Depositional environment of the Owadów-Brzezinki conservation Lagerstätte (uppermost Jurassic, central Poland): evidence from microfacies analysis, microfossils and geochemical proxies

Abstract

The Owadów-Brzezinki quarry is one of the most important paleontological sites in Poland, known for its exceptionally well-preserved Upper Jurassic (Middle Volgian = uppermost Lower Tithonian) fossils. Carbonate deposits of the section record a transition from an offshore to coastal and lagoonal settings and have been studied based on microfacies, micropalaeontological, isotope and chemical proxies. The obtained data point to normal marine conditions during the deposition of the older part of the quarry section in an offshore setting and a gradual transition into lagoonal environment characterized by high-amplitude variations in seawater salinity and oxygenation level of bottom waters, both of which resulted in considerable changes in benthic fauna assemblages or in the total lack of the fauna at some intervals. Above-mentioned conditions during the deposition of the middle part of the quarry section have probably allowed the preservation of diversified fauna with soft tissues. The microfacies and chemical data indicate that dysoxic/anoxic episodes may have occurred not only during the deposition of known fauna-rich beds but also during the deposition of poorly studied, so far, younger part of the section. The uppermost part of the carbonates exposed in the Owadów-Brzezinki quarry originated during the re-appearance of normal marine chemistry mostly in the intertidal-subtidal settings. The depositional conditions of the Owadów-Brzezinki site are nontypical, among famous conservation Lagerstätten, owing to the rapid fluctuations in the oxygenation and salinity of bottom waters. E eschweizerbart_xxx eschweizerbart_xxx Depositional environment of Owadów-Brzezinki conservation Lagerstätte 83 Fig. 2. eschweizerbart_xxx 84 Hubert Wierzbowski et al.

Palaeoenvironmental changes recorded in the oxygen and carbon isotope composition of Kimmeridgian (Upper Jurassic) carbonates from central Poland

“…8). Thresh old lim its of Mn £100 ppm, Fe £250 ppm, and Sr ³490 ppm may be ac cepted as in dic a tive of well-pre served Ju ras sic cal cite bi valve shells ac cord ing to Wierzbowski and Joachimski (2007), and Wierzbowski et al (2016). The given lim its of man ga nese and iron con cen tra tions are in line with the data of Jones et al (1994).…”

“…Higher d 18 O val ues (-0.5 to 0.5‰) are re ported again for the mid-Tithonian oys ters from cen tral Po land (Wierzbowski et al, 2016). The mid-Tithonian fos sils are de rived from open ma rine de pos its be long ing to the Pa³uki For ma tion and the low er most part of the Kcynia For ma tion (Dembowska, 1979;Kutek and Zeiss, 1997;Matyja and Wierzbowski, 2016;Wierzbowski et al, 2016). This may be re lated to a suc ces sive deep en ing of the mid-Pol ish sed i men tary ba sin dur ing a Late Kimmeridgian trans gres sion, which be gan in the Eudoxus Chron (cf.…”

“…Newly ob tained ox y gen iso tope data of well-pre served fossils, along with pub lished d 18 O val ues of Wierzbowski (2015), and Wierzbowski et al (2016), may be used to doc u ment tem -per a ture and sa lin ity vari a tions in the epicontinental Pol ish ba sin dur ing the ma jor Late Oxfordian-ear li est Kimmeridgian re gression and the con sec u tive trans gres sions, which started, de pending on the lo ca tion, in the lat est Hypselocyclum or the Divisum chrons of the lat est Early Kimmeridgian. The pres ent and published data sug gest that d 18 O val ues of Up per Ju ras sic fos sils from cen tral Po land cor re spond closely to sea level vari a tions.…”

Late Jurassic facies succession of the Kleszczów Graben area (southern border of the Łódź Depression, peri-Tethyan shelf, central Poland)

“…De pos its of the Kcynia for mation in cen tral Po land con sist in gen eral of lime stones, marls and sulphates (Dembowska, 1979). The lith o logic pro file of 25 m thick Kcynia for ma tion de pos its dom i nated by limestones is pre sented by Wierzbowski et al (2016) from the Owadów -Brzezinki Quarry lo cated 70 km north-east from the study area. Li thol ogy of the youn gest sed i ments (F22) in the study area seems to cor re spond to the Tithonian Wieniec unit of the Kcynia for ma tion (Dembowska, 1979;Marek et al, 1989) in which some palaeontological lev els are char ac ter ized by lime stones and marls with sulphates (ostracod lev els D and E) (Marek et al, 1989).…”

A new pancryptodiran turtle from the Late Jurassic of Poland and palaeobiology of early marine turtles

“…Unit I (ca. 9.1 m thick) consists of massive, fine‐grained, chalky limestone characterized by a general absence of sedimentary structures with occasional distinctive parallel lamination only (Wierzbowski et al, ). Deep‐burrowing bivalves Pleuromya sp.…”