B3: FAULT SYSTEMS OF THE TACONIC FORELAND; WHITEHALL, NY TO WEST HAVEN, VERMONT [ALL KINDS OF FAULTS!]
William S.F. Kidd
Chul Lim
formerly of Geological Sciences
University at Albany,
Albany, NY 12222
wkidd@albany.edu
Stephen S. Howe,
Atmos. & Environmental Sciences
University at Albany
INTRODUCTION AND SUMMARY
Map-influencing faults of all displacement kinds are observed in the anomalously narrow Taconic orogenic foreland belt in the region where it crosses the New York - Vermont border between Whitehall, NY and West Haven, VT. Outcrop and map evidence for the relative age and displacement of these faults can be seen on this trip. In general, transported Cambro-Ordovician rocks of the continental shelf/platform and of the off-shelf strata in the Taconic Allochthon are affected by thrust faults of a range of ages relative to development of folding and cleavage in particular rock packages. The thrusts all predate large-scale strike-parallel east-side-down normal faulting, in most places in the area to be visited apparently localized, in a large displacement (1000m or more), on one such fault, the Mettawee River Fault. The youngest of the fault sets consist of cross-strike, strike-slip faults, mostly ENE- to NE-trending, some of which have mappable apparent left-lateral displacement, cutting thrusts and the normal fault. Movement on the strike-slip fault system at West Haven was accompanied in this area by fluids shown by our measurements of fluid inclusion homogenization to have been at temperatures sufficiently high to be most likely of Ordovician (Taconic) age. These oblique faults probably had a prior history as components of a trench forebulge normal fault system; they may have influenced at that time and perhaps also earlier the sedimentation on the Laurentian continental shelf, and therefore they may have been localized by an old inherited fracture/fault system in the underlying Grenville basement of this area. More generally, forebulge normal fault scarp topography, whose development mostly predated thrust arrival at any position, are perhaps also responsible for the repeated detachment and stacking of thin slices of the medial Ordovician limestones of the uppermost carbonate shelf which are extensively developed in the area of this field trip. The lower contacts of these slices show evidence of thrust fault transport, and do not support a model of large-scale olistostromal origin. Because the trip is confined to the area affected by thrusts, we will not see unmodified forebulge-type normal faults in autochthonous basement and platform strata, but they occur just to the west along southernmost Lake Champlain. And there are other kinds of fault affecting geological maps of the area which may be mentioned during the trip.

B3: FAULT SYSTEMS OF THE TACONIC FORELAND; WHITEHALL, NY TO WEST HAVEN, VERMONT [ALL KINDS OF FAULTS!]

STOP 1A. Mettawee River Fault at the Type Locality
[NO HAMMERS OR SAMPLING PLEASE - NY DEC REGULATIONS]
The carbonates here along the west bank of the river are mapped by Fisher (1985) as early Ordovician Providence Island Formation, and dip about 10-20 degrees east; they are the upper part of a thrust transported section above the Comstock (= Pinnacle) Thrust. The lowest part of the section here consists of dolostones; the upper 4 meters contains limestone beds; we think it is possible that the part of the section containing limestones is either basal Chazy or Black River. These show some bedding surfaces with well developed ripples, and small mudcracks, and selectively dolomitized burrows. Local meter-scale folding of periclinal geometry affects these beds near this end of the section. Across the river at this point, you can see the dark mid-Ordovician non-calcareous shales which are there partly disrupted with phacoidal melangetype fabric. In the low cliff, a gently east-dipping planar vein of fibrous quartz cuts the deformed shales; the vein has top to west, thrust sense of shear. Walk north along the west bank of the Mettawee River on the mostly dolostone outcrop. About 170 meters north [43.473241; -73.368196], dark highly deformed mid- Ordovician shales extend from the east bank across the river to an almost complete section at the small rapids. Depending on the streamflow, it may or may not not be possible to examine the shale closely. The contact of the deformed shale with the dolostone beds at the west side of the stream is not quite fully exposed (even at the lowest water we have seen, there is a gap of 10 cm or so), but is clearly sharp, and parallel with bedding in the dolostones. This is somewhat surprising, for a contact which maps out a short distance to the north as a sharp fault that unquestionably truncates this and other lower units of the carbonate shelf stratigraphy, as well as the major thrust fault which duplicates this sequence (see the map of Fisher, 1985). Also surprising, for a fault that must have substantial normal sense displacement, is the fact that most or all quartz fiber slickensides in the shale here give thrust sense of displacement. We could infer either that the normal fault mapped to the north passes east of this outcrop within the shale belt, or west within the transported shelf carbonate section (of course badly exposed in that particular place), or that the motion is confined to a surprisingly narrow zone along the contact; the full exposure at Stop 6B suggests the latter possibility is more likely than one might be inclined to think based on this outcrop at Stop 11 alone.

STOP 1B. Deformed Flysch and Melange
Deformed Flysch and Melange Below Contact With Transported Chazyan Shelf Carbonates, in the Banks of the Mettawee River
Walk back to the south end of the carbonate outcrop on the west bank of the river [43.471240, - 73.368354]. If the water is high or it is raining, Stop 1B will be omitted. If conditions permit, scramble along the west bank to the south, and through the scrub along the west side of the old mill race cut at the waterfall, then walk south along the west bank of the river for about 1 km.
The Mettawee River here provides a superb series of exposures (location in Fig 3) that cross from parautochthonous shelf carbonates (mostly dolostones) at the access point, south past the waterfall (43.470990; -73.367826) through alternating zones of flysch-type dark shales, and shale melange, to a large sliver of Chazyan carbonate (mostly limestones, starting at 43.462450; -73.362534) (Fig. 3). The eastern part of the carbonate sliver is poorly exposed in the river, but mapping demonstrates that this fault contact (the Taconic Frontal Fault) cuts obliquely across Taconic stratigraphy and large-scale fold axial traces, and is therefore a post-slaty cleavage generation structure (Fig. 3).
The allochthonous carbonate at this locality and along the western edge of the Allochthon in general has been interpreted and shown on a published map by Fisher (1985) as blocks-in-shale (i.e., olistoliths) rather than as coherent fault slivers. This locality (and stop 5) provide excellent examples to test these two alternative hypotheses. The carbonate/melange contact exposed in the woods across the river here can be walked for nearly 2 kilometers as a continuous, unbroken structure along strike, with internal fold axes in the carbonates approximately parallel to the general contact trend (Selleck and Bosworth, 1985, Plate 1A). The carbonate must be in the form of a large, probably composite sheet. Minor secondary disruption near its margins is undoubtedly present (of structural and perhaps sedimentary causes), but we maintain that the origin of this and other km-(length)-scale carbonate sheets adjacent to the Allochthon was by detachment of thin slices from the top part of the underthrusting shelf rocks and their incorporation to and imbrication at the base of the advancing thrust pile. We think based on our mapping of all this belt north to West Haven that it is highly misleading to describe the geometry of the large carbonate bodies along the western edge of the Allochthon as "blocks-in-shale", and that it is most unlikely that they arose as primary sedimentary slump features (further discussed in Rowley and Kidd, 1982).

STOP 1C. Mettawee River Fault Along Upper Turnpike
**Please stay on the road and its margins; we do NOT have permission to enter the field or woods here**
Two outcrops of shale melange occur a short distance into the field to the east, where outcrop on the west side of the road and into the woods adjacent exposes dolostones of the Cambro-Ordovician shelf (here Fort Ann Fm according to Fisher, 1985; see Fig. 3). These outcrops demonstrate the existence of the Mettawee River Fault as an east side down normal fault and closely constrain its position.

STOP 2. Potsdam/Ticonderoga Arenites and the Comstock (Pinnacle) Thrust.
In low roadside exposure on the west side of the road gently-dipping Upper Cambrian sandstones can be seen, mapped by Fisher (1985) as Ticonderoga and upper Potsdam Formations. The map shows they can be systematically traced for 9 kilometers to the south and, for a shorter distance, to the northeast of this place. Along with the overlying carbonate shelf sequence they demonstrate a major thrust duplication of almost the whole thickness of the local Cambro-Ordovician continental shallow marine platform/shelf sequence. The thrust carrying these strata was termed the Comstock Thrust by Fisher (1985); it climbs rapidly at a lateral ramp 9 km south of this locality (see Fig. 4, and Hayman & Kidd, 2002a; Stop 12) and can be traced a further 11 km carrying limestones of the uppermost part of the Ordovician shelf sequence before it climbs again, into the shale-melange belt, near Smiths Basin.
This small outcrop is not photogenic, and the thrust itself is not exposed here (exposures of it have been found in the woods to the west and southwest), but the map demonstrates its reality, and also that it and the sheet of shelf strata it carries are cut and truncated by the Mettawee River Fault (normal, east side down). Limestones of medial Ordovician age form a low outcrop at the sharp corner in the road to the north, and a larger outcrop on the other side beyond, and are shown by Fisher as Isle La Motte Formation (= Middlebury limestones) and form the foot wall of the Comstock Thrust here. It is probable that the original thrust relationship has been modified at this location by a later ENE-trending fault, but this does not significantly change the basic overthrust relationship.
Hayman & Kidd (2002a, b) provide reasons why this thrust should be specifically identified structurally as the southern extension of the Pinnacle Thrust exposed near Shoreham VT, but it is also helpful to understand that this thrust is the lowest (westernmost) thrust of the overall Champlain Thrust system in this area from Whitehall south to Fort Ann; lower components seen in Vermont (Shoreham Thrust; Main Champlain Thrust) die out southward with their displacements transferred upward along lateral ramps.

STOP 3: Frontal Fault of the Taconic Allochthon as a Post-Cleavage Thrust
**Warning - poison ivy occurs on this outcrop, and most abundantly in the road verge in front of it**
This outcrop (location shown on Fig. 4) is one of a very few places where the western fault contact of rocks of the main Taconic Allochthon is fully exposed; you will see three of them on this field trip. The roadcut exposes cleaved arenites and siltstones belonging to the early Cambrian/latest preCambrian Bomoseen unit of the Taconic Allochthon stratigraphy (a member of the Bull Fm. of Zen, 1967). A gently east-dipping fault contact on a meter or less thickness of dark phacoidal melange-fabric shale is present, although it may require a small amount of digging to complete the exposure. Below the shale, fine-grained medial Ordovician limestones (Glens Falls/Orwell) dipping gently eastward form the western part of the outcrop. The limestones map as a thin (c.10m.) slice above a much larger thickness of medial Ordovician shale and shale melange exposed to the west. This is the same relationship inferred in the Mettawee River section at Stop 1B, although there a different and younger Taconic rock unit locally maps adjacent to the fault. Note that the cleavage in the Bomoseen dips moderately to steeply east and must be truncated by the more gently east-dipping fault. This relationship is consistent with the oblique truncation of map-scale tight-isoclinal folds and their axial traces at the fault in this region, folds to which this cleavage is an axial surface fabric. Bomoseen arenites and siltstones are typically greenish chloritic colors, but in this exposure they are grey to dark grey, particularly near the fault contact with dark medial Ordovician shales affected by phacoidal melange-fabric cleavage. We think that fluid hydrocarbons migrating in the fault channel while it was active penetrated into the lowest Taconic rocks here and (now dehydrogenated carbon) are the cause of the colour difference. The low-angle attitude of the fault exposed here (and shown by local detailed mapping into the stream just to the north) suggests it is a thrust.
Near Troy, NY, in the gorge of the Poestenkill, sense of shear evidence suggests that the more steeply dipping fault exposed there is an east-side-downthrown normal fault which has cut and displaced the original Taconic thrust contact (Lim & Kidd, 2008). Similarly, a large roadcut on NY route 9G west of Hudson, NY exposes a sharp vertical fault contact that is also probably a normal fault. Such post-thrust normal faulting is also seen in calcite veins developed within the Ordovician melange terrain of the NY Capital District (Lim et al, 2005), and in the Mettawee River Fault seen at stops 1, 6B, and 7C on this trip (the trace of which projects well to the west of this locality; see Fig. 4). In this outcrop and more generally in the northern part, however, we think that an older thrust relationship is preserved at the western margin of the Taconic Allochthon, with the transport at this place being post-folding and cleavage development in the Taconic Allochthon strata.

STOP 4. Folded Thrusts of Taconic Allochthon Slates (Plude's Quarry).
Locality marked on Fig. 6. Plude's Quarry (Fig. 5) provides another of the few known exposures of Taconic Allochthon continental rise rocks lying upon the underlying melange/flysch sequence. Along Carlton Road the shales and minor thin silty wackes of the Taconic flysch are broken into a phacoidal melange fabric, seen in the lowest part of the western face of the outcrop. Going up the western outcrop face, a contact of this material overlain by slates with a planar slaty cleavage can be found. This is the Taconic Frontal Fault, again; but mapping by us (as shown in Fig. 6) clearly demonstrates that here, this fault, and the immediately underlying carbonate slice (not exposed in this outcrop), are folded on a map scale. Higher up the outcrop face, harder grayish-green slates contain thin fine-grained ribbon arenites and are consequently identified as belonging to the Poultney Formation of the Taconic Allochthon sequence. In the northern outcrop face of the old quarry, the regional slaty cleavage in those rocks passes down into the grey slates without arenites, that are above grey "shales" with phacoidal melange fabric at the western base of this face. The Poultney rocks above are clearly folded with the slaty cleavage as an axial surface fabric. A previous description of this outcrop (Bosworth and Kidd, 1985), suggested that there is an older, folded (thrust) fault, crossed by the slaty cleavage, that occurs between the Poultney slates above, and the grey slates below, and that this structure may be of the same generation as the early, folded, "Taconic Basal Thrust" of Rowley and Kidd (1981). The gray slates in this interpretation would be a transported constituent of the Middle Ordovician flysch ("Hortonville" lithology). Alternatively, but perhaps less likely, they might be an arenite-poor section of the Poultney unit and that no significant fault occurs at this contact internal to the rocks showing slaty cleavage in this outcrop. What do you think?
In either case, the local geological map shows that the fault expressed by melange fabric at the lower western side of the quarry is also folded, but this fault structure is not required to pre-date or overlap in time the cleavage affecting Taconic Allochthon rocks. The underlying limestone slice that is also affected by folding shows a solution cleavage, variably developed; while this is plausibly the product of the local strain that transported and folded the limestones, this does not mean that it is the same age as the slaty cleavage expressed in the Poultney slates in the quarry. This solution cleavage is more likely to have developed later in the overall Taconic imbrication/transport sequence, just before or during the transport of the shelf limestone, and after the thrust emplacement of the Taconic Allochthon above the limestone.

STOP 5. Thrust of Medial Ordovician Limestones Over Shaly Melange
**Warning - be cautious about where you step up to the rock face - in places, large blocks are visibly detached, and may be very unstable**
Locality indicated on Fig. 6. Carbonate exposures such as this one form lenticular belts bounded by medial Ordovician shales and shale melange (flysch) in a zone near this vicinity up to a few kilometers wide between the western edge of the Taconic Allochthon and the eastern edge of gently east-dipping, unfolded strata that rest with intact unconformable relationship on crystalline Grenville basement (such as those exposed along Rt 4 just east of Whitehall, and on Warner Hill visible a few kilometers due west of this locality). Where contacts are exposed, such as here, evidence for faulted lower contacts of limestone over shale are seen. In particular, the underside of the limestone is coated with fibrous vein-type slickensides, the lineation plunging ∼120º close to down-dip. Truncation of stratification in the limestone is seen locally. An abundance of veins in the limestone within about 50cm of the thrust surface suggests hydrofracturing and high fluid pressures during thrusting. A crude, lenticular cleavage in the underlying shales is deflected adjacent to the fault surface. A small horse of shale, isolated above the main thrust surface by a duplex mechanism, can be seen about half way along the exposure of the thrust (Fig. 7).
Towards the western limit of the overlying carbonate sheet a detached sliver of carbonate about a meter long lies in the cleaved shale just below the prominent fault surface. This may be a structurally detached piece or (less likely because of its shape) an olistolith. Similar lozenge-shaped pieces of medium-grained graywacke up to about ½ m long occur sparingly in the phacoidally-cleaved shale in the western part of the cut. Slickensided surfaces suggest that they too are products of structural disruption ("structural slicing"), although an olistolithic origin for these small objects cannot be discounted.
The shale and siltstone is locally bedded, with minor folds in part of the outcrop. Most is pervasively disrupted by the phacoidal cleavage whose microstructural character, with abundant evidence for shear offsets, is clearly related to faulting (Bosworth and Vollmer, 1981; Bosworth, 1982, 1984). This carbonate and other exposures like it are shown on the New York State geological map and by Fisher (1985) as giant olistolithic blocks. We find this interpretation of the outcrops to be unconvincing and prefer an interpretation, as shown on Fig. 6, where the carbonates and stratigraphically overlying shales form thin thrust sheets accreted beneath the Taconic Allochthon. Demonstrable tight folds and internal duplex faults within these carbonate sheets account for the many places where stratigraphic continuity is disrupted within them.

STOP 6A. Shoreham Thrust Exposure on Book Road
In the center portion of this roadcut exposure, grey-black non-calcareous shale (mid-Ordovician) up to 1 meter thick, with a pronounced phacoidal cleavage indicative of large shear strain, occurs below a sharp contact with highly fractured massive dolostones ("Providence Island" lithology). This is the Shoreham Thrust, and mapping of the surrounding area (Fig. 8) shows unequivocally that it is here the westernmost thrust in the Champlain System - in other words that the "Main Champlain", or Orwell Thrust farther north has disappeared (Hayman and Kidd, 2002a, b). To the south across the Vermont-New York border, near the Poultney River, the Shoreham Thrust also disappears, first because it is truncated by the Mettawee River normal Fault, although minor folding and incipient ramps can be detected in shelf rocks at its expected position in a outlier which occurs east of Whitehall. A major WSW-ENE cross-fault (the Book End Fault) passing north of this outcrop at stop 6A cuts and displaces the autochthonous shelf section and the Champlain Thrust System stack, crossing Book Road at the parking spot. The Shoreham Thrust is offset by this structure with an apparent left lateral displacement of about 2 kilometers. Two other faults like this one pass through the next valley north near West Haven hamlet. These cross faults are discussed in the description of Stops 6B and 7 below.

STOP 6B. Mettawee River Fault Near West Haven
ASK PERMISSION AT BOOK FARM BEFORE ENTERING - find Book Farm along Book Road 1.1 miles south of specified parking place
From parking place, enter field on east by walking between the two fences, opening the gate if necessary (and closing it behind you) - please do not climb over it or the fence. Follow the grassed-over track into the edge of the woods (about 100 meters), then along the edge of the woods (about another 200 meters), then angle down the crest of a low ridge in the meadow (about another 100 meters) to the edge of the woods crossing the low ridge. Outcrop of fractured tan-weathering dolostone ("Providence Island" lithology) is found just inside the woods at this point.
Use the sketch map below to navigate and understand the geology from this point on. About 60 meters east of the first dolostone outcrop, in the bed of the stream near the south end of the small ravine, dark slates ("Hortonville"), of presumed mid-Ordovician age, are exposed in contact with the dolostones [43.647590, -73.341250] . This contact is clearly a steep (60º) east-dipping fault, truncating the moderately east- dipping thick bedding in the dolostones, and the cleavage in the slates. Given the regional context, with no thick dark slates occurring west of this point, but rather the carbonates of the Shoreham Thrust slice, then the underlying autochthonous Cambro-Ordovician "Whitehall facies" shelf sequence, with Potsdam sandstone/quartzite at its base lying unconformably on Grenville basement, this fault must be a normal fault, and is in fact the Mettawee River Fault first proposed by Fisher (1985) in New York. It is the only complete exposure of this fault, although our mapping demonstrates that it runs continuously from the Mettawee River (stop 1A) north through this locality at least as far north as the latitude of Shoreham, VT, and all along this length it truncates regionally the thrust stack of the Champlain Thrust System.
We suspect that it extends significantly farther north and south than this, but there is a lack of clear truncation of components of the Champlain Thrust System beyond these extents. One reason for suspecting a larger along-strike extent is the minimum displacement, which can be constrained from cross-sections, and which demand at least 1000 meters of throw, and perhaps more than 1500 meters. This fault cuts out large, significant parts of the Champlain Thrust stack, and is one of the main reasons why previous attempts failed to trace the major thrust faults of the System southward. What age is this normal fault? We have no direct younger age limit in the mapped area, other than the observation that it is cut and displaced by the WSW-ENE faults which also cut the Shoreham Thrust. In fact this set of local outcrops (see Fig. 9 sketch map) shows that relationship directly, with a smaller splay of the larger WSW-ENE fault displacing in an apparent left-lateral sense the dolostone-slate contact (the Mettawee River Fault).
Evidence to be shown in the outcrop of the next stop (Stop 7A) demonstrates that these apparent strike-slip offsets on the WSW-ENE faults are from actual strike-slip displacement; discussion of the age and origin of this youngest faulting type and orientation is included with Stop 7A.

Parking for stop 7

STOP 7A. Veins and Left-Lateral Strike-Slip Faulting in Limestone at West Haven
ASK PERMISSION AT THE FARMHOUSE TO VISIT THIS OUTCROP AND THE OUTCROP OF STOP 7B. DO NOT GO TO THE OUTCROP UNLESS YOU HAVE PERMISSION. NO HAMMERS ALLOWED.
At the barns, follow the track west 50 meters to the low lying limestone outcrop surfaces.
On the main part of the outcrop, abundant calcite veins of two generations can be seen. The older set strike about N-S and mostly dip moderately to very steeply east. Their displacement sense is not particularly significant for this field trip, and is undetermined in most cases, but east-over-west thrust sense has been seen, as well as some strike-slip component in places, of dextral sense. The significant vein set for our purpose is the one striking between E-W and WSW-ENE, which in all cases cut N-S veins, and can be shown in a number of examples to displace subvertical instances in a sinistral sense. From this outcrop, the only one around West Haven where we have found this evidence, we infer that the apparent displacements on the WSW-ENE faults mapped here resulted from real left-lateral strike-slip displacement, not entirely from steeply directed north-side-down slip cutting gently-moderately east-dipping strata and thrust faults.
We sampled by drilling short cores of some of the veins in this outcrop, and looked for suitable fluid inclusions in doubly polished sections to measure fluid homogenization temperatures, and freezing temperatures, to determine the salinity for the fluids forming the veins. Refer to the vein fluid inclusion discussion in the introduction for overview and details. To summarise the essential point: low salinity fluid inclusions having homogenization temperatures up to 205-215C were found in the younger WSW-ENE veins having left-lateral strike-slip offset. Fluids in the fractures at burial depth when the veins formed would have been above this temperature, the amount depending on the depth, which we do not know. However, by comparison with results from Ordovician (Taconic) and Devonian (Acadian) vein fluid inclusions in the Albany area, we think this temperature is high enough to be indicative of an Ordovician age. Devonian veins (thrust sense only) from the Acadian foreland fold and thrust belt there are distinguishably lower, most around 120-130C. We are not aware of any reason to suppose that Acadian fluids are likely to have been significantly hotter in western Vermont compared with the Albany area, and we note an absence of both strike-parallel normal faults and WSW-ENE cross-faults cutting the Acadian Helderberg fold-thrust belt. So we think the WSW-ENE faults crossing the Taconic foreland thrust belt in this area are strike-slip faults (at least in their later/last slip episodes), and Ordovician (Taconic) in age, and are the youngest of the sets of structures of the Taconic event.
Whether they are Ordovician, or younger, what is their tectonic origin? Thrust faults are easy to understand in the context of the Taconic arc-continent convergence (Bird and Dewey, 1970), and strike-parallel normal faults in that general context similarly have modern exemplars, both of pre-thrusting origin from slab-pull on the down-going lithosphere (Schoonmaker et al, 2005), and extension late in and/or after convergence from slab detachment (Davies and Blanckenburg, 1995) or regional stress removal by large- scale plate boundary reorganisation. Strike-parallel strike-slip faults also are no problem to accommodate by strain partitioning of plate motion (McCaffrey, 1996). Cross-strike strike-slip faults of small displacement, on the other hand, are usually secondary linking structures (tear faults) for thrust (or perhaps with oblique slip for normal fault systems), and these commonly also serve as fault segment delimiters for earthquake slip zones. We think this may be the explanation for these WSW-ENE faults in the Taconic foreland but there is a problem; there are no known contemporary thrust or normal faults of the right relative age, nor any of a compatible slip direction! The WSW-ENE faults cut the Mettawee River normal fault, which itself cuts the youngest thrust in the Champlain Thrust stack. Even if we are wrong about the age constraint inferred from the fluid inclusion minimum temperature, the Acadian thrust slip direction for this sector of the northern Acadian Appalachians is also not towards WSW. Perhaps there could be small displacement blind thrust segments in the flat-lying platform sediments of the Taconic foreland, with WSW-directed slip, that would be the very last activity of the Taconic orogen, and to which these strike-slip faults form tear fault linking structures?
There are other features of the geology apparently associated with the West Haven cross-fault zone that we have noted: a) the abrupt change in the medial Ordovician strata across it from non-calcareous shales occurring to the south, to significant thicknesses of calcareous shales (Cumberland Head and Stony Point Fms) to the north. In addition, b) changes in thickness of the early Ordovician Ward Siltstone appear to be associated with this zone, and perhaps also with other faults of this orientation near and south of Whitehall. The implication is that these faults have developed using older fractures in the basement, and that these older structures also may have influenced subsidence patterns and deposition of sediments of the shelf both before and during the approach of the Taconic thrust stack.
Also, c) the map complexity near West Haven implies that the Shoreham Thrust interacted with an already fault-displaced irregular floor, from normal faulting on these oblique structures before the thrust stack interacted with it; it is admitted that inadequate outcrop and want of 3-D information prevent any clear demonstration of this. However, the same structural history inferred here can be observed if you visit outcrop adjacent to the Split Rock Point Fault [44.267592; -73.337305] near Westport NY where normal displacement on the NE-striking fault is expressed by the juxtaposition of Grenville gneisses and medial Ordovician calcareous shales; the dipping shales bent up by the normal-sense shear strain are cut by calcite veins showing clear evidence of strike-slip displacements, of both dextral and sinistral sense.

STOP 7B. Flat-Lying Thrust Fault of Taconic Slates Over Calcareous Shales and Limestones South of Coggman Creek
The small waterfall cliff, and the stream bed above, expose grey slates with a well-developed, moderately east-dipping cleavage. At the base of the small cliff, these slates rest on a practically flat thrust fault carrying them over dark calcareous shales. These calcareous shales pass down into limestones which form the rest of the outcrop in the stream bed and on the valley walls adjacent. The limestones are medial Ordovician Glens Falls, Orwell, and perhaps Middlebury equivalents, similar to those seen at stop 3, 5, and 7A (but are, we think - see map of Fig. 8 - not part of the same thrust slice as at stop 7A). The transported slates possess a well-developed planar slaty cleavage and so in a structural sense belong with the Taconic Allochthon. Their lithology, the same seen at stop 6B, monotonous, slightly silty, pale to medium grey slate, with thin silty laminations seen in some places, has been given the name Hortonville Slate by Zen (1967) in the area of the main Taconic Allochthon to the east. It is probably a medial Ordovician-age deposit, a facies of the orogenic flysch clastics accompanying the Taconic convergence, but significantly farther-transported than the melange, shales and turbidites of the Hudson Valley. Along structural strike, to the NNE near Benson, these rocks adjoin the Sunset Lake slice of the Taconic Allochthon, and we regard them as an enlarged addition/extension of the Sunset Lake slice. If this interpretation is valid, then the thrust exposed here is essentially another exposure of the western marginal fault of the Taconic Allochthon.
If you are using this field guide independently, you need to return to the Main Road at West Haven, go west along the road 0.3 mile, and ask permission at the house on the north side of the road to visit the outcrop of Stop 7C. If permission is obtained, the outcrop is about 150 meters north of the house.
If permission was previously obtained, return from Stop 7B to the edge of the woods and walk west along the edge for about 450 meters, passing limestone outcrops in the woods extending from near stop 7B until reaching the point where the ridge crest starts descending towards the west and enters the woods. Down the slope to the north at this point, the last limestone outcrop occurs above an exposure of dark melange-fabric shale just below it, showing that the thrust at the base of this limestone sheet runs here. From the point on the ridge, go approximately southwest contouring around the ridge end, and descend slightly into another (usually dry) streambed running roughly west.

STOP 7C. Metawee River Fault and Quartzites of the Pinnacle Thrust West of West Haven
See Fig 8 for location and geological surroundings. Exposures of dark partly melange-fabric shale occur intermittently in the bed and low bank of the stream to just before a sharp increase in the gradient over a rock ledge exposing well-lithified quartz arenites/quartzites. Below these, down stream, dolostones also outcrop. These arenites are part of the Potsdam/Ticonderoga unit of the Cambro-Ordovician shelf sequence, lying above the (here unexposed) Pinnacle Thrust, and must be separated from the melangy shales seen a few feet upstream by the principal strand of the Mettawee River Fault.
These quartzites also outcrop on the crest of the hill across Coggman Creek to the north, where they form an isolated erosional outlier of the Pinnacle Thrust, which overlies mainly dolostones of the Shoreham (locally termed Shaw Mountain) Thrust. We think the quartzite exposures near Root Pond a few kilometers to the northeast also form isolated remnants of the Pinnacle Thrust sheet, and that isolation by truncation of the Mettawee River normal Fault is a key to understanding their relationships, as it is for the similar occurrences of such quartzites in the same structural setting all the way from here at Stop 7C to Whitehall NY, where they can be shown to continue in the hanging wall of the Comstock thrust, as seen at Stop 2.