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  • Geological Society of America (GSA)  (12)
  • American Association for the Advancement of Science (AAAS)
  • 1
    Publication Date: 2015-11-22
    Description: Polyploidy is a common mode of speciation and evolution in angiosperms (flowering plants). In contrast, there is little evidence to date that whole genome duplication (WGD) has played a significant role in the evolution of their putative extant sister lineage, the gymnosperms. Recent analyses of the spruce genome, the first published conifer genome, failed to detect evidence of WGDs in gene age distributions and attributed many aspects of conifer biology to a lack of WGDs. We present evidence for three ancient genome duplications during the evolution of gymnosperms, based on phylogenomic analyses of transcriptomes from 24 gymnosperms and 3 outgroups. We use a new algorithm to place these WGD events in phylogenetic context: two in the ancestry of major conifer clades (Pinaceae and cupressophyte conifers) and one in Welwitschia (Gnetales). We also confirm that a WGD hypothesized to be restricted to seed plants is indeed not shared with ferns and relatives (monilophytes), a result that was unclear in earlier studies. Contrary to previous genomic research that reported an absence of polyploidy in the ancestry of contemporary gymnosperms, our analyses indicate that polyploidy has contributed to the evolution of conifers and other gymnosperms. As in the flowering plants, the evolution of the large genome sizes of gymnosperms involved both polyploidy and repetitive element activity.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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  • 2
    Publication Date: 2019
    Description: 〈p〉In the 1950s the myxoma virus was released into European rabbit populations in Australia and Europe, decimating populations and resulting in the rapid evolution of resistance. We investigated the genetic basis of resistance by comparing the exomes of rabbits collected before and after the pandemic. We found a strong pattern of parallel evolution, with selection on standing genetic variation favoring the same alleles in Australia, France, and the United Kingdom. Many of these changes occurred in immunity-related genes, supporting a polygenic basis of resistance. We experimentally validated the role of several genes in viral replication and showed that selection acting on an interferon protein has increased the protein’s antiviral effect.〈/p〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2015-12-24
    Description: Upper Cretaceous sandstones from 17 localities from California to southeastern Alaska (United States) contain unexpectedly large populations of detrital zircons with Proterozoic U-Pb ages, with age peaks at 1800–1650 and 1380 Ma. These peaks are indicative of a sediment source region in the southern part of the Proterozoic Belt Supergoup basin in central Idaho, which hosts 1800–1650 Ma detrital zircons and which was intruded by rift-related 1380 Ma bimodal plutons and sills. Belt rocks were strongly uplifted and eroded during Late Cretaceous Sevier shortening and fed four paleoriver systems. The Lemhi Pass–Hawley Creek river system flowed east and sourced the Beaverhead-Harebell-Pinyon nonmarine megafan in the Cordilleran foreland basin. The Kione River flowed southwest to northern California, where it sourced a very large, ca. 82–80 Ma, ~600-m-thick delta and submarine fan complex within the northern Great Valley forearc basin. Considerable Kione detritus also transited the forearc basin to reach the Franciscan trench, sourcing a pulse of deposition and subduction accretion in central California and even part of southern California. The Swakane River flowed northwest out of Idaho into Washington, sourcing the protolith for the high-grade Swakane gneiss. More speculatively, a Yakutat River may have flowed northwest and deposited Yakutat strata in a trench off Washington or British Columbia, before those rocks were translated north to southeastern Alaska. Recognition of a major source area in central Idaho for zircons with an uncommon age of 1380 Ma helps constrain the ca. 85–65 Ma paleogeography and paleotectonics of major sectors of the North American convergent margin orogen.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 4
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    Geological Society of America (GSA)
    In: Geology
    Publication Date: 2015-05-23
    Description: To understand linkages among processes that combined to build the North American Cordillera, we synthesize its tectono-magmatic history from the California accretionary wedge to the retroarc foreland of Wyoming. At this latitude, the Cordilleran magmatic arc experienced high-flux events (HFEs) at ca. 160–150 Ma and ca. 105–90 Ma. Retroarc shortening provided the main source of HFE magmas, which in turn created eclogitic arc roots that later foundered into the mantle and cleared the sub-arc region of excess mass, and provided space to accommodate renewed retroarc shortening. The forearc, arc, and retroarc regions all responded variably to this cycle of tectono-magmatic processes, and Laramide flat-slab subduction may have both disrupted and been enhanced by events within this cycle.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 5
    Publication Date: 2016-01-20
    Description: The Andean Cordillera is widely considered to be one of the type examples of a convergent margin setting. In the southernmost Andes, however, rifting and volcanism predated mid-Cretaceous breakup of Gondwana and formation of the South Atlantic Ocean by up to 40 m.y. and culminated in the opening of the Rocas Verdes backarc basin east of the Mesozoic Patagonian Batholith. We present new U-Pb geochronology from the Austral sector (49°S–50°S) that indicates rift volcanism occurred between 154 and 147 Ma near the northern terminus of the basin. Available data and observations from the southern Rocas Verdes Basin indicate larger-magnitude and longer-duration extension compared to the northern basin region. The Rocas Verdes Basin underwent progressive northward propagation and opening and was later backfilled concomitantly with the opening of the southern Atlantic Ocean by north-to-south deposition within a retroarc foreland setting. The influence of the inherited tectonic fabric of the Rocas Verdes backarc basin on the subsequent foreland basin explains many unique characteristics of the Patagonian Andes, such as a protracted deep basin that formed atop the previously rifted and weakened crust. Moreover, the early rift history helps account for intraplate deformation of southernmost South America during the opening of the South Atlantic Ocean.
    Print ISSN: 1941-8264
    Electronic ISSN: 1947-4253
    Topics: Geosciences
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  • 6
    Publication Date: 2016-01-22
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 7
    Publication Date: 2016-03-01
    Description: Despite broad interest in determining the topographic and climatic histories of mountain ranges, the evolution of California’s Sierra Nevada remains actively debated. Prior stable isotope–based studies of the Sierra Nevada have relied primarily on hydrogen isotopes in kaolinite, hydrated volcanic glass, and leaf n -alkanes. Here, we reconstruct the temperature and elevation of the early Eocene Sierra Nevada using the oxygen isotope composition of kaolinitized granite clasts from the ancestral Yuba and American Rivers that drained the windward (Pacific) flank of the Sierra Nevada. First, we evaluated the possible contributions of hydrogen isotope exchange in kaolinite by direct comparison with oxygen isotope measurements. Next, we utilized differences in the hydrogen and oxygen isotope fractionation in kaolinite to constrain early Eocene midlatitude weathering temperatures. Oxygen isotope geochemistry of in situ kaolinites indicates upstream (eastward) depletion of 18 O in the northern Sierra Nevada. The 18 O values, ranging from 11.4 to 14.4 at the easternmost localities, correspond to paleoelevations as high as 2400 m when simulating the orographic precipitation of moisture from a Pacific source using Eocene boundary conditions. This result is consistent with prior hydrogen isotope studies of the northern Sierra, but oxygen isotope–based paleoelevation estimates are systematically ~500–1000 m higher than those from hydrogen-based estimates from the same samples. Kaolinite geothermometry from 16 samples produced early Eocene weathering temperatures of 13.0–36.7 °C, with an average of 23.2 ± 6.4 °C (1). These kaolinite temperature reconstructions are in general agreement with paleofloral and geochemical constraints from Eocene California localities and climate model simulations. Our results confirm prior hydrogen isotope–based paleoelevation estimates and further substantiate the existence of a hot and high Eocene Sierra Nevada.
    Print ISSN: 0016-7606
    Electronic ISSN: 1943-2674
    Topics: Geosciences
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  • 8
    Publication Date: 2015-03-24
    Description: The Late Cretaceous (late Campanian to Maastrichtian) was characterized by a variable greenhouse climate, with evidence for cooling and/or glaciation and warming events. Most of these climatic signals are derived from marine records, and knowledge of the terrestrial climate, especially in the mid-latitudes, is limited due to fragmentary geological records on continents. Here we report mid-latitude terrestrial stable oxygen and carbon isotope data from pedogenic carbonates in the nearly continuous Late Cretaceous age SK-1 core drilled in the Songliao Basin, northeastern China. Our data indicate a punctuated, mid-latitude terrestrial climate in the Late Cretaceous. We interpret the negative excursion of pedogenic carbonate 18 O in the early Maastrichtian to be the result of decreasing temperature and/or strengthened westerlies during global cooling and possible glaciation, providing valuable mid-latitude terrestrial evidence for this event. The negative 13 C isotopic excursion ca. 66 Ma is modeled as higher primary productivity caused by increasing temperature and precipitation in response to a warming climate in the latest Cretaceous. Our continuous stable isotopic records in the Songliao Basin are in accordance with previously published global Late Cretaceous records of climate variability from marine and terrestrial regions, and demonstrate the sensitivity of mid-latitude terrestrial climate in a greenhouse world.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 9
    Publication Date: 2015-03-31
    Description: This study describes the character of submarine mass movement and associated deformation as revealed by an exceptionally well-exposed portion of a seismic-scale mass-transport deposit (MTD) within the upper Miocene Mohakatino Formation (Taranaki Basin, New Zealand). The North Awakino MTD is at least 55 m thick and crops out along the northern Taranaki coastline for ~11 km in wave-cut platforms and in cliffs as much as 100 m high. Spectacular soft-sediment deformation features are developed in remobilized sediment gravity flow deposits that initially accumulated within a low-gradient intraslope basin. Sedimentary facies within the North Awakino MTD comprise laterally extensive, thick- to thin-bedded volcaniclastic sandstone and mudstone. Distinct postdepositional deformation styles are associated with bedding type: folds developed in thick-bedded sandstone are larger (fold heights to tens of meters) and more laterally continuous (to 1 km) than those developed in thinner bedded facies. Regional geologic relationships suggest that nearly the full width of the North Awakino MTD is exposed in outcrop, providing a rare opportunity to observe lateral relationships between the marginal and central portions of the MTD. We conducted a rigorous paleoslope analysis of slump fold, fault, and bedding orientations using both existing and newly proposed methodologies. Separate analysis of seven subregions within the North Awakino MTD reveals that the predicted MTD transport direction varies widely along the outcrop extent. Most notably, slump folds and faults within the inferred margins have mean orientations that are suborthogonal to those within the central portions of the MTD. This relationship is hypothesized to be a consequence of edge effects that may be related to lateral compression along the margins of the MTD. Our analysis demonstrates the importance of accounting for spatial heterogeneity in slump structure orientations when determining the paleoslope orientation through kinematic analysis. Our inference of west-directed translation suggests that the North Awakino MTD formed in response to a local change in the bathymetric slope orientation that was likely the result of tectonically induced basin deformation.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
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  • 10
    Publication Date: 2014-12-31
    Description: Upper Cretaceous–Eocene forearc strata deposited along the California continental margin record a complex history of plate convergence that shaped the tectonic development of the U.S. Cordillera. Synthesis of new and published detrital zircon U-Pb ages over a 2000 km length of the southern Oregon–California–northern Baja forearc clearly demonstrates spatial and temporal changes in sandstone provenance that reflect evolving sediment dispersal patterns associated with the extinction of continental margin arc magmatism and transfer of deformation to the continental interior during latest Cretaceous–early Cenozoic Laramide low-angle subduction. Measured age distributions from Cenomanian to Campanian forearc strata indicate the existence of a drainage divide formed by a high-standing mid-Cretaceous Cordilleran arc that crosscut older, Late Permian–Jurassic arc segments. Progressive influx of 125–85 Ma detrital zircon in the Great Valley forearc reflects ongoing denudation of the Sierra Nevada batholith throughout Late Cretaceous–early Paleogene time. In contrast, age distributions in the Peninsular Ranges forearc indicate early denudation of the Peninsular Ranges batholith that is hypothesized to have resulted from the initial collision of an oceanic plateau with the southern California margin; as a result, these age distributions exhibit little change over time until delivery of extraregional detritus to the margin in Eocene time. Maastrichtian through middle Eocene strata preserved south of the Sierra Nevada record a pronounced shift from local to extraregional provenance caused by the development of drainages that extended across the breached mid-Cretaceous continental margin batholith to tap the continental interior. This geomorphic breaching of the mid-Cretaceous arc, and associated inland drainage migration, represents the culminating influence of Laramide low-angle subduction on the continental margin and likely occurred following subduction of the Shatsky conjugate plateau beneath the western United States.
    Print ISSN: 0016-7606
    Electronic ISSN: 1943-2674
    Topics: Geosciences
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