EVIDENCE FOR PRE-WISCONSINAN AND LATE PLEISTOCENE-EARLY HOLOCENE TECTONIC UPLIFT IN SOUTH-CENTRAL CONNECTICUT FROM AN INTEGRATION OF GEOMORPHIC DATA AND STREAM VECTOR ANALYSES

Both the modern Quinnipiac River valley and its pre-Wisconsinan valley, which is eroded into the underlying bedrock surface formed by the Triassic-age New Haven Formation (arkose) of the Hartford basin, display down-to-the-west tilting along its southernmost 20-km-long reach. This tilt is opposite to the eastward dip of bedding in the New Haven Formation, which argues against homoclinal shifting of the ancient Quinnipiac River as a cause of the tilt. Stream basin asymmetry vectors of higher-order streams in southern Connecticut suggest that the tilt was produced by westward migration of the river against bedrock dip during late Pleistocene or early Holocene time in response to gentle uplift from the east. The westward tilt of the underlying pre-Wisconsinan valley suggests an earlier episode of gentle uplift before Wisconsinan time.

The source of the uplift may be from either of two NE-trending structures to the east: the Eastern Border Fault (EBF) of the Hartford basin and the fracture zone along which the ~200-my-old Higganum dike system (HDS) intruded. There is no direct evidence for reactivation of the EBF while a few observations suggest that the fracture zone into which the HDS intruded has repeatedly been reactivated since Permian time, suggesting that it may be a zone of crustal weakness and possibly the source of the uplift. Thus, additional studies are needed to more accurately determine the timing of the inferred uplift and whether the HDS-related fracture zone is indeed the source.