Geologic Map of the Kilbride Peninsula (County Mayo) and Bencorragh (County Galway), Ireland James Madison University

GEOLOGIC MAP OF THE KILBRIDE PENINSULA (COUNTY MAYO) AND BENCORRAGH (COUNTY GALWAY), IRELAND DESCRIPTION OF MAP UNITS WILLIAM R. SWANGER AND STEVEN J. WHITMEYER SILURIAN SYSTEM 2018 Lettergesh Formation – Greenish-grey, fine-to coarse grained, sandstones and Sl siltstones. Sandstones are medium-to thick bedded with occasional cross-beds, 9° 34’ 31’’ 9° 26’ 9’’ convolute bedding, and soft-sediment deformation. Greenish-grey siltstones are 53° 35’ 3’’ 53° 35’ 3’’ B found at the base of the section near the Tonalee contact.

Slmb Oln Skt Tonalee member (Kilbride Formation) – Red siltstones and shales. 1-3 cm Slm fine- to medium-grained, tan to grey sandstones are present. Or Kilbride Formation – Green to buff, fine- to medium-grained sandstones and Slmb Sk siltstones. Occasional cross-beds, brachiopod casts, and quartz pebble Slm conglomerate bands. Tan to red, medium-grained sandstones, and some thicker Slmb skolithos bearing beds are found near the base of the formation. Oln Sk Slm Slm Lough Mask Formation – Red/purple mudstones, siltstones, and sandstones. Cross-beds abundant; occasional rip-up mud clasts. Sk Slmb Or Basal Lough Mask member (Lough Mask Formation) – Red to pink-stained Slmb Slm Skt trachyte. Abundant 2-3 cm, elongated quartz-filled phenocrysts; occasional Slmb Sk A Skt columns. Slm Slmb Skt Sk

Slm ORDOVICIAN SYSTEM Or Oln Slmb Sk Skt Rosroe Formation – Conglomerates and coarse sandstones; occasional Or Sl Or Slmb breccias. Graded gravity mass flow deposits. Unconformably overlies the Lough Sk Slm Skt Nafooey Formation.

Slm Slmb Skt Lough Nafooey Formation – Massive pillow basalts and brecciated basalt Oln Oln Oln flows. Sk Sl Slm Sk Slmb Skt Skt Sk Slm Slm MAP SYMBOLS Slmb Oln Slmb Oln Skt Sl For all contact and fold symbols, lines are solid where the location is exact, Slmb Slmb Sk long-dashed where the location is approximate, and short-dashed lines where the Slm Sk location is inferred. For geologic observation symbols, observation sites are Slm Slm Skt centered on the strike bar or at the intersection point of multiple symbols. Strike Slmb Slm Skt bars are colored to reflect lithology, with the exception of outcrop scale fault Sk planes, which are colored black. Stations that do not have a strike measurement Sk Slmb Sl Sk Sk Slm B’ are symbolized as colored dots. Skt Oln Slmb Skt Slmb Skt Slmb Slm Sk Skt Slm Contacts Slm Sl Sk Skt Sk Sk Skt Fault Contacts Skt Skt

Sl Unconformable Contact (cross section only) Sl Sl Sl

Folds - showing direction of plunge where appropriate Sl Anticline

Syncline A’

53° 33’ 13’’ 53° 33’13’’ Geologic Observations - All non-black strike symbols are 9° 34’ 31’’ 9° 26’ 9’’ colored to represent the rock formation that they are in. Topographic and Satellite Imagery basemaps, modified MN SCALE 1:24000 Strike and dip of inclined bedding plane from Mapbox.com GIS server 1 0.5 0 1 MILE Lough Mask 4 o18' 1000 0 1000 2000 3000 4000 5000 6000 7000 FEET Strike and dip of incline outcrop scale fault plane Projection: TM65 Irish Grid, Transverse Mercator 76 MILS 1 0.5 0 1 KILOMETER D TM65 Datum Vertical bedding

Digital Cartography by William Swanger County Mayo Strike and dip of overturned beds 2018 MAGNETIC NORTH County Galway DECLINATION AT CENTER OF SHEET Station o . ANNUAL VARIATION 0.17 E (3.02 MILS)

Clonbur

Figure 1. Inset map showing map location captured from Google Maps. CORRELATION OF MAP UNITS

A A’ Sl METERS Bencorragh Unconformity METERS Northwest Southeast 500 500 GEOLOGIC AGE GEOLOGIC Slmb Skt Skt FORMATION Unconformity INTERPRETATION SILURIAN Sk

LETTERGESH (Sl) Slm Lough Nafooey LETTERGESH Marine Turbidites Sea Level Sea Level Slmb Slm Oln Sk PALEOZOIC unconformity Or Sl TONALEE Near-shore System TONALEE (Skt) Or

ORDOVICIAN unconformity - 500 - 500 KILBRIDE Near-shore System KILBRIDE (Sk) Oln

LOUGH MASK Fluvial System LOUGH MASK (Slm) 500 500 ACKNOWLEDGEMENTS Columnal Basalts and Lavas Slmb B B’ BASAL LOUGH unconformably overlie the Rosroe BASAL LOUGH MASK (Slmb) Skt MASK This geologic map was funded in part by the NSF – DUE/TUES “Collaborative METERS Unconformity METERS and Lough Nafooey Research: Google Earth for Onsite and Distance Education (GEODE)” grant. 500 500 PALEOZOIC Kilbride Peninsula Unconformity Gravity mass flows of the Rosroe Sea Level Sea Level ROSROE ROSROE unconformably overlie the Lough LOUGH NAFOOEY Slm Sk (Or) (Oln) Oln SOURCES AND REFERENCES Route 300 Skt Nafooey volcanics Or Lough Mask Sl Sea Level Sea Level Geological Survey of Ireland, 2003, GSI Bedrock Geology 1:100,000 Series: Bedrock Geology 100K Series Data Services Provided by DCENR and Oln Slmb Slm Or Sk Sl LOUGH Pillow basalts and brecciated lava - 500 - 500 GSI (accessed May 2018). NAFOOEY flows Figure 3. Projected contacts and stylized form lines have been added to the cross section view (A toA’) of the area in an attempt to help ORDOVICIAN SILURIAN Tectonic events during the end of the Ordovician rotate the Rosroe and Nafooey. Holland, C.H., 2001, The Geology of Ireland: Dunedin Academic Press Ltd., visualize the structural complexities of the unconformity bound Lough Nafooey Formation (Oln). The simplified geology seen in Figure 531 p. - 500 - 500 2 was exposed to compressional forces creating a series of anticlines and synclines in the South Mayo Trough. There are no arrows or Figure 2. Generalized depositional interpretation of the formations and their stratigraphic relationship in the mapping area.The jagged contacts represent other sense of movement indicators in the map area or cross sections. This is because it is unclear whether strike-slip or normal faulting Meere, P., MacCarthy, I., Reavy, J., Alistair, A., and Higgs, K., 2013, Geology of Ireland, A Field Guide: The Collins Press, 372 p. unconformities found between the Lough Nafooey, Rosroe, and Basal Lough Mask Formations. affected the region post-compression.