NPS Paleontology Research Abstract Volume


GRAPTOLITE BIOSTRATIGRAPHY OF THE
ORDOVICIAN MARTINSBURG FORMATION IN
THE DELAWARE WATER GAP REGION

David C. Parris
Natural History Bureau, New Jersey State Museum
205 West State Street, CN-530
Trenton, New Jersey 08625-0530

Kenneth M. Cruikshank
M. King Hubbert Geomechanics Laboratory
Department of Earth & Atmospheric Sciences
Purdue University
West Lafayette, Indiana 47907

Within the Delaware Water Gap National Recreation Area (New Jersey & Pennsylvania) are many fossil localities that are significant in the biostratigraphy of the Silurian and Devonian Systems. Shelly invertebrate fossils are abundant in the formations of Silurian and Devonian age and have been studied for more than a century.

The fossils of the Ordovician System are less well known, and the rocks are structurally complicated. Biostratigraphy of such formations generally is based on graptolites rather than shelly fossils. Graptolites were floating colonial marine invertebrates with which widely recognized mappable zones have been established.

As an outgrowth of paleontological resource surveys in the Delaware Water Gap National Recreation Area (funded by the Eastern Parks and Monuments Association), the Ordovician Martinsburg Formation can now be studied with reference to a biostratigraphic framework (New Jersey Geological Survey Report 28, 1992). Historically important to the slate industry, it is one of the most important geologic resources of the region.

The collections, including many new graptolite discoveries from northern New Jersey, eastern Pennsylvania, and southeastern New York, confirm that the Ordovician Martinsburg Formation consists of three members: in ascending order the Bushkill, Ramseyburg and Pen Argyl Members. The Bushkill and Pen Argyl Members are not equivalent in age as previously suggested by some authors. The Bushkill Member correlates with the Climacograptus bicornis to Corynoides americanus Zones. The Ramseyburg Member correlates with the interval represented by the Orthograptus ruedemanni Zone and the lowest part of the Climacograptus spiniferus Zone. The Pen Argyl Member correlates with the upper part of the Climacograptus spiniferus Zone.



Back to Table of Contents

United States Department of the Interior, National Park Service