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Current Projects |
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Todd A. LaMaskin, Ph.D. Assistant Professor Department of Geography and Geology
(p) 910-962-2655 (f) 910 962-7077
lamaskint(AT)uncw.edu |
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Contact: |
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Basin Analysis Research Group The LaMaskin Lab |
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Testing models for the timing and magnitude of stable carbon isotope excursions during the Middle Devonian punctata event
Krysden Schantz
The punctata carbon isotope excursion (CIE) occurred ca. 382 Ma (Late Devonian) and represents a series of positive and negative CIEs (Fig. 1A). Authors agree that the punctata CIE represents an oceanographic disturbance and have developed models for global paleoenvironmental change caused by this CIE (Pizarzowska and Racki, 2012); however, temporally consistent CIE trends and magnitudes have not been demonstrated worldwide due to stratigraphic disruption, alteration, and low-resolution sampling. Our objective is to generate a high-resolution stable carbon isotope record from relatively undisturbed, unaltered rocks of the punctata zone in Nevada (Fig. 1B) that will test the model of Pizarzowska and Racki (2012) for the timing and magnitude of globally coincident CIEs during the punctata zone (Fig. 1A). |
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High-resolution stable carbon isotope record across the Alamo meteorite-impact horizon in eastern central Nevada.
Olivia Koster
The Alamo impact took place on the shallow continental shelf of western North America in Late Devonian time during the punctata conodont zone, a time interval known worldwide for a series of large magnitude (i.e., 5 to 7‰) positive and negative carbon isotope excursions (CIEs; Fig.1.A, B; Pisarzowska and Racki, 2012). Some authors suggest that the Alamo impact was the cause of a 5‰ negative isotope excursion within the upper portions of the punctata zone CIE, and that the impact resulted in global ecological perturbations (Sandberg et al., 1997; Sim et al., 2015); however, it has not yet been established if the Alamo event occurred before or after the 5‰ negative isotope excursion. A previous study in Nevada identified a negative carbon isotope excursion that appears to have occurred prior to the Alamo event (Morrow et al., 2009) but intense stratigraphic disruption associated with the Alamo impact at the study site, coupled with a low sampling resolution, yielded inconclusive evidence for a negative isotope excursion that could be associated with the impact. Data from outside of the impact zone—but that still records the impact—are needed to assess if the Alamo event caused a disturbance of the global carbon cycle or the ensuing ecological perturbations as suggested by others (i.e., Sandberg et al., 1997; Morrow et al., 2009; Sim et al., 2015). Our results will enable me to (1) test if the Alamo impact occurred before or after a negative isotope excursion by comparing my isotope record with my detailed stratigraphic observations to determine the exact temporal relationship between the impact and any excursions in the isotope data, and (2) establish an unambiguous stable carbon isotope stratigraphic record of the Alamo event that is at a high enough resolution to draw conclusions about the relationship between bolide impacts and ocean chemistry. |
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Testing an exotic vs. endemic origin for the Rattlesnake Creek terrane, Klamath Mountains, California
Johnathan Rivas
Despite a rich history of investigation, there is still controversy regarding the assembly of the western U.S. Cordillera during Mesozoic time. Some researchers have proposed that expansion of the western U.S. Cordillera occurred through the accretion of exotic arcs to the continental margin (1, 2; Fig, 1A). In contrast, other researchers suggested that periods of in situ extension on the plate margin generated endemic fringing arcs and that subsequent contraction led to accretion and thus expansion (3, 4; Fig. 1B). My objective is to use detrital zircon U-Pb ages to test these two models on rocks of the Rattlesnake Creek and associated accreted terranes in the Klamath Mountains of California. Based on limited existing data, I hypothesize that the Rattlesnake Creek terrane is endemic to the western North American continental margin, supporting the model of in situ extension and contraction (Fig. 1B). |
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Earth and Ocean Sciences |
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Correlating magnetic susceptibility and geochemical proxies with δ13C data during the Late Devonian punctata event, Gap Mountain, eastern Nevada, USA: Does paleoclimate drive Carbon Isotope Excursions?
Amelia Perry
The Late Devonian transitans and punctata events are recorded as a series of positive excursions in δ13C values worldwide; however, the mechanisms responsible for the observed changes in the carbon pool are unknown. A strong positive correlation is observed in a comparison of δ 13C data from the Late Devonian Guilmette Formation (Fig. 1A), eastern Nevada continental shelf (ENCS; Fig. 1B) versus magnetic susceptibility (MS) values (a proxy for wind-blown dust) and geochemical variations of major, minor, and trace elements (paleoproductivity proxies) from Late Devonian rocks of the western Canada sedimentary basin (WCSB; Fig. 1C, 1D). I hypothesize that episodes of increased δ13C values, relative to the Late Devonian background, in samples from the ENCS may be a result of increased wind-blown dust and associated enhanced paleoproductivity. My objective is to test this hypothesis by analyzing MS and selected elements in the same ENCS samples that were analyzed for δ13C. |
