Basin-wide turbidites in a Miocene, over-supplied deep-sea plain: a geometrical analysis

Eighteen stratigraphic sections, 200 m thick on average, were logged in basin plain deposits of the Marnoso-arenacea Formation (Miocene, northern Apennines) over an area of 123 × 27 km. Turbidites form 80–90% of the facies association, hemipelagites the remainder. Thin and thick-bedded turbidites are separated by an approximate statistical boundary at 40 cm; most prominent beds (> 1 m thick) are qualified as megaturbidites. With reference to the main supply-dispersal system (NW to SE), the basin plain can be axially subdivided into proximal, intermediate and distal segments by means of the following parameters: bulk sand content, sand/shale ratio in turbidites, mean thickness of individual layers and component beds, and frequency of thick layers. Almost 40% of thick-bedded turbidites can be traced over the whole study area. These basin-wide deposits form the bulk of the basin fill. Geometrical reconstruction shows that some sandstone beds taper downcurrent from the proximal plain or the adjacent fan area while others thin upcurrent suggesting sand by pass of the fan. Mudstone beds in general thicken towards the end and the margins of the plain indicating that turbidite mud, besides bypassing the fan as a rule, was affected by ponding in the plain. Thin-bedded turbidites have a low sand/shale ratio or are completely muddy representing either tails of sandier turbidites of the outer fan (lobe and fringe deposits) or sheets extending to a great part of or to the whole plain. Sandstone lobes advanced from fans into the plain for 40–50 km gradually thinning and shaling out over a transitional zone of 10–20 km. Their internal geometry shows simple and complex growth patterns: end members are defined as progradational and aggradational. Estimates of original length, width and volume of individual turbidites strongly suggest that flows were usually confined and deflected by basin slopes regardless of source location. Basinal deposits are thus characterized by great thickness and volume, abundance of mud and fine sand, extremely low lateral gradients of thickness and grain size (but rapid wedging near the sides). The basin plain developed as a part of an elongated, oversupplied basin with a ‘highly efficient’, probably delta-fed, dispersal system.     

海绵和海鞘中可培养放线菌的分离与多样性比较

在相同的分离培养条件下,为比较地域差别较大的福建海域海绵动物(山海绵Mycale sp.和网架海绵Stylissa sp.)和海南海域海鞘动物(皱瘤海鞘Styela plicata和乳突皮海鞘Molgula manhattensis)之间可培养放线菌多样性的差异,作者采用5种放线菌分离培养基和1种细菌通用培养基,对海绵和海鞘中的放线菌进行分离培养。采用16S rRNA 基因限制性片段长度多态性(Restriction Fragment Length Polymorphism, RFLP)分析和序列分析,揭示其多样性。共获得可培养放线菌198株,其中从海绵中分离到87株放线菌,从海鞘中分离到111株放线菌。RFLP分析表现为38种不同的图谱类型。16S rRNA基因序列分析表明,从海绵中分离到的放线菌包括6个放线菌属,其中有2株菌的16S rRNA基因序列与最相近的菌株相似性低于97%,可能是潜在的新菌株;从海鞘中分离到的放线菌包括7个放线菌属,有8株可能是潜在的新菌株。比较海绵和海鞘中可培养放线菌的多样性发现,从海绵中分离到的放线菌,除节细菌(Arthrobacter)以外,均包括在海鞘分离的放线菌属中。海鞘相关放线菌多样性水平不容忽视,是除海绵之外另一获得新型放线菌资源以及药用天然活性产物的重要来源。     

EXPERIMENTAL STUDY ON DAM-BREAK FLOOD WAVES OVER MOVABLE BED CHANNEL

1 INTRODUCTION During the last century, the propagation of dam-break flood waves has been the object of intense scientific and technical activity. The topic was initially approached by finding analytical solutions for the shallow-water equations in schematic situations featuring fixed bed and nil flow resistance. An example of this approach can be found in Stoker (1957). The vertiginous increase of automatic calculus which occurred during the last few decades has made it possible to ach…