Hypogene calcitization: Evaporite diagenesis in the western Delaware Basin

Abstract

Evaporite calcitization within the Castile Formation ofthe Delaware Basin is more widespread and diverse than originally recognized. Coupled field and GIS studies have identified more than 1000 individual occurrences of calcitization within the Castile Formation outcrop area, which includes both calcitized masses (limestone buttes) and laterally extensive calcitized horizons (limestone sheets). Both limestone buttes and sheets commonly contain a central brecciated zone that we attribute to hypogene dissolution. Lithologic fabric of calcitized zones ranges from little alteration of original varved laminae to fabrics showing extensive laminae distortion as well as extensive vuggy and open cavernous porosity. Calcitization is most abundant in the western portion of the Castile outcrop region where surface denudation has been greatest. Calcitization often forms linear trends, indicating fluid migration along fractures, but also occurs as dense clusters indicating focused, ascending, hydrocarbon-rich fluids. Native sulfur, secondary tabular gypsum (i.e. selenite) and hypogene caves are commonly associated with clusters of calcitization. This assemblage suggests that calcium sulfate diagenesis within the Castile Formation is dominated by hypogene speleogenesis.

Unconfined hypogene evaporite karst: West Texas and southeastern New Mexico, USA

“…3E), as well as extensive native sulfur deposits that were economically mined throughout the twentieth century (Lee & Williams, 2000). Hill (1996) and Stafford et al (2008c) have documented active degassing still occurring at several "castile buttes" within the Gypsum Plain, indicating that these processes are still active in the region. Evaporite calcitization occurs commonly near the contact between the Bell Canyon and Castile formations, but is most often observed and associated with intrastratal brecciation (Wallace & Crawford, 1992) where these high permeability structures provided preferential flow paths for upward migration of light hydrocarbons.…”

“…Evaporite calcitization is common throughout the Gypsum Plain where light hydrocarbons have migrated updip through the Bell Canyon and Castile formations, fueling sulfate reduction (Kirkland & Evans, 1976). Although it is inconclusive at this point as to whether calcitization was dominantly produced through bacterial sulfate reduction or thermochemical sulfate reduction (Stafford et al, 2008c), the resulting manifestations include calcitized masses, often referred to as "castile buttes and masses" (Fig. 3E), as well as extensive native sulfur deposits that were economically mined throughout the twentieth century (Lee & Williams, 2000).…”

“…3D) both as vertically-extensive breccia pipes and laterally-extensive blanket breccias (Anderson et al, 1978;Stafford et al, 2008c). Intrastratal brecciation results from solutionally-aggressive fluids delivered either vertically or laterally into preferentially soluble zones such that the resulting void structure can no longer support overlying strata.…”

“…Evaporite calcitization occurs commonly near the contact between the Bell Canyon and Castile formations, but is most often observed and associated with intrastratal brecciation (Wallace & Crawford, 1992) where these high permeability structures provided preferential flow paths for upward migration of light hydrocarbons. In many instances, calcitized masses that have been exposed at the land surface through surface denudation continue to expel hydrocarbon-rich gases, based on discernable odor and the presence of powdery, secondary gypsum deposits at degassing locations (Stafford et al, 2008c).…”

Evaporite karst geohazards in the Delaware Basin, Texas: review of traditional karst studies coupled with geophysical and remote sensing characterization

“…Ascending light hydrocarbons from deep sources have migrated upwards through the Castile Formation providing the source material for sulfate reduction (Lee & Williams, 2000); however, the exact mechanism of sulfate reduction is still debated in the region as being either bacterial sulfate reduction (BSR) or thermal sulfate reduction (TSR) (Stafford et al, 2008d). As a byproduct of sulfate reduction, evaporite calcitization is widespread but most frequently associated with breccias.…”