Easily altered minerals and reequilibrated fluid inclusions provide extensive records of fluid and thermal history: gypsum pseudomorphs of the Tera Group, Tithonian-Berriasian, Cameros Basin

Abstract

This study reports a complex fluid and thermal history using petrography, electron microprobe, isotopic analysis and fluid inclusions in replacement minerals within gypsum pseudomorphs in Tithonian-Berriasian lacustrine deposits in Northern Spain. Limestones and dolostones, formed in the alkaline lakes, contain lenticularly shaped gypsum pseudomorphs, considered to form in an evaporative lake. The gypsum was replaced by quartz and non-ferroan calcite (Ca-2), which partially replaces the quartz. Quartz contains solid inclusions of a preexisting non-ferroan calcite (Ca-1), anhydrite and celestine.High homogenization temperatures (T h) values and inconsistent thermometric behaviour within secondary fluid inclusion assemblages in quartz (147–351°C) and calcite (108–352°C) indicate high temperatures after precipitation and entrapment of lower temperature FIAs. Th are in the same range as other reequilibrated fluid inclusions from quartz veins in the same area that are related to Cretaceous hydrothermalism.Gypsum was replaced by anhydrite, likely during early burial. Later, anhydrite was partially replaced by Ca-1 associated with intermediate burial temperatures. Afterward, both anhydrite and Ca-1 were partially replaced by quartz and this by Ca-2. All were affected during higher temperature hydrothermalism and a CO2-H2O fluid. Progressive heating and hydrothermal pulses, involving a CO2-H2O fluid, produce the reequilibration of the FIAs, which was followed by uplift and cooling.

Pseudomorphic Replacement of Mg–Ca Carbonates after Gypsum and Anhydrite

“…This is commonly referred to as mineral pseudomorphism. Under certain conditions, mineral pseudomorphs can even record some crystallographic, chemical, or even isotopic information from the parent phases. − Moreover, the composition of the fluids that promote mineral replacement is occasionally recorded in the pseudomorphs, providing interesting information about the replacement environment. , Therefore, the investigation of the interplay between the kinetics of dissolution–crystallization reactions and the composition of fluids, parent phases, and pseudomorphs is fundamental to gain a better understanding of geological processes such as diagenesis, metamorphism, and formation of sedimentary and secondary minerals during weathering.…”

European Current Research on Fluid Inclusions — ECROFI XXI Leoben (Austria)

“…The influence of diagenetic processes on fluid inclusion formation in Tithonian-Berriasian lacustrine deposits in Northern Spain is studied by Laura Gonzales Corazon et al [9]. Gabriela Kiss et al [10] investigated epigenetic processes in Jurassic pillow basalts.…”