JOURNAL OF PALEONTOLOGY A publication of THE SOCIETY OF ECONOMIC PALEONTOLOGISTS AND MINERALOGISTS and THE PALEONTOLOGICAL SOCIETY with the generous support and cooperation of THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS VOLUME 41 JANUARY 1967 NUMBER 1 BRACHIOPODA AND STRATIGRAPHY OF THE RONDOUT FORMATION IN THE ROSENDALE QUADRANGLE, SOUTHEASTERN NEW YORK FLORENCE GROSVENOR HOAR AND ZEDDIE PAUL BOWEN Shenandoah National Park, Luray, Virginia, and University of Rochester, Rochester, New York ABSTRACT-Study of the stratigraphy and paleontology of the Rondout Formation in the type area, the Rosendale and Rhinebeck quadrangles in southeastern New York, suggests that the formation was deposited in very shallow water with periodic emergence on a broad, carbonate mud flat sloping toward the west and southwest. The sequence represents accumula- tion in shifting subtidal, intertidal, and supratidal environments. Fossiliferous limestones were deposited in very shallow water on an offshore bar and/or a near shore bank; while at the same time, unfossiliferous, laminated carbonates, now dolomites, were deposited in quieter and slightly deeper water between the limestone areas. A thin, stromatoporoid bioherm in the Glasco Member apparently developed on an offshore bar. Mudcracks in the laminated dolo- mites of the Whiteport Member indicate frequent subaerial desiccation and suggest penecon- temporaneous dolomitization of these beds in a shifting subtidal to supratidal environment similar to that recently described in Florida and the Bahamas. Thirty-five stratigraphic sections were studied; twenty were measured in detail. Polished, stained and etched rock specimens were examined from each section, but thin sections were not made. Type sections are proposed for the Wilbur and Rosendale Members, and a reference section for the Glasco Member in the Rosendale quadrangle is suggested. Fourteen brachiopods, one colonial coral, and one bryozoan species are described. On the basis of these fossils, the Rondout Formation is correlated with the Decker Formation of New Jersey, the Cobleskill Formation of central New York, and the Eccentricosta jerseyensis Zone of the Keyser Limestone of Maryland, West Virginia, and Pennsylvania, and the Rondout is judged to be Late Silurian in age. INTRODUCTION The stratigraphy of the Rondout has been THE Rondout Formation of New York is studied by a number of other workers in varying composed of argillaceous and silty carbon-detail since 1843, most recently by Rickard ates and calcareous sandstones of Late Silurian (1962), but no systematic paleontological study age cropping out in two belts across New York has been made. The present work was undertaken State, an east-west belt from Albany to Seneca to describe the stratigraphy of the Rondout Falls, and a northeast-southwest belt from Al- Formation in the type area near Rondout, New bany to Port Jervis on the New Jersey border. York, to describe and illustrate some of the fos- Both lithologically and faunally these belts are sils, especially the brachiopods, and to discuss the dissimilar and represent two broad facies com- environmental conditions under which these plexes: west of Albany the Rondout consists of animals lived and the rocks were depostied. The unfossiliferous dolomite beds, the Chrysler Mem- area of study extends from Glasco, in the Cats- ber of Rickard (1962), whereas southwest of kill quadrangle, to Port Jackson, in the Rosen- Albany the formation contains several variable dale quadrangle, as shown in text-figure 1. limestone, dolomite, and sandstone members Field work was done during the summer of and a rich and varied fauna. 1964. Thirty-five sections were examined, and of 1 This content downloaded from 137.140.1.131 on Thu, 09 Apr 2020 01:13:30 UTC All use subject to https://about.jstor.org/terms 2 FLORENCE GROSVENOR HOAR AND ZEDDIE PAUL BOWEN LOCATI ON MAP RONDOUT FORMATION Numbers correspond to stratigraphic sections described in the text. Scale 0 1 1 3 4 5 b I I I I I I miles TEXT-FIG. 1-Map showing locations of stratigraphic sections of the Rondout Formation from which fossils were collected. these, twenty were measured in detail. Fossils, We are grateful for support of the field work where present, and rock specimens were collected by an honorarium from the State of New York from each unit at each of the localities. The and by a grant from the Society of Sigma Xi. We rock specimens were cut, polished, and stained also thank Dr. Lawrence V. Rickard, Senior with cupric nitrate, according to the method Paleontologist, de- New York State Museum, for scribed by Rodgers (1940), to determine information tex- about Rondout exposures, and Drs. tures and to distinguish between calcite Robert and G. Sutton and Lawrence W. Lundgren of dolomite. The specimens were also etched thewith University a of Rochester for helpful sugges- 10 percent hydrochloric acid solution to permittions which improved the manuscript. Mrs. rapid visual estimation of the percent of Hoarargil- also thanks Mr. and Mrs. G. Gordon Con- laceous material present. All but two of nally the for providing food and lodging during the stratigraphic sections listed have been measured completion of the field work and Leigh D. Hoar, by previous workers, but all were remeasured Jr. for help in collecting rock specimens. and redescribed for this study. STRATIGRAPHY This work was begun as a Master of Science dissertation project by Hoar under the direction The name Rondout was proposed by Clarke & of Bowen at the University of Rochester. Schuchert In the (1899) for rocks exposed in the vicin- present paper, the original report has been ity re- of the town of Rondout in southeastern New vised and enlarged upon by Bowen. Descriptions York. In this region, the Rondout has been sub- of each of the measured sections can be found in divided into four members, which are, from Mrs. Hoar's thesis. bottom to top: the Wilbur Limestone, the Rosen- This content downloaded from 137.140.1.131 on Thu, 09 Apr 2020 01:13:30 UTC All use subject to https://about.jstor.org/terms BRA CHIOPODA OF THE RONDOUT FORMATION 3 dale Dolomite, the Glasco Limestone, and the Bossardville? Formation Whiteport Dolomite. A fifth member, The the Rondout Fuyk in the Port Jackson area (loc. Sandstone, interfingers with the carbonate 1 and 3)mem- is underlain by an extremely fine- bers in the northern and central parts grained of andthe thinly laminated dolomite unit Catskill quadrangle but is not exposed with inalternating the light and dark laminae. In- area studied. The formation is overlain conform- cluded within some of the laminae is silt sized ably throughout eastern New York by the quartz, and in some beds, fragments of the lam- Thacher Member of the Manlius Formation. It inae appear to have been torn up and rotated. overlies highly deformed Ordovician siltstones A 1- to 2-inch thick layer of grayish black shale and shales in the northeastern part of the areamarks the boundary between the Rondout and at Flatbush School (text-fig. 1, loc. 19) and this dolomite unit, which is distinctly different Rondout (loc 18), the Binnewater Formation from the Rondout in its extremely fine grain from Wilbur (loc. 17) to High Falls (loc. 7), and size. Wanless (1921 unpublished M.A. thesis, the Bossardville? Formation at the southwestern Princeton Univ.) suggested that these beds are edge of the area at Port Jackson (loc. 1). the northern equivalent of the Bossardville Binnewater Formation Limestone of New Jersey. The Bossardville Limestone at the old Nearpass Quarries in New The Binnewater Formation underlies the Jersey, where it underlies the Decker Formation, Rondout throughout most of the Rosendale is a "compact, fine-grained, bluish grey, banded quadrangle. It is a thin- to medium-bedded, limestone," (Weller, 1903, p. 61). Wanless' cor- gray, red, or green, dolomitic sandstone relation unit is accepted here but queried because the which is easily distinguished by its high only sandevidence to support it is the correlation of content from the overlying Rondout carbonates. the overlying Rondout and Decker Formations Cross-bedding and ripple marks are prominent as discussed later in this paper. throughout all but the upper 3 feet of the forma- tion, and mudcracks are present on some beds. Manlius Formation, Thacher Member The uppermost 3 feet differ in character from The Thacherthe Member of the Manlius Forma- beds below, in that they show little cross-bedding tion conformably overlies the Rondout in eastern and contain the few fossils, fragments Newof cup York, and the boundary between the two is corals and stromatoporoids, that have been sharp. Only the lower two units of the Thacher found in the formation. Interbedded with the were measured in this study, the lower "curly sandstone are irregular fragments or thin, beds,"dis- and the overlying "Leperditia limestone." continuous layers of argillaceous dolomite upThese to are local names used to refer to the lower 3 inches thick. At Wilbur (loc. 17), the argil- part of the Manlius in the Rosendale-Rondout laceous dolomite is present only as abundant, area an- (Rickard, 1962). The curly beds are fissile, gular fragments within the sandstone beds; laminated, but fine-grained, gray, calcareous shales, to the southwest, thicker and more persistent which in some localities contain impressions of beds are present. At Fourth Lake (loc. 14), ostracods. the The Leperditia limestone is very fos- individual dolomite beds are from 2 to 10 feet siliferous and consists of interbedded argillaceous long and over 1 inch thick. At the southwestern- limestone, dolomite, and shale. The combined most exposure of the Binnewater, at High Fallsthickness of the two units varies from 2 to 6 feet, (loc. 7), the upper 14 feet of the formation butcon- both are present and recognizable through- sist of alternating layers of thinly laminated, out the outcrop area. Rickard (1962) defined the argillaceous dolomite and dolomitic sandstone.