Savoie University
Sciences de la Terre
Lake Mucubají is a moraine-dammed lake, crossed by the Boconó Fault, in the Mérida Andes, Venezuela. Four long pistoncores (up to 8 m long) and 24 short gravity cores (0.6 to 0.8 m long) were collected to study the sedimentary fill of the... more
Lake Mucubají is a moraine-dammed lake, crossed by the Boconó Fault, in the Mérida Andes, Venezuela. Four long pistoncores (up to 8 m long) and 24 short gravity cores (0.6 to 0.8 m long) were collected to study the sedimentary fill of the lake. Lithostratigraphy, magnetic susceptibility, organic and inorganic contents, and 14 C ages, permit lateral correlations between the cores, and with an emerged part of the former larger lacustrine basin fill. The cored succession spans the last 16,000 years. Several abrupt changes in sediment texture and composition are ascribed to depth and surface modifications. Together with soft-sediment disturbances, they are related to the seismo-tectonic activity of the Boconό Fault: shock-induced phenomena (slumps, seiche effects, liquefaction) and co-seismic scarps. Four major earthquakes indicate a mean minimum recurrence interval of 1200 years, which is consistent with trench data obtained from a neighbouring active trace of the Boconó Fault system. Despite the seismotectonic imprint, a general post-LGM climatic trend can be traced and correlated with northern-hemisphere global evolution, in particular for the last 13,000 years.
- by Franck Audemard and +1
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- Evolutionary Biology, Palaeogeography, Geology, Ecology
The right-lateral strike-slip El Pilar Fault is one of the major structures that accommodate the relative displacement between the Caribbean and South-America Plates. This fault, which trends East-West along the northeastern Venezuela... more
The right-lateral strike-slip El Pilar Fault is one of the major structures that accommodate the relative displacement between the Caribbean and South-America Plates. This fault, which trends East-West along the northeastern Venezuela margin, is a seismogenic source, and shows numerous evidence for active tectonics, including deformation of the Quaternary sediments filling the Cariaco Gulf. Because the main El Pilar Fault strand belongs to a set of strike-slip faults and thrusts between the stable Guyana shield (South) and the Caribbean oceanic floor (North), a GPS network was designed and installed to measure the relative motion of the El Pilar Fault and other faults. The results obtained from the comparison of 2003 and 2005 surveys indicate: (i) a lack of significant displacement (especially shortening) in the Serrania del Interior (Neogene cordillera overthrusted above the Guyana craton), (ii) an eastward displacement (relative to fixed south America plate) up to 22 mm/year of benchmarks located north of the El Pilar Fault.
Two very large deep-seated gravitational slope deformations in the highlands of the Mérida Andes, Venezuela, are herein described: the Mucubají Pass and Cerro La Camacha. These slope movements have slid in post-Last Glacial Maximum times.... more
Two very large deep-seated gravitational slope deformations in the highlands of the Mérida Andes, Venezuela, are herein described: the Mucubají Pass and Cerro La Camacha. These slope movements have slid in post-Last Glacial Maximum times. In addition, both landslides are in very close association with the active Boconó Fault trace. The Cerro La Camacha (Camacha Range) landslide is fault bounded along its northwest flank, whereas the Mucubají pass mass movement is even cut by the active fault trace. The almost 10 km long Mucubají slide mobilizes LGM moraine deposits along the unconformable basement contact. La Camacha slope movement is a sackung-type landslide, involving two huge masses that affect the entire northwestern slope of the La Camacha Range. This sackung is at least 20 km long, paralleling the active Boconó Fault trace. Combination of high relief energy (gravitational forces) and seismic shaking related to an on-site active fault could be responsible for the destabilization of the slopes or massif in both cases. Although the seismicallyinduced (re-)activation of the La Camacha landslide is very likely, there is no proof for that yet. Conversely, the Mucubají slide shows geomorphic, geodetic and sedimentary evidence of episodic activity in recent times, which could be ascribed to seismic triggering. In the particular case of the La Camacha sackung, the combination of dextral slip along the Boconó Fault and a SE-dipping fault plane could additionally favor the destabilization of the NW slope of the La Camacha Range.
- by Franck Audemard and +1
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- Psychology, Archaeology, Geology, Geochemistry
El estudio de los glaciares tropicales es una temática de gran importancia para las áreas de paleo-clima, gestión de riesgos naturales, manejo del recurso agua, generación de energía, etc. El presente trabajo muestra algunos adelantos en... more
El estudio de los glaciares tropicales es una temática de gran importancia para las áreas de paleo-clima, gestión de riesgos naturales, manejo del recurso agua, generación de energía, etc. El presente trabajo muestra algunos adelantos en el estudio de la dinámica glaciar cuaternaria en Los Andes Centrales de Mérida. La reconstrucción de los glaciares deducida de la geocronología con el 10 Be in-situ, contribuyen con el conocimiento climático regional y global desde el Último Máximo Glaciar. En el valle de Mucubají, el avance máximo del glaciar ocurrió hace más de18000 años y el retiro definitivo hace menos de 9000 años. El proceso transcurrió en dos grandes etapas. El glaciar retrocedió durante el Pleistoceno de ~3500 m a ~3850 m. La parte superior del glaciar estuvo confinado y desapareció rápidamente durante el Holoceno. En Los Zerpa el avance máximo ocurrió hace aproximadamente 13000 años.
- by Isandra Fortuna and +2
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- Glaciology
In the tropical Mérida Andes (northwestern Venezuela), glacial landforms were found at altitudes between 2600 and 5000 m, corresponding to 600 km 2 of ice cover during the maximum glacial extension. However, the lack of sufficient... more
In the tropical Mérida Andes (northwestern Venezuela), glacial landforms were found at altitudes between 2600 and 5000 m, corresponding to 600 km 2 of ice cover during the maximum glacial extension. However, the lack of sufficient absolute age data prevents detailed reconstruction of the timing of the last deglaciation. On the northwestern flank of the Mucuñuque Massif, successive moraines and striated eroded basement surfaces were sampled for cosmogenic 10 Be investigation. Their compilation with published data allows the establishment of a detailed chronology of the post-LGM glacier history. The oldest moraines (18.1 and 16.8 ka) correspond to the Oldest Dryas. Successive moraine ridges indicate stops in the overall retreat between the LGM and the Younger Dryas. The cold and short Older Dryas stadial has been identified. Results indicate that most of the ice withdrew during the Pleistocene. The dataset supports an intensification of the vertical retreat rate from~25 m/ka during the late Pleistocene to~310 m/ka during the Pleistocene/Holocene. Afterwards, the glacier was confined and located in the higher altitude zones. The altitude difference of the Younger Dryas moraines in the Mucubají, La Victoria and Los Zerpa valleys indicates a strong effect of valley orientation on the altitude of moraine development.
- by Franck Audemard and +1
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We use GNSS observations in northeastern Venezuela to constrain the El Pilar Fault (EPF) kinematics and to explore the effects of the variable elastic properties of the surrounding medium and of the fault geometry on inferred slip rates... more
We use GNSS observations in northeastern Venezuela to constrain the El Pilar Fault (EPF) kinematics and to explore the effects of the variable elastic properties of the surrounding medium and of the fault geometry on inferred slip rates and locking depth. The velocity field exhibits an asymmetric velocity gradient on either side of the EPF. We use five different approaches to explore possible models to explain this asymmetry. First, we infer a 1.6-km locking depth using a classic elastic half-space dislocation model. Second, we infer a 1.5-km locking depth and a 0.33 asymmetry coefficient using a heterogeneous asymmetric model, including contrasting material properties on either side of a vertical fault, suggesting that the igneous-metamorphic terranes on the northern side are ~2 times more rigid than the sedimentary southern side. Third, we use a three-dimensional elasto-static model to evaluate the presence of a compliant zone (CZ), suggesting a 30% reduction of rigidity in the upper 3 km at the depth of a 1- to 5-km wide fault zone. Fourth, we evaluate the distribution of fault slip, revealing a widespread partial-creep pattern in the eastern upper segment, while the upper western segment exhibits a partially locked area, which coincides with the rupture surface of the 1797 and 1929 earthquakes. To supplement these models, we upgrade the previously published displacement simulation method using non-vertical dislocations with data acquired between 2003 and 2013. The localized aseismic displacement pattern associated with creeping or partially creeping fault segments could explain the low level of historic seismicity.
III-1-Correlation between Cores MD-2431 and MD-2429. III-2-Strong lateral thickness increase in the marine sedimentary sequence. III-3-Specific imprints of major earthquakes in the marine sedimentary sequence.
- by Christian Beck and +2
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- Earth Sciences, Geology, Oceanography, Remote Sensing
The Howardite-Eucrite-Diogenite (HED) suite is a family of differentiated meteorites that provide a unique opportunity to study the differentiation of small bodies. The likely parent-body of this meteorite group, (4) Vesta is presently... more
The Howardite-Eucrite-Diogenite (HED) suite is a family of differentiated meteorites that provide a unique opportunity to study the differentiation of small bodies. The likely parent-body of this meteorite group, (4) Vesta is presently under study by the Dawn mission, scrutinizing its surface in the visible and NIR infrared range. Here, we discuss how well the magmatic trends observed in HED might be retrieved from NIR spectroscopy, by studying laboratory spectra of 10 HED meteorites together with spectra from the RELAB database. We show that although an exsolution process did occur for most eucrites (i.e. decomposition of a primary calcic pyroxene into a high-Ca and low-Ca pyroxene), it does not affect the ''bulk pyroxene'' trend retrieved from the location of the pyroxene crystal field bands (Band I with a maximum of absorption around at about 1 lm and Band II around 2 lm). Absolute values of the chemical composition appears however to deviate from the expected chemical composition. We show that mechanical mixture (i.e. impact gardening) will produce a linear mixing in the pyroxenes band position diagram (Band I position vs Band II position). This diagram also reveals that howardite are not pure mixtures of an average eucrite and average diogenite. Because asteroid surfaces are expected to show topography, we also study the effect of observation geometry on the NIR spectra of an eucrite and a diogenite by measuring the bi-directional reflectance spectra from 0.4 to 4.6 lm. Results show that these meteorites tend to act as forward scatterers, leading to a decrease of integrated band area (relative to the continuum) at high phase angles. The position of the two strong crystal field bands shows only small variability with observation geometry. Retrieval of the magmatic trends from the Band I vs Band II diagram should not be affected by observation geometry effects. Finally we performed NIR reflectance measurement on olivine diogenites. The presence of olivine can be suggested by using the Band Area Ratio vs Band I diagram, but this phase might affect the retrieval of pyroxene composition from the position of Band I and Band II.
The right-lateral strike-slip El Pilar Fault is one of the major structures that accommodate the relative displacement between the Caribbean and South-America Plates. This fault, which trends East-West along the northeastern Venezuela... more
The right-lateral strike-slip El Pilar Fault is one of the major structures that accommodate the relative displacement between the Caribbean and South-America Plates. This fault, which trends East-West along the northeastern Venezuela margin, is a seismogenic source, and shows numerous evidence for active tectonics, including deformation of the Quaternary sediments filling the Cariaco Gulf. Because the main El Pilar Fault strand belongs to a set of strike-slip faults and thrusts between the stable Guyana shield (South) and the Caribbean oceanic floor (North), a GPS network was designed and installed to measure the relative motion of the El Pilar Fault and other faults. The results obtained from the comparison of 2003 and 2005 surveys indicate: (i) a lack of significant displacement (especially shortening) in the Serrania del Interior (Neogene cordillera overthrusted above the Guyana craton), (ii) an eastward displacement (relative to fixed south America plate) up to 22 mm/year of benchmarks located north of the El Pilar Fault.
- by Christian Beck and +1
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- Geology, Geophysics, Active Tectonics, North Anatolian Fault
The Gulf of Cariaco is a marginal basin located between the Cariaco Basin and the Paria Gulf, offshore NE Venezuela, along a system of active right-lateral strike-slip faults. It is connected to the Caribbean Sea via a shallow 58-m-deep... more
The Gulf of Cariaco is a marginal basin located between the Cariaco Basin and the Paria Gulf, offshore NE Venezuela, along a system of active right-lateral strike-slip faults. It is connected to the Caribbean Sea via a shallow 58-m-deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands. A dense grid of high-resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill. Six unconformity-bounded seismic-stratigraphic units were identified in the upper~200 m of the sedimentary infill. Detailed seismic-stratigraphic and seismic-facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the Gulf of Cariaco: i) delta offlap breaks, ii) evaporites, and iii) erosional unconformities. Using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model, a relative sea/lake-level history encompassing the last 130 kyr could be reconstructed. In periods of connection with the open ocean, reconstructed relative sea level correlates well with eustatic sea level. In times of disconnection, distinct lakelevel fluctuations occurred, which sometimes resulted in total dessication of the gulf. Lake-level fluctuations appear to correlate with major Heinrich Events, stadials and interstadials. MIS 4, the LGM and the Younger Dryas were thus identified in the Gulf of Cariaco sedimentary record. The last reconnection to the Caribbean Sea occurred during MWP1b (around 11.5 kyr). The very good fit of the Cariaco sea/lake-level curve with the eustatic sea-level curves (both in terms of amplitude and of timing) underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin, despite its active tectonic setting.
Lake Mucubají is a moraine-dammed lake, crossed by the Boconó Fault, in the Mérida Andes, Venezuela. Four long pistoncores (up to 8 m long) and 24 short gravity cores (0.6 to 0.8 m long) were collected to study the sedimentary fill of the... more
Lake Mucubají is a moraine-dammed lake, crossed by the Boconó Fault, in the Mérida Andes, Venezuela. Four long pistoncores (up to 8 m long) and 24 short gravity cores (0.6 to 0.8 m long) were collected to study the sedimentary fill of the lake. Lithostratigraphy, magnetic susceptibility, organic and inorganic contents, and 14 C ages, permit lateral correlations between the cores, and with an emerged part of the former larger lacustrine basin fill. The cored succession spans the last 16,000 years. Several abrupt changes in sediment texture and composition are ascribed to depth and surface modifications. Together with soft-sediment disturbances, they are related to the seismo-tectonic activity of the Boconό Fault: shock-induced phenomena (slumps, seiche effects, liquefaction) and co-seismic scarps. Four major earthquakes indicate a mean minimum recurrence interval of 1200 years, which is consistent with trench data obtained from a neighbouring active trace of the Boconó Fault system. Despite the seismotectonic imprint, a general post-LGM climatic trend can be traced and correlated with northern-hemisphere global evolution, in particular for the last 13,000 years.
l Nororiente venezolano presenta, a lo largo de la historia, la mayor actividad sísmica a escala nacional , siendo la fuente sísmica de los eventos más significativos la extremidad sur de la subducción de las Antillas... more
l Nororiente venezolano presenta, a lo largo de la historia, la mayor actividad sísmica a escala nacional , siendo la fuente sísmica de los eventos más significativos la extremidad sur de la subducción de las Antillas me-0378-1844/07/11/735-07 $ 3.00/0 nores o la falla de El Pilar. Son numerosos los sismos históricos con testimonios escritos de daños sobre la población y el medio construido de la región, desde los comienzos de la dominación española a principios del s. XVI . Particularmente, la ciudad de Cumaná ha sido afectada, hasta llegar a su destrucción parcial, por los eventos de: 1530, 1684, 1766, 1797 y 1853, así como por dos sismos contemporáneos en el s. XX, en 1929 y 1997.
- by Christian Beck and +2
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The sediments of the two largest post-Riss and post-Würm lakes, in the northwestern Alps and southern Jura, contain possible records of seismo-tectonic instability: earthquake triggering of gravity reworking, and direct stratification... more
The sediments of the two largest post-Riss and post-Würm lakes, in the northwestern Alps and southern Jura, contain possible records of seismo-tectonic instability: earthquake triggering of gravity reworking, and direct stratification disturbance.In Lake Annecy, the lacustrine s.s. (non-proglacial) part of a 40 meters-thick rhythmic sediment pile has been investigated for this purpose by CLIMASILAC coring. For the last 15,000 to
Two very large deep-seated gravitational slope deformations in the highlands of the Mérida Andes, Venezuela, are herein described: the Mucubají Pass and Cerro La Camacha. These slope movements have slid in post-Last Glacial Maximum times.... more
Two very large deep-seated gravitational slope deformations in the highlands of the Mérida Andes, Venezuela, are herein described: the Mucubají Pass and Cerro La Camacha. These slope movements have slid in post-Last Glacial Maximum times. In addition, both landslides are in very close association with the active Boconó Fault trace. The Cerro La Camacha (Camacha Range) landslide is fault bounded along its northwest flank, whereas the Mucubají pass mass movement is even cut by the active fault trace. The almost 10 km long Mucubají slide mobilizes LGM moraine deposits along the unconformable basement contact. La Camacha slope movement is a sackung-type landslide, involving two huge masses that affect the entire northwestern slope of the La Camacha Range. This sackung is at least 20 km long, paralleling the active Boconó Fault trace. Combination of high relief energy (gravitational forces) and seismic shaking related to an on-site active fault could be responsible for the destabilization of the slopes or massif in both cases. Although the seismicallyinduced (re-)activation of the La Camacha landslide is very likely, there is no proof for that yet. Conversely, the Mucubají slide shows geomorphic, geodetic and sedimentary evidence of episodic activity in recent times, which could be ascribed to seismic triggering. In the particular case of the La Camacha sackung, the combination of dextral slip along the Boconó Fault and a SE-dipping fault plane could additionally favor the destabilization of the NW slope of the La Camacha Range.