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Geology of the Mokelumne Paleochannel at the Miocene Zoo, Sierra Nevada Foothills, California; And Volcanology and Structure of the Leviathan Peak Arc Volcanic Center, Ancestral Cascades Arc, Monitor Pass Region, Central Sierra Nevada, California
Get PDFThe Mokelumne paleochannel is one of a series of E-W oriented, Eocene to Late Miocene paleochannels that provide constraints on the topographic and tectonic evolution of the Sierra Nevada. One of the largest fossil troves in California, hereafter referred to as the “Miocene Zoo” was recently discovered in the Miocene Mehrten Formation, in the lower reaches of Mokelumne paleochannel in the western Sierra Nevada foothills. The site has captured media attention and is now the subject of intense paleontological study. U-Pb detrital zircon geochronology indicates a maximum depositional age of 8.23 ± 0.08 Ma for the fluvial tuffaceous sandstone and conglomerate of the Mehrten Formation that contain the fossils (Hodges et al., 2022). In Chapter 1, we focus on the geologic setting of the Miocene Zoo, by making digital map compilations and contour maps, a series of measured sections, and by characterizing tephras discovered at the fossil site. New compilation mapping shows that the Mokelumne paleochannel contains a series of erosional unconformities before its deposits fan out down-paleoslope into a broad apron about 15 km east of the modern eastern edge of the California Central Valley. The unconformity at the base of the Mehrten Formation where it rests on the Oligocene Valley Springs Formation is approximately 20 to 60 m deep. A series of measured sections shows that the fossil site lies within a network of braided channels in the axis of the Mokelumne paleovalley, exposed on the north shore of the Camanche Reservoir, with overbank deposits exposed on the south shore of the reservoir. Tephras are also concentrated in the channel axis deposits and include fine-grained water-lain tuff, as well as three types of rounded pumice clasts distinguished by petrography and geochemistry: white hornblende andesite pumices, white biotite dacite pumices, and black biotite trachydacite pumices. 40Ar/39Ar geochronology on plagioclase and hornblende from single pumice clasts provides an age of 8.64 ± 0.04 Ma. We suggest that the younger 8.23 ± 0.08 Ma U-Pb detrital zircon age should be taken as the approximate reference age for the fossiliferous deposits, because we interpret that ash was rapidly deposited in flooding events accompanying volcanic eruptions. These results show that paleochannel re-incision events, well demonstrated for more proximal reaches of paleochannels in the Sierra, also affected the lowermost reach of Mokelumne paleochannel, a fact that must be taken into consideration in models for the topographic evolution of the Sierra Nevada. About 100 km east of the Miocene Zoo, Henry et al. (2012) projected the Mokelumne paleochannel through Ebbetts Pass and Monitor Pass at the modern Sierra Nevada crest, where the Ancestral Cascades arc was active during Miocene time. In the Monitor Pass region, volcanic rocks and faults had not been mapped since 1981, and many units were left undivided (John et al., 1981). In Chapter 2, we present new geologic mapping, cross sections, petrography, geochemistry, and in-progress 40Ar/39Ar geochronology in the newly-defined Leviathan Peak volcanic center in the Monitor Pass region, which allows correlation with regional magmatic and structural events and shows that the Mokelumne paleochannel was disrupted by volcanism or eroded away at this latitude. We infer that the Leviathan Peak volcanic center developed within a large ca. 11 Ma basin which accumulated volcanic debris flow deposits, as well as the tuff of Diamond Valley, which was erupted to the northwest (Wesoloski, 2018). Only one eruptive unit in the center is preserved, consisting of extensive ca. 8 Ma andesite lavas, block-and-ash-flow tuffs and tuffs with large quartz xenocrysts derived from the granitic basement. The rest of the center is preserved as a series of ca. 6 Ma andesite hypabyssal intrusions. Units are cut by a series of normal faults which mainly step down to the east, although one full graben (Bagley Valley) is present. The range front faults include the seismically active Slinkard Valley and Antelope Valley faults. We calculate total offsets and minimum average slip rates on faults where possible. Total offset on the Slinkard Valley fault, which slipped during the 2021 Antelope Valley earthquake (M 6.0; Pollitz et al., 2021; Wang et al., 2023), is estimated at 1.2 km. Offset on the Antelope Valley fault is unknown because the hanging wall lies below the Antelope Valley and Topaz Lake. We combine structural measurements and dates on faulted units to show that at least one fault in this area (the Monitor Pass fault) initiated prior to 8.25 Ma, at least ~3.25 million years before faulting began at the Ebbetts Pass volcanic center to the west. The Leviathan Peak volcanic center represents an anomaly in the Sierra Nevada Ancestral Cascades arc, which is dominated by volcanic rocks, with few exposed hypabyssal intrusions (Busby et al., 2008a, 2013a, 2013b, 2016, 2018; Hagan et al., 2009; Wesoloski, 2018). We suggest that the volcanic cover was largely stripped off the Leviathan Peak volcanic center, exposing the hypabyssal intrusions by footwall uplift and erosion along the Antelope Valley fault. We infer that the Mokelumne paleochannel at Monitor Pass was disrupted by ca. 6 Ma volcanism or eroded away as a result of this footwall uplift. These discoveries shed insight into the volcanic and tectonic evolution of the Monitor Pass Region
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Late Jurassic dike swarms in the southwestern Sierra Nevada Foothills terrane, California: Implications for the Nevadan orogeny and North American plate motion
No full textA previously unrecognized sheared dike swarm has been identified in a southern fragment of the western Foothills terrane—the Owens Mountain area of the western Sierra Nevada foothills, northeast of Fresno, California. It may be the southern extension of the Bear Mountains fault zone. The dike swarm, sheeted in places, consists predominantly of tonalitic tabular bodies and coeval, mutually cross-cutting tonalitic and mafic dikes. Textures and fabrics within the dike swarm range from partially recrystallized igneous to strongly deformed metamorphic tectonites, implying that dike emplacement occurred during ductile deformation. Mylonitization has transposed layering parallel to foliation and has greatly thinned many of the dikes. Layering and foliation dip subvertically and strike NNW–SSE. Post-tectonic annealing has destroyed most microscopic shear indicators, but macroscopic intrafolial folds are common and have steeply southeast-plunging fold axes and S-fold geometries that may indicate a sinistral sense of shear. Age data (U-Pb zircon) from the tonalites reveal that emplacement and crystallization occurred over a 7-m.y. period, from 155 Ma to 148 Ma, at an estimated depth of 10 km (from AlTotal in hornblendes). A correlation between age and degree of deformation and recrystallization of the tonalites implies syntectonic dike emplacement. Intrusion began within 5 m.y. of deposition of the strata into which the dikes were emplaced. Granitic dikes that cut the complex at 123 Ma are nondeformed. The duration of the Nevadan orogeny is shown to have lasted from Late Jurassic to Early Cretaceous (160–137 Ma and possibly to 123 Ma) and thus is more protracted that has been postulated.
The regional tectonics of the Owens Mountain and other Cordilleran dike swarms can be related in a broad dynamic sense to the absolute motion of North America by using the apparent polar wander (APW) analysis of May and Butler (1986). The Nevadan orogeny may be the manifestation of drastic changes in magnitude and direction of North American motion (from ~45 km/m.y. to the NNE to ~200 km/m.y. to the NW; May and Butler, 1986). The Late Jurassic dike swarms record a complex pattern of sinistral-sense transtension-transpression that may have developed at the J2 APW cusp (ca. 150 Ma; see May and Butler, 1986) and during subsequent, rapid northwestward acceleration of North America
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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