Browsing by Author "Wilson, James Lee"
Now showing 1 - 8 of 8
Results Per Page
Sort Options
Item A diagenetic study of the lower coralline limestone (oligocene), the Maltese Islands(1980) Budai, Joyce M.; Wilson, James Lee; Baker, Donald R.; Warme, John E.The Maltese Islands are located on a broad platform extending from northern Africa to Sicily which divides the Mediterranean Sea into an eastern and western basin. Strata exposed on the islands range from Upper Oligocene to Upper Miocene in age and are predominantly carbonates with one pelagic shale unit. This study focuses on the lowest formation, the Lower Coralline Limestone which is of Upper Oligocene (Chattian) age. The mid-Tertiary was a tectonically active time in the central Mediterranean. The western Mediterranean basin was forming during the Neogene and tectonic thrusting occurred to the west, north and east of the study area. Malta's location on a shallow, relatively stable platform in the center of a tectonically active Mediterranean places it in an interesting setting for diagenetic study. Unlike Recent carbonate sediments, the original mineralogic composition of the Lower Coralline Limestone was dominated by high magnesian and low magnesian calcite with only minor amounts of aragonite. Such a mineralogic assemblage would stabilize to low magnesian calcite rapidly and could conceivably affect early marine cementation and later episodes of fresh-water diagenesis. Fine-grained, fibrous marine cementation is present, but poorly preserved and limited to packstones and grainstones. Fresh-water, phreatic cements occurring in the Lower Coralline are more varied in crystal habit and abundant than the early marine cements. Three stages of meteoric cementation are recognized. An early period of syntaxial rim cements on echinoid fragments, accompanied or followed by grain compaction, forms the dominant cement type found in these rocks. These overgrowths display stratigraphically continuous luminescent zones like those reported in Mississippian limestones in New Mexico (Meyers, 1974) . The second phase of meteoric cementation produced fine- to medium-grained scal enohedra cement that clearly follows compaction and echinoid overgrowth development. These cements do not luminesce and constitute less than 20 percent of the fresh-water cements. The final stage of fresh-water cementation produced fine to medium grained, equant granular. void-filling spar. Diagenetic features examined in the Lower Coralline Limestone indicate at least two separate episodes of emergence and fresh-water cementation. Timing of emergent periods can be limited by extent of phreatic diagenesis within the lower units exposed on Malta. Stratigraphic relations of overlying formations that have been down-faulted into subsidence structures created by collapse of solution caverns within the Lower Coralline Limestone (Pedley, 1974) and limited erosional contacts in the lower part of the section provide possible times of fresh-water influence. In addition, proposed periods of subaerial exposure coincide closely with eustatic sea level drops described by Vail et al. (1978) .Item Deposition and diagenesis of the Mississippian Lodgepole Formation, central Montana(1973) Jenks, Susan Elizabeth; Wilson, James LeeThe lower Mississippian Lodgepole Formation is exposed in central Montana in the anticlines which form the Big Snowy and Little Belt Mountains. Four sections averaging 130 feet in length were measured at the base of the Woodhurst Limestone, the uppermost member of the Lodgepole. Three of the sections were located in the western end of the Big Snowy Mountains. These were composed of two major bioclastic and ooid grainstone units, and a succession of mudstones, wackestones, packstones and argillaceous dolomites and pellet grainstones and pelleted mudstones. Field, faunal, and petrographic evidence indicate these rocks were deposited in very shallow water, the grainstones in the form of carbonate sand shoals, the remaining rock types in a broad lagoon behind the shoals. One section was measured 70 miles to the west in the Little Belt mountains. Rocks here consist of crinoid grainstones and packstones, skeletal and ooid grainstones, mudstones, bryozoan packstones and wackestones, and calcareous shales. Evidence suggests these rocks formed down paleoslope from those in the Big Snowys, some of the sediments being deposited in deeper water in a normal marine shelf environment. A number of diagenetic processes affected the sediments after deposition. Morphology and distribution of cements and evidence of timing relative to other diagenetic events indicate cementation of the carbonate sands took place in the intertidal or shallow subtidal environment soon after deposition. Dolomitization of crinoid debris with magnesium derived from the high magnesian calclte of the crinoid skeletons themselves also took place very early in the history of the sediment. This was followed by silicification and pyritization of skeletal debris and ooids. Another, more extensive period of dolomitization occurred which affected micrite and, to a lesser extent, ooids and tended to avoid skeletal material and spar. The last diagenetic event to affect these rocks was compaction and stylolitization filled remaining pore space as coarse blocky calcite spar.Item Late Pleistocene stratigraphy and geologic development of Cozumel Island, Quintana Roo, Mexico(1977) Spaw, Richard Hoencke; Wilson, James LeeKnowledge of the depositional history of Cozumel Island is important for an understanding of the tectonics of the block-faulted eastern Yucatan and Belize continental margin. Basic information was derived from field reconnaissance and petrographic and mineralogic descriptions of thin sectioned and x-rayed samples. Two older Pleistocene, ten late Pleistocene, and one Holocene shallow-water carbonate facies are differentiated by their geometries and positions, megafauna, sedimentary structures, textures, carbonate grain-types, mineralogies and cements. The two older Pleistocene facies represent patch reef and sandy backreef environments of deposition. The late Pleistocene facies were deposited in windward and leeward coral reef, reef pass, seagrass-stabilized backreef, oolite shoal, storm channel, beach, and dune environments. Beachrock is the only Holocene rock on the island. Previously described 125, + 15, B.P. reef, backreef, and beachnearshore facies on the eastern Yucatan coast are in the same positions as the late Pleistocene facies on Cozumel Island; thus, the late Pleistocene Cozumel facies probably were deposited during the Sangamon Interglacial. A world-wide sea level fluctuation curve compiled from the literature is applied to deposition on Cozumel. Rocks from the island record two periodsof submergence with associated shallow-water carbonate deposition, and two intervening periods of emergence with associated subaerial vadose diagenesis. In reconstructing the depositional history of the island, it is determined that no tectonic activity has occurred since the latter part of the middle Pleistocene.Item Origin and silica-carbonate relations of cherts of the Upper Cretaceous of Venezuela(1973) Marcucci, Ettore; Wilson, James LeePetrographic and chemical studies were made on the black cherts of the San Antonio formation (eastern Venezuela) and of the Ftanita del Tachira member (western Venezuela), both of Upper Cretaceous age. The AI2O3, Fe2 (total), MnO, CaO, MgO, K2O and Ti2 contents were analyzed by X-ray fluorescence; S12 contents were analyzed by X-ray fluorescence and gravimetric methods. Na2 was measured using atomic absorption techniques. Gammaray spectrometric methods were used for the determination of U and Th in the rocks from eastern Venezuela. The type of carbonate present was identified by staining the thin sections with K ferricyanide and Alizarin red S. At the microscope, the cherts can be divided into three broad types: (a) pure cherts, with microquartz in the matrix and few microfossils; (b) shaly cherts, with variable amounts of calcite, clay minerals and microfossils; (c) calcareous cherts, with abundant microfauna and calcareous matrix. A fourth type of rock present in the cherts is represented by the calcareous nodules. Combined stratigraphic, lithologic and petrographic data show that the sediments from which the cherts of eastern and western Venezuela derived, were deposited in similar euxinic environments. The Fe/Mn ratios suggest that the sedimentation happened in deep waters. The low Th/U ratios of the rocks from eastern Venezuela are consistent with low rates of sedimentation. The low TiOg/AO and FegO-AlO ratios exclude that the source of Si2 was basic volcanism. The low Th contents in the San Antonio formation suggest that acidic volcanism was not an important source of silica. The presence of partially preserved radiolarians supports the biogenic origin of silica for both cherts. A simplified model of sedimentation in euxinic basins, which explains the alternation of deposition of siliceous and calcareous sediments, is proposed. According to this model, the pH is the factor controlling the solution of the calcareous tests and the consequent concentration of biogenic silica. The deposition of the more argillaceous sediments from which the shaly cherts originated, was probably related to the flushing of the basins by oxygenated currents. The pure cherts were formed by solution of opaline tests of radiolarians and redeposition of the Si2 as void filling, before compaction. The silicification of the matrix and of the calcareous tests happened probably in a later stage. Plots of Si2 contents vs Si2/Al2 ratios and of CaO contents vs SiOg/A^O-j ratios show that the chemical composition is consistent with the formation of these cherts by introduction of Si2 to an original siliceous ooze. The formation of the calcareous cherts In which many calcareous tests are preserved, and the variable proportions of calcite and silica filling the tests, must be related to different production of NH^ and COg by bacterial decay in the early diagenesls. Plots of Si2 contents vs Si2/Al2 ratios and CaO contents vs SlOg/AO ratios show that the derivation of these cherts from a globigerinld ooze, by introduction of silica, would agree with their chemical composition. The calcareous nodules were formed during the early diagenesis of the sediments, before compaction. The replacements of S12 by rhombs of calcite, present in the calcareous cherts, happened after lithiflcation of the sediments.Item Paleo-environments of Middle Pennsylvanian Chaetetes lithotopes, Texas and New Mexico(1977) Spaw, Joan Mussler; Wilson, James LeeDetailed field studies and petrographic analyses of Chaetetes-bearing sections reveal Chaetetes in the presence of Profusulinella in the La Tuna and Berino Formations (Morrowan-Atokan) of the Magdalena Group in the Northern Franklin and Hueco Mountains, Texas and New Mexico. Chaetetes and non-Chaetetes lithotopes are characterized by a diverse and abundant assemblage of benthonic organisms typical of a clear, well-illuminated shallow-water carbonate platform of the late Paleozoic. Two chaetetid growth forms with apparent écologie significance were observed: shingle-form Chaetetes and club-form Chaetetes. Shingle-form Chaetetes are characterized by numerous increases or decreases in width of the upward-growing colony, and commonly form anastomosing complexes of colonies. Club-form Chaetetes evidence subtle changes in width, emphasizing growth along the vertical axis; clustering of solitary club forms is common. Both growth forms are excluded from high-energy shoaling environments. Shingle-form Chaetetes are restricted to the base of lithotopes characterized by prolific growths of phylloid algae. Cuneiphycus, and tubular organisms. Competition with these organisms for substrate space apparently limits Chaetetes distribution on the platform. Common, erratic growth discontinuities in shingle forms and associated burrow-churned wackestones and packstones imply frequent fluctuations in the physical and biological environment. Stagnant, poorly oxygenated conditions on the sea floor limit solitary clubform Chaetetes to the base of a laminated bioclastic mudstone lithotope. Relatively stable conditions in quieter, deeper water are suggested by the associated discretely burrowed, well-laminated mudstones and wackestones.Item Patch reefs off Bermuda(1970) Jordan, Clifton Francis; Wilson, James LeePatch reefs living on the Bermuda Platform provide excellent models for detailed investigation of bioclastic sediment dispersion. Skeletal debris is shed from the reef top to form a wedge of reef flank sediments which angularly onlaps the reef mass at the uppermost reef flank and grades into lagoonal sediments in deeper water. Major avenues of sediment transport are reef face channels, which connect sand channels of the reef top with upper sections of the reef flank. Distance of sediment transport off the reef top is small--less than 100 meters. Compositional and textural trends across patch reefs are interpreted using a working model based on substrate control, biofacies development, particle breakdown, and sediment transport by wave action. Sediment composition provides the basis for recognition of the following microfacies: sediment pockets, sand channels, reef face channels, reef flank, interreef lagoon, and open lagoon. These microfacies are transitional and, in the above order, display the following trends: from the reef top lagoonward, the abundance of Homotrema, coral, and red algae in the sediment increase and the abundance of Halimeda and Foraminifera (excluding Homotrema) decreases. Interreef lagoons are distinguished from open lagoons by a lower mollusc content in the sediment. From the reef top lagoonward, mean grain size generally decreases (with certain anomalies explainable by the patch reef model of sediment dispersion), sorting progresses from poor to very poor, and skewness becomes relatively higher (due to winnowing of fine particles and addition of coarse reef material on the reef top). All kurtosis values indicate non-normal particle-size distributions and support the observed bimodality of sediments associated with patch reefs. Sand-size particles dominate sediments of patch reef facies. The absence of silt and clay is characteristic of the reef top. Gravel is nearly evenly distributed, owing in part, to the large Halimeda content of the sediments (25%-60%) which is significant in this size fraction. Grain size distributions were obtained from a combination of sieving, Emery settling tube, and hydrophotometer analyses. Owing to the effects of irregular particle shapes, Emery tube data must be adjusted if a combination with sieve data is made. A graphic adjustment of such data is made which provides good approximations for mean and standard deviation, while maintaining relative relationships for skewness and kurtosis. Textural trends are displayed more accurately and are more easily recognized when moment calculations are used rather than graphic determinations of sediment parameters. Thus, distribution of bioclastic sediments from Recent Bermudan patch reefs takes place on a small, local scale to form reef flank sediments, results in recognizable sediment microfacies, and is explainable by a sediment dispersion model.Item Provenance and paleotectonic setting of conglomerates in the Virgilian Holder Formation, northern Sacramento Mountains, New Mexico(1978) Dunning, Charles Preston; Wilson, James LeeThe Late Pennsylvanian (Virgilian) Holder Formation of the Sacramento Mountains, south central New Mexico, is composed of clastic and carbonate rocks cyclically deposited on the narrow Sacramento Shelf. Coarse channel fill conglomerates are often found in the lower terrigenous member of the cycles. The cycle thicknesses, coarse terrigenous clastic thicknesses and the trend of the conglomerate channels respond to both the pre-cycle topography and the growth of topographic structures during deposition of the cycle. The prominence of the tectonic structures appear to have increased during the early Virgilian to a maximum during cycle 6. The relatively thin and uniform thicknesses during cycle 7 indicates that growth of shelf structures was at a minimum. Growth was renewed during cycles 8 and 9, documented by the rejuvenation of the La Luz Anticline and the Dry Canyon Syncline. Paleotransport directions from the lower 9 cycles generally indicate southwesterly transport, away from the Pedernal Uplift and into the Orogrande Basin. Where channels are recognized, there is good correlation between channel trends and transport directions. During the height of the transgressive phase of the cycle, the Paleozoic detritus derived from the Pedernal Uplift was involved in high energy coastal processes at the base of the escarpment. It was in this environment that Paleozoic chert and Cambro-Ordovician Bliss Formation quartzite clasts were rounded, and whatever feldspars and Pre-Pennsylvanian limestones that has not been reduced insitu on the uplift or in transport, were destroyed. High energy runoff from the uplift spread the cherts, quartzites and quartz sand across the shelf as clastic flows. These flows cut the channels, incorporating shelf linestones of Virgilian age into the Virgilian conglomerate deposits.Item Speleogenesis in Comal County, Texas(1968) Beck, Barry Frederick; Wilson, James LeeCaves in Corral County, Texas, were examined with regard to their lithologic and geomorphic setting, paying particular attention to controls such as stratigraphic variation, topography, jointing, and ground-water flow. In the light of these data, a new classification of caves is proposed based upon the mode of water flow involved in their formation. Influent caves are formed by water flowing from the surface to the ground-water table. Effluent caves are formed by water flowing from the ground-water reservoir to the surface. Conduit caves are formed principally by phreatic flow with little, or no, surface relationship. This classification is extremely useful in identifying the factors involved in speleogenesis when used in conjunction with areal maps of the aforementioned controls. Effluent caves in the lower Glen Rose Formation are localized within a massive, fossiliferous aquifer and oriented generally down-dip, thus substantiating Gardner's (1935) theory of speleogenesis. Influent caves in both the upper and lower Glen Rose Formation are developed in areas with low surface gradient and consequently high infiltration. They develop vertically until the water reaches a suitable calcareous stratum which conducts it away laterally. A later change of conditions may cause further deepening and a series of pits and passages may develop. Conduit caves in the upper Glen Rose Formation appear to be localized within the more calcareous strata because of the high solubility of these layers in contrast to the shales, marls, and dolomites composing the major part of the section. Secondary collapse of the overlying less soluble strata may provide access for additional inflow, but in most cases this can be eliminated as the primary cause of cavern development. Vadose inflow and the mixing effect which Thrailkill (1968) has postulated as causes of increased solution do not seem responsible either. All the conduit caves examined in detail, however, occur in areas of ground-water convergence. It is hypothesized that the abnormally high flow rate and volume due to this convergence is responsible for their development, thus supporting the mechanism proposed by Swinnerton (1932) and Davies (1957). A cursory examination of caves in the Edwards Limestone reveals that effluent caves may also be caused by the overflowing of a perched aquifer into surface valleys. In the Edwards Limestone it also appears that conduit caves may be localized in a horizon which has high permeability, even within a compositionally homogeneous section.