Internal Troughs Research Articles

New and Interesting Diatoms from the Shiwan Wetwalls, Yunnan Province, China. III. Valve ultrastructure of four new species of Eunotia (Bacillariophyceae: Eunotiales)

Four new Eunotia (Bacillariophyceae: Eunotiales) species are described from the Shiwan Wetwalls in Yunnan Province, China, based on light and scanning electron microscopy. The four species all share the features that assign them to the genus, including asymmetry about the apical axis, raphe predominantly on the valve mantle, and presence of one or more rimoportulae, and they all possess pseudosepta. They differ from one another in several attributes, however. Three of the species possess striae contained in internal troughs, two have spines (either one stout spine at each apex or blunt spines along the dorsal margin) and one has thickened ridges between the striae. These observations of four new Eunotia species further demonstrates the diversity and uniqueness of this wetwall community in Yunnan.

Continental Slopes of the West Africa Region: A Unique Treasure of Hydrocarbons

The West African region embraces a number of coastal sedimentary basins, which continued in deep-water areas of the Atlantic Ocean. It includes the following oil-and-gas-bearing basins: the Gulf of Guinea, the Kwanza–Cameroonian, and the Namibian. The sedimentary cover of the basins of this passive margin is represented by Mesozoic–Cenozoic deposits. The composition of sediments accumulated in them is quite specific and surprisingly units over the vast areas. The tectonic structure of the majority of the continental margins of West Africa makes possible to refer them to the margins of epiplatform orogenic belts. The existence of two systems of linear troughs—internal and external—on the passive margins at the early stages of continent–ocean transition zones relates deep-water hydrocarbon deposits to internal troughs filled by younger sediments: the alluvial fans of submarine rivers and landslide fronts with prograde formations (turbidites, debris flows, etc.). Late Cretaceous and Middle Paleogene clay formations played the role of source beds in the region, so-called “black clays.” An analysis of over 200 hydrocarbon fields, mainly petroleum, discovered in the past 10–15 years in the region revealed a clear tendency of these fields occurring in a productive zone of oil pools extending in a sea depth interval of 400–3000 m on the continental slope and possibly to 4000 m at the continental rise. Moreover, all discovered fields have been estimated in terms of reserves from large to giant. It is also noteworthy that within the shallow of this region, which includes the shelf and the coastal plain, only a number of small, insignificant oil and gas pays have been discovered. The main of oil and gas bearing potential prospects are related to deposits in the middle and lower parts of the continental slope and possibly adjacent areas of the continental rise. In the long term, the drilling objectives will be both postsalt and presalt deep-water oil-and-gas fields.

Cell Washing Centrifuges

Cell Washing Centrifuges

Host location and oviposition in a basal group of parasitic wasps: the subgenual organ, ovipositor apparatus and associated structures in the Orussidae (Hymenoptera, Insecta)

Anatomical studies and behavioural observations indicate that representatives of the Orussidae use vibrational sounding to detect suitable oviposition sites. During host location, vibrations generated by tapping the tips of the antennae against the wood are picked up by the fore legs through the basitarsal spurs, transmitted along the basitarsi to thin-walled areas on the tibiae and through haemolymph to the subgenual organs, where they are transduced into nerve impulses. The apical antennomeres are distinctly shaped and have the cuticle thickened distally. The fore basitarsi have weakly sclerotised basitarsal lines proximally and membranous basitarsal spurs distally. The external wall of the fore tibiae have thin-walled areas distally on their posterior parts. Internally, large subgenual organs are situated opposite the thin-walled areas and each organ consists of 300–400 scolopidial units suspended between a lateral cuticular spine, a ventral sheet and a median ridge. The ovipositor is several times the length of the body of the wasp. When at rest, it extends all the way into the prothorax, where it is coiled before extending posteriorly to lie between the third valvulae distally. The ovipositor lies in a membranous ovipositor sac attached posteriorly to the proximal parts of the ovipositor apparatus and the posterior margin of sternum 7. In the ovipositor apparatus, the anterior parts of the second valvifers are displaced and expanded anterodorsally, inverting the first valvifers and the base of the ovipositor. When in use, the ovipositor is extended and retracted by median apodemes situated on the anterior margins of abdominal sterna 3–7. Longitudinal muscles between the apodemes allow the latter to grip the ovipositor in troughs between them. The ovipositor extends from the abdomen at the tip of sternum 7, and an internal trough on sternum 7 serves to guide the ovipositor into the wood. Despite the alterations observed in the ovipositor apparatus in the Orussidae, the musculature is almost complete and the mode of operation presumably not much different from that of other representatives of the Hymenoptera. The different ways parasitic wasps with very long ovipositors handle and accommodate these and the implications for the evolutionary history of Hymenoptera are discussed.

Enregistrement sédimentaire de la tectonique extensive et de l'eustatisme dans le Jurassique terminal et le Crétacé basal du Prébalkan central et oriental (Bulgarie)

The thick (2 000 m) siliciclastic-dominated synrifi series, which fills up most of the internal troughs of the Central Fore Balkan from Uppermost Tithonian to Valanginian, is subdivided into ten tectono- eustatic depositional sequences. The sequences consist of a coarse and voluminous low stand wedge (block complex, canyon-cone conglomerates, megaslumps, calcareous breccias, etc.) induced by extensional tectonics; and above, a pelite-dominated high stand wedge, of eustatic origin, which contains most of the zonal and subzonal Ammonites allowing datations and correlations. To the NE, towards the Moesian Platform, only the high stand wedges (with or without the transgressive system tracts) of the successive sequences overflow the troughs and become richer in carbonates to the top of the parasequences.

Structure and acoustic stratigraphy of the Manihiki Plateau

The Manihiki Plateau is a large, shallow area of old oceanic crust near the southwest margin of the Pacific Plate. Recent geophysical surveys and traverses have allowed the preparation of a new bathymetric chart showing three distinct provinces, the High, the North, and the Western plateaus, and systems of deep internal troughs. Up to 1 km of sediment occurs both in the troughs and on the shallow plateaus. From seismic reflection profiles we infer that there is a major, sometimes angular, early Tertiary unconformity, that the plateau has always been relatively shallow, and that the High Plateau may originally have been close to sea level. The unusual character of this area of crust is probably inherited from a period of unusually voluminous volcanic eruptions at the time of lithospheric generation when the plateau was at or near the middle Cretaceous triple junction between the Pacific, Antarctic, and Farallon plates.

Regional Geology of Circum-Mediterranean Region

Paleogeographic evidence suggests the presence of five major tectonic elements in the Circum-Mediterranean region. Starting from either the Afro-Arabian or Eurasian continental masses these tectonic units are: (1) shield or craton areas bounded by (2) marginal troughs of relatively low mobility, uniformly filled with normal sediments; (3) geanticlines or upwarps with a thin sequence of sediments, which generally separate the marginal trough from (4) internal troughs filled with a variable thickness of highly plastic sediments and zones of initial ultrabasic activity which were arcuate to (5) nuclei or minor cratons which furnished plastic sediments to the internal troughs. Nuclear areas in the Turko-Balkan region and in the western Mediterranean grew progressively outward by incorporating the folds which developed from a series of internal troughs bordering the nuclei. The high mobility of the internal troughs--displayed in parts of the Taurus, Olnos-Pindos, southern Alps, northern and southern Apennines, Tellian Atlas, and Pyrenean foothills--has resulted in a variety of surficial gravity slides caused by the initial plasticity of the sediments rather than intense crustal shortening or buckling. The shield areas of Afro-Arabia and Fennoscandia have enlarged their cratonic dimensions by the welding and incorporation of successive marginal troughs. The relatively competent sediments of the uniform marginal troughs, when orogenically deformed and later xposed by epeirogenic uplift, as in the Saharan, High and Middle Atlas, and the Iberian Range, produce normal structural types oriented parallel with the configuration of preceding trough trends. In the marginal troughs both deformational intensity and local structural trends seem to be related to the original thickness of sediments and trough orientation, whereas in the internal troughs these features are in many places unpredictable. Outward growth of the continental areas and the arcuate expansion of the nuclei have shifted the two trough types toward each other. This convergence has tended ultimately to fill in the thin crust of the Tethyan area creating a cratonic-like aspect. When the pattern of this postulated tectonic framework is related to current concepts of earth deformation, conclusions drawn from the Circum-Mediterranean region seem to be contrary to the majority of the theories, although at various stages of the orogenic cycle there are analogies to all the proposed concepts.