Abstract
High-latitude continental response to Cenozoic climate change in southern Alaska based on volcanic glass hydrogen isotope compositions
Abstracts with programs - Geological Society of America, Vol.49(6)
Geological Society of America, 2017 annual meeting & exposition
2017
Abstract
The Cenozoic Era is marked by episodes of warming and cooling based on high-resolution marine geochemical records. High-latitude continental responses to these events are poorly documented. In this study, we aim to understand continental paleoclimate response to global events in southern Alaska by studying the hydrogen isotope composition of hydrated volcanic glass. 20 volcanic ash samples were collected from the fluvial Sterling Formation on lowland (<200 m) of the southwestern end of Kenai Peninsula. These ashes are younger than 12 Ma based on previous radiometric dating. Three ash samples were collected from the late Eocene fluvial Hemlock Conglomerate in the Talkeetna and Tordrillos Mountains with a sampling elevation of nearly equal 800 m. Because the rain shadow effect of mountain ranges in southern Alaska may have affected the stable isotope composition of paleo-meteoric water, tectonic uplift is also considered when interpreting the stable isotope record. The hydrated volcanic glass delta D values range from -181 ppm to -97 ppm. After converting these glass values to environmental water delta D values, the reconstructed paleo-meteoric water delta D values for < 12 Ma range from -153 ppm to -66 ppm, and for the late Eocene range from -139 ppm to -98 ppm. The most positive values must be influenced by evaporation of surface water. Modern mean annual surface water delta D values in the study areas range from -150 ppm at nearly equal 1000 m to -110 ppm on lowland (Johnson, 2014). The most negative late Eocene paleo-meteoric water delta D value is only about 10 ppm higher than modern water delta D value at nearly equal 1000 m. Warm late Eocene paleoclimate most likely caused the small isotopic difference, and surface uplift (> 1000 m) of the sampling area was very unlikely during the late Eocene. The late Neogene paleo-meteoric water has lower delta D values than modern lowland surface water, and the values have larger magnitude of variation during 12-6.3 Ma than after 6.3 Ma. Given the well-documented late Neogene global cooling, the lower isotope values and larger variation suggest that the paleoclimate in the Kenai lowland may be more seasonal during 12-6.3 Ma than 6.3 Ma.
Details
- Title: Subtitle
- High-latitude continental response to Cenozoic climate change in southern Alaska based on volcanic glass hydrogen isotope compositions
- Creators
- Benjamin J Deans - University of Texas at Arlington, Department of Earth and Environmental Sciences Arlington, TX USA United StatesMajie FanJeffrey A BenowitzEmily S Finzel
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.49(6)
- Conference
- Geological Society of America, 2017 annual meeting & exposition
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, 2017 annual meeting & exposition
- Language
- English
- Date published
- 2017
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240803302771
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