ThisdatumwasobtainedfromthetopIcmofthe6cmthickBed3,whereasthedatum0.40isthemeanvalueof6samplesofBed26.TABLE3SUCCESSIONOFTHEPTBMARKERStogetherwithunevenlydistributCdirspikeareheresuggestedasauxiliarymarkersoftheboundary.Significanceofthechemicalanomalieswillbefurtherdiscussedintheparagraphofeventostratigraphy.EVENTOgyRATIGRAPHYACROSSTHEPTBOFMEISnANVolcedcEventThe'WhiteClay'orBed25iscomposedofinterbedsofilliteandaxxedmontmorillonite--illitelayerswithsubordinatekaolinite.The'BlackClay'orBed26isofmixedmontmori