Tuesday, April 7, 2015

Highlights—Concretions: What goes down must come up!?

Septarian concretions provide potential geochemical archives of diagenetic evolution. Many previous studies have employed traditional oxygen isotope analyses as a major guide for paragenetic interpretation. However, the oxygen isotope compositions of carbonates are controlled by both temperature and fluid compositions, generating interpretive ambiguity, particularly in diagenetic systems where these controls are difficult to constrain. Here, Loyd et al. use the clumped isotope paleothermometer, an independent temperature proxy, to better characterize paragenesis of septarian concretions from multiple localities. Although originating from different locations and depositional systems, most concretion geochemical compositions conform to a common paragenesis. Particularly intriguing are signals of late-stage spar precipitation from meteoric fluids, interpreted to occur during uplift. These findings are inconsistent with progressive cementation during burial ('on the way down'), and instead suggest that septarian concretions form over relatively long time scales.

Clumped-isotope constraintson cement paragenesis in septarian concretions by Sean J. Loyd, J.A.D Dickson, James R. Boles, and Aradhna K. Tripati

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