Dennis W. Powers

Discovery of abundant cellulose microfibers encased in 250 Ma Permian halite: a macromolecular target in the search for life on other planets.

In this study, we utilized transmission electron microscopy to examine the contents of fluid inclusions in halite (NaCl) and solid halite crystals collected 650 m below the surface from the Late Permian Salado Formation in southeastern New Mexico (USA). The halite has been isolated from contaminating groundwater since deposition approximately 250 Ma ago. We show that abundant cellulose microfibers are present in the halite and appear remarkably intact. The cellulose is in the form of 5 nm microfibers as well as composite ropes and mats, and was identified by resistance to 0.5 N NaOH treatment and susceptibility to cellulase enzyme treatment. These cellulose microfibers represent the oldest native biological macromolecules to have been directly isolated, examined biochemically, and visualized (without growth or replication) to date. This discovery points to cellulose as an ideal macromolecular target in the search for life on other planets in our Solar System.

The Salt That Wasn't There: Mudflat Facies Equivalents to Halite of the Permian Rustler Formation, Southeastern New Mexico

Four halite beds of the Permian Rustler Formation in southeastern New Mexico thin dramatically over short lateral distances to correlative clastic (mudstone) beds. The mudstones have long been considered residues after post-burial dissolution (subrosion) of halite, assumed to have been deposited continuously across the area. Hydraulic properties of the Culebra Dolomite Member have often been related to Rustler subrosion. In cores and three shafts at the Waste Isolation Pilot Plant (WIPP), however, these mudstones display flat bedding, graded bedding, cross-bedding, erosional contacts, and channels filled with intraformational conglomerates. Cutans indicate early stages of soil development during subaerial exposure. Smeared intraclasts developed locally as halite was removed syndepositionally during subaerial exposure. We interpret these beds as facies formed in salt-pan or hypersaline-lagoon, transitional, and mudflat environments. Halite is distributed approximately as it was deposited. Breccia in limited areas along one halite margin indicates post-burial dissolution, and these breccias are key to identifying areas of subrosion. A depositional model accounts for observed sedimentary features of Rustler mudstones. Marked facies and thickness changes are consistent with influence by subsidence boundaries, as found in some modern continental evaporites. A subrosion model accounts for limited brecciated zones along (depositional) halite margins, but bedding observed in the mudstones would not survive 90% reduction in rock volume. Depositional margins for these halite beds will be useful in reconstructing detailed subsidence history of the Late Permian in the northern Delaware Basin. It also no longer is tenable to attribute large variations in Culebra transmissivity to Rustler subrosion.

Depth indicators in Permian Basin evaporites

Abstract The Permian Basin of West Texas and New Mexico contains one of the worlds best-preserved and most extensively studied evaporite basin-to-platform sequences. From analysis of fabrics and small-scale cycle patterns, reconstruction of the position of these elements in the basin-filling sequence and comparison to laboratory-grown and modern evaporite fabrics, we created a table of fabrics that serve as water-depth indicators. Evaporites formed in deeper water (more than a few to hundreds of metres) in both halite- and gypsum-precipitating settings in the Permian Basin are characterized by cumulate fabrics. Cumulates are fine crystals or rafts of fine crystals formed at the air – brine interface that fall though the water body and accumulate on the basin floor with fine lamination, draping relationships, dark colours and minimal early diagenesis. Intervals of coarser crystals precipitated on the basin floor are interpreted as evidence for episodic transport of saturated surface water to the basin floor during perturbation of stratified conditions. Shallow water evaporites in the Permian Basin are dominated by bottom-growth fabrics such as halite chevrons and near-vertically oriented gypsum crystals. Bands of fluid and other inclusions record high frequency changes in depositional rate. Truncated crystals document flooding by undersaturated fresh or marine water under shallow conditions where mixing was adequate to cause undersaturated low-density water to contact the basin floor. Formation of base-of-cycle insoluble residues is a strong indicator of shallow water during the flooding event that initiated each sedimentary cycle. In the Permian Basin, exposure is documented by formation of synsedimentary evaporite karst pits and pipes, truncation, dissolution and recrystallization of earlier fabrics, and precipitation of cements. Red siliciclastic mudstones are associated with the late stages of depositional cycles when the surface was subaerially exposed. Repetition of alternately exposed and saline water table conditions created an array of distinctive fabrics including chaotic mudstone–salt mixtures, karst fills, replacement and recrystallization fabrics, and cracks and saltpolygons.

Synsedimentary Dissolution Pits in Halite of the Permian Salado Formation, Southeastern, New Mexico

ABSTRACT Mining operations in the Permian Salado Formation for the Waste Isolation Pilot Plant (WIPP) reveal filled pits in halite beds which are interpreted as synsedimentary dissolution features. The pits range from a few centimeters to as much as 1 m wide and 1 m deep, and they clearly truncate thin, underlying beds. Halite hopper crystals and possible chevron halite structures occurring in the pits and continuous, undeformed bedding in overlying units demonstrate that the pits formed and filled before deposition of the overlying unit. Pseudomorphs of halite after gypsum swallow-tail crystals are part of the evidence that the dissolution pits formed in shallow water.

Predicting fractured zones in the culebra dolomite.

Fracturing in the Culebra Dolomite Member of the Permian Rustler Formation exhibits a high degree of spatial variability in the vicinity of the Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico. The WIPP is the U.S. Department of Energys deep geological repository for transuranic and mixed wastes resulting from the nations defense programs. The WIPP repository is located 655 m below ground surface in bedded halite of the Permian Salado Formation, which underlies the Rustler and Culebra. Culebra transmissivities (Ts) in the vicinity of the WIPP vary over six orders of magnitude, with higher Ts (log 10 T (m 2 /s) > -5,4) reflecting zones of well-interconnected fractures. We develop, test, and refine a conceptual model for predicting fracture zones within the Culebra. We define three regional-scale controls on Culebra fracturing, including the dissolution of salt from below the Culebra, the presence of halite above and below the Culebra, and overburden thickness. We also identify two local-scale controls on Culebra fracture zones including fracture-filling cements and localized deformation due to ductile flow of the mudstone that underlies the Culebra. The spatial distribution of the regional-scale controls is easily predicted. However, the influence of local controls can only be uniquely identified in hydraulic test data. A drilling program initiated in 2003 tests aspects of this conceptual model and leads to minor revisions of our conceptual understanding of the geologic controls on fracturing in the Culebra.

Evaluation of halite dissolution at a radioactive waste disposal site, Andrews County, Texas

Waste Control Specialists (WCS) has been granted permits to dispose of radioactive waste at their surface facility in western Andrews County, Texas, U.S.A. The facility is located over Permian-age, halite-bearing formations, and the possibility of dissolution and its effects on the long-term performance of the disposal site must be considered. We compare data from the WCS site and vicinity to three conceptual hydrologic models of dissolution processes (shallow, deep, and stratabound). Geophysical logs yield stratigraphic and lithofacies data from the underlying halite-bearing units, the Permian Rustler and Salado Formations. The halite units are continuous, and thickness and lithofacies vary by depositional process, with no discernible postdepositional dissolution. Modest structural trends in these units differ from local changes in evaporite thickness. Therefore, deformation is not related to thickness differences. Local thickness changes in the middle of the Salado Formation indicate depositional variations. Core obtained from upper evaporite-bearing formations at the WCS site show normal depositional features and no brecciation that would be associated with postdepositional dissolution. Deeply buried bedded halite behaves as a ductile material, and the effective stress is close to zero, so that the pressure in pore fluids approaches lithostatic. Hydraulic gradients are outward from halite toward overlying and underlying rocks, eliminating access for low-salinity fluids. Formation fluids at depth are commonly saline and slow moving, further limiting the dissolution process. The hydrologic systems at the site limit the potential for future dissolution.

Synsedimentary dissolution pipes and the isolation of ancient bacteria and cellulose

Coarse, clear halite from synsedimentary dissolution pipes in the Permian Salado Formation in southeastern New Mexico (USA) yielded viable halotolerant bacteria and well-preserved cellulose believed to be Permian in age. Here, we show that geologic and hydrologic conditions have isolated these rocks since Permian time. Pipes were dissolved, most likely along cracks (created by thermal contraction or desiccation) and the boundaries of salt polygons (saucers), on exposed Salado Formation salt-pan surfaces down to the level of the water (brine) table. Macropores developed at the brine level in some horizons. As the water level rose, coarse halite cemented the open space. Fluid inclusions (millimeter-scale) trapped bacteria, which were probably in a spore state, as well as cellulose. Inclusion water from pipes in some cycles may have isotopic values reflecting Permian meteoric water, while other cycles may show evaporated Permian seawater. Exposure surfaces are more prominent in the upper part of Salado Formation depositional cycles due to basin desiccation, as indicated by cracks and dish-shaped laminae. Clays were concentrated on many exposure surfaces by floods, wind, and dissolution. Dissolution pipes formed from these surfaces, and a synsedimentary age is confirmed by undisturbed overlying halite beds. Salado Formation halite has very low permeability (∼10 −22 m 2 ), effectively preventing significant fluid flow and passage of fluids through the formation, either to recrystallize salt or to introduce modern bacteria. Stratigraphic relationships, halite textures, fluid inclusion chemistry, and hydraulic properties are all consistent with a synsedimentary origin of the dissolution pipes, their crystals, and the bacteria and cellulose recovered from the Salado Formation.

The Salt that Wasn't there: Mudflat Facies Equivalents to Halite of the Permian Rustler Formation, Southeastern New Mexico: CURRENT RIPPLES

ABSTRACT Four halite beds of the Permian Rustler Formation in southeastern New Mexico thin dramatically over short lateral distances to correlative clastic (mudstone) beds. The mudstones have long been considered residues after post-burial dissolution (subrosion) of halite, assumed to have been deposited continuously across the area. Hydraulic properties of the Culebra Dolomite Member have often been related to Rustler subrosion. In cores and three shafts at the Waste Isolation Pilot Plant (WIPP), however, these mudstones display flat bedding, graded bedding, cross-bedding, erosional contacts, and channels filled with intraformational conglomerates. Cutans indicate early stages of soil development during subaerial exposure. Smeared intraclasts developed locally as halite was removed syndepositionally during subaerial exposure. We interpret these beds as facies formed in salt-pan or hypersaline-lagoon, transitional, and mudflat environments. Halite is distributed approximately as it was deposited. Breccia in limited areas along one halite margin indicates post-burial dissolution, and these breccias are key to identifying areas of subrosion. A depositional model accounts for observed sedimentary features of Rustler mudstones. Marked facies and thickness changes are consistent with influence by subsidence boundaries, as found in some modern continental evaporites. A subrosion model accounts for limited brecciated zones along (depositional) halite margins, but bedding observed in the mudstones would not survive 90% reduction in rock volume. Depositional margins for these halite beds will be useful in reconstructing detailed subsidence history of the Late Permian in the northern Delaware Basin. It also no longer is tenable to attribute large variations in Culebra transmissivity to Rustler subrosion.