The Stratigraphy of the Stony Brook University Campus

Jessica Nienstedt and Gilbert Hanson

Department of Geosciences, SUNY Stony Brook, Stony Brook, NY

Stony Brook University is located in central Suffolk County on the north shore of Long Island (Figure 1), and overlies some 900 feet of Pleistocene and Cretaceous unconsolidated sediments, which overlie early Paleozoic and Precambrian bedrock. Well logs available at the New York State Department of Conservation for water wells and borings for engineering purposes as well as logs from Suffolk County Water Authority were used to evaluate the underlying strata. Ten boreholes penetrate the Magothy Formation as well as the Pleistocene sediments; in addition five shallow boreholes and a cliff face exposed during construction give a more detailed description of the Pleistocene sediments. Lithologic logs for each of the boreholes and an exposed cliff face on campus are in the appendix.

Fig. 1 Map of Long Island.

Fig. 2. North-south cross section from Long Island Sound to the Atlantic Ocean showing the underlying strata. Modified from Jenson and Soren (1974).

            Jenson and Soren (1974) mapped the hydrological units beneath Suffolk County, Long Island based on well logs from municipal water well borings. Smolensky, Buxton and Shernoff (1989) remapped the hydrologic units. Fig. 2 is a north-south cross-section from Long Island Sound to the Atlantic Ocean that goes through Stony Brook University modified from Jensen and Soren (1974). According to Jensen and Soren (1974) and Smolensky, Buxton and Shernoff (1989), the basement is early Paleozoic and Precambrian bedrock which is overlain by the Lloyd Sand and Raritan Clay Members of the Raritan Formation, these are overlain by  Magothy Formation and the Pleistocene sediments. The type of sediment found in each geologic unit and their thickness are shown in Table 1. The Cretaceous sediments and the top of the basement dip about 1^o to the south (Jensen and Soren, 1974).

Krulikas and Koszalka (1983) describe a lacustrine clay known informally as the Smithtown clay, found within the Pleistocene sediments. The clay is mainly found between the Ronkonkoma and Harbor Hill Moraines in north-central Suffolk County. They suggested that the lake resulted from the damming of water by the Ronkonkoma Moraine upon the retreat of the glacier that formed the Ronkonkoma Moraine. The clay was then buried by sediments associated with the next glacial advance that created the Harbor Hill Moraine.

Most of the Stony Brook University campus is on the Harbor Hill Moraine. The Stony Brook portion of the Harbor Hill Moraine was formed by glacial tectonics. Tzakas and others (2002) describe how pushing of unconsolidated sediments in front of the glacier formed the moraine. Tingue and others (2004) have use ground penetrating radar to show that underlying sediments in the Ashley Schiff Preserve have features typical of a fold and thrust terrane.

While no bore holes penetrate the bedrock on campus, it is most likely that the basement is part of the Avalon Terrane exposed in eastern Connecticut and thought to underlie Long Island Sound immediately to the north (Pacholik and Hanson, 2001). The Avalon Terrane consists of 600 to 700 Ma old dominantly leucocratic gneisses and 300 Ma granitic intrusions. In many places the top of the basement rocks consists of a regolith of residual clay. The Magothy Formation, which is part of the Matawan Group, is separated from the Raritan Formation by an unconformity. Near the base of the Magothy Formation is a coarse basal zone which is overlain by a fining upward sequence consisting mainly of fine sands and clay, typical of a delta environment (Smolensky, Buxton and Shernoff, 1989). The Magothy Formation is overlain by Pleistocene sediments. During the Pleistocene, continental glacial advance and retreat occurred many times. It is not clear how many times this area was glaciated. Glacier scour and melt water valleys have created an irregular surface between the glacial sediments and the Magothy Formation.

Ten deep wells (hundreds of feet) and five shallow wells (less than 100 feet) were chosen for analysis based on quality of the logs and their location. A stratigraphic column was also constructed based on a section on campus that was exposed during construction of a recharge basin (see Appendix).  Figure 3 locates the wells, with letters A through J for the deep wells, ESS gives the location of a shallow borehole near the Earth and Space Sciences Building, S shows the location of a shallow borehole on South Campus and Cliff marks the location of the sedimentary section exposed during construction of a recharge basin. Suffolk County Water Authority (SCWA) well A is the northern most well which is on Mud Road, followed by wells at the Student Union (B), Arts and Science Center (C), Old Chemistry (D), Daniel Webster Drive SCWA Well 1 (E), Daniel Webster Drive SCWA Well 2 (F), Javits Lecture Hall (G), Heavy Engineering (H), Henry Clay Drive SCWA (I) and the southern most well, Oxhead Road SCWA (J). The driller’s information is presented in Table 2; this includes well location, contractor, date, drill type, depth, elevation and reason for drilling. The shallow borehole information is provided in Table 3 and the stratigraphic columns are found in the appendix)

                NS – Not Specified

Results

For each deep borehole, the driller provided the depth of the well relative to land surface, however, the surface elevation was not always provided. Elevation for these wells was determined based on located the site on a topographic map and interpolating the elevation. The depth to the water table relative to the land surface was provided in all logs, except the one at Henry Clay Drive. The depth of the well and elevation of water table are provided in Table 4. In some logs the driller or geologist noted the upper surface of Magothy Formation. When this information was not provided, or its placement was not consistent with the description of the sediments, the upper surface of the Magothy Formation was determined by comparing the sediment descriptions in the logs to descriptions in the literature. Generally the Pleistocene sediments are tan, whereas the Cretaceous sediments are a variety of brighter or more distinct colors, such as red, black, white, gray etc.

Based on the stratigraphic columns of the deeper borehole, the depth of specific units relative to mean sea level were determined and displayed in Table 5. The logs of the Student Union Building (B) and Daniel Webster Road 1 (E) include a gravelly unit that the loggers call the “basal unit”; Table 5 gives the elevation of the “basal unit” described by the drillers of logs B and E, but in the Table 5 it is identified as gravelly which was also identified in boreholes A, C, D, F, I, and J. The surface of the gravelly units in boreholes B and E differs by 85 ft. The position of the gravelly unit within the other boreholes does not show a trend, suggesting that this describes channel fill in multiple channels and not a well-defined stratigraphic unit.

Lignite was identified in the Magothy Formation in boreholes B, C, D, F and J. The elevation of these units, displayed in Table 5, range from –155 to –377 ft relative to mean sea level. In addition to the elevation of the lignite layers, the thickness of each layer is provided in Table 5. In borehole B, Student Union building, the lignite is found in two units. The deeper unit is 12 ft thick with lignite located in fine to medium gray sand, with pieces of clay. The 8 ft thick unit directly above consists of sandy gray clay, pyrite and lignite. To summarize, the sediments found with the lignite are gray, fine to coarse sands and clays, and occasionally pyrite probably representing overbank deposits formed in a swampy environment. Lignite is deposited in an environment that is humid and wet, allowing the preservation of organic material.