ABSTRACT This one-day field trip will visit northern Erie County in northwestern Pennsylvania, USA, and is divided into two parts. The first part will highlight brittle and ductile deformation preserved in Upper Devonian bedrock. It is possible that this deformation occurred in relation to the Alleghenian orogeny during the late Paleozoic. However, some of this deformation displays possible evidence of postdating Wisconsin glaciation, but this interpretation is speculative and based largely on possible topographic disruption of Quaternary river terrace deposits. Morphologic characteristics of outcrops in creeks that expose these tectonic structures will be used as a starting point to discuss structure origin, timing, and their implications. The second part of the trip will visit Erie Bluffs State Park (EBSP) and will examine ongoing mass wasting of bluffs along the southern Lake Erie shoreline. The timing (as determined from dendrochronological analyses) and styles of mass wasting that have occurred at EBSP will be discussed and compared to two other locations along Pennsylvania’s Lake Erie shoreline. An appended road log serves as a geologic guide to the features and processes highlighted on this trip.

ABSTRACT The Erie lakeshore in Pennsylvania, west of the city of Erie, has many geological features that are ripe for study, teaching, and use as a vehicle for public science outreach. Features and processes on display include rapid slope failure and erosion of lakeshore bluffs, Pleistocene till in the bluffs, well-developed ancient sandy beach ridges atop till, and thin Upper Devonian sandstones that were deposited by storms. A wide variety of sedimentary, igneous, and metamorphic rocks can be found among cobbles eroded from till and rounded on lakeshore beaches, providing opportunities for teaching the identification of rocks, minerals, and Paleozoic marine fossils. Small fans at the bases of lakeshore bluffs have morphologies derived from distinct modes of sediment transport and deposition, with the potential to serve as analogs in better understanding large submarine fans. In winter, ice volcanoes can occur on the shoreline. Opportunities for teaching about geologic time are provided by localities where recent sedimentary processes, Pleistocene deposits, Paleozoic sedimentary rocks, and Precambrian igneous and metamorphic rocks can all be seen.

The Bradtville drift, the Canning till, and their correlatives in southwestern Ontario have been previously thought to be early Wisconsinan in age. Here another alternative is offered, whereby the Bradtville drift is assigned to the Illinoian stage, the lowermost Member A of the overlying Tyrconnell Formation to the late Sangamonian; Eowisconsinan, or the earliest part of early Wisconsinan, and its Member B to the early Wisconsinan substage. The age of the Canning till is still unknown. Member A of the Tyrconnell Formation is an accretion gley that formed about 20 m below the present level of Lake Erie, thus requiring a low outlet for the Erie basin. At that time, the Erie basin was drained probably by the buried Erigan channel, which extends about 50 m below the present level of Lake Erie. Member B of the Tyrconnell Formation is varved glaciolacustrine silt and clay, the deposition of which required a rise of lake level above the present one. This rise could have been caused by the Ontario lobe overriding the Niagara peninsula, possibly as far as Gowanda, New York; however, the ice margin remained in the eastern part of Lake Erie. The above hypothesis is supported by available lithologic and paleoecologic data from the region adjoining the north-central and eastern part of Lake Erie, but supporting numerical age determinations beyond the range of radiocarbon dating are still lacking.

Abstract The New York bluffs of Lake Erie, which stretch northeastward 100 km from the Pennsylvania border, and those of Lake Ontario, which extend eastward 212 km from the Niagara River along the south shore of the lake, expose one of the most continuous sets of glacial drift in the northeast. The Erie bluffs are predominantly Devonian shale. However, the shale is mantled by sandy-silt till remarkable for its lateral uniformity in texture, but with distinct “down-ice” trends in lithologic properties relating to the regional bedrock or glacial reworking. Proglacial lacustrine silt, clay, and sand, deposited in 90 to 50 m of water in glacial Lakes Whittlesey and Warren between 13.5 and 12 ka, overlie the till. The bluffs of Lake Ontario are cut only sparingly in Ordovician red sandstone and shale and expose three major lithostratigraphic units. A lower red or pink sandy-till sheet is overlain by widespread gray and red glaciolacusrrine silt and clay. These fines provide major input to a younger, sillier, purplish-gray or gray till marked by both massive basal facies and upper subaqueous-flow or basal melt-out diamicton. A blanketing glaciolacustrine sequence occurring in the lower, nondrumlin areas is largely related to glacial Lake Iroquois. Locally, proglacial sands, lenses of flow till, or stone concentrations indicate a short readvance during lake formation. The two major tills of the Lake Ontario bluffs correlate with a similar sequence in adjacent Ontario, Canada. These, in turn, are tied to the Halton Till of the Port Huron advance. The lower till sheet of the United States Erie shore is related to a preceding advance, which is tentatively identified as the Lake Escarpment glaciation, and the Wentworth Till of nearby Canada.

Abstract Holocene sediments from three deep boreholes from Long Point, a 35-km-long sandy foreland on the Canadian side of eastern Lake Erie, display a consistent coarsening-upward trend from sheltered-water clays and silts to well-sorted shoreface sands. This trend persists in spite of the documented record of lake-level rise, due primarily to postglacial isostatic rebound of the Niagara River outlet. To resolve this contradiction within the context of shoreline evolutionary trends in eastern Lake Erie, sediment data from the boreholes are analyzed in combination with data from other sources. The analysis suggests that the sedimentary sequence is linked to the history of the Long Point foreland and its precursors. The resulting evolutionary model, supported by relict shore features, postulates that Long Point began as a north-south-trending cuspate peninsula, once linked to the ancestral Presque Isle spit on the United States side. The location of the feature was controlled by the Norfolk moraine, a cross-lake ridge of glacial origin. As lake levels rose, the foreland retreated northward with the shoreline as a whole, becoming smaller and more rounded but with well-developed recurves extending northeast. Around 5 to 4 ka, an abrupt rise in lake levels, related to resumption of drainage from the Nipissing Phase in the Upper Great Lakes into the Erie basin, resulted in inundation of most of the ancestral foreland. When the lake later fell to previous levels, presumably due to widening of the Niagara River outlet, the foreland commenced its present east-west orientation. At present, the distal portions of the spit are prograding southward, while the proximal areas are still retreating northward; in other words, the feature is slowly rotating clockwise. The pattern of landward retreat of parts of the foreland over sheltered (lagoonal) deposits and the rotation of the distal portions are also noted in the two other north-shore forelands. Point Pelee and Pointe-aux-Pins, and comparison is made with the transgressive marine barrier islands of the United States east coast.