Improved Geometric Model of Extensional Fault–bend Folding

Extensional fault–bend folds, also called rollovers, are one of the most common structures in extensional settings. Numerous studies have shown that oblique simple shear is the most appropriate mechanism for quantitative modeling of geometric relations between normal faults and the strata in their hanging walls. However, the oblique simple shear has a rather serious issue derived from the shear direction, particularly above convex bends. We use geometric and experimental methods to study the deformation of extensional fault–bend folds on convex bends. The results indicate that whether the fault bends are concave or convex, the shear direction of the hanging wall dips toward the main fault. On this basis, we improve the previous geometric model by changing the shear direction above the convex bends. To illustrate basin history, our model highlights the importance of the outer limit of folding instead of the growth axial. Moreover, we propose a new expression for the expansion index that is applicable to the condition of no deposition on the footwall. This model is validated by modeling a natural structure of the East China Sea Basin.     

Formation and Evolution of a Paleosol across the Lower Silurian-Lower Permian Boundary in Zunyi District, Northern Guizhou, China and Its Paleoenvironment and Paleoclimate Implications

This paper presents a set of bulk geochemical and mineralogical data from a paleoweathering profile located in Zunyi District, Northern Guizhou, China. It was formed at the top of the Hanjiadian Formation of the Lower Silurian. A truncated, argillic, gleyed, kryptic paleospodosol is recognized in the paleoweathering profile. Ratios of immobile elements (Ti/Zr, Ti/Al) and their binary (e.g., Nb vs. Zr/TiO2 and Th/Sc vs. Zr/Sc), triangular diagrams (La-Th-Sc, Th-Sc-Zr/10, Zr-Cr-Ga) reflect that the Gaojiayan paleosol is the product of in-situ weathering of gray-green silty mudstone of the underlying Hanjiadian Formation. Mass balance calculations indicate K enrichment and Na enrichment in the upper and lower portions of paleosol, respectively. These findings both are the results of transgression, which brings substantial concentrations of such elements as K, Na, and Sr. In particular, K enrichment is achieved by the illitization of kaolinite. The biological processes of terrestrial vascular plants also enhance K concentration, especially at the top of the paleosol. Na enrichment is a consequence of albitization and/or adsorption by clay minerals through cation exchange. The mass distributions and relative mass changes of rare earth elements (REEs) in the studied profile display characteristics of vertical zonation. Three peaks in total REEs content are observed, indicating two paleoclimatic or paleoenvironmental changes. Mineralogical characteristics indicate that the paleoclimate changed first from warm and humid to cold and dry and later, to dry and lightly warmer. The corresponding soil environment varies from weakly acidic to strongly alkaline and later, to weakly acidic. Mass translocation characteristics of REEs and several transition metals suggest that the Gaojiayan paleosol may have undergone top erosion.     

内蒙古敖汉旗艮兑营子地区三面井组层序地层

内蒙古赤峰敖汉旗艮兑营子附近二叠系地层比较发育,下二叠统三面井组为一套陆源碎屑岩组合,在区域上较为特殊。在野外实测剖面的基础上,根据岩石组合特征、组构特征、垂向变化规律,将三面井组划分为一个Ⅲ级层序,两个Ⅳ级层序,六个Ⅴ级层序(高频旋回层序)。     

基于多方法手段的开山岛海域淮阴-响水口断裂走向研究

淮阴—响水口断裂为江苏地层分区的重要界线,其陆域位置研究历来已久,但海域位置至今尚未明确。本次研究利用多方法手段,首次确定了淮阴-响水口断裂在南黄海海域的具体位置走向,并明确了开山岛地层归属。     

A new genus of Scoliidae (Insecta: Hymenoptera) from the Lower Cretaceous of northeast China

A new genus and species of Scoliidae (Hymenoptera), Sinoproscolia yangshuwanziensis gen. et sp. nov., is described from the Lower Cretaceous Yixian Formation in Inner Mongolia, China and attributed to the subfamily Proscoliinae. Some characteristics, including complete crossveins 1r-rs and 2r-m in the forewing, and a free section present in almost all longitudinal veins indicate a basal position of the new genus in Proscoliinae. The presence of vein 2A suggests its atavistic origin in Sinoproscolia gen. nov. rather than a true plesiomorphy.     

Ruffordia goeppertii (Schizaeales,Anemiaceae) – A common fern from the Lower Cretaceous Crato Formation of northeast Brazil

Extraordinarily well preserved fern macrofossils of Ruffordia goeppertii (Dunker) Seward (Schizaeales, Anemiaceae) are described from the Lower Cretaceous (late Aptian) Nova Olinda Member of the Crato Formation, northeast Brazil. The identification is based on the morphology of macrofossils and in situ spores, taken from organically preserved material. This extinct, relatively small fern exhibits dimorphic fronds with sterile and fertile pinnules and schizaeoid sporangia, including cicatricose spores. The growth form with clearly differentiated sterile and fertile pinnae may be interpreted as an ancestral state in the phylogeny of the extant genus Anemia. The abundance of this fern reflects its role as ground cover in at least partly (dry) sunny areas, possibly in fern savannah-like habitats, with adaptations to survive drought stress. Finds of Ruffordia in northern Gondwana extend the wide palaeogeographic range of this taxon.     

Second species of enantiornithine bird from the Lower Cretaceous Changma Basin,northwestern China with implications for the taxonomic diversity of the Changma avifauna

We report on a new enantiornithine bird, Dunhuangia cuii, gen. et sp. nov., from the Lower Cretaceous Xiagou Formation of the Changma Basin, northwestern China. Although the material is incomplete, Dunhuangia cuii preserves unique coracoidal and sternal morphologies that distinguish it from other known enantiornithines; this specimen represents only the second enantiornithine reported from the Changma Basin that is diagnostic at the species level. This study enriches our understanding of the enantiornithine component of this ornithuromorph-dominated, Early Cretaceous avifauna.     

Amber‐bearing Bed in a Shallow Marine Setting,an Example from the Lower Cretaceous Miyako Group,Northeastern Japan

A previously unknown amber‐bearing bed in the Lower Cretaceous Miyako Group, northeastern Japan, was deposited within a sequence that contains abundant marine macrofossils and wave‐generated sedimentary structures that suggest deposition in an open shallow marine environment. How the amber was transported from its terrestrial origin to the marine environment is unclear, but sedimentary gravity flow is a strong candidate. Our observations suggest that the occurrence of amber clasts in sediments deposited in open and closed shallow marine environments is not uncommon. Thus, in addition to terrestrial sediments, sediments of marine origin have potential as targets for amber exploration.     

An intercomparison of two rawinsonde systems

Abstract

An intercomparison of the Väisälä MicroCora system used in the Automated Shipboard Aerological Program (ASAP) and the Atmospheric Environment Service upper‐air system (GMD/ADRES) was conducted in May‐June 1983. Thirty‐three paired ascents were made. The ASAP system dry‐bulb temperatures averaged 0.3°C warmer. For the lowest 100 mb, the dew‐point temperature difference (ASAP ‐ GMD/ADRES) was near ‐1°C whereas for the 780–500 mb layer, the difference was 1°C. The wind component mean differences averaged were small but with a 4 m s^?1 standard deviation.     

E24 profile slope stability analysis in Haizhou Opencast Coal Mine of Fuxin

The E24 profile slope analyzed belongs to a series of excavated slopes of the Haizhou Opencast Coal Mine. It seems to be divided into Downslope Part and Upslope Part. Its profile comprises two noticeable coal seams, called the 8# and 9# weak layers, considered as the potential failure surfaces. In consideration of the actual configuration as in the perspective of any modification, assessing the stability of this slope with various profile forms under given conditions, and assessing the risk of instability and quantifying the influence of earthworks or other modifications to the stability of this slope, have constituted the primordial objectives carried out. From assumed potential failure surfaces, any specific profiles and specified slip surfaces are defined. A factor of safety (FoS) is computed for each specified slip surface; the smallest FoS found corresponds to the least favorable slip surface. The safety factor values obtained are compared to the suggested safety factor. Limit equilibrium methods of vertical slices implemented in Slope/W, computer program for slope stability analyses, have been adopted to perform the E24 slope stability analysis. The safety factor values computed with 9# weak layer are lower than for 8#; the factors of safety obtained with Sarma's method are the smallest; more, without groundwater (long term) overall values are greater than those determined under groundwater condition (short term). The lowest safety factor value is found for a profile depending on an adopted earthwork sequence. The E24 profile slope stability analysis shows the instability risk for the deepest weak layer, and also shows the short and long term stability of this slope for the envisaged earth movements. However it demonstrates the existence of instability risk for any earthwork firstly affecting the downslope part.