Sally Potter-McIntyre

Dense urban areas like Berlin face unique challenges when instituting geothermal energy, especially understanding how subsystems (e.g., transportation, people, legal framework, deep subsurface, drinking water, etc.) are linked and how the larger system is affected by changes to subsystems. The innovative approach to viewing a city as a system composed of subsystems and integrating the subsystems in a holistic energy efficiency framework is required to prevent unforeseen adverse consequences of actions such as heat pollution from thermal energy storage in deep reservoirs. The interaction between U-Bahn tubes, HT-ATES/BTES systems, groundwater flow, and the urban heat island creates a tightly coupled thermomechanical environment in which temperature, pore pressure, strain, and geochemical states evolve simultaneously and govern system efficiency and structural stability. In Berlin-Adlershof, an HT-ATES research well was completed in 2024 and drilling of the injection and production wells are slated for this year. Our new work will demonstrate the efficacy of: 1. HT-ATES in Berlin for thermal heat storage and production, 2. Using the subway system to collect heat and mitigate heat waste from the shallow subsurface heat island and heat pollution produced by HT-ATES wells. The interaction data from monitoring wells and a fiber optic experiment within the subway will provide parameters for thermomechanical models on granular scales (e.g., directly adjacent to wells, subway) and we will scale up models to interconnect ATES, subway, and groundwater, and then to district, city, and national levels. Social science and humanities data will be incorporated into the large-scale models to produce a structure for establishing UTES in other cities with unique settings in terms of geology, legal framework, drinking water sources, presence/ absence of mining, and other differences.

Iron (oxyhydr)oxide concretions are cemented mineral masses formed via authigenic cements in sedimentary rocks at any time during diagenesis (syndepositional, burial, and late-stage). These features are common in porous and permeable sandstone and even present on Mars in at least two different locations and formations. One notable study area for the spherules is within the Navajo Sandstone in the Grand Staircase Escalante National Monument (GSENM) in southern Utah. Diagenetic concretions, particularly iron (oxyhydr)oxide mineralogies, are thought to form via a two-fluid mixing model where one fluid has the reactants in solution, then another fluid meets and mixes with the reactant-bearing fluid, and the concretions precipitate. These two fluids could be a reducing fluid that mobilizes iron as Fe2+ and then mixes with an oxidizing fluid to precipitate iron oxyhydr(oxide), but an acidic fluid could mobilize iron as Fe3+ and then interact with a neutral fluid for the same result. Another proposed model for iron (oxyhydr)oxide concretions calls for calcium carbonate precursor concretions and mobilization of iron by acidic fluids. The acidic, iron-bearing fluid then dissolves the carbonate concretion, which buffers the solution enough to precipitate iron oxyhydr(oxide) in the same morphology as the original calcite concretion. Our research shows that in GSENM, iron concretions and calcite concretions are present within the same stratigraphic horizon and in close proximity. Another field observation is the presence of calcite concretions in clusters along paleo water tables, rather than dispersed in a self-organized spacing within three dimensions like the iron features. Also present within the region are concretions with manganese oxide phases and the iron concretions tend to include manganese oxide, but not calcite. Calcite concretions do commonly contain some iron (oxyhydr)oxides, particularly as rims around grains. In the Entrada Sandstone, also in southern Utah, iron concretions are precipitated from fluid brought in with an igneous intrusion that mobilized the iron within the host rock. Structures in the area acted as baffles keeping the fluid stagnant and iron (oxyhydr)oxide concretions are only present between the igneous dike and the nearest baffle. Calcite concretions in the area are dispersed throughout the host rock (both within and outside of the baffles), suggested that mineral precipitation rates control concretion formation and that iron (oxyhydr)oxide concretions need a longer period of fluid stagnation for formation than do calcite concretions. Understanding the complex formation mechanisms can help to unravel the history of diagenetic fluids of varying chemistries and therefore, the habitability of subsurface environments on both Earth and Mars.

Stratigraphic units of the Colorado Plateau comprise a remarkable Mesozoic section in Utah. Thse units are ideal for studying sandstone diagenesis where there is established basinal context of depositional facies and tectonics, as well as continuity of exposure. To untangle the complex relationships and diagenetic histories, it is crucial to understand host rock properities (porosity and permeability), authigenic mineralogies (that give clues to fluid composition), diagenetic textures, and age dating. This study is a review and synthesis of previous work that has contributed to the understanding of the diagenetic history recorded in authigenic iron oxide precipitates. We discuss cement generations and mineralogies, fluid chemistries, origins and mobilization of iron, and timing of precipitation. Spheroidal cemented mineral masses (concretions) are common within many Mesozoic units of Utah – most notably the Jurassic Navajo Sandstone.  However, formation of these concretions is still not completely understood. Spheroidal concretions are currently a “hot topic”, especially since the discovery of similar “blueberry” features on Mars with their implications for habitability, and the potential for these nodules to host biosignatures. Several models for spheroidal concretion formation are evaluated. Understanding how iron is mobilized and precipitated and how spheroidal concretions form have implications for similar geometries and mineralogies in many terrestrial regions, but will require continued integrated studies across multiple scales (see Baker and Potter-McIntyre, this session). These scales include the submicroscopic levels of understanding and detecting the potential role of microbes in mineral precipitation, to the larger scale mapping of regional diagenetic coloration and mineral patterns that could represent records of basinal fluids and the response to climate, tectonics, and regional hydrology.

Mollies Nipple—a butte located in the Grand Staircase-Escalante National Monument (GSENM)—is of special interest because of the presence of unusual alunite and jarosite cements within the caprock. These minerals precipitate in hyperacidic environments (pH1-2) and are not stable over ~pH5; yet they are abundant on Mars where they are used to interpret depositional and diagenetic environments. The caprock at Mollies Nipple is historically interpreted as Navajo Sandstone via photogeologic mapping; however, it is ~200 m above the mapped upper extent of the Navajo Sandstone in this region. The units overlying the Navajo Sandstone have complex stratigraphic relations in this region and the caprock could be the Carmel or Temple Cap Formations, or the Page Sandstone. This study aims to characterize Mollies Nipple through measured sections, mineralogical analyses, palynomorph analysis, and radiometric age dates from ash lenses present in the caprock. The results will better define the stratigraphy of Mollies Nipple and determine the regional correlation of the caprock. Ultimately, this work will contribute to the understanding of how alunite and jarosite were precipitated at Mollies Nipple; why these minerals are still present at Mollies Nipple, and potentially revise the understanding of Martian depositional environments.

Stable δ ¹³ C isotope analysis at hot and cold springs suggests that rapid degassing overprints carbon isotopic biosignatures even when microbial activity produces biogenic textures in the minerals. Mineral precipitation and potential biosignature preservation are evaluated at a cold spring system in Ten Mile Graben, Utah, USA, with scanning electron microscopy, X-ray diffraction, and stable carbon isotopes. Putative biogenic mineral habits such as aragonite microspheres and botryoids, and biologic materials (EPS and diatom tests) are abundant in modern mats, but the δ ¹³ C values are between +2‰ and +7.8‰, consistent with rapid CO ₂ degassing reported by other researchers. Multiple factors, however, influence isotopic signatures of mineral precipitates in this spring system, including rapid degassing, preferential microbial uptake of light carbon isotopes via multiple carboxylation pathways, hydrocarbon-charged fluid, and other inherited isotopic signatures in the fluid, particularly from dissolution of older limestones; therefore, it is not likely that this narrow range of isotopic ratios definitively shows an abiotic signature. A fossil vent preserves biogenic mineral habits, but not microbial body fossils. This study highlights the need for novel biosignature detection methods—and an understanding of what an abiotic signature definitively is—as we prepare for sample caching of carbonate rocks by the Mars2020 mission and future sample return.

Clay mineralogy and diagenesis affect the reservoir quality of the Neogene Surma Group in the Hatiya trough of Bengal Basin, Bangladesh. X-ray diffraction and scanning electron microscopic analyses of diagenetic clay minerals from Shahbazpur#2 well reveal that on average illite is the dominant clay mineral (50%), followed by chlorite (24%), kaolinite (23%) and smectite (2.50%). The absence of smectite at Core-2 (3259.80 m to 3269 m) results from the total transformation of smectite to illite owing to burial depth and high K–feldspar. The diagenetic changes are a result of chemical processes such as cementation, chlorite authigenesis, dissolution, alteration and replacement that have significantly affected the reservoir properties. Cementation plays an important role in reducing reservoir properties with pore and fracture filling cement. The relative percentage of illite and smectite minerals (>90% illite in I/S mixed layer) and Kübler index value (0.34° to 0.76° Δ2θ) indicate a diagenetic zone with subsurface temperatures of 120–180 °C in the studied samples. The temperature range determined using clay percentages and the Kübler index as a geothermometer is supported by observed diagenetic features such as quartz overgrowths, smectite to illite transformations and chlorite coatings. The diagenetic features cause variable reservoir porosity and permeability that are critical in planning exploration and development programs of this field or analog fields across the Bengal Basin.

Directly west of the San Rafael Swell on the Colorado Plateau in the western U.S., the Jurassic Entrada Sandstone is intruded by a ~2 km long mafic dike. The dike is Miocene; however, the area is also crosscut by Laramide (~50Ma) clusters of deformation bands that are up 500 m long and up to ~3 m wide. The mafic intrusions infused the area with fluids that bleached the red sandstone directly surrounding the dike. On one side of the dike, the bleached area terminates at an adjacent deformation band set ~475 m south of the dike. Field observations suggest that the dike acted as a baffle preventing fluids from migrating further into the sandstone. Spheroidal calcite and iron (oxyhydr)oxide concretions are present in the bleached host rock, although calcite concretions (1-3 cm diameter) are present throughout the area on both sides of the deformation bands and in both red and white host rock. Iron (oxyhydr)oxide concretions (1-5 cm diameter) are limited to the uppermost bleached section between the dike and the deformation band set. Some iron concretions have solid interiors, and some have well-cemented rinds with interiors depleted of cement. Additionally, some iron concretions are nucleated on individual deformation bands that are ~2 mm wide and iron (oxyhydr)oxide cemented joint faces are also present. Thermochemical modeling shows the infiltrating Miocene fluids were CO2-bearing, but near neutral pH. The restricted location of the iron (oxyhydr)oxide concretions and relation to the calcite concretions suggest that stagnation of fluid is needed for spheroidal iron oxyhydroxide concretion formation. Calcite concretion nucleation and growth may be quicker resulting in more widespread occurrences, and/or may have preceded the Miocene fluids that infiltrated the unit. The evidence presented here shows that recently proposed models calling for calcite concretion precursors and acidic fluids for iron (oxyhydr)oxide concretion formation may not be correct.

Members of the alunite group are precipitated at low pH (<1 to ~4) in oxidizing environments, are unstable in circumneutral conditions, and are widespread on Mars. At Mollies Nipple in Kane County, Utah, USA, jarosite and alunite are abundant as diagenetic cements in Jurassic sandstones. This research characterizes the jarosite and alunite cements with the goal of determining their origin, and tests the hypothesis that jarosite and alunite may be more stable than the current understanding indicates is possible. Previous studies have placed the jarosite- and alunite-bearing caprock at Mollies Nipple in the Navajo Sandstone, but the presence of water-lain deposits, volcanic ash, volcanic clasts, and peloids show that it is one of the overlying Middle Jurassic units that records sea level transgressions and regressions. A paragenetic timing, established from petrographic methods, shows that much of the cement was precipitated early in a marginal marine to coastal dune depositional environment with a fluctuating groundwater table that drove ferrolysis and evolved the groundwater to a low pH. Microbial interaction was likely a large contributor to the evolution of this acidity. Jarosite and alunite are clearly more stable in natural environments than is predicted by laboratory experiments, and therefore, the Martian environments that have been interpreted as largely acidic and/or dry over geologic time may have been more habitable than previously thought.

On Earth, microorganisms commonly enhance mineral precipitation and mediate mineralogical and chemical compositions of resulting deposits, particularly at spring systems. However, preservation of any type of microbial fossil or chemical or textural biosignature depends on the degree of alteration during diagenesis and factors such as exposure to diagenetic fluids. Little is known about the transformation of biosignatures during diagenesis over geologic time. Ten Mile Graben, Utah, USA, hosts a cold spring system that is an exceptional site for evaluation of diagenetic alteration of biosignatures because of the presence of modern springs with actively precipitating microbial mats and a series of progressively older tufa terraces (<400 ka) preserved in the area from the same spring system. A previously undescribed Jurassic laminated carbonate unit within the upper part of the Brushy Basin Member of the Morrison Formation is also exposed in Ten Mile Graben. This research characterizes the geology of these modern and Quaternary saline, Fe-undersaturated, circumneutral Ten Mile Graben cold springs and provides the first description in the literature of the Jurassic Brushy Basin Member of the Morrison Formation carbonate deposit. Taphonomy of microbial fossils is characterized by scanning electron microscopy (SEM). The data highlight two distinct methods of biosignature formation: (1) precipitation of minerals from an undersaturated solution owing to metabolic activity of the cells and (2) mineral precipitation on charged cell surfaces that produce distinctive microbial trace fossils. Although diagenesis can destroy or severely degrade biosignatures, particularly microbial fossils, some fossils and trace fossils are preserved because entombment by Ostwald ripening limits diagenetic alteration. Recognizing spring-fed, biogenic tufas is crucial for astrobiological research and the search for life on Mars. Key Words: Biosignatures—Taphonomy—Diagenesis—Carbonates—Hot springs. Astrobiology 17, 216–230.