R. B. Halley C.E. Barker 1988 <p>Vadose cements in the Late Pleistocene Miami Limestone contain regions with two-phase aqueous fluid inclusions that have consistent vapor to liquid (V-L) ratios. When heated, these seemingly primary inclusions homogenize to a liquid phase in a range between 75°C and 130°C (mean = 100°<i>C</i>) and have final melting temperatures between −0.3° and 0.0°C. The original distribution of<span>&nbsp;</span><i>T</i>_<i>h</i><span>&nbsp;</span>was broadened during measurements because of fluid inclusion reequilibration. The narrow range of<span>&nbsp;</span><i>T</i>_<i>h</i><span>&nbsp;</span>in these fluid inclusions suggest unusually consistent V-L ratios. They occur with small, obscure, single phase liquid-filled inclusions, which infer a low temperature origin (less than 60°C), and contradict the higher temperature origin implied by the two phase inclusions.</p><p>The diagenetic environment producing these seemingly primary fluid inclusions can be inferred from the origin of the host calcite enclosing them. The δ¹⁸O composition of these cements (−4 to−5.5%., PDB) and the fresh water in the fluid inclusions are consistent with precipitation from low-temperature meteoric water. The carbon-isotope composition of the vadose cements that contain only rare two-phase fluid inclusions are comparable to the host rock matrix (δ¹³C between 0 and +4%., PDB). Cements that contain common two-phase fluid-inclusions have a distinctly lighter carbon isotopic composition of −3 to −5%.. The carbon isotope composition of cements that contain common two-phase inclusions are about 6%. lighter than those of other vadose cements; models of early meteoric diagenesis indicate that this is the result of precipitation from water that has been influenced by soil gas CO₂.</p><p>Our hypothesis is that the primary fluid inclusions, those with consistent V-L ratios and the single-phase liquid inclusions, form at near-surface temperature (25°C) and pressure when consistent proportions of soil gas and meteoric water percolating through the vadose zone are trapped within elongate vacuoles.</p><p>This study corroborates that<span>&nbsp;</span><i>T</i>_<i>h</i><span>&nbsp;</span>measurements on two phase inclusions in vadose cements can be misleading evidence of thermal diagenesis, even if the measurements are well grouped.</p> application/pdf 10.1016/0016-7037(88)90256-6 en Elsevier Fluid inclusions in vadose cement with consistent vapor to liquid ratios, Pleistocene Miami Limestone, southeastern Florida article