Structural Evolution Characteristics Research Articles

Tectonic and climatic controls on the development of foreland fan deltas: Montserrat and Sant Llorenç del Munt systems (Middle Eocene, Ebro Basin, NE Spain)

Along an early Cenozoic foreland–hinterland boundary in northeastern Spain, we synthesize the depositional environment, climatic conditions, structural evolution, age, catchment geometry, and altitudinal characteristics from sedimentologic, palynologic, stratigraphic, structural, and paleomagnetic data. As the transpressional Catalan Coastal Ranges rose during the Paleogene, two large fan deltas prograded into the Ebro foreland basin adjacent to the northeastern part of the range. The apices of the fans likely were localized by lateral ramps or tear faults along which rivers from hinterland catchments debouched into the foreland. Beginning in the late Lutetian, proximal debris-flow, sheetflood, and distal fluvial deposits maintained the fan surface at or above sea level, despite rapid basin subsidence during the succeeding 4.4 my. Palynological data suggest that a warm, humid climate prevailed throughout this interval. The mapped extent of the two fans permits an estimation of their volumes, whereas the spatial distribution of distinctive lithologies within the ancestral Catalan Coastal Ranges serves to delimit the approximate catchment areas for each of the fans. We estimate mean hinterland denudation rates to range from 100 to 180 m/my and mean catchment elevation to range from 700 to 1250 m. The steep gradients between these catchments and the low-lying fan deltas is attributed to the tectonic style of the ancestral Catalan Coastal Ranges, which are characterized by an uplifted basement block along a steep frontal thrust accompanied by folding of cover rocks. The considerable topographic relief of these catchments is inferred to have combined with co-seismic shaking to produce landslides and rockfalls, which were reworked as debris- and fluid-gravity deposits on the fan surfaces.

Structure Evolution of NdF3 Optical Thin Films

The structure evolution characteristics of NdF3 thin films has been analysed concerning texture and grain morphology. The structure could be classified according to the structure zone models, and the growth mode could be related to zone T and zone II. Contamination of the films by residual gases was found to inhibit the migration of grain boundaries and therefore, zone II does not appear even at high substrate temperatures in contaminated films. Stratification by MgF2 interlayers may also result in a decrease of grain size and a smaller surface roughness. The correlation between deposition conditions, stratification, growth mode and optical properties is discussed.

Sedimentary Basins of the Republic of Yemen : Their Structural Evolution and Geological Characteristics

The distribution and evolution of the sedimentary basins of Yemen was, until recently, poorly understood as this was based entirely on surface geology and correlations of the older stratigraphic units which were exposed only in the deeply dissected bordering uplifts of the Gulf of Aden and Red Sea or the high plateau of the north west. Elsewhere cover by the tabular Tertiary sedimentary blanket and the Tertiary Volcanic Group lavas masked the major underlying pre-Cenozoic structural elements and sedimentary successions. Earlier attempts at the delineation of the country's structural framework were, thus, sketchy and/or only partially correct. The discovery of commercial oil and gas in several interior Mesozoic rift basins of Yemen in the late 1980s and in the early 1990s after unification of the former two Yemens, spured many oil companies to enter the exploration race and carry out detailed seismic surveys and intensive exploration drilling in many areas. This resulted in a rapid rise in overall new subsurface geological data acquisition and an increasingly clearer perception of the distribution, orientation and inception times of the main basins. No overall synthesis of results was, however, undertaken since each individual company was primarily concerned with its own concession area and its immediate surroundings. Recent studies involving the review, correlation and synthesis of the mass of new subsurface stratigraphic data in connection with standardisation of lithostratigraphic nomenclature in use in Yemen and its further formalisation in accordance with internationally accepted rules, have, perforce, required the establishment of an overall structural framework within which inter and intra-basinal stratigraphic correlation could be carried out. It is this new framework of depositional basins and interbasinal uplifts that is discussed here. The main Mesozoic basins are related to late Jurassic extension and rifting, principally involving rejuvenation of the ancient NW-SE Najd fault system with subordinate strike-slip motion. The Tertiary basins are related to separation of Arabia from Africa in the Neogene along the Gulf of Aden and Red Sea trends. The principal uplifts are of equal antiquity, the oldest and most persistent being the Hadhramawt Arch. All the tectonic activity is linked to Gondwanan fragmentation and breakup from the initial closure of the paleo-Tethys and opening of the neo-Tethys in late Carboniferous to Permian times, and the development of the African Karoo system, through separation of India from Afro-Arabia in the Cretaceous to ultimate separation of Arabia from Africa in the Neogene. Within individual basins, compartmentalisation by sub-parrallel highs into graben-like and half-graben sub-basins or sectors is related to local adjustments to this continuing motion within the overall structural framework.