Geology topics

Michael Miner

Publications and source records attributed to Michael Miner.

5 recordsLinked to original sources

USGS2024

Short-term sediment dispersal on a large retreating coastal river delta via 234Th and 7Be sediment geochronology: The Mississippi River Delta Front

Many Mississippi River Delta studies have shown recent declines in fluvial sediment load from the river and associated land loss. In contrast, recent sedimentary processes on the subaqueous delta are less documented. To help address this knowledge gap, multicores were collected offshore from the three main river outlets at water depths of 25–280 m in June 2017 just after the peak river discharge period, with locations selected based on 2017 U.S. Geological Survey seabed mapping. The coring locations included the undisturbed upper foreset, mudflow lobes, gullies, and the undisturbed prodelta. Nine multicores were analyzed for Beryllium-7 activity, and four cores were analyzed for excess Thorium-234 activity via gamma spectrometry, granulometry and X-radiography. Our results indicate a general trend of declining 7 Be and 234 Th activities and inventories with increasing distance from sources and in deeper water. The core X-radiographs are graded from the predominantly physically stratified nearshore to the more bioturbated offshore, consistent with the sedimentation patterns. Sediment focusing assessed via the 7 Be and 234 Th sediment inventories shows preferential sedimentation in gully and lobe environments, whereas the upper foreset and prodelta focusing factors are relatively depleted. Overall, short-term sediment deposition from the main fluvial source remains active offshore from all three major river outlets, despite the overall declining river load.

Louisiana↗

USGS2021

Influence of antecedent geology on the Holocene formation and evolution of Horn Island, Mississippi, USA

Horn Island, one of the two most stable barriers along the Mississippi-Alabama chain (Cat, East and West Ship, Horn, West Petit Bois, Petit Bois, and Dauphin), provides critical habitat, helps regulate estuarine conditions in the Mississippi Sound, and reduces wave energy and storm surge before they reach the mainland shore. However, important details of the formation and evolution of the island in response to sea-level rise, storms, and antecedent geology remain unclear. This study integrates 2200 km of high-resolution geophysical data, 35 sediment cores, and 18 radiocarbon ages to better understand the geologic history of the island. Incised valleys of the Biloxi and Pascagoula Rivers underlie Horn Island and played a profound role in the evolution of the system. Within the incised valleys, sandy paleochannel deposits represent potential sediment sources during island development. Scour associated with wave and tidal ravinement processes liberated sand from the paleochannels and along with numerous other sizable sand sources on the shelf contributed to the formation and continued maintenance of Horn Island. Based on radiocarbon ages, transgressive ephemeral islands/shoals with no preserved shoreface existed at least 8000 cal yr BP and were frequently overwashed when sea-level rise rates were ~ 4–5 mm/yr. Approximately 5000 cal yr BP, coinciding with a deceleration in sea-level rise to about 1.4 mm/yr and attendant increased sand supply, radiocarbon ages associated with Horn Island's barrier complex and lower shoreface indicate a period of island stabilization. Seismic and sediment core data show a long history of westward lateral migration by longshore currents through tidal ravinement and inlet fill. Subsurface sand packages associated with tidal inlet fill and paleochannels are available for ravinement and may be important sand sources for Horn Island to maintain subaerial exposure with the expected accelerated future sea-level rise.

Mississippi↗

USGS2020

Short and long-term movement of mudflows of the Mississippi River Delta Front and their known and potential impacts on oil and gas infrastructure

Mudflows on the Mississippi River Delta Front (MRDF) are recognized hazards to oil and gas infrastructure in the shallow (20 – 300 m water depth) Gulf of Mexico. Preconditioning of the seafloor for failure results from high sedimentation rates coupled with slope over-steepening, under-consolidation, and abundant biogenic gas production. Catastrophic failure of production platforms and pipelines due to seafloor displacement during infrequent large hurricanes such as Camille in 1969 and Ivan in 2004, point to cyclical loading of the seafloor by waves as a primary movement trigger. Due to data limitations, the role of smaller storms and background oceanographic processes in driving seafloor movement have remained largely unconstrained, but are thought to contribute to significant seafloor change. With the aid of new high-resolution multibeam mapping and seismic reflection profiling across sections of the MRDF, several moving features within the deforming delta-front environment are investigated and potential hazards to infrastructure installed and adjacent to the region are discussed. Via repeat mapping surveys of selected areas and records of changing shipwreck locations, we highlight significant seafloor displacement across annual to decadal timescales. For example, individual blocks mapped within mudflow gullies adjacent to Southwest Pass show downslope transport of more than 80 m in a single year, while the S.S. Virginia, a 153 m-long oil tanker sunk in 1942 has been relocated and found to have moved downslope more than 400 m in 14 years, without a major hurricane (> Category 2) passing through the region.

Louisiana↗

USGS2012

Geologic controls on sediment distribution and transport pathways around the Chandeleur Islands, LA., USA

Geophysical surveys around the Chandeleur Islands provide the necessary data to map the thickness and distribution of the Holocene deposit associated with this barrier island system. This system rests uncomformably on St. Bernard Delta deposits of the Mississippi Delta plain and is thinnest under the central part of the island chain and thickest at the northern and southern ends. The zone of divergence in the bidirectional littoral transport system coincides with the thin central part. An estimate of northward littoral transport rate based on lithosome age and the volume of sediment that has accumulated at the northern end of the transport cell suggests the average transport rate over the life of the system is greater than present day fair-weather estimates. This difference may be attributed to changes in transport rates through the life of the system, to changes in the rate of sea-level rise or to storms playing a more dominant role than fair-weather waves in littoral transport.

Louisiana↗

USGS2011

Hurricane impact and recovery shoreline change analysis of the Chandeleur Islands, Louisiana, USA: 1855 to 2005

Results from historical (1855-2005) shoreline change analysis of the Chandeleur Islands, Louisiana, demonstrate that tropical cyclone frequency dominates the long-term evolution of this barrier-island arc. The detailed results of this study were published in December 2009 as part of a special issue of Geo-Marine Letters that documents early results from the Northern Gulf of Mexico (NGOM) Ecosystem Change and Hazard Susceptibility Project.

Fact Sheet↗