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Yang T.,Key Laboratory of Seismic Observation and Geophysical ImagingInstitute of Geophysics | Yang X.,State Key Laboratory of Earthquake DynamicsInstitute of Geology | Duan Q.,State Key Laboratory of Earthquake DynamicsInstitute of Geology | Chen J.,State Key Laboratory of Earthquake DynamicsInstitute of Geology | Dekkers M.J.,Paleomagnetic Laboratory Fort Hoofddijk
Geochemistry, Geophysics, Geosystems | Year: 2016

Fluid infiltration within fault zones is an important process in earthquake rupture. Magnetic properties of fault rocks convey essential clues pertaining to physicochemical processes in fault zones. In 2011, two shallow holes (134 and 54 m depth, respectively) were drilled into the Yingxiu-Beichuan fault (Longmen Shan thrust belt, China), which accommodated most of the displacement of the 2008 Mw 7.9 Wenchuan earthquake. Fifty-eight drill core samples, including granitic host rock and various fault rocks, were analyzed rock-magnetically, mineralogically, and geochemically. The magnetic behavior of fault rocks appears to be dominated by paramagnetic clay minerals. Magnetite in trace amounts is identified as the predominant ferrimagnetic fraction in all samples, decreasing from the host rock, via fault breccia to (proto-)cataclasite. Significant mass-losses (10.7-45.6%) are determined for the latter two with the "isocon" method. Volatile contents and alteration products (i.e., chlorite) are enriched toward the fault core relative to the host rocks. These observations suggest that magnetite depletion occurred in these fault rocks-exhumed from the shallow crust-plumbed by fluid-assisted processes. Chlorite, interpreted to result from hydrothermal activity, occurs throughout almost the entire fault core and shows high coefficients of determination (R2>0.6) with both low and high-field magnetic susceptibility. Close relationships, with R2>0.70, are also observed between both low and high-field magnetic susceptibility and the immobile elements (e.g., TiO2, P2O5, MnO), H2O+, and the calculated mass-losses of fault rocks. Hence, magnetic properties of fault rocks can serve as proxy indicators of fluid infiltration within shallow fault zones. © 2016. American Geophysical Union. All Rights Reserved.

Ao H.,CAS Institute of Geology and Geophysics | Ao H.,CAS Institute of Earth Environment | Ao H.,University of Chinese Academy of Sciences | Deng C.,CAS Institute of Geology and Geophysics | And 2 more authors.
Earth and Planetary Science Letters | Year: 2010

The Nihewan fluvio-lacustrine sequence (North China) has recorded late Pliocene-Pleistocene climatic and environmental changes, and contains valuable information on early human evolution in high-latitude East Asia. We carried out a combined mineral-magnetic and geochemical investigation on a sequence from the Xiantai section, eastern Nihewan Basin. Results suggest that large-amplitude magnetic-property variations between so-called 'high-magnetic' and 'low-magnetic' units mainly result from preservation/dissolution cycles of detrital magnetic minerals in alternating oxic and anoxic depositional environments. In our preservation/dissolution model, the high- and low-magnetic units represent glacial and interglacial deposits, respectively. This contributes to a better understanding of the link between magnetic properties and climate in the Xiantai fluvio-lacustrine sequence. Based upon this relationship, early humans may have occupied the Xiantai and Xiaochangliang sites during an interglacial period, during both interglacial and glacial periods at the Donggutuo site, and during a glacial period at the Maliang site. Our work provides a paleoenvironmental context for early human adaptation and occupation in mainland East Asia during the early Pleistocene. © 2010 Elsevier B.V. All rights reserved.

Husing S.K.,Paleomagnetic Laboratory Fort Hoofddijk | Oms O.,Autonomous University of Barcelona | Agusti J.,Institute Catala Of Paleoecologia Humana I Evolucio Social | Garces M.,University of Barcelona | And 3 more authors.
Geobios | Year: 2012

The chronology of the Late Miocene Mediterranean-Atlantic gateways through southern Iberia is a key issue to better understand the geodynamic processes that lead to the Messinian salinity crisis. The timing of the North Betic corridor continentalization has recently been constrained by integrated magnetobiostratigraphic dating of the La Lancha section in the Guadix basin (Hüsing et al., 2010: Palaeogeography Palaeoclimatology Palaeoecology 291, 167-179). This work showed that the continentalization of the Guadix basin encompasses an approximately 2 myr hiatus, with the interval between ∼7.7 to ∼5.5 (or 5.0) Ma missing in the stratigraphic record. Minwer-Barakat and colleagues comment that this hiatus could be slightly shorter, but they base their hypotheses solely on an interval without any reliable magnetostratigraphic data. Their key localities Negratín 1 and Rambla de Chimeneas 3 (MN13), however, confirm that the oldest faunas found at La Lancha section correlate with the upper part of chron C3r (∼5.5 Ma). These continental faunas thus provide more evidence on the presence of a major Messinian hiatus in the Guadix record. © 2012 Elsevier Masson SAS.

van den Berg B.C.J.,University of Salamanca | Sierro F.J.,University of Salamanca | Hilgen F.J.,University Utrecht | Flecker R.,University of Bristol | And 7 more authors.
Global and Planetary Change | Year: 2015

We present a new high-resolution cyclostratigraphic age model for the Messinian sediments of the Montemayor-1 core. This core was drilled in the Guadalquivir Basin in southern Spain, which formed part of the marine corridor linking the Mediterranean with the Atlantic in the Late Miocene. Tuning of high-resolution geochemical records reveals a strong precessional cyclicity, with maximum clastic supply from river run off coinciding with maximum summer insolation. We recognize a gradual change in the nature of the typical cyclic fluctuations in elemental compositions of the sediments through the core, which is associated with a gradual change in depositional environment as the basin infilled. After applying the new age model, the upper Messinian glacial stages and deglaciation are clearly identified in the oxygen isotope records of the Montemayor-1 core. Reinterpretation of existing planktonic and benthic oxygen isotope records for the core and comparison with equivalent successions in the Rifian Corridor in northern Morocco allow the re-evaluation of the influence of the different water masses in the region: North Atlantic Central Water and Mediterranean Outflow Water. We observe no direct influence of MOW immediately before or during the Messinian Salinity Crisis. © 2015 Elsevier B.V.

Vasiliev I.,Paleomagnetic Laboratory Fort Hoofddijk | de Leeuw A.,Paleomagnetic Laboratory Fort Hoofddijk | Filipescu S.,Babes - Bolyai University | Krijgsman W.,Paleomagnetic Laboratory Fort Hoofddijk | And 3 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2010

A marked paleoenvironmental change took place at the beginning of the late Miocene in the Central Paratethys, with dominantly marine Sarmatian successions grading rapidly into mainly brackish Pannonian deposits. A long and excellently exposed section comprising the Sarmatian-Pannonian transition has been investigated at Oarba de Mure? in the Transylvanian basin (Romania). In this paper, we focus on both radiometric and magnetostratigraphic dating to provide a chronology for the Sarmatian-Pannonian transition in Transylvania. Two volcaniclastic layers, located approximately 40m below the Sarmatian-Pannonian transition, yield excellent 40Ar/39Ar ages. The weighted mean plateau age for biotite and sanidine separates provided isotopic ages of 11.62±0.12Ma and 11.65±0.13Ma. This implies deposition during the magnetic chron C5r.2r, which is in agreement with the magnetostratigraphic results of the Oarba de Mure? composite section. Rock magnetic analyses indicate greigite as the main magnetic carrier, with characteristics very similar to the magnetosomal greigite found in the Carpathian foredeep. The newly obtained chronology at Oarba de Mure? constrains the age of the Sarmatian-Pannonian transition in the Transylvanian basin to 11.3±0.1Ma, slightly younger than the 11.61Ma postulated in the Styrian and Vienna Basins. © 2010 Elsevier B.V.

Husing S.K.,Paleomagnetic Laboratory Fort Hoofddijk | Cascella A.,Italian National Institute of Geophysics and Volcanology | Hilgen F.J.,University Utrecht | Krijgsman W.,Paleomagnetic Laboratory Fort Hoofddijk | And 3 more authors.
Earth and Planetary Science Letters | Year: 2010

An integrated high-resolution magnetobiocyclostratigraphy including radioisotopic dating and astronomical tuning is presented for the interval between 15.29 and 14.17 Ma in the marine La Vedova section in northern Italy. The natural remanent magnetization is carried by the iron sulphide greigite and the resultant magnetostratigraphy can be correlated straightforwardly to the interval ranging from C5Bn.2n to C5ADn in the Astronomically Tuned Neogene Time Scale (ATNTS2004). Spectral analysis on high-resolution magnetic susceptibility and geochemical proxy records in the depth domain and, using our magnetobiostratigraphic age model, in the time domain demonstrate that the various scales of cyclicity in the section are related to astronomical climate forcing. Starting from our initial age model, larger-scale cycles were first tuned to eccentricity. This first-order tuning was followed by tuning the basic cycle to precession and boreal summer insolation using inferred phase relations between maxima in Ca/Al, redox-sensitive elements and Ba, and minima in magnetic susceptibility, and maxima in precession and minima in obliquity and boreal summer insolation. Our astronomical ages for reversal boundaries are supported by analysis of sea floor spreading rates and should replace the existing ages in the ATNTS2004 lacking direct astronomical control. Two major steps in the geochemical proxy records, astronomically dated at 15.074 and 14.489 Ma, coincide with abrupt changes in sedimentation rate, and are the result of the combined effect of the ∼ 400-kyr eccentricity cycle superimposed upon a longer-term climatic or tectonic induced trend. © 2009 Elsevier B.V. All rights reserved.

Mourik A.A.,University Utrecht | Bijkerk J.F.,University Utrecht | Cascella A.,Italian National Institute of Geophysics and Volcanology | Husing S.K.,Paleomagnetic Laboratory Fort Hoofddijk | And 3 more authors.
Earth and Planetary Science Letters | Year: 2010

Continuous marine successions covering the Middle Miocene Climate Transition (MMCT; ~15-13.7Ma) are scarce and the lack of a high-resolution magnetobiostratigraphic framework hampers the construction of astronomically tuned age models for this time interval. The La Vedova High Cliff section, exposed along the coast of the Cònero Riviera near Ancona (Italy), is one of the few Mediterranean sections covering the critical time interval of the MMCT. Starting from an initial magnetobiostratigraphic age model, a robust astronomical tuning was constructed for the interval between 14.2 and 13.5Ma, using geochemical element data and time series analysis. A shift in δ18O of bulk sediment towards heavier values occurs between ~13.92 and 13.78Ma and could be related to the Mi3b oxygen isotope event, which reflects the rapid expansion of the East Antarctic Ice Sheet in the middle Miocene. The onset of the CM6 carbon excursion is reflected in the bulk record by a rapid increase in δ13C at 13.86Ma. Our results confirm the proposition that these events coincide with a 405-kyr minimum in eccentricity and a node in obliquity related to the ~1.2Myr cycle. From 13.8Ma onwards, distinct quadruplet cycles containing sapropelitic sediments were deposited. This may suggest a causal connection between the main middle Miocene cooling step and the onset of sapropel formation in the Mediterranean. © 2010 Elsevier B.V.

Husing S.K.,Paleomagnetic Laboratory Fort Hoofddijk | Deenen M.H.L.,Paleomagnetic Laboratory Fort Hoofddijk | Koopmans J.G.,Paleomagnetic Laboratory Fort Hoofddijk | Krijgsman W.,Paleomagnetic Laboratory Fort Hoofddijk
Earth and Planetary Science Letters | Year: 2011

The Global Stratotype Section and Point (GSSP) for the Rhaetian Stage has recently been proposed at Steinbergkogel in Austria. We re-sampled the Steinbergkogel sections (STK-A and STK-B + C) in high-resolution to establish a robust magnetostratigraphy that allows global correlation. The palaeomagnetic signal at Steinbergkogel is composed of three components, which can be separated by thermal demagnetization. The highest temperature component, revealed between 280/300 and maximum 600 °C is of dual polarity and is interpreted as primary. Rock magnetic experiments showed that the signal is carried by magnetite. Our results allow correlation between the two individual Steinbergkogel outcrops. Subsequently, we correlate the two key biostratigraphic horizons for the base of the Rhaetian, the FO of M. hernsteini and the FAD of M. post-hernsteini to other sections of the Tethys domain. The correlation to the astronomically dated continental successions of the Newark basin indicates that these positions for the base of the Rhaetian are most likely determined in chrons E16n and E16r, respectively. This correlation is confirmed by cyclostratigraphic control on the marine Pizzo Mondello (Italy) section, where a combination of long period Milankovitch cycles (~. 175-Myr) and short-eccentricity cycles (~100-kyr) provide additional correlation constraints, respectively supporting a long duration of the Rhaetian. Our study implies that the Norian and Rhaetian Stages have durations of ~17 and ~9 Myr. © 2010 Elsevier B.V.

Husing S.K.,Paleomagnetic Laboratory Fort Hoofddijk | Oms O.,Autonomous University of Barcelona | Agusti J.,Institute Of Paleontologia M Crusafont | Garces M.,University of Barcelona | And 3 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2010

The late Miocene Mediterranean-Atlantic connection through southern Spain is generally thought to have closed during the late Tortonian, but accurate constraints on palaeobathymetry, shallowing rates and closure age are still lacking. We present integrated biostratigraphic (planktonic, benthonic foraminifera and mammals) and magnetostratigraphic results from the marine to continental La Lancha section of the Guadix Basin, refining the chronology for the Miocene-Pliocene sedimentary sequences of this basin that occupied a central position in the marine gateway. In addition, we perform palaeobathymetric analyses on the marine sedimentary sequence to reconstruct sea level fluctuations and vertical motions. Deposition of the Lower Marine Unit took place between 8.1 and 7.85 Ma with accumulation rates of ~1 m/kyr. A rapid shallowing from palaeodepths of 500-300 m to a depth of 300-200 m took place at ~8.0 Ma coinciding with a decrease in downslope transport. Surprisingly, no shallowing trend has been observed towards the unconformable contact with the Transitional Unit, which was deposited in a shallow (~90 m) marine environment. The youngest open marine marls are still indicative for a palaeodepth of N200 m. This leads to the conclusion that fully marine environments in Guadix persisted until at least 7.85 Ma. The palaeomagnetic polarity pattern of the Upper Continental Unit, in combination with the presence of the murid Paraethomys meini in the basal part of this sequence, indicates that the entire continental unit at La Lancha is attributed to the latest Messinian-Zanclean time. This age is in strong contradiction with previous correlations to the late Tortonian. Consequently, we conclude that a major hiatus of at least 2 Myr, comprising most of the Messinian stage, is present in the Guadix basin. Therefore a late Tortonian closure age of the Mediterranean-Atlantic gateway through Guadix has not been confirmed by our results, so that the possibility of a Messinian gateway through southern Spain cannot be completely ruled out. © 2010 Elsevier B.V. All rights reserved.

Mullender T.A.T.,Paleomagnetic laboratory Fort Hoofddijk | Frederichs T.,Research Group Marine Geophysics | Hilgenfeldt C.,Research Group Marine Geophysics | de Groot L.V.,Paleomagnetic laboratory Fort Hoofddijk | And 2 more authors.
Geochemistry, Geophysics, Geosystems | Year: 2016

Today's paleomagnetic and magnetic proxy studies involve processing of large sample collections while simultaneously demanding high quality data and high reproducibility. Here we describe a fully automated interface based on a commercial horizontal pass-through "2G" DC-SQUID magnetometer. This system is operational at the universities of Bremen (Germany) and Utrecht (Netherlands) since 1998 and 2006, respectively, while a system is currently being built at NGU Trondheim (Norway). The magnetometers are equipped with "in-line" alternating field (AF) demagnetization, a direct-current bias field coil along the coaxial AF demagnetization coil for the acquisition of anhysteretic remanent magnetization (ARM) and a long pulse-field coil for the acquisition of isothermal remanent magnetization (IRM). Samples are contained in dedicated low magnetization perspex holders that are manipulated by a pneumatic pick-and-place-unit. Upon desire samples can be measured in several positions considerably enhancing data quality in particular for magnetically weak samples. In the Bremen system, the peak of the IRM pulse fields is actively measured which reduces the discrepancy between the set field and the field that is actually applied. Techniques for quantifying and removing gyroremanent overprints and for measuring the viscosity of IRM further extend the range of applications of the system. Typically c. 300 paleomagnetic samples can be AF demagnetized per week (15 levels) in the three-position protocol. The versatility of the system is illustrated by several examples of paleomagnetic and rock magnetic data processing. © 2016. American Geophysical Union.

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