Diagenesis of Lower Ordovician hardgrounds in Sweden

l m of Arenigian orthoceratite limestone has at !east 10-20 hardgrounds. Glauconite crusts postdate some calcite cement. Calcite crystals are intergrown with glauconite, pyrite, and goethite. lnclusion in calcite protected some goethite from dehydration to hematite. No evidence of aragonite or Mg-calcite was found. »Ant-egg spar« (AES), a variety of microspar, consists of redeposited calcite crystals of early cement origin. Hardgrounds may represent much longer time than the sediment; they show evidence of highly impoverished biota. The carbonate mud is essentially allochthonous.