A detailed sedimentological features of the Slatinski plaz section with a transition from the deep-water Anisian (Illyrian) Strelovec Formation to the Ladinian shallow-water Contrin Formation have been presented. The Strelovec Formation is divided into five different lithostratigraphic units that are characterised by dark hemipelagic and pelagic thin-bedded limestones and dolomitic mudstones that are frequently intercalated with deposits of gravitymass flows, slump and slide to fine-grained low-density turbidity origin. The Strelovec Formation was deposited in a hydrodynamically quiet, pelagic deeper-water anoxic environment, most probably on a gentle platform slope. In the upper part of the formation, the presence of olistolith blocks of shallow-water limestones indicates the closing of the prograding shallow-water platform wedge. Massive dolostones of Unit 6 mark the complete filling of the basin and the beginning of the shallow-water sedimentation of the Contrin Formation in the Early Ladinian. Izvle~ekV članku predstavljamo detajlni sedimentološki profil Slatinski plaz, v katerem lahko opazujemo prehod iz anizijske (ilirske) globljevodne Strelovške formacije v ladinijsko plitvomorsko Contrinsko formacijo. Strelovško formacijo smo razdelili na pet litostratigrafskih enot, za katere je značilno menjavanje temnih hemipelagičnih tankoplastnatih apnencev in dolomitov (mudstone), med katerimi so pogosti sedimenti gravitacijskih tokov (od zdrsov do zdrobnozrnatih turbiditov). Strelovška formacija se je odlagala v hidrodinamsko mirnem, pelagičnem, globljevodnem anoksičnem okolju, najverjetneje na blagem pobočju. V zgornjem delu formacije se pojavijo olistolitni bloki plitvovodnih apnencev, ki nakazujejo približevanje progradacijskega klina napredujoče platforme. Šesta litostratigrafska enota vsebuje plivovodne kamnine zgodnjeladinijske Contrinske formacije, ki kažejo, da se je globljevodni bazen v tem času že popolnoma zasul. GEOLOGIJA 59/1, 23-34, Ljubljana 2016 http://dx
Horseshoe crabs are an archetypal chelicerate group with a fossil record extending back to Early Ordovician time. Although extensively studied, the group generally has a low diversity across the Phanerozoic Eonothem. Here, we expand the known diversity of true horseshoe crabs (Xiphosurida) by the description of a new taxon from the Middle Triassic Strelovec Formation of the Slovenian Alps. The mostly complete fossil is preserved as an external mould and assigned to the family Limulidae Zittel, 1881 as Sloveniolimulus rudkini, n. gen., n. sp. The use of landmark and semilandmark geometric morphometrics is explored to corroborate the systematic palaeontology and suggests that the new genus and species are valid. We also provide the first quantitative evidence for the extensive diversity of Triassic horseshoe crabs. We suggest that Triassic horseshoe crabs likely filled many ecological niches left vacant after the end-Permian extinction.
The Raduha section represents a continuation of the research of the Anisian Strelovec Formation in the Kamnik-Savinja Alps. The Strelovec Formation was deposited during the Anisian on a drowned section of the Serla Dolomite carbonate platform in a restricted probably outer ramp environment associated with an intraplatform basin. The base of the section is represented by dolostone breccia containing angular carbonate lithoclasts of shallow-marine origin. This is followed by alternations of laminated and homogenous hemipelagic limestones deposited in a restricted and anoxic environment. Hemipelagic sedimentation was occasionally interrupted by clay input and deposition of sediments from gravity mass flows. Slow filling of the basin lead to a gradual cessation of anoxic conditions and sedimentation of bedded shallow-marine limestones. After shallow water conditions were established, bioclastic dolostone of the Contrin Formation was deposited.
Xiphosura are a group of marine euchelicerates with a fossil record spanning the majority of the Phanerozoic. Despite this longevity, horseshoe crab fossils are uncommon. This rarity is a result of their cuticular exoskeleton that limits the preservational potential of xiphosurid specimens. Nonetheless, a xiphosurid evolutionary radiation is recorded in Triassic-aged deposits. This event likely reflects the occupation of vacant niches after the end-Permian extinction. Here, we revisit Sloveniolimulus rudkini Bicknell et al., 2019b-a Middle Triassic horseshoe crab from the Strelovec Formation that was previously known from one specimen-and include newly identified material to explore the validity of the taxon. We demonstrate that unique genal spine morphologies are observed in all specimens, supporting the maintenance of S. rudkini. In documenting this material, we also considered the preservational pathways for horseshoe crabs in limestone and document other metazoan groups from this as-of-yet underexplored Konservat-Lagerstätte.
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