Project

Conglomeratic tide-dominated shoreline - Upper Devonian (Fammenian) S.W. New York State

Goal: Document the sedimentary processes and depositional environments of a prograding late Devonian high-energy (coarse quartz sand w/abundant, well-rounded, discoidal quartz pebbles) shoreline.

The Salamanca Conglomerate is composed of a 2-10 meter thick coarsening-upward sequence of apparent shoreface, foreshore/beach, tidal bar/sandwave (cross-bedding up to 6m thick), and tidal/fluvial channel deposits. It forms an extensive escarpment with large joint-separated blocks ("rock cities" where concentrated) on/near hilltops as first noted and superbly described by James Hall (1843).

Investigate paleohydraulic conditions; entrainment/transport thresholds for pebbles of various size (0.5 - 10 cm) suggest currents well in excess of 1m/sec.

Prepared an article for the fall 2017 NYSGA meeting in Alfred, NY.

Ongoing work on regional correlation and unit description of the Salamanca and other conglomerates. Use of 1m-DEM/GIS over a 2000 km2 area is facilitating the search and correlation of disparate outcrops and indicating structural complications in certain areas.

Date: 1 November 2016 - 1 November 2021

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James Craft
added 2 research items
The orthoquartzitic Salamanca conglomerate evidently records a high-energy Upper Devonian seacoast, with at least meso-tidal range, as indicated by a sand-pebble beach, a flood-dominated delta prograding over marine wave-rippled fine sands, large-scale and coarse-grained HCS, and a sub-aqueous large-scale dune field formed by strong flood tides. Most of the sequence records delta progradation and sediment transport/redistribution along shore by waves and tides and most significantly, storm circulation of longshore/rip currents in the breaker/surf zone to the shoreface. Well-exposed channel deposits at the top (which overlie wave-truncated dunes and beach deposits at a similar elevation) suggest either expansion of the delta-delta plain or a transition to a coastal plain terrestrial environment (perhaps including a major flood event as suggested by localized large clasts of quartz, sandstone, mud rip-up clasts, and abundant plant fossils) followed by an apparent abrupt rise in relative sea level and a transgression as indicated by subsequent fine-grained wave-formed strata with an abundant marine fossil fauna.
The final stages of the Devonian Period is recorded in the hills of Allegany State Park and surrounding area (NY/PA contain the most complete and accessible Upper Devonian stratigraphy on Earth). Extensive outcrops are uncommon on the well forested hillsides with the exception of the escarpment/ block-forming Salamanca Conglomerate: ● House-sized blocks of rock (exceptional 3-D views) ● Very large-scale cross-bedding (> 5 meters to ~ 0.05 meters) ● Trillions of pebbles - well-rounded discs of milky vein quartz ● A rock city without peer (“Little” Rock City extends > 10 km along trails in Rock City State Forest). ● Inferred high-energy coastal deposits: - abundant low-angle/large-scale inclined strata = point bars with subjacent marine strata and very coarse mouth bars = flood-dominated delta; - large-scale/very coarse HCS = intense storms (hurricanes based in paleolatitude); - very large shoreward-directed dunes = flood tides and common bi-directional cross- beds.
James Craft
added a project goal
Document the sedimentary processes and depositional environments of a prograding late Devonian high-energy (coarse quartz sand w/abundant, well-rounded, discoidal quartz pebbles) shoreline.
The Salamanca Conglomerate is composed of a 2-10 meter thick coarsening-upward sequence of apparent shoreface, foreshore/beach, tidal bar/sandwave (cross-bedding up to 6m thick), and tidal/fluvial channel deposits. It forms an extensive escarpment with large joint-separated blocks ("rock cities" where concentrated) on/near hilltops as first noted and superbly described by James Hall (1843).
Investigate paleohydraulic conditions; entrainment/transport thresholds for pebbles of various size (0.5 - 10 cm) suggest currents well in excess of 1m/sec.
Prepared an article for the fall 2017 NYSGA meeting in Alfred, NY.
Ongoing work on regional correlation and unit description of the Salamanca and other conglomerates. Use of 1m-DEM/GIS over a 2000 km2 area is facilitating the search and correlation of disparate outcrops and indicating structural complications in certain areas.
 
James Craft
added an update
Summary of Investigations to date:
● After a glimpse of gigantic (> 5 meters high) cross-bedding in Rock City State Forest (RCSF) in fall 2016, a study of the Salamanca Conglomerate (SC) began in earnest that winter. A busy field season resulted in a 2017 NYSGA publication describing and interpreting the SC as tide-dominated coastal deposits. ● Field work continued in 2018 defining large channel deposits overlying marine strata (inferred delta) on the west flank of RCSF and a recon of the Bear Caves outcrop (~ 15 miles south in ASP; similar deposits). ● Search for additional outcrops to assess spatial variation and correlation of the SC was facilitated by remote sensing: Online viewing of high-resolution 2016 orthoimagery and then 2017 LIDAR/DEM (Digital Elevation Model) data: http://gis.ny.gov/elevation/lidar-coverage.htm. ● With 2017-2018 release of multi-county 1-meter DEM coverage, 1800 sq.km. (1200 DEM tiles) were downloaded for use in the open-source/ free-ware Quantum GIS. Outcrop search and analysis is ongoing.
DEM – GIS Approach
● Problem – “Several” conglomerate beds have been variously identified and correlated since James Hall visited the area during the Geologic Survey of New York in the late 1830s. ● Hypothesis – One-meter DEMs should allow for remote recon of conglomerate blocks and outcrops. GIS plotting and analysis could provide rather precise formation dip (angle and azimuth). Such data could help untangle long-standing correlation issues and pinpoint outcrops for further study. ● Assumptions – The conglomerate beds are planar, continuous over some distance, and the tops (caprock) are thinly-covered or exposed. The beds may form stratigraphic markers in an otherwise monotonous sequence of shale and sandstone.
DEM - GIS Methods
● Digital Elevation Models are typically processed from LIDAR data to “bare-earth” surface. ● With “1 meter-DEM”s, relatively small features are visible (~ 1m horizontal & ~ 0.1m vertical accuracy/resolution). ● The 1800 sq.-km. DEM study area (1200 DEM 1.5km2 tiles) shows numerous block fields and outcrops gracing the hillsides. ● The “crumb” trails produced by downslope block movement (“creep”) can point to the source/outcrop. And springs are common at outcrop bases. ● Using “best-fit plane” GIS plugin, the x,y,z position of selected outcrop/block tops yield dips and azimuths of best-fit planes/beds. ● Using “plane-DEM intersection” GIS plugin, bed dips and azimuths yield intersections of planes/beds in the landscape.
DEM - GIS Preliminary Results
● The Salamanca Conglomerate can be traced ~ 18 miles southward from the hilltop at Holiday Valley Ski Resort (708m amsl) to Bear Caves/Quaker Run/ASP outcrop (540m). ● From the west, S.C. outcrops near the Catt./Chat. County line (and glaciation margin) extend 25 miles through ASP & beyond the Tuna Creek valley where apparent structural complications impede correlation. ● Dips range from 0.3 to 0.5 degrees; azimuths from 150 to 180 degrees. North of the Allegany river, azimuths range 150 to 160 and tend toward 180 near the State line (reflected generally by the Lower Devonian Oriskany Fm. structural map).
● A “new” Rock City/Village (dubbed “Hourglass”) and nearby “blocky” outcrops were located in the SW corner of the park. ● Based on a conglomeratic formation of Mississippian-age at the same elevation (640m) mapped to the west and to the east in NY and direct correlation with the PA geologic map, this unit is likely Mississippian age (rather than Devonian as mapped). ● The GIS “best-fit” plane of these “new” outcrops (65 x,y,z pts) = dip of ~0.3O on a bearing of ~196O ● Intersection of this plane with the DEM terrain (GIS plugin; computationally intensive) yielded numerous other possible Mississippian-age outcrops including the “headwaters” area of ASP and Thunder Rocks.
 
James Craft
added a research item
The orthoquartzitic Salamanca conglomerate records a high-energy Upper Devonian seacoast, with at least meso-tidal range, as indicated by a pebbly shoreface and beach, a tide-dominated delta prograding over marine wave-rippled fine sands, and a sub-aqueous large-scale (4m-6m foresets) dune field formed by strong flood tides. Most of the sequence records delta progradation and sediment transport/redistribution along shore to dunes and beaches by tides and waves. Unusual occurrences include large (L= dm to m; H= dm), coarse-grained (sand to pebbles), 2D and 3-D wave ripples with rounded crests (coarse hummocky cross-strata?) and a well-preserved formset (foresets/topset/stoss) of a very large dune. Well-exposed channel deposits at the top of the sequence (which overlie wave-truncated dunes and beach deposits at a similar elevation) suggest either expansion of the delta/delta plain or a transition to a coastal plain terrestrial environment. A major flood event is suggested by the caprock locally composed of large (up to 7 cm) well-rounded clasts of vein quartz with subordinate sandstone, rock, and mud rip-up fragments and abundant aligned plant fossils. Wave-formed strata with abundant marine fossils directly overlie the caprock indicating a transgression with an apparent abrupt rise in relative sea level.
James Craft
added an update
Attached is a compilation of channel deposits at several outcrops in Rock City State Forest.
 
James Craft
added an update
On a hilltop in Rock City State Forest (http://www.dec.ny.gov/lands/77184.html), three miles north of Salamanca, NY (Fig. 1), the Salamanca Conglomerate outcrops in spectacular fashion. Part of the Upper Devonian (late Fammenian) Cattaraugus formation, the quartz-pebble conglomerate forms a five to ten-meter high escarpment and topographic bench at ~ 2200 feet amsl amid a mature cherry-maple-oak forest. In places, house-sized blocks have separated from the escarpment along orthogonal joint sets and variably “crept” downhill. Where concentrated, a maze of passageways and blocks may form so-called “rock cities”, an impressive example of which is Little Rock City. These monolithic blocks permit extraordinary 3-D views of diverse sedimentary structures such as ubiquitous cross-bedding and channel deposits.
Six outcrop areas with the most significant exposures were logged over a four-kilometer north-south traverse. The traverse largely follows the east-facing hillside which roughly parallels the presumed paleo-shore of the Devonian Catskill Sea. Extensive “bookend” outcrops at the north face (off the Rim Trail) and at the southeast perimeter (“Little Rock City” along the North Country-Finger Lakes Trail) along with close vertical (time) control allow a nearly continuous look at spatial and temporal changes in sedimentary deposits along a four-kilometer stretch of inferred late Devonian seacoast.
Six major outcrops over a ~ 4K paleoshore-parallel traverse, appear to record three major depositional environments from north to south:
- shoreface-foreshore (beach) sequence on the north (wave-ripple laminated fine sands - coarse-grained wave ripples/dunes - parallel/low-angle coarse sand-pebble beds);
- a prograding tide-dominated delta and tidal flats (abundant channel-form/coarse sand-pebbly lateral-accretion deposits, currents directed mainly shoreward); and
- a sub-aqueous tidal dune field (~5+m cross-beds; wavelengths up to ~100m, fine-coarse sand with abundant granule concentrations and occ. pebbles, inclined shoreward; an intact 2m "formset" offers insights into dune genesis).
The entire sequence is capped/overridden by ~ 3m thick channel deposits and in places, a 15-30 cm caprock with densely-packed vein-quartz (and minor "exotics" such as sandstone, metamorphic, and mudstone rip-up clasts - the only mud observed) pebbles/cobbles with abundant plant remains. Finally, draped directly over the pebbly conglomerate caprock are wave-rippled fine-med. sandstones with marine fossils (similar to the those at the base of beach sequence and beneath a channel sequence).
This conglomerate appears to record a high-energy seacoast, with at least a meso-tidal range and strong storms, as indicated by a pebbly beach (or delta front), a tide-dominated delta prograding over marine wave-rippled fine sands, and a sub-aqueous large-scale dune field formed by strong flood tides. Most of the sequence records delta progradation and sediment transport/redistribution along shore to dunes and beaches by tides and waves. The intact tidal dune (1st pic below; formset with preserved stoss/topset, foreset, and bottomset beds) appears to show vertical aggradation due to competing ebb and flood tides and an abundant sediment supply. As the dune grew to ~2m, flood tides began to dominate with subsequent migration by foreset deposition as supplied by the stoss/topset "conveyor belt". Well-exposed channel deposits at the top overlie dune and beach deposits (which appear truncated at a similar elevation by apparent storm waves) suggest either lateral expansion of the delta or a transition to a fully fluvial-coastal plain environment (perhaps including a major flood(s) event as suggested by ~ up to 7 cm clasts). An abrupt rise in relative sea level is suggested by subsequent fine-coarse grained wave-formed strata with marine fossils which drapes and conforms to the very coarse caprock. Some wave reworking of the caprock may have occurred (i.e., a transgressive lag deposit) but it was likely insignificant since mud rip-up clasts are preserved in places, plant fossils are generally aligned normal to shore, and the overlying marine deposits are thin-bedded and finer-grained (probable shoreface to offshore deposits).
 
James Craft
added an update
Project goal
Document the depositional environments and sedimentary processes of a prograding late Devonian high-energy (coarse quartz sand w/abundant, well-rounded, discoidal vein-quartz pebbles) shoreline.
The Salamanca Conglomerate is composed of a 2-10 meter thick coarsening-upward sequence of apparent shoreface, foreshore/beach, tidal bar/sandwave (cross-bedding up to 6m thick), and tidal/fluvial channel deposits. It forms an extensive escarpment with large joint-separated blocks ("rock cities" where concentrated) on/near hilltops as first noted and superbly described by James Hall (1843).
Investigate paleohydraulic conditions; entrainment/transport thresholds for pebbles of various size (0.5 - 10 cm) suggest currents well in excess of 1m/sec.
Prepared an article for the fall 2017 NYSGA meeting in Alfred, NY.
Ongoing work on regional correlation and unit description of the Salamanca and other conglomerates. Use of 1m-DEM/GIS over a 2000 km2 area is facilitating the search and correlation of disparate outcrops and indicating structural complications in certain areas.
Background and motivation
Master's degree - SUNY-Binghamton (1985); published an article on Upper Devonian shallow-marine/hummocky x-strata with J. Bridge (GSA; 1987).
Worked for NYSDEC for 31 years (Engineering Geologist); retired fall 2016. Studied/published on some karst hydrogeologic and contaminant transport problems with Paul Richards (SUNY-Brockport).
Been wandering the "Rock Cities" of SW-NY with great fascination for years and now have time to take a better look.