Interpretation of recent structures in an area of cryptokarst evolution—neotectonic versus subsidence genesis

Dias, Ruben P.; Cabral, João

doi:10.1080/09853111.2002.10510756

Cited by 26 publications

(23 citation statements)

References 11 publications

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“…occurrence of bioturbated massive and horizontally laminated marl facies in the core of some of these structures indicates that the synsedimentary passive bending caused by the interstratal and suballuvial karstification of the evaporites led to the generation of poorlydrained subsidence depressions in the pediment surface. The reverse faults observed in the central part of some synforms may be explained as rotated normal faults or as bending-moment faults generated in the concave part of the fold to accommodate length changes produced by the gravitational bending (Ge and Jackson, 1998;Gutiérrez, 1998a;Dias and Cabral, 2002). Some abandoned gypsum quarries excavated in this pediment display the upper part of a dense network of openings in the gypsum bedrock filled with sediments derived from the overlying alluvial cover.…”

Section: Intermediate Terraces (T5 To T7)mentioning

confidence: 96%

Impact of halite dissolution subsidence on Quaternary fluvial terrace development: Case study of the Huerva River, Ebro Basin, NE Spain

2008

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Section: Intermediate Terraces (T5 To T7)mentioning

confidence: 96%

Impact of halite dissolution subsidence on Quaternary fluvial terrace development: Case study of the Huerva River, Ebro Basin, NE Spain

2008

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“…10), acquired over a very thin layer of alluvium surrounded by Cretaceous rocks has a totally different seismic pattern, composed of chaotic reflections that we have interpreted as highly folded and faulted clastics of Cretaceous age. The poor aspect of this stacked section is probably due, not only to the high deformation expected in the area (from geological data), but also due to severe statics problems caused by the presence of a karst developed in the cretaceous limestones, filled with Plio-Quaternary sediments (DIAS and CABRAL, 2002b), and to the lack of acoustic impedance contrasts in these layers.…”

Section: Reflection Datamentioning

confidence: 99%

A Geophysical Study of the Carcavai Fault Zone, Portugal

Carvalho

Ramalho

Dias

et al. 2011

Pure Appl. Geophys.

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The Algarve province is located a few hundred kilometres north of the crossing of the E-W Eurasia-Africa plate boundary in an area of diffuse seismicity and broad deformation. It is characterised by a moderate seismicity, with some important historical and instrumental earthquakes causing loss of lives and significant material damages. The area is affected not only by plate boundary earthquakes but also by moderate to large events generated by local sources. The assessment of onshore local sources is, therefore, of vital importance for an evaluation of the regional seismic hazard. This paper discusses the application of geophysical data to the study of the Carcavai fault zone, an outcropping structure more than 20 km long which is seen to deform sediments of the Plio-Quaternary age. The location of some sectors of the fault zone, as well as the vertical offsets of the structure, are still to be confirmed. In order to estimate these and to study the geometry of the fault zone at depth, geophysical data were acquired together with new geological data. Where the location of the fault was less certain, EM and seismic reflection profiles with coarse spatial sampling were carried out. After the detailed location of the fault zone, seismic reflection profiles with a more dense spatial resolution were acquired. The integrated interpretation of the geological and geophysical data confirmed the presence of a large fault zone. The total fault length is still unknown as its extension offshore is still being studied. Together with estimated values of the throw obtained, this data set has improved understanding the seismic hazard in the area by providing more refined estimates of coseismic rupture, maximum expected earthquake and return periods.

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“…The metre scale secondary structures typical of the lowermost exposed parts strongly suggest a bedrock morphology (Fig. 7) similar to that seen in the Portuguese cryptokarsts (''basin and dome'' structure, Dias and Cabral 2002). The Pays Bruˆle´deposit has a more complex geometry.…”

Section: Nature Of the Trapmentioning

confidence: 92%

“…Faults with normal and reverse geometries (Fig. 3d) are also very much a part of this setting as a result of accommodation to a very irregular bedrock lowering (Dias and Cabral 2002;Dupuis et al 2003). In this environment, faults with reverse geometry may be explained by several mechanisms, including a geometrical control imposed by the substratum morphology, by the formation of synthetic faults accompanying a normal fault, by a permutation of the maximum principal stress from vertical to horizontal direction due to a stress relief in the vertical direction resulting from a sinking of the well floor or a sudden cavity collapse (Odonne et al 1999;Dias and Cabral 2002).…”

Section: Nature Of the Trapmentioning

confidence: 95%

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Genesis of the Dordogne (France) high-purity silica placers

Désindes¹,

Durand²,

Bailly³

et al. 2005

Int J Earth Sci (Geol Rundsch)

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International audienceThis article describes the formation of the principal French high-purity silica placer (source for electrometallurgy of silicon and ferrosilicon), the Boudeau deposit in Dordogne, and of one of its subordinate deposits, the Pays Brûlé deposit. Boudeau has always been considered to be a colluvial deposit, formed in a trap produced by extensional tectonism. The present work suggests a new genetic interpretation, based on a combined study of the deposits and their underlying rocks. It shows that the quartz gravel deposits, laid down by stream flow within braided channels, were reworked by karstic progressive sinking, and that the mechanism responsible for the increase in the thickness of the economic formations is cryptokarstic corrosion. This undercovers weathering process, which involves dissolution of karstifiable rocks (oolitic and bioclastic limestones) at their interface with a permeable, non-karstifiable cover composed of chemically pure quartz gravels in a sandy-argillaceous matrix. A typological study of the gravels provides a basis for tackling the problem of their origin and their purity. They seem to be derived mainly from the synmetamorphic quartz mobilisates of the stripped metamorphic units (the lower and upper gneiss units forming the western edge of the Massif Central). Lastly, a dynamic model is suggested for the genesis of the high-purity silica deposits of Dordogne

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Interpretation of recent structures in an area of cryptokarst evolution—neotectonic versus subsidence genesis

Cited by 26 publications

References 11 publications

Impact of halite dissolution subsidence on Quaternary fluvial terrace development: Case study of the Huerva River, Ebro Basin, NE Spain

Impact of halite dissolution subsidence on Quaternary fluvial terrace development: Case study of the Huerva River, Ebro Basin, NE Spain

A Geophysical Study of the Carcavai Fault Zone, Portugal

Genesis of the Dordogne (France) high-purity silica placers

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