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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 56 (1972)

Issue: 3. (March)

First Page: 434

Last Page: 453

Title: Sedimentology and Dolomitization of Muschelkalk Carbonates (Triassic), Iberian Range, Spain

Author(s): Tom Freeman (2)


Triassic rocks of the Iberian Range consist of a succession of continental sandstones (Buntsandstein), peritidal carbonates and shales (Muschelkalk), and continental claystones and evaporites (Keuper). This "Germanic" platform facies closely resembles equivalent rocks in the Balearic Islands; consequently, any hinge line separating platform from geosynclinal facies must lie an undetermined distance southeast of the Balearics.

Dolostone, which comprises 75 percent of Muschelkalk carbonates, bears no relation to sedimentary facies; to the contrary, it is demonstrably joint controlled. This fact, together with the near absence of "dedolomite," indicates a late and sustained magnesium/calcium ratio in excess of that expected from an evaporite-bearing assemblage.

Water samples from Keuper "salinas" (salt-producing evaporating pans) show that meteoric water descending through the Keuper evolves into a brine with Mg:Ca ratios locally 4:1, in spite of the abundant gypsum and anhydrite. X-ray analysis suggests chlorite as a source of the magnesium, the solubility of which probably reflects diagenetic fixing in the Keuper evaporite basin. The composition of Keuper water, aided prior to unloading by geothermal gradient, is thought to be responsible for Muschelkalk dolomitization.

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