The Seoca Lithiotis Limestone ("Budoš Mountain Limestone", also known simply as High Karst Bioclastic limestone) is a geological formation in Montenegro and possibly Albania that dates to 185-183 million years ago, covering the Pliensbachian-Toarcian stage of the Jurassic Period. It is located within the high karst zone and represents a unique terrestrial setting with abundant plant material, one of the few known from the Toarcian of Europe. It is the regional equivalent to the Toarcian-Aalenian units of Spain such as the Turmiel Formation and the El Pedregal Formation, the Sinemurian Coimbra Formation in Portugal, units like the Aganane Formation or the Tafraout Group of Morocco and others from the Mediterranean such as the Posidonia Beds of Greece and the Marne di Monte Serrone of Italy. In the Adriatic section, this unit is equivalent to the Calcare di Sogno of Northern Italy. It represents almost the same type of ecosystem recovered in the older (Pliensbachian) Rotzo Formation of the Venetian region and the Podpeč Limestone of Slovenia, also known for its rich floral record.
Regional Context In Montenegro, Lower Jurassic carbonate deposits are seen intermittently along the Adriatic Carbonate Platform extending from Herzegovina into the region and reaching northern Albania. The Toarcian palaeogeography of Montenegro was characterised by two major units, mostly found in the Dinarides: the High Karst Zone, representing the Carbonate Platform, and the Budva Basin, which represented a shallow marine setting where ammonites are abundant, separated at the W of the Apulian Carbonate Platform by the "deep-water Adriatic Basin". The previous Pliensbachian platform suffered partial flooding in some sectors and simultaneous emergence in others during the Toarcian, with the carbonate facies recovered at S of Nikšić, northeast of Podgorica and in the Rumija Mt remaining as environments close to the marginal part. These layers, generally overlaid by younger sediments, exhibit oolitic limestone characteristics, with late-diagenetic dolomite intercalations indicative of formation near the platform's margin. Key exposures appear west of Nikšić, northeast of Podgorica, and within the Rumija Mountain range.
During the Pliensbachian, most of the area was dominated by the "Lithiotis Facies" from Tolmin to Podgorica, with no proper emergent lands nearby, In the Toarcian, the nearest emergent lands were located to the northeast–southeast, from the west of Zagreb to Prozor, while the sectors at Montenegro and Albania were located in between ooid grainstone levels, representing a proximal carbonate ramp. The Budva basin evolution in the Toarcian was marked by the changes in the sea level, developing a distally steepened ramp until the Lower Toarcian, and an accretionary rimmed platform in younger layers. The Adriatic-Dinaric Carbonate Platform is well measured at the Mount Rumija where the transitional facies between the platform setting and the deeper pelagic environment is seen, recovering a lateral transition from a lagoonal environment exposed in Seoce to the platform edge, exposed in Tejani (called Tejani section), and finally the deeper water environment, called Livari section can be observed at the own Mount Rumija.
Description The formation is ~450 m thick and comprises well-bedded light brown to light grey limestones organized into meter-scale shoaling-upward cycles. Typical microfacies include lumachelle beds of Plicatostylidae, bioclastic packstone/wackestone, oncoid–peloid grainstone, and fenestral pelmicrites. Fenestral textures, vadose features (mouldic/corrosion voids with meteoric cements) and intermittent nodular horizons occur toward the top of cycles. Deposition took place in intratidal to supratidal lagoons along the platform interior; the uppermost part records opening toward deeper settings that were rapidly blanketed by Aalenian oolites. The base lies on Late Triassic Lofer Limestones without angular discordance; the top transitions sharply to Aalenian oolitic sands (Oolites of Mt. Rumija II). The Liassic age (likely Pliensbachian–early Toarcian) is constrained by the Plicatostylidae facies, Foraminifera content and upward passage into Middle Jurassic oolitic units documented on Rumija. The main unit at Budoš is lithologically almost identical to the major fossiliferous levels of the Rotzo Formation, composed of bituminous limestones and marly limestones (fenestrate limestones and tempestites) with several episodes of emersion, all of coastal origin and rich in plant detritus and leaf remains, connected to the typical Lithiotis reefs found in the Pliensbachian–Toarcian carbonate platforms of the Adriatic region.
The unit is mostly known by its rich macroflora, the most complete of the Mediterranean Toarcian realm along with the Marne di Monte Serrone, with several characteristics, such as the abundant presence of thermophilic Bennettitales and the dominance of the Seed Fern Pachypteris, that grew in semi-arid climates. This particular province is characterized by fossil plants that belonged to the specific vegetation of intra-oceanic islands with the dominance of "mangrove"-type swamps where ''Pachypteris'' dominated, and drier vegetation within the island regions of "Maquis shrubland" type (probably a number of species of the genera Brachyphyllum and Pagiophylum). The nearest emerged areas were present in the terrains of Sinjavina and Durmitor, marked by a paleorelief of Jurassic Bauxite-abundant deposits within karstified limestones and rare dolomites.
Paleoenvironment
Facies architecture and fossil content indicate a low-energy, protected lagoon on the inner to middle ramp, with repeated shoaling-upward parasequences from Plicatostylidae-rich subtidal packstones to fenestral supratidal mud-rich beds. Local hardgrounds, vadose cements and rare breccias record brief emersion events before progradation of oolitic shoals during the Middle Jurassic. Local Budos flora developed on an island setting in the Dinaric Carbonate Platform, likely linked with the exposed layers of Seoce. This setting would be made of the emerged Budoshi High, representing an island flora; a humid belt would have existed along the shore, while coniferous vegetation would have prevailed in the drier interior. The Budoš flora, as well as the Rumija and Seoce ''Lithiotis'' facies, developed after the Livari supersequence created a massive lagoon on the inner ramp. A common facies in the 3 locations shows about 1–2 m thick lagoon parasequences, from lithiotis rich subtidal packstone to shallower wackestone, where the lagoonal shale facies recovering the flora is deposited.
The main consensus is that the layers rich in flora belong to a Bahamian-type Mangrove system developed on a coastal setting with a nearby Macchia arid inland setting dominated by Hirmeriellaceae and Araucariaceae conifers, as well as Bennettites, that was either an island inside a Carbonate platform or part of a larger landmass. The mangrove system was mostly composed of seed ferns bearing the leaf genus Pachypteris linked with complex root systems that cover most of the layers, developed over and linked with the local aberrant bivalve (Lithiotis) reefs, developed together as a belt around the coast, yet it is unknown how far it reached. The inland setting was dry and with common wildfire activity, as proven by the great amount of charcoal recovered in some of the layers. The Lithiotis layers are intercalated by oolitic and oncolitic layers of likely subtidal/lagoonal origin, with several coastal cycles measured, such as development of lagoons and complete flooding of the vegetation levels, as well small coal-dominated sections. The ingression-regression trend allowed the development of the local mangroves.
The same type of ecosystem was also recovered more recently on slightly older (Late Pliensbachian) rocks on Albania that may belong to the same unit, with also great dominance of the genus Pachypteris linked with root systems along Lithiotis reefs, with evidence of catastrophic events which "killed" the flora. These types of layers have been vinculated with the early evolution of crabs.
Fossil content
Foraminifera GenusSpeciesLocationMaterialNotesImagesGlomospira G. sp.SeoceIsolated Tests/ShellsAmmodiscidaeInvolutina I. jurassicaSeoceIsolated Tests/ShellsTrocholinidaeOrbitopsella O. praecursor Seoce Isolated Tests/ShellsMesoendothyridaePseudocyclammina P. liasica P. spp.SeoceIsolated Tests/ShellsPfenderinidaeSpirilina S. spp.SeoceIsolated Tests/ShellsSpirillinidaeVidalina V. martanaSeoceIsolated Tests/ShellsCornuspiridae
Brachiopoda GenusSpeciesLocationMaterialNotesImagesCuneirhynchia C. dalmasi Livari, Rumija Isolated ShellsA Rhynchonellidan brachiopoda, member of PrionorhynchiidaeLivarirhynchia L. rajkae Livari, Rumija Isolated ShellsA Rhynchonellidan brachiopoda, member of AllorhynchidaeHomoeorhynchia H. lubrica Livari, Rumija Isolated ShellsA Rhynchonellidan brachiopoda, member of RhynchonellidaePrionorhynchia P. fraasi Livari, Rumija Isolated ShellsA Rhynchonellidan brachiopoda, member of PrionorhynchiidaeRhapidothyris R. sp. Livari, Rumija Isolated ShellsA Terebratulidan brachiopoda, member of LobothyrididaeSepkoskirhynchia S. sphaerica Livari, Rumija Isolated ShellsA Rhynchonellidan brachiopoda, member of BasiliolidaeSkadarirhynchia S. semicostata Livari, Rumija Isolated ShellsA Rhynchonellidan brachiopoda, member of Basiliolidae
Mollusks Accumulations of Nerineidae gastropods are common. Large, thick-walled gastropods are common in the middle and upper parts of the section. High-spired lagoonal gastropods (non-marine tolerant taxa) are found.
Genus Species Location Material Notes ImagesCochlearitesC. loppianusBudos Mountain Livari, Rumija Seoce Tejani Isolated & acummulated ShellsAn oyster of the family Plicatostylidae.GervilleiopernaG. ombonii G. sp.Budos Mountain Livari, Rumija SeoceIsolated & acummulated ShellsAn oyster of the family Plicatostylidae.Lithioperna L. (Lithiopedalion) kuehni L. scutata L. spp.Budos Mountain Livari, Rumija Seoce Tejani Isolated & acummulated ShellsAn oyster of the family Plicatostylidae.LithiotisL. problematica L. sp.Budos Mountain Livari, Rumija SeoceIsolated & acummulated ShellsAn oyster of the family Plicatostylidae.Manticula M. problematica Budos MountainIsolated ShellsAn oyster of the family Pergamidiidae.Mytiloperna M. lepsiiBudos Mountain Livari, Rumija SeoceIsolated ShellsAn oyster of the family Malleidae. Mytilus M. spp.Budos Mountain Livari, Rumija SeoceIsolated ShellsA mussel of the family MytilidaePleurotomaria P. sp.Budos Mountain Livari, Rumija SeoceShellsA Snail of the family Pleurotomariidae.
Echinodermata Common crinoid ossicles and sea urchin fragments mark brief open-marine incursions into the lagoons. GenusSpeciesLocationMaterialNotesImagesCotylederma C. sp.Tejani Multiple ossiclesA Crinoidean, member of the family Cotyledermatidae Isocrinus I. psilonoti I. spp.Tejani Multiple ossiclesA Crinoidean, member of the family IsocrininaePentacrinites P. cf. fossilisTejani SectionsA Crinoidean, member of the family Pentacrinitidae
"Algae" Unspecified stromatolitic laminae (Cyanophyceae?) is found in multiple levels. Genus Species Location Material Notes ImagesCayeuxia C. liasica C.? piae C. spp.SeoceImprintsA Green alga of the Halimedaceae or Udoteaceae family.Palaeodasycladus P. mediterraneus P. spp.SeoceImprintsA green alga of the family Dasycladaceae.ScrinocassisS. sp.BudošCystsAffinities with Scriniocassiaceae. Brackish Green Algae, related to lagoonar water bodiesThaumatoporella T. parvovesiculiferaSeoceImprintsA encrusting green alga of the Thaumatoporellales group. The dominant alga locally
Bryophyta Genus Species Location Material Notes ImagesPorcellisporaP. longdonensisBudošSporesIncertae sedis; affinities with Bryophyta.
Lycophytes