Use of Clumped-Isotope Thermometry To Constrain the Crystallization Temperature of Diagenetic Calcite

Abstract

We describe an approach to estimating the crystallization temperatures of diagenetic calcites using clumped-isotope thermometry, a paleothermometer based on the 13 C- 18O-bond enrichment in carbonates. Application of this thermometer to calcified gastropod shells and calcite cements in an early Eocene limestone from the Colorado Plateau reveals a record of calcite precipitation and replacement at temperatures varying from 14 to 123uC. The early Eocene host sediments were never deeply buried, but they experienced a significant thermal pulse associated with the emplacement of a late Miocene basalt flow. The combination of independent constraints on thermal history with clumped-isotope thermometry, petrographic (including cathodoluminescence) observations, and oxygen isotopic data provides an improved basis for estimation of the temperature and timing of diagenetic events and fluid sources. The petrography and calcite d 18O values, taken alone, suggest that the aragonite-tocalcite transformation of gastropod shell material occurred simultaneously with early formation of cements and lithification of the matrix in the same sample. However, addition of clumped-isotope thermometry demonstrates that this phase transformation of shell material occurred at temperatures of 94-123uC in a highly rock-buffered microenvironment (i.e., with the isotopic composition of fluid buffered by coexisting carbonate), millions of years after lithification of the matrix and formation of initial low-temperature (14-19uC) calcite cements within shell body cavities. Clumped-isotope temperatures in excess of reasonable Earth-surface conditions recorded by later-formed cements demand that cement growth occurred in association with the lava emplacement. Our results illustrate the potential for clumped-isotope thermometry to constrain conditions of diagenesis and guide interpretations that would not be possible on the basis of conventional stable-isotopic and petrographic data alone, and demonstrate how petrographic characterization of clumped-isotope thermometry samples can benefit paleoclimate studies.

Evolution of Neoproterozoic Wonoka–Shuram Anomaly-aged carbonates: Evidence from clumped isotope paleothermometry

“…The model allows for the generation of temperature-isotope trajectories for the evolution of carbonate minerals and fluids in equilibrium at variable water-rock ratios (W/R). A similar approach was used to explore clumped isotope temperature and isotope relationships of diagenetic calcites within an Eocene limestone (Huntington et al, 2011). The Neoproterozoic units explored here exhibit similar trends, with temperature and oxygen values that conform to those expected for mineral reequilibration with increased temperature at relatively low W/R (Figs.…”

“…Clumped isotope-derived temperatures can be combined with ␦ 18 O carb to uniquely determine ␦ 18 O w through application of an appropriate carbonate-water oxygen isotope fractionation factor (Kim and O'Neil, 1997;Vasconcelos et al, 2005). The tool has been used for a range of applications including the study of primary and diagenetic processes in terrestrial and marine samples of a wide range of ages (Came et al, 2007;Affek et al, 2008;Dennis and Schrag, 2010;Eagle et al, 2010Eagle et al, , 2011Eagle et al, , 2013Passey et al, 2010;Tripati et al, 2010Tripati et al, , 2014Bristow et al, 2011;Ferry et al, 2011;Finnegan et al, 2011;Huntington et al, 2011;Keating-Bitonti et al, 2011;Loyd et al, 2012aLoyd et al, , 2013aLoyd et al, , 2014Passey and Henkes, 2012;Swanson et al, 2012;Dale et al, 2014).…”

Terrestrial cooling in Northern Europe during the Eocene–Oligocene transition

“…Second, Solent Group sediments have not been deeply buried, heated, or extensively altered, and most sediments remain unlithified (14)(15)(16)26). Although low-temperature diagenetic alteration of aragonite to secondary calcite is commonly observed in the rock record (27), all samples were analyzed by X-ray diffraction and produced patterns consistent with aragonite (28). Third, thin-section analyses of individual shells showed an outer layer with vertical crystals in all shells.…”

Extensive, uplift-related and non-fault-controlled spar precipitation in the Permian Capitan Formation

“…As demonstrated elsewhere, the clumped isotope paleothermometer provides a unique opportunity to probe pore water δ 18 O values in diagenetic systems (Huntington et al, 2011;Bristow et al, 2012;Loyd et al, 2012;Budd et al, 2013). The pore fluids responsible for the generation of the Capitan spar calcites exhibited negative values, some of which were quite depleted in 18 O (with δ 18 O fluid values down to~−10‰).…”

“…Additional information can be acquired via a simple water/rock model first introduced by Banner and Hanson (1990) and similarly utilized by Huntington et al (2011). The model is based on the following equations:…”