LATE CAMBRIAN AND EARLY ORDOVICIAN FAUNAS FROM THE WILBERNS FORMATION OF CENTRAL TEXAS

The San Saba Member of the Wilberns Formation of central Texas is mostly coarse-grained, trilobitic limestone that grades eastward to dolomite and contains sandstone intervals in its westernmost exposures. Faunas from the limestone place the middle part of the San Saba within the Trempealeauan Stage (Saukia zone) of the Upper Cambrian, but the uppermost part belongs to the Lower Ordovician. Three subzones within the Saukia zone are described. In ascending order they are: the Saukiella junia subzone containing Bayfieldia, Briscoia, Corbinia, Euptychaspis, Eurekia, Saukia, Saukiella, Stenopilus, Triarthropsis, and Finkelnburgia; the Saukiella norwalkensis subzone containing Bayfieldia, Bowmania, Briscoia, Calvinella, ?Dikelocephalus, Eurekia, Euptychaspis, Heterocaryon, Idiomesus, Keithiella, Leiocoryphe, Macronoda, Plethometopus, Prosaukia, Saukiella, Stenopilus, Theodenisia, and Finkelnburgia; the Corbinia apopsis subzone containing A cheilops, Apatokephaloides, Corbinia, Eurekia, Idiomesus, Leiobienvillia, Leiocoryphe, Plethometopus, Theodenisia Triarthropsis, Apheoorthis, Finkelnburgia, Glyptotrophia, and Nanorthis. Trilobites of the Saukiella junia and Saukiella norwalkensis subzones are closely allied to those of the Trempealeauan of the upper Mississippi Valley, whereas the trilobites of the Corbiuia apopsis subzone represent an influx of the Hungaia magnifica fauna. The low Ordovician faunas are subdivided into two zones. The lower zone is named the Missisquoia zone and contains Highgatella, Homagnostus, Hystricurus, Missisquoia, Para- bolinella, Symphysurina, Apheoorthis, Conotreta and Syntrophina. It correlates closely with a low Ordovician fauna from Vermont described by Shaw. The upper zone is the Symphysurina zone and contains Clelandia, Homagnostus, Hystricurus, Jujuyaspis, Symphysurina, Apheo- orthis, and Syntrophina. It correlates most closely with the Symphysurina zone of Utah and Nevada. New trilobite species are Acheilops masonensis, Bayfieldia simata, Bowmania sagitta, Briscoia llanoensis, Calvinella procera, Clelandia texana, Corbinia apopsis, Corbinia implumis, Euptychaspis jugalis, Homagnostus reductus, Keithiella patula, Leiobienvillia leonensis, Leio- coryphe halei, Missisquoia infiata, Missisquoia nasuta, Saukiella planata, and Symphysurina bubops.

[1]  R. E. Grant.  FAUNAS AND STRATIGRAPHY OF THE SNOWY RANGE FORMATION (UPPER CAMBRIAN) IN SOUTHWESTERN MONTANA AND NORTHWESTERN WYOMING , 1965 .

[2]  Christina Lochman.  Upper Cambrian faunas from the subsurface Deadwood Formation, Williston Basin, Montana , 1964 .

[3]  F. Rasetti.  Trempealeauian trilobites from the Conococheague, Frederick, and Grove limestones of the central Appalachians , 1959 .

[4]  H. B. Whittington,et al.  STRATIGRAPHY OF THE COW HEAD REGION, WESTERN NEWFOUNDLAND , 1958 .

[5]  W. K. Hamblin.  The Cambrian sandstones of northern Michigan , 1958 .

[6]  C. W. Merriam,et al.  The stratigraphic section in the vicinity of Eureka, Nevada , 1956 .

[7]  A. R. Palmer.  Upper Cambrian Agnostidae of the Eureka District, Nevada , 1955 .

[8]  Christina L. Balk.  Lower Ordovician Trilobites from Western Utah and Eastern Nevada , 1954 .

[9]  J. L. Wilson.  Late Cambrian and early Ordovician trilobites from the Marathon Uplift, Texas , 1954 .

[10]  C. A. Nelson.  Cambrian trilobites from the Saint Croix valley [Minnesota-Wisconsin] , 1951 .

[11]  A. Shaw.  New late Cambrian trilobites, [Part] 1 of The paleontology of northwestern Vermont , 1951 .

[12]  A. Shaw.  THE PALEONTOLOGY OF NORTHWESTERN VERMONT. I. NEW LATE CAMBRIAN TRILOBITES , 1951 .

[13]  T. H. Clark.  Theodenisia, new name, replacing Denisia Clark , 1948 .

[14]  P. Cloud,et al.  STRATIGRAPHY OF THE UPPER CAMBRIAN, LLANO UPLIFT, TEXAS , 1947 .

[15]  E. A. Frederickson.  Correlation of Cambro- Ordovician trilobites from Oklahoma , 1941 .

[16]  C. R. Stauffer.  Fauna of the Van Oser beds [Minnesota] , 1940 .

[17]  P. Raymond.  Upper Cambrian and Lower Ordovician Trilobita and Ostracoda from Vermont , 1937 .

[18]  G. A. Cooper,et al.  New genera and species of Ozarkian and Canadian brachiopods , 1936 .

[19]  C. E. Resser.  Nomenclature of some Cambrian trilobites , 1935 .

[20]  J. Bridge,et al.  Faunal Correlation of the Ellenburger Limestone of Texas , 1932 .

[21]  R. Ruedemann,et al.  The Cambrian of the upper Mississippi valley , 1930 .

[22]  C. L. Fenton,et al.  Ecologic Interpretations of Some Biostratigraphic Terms , 1928 .