Paleoclimate and tectonic controls on the depositional and diagenetic history of the Cenomanian–early Turonian carbonate reservoirs, Dezful Embayment, SW Iran

Scarab beetles (Coleoptera: Scarabaeidae) can exhibit striking colours produced by pigments and/or nanostructures. The latter include helicoidal (Bouligand) structures that can generate circularly polarized light. These have a cryptic evolutionary history in part because fossil examples are unknown. This suggests either a real biological signal, i.e. that Bouligand structures did not evolve until recently, or a taphonomic signal, i.e. that conditions during the fossilization process were not conducive to their preservation. We address this issue by experimentally degrading circularly polarizing cuticle of modern scarab beetles to test the relative roles of decay, maturation and taxonomy in controlling preservation. The results reveal that Bouligand structures have the potential to survive fossilization, but preservation is controlled by taxonomy and the diagenetic history of specimens. Further, cuticle of specific genus ( Chrysina ) is particularly decay-prone in alkaline conditions; this may relate to the presence of certain compounds, e.g. uric acid, in the cuticle of these taxa.

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Ultrastructure, dissolution and "pyritization" of Late Quaternary and Recent echinoderms

Bulletin of the Geological Society of Denmark ◽

10.37570/bgsd-1988-36-09 ◽

1987 ◽

Vol 36 ◽

pp. 275-287

Author(s):

Margit Jensen ◽

Elsebeth Thomsen

Keyword(s):

Late Pleistocene ◽

Sea Water ◽

Late Quaternary ◽

Pore Space ◽

Water Interface ◽

Sea Stars ◽

Northern Norway ◽

History Of ◽

Organic Tissue ◽

Diagenetic History

The diagenetic history of the skeletal elements of Late Pleistocene-Holocene Ophiura sarsi from the shelf off northern Norway (Andfjorden, Malangsdjupet) is elucidated by comparison with natural and induced degradation of the skeletal elements of Recent ophiuroids (brittle stars) and asteroids (sea stars) from Danish waters. Dissolution features ("core-and-rind") in the trabeculae of fossil and Recent echinoderm stereom are initiated during death and early decay of organic tissue in the animals. The trabeculae have a polycrystalline lamellar ultrastructure and lose their older central part during later stages of dissolution, which are dependant on undersaturation of the sea-water with regard to CaC03• The presence of undersaturated sea-water is supported by palaeoecological studies (Thomsen & Vorren 1984, 1986) implying oxygen deficient periods in the Late Pleistocene and an increased biogenic production in the Holocene. Pyrite framboids are situated in the secondary voids within the trabeculae and in the pore space of the stereom of the Late Pleistocene elements. No pyrite is observed within the polycrystalline lamellar ultrastructure of the trabeculae. The Late Pleistocene "pyritization" took place during oxygen deficient periods at the sediment-water interface or within the reduced zone of the topmost sediment.

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Sedimentologic and diagenetic history of the Mission Canyon Formation (Mississippian) and stratigraphic equivalents, southwestern Montana and east-central Idaho and determination of rare earth element abundances in diagenetic carbonates

10.2172/565352 ◽

1998 ◽

Author(s):

Keyword(s):

Rare Earth ◽

Rare Earth Element ◽

Earth Element ◽

East Central ◽

Element Abundances ◽

Southwestern Montana ◽

History Of ◽

Diagenetic History ◽

Central Idaho

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