Recent Oneonta State Masters Program graduate Randall Willson was kind enough to send me a copy of his masters thesis and I decided (with his permission) to post it on here. The following excerpt is only the abstract to his 148 page thesis. Enjoy.
THE SEDIMENTOLOGY AND STRATIGRAPHY OF THE MANLIUS FORMATION (PŘÍDOLÍ?) AND ADJACENT UNITS: LOWER HELDERBERG GROUP, CENTRAL NEW YORK
The correlation of disconformities within western portions of the Helderberg outcrop belt in New York State has clarified stratigraphic relationships within the Manlius Formation and between the Manlius and adjacent units. Throughout the region, the Minelot Falls Unconformity marks the contact between the Thacher Member of the Manlius and the underlying Rondout Formation. However, at Skaneateles Falls, the Elmwood C Member of the Manlius rests on the Rondout Formation owing to onlap along the edge of the basin.
The Clockville discontinuity that marks the top of the Thacher Member and the base of the overlying Green Vedder Member (GVM), has been correlated westward, nearly to the limit of the outcrop belt. The GVM persists through this area, though it is significantly thinner than in eastern localities.
Tracing of the Olney Member has revealed a previously undocumented occurrence of branching stromatoporoids (Clavidictyon) in upper portions of the member, stratigraphically much lower than previous reports. Rather than grading imperceptibly into the Dayville Member, the Olney is unconformably (Terrace Mountain Unconformity) overlain by the Dayville, a relationship that is clearly displayed in the town of Manlius. Therefore, strata previously assigned to the Olney east of Manlius, N.Y. are herein considered to be parts of the Dayville Member.
A subaerial unconformity preceded Elmwood deposition and progressively beveled older units westward. The “Manlius tongue,” mapped by Rickard (1962), is not a simple progradation of Manlius strata into the surrounding Coeymans facies, but is a result of the misinterpretation of the uppermost Dayville strata as “undifferentiated Elmwood.” The top of the Elmwood/base of the Clark Reservation Member is also unconformable. Trypanites-bored hardgrounds throughout the Clark Reservation suggest significant stratigraphic condensation within this unit. The notion of a “Manlius tongue” is further compromised by recognition of a second subaerial unconformity that preceded deposition of the Jamesville Member. Traced eastward, this unconformity truncates the Clark Reservation, the Elmwood and then the uppermost portion of the Dayville Member before it is cut by the descending Howe Cave Unconformity near Cherry Valley. These stratigraphic relationships further emphasize the need to reassign the Dayville Member from the Coeymans Formation to the Manlius Formation as suggested by Ebert and Matteson (2003).
The GVM (informal, upper thin-bedded Thacher) of the Manlius Fm. is present within most sections studied, and is characterized by hummocky cross-stratified wackestones and packstones interbedded with mudstones and calcareous shales. Beds of the GVM typically display flat basal contacts overlain by planar to cross-laminae and less commonly rippled caps, a sequence typical of tempestitic shelf deposits. Firmgrounds to hardgrounds developed on upper surfaces of many beds (mm to few cm) are strewn with ostracods, brachiopods, encrusting bryozoans and horizontal burrows of Planolites indicative of post-storm recolonization. Equant spar-filled fractures (mudcracks of Laporte (1969), and others) are common along hardground horizons in mudstone-wackestone beds and are interpreted as subaqueous in origin. Interbedded calcareous shales and mudstones exhibit ramifications of Medusaegraptus (a dacycladacean alga), vascular plant debris, soft tissues of annelids, microbial mats, and rare tentaculites.
Thicknesses of the GVM at Oriskany Falls and Munnsville indicate maximum basinal subsidence in this area during deposition. At western outcrops, hummocks are much broader (> 1m) than their counterparts to the east. Shallower facies to the east are demonstrated by hummocks with much shorter wavelengths, sometimes displaying a nodular appearance associated with large ripple/dune forms. Correlations between outcrops displaying the GVM indicate an eastward shallowing from Oriskany Falls to Schoharie. To the west of Clockville, upper beds of the GVM are truncated by the overlying Olney Member of the Manlius Formation via the Terrace Mountain Unconformity. The presence of this sediment-starved, storm-dominated shelf setting in the presumed peritidal Manlius Formation raises new questions regarding the evolution of the Appalachian Basin during Helderbergian time.
Interview: Ross Campbell
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