Synthesis and revision of groups within the Newark Supergroup, eastern North America Robert E. Weems U.S. Geological Survey, M.S. 926A, Reston, Virginia 22092 Paul E. Olsen Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964 ABSTRACT sills, places Newark Supergroup rocks in the basins; and the Fundy Group in various areas of Agawam Group. Application of this new re- the Fundy basin), one group encompasses the en- The Newark Supergroup currently includes gional group stratigraphy to the early Meso- tire column of a single basin (Hartford Group in nine stratigraphic groups, each of which ap- zoic rift basins requires revision of the stratig- the Hartford basin), and one group encompasses plies to part or all of the rock column of only raphy of several basins to make formation only part of the sequence in three basins (Bruns- one or a few basins. Because the group nomen- boundaries match group boundaries. wick Group in the Newark basin; Meriden Group clature within the Newark Supergroup is nei- in the Pomperaug and Hartford basins). In other ther inclusive nor parallel in its concepts, INTRODUCTION early Mesozoic basins, no groups have been pro- nearly half of the strata within the Newark Su- posed (Scottsburg, Randolph, Roanoke Creek, pergroup lacks any group placement. A new The Newark Supergroup (Fig. 1) is an inclu- Briery Creek, Farmville, Taylorsville, Scottsville, system is proposed herein that (1) establishes sive stratigraphic term for all continental sedi- Gettysburg, Cherry Brook, Deerfield, Northfield, unambiguous group boundaries, (2) places all mentary and extrusive volcanic rocks of Middle and Middleton basins). Thus some groups corre- Newark Supergroup strata into groups, (3) re- Triassic through Early Jurassic age that are pre- spond to one basin, some groups are present in duces the number of group names from nine to served in 29 rift basins exposed in eastern North more than one basin, some groups include only three, (4) creates parallelism between groups America (Olsen, 1978; Froelich and Olsen, part of one basin, and some basins have no group and three major successive tectonic events that 1984). Age-equivalent rocks lie buried beneath assignment. created the rift basins containing the Newark the Atlantic Coastal Plain, but these have not This approach to the group concept has unnec- Supergroup, and (5) coincidentally provides been added to the Newark Supergroup because essarily fragmented a relatively uniform regional isochronous or nearly isochronous group their age, areal extent, and lithologic composition lithostratigraphic and tectonostratigraphic pat- boundaries. These proposed groups are (1) the remain unknown (Luttrell, 1989, p. 2). The New- tern, because the depositional history of the entire Chatham Group (Middle Triassic to basal ark Supergroup is bounded by profound regional Newark Supergroup can be divided into three Lower Jurassic sedimentary rocks), (2) the unconformities, each representing 90 m.y. or discrete and successive phases. In the first phase, Meriden Group (Lower Jurassic extrusive vol- more. Although local internal unconformities separate basins formed and clay, silt, sand, and canic and sedimentary rocks), and (3) the Aga- have been documented, the Newark Supergroup gravel were deposited in fluvial, lacustrine, and wam Group (new name) (Lower Jurassic sedi- regionally represents nearly continuous deposi- alluvial fan environments. This phase persisted mentary rocks above all early Mesozoic tion from Middle Triassic into Early Jurassic time about 35 m.y., from the Middle Triassic to the be- igneous intrusive and extrusive rocks). (Olsen, 1986). ginning of the Jurassic (Olsen, 1986). A second This new rock classification system makes Formational nomenclature within the Newark depositional phase occurred within the Early use of the fact that a discrete interval of syn- Supergroup generally is adequate (Luttrell, 1989, Jurassic, when large volumes of basaltic magma chronous or nearly synchronous volcanism Plate 1), but group-level stratigraphy remains dis- spread as basalt flows across the basin floors. and plutonism occurred throughout the early organized and incompletely applied (Fig. 2). These flows are interbedded with sedimentary Mesozoic rift system of eastern North Amer- Four group names (Conewago, Lewisburg or rocks, formed from continental sediments that ica. The presence or absence of volcanic rocks Lewisberry, Lisbon or Lisburn, and Manchester) continued to accumulate between basaltic erup- provides a powerful stratigraphic tool for es- have been proposed and subsequently abandoned tions. On the basis of analysis of Milankovitch- tablishing regional groups and group bound- (Luttrell, 1989); these are not discussed further. type cycles, volcanic extrusions began synchro- aries. The presence of sedimentary rocks in- Among groups currently accepted in the litera- nously within 21 k.y., ended synchronously, and jected by diabase dikes and sills, in the absence ture, two groups occur within one basin (Tucka- lasted for 580 ± 100 k.y. (Olsen and Fedosh, of extrusive volcanic rocks, places Newark Su- hoe and Chesterfield Groups in the Richmond 1988; Olsen et al., 1996). The third phase com- pergroup rocks in the Chatham Group. The basin); one group encompasses the entire column menced after volcanism ceased and sedimenta- presence of extrusive volcanic rocks, interbed- in several basins (Chatham Group in the Crow- tion resumed without volcanic interruption in at ded with sedimentary rocks injected by dia- burg, Wadesboro, Ellerbe, Sanford, and Durham least two of the rift valleys. base dikes and sills, places Newark Super- basins; Dan River Group in the Davie County Wherever the middle stage of the Newark Su- group rocks in the Meriden Group. The and Dan River–Danville basins; Tuckahoe Group pergroup rock column is fully preserved, the in- presence of sedimentary rocks lacking both ex- in the Deep Run and Flat Branch basins; Cul- terval of basaltic magmatism is represented by trusive volcanic rocks and diabase dikes and peper Group in the Barboursville and Culpeper three successive stratigraphic suites of multiple GSA Bulletin; February 1997; v. 109; no. 2; p. 195–209; 9 figures. 195 WEEMS AND OLSEN Figure 1. Areal distribution of the Newark Supergroup in eastern North America. Basins in which the Newark Supergroup is preserved are listed by numbers (from Lut- trell, 1989). tholeiitic lava flows. Extensive local and regional and Olsen, 1985; Traverse, 1986; Litwin et al., unstudied. Tollo and Gottfried (1992) defined mapping throughout the early Mesozoic rift ba- 1991). Although Early Jurassic diabase dikes and three volcanic intervals, each with a distinctive sins has revealed no evidence for any extrusive sills are common in the southerly and easterly rift chemistry probably derived from a separate volcanic rocks below this interval or above it. basins, any flows formerly associated with them magma source. The lowest suite of flows (vol- Thus flow units are found in the northerly and have been removed by erosion. canic interval I), which includes the correlative westerly early Mesozoic rift basins that still con- The geochemistry and petrology of the lava Mount Zion Church, Aspers (named below), Or- tain Jurassic rocks (Culpeper, Gettysburg, New- flows have been extensively studied in the ange Mountain, Talcott, and North Mountain ark, Pomperaug, Hartford, Deerfield, and Fundy), Culpeper, Gettysburg, Newark, Hartford, Deer- Basalts (Fig. 3), consists of very similar high-ti- and none are found in the southerly and easterly field, and Fundy basins (Smith et al., 1975; Puffer tanium quartz-normative (HTQ) basalts (Puffer basins where extensive palynological studies et al., 1981; Philpotts and Reichenbach, 1985; et al., 1981; Tollo and Gottfried, 1992). The sec- show that all preserved strata are Triassic in age Tollo, 1988; Dostal and Greenough, 1992; Ho- ond suite of flows (volcanic interval II), which in- (Dunay and Fisher, 1974; Cornet, 1977; Schaeffer zik, 1992; Puffer, 1992; Tollo and Gottfried, cludes the correlative Sander, Preakness, Holy- and McDonald, 1978; Olsen et al., 1982; Cornet 1992). The flows in the Pomperaug basin remain oke, and Deerfield Basalts and the slightly older 196 Geological Society of America Bulletin, February 1997 NEWARK SUPERGROUP, EASTERN NORTH AMERICA Figure 2. Currently accepted group nomenclature for the Newark Supergroup. Unnumbered portions of stratigraphic columns are not placed in any group. 1—Chatham Group, 2—Dan River Group, 3—Tuckahoe Group, 4—Chesterfield Group, 5—Culpeper Group, 6—Brunswick Group, 7—Meri- den Group, 8—Hartford Group, 9—Fundy Group. Data compiled from Luttrell (1989) except as follows: Hartford Group from Lorenz (1988) and Hu- bert et al. (1992). Jurassic stage assignments based on work by Padian (1989). Work by Litwin and Weems (1992) and Litwin and Ash (1993) take the columns of the Wadesboro, Sanford, Durham, Dan River, and Taylorsville basins well into the Norian; the top of the Richmond basin column is raised to match correlative Taylorsville basin strata. Position of the columns for the Scottsburg, Randolph, Roanoke Creek, Briery Creek, Farmville, and Scottsville basins are based partly on work by Robbins (1985) in the Farmville basin, Olsen (cited in Schaeffer and McDonald, 1978), and on extensive fieldwork by Weems. The base of the Barboursville and Culpeper columns are raised because no direct evidence exists for Carnian strata; the top of the Culpeper column is lowered on