ABSTRACT
Tepee-associated sheet-crack structures and carbonate cements that largely fill them are developed in the carbonate facies of the back-reef Capitan Reef complex, Guadalupe Mountains, New Mexico. Sheet cracks, their cements, and associated teepee structures were studied to better understand the timing, nature of precipitating waters, and environment of deposition of the sheet-crack cements. Sheet-crack cements were field classified into 8 morphologic fabrics.
Contrary to previous work, this study found that sheet-crack fillings developed symmetrically from roofs and floors. Sheet-crack cements, the sheet cracks, and associated teepee structures developed repeatedly and episodically. Most are erosionally truncated and cross-cut by overlying surfaces. Most cements show isopachous growth indicative of precipitation under phreatic conditions. Some pendant cements suggest precipitation in a vadose environment, indicating occasional exposure of the outer-shelf and shelf-crest facies.
Calcite-cement fabrics (39 samples) were analyzed for Sr, Mg, Fe, δ13C, and δ18O. Chemical compositions range from: Sr = 116 to 5,244 ppm; Mg = 215 to 9,188 ppm; Fe = 7 to 758 ppm; δ18O = -5.6 to + 0.4‰; and δ13C = +4.9 to 7.5‰ (PDB). Sr exhibits distinct groupings of more than 2,000 ppm and fewer than 500 ppm. Samples with high Sr are associated with lower δ13C, δ18O, and Mg compositions. The converse is true for the low Sr values.
Isotopically heavier samples are interpreted as precipitated from restricted marine waters. Isotopically lighter samples are interpreted as precipitated from mixed meteoric and marine waters. The meteoric water is inferred to have originated from shelfward, terrestrial source areas. It is hypothesized that these waters traveled through an aquifer system and percolated upward as springs to the sheet-crack area.
