Simulating the Greenland atmospheric boundary layer     

BRUCE DENBY  WOUTER GREUELL  JOHANNES OERLEMANS 《地球，A辑:动力气象学与海洋学》2002,54(5):529-541

  相似文献   

Columnar calcites as testimony of diagenetic overprinting at the boundary between Upper Tournaisian dolomites and limestones (Belgium): multiple origins for apparently similar features     

PETER NIELSEN  PHILIPPE MUCHEZ  WOUTER HEIJLEN  A. E. TONY FALLICK†  EDDY KEPPENS‡  DOMINIQUE WEIS§  RUDY SWENNEN 《Sedimentology》2005,52(5):945-967

In topographic flat areas, sedimentary settings may vary from one outcrop to another. In these settings, calcite precipitates may yield macroscopically similar columnar features, although they are products of different sedimentary or diagenetic processes. Three columnar calcite crystal fabrics, i.e. rosettes, palisade crusts and macro-columnar crystal fans, have been differentiated near and at the contact between Upper Tournaisian dolomites and limestones along the southern margin of the Brabant-Wales Palaeohigh. Their petrographic characteristics, and geochemical and fluid inclusion data provide information on the (dia)genetic processes involved. Rosettes composed of non-luminescent columnar calcite crystal fans (1–5 cm in diameter) developed on top of one another, forming discrete horizons in repetitive sedimentary cycles. The cycles consist of three horizons: (I) a basal horizon with fragments from the underlying horizon, (II) a micrite/microspar horizon with incipient glaebules, (III) an upper horizon consisting of calcite rosettes, with desiccation features. The petrographical features and δ¹⁸O signatures of −10·0 to −5·5‰ and δ¹³C values of −5·5 to −3·2‰ support either evaporative growth, an evaporative pedogenic origin, or overprinting of marine precipitates. Palisade crusts, composed of a few to 10 mm long non-luminescent calcite crystals, coat palaeokarst cavities. Successive palisade growth-stages occur which are separated by thin laminae of micrite or detrital quartz, displaying a geopetal arrangement. Palisade crusts are interpreted as intra-Mississippian speleothems. This interpretation is supported by their petrographic characteristics and isotopic signature (δ¹⁸O = −8·7 to −6·5‰ and δ¹³C = −4·8 to −2·5‰). Macro-columnar crystals, 1–50 cm long, developed mainly perpendicular to cavity walls and dolomite clasts. Crystal growth stages in the macro-columnar crystals are missing. δ¹⁸O values vary between −16·4 and −6·8‰ and δ¹³C values between −5·2 and −0·9‰. These features possibly support a late diagenetic high temperature precipitation in relation to hydrothermal karstification.  相似文献   

Architecture of the Castissent fluvial sheet sandstones, Eocene, South Pyrenees, Spain   总被引：1，自引：0，他引：1  

MARIANO MARZO  WOUTER NIJMAN†  CAI PUIGDEFABREGAS‡ 《Sedimentology》1988,35(5):719-738

The Castissent Formation represents a phase of strong fluvial progradation within the fluvio-deltaic Montanyana Group, probably enhanced by the late Ypresian sea-level fall. The structural setting is characterized by the emplacement of the South Pyrenean nappes. The major architectural feature of the Formation is the superposition of three multilateral and multistorey sheet sandstone complexes (A, B and C), interbedded in finer floodplain deposits and dark-grey mudstones of brackish transitional origin. The structure of the sheet sandstone complexes is exemplified by the detailed analysis of the lower sheet sandstone complex (A), 25 m thick, 6 km wide and exposed over 25 km of its length. Three types of channel-fill sandstones serve as components: (1) lenticular-bedded bodies, interpreted as braided stream deposits, (2) lateral accretion-bedded bodies, intepreted as meandering stream deposits, and (3) ribbons, originating from laterally stable and short-lived offshoot or crevasse channels. By coalescence and/or stacking of these channel-fill types, higher-order architectural units (A1, A2, A3) have been formed that together build the sheet sandstone complex. On the basis of downstream variation in proportion and geometrical relation between the channel-fill components, three depositional zones have been differentiated within the fluvial system. Each zone is characterized by specific architectural processes: (1) alternation of minor aggradational-degradational cycles in the proximal valley, (2) generation of new alluvial belts in the intermediate nodal avulsion zone, and (3) successive random avulsion processes with development of semipermanent crevasse channels or minor distributaries in the distal distributive zone. The sedimentation of the Castissent Formation was structurally controlled by an interplay of vertical basement movement due to thrust stacking in the hinterland and surficial thrust displacement to the foreland resulting in alternating southward and northward shift of the fluvial system.  相似文献