UNCONFORMITIES AND STRATIGRAPHIC RELATIONSHIPS WITHIN THE MANLIUS FORMATION, HELDERBERG GROUP (PRÍDOLÍ?) OF CENTRAL NEW YORK STATE

Correlation of disconformities in western portions of the Helderberg outcrop belt has clarified stratigraphic relationships within the Manlius Fm. and between the Manlius and adjacent units. Throughout the region, the Minelot Falls Unconformity marks the contact between the Thacher Mbr. of the Manlius and the underlying Rondout Fm. However, at Skaneateles Falls, the Elmwood C Mbr. of the Manlius rests on the Rondout Fm. owing to onlap along the edge of the basin.

The Clockville Unconformity at the top of the Thacher Mbr. and the overlying Green Vedder Mbr. (GVM), have 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 Mbr. 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, NY are now considered to be parts of the Dayville Mbr.

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 (CR) Mbr. is also unconformable. Trypanites-bored hardgrounds throughout the CR Mbr. 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 Mbr. Traced eastward, this unconformity truncates the CR Mbr., the Elmwood and then the uppermost portion of the Dayville Mbr. before it is cut by the descending Howe Cave Unconformity near Cherry Valley. These stratigraphic relationships further emphasize the need to reassign the Dayville Mbr. from the Coeymans Fm. to the Manlius Fm. as suggested by Ebert and Matteson (2003).