Stratigraphy and paleogeography of the Ediacaran Doushantuo Formation (ca. 635-551Ma) in South China

Investigating the use of sedimentary geochemical proxies for paleoenvironment interpretation of thermally mature organic-rich strata: Examples from the Devonian–Mississippian shales, Western Canadian Sedimentary Basin

Chert deposits preserve a record of secular change in the oceanic silica cycle. The evolutionary radiation of silica-secreting organisms resulted in a transition from abiological silica deposition, characteristic of the Archean and Proterozoic eons, to the predominantly biologically controlled silica deposition of the Phanerozoic. Comparative petrography of Phanerozoic and Precambrian cherts indicates that an earlier change in chert deposition occurred toward the end of the Paleoproterozoic era (ca. 1.8 Ga). In Neoproterozoic and Mesoproterozoic strata, early diagenetic chertification is largely restricted to peritidal environments. These early diagenetic cherts typically occur as nodules or discontinuous beds within carbonate deposits that have similar depositional textures. The cherts formed primarily by carbonate replacement with subsidiary direct silica precipitation. Some of the Paleoproterozoic cherts associated with iron formations, however, are distinctly different from younger cherts and appear to have formed largely by direct silica precipitation at or just below the seabed. These primary cherts lack ghosts or inclusions of carbonate precursors, have fine-scale grain fracturing (possibly from syneresis), exhibit low grain-packing densities, and are not associated with unsilicified carbonate deposits of similar depositional composition. Cherts in some Paleoproterozoic iron formations (e.g., the Gunflint Formation, northwestern Lake Superior region) are composed of silica types similar to those in Phanerozoic sinters (e.g., the Devonian Rhynie and Windyfield cherts, Scotland). Such cherts may provide evidence that basinal, and perhaps global, oceanic silica concentrations were higher during the Paleoproterozoic era than at later times.

Secular change in the Precambrian silica cycle: Insights from chert petrology

The Cretaceous to Eocene succession in central and south Jordan is characterised by passive
continental margin depositional sequences, which pass upward from alluvial/paralic to
carbonate shelf and pelagic ramp settings. Detailed section logging and outcrop mapping have
produced robust lithostratigraphic and lithofacies schemes that can be correlated throughout
the region and in the subsurface. These schemes are set in a sequence stratigraphic context
in relation to the evolution sedimentation on the Arabian and Levant plates. Three major
megasequences are described (Kurnub, Ajlun and Belqa), and these are further subdivided
into large-scale depositional sequences separated by regional sequence boundaries that
represent maximum flooding surfaces. There is close correspondence between maximum
flooding surfaces recording major sea-level rise with those derived for the Arabian and
Levant plates, although there are some discrepancies with the precise timing of global sealevel
fluctuations.
An upward change from braided to meandering stream fluvial environments in central
and south Jordan during the Early Cretaceous, reflects a decreasing geomorphological
gradient of the alluvial plain, declining siliciclastic sediment flux, and increased floodplain
accommodation, associated with a regional Late Albian (second-order) rise in relative sealevel.
The Late Albian to Early Cenomanian marine transgression across the coastal alluvial
plain marks a major sequence boundary. During Cenomanian to Turonian times a rimmed
carbonate-shelf was established, characterised by skeletal carbonates showing small-scale,
upward-shallowing cycles (fourth- to fifth-order parasequences) ranging from subtidal to
intertidal facies, arranged into parasequence sets. Rimmed carbonate shelf sequences pass
laterally to coeval coastal/alluvial plain facies to the south and east. Eustatic (third-order)
fluctuations in relative sea level during the Cenomanian and Early Turonian resulted in
deposition of ammonite-rich wackestones and organic-rich marls, during high sea-level
stands (maximum flooding surfaces). Progradational sabkha/salina facies passing landwards
to fluvial siliciclastics were deposited during an Early Turonian sea-level low stand, marks a
regional sequence boundary, above which a highstand carbonate platform was established.
A second-order, regional rise in sea level and marine transgression during the Early Coniacian
marks a Type 2 sequence boundary, and subsequent drowning of the rimmed carbonate
shelf by Late Coniacian times. Sedimentation during the Santonian to Maastrichtian was
characterised by a hemi-pelagic chalk-chert-phosphorite lithofacies association, deposited in
shallow to moderate water depths on a homoclinal ramp setting, although thicker coeval
sequences were deposited in extensional rifts. The marked change in sedimentation from
rimmed carbonate shelf to pelagic ramp is attributed to Neo-Tethyan mid-oceanic rifting,
tilting, intracratonic deformation and subsidence of the platform; this is reflected in changes in
biogenic productivity and ocean currents. Oceanic upwelling and high organic productivity
resulted in the deposition of phosphorite together with giant oyster banks, the latter developing
within oxygenated wave-base on the inner ramp. Chalk hardgrounds, sub-marine erosion
surfaces, and gravitational slump folds indicate depositional hiatus and tectonic instability
on the ramp. In the Early Maastrichtian, deeper-water chalk-marl, locally organic-rich, was
deposited in density-stratified, anoxic basins, that were partly fault controlled.
Pulsatory marine onlap (highstand sequences) during the Eocene is manifested in pelagic
chalk and chert with a paucity of benthic macro-fauna, indicating a highly stressed, possibly
hypersaline, and density-stratified water column. Comparison with global and regional
relative sea-level curves enable regionally induced tectonic factors (hinterland uplift and
ocean spreading) to be deduced, against a background of global sea-level rise, changing
oceanic chemistry/productivity and climatic change.

Evolution of Cretaceous to Eocene alluvial and carbonate platform sequences in central and south Jordan.

Oxygenation of the Earth's atmosphere–ocean system: A review of physical and chemical sedimentologic responses

http://kenanaonline.com/files/0012/12107/jordan-phosphate.pdf

Upper Cretaceous (Campanian) phosphorites in Jordan: implications for the formation of a south Tethyan phosphorite giant

Irrespective of geologic age, Phanerozoic coated phosphate grains deposited beneath productive surface waters in organic-rich paleoenvironments are of only two types. Unconformity-bounded grains contain internal discordances and erosional surfaces, attributable to multiple episodes of phosphogenesis and sedimentary reworking during periods of stratigraphic condensation. Redox-aggraded grains consist of concordant concentric phosphate laminae that are intimately interlayered with circumgranular layers containing pyrite, chamosite, or barite, recording in situ diagenetic mineralization driven by changes in pore-water redox potential. Such changes can be attributed to variations in biological oxygen demand within suboxic pore-water environments resulting from fluctuations in sedimentation rate of organic carbon. Redox-aggraded grains are thus sensitive indicators of variations in organic carbon export and record changes in primary productivity and/or ecological dynamics of the surface ocean. This concept of coated-grain formation necessitates a long residence time just below the sediment-water interface. If sedimentation rate is too high, grains are rapidly buried and so removed from the zone of active phosphate precipitation. Coated phosphate grains can therefore be considered the granular equivalents of condensed beds. These concepts are equally applicable to the interpretation of other types of coated grains and concretions that contain Eh-sensitive minerals, such as iron-bearing ooids and polymineralic concretions.

Coated phosphate grains: Proxy for physical, chemical, and ecological changes in seawater

The importance of Rare Earth Elements (REE) in phosphorites had attracted attention in the last few years, since these enriched elements could be subtracted as by product in the fertilizer industry. In addition, their role in depositional environment is well established.
Therefore, thirty seven phosphorite samples from all over Jordan; twelve from SE, fourteen from central and eleven from NW were analyzed for REE and other elements.
The results show that REE are depleted relative to worldwide phosphorites (35.64- 85.23ppm) and have seawater pattern indicating the incorporation from seawater. The depletion increases southwards due to (i) less time for incorporation of the REE at the sea floor, (ii) source rock of REE which is sandstone, (iii) very shallow burial, (iv) slight weathering of phosphorites. Ce shows a negative anomaly increasing northwards indicating more oxic environment.
Y and Sc also are analyzed and treated in this manuscript since Y has similar behavior to REE and Sc lies in the same column at the periodic table. 
Other major, minor and trace elements are also studied and will be treated in another article.

https://journals.ju.edu.jo/DirasatSci/article/download/1454/4983

Peir K. Pufahl

Papers

Upper Cretaceous (Campanian) phosphorites in Jordan: implications for the formation of a south Tethyan phosphorite giant

Coated phosphate grains: Proxy for physical, chemical, and ecological changes in seawater

The Geochemistry of Rare Earth Elements (REE), Yttrium (Y) and Scandium (Sc) in Some Upper Cretaceous Jordanian Phosphorites