B4: EURYPTERIDS AND FACIES CHANGES WITHIN SILURIAN/DEVONIAN 'EURYPTERID BEDS' OF NEW YORK STATE
Samuel J. Ciurca, Jr.
Rochester, New York
INTRODUCTION
Perhaps nowhere else in the world are eurypterids found in the abundance they are within the Siluro-Devonian strata of New York State. More importantly, little-understood cyclic sequences, mostly within an evaporite basin, preserved a multitude of distinctive eurypterid faunas. Many of these are currently known, and several now known, need to be better understood. This is especially true of Akron-Cobleskill horizons (see Ciurca 1978, 1994) that are providing abundant remains of successor faunas to those of the well-known Bertie faunas, viz. Eurypterus remipes (older) and Eurypterus lacustris Faunas.
The purpose of this paper is to comment on Bertie Group and overlying Akron-Cobleskill occurrences – their distribution geographically and stratigraphically of microbialites and eurypterids – and suggest that much more research is required if we are to truly understand the paleoenvironment not only of the sedimentary rocks in which we find specimens, but the environment in which the animals actually lived. The association of many of the eurypterid horizons with stromatolites/thrombolites is particularly emphasized. This is an exciting new area of observation and research.
The evolution of fish, and other organisms, has taught us that given enough time, many animals evolve to occupy disparate environments within the marine realm and often within the fresh water realm (rivers and lakes). Many authors have already suggested that the various eurypterid morphologies we encounter can be attributed to their existence in a variety of environments. Yet, it has proved difficult to provide specific environments for specific eurypterids – especially faunas that contain a great variety of species (forms) co-mingled like those of the Bertie Group assemblages.
The discovery of numerous post Akron-Cobleskill eurypterid horizons (Ciurca 1973, 1994) and horizons within the Cobleskill Limestone (itself) of eastern New York suggested lithologically and faunally that the Bertie Group needed redefinition. Redefinition was proposed previously (Ciurca 1980) and provided for practical recognition of the Silurian-Devonian boundary across New York State from Albany westward to Buffalo and into the Niagara Peninsula of Ontario, Canada based upon the abrupt appearance of Erieopterus.
In addition, examination of the typical Bertie Group lithologies and faunas can help us look for and understand newly discovered eurypterid horizons. An example of this, discussed below, is the occurrence of numerous stromatolite horizons within most sequences (See section on Microbialites within the Bertie Group).
The eurypterid-bearing horizons mostly begin in basal Salina Group units that are more argillaceous than Bertie Group (and higher) horizons. While not much is known about facies relationships within these lower horizons (e.g. Pittsford and other members of the Vernon Formation), some observations have been made (Ciurca in NYSGA 1990). Of course, during the deposition of the Salina sequence, the thick red beds of the Vernon-Bloomsburg to the south and east were important to the paleoenvironmental setting in which we find the eurypterids. To the west of the basin were the ‘Niagaran’ reefs, some of which are believed to have continued growth into late Salina and Bertie time.
All of the Late Silurian and Early Devonian eurypterid ‘deposits’ indicate formation in shallow water and most are associated with features of desiccation represented by the numerous (cyclical) horizons bearing mudcracks, occasional ripple marks, rip-up clasts and probable strandline deposits. Uniquely, the Yale Peabody Museum ory is now the repository of a great collection of the sedimentary structures and sedimentological features, including a suite of associated lithological samples personally observed and collected over a period of about 40 years.

>B4: EURYPTERIDS AND FACIES CHANGES WITHIN SILURIAN/DEVONIAN 'EURYPTERID BEDS' OF NEW YORK STATE

Remington Arms Factory on left

Entering Illion Gorge (Steele Creek)
Ordovician Time Zone

Entering Silurian Time Zone

Vernon Red Shale

Syracuse Formation on left

Early Devonian limestones on left

STOP 1. Exposures of the Late Silurian Fiddlers Green Fm
Approximately the upper half of the Fiddlers Green Fm. (Bertie Group) is exposed along the road directly opposite the Litchfield Town Hall (Ciurca Locality 56, Cedarville at Jerusalem Hill Roads). In 1966, the exposure was a glacially polished surface on the Phelps Waterlime Member and very resistant to excavation. However, during this and many subsequent years, hundreds of specimens of eurypterids and associated fauna were obtained from this relatively small outcrop. This material is now in the Yale Peabody Museum in New Haven, Connecticut. The eurypterid-bearing units here are the Phelps Waterlime at the top of the exposure and the underlying finely-crystalline Victor Member. Eurypterus remipes is the common element of the eurypterid fauna here and has drawn collectors from all over to this area trying to find one.

POW/MIA Remembrance Bridge.

STOP 2. Exposures of the Late Silurian and Early Devonian Strata
Stratigraphically, this is an important section. At the base is the uppermost Fiddlers Green Fm. (Bertie Group) with eurypterids and salt hoppers. Overlying strata include the Forge Hollow, Cobleskill, Chrysler, Thacher and part of the Olney Formations. There are at least three eurypterid horizons present in the section. The Silurian/Devonian boundary lies within the lower part of the Chrysler Fm. here – this lower portion is rich in strontium (celestite) at Chittenango Falls. This section, again, exhibits the importance of microbialites in sections preserving eurypterid remains. In the upper portions of this section, within the ‘Thacher’ here, are more than two thick beds (more than 2.5 m) of stromatolites (including digitate forms) and thrombolites intimately associated with the Early Devonian eurypterid, Erieopterus.

STOP 3. Rock Cut Bioherm (New Name)
This road cut exposes what is here interpreted as another example of a patch reef within the Akron/Cobleskill sequence like that proposed for the Marcellus Falls area (Martisco Reef Complex). Above the sequence here is the lower portion of the overlying Chrysler Formation. While chert is a minor component there, as compared to the Marcellus Falls exposures, it allows for a direct correlation with the units exposed at Marcellus Falls. Both localities record the same post-Bertie eurypterid facies.

STOP 4. Martisco Reef Complex, Marcellus Falls
And Overlying Chrysler Formation
Interpreted herein (and associated website) to be a Late Silurian patch reef associated with the Akron/Cobleskill sedimentation in upstate New York in this area, and eastward to the Rock Cut Gorge and also westward to the Auburn area. Eurypterid paleoenvironments can only legitimately be interpreted if we take into account the known distribution of stromatoporoids biohermal and biostromal deposits and understand the impact of the variety of morphotypes exhibited within the Bertie Group (and overlying sequences) of microbialites as we come to recognize them within the eurypterid-bearing Late Silurian and Early Devonian sequences.
The most notable feature here is the dark chert facies which is seen to laterally replace the reef but also overlies what looks like the core of the reef – a highly dolomitized massive section with vugs, dolomite crystals, and silicified stromatoporoids. This lithology resembles parts of the Lockport Dolostone of western New York.

STOP 5. Cobleskill Limestone Stromatoporoid Biostrome
The intimate contact of an eurypterid horizon with deeper water facies is illustrated at this site. This may represent an extreme regression as eurypterid beds lie upon a massive stromatoporoid biostrome. And to complicate matters more, there are higher Eurypterus-bearing, pre-Erieopterus, units preserved upstream. This is the most complex area of eurypterid stratigraphy in upstate New York and is especially important because the units are all post-Bertie Group, i.e. post Eurypterus lacustris Biofacies. Thus, there are numerous eurypterid horizons exposed in the Owasco Outlet and we need to know why they are preserved here and how this important section relates to those to the west, south and east.