Using oxygen isotopes from apatitic conodonts to understand the origins of Paleozoic-Triassic 3rd-order (My-scale) sea-level changes

点击翻译按钮获取中文摘要

Precambrian through Phanerozoic marine deposits are dominated by lithological, geochemical, and biological records of repeated sea-level changes ranging in duration from 10 thousand to 10 million years. The objectives of the proposed research are to understand the origin of persistent, but enigmatic ~1-5 My-scale sea-level changes which result in the deposition of transgressive-regressive marine sequences tens to about a hundred meters thick. The method used to evaluate the origin of these sequences is to analyze the delta-18 Oxygen values of conodonts (extinct apatitic marine microfossils) from selected Ordovician through Triassic sequences to determine if a systematic relationship exists between del 18-O values and transgressive-regressive facies trends.If a systematic relationship between del 18-O values and transgressive/regressive facies trends is observed, then this will indicate that My-scale climate changes are responsible for sequence development. If no relationship between del 18-O values and facies changes is observed, then tectonic process(es) unrelated to climate change are responsible. The research will also evaluate the depth habitat of certain Ordovician and Triassic conodonts; this is crucial for reconstructing depth-dependent marine paleotemperatures and isotopic compositions. This research is primarily focused on understanding the My-scale controls on the infilling of marine basins. If the sea-level changes are, in fact, controlled by climate variations, facies-independent sea-level curves can be constructed and the argument for long-period orbital forcing modulation is supported. This may permit using these sequences for calibrating the Paleozoic-Triassic geological time scale, much like shorter term orbital cycles (~20-100 ky) are being used to calibrate the Cenozoic time scale. The techniques, data, and results will be utilized to develop hands-on, inquiry-based laboratory exercises for undergraduate Earth History and Sedimentology-Stratigraphy classes at UNM. The techniques and results will also be incorporated into graduate-level lectures in Carbonate Stratigraphy, Paleoclimatology, and Stable Isotope Geology. Results from this research will be presented at conferences (GSA, AGU, AAPG), in appropriate journal publications, and invited university seminars.