Abstract: Recycled, Resurrected "Put-back" Clasts of Lower Paleozoic Carbonates: Clues to Extent of Taconian Obduction, Eastern NY

John E. Sanders

Carbonate clasts composed of Lower Paleozoic limestones and found as isolated blocks in Middle Ordovician black siltstones (Snake Hill Formation) yield clues about the extent of obduction of the Taconic allochthons. The stratigraphic units evolved from three Early Paleozoic paleotectonic/paleogeographic settings when NY lay in the Southern-Hemisphere tropics (Paleozoic S and N corresponded to present-day E and W, respectively): (1) Cambrian-Early Ordovician passive margin with carbonate shelf (Sauk Sequence; dolostones on former landward side to N grading seaward into more-abundant limestones at former shelf edge) situated landward of a continental rise (setting of Taconic Sequence). (2) After continent-wide emergence, continuation of (1) with but minor dolostones (basal ippecanoe limestones and coeval top of Taconic Sequence). (3) Convergent-margin phase featuring foreland basin whose floor was crossed by N-moving thrusts (setting of "blocks-in-shale" units). Some carbonate clasts, originally shed S from the former shelf edge into deep water and enclosed within the terrigenous Taconic pelites, were obducted back onto the shelf to sites tens of km inboard of the former shelf edge, and recycled as resurrected clasts that traveled N into the foreland-basin black muds.

AAPG Search and Discovery Article #90954©1995 AAPG Eastern Section, Schenectady, New York