Browsing by Subject "Karst"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Evolution of a regionally extensive evaporite removal paleokarst complex : Mississippian Madison Group, Wyoming(2011-12) Kloss, Travis T.; Zahm, Christopher Kent; Kerans, C. (Charles), 1954-; Fisher, William L.Paleokarst systems owe their complex geometries to the interaction between the karst aquifers and the host rock being dissolved. The majority of paleokarst research to date has considered dissolution of carbonate strata (James and Choquette 1987), but rapid and extensive dissolution of interstratified evaporites can be an important if largely undocumented style of paleokarst that may play an important role in near-surface environmental settings as well as providing a unique style of reservoir heterogeneity in the subsurface (Sando 1967, 1974, 1988; Smith et al. 2004). This study is designed to answer the question, “How do we recognize evaporite paleokarst as distinct from standard meteoric carbonate paleokarst?” using spectacular, laterally continuous exposures in the upper Madison Formation within Bighorn Canyon, Wyoming. Key characteristics of the Madison intrastratal evaporite karst complex were documented and contrasted with the top-Madison surficial karst system resulting in a suite of data that includes detailed section measuring, facies mapping using high resolution photo panels and ground based LiDAR for control. Hand samples, thin sections and x-ray diffraction analysis also contributed to this study. High resolution mapping of key surfaces, karst facies and petrophysical properties were used to develop a stepwise evolutionary model of the evaporite removal paleokarst complex. The interplay between surficial karstification, solution enhanced fractures, subsurface intrastratal evaporite dissolution, collapse and infill, were considered in constructing this model. Similar to standard meteoric paleokarst systems, the Madison evaporite paleokarst has been divided into 7 distinct karst “facies” including laminated cave floor fill, roof collapse chaotic breccias, and suprastratal dissolution complexes. Features proposed to be unique to evaporite paleokarst that will aid in future studies are (1) presence of relic gypsum breccia clasts within cave-fill facies, (2) the near absence of cave pillars or roof touch down within the chaotic breccia zones, indicating removal of a laterally extensive soluble stratum, (4) a striking absence of sub-cave floor breccias or fractures, (5) a distinct breccia matrix consisting of primarily autochthonous detrital dolomite with a minor component of allochthonous detrital clays from the overlying Amsden, suggesting that the bulk of the breccia matrix is locally sourced insoluble residue from evaporite dissolution, and finally (6) close facies associations of the depositional sequence suggesting that evaporites were a likely part of the original stratigraphic record in the Madison. These criteria are considered to be a solid starting point for an evaporite paleokarst model and should assist in the recognition of similar paleokarst breccias in the ancient rock record.Item Microbe-mineral affinity in sulfuric acid karst systems(2011-08) Jones, Aaron Alexander; Bennett, Philip C. (Philip Charles), 1959-; Breecker, Daniel O.; Omelon, Christopher R.Microbial communities influence the kinetics and pathways of reactions involved in the dissolution of a number of minerals (Ehrlich 1996). On a smaller scale these interactions can affect substrate permeability, porosity, and create highly localized biogeochemical conditions. However, a mechanistic understanding of the consequences of microbial surface colonization on calcite dissolution rate has yet to be achieved. More specifically, little is known about the impact of sulfur-oxidizing bacteria activity on the rate of carbonate mineral dissolution, or the nature of the microbe-limestone attachment and interaction. Through a series of laboratory and field experiments the effect of mineral surface colonization by microbial communities, obtained from an active sulfuric acid cave (Lower Kane Cave (LKC), Big Horn Basin, WY), on the dissolution rate of Madison Limestone was quantified. Results from laboratory experiments showed that a microbial biofilm, composed primarily of Epsilonproteobacteria and Gammaproteobacteria growing on a limestone surface oxidized thiosulfate and increased carbonate dissolution rates up to 3.3 times faster than abiotic rates. When all thiosulfate substrate was withheld the community oxidized stored intracellular sulfur, continuing to accelerate limestone dissolution and decreasing pH. This process is sensitive to O2 limitations. Characterization of this aggressive sub-biofilm corrosion was more closely examined by SEM imaging. By comparing mineral surface morphology of colonized chips to non-colonized chips of various carbonate substrates, it was shown that even under conditions near equilibrium with calcite, aggressive dissolution of carbonate substratum occurs exclusively beneath the biofilm. These findings support the hypothesis that (1) sulfur-oxidizing microbial communities aggressively dissolve carbonates in order to buffer the production of excess acidity by neutrophilic communities and (2) biofilm presence affects carbonate mineral dissolution by physically separating a bulk stream water from the sub-biomat environment. Furthermore, it was found that mineralogy affects the degree of establishment of microbial communities in this environment. Results from a series of four laboratory and one in situ reactor experiment showed that limestone and dolostone substratum consistently had higher biomass accumulations than silicate minerals or pure Iceland spar calcite in the same reactor. These results provide evidence to support the hypothesis that mineralogy influences microbial accumulation in sulfuric-acid karst systems. Particularly, neutrophilic sulfur-oxidizing communities accumulate in greater quantities on solid substrates that buffer metabolically-generated acidity. These results also demonstrated the dependence of microorganisms on colonization of a particular mineral surface, possibly in order to gain access to micronutrients bound within solid substrates when exposed to nutrient-limited conditions.Item Modeling the Hydrologic Impact of Arundo Donax on the Headwaters of the Nueces River Using the Swat Model(2014-08-06) Jain, ShaileeThe invasive species Arundo donax (hereafter Arundo), has invaded the riparian zones of the Rio Grande River and the rivers of the Texas Hill Country over the last two decades. Arundo, also known as the giant cane, is a robust herbaceous plant that can grow in many different climatic conditions. Arundo was first observed along the Nueces River in 1994 by the Nueces River Authority (NRA). It then spread rapidly downstream due to its high growth rate and/or stream flow and completely displaced the native vegetation, primarily P. virgatum (hereafter switchgrass), in the riparian zone wherever it got established. An eradication program was started in 2010 by the NRA to remove Arundo from the Nueces River. The objective of this research project was to (1) develop an algorithm to simulate the propagation of Arundo, (2) study changes in streamflow patterns during pre- and post- Arundo invasion periods, (3) calibrate and validate the Soil Water Assessment Tool (SWAT) for the Nueces River Headwater (HUC 12110101) watershed in central Texas, and (4) assess the effects of the invasion of Arundo on the watershed hydrology by comparing it to the native grass species switchgrass (Panicum virgatum) that used to be the dominant species in the watershed. Arundo parameters appropriate for the Nueces River were added to create a new crop category in the SWAT database. Calibration and validation of SWAT were based on measured streamflow data available at the USGS gage (USGS 08910000) on the Nueces River for the period 1960 to 1994. Switchgrass, the native vegetation, was chosen as the plant to compare Arundo with so that the difference in hydrology could be understood. The results revealed that accumulated evapotranspiration was not statistically different between Arundo and switchgrass for the period of 16 years (1995-2010). There was also no difference in the water yields of Arundo and switchgrass. In conclusion it appears that Arundo in the Nueces River has not caused any changes in water uptake compared to the native grass, switchgrass, that previously dominated the headwaters.Item Morphologies and controls on development of Pliocene-Pleistocene carbonate platforms : Northern Carnarvon Basin, Northwest Shelf of Australia(2013-08) Goktas, Pinar; Fulthorpe, Craig Stephen, 1954-; Austin, James AlbertThe detailed morphologies, evolution and termination of Neogene tropical carbonate platforms in the Northern Carnarvon Basin (NCB) on the passive margin of the Northwest Shelf of Australia reveal information on the history of local oceanographic processes and changing climate. Cool-water carbonate deposition, dominant during the early-middle Miocene, was superseded by a siliciclastic influx, which prograded across the shelf beginning in the late-middle Miocene during a period of long-term global sea-level fall. The resulting prograding clinoform sets, interpreted as delta lobes, created relict topographic highs following Pliocene termination of the siliciclastic influx (Sanchez et al., 2012a; 2012b). These highs created a favorable shallow-water environment for subsequent photozoan carbonate production. A composite, commercial 3D seismic volume allows investigation of the temporal and spatial evolution of the resulting Pliocene-Pleistocene carbonate platforms. Initiation of carbonate development, in addition to being a response to cessation of siliciclastic influx and the existence of suitable shallow-water substrate, was also influenced by the development of the warm-water Leeuwin Current (LC), flowing southwestward along the margin. Four flat-topped platforms are mapped; each platform top is a sequence boundary defined by onlap above and truncation below the boundary. Successive platforms migrated southwestward, along-strike. Internally, platforms have progradational seismic geometries. The mapped platform tops are large (≥ 10 km wide). Evidence of karst (e.g., v-shaped troughs up to 50m deep and ~1 km wide and broader karst basins up to 20 km2 coverage area) on platform tops suggests episodic subaerial exposure that contributed to the demise of individual platforms. The most recent platform, platform 4, is unique in having interpreted reefs superimposed on the progradational platform base. The base of these reefs now lies at ~153 m and the reefs may therefore have developed post-LGM (~21 Ka). The reefs subsequently drowned, with drowning possibly aided by turbidity associated with formation of adjacent sediment drifts and weakening and strengthening LC during the late Pleistocene. The progressive drowning and termination of platforms from northeast to southwest along strike may result from differential compaction of the deltaic substrate or differential tectonic subsidence caused by the collision at the Banda Arc between the Australian and Pacific platesItem Structural controls on evaporite paleokarst development : Mississippian Madison Formation, Bighorn Canyon Recreation Area, Wyoming and Montana(2012-05) Eldam, Nabiel S.; Kerans, C. (Charles), 1954-; Zahm, Christopher Kent; Steel, RonThis study provides new insights on the mechanisms that controlled the development of solution-enhanced fractures and suprastratal deformation associated with the Mississippian Madison Sequence IV evaporite paleokarst complex. Based on detailed field mapping utilizing LiDAR, GPS, and field observations, we document a paleostructural high (oriented 145º) associated with the Ancestral Rockies uplift within the study area. One hundred twenty-one sediment-filled, solution-enhanced fractures within the Seq. IV cave roof were mapped and characterized by their dominant fill type (Amsden or Madison) and vertical extent. Spatial analysis reveals minimum spacing of these features occurs in areas uplifted during the Late Paleozoic suggesting a link between paleostructural position and solution feature spacing. Shape analysis of these solution features also supports structural position during the Late Paleozoic acted as a dominant control on fracture morphology: (1) downward tapering and fully penetrative features concentrate in areas that experienced uplift; (2) upward tapering concentrate in areas that were undeformed. Mapping of Seq. IV cave roof strata demonstrates vertical collapse variability exceeds 22 m and fault intensity increases in areas of increased collapse. These findings have significant implications for prediction and characterization of solution-enhanced fractures and suprastratal deformation within evaporite paleokarst systems.Item Surface water recharge in karst : Edwards-Trinity Aquifers-Nueces River system(2015-05) Kromann, Jenna; Sharp, John Malcolm, Jr., 1944; Gary, Marcus O.; Johnson, Joel PThe karstic Edwards Aquifer is a primary source of water in south-central Texas for domestic, agriculture, and industrial uses. Significant recharge into the aquifer occurs as surface water streams, including the Nueces River, cross the Recharge Zone (RZ). Recharge models use data from two stream gauges, located above and below the RZ. These gauges are used to compute recharge into the aquifer; this may underestimate recharge volume because the actual water balance is complex. Synoptic gain/loss studies show that: flow rates change significantly as the river passes through extensive unconsolidated alluvium, gain/loss in reaches varies temporally, and recharge may be occurring in the Contributing Zone (CZ). From these synoptic studies, a 10-km reach of the Nueces River near Montell, TX, was identified that loses 100% of flow over the CZ during low stream flows. In this study reach, Candelaria Creek runs parallel to the dry segment of the Nueces River for 2.5 km; the creek contributes 52-64% of flow measured at the USGS recharge index gauge. The main sources of flow to the creek are two springs, hypothesized as possibly being sourced from: underflow from the Nueces River, a combination of Trinity Aquifer groundwater and river underflow, or solely groundwater from the Trinity Aquifer. To investigate recharge in the CZ and the source water for springs that contribute flow to Candelaria Creek, a variety of methods were used including: hydrograph and gain/loss analyses, potential evapotranspiration calculations, and interpretation of specific conductance, temperature, chemical, isotopic, and near surface geophysical data. The data suggest that the springs are likely sourced from both Nueces River underflow and Trinity Aquifer groundwater. Defining the source of the springs that contribute to Candelaria Creek is important to understand the complex water balance in the Nueces River and the role of underflow/storage in this system. It was found that underflow was a significant source of spring flow, but could not account for the total amount of spring flow; this suggests the Trinity Aquifer also contributes flow to the springs. A water balance estimates that recharge in the CZ at 6,213,048-9,814,814 m3 per year, which is between 0.9 to 2% of total recharge to the Edwards Aquifer and 4 to 11% of Nueces Basin recharge may be unaccounted for over the CZ during low hydrologic flow conditions. This water balance suggests that there is significant recharge occurring over the CZ and some recharge may be unaccounted for based on the current method used to calculate recharge.