Abstract

From eastern Gaspe southwest to central Chihuahua the Lower Devonian marine sedimentary sequence carries brachiopod faunas of singular provincial affinity. Four zones, based on rensselaeriid evolution, are recognized: (1) Nanothyris Zone, comprising the Manlius-Coeymans and Kalkberg-New Scotland intervals (Gedinnian), (2) Rensselaeria Zone, comprising the Becraft-Port Ewen plus the Oriskany (Siegenian), (3) Etymothyris Zone, and (4) Amphigenia Zone. The latter two zones comprise the Esopus and Schoharie-Bois Blanc (Emsian).

Manlius-Coeymans equivalents are not widespread and are surely recognized, beyond the New York-Pennsylvania-Maryland-West Virginia region, only in Gaspe (St. Albans Formation) and as far southwest as western Tennessee (Rockhouse Formation). The Bailey Limestone of Missouri could include Manlius-Coeymans equivalents, but fossils of that age are unreported. The belt of marine rocks appears to be narrow and is represented predominantly by limestone and calcareous shale.

In the middle and upper part of the Helderbergian, including Kalkberg-New Scotland and Becraft-Port Ewen equivalents, brachiopod - rich limestones, terriginous rocks, and volcanics are far more widespread. Southwest of New York, Pennsylvania, Maryland, Virginia, and West Virginia, there is a broad expanse inclusive of southeastern Missouri, Oklahoma, Texas, and Chihuahua where this interval is represented principally by limestone. Northeast of New York the limestone belt gave way to one rich in terriginous rocks with a central core of volcanics from northern New Brunswick to northcentral Maine.

Oriskany equivalents are equally widespread, but in many places lie unconformably upon upper Helderbergian or older rocks. In the southern United States and Chihuahua. limestone and chert predominate, but the Oriskany Sandstone and its equivalents span a broad area in New York, Pennsylvania, and southwest to westernmost Virginia. A limestone belt can be traced from eastern New York, through Montreal, and thence northeast to eastern Gaspe. An argillaceous belt is widespread through the Connecticut Valley region of New England to Gaspe.

Esopus time saw a restriction of marine faunas to terriginous facies occurrences in Gaspe and in the Matapedia Valley of Quebec as well as in eastern New York, Pennsylvania, West Virginia, and to limestone in central Texas. Most of the rest of eastern and southern North America apparently was emergent during Esopus time.

Schoharie time was again represented by widespread marine sediments. Terriginous rocks occur in a belt west of a land area extending from Gaspe to the southwest, traceable through New York, Pennsylvania, and as far south as northern Alabama. A broad inner, limestone belt, containing much chert, occupied the area around the Great Lakes and to the west and south of central Tennessee and stretching into west Texas and northern Mexico.

During early Gedinnian time beds equivalent to the Manlius and Coeymans, representing a terriginous marine facies, were being deposited in Nova Scotia, southern New Brunswick, and eastern Maine and were characterized by brachiopods belonging to the Old World Province (Rhenish Community). A land area from northern New Brunswick through and including much of Maine lay between the Old World and Appalachian Province occurrences. During the interval including late Gedinnian, Siegenian, and Emsian (equivalent to the New Scotland and higher parts of the Helderberg, the Oriskany, Esopus, and Schoharie) terriginous marine sediments were deposited in southern Nova Scotia carrying brachiopods belonging to the Old World Province (Rhenish Community) and were separated from Appalachian Province marine areas by a land area in southern New Brunswick, eastern Maine, and northern Nova Scotia.

Several animal communities, based on brachiopods, have been delineated in the Lower Devonian of the Appalachian Province. These are best understood for deposits of Oriskany age and prove not to coincide with the distribution of Oriskany age lithofacies belts.

Age and correlation of Helderbergian to Oriskany (Gedinnian to Siegenian) formations are discussed separately. Arguments are advanced to show that the New Scotland Brachiopod-rich Community has an age essentially equivalent to the whole of the Helderbergian, but that Manlius-Coeymans, Kalkberg-New Scotland, and Becraft-Port Ewen should be separately recognizable on faunal grounds (other than those controlled by community) beyond the belt of outcrops from New York to westcentral Virginia and West Virginia.