Organic Matter Distribution, Water Circulation and Dolomitization Beneath the Abu Dhabi Sabkha (United Arab Emirates)

Baltzer, F.; Kenig, Fabien; Boichard, R.; Plaziat, Jean-Claudé; Purser, B. H.

doi:10.1002/9781444304077.ch23

Cited by 25 publications

(32 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Accelerating effect of bio-and/or rhizoturbation on seepage reflux: burrows and hollow root debris, partly empty at low tide (a), are rapidly filled by flood tide (b-c) forming a perched reservoir ensuring percolation of dolomitizing fluid (sea water of elevated salinity) during falling tide (d). After Baltzer et al (1994). Mazullo et al, 1995) similar to the values measured in Upper Jurassic tidal-flat dolomites (Fig.…”

supporting

confidence: 84%

Early diagenetic dolomitization and dedolomitization of Late Jurassic and earliest Cretaceous platform carbonates: A case study from the Jura Mountains (NW Switzerland, E France)

Rameil

2008

Sedimentary Geology

105

View full text Add to dashboard Cite

Early diagenetic dolomitization is a common feature in cyclic shallow-water carbonates throughout the geologic record. After their generation, dolomites may be subject to dedolomitization (re-calcification of dolomites), e.g. by contact with meteoric water during emersion. These patterns of dolomitization and subsequent dedolomitization frequently play a key role in unravelling the development and history of a carbonate platform. On the basis of excellent outcrops, detailed logging and sampling and integrating sedimentological work, high-resolution sequence stratigraphic interpretations, and isotope analyses (O, C), conceptual models on early diagenetic dolomitization and dedolomitization and their underlying mechanisms were developed for the Upper Jurassic / Lower Cretaceous Jura platform in north-western Switzerland and eastern France. Three different types of early diagenetic dolomites and two types of dedolomites were observed. Each is defined by a distinct petrographic/isotopic signature and a distinct spatial distribution pattern. Different types of dolomites are interpreted to have been formed by different mechanisms, such as shallow seepage reflux, evaporation on tidal flats, and microbially mediated selective dolomitization of burrows. Depending on the type of dolomite, sea water with normal marine to slightly enhanced salinities is proposed as dolomitizing fluid. Based on the data obtained, the main volume of dolomite was precipitated by a reflux mechanism that was switched on and off by high-frequency sea-level changes. It appears, however, that more than one dolomitization mechanism was active (pene)contemporaneously or several processes alternated in time. During early diagenesis, percolating meteoric waters obviously played an important role in the dedolomitization of carbonate rocks that underlie exposure surfaces. Cyclostratigraphic interpretation of the sedimentary succession allows for estimates on the timing of early diagenetic (de)dolomitization. These results are an important step towards a better understanding of the link between high-frequency, probably orbitally forced, sea-level oscillations and early dolomitization under Mesozoic greenhouse conditions.

show abstract

supporting

confidence: 84%

Early diagenetic dolomitization and dedolomitization of Late Jurassic and earliest Cretaceous platform carbonates: A case study from the Jura Mountains (NW Switzerland, E France)

Rameil

2008

Sedimentary Geology

105

View full text Add to dashboard Cite

show abstract

“…Although Nitti et al (2012) explored the vertical changes in the microbial community in lacustrine stromatolites, only a few studies have explored the vertical variation in bacterial and archaeal communities in zones of carbonate and evaporite precipitation (Kenig et al, 1990;Kendall et al, 2002). Kenig et al (1990), together with Baltzer et al (1994), analysed the OM in shallow-water lagoonal and intertidal sediments in Abu Dhabi. Three different organo-sedimentary facies were distinguished, with distinct organic signatures that persisted after burial and which are related to the rate of change of sea level, substrate morphology and rates of sedimentation.…”

Section: Introductionmentioning

confidence: 99%

Biogeochemistry of intertidal microbial mats from Qatar: New insights from organic matter characterisation

Słowakiewicz

Whitaker

Thomas

et al. 2016

Organic Geochemistry

View full text Add to dashboard Cite

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms AbstractUnderstanding early organic matter alteration and preservation in marine carbonate-evaporite systems could improve understanding of carbon cycling and hydrocarbon source rock prediction in such environments. It is possible that organic-rich microbial mats are important contributors to preserved hydrocarbons, and to explore this we examined changes in lipid composition in such a mat from a mesohaline intertidal lagoon, eastern Qatar. The mat reaches > 5 cm thickness over a carbonate mud substrate, rich in seagrass, gastropods and other small bioclasts. Clear lamination, with distinct downward colour changes from green to pink to brown, reflects different microbial mat communities. The layers contain spheroids of probable dolomite, the precipitation of which was plausibly bacterially-mediated. Lipids [n-alkanes, fatty acids (FAs), hopanoids, isoprenoid hydrocarbons, dialkyl glycerol diethers (DAGEs), and isoprenoid (0 to 4) and branched (Ia to IIIa) GDGTs] reflect the diverse mat-building phototrophic, heterotrophic and chemoorganotrophic microorganisms, as well as some likely allochthonous material (i.e. steroids, n-alkanols, high molecular weight nalkanes). The lipids clearly document the change in microbial community, with phytene being the predominant hydrocarbon in the phototrophic surface layer. Oxygen and pH drop significantly 0.2 cm below the mat surface, coincident with the predominance of Deltaproteobacteria and increased concentrations of archaeal and bacterial glycerol dialkyl glycerol tetraether lipids andC 15 /C 16 and C 16 /C 17 dialkyl glycerol ether lipids in the deeper layers. Archaeol, likely of methanogen origin, is most abundant in the deepest layer. Allochthonous inputs occur throughout the mat, including abundant steroids, especially dinosterol and dinostanol, that are possibly related to periodic algal (dinoflagellate) blooms in the Arabian Gulf. Both n-alkanes and n-alkanols appear to be derived from seagrass. Organic matter contents decrease in the deepest mat; this suggests an overall low preservation potential of OM in intertidal mesohaline-hypersaline mats of the Arabian Gulf, which in turn suggests that these are not the major source of hydrocarbons in microbially-dominated carbonateevaporite systems.2

show abstract

“…For example, the regressive mangal palaeosol that was observed by Kenig (1991) and Baltzer et al (1994) at Ras Ghanadah was not observed at all on the channel banks. The distribution of the organic facies in both the transgressive and regressive sequences seems to be dictated by a number of parameters: rate of sea-level change; aggradation and progradation rate; slope of the substrate; and formation of the barrier islands.…”

Section: Distribution Of Organic Matter In Abu Dhabi Sabkha Sedimentsmentioning

confidence: 99%

“…The past presence of mangals is only indicated by rare Avicennia horizontal roots and pneumatophores below the microbial mat. A 25 cm thick mangal palaeosol with a TOC content of up to 8.2 % was observed at Ras Ganadah, where the narrow sabkha had a progradation rate of 0.35-0.75 m yr À1 (Kenig et al, 1990;Kenig, 1991;Baltzer et al, 1994). This low rate, associated with a slow lateral movement of the intertidal zone, allowed several generations of Avicennia to grow at the same place, providing enough sedimentary organic carbon to create a significant accumulation.…”

Section: Regressive Sequencementioning

confidence: 99%

“…Total organic carbon (TOC) content may locally reach 11 wt % (Kenig et al, 1990;Kenig, 1991) and organic matter is playing an important role in diagenetic processes that include dolomitization (e.g. Baltzer et al, 1994). Intertidal microbial mats and Avicennia marina mangals (mangroves), as well as subtidal seagrass fields dominated by Halodule uninervis, provide significant amounts of organic matter to modern sediments, each forming a distinct sedimentary facies or biocoenoses (Kenig, 1991;Kenig et al, 1990).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Distribution of organic matter in the transgressive and regressive Holocene sabkha sediments of Abu Dhabi, United Arab Emirates

Kenig

2010

Quaternary Carbonate and Evaporite Sedimentary Facies and Their Ancient Analogues

View full text Add to dashboard Cite

Two navigation channels dredged in the 1980s across the hypersaline coastal plain of Abu Dhabi (UAE) offered a unique opportunity to study the distribution of organic matter in transgressive and regressive, subtidal, intertidal and supratidal sediments that accumulated during the Holocene. In modern Abu Dhabi lagoons, intertidal microbial mats and Avicennia marina mangals (mangroves), as well as subtidal seagrass fields dominated by Halodule uninervis, provide significant amounts of organic matter to modern sediments. Each of these primary producers is associated to a distinct sedimentary facies and biocoenosis recognizable in Holocene sediments. The distribution of these biocoenoses obeys a number of rules deriving from the ability of each of the primary producers to adapt to salinity changes in response to lagoon closure, rate of sealevel change, and associated rate of displacement of the intertidal zone, as well as changing progradation and aggradation rates. The subtidal seagrass biocoenosis is mostly part of the transgressive sequence, as the salinity in the Abu Dhabi lagoon was lower prior to barrier island development. In the transgressive sequence, Avicennia marina mangal palaeosols are sparse and formed only where the slope of the substrate was steep enough to allow minimal lateral displacement of the mangal community during transgression. The thin intertidal transgressive sequence is mostly characterized by burrowed microbial mat.The regressive sequence is dominated by the microbial mat biocoenosis in areas of fast progradation of the sabkha (> 1 m yr À1 ) as this community is well adapted to the hypersaline conditions of the intertidal zone. A regressive A. marina mangal palaeosol was observed only where progradation rates were between 0.35-0.75 m yr À1 . The mangal community in Abu Dhabi lagoons is stressed by salinity and fast progradation rates. This contrasts with the dominance of mangal soils in humid tropical environments, where highly productive mangals produce thick and organic matter-rich soils irrespective of the rate of sea-level change and rates of progradation.

show abstract

Organic Matter Distribution, Water Circulation and Dolomitization Beneath the Abu Dhabi Sabkha (United Arab Emirates)

Cited by 25 publications

References 0 publications

Early diagenetic dolomitization and dedolomitization of Late Jurassic and earliest Cretaceous platform carbonates: A case study from the Jura Mountains (NW Switzerland, E France)

Early diagenetic dolomitization and dedolomitization of Late Jurassic and earliest Cretaceous platform carbonates: A case study from the Jura Mountains (NW Switzerland, E France)

Biogeochemistry of intertidal microbial mats from Qatar: New insights from organic matter characterisation

Distribution of organic matter in the transgressive and regressive Holocene sabkha sediments of Abu Dhabi, United Arab Emirates

Contact Info

Product

Resources

About