National Park Service geologic type section inventory: National Capital Region Inventory & Monitoring Network
Authors: Henderson Tim , Santucci Vincent , Connors Tim , Tweet Justin 
Published: July 2022

Type sections are one of several kinds of stratotypes. A stratotype is the standard (original or subsequently designated), accessible, and specific sequence of rock for a named geologic unit that forms the basis for the definition, recognition, and comparison of that unit elsewhere. Geologists designate stratotypes for rock exposures that are illustrative and representative of the map unit being defined. Stratotypes ideally should remain accessible for examination and study by others. In this sense, geologic stratotypes are similar in concept to biological type specimens, however they remain in situ as rock exposures rather than curated in a repository. Therefore, managing stratotypes requires inventory and monitoring like other geologic heritage resources in parks. In addition to type sections, stratotypes also include type localities, type areas, reference sections, and lithodemes, all of which are defined in this report. The goal of this project is to consolidate information pertaining to stratotypes that occur within NPS-administered areas, in order that this information is available throughout the NPS to inform park managers and to promote the preservation and protection of these important geologic heritage resources. This effort identified 20 stratotypes designated within seven park units of the National Capital Region I&M Network (NCRN): Chesapeake and Ohio Canal National Historical Park (CHOH) contains three type sections, two type localities, one type area, and eight reference sections; George Washington Memorial Parkway (GWMP) contains one type locality; Harpers Ferry National Historical Park (HAFE) contains two type sections, and one type locality/type area; Manassas National Battlefield (MANA) contains two type areas; Monocacy National Battlefield (MONO) contains one type section; National Capital Parks-East (NACE) contains one type locality; Prince William Forest (PRWI) contains one type section. Note that two stratotype designations (for the Harpers and Mather Gorge Formations) are shared amongst multiple park units. Table 1 provides information regarding the 20 stratotypes currently identified within the NCRN. There are currently no designated stratotypes within Antietam National Battlefield (ANTI), Catoctin Mountain Park (CATO), Rock Creek Park (ROCR), and Wolf Trap National Park for the Performing Arts (WOTR). However, CATO, CHOH, and GWMP contain important rock exposures that could be considered for formal stratotype designation as discussed in the Recommendations section. The inventory of geologic stratotypes across the NPS is an important effort in documenting these locations in order that NPS staff recognize and protect these areas for future studies. The focus adopted for completing the baseline inventories throughout the NPS has centered on the 32 inventory and monitoring (I&M) networks established during the late 1990s. Adopting a network-based approach to inventories worked well when the NPS undertook paleontological resource inventories for the 32 I&M networks and was therefore adopted for the stratotype inventory. The Greater Yellowstone I&M Network (GRYN) was the pilot network for initiating this project (Henderson et al. 2020). Methodologies and reporting strategies adopted for the GRYN have been used in the development of this report for the NCRN. This report includes a recommendation section that addresses outstanding issues and future steps regarding park unit stratotypes. These recommendations will hopefully guide decision-making and help ensure that these geoheritage resources are properly protected and that proposed park activities or development will not adversely impact the stability and condition of these geologic exposures.