Joint orientations from Paleozoic sedimentary rocks in the Kyzyl Kum region, Uzbekistan, Central Asia

Abstract

Over 18,000 joint orientations were measured from a spectrum of lithologies of various ages at natural exposures in the Central Kyzyl Kum region. For each exposure, we plotted joint orientation diagrams and identified local joint systems. Orientations of these systems were established from both (i) density maxima of poles to joints on stereograms and (ii) cluster analysis. Tilt-corrected data from coeval strata integrated over all the measurement localities were used to identify regional joint directions and their relative development. In Paleozoic sedimentary rocks these directions are, overall, close to fault and fold trends in structures related to pre-Paleozoic, Caledonian, and Hercynian evolutionary stages. However, regional joint systems display certain changes in their direction and development depending on rock age. In Cretaceous deposits, regional joint directions are chiefly inherited from those in Paleozoic strata. Our study of time-dependent changes in regional jointing characteristics proves that, as the region kept developing, the primary jointing became overprinted by additional random joints and tectonic joint systems. Our previous attempt to reconstruct paleostresses in the study region from joints in sedimentary rocks yielded results closely similar to fold trend data.