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Fossil bacteria in Cenomanian–Turonian phosphate nodules and coprolites, Bohemian Cretaceous Basin, Czech Republic

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Al-Bassam K. , Halodová P.

Annales Societatis Geologorum Poloniae

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2018

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tom Vol. 88, No. 3

257--272

EN

Phosphatized biomorphs, resembling modern and ancient bacteria, were identified for the first time in phosphate nodules, present at the base of the Bílá Hora Formation (uppermost Cenomanian - lower Turonian), and in phosphate coprolites at the base of the Teplice Formation (upper Turonian) in the Bohemian Cretaceous Basin. They are present in colonies as filaments, coccoids, strings, rods and outgrowths, associated with the phosphate as part of the rock constituents and display the characteristics of fossilized bacteria. Two types of bacteria were identified: chemotrophic, sulphur-reducing bacteria in the phosphate nodules and phototrophic cyanobacteria in the phosphate coprolites. Microanalysis of some of the fossil bacteria revealed a fluoride-rich calcium phosphate composition, compatible with the composition of bulk samples, in which carbonate-fluorapatite is the main mineral in the phosphate nodules and coprolites. The environmental indications of these fossil bacteria support the interpretation of an anoxic environment of phosphogenesis in the latest Cenomanian - earliest Turonian and variable redox conditions of coprolite phosphatization in the late Turonian. The potential microbial role in phosphogenesis in the former may have involved the suboxic breakdown of P-rich organic matter by sulphur-reducing bacteria and the release of phosphorus in the pore water, leading to the biochemical precipitation of phosphate. The latter involved initial P-storage by phototrophic bacteria in an oxic environment, followed by P-release below the sediment-water interface under suboxic conditions and subsequent phosphatization of the coprolites.

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Isotopic composition of apatite-bound sulphur in the Triassic phosphogenic facies in Svalbard

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Krajewski K. P.

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2000

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tom Vol. 116

85--109

EN

Isotopic composition of apatite-bound sulphate sulphur in the Middle Triassic phospho- genic facies in Svalbard (Bravaisberget and Botneheia formations) shows wide lateral variation, with d34S values ranging from +24.9‰ to -2.0‰. After correction for likely value of coeval seawater sulphate (d34S = +15.1‰ š 1.5‰), the D34S (= d34SCFA - d34Scoeval evaporite) values of the Middle Triassic apatites fall in a range between approx. +10‰ and -17‰, suggesting complex and variable isotopic modifications of seawater sulphate in bottom phosphogenic environments. This variation was primarily forced by changing bottom depositional conditions along the Svalbard shelf which affected the nature, allocation, and intensity of phosphogenic processes in surficial sediments. Four bottom diagenetic systems leading to different isotopic ranges of apatite-bound sulphur are suggested: (1) rapid burial semi-closed system (D34S = +10‰ to +5‰); (2) shielded interface semi-closed system (D34S = 0‰ to -17‰); (3) open oxic/anoxic system (D34S = +3‰ to -1‰); and (4) semi-closed anoxic system (D34S = +6‰ to +4‰). The rapid burial semi-closed system and the open oxic/anoxic system dominated the formation of apatite in the shallow and deep parts of the Svalbard shelf, respectively. Seawater sulphur values of apatites formed in organic-rich deep shelf facies of the Botneheia Formation in central and eastern Svalbard reflect high original porosity of the sediment and nearsurface location of the phosphogenic zone in a thin suboxic and in the upper part of anoxic sulphidic pore environments. Heavier sulphur values of apatites formed in silty to sandy shallow shelf facies of the Bravaisberget Formation in western and southwestern Spitsbergen also reflect phospho- genesis in the suboxic/upper anoxic sulphidic pore environment, but located deeper in sediment column and characterized by limited sulphate exchange with shelf water. The semi-closed anoxic system and the shielded interface semi-closed system developed locally in bottom shelf environ- ments, reflecting peculiar, spatially restricted depositional conditions. Isotopically heavy apatitic sulphur in organic-rich facies of the Botneheia Formation deposited to the east of the Billefjorden Fault Zone in Spitsbergen reflects phosphogenesis in semi-closed anoxic system developed in surficial sediments overlain by anoxic bottom water enriched in residual dissolved sulphate. Isotopically light apatitic sulphur in microbial mat-generated phosphorite horizons occurring locally in both the shallow (Bravaisberget Formation) and deep shelf (Botneheia Formation) facies in Spitsbergen reflects phosphogenesis in nearsurface environment shielded by gradient-type microbial mats. The light apatitic sulphur originated from intense oxidation of hydrogen sulphide at a narrow oxic/anoxic interface stabilized by the growth and metabolic activity of the mat-forming communities.

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Phosphorus concentration and organic carbon preservation in the Blanknuten Member (Botneheia Formation, Middle Triassic), Sassenfjorden, Spitsbergen

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Krajewski K. P.

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2000

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tom Vol. 116

139--173

EN

The paper attempts to reconstruct depositional to diagenetic processes that led to the increased contents of mineral phosphorus and organic carbon in the Middle Triassic organic-rich phosphatic Blanknuten Member sequence in Sassenfjorden, Spitsbergen. The results of petrographic and geochemical analyses suggest that enhanced preservation of both organic carbon (1-8%) and mineral phosphorus (3-26% P2O5) in the sequence is a result of excess production, deposition, and diagenesis of indigenous marine organic matter in the shelf environment under prevailing oxygen- deficient bottom conditions. The nature of organic sources and the character of depositional environment aided the preferential preservation of oil-prone kerogen of the Type II. Diagenesis of organic phosphorus in surficial sediments led to the formation of phosphate peloids and nodules that occur dispersed in fine-grained facies (3-10% P2O5), or are concentrated at recurrent granular horizons due to dynamic environmental processes (12-18% P2O5). Maximum phosphorus concentra- tion (up to 26% P2O5) is noted in granular phosphorite horizons that were covered and stabilized by deep-water microbial mats during periods of diminished bottom dynamics and non-deposition. An interplay between the deposition and diagenesis of organic matter in oxygen-deficient environment, the dynamic processes leading to reworking and redeposition of sediments, and the growth and phosphatization of microbial mats accounts for the observed complexity of the phosphorus and organic carbon distributions in the Blanknuten Member sequence.

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Type section of the Bravaisberget Formation (Middle Triassic) at Bravaisberget, western Nathorst Land , Spitsbergen, Svalbard

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Krajewski K. P. , Karcz P. , Woźny E. , Mørk A. , Krajewski K. P. , Karcz P. , Woźny E. , Mørk A.

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nr 2

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Type section of the Bravaisberget Formation [Middle Triassic] at Bravaisberget, Western Nathorst Land, Spitsbergen, Svalbard

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Krajewski K. P. , Karcz P. , Wozny E. , Mork A.

Polish Polar Research

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2007

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tom 28

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nr 2

EN

The Bravaisberget Formation in Spitsbergen embraces an organic carbon-rich, clastic sequence that reflects a general shallow shelf development of the Middle Triassic depositional system in Svalbard. New observations and measurements of the type section of the formation at Bravaisberget in western Nathorst Land allow to present detailed litho- stratigraphical subdivision of the formation, and aid to reconstruct its depositional history. The subdivision of the formation (209 m thick at type section) into the Passhatten, Somovbreen, and Van Keulenfjorden members is sustained after Mørk et al. (1999), though with new position of the boundary between the Passhatten and Somovbreen mbs. The Passhatten Mb is defined to embrace the black shale-dominated sequence that forms the lower and middle parts of the formation (160 m thick). The Somovbreen Mb (20 m thick) is confined to the overlying, calcite-cemented sequence of marine sandstones. The Van Keulenfjorden Mb (29 m thick) forms the topmost part of the formation composed of siliceous and dolomitic sandstones. The formation is subdivided into twelve informal units, out of which eight is defined in the Passhatten Mb (units 1 to 8), two in the Somovbreen Mb (units 9 and 10), and also two in the Van Keulenfjorden Mb (units 11 and 12). Units 1, 3,5,7 and 9 contain noticeable to abundant phosphorite, and are interspaced by four black shale sequences (units 2,4,6, and 8). Unit 9 passes upwards gradually into the main sandstone sequence (unit 10) of the Somovbreen Mb. The base of the Van Keulenfjorden Mb is a discontinuity surface covered by thin phosphorite lag. The Van Keulenfjorden Mb consists of two superimposed sandstone units (units 11 and 12) that form indistinct coarsening-upward sequences. The Bravaisberget Fm records two consequent transgressive pulses that introduced high biological productivity conditions to the shelf basin. The Passhatten Mb shows pronounced repetition of sediment types resulting from interplay between organic-prone, fine-grained environments, and clastic bar environments that focused phosphogenesis. The lower part of the member (units 1 to 5) contains well-developed bar top sequences with abundant nodular phosphorite, which are under- and overlain by the bar side sequences grading into silt- to mud-shale. The upper part of the member (units 6 to 8) is dominated by mud-shale, showing the bar top to side sequence with recurrent phosphatic grainstones in its middle part. Maximum stagnation and deep-water conditions occurred during deposition of the topmost shale sequence (unit 8). Rapid shallowing trend terminated organic-rich environments of the Passhatten Mb, and was associated with enhanced phosphogenesis at base of the Somovbreen Mb (unit 9). Bioturbated sandstones of the Somovbreen Mb (unit 10) record progradation of shallow-marine clastic environments. The sequence of the Van Keulenfjorden Mb (units 11 and 12) was deposited in brackish environments reflecting closure of the Middle Triassic basin in western Svalbard.