The landscape of southwest Montana is dominated by topography and adjacent sedimentary basins that resulted from deformation associated with the Sevier and Laramide orogenies140-50 million years ago and ~70-40 million years ago, respectively. Stark changes in drainage and deposition from Permian to Miocene (300 to 5 million years ago) have been described from uplifted sedimentary sequences. Despite numerous studies, the precise timing of eastward propagation of the Sevier fold‐thrust belt and its impact on drainage, as well as the timing of sedimentary basin partitioning into smaller intra-basins remain unclear. For this project, I worked under the guidance of Dr. Licht and Megan Mueller to collect field samples in Montana, isolate zircon grains for analysis and synthesize the results. Here we present geochronological and petrographic data that explain the timing of changes in drainage patterns, and place constraints on the chronology of orogenic development from Permian through Miocene sedimentary rocks exposed near Dillon, southwest Montana. The techniques used in this study are zircon geochronology and sandstone petrography. Zircon geochronology determines the age of zircon minerals found in sediment and offers insights into the ages of the sediment source areas. Sandstone petrography is used to classify the mineralogy of grains in sandstones and allow us to determine potential sediment sources. Understanding the evolution of drainages and changes in sediment transportation is critical to reconstruct the complex tectonic history of this region and aid in uncovering the chronology of Sevier and Laramide deformation.

The uplift of the Cascade Range in Washington had a dramatic impact on regional ecosystems and global climate by creating continent-scale rain shadow effects, enhancing regional aridity, and providing an anchor to the North American ice-sheet during glacial ages. Despite their importance, however, the chronology of the Cascades uplift remains poorly understood, with proposed ages for the uplift ranging from Eocene (~40 million years ago) to Pliocene (~4 million years ago). Before the onset of uplift, rivers would have drained westwards across Washington State; the uplift would have disrupted these river systems and separated river drainages on both sides of the mountain range. The goal of this study is to determine when uplift began by determining when this drainage disruption occurred. To do so, we propose to compare the sedimentary provenance of geological units of various ages on both sides of the mountains. Our methods include U-Pb dating of detrital zircons and sedimentary petrography of sandstones. Sediment samples on the west side of the Cascade Mountains have previously been analyzed for these two methods on an earlier research project. We will focus here on new results from multiple samples from the east side of the Cascade Mountains, and compare them with samples from the west side to propose a time window for the onset of uplift.

The Pondaung Formation of central Myanmar consists of fluvial and alluvial sedimentary rocks deposited during the Middle Eocene, 40 million years ago. The formation has yielded fossils of some of the earliest anthropoid primates, coeval with the first primate dispersal from Asia to Africa. Previous sedimentological and paleobotanical studies have shown that the Pondaung Formation was deposited in a landscape of open-forested seasonal wetlands with isolated riparian and monsoonal deciduous forests. However, the spread of these forests and locations of primate habitats within this mosaic landscape remains unclear. This project aims to provide a more precise reconstruction of the landscape at primate-bearing fossil sites using isotopic data gathered from paleosols as proxies for vegetation and climate during its deposition. We propose to use carbon isotope data collected from soil organic matter to produce estimates of precipitation. They are combined with the carbon isotopic composition of pedogenic carbonates to give direct estimates of soil productivity and vegetation cover. Together, these data allow us to decipher the landscape at the fossil sites, providing context for the evolution and dispersal of these primates. Our preliminary results agree with previous studies of the region, showing that the landscape was forested and flooded for considerable periods of time, experiencing strong seasonality in precipitation.

Recent increases in atmospheric carbon dioxide levels have led to a decrease in the pH of the world’s oceans. These changes in seawater chemistry could have severe consequences for calcifying organisms such as corals. Ocean acidification (OA) poses an imminent threat to the world’s coral reef ecosystems, which could lead to massive reductions in global marine biodiversity. Much of the response of corals to OA is still poorly understood from a detailed physiological perspective, particularly the impact of OA on a fundamental process of skeletal growth called nucleation. Nucleation is the process by which calcium and carbonate ions combine in solution to form a new piece of solid calcium carbonate, which corals use to build their skeleton. While calcification has been measured in corals, the specific step of nucleation has not been quantified and has the potential to be more sensitive to ocean acidification. Coral fragments of Stylophera pistillata and Acropora microphthalma were grown on microscope slides secured in petri dishes in normal ocean conditions suitable for growth. Half of the fragments will be placed into another tank that has constant alkalinity and a set pH of about 7.8 controlled with bubbling air at 800ppm carbon dioxide into the water, the predicted level of atmospheric carbon dioxide in 2100 with the current rate of emissions. This will allow for a big enough change in pH to clearly determine if nucleation is affected by lower pH. With an inverted microscope, the calcifying space was visible through the glass slides, and time-lapses were taken to quantify nucleation rates of corals in the normal ocean conditions. Reefs play a huge role in supporting biodiversity, economies, and population health. Understanding how nucleation rates are changing in variable ocean conditions is a key step in developing new ways to conserve reefs.

The Paleocene-Eocene Thermal Maximum (PETM), a period of intense warming 56 million years ago, is our closest analog to the present-day global warming phenomenon and is well documented in past studies. However, the warming trends and climatic shifts prior to it, though crucial to our understanding of the driving processes behind the PETM, have been largely overlooked. The shale fossil beds at Bison Basin, Wyoming feature abundant paleobotanical evidence from the middle Paleocene that will be used in this study to document environmental changes that took place in central Wyoming during the middle-late Paleocene, supplementing sedimentological and stratigraphic evidence. In doing so, this study will provide a paleoenvironmental context to aid in interpreting fossil faunas collected from the same site.The fossils, primarily leaves, were collected using census collection techniques from two distinct stratigraphic layers and will be characterized by designating morphotypes, identifying relative abundance and diversity, and identifying their taxonomic affinities per previous work on this site and the generalized region. The mean annual temperature and precipitation will be reconstructed using Leaf Margin Analysis and Climate Leaf Analysis Multivariate Program (CLAMP). Preliminary analysis indicates some change in the environment between the two stratigraphic layers but it is unclear whether the changes are to be attributed to climate or landscape. Further investigations seek to better understand the cause of this significant change and provide perspective to the global warming trends before the onset of the PETM.

The Ayeyarwady River Delta, Myanmar is the third largest fluvial source of sediment to the global ocean. This river is an ideal natural laboratory in comparison to other nearby Southeast Asian rivers. This is due to the lack of construction of dams or other alterations to its flow. The UW Sediment Dynamics Group is investigating three distributaries of the Ayeyarwady: the Pathein, the Bogale, and the Yangon Rivers in the west, central, and eastern regions of the delta respectively. These rivers experience differences in discharge, tides, and waves, resulting in different morphologies. The river experiences high seasonal flow during the summer monsoon and low flow during the winter. During the high flow season, the interface between freshwater tidal river and salty estuary is relatively far downstream, and the deposited bed sediment is sourced from the river. During low flow however, the estuary interface migrates upstream and the tides have a stronger influence on the flow, with bed sediment sourced from the continental shelf. In both seasons, bed sediment was collected along the lengths of each distributary in order to understand the patterns of mud and sand deposition in the delta. Disaggregated samples were analyzed for grain size using a LS13-320 Laser Coulter Counter. The percent mud and median grain size was used to determine where mud is being deposited and what causes it to be deposited there. It is expected that during low flow, sediment gets more muddy towards the mouth of the river, and during high flow the bed sediment will be more sandy. Initial findings show that in the Pathein River, sediment indeed does get muddier with downstream distance, supporting the hypothesis. By examining the spatial patterns, our research group will be able to better understand where and when sediment is retained in this relatively natural deltaic environment.