Dresbachian
The Dresbachium is (or was ) in the Earth's history, a period in the hierarchical rank of a stage in the Upper Cambrian of North America. The Dresbachium followed the Alberta series. About or after Dresbachium followed the Franconium. The stage is now obsolete and is no longer used, but it is very common to find in the literature of the 20th century. The Dresbachium corresponds today to the global levels of Guzhangium and Paibium and still reaches a very short period of time in the Jiangshanium into it. The Dresbachium corresponds in geochronology and after today's correlation ( 2012) during the period from 499.5 to 493.9 ma
Naming and history
The concept of Dresbachium goes back to Newton Horace Winchell basically, the first of a " Dresbach Stone " said 1884. He figured this Dresbach Stone but for St. Croix St. Croix formation or Sandstone. From the context it is clear that only Winchell introduced a lithostratigraphic unit within another formation. In 1886 and 1888, he described the unit as Dresbach Sandrock (within the St. Croix Formation). The term Dresbach Stone ( or Dresbach Sandrock ) is named after the place Dresbach in Winona County in the southeastern corner of Minnesota on the Mississippi. 1924 Edward Oscar Ulrich defined the Dresbach Sandstone as lithostraphische unity between the Franconia Sandstone and the Eau Claire Shale. Peterson led 1929 Dresbach formation and divided the Eau Claire Sandstone and Shale in the Dresbach formation a. Trowbridge and Atwater expanded the Dresbach formation again and set the beginning of the Dresbach formation to the base of Mount Simon Sandstone at .. 1938 was limited to the U.S. Geological Survey, the Dresbach Sandstone strong again one, to the exclusion of Eau Claire Sandstone and Mount Simon Sandstone. This lithologic unit is now divided into the Mount Simon Formation, the Eau Claire Formation and Wonewoc formation. The term Dresbach designated thus originally not period.
Edward Oscar Ulrich named in his 1911 published work Revision of the Paleozoic systems in question period as Saint Croixan, is being left open, what amount of time the Saint Croixan included (or should include ). Only in 1944 led BF Howell next Franconian and Tempealeauian the concept of time Dresbachian one.
Definition and correlation
In the original definition by Benjamin Franklin Howell et al. (1944 ) included the Dresbachium the Cedaria, the Crepicephalus and the Aphelaspis - Trilobitenzonen. 1958 beat Christina Lochman - Balk and James Lee Wilson before the Dunderbergia - Faunenzone. They limited the Dresbachian on the Cedaria and the Crepicephalus zone. They wanted to propose at a later time a new level, which included Aphelaspis and the Dunderbergia - Trilobitenzone. This proposal did not sit through, but the following about the Aphelaspis zone Dunderbergia zone was added to the Dresbachium. These four zones are correlated to meet with the upper two thirds of the global Guzhangium stage, the entire global Paibium stage and a very short period of time in the lowest part of the global Jiangshanium stage. Ludvigsen & Westrup (1985 ) replaced the structure of the Oberkambriums in Dresbachium, Franconium and Tempealeauium by the new name Marjuman, Steptoean and Sunwaptan. These new steps have not been successful internationally and regionally. However, the limitations of these new levels do not match with the old steps. The Marjuman begins deeper than the Dresbachium with the Ptychagnostus atavus zone, three Trilobitenzonen and ends with the Crepicephalus zone, in the very Dresbachium. The above includes the following Steptoean the remaining two Trilobitenzonen of Dresbachium plus the Elvinia zone, the lower zone of the former Franconiums.
Events in Dresbachium
In the lower Dresbachium a second extinction event in the Cambrian was held to Upper Botomium. A third extinction event followed in Tempealeauium and at the end of the Cambrian.