A genetic classification of sinkholes illustrated from evaporite paleokarst exposures in Spain |
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| Authors: | Francisco Gutiérrez Jesús Guerrero Pedro Lucha |
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| Institution: | (1) Earth Science Department, Edificio Geológicas, Universidad de Zaragoza, C/. Pedro Cerbuna, 12, 50009 Zaragoza, Spain |
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| Abstract: | This contribution analyses the processes involved in the generation of sinkholes from the study of paleokarst features exposed
in four Spanish Tertiary basins. Bedrock strata are subhorizontal evaporites, and in three of the basins they include halite
and glauberite in the subsurface. Our studies suggest that formation of dolines in these areas results from a wider range
of subsidence processes than those included in the most recently published sinkhole classifications; a new genetic classification
of sinkholes applicable to both carbonate and evaporite karst areas is thus proposed. With the exception of solution dolines,
it defines the main sinkhole types by use of two terms that refer to the material affected by downward gravitational movements
(cover, bedrock or caprock) and the main type of process involved (collapse, suffosion or sagging). Sinkholes that result
from the combination of several subsidence processes and affect more than one type of material are described by combinations
of the different terms with the dominant material or process followed by the secondary one (e.g. bedrock sagging and collapse
sinkhole). The mechanism of collapse includes any brittle gravitational deformation of cover and bedrock material, such as
upward stoping of cavities by roof failure, development of well-defined failure planes and rock brecciation. Suffosion is
the downward migration of cover deposits through dissolutional conduits accompanied with ductile settling. Sagging is the
ductile flexure of sediments caused by differential corrosional lowering of the rockhead or interstratal karstification of
the soluble bedrock. The paleokarsts we analysed suggest that the sagging mechanism (not included in previous genetic classifications)
plays an important role in the generation of sinkholes in evaporites. Moreover, collapse processes are more significant in
extent and rate in areas underlain by evaporites than in carbonate karst, primarily due to the greater solubility of the evaporites
and the lower mechanical strength and ductile rheology of gypsum and salt rocks. |
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| Keywords: | Sinkholes Sinkhole classification Paleokarst Subsidence mechanisms Evaporite karst |
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