Calpionellid biostratigraphy of the Upper Tithonian–Upper Valanginian interval in Western Sicily (Italy)

A revision of the calpionellid bio-chronostratigraphy in Western Sicily (Italy) was carried out, in order to update the taxonomy of this group, through the identification of some genera (Borziella, Longicollaria, Chitinoidella, Dobeniella, Sturiella, Borzaiella and Praecalpionellites) and species (Remaniella catalanoi Pop, Remaniella duranddelgai Pop, Remaniella colomi Pop, Remaniella borzai Pop, Remaniella filipescui Pop) recorded for the first time in the area. The studied sections, belonging to the Trapanese and Saccense Domains (Western Sicily), include at the base the upper portion of the Rosso Ammonitico Unit (Upper Tithonian), followed by the Lattimusa Formation (Lower Cretaceous). The quantitative and biostratigraphic analysis of the calpionellid assemblages allowed us to identify 13 assemblages and to define some important bioevents for the Upper Tithonian–Valangianian interval. The recorded calpionellid bioevents allowed us to recognize Zone/Subzone schema, which have been correlated with the bio-chronostratigraphy previously proposed for the Western Tethys. Editorial handling: M. Chiari (Guest) & J.-P. Billon-Bruyat     

Laboratory sustained turbidity currents form elongate ridges at channel mouths

The turbulent flow structure, suspended sediment dynamics and deposits of experimental sustained turbidity currents exiting a channel across a break in slope into a wide tank are documented. The data shed light on the flow evolution and deposit geometry of analogous natural channel‐fed submarine fans. Flows generated in a 0·3 m wide, sloping (0°, 6°, 9° or 20°) channel crossed an angular slope break and spread onto a horizontal tank floor. Flow development comprised: (i) channelized phase (unsteady channel flow developing into steady channel flow); (ii) initial lateral expansion phase (unsteady‐spreading wall jet phase); (iii) constant lateral expansion phase (steady‐spreading wall jet phase); and (iv) rapid waning phase. Phases (i) and (iv) are similar to laterally constrained turbidity currents, but phases (ii) and (iii) are considerably different from such two‐dimensional currents. Steeper channel slopes produced greater flow velocities and turbulence intensities, but these effects diminished markedly with distance from the channel mouth. Flow velocity vectors in the tank had similar patterns for all channel slopes, with a central core of faster velocity and narrow vector dispersion and slower flow with larger dispersion at the jet margins. Suspended sediment concentrations were higher within flow heads and dense basal layers in flow bodies. Time‐averaged acoustic backscatter data showed vertical concentration gradients, confirmed by siphon samples. The deposits comprised a thick central ridge, of similar order width to the channel mouth, with abrupt margins and a surrounding, very thin, fan‐like sheet. The ridge was coarser grained and better sorted than the original sediment, with grain‐size fining downstream, particularly over the fan‐like sheet. The formation of a central ridge suggests that, in the tank, vertical turbulent momentum exchange is more significant for sediment dynamics than spanwise momentum exchange due to lateral expansion. The streamwise elongate geometry of the ridge contrasts with conventional fan‐like geometry found with surge‐type turbidity flows, a result that has widespread stratigraphic and economic implications.     

利用地层切片研究河道砂体发育特征——以南图尔盖盆地Doshan地区为例

针对目的层埋深大、钻井稀少且分布不均所造成的沉积相研究和砂体预测的难题,以哈萨克斯坦南图尔盖盆地Doshan地区为例,在层序地层学和沉积学研究的基础上,充分挖掘三维地震数据的横向分辨能力,利用90°相位转换、地层切片、分频处理等地震沉积学关键技术,通过单井相标定地层切片属性的实际地质意义,应用纵向关联的多张地层切片,识别出阿克沙布拉克组(SQ_8层序)至少发育六期河道,其中SQ_(8-1)旋回内发育两期,为河道发育最广泛、最强烈的时期;SQ_(8-2)旋回内河道稀疏,纵向连续性差;SQ_(8-3)旋回河道分布局限,水体范围缩小,与SQ_(8-1)、SQ_(8-2)相比较具有沉积的继承性特征,反映出水体深度有所变浅,经历了一期以水进为主的水进—水退过程。研究表明,地层切片技术有效地描述了河道的平面几何形态与不连续性,这为本区岩性地层圈闭的描述与预测提供了地质依据。     

Small- to large-scale geographical patterns within the macrobenthic Abra alba community

The Abra alba community is widely spread in the coastal zone of the English Channel and the Southern Bight of the North Sea. The community is located on shallow, fine muddy sands. Its spatial distribution can be broken up into a number of isolated patches (Atlantic French, British and German coast) and one large continuous distribution area (northern France up to the Netherlands). The aim of this study is to investigate the geographical patterns within the macrobenthic A. alba community at different scales: the community's full distribution range (i.e. large scale) and a selected area with a continuous distribution of the A. alba community (i.e. small scale) in relation to structuring environmental variables. Therefore, an analysis of newly collected samples along the Belgian coastal zone was combined with available information on the A. alba community throughout its distribution range. Although the community structure shows a high similarity across the full distribution range of the A. alba community, large- as well as small-scale changes in community composition were observed: the Belgian Continental Shelf (BCS) should be considered as a major transition from the rich southern to the relatively poorer northern distribution area of the A. alba community. At a large scale (i.e. full distribution range), the differences in community structure are expected to result from (1) the specific hydrodynamic conditions in the English Channel (Atlantic ocean waters) and the Southern Bight of the North Sea, with a consequent differential connectivity between the different areas and (2) the climatological and related faunal shift from temperate (English Channel) to boreal conditions (German Bight). At a small scale (i.e. within the continuous distribution area), structural and functional community aspects may result from geographic differences in (1) detrital food availability, related to riverine input and pelagic productivity, along and across the coastline and (2) the amount of suspended matter, impoverishing the A. alba community when excessively available.     

Active folding along a rift-flank: The Catania region case history (SE Sicily)

In this paper a new kinematic and dynamic model on the Recent and active contractional deformation of the Catania region, eastern Sicily, is discussed. The study area represents one of the most seismically active region of the Mediterranean, located at the intersection between the front of the Sicily collision belt and the seismogenic Siculo-Calabrian Rift-Zone. The analysed contractional tectonics form an active triangle zone that originated from the tectonic inversion of a Lower-Middle Pleistocene extensional basin, which was located at the northern edge of the African foreland. The triangle zone consists of two antithetic ENE–WSW oriented thrust-ramps that show evidence of motion during the Holocene and bound a folded belt that involves alluvial deposits as young as 40 ka. These contractional structures represent the final product of the positive tectonic inversion of extensional features located, in the Hyblean Plateau in SE Sicily, along the flank of the active rift zone. The Late Quaternary motions along the inverted structures was accommodated to the west by a major N–S oriented left-lateral fault zone, which separates the active contractional domains from the adjacent sectors of the African margin. As a whole, the Late Quaternary contractional tectonics of SE Sicily have been related to a NW-verging crustal stacking, related to a Mantle intrusion beneath the Hyblean Plateau that developed as effect of the rift-flank deformation. The crustal lineaments, which compose the new kinematic model, represents potentially active seismogenic sources that might be considered in the frame of the seismotectonic picture of the Catania region.     

渤海东部潮流沉积特征及MIS4以来的沉积环境演化

渤海东部发育了典型的潮流沉积,由老铁山水道冲刷槽、辽东浅滩沙脊和渤中浅滩沙席组成。该文基于中国海洋地 质调查最新获取的高分辨率单道地震数据,与水深变化进行对比,将该区的潮流沉积特征与其地震相特征进行精细分析, 同时结合晚第四纪CD5孔的岩性、14C测年和层序地层划分,识别出晚更新世以来的四期层序地层,分别是MIS4以细砂为 主的陆相地层、MIS3以粉砂和黏土为主的滨浅海相沉积地层、MIS2末次盛冰期形成的以粉砂质粘土和细砂质粉砂为主的陆 相沉积地层和全新世（MIS1） 发育的以粉砂质黏土和细砂组成的海相沉积地层。其中全新世地层分别由早期的滨海相沉 积、中期的浅海沉积和晚期的潮流沉积组成。通过这四期层序的研究,揭示了该区MIS4期以来的沉积环境演化。     

Stream response to subsidence from underground coal mining in central Utah

 Short-term geomorphic and hydrologic effects of subsidence induced by longwall mining under Burnout Creek, Utah were evaluated. During the year after longwall mining, 0.3–1.5 m of subsidence was measured near impacted reaches of the mountain stream channel. The major channel changes that occurred in a 700-m reach of Burnout Creek that was subsided from 1992 to 1993 were: (1) increase in lengths of cascades and to a lesser extent glides; (2) increases in pool length, numbers and volumes; (3) increase in median particle diameter of bed sediment in pools; and (4) some constriction in channel geometry. Most of the changes appeared short-lived, with channel recovery approaching pre-mining conditions by 1994. In a 300-m reach of the South Fork that was subsided from 1993 to 1994, only channel constriction was observed, although any impacts on pool morphology may have been confounded by heavy grazing in the riparian reaches during the dry summer of 1994. Similar near-channel sedimentation and loss of pool volume between 1993 and 1994 were noted throughout Burnout Creek and in adjacent, unmined James Creek. Subsidence during the 3-year period had no effect on baseflows or near-channel landslides. Received: 10 April 1998 · Accepted: 21 September 1998     

SEDIMENT LOAD AND ITS INFLUENCE ON CHANNEL PROCESSES OF SOME LARGE RIVERS IN RUSSIA AND CHINA~1

I INTRODUCTIONThe volume and regime of sediment load are the most important factors, which are responsible for theformation, direction and deformation rate of the river channels. Despite the long history of study anddevelopment of sediment load calculation methodology, there are still numerous problems that remain tobe solved such as river pattern and sediment movement and so on (Wang et al, 1997).In this respect, the comparative analysis of sediment load and river channel processes of la…     

延安市冬季边界层风、温场特征分布

本文利用1985年12月25日—1986年1月9日的实测资料,分析了延安市冬季边界层风、温场特征。结果表明:延安市冬季低层逆温持续时间长、强度大,逆温持续期近地面几十米表现为混合层结构。边界层风场十分复杂,时空变化大,地面常为小风状态,风向、风速沿垂直方向有明显切变,低层流场有显著渠道效应,山谷风明显。