Conodonts and chitinozoans were studied from the Neitla section, which exposes the boundary between the Porkuni and Juuru regional stages. This level, although not proved biostratigraphically, has been traditionally considered to correspond to the Ordovician–Silurian boundary. However, stable carbon isotope data indicate that the system boundary lies higher in the succession, in the lower part of the Juuru Regional Stage. Rare conodonts and chitinozoans discovered in the section do not provide any criteria for locating the boundary. Although conodonts are represented by taxa characteristic of the Silurian, all of them are known to have already appeared elsewhere in the Upper Ordovician.
Armstrong, H. A. 1996. Biotic recovery after mass extinction: the role of climate and ocean-state in the post-glacial (Late Ordovician–Early Silurian) recovery of the conodonts. Geological Society, London, Special Publications, 102, 105–117.
https://doi.org/10.1144/GSL.SP.1996.001.01.08
Einasto, R. 2007. Ordoviitsiumi ja Siluri ladestu piiri leidmine Neitla kruusakarjääris (Discovery of the Ordovician and Silurian boundary in the Neitla gravel quarry). Keskkonnatehnika, 7, 60–61.
Gul, B., Ainsaar, L. and Meidla, T. 2021. Latest Ordovician–early Silurian palaeoenvironmental changes and palaeotemperature trends indicated by stable carbon and oxygen isotopes from northern Estonia. Estonian Journal of Earth Sciences, 70, 196–209.
https://doi.org/10.3176/earth.2021.14
Hints, L. and Männik, P. 2014. Stop A10: Porkuni quarry. In 4th Annual Meeting of IGCP 591, Estonia, 10–19 June 2014. Abstracts and Field Guide (Bauert, H., Hints, O., Meidla, T. and Männik, P., eds). University of Tartu, Tartu, 167–172.
Hints, L. and Meidla, T. 1997. Keila Stage. Oandu Stage. Rakvere Stage. Nabala Stage. Vormsi Stage. Pirgu Stage. Porkuni Stage. In Geology and Mineral Resources of Estonia (Raukas, A. and Teedumäe, A., eds). Estonian Academy Publishers, Tallinn, 74–88.
Jeppsson, L. and Anehus, R. 1995. A buffered formic acid technique for conodont extraction. Journal of Paleontology, 69, 790–794.
https://doi.org/10.1017/S0022336000035319
Jeppsson, L., Anehus, R. and Fredholm, D. 1999. The optimal acetate buffered acetic acid technique for extracting phosphatic fossils. Journal of Paleontology, 73, 964–972.
https://doi.org/10.1017/S0022336000040798
Kaljo, D., Nestor, H. and Põlma, L. 1988. East Baltic Region. Bulletin of the British Museum (Natural History), Geology, 43, 85–91.
Männik, P. 1994. Conodonts from the Pusku quarry, lower Llandovery, Estonia. Proceedings of the Estonian Academy of Sciences. Geology, 43, 183–191.
https://doi.org/10.3176/geol.1994.4.03
Meidla, T., Hints, O. and Ainsaar, L. 2023. Searching for the Ordovician–Silurian boundary in Estonia, Latvia and Lithuania. Estonian Journal of Earth Sciences, 72, 70–73.
