Dissolution-collapse breccias and paleokarst resulting from dissolution of evaporite rocks, especially sulfates

Ortı́

et al. 2001

Carbonates Evaporites

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...

Section: Dissolution-induced Subsidence Recorded In Mesozoic Sedimentmentioning

confidence: 99%

The stratigraphical record and activity of evaporite dissolution subsidence in Spain

Ortı́

et al. 2001

Carbonates Evaporites

“…2,3). In fact, paleokarst, brecciated zones,and otherkarstfeatures foundin somecarbonates mayhavebeeninitiated byearlierdissolution and karstdevelopment in gypsumthatis interbedded withthe carbonates; Sando (1988), Friedman (1997, and Palmerand Palmer (in preparation) provideexamples and a summary of this carbonate/sulfate relationship. Gypsum-karst features commonly have a linear orientation, and these appear to be controlled by joints or fractures in the rock; however, some karst features have a seemingly random orientation, wherein the controls are not understood.…”

Section: Gypsum-karst Processesmentioning

confidence: 99%

Evaporite karst in the United States

Johnson

1997

Carbonates Evaporites

Evaporites, includinggypsum(or anhydrite)and salt, arethemostsolubleof commonrocks; they are dissolvedreadilyto form caves, sinkholes. disappearing streams, and other karst features that typically are found in limestones and dolomites. The four basic requirementsfor evaporitekarst to develop are: (1) a deposit of gypsumor salt; (2) water, unsaturatedwith caSO. or NaCl; (3) an outlet for escape of dissolvingwater; and (4) energyto cause water to flow throughthesystem. Evaporitesarepresentin 32 of the48 contiguousstates, and they underlie about 35-40% of the land area; they are reported in rocks of every geologic system from the Precambrian through the Quaterruuy. Evaporitekarst is known at leastlocally(and sometimesquiteextensively)in almost all areas underlainby evaporites. Themost widespread and pronounced examples of both gypsum and salt karst are in the Permian basin of the southwestern United States,but many other areas are also significant. Human activities have caused some evaporite-karst development,primarilyin salt deposits. Boreholesmay enable (either intentionallyor inadvertently) unsaturatedwater to flow throughor against salt deposits,thus allowing developmentof small to large dissolutioncavities. If the dissolutioncavity is large enough and shallowenough.successiveroof failuresabove thecavitycan cause land subsidence or catastrophic collapse.

“…In fact, paleokarst, becciated zones, anc! other karst features found in some carbonates may have been initiated by earlier dissolution and karst development in gypsum that is interbedded with the carbonates; Sando (1988), Friedman (1997, and Palmer & Palmer (1997) provide examples and a summary of this carbonate/sulfate relationship. Gypsum-karst features commonly have a linear orientation, anc!…”

Section: Gypsum Karst Processesmentioning

confidence: 99%

Gypsum karst in the United States

Johnson¹

1996

IJS

Gypsum is one of the most soluble of common rocks; it is dissolved readily to form caves, sinkholes, disappearing streams, and other karst features that typically are found in limestones and dolomites. The four basic requirements for gypsum karst to develop are: (1) a deposit of gypsum; (2) water, unsaturated with CaS04; (3) an outlet for escape of dissolving water; and (4) energy to cause water to flow through the system. Gypsum deposits are present in 32 of the 48 conterminous United States, and they underlie about 35--40% of the land area; they are reported in rocks of every geologic system from the Precambrian through the Quaternary. Gypsum karst is known at least locally (and sometimes quite extensively) in almost all areas underlain by gypsum, and commonly extends down to depths of at least 30 m below the land surface. The most widespread and pronounced examples of gypsum karst are in the Permian basin of southwestern United States, but many other areas also are significant. Human activities may also cause, or accelerate, development of gypsum karst.