Trilobites are Paleozoic fossil animals that appeared in the Cambrian period and died out in the Permian period. They lived in sea waters of normal salinity, leading a mobile nektonic or planktonic mode of life. The shell of trilobites consisted of individual plates connected by soft tissues. After the animal’s death, it disassembled easily.
Because of that, trilobite remains can be found in any normal marine sediments of Paleozoic age. However, whole shells are found only in rocks formed in calm conditions with no bottom currents. While shell fragments are found in coarse-grained sandstone and even in conglomerates, complete specimens can be found only in clay, clay shale, layered siltstone, and marl, marlstone, and, less often, in massive limestone and dolomites.
The best-preserved trilobites are found only in rocks that haven’t undergone significant post-diagenetic changes. Tectonic movements cause deformation of shells — hydrothermal processes often lead to the dissolution of trilobite skeletons and its replacement by shapeless masses such as calcite aggregates, as well as iron or manganese oxides. At the same time, superimposed silicification processes can lead to the replacement of the shell with silicon or chalcedony. In that case, the skeleton remains perfectly preserved in every tiny detail. In short, if you want to collect some good-quality trilobites, consider starting your search in areas where the Paleozoic strata were not exposed to any noticeable tectonic cataclysms. Two such areas are best known in Russia: the East European Craton and the Siberian Craton.
The Cambrian trilobites are mainly found in two regions of Russia: the Altai-Sayan region and the Siberian Craton. Regarding the Altai-Sayan region, the popular location on the Orlinaya Gora near the village of Guryevsk, on the north-eastern spurs of the Salair Ridge, is worth mentioning. Here, in the thick greenish shale and siltstone, numerous trilobites can be found, although those are usually not very well preserved. Regarding the Siberian Craton, the Cambrian trilobites are known to be found in many places, with the Lena River basin being the most popular location. One of the best spots is in the Lena Pillars area. Here, trilobites, although mostly small in size, are often found whole. Their dark shells are easy to spot on top of light sheered limestone and dolomites.
Ordovician trilobites are remarkable for their diversity and distribution. They can be found in almost all areas where the Ordovician strata come to the surface. In Russia, such areas include northwest and north of the East European Craton, the Urals from the southern foothills to the Arctic regions, Pay-Khoy Ridge, the Arctic islands, the south of Western Siberia (Altai, Salair, Sayany), Central Siberia (mainly the basins of the Lena and Podkamennaya Tunguska rivers), Arctic Siberia (Taymyr, Norilsk region, and the islands), Southern Siberia (Tuva, Transbaikal), Eastern Siberia (the basins of the Indigirka and Kolyma rivers, the coast of the Sea of Okhotsk, Chukotka). Several hundred locations are known across this region, with about 2,500 trilobite species occurring there. Of course, good specimens are hard to come by.
Of the several hundred known locations where Ordovician trilobites are found, three should be mentioned. First of all, Leningrad Oblast located in the northwest of the East European Craton. Here, along the Ladoga Glint, there are numerous outcrops, trial pits, and quarries, in which horizontally bedded limestone, marl, and clay of Ordovician age are uncovered. In some horizons of this stratum, along with numerous fragmentary remains, whole trilobite shells are often found, some reaching 30 cm in length. Trilobites found in the vicinity of St. Petersburg are remarkable for their diversity (more than 250 species are described), excellent conservation of shells, and endemism of species. Many trilobites from Leningrad Oblast are found only in Baltoskandia and are not known outside this region. It should be added that the Ordovician fauna of the St. Petersburg Province has been described since the beginning of the 19th century, and the trilobites became particularly well-known following the works published by the Russian geologist F. B. Schmidt in 1858–1907.
Another popular location where Ordovician trilobites are common is located near the village of Bugryshikha on the left bank of the Belaya River in Altai Krai. Numerous trilobites can be found here, in the thick of intertwined dark grey shale and siltstone with limestone lenses. Unfortunately, the shells found in these locations usually have poor quality, and whole specimens are extremely rare.
The Siberian Craton is home to hundreds of locations of Ordovician trilobites. They are located mainly in the basins of the rivers Khantaika (northwest of Central Siberia), Tunguska (west of Central Siberia), and Lena (east of Central Siberia). On both banks of the Lena river, near the villages of Volgino, Yelovka, Zmeinovo, Krivolutskoye, Kudrino, Povoroty, etc. Ordovician deposits are represented by green and red siltstone, argillite, and marl with beds of limestone. Trilobite remains are found in individual bands of this stratum, sometimes numerous. By the way, the location in the vicinity of the village Krivolutskoye was discovered in the middle of the 19th century.
The Silurian trilobites are common in roughly the same areas as the Ordovician trilobites but are much rarer. They are known to be foundin the Urals, Pay-Hoy, on the island of Vaigach, in the Altai-Sayan region, on the Taimyr peninsula, and across the Siberian Craton. Here we will mention only some of the locations in the Urals. In the republic of Bashkortostan, trilobites from the Silurian sequence of limestone and shale, found in the basins of the Kaga and Belaya rivers, are described. Trilobites were also found, sometimes numerous, in the thick of pink or yellowish limestone in the basins of the Istok and Kedrovaya rivers (Middle Urals). It should be noted, however, that Silurian trilobites from the Urals are usually not well preserved, and whole specimens are extremely rare there.
Devonian trilobites are mainly found in the Urals, less commonly in the Altai-Sayan region and Central Siberia. Information about the Altai and Siberian specimens is fragmentary, so let’s dwell on the much more well-known locations in the Urals. In the east of Southern Urals, in the basins of the rivers Ay, Sim, and Ural, Devonian limestone sequences contain rich and various fauna, including trilobites. There are locations in the west of the Southern Urals, in Bashkortostan, in the basins of the rivers Bolshoi Ik, Inzer, Zigan, Ryauzyak, and Sikasya, where organogenic limestones are known to contain numerous corals, brachiopods, ammonoids, as well as trilobites. Trilobites were also found in the Middle Urals, in the basin of Vishera river, in rocky coastal outcrops and pits. It should be kept in mind that trilobites occur sporadically rather than regularly in the locations mentioned above, although in some cases they can form clusters. It seems that persistent research into Devonian trilobites of the Urals can offer wonderful discoveries.
Carboniferous trilobites are common in many locations but are quite rare. Those are also usually small in size, so they’re easy to miss when taking a quick look at the outcrops. Carboniferous trilobites have long been found in two regions: in the European part of Russia (the East European Craton) and in the Urals. Trilobites are also found in limestone quarries and pits near the Moscow, Tula, and Kaluga Oblasts, along with the rich fauna of brachiopods, and crinoids. The specimens from these areas have been described since the early 19th century. Trilobites also occur in the Novgorod Oblast, in outcrops of light limestone on the rivers Okhomlya and Msta, sometimes forming clusters. Similar findings are known to be found around the Don river in the Volgograd Oblast.
In the Urals, сarboniferous trilobites have been found in dozens of locations, but even there they are not common, although they can sometimes form clusters. On the Ural river, in the Chelyabinsk Oblast, for example, there are frequent exposures of light limestone, where nests with rich fauna are marked, including those containing trilobites. Clusters of trilobites were also found in limestone quarries of the Orsk plant in the Orenburg Oblast. The same situation occurs in Bashkortostan, in the outcrops of light reefogenic and biogenic limestone on the rivers Ai, Zilim, Tastuba, Yuryuzan, Ural, etc. To the north, across the Middle Urals (Perm Oblast), coal trilobites from limestone and argillite in the basins of the rivers Irgina, Kolva, Kosva, Kyn, and Yaiva, as well as from numerous quarries, are described.
Trilobites of Permian age are extremely rare. Authentic findings are known only in the Middle Urals. Trilobites were also found in the outcrops and quarries of light reef limestone along the Ufa river (Sverdlovsk Oblast) and the Syva river (Perm Krai), along with the rich fauna of brachiopods, corals, crinoids, and gastropods. Like coal trilobites, they are very small in size and can easily be missed when gathering fossil fauna.
