The island of Fuerteventura offers a unique possibility for studying mineralogical, chemical, and textural changes in Holocene and Pleistocene skeletal carbonate sands which, due to eustatic sea level changes, have been exposed to one or more diagenetic environments. An example is the diagenetic development of a 30,000-year old dolomitized calcarenite from the Jandia Peninsula.

Stage 1 (intertidal or beachrock stage):
Precipitation of magnesian calcite leads to the formation of beachrock in the intertidal zone.

Stage 2 (supratidal marine evaporitic stage):
Lowering of the sea level (about 2-3 m compared with stage 1) has exposed the beachrock to the supratidal zone which, however, still remains under the influence of the sea and of the evaporating seawater. After the retreat of heavy seas, seawater accumulated on the surface or within the pores of the beachrock evaporates and percolates through the calcarenite. The high Mg/Ca ratio (> 15) of the percolating brines causes dolomitization of the magnesian calcite cement as well as of allochems consisting of the same mineral (red algae, echinoderms).

Stage 3 (supratidal meteoric stage):
When, by further lowering of the sea level, the partly dolomitized beachrock is exposed to meteoric (freshwater) conditions, the supratidal meteoric stage is achieved. Aragonite of the allochems is converted to calcite by wet transformation and calcite is precipitated in the interstitial spaces of the calcarenite as second-generation cement (cement B).

Other interesting examples are calcarenites (eolianites) which originally were exposed to the meteoric diagenetic environment and are now in the intertidal zone; a first-generation cement consisting of calcite is followed by a second-generation cement consisting of magnesian calcite!

Calcarenites overlain by basaltic lavas permit the study of hydrothermal alteration of carbonate rocks.

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