Seoca Lithiotis Limestone
The Seoca Lithiotis 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 know 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 an equivalent of the Calcare di Sogno of north Italy. It represents almost the same type of ecosystem recovered in the older Rotzo Formation of the Venetian region and the Podpeč Limestone of Slovenia, known also 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 paleogeography 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, that 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 in the Toarcian a partial flooding in some sectors and simultaneous emergence in others, with the carbonate facies recovered at S of Nikšić, NE 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.At 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 expanded were located at the NE-SE, 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, 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 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. The Liassic age 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 by bituminous limestones and marly limestones with several episodes of emersions, 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 in 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 on 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 were Pachypteris dominated, and drier vegetation within the island regions of "Maquis shrubland" type. The nearest emgerged 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 Rumija and Seoce lithiotis facies were made after the Livari supersequence created a massive lagoon in 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 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 reefs, together developed as a belt around the coast, yet is unknown how far 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 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
Mollusks
Accumulations of Nerineidae gastropods are common. Large, thick-walled gastropods common in the middle and upper parts of the section. High-spired lagoonal gastropods are found.| Genus | Species | Location | Material | Notes | Images |
Cochlearites' |
| Isolated & acummulated Shells | An oyster of the family Plicatostylidae. | ||
Gervilleioperna' |
| Isolated & acummulated Shells | An oyster of the family Plicatostylidae. | ||
Lithioperna' | L. kuehniL. scutataL. spp. |
| Isolated & acummulated Shells | An oyster of the family Plicatostylidae. | |
Lithiotis' |
| Isolated & acummulated Shells | An oyster of the family Plicatostylidae. | ||
| Manticula | M. problematica |
| Isolated Shells | An oyster of the family Pergamidiidae. | |
| Mytiloperna | M. lepsii |
| Isolated Shells | An oyster of the family Malleidae. | |
| Mytilus | M. spp. |
| Isolated Shells | A mussel of the family Mytilidae | |
| Pleurotomaria | P. sp.'' | Shells | A Snail of the family Pleurotomariidae. |
Echinodermata
Common crinoid ossicles and sea urchin fragments mark brief open-marine incursions into the lagoons.| Genus | Species | Location | Material | Notes | Images |
| Cotylederma | C. sp. | Tejani | Multiple ossicles | A Crinoidean, member of the family Cotyledermatidae | |
| Isocrinus | I. psilonotiI. spp. | Tejani | Multiple ossicles | A Crinoidean, member of the family Isocrininae | |
| Pentacrinites | P. cf. fossilis | Tejani | Sections | A Crinoidean, member of the family Pentacrinitidae |
"Algae"
Unspecified stromatolitic laminae is found in multiple levels.| Genus | Species | Location | Material | Notes | Images |
| Cayeuxia | C. liasicaC.? piaeC. spp. | Seoce | Imprints | A Green alga of the Halimedaceae or Udoteaceae family. | |
| Palaeodasycladus | P. mediterraneusP. spp. | Seoce | Imprints | A green alga of the family Dasycladaceae. | |
| Scrinocassis |
| Budoš | Cysts | Affinities with Scriniocassiaceae. Brackish Green Algae, related to lagoonar water bodies | |
| Thaumatoporella | T. parvovesiculifera | Seoce | Imprints | A encrusting green alga of the Thaumatoporellales group. The dominant alga locally |