The structure and kinematics of substrate entrainment into high-concentration sandy turbidites: a field example from the Gorgoglione 'flysch' of southern Italy

Sandy turbidites commonly show evidence for significant dynamic coupling with their substrate. The resulting deformation can be described using structural kinematic methods, linked to palaeoflow indicators, to better understand the links between flow and entrainment processes. A field example from the syn‐orogenic Gorgoglione Flysch, a succession of upper Miocene turbidites deposited into a deforming array of thrust‐top basins in the southern Apennine thrust belt, Italy, is described. The succession contains metre‐scale packages of alternating sandy turbidites and shales but is notable for containing > 100 m thick, massive sandbodies. These are structureless apart from sporadic horizons of aligned mud clasts. Commonly, the substrate beneath the massive sandbodies is deformed, with minor folds and thrusts verging in the direction of palaeoflow determined from tool marks and flutes at the base of these sandbodies. Structural studies from the base of a selected massive sandbody have identified that the substrate mud has been injected upwards, with flames sheared over in the direction of palaeoflow. Thus the substrate has deformed and become entrained during emplacement of the massive sandy body. At some locations, the substrate can be traced into the overlying deposit, with substrate clay beds becoming boudinaged and entrained into the sandbody. Analysis of the orientation of the mud clasts indicates that this bed disruption and incorporation into the sandy massive‐bed turbidite was an organized, viscous process. These features indicate that significant shear stress was partitioned out of the flow and onto the substrate. The incorporation and disruption of substrate into the sandbody suggest that post‐disruption strains increase upwards – implying that displacement gradients increased into the flow. These behaviours, showing variations in strain partitioning between the flow and its substrate, are explored in terms of evolving flow dynamics and substrate rheology.     

Discrete visibility problems and graph algorithms

Many problems of practical interest involve line-of-sight on a topographic surface. Some such problems can be successfully studied on the basis of the mutual visibility among a finite number of representative points. Such visibility problems can be formalized and resolved as graph problems. In this paper, we show that graph algorithms can be useful to find efficient solutions for discrete visibility problems in several cases. On the basis of results from the theory of complexity, we give some practical rules to apply such an approach. We further investigate the solution of some relevant visibility problems under this perspective.     

青藏高原东缘九寨沟高寒钙华分类与命名

九寨沟钙华景观不仅有着独特的旅游与美学价值,在古气候、古灾害、古地震/活动构造、高原隆升以及人类世等研究中也能提供重要的地质档案。无论从旅游与科普的角度,还是从科学研究出发,开展钙华分类研究必然是前提、也是基础。基于地球系统科学理论,从物质来源到沉积环境,分析了无机和有机对钙华沉积的控制因素,按照相（分为亚相、微相）、类（分为大类、亚类）的沉积特征对钙华进行了分类,划分依据是:沉积环境决定了水动力条件与生物参与度,进而形成了千变万化的钙华沉积形态,最终架构了丰富多彩的钙华景观。所划分的结构—成因类型对“九寨沟式钙华”的科学研究有重要指导意义;从旅游与科普角度开展的钙华地貌—形态分类,可为大众旅游、科普以及管理部门提供更高的辨识度及生态保育参考。      

Discontinuous Melt Extraction and Weak Refertilization of Mantle Peridotites at the Vema Lithospheric Section (Mid-Atlantic Ridge)

Melting processes beneath the Mid-Atlantic Ridge were studiedin residual mantle peridotites sampled from a lithospheric sectionexposed near the Vema Fracture Zone at 11°N along the Mid-AtlanticRidge. Fractional and dynamic melting models were tested basedon clinopyroxene rare earth element and high field strengthelement data. Pure fractional melting (non-modal) cannot accountfor the observed trends, whereas dynamic melting with criticalmass porosity <0·01 fits better the measured values.Observed microtextures suggest weak refertilization with 0·1–1%quasi-instantaneous or partially aggregated melts trapped duringpercolation. The composition of the melts is evaluated, togetherwith their provenance, with respect to the garnet–spineltransition. Partial melts appear to be aggregated over shortbut variable intervals of the melting column. Deep melts (generatedwithin the garnet stability field at the base of the meltingcolumn) escape detection, being separated from the residuesby transport inside conduits or fractures. The temporal evolutionof the melting process along the exposed section shows a steadyincrease of mantle temperature from 20 Ma to present. KEY WORDS: mantle partial melting; abyssal peridotite; trace element; refertilization; Vema Fracture Zone     

COMPARISON AMONG EMPIRICAL PROBABILITY DENSITY FUNCTIONS OF THE VERTICAL VELOCITY IN THE SURFACE LAYER BASED ON HIGHER ORDER CORRELATIONS

Vertical velocity fluctuations were measured in theatmospheric surface layer by means of an ultrasonic anemometer andhigher order correlations were calculated on two time series, recordedin unstable and neutral conditions, and selected for the wholemeasurement period on the basis of the inversion test (stationaritytest). Comparisons have been made between observed and predictedcorrelations by considering Gaussian joint-PDF and Gram-Charlierseries expansions truncated to the fourth and sixth order as doneearlier by Frenkiel and Klebanoff. A bi-Gaussian PDF, given by amixture of two Gaussian PDFs, has also been considered. This lasthas been constructed assuming that either the first three or the firstfour moments are given, and the relationships between correlationfunctions of different order are derived. The departure from Gaussianbehaviour in both stability conditions is derived. Though Gram-Charlier series expansions show a good correspondence toexperimental reality, their use as non-Gaussian probabilitydistributions cannot be suggested in theoretical approaches andshould be considered with care in practical applications, due topossible occurrences of small negative probabilities. The resultsshown in this paper support the applicability of the bi-Gaussian PDFcreated using up to the fourth moment.