Boulder, Colo., USA – Learn more about river morphology in Oregon; coastal responses to sea level; the Tertiary Sabzevar Range, Iran; carbon-dioxide sequestration; fault systems in the Blue Mountains of Jamaica; Villarrica Volcano, Chile; landslide modeling; the southern Bighorn Arch, Wyoming; high-diversity plant fossil assemblages of the Salamanca Formation, Argentina; Upper Cretaceous strata, Western Interior Seaway; stratigraphy in Italy; the Soreq drainage, Israel; faulting in Surprise Valley, California; and the Qiantang River estuary, eastern China.
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Geologic and physiographic controls on bed-material yield, transport, and channel morphology for alluvial and bedrock rivers, western Oregon
Jim E. O'Connor et al., U.S. Geological Survey, Oregon Water Science Center, 2130 SW 5th Ave., Portland, OR 97201, USA; oconnor@usgs.gov. Posted online ahead of print on 7 Jan. 2014; http://dx.doi.org/10.1130/B30831.1.
The rivers of western Oregon have diverse forms and characteristics with channel substrates ranging from continuous alluvial gravel to bare bedrock. These differences owe to variable supply of gravel to the channel, and to gravel comminution during fluvial transport. The primary factors controlling gravel supply are rock type and the slope of the contributing basins. The primary control of bed-material comminution, which can reduce gravel flux by 50%-90% along the length of the larger rivers in western Oregon, is rock type. At the scale of western Oregon, these controls exert far-reaching influence on the distribution of alluvial and non-alluvial channels and their consequently distinctive morphologies and behaviors --differences germane for understanding river response to tectonics and environmental perturbations, as well as for implementing effective restoration and monitoring strategies.
Coastal response to late-stage transgression and sea-level highstand
Christopher J. Hein et al., Department of Physical Sciences, Virginia Institute of Marine Science, College of William and Mary, Post Office Box 1346, 1375 Greate Road, Gloucester Point, Virginia 23062-1346, USA; hein@vims.edu. Posted online ahead of print on 7 Jan. 2014; http://dx.doi.org/10.1130/B30836.1.
The records of shoreline responses to past changes in sea level provide insights into how coasts will respond to future accelerated sea-level rise. In much of the Southern Hemisphere sea level was 1 to 4 m higher than present 5000 to 7000 years ago. Since that time it has fallen, stranding beaches and barriers several kilometers inland from the modern shoreline. This study looks at several coastal systems associated with the highstand in southern Brazil and compared these examples to published records of 5000- to 7000-year-old highstand deposits across the Brazilian coast. Christopher J. Hein and colleagues identified multiple types of highstand deposits, which range from bedrock cliffs, to marsh/lagoon deposits, to complete barrier islands. The type of deposit was controlled by wave exposure, rate of sediment supply, and the ability of coastal features to migrate landward as sea-level rose. The two most important findings from this work are (1) coastal features varied greatly even within small embayments; and (2) the rate of sea-level rise had to reduce to about 2 mm/yr before barriers could form and stabilize. These results imply that coastal barriers are highly sensitive to the rate of sea-level rise, but that responses to future sea-level rise will be highly variable along even along short stretches of coast.
Adakite differentiation and emplacement in a subduction channel: The late Paleocene Sabzevar magmatism (NE Iran)
Federico Rossetti et al., Dipartimento di Scienze, Università Roma Tre, Roma, Italy; rossetti@uniroma3.it. Posted online ahead of print on 7 Jan. 2014; http://dx.doi.org/10.1130/B30913.1.
Various Mesozoic-Tertiary ophiolitic suture zones surround the Central East Iranian Microcontinent. These ophiolitic domains are the remnants of oceanic marginal back-arc basins formed in the in the upper-plate of the Neotethyan subduction and they record a prolonged history of continental break-up, oceanic lithosphere production, and consumption. This paper describes the mode of emplacement, petrology and geochronology of a suite of arc granitoids intruded within the ophiolitic suture zone exposed along the Tertiary Sabzevar Range, NE Central Iran. Evidence is provided for Late Paleocene magma generation and emplacement at depth within the subduction channel during consumption of the Late Cretaceous Sabzevar ocean. The study provides an outstanding example of a Tertiary fossil subduction channel and processes associated with formation of plutonic rocks from partial melting of oceanic crust, magma differentiation and emplacement in convergent margins. Implications in terms of the regional tectonic scenario are discussed and framed within the history of the Neotethyan subduction during the Mesozoic-Tertiary time lapse.
Physical constraints on geologic CO2 sequestration in low-volume basalt formations
Ryan M. Pollyea et al., Department of Geology & Environmental Geosciences, Northern Illinois University, DeKalb, Illinois 60115, USA; rpollyea@niu.edu. Posted online ahead of print on 7 Jan. 2014; http://dx.doi.org/10.1130/B30874.1.
In 2012, global CO2 emissions from fossil fuel combustion increased 1.4% to 31.6 Gt (a 37 record high), and in May 2013, average daily atmospheric CO2 concentrations exceeded 400 ppm for the first time since such data have been recorded. In response to steadily increasing atmospheric CO2 concentrations, a number of strategies have been proposed for managing anthropogenic CO2, including disposal in deep underground reservoirs, i.e., geologic carbon sequestration. In basalt-hosted reservoirs, isolating CO2 from the atmosphere is based on geochemical reactions between water, CO2, and basalt rock, the result of which is permanent trapping in the form of solid phase mineral precipitates. In addition to the geochemistry, understanding the how the disposal reservoir responds to industrial-scale injection rates is an important criteria for feasibility assessment. In this paper, a non-reactive numerical modeling experiment of CO2 sequestration in a fractured basalt reservoir reveals several promising attributes, including (1) injection pressures below the hydraulic fracture gradient in 96% of the model scenarios, (2) low potential for shear failure under assumed stress conditions, and (3) favorable physical isolation in the first twenty years of injection, i.e. prior to widespread mineralization.
Protolith provenance and thermotectonic history of metamorphic rocks in eastern Jamaica: Evolution of a transform plate boundary
David P. West Jr. et al., Middlebury College, Geology, Middlebury, VT 05753, USA; dwest@middlebury.edu. Posted online 21 January 2014, http://dx.doi.org/10.1130/B30704.1.
The Blue Mountains of eastern Jamaica are located along the western extension a regional fault system that is notable for producing the devastating Haiti earthquake of 2010. Over millions of years this fault system has slowly uplifted the Blue Mountains to elevations over 7000 feet and through this process exposed older rocks which provide windows into the ancient geologic history of the northern Caribbean region. This paper presents new data from these older rocks and the findings not only include information on their origins, but also details on when they were uplifted along this regional fault system. Interestingly, sequences of rocks in the Blue Mountains that are currently in direct contact with one another preserve very different histories and have only been relatively recently juxtaposed through faulting. Reconstructions of the past histories of rocks exposed along major fault systems such as this can provide clues as to the future evolution of these active tectonic zones.
The 600 yr eruptive history of Villarrica Volcano (Chile) revealed by annually laminated lake sediments
M. Van Daele et al., Renard Centre of Marine Geology (RCMG), Department of Geology and Soil Science, Ghent University, Krijgslaan 281/S8, B-9000 Gent, Belgium; maarten.vandaele@ugent.be. Posted online 21 January 2014, http://dx.doi.org/10.1130/B30798.1
This study of the eruption history of Villarrica Volcano (Chile) statistically demonstrates that a volcanic quiescence of more than two decades, as currently occurring, has been exceptional during the last 600 years. Our research indicates that in this time period the Villarrica Volcano erupted 112 times, and at least 22 times the eruption also triggered destructive volcanic mud flows. Consequently the potential risk for a new eruption in the near future is high. This 600-year volcanic record significantly expands our knowledge on the eruptive frequency of this volcano, compared to what was previously known from historical records. A volcanic hazard assessment for this rapidly expanding tourist region will be greatly improved thanks to this new perspective on the recurrence interval of eruptions and volcanic mud flows. This study also highlights how lake records are a very useful tool to improve historical eruption records in areas that were previously uninhabited. In this research we retrieved a 600-year-long sedimentary record with an almost yearly resolution from two neighboring lakes at the foot Villarrica Volcano. Using a range of high-resolution analytical methods we detected three types of deposits triggered by often undocumented historical volcanic activity.
An experimental method for testing soil mobility of landslides
Jonathan P. McKenna et al., U.S. Geological Survey, Box 25046, MS-966, Denver, Colorado 80225, USA; jmckenna@microseismic.com. Posted online 21 January 2014, http://dx.doi.org/10.1130/B30870.1
Debris flows can travel great distances from their sources and pose hazards to communities downstream. Identification of soils susceptible to liquefaction during slope failure could aid in locating potential debris-flow sources. We used a modified version of the slump test, typically used to measure the consistency of wet concrete mix, to test the tendency of soil to flow. The large diameter test mold can accommodate gravelly soils and tests can be run at low normal stresses to accommodate loosely packed soils. Soils deform by gravitational failure so a prescribed strain rate is not required. This method can be used to identify a threshold density below which a soil will flow under field-saturated conditions.
Towards a better understanding of the influence of basement heterogeneities and lithospheric coupling on foreland deformation: A structural and paleomagnetic study of Laramide deformation in the southern Bighorn Arch, Wyoming
Arlo Brandon Weil et al., Department of Geology, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, USA; aweil@brynmawr.edu. Posted online 21 January 2014, http://dx.doi.org/10.1130/B30872.1.
An integrated geologic study of deformed sedimentary rocks along the flanks of the southern Bighorn Arch, Wyoming, was undertaken to test models of Laramide foreland (Rocky Mountain) tectonics. The Laramide foreland is characterized by a system of basement-cored ranges and associated folds that trend overall NW-SE (e.g. Wind River Arch), but in detail are curved, and range from N-S (southern Bighorn Arch) to E-W trending (Uinta Arch). Within the Bighorn Arch, small-scale faults and subtle grain fabrics record widespread, but limited early tectonic shortening, which was followed by large-scale fault slip and folding during arch growth. Structurally restored paleomagnetic directions record only limited, non-systematic vertical-axis rotations, indicating that the map-scale curvature of the Bighorn Arch observed today is a primary feature. Restored shortening directions are on average WSW-ENE along the southern Bighorn Arch, but display local deflections related to heterogeneities of underlying basement blocks and proximity to major crustal weaknesses. Regional shortening patterns across the Laramide foreland are interpreted to reflect deformation partitioning in response to far-field tectonic stress related to low-angle subduction along the ancient Cordilleran margin and to local interactions with preexisting basement weaknesses.
New age constraints for the Salamanca Formation and lower Río Chico Group in the western San Jorge Basin, Patagonia, Argentina: Implications for Cretaceous-Paleogene extinction recovery and land mammal age correlations
William C. Clyde et al., University of New Hampshire, Earth Sciences, 56 College Rd., James Hall, Durham, NH 03824, USA; will.clyde@unh.edu. Posted online 21 January 2014, http://dx.doi.org/10.1130/B30915.1.
The timing of biotic recovery after the Cretaceous/Paleogene (K/Pg) boundary mass extinction is poorly resolved in South America. This paper reports new geochronological data from two well-known geological units (Salamanca Formation and Río Chico Group) in Patagonia (Argentina) that preserve important early Paleogene floral and faunal fossil assemblages but are imprecisely dated. Our results suggest that the Salamanca Formation was deposited between ~65.7 and ~63.5 million years ago, just after the K/Pg boundary extinction, and Río Chico Group deposition began ~62.5 million years ago. These new age constraints indicate that high diversity plant fossil assemblages from the Salamanca Formation and important vertebrate assemblages from the Río Chico Group are older than previously thought supporting previous evidence for more rapid biotic recovery from the K/Pg boundary extinction in the southern hemisphere compared to the northern hemisphere.
Interregional correlation of disconformities in Upper Cretaceous strata, Western Interior Seaway: Biostratigraphic and sequence-stratigraphic evidence for eustatic change
Ireneusz Walaszczyk et al., Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada (corresponding author: G. Plint, gplint@uwo.ca). Posted online 24 Jan. 2014, http://dx.doi.org/10.1130/B30823.1.
Our study of Upper Cretaceous shallow marine rocks (about 89 million years old) in southern Alberta and northern Montana revealed a succession of evolving bivalve species that was the same as that seen in European strata. Study of equivalent Upper Cretaceous strata in southern Colorado revealed that one of the key species was absent. It was realized that this was due to a subtle erosional break, rather than the result of inhibition of the fauna from the region by ecological factors. Erosional surfaces due to sea-level rise and fall could be traced in borehole data for more than 300 km from Alberta to Montana; new bivalve faunas appeared following pulses of sea-level rise. Prompted by the results from Alberta, renewed study in southern Colorado showed that new bivalve faunas also appeared above subtle erosion surfaces. This observation suggested that simultaneous sea-level changes and faunal colonization events occurred at sites located more than 1000 km apart. Because sea-level changes occurred on a time-scale of less than one million years, they were most reasonably attributed to the waxing and waning of small Antarctic ice sheets, supporting the idea that the "greenhouse" world of the Cretaceous was not ice-free, as has traditionally been thought.
Facies architecture and depositional model of a macrotidal incised-valley succession (Qiantang River estuary, eastern China), and differences from other macrotidal systems
Xia Zhang et al., State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210046, Jiangsu, China, zhangxiananjing@163.com. Posted online 24 Jan. 2014, http://dx.doi.org/10.1130/B30835.1.
The present-day Qiantang River estuary is a word-famous macrotidal-dominated estuary. The maximum tidal range and tidal-current speed could reach up to 8.93 m and 5.16 m/s, respectively causing the formation of tidal bores, which extend landward roughly 90 km. The Qiantang River tidal bore is one of the world's three major tidal bores, with the other two being Amazon River and Ganges River tidal bores. The Qiantang River incised valley is buried beneath the present-day Qiantang River estuary with the maximum depth of 125 m. This incised valley underwent three evolutional stages since the last glaciation: formation stage (20,000-15,000 years before present [yr B.P.]), filling stage (15,000-7,500 yr B.P.), and burial stage (7,500 yr B.P. to present). A paleo-estuary, formed between 12,000-7,500 yr B.P., was well-preserved within the Qiantang River incised-valley filling. Compared with the present-day Qiantang River estuary, a series of tidal channel sand bodies are present within it, occurring as the main reservoirs for the late Quaternary shallow biogenic gas. Since 1991, seven shallow gas fields have been discovered in these sand bodies, with the predicted total gas amount of 2445 times 108 cubic meters.
Controls on denudation rates in tectonically stable Mediterranean carbonate terrain
Uri Ryb et al., The Fredy and Nadine Herrmann Institute of Earth Sciences, The Hebrew University, Jerusalem, Israel; uri.ryb@mail.huji.ac.il. Posted online 24 Jan. 2014, http://dx.doi.org/10.1130/B30886.1.
Erosion rates dependency in topography, climate, rock composition and soil cover was explored in the Soreq drainage, Israel. A region that is tectonically stable, has a typical Mediterranean climate, and is governed by limestone and dolomite rocks. Erosion rates were calculated over annual and 104 year timescales using measurements of groundwater geochemistry and bedrock and sediment chlorine-36 isotope content. In all timescales, erosion rates depend mostly on precipitation, which indicates that rock-dissolution processes are the most important erosive process in these settings .This is in contrast to landscapes controlled by silicate rocks such as granite, sandstone, and basalt. The results of the paper show that the intensity of erosion decreased significantly between the last glacial period and the present interglacial. This difference is attributed to increased precipitation in the Eastern Mediterranean region during the last glacial period.
Structural controls on geothermal circulation in Surprise Valley, California: A re-evaluation of the Lake City fault zone
Anne E. Egger et al., Central Washington University, Geological Sciences, 400 E. University Way, Ellensburg, WA 98926-7418, USA; eggera@cwu.edu. Posted online 24 Jan. 2014, http://dx.doi.org/10.1130/B30785.1.
The Lake City Fault Zone in northeastern California has appeared on published maps since 1981. This NW-trending structure has been considered as a possible source of earthquakes and as a controlling structure for circulation of hot water in the geothermal system across Surprise Valley. Given its potential importance, several methods were used to assess the nature of this fault zone. A complimentary suite of geophysical methods that highlight density and magnetic contrasts as well as subsurface resistivity failed to produce any evidence for a through-going structure in the vicinity of the mapped Lake City Fault Zone. These findings are supported by a lack of surface features like fault scarps that would indicate recent activity along this fault zone. The evidence suggests instead that both seismic activity and geothermal fluid circulation are controlled by N-trending faults and the interactions between them, and the Lake City Fault Zone should be removed from consideration as a hazard or fluid pathway.
Unraveling tectonic and climatic controls on synorogenic growth strata (Northern Apennines, Italy)
Kellen L. Gunderson et al., Chevron Energy Technology Company, 1500 Louisiana St., Houston, TX 77044, USA; kellen.gunderson@lehigh.edu. Posted online 24 Jan. 2014, http://dx.doi.org/10.1130/B30902.1.
Tectonic, climate, and sedimentological processes all leave an imprint on the stratigraphic rock record. It can be difficult to separate the individual effects of these processes when all that is available to interpret in the stratigraphic record is the end result of these process interactions. Consequently, stratigraphic interpretations are commonly non-unique and subject to the background and biases of the interpreter. A new study of a stratigraphic section in the Northern Apennines, Italy, successfully disentangles the effects of climate, tectonics, and sedimentological processes. This study uses a variety of geochronological techniques to date marine and terrestrial strata and uses these high-resolution ages to unravel the effects of climate and tectonics on the stratigraphy.
Detrital zircon lineages of late Neoproterozoic and Cambrian strata, NW Laurentia
Larry S. Lane and George E. Gehrels, Geological Survey of Canada, 3303 33 Street NW, Calgary, Alberta T2L 2A7, Canada; llane@nrcan.gc.ca. Posted online 24 Jan. 2014, http://dx.doi.org/10.1130/B30848.1.
From the abstract: The Phanerozoic tectonic evolution of the Arctic is a field of escalating scientific interest. Detrital zircon provenance studies provide vital contributions to clarify the region's tectonic evolution. Northwest Laurentia exposes a broad expanse of Proterozoic and Paleozoic sedimentary strata for which detrital zircon populations are poorly characterized. Moreover, the significance of sedimentary recycling is becoming better appreciated in light of detrital zircon studies. As more data become available, our understanding of the detrital zircon character of NW Laurentia improves, providing an increasingly reliable baseline at subcontinental resolution against which potentially allochthonous terranes, such as Arctic Alaska, can be assessed. Sandstones of late Neoproterozoic and Cambrian age from NW Canada yield detrital zircon signatures dominated by zircon grains recycled from Proterozoic sedimentary strata. Two Neoproterozoic sandstones from the northern Mackenzie Mountains yield zircon populations sourced from the Mackenzie Mountains Supergroup. Two Lower Cambrian sandstones sourced from the Yukon stable block and deposited in Richardson Trough have zircon populations nearly identical to those of the upper Wernecke Supergroup, locally exposed across the southern Yukon stable block, where they are unconformably overlain by Cambrian strata. Comparisons with similar studies from NW Canada permit generalizations of the patterns of zircon recycling. Four provenance lineages are described that characterize Laurentia-derived successions in NW Canada.
Journal
Geological Society of America Bulletin