Browsing by Subject "Stratigraphic -- Paleozoic"
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Item Contact aureole rheology of the White Horse pluton(Texas Tech University, 2004-08) Marko, Wayne T.The 160 Ma White Horse pluton intruded a thick sequence of miogeoclinal Paleozoic carbonate rocks in the northeastern Great Basin Region, Nevada. The dominantly quartz monzonite pluton (-16 km^ of exposure) lacks internal fabric, concentric zoning, and stoped blocks, but hosts several smaller granite and granodiorite bodies as well as numerous microdiorite mafic enclaves. The structural aureole extends 7 km along the eastern side of the elliptical intrusive body. Continuous and discontinuous spaced axial planner foliations and harmonic to disharmonic, tight to isoclinal folds wrap around the western margin of the pluton. Folds verge toward and away from the pluton and a rim anticline is preserved along the pluton margin. In several locations fold axes are cut by the pluton host rock contact. The aureole was shortened approximately 54% during emplacement. However, a maximum of 52 % of the exposed pluton area is unaccounted for after the ductile aureole strain is restored. The pluton contact geometry is highly variable and parallel to subparallel with host rock anisotropy. Along the southern aureole the contact dips 14° to the north (towards the intrusion) and in the southeast the contact turns over to dip 45° to the southeast (away from the intrusion). In the northeastern aureole the contact dips 31° to the northeast while at structurally higher elevations the contact dips 45° to the southwest. Several dikes cut host rock structure and turn to propagate towards one another, preserving the late stage stoping process. Aureole tectonites consist of carbonate mylonites and coarse mylonites interlayered with annealed marble. Intracrystalline slip, grain boundary migration, subgrain rotation and grain size sensitive diffusion creep accommodated ductile deformation. Significant syntectonic grain growth occurred during carbonate grain recrystallization. Minimum stress estimates from piimed calcite tectonites range from 30 to 34 MPa. Minimum strain rate estimates range from 10""s'' at 600° C to 10''^s"' at 400° C. Temperatures correspond with the peak thermal gradient predicted for the aureole. Magma chamber construction was accomplished by contemporaneous brittle and ductile translation of host rocks. Stoping accounts for missing host rock area, truncated bedding, and the consistent subparallel orientation of the pluton contact with host rock structure. Ductile deflection of the host rocks was accomplished by lateral expansion of the magma chamber after magma ascent had ceased. This process produced plutonvergent and divergent folds and a rim anticline. Calculated aureole strain rates preclude the possibility of simple end-member emplacement diking and diapiric models. The large viscosity contrast between the host rocks and the magma as well as the lack of fabric within the intrusion suggests aureole deformation (chamber construction) was driven by buoyancy and/or overpressure and was completed before the magma had achieved a yield strength.Item Depositional history of Cisco-Wolfcamp strata, Bend Arch, north-central Texas(Texas Tech University, 1973-05) Harrison, Earl Preston,Not availableItem Depositional history of Cisco-Wolfcamp strata, Bend Arch, north-central Texas(Texas Tech University, 1973-05) Harrison, Earl Preston,Not availableItem Lower Pennsylvanian stratigraphy of the Central Colorado Trough(Texas Tech University, 2003-08) Musgrave, Bryan EdwardThe Central Colorado Trough formed as a result of the uplift of the Ancestral Rocky Mountains. With uplift, sediments were eroded from the adjacent highlands and deposited in the trough. The Lower Pennsylvanian stratigraphy of the Central Colorado Trough was determined based on outcrops in the southern Mosquito Range and Arkansas River Valley east of Salida, Colorado. The Kerber Formation is the oldest Pennsylvanian strata in the Central Colorado Trough and was derived from the erosion of older Paleozoic sedimentary rocks and some crystalline basement rocks. It was deposited in alluvial fan and braided streams environments near the edges of the trough. Along the axial portion of the Trough, it was deposited in braid-delta and shallow marine environments. As marine incursion occurred from the northwest, a retrogradational sequence developed. Based on conodont faunas, the upper Kerber Formation is late Morrowan to Atokan in age. Because the strata of the Central Colorado Trough are intimately related to the initial uplift of the Ancestral Rocky Mountains, the formation of the Ancestral Rocky Mountains began no later than the late Morrowan. The Kerber Formation correlates with the Belden Formation of the northern portion of the Trough based on the first appearance of the conodonts Idiognathoides sinuatus, Idiognathodus sinuosus, and Idiognathodus parvus. At Willard Springs they occur within the Belden, whereas they occur within the Kerber at Wells Gulch, 8 km to the south. The dark marine sediments of the Belden Formation extend further southward than previously documented, and approximately 127 m of section occurs at Willard Springs, northeast of Salida. At Willard Springs, the Belden Formation lies conformably above the Kerber Formation and conformably below the Sharpsdale Formation. This is the first time that the Belden has been documented m contact with the Sharpsdale Formation. At Wells Gulch and Box Canyon to the south, the Belden Formation grades into shallow-water carbonates and shales interbedded with Kerberand Sharpsdale-type elastics. The Sharpsdale Formation was derived from the erosion of Precambrian crystalline basement rocks of the Uncompahgre Highland as the climate of the Pennsylvanian grew more arid. It was deposited in alluvial fan and braided stream environments near the edges of the trough. Along the axial portion of the trough, it was deposited in braid-delta and rare shallow marine environments. A northward prograding sequence developed as sediment influx exceeded local sea-level rise.Item Sedimentology and diagenesis of the basinal facies of the Dimple Limestone, Marathon Basin, West Texas(Texas Tech University, 1985-05) Baker, Lisa MarieThe Dimple Limestone (Morrowan?-Atokan), Marathon Basin, Texas, represents a break in the Ouachita clastic flysch sequence. Carbonate material was transported from the present northwest into the Ouachita trough, an abrupt change from influx of clastic flysch derived from a southern source. The basinal facies of the Dimple Limestone was deposited in the mid- to lower portions of a submarine fan system, and is represented by allodapic limestones, turbidite and hemipelagic shales, and thin black chert beds, also interpreted as turbidites. The basinal facies may be divided into sedimentary packages, reflecting the ^ode of deposition. A package consists of a thick, coarse-grained, basal member with an overlying mudstone, followed by thinner interbedded limestones, shales, and cherts. The thick basal members of the oobiolithoclastic packstone and spiculiferous packstone lithofacies, show evidence of scouring. They represent the main locus cf the turbidity flows, channelized areas, or perhaps stronger flows with disturbance in shelf environments. Thick basal units typically fine upward into mudstones of the spiculiferous shale lithofacies. All sediments from the base through the mudstone were deposited by one continuously decelerating turbidity current. The thinner, interbedded turbidites within each sedimentary package represent weaker currents, with instability in upper slope, spicule-rich environments. They represent shifting of the main locus of the flows within the submarine fan system. Pelagic shales represent periods of relative quiescence, during which normel marine deposition resumed. At least seven stages of diagenesis have altered the basinal Dimple sediments. These include: 1) post-burial diagenesis, 2) fresh-water diagenesis, 3) dolomitization, 4) precipitation of siderite, 5) precipitation of celbar, 6) fresh-water diagenesis, and 7) ferroan dolomitization. Virtually all effective porosity has been occluded, with no remaining reservoir potential. Potential as a hydrocarbon source is possible due to abundant organic matter, and depending on the burial history.Item Sedimentology, petrography, and diagenesis of selected Paleozoic source rocks from the Permian Basin(Texas Tech University, 1990-12) Trabelsi, Ali M. S.Sedimentological and paleontological investigations of the Upper Devonian Woodford, Pennsylvanian (Missourian), and Permian (Wolfcampian) shales from the Permian Basin of west Texas and southeastern New Mexico indicate that these shales were deposited in deep-water environments, whereas the Atokan shales were deposited in a shallow-water open shelf environment. Woodford, and Wolfcampian shales were deposited as hemipelagic sediments in environments having little wave and current action, while Canyon shales were deposited by turbidity currents and are associated with submarine fan facies. Integrated sedimentological, paleontological and geochemical data indicate that these Paleozoic shale sequences were accumulated in stratified water columns and anoxic to near-anoxic conditions prevailed during their deposition. Hence, large amounts of marine organic matter are preserved in these shales, as indicated by the relatively high total organic content (TOC) values. TOC for all shales exceeds 5 wt% and reaches up to 26 wt%. Shales are classified as, lutite, granolutite, granopackite, and compackite. Lutite is a clay-supported rock with less than 10% grains, whereas granolutite is a claysupported rock with more than 10% grains. Granopackite is a grain-supported rock, having a texture in which grains are in contact and detrital clay is dispersed among the grains. Compackite is characterized by a grain-supported fabric, but the grains are separated by clay platelets which have been bent and distorted owing to compaction. Canyon turbiditic shales exhibit much more shale rock type diversity than any of the Woodford, Atokan, and Wolfcampian hemipelagites. Appreciable amounts of diagenetic minerals were precipitated in these shales. Framboidal and cubic pyrite and silica are common minerals in all shale sequences. Dolomite, calcite, ferroan dolomite and ferroan calcite are abundant in Wolfcampian shales and significant amounts of ferroan dolomite occur in Woodford silty black shales. Celestite and anhydrite were detected only in the Wolfcampian shales from the Delaware Basin and siderite is only found in the Canyon shales. The significance of abundant authigenic minerals in these shales, is that they occur early, possibly before hydrocarbon generation, hence producing a very impermeable medium which would obstruct migrating pore fluids and/or oil. Clay-mineral diagenesis (conversion of illite smectite mixed layers to illite) appears to partially have influenced the diagenesis or precipitation of the authigenic nonclay minerals in these shales, and played an important role in the evolution of ferroan calcite and ferroan dolomite in Woodford and Wolfcampian shales. Petrographic analyses of the studied (Woodford, Atokan, Canyon, and Wolfcampian) shales, in conjunction with examination of geophysical density and porosity logs (FDC and CNL) indicate that some shales are compacted, while others are less compacted. Compacted shales are characterized by low densities, contain flattened palynomorphs and shale fabrics compressed around sand grains, bioclasts, and pyrite and phosphatic nodules. Less compacted shales (Wolfcampian shales) contain appreciable amounts of diagenetic minerals which resulted in differential cementation of these shales, increasing their density and arresting compaction.Item Skarn formation adjacent to the Whitehorn Stock, Chaffee County, Colorado(Texas Tech University, 1986-05) Wofford, Melissa K YoungPaleozoic sediments in the Calumet Mining District were metamorphosed by emplacement of the Whltehorn Granodiorite and related sills during Late Cretaceous time producing metamorphic zonations. Carbonates in the Manitou Dolostone were metamorphosed to dolomite, tremolite and calcite assemblages. The Fremont Dolostone and Leadville Limestone were metamorphosed to dolomite, calcite, muscovite, tremolite, chlorite and minor diopside assemblages. The greatest effects of metamorphism and hydrothermal activity occur in the Pennsylvanian Kerber Sandstone that lie between the stock and a sill that intruded subjacent Leadville Limestone. Numerous vein-like sills intruded the Kerber Sandstone, producing mixtures of hypidiomorphic-granular igneous rocks and calc-silicate assemblages of diopside, plagioclase, scapolite and spinel. These rocks are hosts for large veins of massive epidote, garnet, calcite and wollastonite formed as a result of mass transfer by fluid infiltration in the sediments. Original sand-rich and carbonate layers were metamorphosed to quartzites and wollastonitic marbles, respectively. Pelitie rocks form the central part of the Kerber Sandstone. In these rocks, the andalusite zone lies furthest from the stock and is succeeded by the andalusite + sillimanite and sillimanite zones toward the stock. Cordiarite is a major phase in all three zones. Graphite is abundant in the second and third zone and as inclusions in andalusite in the first zone. Fibrolite is a retrograde (?) mineral in all three zones. Corundum-bearing pelites formed in the sillimanite zone. The pressure of skarn formation was estimated to be 1.4 kbars by determining thickness of overburden at the time of intrusion. Temperature of formation of the carbonates in the Fremont Dolostone and Leadville Limestone was estimated to be 569°C to 583°C with a fluid composition of XC02 = 0.55 to 0.62. A temperature of 670°C for the pelitic rocks was estimated from the aluminum silicate phase diagram. Fluid composition in the pelitic rocks could not be determined but were estimated to be H20~rieh. The position of the P-T equilibria for the cale-silicate rocks are greatly affected by the fluid composition and/or the mineral composition and did not yield meaningful temperatures. Since the cale-silicate rocks and pelitic rocks are equidistant from the stock, a similar temperature of formation would be expected. At a temperature of 670°C, XC02 = 0.22 for the cale-silicate rocks. The magmatic veins that intruded the Kerber Sandstone must have been at temperatures greater than 725"C (granitic solidus).Item Structural Analysis of Folding of Paleozoic Sequence, Solitario Uplift, Trans-Pecos Texas(Texas Tech University, 1981-08) Bagstad, David PeterThe Solitario is an eroded dome of about nine miles diameter located in southwest Texas. Its core is chiefly of deformed Paleozoic sedimentary rocks, which are overlain unconformably by outward-dipping Cretaceous limestones that constitute the rim rocks. Earlier work on the Solitario focused mainly on the stratigraphy and igneous geology, correlation of Paleozoic Ouachita facies rocks with those in the Marathon region, and doming as a product of interpreted laccolithic intrusion. Less attention was given to structural studies, but tectonic correlation between the Solitario and Marathon regions was suggested on the basis of general deformational style and trend. Affects of doming are removed to obtain late Paleozoic structural configurations. The resulting pattern of bedding, as displayed on equal-area projections, shows a major fold system the attitude (45°4°NE) of which matches closely that of the Ouachita system in the Marathon region; 15 axes of minor folds also have Ouachita orientations. Unexpectedly 13 minor fold axes have different, deviant, trends. A second rotation to remove the effects of Ouachita folding, shows a poorly defined girdle of deviant minor folds approxi'mately perpendicular to the Ouachita system. These folds could represent a pre Ouachita deformation, but such a deformation is problematical.Item Structural Relationships of Paleozoic and Mesozoic Rocks, Northeastern Placer County, California(Texas Tech University, 1977-08) Morahan, George ThomasIn northeastern Placer County, California, along the North Fork of the American River, folded and metamorphosed Paleozoic rocks are in contact with a homoclinal succession of Mesozoic rocks. The Paleozoic rocks, part of the Blue Canyon Formation of the Calavaras Group, consist predominately of quartz metawacke, metasiltstone, slate, and metachert. The Mesozoic rocks crop out to the northeast of the Blue Canyon Formation. They are mainly of the Early to Middle Jurassic Sailor Canyon Formation, which is composed of feldspathic graywacke, siltstone, shale, and volcanogenic rocks. Between the Blue Canyon and Sailor Canyon Formations are conglomerate, limestone, and siltstone of Triassic(?) age. In the Blue Canyon Formation layering (S^.) and foliation (S„) mainly strike northwest and dip steeply southwest; however, orientations of S_ are also distributed about a beta-axis (3), which plunges moderately to the northwest and is parallel to the plane of S„. Mesoscopic fold axes and lineations are sub parallel to 3« A. metamorphic alignment of micas (S-) parallels S„ and is transected by S_ in pelitic rocks. In the Sailor Canyon Formation bedding (S, ) consistently strikes northwest and dips moderately to the northeast. Metamorphic foliation is absent except for a weak alignment of micas near the contact with the Triassic(?) units. At most other localities metamorphism is weak and static, and sedimentary textures are well-preserved. The Triassic(?) units contain a foliation which parallels S^ of the Blue Canyon Formation, but bedding in these units appears conformable only with S^^ of the Sailor Canyon Formation and not with S . Apparently, V the contact between the Triassic(?) units and the Blue Canyon Formation is an angular unconformity. Possibly, rocks of the Blue Canyon Formation were folded or tilted during an early period of deformation (D^?) which preceded deposition of the Triassic(?) units and during which S formed. A later deformational event (D_) involved penetrative shear and incomplete transposition of S and S into the plane of S in the Blue Canyon Formation and northeastward tilting, possibly in association with major fold development, in the Mesozoic units. During D , shearing associated with the development of S_ attenuated upward and eastward, dying out in the Sailor Canyon Formation. D (?) may be an expression of the Permian-Triassic Sonoma Orogeny, D apparently corresponds to the classical Nevadan Orogeny, which affected rocks of the Sierra Nevada during Late Jurassic time. VI