2026-09-24T02:18:19Zhttps://api.repository.cam.ac.uk/server/oai/requestoai:www.repository.cam.ac.uk:1810/2901362021-04-21T19:32:15Zcom_1810_195764com_1810_256064col_1810_219098
Isotope Systematics of Gypsum and its Hydration Water
10.17863/CAM.37364
Evans, Nicholas Philip
0000000298138811
Hodell, David A
0000000185371588
Triple oxygen and hydrogen isotope analysis of the structurally-bound water in gypsum can
provide a direct measure of past hydrologic variability. This thesis presents the development
of the water extraction and isotopic measurement procedures, the calculation of the gypsum-water
isotope fractionation factors, and the application of the method to constrain the palaeohydrologic
conditions in two temporally and geographically disparate sites.
Measurement of the isotopic composition of gypsum hydration water is used to examine
the hydrological changes that occurred during the Terminal Classic Drought of the Maya
lowlands (~800-1000 CE), coincident with the period when the Classic Maya Civilization
of Mesoamerica collapsed. The data provide a complete and direct archive of hydrological
conditions that have previously been limited to ice core records. Mean annual rainfall is
shown to have decreased by between 41% and 54%, with intervals of up to 70%, compared
to present-day conditions. This study has also shown for the first time that relative humidity
was 2%-7% lower during the Terminal Classic Drought compared to today.
The methodology is also applied to the massive gypsum deposits in the marginal and
deep basins of the Mediterranean to interpret the chemical evolution of parent water bodies
during the Messinian Salinity Crisis (5.97-5.3 Ma). By combining the measurement of
gypsum hydration water with other traditional (e.g. strontium) and novel (e.g. calcium
and barium) isotope tracers, the hydrological changes during the deposition of Primary
Lower Gypsum units of the Sorbas Basin in southeastern Spain, the Upper Gypsum units
of Sicily, and deep basin deposits have been constrained. The results indicate that all
deposits experienced a significant freshwater contribution to the mother fluids from which
they formed. It is proposed that obliquity-controlled sea level and eccentricity-modulated
precession, superimposed on longer-term tectonic restriction of the Mediterranean-Atlantic
exchange, together controlled the varying depositional environments during the formation
of the Messinian Salt Giant.
This thesis demonstrates that the analysis of gypsum hydration water is a powerful tool
for palaeoclimate reconstruction. The methodology can be applied to gypsum (and other
hydrated minerals) in a wide range of settings across geological space and time, providing
a rich source of information about the environmental conditions under which they formed.
University of Cambridge
2019-03-30
Thesis
Doctoral
Doctor of Philosophy (PhD)
en
This research was supported by the ERC WIHM Project #339694 to DAH.
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Climate
Gypsum hydration water
Fractionation factors
Classic Maya civilization
Maya
Terminal Classic Drought
Drought
Messinian Salinity Crisis
Triple oxygen isotopes
Stable isotopes
Isotopes
Gypsum
Calcium Sulfate
Palaeoclimate
Hydrated minerals
Evaporites