Middle Trinity Research Articles

Development of a Flow‐Specific Floodplain Inundation Model to Assess Alligator Gar Recruitment Success

AbstractAlligator Gars Atractosteus spatula historically ranged throughout the lower Mississippi River basin and in the coastal river basins of the Gulf of Mexico from Florida to Mexico, but they have now experienced population reductions or extirpations in many parts of their range. Hydrologic alterations of river systems leading to reduced river–floodplain connectivity are thought to be a main contributor to these declines. To better conserve and manage this species, it is important to understand how hydrologic processes influence floodplain connectivity and ultimately the recruitment success of Alligator Gars. Utilizing a one‐dimensional hydraulic model combined with high‐resolution digital elevation models, a high‐resolution floodplain inundation model for the middle Trinity River, Texas, was created. Available land use and vegetation data layers were overlaid to identify and quantify suitable Alligator Gar spawning habitat based on recently developed habitat suitability criteria. Finally, we used this model to estimate historic spawning habitat availability using a hydrologic time series analysis. These spawning habitat availability data were combined with hydrologic and water temperature data and correlated with historic Alligator Gar recruitment success using published year‐class strength data. Our results show that in the middle Trinity River Alligator Gar recruitment success was correlated with variables associated with spawning habitat availability from May to July. The multiple characteristics reflecting the extent, duration, and time that spawning habitats were available appeared to interact to produce exceptional Alligator Gar recruitment.

Sporadic gastrinoma - Diagnose and treatment - Case report

The Aptian–Albian Glen Rose Limestone (GRL) is an argillaceous shallow-marine carbonate deposit on the Central Texas Platform and contains the upper Trinity aquifer and the upper part of the middle Trinity aquifer. The GRL is divided into Upper and Lower GRL members, which have been further subdivided into hydrostratigraphic units (HSUs). This study uses an integrated ichnological and sedimentological approach to record changes in ichnofabric index (ii) as a proxy for bioturbation within the GRL and relates these changes to fluid flow. Fluid pathways within HSUs are controlled by the complex interaction of faults and fractures, karst development, and large-scale bioturbation-influenced porosity and permeability. The effect of bioturbation-influenced porosity as an aquifer characteristic is the least studied of these factors. Post-depositional solution enhancement of ichnofossils is also common and has increased lateral and vertical fluid connectivity in some HSUs. Most GRL strata are dominated by Thalassinoides networks, but also contain Palaeophycus, Planolites, Ophiomorpha, Serpulid worm tubes, rhizoliths, and Cruziana. Thalassinoides are commonly filled with coarser sediment than the surrounding matrix and act as fluid conduits within an otherwise low permeability matrix. Beds with ii3–4 and burrows with permeable fill transmit water readily. Beds with ii5–6 are commonly muddy and heavily homogenized, restricting fluid flow. Grainstone beds commonly have ii1–2 and are well cemented, restricting fluid flow to low intergranular flow. Pore systems dominated by Thalassinoides ichnofabrics, such as the GRL, are difficult to characterize on a large scale using many laboratory methods because they create heterogeneous flow paths depending on difference in permeability between the matrix and burrow fill. Understanding the effects of bioturbation-influenced porosity and permeability on subsurface fluid pathways is vital for creating a geologic and hydrostratigraphic framework for the Trinity aquifer.

Effects of Thalassinoides ichnofabrics on the petrophysical properties of the Lower Cretaceous Lower Glen Rose Limestone, Middle Trinity Aquifer, Northern Bexar County, Texas

The combined Edwards and Trinity aquifer system is the primary source of freshwater for the rapidly growing San Antonio and Austin metropolitan areas. The karstic Lower Cretaceous (Aptian–Albian) Lower Glen Rose Limestone (GRL) contains the middle Trinity aquifer and has been subdivided into six hydrostratigraphic units (HSUs) with distinct hydrologic characteristics. These HSUs were first identified in the subsurface via core examination at the Camp Stanley Storage Activity (CSSA) in northern Bexar County, Texas and were then correlated to associated gamma-ray and resistivity logs. The Trinity aquifer system is a telogenetic karst and fluid flow is directed primarily through solution-enhanced faults, fractures, and pervasive Thalassinoides networks because matrix porosity of both transmissive and confining HSUs is very low. Meteoric water infiltrates the Trinity aquifer through vertically-oriented faults and likely moves laterally through biogenic pores. Two 7.62cm diameter GRL cores and well logs from monitoring wells CS-MW9-CC and CS-MW5-LGR recovered from the CSSA were used to characterize the effect such large-scale Thalassinoides networks have on the petrophysical properties (resistivity and natural gamma-ray) of four HSUs (Honey Creek, Rust, Doeppenschmidt, and Twin Sisters HSUs). Resistivity logs show that resistance values >300Ω-m correlate with well-developed biogenic porosity and values of 650Ω-m are associated with solution enhancement of the Thalassinoides networks. These high resistivity zones are cyclical and are identified in muddy confining units, even when no changes in lithology or karstic development are identified. Pervasive Thalassinoides networks act as starting points for wide spread dissolution and lead to advanced karst development in transmissive HSUs. Natural gamma-ray logs do not reflect hydrologic characteristics directly, but are inversely correlated to resistivity logs and display m-scale cyclicity. Resistivity logs suggest that Thalassinoides networks are interconnected throughout strata within the GRL and when coupled with natural gamma-logs, the lateral distribution of these networks within HSUs can be correlated. Identifying such fluid pathways is of particular importance for wells not located in proximity to major faults and karstic features.

Bioturbation-influenced fluid pathways within a carbonate platform system: The Lower Cretaceous (Aptian–Albian) Glen Rose Limestone

The Aptian–Albian Glen Rose Limestone (GRL) is an argillaceous shallow-marine carbonate deposit on the Central Texas Platform and contains the upper Trinity aquifer and the upper part of the middle Trinity aquifer. The GRL is divided into Upper and Lower GRL members, which have been further subdivided into hydrostratigraphic units (HSUs). This study uses an integrated ichnological and sedimentological approach to record changes in ichnofabric index (ii) as a proxy for bioturbation within the GRL and relates these changes to fluid flow. Fluid pathways within HSUs are controlled by the complex interaction of faults and fractures, karst development, and large-scale bioturbation-influenced porosity and permeability. The effect of bioturbation-influenced porosity as an aquifer characteristic is the least studied of these factors. Post-depositional solution enhancement of ichnofossils is also common and has increased lateral and vertical fluid connectivity in some HSUs. Most GRL strata are dominated by Thalassinoides networks, but also contain Palaeophycus, Planolites, Ophiomorpha, Serpulid worm tubes, rhizoliths, and Cruziana. Thalassinoides are commonly filled with coarser sediment than the surrounding matrix and act as fluid conduits within an otherwise low permeability matrix. Beds with ii3–4 and burrows with permeable fill transmit water readily. Beds with ii5–6 are commonly muddy and heavily homogenized, restricting fluid flow. Grainstone beds commonly have ii1–2 and are well cemented, restricting fluid flow to low intergranular flow. Pore systems dominated by Thalassinoides ichnofabrics, such as the GRL, are difficult to characterize on a large scale using many laboratory methods because they create heterogeneous flow paths depending on difference in permeability between the matrix and burrow fill. Understanding the effects of bioturbation-influenced porosity and permeability on subsurface fluid pathways is vital for creating a geologic and hydrostratigraphic framework for the Trinity aquifer.

Geophysical mapping of Mount Bonnell fault of Balcones fault zone and its implications on Trinity-Edwards Aquifer interconnection, central Texas, USA

Geophysical surveys (resistivity, natural potential [self-potential], conductivity, magnetic, and ground penetrating radar) were conducted at three locations across the Mount Bonnell fault in the Balcones fault zone of central Texas. The normal fault has hundreds of meters of throw and is the primary boundary between two major aquifers in Texas, the Trinity and Edwards aquifers. In the near surface, the fault juxtaposes the Upper Glen Rose Formation on the Edwards Plateau, consisting of interbedded limestone and marly limestone, against the Edwards Group, which is mostly limestone, on the eastern down-thrown side (coastal plain). The Upper Glen Rose member is considered to be the Upper Trinity Aquifer and also a confining zone underlying the Edwards Aquifer. However, recent studies have documented a hydraulic connection between the Edwards and Upper Trinity aquifers. The uppermost portions of the Upper Trinity and the Edwards aquifers, in some places, operate as a single aquifer system, while the lowermost units of the Upper Glen Rose are confining layers between the Edwards Aquifer and the Middle Trinity Aquifer. Geophysical data, which include resistivity, natural potential, magnetic, conductivity, and ground penetrating radar, indicate not only the location of the fault but additional karstic features on the west side (Upper Glen Rose Fm.) and on the east side (Edwards Group) of the Mount Bonnell fault. Resistivity values of the Glen Rose and Edwards Group do not appear to have significant lateral variations across the fault. In other words, the Mount Bonnell fault does not appear to juxtapose different resistivity units of the Edwards Group and Upper Glen Rose member. Thus, the fault may not be a barrier for groundwater flow. With the abundant karstic features (caves, sinkholes, fractures, collapsed areas) on both sides of the fault, determined by the geophysical data, one can conclude that lateral groundwater flow (intra-aquifer) between the Edwards Aquifer and Upper Trinity is likely.

Investigating Groundwater Flow Between Edwards and Trinity Aquifers in Central Texas

Understanding the nature of communication between aquifers can be challenging when using traditional physical and geochemical groundwater sampling approaches. This study uses two multiport wells completed within Edwards and Trinity aquifers in central Texas to determine the degree of groundwater inter-flow between adjacent aquifers. Potentiometric surfaces, hydraulic conductivities, and groundwater major ion concentrations and Sr isotope values were measured from multiple zones within three hydrostratigraphic units (Edwards and Upper and Middle Trinity aquifers). Physical and geochemical data from the multiport wells were combined with historical measurements of groundwater levels and geochemical compositions from the region to characterize groundwater flow and identify controls on the geochemical compositions of the Edwards and Trinity aquifers. Our results suggest that vertical groundwater flow between Edwards and Middle Trinity aquifers is likely limited by low permeability, evaporite-rich units within the Upper and Middle Trinity. Potentiometric surface levels in both aquifers vary with changes in wet vs. dry conditions, indicating that recharge to both aquifers occurs through distinct recharge areas. Geochemical compositions in the Edwards, Upper, and Middle Trinity aquifers are distinct and likely reflect groundwater interaction with different lithologies (e.g., carbonates, evaporites, and siliceous sediments) as opposed to mixing of groundwater between the aquifers. These results have implications for the management of these aquifers as they indicate that, under current conditions, pumping of either aquifer will likely not induce vertical cross-formational flow between the aquifers. Inter-flow between the Trinity and the Edwards aquifers, however, should be reevaluated as pumping patterns and hydrogeologic conditions change.

Identifying Flow Intervals by Pore Geometry and Petrophysics: Middle Trinity Aquifer (Lower Cretaceous Limestone)

A core from the Lower Cretaceous middle Trinity aquifer of southern Kendall County, Texas, was analyzed to compare its petrographic and petrophysical properties to its hydraulic flow characteristics. The analyses helped determine flow intervals in the core. Flow intervals are defined as vertical zones having similar geologic (depositional and diagenetic) history, petrophysical properties, and hydraulic conductivity characteristics. The information gathered from the study of a single core may be integrated with similar data from other cores or well logs to define 'flow units.' Methodology involved visual and image analysis examination of thin sections and epoxy pore casts of samples to evaluate pore geometry (pore size, pore throat size, pore interconnectivity, and pore throat size heterogeneity). Samples were thus grouped into pore-type families. Representative samples from each pore-type family were tested for air and brine permeability, porosity, and mercury injection capillary pressure. Pore throat size distributions obtained from the capillary pressure analyses were compared to the data derived from the pore casts and thin sections. Pore geometry evaluated correlated well with mercury capillary pressure data for the most permeable zone of the core. Geologically, this flow interval consists of a porous, medium-grained peloid grainstone that is characterized by large pores connectedmore » by large pore throats. Wherever present, such pore throat to pore body size ratios enhance flow through the rock. Correlation between pore geometry and capillary pressure data deteriorate in packstones with increasing micrite mud content and wackestones with increasing dolomitization. These lower correlations are due to decreasing pore throat size and increasing pore throat size heterogeneity in these rocks.« less

STratigraphic Petrology as Aid to Mapping Calcarenite Bodies in Lower and Middle Trinity Cretaceous Rocks of San Marcos Platform, Texas: ABSTRACT

Lower Trinity rocks (Sycamore sandstone, Hosston sandstone, and Sligo limestone) and middle Trinity rocks (Hammett shale and Cow Creek limestone) represent two depositional cycles, bounded by regional disconformities, in the basal Lower Cretaceous section of south-central Texas. The cyclic units contain alluvial sandstone, alluvial and lagoonal terrigenous mudstone, lagoonal carbonate mudstone, and oolitic and skeletal calcarenites. Study of outcrops, cores, well cuttings, and electric logs demonstrates that these lithofacies are in ordered belts parallel with paleoslope contours on the depositional shelf. Calcarenites formed where highly agitated marine water impinged on the shelf surface. At different times, belts of calcarenite were formed at the shoreline, about 50 mi offshore, and 75-90 mi offshore. The resulting bodies are 5-25 ft thick, 5-10 mi wide, and tens of miles long. The approximate location of each offshore body can be determined by mapping lithofacies belts landward. Seaward from the calcarenite bodies, ooliths and well-rounded skeletal fragments are present as exotic grains in mud. These round grains range from 0.05 to 0.1 mm in diameter and are in quiet-water, open-marine sediments characterized by calcareous mud, terrigenous silt, glauconite silt, large angular shell fragments, and fragile whole fossils. Careful correlation of electric logs on the basis of scattered cores, plus thorough examination of well cuttings and cores, provides the ability to predict locations of calcarenite belts within these cyclic deposits. End_of_Article - Last_Page 600------------

Paleogeography, Paleohydrology, and Diagenesis of Middle Trinity (Lower Cretaceous) Carbonate Beach Sequence, Texas: ABSTRACT

The Hammett Shale, Cow Creek Limestone, and overlying Hensel Sandstone represent a transgressive-regressive depositional cycle. Hammett shales and carbonates were deposited in low-energy marine lithotopes seaward of nearshore shoal, lagoonal, and beach environments represented in Cow Creek lithofacies. Fungalgal caliches and supratidal marshes developed in places in the beach backshore. Contemporaneously, smectitic red muds, caliches, and lenticular sands were deposited on the arid Hensel alluvial plain. Statistical analysis of matrix, cement, and allochems reveals that early diagenetic modifications in the marine carbonate sequence have distinctive vertical distributions. Fewer beds are dolomitized above the Hammett Shale. Lagoonal strata consist mainly of recrystallized pelleted nodules and pseudospar lime packstones; and beach grainstones are never dolomitized. Aragonitic bioclasts underwent dissolution in the beach but stabilized by inversion in lower facies. Iron-free calcites predominate in the beach foreshore beds; ferroan calcites predominate in underlying units. Micritized and enveloped grains are most abundant in mud-free beach sediments. The strandline meteoric-vadose zone and the mixed zone separating local and regional meteoric-phreatic waters from marine interstitial fluids were the loci of most diagenetic alteration. Caliche development, early cementation, and grain leaching were affected by equilibrating vadose waters. Cementation was inhibited and inversion allowed to proceed in the local mixed-phreatic zone, whereas dolomitization of Hammett carbonates took place in regional mixed-phreatic waters. Iron-free cements were precipitated in oxidized, phreatic, or vadose zones. End_of_Article - Last_Page 630------------

Deep Lower Cretaceous Exploration on the Western Gulf Coastal Plain: ABSTRACT

Hydrocarbon exploration in Lower Cretaceous rocks of western Gulf Coastal Plain dates from 1920's when such shallow fields as Luling, Darst Creek, and Salt Flat were discovered. Deeper exploration for objectives in Lower Cretaceous increased sharply following 1954 discovery of Stuart City field, LaSalle County, Texas. The rock column under consideration, dates from Neocomian to upper Albian including, in ascending order, following stratal units: Trinity, Fredericksburg, and Washita. While deep Lower Cretaceous activity is often referred to as the Edward play, objective horizons actually fall within Edwards, Glen Rose, and Sligo limestones. The middle Trinity Pearsall shale and middle to late Washita Del Rio shale are widely distributed, easily mapped units. Limestones between these key beds are composed of three generalized lithofacies grading from north-northwest to south-southeast as follows: (1) Carbonate rocks of shallow-water origin characterized by mudstones, wackestones, and packstones in which miliolid and larger foraminifers, oolites, and algal structures are common. Evaporites are locally abundant and dolomite is widely developed; (2) Wackestones, boundstones, and grainstones of shallow-water origin in which dominant faunal elements are rudistids, corals, algae, and stromatoporids; (3) Carbonate mudstone of somewhat deeper-water and more open-sea origin bearing pelagic foraminifers and calcispheres. Lithofacies 1 and 3 have widespread distribution whereas rudistid-bearing rocks are limited to a rather narrow band along platform margins, and have thus become known as the Edwards reef. These Lower Cretaceous rocks produce from fault closures in Edwards and Glen Rose where dolomitization and dissolution have greatly improved reservoir End_Page 353------------------------------ and from structural closures coexistent with rudistid facies. Initial production and productive history of reservoirs in rudistid-bearing rocks have been disappointing. Exploration in trend has been based on close correlation of seismic field efforts and regional stratigraphic studies. Detailed studies of reef complex in an attempt to determine areas of best porosity and engineering studies related to reservoir stimulation, are necessary before this trend becomes economically more attractive. End_of_Article - Last_Page 354------------