USGS formalizes a new Pleistocene geological unit in Virginia

A unit defined by its boundaries and topography

The United States Geological Survey (USGS) formalized the Elsing Green Alloformation as a new Pleistocene allostratigraphic unit in Virginia’s coastal plain. The unit comprises a terrace deposit bounded by unconformities and occupies a relatively flat surface, whose mapped elevation is approximately between 26 and 38 feet (7.9 and 11.6 meters). The report describes these features as part of the unit’s characterization, not as a direct dating of each deposit.

At its landward boundary, the unit is usually marked by the base of an erosional escarpment; the foot of the escarpment is typically at 38 feet (11.6 meters). Its identification is based on both this topographic expression and its stratigraphic position. In other words, the proposal is not based only on the height of the land: it also considers the geometry of the boundaries and the deposit’s relationship to neighboring units.

What changes from the earlier mapping

The sediments now included in the Elsing Green Alloformation had been mapped as part of the Shirley Formation or the Sedgefield Member of the Tabb Formation. According to USGS, the new unit is distinguished from those assignments by significant differences in the escarpments that bound it and in the terrace morphology. The formalization therefore modifies the geological classification of previously described deposits, rather than announcing the discovery of a new material or a process observed in real time.

The type area provides the reference location for identifying the unit: it is in the Tunstall 7.5-minute quadrangle, near Elsing Green Plantation, in King William County, Virginia. The report identifies borehole 2012270-2 as the reference section. These details locate the formal definition; by themselves, they do not indicate that the entire unit has been sampled uniformly.

Age and correlation interpretations

USGS interprets the Elsing Green Alloformation as corresponding to Marine Isotope Stage 9e, with an approximate age of 330,000 years. This is a chronological interpretation, not a figure presented as exact. The available summary does not detail the methods used to establish that age, so it does not allow the uncertainty or specific dating evidence to be evaluated here.

The report also proposes correlating the unit with other Middle Pleistocene terrace deposits in the Atlantic Coastal Plain. The examples mentioned include the younger Lynch Heights Formation, located in Delaware, and the Butlers Bluff Member of the Nassawadox Formation, on Virginia’s Eastern Shore. Correlation is a proposal to relate deposits from different areas; the summary does not provide an independent demonstration that they are equivalent in all their features or history.

Scope of the announcement

The publication appears as chapter D of Stratigraphic notes—Volume 3, 2026, a six-page USGS professional report. Its described contribution is to formally establish a unit and specify its characteristics, type locality, and reference section. To understand how stratigraphic classifications are constructed and revised, these descriptions are considered within the region’s geology; general information about NSF’s institutional support for research does not constitute independent corroboration of this result.

The available documentation also does not allow the news report to be expanded with details about field methods, materials analyzed, or the degree of uncertainty in the proposed correlations. NSF’s information on materials research describes programs in another scientific area and provides no relevant evidence about this geological unit.