The Zagaje Formation is a Latest Triassic-Early Jurassic Epoch (Rhaetian-Sinemurian) geologic formation located mostly in Poland with layers also exposed in north Germany. This unit is known for its diverse Ichnofossil assemblages, with traces of invertebrates along vertebrate footprints, as well plants, large coal accumulations, invertebrate remains and ichnofossils. The Zagaje Formation correlates with The lower part of the Höganäs Formation in Scania, as well the Munkerup Member and the Gassum Formation in Denmark.

Paleoenvironment

The Zagaje Formation is particularly visible in the Sołtyków region and is made mostly of Early Jurassic continental mudstone-sandstone deposits linked to the onset of "depositional sequence I". Its age is confirmed as mostly Early Hettangian through stratigraphic and paleontological analyses, including fossil flora and conchostraca findings. Sedimentological studies divide the Sołtyków profile into three parts: ephemeral reservoir deposits, floodplain and lacustrine sediments, and river channel deposits, highlighting dynamic depositional environments influenced by tectonic subsidence and varying hydrological conditions. Climate wise, the area was located back in the Hettangian around 45°N paleolatitude in Laurasia within a rise of 5–10°C above present, were it experienced significant climatic and environmental change related with sea-level fluctuations, manifested locally with a notorious retrogradational fluvial-lacustrine sedimentation, with evidence of a humid climate interspersed with drier seasons. Some plant fossils like Hirmeriella mark points of aridity on what was mostly a humid swampy alluvial-lacustrine habitat. The Zagaje Formation’s deposits are know from both outcrops and borehole profiles that consist primarily of sandstones, mudstones, and interspersed coal and siderite layers. It represents a stratigraphic gap with the underlying Upper Triassic formations and is capped by a transgressive contact with the Skłoby Formation. This unit contains freshwater fauna and diverse trace fossils, including vertebrate tracks. The paleoenvironment reflects a dynamic alluvial plain shaped predominantly by high-sinuosity stream processes, transitioning from earlier braided and low-sinuosity stream systems. This evolution is attributed to climatic changes, rising base levels, and decreasing geomorphological gradients. Observations, both from exposures and borehole data, highlight the dominance of avulsion processes, with several depositional subsystems identified. Facies with organic remains are diverse: riverbed biofacies, derived from meandering channels characterized by fining-upward sequences composed of channel lag deposits, point-bar sands, and finer overlying sediments. These deposits exhibit lateral accretion bedding and significant fossil bivalves and large-sized floated plant remains (stems and trunks of large plants) consistent with subaqueous dune migration within the channels; levee deposits derived from successive floods with scarce root traces, while plant remnants are common; Paleosoils with sparse traces of plant roots and remains of floating plants of highly variable size (mainly organic detritus, but also fragments of wood), fragments of bivalve shells and vertebrate remains (amniote bones, tracks, fish scales); the biofacies of the ephemeral water reservoir with plant remains, mainly horsetails, and fossils of insects, ostracods, and conchostraca; The pedogenic soil biofacies with remains of plant roots with preserved organic matter and rhizomes and stems in a living position; Floodplain biofacies with traces of numerous plant roots and plant macroremains, and remains of sedge stems preserved in a living position; Lake-marsh biofacies, dark, laminated mudstones with plant roots and coal, with few fossil bivalves, a large amount of organic matter in the form of plant detritus, and layers of coal and numerous finds of miospores and megaspores. The local presence of charcoal fragments and high concentrations of PAHs, along with possible burnt plants, provides evidence for wildfires in the region, that likely occurred near the surface with charred wood fragments were subsequently incorporated into sediments by river transport. The high presence of coprolites has allow also to stablish the tropic chain of the local biota, with a clear full ecosystemical substitution of the older Triassic archosaurs by Dinosaurs.

Biota

Indet. Invertebrates

Several unname Ichnofossils are recovered at Soltyków, including conical domichnia (Conichnus?), bivalve straight to winding linear trails, smooth vertical and subvertical branching tunnels, knob-walled tunnels, mace-shaped or irregular ellipsoid chambers, etc.

Molluscs

Indeterminate gastropod egg capsules are know, similar to the ones recovered in the extant Neritina. 4 unnamed morphotypes of freshwater bivalves of the family Unionidae are know.

Crustacea

Insects

Radial chambers around large tunnels have been recovered, they may be arthropod burrows or traces of roots. Large nest structures with septa, similar to nesting behaviour of insects like Cicadas are know.

Fish

Unidentified Actinopterygian fish scales and teeth were collected from clayish, organic-rich lake deposits, while some coprolites have been referred to Hybodontiform sharks.

Testudinata

Synapsids

Rhynchocephalia

Crocodrylomorphs

Pterosauria

Theropods

Some elliptical "post-egg" structures egshells & eggs with embryo remains have been referred to theropods, yet may also belong to Ornithischians.

Sauropodomorpha

Ornithischia

Plants

In Palynology, the Zagaje Formation belongs to the Nathorstisporites hopliticus assemblage (Isoetales), indicating a spike in marshland and lacustrine settings. The Sołtyków outcrop is dominated by Classopollis (Cheirolepidiaceae), Aratrisporites (Cycadidae), Concavisporites (Dipteridaceae) and Cyathidites (Cyatheaceae).