Origin of Phosphorites, Glauconites and Associated Facies Through Time: Case Studies
Study of the carbonate micrite phase of laminated pelletal phosphorites from various phosphate fields of the Negev reveals that this phase was largely formed in situ, and that bacterial mats are principally the frame-builders of this phase. These mats are composed of vertically stratified, calcite-mineralized assemblages of bacterial bodies of various shapes, sizes, and organizations. This biostratification is believed to represent the fossilized record of time-successive consumer bacterial populations that degraded planktonic detritus, and mats of filamentous and coccoid microphytes, which colonized the Mishash seafloor during phosphorite formation and were partly preserved in these rocks as apatitic sheaths and envelopes. Carbonate mineralization of the bacterial consumers probably took place during anaerobic degradation of the matted sediments, as indicated by low δ13C values in many of these carbonates. The diagenetic fate of the filamentous and coccoid Mishash bottom-dwelling microphytes (apatite mineralization versus turnover as bacterial carbonates) was dependent on the balance between the rate of organic matter accumulation and the extent of bottom sediment ventilation, which together controlled the redox conditions of organic matter decomposition and pore-water carbonate ion concentrations. This may explain why primary (pristine) apatite beds are common in condensed proximal Mishash sections around Negev Campanian highs, whereas they are more sporadic in basinal carbonate-rich Mishash sections. It might also explain why the coccoid and filamentous microphyte structures, which matted the Mishash seafloor and are now preserved in many of the Negev phosphorite rocks, were found to be mineralized only by phosphate and never by carbonate.
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Marine Authigenesis: From Global to Microbial
This volume is a collection of 33 state-of-the-art papers focusing on various aspects of authigenic and diagenetic marine minerals and related global elemental cycling. The commingling of the various studies of authigenic minerals in this volume, including the most recent advances in knowledge concerning the occurrence and origins of phosphorites, glauconites, dolomites, siderites, manganese-iron associations, barites, ironstones, and other marine chemical sediments/sedimentary rocks of early authigenic/diagenetic origin, is partly the result of the increasing awareness that there are many overlaps, even direct co-associations, between different authigenic minerals, both in time, space, and genesis. Taken together, this compilation represents a holistic approach towards marine authigenesis that considers the integrated whole more than the simple sum of its parts.