A2: DEPOSITIONAL AND TECTONIC MODELS FOR UPPER DEVONIAN SANDSTONES IN WESTERN NEW YORK STATE
Saturday Field Trip A2
Sandstone Outcrops from Allegany, Cattaraugus and Wyoming counties.
Guidebook for the field trip held October 7th, 2006 in
conjunction with the 35th Eastern Section AAPG Meeting and 78th
NYSGA Field trips held in Buffalo, New York
Gerald J. Smith and Robert D. Jacobi,
Field trip leaders and guidebook authors
UB Rock Fracture Group
Department of Geology
University at Buffalo
Buffalo, New York
Field trip sponsored in part by NYSERDA (New York State Energy
Research and Development Authority)
October 7th, 2006
We thank STATEMAP, EDMAP, NYSERDA, and Industrial Associates for
funding the research reported herein.
INTRODUCTION
Goals and Objectives
The intention of this field trip is to visit examples of the major clastic depositional environments prevalent in the Late Devonian Appalachian foreland basin. Additionally, we will examine how syndepositional faulting influenced, and in some cases controlled, the deposition of the major petroleum reservoirs. This field trip represents a continuing evolution in our understanding of the Upper Devonian depositional controls. Our earliest sandstone field trip (Jacobi et al., 1990) proposed turbiditic and storm depositional environments in a basin setting, consistent with the views of the time that the Appalachian Basin in New York State was essentially structurally featureless (except for rare folds in the south and the Clarendon-Linden Fault), and that the shorelines had been muddy. Our next field trip (Jacobi and Smith, 1999) showed that post-depositional faulting was likely, that sandy/silty shoreface environments were possible farther east, and that syndepositional faulting affected the Rushford Formation.
In this field trip, we will visit outcrops representing the major sandstone depositional systems (turbidites, shelf-ridges, beaches, and fluvial) which correlate with the main Upper Devonian oil and gas reservoir sandstones of the Elk, Bradford and Venango groups. At each stop we will point out sedimentary structures, trace fossils and bedding relationships that assist in determining the depositional environment. We will also discuss the significance of syndepositional deformation structures that occur ubiquitously within Allegany and Cattaraugus counties ofNew York State. These deformation structures, as well as other data sets (e.g., paleoflow indicators, structure contour maps, isopach maps, and ichnofacies), indicate that the depositional systems were influenced by an interplay among fault block rotation, eustatic sea level and sediment supply.
OUTCROP EXAMPLES OBSERVED ON THE FIELDTRIP
Our field trip will examine outcrop examples of the depositional environments that represent the major clastic reservoirs in the Upper Devonian that correlate with the Elk, Bradford and Venango reservoir sands to the south. Additionally, the fieldtrip shows examples of syndepositional faulting and the faulting influence/control on depositional environments. To cover as much ground as possible in the time allotted, we have chosen outcrops near roads, although these outcrops do not necessarily represent the best outcrop possible. Several stops are located on state property, or along roadcuts, and do not require obtaining landowners permission (although entry to Letchworth State Park will require an admission during certain periods of the year). Two stops are located on private property and will require obtaining permission from the landowner prior to visiting. Most landowners we have encountered are reasonable and offer no objection, unless they regularly discover trespassers or signs of trespasser. Please respect the wishes of the landowner.

A2: DEPOSITIONAL AND TECTONIC MODELS FOR UPPER DEVONIAN SANDSTONES IN WESTERN NEW YORK STATE

STOP 1. Letchworth Upper Falls Trail
Letchworth State Park contains a remarkable exposure of the Frasnian stratigraphic section along the 400 foot high cliffs and waterfalls carved by the Genesee River. Three major waterfalls are viewable in the park, the Lower, Middle and Upper Falls. Whereas much of the cliff sections are comprised of Gardeau Fm. shales and silty shales interbedded with thin turbidite/storm sandstones, the stratigraphic section above the Upper Falls exposes outcrops of the Nunda Formation (Clarke, 1897; Figure 23). The Nunda Formation is correlative to Elk reservoir sands, and is a good example of a thick turbidite sandstone TA8 ; however dewatering structures and wave-modification provide more variability than the original Bouma model (See figure 12).
The outcrop we will examine is exposed along the trail toward the Upper Falls and the High Bridge. The path and stairs were cut through 24 m of stratigraphic section, mostly fine-grained sandstone. In addition to examples of primary bedforms and sedimentary structures typical of turbidites, soft-sediment deformation and liquefaction features including sandstone dikes, roll ups, load casts, and zones of liquefaction with sharp boundaries are quite common in both the sandstones and the interbedded shales. Small down-on-the-east stratigraphic offsets ( -6 em) along northwest-trending (317} fractures typically coincide with observable deformation zones in the outcrop.
Bedding within some of the thicker sandstones appears similar to swaley-cross stratification, which suggests storm-wave modification/influence. Storm influence within the Nunda Formation is consistent with observations made higher in the stratigraphic section where "deep" water depositional environments (black shales and turbidites) show numerous bedforms (such as hummocky cross-stratification, 3-D ripples, linguoid ripples, e.g., Smith and Jacobi, 2002) that indicate depositional depth was within storm-wave base (Myrow et al., 2002; Pattison, 2005).
The specific depositional environment of the thick sandstones of the Nunda exposed at Letchworth is ambiguous. The thick nature of the sandstone beds, the striations on the base of the sandstone beds, the massive to planar (to possibly swaley bedding) all indicate proximal turbidites (TAB to T A-c). Such turbidites were typically are thought to represent submarine channel deposits. However, the lack of coarse basal sediments, and the constant thickness of the thick beds exposed along the High Cliffs at Inspiration Point suggest that either the channels were very wide, or that these represent a non-point source, more on the order of a storm-generated wash with a shoreface source. To the east we have found an erosional channel wall, indicating a channel (or slump scar) (Jacobi et al, 1994), and to the west, we suggested relatively thick Nunda sand beds represented sand lobe at the end of a channel (Jacobi et al, 1994), so it is possible that these sands at Letchworth do represent wide channels (or storm-generated wash that funneled into channels downslope).

STOP 2. Mills-Mills - Wiscoy Creek exposure (Figures 24, 25).
Wiscoy Creek at Mill-Mills where Mills-Mills Rd. crosses Wiscoy Creek. This is the upstream end of a fairly continuous outcrop that extends down to the village of Wiscoy. Roadcuts on either side of the bridge contain weathered exposures of the Hume Fm. black shale (Pepper and deWitt, 1951). The basal contact of the Hume Fm. with the underlying Mills-Mills Fm. (Smith and Jacobi, 2000) occurs below the Mills-Mills dam. The sandstones near the contact have a distinct petroliferous odor.
The underlying Mills-Mills Fm. (Smith and Jacobi, 2000) is lowest, thick sandstone package in the Famennian stratigraphic section in Allegany County. The Mills-Mills Fm. can be separated into upper and lower sandstone packets. The lower sandstone packet is a thick (∼3 m), upward fining sequence of fine- to medium-grained sandstone interbedded with thin gray shales and siltstone. The lower sandstones have tabular cross-stratification and displays prominent climbing ripples. The lowermost sandstone is thick (20-40 cm) and fine-grained sand; the sand bed has an erosional base and is channelized in cross-section. The upper sandstone packet ranges from 1 to 2 m thick and consists of thick beds (40 to 60 cm) of medium sandstones. Flute casts are observed on the soles of sand beds. Between the two sandstone packets is an interbedded section of thin gray sandstones, siltstones and shales that change upsection from gray to black. We have interpreted the Mills-Mills Fm. as offshore to restricted circulation deposits (Figure 12), with the sandstone packets deposited as TAB to TAC turbidites with TC -starting turbidites in the upper packet. Many of the lower turbidites are consistent with proximal turbidites deposited in channels, whereas the TC - starting turbidites appear more like lobe fringe sands.
The contact between the Mills-Mills Fm. and the underlying South Wales Fm. (Pepper and deWitt, 1951) is located downstream at the waterfall near the old RG&E powerhouse. The caprock of the waterfall is the basal thick fine-grained sandstone bed of the Mills-Mills Fm. The exposure of the Mills-Mills continues upstream with the sandstone beds forming small cascades up to the dam at Mills-Mills. The interbedded shales and siltstones grade from gray to black at the top of the formation.
Farther downstream, additional outcrops of the South Wales Fm. and Dunkirk Fm. (Clarke, 1903), are exposed along the southern bank, and in the north-flowing tributaries. Correlation of marker beds, such as the basal sandstones of the Mills-Mills and South Wales formations) indicate possible uplift along the fault east of STOP 2 (Figure 26).

STOP 3. Hillcrest Rd. Roadcut (Figures 27, 28)
Thick laminated sandstone (>3 meters thick) is exposed on either side of the road, where Hillcrest Rd. begins to climb the hill. The western side of the road exhibits the sharp contact between the Rushford Fm. (Luther, 1902) and the Caneadea Fm. (Chadwick, 1933), whereas the fracture controlled exposure on the eastern side gives an excellent view of the planar laminations and small, white, cloudy quartz pebbles incorporated into the fine-grained sandstone matrix.
The exposure of the Lower Rushford Mbr. here is interpreted as three stacked shore faces. The upper shoreface (planar beds) and foreshore (planar laminations) facies of each shoreface is eroded by an overlying transgressive surface of erosion. The Lower Rushford Member is correlative to the Bradford 3rd reservoirs along the New YorkPennsylvania border (Fettke, 1939; Manspeizer 1963; Smith, 2006).

STOP 4. Lunch Stop - Caneadea Dam and Rushford Lake.
STOP 4 - Lunch Stop -Caneadea Dam and Rushford Lake.
Beyond the fence is Caneadea Dam and Rushford Lake. Old photographs of the construction of the Caneadea Dam in 1929 show the north wall of the gorge (the side we are on) devoid of trees, and show quarries of the Rushford sandstones. By the dam, and around the eastern end of Rushford Lake, is the type exposure of the Rushford Formation as defined by Luther (1902), although close, hands-on access to these outcrops can be difficult depending on the lake level. When the lake level is lowered in the Fall, along the south gorge wall of the dam can be seen a series of north-striking, east-dipping, closely-spaced step faults; each with minor offsets (on the order of a few centimeters; Jacobi and Fountain, 2002). These small faults are consistent with well-logs that indicate a down-on-the-west fault of the Clarendon-Linden Fault System (Jacobi and Fountain, 2002) just west of this location. Other indicators of the fault include: 1) the north-striking valley (topographic lineament) where well-logs indicate a fault (Jacobi and Fountain, 1993), and 2) surface stratigraphy that suggests about 15.25 meters of offset across the fault (from Hillcrest Rd. outcrop (STOP 3) to the lake-level outcrops along the eastern edge of Rushford Lake.

STOP 5. White Creek at the Little John Rd. crossing (Figures 29, 30)
White Creek contains some of the best exposures of Luther's (1902) Rushford Fm. Road cuts north of Little John Rd. display the vertical section; creek exposures show the three, stacked shoreface sequences as well as exhibiting syn- and post-depositional deformation.
North of the bridge is a large exposure of the three-shoreface sequences that comprise the Lower Rushford Mbr. of the Rushford Formation. Basically similar to the Lower Rushford Mbr outcrops we examined near Rushford Lake, the outcrop here is much thicker (∼8.5 m). The variation of thickness of the Lower Rushford Mbr. coincides with faults of the Clarendon-Linden Fault System (Figure 31 ). The thicker regions possess preserved transgressive lags on offshore sequences, whereas the thinner regions possess eroded upper-shoreface and foreshore zones.
At the northernmost exposure of the outcrop, the 1st shoreface sequence forms the lowest step in the small falls of the outcrop. The top bed is a fossiliferous, medium to coarse sandstone that typifies the transgressive lags that occur on top of the shoreface sequences in the lower sandstone packet. Overlying the 1st shoreface is a thick interbedded section that is well exposure on the east cliff exposure. Soft-sediment deformation, primarily ball-and-pillow structures are well exhibited in the sandstone beds beneath the 2nd shoreface sequence. The 2nd shoreface sequence displays planer laminated beds typical of the shoreface sequence, but also includes a sediment slide (debrite) with a large sandstone olistolith surrounded by a muddy debris flow with deformed sand clasts. The top of the 2nd shoreface sequence occurs near the main falls/cascade. The sandstone displays small dunes (amplitude- ∼0.5 m, wavelength ∼2.0 m) that are a classic example of symmetrical ripples with tuning forks. The 3rd sandstone sequence forms the upper part of the cascade. The most noticeable feature is the transgressive lag that caps the sequence and the falls. This lag deposit contains large clasts of white, cloudy quartz as well as numerous brachiopod shell fragments and large red silt clasts. The underlying sandstone contains Rhizocorallium, Arenicolites and Thalassinoides, typical of a Glossifungites firmground. Overlying the 3rd shoreface sequence is the thick interbedded sequence that separates the lower sandstone packet from the upper sandstone packet.
We propose that the stress associated with the Acadian Orogeny caused a reactivation of basement faults, including those of the Clarendon-Linden Fault System and the Iapetan opening faults. Motion on these faults resulted in a number of small fault blocks that affected the basin topography. The motion and rate of slip and rotation among the faults was not identical, with the result that minor topographic highs and lows within the basin were created by small fault block motion that would create variable accommodation space over the faulted area (Figure 32).
We first proposed fault control of Upper Devonian sandstones to explain the occurrence - and preservation of shoreface sandstones in the Lower Rushford Member (Smith and Jacobi, 1998, 2000, 2001, 2003 and 2005; Jacobi and Smith, 2004). Syndepositional fault activity would enable coarser sediments to accumulate along active fault blocks at and adjacent to the intersection of the north-south trending Clarendon-Linden Fault System, and the northeast trending shoreline would act as a groin (Figure 33).
Upstream from the waterfalls located north of the bridge, deformation in the shales, silty shales and siltstones are readily observed; both deformed sandstones (ball and pillow) and pencil cleavages occur. At 0.25 mi (0.4 km) south of Little John Bridge, a repetition of the section appears to outcrop in White Creek. The upper part of the 2nd shoreface sequence and all of the 3rd shoreface sequence outcrops again at a small waterfall/cascade. Unlike the outcrop to the north of the bridge at Little John Rd., this outcrop does not have the thick transgressive lag deposits. However, a thin coquinite is observed at the top of the 3rd shoreface sequence and on top of the 2nd shoreface sequence, large cloudy quartz pebbles can be observed. The offset between the outcrop by the bridge and the repeated(?) section is approximately 11.6 m (∼38 ft), down on the west (or north).

STOP 6. Farnsworth Road - road cut (Figures 34, 35).
The roadcuts along the northern side of Farnsworth Road are exposures of the Hinsdale Fm. (Chadwick, 1933), (possibly a correlative to the "Pink Rock", an old drillers name), one of the stratigraphically higher Bradford reservoir sandstones. The Hinsdale Formation is comprised of thick sandstone beds that can be roughly separated into three packets. The thick sandstone lenses are typically fine-grained sandstone with thick lenses of coquinite that typically form basal lags, but also occur as small internal lenses (Figure 35). Thickness variability within the sandstones is high, further compounded by variable erosion of lower units by overlying sandstones.
Sedimentary structures are typically SCS with less frequent occurrences of TCS and tabular cross-beds. Small amplitude (and wavelength) symmetrical and interference ripples are commonly observed on the inner surface of large troughs and swales, implying complex, combined-flow during time of deposition (Figure 17). Thinner sandstones within the interbedded sections contain both asymmetric and 3-dimensional ripples and HCS; several thin sandstones also contain grooves and striations on the sole of the beds. Both the sandstones of the interbedded sections and the thick sandstone packets contain an abundant, but still low-diversity Skolithos ichnofacies. High frequency of Arenicolites and Skolithos occur in both the thinner sandstones as well as in the thick sandstone packets. A poorly developed Cruziana ichnofacies consisting of sporadic occurrences of Planolites and Teichichnus is found in the thicker interbedded sections.
We interpret the Hinsdale Formation as being deposited well above storm wave base, but still below fair weather wave base, most likely upper offshore to lower shoreface. The dominance of SCS and typical tempestite packets imply the Hinsdale Formation was deposited primarily by storms; the large amounts of fossils and the singular occurrence of red shales and sandstones suggest the shoreline was moving westward and terrestrial sediments were now being incorporated into the marine sedimentary deposits. The interpreted depositional environment is likely to be either nearshore storm-generated sand ridges or a storm-influenced barrier bars (Miall, 2000)
The roadcut displays the sharp-based sandstones that have lenses of coquinite throughout, but generally a thicker lag deposit at the base. Bedding in the sandstone is distinctly swaley, with large erosional surfaces cutting down into underlying units. At the lower roadcut, above the prominent, thick sandstone is a red to purplish red shale which aids the identification of the formation. The depositional environment for the Hinsdale and many of the similar thick sandstones between the Lower Rushford Member (STOPS 3, 4 and 5) and the Hinsdale Fm. are probably storm shelf ridges to storm-dominated barrier bars. The lateral variability observed at this location and many similar outcrops may explain the "lensing" nature of the Upper Devonian reservoir sands.

STOP 7. Little Rock City (Figures 36, 37).
Little Rock City is a State Forest under the supervision of the NYS Department of Environmental Conservation. The Salamanca Conglomerate (Carll, 1880) marks the basal contact of the Conewango Group with the underlying Conneaut Group. Sands and coarser units of the Conewango Group are correlative to the Venango reservoir sands in Pennsylvania. At this site exposures of thick orthoconglomerate (between 2 and 12 m thick) occur along the northern and eastern sides of the hill. House-size blocks separated along joints by periglacial expansion are abundant throughout the area; at least one was redeposited upside-down on top of another block by glacial activity.
Lithologically the Salamanca is an oligomictic quartz orthoconglomerate. The conglomerate consists of a medium to coarse sand matrix with clasts of cloudy white quartz. The clasts are oblate discoids that range from 0.5 centimeters up to 6+ centimeters in diameter. The oblate discoid shapes of the pebbles are typical of a wave-dominated shoreface. Large downlapping, graded cross-sets (1 to 4 meters high) and channels occur throughout the lower section of the outcrop. These bedforms may represent alluvial gravel bars. The form of the large cross sets is also similar to that found in estuarine tidal sand bars, but the thickness of the sets is high for the low (about 2 m) tidal fluctuations thought to characterize the Acadian Catskill Sea (e.g., Woodrow and Isley, 1983). However, the coarseness of the conglomerate indicates a high energy system, consistent with a tidal prism or bore in an estuary (and also consistent with the tidal gravels in the English Channel) that could have had a higher tidal range than the assumed 2 m Catskill Sea tidal range. Thus, these large crossbeds could be fluvial bars or tidal. Tabular crosssets and crossbeds with a herringbone pattern are observed above the large cross sets (although some of the herringbone is a "pseudo-herringbone" that results from trough cross sets in opposite directions). Both herring bone patterns, however, are consistent with reversing currents of tidal flux, as in a tidal channel. Overall, the large scale crossbeds, trough cross-sets, and the herringbone pattern suggest an estuarine/estuarine mouth depositional environment (Dalrymple, 1992) with a strong tidal influence. Paleoflow indicators from sedimentary structures are few, ripples and troughs on the upper surface occur sporadically.
We recognized several distinct facies within the Salamanca Conglomerate: facies A is the caprock of the Salamanca Conglomerate with the largest quartz clasts (5 cm). The conglomerate is generally disorganized with clasts orientated obliquely and perpendicular to bedding, except for the top surface; large carbonized wood fragments also occur. Facies B is a less resistant, more friable unit that exhibits herringbone bedding marking current reversals. Facies C is comprised of two thick, graded foreset packets each ranging 1 to 4 meters thick with large clasts accumulating along bedding planes with some asymmetric ripples. Facies D is a less resistant, more friable unit that contains fewer clasts, but generally does not exhibit reversals in bedding (Figure 47).
We have observed similar arrangement of facies at conglomerate blocks loose in Allegany State Park and adjacent areas, and at the "Bear Caves" area outcrops at Mount Seneca in Allegany State Park. The outcrops and loose blocks examined south of Little Rock City were generally sandier than the Little Rock City conglomerates, with clasts occurring only along bedding planes, and the clasts typically are not as large (maximum clast- 2 cm) as the clasts measured at Little Rock City.