This study investigates the stratigraphy of the newly defined mid-Carboniferous boundary. The selection of the mid-Carboniferous stratotype section should reconcile problems between the different mid-Carboniferous\ud biostratigraphies developed throughout the world and provide a standard against which other successions can be correlated.\ud \ud The nature of the mid-Carboniferous boundary in the Clare Basin has been investigated. Various geochemical analyses have been conducted on a mid-Carboniferous section and it has been possible to construct a chart relating these various geochemical parameters to relative sea-level. It is shown that although deposition is complete through the interval, there is a geochemical expression of a lowstand during the lowest Chokierian. Additionally, doubt is cast on the presumption that all sediments deposited outside 'marine bands' are non marine. A model has been developed for mid-Carboniferous deposition in the Clare Basin. It is envisaged that the shelves of the Clare Basin were flooded during the early Namurian leading to an environment suitable for phosphate authigenesis. During a major regression in the Pendleian/lower Arnsbergian the phosphate was reworked into a lag. The lowstand of the basal Chokierian is marked by a thin lag on the shelves, whilst deposition was continuous in the basin centre. Later Chokierian times are marked by a widespread transgression.\ud \ud The mid-Carboniferous stratotype has been chosen at Arrow Canyon,Nevada. Microfacies studies show that deposition was on a winnowed carbonate platform showing reworking of bioclasts. Faunal diversity and eveness studies have also been conducted on this section. No drop in diversity is seen at the mid-Carboniferous boundary, although a drop in\ud eveness is seen, whether this relates to a specialised fauna or selective winnowing of bioclasts is unknown.\ud \ud Correlations between America and western Europe show that conodonts are strongly facies controlled and it is unlikely that the appearance of Declinognathodus noduliferus is truly isochronous between sections, and thus is an unwise choice for defining the mid-Carboniferous boundary.\ud Additionally it is suggested that Arrow Canyon was a poor choice for the stratotype section due to both the possibility of reworking, the presence of an\ud unconformity in the section and possible doubts over the conodont record at this locale.\ud \ud The Rhachistognathus minutus zone is recognized as a new conodont zone across the Arnsbergian/Chokierian boundary
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