of The Iberian Plate. Huérteles Afm. was deposited in a trough with a NW-SE orientation and strong subsidence. In this trough the sedimentary record exceeds 1000 m in thickness for this alloformation. The Basin shows a marked asymmetry, with the highly subsident trough displaced to the NE.The sedimentary system consists of a playa complex, in which several subenvironments can be distinguished. The proximal or bajada environments were located to the west. The terrigenous materials, that constitute the sediments of these areas, come from the erosion of materials previously deposited in the Basin. To the East the environments were mainly saline lakes, that received siliciclastic materials from the Northeast, where the main border fault system was situated.The vertical sequence in the central part of the Basin (where a perennial saline lake was located) shows a marked cyclicity, with primary sequences about 10 m thick. These consist of laminated limestones in their lower part, and carbonate breccias at the top. These primary sequences represent the filling of a lake, with relatively dilute waters at first, passing gradually into a saline lake. This reflects a transition from humid to arid climatic periods.Additionally there is another cyclicity of a higher rank indicated by sequences about 300 m thick These major sequences are formed by primary sequences. The minor primary sequences are mainly composed of laminated limestones in the lower part of the major sequences, and the carbonate breccias dominate in the upper part of the major sequences. These major sequences may indicate longer periods of climatic variation, that varied from a relatively humid to an arid climate. This sequential arrangement was accentuated by the strong tectonic activity during sedimentation, that produced large slump structures where evaporites were more abundant.This is the sixth paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits.