At the Illinois Basin–Decatur Project, a large-scale CO2 capture and geologic storage demonstration project in the saline Mount Simon Sandstone in central Illinois, three overlying and laterally continuous shale formations (the Eau Claire, Maquoketa, and New Albany) are considered confining units overlying the sandstone reservoir. The Mount Simon reservoir contains internal mudstone baffles that will influence CO2 migration pathways and future interaction with seals. Understanding the sealing properties of rock units deemed seals or confining units is vital to commercialization of geologic carbon storage. For this article, nanoscale-resolution focused ion beam scanning electron microscopy (SEM), mercury injection capillary pressure (MICP), X-ray diffraction (XRD) spectroscopy, and quantitative evaluation of minerals by SEM were used to characterize the controls on the sealing integrity of these seals and reservoir confining units. Results show that porosity and pore size generally decrease with depth, except in the carbonate-rich Maquoketa Shale. The Maquoketa contains the highest pore volume owing to abundant dolomite in the mineral matrix compared with the other mudstone and shale intervals, which are clay rich. The shallowest seal sample, the organic-rich New Albany Shale, contains the highest frequency of the smallest pore throat size and is most comparable, with respect to pore sizes and entry pressures, to the deepest black shale and primary Mount Simon reservoir seal, the Eau Claire. Point-specific MICP threshold pressure results, theoretical calculations based on a range of permeabilities, and column height calculations indicate that the internal Mount Simon mudstone and Eau Claire Shale are effective seals of CO2 in the Mount Simon reservoir.

An Early Jurassic (∼196 Ma, laser ablation multiple-collector ICP-MS zircon U-Pb ages) suite of diabase dikes and sills has been identified within the Late Triassic Langjiexue Group, part of the Tethyan sedimentary sequence that is composed of shale and fine-grained sandstone. More primitive rocks (MgO>8.0 wt%) from this suite are characterized by mid-ocean ridge basalt–like rare earth element distribution patterns and isotope (Sr and Nd) compositions, as well as relatively high contents of mantle-compatible elements (e.g., Cr, Ni, and Co), which indicates that they were derived from partial melting of depleted mantle. Younger (∼140 Ma) mafic magmatism in the region has been proposed to represent the initial breakup of the eastern Gondwana continent and the opening of the Indian Ocean. We propose that the ∼196 Ma diabases developed in a continental extension setting and represent the products of melting of depleted mantle within or on the margin of the Neo-Tethyan Ocean.

Postcollisional magmatism is widely distributed in southern Sinai, the extreme northern part of the Neoproterozoic Arabian-Nubian Shield. This article deals with mineral and whole-rock chemistry of postcollisional syenogranites and associated volcanic rocks from three localities in southern Sinai: Iqna Sharay’a, Rusis-Rutig, and Um Shuki–Abu Khusheib. The studied volcanic rocks have compositions between rhyolites and dacites with minor andesite. The whole-rock chemical compositions of the investigated rock types together with the biotite chemistry are consistent with high-K calc-alkaline and alkaline/peralkaline magma. The studied syenogranites and most volcanic rocks are more akin to anorogenic alkaline within-plate environments. Only a few samples of Um Shuki–Abu Khusheib volcanic rocks display some characteristics of orogenic arc-type environments. The high-K calc-alkaline to alkaline affinity and the relative enrichments in large ion lithophile elements (especially K, Rb, and Ba) and light rare earth elements together with a significant negative Eu anomaly imply that the studied granites and volcanic rocks were generated by partial melting of lower to middle crustal materials accompanied by the underplated mafic magma produced in the lithospheric mantle (convective diffusion). This convective diffusion describes a specific scenario of active chemical interaction between mafic and silicic magmas in order to explain formation of voluminous high-K calc-alkaline and alkaline/peralkaline magmatism in postcollisional tectonic environments. The enhanced temperatures of A-type silicic magmas of more than 1000°C suggest that magma generation could occur even at the depth of the uppermost lithospheric mantle.

Next article FreeFront MatterPDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 130, Number 2March 2022 Article DOIhttps://doi.org/10.1086/720759 Views: 57Total views on this site © 2022 The University of Chicago. All rights reserved.PDF download Crossref reports no articles citing this article.

Hydrodynamic equations are frequently employed in the study of coastal boulder movement to estimate the height of tsunami or storm waves responsible for initiating dislodgement. A recent review has challenged the use of such equations and, through a test using a data set of boulders that were moved during storms over winter 2013–14 in the Aran Islands (Ireland), concludes that the equations are flawed. To evaluate this claim, this study revisits the foundation of the equations and reflects on the recent review. We conclude that, although the review is timely and welcomed for the questions it prompts, it arguably does not provide grounds to pronounce the equations flawed. This is due to various considerations, including (1) the equations have been misapplied to physical settings other than as originally intended, (2) wave-type parameters for estimating tsunami and storm wave heights from boulder measurements appear reasonable and not flawed when used within the intended physical settings, (3) the Aran Islands may not be an appropriate location to test the equations because of their physical setting, (4) the exclusion of storm surge and wave setup effects in the test is likely to underestimate the calculated height attained by storm waves, and (5) for comparison, recently revised equations are used to recalculate the Aran Islands boulder data set, indicating that all but 33 boulders demonstrably moved by the 2013–14 storms may be explained by the maximum storm wave height proposed by the review and that all these moved boulders might be explained if the effects of storm surge are included. Analytical tools, such as provided by hydrodynamic equations for boulder dislodgement, are considered important in the contribution they make to coastal risk assessment and hazard management.