The Drzewica Formation (also called Drzewica Series, gen. serii drzewickiej and in older literature Bronów Series,named for Bronów village (gmina Żarnów, Opoczno County, Łódź Voivodeship). or Komorowo Beds,named for Komorowo, Łobez County village, gmina Resko, Łobex County, West Pomeranian Voivodeship. ) is a geologic formation in Poland. It is Pliensbachian in age. Vertebrate fossils have been uncovered from this formation, including dinosaur tracks. The Drzewica Formation is part of the Depositional sequence IV-VII of the late lower Jurassic Polish Basin, with the IV showing the presence of local Alluvial deposits, with possible meandriform deposition origin, dominated in Jagodne and Szydłowiec, while delta system occurred through the zone of the modern Budki. The sequence V shows a reduction of the erosion in the Zychorzyn borehole of the Drzewica Formation, showing changes on the extension of the marine facies, where upper deposits change from Alluvial to Deltaic-Seashore depositional settings. VI-VII facies were recovered on the Brody-Lubienia borehole, with a lower part exposed on the village of Śmiłów that shows a small fall of the Sea level. The stathigraphic setting of the dinosaur tracks reported from the formation suggest a Seashore or Deltaic barrier. Body fossils reported include bivalves, palynology, fossil trunks, roots. Trunks of coniferous wood, especially Cheirolepidiaceae and Araucariaceae trees show the occurrence of vast coniferous forests around the tracksite. The association of forests and dinosaur megafauna on the Pliensbachian suggests also a colder and specially dry ecosystem. Drzewica deposits where in part to be a gigantic shore barrel, setting at the time where the Polish basin sea was at its lowest point. Other related units are Fjerritslev or Gassum Formation (Danish Basin), Hasle & Sorthat Formation (Bornholm), upper Neringa Formation (Lithuania) and abandoned informal units in other regions of Poland: upper Sławęcin Beds (),named for Sławęcin, Włocławek County Wieluń series () or Bronów series.
Description The Drzewica Formation between Gowarczów and Rozwady, forms sandstone complexes of +10 or so meters, usually uniformly formed, finely less often medium-grained, separated by Silt-sandstone blocks, sandstone-like places or Siltstones. In these sediments there are worm tubules (Ichnofossils), Rhizoids and the remains of Charred plants, sometimes thin carbon inserts. This section on the area of Gowarczów-Rozwady wasn't completely covered, but connects the appearance of the Drzewica Formation strata with several coeval Boreholes: Gowarczów (GW-1 and GW-2), Kuraszków (KP-1 and KP-4), Sielec (A2), Adamów (Al), Kraszków (MG-2), Gielniów (GG-1) and in a few exposures (quarries) from the vicinity of Kraszków and Gielniów. On this region the most complete profile of this formation was obtained in the Sielec Borehole (A2), which was pierced by the geological structure of the outcrop zone, covering the middle and upper section of the Drzewica Formation with a thickness of 146.7 m. Locally, the thickness of this series is estimated at 175–180 m.
Profile +Stratigraphy on the Bodzanów IG 1 BoreholeUnitLithologyThickness (metres)Fossil Palynology/FloraFossil FaunaYoungestsandstones2630.0–2632.0 m depth on the General Lithological ProfileNon ReportedNon ReportedN12.6 m of core, including: 0.7 m-fine grained sandstone, light gray, almost white, solid/compact. 0.8 m-fine grained sandstone, light gray, almost white, with a tabular diagonal layering, emphasized by accumulations of carbonated organic matter and Muscovite. 1.1 m -fine grained sandstone, light gray, almost white, with blurry layering.2632,0–2638,0 m depth on the General Lithological ProfileCupressacites subgranulatus (Cupressaceae Conifers) Ischyosporites variegatus (Dicksoniaceae Ferns) Carnisporites granulatus (Selaginellaceae Lycopsids) Taurocusporites verrucatus (Notothyladaceae Bryophytes) Classopollis classoides (Cheirolepidiaceae Conifers) Trachysporites sp. (Pteridophyta Ferns) Tsugaepollenites macroverrucosus (Pinaceae Conifers) Corrugatisporites scanicus (Lygodiaceae Ferns) Deltoidospora minor (Cyatheaceae Ferns) Carbonized vegetable chaffNon ReportedDownwards lutite turning into mudstones. At a depth of 2638.0–2794.0 m, interpretation based on geophysical measurements and crumb samples2638,0–2642,0 m depth on the General Lithological ProfileNon ReportedNon ReportedOldestsandstones and inverted sandstones, with individual inserts of sandy mudstones2638,0–2642,0 m depth on the General Lithological ProfileNon ReportedNon Reported
Paleogeography At the Late Pliensbachian (Margaritatus-Spinatum) several changes occur on the Polish Basin. The last section, latest Raricostatum subzone, there were a series marine transgressive surfaces, linked with the called Pli1 transgressive phase, known thanks to molluscs and ooids, along with an increase of marine macrofauna and microfauna. A marine Ingression filled the Polish basin, depositing marine dark Clay, Mudstone and lenticular Heteroliths, that are abundant on the lower-Middle Pliensbachian Łobez Formation and Poland, where dark-grey marine Claystones appear on the Kaszewy 1 borehole. There was a visible shoreline retreat that ends on the beginning of the Late Pliensbachian Margaritatus Chronozone. After the Pli1, a series of local subordinate retrogradational stratal-pattern architectures indicate the transgressive phase of the sequence Pli2. Pli2 The transgressive phase led to a maximum flooding level at the middle Spinatum. That was known thanks to Ammonites found on an 85 m basin at NW Poland, on the Wolin IG-1 borehole. This transgression also impacted deposition, with 265 m sequences of Mudstones and sandstones in a syndepositional tectonic graben at the Wolin-Recław Zone. After the maximum peak of the flooding basin it followed a regressive phase, characterized by progradational fluvio-deltaic sandstones, like the series of sandstones that recover the major tracksites of the Drzewica Formation, the Śmiłów Quarry Tracksite and the Wólka Karwicka Tracksite, both know from a regression nearshore/barrier lagoonal derived sandstone deposit. The Coeval deposits of Usedom and East Prignitz on Germany contain numerous Glendonites (Calcite pseudomorphs after Ikaite), what lends support to the possibility of a Late Pliensbachian cooling event and polar Glaciation at that time. Mostly of the authors, based on the current scientific quorum and the wide distribution of Glendonites in Upper Pliensbachian strata, tend to support a glacial-derived hypothesis.
The Spinatum regression collides with the worldwide Toarcian Oceanic Anoxic event. The oldest deposits of the sequence (Latest Pliensbachian-Lowermost Toarcian), partly of an age resting on a regional erosional surface, comprise alluvial and deltaic sediments assigned to a number of lithostratigraphic units of local significance. The sequence recovers significant sea-level falls, that are related with the recurrent Late Pliensbachian glaciation, that would be followed at the start of the Toarcian with Global warming and a large scale transgression, recovered locally on the Ciechocinek Formation.
Thanks to data from the Kaszewy 1 borehole levels of 1200 pCO2 were recovered, thanks to Plant stomatal index, being the highest amount recovered on the whole Lower Jurassic interval. The studied strata also led to know a great variability in Total Organic Content, interpreted as result of a greater terrestrial biodegradation. This led to knowing that the lower temperatures recovered from the Polish Basin in this interval occurred in the latest Rhaetian/earliest Hettangian, the late Hettangian, early Pliensbachian and especially in the Late Pliensbachian (Stokesi, Gibbosus, Spinatum), being this last the coolest period in the whole Early Jurassic.
Sedimentological evolution The Formation strata starts on the Polish Jurassic Depositional sequence V, that besides Drzewica area and Budki–Szydłowiec–Jagodne area, is also known from the Brody-Lubienia borehole (with a massive exposure of the sequence V in an operating quarry near Bielowice, the major one along with Skrzynno near Przysucha), that is located on the eastern part of the Świętokrzyskie Mountains region, giving insight into development of Pliensbachian deposits in the marginal parts of this basin. The initial part of this sequence is associated with a local fall of the sea level, where the lower IV level transition exposes with erosion, on locations such as the Zychorzyn borehole (at depth of 96.1 m) on Drzewica. The latter sedimentation is marked with thin deposits from delta-distributary depositional subsystem, that become thicker around the Budki, where in the zone of the Brody-Lubienia borehole an alluvial-meandering channel deposition system developed. After this initial regression there was a local transgression that led to abundance of local trace fossils and the formation of barrier-lagoonal deposits on Budki and in Brody-Lubienia, along with the increased presence of marine bivalves. In the Brody-Lubienia borehole were developed in embayment-lagoon facies. After the major marine transgression there was a visible change on Budki–Szydłowiec–Jagodne, shifting to fluvial discharge continuously moving along the Nowe Miasto–Iłża fault to the NE direction during the Pliensbachian times. At this time on the Jagodne 1 borehole it was deposited the development of a barrier-lagoon linked with a delta.
The Depositional sequence VI starts on the Jagodne 1 borehole with very large Mud clasts, pointing to intensive erosion of the underlying lagoonal sediments, while on the basin center, on the Zychorzyn borehole the erosion on lower sediments was lesser aggressive. The sediments that were deposited at the start of this sequence are uniformly represented by coarse alluvial deposits, interpreted as meandering river with possible conspicuous share of bed load transport. On the Budki 1 borehole series of coarse-grained alluvial package (especially large scale tabular cross-bedding sets dominate and quartz pebbles association), can represent low-sinuosity braided channels. Another transgressive phase on this sequence led to the formation of foreshore/shoreface/barrier deposits, and a local event on the Polish Basin, where there was a rapid drowning of the paleorelief with alluvial valleys and coastal plains, resulting in embayed coastline with detached beach andor barrier ridges. There was equilibrium with the sea level, with periodical little regressions and transgressions. The maximum flooding range of this phase is represented by the Szydłowiec sandstones, developed on a regressive period where on Śmiłów was developed an eolian dune depositional subsystem linked with a barrier-lagoon, know due to the presence of barrier crest eolian deposits with plants buried. In this environment, the major Tracksites of the formation were developed. Linked with the Śmiłów Quarry sandstone appear deltaic deposits on the Brody-Lubienia borehole and on Zychorzyn.
The Depositional sequence VII is the last Pliensbachian major sequence, know especially from the Brody-Lubienia borehole and the continuation of an alluvial portion exposed also at Śmiłów, where an exposure exhibits sequence VI/VII characters, showing that the sea level fall was not so significant, as it was in the base of the previous sequence. This sequence starts with a rise of sea level and quick drowning of the whole area, destroying the previous delta system/marsh subsystem development measured at the Brody-Lubienia borehole, that shows that the amplitude of this transgression was quite high, as is represented by a thickness of 16 m.