CYNGOR CEFN GWLAD CYMRU
COUNTRYSIDE COUNCIL FOR WALES
SITE OF SPECIAL SCIENTIFIC INTEREST: CITATION
National Grid Reference: SH 375838
Site Area: 4.6 ha
Nantannog is of special interest for its geology. The site consists of rock exposures in a ravine and stream section 3.5 km west of Llanerchymedd.
The site exhibits important sedimentary features peculiar to the Arenig-Llanvirn Series on Anglesey, and is the type locality for the Nantannog Formation. The exposure features a bedded sequence of shales and sandstones of the Nantannog Formation, with shelly and graptolitic faunas. In the middle of the section, a 20m thick slide conglomerate, derived ultimately from the Precambrian Mona Complex, lies above graptolite-bearing hirundo zone shales. The site contains excellent exposures, illustrative of the sedimentation and stratigraphy of Anglesey in the Lower Ordovician.