- journal_title：Geology
- Contributor：M. Elrick ; D. Reardon ; W. Labor ; J. Martin ; A. Desrochers ; M. Pope
- Publisher：Geological Society of America
- Date：2013-07-01
- Format：text/html
- Language：en
- Identifier：10.1130/G34363.1
- journal_abbrev：Geology
- issn：0091-7613
- volume：41
- issue：7
- firstpage：775
- section：Articles
This study focuses on the ∼10 m.y. before the latest Ordovician (Hirnantian) glaciation; we test whether orbital-scale climatic fluctuations controlled the growth and melting of continental glaciers, resulting in glacioeustatic sea-level changes and the development of widespread marine sedimentary cycles. δ18O values of conodont apatite from 14 Late Ordovician (Katian) cycles range from ∼17‰ to 21‰. Isotopic values decrease and are lowest in the deepest water facies and increase and are highest in shallow-water facies, supporting the hypothesis that glacioeustasy was the dominant control on water-depth changes. Measured intracycle δ18O changes of 0.7‰–2.5‰ were controlled by changes in ice volume (<60 m sea-level changes), sea-surface temperatures (<5 °C), and potentially local increases in seawater evaporation during drier and/or windier glacial stages. These interpreted orbital-scale climate changes and resultant large glacial ice-volume changes support recent interpretations of a dynamic and prolonged Ordovician greenhouse to icehouse transition.