Michael J. Simms Department of Geology, Ulster Museum, Botanic Gardens, Belfast BT9 5AB, Northern Ireland. [email protected] Andrew J. Jeram, Mullaghdubh House, 27 Gobbins Path, Islandmagee, Co. Antrim BT40 3SP, Northern Ireland. [email protected] ammonites absent Planorbis Subzone Lilstock Fm Langport Member 29 Blue Lias Formation 25 16 12 8 7 6 5 4 3 2 1 14 16 18 20 22 24 18 LIAS GROUP PENARTH GROUP m s fs 1 2 3 4 5a 5b 6 7 10 9 8 100 200 300 400 500 600 700 cm 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 SB TST SB HST 21 20 19 22a 18 17 16 14 15 13 12 11 FSST echinoid horizon mudcracked horizon gutter casts gutter casts ripples ? 3rd order cycles ? 4th order cycles CYCLOSTRATIGRAPHY pale grey mudstone/shale dark grey mudstone/shale medium grey mudstone/shale very dark grey mudstone/shale limestone marl heterolith, mm-cm scale shale KEY articulated ichthyosaur bone bed bivalve bed with Cardinia in life position ? 2nd order rise fall > > continues up to Bucklandi Zone continues down to Mercia Mudstone Group (Norian) LO conodonts (England) dysaerobic? FO - crinoids (Isocrinus sp. nov.) Psiloceras erugatum Neophyllites imitans Neophyllites antecedens 29 28c 28b 28a 27 26 25 24 23b 23a 30 31 32 33a 33b 34 33c 33d 33e 33f 33g TST HST MFS FSST 22b 22c 22d recovery fauna top Cotham Member Langport Member HST/Regression Asymmetric Bundle MFS Condensed Bundle Transgressive Bundle Erosional truncation TC TC? TC bivalve concentrations Modiolus horizons Liostrea bands abundant trace fossils SEQUENCE STRATIGRAPHY turbidites Psiloceras planorbis Psiloceras sampsoni and cf. sampsoni Psiloceras plicatulum and cf. plicatulum Caloceras spp. on this poster What has the Larne section to offer as a potential GSSP? Exceptional stratigraphic thickness The Triassic-Jurassic boundary succession at Larne is significantly thicker, and experienced more continuous deposition, than correlative strata at St Audrie’s Bay or at any other site in NW Europe. It offers potential for refining the isotope curve of Hesselbo et al. (2002; Geology, 30, 251-254) to a significantly higher resolution. Diverse macro- and microfauna and flora The fossil macro- and microfauna (ammonites, bivalves, gastropods, echinoids, crinoids, trace-fossils, vertebrates, ostracods, foraminifera) are abundant and diverse. Data for the nearby Larne borehole are already published. The diversity and preservation of the earliest Jurassic ammonite fauna in the Larne Basin is superior to that at St. Audrie’s Bay or at any other UK site (see poster below). Potential for global correlation Two orders of sedimentary cycles, largely unaffected by diagenetic limestones, can be recognised at this site (this poster, far right). Analysis, combining sequence stratigraphy and cyclostratigraphy, indicates that these cycles reflect eustatic fluctuations and hence have significant potential for global correlation (see website for more detailed discussion). The foreshore at Waterloo Bay, Larne, on the east coast of Northern Ireland, exposes an almost uninterrupted succession from the upper part of the Mercia Mudstone Group (Triassic, Norian) through to the Bucklandi Zone of the Lias Group (Jurassic, Sinemurian). The Triassic-Jurassic boundary succession at Waterloo Bay is proving to be superior in many respects to that at St. Audrie’s Bay, in south-west Britain, which, for decades, has been cited as a candidate Global Stratotype Section and Point (GSSP) for the base of the Jurassic System. Waterloo Bay, Larne, Northern Ireland: A potential Global Stratotype Section and Point (GSSP) for the base of the Jurassic System early diagenetic carbonate nodule Highstand Bundle Dublin Belfast Cork Galway Larne Waterloo Bay fault fault Langport Member Langport Member Lias Group Lias Group (first ammonites) (first ammonites) upper upper Cotham Cotham Member Member upper upper Planorbis Planorbis Subzone Subzone Penarth Group Penarth Group Bed 24 Bed 24 Location of Waterloo Bay, Larne, and a view from the adjacent cliff-top of part of the foreshore section at low tide. Strata dip at about 25 o to the north-west. Access to the site is exceptionally good via the promenade in the foreground. Figure for scale at the seaward end of the top of the Langport Member. Triassic-Jurassic boundary stratigraphy (preliminary results) Log and analysis by A.J.Jeram and M.J.Simms July 2006 Planorbis Subzone Johnstoni Subzone Correlative section at St Audrie’s Bay for comparison (after Hesselbo et al. 2002, Geology, 30, 251-254).