干旱区生态环境知识资源中心

Remote sensing images and recent field studies provide important morphological and structural constraints for the BP and Oasis impact structures in Libya. The BP structure (25 degrees 19'N, 24 degrees 20'E) is highly eroded and appears on satellite images in the form of a set of concentric rings. The rocks are composed of sandstones of the Jurassic to Cretaceous Nubia Formation. The Landsat image allows division of the structure into inner, middle, and outer rings. The ERS1 and Radarsat radar images do not show much detail, but the rings are more pronounced than in the visible wavelengths, probably because the radar penetrates the sand cover. In the field it became obvious that the cited diameter of 2.8 or 3.2 km for the outer ring does not represent the actual crater diameter, as the "middle ring" represents the actual crater rim with a diameter of about 2 km. The middle ring is characterized by a distinct series of hills of up to about 30 m elevation above the surrounding desert, with rocks dipping at 30 to 50 degrees outwards. Some parts of the rim are characterized by intense folding and faulting. The "outer ring" is a discontinuous ring of low hills with 1-2 m average elevation, dipping at 10 degrees inwards. The "inner ring" is interpreted as a small central uplift structure (ca. 500 m in diameter) with steeply upturned strata that are intensely folded, faulted, and - in places - brecciated.