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'''Laurentia''' ('''North American Craton''') is a large continental [[craton]], which forms the ancient geological core of the [[North America]]n continent.  

'''Laurentia''' ('''North American Craton''') is a large continental [[craton]], which forms the ancient geological core of the [[North America]]n continent.  

[[file:NacratonUSGS.jpg|thumb|300px|The North American continent, USGS. The brown area shows the part of the North American continent that has been stable for over 600 million years. This region is made up of a basement older Precambrian metamorphic and igneous rock that is mostly covered by a relatively thin cover of younger sedimentary rock. Geologists call these long-stable continental cores cratons. The green area on the illustration shows new continental material that was added relatively recently, within the last 600 million years or so. Continents can grow when two plates collide, welding, or accreting, the two pieces together. Continents also grow when oceanic crust is scraped off oceanic plates as they sink in subduction zones. The purple area fringing the stable continental core is made up of older Precambrian basement that was deformed during plate collisions that occurred within the last 600 million years. The force of collision produced great folds and faults that sometimes penetrated deep into the continental interior. Where the crust was uplifted, these folds and faults are exposed at the surface, allowing geologists to piece together the ancient history of our continent.<ref name=USGS>USGS Geology in the Parks, , http://geomaps.wr.usgs.gov/parks/pltec/nacraton.html</ref>]]

The great American carbonate bank (GACB) refers to a system of carbonates and related siliciclastics that were deposited on and around the Laurentian continent during the [[Cambrian]], Early [[Ordovician]], and earliest Middle Ordovician. This laterally continuous and diverse sequence has been assigned different sets of formation and group names across the GACB, such as [[Arbuckle]], [[Beekmantown]], [[Bonanza King]], [[Deadwood]], [[Ellenburger]], [[El Paso]], [[Knox]], [[Prairie du Chien]], and [[Potsdam]] (to name just a few of the more widely used), but characteristic lithofacies and fauna that are found throughout North America, Greenland, northwestern Scotland, Svalbard, and the pre-Cordillera of Argentina are observed.

The great American carbonate bank (GACB) refers to a system of carbonates and related siliciclastics that were deposited on and around the Laurentian continent during the [[Cambrian]], Early [[Ordovician]], and earliest Middle Ordovician. This laterally continuous and diverse sequence has been assigned different sets of formation and group names across the GACB, such as [[Arbuckle]], [[Beekmantown]], [[Bonanza King]], [[Deadwood]], [[Ellenburger]], [[El Paso]], [[Knox]], [[Prairie du Chien]], and [[Potsdam]] (to name just a few of the more widely used), but characteristic lithofacies and fauna that are found throughout North America, Greenland, northwestern Scotland, Svalbard, and the pre-Cordillera of Argentina are observed.

file:NacratonUSGS.jpg|The North American continent, USGS. The brown area shows the part of the North American continent that has been stable for over 600 million years. This region is made up of a basement older Precambrian metamorphic and igneous rock that is mostly covered by a relatively thin cover of younger sedimentary rock. Geologists call these long-stable continental cores cratons. The green area on the illustration shows new continental material that was added relatively recently, within the last 600 million years or so. Continents can grow when two plates collide, welding, or accreting, the two pieces together. Continents also grow when oceanic crust is scraped off oceanic plates as they sink in subduction zones. The purple area fringing the stable continental core is made up of older Precambrian basement that was deformed during plate collisions that occurred within the last 600 million years. The force of collision produced great folds and faults that sometimes penetrated deep into the continental interior. Where the crust was uplifted, these folds and faults are exposed at the surface, allowing geologists to piece together the ancient history of our continent.<ref name=USGS>USGS Geology in the Parks, , http://geomaps.wr.usgs.gov/parks/pltec/nacraton.html</ref>

file:M98Ch2Fig1.JPG|Restored extent of the great American carbonate bank (GACB) during the earliest Ordovician (early Tremadocian) Stonehenge transgression. This transgression occurred during deposition of the Early Ordovician Symphysurina trilobite Zone or during deposition of the Cordylodus angulatus and basal Rossodous manitouensis conodont Zones. This period probably does not represent the maximum transgression during deposition of the Sauk III but is commonly preserved and recognized across Laurentia. The records of younger transgressions, which may have been more extensive, are commonly removed by erosion. Consequently, this map records the maximum documented (at this time) extent of the GACB across Laurentia.<ref name=Derbyetal_2012>Derby, James R., Robert J. Raine, Anthony C. Runkel, and M. Paul Smith, 2012, [http://archives.datapages.com/data/specpubs/memoir98/CHAPTER02/CHAPTER02.HTM Paleogeography of the great American carbonate bank of Laurentia in the earliest Ordovician (early Tremadocian): The Stonehenge transgression], in J. R. Derby, R. D. Fritz, S. A. Longacre, W. A. Morgan, and C. A. Sternbach, eds., The great American carbonate bank: The geology and economic resources of the Cambrian–Ordovician Sauk megasequence of Laurentia: AAPG Memoir 98, p. 5–13.</ref>

Fundamental to our understanding of the components of the GACB is the biostratigraphy that ties the disparate parts into a cohesive whole. Biostratigraphic zonation has advanced considerably since the days when Sloss et al.<ref name=Slossetal_1949>Sloss, L. L., W. C. Krumbein, and E. C. Daples, 1949, Integrated facies analysis, in C. R. Longwell, ed., Sedimentary facies in geologic history: Geological Society of America Memoir 39, p. 91–124.</ref> coined the term ''Sauk sequence'' and Palmer<ref name=Palmer_1981>Palmer, A. R., 1981, Subdivision of the Sauk sequence, in M. E. Taylor, ed., Short papers for the 2nd International Symposium on the Cambrian System: U.S. Geological Survey Open File Report 81-743, p. 160–162.</ref> subdivided the Sauk into three subdivisions. It is now possible to identify more than 20 biostratigraphic zones within the Sauk succession for the Laurentian continent (with finer subdivision possible on a more local basis) using mostly trilobites and conodonts.  

Fundamental to our understanding of the components of the GACB is the biostratigraphy that ties the disparate parts into a cohesive whole. Biostratigraphic zonation has advanced considerably since the days when Sloss et al.<ref name=Slossetal_1949>Sloss, L. L., W. C. Krumbein, and E. C. Daples, 1949, Integrated facies analysis, in C. R. Longwell, ed., Sedimentary facies in geologic history: Geological Society of America Memoir 39, p. 91–124.</ref> coined the term ''Sauk sequence'' and Palmer<ref name=Palmer_1981>Palmer, A. R., 1981, Subdivision of the Sauk sequence, in M. E. Taylor, ed., Short papers for the 2nd International Symposium on the Cambrian System: U.S. Geological Survey Open File Report 81-743, p. 160–162.</ref> subdivided the Sauk into three subdivisions. It is now possible to identify more than 20 biostratigraphic zones within the Sauk succession for the Laurentian continent (with finer subdivision possible on a more local basis) using mostly trilobites and conodonts.