SEDIMENT STARVATION ALONG THE PUNCH KILL UNCONFORMITY AND WESTWARD ONLAP OF THE KALKBERG FORMATION (LOCHKOVIAN, HELDERBERG GROUP) IN NEW YORK STATE

The Punch Kill Unconformity (PKU) marks the contact between the Coeymans and Kalkberg formations. At Cherry Valley (CV) and Cobleskill (CBL), the uppermost Coeymans Fm. comprises skeletal grainstones with abundant holdfasts of the cystoid Lepocrinites gebhardi. However, this unit is missing at Catskill in the Hudson Valley (HV). In each outcrop, the PKU is marked by an irregular, pyrite-mineralized surface which records maximum flooding (MFS) at the base of a fourth order sequence. At CBL, this surface caps several dm of well-sorted, pyritic, nodular echinoderm grainstones which record in situ reworking of resistant skeletal debris during stratigraphic condensation. We interpret this as a thin remnant of the transgressive systems tract (TST).

In the HV, the lowest Kalkberg is divisible into 4 units. Unit A (lowest) comprises cherty, skeletal packstones to grainstones, which are overlain by muddier beds with less chert (unit B). Unit C comprises nearly 1 m of pyritic, shaly mudstones with packstone interbeds, followed by interbedded packstones and shaly wackestones with holdfasts of Mariacrinus stoloniferous (unit D). At CBL, a more fossiliferous equivalent of unit B overlies the PKU and is followed by thinner and more fossiliferous occurrences of units C and D. At CV, unit D (M. stoloniferous beds) rests directly on the PKU. The westward younging of units that overlie the PKU demonstrates that the Kalkberg Fm. onlapped from east to west.

At CBL, textural trends in unit B indicate aggradation in the high stand systems tract (HST). Units C and D comprise a second fourth order cycle with initial deepening (TST) recorded by unit C. Unit D represents the HST, but evidence for aggradation is lacking.

In the studied sections, all units thicken eastward into the HV. Comparison of facies within Kalkberg subunits reveals increased siliciclastics and pyrite eastward. Faunal content and diversity decrease eastward. These changes signal greater water depth and dysoxia in the HV. Rapid changes in thickness and relative bathymetry over small distances suggest that Kalkberg onlap was driven by increased subsidence rather than eustatic deepening. Deepening of the basin continued with the overlying New Scotland Fm. We interpret these stratigraphic changes as distal responses to earliest Acadian tectonism.