J.C. Ridge | Geology Reports

USGS2016

Glacial Lake Hitchcock and the sea: Fieldtrip Guidebook for the 78th Annual Reunion of the Northeast Friends of the Pleistocene

The fieldtrip will demonstrate the evidence for a close connection of Lake Hitchcock levels with lake levels and the position of sea level in Long Island Sound via a channel cut into glacial lake deposits in the lower Connecticut River valley, which issuperposed on a bedrock ridge at the mouth of the Connecticut River. On the trip we will explain important offshore features like an extensive ‐40‐m marine delta, and the altitudes of “The Race” spillway cut through the Harbor Hill moraine, Block Channel spillway cut through the terminal moraine, and the ‐85‐m Block Delta built into Last Glacial Maximum (LGM) eustatic sea level 115 km south of the terminal moraine. The history of lake levels and knowledge of eustatic sea levels provided by the Barbadossea level curve (Bard and others, 1990) have implications for the magnitude of glacio‐ isostatic depression and the timing of rebound. We will also review recent refinements to the chronology of ice retreat through the region as a result of new varve cores and the newly calibrated North American Varve Chronology (NAVC) (Ridge, 2004, Ridge and others, 2012) and discuss implications for the timing and mechanism of glacial Lake Hitchcock drainage in Connecticut.

Connecticut, Massachusetts↗

USGS1992

A model of late quaternary landscape development in the Delaware Valley, New Jersey and Pennsylvania

In the Delaware Valley of New Jersey and eastern Pennsylvania the late Quaternary history of colluviation, fluvial adjustment, and soil formation is based on the ages of pre-Wisconsinan soils and glacial deposits which are indicated by feld relationships and inferred from mid-latitude climate changes indicated by marine oxygen-isotope records. The area is divided into four terranes characterized by sandstone, gneiss, slate and carbonate rocks. Since the last pre-Wisconsinan glaciation (> 130 ka, inferred to be late Illinoian), each terrane responded differently to chemical and mechanical weathering. During the Sangamon interglacial stage (∼ 130-75 ka) in situ weathering is inferred to have occurred at rates greater than transportation of material which resulted in the formation of deep, highly weathered soil and saprolite, and dissolution of carbonate rocks. Cold climatic conditions during the Wisconsinan, on the other hand, induced erosion of the landscape at rates faster than soil development. Upland erosion during the Wisconsinan removed pre-Wisconsinan soil and glacial sediment and bedrock to produce muddy to blocky colluvium, grézes litées, and alluvial fans on footslopes. Fluvial gravel and overlying colluvium in the Delaware Valley, both buried by late Wisconsinan outwash, are inferred to represent episodes of early and middle Wisconsinan (∼ 75-25 ka) upland erosion and river aggradiation followed by river degradation and colluvium deposition. Early-middle Wisconsinan colluvium is more voluminous than later colluvium despite colder, possibly permafrost conditions during the late Wisconsinan ∼ 25-10 ka). Extensive colluviation during the early and middle Wisconsinan resulted from a longer (50 kyr), generally cold interval of erosion with a greater availability of easily eroded pre-Wisconsinan surficial materials on uplands than during the late Wisconsinan. After recession of late Wisconsinan ice from its terminal position, soil formation and landscape stability were delayed until the Holocene by a lingering cold climate, slope erosion, colluvium and alluvial fan deposition, and eolian sedimentation. Late Quaternary erosion in the Delaware Valley was dominated by glacial and periglacial processes during glacial stages. During the warm interglacial stages, soils developed on a more stable landscape. These souls were easily colluviated by periglacial erosion during periods of intermittent cold climate.

Geomorphology↗