TY - JOUR ID - 119416 TI - Climatic changes and astrochronology: an Ordovician perspectiv JO - پژوهش‌های تغییرات آب و هوایی JA - CCR LA - fa SN - AU - Ghobadi Pour, Mansoureh AU - Popov, Leonid AU - Cherns, Lesley AD - Department of Geology, Faculty of Sciences, Golestan University, Gorgan 49138-15739, Iran AD - Department of Natural Sciences, National Museum of Wales, Cardiff CF10 3NP, United Kingdom AD - School of Earth and Environmental Sciences, Cardiff University, Cardiff CF10 3AT, United Kingdom Y1 - 2020 PY - 2020 VL - 1 IS - 4 SP - 89 EP - 109 KW - Ordovician KW - orbital forcing KW - astrochronology KW - Cyclostratigraphy KW - Biostratigraphy DO - 10.30488/ccr.2020.255527.1030 N2 - Review of current progress in Mid to Late Ordovician astrochronological studies exposes some important issues related to cyclostratigraphical studies, including the completeness and correlation of successions, and the connection between inferred astronomical cycles and geological events recorded in the sedimentary record. While bulk, low-field, mass specific magnetic susceptibility methods are widely applied in studies of high resolution cyclostratigraphy, they require close support from sequence stratigraphy and biostratigraphy, and should be linked back to outcrop patterns. Otherwise they risk distortion in the calibration against geological time, through lack of anchoring to well-defined biostratigraphical horizons and unrecognised condensed intervals and larger hiatuses. A significant limitation currently is that few high-resolution radio-isotope ages are linked to well-defined biostratigraphical boundaries. Nevertheless, fourth order sedimentary sequences linked to 405 ky orbital eccentricity cycles, and longer orbital cyclicity impressed in third-order sequences, represent good grounds for development of a reliable astrochronological scale. The astrochronologically calibrated sequence-stratigraphical record documented from high latitude Gondwana shows significant impact from orbital forcing on the Mid to Late Ordovician global climate. UR - https://ccr.gu.ac.ir/article_119416.html L1 - https://ccr.gu.ac.ir/article_119416_bc9a0295fb85f864b1b43ec11172821b.pdf ER -