GEOLOGIC MAPPING IN THE GREENSBORO, NC AREA: CITIZEN SCIENCE CONTRIBUTIONS TO UNDERSTANDING THE GEOLOGY OF THE AREA

In the North Carolina Piedmont, detailed geologic mapping is typically considered too difficult for a citizen scientist project due to the lack of rock exposure, deep weathering profile and need of an advanced knowledge in the identification of metamorphosed rocks. We present a preliminary 1:24,000-scale geologic map of the southern third of the Lake Brandt Quadrangle created from data collected through citizen science and verified through detailed rock sample identification and accurate sample location data.

The quadrangle straddles the Hyco Shear Zone - the contact between the Carolina and Milton terranes with the intervening Churchland pluton. The southeast portion of the map area is underlain by metamorphosed granodiorites to gabbros and volcaniclastic rocks of the Carolina terrane. The northwest portions of the map area are underlain by fine to coarse grained granite of the Churchland pluton. The Churchland ranges from unfoliated, to foliated and strongly foliated. Strongly foliated locations are interpreted as mylonitic fabrics from deformation along the Hyco Shear Zone. Amphibolite and biotite gneiss and schist are present locally within the Churchland pluton and are interpreted as xenoliths of Milton terrane lithologies.

Multiple traverses were conducted and data collected along greenway trails and other streams and drainages. The latitude and longitude of outcrop and/or float locations were collected utilizing a smart phone GPS (accuracy +-40 feet). Station locations were photographed, rock samples collected and stored in Ziploc-style bags and labeled. Station location data was tabulated in excel spreadsheet format and preliminary rock type information entered for each station location by the citizen scientist. Periodic work sessions were conducted with staff from the North Carolina Geologic Survey (NCGS) in which: 1) the excel spreadsheet was imported into a GIS so rock sample locations could be viewed spatially with respect to the study area; 2) the rocks samples from each station were reviewed and the preliminary rock types were modified as needed; and 3) geologic contacts were drawn by NCGS staff based on the data. This method proved successful in providing accurately located data to allow for the drafting of geologic contact lines.