Marine Phosphogenesis in Shallow-Water Environments: Cambrian, Tertiary, and Recent Examples

Schwennicke, Tobias; Siegmund, Hendrik; Jehl, Caroline

doi:10.2110/pec.00.66.0481

Cited by 7 publications

(9 citation statements)

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“…These results as well as those of previous studies of Delle-event phosphorites in the Antler orogenic belt add to a growing body of literature documenting phosphorite deposition in relatively shallow water (Lucas and Prèvôt-Lucas 2000;Schwennicke et al 2000). These results also point the way for possible additional detailed study of carbonate sequences that are succeeded by condensed phosphate sections (e.g., Föllmi et al 1994).…”

Section: Discussionsupporting

confidence: 78%

Geochemistry of the Mississippian Delle Phosphatic Event, Eastern Great Basin, U.S.A.

Jewell

Silberling

Nichols

2000

Journal of Sedimentary Research

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The Middle Mississippian Delle phosphatic event marks a significant change in depositional conditions in the Devonian-Mississippian Antler foreland basin of North America. Stratigraphic and petrographic studies show that deposition of Delle-event rocks ended a long period of open-marine carbonate sedimentation when facies shifted to phosphorites, cherts, fine-grained siliciclastics, and lime mudstones from highly productive waters that may have been episodically anoxic. This drastic change in lithology is reflected in the chemistry of the two suites of rocks. ␦ 18 O values of the Delle-event lime mudstones and phosphatized wackestones-packstones affected by the Delle event are 3-5‰ lighter than underlying and overlying open marine wackestones-packstones. Sr concentrations of Delle-event lime mudstones and open marine wackestone-packstone facies are low, suggesting that both of these lithologies have undergone similar postdiagenetic alteration. The uniform Sr concentrations and variable ␦ 18 O data suggest that either the younger Delle-event rocks were exposed to meteoric water during diagenesis or that the relatively light ␦ 18 O values represent a primary brackish-water depositional signal. Either interpretation is consistent with sedimentological evidence of the Delle event occurring in a predominantly shallow-water setting. ␦ 13 C values of Delle-event lime mudstones are also anomalously light, indicating a high input of organic carbon during their formation. Mn concentrations of the Delle-event lime mudstones and stratigraphic equivalents are highly variable, suggesting fluctuating oxygen concentrations during their deposition and diagenesis. Rare-earth-element data from phosphorites and cherts of the Delle event indicate oxic to suboxic depositional conditions.

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Section: Discussionsupporting

confidence: 78%

Geochemistry of the Mississippian Delle Phosphatic Event, Eastern Great Basin, U.S.A.

Jewell

Silberling

Nichols

2000

Journal of Sedimentary Research

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“…Microcrystalline carbonate‐fluorapatite is normally associated with the formation of marine phosphorites or microphosphorites (Cook et al. , 1990; Schwennicke et al. , 2000).…”

Section: Discussionmentioning

confidence: 99%

“…Fluorapatite precipitation is generally rapid, having growth times between 500 and 2000 years in modern phosphorites within the top few tens of centimetres of the sediment–water interface, where microbial activity is greatest (Glenn, 1990). Schwennicke et al. (2000) describe phosphatic ooids, pelloids, multiply coated detrital grains, sections of colloform veinlets and lithified phosphatic mud in shallow‐marine Cambrian phosphorites from China.…”

Section: Discussionmentioning

confidence: 99%

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Microtextures, geochemistry and geochronology of authigenic xenotime: constraining the cementation history of a Palaeoproterozoic metasedimentary sequence

et al. 2005

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An ≈ 26 m thick unit of phosphatic sandstone and black shale (the Phosphatic Unit) in the Palaeoproterozoic Mount Barren Group of south‐western Australia contains abundant authigenic xenotime crystals showing well‐preserved diagenetic textures. Despite extensive regional deformation and thermal metamorphism, the peak of which occurred at ≈ 1205 Ma, the Phosphatic Unit was preserved as a low‐strain envelope because of its pre‐compaction carbonate and phosphate cementation. In situ U–Pb geochronology of xenotime reveals four discrete age populations at 1693 ± 4, 1645 ± 3, 1578 ± 10 and 1481 ± 21 Ma. When integrated with petrography, the age data place a timeframe on: (i) sediment deposition; (ii) phosphogenesis; (iii) diagenetic cement infilling; (iv) diagenetic pyrite formation; (v) secondary porosity generation; (vi) hydrocarbon migration; (vii) burial compaction; and (viii) hydrothermal alteration, up until peak thermal metamorphism. Xenotime growth at ≈ 1693 Ma occurred prior to compaction, whereas xenotime growth at ≈ 1645 Ma occurred during burial. Xenotime growth at ≈ 1580 Ma and at ≈ 1480 Ma appears to be the far‐field record of thermotectonic events associated with intracontinental extension and magmatism recorded elsewhere in Australia. Geochemical analysis, integrated with geochronology, shows a systematic increase in MREE/HREE in xenotime crystals with decreasing age and with increasing stratigraphic depth. Coupled with a decrease in xenotime abundance and age with depth, it suggests that: (i) the main focus of porosity infilling was at the top of the Phosphatic Unit and progressed downwards over the > 200 Myr period of porosity infilling, and (ii) the changes in xenotime REE chemistry may be due to an influx of MREE from increasing amounts of dissolved apatite or changes, with respect to REE solubility, in the physiochemical nature of the fluids with burial depth.

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“…Recent phosphorite formation occurs in the following depositional environments: (1) upwelling conditions off the American and African west coasts, characterized by high primary organic production, lead to the accumulation of organic-rich ooze in shallow waters (e.g. Burnett, 1977;Jahnke et al, 1983;Thomson et al, 1984;Baturin, 2000), (2) off east Australia, phosphorites form in organic-poor sediments at about 400 m water depth due to low accumulation rates (O'Brien and Veeh, 1980), (3) apatite formation in nearshore carbonate sediments at Bermuda (Gaudette and Lyons, 1980) depends on a high amount of organic matter and (4) Schwennicke et al (2000) concluded that restricted water circulation and high bioproductivity may cause phosphogenesis in shallow marine environments from Cambrian to Recent. None of these examples show similar conditions of phosphatization described in the present study, which shows that phosphorite nodules may form in coarse bioclastic grainstones, without significant amounts of organic matter.…”

Section: Formation Of Phosphoritesmentioning

confidence: 99%

Phosphatic black pebbles and nodules on a Devonian carbonate shelf (Anti-Atlas, Morocco)

Fröhlich

2004

Journal of African Earth Sciences

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Marine Phosphogenesis in Shallow-Water Environments: Cambrian, Tertiary, and Recent Examples

Cited by 7 publications

References 0 publications

Geochemistry of the Mississippian Delle Phosphatic Event, Eastern Great Basin, U.S.A.

Geochemistry of the Mississippian Delle Phosphatic Event, Eastern Great Basin, U.S.A.

Microtextures, geochemistry and geochronology of authigenic xenotime: constraining the cementation history of a Palaeoproterozoic metasedimentary sequence

Phosphatic black pebbles and nodules on a Devonian carbonate shelf (Anti-Atlas, Morocco)

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