Vol 50, No 12 (2016)

The Mongolian Precambrian and Cambrian event chronostratigraphic classification of sedimentary, sedimentary—volcanogenic, volcanogenic, and metamorphic rock sediments spread over the territory of Mongolia according to the new chronostratigraphic classification approved by the International Stratigraphic Commission is discussed. These ancient rock units are readily divided into two independent complexes. The lower complex (1000–3500 m) is represented by the Archean and Early Proterozoic crystalline basement and the upper complex is the latest Precambrian–Cambrian sediments (220–7500 m). A detailed study of abundant Neoproterozoic and Early Cambrian faunal (ichnofossils, hexactinellid sponges, archaeocyaths, trilobites, etc.) and floral (stromatolites, microphytolites, cyanobacterial mats, microfossils, etc.) fossils provides the first regional chronostratigraphic subdivision of different facies sediments. Every stage is characterized by distinctive geohistorical and biological events.

At present, in Mongolia crystalline complexes are reliably established in almost all major structural elements. The largest field of these complexes is recognized in the Early Caledonian structures of the North-Mongolian Folded Belt, in the Tarbagatai and Baidarik blocks. The crystalline complexes of the South Altai Belt have previously been interpreted as fragments of the Precambrian basement. Recent geochronological and isotope geochemical data have shown that pre-Riphean and Early Hercynian formations can be recognized in the Precambrian of Mongolia. These complexes show evidence of similar metamorphic processes, but are different in structural position and geological history. The paper contains new stratigraphic schemes for metamorphic complexes of the Baidarik and Tarbagatai blocks and also the South Altai Metamorphic Belt (SAMB).

Biotic associations are indispensable components in the development of all phosphoric deposits, including the Cambrian deposit in western Mongolia. The biota contributes to the enrichment of the rocks by phosphates in the following way: organisms absorb phosphorus from the water solution, store it in the cells, and after they die, phosphorus is returned to the water, where part of it participates in the mineralization of the mucous sheaths formed of bacteria, dead bacteria, and other organic matter. This cycle repeats until the mineralized phosphate compounds integrate with the sedimentary rocks.

Fossil brachiopods from the Ordovician, Silurian, Devonian, Carboniferous, and Permian deposits of Mongolia have been studied for the last forty-five years by the Joint Soviet-Mongolian (later RussianMongolian) Paleontological and Geological Expeditions. New data on the taxonomic composition, stratigraphic and geographic distribution of the brachiopod assemblages have been obtained. The brachiopod systematics has been further refined and detailed, and the stratigraphic and correlation scales and biogeographic reconstructions have been elaborated for the Paleozoic of Mongolia.

The scientific value of insect fossils is very high. The first remains of insects were discovered during the third Asian expedition of the American Museum of Natural History (1923) to the Anda-Khuduk locality. To date, 112 localities, from the Permian to Neogene, have been found in Mongolia, including the world’s largest lagerstätten Böön Tsagaan and Shar Teg. Most of them are Jurassic and Lower Cretaceous localities; Jurassic localities are significantly less numerous than Lower Cretaceous ones, which account for more than half of all known localities. Paleoentomological surveys have been performed with a varying intensity by the Joint Soviet–Mongolian Paleontological Expedition (JSMPE) and Joint Russian–Mongolian Paleontological Expedition (JRMPE) since 1970. A total of 17 expedition trips have been carried out. As a result, several tens of thousands of insect remains representing 29 orders, 299 families, 695 genera, and 870 species were obtained. However, the systematic position of many forms, especially homopetrans, coleopterans, and dipterans, has not been described or often even identified. More than 300 works have been published on the fossil insects of Mongolia, but less than half of the collected material has been described. Along with the paleontological collections, considerable attention was paid to paleoecological observations. To understand the history of water bodies, detailed studying and description of the structure of sediments and their stratigraphy have been performed. It has been revealed that ecosystems of ancient water bodies differed significantly from what could be restored based on Recent analogues. A new scheme of stratigraphic relationships between Jurassic and Cretaceous localities is provided. The analysis of paleogegraphic distribution of insect remains showed that localities of western Mongolia belong to a different paleozoogeographic division than the rest of its territory, which is biotically similar to Transbaikalia and China.

The “Fighting Dinosaurs” from Mongolia are discussed. The observable positions of two coupled dinosaur skeletons are explained based on their postmortem displacement.

A complete taxonomic review of Neogene birds of continental Asia is provided. To date, avifauna from the latter half of the Miocene and Pliocene of Central Asia (Mongolia and adjacent regions of Inner Asia) are most thoroughly investigated. Available data enable a reconstruction of successive replacement of Early and Middle Miocene avifaunas by communities of the Recent type. Middle Miocene avifaunas of Mongolia include a great number of extinct genera and species, many of which were widespread in Eurasia. Extant genera became dominant in the Late Miocene and taxa close to living species appear in the Late Pliocene fossil record. Late Pliocene communities of birds of Central Asia were complex in genesis, composed of Miocene relicts (Struthio), immigrants from the European regions of the Palearctic (phasianid Plioperdix), North American immigrants (Calcarius), and also autochthonous elements, the origin of which is apparently connected with the arid belt of Central Asia (diverse passerines).

Floras of Oshin-Boro-Udzyur-Ula, Tsagan-Ovoo, and Nariin-Sukhait of Mongolia are reviewed. Their composition suggests a Middle Jurassic age for these floras. They resemble the synchronous floras of the West Siberian Province of the Siberian Paleofloristic Region. The boundary between this province and North Chinese Province of the same region should be drawn further to the south than was previously thought. The Middle Jurassic floras of Mongolia existed in a warm temperate, humid climate.

An assemblage of charophyte algae from the Upper Oligocene Beger Formation in the Shine Us locality (Mongolia) is characterized and a new species, Charites badamica, is described.