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Cyanobacterially generated peloids in laminated, organic‐matter rich, limestones: an unobtrusive presence
Author(s) -
Tribovillard NicolasPierre
Publication year - 1998
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1046/j.1365-3121.1998.00177.x
Subject(s) - geology , cyanobacteria , facies , carbonate , organic matter , alkalinity , settling , carbonate platform , geochemistry , mineralogy , paleontology , chemistry , ecology , biology , structural basin , environmental science , bacteria , organic chemistry , environmental engineering
The late‐Kimmeridgian Southern Jura (France) is a carbonate platform where laminated limestones accumulated locally (notably at Orbagnoux). The two types of laminations encountered result either from particle settling in a very quiet environment or from bacterial mat growth. In the latter case, as revealed by acid etching, the dark‐coloured laminae result from filamentous cyanobacteria developments, whereas the light‐coloured laminae appear, surprisingly, to comprise packed peloids. These peloids are interpreted as originating from the in vivo or shortly post mortem calcification of sheaths of coccoid cyanobacteria in an environment loaded by temporary excess alkalinity (and possible H 2 S emissions). Thus, a simple etching treatment reveals the unsuspected, albeit prominent, role of cyanobacteria in the genesis of the limestones from Orbagnoux. As such facies are widespread in Late Jurassic records, the role of cyanobacteria in their formation deserves re‐evaluation.