PALAEOZOIC/Carboniferous 201 have been amongst the most widely studied, very few formal definitions of the units of the Carboniferous have been internationally ratified Historical Setting The Carboniferous was named by William Conybeare and William Phillips in 1822, based upon their work in northern England From their studies, particularly in Yorkshire, they recognized a distinctive coalbearing sequence, which had an important limestone sequence below The frequent coals, which were economically important, are reflected in the name The lower limestone unit became known as the Mountain Limestone, and the coal series became known as the Coal Measures This sequence of rocks was found across much of Western Europe, and the Carboniferous was divided into the Lower Carboniferous, comprising predominantly marine limestones, and the Upper Carboniferous, comprising clastic and coal-bearing strata In continental Europe these two major divisions were termed the Dinantian and Silesian In North America, however, whilst a similar sequence of limestones and coals was found, the divisions were named the Mississippian by Winchell and the Pennsylvanian by Williams Unfortunately, the boundary between them did not coincide with the boundary defined in western Europe To complicate matters even further, a three-fold division of the Carboniferous was recognized in Russia Chronostratigraphy and Biostratigraphy Through the Heerlen congresses, and later the International Carboniferous Congress, held in Europe, North America, South America, and China through the twentieth century, a number of attempts to divide the Carboniferous into stages and to correlate local stages worldwide were made Local stages were erected with formal boundary stratotypes, but there is often confusion as to usage in the literature Currently, whilst the Carboniferous stage nomenclature has been agreed, few boundaries have yet been defined by the International Commission on Stratigraphy (ICS) (Figure 1) Devonian–Carboniferous Boundary The base of the Carboniferous System (also the base of the Tournaisian Stage) has now been formally defined as the first appearance of the conodont Siphonodella sulcata within the evolutionary lineage from Siphonodella praesulcata to Siphonodella sulcata Figure Current statigraphical nomenclature for the Car boniferous Reproduced from the International Commission on Stratigraphy Taken from ICS website The Global Standard Section and Point is at the base of Bed 89 in Trench E0 at La Serre in southern France The rocks in the La Serre sequence are marine, belonging to the ‘klippen of cabrie`res’, comprising biodetrital oolitic limestones within a pelagic matrix of shale and cephalopod-bearing calcilutites The fauna is varied and includes trilobites Carboniferous–Permian Boundary The base of the Permian System (and hence the top of the Carboniferous System) is defined as the first occurrence of the ‘isolated-nodular’ morphotype of Streptognathodus ‘wabaunsensis’ conodont chronocline, 27 m above the base of Bed 19, Aidarabsh Creek, northern Kazakhstan, which is in the southern Ural Mountains The strata comprise hemipelagic silt and clay, with occasional lenses of sand and very course sand The marine fauna, in addition to conodonts, includes ammonoids and fusilinid benthic foraminifera Mississippian–Pennsylvanian Boundary Following considerable debate, the division of the Carboniferous System into two subsystems has been agreed These two subsystems have been named the Mississippian and Pennsylvanian, although their usage may not always correspond with previous usage The mid-Carboniferous boundary does not coincide with the boundary between either the Lower and Upper Carboniferous or the Dinantian and Silesian of previous schemes In Europe the boundary is within the Namurian of older usage (Figure 2) The base of the Pennsylvanian is also the base of the Bashkirian stage The Global Standard Section and Point has been located at the lowest occurrence of the conodont Declinognathodus nodiliferus s.l., 82.9 m above the top of Battleship Wash Formation, Arrow Canyon, southern Nevada, USA