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| Titel |
Isostasy-controlled thinning-upward cycles in the Mediterranean?; a comparison with the Zechstein salt giant |
| VerfasserIn |
Frank J. G. Van den Belt, Poppe L. de Boer |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094480
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| Publikation (Nr.) |
 EGU/EGU2014-9890.pdf |
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| Zusammenfassung |
| The desiccated deep-basin model, originally developed for the Mediterranean salt giant,
deviated significantly from existing models and it has never been satisfactorily translated into
a general concept. With time, however, Mediterranean models evolved towards moderate
basin depths and the view that deposition took place in a flooded basin has gained
reputation. These new insights have bridged the gap with general evaporite models and
open possibilities of integrating concepts developed for other salt giants into the
model.
Recent modelling work (Van den Belt & De Boer, 2012) based on the Zechstein salt basin
has shown that the thickness and composition of subsequent evaporite cycles can be
explained by a model that involves a repetition of a three-stage process of 1) progressive
narrowing of an ocean corridor in response to sulphate-platform progradation, resulting in 2)
brine concentration and rapid infilling of the basin with halite and potash salts, the
load of which causes 3) isostatic creation of accommodation space for the next
cycle.
Isostatic theory predicts that each cycle has approximately half the thickness of the
previous one, e.g. 1.0 > 0.50 > 0.25 > 0.125 followed by a number of (coalesced) smaller
cycles with a joint thickness of 0.125. The sequence in the basin centre then adds up to 2,
which is two times the original basin depth. For the Zechstein case actual cycle thickness well
matches these predicted values with cycle thicknesses of about 1.06 > 0.54 > 0.18 > 0.10
and 0.12.
The cycle build-up of the Mediterranean salt giant is less well known, because of limited
deep drilling. There are at least two cycles, a thin upper overlying a thick lower unit, but
comparison of Zechstein patterns with Mediterranean sections has shown that more cycles
may be present. Typical cycle boundaries include K/Mg-salt interbeds in halite units, and
halite interbeds in sulphate units. Interestingly, analysis has shown that such indicators in
Mediterranean sections indicate that cycles may indeed be stacked according to the 50%
thickness rule. Examples are the K-salt halfway up the Sicilian section and the regular halite
interbeds in the Upper Evaporite of the Western Mediterranean. In addition, the
Lago Mare clays that define the top of the Mediterranean section are reminiscent
of the Zechstein claystone cap. If the proposed mechanism indeed applies to the
Mediterranean it would point at an initial basin depth of about 600-700 for the Western
Mediterranean.
Van den Belt & De Boer (2012) Utrecht Studies in Earth Sciences, v. 21, p. 59-65. |
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