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