All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1819.
All together now: an international palynological team documents vegetation and climate changes during the last 500 kyr at Lake Ohrid (SE Europe)
Alpine and Mediterranean Quaternary,
29
(2)
201 – 210
2016
ISSN: 22797327
Publisher: AIQUA - Associazione Italiana per lo Studio del Quaternario
Abstract: ▾ Lake Ohrid (Balkan peninsula) is the oldest European extant lake and one of the deepest and largest. Such a unique, terrestrial natural archive is especially relevant for both paleoenvironmental and paleoclimatic reconstructions but also for genetic studies. In the frame of the International Continental Scientific Drilling Program (ICDP), a deep drilling campaign was carried out within the scope of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project in 2013. Here, we present the summary of palynological analyses carried out in the upper 200 m of the overall 569 m long DEEP site sediment succession from the central part of the lake. These studies, performed by an international palynological team, document the main floristic, vegetation and climate changes during the last ca 500 kyr, at a millennial-scale resolution (~1.6 kyr). The continuous sediment infill permitted to trace multiple non-forested/ forested phases as a response to Glacial/Interglacial cycles as well as to sub-Milankovitch climate changes. The pollen record, corresponding with marine isotope stages MIS 13 to MIS 1, points to a progressive change from cooler and wetter to warmer and drier interglacials. New palynological studies are underway to reconstruct vegetational and climatic conditions over older intervals as well as to obtain high resolution data for some key intervals such as MIS 5-6, MIS 11-12, MIS 35-42. The complete record of changes in flora composition and vegetation during both glacials and interglacials will furnish indispensable insights for understanding the role of refugia, ecosystem resilience and maintenance of terrestrial biodiversity in the Mediterranean area.
1818.
Aligning and synchronization of MIS5 proxy records from Lake Ohrid (FYROM) with independently dated Mediterranean archives: Implications for DEEP core chronology
Biogeosciences,
13
(9)
2757 – 2768
2016
ISSN: 17264170
Publisher: Copernicus GmbH
Keywords:▾
Lake Ohrid; Mediterranean Sea; age determination; cyclostratigraphy; glacial-interglacial cycle; marine isotope stage; marine record; Ocean Drilling Program; paleoclimate; proxy climate record; radiometric method; tephra; tephrochronology
Abstract: ▾ The DEEP site sediment sequence obtained during the ICDP SCOPSCO project at Lake Ohrid was dated using tephrostratigraphic information, cyclostratigraphy, and orbital tuning through the marine isotope stages (MIS) 15-1. Although this approach is suitable for the generation of a general chronological framework of the long succession, it is insufficient to resolve more detailed palaeoclimatological questions, such as leads and lags of climate events between marine and terrestrial records or between different regions. Here, we demonstrate how the use of different tie points can affect cyclostratigraphy and orbital tuning for the period between ca. 140 and 70 ka and how the results can be correlated with directly/indirectly radiometrically dated Mediterranean marine and continental proxy records. The alternative age model presented here shows consistent differences with that initially proposed by Francke et al. (2015) for the same interval, in particular at the level of the MIS6-5e transition. According to this new age model, different proxies from the DEEP site sediment record support an increase of temperatures between glacial to interglacial conditions, which is almost synchronous with a rapid increase in sea surface temperature observed in the western Mediterranean. The results show how a detailed study of independent chronological tie points is important to align different records and to highlight asynchronisms of climate events. Moreover, Francke et al. (2016) have incorporated the new chronology proposed for tephra OH-DP-0499 in the final DEEP age model. This has reduced substantially the chronological discrepancies between the DEEP site age model and the model proposed here for the last glacial-interglacial transition. © 2016 Author(s).
1817.
Aftershocks triggered by fluid intrusion: Evidence for the aftershock sequence occurred 2014 in West Bohemia/Vogtland
Journal of Geophysical Research: Solid Earth,
121
(4)
2575 – 2590
2016
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
Bohemia; Czech Republic; Germany; Vogtland; aftershock; earthquake magnitude; earthquake swarm; fault plane; focal mechanism; stress field
Abstract: ▾ The West Bohemia/Vogtland region, central Europe, is well known for its repeating swarm activity. However, the latest activity in 2014, although spatially overlapping with previous swarm activity, consisted of three classical aftershock sequences triggered by ML3.5, 4.4, and 3.5 events. To decode the apparent system change from swarm-type to mainshock-aftershock characteristics, we have analyzed the details of the major ML4.4 sequence based on focal mechanisms and relocated earthquake data. Our analysis shows that the mainshock occurred with rotated mechanism in a step over region of the fault plane, unfavorably oriented to the regional stress field. Most of its intense aftershock activity occurred in-plane with classical characteristics such as (i) the maximum magnitude of the aftershocks is significantly less than the mainshock magnitude and (ii) the decay can be well fitted by the Omori-Utsu law. However, the absolute number of aftershocks and the fitted Omori-Utsu c and p parameters are much larger than for typical sequences. By means of the epidemic-type aftershock sequence model, we show that an additional aseismic source with an exponentially decaying strength triggered a large fraction of the aftershocks. Corresponding pore pressure simulations with an exponentially decreasing flow rate of the fluid source show a good agreement with the observed spatial migration front of the aftershocks extending approximately with log(t). Thus, we conclude that the mainshock opened fluid pathways from a finite fluid source into the fault plane explaining the unusual high rate of aftershocks, the migration patterns, and the exponential decrease of the aseismic signal. ©2016. American Geophysical Union. All Rights Reserved.
1816.
Advanced seismic imaging techniques characterize the Alpine Fault at Whataroa (New Zealand)
Journal of Geophysical Research: Solid Earth,
121
(12)
8792-8812
2016
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
fault zone; P-wave; prestack migration; seismic data; seismic reflection; seismic tomography; seismic velocity; structural geology; transpression, Alpine Fault Zone; New Zealand; South Island; West Coast [South Island]; Whataroa
Abstract: ▾ The plate-bounding Alpine Fault in New Zealand is an 850 km long transpressive continental fault zone that is late in its earthquake cycle. We have acquired and processed reflection seismic data to image the subsurface around the main drill site of the Deep Fault Drilling Project (DFDP-2). The resulting velocity models and seismic images of the upper 5 km show complex subsurface structures around the Alpine Fault zone. The most prominent feature is a strong reflector at depths of 1.5–2.2 km with an apparent dip of 48° to the southeast below the DFDP-2 borehole, which we assume to be the main trace of the Alpine Fault. Above the main reflector, parallel reflectors suggest the presence of a ∼600 m wide damage zone. Additionally, subparallel reflectors are imaged that we interpret as secondary branches of the main fault zone. Conjugate faults imaged by the data show the complexity of the subsurface. The derived P wave velocity model reveals a 300–600 m thick sedimentary layer with velocities of ∼2.3 km/s above a schist basement with velocities of 4.5–5.5 km/s. A low-velocity layer can be observed within the basement at 0.8–2 km depth. A small-scale low-velocity anomaly appears at the top of the basement that can be correlated to the fault zone. The results provide a reliable basis for a seismic characterization of the DFDP-2 drill site that can be used for further structural and geological investigations of the architecture of the Alpine Fault in this area. ©2016. American Geophysical Union. All Rights Reserved.
1815.
A progressively wetter climate in southern East Africa over the past 1.3 million years
Nature,
537
(7619)
220-224
2016
ISSN: 00280836
Publisher: Nature Publishing Group
Keywords:▾
carbon dioxide; rain; alkane; calcium; carbon dioxide; dust; ice; rain; wax, arid environment; carbon dioxide; climate conditions; glacial-interglacial cycle; global climate; greenhouse gas; insolation; orbital forcing; paleoclimate; proxy climate record; sea surface temperature; spatiotemporal analysis; terrigenous deposit, Article; climate; climate change; Indian Ocean; interglacial; lake sediment; Malawi; Northern Hemisphere; paleoclimate; priority journal; sea surface temperature; summer; sunlight; thermoregulation; Africa; analysis; atmosphere; chemistry; desert climate; dust; history; lake; plant; plant leaf; season; temperature, East Africa; East African Lakes; Indian Ocean; Lake Malawi; Pacific Ocean, Africa, Eastern; Alkanes; Atmosphere; Calcium; Carbon Dioxide; Climate; Desert Climate; Dust; History, Ancient; Ice; Indian Ocean; Lakes; Malawi; Plant Leaves; Plants; Rain; Seasons; Temperature; Waxes
Abstract: ▾ African climate is generally considered to have evolved towards progressively drier conditions over the past few million years, with increased variability as glacial-interglacial change intensified worldwide. Palaeoclimate records derived mainly from northern Africa exhibit a 100,000-year (eccentricity) cycle overprinted on a pronounced 20,000-year (precession) beat, driven by orbital forcing of summer insolation, global ice volume and long-lived atmospheric greenhouse gases. Here we present a 1.3-million-year-long climate history from the Lake Malawi basin (10°-14° S in eastern Africa), which displays strong 100,000-year (eccentricity) cycles of temperature and rainfall following the Mid-Pleistocene Transition around 900,000 years ago. Interglacial periods were relatively warm and moist, while ice ages were cool and dry. The Malawi record shows limited evidence for precessional variability, which we attribute to the opposing effects of austral summer insolation and the temporal/spatial pattern of sea surface temperature in the Indian Ocean. The temperature history of the Malawi basin, at least for the past 500,000 years, strongly resembles past changes in atmospheric carbon dioxide and terrigenous dust flux in the tropical Pacific Ocean, but not in global ice volume. Climate in this sector of eastern Africa (unlike northern Africa) evolved from a predominantly arid environment with high-frequency variability to generally wetter conditions with more prolonged wet and dry intervals. © 2016 Macmillan Publishers Limited, part of Springer Nature.
1814.
A microphysical interpretation of rate- and state-dependent friction for fault gouge
Geochemistry, Geophysics, Geosystems,
17
(5)
1660-1677
2016
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Activation energy; Chemical activation; Creep; Deformation; Earthquakes; Faulting; Friction; Geophysics; Shear strength; Tribology, Ambient conditions; Constitutive parameters; Earthquake nucleation; Frictional strength; Inverse relationship; Microphysical models; Microphysical process; Seismogenic faults, Fault slips, asperity; creep; earthquake mechanism; earthquake rupture; fault gouge; fault slip; fault zone; plastic deformation; shear strength; tectonic evolution; tectonic setting
Abstract: ▾ The evolution of fault strength during the seismic cycle plays a key role in the mode of fault slip, nature of earthquake stress drop, and earthquake nucleation. Laboratory-based rate- and state-dependent friction (RSF) laws can describe changes in fault strength during slip, but the connections between fault strength and the mechanisms that dictate the mode of failure, from aseismic creep to earthquake rupture, remain poorly understood. The empirical nature of RSF laws remains a drawback to their application in nature. Here we analyze an extensive data set of friction constitutive parameters with the goal of illuminating the microphysical processes controlling RSF. We document robust relationships between: (1) the initial value of sliding (or kinetic) friction, (2) RSF parameters, and (3) the time rates of frictional strengthening (aging). We derive a microphysical model based on asperity contact mechanics and show that these relationships are dictated by: (1) an activation energy that controls the rate of asperity growth by plastic creep, and (2) an inverse relationship between material hardness and the activation volume of plastic deformation. Collectively, our results illuminate the physics expressed by the RSF parameters, and which describe the absolute value of frictional strength and its dependence on time and slip rate. Moreover, we demonstrate that seismogenic fault behavior may be dictated by the interplay between grain properties and ambient conditions controlling the local shear strength of grain-scale asperity contacts. © 2016. American Geophysical Union. All Rights Reserved.
1813.
A high-resolution mid-Pleistocene temperature record from Arctic Lake El'gygytgyn: A 50 kyr super interglacial from MIS 33 to MIS 31?
Earth and Planetary Science Letters,
43656-63
2016
ISSN: 0012821X
Publisher: Elsevier
Keywords:▾
Glacial geology; Glycerol; Isotopes, Arctic; Branched GDGT; Marine isotope stages; Paleoclimatology; Super interglacial, Lakes, interglacial; marine isotope stage; Northern Hemisphere; paleoclimate; paleotemperature; Pleistocene, Arctic; Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ Previous periods of extreme warmth in Earth's history are of great interest in light of current and predicted anthropogenic warming. Numerous so called "super interglacial" intervals, with summer temperatures significantly warmer than today, have been identified in the 3.6 million year (Ma) sediment record from Lake El'gygytgyn, northeast Russia. To date, however, a high-resolution paleotemperature reconstruction from any of these super interglacials is lacking. Here we present a paleotemperature reconstruction based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) from Marine Isotope Stages (MIS) 35 to MIS 29, including super interglacial MIS 31. To investigate this period in detail, samples were analyzed with an unprecedented average sample resolution of 500 yrs from MIS 33 to MIS 30. Our results suggest the entire period currently defined as MIS 33-31 (~1114-1062 kyr BP) was characterized by generally warm and highly variable conditions at the lake, at times out of phase with Northern Hemisphere summer insolation, and that cold "glacial" conditions during MIS 32 lasted only a few thousand years. Close similarities are seen with coeval records from high southern latitudes, supporting the suggestion that the interval from MIS 33 to MIS 31 was an exceptionally long interglacial (Teitler et al., 2015). Based on brGDGT temperatures from Lake El'gygytgyn (this study and unpublished results), warming in the western Arctic during MIS 31 was matched only by MIS 11 during the Pleistocene. © 2016 Elsevier B.V.
1812.
3D reflection seismic imaging at the 2.5km deep COSC-1 scientific borehole, central Scandinavian Caledonides
Tectonophysics,
68940--55
2016
ISSN: 004019511811.
15 Years of Hardship and Struggle History and the Prospects for the Future of the Chinese Continental Scientific Drilling Program(CCSD):In Memory of the 15 Year Anniversary of CCSD and 20 Year Anniversary of ICDP (in Chinese with English abstract);[中国大陆科学钻探的过去、现在和未来——纪念中国大陆科学钻探实施15周年、国际大陆科学钻探委员会成立20周年]
Acta Geologica Sinica,
90
(09)
2109-2122
2016
1810.
Megaspores attributable to Ghoshispora in Late Cretaceous deposits of the Songliao Basin, north-east China: Taxonomic clarification and distribution
Review of Palaeobotany and Palynology,
23240-60
2016
ISSN: 00346667
Publisher: Elsevier B.V.
Keywords:▾
biogenic deposit; biostratigraphy; Cretaceous; fern; fossil assemblage; geographical distribution; identification method; morphology; morphotype; nomenclature; paleoenvironment; palynology; scanning electron microscopy; spore; taxonomy, China; Songliao Basin
Abstract: ▾ The composite SK-1 borehole drilled in the Songliao Basin, north-east China penetrated non-marine rocks of Late Cretaceous age, some of which yielded assemblages of Ghoshispora. Species of this megaspore genus have palaeoenvironmental and potentially also biostratigraphic significance. Their value as determinants of age is, however, currently limited because many are difficult if not impossible to differentiate as our appraisal of their morphological characters reveals. This review helped to put the specimens recovered from the SK-1 borehole into context and led to the identification of a few of the specimens as Ghoshispora kondinskayae (Srivastava et Binda) Srivastava, G. sp. cf. G. bella (Kondinskaya) subsp. deltoidea Kutluk et al., and G. sp. cf. G. rara (Kondinskaya) Srivastava. Several revealed characters under the scanning electron microscope that differ from those of previously published species: two of these are described as new, namely Ghoshispora zhaoi sp. nov. and G. bulbosa sp. nov. Owing to a lack of sufficient specimens six other morphotypes have had to be identified in open nomenclature as G. sp. A-F. It is likely that the parent plants of all of the species grew in and/or close to standing water. The comparatively large number of very small specimens in association with, and having some of the characters of, the larger representatives of G. zhaoi suggests that a few might be the microspores of this species rather than incompletely developed megaspores. © 2016 Elsevier B.V.
1809.
Drilling fluid technology applied in a large hole of the second spudding of the scientific drilling well in the Songliao basin (in Chinese with English abstract); [松辽盆地大陆科钻二开段大井眼钻井液技术]
Geology and Exploration,
52
(5)
931-936
2016
1808.
A 400-ka tephrochronological framework for Central America from Lake Petén Itzá (Guatemala) sediments
Quaternary Science Reviews,
150200 – 220
2016
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Guatemala [Central America]; Lake Peten Itza; Pacific Ocean; Pacific Ocean (East); Peten; Yucatan Peninsula; Sediments; Trace elements; Volcanoes; CAVA; Explosive volcanism; ICDP; Paleoclimates; Tephrochronology; caldera; drilling; explosive volcanism; island arc; lowland environment; Neotropical Region; paleoclimate; Pleistocene; sediment analysis; sedimentation; tephrochronology; volcanic eruption; Lakes
Abstract: ▾ Lake Petén Itzá, northern Guatemala, lies within a hydrologically closed basin in the south-central area of the Yucatán Peninsula, and was drilled under the auspices of the International Continental Scientific Drilling Program (ICDP) in 2006. At 16°55′N latitude, the lake is ideally located for study of past climate and environmental conditions in the Neotropical lowlands. Because of its great depth (>160 m), Lake Petén Itzá has a record of continuous sediment accumulation that extends well into the late Pleistocene. A key obstacle to obtaining long climate records from the region is the difficulty of establishing a robust chronology beyond ∼40 ka, the limit of 14C dating. Tephra layers within the Lake Petén Itzá sediments, however, enable development of age/depth relations beyond 40 ka. Ash beds from large-magnitude, Pleistocene-to-Holocene silicic eruptions of caldera volcanoes along the Central American Volcanic Arc (CAVA) were found throughout drill cores collected from Lake Petén Itzá. These ash beds were used to establish a robust chronology extending back 400 ka. We used major- and trace-element glass composition to establish 12 well-constrained correlations between the lacustrine tephra layers in Lake Petén Itzá sediments and dated deposits at the CAVA source volcanoes, and with their marine equivalents in eastern Pacific Ocean sediments. The data also enabled revision of eight previous determinations of erupted volumes and masses, and initial estimates for another four eruptions, as well as the designation of source areas for 14 previously unknown eruptions. The new and revised sedimentation rates for the older sediment successions identify the interglacial of MIS5a between 84 and 72 ka, followed by a stadial between 72 and 59 ka that corresponds to MIS4. We modified the age models for the Lake Petén Itzá sediment sequences, extended the paleoclimate and paleoecological record for this Neotropical region to ∼400 ka, and determined the magnitude and timing of CAVA eruptions. © 2016 Elsevier Ltd
1807.
Ecology of cladocera species from central America based on subfossil assemblages
Advances in Oceanography and Limnology,
7
(2)
151 – 162
2016
ISSN: 19475721
Publisher: Page Press Publications
Keywords:▾
El Salvador [Central America]; Guatemala [Central America]; Honduras; Bosminidae; Chydoridae; Chydorus sphaericus; Cladocera; Daphniidae; cluster analysis; crustacean; fossil assemblage; lacustrine deposit; morphotype; paleoecology; paleontology; plankton
Abstract: ▾ Cladocera species composition was analyzed in surface sediments of 29 lakes in Central America (Guatemala, El Salvador and Honduras). The material studied was collected with an Ekman grab in autumn 2013 from lakes located in lowland, highland and mountain regions. The study revealed high variability in qualitative and quantitative composition of subfossil Cladocera. A total of 31 Cladocera species (5 planktonic and 26 littoral) were identified, as well as 4 morphotypes that could not be identified (NRR 1-4). Planktonic Bosminidae and Daphniidae were the most abundant families. Daphniidae were restricted to water bodies in mountain regions, whereas Bosminidae were widely distributed in lakes with different abiotic conditions. Moreover, Bosminidae species also occurred in highly mineralized waters (> 900 μS cm–1). The great majority of the identified Cladocera species belonged to the littoral family Chydoridae. Chydorus cf. sphaericus was the most common species (found in 20 lakes), which probably reflects its tolerance to a wide spectrum of habitat conditions. Cluster analysis discriminated 6 groups of Cladocera species with a high correlation level within groups (≥0.8), which showed different types of correlation with lake characteristics and environmental variables. Canonical correspondence analysis (CCA) showed that altitude and secondly water electrical conductivity were the most important drivers of Cladocera species composition in the region studied. Furthermore, CCA analysis indicated lowland lakes with low water transparency were also characterized by peculiar species assemblages. © 2016, Page Press Publications. All rights reserved.
1806.
High elevation of Jiaolai Basin during the Late Cretaceous: Implication for the coastal mountains along the East Asian margin
Earth and Planetary Science Letters,
456112-123
2016
ISSN: 0012821X
Publisher: Elsevier B.V.
Keywords:▾
Climate change; Isotopes; Stratigraphy, Clumped isotopes; coastal mountains; East Asia; Jiaolai Basin; Late cretaceous; Paleoelevation, Landforms, continental margin; Cretaceous; elevation; paleoclimate; paleogeography; stratigraphy, China; Jiaolai Basin; Shandong
Abstract: ▾ A large body of evidence suggests that there were extensive coastal mountains along the East Asian margin during the Late Cretaceous. However, current knowledge of the paleo-mountains — the period, range, and elevation — is limited. Therefore, direct paleoaltimetry is needed to validate and evaluate the paleo-mountains in East Asia. Our study area is Jiaolai Basin, which is located at the East Asian continental margin. We estimate the paleoelevation of Jiaolai Basin during the Late Cretaceous using carbonate clumped isotope paleothermometry. After correcting for seasonal preference, latitudinal difference, and secular climate change, we conclude that the paleoelevation of Jiaolai Basin was almost certainly ≥2.0 km at ∼80 Ma. Combined with the evidence from stratigraphy, paleogeography, and paleoclimatology, our results suggest that the existence of coastal mountains along East Asia during the Late Cretaceous is likely and the model of Okhotomorsk–East Asia collision is preferred. © 2016 Elsevier B.V.
1805.
Ecosystem regimes and responses in a coupled ancient lake system from MIS 5b to present: The diatom record of lakes Ohrid and Prespa
Biogeosciences,
13
(10)
3147-3162
2016
ISSN: 17264170
Publisher: Copernicus GmbH
Keywords:▾
aquatic ecosystem; climate change; climate forcing; diatom; ecosystem resilience; fossil record; hydrological change; lacustrine environment; Last Interglacial; microbial community; micropaleontology; paleoclimate; paleoecology; paleolimnology; physicochemical property; reconstruction, Lake Mikri Prespa; Lake Ohrid, Bacillariophyta
Abstract: ▾ We reconstruct the aquatic ecosystem interactions since the last interglacial period in the oldest, most diverse, hydrologically connected European lake system, by using palaeolimnological diatom and selected geochemistry data from Lake Ohrid "DEEP site" core and equivalent data from Lake Prespa core, Co1215. Driven by climate forcing, the lakes experienced two adaptive cycles during the last 92 ka: "interglacial and interstadial" and "glacial" cycle. The shortterm ecosystems reorganizations, e.g. regime shifts within these cycles substantially differ between the lakes, as evident from the inferred amplitudes of variation. The deeper Lake Ohrid shifted between ultra oligo- and oligotrophic regimes in contrast to the much shallower Lake Prespa, which shifted from a deeper, (oligo-) mesotrophic to a shallower, eutrophic lake and vice versa. Due to the high level of ecosystem stability (e.g. trophic state, lake level), Lake Ohrid appears relatively resistant to external forcing, such as climate and environmental change. Recovering in a relatively short time from major climate change, Lake Prespa is a resilient ecosystem. At the DEEP site, the decoupling between the lakes' response to climate change is marked in the prolonged and gradual changes during the MIS 5/4 and 2/1 transitions. These response differences and the lakes' different physical and chemical properties may limit the influence of Lake Prespa on Lake Ohrid. Regime shifts of Lake Ohrid due to potential hydrological change in Lake Prespa are not evident in the data presented here. Moreover, a complete collapse of the ecosystems functionality and loss of their diatom communities did not happen in either lake for the period presented in the study. © 2016 Author(s).
1804.
Maximum earthquake magnitudes along different sections of the North Anatolian fault zone
Tectonophysics,
674147-165
2016
ISSN: 00401951
Publisher: Elsevier B.V.
Keywords:▾
Earthquakes; Hazards; Seismology; Strike-slip faults; Structural geology; Transform faults, Continental transform; Earthquake magnitudes; Fault zone; Historical seismicity; North Anatolian Fault Zone, Fault slips, continental margin; earthquake catalogue; earthquake magnitude; fault zone; hazard assessment; North Anatolian Fault; San Andreas Fault; seismic source; seismicity; seismology; transform fault, Dead Sea; Istanbul [Turkey]; Marmara [Turkey]; Turkey
Abstract: ▾ Constraining the maximum likely magnitude of future earthquakes on continental transform faults has fundamental consequences for the expected seismic hazard. Since the recurrence time for those earthquakes is typically longer than a century, such estimates rely primarily on well-documented historical earthquake catalogs, when available. Here we discuss the maximum observed earthquake magnitudes along different sections of the North Anatolian Fault Zone (NAFZ) in relation to the age of the fault activity, cumulative offset, slip rate and maximum length of coherent fault segments. The findings are based on a newly compiled catalog of historical earthquakes in the region, using the extensive literary sources that exist owing to the long civilization record. We find that the largest M7.8-8.0 earthquakes are exclusively observed along the older eastern part of the NAFZ that also has longer coherent fault segments. In contrast, the maximum observed events on the younger western part where the fault branches into two or more strands are smaller. No first-order relations between maximum magnitudes and fault offset or slip rates are found. The results suggest that the maximum expected earthquake magnitude in the densely populated Marmara-Istanbul region would probably not exceed M7.5. The findings are consistent with available knowledge for the San Andreas Fault and Dead Sea Transform, and can help in estimating hazard potential associated with different sections of large transform faults. © 2016 The Authors.
1803.
Mass wasting history within Lake Ohrid basin (Albania/Macedonia) over the last 600 ka
Advances in Natural and Technological Hazards Research,
41291-300
2016
ISSN: 18789897
Publisher: Springer Netherlands
Abstract: ▾ Lake Ohrid (LO), a transboundary lake shared by Macedonia and Albania on the Balkan Peninsula, is not only considered to be the oldest lake in Europe (~2 Ma) but has a long and continuous sedimentary history. An advantage at LO is the availability of hydroacoustic data sets of good quality covering the entire lake basin. The tectonically formed basin is filled with thick undisturbed sediments. However, the overall internal structure of LO is characterized by numerous faults, clinoform structures, and several Mass Transport Deposits (MTDs). By using a seismic chronology model (SCM) correlating seismic reflector packages with Marine Isotope Stages (MIS) we estimate the occurrence of the deepest MTD detected in the southern basin at the transition of MIS9 to MIS8 (~300 ka) defining the onset of the sliding history in LO that is still ongoing today. In general, MTDs are widespread within the basin but they do cluster at active faults. Two large MTDs occurred in the early MIS7 (~230 ka, ~220 ka) and after a quiesence period of about ~70 ka two additional large MTDs have been detected in the late penultimate glacial period MIS6 (~150 ka, 130 ka). MIS5 seemed to be another quiet period with respect to mass wasting. In the younger sedimentary history mass movement is a common process with several large and mid-sized deposits mapped at all stratigraphic levels. The youngest slide deposits are estimated to occur within the last 2,000 years. The main outcome of this paper is a model for the spatial and temporal distribution of mass wasting for Lake Ohrid. © Springer International Publishing Switzerland 2016.
1802.
Late Cretaceous marine fossils and seawater incursion events in the Songliao Basin, NE China
Cretaceous Research,
62172-182
2016
ISSN: 01956671
Publisher: Academic Press
Keywords:▾
biostratigraphy; bivalve; Cretaceous; dinoflagellate; fish; foraminifera; lacustrine environment; nanofossil; paleoenvironment; seawater, China; Songliao Basin, Bivalvia; Dinophyceae; Foraminifera
Abstract: ▾ The Songliao Basin is the largest non-marine oil-bearing basin in China. Because of the absence of substantial evidence, the hypothesis of seawater incursion events into the Songliao Basin remains controversial. The presence of marine fossils could provide direct proof to support this supposition. Here, we report new discoveries of foraminifera, calcareous nannofossils, brackish dinoflagellates, and other marine and brackish-water fossils to support the suggestion of seawater incursion events in the Songliao Basin. Relatively abundant benthic and planktonic foraminifera, calcareous nannofossils, marine and brackish-water dinoflagellates, fish, and bivalves have been discovered in Members 1 and 2 of the Nenjiang Formation, a few foraminifera and brackish-water dinoflagellates have been found in the lower Qingshankou Formation, and just a few brackish-water bivalves have been found in the uppermost Qingshankou Fm. Based on the presence of marine molecular fossils and other evidence, we suggest that relatively large seawater incursion events occurred during the sedimentation of the lower Nenjiang Fm., relatively smaller seawater incursions occurred during the deposition of the lower Qingshankou Fm., and possibly a very small seawater incursion occurred during the sedimentation of the uppermost Qingshankou Fm. These seawater incursion events in the Songliao Basin were controlled by regional tectonic activity, evolution of the palaeo Songliao Lake, and global sea level change. These periodic seawater incursions brought marine biota into the palaeo Songliao Lake. © 2015 Elsevier Ltd.
1801.
Large-displacement, hydrothermal frictional properties of DFDP-1 fault rocks, Alpine Fault, New Zealand: Implications for deep rupture propagation
Journal of Geophysical Research: Solid Earth,
121
(2)
624-647
2016
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
earthquake rupture; fault; fault displacement; fault gouge; friction; hydrothermal system; plate tectonics; strain rate, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ The Alpine Fault, New Zealand, is a major plate-bounding fault that accommodates 65-75% of the total relative motion between the Australian and Pacific plates. Here we present data on the hydrothermal frictional properties of Alpine Fault rocks that surround the principal slip zones (PSZ) of the Alpine Fault and those comprising the PSZ itself. The samples were retrieved from relatively shallow depths during phase 1 of the Deep Fault Drilling Project (DFDP-1) at Gaunt Creek. Simulated fault gouges were sheared at temperatures of 25, 150, 300, 450, and 600°C in order to determine the friction coefficient as well as the velocity dependence of friction. Friction remains more or less constant with changes in temperature, but a transition from velocity-strengthening behavior to velocity-weakening behavior occurs at a temperature of T = 150°C. The transition depends on the absolute value of sliding velocity as well as temperature, with the velocity-weakening region restricted to higher velocity for higher temperatures. Friction was substantially lower for low-velocity shearing (V < 0.3 μm/s) at 600°C, but no transition to normal stress independence was observed. In the framework of rate-and-state friction, earthquake nucleation is most likely at an intermediate temperature of T = 300°C. The velocity-strengthening nature of the Alpine Fault rocks at higher temperatures may pose a barrier for rupture propagation to deeper levels, limiting the possible depth extent of large earthquakes. Our results highlight the importance of strain rate in controlling frictional behavior under conditions spanning the classical brittle-plastic transition for quartzofeldspathic compositions. ©2016. The Authors.
1800.
Laboratory observations of time-dependent frictional strengthening and stress relaxation in natural and synthetic fault gouges
Journal of Geophysical Research: Solid Earth,
121
(2)
1183-1201
2016
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
earthquake event; fault; fault gouge; friction; mineralogy; observational method; relative humidity; slip; stress
Abstract: ▾ Interseismic recovery of fault strength (healing) following earthquake failure is a fundamental requirement of the seismic cycle and likely plays a key role in determining the stability and slip behavior of tectonic faults. We report on laboratory measurements of time- and slip-dependent frictional strengthening for natural and synthetic gouges to evaluate the role of mineralogy in frictional strengthening. We performed slide-hold-slide (SHS) shearing experiments on nine natural fault gouges and eight synthetic gouges at conditions of 20 MPa normal stress, 100% relative humidity (RH), large shear strain (~15), and room temperature. Phyllosilicate-rich rocks show the lowest rates of frictional strengthening. Samples rich in quartz and feldspar exhibit intermediate rates of frictional strengthening, and calcite-rich gouges show the largest values. Our results show that (1) the rates of frictional strengthening and creep relaxation scale with frictional strength, (2) phyllosilicate-rich fault gouges have low strength and healing characteristics that promote stable, aseismic creep, (3) most natural fault gouges exhibit intermediate rates of frictional strengthening, consistent with a broad range of fault slip behaviors, and (4) calcite-rich fault rocks show the highest rates of frictional strengthening, low values of dilation upon reshear, and high frictional strengths, all of which would promote seismogenic behavior. ©2016. American Geophysical Union. All Rights Reserved.
1799.
Improved end-member characterisation of modern organic matter pools in the Ohrid Basin (Albania, Macedonia) and evaluation of new palaeoenvironmental proxies
Biogeosciences,
13
(3)
795 – 816
2016
ISSN: 17264170
Publisher: Copernicus GmbH
Keywords:▾
Albania; Lake Ohrid; Macedonia [Southern Europe]; biomarker; biome; catchment; climate effect; environmental change; geochemistry; Holocene; inorganic carbon; leaf litter; paleoenvironment; sediment analysis; soil organic matter; vegetation history
Abstract: ▾ We present elemental, lipid biomarker and, in the supplement, compound-specific isotope (δ13C, δ2H) data for soils and leaf litter collected in the catchment of Lake Ohrid (Albania, Macedonia), as well as macrophytes, particulate organic matter and sediments from the lake itself. Lake Ohrid provides an outstanding archive of continental environmental change of at least 1.2 million years and the purpose of our study is to ground truth organic geochemical proxies that we developed in order to study past changes in the terrestrial biome. We show that soils dominate the lipid signal of the lake sediments rather than the vegetation or aquatic biomass. There is a strong imprint of suberin monomers on the composition of total lipid extracts and chain-length distributions of n-alkanoic acids, n-alcohols, ω-hydroxy acids and α, ω-dicarboxylic acids. Our end-member survey identifies that ratios of mid-chain length suberin-derived to long-chain length cuticular-derived alkyl compounds as well as their average chain length distributions can be used as new molecular proxies of organic matter sources to the lake. We tested these for the 8.2 ka event, a pronounced and widespread Holocene climate fluctuation. In SE Europe climate became drier and cooler in response to the event, as is clearly recognisable in the carbonate and organic carbon records of Lake Ohrid sediments. Our new proxies indicate biome modification in response to hydrological changes, identifying two phases of increased soil organic matter (OM) supply, first from soils with moderately degraded OM and then from more degraded soils. Our study demonstrates that geochemical fingerprinting of terrestrial OM should focus on the main lipid sources, rather than the living biomass. Both can exhibit climate-controlled variability, but are generally not identical. © Author(s) 2016.
1798.
Implications of structural inheritance in oblique rift zones for basin compartmentalization: Nkhata Basin, Malawi Rift (EARS)
Marine and Petroleum Geology,
72110-121
2016
ISSN: 02648172
Publisher: Elsevier Ltd
Keywords:▾
Geologic models; Hydrocarbons; Sediments; Strike-slip faults, East African Rift; Existing structure; High resolution seismic; Hydrocarbon distribution; Normal faults; Sediment distribution; Strike-slip deformation; Structural inheritance, Fault slips, basin evolution; compartmentalization; deformation; extensional tectonics; hydrocarbon; normal fault; rift zone; sediment transport; strike-slip fault, East African Rift
Abstract: ▾ The Cenozoic East African Rift System (EARS) is an exceptional example of active continental extension, providing opportunities for furthering our understanding of hydrocarbon plays within rifts. It is divided into structurally distinct western and eastern branches. The western branch comprises deep rift basins separated by transfer zones, commonly localised onto pre-existing structures, offering good regional scale hydrocarbon traps. At a basin-scale, local discrete inherited structures might also play an important role on fault localisation and hydrocarbon distribution. Here, we consider the evolution of the Central basin of the Malawi Rift, in particular the influence of pre-existing structural fabrics.Integrating basin-scale multichannel 2D, and high resolution seismic datasets we constrain the border, Mlowe-Nkhata, fault system (MNF) to the west of the basin and smaller Mbamba fault (MF) to the east and document their evolution. Intra basin structures define a series of horsts, which initiated as convergent transfers, along the basin axis. The horsts are offset along a NE-SW striking transfer fault parallel to and along strike of the onshore Karoo (Permo-Triassic) Ruhuhu graben. Discrete pre-existing structures probably determined its location and, oriented obliquely to the extension orientation it accommodated predominantly strike-slip deformation, with more slowly accrued dip-slip.To the north of this transfer fault, the overall basin architecture is asymmetric, thickening to the west throughout; while to the south, an initially symmetric graben architecture became increasingly asymmetric in sediment distribution as strain localised onto the western MNF. The presence of the axial horst increasingly focussed sediment supply to the west. As the transfer fault increased its displacement, so this axial supply was interrupted, effectively starving the south-east while ponding sediments between the western horst margin and the transfer fault. This asymmetric bathymetry and partitioned sedimentation continues to the present-day, overprinting the early basin symmetry and configuration. Sediments deposited earlier become increasingly dissected and fault juxtapositions changed at a small (10-100 m) scale. The observed influence of basin-scale transfer faults on sediment dispersal and fault compartmentalization due to pre-existing structures oblique to the extension orientation is relevant to analogous exploration settings. © 2016 Elsevier Ltd.
1797.
Impact processes, permafrost dynamics, and climate and environmental variability in the terrestrial Arctic as inferred from the unique 3.6 Myr record of Lake El'gygytgyn, Far East Russia – A review
Quaternary Science Reviews,
147221-244
2016
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Amplification; Climate change; Drops; Dynamics; Fluorine; Forestry; Glacial geology; Glaciers; Ice; Isotopes; Permafrost; Rock drilling; Sediments; Structural geology; Vegetation; Volcanic rocks, Environmental evolution; Environmental variability; ICDP; Interglacial cyclicity; Interglacials; Mid-Pliocene; Pliocene; West antarctic ice sheets, Lakes, arctic environment; Beringia; climate variation; Cordilleran Ice Sheet; crater lake; environmental change; glacial-interglacial cycle; historical ecology; isotopic analysis; marine isotope stage; nutrient dynamics; paleoenvironment; permafrost; Pliocene-Pleistocene boundary; vegetation dynamics; warming, Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ Lake El'gygytgyn in Far East Russia is a 3.6 Myr old impact crater lake. Located in an area that has never been affected by Cenozoic glaciations nor desiccation, the unique sediment record of the lake represents the longest continuous sediment archive of the terrestrial Arctic. The surrounding crater is the only impact structure on Earth developed in mostly acid volcanic rocks. Recent studies on the impactite, permafrost, and sediment sequences recovered within the framework of the ICDP “El'gygytgyn Drilling Project” and multiple pre-site surveys yielded new insight into the bedrock origin and cratering processes as well as permafrost dynamics and the climate and environmental history of the terrestrial Arctic back to the mid-Pliocene. Results from the impact rock section recovered during the deep drilling clearly confirm the impact genesis of the El'gygytgyn crater, but indicate an only very reduced fallback impactite sequence without larger coherent melt bodies. Isotope and element data of impact melt samples indicate a F-type asteroid of mixed composition or an ordinary chondrite as the likely impactor. The impact event caused a long-lasting hydrothermal activity in the crater that is assumed to have persisted for c. 300 kyr. Geochemical and microbial analyses of the permafrost core indicate a subaquatic formation of the lower part during lake-level highstand, but a subaerial genesis of the upper part after a lake-level drop after the Allerød. The isotope signal and ion compositions of ground ice is overprinted by several thaw-freeze cycles due to variations in the talik underneath the lake. Modeling results suggest a modern permafrost thickness in the crater of c. 340 m, and further confirm a pervasive character of the talik below Lake El'gygytgyn. The lake sediment sequences shed new leight into the Pliocene and Pleistocene climate and environmental evolution of the Arctic. During the mid-Pliocene, significantly warmer and wetter climatic conditions in western Beringia than today enabled dense boreal forests to grow around Lake El'gygytgyn and, in combination with a higher nutrient flux into the lake, promoted primary production. The exceptional warmth during the mid-Pliocene is in accordance with other marine and terrestrial records from the Arctic and indicates a period of enhanced “Arctic amplification”. The favourable conditions during the mid-Pliocene were repeatedly interrupted by climate deteriorations, e.g., during Marine Isotope Stage (MIS) M2, when pollen data and sediment proxies indicate a major cooling and the onset of local permafrost around the lake. A gradual vegetation change after c. 3.0 Ma points to the onset of a long-term cooling trend during the Late Pliocene that culminated in major temperature drops, first during MIS G6, and later during MIS 104. These cold events coincide with the onset of an intensified Northern Hemisphere (NH) glaciation and the largest extent of the Cordilleran Ice Sheet, respectively. After the Pliocene/Pleistocene transition, local vegetation and primary production in Lake El'gygtygyn experienced a major change from relatively uniform conditions to a high-amplitude glacial-to-interglacial cyclicity that fluctuated on a dominant 41 kyr obliquity band, but changed to a 100 kyr eccentricity dominance during the Middle Pleistocene transition (MPT) at c. 1.2–0.6 Ma. Periods of exceptional warming in the Pleistocene record of Lake El'gygytgyn with dense boreal forests around and peaks of primary production in the lake are assigned to so-called “super-interglacial” periods. The occurrence of these super-interglacials well corresponds to collapses of the West Antarctic Ice Sheet (WAIS) recorded in ice-free periods in the ANDRILL core, which suggests strong intrahemispheric teleconnections presumably driven by changes in the thermocline ocean circulation. © 2016 Elsevier Ltd
1796.
Hydrothermal frictional strengths of rock and mineral samples relevant to the creeping section of the San Andreas Fault
Journal of Structural Geology,
89153-167
2016
ISSN: 01918141
Publisher: Elsevier Ltd
Keywords:▾
Landforms; Rocks; Slip forming; Stick-slip; Strike-slip faults, Franciscan Complex; Frictional strength; Great Valley sequence; SAFOD; San Andreas fault; Saponite, Minerals, creep; fault gouge; friction; rock; San Andreas Fault; saponite; seismic zone; slip; strength; strike-slip fault; temperature, California; Central Valley [California]; United States
Abstract: ▾ We compare frictional strengths in the temperature range 25-250 °C of fault gouge from SAFOD (CDZ and SDZ) with quartzofeldspathic wall rocks typical of the central creeping section of the San Andreas Fault (Great Valley sequence and Franciscan Complex). The Great Valley and Franciscan samples have coefficients of friction, μ > 0.35 at all experimental conditions. Strength is unchanged between 25° and 150 °C, but μ increases at higher temperatures, exceeding 0.50 at 250 °C. Both samples are velocity strengthening at room temperature but show velocity-weakening behavior beginning at 150 °C and stick-slip motion at 250 °C. These rocks, therefore, have the potential for unstable seismic slip at depth. The CDZ gouge, with a high saponite content, is weak (μ = 0.09-0.17) and velocity strengthening in all experiments, and μ decreases at temperatures above 150 °C. Behavior of the SDZ is intermediate between the CDZ and wall rocks: μ < 0.2 and does not vary with temperature. Although saponite is probably not stable at depths greater than ~3 km, substitution of the frictionally similar minerals talc and Mg-rich chlorite for saponite at higher temperatures could potentially extend the range of low strength and stable slip down to the base of the seismogenic zone. © 2016.
1795.
Hydrologic testing during drilling: application of the flowing fluid electrical conductivity (FFEC) logging method to drilling of a deep borehole
Hydrogeology Journal,
24
(6)
1333--1341
2016
ISSN: 1431-2174, 1435-0157Abstract: ▾ Drilling of a deep borehole does not normally allow for hydrologic testing during the drilling period. It is only done when drilling experiences a large loss (or high return) of drilling fluid due to penetration of a large-transmissivity zone. The paper proposes the possibility of conducting flowing fluid electrical conductivity (FFEC) logging during the drilling period, with negligible impact on the drilling schedule, yet providing important information on depth locations of both high- and low-transmissivity zones and their hydraulic properties. The information can be used to guide downhole fluid sampling and post-drilling detailed testing of the borehole. The method has been applied to the drilling of a 2,500-m borehole at Åre, central Sweden, firstly when the drilling reached 1,600 m, and then when the drilling reached the target depth of 2,500 m. Results unveil eight hydraulically active zones from 300 m down to borehole bottom, with depths determined to within the order of a meter. Further, the first set of data allows the estimation of hydraulic transmissivity values of the six hydraulically conductive zones found from 300 to 1,600 m, which are very low and range over one order of magnitude.