The contrasting origins of glauconite in the shallow marine environment highlight this mineral as a marker of paleoenvironmental conditions

Glauconite is an authigenic mineral reputed to form during long-lasting contact between a nucleus (a pre-existing phyllosilicate) and seawater. This protracted makes it possible subtract the ions necessary for construction of neoformed phyllosilicate, here, glauconite very close illite, rich in K Fe). As result, often associated with sediments deposited transgressive context strong slowdown rate sedimentation relatively large water layer thickness. case Cenomanian chalk Boulonnais (north France). Being chemically physically resistant, that reworked, like quartz grains. frequently Jurassic deposits Boulonnais, where glauconite, almost ubiquitous, either traces or significant proportions sediments, presents grain size sorting attesting its transport reworking. However, these are shallow (shoreface, upper offshore), which supports idea “glauconite factory” was itself areas Boulonnais. The only identified facies both abundant, unsorted (non reworked) oyster reefs formed at outlet cold seeps linked late-Jurassic synsedimentary tectonic (Kimmeridgian, Tithonian). Our work hypothesize isolated were environments combining redox conditions seawater favoring formation glauconite. weakly reducing here attested by contents metallic trace elements sensitive (vanadium, germanium, arsenic, this case). thus adds new element understanding mechanisms environments.