The development of polygonal fault systems by syneresis of colloidal sediments   总被引：2，自引：0，他引：2  

David N. Dewhurst  Joseph A. Cartwright  Lidia Lonergan 《Marine and Petroleum Geology》1999,16(8):111

Polygonal fault systems occur in numerous sedimentary basins worldwide, are generally located on passive margins in onlap fill units and tend to comprise the finest grained sediments in this geological setting. These fault systems have been most thoroughly described in the central North Sea basin and the detailed structure shows a significant correlation with lithological variations, both vertically and laterally. Extension measured in stacked decoupled tiers of polygonal faults correlates positively with both clay fraction and smectite content. Lateral facies variations are also observed and indicate that time-equivalent sequences upslope from the smectite-rich polygonally faulted sediments are coarse-grained, clay-poor and undeformed. This leads us to believe that the structure and geometry of the fault system are controlled by the colloidal nature of the sediments, and that the volumetric contraction measured on seismic sections can be accounted for by syneresis of colloidal smectitic gels during early compaction. Syneresis results from the spontaneous contraction of a sedimentary gel without evaporation of the constituent pore fluid. This process occurs due to the domination of interparticle attractive forces in marine clays, dependent on environment, and is governed by the change of gel permeability and viscosity with progressive compaction. The process of syneresis can account for a number of structural features observed within the fault systems, such as tiers of faults, the location of maximum fault throw and growth components at upper fault tips. As such, this paper represents the first attempt to correlate microscale properties of clay-rich sediments to their macroscale seismic character.  相似文献   

The Pachuca obsidian source,Hidalgo, Mexico: A geoarchaeological perspective     

Alyson Lighthart Ponomarenko 《Geoarchaeology》2004,19(1):71-91

Sierra Las Navajas, known to archaeologists as “the Pachuca obsidian source,” has been a major source of obsidian to Mesoamerican societies for more than 3000 years, producing a fine green obsidian unique in Middle America. It was the primary source of the obsidian that formed the economic backbone of the major sociopolitical centers of Classic period Teotihuacán, epi‐Classic Toltec Tula, and Aztec Tenochtitlán. In this paper, the obsidian of Sierra Las Navajas is discussed in the following contexts: (1) geologically, because the extraordinary quality of the Pachuca obsidian, its ease of extraction, and its distinctive color and chemistry are a direct result of its geologic emplacement; (2) locally, as the different mining localities within Sierra Las Navajas reflect the varying needs of the cultures working them; and (3) globally, as the obsidians of Las Navajas were used in concert with obsidians from other sources, and were traded great distances across Mesoamerica. © 2004 Wiley Periodicals, Inc.  相似文献