Isotope Stratigraphy and Paleodepth Changes of Pennsylvanian Cyclical Sedimentary Deposits

摘要: Oxygen isotopes can record water depth changes because of the relationship between and temperature, ice volume by its relation to isotopic composition sea water. Because this, oxygen provide an excellent means studying conditions responsible for formation cyclical sedimentary deposits in late Paleozoic. We have determined isotope stratigraphy two Pennsylvanian units north Texas, Necessity Shale Colony Creek Shale, after having carried out detailed stdies depositional environments andfossil biotas these units. Isotope data were obtained from fibrous calcite shells brachiopod Crurithyris planoconvexa, which is present throughout both shales. Preservation original indicated preservation shell microstructure, absence cathodoluminescence, low iron manganese concentrations, high sulfur concentration within shells. These characters plain light cathodoluminescence microscoPy, microprobe, SEM-EDS. In contrast, prismatic outer layer some margins are diagenetically altered. This alteration recognized visible concentration. The cycles studed be divided into as many four zones based on sedimentology, fossil biota, position transgressive regressive sequence. From shallowest deepest, they myalinid zone, fusulinid ammonoid gondolellid zone. deepest faunal defined occurrence conodont Gondolelia, correlates with maximum 8180 C. planoconvexa. indicates that brachiopods recording a decrease emperature associated deepening water, temperature effects major component signal cycles. Using modern tropical ocean profiles analogue interpretation 180 stratigraphy, change estimated deposition cycle Brownwood area Texas at least 70 m. INTRODUCTION