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Calabrian (stage) ：ウィキペディア英語版

Calabrian (stage)

Calabrian is a subdivision of the Pleistocene Epoch of the geologic time scale, defined as ~1.8 Ma.—781,000 years ago ± 5,000 years, a period of ~.
The end of the stage is defined by the last magnetic pole reversal (781 ± 5 Ka) and plunge into an ice age and global drying possibly colder and drier than the late Miocene (Messinian) through early Pliocene (Zanclean) cold period.〔A chronology of Pliocene sea-level fluctuations, U.S. Atlantic Coastal Plain: Quaternary Science Reviews, v. 10, p. 163–174.〕 Originally the Calabrian was a European faunal stage primarily based on mollusk fossils. It has become the second geologic age in the Early Pleistocene. Many of the mammalian faunal assemblages of the Early Pleistocene start in the Gelasian. For example, the Platygonus and other Blancan fauna appear first in the Gelasian.
==History of the definition of the Calabrian==
Because sea shells are much more abundant as fossils, 19th- and early 20th-century geo-scientists used the plentiful and well-differentiatable Mollusca (mollusks) and Brachiopods to identify stratigraphic boundaries. Thus the Calabrian was originally defined as an assemblage of mollusk fossils, most brachiopods being extinct by then. Efforts were then made to find the best representation of that assemblage in a stratigraphic section. By 1948 scientists used the initial appearance of cool-water (northern) invertebrate faunas in Mediterranean marine sediments as the beginning marker for the Calabrian. The 18th International Geological Congress in London (1948) placed the base of the Pleistocene at the base of the marine strata of the Calabrian Faunal Stage and denominated a type section in southern Italy. However, it was discovered that the original type section was discontinuous at that point and that the base of the Calabrian Stage as defined by fauna assemblages extended to earlier levels within the Pleistocene. A new type section was chosen, several miles from the original one, at Vrica, 4 km south of Crotone in Calabria, southern Italy. Analysis of strontium and oxygen isotopes as well as of planktonic foraminifera has confirmed the viability of the current type section. The 27th International Geological Congress in Moscow in 1984 formally ratified the type section. The starting date was originally thought to be about 1.65 million years ago, but has been recalculated as 1.806 Mya.

抄文引用元・出典: フリー百科事典『ウィキペディア（Wikipedia）』
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