Original mineralogy of Carboniferous worm tubes: Evidence for changing marine chemistry and biomineralization

Petrographic and geochemical evidence indicates that the original mineralogy of calcareous worm tubes in Carboniferous limestones changed from calcitic in the Mississippian to aragonitic in the Pennsylvanian. This change in mineralogy of CaCO₃ produced by polychaete worms, which are relatively simple biomineralizers, parallels changes observed in nonbiological Carboniferous marine carbonates, suggesting that skeletal secretion of CaCO₃ by polychaetes responded to a global change in seawater chemistry. This is the first documentation of long-term change in the mineralogy of biologically induced biomineralization. It raises the possibility that other bioinduced biomineralization changed in response to changing marine chemistry, in contrast to biocontrolled biomineralization by more sophisticated organisms that persisted with no mineralogical change.