Anthony W. Walton

Alteration of hyaloclastites in the HSDP 2 Phase 1 Drill Core 1. Description and paragenesis

This is the publishers version. Copyright 2003 by Chinese Geophysical Society. All rights reserved.

History of diagenetic fluids in a distant foreland area, Middle and Upper Pennsylvanian, Cherokee basin, Kansas, USA: Fluid inclusion evidence☆

Abstract Analysis of fluid inclusion data in diagenetic cements from Pennsylvanian limestones and sandstones of the Cherokee basin in southeastern Kansas reveals the succession of diagenetic fluids in a distant foreland of the Arkoma-Ouachita system. This succession includes early low-salinity (0.0–2.4 wt% NaCl eq.) fluids of meteoric affinity (Fluid I) followed by low-temperature Na-Ca-Cl brines (Fluid II with salinities between 8.4 and 24.1 wt% NaCl eq.). Fluids I and II were present in the system during precipitation of early-stage calcite cements at temperatures less than about 50°C. Another Na-Ca-Cl brine (Fluid III with salinity up to 25 wt% NaCl eq.) was present in the system later, at temperatures of maximum burial (at least 80–85°C) and higher. Fluid III is followed by a Na-Cl brine (Fluid IV, with salinities about 19–21 wt% NaCl eq.) characterized by temperatures distinctly higher than maximum burial, up to 150°C. Fluid III and Fluid IV were entrapped during precipitation of late-stage baroque dolomite and Fe-dolomite in Pennsylvanian limestones, and late-stage Fe-dolomite and ankerite in Pennsylvanian sandstones. The record of progression from Fluid III to Fluid IV may have been partially obscured by thermal re-equilibriation of some inclusions during migration of Fluid IV. Fluids with Na-Ca-Cl chemistry (Fluid II and III) were either indigenous subsurface fluids of the Cherokee and Arkoma basins, or might have originated as reflux fluids in a Permian evaporitic basin of Central Kansas. Later Na-Cl brine (Fluid IV) originated in deeper parts of the Arkoma-Ouachita system and might have acquired their salinity by dissolution of hypothetical salts buried beneath the Ouachitas. Temperatures recorded by fluid inclusions in late-diagenetic carbonates are 20–60°C higher than those calculated for the maximum burial of the studied section. This thermal anomaly suggests an advective heat transfer from the Arkoma-Ouachita system onto the shelf of the Cherokee basin related to the invasion of late-diagenetic fluids.

Accumulation of volcaniclastic aprons in the Mount Dutton Formation (Oligocene-Miocene), Marysvale volcanic field, Utah

Volcaniclastic rocks in the Mount Dutton Formation form coalescing aprons of lahar deposits around several volcanoes. The aprons accumulated across a featureless alluvial plain in an arid to semi-arid climate. Under these conditions, debris flows dominated apron construction, building large aprons extending as much as 27 km from the flank of the source volcano. Three distinct but gradational lithofacies assemblages within the aprons show a proximal to distal change from thickly bedded, coarse lahar deposits to thinly bedded, fine-grained ones. This lithofacies change represents a change from channelized flow on the proximal apron to unchannelized flow on the medial apron. Unconfined flow on the medial apron, together with lower slope, caused lahars to deposit the bulk of their sediment load. Most deposition in distal areas resulted from small, dilute lahars. Large lahars capable of transporting coarse sediment into distal areas were rare. The aprons also show a down-apron decrease in abundance of debris-flow deposits, corresponding to an increase in hyperconcentrated flow deposits. This trend represents reworking of more proximal deposits by floods that did not form debris flows, rather than flow transformation from debris flow to hyperconcentrated flow. Arid climate and unchannelized flow prevented the flow transformation that is a common feature of volcaniclastic deposits in the Pacific Northwest, where glacially dissected valleys with permanent streams control flow of lahars away from the volcanoes.

Effect of Oligocene volcanism on sedimentation in the Trans-Pecos volcanic field of Texas

The nature and history of volcanic activity in the Trans-Pecos volcanic field of Texas controlled depositional timing, environmental distribution, and lithologic character of associated sediments. Tuffaceous and epiclastic sedimentary rocks of the Tascotal and Fresno Formations and the Perdiz Conglomerate are part of the intermediate-source facies of the field. Rhyolitic and trachytic activity in major calderas produced abundant pyroclastic debris that has been reworked into sandy alluvial fans adjacent to the caldera complexes, whereas post-volcanic alluvial-fan sediments are tuffaceous or epiclastic conglomerates. The intermediate-source facies consists of four components: active apron, inactive (or epiclastic) apron, eolian sand sheet, and valley facies. The arrangement and timing of development of these facies depend upon the eruptive history of the volcanic centers. The Tascotal, Fresno, and Perdiz contain five depositional units. (1) The Chinati apron unit recorded rhyolitic and trachytic activity in the Chinati Caldera during the 105–106 yr after its collapse. (2) The southern apron unit formed around the San Carlos–Sierra Rica eruptive center in Mexico before eruption of the San Carlos Ignimbrite. (3) The conglomerate and limestone unit formed as epiclastic fans around the Solitario uplift and as braided-stream and lake deposits between aprons and the Solitario. (4) The eolian unit of the Tascotal formed as drainage off the Chinati eruptive center adjusted from carrying fine pyroclasts to coarser epiclasts. (5) The Perdiz Conglomerate and equivalent epiclast-rich, conglomeratic parts of the Tascotal and Fresno are a bajada-like accumulation of fluvial epiclastic conglomerate from non-volcanic sources and the Chinati eruptive center after its activity ceased. Framework mineral composition is a function of grain size; very fine and fine tuffaceous sandstones consist mostly of reworked glass shards, and rocks that have textures coarser than medium sand are mostly epiclastic VRFs. Active apron rocks formed by deposition from sheet-floods and poorly defined channels in a bajada-like accumulation that resembles sandy distal alluvial-fan deposits because the volcanos provided so much sand-sized debris, but little clay.

EUENDOLITHIC MICROBORINGS IN BASALT GLASS FRAGMENTS IN HYALOCLASTITES: EXTENDING THE ICHNOFABRIC INDEX TO MICROBIOEROSION

Abstract A systematic, semiquantitative measurement of intensity of euendolithic microbioerosion aids in understanding the interactions between microorganisms and basalt glass. These interactions are important because they occur widely in ocean basins and lead to incongruent dissolution of glass. No semiquantitative method currently exists for measuring euendolithic microbioerosion. We modify the ichnofabric index (ii of Droser and Bottjer, 1986) to the microendolithic ichnofabric index (MII), a scale-independent, orientation-independent, semiquantitative classification scheme specifically for euendolithic microborings in volcanic glass, but applicable to any medium. Material used to develop the MII comes from the phase one core, Hawaii Scientific Drilling Project #2 well and ranges in age from ~636 to 413 ka. Microtubular features in the glass are linear or curvilinear, ~0.5–2 µm in diameter, 1 µm to >100 µm long, and originate from the margins of glass fragments found in hyaloclastites and pillow lavas. Standard categories of the ii were modified to address the circumstances of the microborings. Percent disruption of primary fabric is the basis of the MII rather than percent disruption of bedding. Six categories are used ranging from no (MII  =  1) to complete disruption (MII  =  6). Modification of the ii extends the measuring scale of bioerosion to near the minimum size range for trace fossils. By extension, MII can be used for any traces that penetrate the associated medium, from microbial borings to dinosaur footprints, if the ratio of measurement length to diameter of the traces is ~30 : 1.

Stratigraphy and Depositional Environments--Krebs Formation in Southeastern Kansas: ABSTRACT

End_Page 1317------------------------------The Krebs Formation (Middle Pennsylvanian-Desmoinesian) forms the lower portion of the Cherokee Group in the Cherokee basin of southeastern Kansas. The Krebs Formation near its outcrop in Cherokee and Crawford Counties consists of 78% shale and mudstone, 18% sandstone and siltstone, 3% coal, and 1% limestone, comprising a total thickness of 120 to 220 ft (37 to 67 m). Integration of data from continuous cores, outcrops, and geophysical logs provides a detailed stratigraphic framework and facilitates interpretation of depositional environments. Coal beds and associated seat-rock units, some having an areal extent of several thousand square miles, provide excellent stratigraphic marker beds for correlation of discontinuous reservoir sandstones. Radioactive dark-gray shale units and argi laceous limestone units often overlie coal beds and may be equally widespread. Net-sandstone isolith maps reveal the presence of a lobate deltaic complex in southwestern Missouri, characterized by both stacking and offset of major sandstone bodies. Coal beds commonly cap upward-coarsening, mud-dominated sequences consisting of dark-gray shale with occasional argillaceous limestones overlain by lenticular-bedded shale or wavy-bedded siltstones. This vertical transition of lithofacies is interpreted to result from the progradational infilling of large interdistributary bays. Coarsening-upward sandstone sequences--consisting of lenticular-bedded shale grading upward into wavy-bedded siltstone, flaser-bedded sandstone, and rippled or cross-bedded sandstone--represent distributary mouth-bar or crevasse-splay deposits. Fining-upward sequences--composed of a basal scou surface overlain by mud-clast conglomerates, large-scale cross-bedded sandstone, and rippled or flaser-bedded sandstone--are interpreted to be channel-fill or point-bar deposits. End_of_Article - Last_Page 1318------------

Evaluation of Uranium Potential of Frontier Areas by Functional Source-Rock Analysis: ABSTRACT

Rapid, inexpensive evaluation of the potential of frontier areas for epigenetic uranium deposits can be conducted using functional source-rock analysis analogous to that employed in the petroleum industry. Association of uranium-rich volcanic glass with nearly all such deposits suggests that their uranium came from glass. Concentration of uranium in ores is about 103 times that in glass-rich sources, so great volumes of depleted rock should mark favorable areas. Fresh rhyolite glass contains uranium adsorbed on shard surfaces, soon washed off, and 5 to 10 ppm internal uranium, which is released when the glass converts to a crystalline assemblage. Only under certain circumstances does released uranium migrate. Studies conducted in south and west Texas and in Nevada on volcanic rocks and sediments that originally contained abundant volcanic glass lead to the following conclusions: conversion in soil or by very early diagenesis, and low temperature conversion of glassy ash flows to clay release uranium for migration; high temperature conversion by divitrification or vapor phase crystallization and diagenesis in open hydrologic systems trap uranium near its site of release. Structures and textures produced during each of these processes are disti ctive and can be recognized in the field or in thin section. Furthermore, the processes probably produce distinctive chemical effects other than depletion of uranium. Functional source rock exploration for uranium consists of field, petrographic, and geochemical detection of depleted rock that altered in a favorable fashion. Evaluation of likely migration routes; geologic, geochemical, and radiometric exploration for traps; and drilling programs can then be concentrated in the most favorable areas. End_of_Article - Last_Page 798------------