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xvii, 106 p. : ill., maps. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / This dissertation establishes the age, depositional environment, composition, and climatic conditions for the Cape Blanco flora. The paleotemperature estimated by the Cape Blanco flora, the Temblor flora of California, and the Seldovia flora of Alaska are then compared with sea surface temperatures estimated from oxygen isotope analysis of benthic foraminifera. The unconformity-bound shallow marine sandstone of Floras Lake includes a redeposited tuff bed which contains fossil leaves at Cape Blanco. An 40 Ar/ 39 Ar age of 18.26 ± 0.86 Ma is presented for the tuff as well as a paleomagnetic stratigraphy of the sandstone. Sedimentary structures of the tuff bed are evidence that the tuff was deposited at or just above the strand line. The depth of tuff deposition was shallower than the adjacent marine sands, and this short-lived shoaling may have been a result of increased sediment supply. The fossil flora was an oak forest with numerous species of Fagaceae. Additional components include lanceolate Salicaceae leaves, entire margined Lauraceae, fragmentary Betulaceae, and lobed Platanaceae. Coniferous debris, charcoal, Equisetales, and Typhaceae forms are also figured. Ten leaf forms could not be confidently assigned to established names but are described, figured, and called angiosperm forms 1-10. In total 44 unique forms are identified. The size and margin type of the dicot specimens are quantified, and by comparison with known modern floras, a former mean annual precipitation of 201 (+86, -61) cm and a former mean annual temperature of 18.26 ± 2.6°C are estimated. The paleotemperature of the ∼17.5 Ma Seldovia Flora and the ∼17.5 Ma Temblor Flora are estimated using the same method, establishing a ∼0.7°C per degree of latitude temperature gradient for the northern hemisphere temperate zone. The leaf based gradient is steeper than the sea surface temperature gradient, of ∼0.26°C per degree of latitude as estimated from oxygen isotopic composition of foraminifera collected from ocean sediment cores. Both fossil leaf and isotope methods suggest that the early Miocene was ∼5°C warmer than today. This thesis includes unpublished co-authored material. / Committee in charge: Gregory Retallack, Chairperson, Geological Sciences; Rebecca Dorsey, Member, Geological Sciences; Joshua Roering, Member, Geological Sciences; Barbara Roy, Outside Member, Biology

The Sucker Creek Formation exposures at Devils Gate in southeastern Oregon have yielded a significant small mammal fauna of at least thirty small mammal taxa from five stratigraphic horizons. The mammal-bearing portion of the Devils Gate section is more than 200 m thick. Fossil mammals occur in lacustrine and marginal lacustrine deposits lower in the section and occur in overbank and paleosol deposits higher in the section. ⁴⁰Ar/³⁹Ar single-crystal laser-fusion dates on three Devils Gate ashes shows that the age of the mammal-bearing sequence at Devils Gate spans the late early Barstovian land-mammal age with possible overlap into the late Barstovian, as currently defined. Duration of the entire mammal-bearing portion of the Devils Gate section was less than a million years. Both a new ash date from the type section and biostratigraphic correlations between Devils Gate and the type section support considerable temporal overlap between the two exposures. The Devils Gate Local Fauna includes several new taxa: a phyllostomatid bat; two "flying squirrels", Petauristodon sp. A and Petauristodon sp. B; and an eomyid rodent, Leptodontomys sp. A. Several fossil occurrences represent the first record of a taxon in the northern Great Basin and/or in the Barstovian land-mammal age, including: Blackia sp., Schaubeaumys grangeri, Protospermophilus quatalensis, and Pseudadjidaumo stirtoni. The Stagestop locality produced two new taxa, Copemys sp. aff C. esmeraldensis and Mystipterus sp. The Stagestop local fauna is Clarendonian in age. Concretions are an important source of fossil mammals in exposures of the Sucker Creek Formation. Geochemical analyses show that concretions formed through a complex interaction between bone and surrounding volcaniclastic material. Although some superficial bone was consumed during concretion diagenesis, concretion development reduced the chance of prolonged chemical and physical destruction of bone during later soil development. The broad ecological diversity of small mammals recovered from Devils Gate supports an interpretation of the local paleoecology as a mosaic of grassland, forest, and pond/lake-bank environments. Sequential small mammal faunas across a prominent ash event show a generally stable composition with no pronounced ecomorphic differences in pre- and post-volcanic disturbance intervals. Therefore, small mammals do not show analogous ecological patterns to disturbance-driven plant successions in the Sucker Creek Formation. I infer that the local ecosystem recovered from volcanic blasts at a temporal scale below the resolution of time-averaged, post-disturbance paleosols.