New Mexico Geological Society Annual Spring Meeting — Abstracts

Whole rock isotope analysis of carbonate samples from the upper 30 m of Paradise Formation and the lower 5 m of the overlying Horquilla Limestone in Chaney Canyon resulted in average isotopic values of 2 δ¹³C and -6 δ¹⁸O. These values on the average are isotopically lighter than those published for age equivalent strata. A plot of oxygen vs. carbon shows a distinctive linear trend toward lighter isotopic values (Fig. 1).

By plotting the isotopic data in correct stratigraphic order several distinctive patterns come out (Fig. 2). Carbon values vary by 2 per mil throughout the section in a random pattern. Oxygen values, however, show considerable variation when plotted in stratigraphic order. This variation is shown by the distinctive patterns that sweep from a more marine value of -4 δ¹⁸O to a much lighter diagenetic value around -8 δ¹⁸O. This sweeping pattern is observed twice in the oxygen isotope record from Chaney Canyon. Note that there does not appear to be any significant change in isotope values across the Mississippian/Pennsylvanian boundary, a recognized regional disconformity.

The variations observed in the isotopic record from this stratigraphic section can be attributed to several geologkal processes. Such processes include diagenetic alteration of the carbonates by meteoric waters, or burial diagenesis.