FRACTURES IN LATE CENOZOIC SEDIMENTS: NEW POSSIBILITIES FOR STRUCTURAL ANALYSIS

Abstract

Direct observations of fractures and tectonic jointing are crucial for the study of fault systems in any region. They provide information needed for the mapping of the internal structure of fault zones, determination of stages of their kinematics and amplitudes, and reconstruction of tectonic stress fields. Of particular importance are similar observations in active fault zones where strong earthquakes can be generated. The study of fractures and fissures in well-exposed areas is a relatively easy task, whereas areas with a soft sedimentary cover provide little information during structural mapping. Physicochemical properties of nonlithified (weakly cemented) sequences are such that traces of tectonic movements are rapidly masked under the influence of exogenic transformations. In addition, manifestations of tectonic movements and exogenic fractures are frequently similar and cannot always be distinguished with certainty. In this connection, of particular interest is the study of fractures in soft sediments with abundant coarse-clastic material (sandy-pebbly, pebbly-boulder, boulder, and other sequences). Our data show that tectonic fractures are rather prominent in these sequences and they can be studied by the existing methods of structural analysis commonly used for the study of fractures in rocks.