The Barby Formation makes up part of the Konkiep Terrane, which is a major Mesoproterozoic arc complex along the Kalahari craton margin in southwest Namibia. Previous mapping indicates that the Barby Formation contains a laterally and vertically complex series of basaltic to rhyolitic lavas, rhyolitic ignimbrites, and associated hypabyssal intrusions. Our new work shows that significant basaltic to andesitic pyroclastic successions are also present within the unit and record a wide variation in eruption styles.
Detailed mapping reveals the presence of Hawaiian, Strombolian and phreatomagmatic pyroclastic deposits forming successions up to X m thick emplaced close to source vents and intercalated with fine-grained lacustrine strata in an area ~20 km2. The most abundant deposits consist of basaltic to andesitic spatter accumulations formed from vigorous lava fountains during Hawaiian-style eruptions. These sequences show random vertical transitions on the scale of a few meters from moderately agglutinated to densely welded spatter, which reflect variations in pyroclast accumulation rates. Individual spatter pieces are up to x cm long. The densely welded spatter forms lava-like units, but we see no evidence of clastogenic lava flows. Sequences of basaltic lapillistone with dispersed ribbon and fusiform bombs up to 50 cm across record Strombolian eruptions during episodes of lower magma flux without involvement of external water. The spatter accumulations typically grade upward into phreatomagmatic deposits containing minor amounts of spatter and cauliflower bombs mixed with poorly vesicular lapilli tuff, in which particle shapes are controlled mostly by fracture surfaces rather than broken bubble walls; up to 30% lacustrine sediment is intermixed with juvenile lapilli and ash in these deposits. We infer that changes in eruptive style in this part of the arc sequence were controlled at least partly by variations in magma ascent rates at shallow depths, as documented in numerous other volcanic provinces. Transitions from Hawaiian to phreatomagmatic eruptions may at least partly reflect a decrease in magma flux in the presence of external water, lowering the magma-to-water mass ratio so that hydrovolcanic explosions became possible.
The Eagle For Shale is a cretaceous geological formation that contains vast amounts of hydrocarbons. It is located in South Texas and is home to the largest oil and gas development in the world based on capital invested. The Eagle Ford play is shallower compared to other formations, and due to its high carbonate content and lack of clay content, the shale is more brittle allowing higher production rates through the process of hydraulic fracturing.
A GIS analysis of the Eagle Ford formation has been prepared in Lavaca County, Texas focusing on the producing trend that ceased development when crude oil prices dropped. This analysis will pay close attention to the San Marcos Arch and its impact on the Eagle Ford thickness adjacent to it and over it. This analysis discusses the arch itself, when in geologic time it occurred and what impact that event may not have had on the formation of the Eagle Ford.
Unconventional resources have become increasingly important in the production of petroleum. Shales, which are one of the unconventional resources being explored, are generally very difficult to work with due to their apparent homogeneous, fine-grained nature. Detailed studies often require the use of specialized tools to analyze and understand the rock. X-ray fluorescence, X-ray powder diffraction, carbon analyzers, and mechanical strength testers are commonly used tools to analyze shale cores. Results from these tools provide a wealth of data that allow detailed understanding of these resource rocks.
The Barnett Shale is one such resource and serves as the primary source rock for oil and gas reservoirs in the Bend arch/Fort Worth Basin area. Recently, the Barnett Shale itself has been an exploration target and now is a significant gas-producing formation in Texas. Research has shown that the Barnett Shale is organic rich and thermally mature for hydrocarbon generation. The estimated maximum gas storage capacity of the Barnett Shale is 540 mcf/acre-foot.
The Barnett Shale is an excellent formation to study as there is an abundance of data and cores. A single core will be analyzed using the above-mentioned devices. This study will lead to a better understanding of how unconfined compressive strength (UCS), composition, TOC, and core dimensions correlate and affect one another. By completing various analyses, several questions can be addressed including: 1) How does the sample volume affect micro-rebound hammer readings? 2) Which minerals control UCS? 3) Are X-ray fluorescence data sufficient to characterize the mineralogy or are X-ray powder diffraction data advantageous? 4) How do mechanical stratigraphy and XRD data correlate and are correlations comparable to mechanical stratigraphy and XRF data? 5) Which trace elements represent the best proxy for total organic carbon (TOC) content? Answering these questions will add new data to a growing database on the Barnett Shale and help us better understand this unconventional resource play.
In 1983 the American Association of Petroleum Geologist published a geologic guidebook called “Stratigraphic and Structural Overview of the Upper Cretaceous Rocks exposed in the Dallas Vicinity” written by Robert T Clarke and David E. Eby. This field publication outlined a guided field trip of stops of interest in Dallas County and the surrounding counties. The user can follow the guidebook with an outlined travel route to a series of designated stops of known outcrops. The Upper Cretaceous rocks exposed in the Dallas vicinity area were designated by Adkins in 1932 from oldest to youngest; the Grayson Formation (Washita Group) and the Woodbine, Eagle Ford, Austin, and Taylor Groups. The trip begins on the Black Prairie in Dallas and proceeds westward across the Eastern Cross Timbers to Arlington. The field trip area follows roughly along the structural boundary between the Fort Worth basin in the northwest and the Ouachita fold belt in the southeast. This field guide includes hand drawn maps, hand drawn stratigraphic sections and black and white reprinted photographs of the outcrops described. Each stop has a detailed description to allow the user to find the outcrop and details about fossil assemblages and particular characteristic of the formation at the location. The information in the guidebook is very useful but the media used at the time is now considered outdated.
To update this detailed field guide with more modern technology and locational accuracy, a GIS project was conducted to assimilate all the necessary geospatial data layers, traveling routes, GPS location of each designated stop and new color photography of the outcrops visited. All of this geospatial data was collected and formatted to allow a user of the field guide to traverse the entire field trip by accessing an integrated geospatial map. The ultimate goal of this project is to publish this material as a web based story map to allow easy web access to anyone interested in outcrops and provided information. This story map would make this information available to users on mobile products and allow users to contribute remarks and additional important outcrop locations to the product.
Adkins, W.S., 1932, The Mesozoic systems of Texas, in The Geology of Texas:
Univ. Texas Bull., no. 3232, p. 239-518.
Northwestern South America is highly deformed due to the transpressive boundary with complex interactions among the Caribbean plate, the South American plate, the Nazca plate and the Panama arc. Previous studies suggest that the Cenozoic uplifting of the Mérida Andes and Eastern Cordillera of Colombia affected sediment dispersal patterns in the region, shifting from a Paleocene foreland basin configuration with an axial major fluvial system, to the modern configuration of isolated basins with distinctive sediment dispersal patterns. Well-exposed Cretaceous to Pliocene strata in the Táchira saddle between the Easter Cordillera and Merida Andes provide a unique opportunity to test proposed sediment dispersal patterns in the region. U-Pb detrital zircon geochronology and supplementary XRD heavy mineral identification were used together to document provenance of Cretaceous to Pliocene clastic rocks collected from the area of La Alquitrana. Results from the U-Pb detrital zircon geochronology show that there are six age groups recorded in this samples. Two groups related with Precambrian Guyana shield Terranes and Putumayo basement in the Eastern Cordillera, and four groups related to different magmatic episodes during the Andean Orogenic process. Three major paleogeography changes were also recorded in these detrital signatures, including a transition between the Cretaceous passive margin and the Paleocene foreland basin, the initial uplifting of the Eastern Cordillera with the isolation the Llanos Basin and Táchira Saddle from the Central Cordillera and the Magdalena Valley in the Early Oligocene, and the uplifting of the Mérida Andes by the Early Miocene. The outcomes of this study emphasize the importance of the Mérida Andes and Eastern Cordillera Uplift in controlling the evolution of the sediment dispersal patterns in northern South America and represent a contribution in the understanding of the paleogeographic evolution in the region.
Fluvio-lacustrine systems are prone to experiencing significant flood events separated by longer low energy periods. During low flow, sediment is stored upstream of the lake as mid-channel and side-attached bars. During high-discharge events, water level rises above the topographically low delta front levees, the turbulent jet of the river is positioned upstream of the levee terminus where levees are less confining, and the previously stored sediment is flushed from the channel into the lake basin laterally as sheets. This process forms a laterally extensive, well sorted wedge shaped deposit of fine grained sand called a blowout wing (after Tomanka, 2013). These wings are documented in the ancient within the Kayenta Formation, UT, where the sand wings demonstrated a significant increase in connectivity between statistically clustered fluvio-lacustrine channel belts. In this research, we document two examples of blowout wings forming in the modern. The first example is a lake sourced by a mud dominated river (Denton Creek, Lake Grapevine, TX), and the second is a lake sourced by a sandy, bedload dominated river (Red River, Lake Texoma, TX). Wings are composed of fine to medium grained, well sorted, and clean sand. The deposits are thin and laterally continuous, with measured thicknesses of 5-10 cm that thin away from channel axis. Wings have an aerial extent up several hundred meters, scaling to 4-6 times the channel width. The Red River at Lake Texoma has a channel width of 125m and deposits wings with an aerial extent of 250-350m long along the levee of the delta channel and 300-500m laterally. As the Red River has prograded into the basin, 5-6 individual blowout wings form a wing complex 1500m long and 500-600m laterally from the channel. Denton Creek at Lake Grapevine has a channel width of 25m and deposits wings on the order of 50-125m along the levee of the delta channel and 60-150m laterally. Three wings at Lake Grapevine form a wing complex 300m long and 100-150m laterally. The amalgamation and statistical clustering of fluvio-deltaic channel belts is increased by the presence of blowout wings, resulting in higher total reservoir size and connectivity. Blowout wings should be, and are, found in modern systems and subsequently the rock record recording fluvio-lacustrine environments of deposition.
Thin sand sheets presumed to be terminal splay bodies have potential to serve as hydrocarbon reservoirs. The few studies of terminal splays managed from arid systems has provided insight, but ground study of the humid equivalent is lacking. Deposited in the distal zone of a distributary fluvial system (DFS), the splay bodies are formed as rivers terminate from loss of slope into unconfined dispersive flow and deposit bed load as splays and advect mud to more distal floodplains. The splay sheets and floodplain together provide potential for both reservoir and seal. We examined terminal splay deposits in a modern humid terminal splay system, Andean foreland of northern Argentina, and in ancient foreland deposits, Paleocene Raton Formation of the Colorado Raton Basin. I am going to compare the two locations in terms of grain-size, sedimentary structures, geometry, and scale and see how they relate. I hypothesize that the two are going to have similar grain sizes, and that the sedimentary structures and geometries will also be analogous but expect them to be scaled down in the Raton Basin.
The modern splay in Argentina is nearly 1.3 km wide and 1.9 km long and was deposited during a single large flood in 2012. Cross sections generated by hand augers show a maximum thickness of 0.8 m, an average of 0.5 m, and a consistently very fine-grained to lower medium-grained sand texture throughout. Total sand deposited in the flood event is ~ 1.2 million cubic meters (~2.0 million cubic meter maximum), and accumulates over earlier splay deposits separated by weakly developed soils that are locally removed by splay incision. Subsequent dissection of the splay permits examination of sedimentary structures, which are dominantly climbing ripples, planar laminations, and cross sets, but climbing antidunes are locally found near the splay apex. Ancient terminal splays of the Raton Formation are made of thinner sand sheets (~0.25 m) and tend to have thicker muddy floodplain deposits between. Grain-size distribution, sheet geometry, and sedimentary structures however are consistent between the modern and ancient examples. Both the Argentina and Raton examples reflect the distal end of a humid Distributive Fluvial System, however, the Raton system appears to have been of smaller scale. This is consistent with the comparatively smaller scale of the Raton vs. Andean tectonic system.
The Late Paleozoic Ouachita fold-and-thrust belt extends from the southern terminus of the Appalachian thrust belt in eastern Mississippi up through central Arkansas, southeastern Oklahoma, and Texas terminating in northeastern Mexico. A series of Carboniferous foreland basins were formed sequentially to the thrust front. The interaction between the Laurentian craton and the Appalachian-Ouachita orogenic belts controlled sedimentation in the southern midcontinent region throughout the Paleozoic. In contrast to the Appalachian orogenic belt to the east, the Ouachita orogenic belt and associated sediments remain poorly documented and less constrained.
In this study, seven Ordovician to Mississippian aged clastic units from the Ouachita Mountain in central Arkansas were sampled and tested using U-Pb detrital zircon geochronology. Three major age peaks are prominent, including the Grenville Province (~0.95-1.2 Ga), the Granite-Rhyolite Province (~1.3-1.5 Ga), and the Superior Province (>~2.5 Ga) in Ordovician to Silurian aged rocks. A change in this signature becomes clear at the beginning of the Carboniferous from Early Mississippian Stanley Group samples showing the additional Paleozoic age peak (~490-520 Ma) potentially derived from the Appalachian orogenic belt to the east, and/or from peri-Gondwanan terranes accreted to Laurentia just before the collision with Gondwana. This stratigraphic variation of detrital zircon age signature suggests that the transition from a passive to an active margin in the Ouachita trough started, at the latest, in early Mississippian times. Results of this study is the first systematic study of the U-Pb detrital zircon signature of the Ouachita orogenic belt and have important implications in sediment dispersal, provenance interpretations, and paleogeography reconstructions in North America, especially in the southern mid-continent and surrounding areas.
A GIS site assessment and building plan was performed on approximately 20 acres located near Edna, Texas. The property surrounds a 5 acre lake with three existing small houses facing the lake. The site assessment evaluated the potential for construction of additional single story 2 bedroom homes. Using aerial photography, digital elevation data, and a soil survey; a map of the project area and site conditions was created. Elevation and soil suitability were used to determine drainage and suitability of the soil for foundation support. Color aerial photography was essential in developing layout of boundaries, existing structures and lake location. A viewshed analysis from the front porch of each of the proposed new structures was performed to evaluate the quality of view angle to the lake.
This study involved the examination of core samples from the Lower Cretaceous aged Kiamichi Formation of the East Texas Basin in order to interpret its organic and elemental geochemistry using various techniques. The Kiamichi Formation may have the potential to be a source rock for hydrocarbons, and may be a plausible target for oil and gas companies to produce using unconventional techniques. Since this formation has yet to be thoroughly analyzed, this project has lead to further understanding of its potential by using techniques such as handheld x-ray ﬂuorescence tool to estimate for the abundance of rare earth elements and trace metals, as well as a CHNS analyzer to determine the amount of organic carbon of the formation. Upon completion of the sample analysis, this geochemical information about the Kiamichi Formation provides beneficial information for further research on the overall Kiamichi Seaway.
The Eagle Ford Shale in south Texas is one of the most prolific unconventional hydrocarbon plays in the world (Breyer, 2016). In 2015, natural gas and oil from this field hit peak production numbers at 5,539 MMcf (million cubic feet) and 1,118,648 Bbl (barrels) per day, respectively (Texas RRC, 2016). In order for this low-permeability formation to produce, companies are using hydraulic fracturing, a stimulation treatment used in low-permeability rock whereby fluids are pumped at high pressures into reservoirs, causing new fractures to form and possibly reactivating existing fractures (Schlumberger, 2016). The aim of this study is to identify any geomechanical and geochemical properties that optimize fracture connectivity within the Boquillas Formation, the West Texas Eagle Ford equivalent. Energy-dispersive x-ray fluorescence (ED-XRF) and strength/hardness data from this study suggests that fracture frequency and length are affected by the clay and calcium carbonate content, and, by inference, the strength of the rock.