Abstract Regional facies for the Upper Ordovician Series (global classification) of eastern North America consist of clean (pure) carbonates, mixed carbonates and terrigenous clastics, shale, terrigenous clastics coarser than shale, and terrigenous clastics prograding over carbonates. The last facies is characteristic of the Upper Ordovician. Maps and cross sections for stages of the Upper Ordovician demonstrate the influence of regional tectonic events on the sedimentation pattern of these facies.

Abstract Middle and Upper Ordovician sediments in northwest Georgia and northeast Alabama can be separated into three facies complexes. The northwestern complex is dominated by shallow water and peritidal carbonates, the central complex by red, peritidal clastics, and the southeastern complex by basinal black shales.

Abstract Exploration for fractured reservoirs in the non-porous biomicrite of the Trenton Limestone has taken place since 1910. Increased drilling since 1981 has doubled production from this structurally complex area of the Eastern Overthrust.

Abstract Early Paleozoic foredeep evolution in the central Appalachian orogen can be described in terms of five stages: (1) Stable Shelf, (2) Initial Uplift of Shelf, (3) Shelf Exposure, (4) Collapse of Peripheral Bulge, and (5) Basin Fill. In addition, strike-parallel variations in central Appalachian foredeep stratigraphy reflect collision along the irregular, early Paleozoic North American continental margin.

Abstract The carbonate facies of the Middle and Upper Ordovician of Central Pennsylvania show repetitive sequences of micrite, bioclastic limestone and siliciclastic shale. Five repetitive patterns based on sedimentologic and paleontologic data are present. These sequences are a result of storm deposition, as indicated by shell and intraclastic lags, fining upward trends, abrupt contacts between the beds, and the multidirectional sole marks. The series of sequences is a result of the decreasing effects of these storms on the deepening carbonate platform-ramp during the Middle and Late Ordovician.

Abstract Although the Trenton Group of New York State has been studied for more than 150 years, no comprehensive description of its facies patterns has ever been produced. Such a description is presented here. The facies patterns of the Trenton Group reveal that this unit’s deposition was indirectly controlled by the Taconic orogeny then going on in nearby New England.

Abstract The Denley Limestone (Trenton Group) in the Mohawk Valley, New York, is composed of bioclastic turbidites associated with slump fold horizons and syndepositional block faults which indicate that the limestones of the Denley Formation are foreland basin/trench slope deposits.

Abstract The Taconic Foreland Basin formed during the collision between the North American craton and the Ammonoosuc Arc, approaching from the east. Oxygen-depleted conditions in the basin were probably caused by density stratification in the water column due to a locally humid climate, in combination with stagnant conditions in the world ocean. A long-term cyclicity of alternating 500,000 to 1,000,000 year long “anaerobic phases” and “dysaerobic phases” appears to be the result of a combination of variations in the sedimentation rate, climatic conditions, and changes in the world ocean.

Abstract Exploration and development of the Late Ordovician Trenton Limestone has occurred in New York State since the late 1800s. From the early days of exploration to the present, the Trenton has proven to be an elusive target for developers. However, with renewed interest and current activity, coupled with improved drilling and completion techniques, the Trenton Limestone in New York may yet prove to be an important reservoir.

Abstract Numerous high-angle faults that were active during deposition are recognizable within the autochthonous, Upper Ordovician, Trenton Group ramp sequence in southern Quebec/The facies of the Trenton Group in southern Quebec can be compared to those in New York and can be shown to be controlled by proximity to, or position within, the Taconic foreland basin.

Abstract The Trenton Limestone of northwestern Ohio consists of three primary facies: open shelf, platform margin, and platform. The platform margin and platform facies appear to be equivalent to the Point Pleasant Formation. Secondary dolomitization of the Trenton Limestone has resulted in a number of zones and types of dolomite within the unit. A combination of dolomitization models involving shale dewatering and fluid migration along fracture trends are presented to explain the dolomite occurrence. A thorough understanding of Trenton lithologies, depositional and tectonic settings, and diagenesis should aid future exploration efforts within this once prolific producer of northwestern Ohio.

Abstract Six potential trapping plays in northwestern Ohio are recognized in the Trenton Limestone reservoir of the Lima-Indiana Field and surrounding areas. The six plays are: 1) simple anticlinal traps, 2) faulted anticlines, 3) updip facies change, 4) dolomitization along fracture trends, 5) porosity-permeability traps and 6) small anticlinal noses. Limited production records suggest that fracture-enhanced plays are the most productive of oil and gas.

Abstract The Trenton Limestone in Northwestern Ohio has been targeted for hydrocarbon exploration and evaluation because it offers the possibility of good economic returns with low costs, good leasehold availability, and an opportunity to test modern reservoir stimulation technology. Results of exploration efforts have shown that (1) geological high-grading of well site selection was needed, (2) there is a need for stimulation treatments designed to enhance production, (3) there is a marginal return on investment with current economics, and (4) gas pipeline construction should be delayed until larger reserves are found or until a more favorable gas marketing climate develops.

Abstract Prouty (1976) proposed a wrenching model to account for the linear infrastructures of the Michigan basin. This was based first on lineament (fault) patterns and outcrop fracture analyses (“ground truth”). The azimuths of linear producing fields fit closely the shear model. To test the model, analyses (X-ray diffraction) of numerous well samples from several producing fields show a coincidence of the occurrence of epigenetically formed dolomite (porous reservoir rock) channelways along with structural features such as vertical shear faults (shear couples), shear folds, and offshoots from the fault channelways of the wrenching model. This porous dolomite is the reservoir rock of the producing fields. The shear model offers an important additional dimension in field development as well as exploration for new structures.

Abstract There are four generalized zones of dissolution in the Trenton-Black River formations in central southern Michigan, which are interpreted as caves formed during karstification. These caves are recognized as lost circulation zones during drilling. The Trenton-Black River caves are compared and contrasted with the Mammoth Cave System of Kentucky.

Abstract Reservoirs in the Upper Ordovician Trenton Limestone and the Black River Group in Indiana, Michigan, and Ohio form a major oil province, important since 1884. This province (America’s first giant oilfield) has yielded more than 600 MMBO. This includes the giant Albion-Scipio Trend (120 MMBO), discovered in 1956. Although production from the Trenton and Black River carbonates is high, little has been known about the nature and distribution of their reservoirs. Recent research indicates that they do not contain any depositional (primary) porosity. Reservoirs exist only where dolomitization or fracturing or a combination has occurred. Trenton and Black River dolomitization does not conform to facies-related models, but must be related either to fluid movement along fractures associated with tectonic features or to burial dolomitization. A comparison of fields with dolomitization along linear fault (or fracture) zones and those showing regional burial dolomitization indicates the relative importance of faults and fractures. Oil recovery from fault/fracture-dolomite reservoirs is 2500 to 12, 000 bbl/acre, and that from burial-dolomite reservoirs is only 540 to 1000 bbl/acre.

Abstract The Trenton Limestone consists of skeletal sand and organic buildup facies that were deposited on a carbonate ramp under shallow-water open-marine conditions. Petroleum reservoirs occur in the Trenton only where hydrocarbon entrapment in both structural and stratigraphic traps preserved porosity in a regional dolostone.

Abstract The Granville pay zone produces oil and gas from pelecypod/ gastropod rudstone and grainstone carbonate sediment-piles that accumulated as shoal and beach deposits on a shallow-water carbonate platform in Late Ordovician (Edenian) time. Fresh-water vadose diagenesis produced secondary porosity into which hydrocarbons migrated. There is a predictable trend to these Granville pay zone reservoirs, and other similar reservoirs can be predicted using modern sedimentological techniques.