All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1869.
[English]
Application of raman spectroscopy and high-precision geochemistry for study of stromatolites
Biogenic—Abiogenic Interactions in Natural and Anthropogenic Systems
Page 329--341
Institute of Geology, Karelian Research Centre, Russian Academy of Sciences, Petrozavodsk, Russian Federation
Publisher
Springer
2016
329--341Keywords:▾
carbonate sediment; environmental conditions; geochemistry; inductively coupled plasma method; microbialite; Proterozoic; Raman spectroscopy; stromatolite, Baltic Shield; East European Craton
1868.
[English]
P-And S-wave seismic imaging of overdeepened alpine valleys
Publisher
European Association of Geoscientists and Engineers, EAGE
2016
Leibniz Institute for Applied Geophysics (LIAG), Germany1867.
[English]
Microseismic network design in complex 3D velocity models
Volume 35
,
Page 2765-2769
In Sicking C., FergusonSicking J.,
Editor
Publisher
Society of Exploration Geophysicists
2016
NORSAR, Norway1866.
[English]
Integration of geophysical data for deep exploration in the kylylahti cu-mining area, eastern Finland
Page 26 – 30
Publisher
European Association of Geoscientists and Engineers, EAGE
2016
Keywords:▾
Cobalt alloys; Copper alloys; Copper mines; Core drilling; Deposits; Infill drilling; Potassium alloys; Reflection; Seismic waves; Seismology; Sulfur compounds; Zinc alloys; Conductivity anomalies; Density distributions; Exploration potential; High resolution reflection seismic; Inversion results; Seismic reflection data; Subsurface density; Subsurface structures; Mineral exploration
ISBN:
978-151082247-4
1865.
Wellbore and groundwater temperature distribution eastern Snake River Plain, Idaho: Implications for groundwater flow and geothermal potential
Journal of Volcanology and Geothermal Research,
320144-155
2016
ISSN: 03770273
Publisher: Elsevier B.V.
Keywords:▾
Aquifers; Boreholes; Geothermal energy; Geothermal heating; Groundwater; Groundwater flow; Heat transfer; Rivers; Temperature distribution; Thermal gradients, Advective transport; Geothermal potential; Ground water movement; Groundwater temperatures; Hydrothermally altered rocks; Isothermal temperature; Snake river plains; Thermal groundwater, Groundwater resources, aquifer; flow modeling; groundwater; heat flow; permeability; temperature profile; tracer, Idaho; Snake River Plain; United States, Calluna vulgaris
Abstract: ▾ A map of groundwater temperatures from the Eastern Snake River Plain (ESRP) regional aquifer can be used to identify and interpret important features of the aquifer, including aquifer flow direction, aquifer thickness, and potential geothermal anomalies. The ESRP is an area of high heat flow, yet most of this thermal energy fails to reach the surface, due to the heat being swept downgradient by the aquifer to the major spring complexes near Thousand Springs, ID, a distance of 300 km. Nine deep boreholes that fully penetrate the regional aquifer display three common features: (1) high thermal gradients beneath the aquifer, corresponding to high conductive heat flow in low-permeability hydrothermally-altered rocks; (2) isothermal temperature profiles within the aquifer, characteristic of an actively flowing groundwater; and (3) moderate thermal gradients in the vadose zone with values that indicate that over half of the geothermal heat flow is removed by advective transport in the regional aquifer system. This study utilized temperature data from 250 ESRP aquifer wells to evaluate regional aquifer flow direction, aquifer thickness, and potential geothermal anomalies. Because the thermal gradients are typically low in the aquifer, any measurement of groundwater temperature is a reasonable estimate of temperature throughout the aquifer thickness, allowing the construction of a regional aquifer temperature map for the ESRP. Mapped temperatures are used to identify cold thermal plumes associated with recharge from tributary valleys and adjacent uplands, and warm zones associated with geothermal input to the aquifer. Warm zones in the aquifer can have various causes, including local circulation of groundwater through the deep conductively dominated region, slow groundwater movement in low-permeability regions, or localized heat flow from deeper thermal features. © 2015 Elsevier B.V.
1864.
Using palynology to re-assess the Dead Sea laminated sediments - Indeed varves?
Quaternary Science Reviews,
14049-66
2016
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Deposition; Floods; Fungi; Grain size and shape; Multivariant analysis; Particle size analysis; Seawater; Sediments, Air borne; Aragonite; Dead sea; Flash flood; Laminated sediments; Reworked pollen, Carbonate minerals, aragonite; carbon balance; flash flood; fungus; Holocene; lacustrine deposit; lamination; palynology; reworking; runoff; spore; varve; watershed, Dead Sea
Abstract: ▾ Lacustrine laminated sediments are often varves representing annual rhythmic deposition. The Dead Sea high-stand laminated sections consist of mm-scale alternating detrital and authigenic aragonite laminae. Previous studies assumed these laminae were varves deposited seasonally. However, this assumption has never been robustly validated. Here we report an examination of the seasonal deposition of detrital-aragonite couplets from two well-known Late Holocene laminated sections at the Ze'elim fan-delta using palynology and grain-size distribution analyses. These analyses are complemented by the study of contemporary flash-flood samples and multivariate statistical analysis. Because transport affects the pollen preservation state, well-preserved (mostly) air-borne transported pollen was analysed separately from badly-preserved pollen and fungal spores, which are more indicative of water transport and reworking from soils. Our results indicate that (i) both detrital and aragonite laminae were deposited during the rainy season; (ii) aragonite laminae have significantly lower reworked and fungal spore concentrations than detrital and flash-flood samples; and (iii) detrital laminae are composed of recycling of local and distal sources, with coarser particles that were initially deposited in the Dead Sea watershed and later transported via run-off to the lake. This is in line with previous carbon balance studies that showed that aragonite precipitation occurs after the massive input of TCO2 associated with run-off episodes. Consequently, at least for the Holocene Ze'elim Formation, laminated sediments cannot be considered as varves. Older Quaternary laminated sequences should be re-evaluated. © 2016 The Authors.
1863.
Using distributions and stable isotopes of n-alkanes to disentangle organic matter contributions to sediments of Laguna Potrok Aike, Argentina
Organic Geochemistry,
102110 – 119
2016
Keywords:▾
Argentina; Laguna Potrok Aike; Patagonia; Santa Cruz [Argentina]; Biogeochemistry; Biological materials; Chains; Dust; Isotopes; Lakes; Sediments; Chain length distribution; Environmental reconstruction; ICDP; Isotopic composition; Long chain n-alkanes; n-Alkanes; PASADO; Relative contribution; alkane; biomarker; carbon isotope; hydrogen isotope; isotopic composition; lacustrine deposit; macrophyte; organic matter; paleoenvironment; reconstruction; sediment chemistry; spatial distribution; stable isotope; submerged vegetation; Paraffins
Abstract: ▾ When using biomarkers such as n-alkanes as tools for paleo-environmental reconstructions, it is imperative to determine their specific sources for each setting. Toward that goal, we analyzed a set of various potential organic matter (OM) sources such as aquatic and terrestrial plants, dust, and soils from Laguna Potrok Aike (LPA) and surrounding areas in southern Patagonia. We determined chain length distributions and hydrogen (δD) and carbon (δ13C) isotopic compositions of n-alkanes of different OM sources in order to quantify their relative contributions to lake sediments. Our results reveal that the mid-chain n-alkane, n-C23, is predominantly produced by submerged aquatic plants, whereas long-chain n-alkanes (n-C29–n-C31) are derived from various terrestrial sources. We estimated their relative contributions to the sediment using two approaches, i.e., based on the n-alkane distributions and their δD and δ13C values. Both approaches result in similar estimates of aquatic and terrestrial contributions for mid- and long-chain n-alkanes to the sediment. 62–73% of the mid-chain n-C23 alkanes originate from aquatic sources while 66–77% of the long-chain n-alkanes originate from dust and 14–30% from terrestrial plants. Our study shows that mid-chain n-alkanes such as the n-C23 alkane in LPA are derived mainly from aquatic macrophytes and thus have the potential to record changes in lake-water isotopic composition. In contrast, the n-C29 alkane reflects the isotopic signal of various terrestrial sources from southern Patagonia. © 2016 Elsevier Ltd
1862.
Unusual, basin-scale, fluid–rock interaction in the Palaeoproterozoic Onega basin from Fennoscandia: Preservation in calcite δ18O of an ancient high geothermal gradient
Precambrian Research,
281224 – 235
2016
ISSN: 03019268
Publisher: Elsevier B.V.
Keywords:▾
calcite; carbonate; diagenesis; geothermal gradient; oxygen isotope; Proterozoic; water-rock interaction, Arkhangelsk [Russian Federation]; Fennoscandia; Onega Basin; Russian Federation
Abstract: ▾ A variety of carbonates of different geneses, as indicated by petrography and geochemistry, are found throughout 400 m of the volcano-sedimentary rocks of the Zaonega Formation of Palaeoproterozoic age in the Onega basin of Fennoscandia. Following intensive sampling and analysis of varied calcites from drillcore recovered during the ICDP FAR-DEEP program, we report a highly unusual depth distribution of calcite oxygen isotope values (δ18Ocal). Unprecedentedly for such rocks, the δ18Ocal values over the full depth interval of 400 m are strongly linearly correlated with depth (r2 = 0.9015, n = 178). We propose that this is the result of major oxygen isotope resetting through water–rock interaction with a fluid of relatively constant oxygen isotopic composition (δ18Ow). In this model, the observed linear δ18Ocal-depth relationship is then a consequence of the increase in temperature with depth because of the background geothermal gradient. Minor deviations from the overall linear trend are likely due to bed-scale geological factors including locally high impermeability, and oxygen isotope modification of δ18Ow by comparatively intense water–rock interaction. Were the observed δ18Ocal values to have been reset during the greenschist facies Svecofennian metamorphism which affected the rocks at c. 1800 Ma, the implied geothermal gradient of ∼560 °C km−1 is geologically unreasonable and, accordingly, this hypothesis is ruled out. Rather, the δ18Ocal variation of 5‰ over 400 m implies a near-surface depth for the rocks during fluid interaction, and this is consistent with a surface-derived origin of the infiltrating fluid (δ18Ow ∼−13.6‰ for a surface temperature of 15 °C and geothermal gradient of ∼52 °C km−1). It is speculated that the fluid accessed the carbonates from the basin edge by bed-parallel rather than cross-formational flow. There is an intriguing distribution of Na in the sedimentary rocks of the Zaonega Formation. Sodium is relatively abundant in rocks below a certain depth (the lowermost dolostone at ∼258 m), but rare in shallower sequences. It is argued that this distribution did not originate with the basin-scale fluid–rock interaction documented above, but may rather be the result of evaporite dissolution, and subsequent redistribution of soluble elements during fluid flow associated with the syndepositional emplacement of basin-wide igneous rocks. © 2016 Elsevier B.V.
1861.
Two new fossil Cyclotella (Kützing) BrébBisson species from Lake Ohrid, Macedonia/Albania
Fottea,
16
(2)
218 – 233
2016
ISSN: 18025439
Publisher: Czech phycological Society
Abstract: ▾ Lake Ohrid is the oldest existing lake in Europe and it is known for its high diversity with around 200 endemic or relict diatom species recognized. In order to understand this phenomenon, a large project on deep drilling was performed and a core with maximum sediment depth of 569 m which spans > 1.2 million years was recovered. Two new species of Cyclotella were discovered in the core samples, which are described here as Cyclotella cavitata sp. nov. and Cyclotella sollevata sp. nov. The species have been studied with light and scanning electron microscopes, their morphological features and their relevance to other members of the genus Cyclotella are discussed. Cyclotella cavitata sp. nov. is characterized by round to elliptical shape; elliptic and tangentially undulate central area with one to three papillae on the elevated side. Central fultoportulae are absent while marginal fultoportulae internally are located on slightly depressed costae, with short tube openings with two satellite pores surrounded by cowlings. Satellite pores are situated circumferentially. Internally the rimoportula is situated in the marginal area with a sessile labium. Cyclotella sollevata sp. nov. is characterized by round valves with convex or concave central area which is uneven, colliculate, with papillae and granules. Central fultoportulae are present with variable number (9-21), internally with short tube openings with two satellite pores, which are surrounded by cowlings; Internally marginal fultoportulae are located on depressed costae and have short tube openings with two satellite pores situated circumferentially, surrounded by cowlings. The rimoportulae are located in the marginal area with a sessile labium variably orientated. Cyclotella sollevata and Cyclotella cavitata have been observed only in the fossil sediments of Lake Ohrid. Comments on the position of rimoportula, used as synapomorphic character to separate Lindavia from Cyclotella sensu lato are provided. © Czech Phycological Society (2016).
1860.
Treeline dynamics in Siberia under changing climates as inferred from an individual-based model for Larix
Ecological Modelling,
338101-121
2016
ISSN: 03043800
Publisher: Elsevier B.V.
Keywords:▾
Climate models; Dynamics; Ecology; Global warming; Sensitivity analysis, Forest change; Individual based model; Larix gmelinii; Local sensitivity analysis; Model description; Sensitivity values; Spatially explicit modeling; Time-lag effect, Forestry, boreal forest; climate change; climate effect; coniferous forest; ecological modeling; ecotone; experimental study; forest ecosystem; global warming; literature review; permafrost; sensitivity analysis; treeline; twenty first century, Krasnoyarsk [Russian Federation]; Russian Federation; Siberia; Taymyr Peninsula, Larix; Larix gmelinii
Abstract: ▾ Siberian boreal forests are expected to expand northwards in the course of global warming. However, processes of the treeline ecotone transition, as well astiming and related climate feedbacks are still not understood. Here, we present ‘Larix Vegetation Simulator’ LAVESI, an individual-based spatially-explicit model that can simulate Larix gmelinii (Rupr.) Rupr. stand dynamics in an attempt to improve our understanding about past and future treeline movements under changing climates. The relevant processes (growth, seed production and dispersal, establishment and mortality) are incorporated and adjusted to observation data mainly gained from the literature. Results of a local sensitivity analysis support the robustness of the model's parameterization by giving relatively small sensitivity values. We tested the model by simulating tree stands under modern climate across the whole Taymyr Peninsula, north-central Siberia (c. 64–80° N; 92–119° E). We find tree densities similar to observed forests in the northern to mid-treeline areas, but densities are overestimated in the southern parts of the simulated region. Finally, from a temperature-forcing experiment, we detect that the responses of tree stands lag the hypothetical warming by several decades, until the end of 21st century. With our simulation experiments we demonstrate that the newly-developed model captures the dynamics of the Siberian latitudinal treeline. © 2016
1859.
The Sr-isotopic stratigraphy of the northern limb of the Bushveld Complex, South Africa
Journal of African Earth Sciences,
11395--100
2016
1858.
Spatio-temporal trends in normal-fault segmentation recorded by low-temperature thermochronology: Livingstone fault scarp, Malawi Rift, East African Rift System
Earth and Planetary Science Letters,
45562-72
2016
ISSN: 0012821X
Publisher: Elsevier B.V.
Keywords:▾
Apatite; Cooling systems; Fission reactions; Geologic models; Phosphate minerals; Tectonics; Temperature, Apatite fission tracks; Climatic fluctuations; Displacement profiles; East African Rift; Normal faults; Spatial and temporal variation; Thermochronology; Vertical distributions, Fault slips, fault scarp; fault zone; footwall; hanging wall; normal fault; segmentation; spatiotemporal analysis; thermochronology, East African Rift
Abstract: ▾ The evolution of through-going normal-fault arrays from initial nucleation to growth and subsequent interaction and mechanical linkage is well documented in many extensional provinces. Over time, these processes lead to predictable spatial and temporal variations in the amount and rate of displacement accumulated along strike of individual fault segments, which should be manifested in the patterns of footwall exhumation. Here, we investigate the along-strike and vertical distribution of low-temperature apatite (U–Th)/He (AHe) cooling ages along the bounding fault system, the Livingstone fault, of the Karonga Basin of the northern Malawi Rift. The fault evolution and linkage from rift initiation to the present day has been previously constrained through investigations of the hanging wall basin fill. The new cooling ages from the footwall of the Livingstone fault can be related to the adjacent depocentre evolution and across a relay zone between two palaeo-fault segments. Our data are complimented by published apatite fission-track (AFT) data and reveal significant variation in rock cooling history along-strike: the centre of the footwall yields younger cooling ages than the former tips of earlier fault segments that are now linked. This suggests that low-temperature thermochronology can detect fault interactions along strike. That these former segment boundaries are preserved within exhumed footwall rocks is a function of the relatively recent linkage of the system. Our study highlights that changes in AHe (and potentially AFT) ages associated with the along-strike displacement profile can occur over relatively short horizontal distances (of a few kilometres). This is fundamentally important in the assessment of the vertical cooling history of footwalls in extensional systems: temporal differences in the rate of tectonically driven exhumation at a given location along fault strike may be of greater importance in controlling changes in rates of vertical exhumation than commonly invoked climatic fluctuations. © 2016 Elsevier B.V.
1857.
The Lawn Hill annulus: An Ordovician meteorite impact into water-saturated dolomite
Meteoritics and Planetary Science,
51
(12)
2416-2440
2016
Abstract: ▾ The Lawn Hill Impact Structure (LHIS) is located 250 km N of Mt Isa in NW Queensland, Australia, and is marked by a highly deformed dolomite annulus with an outer diameter of ~18 km, overlying low metamorphic grade siltstone, sandstone, and shale, along the NE margin of the Georgina Basin. This study provides detailed field observations from sections of the Lawn Hill annulus and adjacent areas that demonstrate a clear link between the deformation of the dolomite and the Lawn Hill impact. 40Ar-39Ar dating of impact-related melt particles provides a time of impact in the Ordovician (472 ± 8 Ma) when the Georgina Basin was an active depocenter. The timing and stratigraphic thickness of the dolomite sequence in the annulus suggest that there was possibly up to 300 m of additional sedimentary rocks on top of the currently exposed Thorntonia Limestone at the time of impact. The exposed annulus is remarkably well preserved, with preservation attributed to postimpact sedimentation. The LHIS has an atypical crater morphology with no central uplift. The heterogeneous target materials at Lawn Hill were probably low-strength, porous, and water-saturated, with all three properties affecting the crater morphology. The water-saturated nature of the carbonate unit at the time of impact is thought to have influenced the highly brecciated nature of the annulus, and restricted melt production. The impact timing raises the possibility that the Lawn Hill structure may be a member of a group of impacts resulting from an asteroid breakup that occurred in the mid-Ordovician (470 ± 6 Ma). © The Meteoritical Society, 2016.
1856.
The Hominin Sites and Paleolakes Drilling Project: Inferring the environmental context of human evolution from eastern African rift lake deposits
Scientific Drilling,
211 – 16
2016
ISSN: 18168957
Publisher: Copernicus GmbH
Keywords:▾
Core drilling; Deposits; Drills; Environmental protection; Lakes; Sediments; Archaeological site; Drilling projects; Environmental contexts; Environmental history; Evolutionary history; Human evolution; Lake deposits; Paleoclimatic record; Deepwater drilling
Abstract: ▾ The role that climate and environmental history may have played in influencing human evolution has been the focus of considerable interest and controversy among paleoanthropologists for decades. Prior attempts to understand the environmental history side of this equation have centered around the study of outcrop sediments and fossils adjacent to where fossil hominins (ancestors or close relatives of modern humans) are found, or from the study of deep sea drill cores. However, outcrop sediments are often highly weathered and thus are unsuitable for some types of paleoclimatic records, and deep sea core records come from long distances away from the actual fossil and stone tool remains. The Hominin Sites and Paleolakes Drilling Project (HSPDP) was developed to address these issues. The project has focused its efforts on the eastern African Rift Valley, where much of the evidence for early hominins has been recovered.We have collected about 2 km of sediment drill core from six basins in Kenya and Ethiopia, in lake deposits immediately adjacent to important fossil hominin and archaeological sites. Collectively these cores cover in time many of the key transitions and critical intervals in human evolutionary history over the last 4 Ma, such as the earliest stone tools, the origin of our own genus Homo, and the earliest anatomically modern Homo sapiens. Here we document the initial field, physical property, and core description results of the 2012-2014 HSPDP coring campaign. © Author(s) 2016.
1855.
The fluid budget of a continental plate boundary fault: Quantification from the Alpine Fault, New Zealand
Earth and Planetary Science Letters,
445125-135
2016
ISSN: 0012821X
Publisher: Elsevier B.V.
Keywords:▾
Budget control; Carbon dioxide; Earthquakes; Faulting; Flow of fluids; Geochemistry; Geochronology; Geophysics; Helium; Hot springs; Isotopes; Metamorphic rocks; Rocks, Alpine Faults; Fault seal; Fluid fluxes; Helium isotopes; Mantle CO2; Meteoric waters, Transport properties, carbon dioxide; earthquake magnitude; earthquake rupture; fault zone; helium isotope; mantle source; meteoric water; Pacific plate; permeability; plate boundary, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ Fluids play a key role in modifying the chemical and physical properties of fault zones, which may prime them for repeated rupture by the generation of high pore fluid pressures and precipitation of commonly weak, secondary minerals. Fluid flow paths, sources and fluxes, and the permeability evolution of fault zones throughout their seismic cycles remain poorly constrained, despite their importance to understanding fault zone behaviour. Here we use geochemical tracers of fluid-rock exchange to determine budgets for meteoric, metamorphic and mantle fluids on a major compressional tectonic plate boundary.The Alpine Fault marks the transpressional Pacific-Australian plate boundary through South Island, New Zealand and appears to fail in regular (329±68 yrs) large earthquakes (Mw~8) with the most recent event in 1717 AD. Significant convergent motion has formed the Southern Alps and elevated geothermal gradients in the hangingwall, which drive crustal fluid flow. Along the Alpine Fault the Alpine Schist of the Pacific Plate is thrust over radiogenic metasedimentary rocks on the Australian plate. The absence of highly radiogenic (87Sr/86Sr > 0.7200) strontium isotope ratios of hangingwall hot springs and hydrothermal minerals formed at a range of depths in the Alpine Fault damage zone indicates that the fluid flow is restricted to the hangingwall by a cross-fault fluid flow barrier throughout the seismogenic crust. Helium isotope ratios measured in hot springs near to the Alpine Fault (0.15-0.81 RA) indicate the fault is a crustal-scale feature that acts as a conduit for fluids from the mantle. Rock-exchanged oxygen, but meteoric water-like hydrogen isotope signatures of hydrothermal veins indicate that partially rock-exchanged meteoric fluids dominate down to the top of the brittle to ductile transition zone at ∼6 km. Geochemical tracer transport modelling suggests only ∼0.02 to 0.05% of total rainfall west of the Main Divide penetrates to depth, yet this recharge flux is sufficient to overwhelm other fluid contributions. Calculated mantle fluid fluxes of CO2 and H2O (0.2 and 3 to 13 mol/m2/yr respectively) and metamorphic H2O fluxes (4 to 750 mol/m2/yr) are considerably lower than the focused meteoric water discharge flux up the Alpine Fault (4 × 103 to 7 × 104 mol/m2/yr), driven by the >3000 m hydrologic head of the Southern Alps. Meteoric waters are primarily responsible for modifying fault zone permeability during fluid-rock interactions and may facilitate the generation of high pore fluid pressures that could assist episodic earthquake rupture. © 2016 The Authors.
1854.
The coupled 182W-142Nd record of early terrestrial mantle differentiation
Geochemistry, Geophysics, Geosystems,
17
(6)
2168 – 2193
2016
1853.
The Campi Flegrei Deep Drilling Project (CFDDP): New insight on caldera structure, evolution and hazard implications for the Naples area (Southern Italy)
Geochemistry, Geophysics, Geosystems,
17
(12)
4836 – 4847
2016
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Campania [Italy]; Campi Flegrei; Italy; Naples; Napoli [Campania]; Deposits; Geochronology; Hazards; Stratigraphy; Tectonics; Volcanic rocks; Caldera-forming eruption; Campanian Ignimbrite; Campi Flegrei; Collapse mechanism; Neapolitan yellow tuffs; Scientific drilling; Tectonic structure; Volcanic hazards; argon-argon dating; caldera; deep drilling; geochronology; reconstruction; tectonic evolution; volcanic eruption; Volcanoes
Abstract: ▾ The 501 m deep hole of the Campi Flegrei Deep Drilling Project, located west of the Naples metropolitan area and inside the Campi Flegrei caldera, gives new insight to reconstruct the volcano-tectonic evolution of this highly populated volcano. It is one of the highest risk volcanic areas in the world, but its tectonic structure, eruptive history, and size of the largest eruptions are intensely debated in the literature. New stratigraphic and 40Ar/39Ar geochronological dating allow us to determine, for the first time, the age of intracaldera deposits belonging to the two highest magnitude caldera-forming eruptions (i.e., Campanian Ignimbrite, CI, 39 ka, and Neapolitan Yellow Tuff, NYT, 14.9 ka) and to estimate the amount of collapse. Tuffs from 439 m of depth yield the first 40Ar/39Ar age of ca. 39 ka within the caldera, consistent with the CI. Volcanic rocks from the NYT were, moreover, detected between 250 and 160 m. Our findings highlight: (i) a reduction of the area affected by caldera collapse, which appears to not include the city of Naples; (ii) a small volume of the infilling caldera deposits, particularly for the CI, and (iii) the need for reassessment of the collapse amounts and mechanisms related to larger eruptions. Our results also imply a revaluation of volcanic risk for the eastern caldera area, including the city of Naples. The results of this study point out that large calderas are characterized by complex collapse mechanisms and dynamics, whose understanding needs more robust constraints, which can be obtained from scientific drilling. © 2016. The Authors.
1852.
The Campi Flegrei caldera (Italy): Formation and evolution in interplay with sea-level variations since the Campanian Ignimbrite eruption at 39 ka
Journal of Volcanology and Geothermal Research,
327361 – 374
2016
ISSN: 03770273
Publisher: Elsevier B.V.
Keywords:▾
Campania [Italy]; Campi Flegrei; Italy; Napoli [Campania]; Basidiomycota; Buildings; Seismic response; Seismic waves; Seismology; Stratigraphy; Subsidence; Volcanoes; Caldera formation; Caldera resurgence; Campi Flegrei; Fault system; Nested calderas; Reflection seismics; caldera; Campanian; collapse; formation mechanism; ignimbrite; landform evolution; sea level change; seismic reflection; volcanic eruption; Sea level
Abstract: ▾ To date, the origin of the Campi Flegrei caldera is still under debate and may be related to (1) a single caldera collapse associated with the Neapolitan Yellow Tuff (NYT) eruption, (2) two subsequent caldera collapses associated with the NYT and the preceding Campanian Ignimbrite (CI) eruptions forming a nested-caldera complex, or (3) not related to a caldera collapse after all. Here, we study the submerged portion of the caldera, which has favored a marine depositional setting and, thus, represents an ideal location for the reconstruction of its formation history, utilizing multichannel seismic data. Volcanic deposits and edifices were seismically distinguished from sedimentary successions, and the stratigraphy could be refined and extended back to the Campanian Ignimbrite eruption at ~ 39 ka. High-resolution multichannel reflection seismic data revealed the existence of a nested-caldera complex formed during the CI eruption at ~ 39 ka and the more recent NYT eruption at ~ 15 ka. A ring-fault bounding an inner caldera collapse structure was clearly imaged. It appears that this inner ring-fault was initially activated during the CI caldera collapse and later reactivated during the NYT caldera collapse with different amounts of subsidence. The NYT caldera probably formed during an asymmetrical collapse with a maximum subsidence of ~ 75 m in the offshore portion. The vertical displacement related to the CI caldera collapse may be significantly larger. The submerged caldera depression accommodates post-eruption sediments. Within this high-resolution archive, two major unconformities developed at ~ 8.6 ka and 5 ka, when resurgence-related uplift exceeded the rate of sea-level rise concurrent with the emersion of the La Starza terrace. A previously unknown post-collapse submarine volcanic mound located between Nisida Island and Nisida Bank probably formed between 4.8 and 3.7 ka. Also, the Penta Palummo Bank appears to be constructed of at least two monogenetic volcanic edifices, the Penta Palummo volcano formed at ~ 100 ka and a younger mushroom-shaped unit formed between 39 and 15 ka. The main outcome of this study is a conceptual evolutionary model, providing novel insights on the formation of the Campi Flegrei nested caldera in the course of two large-scale eruptions (CI and NYT) with associated caldera collapses along mutual (i.e. reactivated) faults and subsequent caldera resurgence. As both the genesis and subsurface architecture of the Campi Flegrei caldera are still hotly debated topics in literature, our discoveries can be regarded as a substantial advancement in the understanding of the Campi Flegrei volcanic area. © 2016 Elsevier B.V.
1851.
Tenoumer impact crater, Mauritania: Impact melt genesis from a lithologically diverse target
Meteoritics and Planetary Science,
51
(2)
323-350
2016
Abstract: ▾ Impact melt rocks from the 1.9 km diameter, simple bowl-shaped Tenoumer impact crater in Mauritania have been analyzed chemically and petrologically. They are heterogeneous and can be subdivided into three types based on melt matrix color, occurrence of lithic clast components, amount of vesiculation (melt degassing), different proportions of carbonate melt mingled into silicate melt, and bulk rock chemical composition. These heterogeneities have two main causes (1) due to the small size of the impact crater, there was probably no coherent melt pool where a homogeneous mixture of melts, derived from different target lithologies, could be created; and (2) melt rock heterogeneity occurring at the thin section scale is due to fast cooling during and after the dynamic ejection and emplacement process. The overall period of crystal growth from these diverse melts was extremely short, which provides a further indication that complete chemical equilibration of the phases could not be achieved in such short time. Melt mixing processes involved in the generation of impact melts are, thus, recorded in nonequilibrium growth features. Variable mixing processes between chemically different melt phases and the formation of hybrid melts can be observed even at millimeter scales. Due to extreme cooling rates, different mixing and mingling stages are preserved in the varied parageneses of matrix minerals and in the mineral chemistry of microlites. 40Ar39Ar step-heating chronology on specimens from three melt rock samples yielded five concordant inverse isochron ages. The inverse isochron plots show that minute amounts of inherited 40Ar* are present in the system. We calculated a weighted mean age of 1.57 ± 0.14 Ma for these new results. This preferred age represents a refinement from the previous range of 21 ka to 2.5 Ma ages based on K/Ar and fission track dating. © 2016 The Meteoritical Society.
1850.
Tectonics and cycle system of the Cretaceous Songliao Basin: An inverted active continental margin basin
Earth-Science Reviews,
15982-102
2016
ISSN: 00128252
Publisher: Elsevier B.V.
Keywords:▾
collision zone; continental margin; detachment fault; Moho; Pacific plate; rift zone; subduction; tectonic evolution; tectonic setting; three-dimensional modeling; transition zone, China; Songliao Basin
Abstract: ▾ Recent ICDP drilling and deep basin volcanic exploration of 3000 m below the surface in the Songliao Basin (SB) have highlighted the 3-D delineation of the basin. The integrated new data led us to reevaluate the basin tectonics, for which the basin type, basin evolution and a number of geodynamic aspects have been controversial topics. We outline the position of a main lithospheric scale detachment fault beneath the SB, based on apparent crustal scale displacements, Moho breaks, the thinning of the Moho transition zone beneath the SB and the changing mantle thickness. This fault interpretation is consistent with simple shear as the rift mechanism. Based on a comprehensive analysis of the tectonic setting, underlying crust, structural style, sequence stratigraphy, subsidence history and volcanism, we propose an active continental margin model for the SB which shows some similarities to aulacogens but also notable differences. Situated between two Late Mesozoic active continental margins, the northern/northwestern Mongol-Okhotsk and the eastern Sikhote-Alin orogenic belts, the Cretaceous basin evolved on a pre-Triassic structurally weak basement mosaic. Its development began with regional mega-rifting from 150 to 105 Ma, followed by significant sagging between 105 and 79.1 Ma and ended with regional uplift and basin inversion from 79.1 to 64 Ma. Three regional angular unconformities separate the basin fill into three respective tectono-stratigraphic sequences. (1) The syn-rift stage is characterized by widespread fault-bounded grabens and volcanogenic successions, corresponding upward to the Huoshiling, Shahezi and Yingcheng Formations. (2) The post-rift stage includes the Denglouku, Quantou, Qignshankou, Yaojia and Nenjiang Formations. It is a special feature that the subsidence rate is abnormally high (mean of 103 m/Ma), and that flood basalt erupted along an axial wrench fault zone, associated with several marine intervals from the mid-Turonian to early Campanian (K2qn to K2n), possibly (not certainly) indicating incipient sea floor spreading characterized by Moho breaks along the basin axis in the SB around 88 Ma. Stretching stopped abruptly at approximately 79.1 Ma and was followed by uplift and rapid erosion (-145 m/Ma). (3) Recorded by the Sifangtai and Mingshui Formations the structural inversion stage included a continuous depocenter migration to the northwest. The basin was shrinking to demise as a result of changing subduction parameters of the Pacific subduction zone. In addition to the three tectonic basin cycles, a cyclic basin fill pattern exists with three volcanic basin fill intervals of Huoshiling, Yingcheng, and upper Qingshankou Formations that alternate with sedimentary basin fill intervals of Shahezi, Dengloukou-Quantou, and Yaojia-Nenjiang Formations.When determining the subsidence rates, we observed not only anomalously fast subsidence but also found an intricate link between the subsidence rate and type of basin fill. After each volcanic interval, the subsidence rates increased in a cyclic fashion during the sedimentary intervals. Thus, there is a system of three different types of important, basin-wide geological cycles that controlled the evolution of the SB. The subsidence rate was especially high (up to 199 m/Ma) after the last volcanic episode at 88 Ma. In addition to thermal subsidence and loading by the basin fill as causative processes, we also consider magmatic processes related to asthenospheric upwelling beneath the SB. They involve the roof collapse of shallow, depleted magma chambers, the igneous accretion of initially hot, dense, basic rocks, and lithospheric delamination beneath the SB. The difference in the subsidence rates during the volcanic and sedimentary intervals may in part also have been due to heating-related uplift during the volcanic intervals. The particularly high subsidence during the Late Cretaceous sedimentary cycles was partly increased by transtension. We put forward a general model for active continental margin basins. They are generally similar to aulacogens but display the following differences. In active continental margin basins, rifting depends on the subduction parameters that may cause strong to mild extension in the giant marginal region. The geochemical composition of the volcanic rocks is more calc-alkaline in nature because they are suprasubduction-related. These basins will eventually enter a post-rift sag stage that involves thermal subsidence. However, the basin will still be near an active continental margin, and, thus, some dip- and/or strike-slip faulting may occur coevally, depending on the subduction parameters. Sag cycles in active continental margin basins will likely include volcanism. Basin inversion will after all affect active continental margin basins. Such basins strike parallel to the respective continental margin. Thus, basin inversion by subduction/collision may be more intense than in the case of aulacogens, which do not tend to strike parallel to the continental margin. Basin inversion may also precede a collision due to changing subduction parameters. Subsidence behavior may also differ because many aspects of subsidence may be at work. Subsidence curves in active continental margin basins may be fairly individual. The application of our model only requires settings with the presence of one Pacific margin type. © 2016 The Authors.
1849.
Sulphur tales from the early Archean world
International Journal of Astrobiology,
15
(3)
177 – 185
2016
ISSN: 14735504
Publisher: Cambridge University Press
Keywords:▾
Archean; magma; pyrite; sedimentary rock; stable isotope; sulfate; sulfur cycle; sulfur isotope
Abstract: ▾ Sedimentary and magmatic rocks and their distinct sulphur isotopic signatures indicate the sources and processes of sulphur cycling, in particular through the analysis of all four stable sulphur isotopes (32S, 33S, 34S and 36S). Research over the past 15 years has substantially advanced our understanding of sulphur cycling on the early Earth, most notably through the discovery of mass-independently fractionated sulphur isotopic signatures. A strong atmospheric influence on the early Archean global sulphur cycle is apparent, much in contrast to the modern world. Diverse microbially driven sulphur cycling is clearly discernible, but its importance for Earth surface environments remains to be quantified. © 2016 Cambridge University Press.
1848.
Structural modeling of the casings in the IDDP-1 well: Load history analysis
Geothermics,
621-11
2016
ISSN: 03756505
Publisher: Elsevier Ltd
Keywords:▾
Geothermal fields; Geothermal wells; Shoe manufacture; Structural analysis; Thermal cycling, High temperature; IDDP; Krafla geothermal field; Non-linear finite element model; Production casings; Steel casing; Structural modeling; Thermal contraction, Finite element method, finite element method; geothermal energy; geothermal power; numerical model; structural analysis, Iceland
Abstract: ▾ Flow testing of IDDP-1, the first Icelandic Deep Drilling Project (IDDP) well drilled in the Krafla geothermal field in Iceland, demonstrated promising results by producing superheated steam. During an unavoidable quenching of the well the innermost casing failed presumably due to tensile stresses caused by thermal contraction. Since the structural integrity of casings is essential for utilization of high temperature geothermal wells, the well has not been discharged again. In this paper, the casings of the well are analyzed structurally with a nonlinear finite-element model. The load history of the casings is followed from installation and through several thermal cycles, but the well was discharged at least six times before it was quenched with cold water. The results show that changes in stiffness due to the presence of casing shoes and changes in casing thickness have an effect on the stress and strain formations in neighboring casings. The results illustrate that during each thermal cycle, the wellbore thermal load is more severe for the production casing than for the external casings that are somewhat protected, provided that cementing in between is adequate. © 2016 Elsevier Ltd.
1847.
Strontium and neodymium isotope systematics of target rocks and impactites from the El'gygytgyn impact structure: Linking impactites and target rocks
Meteoritics and Planetary Science,
51
(12)
2347 – 2365
2016
1846.
Stratigraphy, sedimentology and structure of the Jurassic (Callovian to Lower Oxfordian) succession at Castle Hill, Scarborough, North Yorkshire, UK
Proceedings of the Yorkshire Geological Society,
61
(2)
109 – 133
2016
ISSN: 00440604
Publisher: Geological Society of London
Keywords:▾
England; North Yorkshire; Scarborough [North Yorkshire]; United Kingdom; Ammonoidea; Dinophyceae; bioturbation; Callovian; Oxfordian; sandstone; sedimentation rate; sedimentology; storm surge; stratigraphy; transgression
Abstract: ▾ Site investigation borehole cores and temporary shaft exposures at the Toll House Pumping Station shaft site, Castle Hill, Scarborough, North Yorkshire, have revealed new data on the Callovian to Lower Oxfordian (Jurassic) succession. The condensed transgressive marine unit, the Lower Callovian Cornbrash Formation, rich in berthierine ooids and abundant shelly fossils, and the attenuated Cayton Clay Formation represent the Early Callovian marine transgression that flooded the low-gradient alluvial plain, which is represented by the underlying Scalby Formation. The Callovian Osgodby Formation (Red Cliff Rock and Langdale members) is an extensively bioturbated, silty sandstone with abundant berthierine-pyrite ooids in the lower part. It was deposited in lower- to upper-shoreface settings. Slow sedimentation rates, with long sediment residence time, resulted in a diverse ichnofauna and a high bioturbation index. Framboidal pyrite ooids in the lower Osgodby Formation sandstones are interpreted as being formed in anoxic lagoons in the nearshore zone; ooids were subsequently swept offshore during storm surge-ebb events. Cold water dinoflagellate cysts of Boreal affinity such as Gonyaulacysta dentata in the lower part of the Oxford Clay Formation indicate an Early Oxfordian age. This is confirmed by the presence of the zonal ammonite species Quenstedoceras mariae and is consistent with a relatively cold, but warming, palaeoclimate at this time. Shaft excavations revealed a new major fault, the Toll House Fault, which is interpreted to be a splay fault bifurcating off the main Castle Hill Fault. Together, the Toll House and Castle Hill faults form the western bounding faults of the Peak Trough, a graben-like structure that extends northwards, offshore.Supplementary material: Supplementary data 1 (Macrofossil identifications from the Toll House shaft) and Supplementary data 2 (List of macropalaeontological specimens from the Toll House Boreholes) are available at https://dx.doi.org/10.6084/m9.figshare.c.3469968. © 2016 The Author(s). Published by The Geological Society of London for the Yorkshire Geological Society. All rights reserved.
1845.
Stochastic exploration and the geologic context of enhanced geothermal system viability on the Snake River Plain, Idaho
Special Paper of the Geological Society of America,
519115-136
2016
ISSN: 00721077
Publisher: Geological Society of America
Keywords:▾
Autocorrelation; Boreholes; Fracture; Geothermal fields; Geothermal wells; Groundwater; Heat exchangers; Heat flux; Hydraulic fracturing; Petroleum reservoir engineering; Stochastic models; Stochastic systems; Welding, Enhanced geothermal systems; Fracture distributions; Geomechanical behavior; Geostatistical techniques; Preexisting fracture; Spatial autocorrelations; Stochastic simulations; Subsurface temperature, Geothermal energy, fracture network; geothermal power; geothermal system; groundwater exploration; heat flux; hydraulic fracturing; permeability; reservoir; surface temperature, Idaho; Idaho; Snake River Plain; United States
ISBN:
9780813725192
Abstract: ▾ Geothermal energy depends on high subsurface temperature, adequate permeability and fracture volume, and accessible groundwater supply to support heat exchange with surrounding rock. Some regions may have adequate thermal resources but lack the necessary permeability or deep circulating water. Exploitation of such areas for geothermal energy could occur if permeability can be enhanced enough to provide the necessary heat exchange. These improvements to the geothermal reservoir would produce what is termed an "enhanced geothermal system" (EGS). The Snake River Plain (SRP) in southern Idaho is a geological region with high heat flux (~110 mW/m2) that has been recommended as an EGS target. In this study, we consider how the geologic and thermal history of the SRP might influence its EGS potential. We describe the fracture distribution (mean = 28.63 fractures/10 m) in a welded tuff core recovered from one of the few deep boreholes located on the SRP and provide a preliminary discussion of the likely geomechanical behavior under in situ stress. Spatial autocorrelation of fracture features is defined with geostatistical techniques and used in a stochastic simulation of possible structures in other welded tuff reservoirs. Autocorrelation scales for the continuous date are on the order of 70 meters with high subsample scale variability (56 m). Results should aid in designing criteria for a hydraulic fracturing plan that would augment the permeability and connectivity of an SRP reservoir's preexisting fracture network. © 2016 The Geological Society of America. All rights reserved.