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A shoreline to deep basin correlation chart for the middle Silurian coupled extinction-stable isotopic event is presented. The chart is a first attempt to synthesise new stratigraphic, faunal and stable isotopic data, as well as diversity changes among organic-walled microplankton (acritarchs), from the Grötlingbo-1 and Hunninge-1 cores on Gotland (Sweden), along with previously published data from the Bartoszyce IG 1 core (Poland), the Gräfenwarth section (Germany), and the Ruhnu (500) and Ohesaare cores (Estonia). Accordingly, the relative timing of biotic, sedimentary, and stable isotopic changes associated with the event can be studied in high stratigraphic resolution across a basin area of ~120 000 km 2 (in the epicontinental Baltic Basin) and further off the Silurian continental margin into the Rheic Ocean (Gräfenwarth section). A graptolite biozonation is presented for the Late Wenlock of the Grötlingbo-1 core and the middle Silurian carbon isotope excursion (CIE) is for the first time detected in stratigraphically continuous sections on Gotland. It starts close above the LAD of Monograptus flemingii and peaks at δ 13 C values of 2.4‰ in the Grötlingbo-1 core and at 3.8‰ in the Hunninge-1 core. The correlation chart forms the basis for several important conclusions for the mid-Silurian event: (a) it is associated with major and synchronous sedimentary changes across the basin independent of palaeodepth, i.e., the entire marine realm, from shoreline to deep basin, was affected; (b) the onset of the CIE is within the latest part of a regressive systems tract and related to carbonate platform exposure and termination; (c) the CIE peak interval correlates with the early transgressive systems tract and the development of laminated strata in the deeper parts of epicontinental seas, as well as with increased accumulation of organic matter in even deeper basins; (d) the major diversity anomalies among planktonic and nektonic taxa precede or occur close to the onset of the CIE.

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Abstracts -A revision of the trilobite fauna from Brzechów in the Holy Cross Mountains (Poland) shows that the assemblage consists of Palaeolenus medius (Bednarczyk), Issafeniella orlowinensis (Samsonowicz), Kingaspidoides sanctacrucensis (Czarnocki), Paradoxides (Acadoparadoxides) oelandicus Sjögren, P. (A.) cf. mureroensis Sdzuy and P. (A.) sp. It is earliest Middle Cambrian in age according to the West Gondwana standard of Geyer & Landing (2004) and can be correlated with the Cephalopyge notabilis Zone of Morocco. Moreover, the co-occurrence of the ranges of P. (A.) oelandicus with P. (A.) cf. mureroensis might suggest that P. (A.) oelandicus appears earlier in the Brzechów sandstones than in Scandinavia, thus the strata exposed here do not find their correlative in the Scandinavian succession. As a result, the Banian/Agdzian boundary (Lower-Middle Cambrian boundary according to the West Gondwana standard) probably lies within the Kamieniec Formation, and also below the Brzechów sandstones, in the upper part of the Ociesęki Formation. Close similarity of the discussed assemblage with contemporaneous assemblages from Morocco, Jordan or New Brunswick indicates that the fauna is generally of peri-Gondwanan and Gondwanan aspect.

3 Pol ish Geo log i cal In sti tute -Na tional Re search In sti tute, Rakowiecka 4, 00-975 Warszawa, Po land Masiak, M., Stempieñ-Sa³ek, M., Podhalañska, T., 2020. Microphytoplankton from mid dle palaeolatitudes of the South ern Hemi sphere -a re cord from cli mate change strata of Baltica's O/S bound ary. Geo log i cal Quar terly, 64 (1): 86-103, doi: 10.7306/gq.1518In the pres ent study, data on the di ver sity of acritarch and prasinophyte microphytoplankton were col lected from Or do vician-Si lu rian tran si tional strata at three dif fer ent geo log i cal lo cal i ties in Po land: south ern part of the Holy Cross Moun tains (Ma³opolska Block, south ern Po land), East Eu ro pean Plat form (Baltica), and Koszalin-Chojnice Zone (NW Po land). The mate rial rep re sents the mucronata (tri lo bite) to vesiculosus (graptolite) biozones. The Or do vi cian microphytoplankton as semblages are char ac ter ized by low fre quency and low di ver sity: up to 110 spec i mens and 12 gen era per slide, in con trast to Si lu rian ones that are more fre quent and more di verse ->3000 spec i mens and 16 gen era per slide (di ver sity at the spe cies level is also higher). Through out the Or do vi cian part of the suc ces sion, typ i cal Or do vi cian gen era oc cur, such as Acanthodiacrodium, Ordovicidium, Orthosphaeridium and large Baltisphaeridium, to gether with iso lated oc cur rences of typi cal Si lu rian gen era, es pe cially in the up per part of the Hirnantian (e.g., Diexallophasis). The Si lu rian as sem blages are typ ified by high fre quency of prasinophytes fol lowed by typ i cal Si lu rian acritarchs: Tylotopalla, Ammonidium, Domasia and Oppilatala. The palynological ma te rial from Po land is com pared with ma te rial known from other lo cal i ties: the Rapla and Valga bore holes (Es to nia) and Anticosti Is land (Can ada), as well as oth ers placed in dif fer ent palaeocontinents and dif fer ent bathymetric zones. Palynological as sem blages ob tained from Pol ish ma te rial con firm that bathymetry played the key role in tax o nomic di ver si fi ca tion of the microphytoplankton as sem blage. This sup ports the ex ist ing mod els of dis tri bu tion: dom inance of prasinophytes (leiospheres) and cryptospores is char ac ter is tic for shal low-wa ter en vi ron ments. In deeper wa ter, dom i nance of acanthomorphs is ob served. In the deep est-wa ter zones -mixed as sem blages oc cur. For the Holy Cross Moun tains, microphytoplankton fre quency is com pared with a TOC curve in the same in ter val.Key words: Po land, Or do vi cian/Si lu rian bound ary, palynology, acritarch fre quency,