Modern lithostratigraphic units
Origin and Type Section: The Selby Formation, originally defined by Marshall Kay (1937) for exposures along Selby Creek, Lennox and Addington County, Ontario, represents the oldest portion of the Rocklandian Stage. The fauna of the lower Rockland was first recognized as a distinct unit in the Ottawa region and assigned a name of "Leray beds, " based on lithologic similarities to a unit in the Black River Group of New York (sensu Wilson, 1921). Having worked extensively on this unit, Marshall Kay (1937) felt the "Leray beds" of Ontario were younger than those of the original Leray Limestone located at Watertown, New York. Because of its distinctive fossil composition, he designated this unit as being separate from the underlying Black River Group and grouped the Selby with the overlying Napanee into his Rockland Formation. Since this assessment was made, the term Rockland was designated as a time-rock term and the Selby Limestone was inturn promoted to formation status.
Description: Physically defined, the Selby Limestone includes the set of limestones "succeeding the Black River group and underlying the Napanee member of the Rockland formation in southeastern Ontario and northwester New York" (Kay, 1937; p. 252). The key characteristic of this stratigraphic unit is the presence of the brachiopod Doleroides ottawanus Wilson.
Lithologically, the Selby consists typically of "dark-gray to black, medium- to fine-textured, petroliferous limestone in thin beds, weathering buff, and having a jointed splintery fracture" (Kay, 1937; p. 252). In outcrop the Selby contrasts with the overlying Napanee in the lack of grey to black shaly interbeds. Moreover, the Selby in most outcrops is a condensed, nodular limestone with an abundance of cephalopod forms including Maclurites logani, so as to almost represent a "cephalapodakaulken" like facies.
Members or marker intervals: The Selby itself is a very thin unit and contains a rather homogeneous lithology. However the upper contact of the Selby, where exposed beneath the Napanee Formation, has a characteristic rusty mineralized contact. In the Mohawk Valley region, where the Selby is mostly absent, one locality (that at Ingham's Mills, on East Canada Creek) has a thin Selby with distinctive black mineralized vertical burrow infillings. Although the exact mineralogy of the infillings is currently unknown, they do appear to be related to condensation and sediment starvation.
An additional key marker lies at the base of the Selby Formation. In the power diversion channel for the Black River Hydroelectric Plant at Glenn Park, New York (near Watertown, NY) a prominent yellow-tan weathering clay seam is well exposed below the typical nodular thin bedded Selby. This K-bentonite, along with at least 3 others below can be raced northwest into Ontario where they are well exposed at Napanee, and Marmora. Moreover, these K-bentonites are traceable toward the southeast into the West Canada Creek Valley, where they are variously exposed in several stream and quarry sections in the vicinity of Middleville. The basal Selby K-bentonite was the focus of several papers by Marshall Kay, and although there is some controversy surrounding the name of this and subjacent K-bentonites, Marshall Kay did refer to this K-bentonite at Middleville as the Hounsfield Metabentonite (Kay, 1935).
Occurrence in Trenton gorge: The lowermost Trenton facies, the Selby Limestone, is not exposed in the type section of the Trenton Group. However, nearby sections in the southern Black River Valley and in a few sections within the Middleville (lower West Canada Creek Valley) area do demonstrate a very condensed, thin bedded limestone similar in character to the Selby.
Origin and Type Section: The Napanee Formation was originally proposed by Marshall Kay (1937) to include the rock overlying the Black River Group in Southeastern Ontario, near the town of Napanee, Ontario. This unit formed the upper portion of the Rockland Limestone (sensu Raymond, 1914; Rockland, Russel County, Ontario). Today Napanee Formation is relegated to its use as a rock-term, while Rockland has been relegated by Kay (1968) to a time-rock term. In this sense the earliest portion of Trenton deposition occurred during the Roclandian Stage.
Description: Prior to its designation as a Napanee, the Rockland Limestones were "described as consisiting of 40 feet of heavy-bedded limestones, separated from the "Lowville" limestone by 18 feet of "Leray beds of the Black River." (Kay, 1937; p. 251; Wilson, 1921). Through his analysis, Kay felt that the 18 feet of "Leray beds" sensu Wilson, 1921) were actually younger than the Leray of the type section (near Watertown, New York) of these beds. Given this difficulty and the application of his term Leray, he chose to rename the "Leray beds" of Ontario, the Napanee Limestones. He chose, at the time to include the Napanee as the upper member of the Rockland Formation (Kay, 1937), however as the Rockland is used as a time-rock term, Napanee has sufficient lithologic distinction to now be considered a formation on its own.
Lithologically, the Napanee Formation has a rather distinctive lithology, which when seen in outcrop juxtaposed against the massive carbonates of the Black River Group tends to stand out. This unit tends to show rather rhythmic interbeds of fine grained calcilutites, calcisiltites and interbedded shales. Depending on the location, the caps of calcilutite beds and the shales can be quite fossiliferous with brachiopods, crinoids, trilobites, and various mollusc types. In weathered sections this unit tends to weather buff tan but in fresh surfaces, the medium to fine textured carbonates tend to be dark gray-blue in color.
Despite its rather distinctive lithologic appearance, the Napanee was first defined on the basis of its faunal composition. Originally, Kay (1937) designated this unit (the upper member of the Rockland) on the presence of the brachiopod Triplecia cuspidata (Hall). These Triplecia bearing strata were superadjacent to the Selby Limestone and subjacent to the Hull (or Kings Falls Limestones). In addition, the Napanee tends to be heavily dominated by the small orthid brachiopod Paucicrura (Dalmanella) rogata (Sardeson).
Members or marker intervals: In most areas of northwestern New York and Ontario, Canada, the Napanee Formation tends to be rather homogenous in its lithic character. However, despite its seemingly regular appearance, the Napanee does have a 0.5 to 1 meter thick middle unit that tends to be slightly more fossiliferous and can even develop into packstone to grainstone facies. This middle unit, can be used to divide the Napanee into a lower and upper unit (Cameron, 1968). In regard to other stratigraphic marker beds, the sharp basal contact of the Napanee with the underlying Selby tends to be its most striking feature. The dramatic shift from a dark gray massive burrow mottled wackestone and micritic packestones to alternating calcilutites, calcisiltites, and shales occurs at a very sharp phosphatic suface which can be traced some distance from Ontario into New York State. In the West Canada Creek to Mohawk Valley's the underlying Selby pinches out below this contact and as such, this contact has been variously interpreted as a subaerial erosion surface (Cameron and Mangion, 1977) or as a maximum flooding surface (Cornell, 2001).
Occurrence in Trenton gorge: Although the Napanee is present in several stream cuts in tributaries of West Canada Creek and downstream from Trenton gorge at Newport, New York, it does not outcrop in the Trenton Falls Gorge. In the schematic south-to-north cross-section shown above, the position of the Napanee is shown in white and is projected based on succession of overlying units. This unit varies in thickness and in some places pinches out beneath the overlying Kings Falls Formation. Further east at Ingham's Mills, on East Canada Creek, the Napanee unit is well developed and several meters thick. Unfortunately, it is not observed in the Trenton gorge sections as they do not cut low enough in the section. As such, the discussion in this context is limited to its basic description.
Origin and Type Section: By 1931, Marshall Kay had begun to publish some of the first reports on the occurrence of altered volcanic ashes from Middle Ordovician limestones. In his first paper on the “Stratigraphy of the Ordovician Hounsfield Metabentonite,” Kay outlined the stratigraphic occurrence of a prominent, unctuous clay within the upper Black River group from northwestern New York State. In his studies, he began to correlate the occurrence of this particular layer into the Mohawk Valley where a similar layer was visible immediately above the Black River limestones and below a series of excellently developed grainstone beds. After discovering a series of other K-bentonite beds, Marshall Kay realized that the correlations were not as simple as he had originally documented and by 1933 he began to publish the results of some of his investigations into the nature of the basal Trenton Limestones in the Northern New York region. For over 30 years, Kay extended the stratigraphic nomenclature of studies of the Trenton equivalent rocks from Quebec (the Hull Limestone) and from southwestern Ontario (the Kirkfield Limestone).
In 1968, Kay introduced the term Kings Falls Formation, for the Hull and Kirkfield equivalent rocks found in the New York region. He had chosen to use Kirkfield as a time-rock term (i.e. Kirkfieldian Stage) and in order to establish a rock-term to use for these strata, he selected the best exposure of the basal Trenton in the northern New York region. For the type section of these near basal, limestones, Kay chose Kings Falls on the Deer River, a tributary to the Black River. The Kings Falls locality exposes both the basal contact with the underlying Napanee limestone, as well as the overlying Sugar River beds.
Description: The Kings Falls limestone is composed of several shallowing-upward cycles of thick ledges of calcarenite or crinoidal grainstones and brachiopod coquinas. Interbedded with these very coarse-grained lithologies are a series of thin dark gray to black shales. Most often the grainstone beds show excellently preserved hummocky cross-stratification, and large-scale pararipples on the top surfaces of many beds. In the type section the Kings Falls Formation reaches its maximum thickness of nearly 100’, but in regions to the north and south, this interval is usually between 50 and 70 feet, except in the eastern Mohawk Valley region, where the Kings Falls thins considerably across the Canajoharie Arch.
The Kings Falls Formation lends itself to easy identification for the faunal composition of this unit is unmistakable. These limestone beds are often full of a variety of echinoderm plates and a wide variety of trilobite types, not recorded in lower formations. The time-equivalent Kirkfield Limestone of southwestern Ontario, displays some of the greatest disparity in echinoderms from any one locality up to that time. However, on the basis of his original description, Kay had indicated that the very basal portion of the Kings Falls contained Triplecia cuspidata and the presence of this brachiopod made the basal Kings Falls Rocklandian in age.
Members or marker intervals: Although, Kay (1968) did not define the exact base of the Kings Falls limestone, he did indicate that its contact was placed at the base of the “first dominant caclarenite” which occurs slightly below the last set of finer-grained Napanee-like calcisiltites. In practice, however, the main contact of the basal Kings Falls shows evidence of truncation, especially in the West Canada Creek Valley (in the area around Middleville), lies slightly above the “first dominant calcarenite.” The upper surface of the Kings Falls is much more discernable as it is marked by the dramatic shift from the coarse-grained, cross-stratified beds into finer grained shaly, interbedded, wackestones and calcisilites of the Sugar River. The contact was drawn near the top of the falls at the type section on Deer River which was located about one foot below the base of a distinctive contorted interval.
Within the context of key marker horizons, the upper surface of the Kings Falls tends to have a very sharp mineralized surface that in many cases is developed into an excellent hardground surface. In northern New York and southern Ontario Canada, the upper surface of the Kings Falls tends to show a wide variety of sedimentologic and faunal components that make it a very unique surface. In fact in several localities in the Lake Simcoe region, the same surface tends to be well colonized by edrioasteroid echinoderms and shows evidence for many types of echinoderm and bryozoan holdfasts as well as a variety of Trypanites borings (Brett and Brookfield, 1984). This same hardground is also unique in that it is smothered by an altered volcanic ash bed, which in Ontario is called the MR K-bentonite (Liberty, 1969). Additional K-bentonite horizons in the Kings Falls are known from the Black River Valley and western Mohawk. In the West Canada Creek Valley, two K-bentonites are known, one from near the base of the formation at Middleville, and the other from near the top of the formation. These K-bentonites are poorly constrained in the regions to north of Trenton Falls, but there are several K-bentonites developed in the Kings Falls in this region.
In addition to its upper hardground bed, the Kings Falls Limestone demonstrates a series of two to three basal polymictic conglomerate beds. The occurrence of these beds is generally limited to the central Mohawk River Valley, where the Kings Falls Formation as exposed at Inghams Mills on East Canada Creek, shows Grenville aged gneiss clasts admixed with the several lithologies of limestone and basal Kings Falls grainstones.
Occurrence in Trenton gorge: Although not present within the main chasm of Trenton Falls gorge, the Kings Falls formation has been reported to outcrop in the banks of West Canada Creek at the village of Trenton Falls. In this position the several feet of coarse-grained limestones that cap the Village Falls (Morgan’s Mill Falls) probably represent the upper few beds of the Kings Falls and are most likely equivalent to the beds that cap the Kings Falls at Deer River. Unfortunately the outcrop exposures today are poor and mostly covered by a smaller dam constructed for the diversion of water for the barge canal.
Origin and Type Section: The Sugar River Limestone, again a relatively recent contribution of Kay (1968), was first established as a rock-term to replace the term Shoreham Limestone, which Kay had elevated to sub-stage status (i.e. Shorehamian substage of the Shermanian Stage). Similar to the Kings Falls, the Sugar River was described from a locality in Lewis County, New York although near the southern limits of the county and in the upper Black River Valley near its drainage divide with West Canada Creek Valley.
Description: In the Black River Valley region and in the nearby West Canada Creek Valley, the upper Kings Falls transitions rapidly into thinly interbedded shales, and fine-grainstones, with thin nodular wackestones and calcisilt stringers common. This lithology is more similar to the Napanee Formation subjacent to the underlying Kings Falls, than it is to the distinctively coarse-grained Kings Falls Formation.
Although the Sugar River is dominantly interbedded shales and fine grainstones, it becomes distinctively more nodular and finer-grained towards the middle of the unit. In the type section at Sugar River, southern Lewis County, the formation is approximately 40’ thick. Near the top of the succession, the Sugar River transitions to a more medium-bedded, calcilutite facies and generally shows fewer fossiliferous horizons. This upper unit has been recognized as a separate unit and named the Rathbun Member of the Sugar River Formation. To the southeast into West Canada Creek and Mohawk Valley regions, the Rathbun Member is traceable into a coarser-grained, crinoidal packstone lithology with minor grainstone stringers, as is exposed south of Middleville, New York. This upper member shows evidence of thinning, and shallowing into the Middleville region and then transitions into the shale dominated facies of the lower Flat Creek Shales in the regions east of Little Falls.
In addition to its distinctive lithology, the Sugar River carries a very distinctive fauna that enables it’s easy field recognition wherever it is exposed. The Shorehamian Stage, of which the Sugar River is the major unit, is demarcated by the first occurrence of two major faunal elements in the New York sections. First, the lace-collared trilobite Cryptolithus tesselatus (Green) is present in large numbers at several horizons but most predominantly in the medial Sugar River. Second, the first occurrence of the gumdrop-shaped bryozoan, Prasopora is within the lower portion of the Sugar River. Both of these faunal elements are abundant and often compose very dense accumulations on some bedding planes.
Like the underlying Kings Falls Formation, the Sugar River demonstrates some lateral thickness variation. In the West Canada Creek Valley, the Sugar River has been measured at approximately 30 feet while in northern New York it maintains nearly this same thickness. However, in the southern Black River Valley region, the Sugar River Formation reaches it maximum thickness near the type section at Sugar River where it is measured at nearly 52’. (Chenoweth, 1952).
Members and key marker intervals: The Sugar River Formation demonstrates several important marker intervals and key contact surfaces that are useful in correlation. The first, and perhaps one of the most distinctive intervals, are the basal disturbed beds of the Sugar River. At the Kings Falls type section on the Deer River, the contact between the Kings Falls Formation and the Sugar River Formation is drawn approximately 1 foot below an interval of contorted strata. These contorted strata show evidence of channeling, disc and saucer structures as well as shale diapers, all of which indicate possible synsedimentary deformation of these sediments on the seafloor. Similar structures are observed in the same stratigraphic position at Whitaker Falls in Martinsburg, New York and again along the Sugar River near Boonville. This series of deformed beds represents the lowest occurrence of such features in the Trenton of New York.
In addition to the basal deformed zone, the top of the Sugar River Formation is denoted by the distinctive interval at the base of the overlying Denley Formation. This extremely condensed bed, named the “Trocholites Zone,” marks the sharp change out of the nodular packstones, and fine grainstones of the Rathbun member into the overlying calcilutites of the Poland Member of the Denley.
Occurrence in Trenton gorge: Within Trenton gorge the lowest rocks exposed, from just below the powerhouse to approximately 15 feet below the rim of Sherman Fall, are now assigned to the upper Sugar River Formation. The exposure here transitions from the upper part of the middle Sugar River into the overlying Rathbun member. In the type section of the Rathbun member at Rathbun Brook in the West Canada Creek Valley, this uppermost Sugar River member is approximately 9’ thick, and although it thins considerably into the Mohawk Valley, it is about this same thickness at Trenton Falls. Subjacent to this upper member, lower in the section, near the powerhouse, the middle Sugar River Formation is excellently exposed. This particular interval shows excellently preserved Cryptolithus trilobites and numerous Prasopora colonies. Approximately 15’ of this interval is exposed.
Origin and Type Section: Although it has been recognized as a very distinctive stratigraphic interval since the first geologic investigations of Trenton Falls, the interval from near the cap of Sherman Fall upward to the base of the coarse-grained carbonate at the top of the gorge was not fully subdifferentiated until the studies of Kay (1943, 1968). Initially, Kay applied the term Denmark Formation to this fossiliferous interval of dominantly fine-grained carbonates and interbedded shales, for exposures of the unit in the central Black River Valley in the town of Denmark. In 1968, Kay relegated the term Denmark for more biostratigraphic purposes and applied the term Denley Formation to denote rock terms.
Description: The Denley Formation has been redefined in the recent publication by Brett & Baird (2002), using two distinctive marker horizons as the lower and upper contacts of the formation. These two marker horizons include the basal “Trocholites beds”, termed the City Brook Bed by Baird and others (1992), and the High Falls K-bentonite. Thus delineated, the Denley Formation now encompasses only a portion of the original Denmark Formation, with the uppermost unit elevated to formation status. As defined, the Denley Formation now contains two members: the lower or Poland member and the upper or Russia member. Collectively grouped the Denley is generally considered to be composed dominantly of nodular fine-grained limestones. Each member of the Denley and their internal marker divisions are discussed in stratigraphic order (oldest first) in the following section.
Poland Member
The Poland Member is defined as the interval between the basal City Brook Bed and the lowermost Kuyahoora K-bentonite. Given this delineation, the Poland is approximately 30’ thick.
City Brook Bed Sub-member
The City Brook Bed, previously referred to as the “Camp Member” by Chenoweth (1952) is the relatively condensed, nodular calcilutite interval containing abundant Trocholites. This interval measures feet in Trenton Falls although it is slightly thicker toward the north and slightly thinner toward the southeast of Trenton. The base of this unit is marked by a sharp discontinuity surface with the underlying coarser-grained lithologies of the Rathbun. Its upper limit is marked by the transition tomore tabular-bedded barren calcilutites which are interbedded with buff weathering shales and thin coquinal grainstone beds.
Upper (Glendale) Sub-Member
The interval immediately above the City Brook Bed, grades into somewhat coarser planar-bedded calcisiltites and calcilutites with buff weathering shale stringers. This particular interval is approximately 35 feet thick in the southern Black River Valley and apparently thins to about 25’ at Trenton Falls. This unit is moderately fossiliferous with species of trilobites especially common. The planar middle to upper Poland interval grades upward into coarser-grained, rippled calcarenites that often contain intraclastic conglomerates showing significant evidence for early cementation and development of storm clasts. This interval is relatively resistant to weathering, and makes up the ledge forming the cap of Sherman Fall.
Key Markers and Contacts: Poland Member: As previously mentioned the Poland Member is a very distinctive interval for correlation. This unit, because of its distinctive basal nodular calcilutitic City Brook Bed, and the planar-bedded calcilutites, shales and calcarenites of the overlying Glendale sub-member is generally very easily identified in outcrop. In addition, the top of the Glendale sub-member is relatively distinctive because of the presence of several intraclastic conglomerates within the wavy-bedded calcarenite interval. Adding to its distinctive lithologic character, this unit has excellently preserved Isotelus and Flexicalymene trilobite beds in some layers. In addition to these highly favored faunal elements, the Poland member contains typical Trenton faunas such as the brachiopods Reserella, Sowerbyella, and Rafinesquina in very large numbers. Moreover, the presence of the graptolite Corynoides americanus helps with biostratigraphic analysis.
Additional maker horizons are denoted by several distinctive K-bentonites, in addition to the lower Kuyahoora K-bentonite located at the top of the member. The additional K-bentonite horizons are present as recessive notches in the face of Sherman Falls. The lower Sherman Fall K-bentonite is located about 14 feet above the base of the Glendale Submember and has been chemically fingerprinted and correlated into equivalent units to the east of Trenton Falls. The upper Sherman Fall K-bentonite, although not yet fingerprinted (?), is located about 9’ above the former and as such these twin K-bentonites can be used for correlation. These two Sherman Fall K-bentonites were called the M8 and M11 K-bentonites by Cisne and Rabe (1978) and Cisne et al. (1982).
Russia Member
The upper member of the Denley Formation was originally named by Kay in (1943) for the upper calcilutite-dominated facies above the Poland and below the coarse-grained carbonates of the overlying Cobourg (now called Rust Formation). This particular member of the Denley is very distinct in that it shows several well-developed cycles, which show very distinctive shallowing upward motifs. Because these cycles are very well developed and easily recognized each have been named as informal subunits of the Russia. Moreover, as the lower series of cycles show slight facies differences between the lower, middle, and uppermost beds (showing a larger-scale shallowing upward pattern), three sub-members have been designated for the Russia. The lower Submember has been named the Lower High Falls Submember, the middle Submember the Cincinnati Creek Submember, and the upper has been termed the Upper High Falls Submember.
- Lower High Falls Submember: “Overhanging Ledge Bed” Cycle
The basal shallowing-upward cycle of the Russia is perhaps one of the most easily recognized of the 5 Russia cycles. This particular interval is denoted at its base by the rather distinctive contact with the subjacent Poland member with the Lower Kuyahoora K-bentonite demarcating the contact between the two units. Moreover, the base of this unit shows a sharp lithologic change from the rippled calcarenites and intraclastic limestones of the underlying Poland into rather homogeneous shaly-nodular fine-grained calcilutite limestones. Within the basal few feet of the lower cycle, a very weak cycle can sometimes be identified between the Lower and Upper Kuyahoora K-bentonites with a somewhat condensed skeletal packstone at the summit. Regardless, this cycle transitions back into shaly nodular fine-grained limestone that persists upward to a compact coarse-grained crinoidal packstone bed that composes the lip of Lower High Falls. Its total thickness is then just over 25’.
- Cincinnati Creek Submember: Castle Road Bed Cycle
The second well-developed cycle is represented by a substantially thinner cycle, which is approximately 13.5’, and within the Cincinnati Creek Submember. Yet because of its distinctive basal and capping beds, it is easily recognized. The unnamed cycle has nearly 1’ of dark gray to black fissile shale which is overlain by thin concretionary calcisiltites which grade upward through interbedded shales, and calcisiltites into a series of compact, condensed crinoidal wackestones and packstones that mark the cap of the cycle and are referred to as the Castle Road Beds from exposures on nearby City Brook. Interrupting this succession is a minor persistent packestone to grainstone bed that is yet “unnamed,” and is present in the middle part of this cycle. However, the Castle Road cycle cap is perhaps the most coarse-grained of the Russia and can be correlated some distance to the southeast of Trenton Falls. Moreover, an additional unnamed K-bentonite has been described from immediately below the base of the capping bed. This K-bentonite has been found in several outcrops to the southeast of Trenton Falls.
- North Gage Road Bed Cycle
Overlying the Castle Road Cycle, another slightly thicker cycle measuring approximately 16’ thick is developed in dark gray shales interbedded with subnodular to subtabular calcisiltites. The succession is then capped by a very distinctive, very widespread, wavy-bedded Prasopora packstone or biorudite demarcating the top of the Cincinnati Creek Submember. This bed and a subjacent 3’ thick bioturbated fine-grained grainstone bed make a distinctive couplet of beds that are easily recognized and traced widely in the West Canada Creek exposures.
- Upper High Falls Submember: Taylor Fork Cycle
The uppermost Submember of the Russia is demarcated by a very distinctive change in lithofacies from the underlying Cincinnati Creek Submember. The Taylor Fork Cycle is approximately 12 feet thick with the basal 6’ composed of very tabular and even-bedded calcilutites that grade upward into more standard nodular wackestones and packstones showing well-developed bioturbation. The cap of this cycle is rather distinctive in that the uppermost beds show evidence of soft-sediment deformation. This unit is sometimes mistakenly referred to as the “Lower Disturbed Zone” which occurs in the base of the overlying Rust Formation. This bed is immediately overlain by a condensed, quartz-rich, crinoidal grainstone that truncates portions of the underlying disturbed interval. The top surface of this bed shows substantial mineralization and chertifiation, with evidence for phosphatization, and dissolution of brachiopod skeletal carbonate. Sitting on this surface is the Upper High Falls K-bentonite, which demarcates the contact between the Russia Member of the Denley Formation and the superjacent Rust Formation.
Key markers and contacts: Russia Member: Due in part to its rather distinctive cyclically bedded nature, the Russia Member is a rather distinct stratigraphic interval within the middle of the Trenton Group. The diversity of cycle caps with unique event beds, faunal epiboles and distinctive lithogic changes in key intervals provide excellent markers for recognition and correlation of the Russia Member into other areas. The series of marker horizons, although previously noted in the discussion of each of the sub-members, include the metamorphosed volcanic ash layers. These K-bentonites, the twin Kuyahoora K-bentonites at the base and the Upper High Falls K-bentonite at the summit, represent geologically instantaneous event deposits that help the stratigrapher to establish chronostratigraphic correlations betweens regions. Likewise, the upper disturbed zone just below the Taylor Fork Bed represents a similar type of event horizon that helps establish a fairly distinctive time marker.
Other key marker horizons, although not precisely time-constrained, can provide assistance with chronostratigraphic assessments. These markers include the small-scale cycles themselves, as well as the larger-scale sequence stratigraphic marker horizons, including sequence boundaries and their correlative non-conformities, as well as maximum flooding surfaces and other internal sequence surfaces. Within the Russia, it appears that the base of the unit represents a rather distinctive maximum flooding surface out of the Poland below, with the top of the succession representing components of the upper highstand systems tract including the forced regression surfaces and sequence boundary.
In addition to the unique event stratigraphic markers discussed above, the Russia displays several faunal signatures that are constrained to characteristic stratigraphic horizons. As discussed, the couplet beds of the upper North Gage Road cycle are unique in their distinctive bioturbated, fine-grained grainstone and Prasopora biorudits. These two beds are utterly unique and easily recognized over wide-regions within this interval. The development of this interval is likely due to unique environmental conditions that existed for a very short time during the deposition of the upper Russia.
Occurrence in Trenton gorge: Within Trenton Gorge, the Denley Formation is very well exposed and despite past arguments to this point, it is exposed in its entirety from base to summit. This interval can easily be viewed from the upper few feet of the capping beds of Sherman Fall, in the gorge walls on either side of West Canada Creek, in the streambed immediately above Sherman Fall through the base of Upper High Falls. Through this distance the total thickness of the Denley Formation is nearly 100’ thick. With some difficulty the Russia Member can be viewed in the vicinity of lower High Falls, but this interval is more easily accessed in the nearby exposures along City Brook.
Origin and Type Section: As originally conceived, Kay in 1943 introduced the term Rust for the lower member of his Cobourg Formation having correlated the interval from Ontario into central New York State. Recognizing two divisions within the Cobourg in West Canada Creek Valley, he named the lower unit Rust, after exposures of the well-known quarries on the William Rust Farm just east of Trenton Falls. Again, because of chronostratigraphic connotations of the term Cobourg (as in Cobourgian), this interval near the top of the Trenton was lacking unifying lithostratigraphic nomenclature. In the more recent studies of Brett and Baird (2002), the Rust member of Kay, was promoted to formation status, in part because of its rather distinctive facies, but also to promote the continuity of lithostratigraphic nomenclature.
Description: As now described, the Rust Formation, in contrast to the finer-grained Russia below, is generally considered to be composed of nodular to wavy-bedded coarse-grained packstones to grainstones and can be divided into three lithologic divisions. These divisions although very similar in overall composition, again can be distinguished as shallowing-upward packages with similar motifs to the underlying Russia. However because of its distinctive internal stratigraphic intervals, as well as its coarser lithology, the Rust is very easily recognized in the West Canada Creek Valley. Further to the east, however, correlations show that this interval becomes substantially modified to the east and transitions into a condensed turbidite-shale succession and then finally into basinal black shale facies of the Valley Brook Member of the Flat Creek Formation.
In addition to lithologic characteristics, the Rust Formation represents one of the best-known stratigraphic intervals in the Trenton Group. In part, this is because of the well-known collection of trilobites, echinoderms, and other fossil specimens collected from this interval, by William Rust and Charles Doolittle Walcott. The small quarry they worked in, known as the Walcott-Rust Quarry, was located near the Rust Farm. In fact it is these fossil specimens that are now housed in the Museum of Comparative Zoology at Harvard, and are a primary focus of this website.
More specifically, with respect to biostratigraphic zonation, the base of the Rust Formation is now clearly established as containing the boundary between the Corynoides americanus and Orthograptus ruedemanni graptolite zones.
As mentioned above, the Rust can be divided into three members, which include the Mill Dam Member, the Spillway Member, and the uppermost Prospect Quarry Member. Each member and their internal marker divisions are discussed in stratigraphic order in the following section.
Mill Dam Member
The basal member of the Rust is represented by the 36’ thick interval above the Upper High Falls K-bentonite. The basal 1 to 2’ of the Mill Dam Member, although similar in lithology to the underlying Russia is composed of tabular lutites and shales which are sharply overlain by much coarser, and more resistant fossiliferous packstone beds that are exposed in the face of Upper High Falls and again in the interval immediately above the High Falls through the top of Mill Dam Fall.
Key markers and contacts: Mill Dam Member: Just above the basal lutite package, and within the base of the massive packstone beds is an important marker horizon, referred to informally by previous workers including Kay (1953), as the “Lower Disturbed Zone.” This particular interval and one in the overlying Spillway Member have been studied since the turn of the century (see Miller, 1917; Hahn 1913). This distinctive, strongly deformed and contorted interval occurs 6 feet above the base of the Mill Dam Member. The remainder of the Mill Dam Member is composed of a rather massive succession of wavy-bedded packstones interrupted by a thin interval of more tabular fine-grained wackestones. This slightly finer interval represents the base of yet another small-scale shallowing-upward cycle within the Trenton. At Trenton Falls, this same interval contains a thin recessive weathering notch that potentially represents another K-bentonite. The bench of limestone above Mill Dam Fall demarcates the cap of the Mill Dam Member, and is represented by a fairly compact interval of grainstones. The cap of these grainstone beds is very sharp with a change into much shalier and fine-grained lithologies of the overlying Rust Quarry Beds.
Spillway Member
The middle or Spillway Member of the Rust Formation is excellently exposed from the base of the Hydro-dam Spillway upward to the floor of the spillway located on the east side of the gorge just upstream from the railroad bridge crossing West Canada Creek. In its entirety, the Spillway Member is roughly the same thickness as the underlying Mill Dam Member, but shows a greater degree of facies heterogeneity from base to summit. The lower portion of limestone composing the base of the Spillway Waterfall is identified as the calcilutite facies of the Rust Quarry. The upper portion, in turn returns to a more distinctive brachiopod-rich, wavy-bedded packstone interval that extends from midway up the face to the floor of the waterfall.
Rust Quarry Submember
Of all Trenton intervals, the paleontology of the Rust Quarry Beds is perhaps the most well known. The rather fine-grained calcilutite and shales of this interval have yielded some of the most-diverse, well-preserved fossil trilobites and echinoderms known from the Trenton. Several publications have been dedicated to the study of this particular interval. Among them is the 1934 paper by Delo, as well as the more recent paper of Brett and others (1999). Sedimentologically, this unit fines upward through a repetitious series of fine-grained normal to reverse-graded peloidal calcilutites, calcisiltites and fine-grained calcarenites. Excellent exposures of this immediate interval are provided in the exposures upstream of Trenton Falls, near Prospect under the Military Road Bridge and in the Rust-Walcott Quarry just east of the gorge.
Upper Spillway Submember
The upper beds of the Spillway Member are very distinctive in their sedimentary character, as this interval of approximately 15’(?) shows an upward coarsening package out of the lutites of the Rust Quarry interval. The upward coarsening continues upward to the floor of the Spillway where the upper 3’ of coarse brachiopod packstone to grainstone beds are heavily deformed and slumped into broad channel-shaped features that have a nearly east to west, long-axis orientation. This same interval has been referred to as the “Upper Disturbed Zone” by Kay (1953) and other previous authors including Sherman, (1826); White (1896), Hahn, (1913), Miller, (1915, 1917
Key Markers and Contacts: Spillway Member: As mentioned above, the Spillway Member succession is excellently constrained above and below by the sharp flooding style contacts with the Mill Dam Member below and the shaly, interbedded calcisiltites of the overlying Prospect Quarry Member. These two contact surfaces are easily recognized by the change from very coarse-grained pack- to grainstone beds into shaly calcilutite to calcisiltite facies. Moreover in the case of the upper contact of the Spillway Member, the development of the “Upper Disturbed Zone” makes this contact even more conspicuous at many localities in the West Canada Creek Valley. The additional occurrence of a uniquely condensed phosphatic lag bed developed immediately on top of the “Upper Disturbed Zone” helps to establish correlations into sections in the southern West Canada and eastern Mohawk Valleys, where the coarse-grained carbonates of Trenton Falls grade into substantially thinner and finer-grained, condensed shaly nodular facies before developing and rethickening into siliciclastic dominated shale successions of the Flat Creek.
In addition to lithologic markers, the unique taphonomic signature of the lower Rust Quarry interval also makes a unique marker that is distinct in the base of the Spillway Member. This interval, which is just under a meter-thick, displays uniquely preserved trilobites of at least 18 species as well as other taxa. Based on the preservation of these specimens and their orientations both at the bases and tops of graded fine-grained calcilutites suggest that these trilobites were transported alive and buried in rapidly deposited distal storm and turbidite horizons. The absence of substantial numbers of bioturbators in this interval helped to preserve these specimens, so much so that some of the trilobites still have appendages preserved. (Brett et al. 1999)
Prospect Quarry Member
As the uppermost member of the Rust, the Prospect Quarry member at Trenton Falls is easily delineated both lithologically and with respect to key marker horizons. Like the underlying Spillway Member, the Prospect Quarry Member is defined as another shallowing-upward succession that is capped by the overlying Steuben Formation. The lower portion of this shallowing-upward succession that is designated the Prospect Quarry Member, is approximately 15’ thick. This succession, named for exposures in the Prospect Quarry on the west bank of WestCanada Creek just south of the village of Prospect, is substantially coarser overall than the subjacent Spillway Member, yet is distinguished from the overlying Steuben Formation in that it still contains a good proportion of finer-grained limestones and interbedded shales.
Lithologically, the Prospect Quarry Member commences immediately above the phosphatic capping bed of the underlying Spillway Member with a very thin (1-2’?) of shales and tabular calcisiltites that grade upward into thin to medium bedded coquinal packstones and grainstones. Near the top of the succession, the beds become less shaly and show evidence of increased amalgamation.
Key Markers and Contacts: Prospect Quarry Member: The Prospect Quarry Member, again is usually very easy to recognize at Trenton Falls by its basal and capping contacts. The presence of the “Upper Disturbed Zone” and superjacent phosphatic capping bed of the Spillway Member below are sharply overlain by much finer-grained calcisiltites and shales. This represents yet another flooding style contact that are so important in the delineation of Trenton lithologic sub-units. The upper contact with the overlying Steuben Formation is also easy to chose, as the base of the Steuben, although apparently an upward-extension of the same shallowing-upward succession, is demarcated by the rapid transition into very coarse-grained, massive bedded, crinoid and brachiopod coquinal grainstones.
Occurrence in Trenton gorge: Within Trenton Gorge, the Rust Formation is excellently exposed in the region from the top of Upper High Falls, just below the base of Mill Dam Fall through the walls of the hydro dam spillway. In this interval the thickness of the Rust is nearly the same as the underlying Denley Formation, which is approximately (100?) thick. Nearly the same interval is exposed again upstream from the hydro dam in the vicinity of Prospect, where due to dip changes, the middle Rust succession is again brought to the surface although at a greater topographic elevation.
Origin and Type Section: In the same paper previously discussed, Kay (1943) established the name Steuben for the upper portion of the Cobourg Formation. The distinctive very coarse-grained lithologies of the Steuben have been recognized since the very first geological surveys of New York, and recognizing their faunal similarity to the Cobourg Limestones in Ontario, Kay established them as upper Trenton. The Steuben Formation takes its name from the exposures on Steuben Creek, just west of Barneveld, New York (just west of Trenton Falls).
Description: As described, the Steuben Formation is the uppermost unit of the Trenton Group. The Steuben Formation is represented by massively bedded, very coarse-grained skeletal grainstones that commonly show evidence for cross-bedding and sediment reworking. In the Trenton Falls region the Steuben is represented by two main coarse-grained intervals interrupted by a thin interval of shaly, wavy-bedded wackestones and packstones. Thus delineated, the Steuben is separated into two main units separated by the middle shaly interval. Due to its association with the underlying Prospect Quarry Member of the Rust Formation, the Lower Member of the Steuben appears as the upper half of a shallowing or coarsening-upward succession. The Upper Member, referred to here as the Remsen Falls Member displays a similar upward-coarsening pattern from the base of the middle shaly interval. In total, the Steuben Formation at Trenton Falls is approximately 30’ thick, although it is difficult to assess given that the top of the gorge is composed of Steuben and the uppermost contact is not observed. However to the north near Remsen on Cincinnati Creek, the total thickness of the entire Steuben is measured at nearly double the former with approximately 70’ of section.
Lower Member
As mentioned, the Lower Member of the Steuben represents the upward-shallowing component of the Prospect Quarry Member. As such, the Lower Member is defined as the succession of coarse-grained grainstones present above the Prospect Quarry beds through the base of the middle shaly wackestones and packstones at the base of the Upper Member. Within this interval, the Lower Steuben Member is essentially a homogeneous cross-bedded coarse crinoidal grainstone.
Key Markers and Contacts: Lower Member: Previously discussed, the basal contact of the Lower Member of the Steuben is generally thought to be conformable with the underlying Rust at Trenton Falls. The disappearance of shaly interbbeds and the increased amalgamation of massive grainstones is the lithologic signature that records the basal Steuben. Although the lower Member is essentially a homogeneous succession of grainstones, the upper few feet of the member show increased rusty mineral staining with some minor evidence of hardground development. This interval appears to represent the transition to a more sediment starved condition, just prior to the deposition of the middle shaly interval.
Upper “Remsen Falls” Member
From the base of the middle shaly, wacke- to packstone interval, the remainder of the Steuben Formation grades upward in one fairly continuous shallowing or coarsening upward succession. This upper member, although very similar in motif to the subjacent shallowing-upward succession (Prospect Quarry to Lower Steuben), is relatively thin and nearly equal in thickness to the Lower Steuben by itself. At about 35’ the Upper Steuben as exposed at Remsen Falls (a few miles north of Trenton), is composed of approximately 18 feet of basal thin to medium bedded shaly bioclastic limestones which grade upward into nearly an equivalent thickness of coarse-grained massively bedded crinoidal limestone similar to the Lower Member.
Key Markers and Contacts: Upper Member: Given the very easily recognized lithologic texture of the Steuben and its members, this interval is readily discerned. As mentioned above, the sharp transition from the massive coarse grainstone facies of the Lower Member into the shalier middle Steuben is a distinctively condensed surface that represents a substantial flooding horizon. Similarly, the upper contact of the Steuben Formation is represented by an even more substantial flooding surface that marks the end of carbonate deposition in the Trenton Falls area. This contact superimposes the dark siliciclastic shales and siltstones of the Frankfort Formation over the top of the carbonate dominated Trenton Group. Aside from containing abundant pelmatozoan and other skeletal fragments, The Steuben does not have many internal marker horizons such as K-bentonites or other event horizons that are useful for correlation. That said, however, it is now believed that within the base of the Upper Steuben Remsen Falls Member, is the biostratigraphic boundary between the Orthograptus ruedemani and Climacograptus spiniferus graptolite zones.
Occurrence in Trenton gorge: Within Trenton Gorge, the uppermost Trenton Group has long been recognized as a very coarse-grained skeletal grainstone and represented by the uppermost cliff exposures along West Canada Creek. Due to the construction of the hydrodam spillway on the eastside of the creek and access roads to the pump houses on the west side of the gorge, relatively good exposures of the Lower Steuben are easily accessed. Unfortunately due to weathering and removal of overlying strata, the Upper Member of the Steuben is not exposed in the Trenton Falls chasm. Instead, nearby exposures along Cincinnati Creek at Remsen provide opportunities to observe both the upper contact of the Lower Steuben as well as the succession toward the top of the formation.
