Geology Research Projects 2023
Wynn Bryant
Advisor: Don Barber
Comparing Stable Carbon Isotope Values Between Underlying Mangrove Sediments and Overwash Layers Deposited by Hurricane Ian in Southwest Florida
Hurricane Ian was a Category 5 tropical cyclone that struck the west coast of Florida in 2022. Its peak winds of up to 160 mph caused considerable damage to Florida infrastructure, economy, and coastal environments. The hurricane also generated intense flooding that deposited allochthonous sediments along the west coast of Florida. My lab is interested in identifying properties of Ian’s overwash deposits that can be used to distinguish them from the underlying non-storm sediments. My project specifically compares bulk stable carbon isotopic composition for this purpose.
Overwash deposits from Hurricane Ian and associated underlying sediment samples were collected along the southwest coast of Florida for examination. My research aims to determine if there is a difference in stable carbon isotope signatures between overwash deposits and underlying mangrove sediments. If there is a clear contrast in stable carbon isotopes, then carbon isotope values can function as a proxy for identifying past storm events buried in the geological record. The sediment samples will be freeze-dried, milled, weighed, and sealed in tin capsules prior to being analyzed in an elemental combustion and cavity ring-down spectroscopy system to measure the stable carbon isotope ratios. I hypothesize that the stable isotopic composition of the overwash deposits and underlying sediment will differ because the allochthonous storm deposits are likely to include carbon that is isotopically distinct from that of the mangrove sediments.
My results will be combined with other sedimentary, micropaleontological and biogeochemical data to provide a full characterization of Hurricane Ian’s overwash deposit. Evaluating proxies to identify storm deposits is valuable because it allows researchers to reconstruct historical storm surge events in the geologic record, and compare their magnitude and frequency with recent storm records. Ultimately, this leads to a better understanding of the impact of current climate change on storms so coastal advisors can make educated decisions on coastal resiliency and adaptation.
Morgan Hanson-Rosenberg
Advisor: Selby Hearth
Interpreting the history of metamorphism in the Wissahickon formation using mineralogy and mapping
This summer I am working with the mineralogy of the Wissahickon formation, trying to expose some of the metamorphic history. The Wissahickon formation is a bedrock unit that underlies much of Philadelphia and is defined mineralogically by abundant mica and garnet. The sequence of metamorphic and orogenic events that produced the underlying rocks of the Philadelphia area are strikingly complex and an ongoing area of debate for geologists.
In order to interpret the metamorphic history, I am using existing data on index minerals in the Wissahickon and strategically mapping where certain minerals have been observed in the Philadelphia area. I will also be reconciling thin section mineral analyses with geologic units and outcrops from Southeastern Pennsylvania and Northern Delaware and using QGIS to map thin section mineral data.
My hope is that this project will deepen my understanding of the history of these rocks and result in an interpretation of the sequence of metamorphic events that created the highly divisive Philadelphia area geology.
Samantha Lyster
Advisor: Arlo Weil
Investigating Laramide Orogeny-Associated Shortening Across the Colorado Plateau
The Laramide orogeny was a period of mountain-building on what is now North America, which began in the Late Cretaceous and ended in the Paleogene period. During this period, an oceanic plate subducted under the western edge of North America at a notably shallow angle, an occurrence known as flat-slab subduction. The general understanding is that deformation caused by this event migrated northeast-ward; for example, activity started in the southern Colorado Plateau around 80 million years ago, but in northern Wyoming around 60 millions years ago. This summer, we will be traveling to the Colorado Plateau to collect rock samples to gain a better understanding of strain and stress orientation at various locations associated with the Laramide orogeny. This research helps us learn how continents are deformed by tectonic processes and develops a model for flat-slab subduction.
In order to quantify shortening directions, we will measure populations of minor faults, both out in the field and from the existing literature. In the lab, we will conduct magnetic susceptibility analyses on the collected rock samples to estimate shortening directions from microscale internal fabrics. We will also use paleomagnetic analysis to quantify any rotation the rock has undergone in order to test whether our measured shortening directions need to be corrected for any post- or syn-tectonic rotations. By investigating stress orientation and shortening directions at many individual localities, we will gain further insight into the big picture of how and when this orogeny occurred.
Adalia Rodriguez
Advisor: Don Barber
Distributions of modern salt-marsh foraminifera in southern New Jersey and their viability for sea-level studies
Currently the United States eastern seaboard is experiencing sea-level rise at a faster rate than the global average. In order to understand the magnitude of local sea-level change and how it may affect coastal habitats and communities in the future, we must look in the past to determine how and why sea level has changed through time. Salt marsh environments, which are prevalent on the US East Coast, can be used to reconstruct past sea level. Although salt marshes often appear flat, there are subtle topographic differences which experience different tidal flooding frequencies. Furthermore, salt-marsh foraminifera species are sensitive to the tidal flooding frequencies, and thus inhabit specific elevation zones within the marsh. Therefore, distinct foraminifera assemblages can be associated with tidal flooding frequency and, hence marsh surface elevation. Characterization of the modern foraminifera assemblages provides a key to interpreting paleo marsh elevation from core samples extracted from older and deeper sediments.
This project will be characterizing the modern salt marsh foraminifera assemblages along two elevation transects across a salt marsh in Dennis Creek, New Jersey. The modern assemblages describe the relative abundances of foraminifera species as a function of marsh surface elevation relative to modern local sea level. In order to analyze foraminiferal assemblages, live and dead foraminifera are counted at each sample site across two transects. The modern foraminifera samples were stained with rose Bengal immediately after collection to differentiate dead and live foraminifera, but ultimately, only dead foraminifera are to be used in analysis. Samples were stored in a buffered ethanol solution and refrigerated prior to analysis. Each sample is wet sieved to isolate the 63-500 µm size fraction, split into eight equal aliquots, and then counted under a microscope in distilled water. In each sample, a minimum of 100 dead foraminifera tests will be counted and identified to species level to observe changes in assemblages across the transects. Ultimately, this data will be used as a modern training set to produce a new sea-level record from Dennis Creek to constrain sea-level variability over time and space. An improved understanding of local sea-level variability is essential for future predictions of coastal inundation by rising seas due to climate change.
Aidan York
Advisor: Arlo Weil
Constructing a History of Laramide-era Tectonism and Deformation in the Colorado Plateau
The Laramide Orogeny is a major deformational, mountain-building event that impacted western North America approximately 80 million years ago due to the low-angle subduction of an oceanic plate under the North American plate. The deformational history of this event, particularly with respect to rigid-body-rotations, translations, and internal strain, is recorded within the remnant paleomagnetism and meso- and micro-scopic structures and fabrics in rocks from the Colorado Plateau, located in the Four Corners area of the United States. Studying this region is of particular interest, as it holds a record of transitioning tectonic environments and mountain-building, spanning before, during, and after the Laramide itself. For my summer research, I am looking to uncover aspects of that history, by quantifying rotations and applying time constraints to the region’s development. This will be done by conducting paleomagnetic and fabric analyses of samples collected from the Colorado Plateau. In particular, I will be measuring anisotropy of magnetic susceptibility (AMS) to infer Laramide shortening directions based on fabrics of deformed rocks, and studying remnant magnetization to determine the orientation of North America at the time of rock formation.
These analyses will be conducted on samples previously collected by Dr. Weil, as well as on samples our team collects this summer. This summer’s research will include a two-week trip to the Colorado Plateau, beginning in Utah and travelling to New Mexico, to visit several Laramide age field sites, collect more samples for analyses, and record observations about mesoscale deformational features, such as faults and fractures. This field data, in conjunction with laboratory analyses of samples, will help to create a fuller picture of the American southwest’s unique and storied geologic history. This, in turn, will ultimately lead to a better understanding of continental tectonism associated with and resulting from low-angle subduction.