Dedolomitization and other diagenesis in the backreef setting of the Permian Reef Complex in Dark Canyon, New Mexico

The presence of dedolomite has only been noted in the backreef setting of the Permian Reef Complex in one previous study. This study closely examines dedolomite in the Tansill Formation in Dark Canyon, New Mexico petrographically, elementally, and isotopically along with other diagenetic cements and replacement phases found in this environment. The focus of this project was to petrographically examine the diagenetic events in the near backreef facies (the Tansill and Yates Formations) of the Permian Reef Complex in research cores from Dark Canyon in order to better understand how dedolomitization fits into the paragenetic sequence and its implications for the diagenetic history of the reef complex. This, coupled with elemental and isotopic analyses, as well as data from previous studies, helped to gain insight into the diagenetic environments in which these events took place.;Aragonite and early calcite cements, evaporite precipitation/growth, and early dolomitization occurred at the surface during deposition of the reef and backreef facies. The higher iron content (2674.35 ppm) and finely-crystalline nature of the early stage dolomite relative to the later dolomite indicate that it is a protodolomite that formed on the surface. Later dolomitization was due to dense brines percolating through the subsurface via fractures and pore spaces. This later dolomite could have occurred during burial as opposed to in a marine setting judging by their more euhedral and clearer crystalline character based on observations from previous studies. Evaporite dissolution coupled with calcium-rich fluids were probably responsible for dedolomitization as well as the late, coarsely crystalline calcite precipitation. The dedolomite was likely a direct replacement of the euhedral dolomite with calcite, which still retains the original dolomitic rhomb morphology. Isotopic values for the dedolomite range from -5.07‰ to -4.03‰ delta18 O and 0.61‰ to 2.14‰ delta13C (VPDB). These values differ from the bulk of previously analyzed calcite (which ranges from about -20‰ to -4‰ delta18O and -14‰ to 2‰ delta13C (VPDB)) and the dolomite both from this study and previous analyses (-3‰ to 6‰ 18O and -2‰ to 7‰ delta13C (VPDB)). These values correspond with fracture related dolomite from previous studies.