Carbonate concretions: An ideal sedimentary host for microfossils
Journal - Geology
Microfossils extracted from carbonate concretions tend to bebetter preserved, more abundant and diverse, and more likelyto retain delicate and fragile structures than those extractedfrom the surrounding rocks. Enhanced preservation correlateswith early diagenetic concretion formation at or near the sediment-waterinterface and with higher carbonate, organic material, and metalliccation content than in surrounding rocks. Early diagenetic growthis inferred by diverging sedimentary laminations and small-scalesedimentary structures in fossiliferous carbonate concretions.High initial concentrations of microorganisms or fecal pelletsmay commonly be responsible for incipient carbonate-concretiongrowth. Excellent preservation is demonstrated by radiolariansand palynomorphs extracted from a carbonate concretion fromthe Middle Jurassic Shelikof Formation, southern Alaska.