Sedimentary Phosphorites Research Articles

Analysis and interpretation of the paleogeographic distribution of marine sedimentary phosphorites

World-wide distribution of marine phosphorite deposits has been plotted on computergenerated paleogeographic maps of specific geologic time intervals in order to determine if and when optimum arrangements of continents and oceans existed for phosphorogenesis. Geographic input data for the program HYPERMAP consists of digitized continental edges and bathymetry and appropriate coordinates for discrete continental structural blocks. Paleopole and block rotation data were used to construct maps for the following time intervals; Recent, 20, 40, 60, 80, 100, 120, 140, 170–190, 250, 280, 325, 350, 375, 400, 450, 500, and 600 Ma. Phosphorite deposits were plotted directly on the appropriate map according to location and age. The major phosphorites have been divided into four types (A, B, C, D)on the basis of the environment of deposition and facies association. A and B types were deposited in water depths of several hundred meters in association with black shales, chert, and dolomite. In terms of reserves of P2O5they show marked distribution peaks in the Lower and Middle Cambrian and the Permian. C and D types were deposited in water depths of tens of meters in association with quartz siltstones, quartz mudstones, and carbonates. Time distribution peaks in the Lower and Middle Cambrian, the Ordovician, Upper Cretaceous-Eocene, and the Miocene are evident for these deposits. The plotted distributions may be related to a recent model of phosphorite deposition (Sheldon, 1980)which suggests that phosphate levels in ocean water have fluctuated with time. Phosphate content built up during times of high-level warm seas was brought into favorable depositional sites by equatorial and tradewind belt upwelling currents. The paleogeographic analysis shows that maximum phosphorite deposition from equatorial upwelling (type C)occurred north and south of narrow constricted equatorial seaways, at times of high-level warm seas. Maximum deposition of phosphorites from tradewind belt upwelling (types A, B, C, D)occurred when polar oceans were wide and there were extensive north-south trending coasts in low latitudes, at times of transition from high-level warm seas to low-level cool seas.

Lower Eocene phosphorites of the western desert, Iraq

Marine sedimentary phosphorites of Eocene age (Upper Ypresian) are exposed in the extreme west of Iraq within the Dammam Formation. They are associated with limestone and chert, and their deposition seems to have taken place in a shallow marine environment within a structurally controlled basin open to the sea from the northern and western sides only. The studied phosphorites are granular in texture, coarse-grained and cemented by calcite which is occasionally silicified. Bone fragments are present in small amounts. Carbonate-fluorapatite is the only phosphate mineral detected in these phosphorites, with relatively high amounts of the components SO 4 −2, CO 3 −2, F −1, H 3O 1 and Na 1 substituting in the crystal structure. The Lower Eocene phosphorites of Iraq are part of the Tethyan phosphorite province, and are comparable in many aspects with those of Paleocene and Upper Cretaceous age in the Western Desert of the country.

The phosphorites of West Thaniyat Turayf, Saudi Arabia

Sedimentary phosphorite has been deposited during a transition from clastic to chemical sedimentation as a result of upwelling of nutrient-rich waters coinciding with a Late Cretaceous (?) transgression of the Tethys sea in a part of northwestern Saudi Arabia. A 3- to 5-m-thick zone of phosphorite, chert, mudstone, and magnesian limestone reflecting this transgression is exposed at West Thaniyat.The phosphorite consists of apatite, mostly in pellet form, and clastic quartz with minor montmorillonite or magnesian calcite, and was deposited on a shallow shelf having a gently undulating configuration of basins and arches with a north-northeast trend. Phosphorite deposited in basins is indurated by clay; on arches it is indurated by limestone.There is a constant positive correlation between conditions of moderate turbulence and phosphorite accumulation--even to the extent that inclusions in pellets are clasts of quartz and microsphorite. Thus, apatite is suggested to be precipitated directly from sediment pore waters under conditions of moderate turbulence. Cessation of turbulence and upwelling results in accumulation of montmorillonite mudstone in basins and calcareous oozes on arches. The culminating event of each of two phosphorite-mudstone-magnesian limestone deposition cycles during this transition is a chert layer. This might result from explosive growth of diatomaceous blooms after completion of phosphorite deposition and may depend on changes in the nature of nutrient supply.

Ancient Marine Phosphorites

Marine phosphorites have been studied for more than a hundred years, both because of their commercial value as fertilizer and because of their importance to sedimentary petrology. Phosphorus is, of course, one of the basic plant nutrients and is intimately involved in biospheric processes ; however, its role in biogenic and chemogenic sedimentation is difficult to study and is not completely understood. Marine phosphorites on the seafloor today occur on continental shelves, rises, and seamounts where they are difficult to observe and collect. In the laboratory, the mineral structure and crystal chemistry of sedimentary apatite has been difficult to analyze because of its complexity and small crystal size, and apatite has not yet been synthesized at low temperatures in solutions that approx­ imate seawater in composition. Physical-chemical equilibrium studies have been difficult because of the slow rates of reaction, the complex composition of apatite, and the formation of complex surface phases and complex phosphorous ions in solution, as well as the complex nature of seawater itself. As a result, progress has been slow in understanding the origin of sedimentary phosphorites, including the source and the processes of concentration of the phosphorus and the processes and the environment of deposition of the phosphorite. Hypotheses and arguments have pro­ liferated; however, in recent years consensus has been reached on many points. Arguments still exist on a number of other points, stimulating continued research in the field. Sedimentation processes commonly can be studied directly in the modern environment, and the results can be applied by analogy to inter­ pret ancient deposits according to Lyell's principle. In the case of phos­ phorites, marine geology studies, particularly in the last decade, have produced information that has been extremely interesting and somewhat

Mineralogy of carbonate fluorapatites

The principal phosphate mineral in sedimentary phosphorites is carbonate fluorapatite of the variety francolite. Francolites exhibit several systematic isomorphous substitutions including sodium and magnesium for calcium, carbonate for phosphate, fluorine for oxygen, and hydroxyl for fluorine. These substitutions result in measurable variations of the crystallographic properties including unit-cell parameters and optical indices. Statistical models have been developed to relate compositional and crystallographic variations in the various francolites. Previous work has shown that francolite compositions are metastable with respect to fluorapatite. The effects of weathering, metamorphism and geological time causing systematic changes in francolite compositions are used as examples of these relationships.

Systematic variations in the contents of Na, Sr, CO 3 and SO 4 in marine carbonate—Fluorapatite and their relation to weathering

The concentrations of the major substitutents Na, Sr, CO 3 and SO 4 in the carbonate—fluorapatite phase of marine sedimentary phosphorites show large systematic variations between, and within, deposits now on land, whilst variations are minimal between, and within, present sea-floor deposits. These variations reflect the influence of weathering and suggest that all marine carbonate—fluorapatite originally has approximately the same chemical composition.

Uranium-series disequilibrium studies in phosphorite nodules from the west coast of South America

Sedimentary phosphorites occurring on the sea floor off Peru and Chile have been analyzed for U and Th isotopes, to establish their ages and hence obtain clues for their mode of formation. Fission-track distribution studies indicate that the U is primarily associated with the apatite fraction. Uranium-series disequilibrium methods, therefore, should be applicable, if the U incorporation is syngenetic with the apatite. The fractionation of U isotopes between oxidation states in the relatively young phosphorites from South America is low compared to that in older deposits. This supports the contention of Kolodny and Kaplan (1970) that the major mechanism of 234U 238U fractionation is displacement of 234U atoms into sites where they are more ‘oxidizable’ than the 238U parent. Age estimates based on 234U(IV) and 230Th contents are internally consistent and range from late Pleistocene to Recent. The results indicate that marine phosphorites are currently forming in this area of intense oceanic upwelling. The age pattern during the last 150,000 yr suggests a correlation with eustatic high sea level stands and implies that conditions were more favorable for apatite genesis in this area during interglacials rather than during glacial times.

Precambrian Stromatolitic Phosphorites of Udaipur, Rajasthan, India

Research Article| August 01, 1971 Precambrian Stromatolitic Phosphorites of Udaipur, Rajasthan, India D. M BANERJEE D. M BANERJEE Department of Geology, University of Delhi, Delhi-7, India Search for other works by this author on: GSW Google Scholar GSA Bulletin (1971) 82 (8): 2319–2330. https://doi.org/10.1130/0016-7606(1971)82[2319:PSPOUR]2.0.CO;2 Article history received: 17 Aug 1970 rev-recd: 18 Feb 1971 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation D. M BANERJEE; Precambrian Stromatolitic Phosphorites of Udaipur, Rajasthan, India. GSA Bulletin 1971;; 82 (8): 2319–2330. doi: https://doi.org/10.1130/0016-7606(1971)82[2319:PSPOUR]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Study of the origin of phosphorite in the Precambrian Aravalli metasediments has involved stratigraphic analyses of the Aravallian rock sequences around Udaipur, petrography of the phosphatic minerals, chemical analyses of representative samples and reconstruction of the environment of deposition. The role of Stromatolitic algae in the formation of the sedimentary phosphorite has been clearly demonstrated. Evidence suggests that the phosphorites of the Udaipur area were deposited in shallow waters where luxuriant growth of Stromatolitic algae helped in trapping and precipitating phosphorus from the basin waters. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Carbon and Oxygen Isotopes in Apatite Co2 and Co-Existing Calcite from Sedimentary Phosphorite

ABSTRACT Carbon and oxygen isotopes were analyzed in carbonate apatite CO2 and in co-existing calcite. Both C and O in apatite CO2 are enriched in the respective light isotopes relative to calcite. These results confirm the proposition that carbonate is part of the apatite structure.