Unatego Area Landowners Association

Otego - Unadilla - Butternuts Area Residents



              The Marcellus Formation - A Gas Bearing Shale

The Marcellus shale runs from the southern tier of New York, through the western portion of Pennsylvania into the eastern half of Ohio and through West Virginia. In Pennsylvania, the formation extends from the Appalachian plateau into the western valley and ridge. This area has produced natural gas for years, but the Marcellus shale, a deep layer of rock, is officially identified as holding a relatively small amount of proven or potential reserves. However, many gas production companies are now interested in the Marcellus.


The natural fractures in the Marcellus shale are the key to recovering large amounts of gas. As heavily organic sediments were laid down 365 million years ago, the black shale of the Marcellus formed. As the organic material decayed and degraded, methane and other components of natural gas formed and dispersed through the pores in the rock. About 300 million years ago, the pressure of the gas caused fractures to form in the shale. It was not until 280 million years ago that the eastern portion of Pennsylvania was pushed into the folding of the ridge and valley province that makes up that area. Gas that occurs in pockets underground is considered a conventional reservoir; gas that is distributed throughout the rock, like the Marcellus, is called an unconventional reservoir.


For further information on the geology of the Marcellus Shale, follow this link:



                                       Utica Shale

 According to the USGS, The Utica Shale is part of Trenton Group 100-300 ft. (30-90 m).  The Utica Shale is divided in the Mohawk Valley into upper and lower parts by a tongue of the Dolgeville Formation and these parts are here assigned member names.

 The lower portion of the Utica is named the Flat Creek Member and the upper, the Indian Castle Member. These lithostratigraphic units replace earlier names such as the Canajoharie Shale, which are primarily biostratigraphic. Revised stratigraphic correlations based on reinterpretation of graptolites and K-bentonites in the area suggest that the lower part of the Utica Shale is the lateral equivalent of a large part of the lower Trenton Group and is older than the Denley Limestone, with which it has been previously equated.

 The Flat Creek Member overlies the early to middle Kirkfieldian Kings Falls Limestone of the Trenton Group at Canajoharie Creek and interfingers with the Sugar River Limestone of the Trenton Group to the west. The Trenton-Utica succession is a transgressive sequence. Westward, the Dolgeville grades into the lower Denley and the Utica (equivalent to only the upper Utica of the east) disconformably overlies the Denley and Steuben Limestones of the Trenton Group.

 The Utica underlies the Frankfort Formation throughout the study area. Age of the Utica between Chuctanunda Creek and Caroga Creek, ranges from Kirkfieldian (Mohawkian) to Edenian (Cincinnatian). Formation youngs westward and at Trenton Falls the entire unit is shown as Maysvillian (Cincinnatian).



  One of the oldest and most widespread black shales is the Ordovician-age Utica Shale. The Utica Shale lies conformably above the Trenton Limestone/Dolgeville Formation in New York (Table 2.1). It was deposited very broadly across the Appalachian Basin and into Ontario, and covers thousands of square miles.  In New York the Utica is found in outcrop along the west and south-southeast sides of the Adirondack Mountains,  and is well exposed in several locals along the northern margin of the Allegany Plateau (Figure 2.3). It is deeply buried over most of the state of New York, and from outcrop it dips to depths over 9,000 feet in the southern portion of the state (Wallace, 1988).

  The Utica is a massive, fossiliferous, organic-rich, thermally-mature black to gray-black shale, and is considered to be the source rock for Lower Devonian through Cambrian production and shows. The Utica was deposited in a deep marine basin with a subsiding trough that generally trended north-south. It interfingers with the basal Dolgeville formation, which is composed of alternating beds of limestone and shale. Source rock for the organic-rich black shale was supplied from the eroding highlands to the east.

  Slowly the deep marine trough was filled in, and deposition of the upper Utica spread westward. The westward migration was periodic which is reflected in the presence of at least five facies intervals, which are bounded by unconformities or condensed beds (Lehmann, 1995). Each unit represents a pulse of subsidence and subsequent sedimentation in the basin, and all have several similarities. Each interval onlaps argillaceous limestone, and has shifted westward with respect to the underlying unit. The base of each unit is defined as a disconformity and/or stratigraphically condensed interval, and each appears to record a localized deepening event. The overlying black shale unit is thinner than the previous unit.

  The thickest section of the Utica is found along the Mohawk Valley and was deposited in the subsiding trough where it is well over 2,000 feet thick. It thins to the north and west to less than 100 feet along the Lake Erie shoreline where it becomes somewhat silty. Over much of New York State, the Utica is less than 300 feet thick (Figure 2.4) (Zerrahn, 1978). The Utica is overlain by coarser clastics of the Lorraine Shale, which consists of shale, siltsone and fine-grained sandstones, which were deposited as the marine environment prograded westward and deltaic deposits pushed across New York from the east. Oil and gas shows have been reported in the black shale of the Utica and in its Dolgeville member, including a recent report of 1 MMscf/day (Trevail, 2003).



                                              The Utica Shale Play of Eastern New York

John P. Martin1, Richard E. Nyahay2, James Leone2, and Langhorne B. Smith2
1New York State Energy Research and Development Authority, Albany, NY
2Reservoir Characterization Group, New York State Museum, Albany, NY

Exploratory drilling is underway to begin producing the Utica Shale of eastern New York State. When developed, this field will represent the easternmost natural gas field in the United States. The prospective fairway includes a 17 county region bounded to the by the Hudson River, the Finger Lakes, the Mohawk Valley and the Pennsylvania border.

The Utica is a massive, fossiliferous, organic-rich, thermally-mature black to gray-black shale deposited in a subsiding trough that generally trended north-south. The Dolgeville, interpreted as a slope facies peripheral to the Trenton platform, interfingers with the basal Flat Creek black shale member. Source rock for the organic-rich black shale was supplied from the eroding Taconic highlands to the east. As the deep marine trough was filled in, the deposition of the lower members of the group onlapped westward over the carbonate platform. The basal Flat Creek member thickens considerably in the eastern half of New York and uppermost Indian Castle member spreads widely across the Appalachian Basin.

The exploration fairway has been defined though an analysis of cuttings and cores defining unit properties, Rock-Eval parameters S2, Tmax , HI (Hydrogen Index), and TR (Transformation Ratio). Current drilling activity to date has concentrated on the shallower northern areas but technical evidence supports much deeper drilling depths. Hydraulic fracture designs include the use of acid to take advantage of the high calcite component. Since this play is within the eastern gas market, producers can expect a price premium for their gas.

Presented AAPG Eastern Section Meeting, Pittsburgh, Pennsylvania 2008 © AAPG Eastern Section




Figure 1. Map showing the thickness of the Utica Shale in New York State and northern Pennsylvania.


Shale schematic - Utica and Lorraine


Utica compared to Barnett shale