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Devonian brachiopods of southwesternmost Laurentia; biogeographic affinities and tectonic significance

Arthur J. Boucot, Forrest G. Poole, Ricardo Amaya-Martinez, Anita G. Harris, Charles A. Sandberg and William R. Page
Devonian brachiopods of southwesternmost Laurentia; biogeographic affinities and tectonic significance (in The terrane puzzle; new perspectives on paleontology and stratigraphy from the North American Cordillera, Robert B. Blodgett (editor) and George D. Stanley (editor))
Special Paper - Geological Society of America (2008) 442: 77-97


Three brachiopod faunas discussed herein record different depositional and tectonic settings along the southwestern margin of Laurentia (North America) during Devonian time. Depositional settings include inner continental shelf (Cerros de Los Murcielagos), medial continental shelf (Rancho Placeritos), and offshelf continental rise (Rancho Los Chinos). Ages of Devonian brachiopod faunas include middle Early (Pragian) at Rancho Placeritos in west-central Sonora, late Middle (Givetian) at Cerros de Los Murcielagos in northwestern Sonora, and late Late (Famennian) at Rancho Los Chinos in central Sonora. The brachiopods of these three faunas, as well as the gastropod Orecopia, are easily recognized in outcrop and thus are useful for local and regional correlations. Pragian brachiopods dominated by Acrospirifer and Meristella in the "San Miguel Formation" at Rancho Placeritos represent the widespread Appohimchi Subprovince of eastern and southern Laurentia. Conodonts of the early to middle Pragian sulcatus to kindlei Zones associated with the brachiopods confirm the ages indicated by the brachiopod fauna and provide additional information on the depositional setting of the Devonian strata. Biostratigraphic distribution of the Appohimchi brachiopod fauna indicates continuous Early Devonian shelf deposition along the entire southern margin of Laurentia. The largely emergent southwest-trending Transcontinental arch apparently formed a barrier preventing migration and mixing of many genera and species of brachiopods from the southern shelf of Laurentia in northern Mexico to the western shelf (Cordilleran mio-geocline) in the western United States. Middle Devonian Stringocephalus brachiopods and Late Devonian Orecopia gastropods in the "Los Murcielagos Formation" in northwest Sonora represent the southwesternmost occurrence of these genera in North America and date the host rocks as Givetian and Frasnian, respectively. Rhynchonelloid brachiopods (Dzieduszyckia sonora) and associated worm tubes in the Los Pozos Formation of the Sonora allochthon in central Sonora are also found in stratiform-barite facies in the upper Upper Devonian (Famennian) part of the Slaven Chert in the Roberts Mountains allochthon (upper plate) of central and western Nevada. Although these brachiopods and worm tubes occur in similar depositional settings along the margin of Laurentia in Mexico, they occur in allochthons that exhibit different tectonic styles and times of emplacement. Thus, the allochthons containing the brachiopods and worm tubes in Sonora and Nevada are parts of separate orogenic belts and have different geographic settings and tectonic histories. Devonian facies belts and faunas in northern Mexico indicate a continuous continental shelf along the entire southern margin of Laurentia. These data, in addition to the continuity of the late Paleozoic Ouachita-Marathon-Sonora orogen across northern Mexico, contradict the early Late Jurassic Mojave-Sonora megashear as a viable hypothesis for large-magnitude offset (600-1100 km) of Proterozoic through Middle Jurassic rocks from California to Sonora.

ISSN: 0072-1077
EISSN: 2331-219X
Serial Title: Special Paper - Geological Society of America
Serial Volume: 442
Title: Devonian brachiopods of southwesternmost Laurentia; biogeographic affinities and tectonic significance
Title: The terrane puzzle; new perspectives on paleontology and stratigraphy from the North American Cordillera
Author(s): Boucot, Arthur J.Poole, Forrest G.Amaya-Martinez, RicardoHarris, Anita G.Sandberg, Charles A.Page, William R.
Author(s): Blodgett, Robert B.editor
Author(s): Stanley, George D., Jr.editor
Affiliation: Oregon State University, Department of Zoology, Corvallis, OR, United States
Affiliation: U. S. Geological Survey, Anchorage, AK, United States
Pages: 77-97
Published: 2008
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 43
Accession Number: 2009-006317
Categories: StratigraphyInvertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 4 plates, 2 tables, sketch map
N26°30'00" - N32°30'00", W115°04'60" - W108°30'00"
Secondary Affiliation: University of Montana, USA, United StatesU. S. Geological Survey, USA, United StatesUniversidad de Sonora, MEX, Mexico
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200904
Program Name: USGSOPNon-USGS publications with USGS authors
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