Abstract
This paper concerns deals with biogeologic accumulation and their peculiarities, lithological unites of the phosphorite-bearing formations of these basins and an evolution of the old biota. Old bedded phosphorites are believed to be connected with specific biogeological events happening in the Neoproterozoic glaciation, which was followed by rapid deglaciation, Ediacaran bioradiation and the “great” postglacial transgression bearing phosphorites at its initial phase. The Mongolian phosphate basins give evidence of this phenomenon. Khubsugul basin is located in the northern Mongolia. The Neoproterozoic-Cambrian phosphorite-bearing khubsugul group is subdivided into 3 formations as ongolik, kheseen and erkhelnuur which are rich in organic fossils (a group of cyanobacterial mats, archaeocyaths, trilobites) in the ascending order. The Zavkhan basin lies in the western Mongolia. The Ediacaran-lower Cambrian sediments are divided into five formations: Maikhanuul (diamictites), Tsagaanolom (phosphorite-bearing carbonate), Bayangol, Salaanygol and Khairkhan. All the formations contain the paleontological fossils (algae, sponges, cyanobacterial mats, ichnocoenosis, soft-bodied fauna, archaeocyaths, etc.). Bedded phosphorites are the object for comprehensive research of bacterial paleontology. It is shown at example of the Mongolian Khubsugul and Zavkhan sea shelf phosphate basins. The expounded actual material clearly shows that the heterogeneous biologic activity, suitable geologic (transgressive systems tracts) and paleogeographic (glaciations, warm climate, etc.) conditions played an important role in the formation and accumulation of the biogenic bedded phosphorites.
Highlights
During the late Precambrian-Early Cambrian period important increases took place in the oxygen concentration of the atmosphere and hydrosphere, the unicellular eucaryotes, procaryotes diversified, stromatolites, microphytolites, and metazoa more appeared
Phosphorite genesis correlates with elevated sea-level resulting from transgression, allowing deposition on shallow shelves, and with warm climate which may be related to an increased phosphorus flux to the oceans during times of increased chemical weathering on land, and to the development of widespread oxygen-depleted waters because rates of oceanic circulation and oxygen solubility are reduced [2]
Khubsugul Phosphate Basin The Khubsugul phosphate basin is located on the Tuva-Mongolian microcontinent, which was carbonate platform in the Ediacaran-Cambrian period (Figure 1)
Summary
During the late Precambrian-Early Cambrian period important increases took place in the oxygen concentration of the atmosphere and hydrosphere, the unicellular eucaryotes, procaryotes diversified, stromatolites, microphytolites, and metazoa more appeared. Dorjnamjaa et al [6], the radiation comprised five episodes or stages of development: 1) Prevendian (Pretonian)-unicellular procaryotes and eucaryotes; 2) Mid-late Vendian (TonianGryogenian) fauna, early trace fossils, and acritarchs; 3) Nemakit-Daldynian (late Vendian or Ediacaran)-phosphatic small shelly fossils, many shallow-water trace fossils, and calcified cyanobacteria; 4) Tommotian (basal Cambrian)-calcareous small shelly fossils with the first archaeocyathans, molluscus and medusoid; 5) Atdabanian-abundant archaeocyathans with trilobites, brachiopods, echinoderms and deeper water trace fossils All these episodes took place at a time when a supercontinent was breaking up, leading to the formation of the Iapetus ocean. Phosphorite sediments in the Khubsugul and Zavkhan bassins are realizable fact for an explanation of this phenomenon
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