Non-calcareous Sandstone Research Articles

Mineralogical and geochemical evidence for biogenic and petroleum-related uranium mineralization in the Qianjiadian deposit, NE China

The sandstone-hosted Qianjiadian uranium deposit, hosted in the Upper Cretaceous Yaojia Formation in the Qianjiadian area, Songliao Basin, NE China, has been studied for over twenty years. However, there exists debate on whether mineralization fluid is low-temperature groundwater in favor of biogenic mineralization or diabase-related magmatic hydrothermal fluid for this deposit and other adjacent geologically linked sandstone-hosted uranium deposits (Baixingtu, Baolongshan and Huitianzhao deposits) in the North China. This study provided new data from petrographic and geochemical analyses, geochronology of uranium minerals (the EMPA chemical dating method) and petroleum hydrocarbon biomarkers in host sandstones. Two types of host sandstone were recognized. In calcareous sandstones, pitchblende coexists with colloform pyrite and poikilitic calcite cement while quartz and feldspars were extensively corroded. In non-calcareous sandstones, coffinite coexists with colloform pyrite and only feldspars were slightly corroded. This suggests that pitchblende formed in high pH (pH > ∼9) fluid, while the pH of ore-forming fluid for coffinite was lower (pH = 7–9). Besides, EMPA chemical dating revealed two stages of uranium mineralization. Stage-A occurred in 43–28 Ma with pitchblende as the only uranium mineral species. Stage-B occurred in 19–3 Ma with the formation of both pitchblende and coffinite. The uranium mineralization was biogenic under low-temperature groundwater condition and thus not from a diabase-related mafic magmatic hydrothermal fluid based on the following lines of evidence: (i) some coffinite occurs as phosphorus-rich microorganism-like microspherules structure; (ii) pyrite aggregates were generated from bacterial sulfate reduction as indicated by the δ34S values as low as −41.4‰; (iii) calcite cement in calcareous sandstone contains only single phase aqueous inclusions, and have δ13C values as low as −11.2‰, indicating that part of the carbon was derived from organic matter oxidation; (iv) the organic matter oxidation is further supported by hydrocarbons extracted from petroleum inclusions within calcite cement, showing occurrence of C26–C31 17α, 21β 25-norhopanes, typically resulting from heavy biodegradation.

A new species ofFellhanera(lichenized Ascomycota:Pilocarpaceae) from central North America

AbstractFellhanera crucitignorum, a blastidiate crustose lichen with anthraquinones and submuriform ascospores, is described as new to science. The species is associated with exposures of non-calcareous sandstones in Kansas and Oklahoma, in the southern portion of North America's Great Plains. The authraquinones are typically concentrated in the blastidia, creating a distinctive grey thallus with localized orange granules.

A Triassic Upwelling Zone: The Shublik Formation, Arctic Alaska, U.S.A.--Reply

ABSTRACT The Shublik Formation (Triassic, North Slope, Alaska) is an organic-, phosphate-, and glauconite-rich unit with abundant fossils of marine vertebrates and mollusks. Four lithofacies are identified in the Shublik Formation: nonglauconitic sandstone--thin- to medium-bedded, fine, quartzose, calcareous to noncalcareous sandstone or silty to muddy sandstone, fossiliferous in places; glauconitic--thin- to medium-bedded, fine, quartzose sandstone, muddy sandstone, or siltstone containing 10% to > 50% glauconite grains phosphatic--thin- to medium-bedded siltstone or sandstone or laminated, black silty limestone or limestone containing phosphate nodules; and organic-rich--laminated, black limestone, marl, and mudstone. The organic carbon content of the organic-rich facies is as high as 5.45 wt %, despite the fact that the rocks are overmature and have generated oil. The mean P content of the phosphatic facies is as high as 14 wt % elemental P. Ichnofabrics are related to lithofacies and consistent with interpreted oxygen levels. Ichnofabrics also provide evidence of fluctuating oxygen levels within the facies, especially the nonglauconitic sandstone and glauconitic facies. The organic-rich facies and, to a lesser extent, the phosphatic facies contain abundant, pristine, disarticulated shells of the clam Halobia. The facies, geochemistry, ichnofabrics, and taphonomy are interpreted to be related to onshore-offshore gradients in biologic productivity and redox conditions. The facies array in the Shublik Formation is more similar to that in modern upwelling zones than facies arrays in other well-studied upwelling deposits. The Shublik Formation is interpreted as an upwelling-zone deposit and can serve as an archetype of such deposits.

Stratigraphy, sedimentology and structure of the Ihungia decollement, Raukumara Peninsula, North Island, New Zealand

The 75 km2 Ihungia catchment, in the extreme northeast of the North Island of New Zealand, includes part of the northeast-trending, complex belt of Cretaceous and Tertiary rocks forming the eastern continental margin sequence of New Zealand (the East Coast Deformed Belt). Upper Cretaceous “autochthonous” rocks, exposed in the north of the region, are mapped as extensions of the Ngaterian Hikurangi Beds(formation)and overlying Teratan–Haumurian calcareous flysch of Tapuaeroa Formation. The Hikurangi Beds contain 2 new units—the lower Mangarakeke lithofacies(300 m thick, alternating noncalcareous sandstone and mudstone), and the Rangikohua lithofacies(200 m thick, massive, noncalcareous sandstones separated by thin siltstone lenses). These rocks were deformed by north–southtrending isoclinal folding before becoming a repository area for 3 thrust sheets, emplaced by gravity sliding from the north over the “autochthonous” material. The lowest thrust sheet, emplaced following Late Oligocene time, is composed predominantly of Mokoiwi Formation mudstones, including blocks of Taitai Sandstone Member (Motuan, Albian age), and blocks of Mangatu Group lithologies, including Whangai and Weber Formations (Dannevirke–Landon, Paleogene),enclosed in bentonite. New lithologies in the Mangatu Group are divided into sandstone, flysch, or greensand lithofacies. The middle thrust sheet contains thick Upper Tertiary mudstone and flysch of the Ihungia Formation, including a 10-15 m thick, normally graded, igneous conglomerate lithofacies, and a 100 m thick, laminated bryozoan, coquina limestone lithofacies. Emplacement postdates the emplacement of the lowest thrust and occurred later than Middle Miocene. Mangatu Group lithologies recur in the uppermost thrust sheet, emplaced after the middle thrust. All lithologies have been influenced by multiphase ENE-WSW to east-west faulting and folding episodes.

Rio Zulia Field, Colombia: ABSTRACT

The Rio Zulia field in northeastern Colombia lies within the southernmost part of the oil-rich Maracaibo basin. The field measures 3.4 by 0.9 mi (5.5 by 1.5 km) and is located on a faulted anticline whose southeastern flank is cut by an east-directed thrust fault. Cumulative production during the 20 years since Chevron discovered it in March 1962 is 125 million bbl. The oil is brown, paraffinic, and has a gravity of 41.5° API. Maximum production of 35,000 BOPD was reached in 1966; present production is about 4,000 BOPD. Almost all the production has come from the Eocene Mirador Formation, a loosely consolidated fine to coarse-grained, non-calcareous sandstone with irregularly distributed clay and siltstone interbeds. The sandstone is part of the Eocene delta built out to the northeast over the Lake Maracaibo region. The Mirador of the Rio Zulia area belongs to the back-delta fluvial system. End_of_Article - Last_Page 984------------

Geochemistry and Petrology of the Morrison Formation, Dillon, Colorado

The Morrison Formation in a measured drill-core section from Dillon, Colorado, is 226 feet thick and is largely a clastic accumulation of wind-and water-transported altered volcanic dust, clay minerals, and angular to rounded sand-size fragments, mainly quartz. The bottom 60 feet of the formation is a fine-grained siliceous marl containing abundant clay minerals, scattered sand grains, calcareous shell fragments, and chemically precipitated carbonates. Above the marl an interval 110 feet thick includes an alternation of more or less sandy mudstones and calcareous mudstones, and calcareous and noncalcareous sandstones. The top 56 feet is noncalcareous mudstone. Altered volcanic dust is abundant in the upper 117 feet of the formation. Chemical analyses and petrographic characteristics indicate that a large fraction of the materials in the formation came ultimately from a rhyolitic volcanic source, but sparse to abundant sand grains in many layers indicate intermixing of materials from other sources. Abundant clay minerals in the formation formed prior to, and after deposition. After deposition, illite and cryptocrystalline quartz developed at the expense of originally deposited components.

Diagenetic Aspects of Lower Morrowan, Pennsylvanian, Sandstones, Northwestern Oklahoma

Diagenesis has profoundly altered the reservoir capacity of some lower Morrowan sandstones in the Anadarko basin. Definitions of sandstone geometry, depositional environment, etc., comprise only part of the information necessary to explore intelligently for hydrocarbons in these rocks. Most of the lower Morrow sandstones were deposited in a broadly transgressive system. Two basic types of sandstone are recognized: (1) Type A is a very nearshore, clean, well sorted, non-glauconitic, non-calcareous sandstone deposited in a high energy environment; (2) Type B is a seaward facies of Type A, deposited under lower energy conditions and is normally poorly sorted, glauconitic, calcareous, and here and there shaly. Petrographic analyses indicate Type A sandstones have either (1) extreme pressure solution and no permeability, or (2) moderate to minor pressure solution with secondary quartz overgrowth cement. These rocks are generally permeable when medium- to coarse-grained and impermeable if fine-grained. Upper and lower edges of some sand bodies are tightly cemented with CaCO3 possibly through ionic impedance at the sand-shale boundary. Type B sandstones have been diagenetically altered by minor secondary quartz overgrowth and pressure solution, extensive carbonate cementation, and some authigenic clay. Commercial permeability is associated with secondary removal of carbonate cements. Such reservoirs have random shapes and are difficult to predict or evaluate. A qualitative petrographic rock fabric classification based on relative degree of pressure solution, type of grain outlines and contacts, amount and type of cement and porosity is useful in mapping their geographic distributions. Integration of this type data into normal subsurface exploration methods is helpful for the understanding of the lower Morrow in the area studied.