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Palaeoenvironmental significance of iron carbonate concretions from the Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków-Silesia Homocline, Poland

Witkowska M.

Acta Geologica Polonica

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2012

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Vol. 62, no. 3

307-324

EN

Iron carbonate concretion horizons are characteristic features of the Bathonian (Middle Jurassic) claystone-mudstone succession at Gnaszyn. They occur in single horizons, which generally represent the same genetic type. The siderite concretions are the main type of iron carbonate concretions at Gnaszyn; a second type is represented by phosphate-siderite concretions. On the basis of the fieldwork, and their petrographical and mineralogical characteristics, the genesis of the concretions and their palaeoenvironmental significance is discussed. The results of this study (based on the localization, mode of occurrence, mineralogy of iron carbonate concretions and also the textural relationship between the concretions and host sediment layers) suggest an early diagenetic origin of the concretions. The preferential occurrence of the concretion horizons in single layers in the ambient sediments was associated with particular conditions of their deposition and early diagenesis, favored by a slower sedimentation rate and more intense bioturbation, and related primarily to the greater availability of reactive iron ions. From the viewpoint of physicochemical conditions the horizons with iron carbonate concretions in the study area reflect the redox boundary between oxic/bioturbated and anoxic/non-bioturbated zones. The conditions favoring the formation of such horizons was possibly due to longer periods of diminished sedimentation rate when the redox boundary remained in the same position within the sediment.

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Zmienność litologiczna osadów ilasto-krzemionkowych z obszaru IOM (strefa rozłamowa Clarion-Clipperton; E Pacyfik)

Maciąg Ł., Kotliński R. A., Borówka R. K.

Górnictwo i Geoinżynieria

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2011

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R. 35, z. 4/1

243-255

PL

W artykule przedstawiono zmienność wybranych cech sedymentologicznych, składu mineralnego w podfrakcjach oraz charakteru procesów wczesnej diagenezy osadów ilasto-krzemionkowych z obszaru złożowego IOM (wschodni Pacyfik, strefa rozłamowa Clarion-Clipperton). Zwrócono uwagę na zróżnicowanie uwarunkowań środowiskowych istotnych z punktu widzenia geologii regionalnej i paleogeografii, wpływających na zmienność litologiczną osadów oraz możliwość formowania się tlenkowych skupień Fe-Mn. W wyniku badań osadów wchodzących w skład tzw. litofacji stropowej FCl iv formacji Clipperton (pliocen-holocen), reprezentowanych przez muły ilaste krzemionkowe, ustalono średnią średnicę ziarna na poziomie x = 6,83 phi. Potwierdzono zdecydowaną jednomodalność rozkładów uziarnienia oraz ich słabe wysortowanie. Stwierdzono różnice ilościowe w składzie mineralnym w obrębie podfrakcji < 0,004 oraz < 0,002 mm, w grupie chlorytów i smektytów. Odnotowano znaczną zmienność pionową w składzie gatunkowym i ilości bioklastów promienic i okrzemek, minerałów ilastych z grupy kaolinitu i illitu oraz w zawartości mikrokonkrecji. Zasygnalizowano, że stabilność czasowo-przestrzenna składowych środowiska w obszarze strefy rozłamowej Clarion-Clipperton warunkuje istnienie atrakcyjnych gospodarczo pól konkrecjonośnych, stanowiących potencjalne źródło pozyskiwania rud w przyszłości.

EN

Authors presented geospatial variability of selected sedimentological, mineralogical and diagenetical features of clayey-siliceous sediments from Interoceanmetal deposit area (eastern Pacific, Clarion-Clipperton fracture zone). Changes of environmental conditions essential to geological and palaeogeographical situation into C-C zone, and also their importance to forming processes of Fe/Mn oxide concentrations have been described. Research studies on sediments, classified to the uppermost part of Clipperton FCl IV Formation (pliocene-holocene), show unimodal distribution of samples, poor sorting and mean grain size of siliceous clayey muds amount to x = 6,83 phi. Some qualitative/quantitative changes into the mineral composition of the clay < 0,004 / < 0,002 mm subfractions (clay minerals from kaolinite/illite/chlorite/smectite groups), perpendicular variability of some Radiolaria/Diatomeae species and also micronodules amount depletion during burial processes have been confirmed. Environmental conditions into the C-C zone enable to form economically attractive depositional fields covered by polymetallic nodules that constitute potential ore sources of Mn, Ni, Co, Cu and other metals in the future.

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Early Diagenetic Processes in the Formation of Carbonate-Hosted Mn Ore Deposit (Lower Jurassic, Tatra Mountains) as Indicated from Its Carbon Isotopic Record

Krajewski K., Lefeld J., Łącka B.

Bulletin of the Polish Academy of Sciences. Earth Sciences

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2001

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Vol. 49, nr 1

13-29

EN

The Lower Jurassic Huciska Limestone Formation (lower Sub-Tatric nappe) in the Western Tatra Mountains locally hosts lens-like bodies of Mn-ore deposit (the Banie Ore Bed). The ore is composed of crinoidal sediment containing both Mn-oxides (bixbyite, hausmannite, todorokite, birnessite) and Mn-carbonates (manganic calcite, kutnahorite, calcic rhodochrosite, rhodochrosite). This composition reflects deposition of Mn oxide-rich sediment as a result of episodes of downslope gravitational transport in a marginal part of the Krizna basin, and early diagenetic formation of Mn-carbonates resulting from bacterial reduction of manganese in a nearsurface environment. The diagenetic reduction of manganese brought about important decrease of d(13)C values (-1.2‰ to +0.5‰) of carbonate carbon in the Mn-ore deposit, which stands in a marked contrast to positive carbon values (+2.0‰ to +3,6‰) of the besting carbonate facies in the Huciska Limestone Formation. Enhanced deposition and diagenesis of manganese in the Huciska Limestone Formation is a result of elevated Mn content in the Toarcian Tethys, reflecting both increased Mn supply associated with initial stage of ocean floor spreading and development of widespread oxygen-minimum zones in basinal settings.

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Early diagenetic collapse and injection microstructures in phosphate nodules of the Brentskardhaugen Bed (Jurassic) in Spitsbergen

Krajewski K.

Bulletin of the Polish Academy of Sciences. Earth Sciences

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2000

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Vol. 48, nr 2

209-229

EN

Fossiliferous phosphate nodules in the condensed Brentskardhaugen Bed (Toarcian-Bathonian) in Spitsbergen show common collapse and injection microstructures associated with stages of phosphatization of biogenic carbonate skeletal remains. These structures provide supporting evidence for the nature of early phosphate replacement of biogenic carbonate in clastic condensed environment of the Jurassic Spitsbergen shelf. The replacement process consisted in phosphate cementation of the original skeletal surfaces and internal skeleton pore spaces. Stages of early diagenetic dissolution of biogenic carbonate and reworking events in the depositional environment led, however, to complex and variable infillings of skeletal moulds. Interplay of recurrent events of phosphate emplacement into sediment, carbonate dissolution, and mechanical reworking of fossiliferous phosphate nodules accounts for a broad spectrum of phosphatic replacement microstructures in the original biogenic carbonate.