Thesis
Comparison between sedimentary geochemistry and detrital zircon U-Pb provenance models, Cook Inlet Basin, south-central Alaska
University of Iowa
Master of Science (MS), University of Iowa
Spring 2022
DOI: 10.17077/etd.006358
Abstract
The provenance of most basin systems today is interpreted based on detrital zircon geochronology, which has all but replaced the use of geochemical approaches that can sometimes better constrain and effectively complement provenance information inferred from isotopic approaches. Here we compare mudstone and sandstone whole rock major and trace element geochemistry of the Late Oligocene-Middle Miocene Tyonek, Late Miocene Beluga and Pliocene Sterling formations in the Cook Inlet Basin, Alaska, with existing detrital zircon U-Pb geochronology to better elucidate the provenance. Zircons are abundant in some lithologies but deficient in others so detrital zircon U-Pb geochronology only detects certain components in a source region. Previous detrital zircon data demonstrate that zircon-bearing source areas for the Cenozoic strata vary dependent upon which margin of the basin they are exposed.Based on detrital geochronology, the Tyonek, Beluga, and Sterling formations exposed along the eastern margin of the basin primarily derived sediment from the adjacent accretionary prism and accreted juvenile (mafic) arc rocks along the eastern margin. The Beluga and Sterling formation exposed along the western margin also match this eastern provenance. In contrast, the Tyonek Formation exposed along the western margin reflects a primarily granitic sediment source to the north. Our new geochemical data from all the formations suggest a mostly juvenile to intermediate sediment source and evidence for sediment recycling from accretionary prism strata is not observed. Discrimination diagrams based on trace elements consistently show a trend from mafic to andesitic sources for the Late Cenozoic strata but rarely reach felsic compositions demonstrating the loss of the granitic signature in the mudstone.
This study demonstrates that combining geochronologic and geochemical data from sedimentary rocks can help to better resolve provenance and provide insight into non-zircon-bearing source areas. Furthermore, geochemical approaches can be applied to both sand- and mud-sized fractions, further expanding our understanding of sediment flux and potential source rocks in a basin.
Details
- Title: Subtitle
- Comparison between sedimentary geochemistry and detrital zircon U-Pb provenance models, Cook Inlet Basin, south-central Alaska
- Creators
- Alethea Kapolas
- Contributors
- Emily S Finzel (Advisor)William C McClelland (Committee Member)David W Peate (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Geoscience
- Date degree season
- Spring 2022
- DOI
- 10.17077/etd.006358
- Publisher
- University of Iowa
- Number of pages
- xi, 39 pages
- Copyright
- Copyright 2022 Alethea Kapolas
- Language
- English
- Description illustrations
- color illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references (pages 34-39).
- Public Abstract (ETD)
- Sedimentary basins are areas where sinking of the Earth’s surface creates accommodation space for the accumulation of sediments. They are commonly formed concurrently with the uplift of mountain regions. This uplift results in sediment being eroded from the mountainous regions and deposited within the sedimentary basin system. Determining the origin of sediments, or provenance, within the basin is important when investigating these systems. Typically, provenance is determined by dating the mineral zircon, which elucidates the maximum depositional age for that sediment and that age can be compared to different source regions in the basin system. Zircons are commonly dated using U-Pb geochronology which utilizes the radioactive nature of the elements to determine how old that mineral is. This is a robust and accurate method that has dominated provenance work. However, zircons are only abundant in some rock types (e.g., sandstones) but deficient in others (e.g., mudstones), so U-Pb geochronology of zircons can only detect certain components in a given source region. Certain elements are effectively transferred from the source regions to sedimentary rocks because they are resistant to post-depositional mobility. By comparing the major and trace element (geochemical) compositions of samples to those of the source areas can also provide valuable insight to the provenance of that sediment. Combining geochronologic and geochemical data from sedimentary rocks, therefore, can help to better resolve provenance and provide insight into non-zircon-bearing source areas. Here, we explore this approach by comparing our new geochemical data from a southern Alaska basin with existing zircon data.
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984271354302771
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