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1. Seismic Response of Cook Inlet Sedimentary Basin, Southern Alaska

   https://doi.org/10.1785/0220190205  

   Smith, Kyle; Tape, Carl (October 2019, Seismological Research Letters)

   null (Ed.)

   Abstract Cook Inlet fore‐arc basin in south‐central Alaska is a large, deep (7.6 km) sedimentary basin with the Anchorage metropolitan region on its margins. From 2015 to 2017, a set of 28 broadband seismic stations was deployed in the region as part of the Southern Alaska Lithosphere and Mantle Observation Network (SALMON) project. The SALMON stations, which also cover the remote western portion of Cook Inlet basin and the back‐arc region, form the basis for our observational study of the seismic response of Cook Inlet basin. We quantify the influence of Cook Inlet basin on the seismic wavefield using three data sets: (1) ambient‐noise amplitudes of 18 basin stations relative to a nonbasin reference station, (2) earthquake ground‐motion metrics for 34 crustal and intraslab earthquakes, and (3) spectral ratios (SRs) between basin stations and nonbasin stations for the same earthquakes. For all analyses, we examine how quantities vary with the frequency content of the seismic signal and with the basin depth at each station. Seismic waves from earthquakes and from ambient noise are amplified within Cook Inlet basin. At low frequencies (0.1–0.5 Hz), ambient‐noise ratios and earthquake SRs are in a general agreement with power amplification of 6–14 dB, corresponding to amplitude amplification factors of 2.0–5.0. At high frequencies (0.5–4.0 Hz), the basin amplifies the earthquake wavefield by similar factors. Our results indicate stronger amplification for the deeper basin stations such as near Nikiski on the Kenai Peninsula and weaker amplification near the margins of the basin. Future work devoted to 3D wavefield simulations and treatment of source and propagation effects should improve the characterization of the frequency‐dependent response of Cook Inlet basin to recorded and scenario earthquakes in the region. 

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2. The end of the Cretaceous: depositional palaeogeographical reconstruction of the Gulf of Mexico and adjacent areas just prior to the Chicxulub impact

   https://doi.org/10.1144/SP545-2023-51  

   Snedden, John William; Lowery, Christopher M; Lawton, Timothy F (November 2023, Geological Society, London, Special Publications)

   Abstract Until recently, information about the end of the Cretaceous was based upon investigation of global outcrop sections. New subsurface drilling and characterization from well cores and logs in the Gulf of Mexico Basin have greatly illuminated the end Cretaceous event. However, the palaeogeography of the late Maastrichtian just prior to bolide impact is less well understood and is of great importance in terms of modelling the resulting distribution and composition of the Chicxulub impact material, as well as tsunami and seiche wave height. Here, we examine the Maastrichtian strata in the basin, synthesizing lithostratigraphy and chronostratigraphy, tectonic plate reconstructions, global and local sea level history, palaeoclimate and depositional systems. Our new Maastrichtian palaeogeographical reconstruction shows the basin prior to the Chicxulub impact at a time of globally high sea level, with widespread deposition of deepwater chalks and shallow marine carbonates and local siliciclastic shorelines fed by the nascent Cordilleran belt. Stratigraphic correlations of wells and outcrops illustrate the range of palaeoenvironments from coastal plain to deep marine. As much as 610 m (2000 ft) of Maastrichtian and Campanian section is mapped around the basin, reflecting accommodation provided by basin subsidence, salt deflation and palaeophysiography. A large thickness of carbonates accumulated in the basin centre, with steep shoreline to basin gradients particularly in Mexico. At the end of the Cretaceous, carbonate palaeoenvironments probably covered 96% of the Gulf of Mexico Basin, with less than 4% of the area likely occupied by siliciclastic systems, a distribution that evolved from the Early Cretaceous. Our maps thus explain dominance of carbonate breccia and chalks in K–Pg boundary units deposited over the basin sites proximal or distal to the Chicxulub impact crater. This also elucidates the large impedance contrast and high amplitude seismic response of the K–Pg boundary horizon, mappable over vast portions of the basin. 

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3. Magnetic susceptibility of the Late Devonian Antrim Shale of the Michigan Basin

   Barker-Edwards, T; Voice, P; Zambito, J (April 2024, Geological Society of America Abstracts with Programs)

   This study utilizes the magnetic susceptibility (MS) of sedimentary strata to correlate the Late Devonian Antrim Formation black shale and calcareous mudstone within the Michigan Basin as well as the Antrim with previously published MS profiles from contemporaneous, shale-dominated strata from the Illinois Basin. MS can be used as a proxy for changes in material composition, which is linked to paleoclimate-controlled sediment fluxes and depositional environments. In the Michigan Basin, MS profiles through the basin-margin State Chester Welch 18 and the more basinal Krocker 1-17 cores show that MS patterns correspond to lithostratigraphic units. For some of these units the MS patterns are similar among the cores, though not for all units. Preliminary interpretation is that MS patterns are a result of proximity to sediment source (Acadian Orogeny versus Transcontinental Arch) as well as intrabasinal early diagenetic processes (pyrite). Furthermore, the lithostratigraphic units in these cores may not be chronostratigraphically equivalent. This study also compares the Michigan Basin MS basinal profile (Krocker 1-17 core) with previously published data from the “Bullitt County Core” from Kentucky, in the southern Illinois Basin. Within a biostratigraphic framework, the Michigan and Illinois Basin cores appear to show similar MS patterns. This is possibly because sediment input to these two locations is primarily sourced from the Acadian Orogeny, and the depositional environment and therefore early diagenetic processes, are similar. Future work will combine mineralogical analysis with the MS profiles to decipher the source of magnetic susceptibility, currently hypothesized to be driven by ilmenite concentration. 

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4. Site U1456

   https://doi.org/10.14379/iodp.proc.355.103.2016  

   Pandey, DK; Clift, PD; Kulhanek, DK; Andò, S; Bendle, JAP; Bratenkov, S; Griffith, EM; Gurumurthy, GP; Hahn, A; Iwai, M; et al (August 2016, Proceedings of the International Ocean Discovery Program Expedition reports)

   International Ocean Discovery Program (IODP) Site U1456 lies offshore the western margin of India, ~475 km from the Indian coast and ~820 km from the modern mouth of the Indus River, which is presumed to be the primary source of sediment to the area (Figure F1). Site U1456 is within Laxmi Basin, which is flanked by Laxmi Ridge to the west and the Indian continental shelf to the east. Laxmi Ridge separates the Eastern Arabian Basin to the east and Western Arabian Basin to the west. Gop Rift lies northeast of Laxmi Ridge and is an along-strike equivalent of Laxmi Basin. Laxmi Basin is a 200–250 km wide depression that runs in a northwest–southeast direction parallel to the west coast of India. A series of isolated seamounts (e.g., Panikkar and Raman Seamounts, together with Wadia Guyot) occur along the axial part of Laxmi Basin, which are collectively referred to as Panikkar Ridge (Krishna et al., 2006) (Figure F2). Site U1456 was positioned in order to core through the Cenozoic sedimentary cover and penetrate into igneous basement to understand the long-term development of the regional tectonics, climate, and erosional history. 

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5. The Role of Atlantic Basin Geometry in Meridional Overturning Circulation

   https://doi.org/10.1175/JPO-D-21-0036.1  

   Ragen, Sarah; Armour, Kyle C.; Thompson, LuAnne; Shao, Andrew; Darr, David (March 2022, Journal of Physical Oceanography)

   Abstract We present idealized simulations to explore how the shape of eastern and western continental boundaries along the Atlantic Ocean influences the Atlantic meridional overturning circulation (AMOC). We use a state-of-the art ocean–sea ice model (MOM6 and SIS2) with idealized, zonally symmetric surface forcing and a range of idealized continental configurations with a large, Pacific-like basin and a small, Atlantic-like basin. We perform simulations with five coastline geometries along the Atlantic-like basin that range from coastlines that are straight to coastlines that are shaped like the coasts of the American and African continents. Changing the Atlantic basin coastline shape influences AMOC strength in a manner distinct from simply increasing basin width: widening the basin while maintaining straight coastlines leads to a 10-Sv (1 Sv ≡ 10⁶m³s⁻¹) increase in AMOC strength, whereas widening the basin with the geometry of the American and African continents leads to a 6-Sv increase in AMOC strength, despite both cases representing the same average basin-width increase relative to a control case. The structure of AMOC changes are different between these two cases as well: a more realistic basin geometry results in a shoaled AMOC while widening the basin with straight boundaries deepens AMOC. We test the influence of the shape of the both boundaries independently and find that AMOC is more sensitive to the American coastline while the African coastline impacts the abyssal circulation. We also find that AMOC strength and depth scales well with basin-scale meridional density difference, even with different Atlantic basin geometries, illuminating a robust physical link between AMOC and the North Atlantic western boundary density gradient. 

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