The stratigraphical record and activity of evaporite dissolution subsidence in Spain

Abstract

The evaporite formations (in outcrop and at shallowdepth) cover an extensivearea of the Spanish territory. These soluble sediments are foundin diversegeological domainsand recorda widetimespan fromthe Triassicup to the presentday. Broadly,the Mesozoic and Paleogene formations (Alpinecycle) are affected by compressional structures, whereasthe Neogene (post-orogenic) sedimentsremain undefonned.The subsidence caused by subsurface dissolution ofthe evaporites (subjacentkarst)takesplace in three maintypes of stratigraphical settings: a) Subsidence affectingevaporite-bearing MesozoicandTertiarysuccessions (interstratalkarst);b) Subsidencein Quaternaryalluvialdeposits relatedto the exorheicevolutionofthepresent-dayfluvialsystems(alluvialor mantledkarst);c) Subsidencein exposedevaporites(uncovered karst). These types may be represented by paleosubsidence phenomena (synsedimentary and/or postsedimentary) recognizable in the stratigraphical record, or by equivalentcurrentlyactive or modemexampleswith surfaceexpression.The interstratal karstification of the Mesozoic marine evaporitesand the consequent subsidenceof the topstrata is revealedby stratiform collapsebrecciasand wedge-outs in the evaporitesgrading intounsoluble residues.InseveralTertiarybasins,the sedimentsoverlyingevaporiteslocallyshowsynsedimentary and/orpostsedimentary subsidencestructures. The dissolution-induced subsidence coeval to sedimentation gives place to local thickenings in basin-like structures with convergent dips and cumulative wedge out systems. This sinkingprocesscontrolsthe generation of depositional environments and lithofaciesdistribution. The postsedimentary subsidenceproducesa greatvarietyof gravitational deformations in the Tertiarysupra-evaporitic units includingbothductile and brittle structures(flexures, synfonns,fractures,collapseand brecciation).The Quaternary fluvial terrace deposits on evaporite sedimentsshow anomalous thickenings (>150 m) caused by a dissolution-induced subsidence process in the alluvial plain which is balanced by alluvial aggradation. The complex space and time evolutionpattern of the paleosubsidence gives place to intricate and anarchical structures in the alluvium which may be erroneously interpreted as pure tectonic deformations. The current subsidence and generationof sinkholes due to suballuvialkarstification constitutesa geohazardwhich affectsto largedenselypopulatedareas endangering human safetyand posinglimitationsto the development. An outstandingexamplecorresponds to Calatayud historicalcity, where subsidence severelydamageshighlyvaluablemonuments. The subsidenceresultingfrom the underground karstification of evaporiteshas determinedor influencedthe generation of some importantmodem lacustrinebasins like Gallocanta, Fuente de Piedra and Banyoles lakes. The suddenformationof sinkholes due to the collapse of cave roofs is relatively frequentin some evaporite outcrops. Very harmful and spectacularsubsidence activity is currently occurring in the Cardona salt diapir where subsidence has been dramatically exac...

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

“…An entrenchment of 115 m and an eastward lateral migration in excess of 2 km have been estimated for the fluvial system since the formation of the oldest mapped terrace. The existence of linear and prominent gypsum scarps is a frequent characteristic of the numerous fluvial valleys excavated in Tertiary evaporites in Spain (Silva et al, 1988;Gutiérrez et al, 1994;Gutiérrez and Gutiérrez, 1998;Gutiérrez et al, 2001Gutiérrez et al, , 2004. In the case studied, the abrupt change from an asymmetric valley with a gypsum escarpment to a relatively symmetric valley may be attributed to the "replacement" of the evaporitic bedrock in the lower reach by more resistant thickened and cemented terrace deposits filling dissolutioninduced troughs and basins.…”

“…Perhaps surprisingly, the great majority of the documented examples of fluvial systems affected by synsedimentary subsidence due to evaporite dissolution are restricted to Spanish territory. The main anomalous morpho-stratigraphical features that produce this type of subsidence include (Gutiérrez et al, 2001: (1) abrupt thickening of fluvial deposits, that may locally reach more than 100 m. These thickened alluvial deposits fill complex dissolution-induced basins and troughs up to several tens of kilometres in size; (2) superposition of the deposits correlative to different terrace levels; (3) the presence of abundant syn-and post-sedimentary gravitational deformations. In Spain, these peculiar features have been reported in numerous fluvial valleys excavated in evaporitic formations, mostly Tertiary in age, although some examples related to Triassic evaporites have also been documented.…”

A review on Quaternary tectonic and nontectonic faults in the central sector of the Iberian Chain, NE Spain

“…Lafuente et al (2010) añaden dos eventos de rotura; un event horizon en la base de la unidad 2, que interpretan como un paelosuelo y el desplazamiento de una supuesta cuña coluvial correspondiente a las unidades 4 y X. Nótese el carácter erosivo de los límites superior e inferior de la unidad 4. long are higher than 0.65 m. Average displacements of such amount are expectable for normal fault surface ruptures around 28 km long (Wells and Coppersmith, 1994). Evidence of stick-slip displacement is commonly used as a criterion to differentiate between tectonic (seismogenic) and dissolution-collapse (nonseismogenic) faults in areas underlain by evaporites (Hanson et al 7KH ¿QG-ings of Gutiérrez et al (2011) strongly suggest that this criterion is not reliable, having relevant implications for seismic hazard assessment in regions where evaporite dissolution plays a role on active deformation, as might be the case in some areas of the Spanish Territory (Gutiérrez et al, 2001.…”

Natural and anthropogenic hazards in karst areas of Albania

“…As floods and mass movements have been the object of several dedicated articles (see for example, Qiriazi and Sala, 1999) attention will be focused on subsidence and sinkholes, which represent a significant geohazards in Albania, as well as in many other parts of Europe (Cooper and Waltham, 1999;Gutierrez et al, 2001;Cooper, 2002;Delle Rose and Parise, 2002;Guerrero et al, 2004).…”