The origin of large gypsum crystals in the Geode of Pulpí (Almería, Spain)
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Mostrar el registro completo del ítemEditorial
Geological Society of America
Fecha
2019-10-15Referencia bibliográfica
Canals, A., Van Driessche, A.E.S., Palero, F., and García-Ruiz, J.M., 2019, The origin of large gypsum crystals in the Geode of Pulpí (Almería, Spain): Geology, v. 47, p. 1161–1165
Patrocinador
Financial support was provided by Projects CGL2010–16882 and CGL2010–12099-E (Ministerio de Educación y Ciencia [MEC]) and CGL2016–78971-P (MEC).Resumen
The Geode of Pulpí (Almería, Spain) is an ∼11 m3 ovoid cavity, the walls of which are covered
with meter-sized idiomorphic and highly transparent gypsum (CaSO4•2H2O) crystals.
We performed a thorough study based on field work, and petrographic and geochemical
data collection, which aimed to reconstruct the geological history leading to the formation of
this geode. The geode is hosted in mineralized Triassic carbonate rocks with a discontinuous
mineral sequence from iron-carbonates and barite to celestine and finally gypsum (microcrystalline
and selenite). Data from fluid inclusions show that barite precipitated above 100 °C,
celestine at ∼70 °C, and gypsum below 25 °C. All δ34S sulfate phases fall between Triassic
and Tertiary evaporite values. Barite and gypsum, either microcrystalline or large selenite
crystals, show variable δ34S and δ18O compositions, whereas celestine and centimetric selenite
gypsum have homogeneous values. We propose that the growth of the large selenite crystals
in the Geode of Pulpí was the result of a self-feeding mechanism consisting of isovolumetric
anhydrite replacement by gypsum at a temperature of 20 ± 5 °C, episodically contributed
by a ripening process enhanced by temperature oscillations due to climatic change.