Geology Scholarly Workshttps://hdl.handle.net/1808/882024-03-28T17:15:00Z2024-03-28T17:15:00ZLand loss in the Mississippi River Delta: Role of subsidence, global sea-level rise, and coupled atmospheric and oceanographic processesBlum, MikeRahn, DavidFrederick, BrucePolanco, Sarahttps://hdl.handle.net/1808/341582023-05-11T06:07:50Z2023-02-05T00:00:00ZLand loss in the Mississippi River Delta: Role of subsidence, global sea-level rise, and coupled atmospheric and oceanographic processes
Blum, Mike; Rahn, David; Frederick, Bruce; Polanco, Sara
The Mississippi River Delta in coastal Louisiana has suffered large-scale land loss during the historic period and is representative of a global phenomenon where low-elevation deltaic coasts are increasingly at risk because of disrupted sediment supply and accelerated global sea-level rise. Land loss is a natural part of deltaic evolution over time, and most of the land loss in the Mississippi River Delta occurred after individual delta-plain headlands were abandoned as active constructional landscapes, but before 1932 when collection of air photos would make repeat land loss measurements possible. A coastwide land loss of ∼5000 km2 is now well documented for the period 1932 to 2016, which corresponds to a mean rate of ∼57 km2 yr−1.
We use a LiDAR digital topobathymetric model to hindcast land-area changes through time for 1950–2010 by incrementally restoring elevation lost due to subsidence, global sea-level rise, and annual anomalies in mean sea level. Our results support the view that the magnitude and spatial distribution of 20th century land loss can be explained by an unfortunate convergence of ongoing subsidence, greatly reduced sediment dispersal due to levee construction, and acceleration of global sea-level rise. Other factors have contributed to land loss on local scales, but the magnitude of land loss that has occurred would have occurred anyway due to subsidence, lack of sediment input, and accelerated sea-level rise.
Multidecadal accelerations and decelerations in land loss from 1950 to 2010 have been observed, and attributed to accelerations and decelerations in subsidence due to subsurface fluid withdrawals. However, non-linear land loss represents measurements that were made when water levels varied due to annual to multidecadal anomalies in mean sea level. Anomalies in mean sea level are driven by flux of water into and out of the Gulf of Mexico from the Atlantic, as well as the Atlantic Multidecadal Oscillation (AMO), which produces precipitation anomalies in the Gulf of Mexico drainage area, anomalies in Mississippi River discharge to the Gulf of Mexico, and changes in wind directions that serve to trap water along the coast and elevate coastal sea level, or advect water away from the coast to lower coastal sea level. Sea-level anomalies of the scale described here amplify or suppress the secular trend of global sea-level rise and its impacts on low-elevation delta plains as they respond to ongoing subsidence and anthropogenic disruption of sediment dispersal.
2023-02-05T00:00:00ZBerriasian–Valanginian Geochronology and Carbon-Isotope Stratigraphy of the Yellow Cat Member, Cedar Mountain Formation, Eastern Utah, USAJoeckel, Robert M.Suarez, Celina A.McLean, Noah M.Möller, AndreasLudvigson, Gregory A.Suarez, Marina B.Kirkland, James I.Andrew, JosephKiessling, SpencerHatzell, Garrett A.https://hdl.handle.net/1808/341402023-05-06T06:07:33Z2023-01-26T00:00:00ZBerriasian–Valanginian Geochronology and Carbon-Isotope Stratigraphy of the Yellow Cat Member, Cedar Mountain Formation, Eastern Utah, USA
Joeckel, Robert M.; Suarez, Celina A.; McLean, Noah M.; Möller, Andreas; Ludvigson, Gregory A.; Suarez, Marina B.; Kirkland, James I.; Andrew, Joseph; Kiessling, Spencer; Hatzell, Garrett A.
The Early Cretaceous Yellow Cat Member of the terrestrial Cedar Mountain Formation in Utah, USA. has been interpreted as a “time-rich” unit because of its dinosaur fossils, prominent paleosols, and the results of preliminary chemostratigraphic and geochronologic studies. Herein, we refine prior interpretations with: (1) a new composite C-isotope chemostratigraphic profile from the well-known Utahraptor Ridge dinosaur site, which exhibits δ13C features tentatively interpreted as the Valanginian double-peak carbon isotope excursion (the so-called “Weissert Event”) and some unnamed Berriasian features; and (2) a new cryptotephra zircon eruption age of 135.10 ± 0.30/0.31/0.34 Ma (2σ) derived from the CA-ID-TIMS U-Pb analyses of zircons from a paleosol cryptotephra. Our interpretations of δ13C features on our chemostratigraphic profile, in the context of our new radiometric age, are compatible with at least one prior age model for the “Weissert Event” and the most recent revision of the Cretaceous time scale. Our results also support the interpretation that the Yellow Cat Member records a significant part of Early Cretaceous time.
2023-01-26T00:00:00ZStraboTools: A Mobile App for Quantifying Fabric in GeologyGlazner, Allen F.Walker, J. Douglashttps://hdl.handle.net/1808/335622022-09-22T08:00:51Z2020-08-01T00:00:00ZStraboTools: A Mobile App for Quantifying Fabric in Geology
Glazner, Allen F.; Walker, J. Douglas
Quantification of field observations is an essential step in making them reproducible and shareable, but field geologists have few tools for quantifying field observations of important features such as foliation intensity, crystal alignment, vesicle elongation, joint intensity, and mineral proportions. Here we describe a mobile app, StraboTools, which offers two ways to rapidly and objectively quantify these variables. The edge fabric tool examines grayscale gradients in a photograph and summarizes them with the edge fabric ellipse. For deformation of a homogeneous material with passive markers, this ellipse tracks the strain ellipse. Edge fabric ellipses can be determined on the outcrop and make quick work (5 seconds) of formerly time-consuming and subjective strain-analysis tasks (e.g., Fry and Rf /Φ analysis). They are remarkably sensitive to subtle deformations that are difficult to see by eye. The color index tool determines the proportion of any component in the photograph whose grayscale level can be isolated (e.g., dark minerals in a granitic rock, feldspar phenocrysts in a lava, or blue epoxy in a thin section). Estimating proportions by eye has poor precision and accuracy; the color index tool is both accurate and precise if a suitable rock face is available. These tools can be used with photomicrographs and aerial photographs as well as in the field.
2020-08-01T00:00:00ZPliocene–Pleistocene basin evolution along the Garlock fault zone, Pilot Knob Valley, CaliforniaRittase, William M.Walker, J. DouglasAndrew, JoeKirby, EricWan, Elmirahttps://hdl.handle.net/1808/335612022-09-22T08:00:54Z2020-08-06T00:00:00ZPliocene–Pleistocene basin evolution along the Garlock fault zone, Pilot Knob Valley, California
Rittase, William M.; Walker, J. Douglas; Andrew, Joe; Kirby, Eric; Wan, Elmira
Exposed Pliocene–Pleistocene terrestrial strata provide an archive of the spatial and temporal development of a basin astride the sinistral Garlock fault in California. In the southern Slate Range and Pilot Knob Valley, an ∼2000-m-thick package of Late Cenozoic strata has been uplifted and tilted to the northeast. We name this succession the formation of Pilot Knob Valley and provide new chronologic, stratigraphic, and provenance data for these rocks. The unit is divided into five members that record different source areas and depositional patterns: (1) the lowest exposed strata are conglomeratic rocks derived from Miocene Eagle Crags volcanic field to the south and east across the Garlock fault; (2) the second member consists mostly of fine-grained rocks with coarser material derived from both southern and northern sources; and (3) the upper three members are primarily coarse-grained conglomerates and sandstones derived from the adjacent Slate Range to the north. Tephrochronologic data from four ash samples bracket deposition of the second member to 3.6–3.3 Ma and the fourth member to between 1.1 and 0.6 Ma. A fifth tephrochronologic sample from rocks south of the Garlock fault near Christmas Canyon brackets deposition of a possible equivalent to the second member of the formation of Pilot Knob Valley at ca. 3.1 Ma. Although the age of the base of the lowest member is not directly dated, regional stratigraphic and tectonic associations suggest that the basin started forming ca. 4–5 Ma. By ca. 3.6 Ma, the northward progradation fanglomerate sourced in the Eagle Crags region waned, and subsequent deposition occurred in shallow lacustrine systems. At ca. 3.3 Ma, southward progradation of conglomerates derived from the Slate Range began. Circa 1.1 Ma, continued southward progradation of fanglomerate with Slate Range sources is characterized by a shift to coarser grain sizes, interpreted to reflect uplift of the Slate Range. Overall, basin architecture and the temporal evolution of different source regions were controlled by activity on three regionally important faults—the Garlock, the Marine Gate, and the Searles Valley faults. The timing and style of motions on these faults appear to be directly linked to patterns of basin development.
2020-08-06T00:00:00Z