Current Research Projects
stratigraphy, diagenesis, and chemostatigraphy of UPPER ORDOVICIAN AND LOWER SILURIAN carbonates in the great basin, USA
Since 2012 my students and I have been studying the sequence stratigraphy, diagenetic history, and carbon isotope stratigraphy of Upper Ordovician and Lower Silurian carbonates exposed in Nevada and Utah. These platform carbonates were deposited during sea level fluctuations associated with the waxing and waning of glaciers on Gondwana during the Ordovician-Silurian icehouse.
Our stratigraphic and carbon isotope studies have documented a latest Ordovician (Hirnantian) depositional sequence that carries a globally-documented positive carbon isotope excursion. This basinward-thickening package of sediment is capped by a regional unconformity interpreted to represent the Hirnantian glacial maximum. Carbon isotope stratigraphy provides a means to correlate the Great Basin depositional sequences to strata exposed in the Cincinnati Arch and across the globe (Jones et al., in press at Palaeo3).
We used field observations and carbon isotope stratigraphy to test the hypothesis that an extensive terrestrial biosphere developed in the Neoproterozoic. The early greening hypothesis could potentially explain the occurence of major negative carbon isotope anomalies associated with global glaciation through incorporation of isotopically depleted remineralized terrestrial organic matter during meteoric diagenesis. However, our observations of the carbon isotope record of dolostones that underwent extensive meteoric diagenesis during the Ordovician-Silurian icehouse do not support this model (Jones et al., Geology, 2015).
We have developed a paragentic model for the Upper Ordovician Ely Springs Dolosone and Lower Silurian Laketown Dolostone (Creel and Jones, 2013; Creel et al., in preparation) based on integrated field observations, petrography, and elemental and isotopic geochemistry. We are using calcium and magnesium isotope ratios in these dolostones to further elucidate the diagenetic history of these strata and quantify alteration pathways of the carbon isotope records.
diagenetic alteration of sulfur isotope ratios in paleozoic carbonates
Carbonate-associated sulfate (CAS) is a trace constituent of many limestones and dolostones. Stratigraphic trends in sulfur isotope ratios of CAS are commonly used to elucidate operation of the ancient sulfur cycle and, in conjunction with other geochemical and geological data, make inferences about redox changes in Earth's surface envelope. We are interested in understanding the fidelity of the CAS sulfur isotope signal during diagenesis. We are currently using our basin transect of Upper Ordovician-Lower Silurian dolostones as a natural laboratory to explore CAS sulfur isotope variability in response to meteoric and burial diagenesis and early dolomitization.
geobiology of dolomite formation at Deep springs lake, ca
The occurence of fine grained dolomite ooze in the unconsolidated playa muds of Deep Springs Lake provide an opportunity to study the geochemical signatures of authigenic dolomite and the waters in which that dolomite forms. We are also investigating the microbiological context in which the sediment is forming to test new models of microbial participation in dolomite nucleation and growth. This interdisciplinary project began with the support of the Keck Geology Consortium and has involved undergraduate students from seven institutions.
Neoproterozoic-cambrian stratigraphy and chemostratigraphy of the khubsugul Basin, mongolia
In an ongoing collaboration with Francis Macdonald and his research group, my students and I are developing integrated stratigraphic and chemostratigraphic records of the Cryogenian and Early Cambrian stratigraphy of the Khubsugul Basin in northern Mongolia. These data help determine the environmental boundary conditions for early animal evolution during the Cambrian Explosion.