Carbonate concretions: An ideal sedimentary host for microfossils

Blome, Charles D.; Albert, Nairn R.

doi:10.1130/0091-7613(1985)13<212:ccaish>2.0.co;2

Cited by 29 publications

(15 citation statements)

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“…The record of these events has eluded us due to diagenetic loss, limited study, or, perhaps the absence of preservable structures. Analysis of sediments cemented by calcium carbonate at the centers of concretions or from within cemented centers of mollusks, is the direction this research should take in order to advance the early history of the diatoms and Chrysophyceans, because the concretions or shells preserve the temporally unstable opal-A (Blome and Albert, 1985;Harwood, 1988).…”

Section: A Discussion On the Origin Of The Diatoms With Reference To mentioning

confidence: 99%

Lower Cretaceous Diatoms from ODP Leg 113 Site 693 (Weddell Sea). Part 2: Resting Spores|Chrysophycean Cysts|an Endoskeletal Dinoflagellate|Notes on the Origin of Diatoms

Harwood¹,

Gersonde²

1990

Proceedings of the Ocean Drilling Program

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A rich assemblage of Lower Cretaceous (lower Albian) siliceous microfossils was recovered at ODP Site 693 on the Weddell Sea margin of East Antarctica during Leg 113. This assemblage includes marine diatoms, silicoflagellates, radiolarians, Chrysophycean cysts, and endoskeletal dinoflagellates that are extraordinarily well preserved and in most cases, radiolarians excluded, represent the oldest known well-preserved assemblages of these groups. This chapter describes and illustrates Lower Cretaceous diatom resting spores, Chrysophycean cysts, and an endoskeletal dinoflagellate from Holes 693A and 693 B. Six new diatom genera and 20 new species of probable diatom resting spores are presented here, in addition to 10 apparently new Chrysophycean cyst taxa and one endoskeletal dinoflagellate species. Diatom assemblages reported here and in the preceding chapter on vegetative forms (Part 1) suggest: (1) that diatoms were a complex, diverse, and widespread group by late Early Cretaceous time; (2) that diversities are high enough to anticipate the construction of a useful biostratigraphic zonation as more data become available; (3) that there is a considerable difference between assemblages in these Albian sediments and younger Senonian diatomites known around the world; (4) that both resting spore formation and the ability to form chains are ancient features of the diatoms; and (5) that diatom distribution in the Early Cretaceous may have been restricted to continental margins and interior seas, areas where resting spore formation is most common. Because these assemblages are the oldest, well-preserved diatom and chrysophycean floras known, this chapter concludes with a brief review and discussion on the origin of the diatoms, addressing both the role of resting spores and postulated links to Chrysophycean flagellates.

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Section: A Discussion On the Origin Of The Diatoms With Reference To mentioning

confidence: 99%

Lower Cretaceous Diatoms from ODP Leg 113 Site 693 (Weddell Sea). Part 2: Resting Spores|Chrysophycean Cysts|an Endoskeletal Dinoflagellate|Notes on the Origin of Diatoms

Harwood¹,

Gersonde²

1990

Proceedings of the Ocean Drilling Program

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“…3). Preservation of radiolarians in calcareous concretions within clay-dominated sediments has been repeatedly recovered from sedimentary successions of different ages (Blome & Albert 1985). Early carbonate precipitation protected the radiolarian skeletons from early diagenetic dissolution, which is otherwise common in clay-rich sediments (Riedel 1959).…”

Section: Xintangwu Concretionmentioning

confidence: 99%

First Early Cambrian Radiolaria

Braun

Chen

Waloszek

et al. 2007

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Radiolarian skeletons are known from a limestone concretion collected from a black shale succession and from black cherts of the Yangtze Platform, China. Both occurrences are of earliest Cambrian age. The findings, reported in this paper, represent the oldest known fossil Radiolaria. Their spherical skeletons display a morphology typical of spherical radiolarians from Ordovician and younger faunas. This occurrence of radiolarians with radial symmetry and, most probably, a planktonic lifestyle can now be traced back into the earliest Cambrian. Thus, radiolarians have been part of the early oceanic plankton and likely played a significant role in the silica cycle of the oceans along with siliceous sponges.

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“…Therefore, the supposed radiolarian shells underwent preferential preservation in the concretions in terms of three-dimensional morphology and abundance (e.g. Blome & Albert, 1985). Differential preservation of microfossils between the carbonate concretions and the carbonate-free host mudstones indicates early, precompactional calcite precipitation and concretion formation (Blome & Albert, 1985;Scasso & Kiessling, 2001).…”

Section: Petrographic Evidence Of Diagenetic Processes and Conditionsmentioning

confidence: 99%

Deep‐burial alteration of early‐diagenetic carbonate concretions formed in Palaeozoic deep‐marine greywackes and mudstones (Bardo Unit, Sudetes Mountains, Poland)

2014

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Carbonate concretions formed in bathyal and deeper settings have been studied less frequently than those formed in shallow-marine deposits. Similarly, concretions affected by catagenetic conditions have rarely been reported. Calcite concretions in deep-marine mudstones and greywackes of the Bardo Unit (Sudetes Mountains, Poland) formed during early diagenesis and were buried to significant depths. Petrographic and geochemical (elemental and stable C and O isotopic) analyses document their formation close to the sedimentwater interface, prior to mechanical compaction within the sulphate reduction zone and their later burial below the oil window. Although the concretions were fully formed during early diagenesis, the effects of increased temperature and interaction with late-diagenetic interstitial fluids can be discerned. During maximum burial, the concretions underwent thorough recrystallization that caused alteration of fabric and elemental and O isotope composition. The initial finely crystalline cement was replaced by more coarsely crystalline, sheaflike, poikilotopic calcite in the concretions. These large calcite crystals engulf and partially replace unstable detrital constituents. The extremely low d18 O values (down to À21Á2& Vienna Pee Dee Belemnite) in the concretions are the result of the increased temperature in combination with alteration of volcanic glass, both causing a significant 18 O-depletion of bicarbonate dissolved in the interstitial fluids. Recrystallization led to uniform O isotope ratios in the concretions, but did not affect the C isotope signature. The d 13C values of the latediagenetic cements precipitated in the greywacke and in cracks cutting through concretions imply crystallization in the catagenetic zone and decarboxylation as a source of the bicarbonate. These late-diagenetic processes took place in a supposedly overpressured setting, as suggested by clastic dykes and hydrofractures that cut through both concretions and host rock. All of these features show how the effects of early and late diagenesis can be distinguished in such rocks.

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Carbonate concretions: An ideal sedimentary host for microfossils

Cited by 29 publications

References 0 publications

Lower Cretaceous Diatoms from ODP Leg 113 Site 693 (Weddell Sea). Part 2: Resting Spores|Chrysophycean Cysts|an Endoskeletal Dinoflagellate|Notes on the Origin of Diatoms

Lower Cretaceous Diatoms from ODP Leg 113 Site 693 (Weddell Sea). Part 2: Resting Spores|Chrysophycean Cysts|an Endoskeletal Dinoflagellate|Notes on the Origin of Diatoms

First Early Cambrian Radiolaria

Deep‐burial alteration of early‐diagenetic carbonate concretions formed in Palaeozoic deep‐marine greywackes and mudstones (Bardo Unit, Sudetes Mountains, Poland)

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