The purpose of this study was to gain insight into the depositional environment, basin architecture, lake dynamics and paleoclimate of the Miocene-Pliocene Verde Formation. The results of this work have broad implications with respect to paleodrainages and processes related to tectonically controlled basins in the southwestern United States. The basin is a large asymmetrical modified half graben in the hanging wall of the Verde fault within the Transition Zone of central Arizona. The Verde Formation in the northern portion of the valley is composed of undeformed strata of alternating micrite and sandy micrite. I present field observations and lithofacies descriptions from five stratigraphic sections totaling 569 meters complemented by petrography, x-ray diffraction, scanning electron microcopy, coulometry and stable isotope analysis.
The lithofacies and stable isotope compositions of the Pliocene terrestrial deposits of the upper Verde Formation suggests a hydrologically open shallow lacustrine marsh depositional system. Stable carbon and oxygen isotope compositions relative to Vienna PeeDee Belemnite (VPDB) of bulk rock samples range from -5.66‰ to 0.35‰ and -11.69‰ to -9.10‰, respectively. The trends in these values aided correlation of measured sections and are incorporated into paleoenvironmental interpretations. Carbon isotope excursions, have been proven useful in correlating three of the five measured sections in this study, which also aided in making lithostratigraphic ties. This is the first record of a discreet, correlative stratigraphic marker in the uppermost Verde Formation.
The lithofacies described in this study are associated with particular depozones which include pedogenic, palustrine, littoral, sublittoral, and spring deposits. The depositional environment is interpreted to have alternated between an overfilled and balanced-fill lake basin setting that included marshes and soil development along its margins with associated springs based on isotopic analysis and field observations. The laterally continuous horizontal strata and narrow range of δ18O values suggests that accommodation was created by frequent small tectonic movements over time rather than fewer larger events. The climate is inferred to have been semi-arid due to the presence of pedogenically modified lacustrine carbonate deposits.
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|Advisor:||Sample, James C.|
|Commitee:||Middleton, Larry T., Saylor, Joel E., Smith, Michael E.|
|School:||Northern Arizona University|
|Department:||School of Earth Sciences and Environmental Sustainability:|
|School Location:||United States -- Arizona|
|Source:||MAI 54/06M(E), Masters Abstracts International|
|Subjects:||Geology, Sedimentary Geology, Geochemistry|
|Keywords:||Chemostratigraphy, Lacustrine, Paleohydrology, Sedimentology, Stable isotopes, Stratigraphy|
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