Ammonoid Succession of Setorym River （Verkhoyansk Area） and Problem of Permian—Triassic Boundary in Boreal Realm

The presence of a single Otoceras species (O.boreale), morphologically very variable, at the base of the Nekuchan Formation in Verkhoyansk, we believe, is to be obvious. Some morphological evidence leaves no doubt that two described morphs of O. boreale are s strictly corresponding sexual dimorphic pair. It is very likely that Kummel‘s idea that Canadian. O. concavum Tozer is an invalid species is truthful, considering the range of variability seen in larger Siberian and Himalayan Otoceras fauna. Just above the upper Tatarian Imtachan Formation, the six stages of ammonoid succession can be recognized within the lower part of the Nekuchan Formation in the Setorym River Section:(a) Otoceras boreale;(b) Otoceras boreale-Tompophiceras pascoei; (c) Otoceras boreale-Tompophiceras pascoei-Aldanoceras;(d)Tompophiceras pascoei-Otoceras boreale-Aldanoceras;(e) Tompophiceras morpheous-T.pascoei-Aldanoceras;(f) Tompophiceras more pheous-T.pascoei-Wordieoceras domokhotovi-Ophiceras transitorium;(g)Tompophiceras morpheous-T.pascoei, corresponding to the Otoceras boreale and Tompophiceras morpheous zones. In spite of the domination of Otocerataceae or Xenodiscaceae in both oif these zones and the presence of some Permian type conodonts in the lower part of the Otoceras boreale Zone, they seem to be early Induan in age on the basis of the following arguments:(1) in contrast to the underlying regressive type sediments of the Upper Tatarian Imtachan Formation, both the Otoceras boreale and the Tompophiceras morpheous zones of the lowermost part of the Nekuchan Formation correspond to the single transgressive cycle;(2)typical early Induan ammonoids (Ophiceras and Wordieoceras) have been recognized in the Tompophiceras morpheous zone; (3) all described ammonoid succession stages (a-g) are characterized by very gradual changes and therefore correspond to the different parts of the single zone or to the different zones of the same stage, but not to the different systems (Permian and Triassic);(4)elsewhere in the Boreal realm (Arctic Canada), the conodont index species for the base of the Triassic, Hindeodus parvus, has been reported from the Otoceras boreale Zone. A new scheme of the phylogeny for the Otocerataceae and its Induan-Olenekian offspring (Araxceratidae-Otoceratidae-Vavilovitidae n.fam.-Proptychitidae-Arctoceratidae) and Xenodiscaceae is offered.     

The Middle and Upper Devonian in southeastern flank of the Siberian platform (Southern Verkhoyansk Region,Sette-Daban Mountain Range)

Data on Middle and Upper Devonian deposits studied in southeastern flank of the Siberian platform are considered. A scheme of stratigraphic zoning in the study region is presented. Nineteen sedimentological and biotic events, which are recorded in the studied sections, are of the regional, interregional and global ranks. Their connection with eustatic sea-level fluctuations is established. Sections of the formation and regional horizon stratotypes and parastratotypes are described. The revision of species Mucrospirifer novosibiricus (Toll) is carried out.     

The Zaderzhninskoe gold deposit: Mineral composition,fluid inclusions,and age (South Verkhoyansk region)

Based on results of study of the regional position, chemical composition of ores, fluid inclusions, and age relationships between mineralization and igneous rocks, we propose a geological and genetic model for the formation of gold mineralization of the Zaderzhninskoe deposit. Mineralization is located in the tectonic node of the intersection of two regional structures in the supraintrusive zone of a latent granitoid pluton among the terrigenous rocks of the Verkhoyansk complex, which are regionally metamorphosed to the greenschist facies. The sequential deposition of three types of mineralization—Au-quartz (including early low-gold Au-As and late productive Au-Pb-Zn mineralization), Au-rare-metal, and Au-silver—has been established. The Au-Bi (Te) assemblage contains native bismuth, bismuthinite, hedleyite, Bi sulfotellurides, gustavite group minerals, and secondary minerals—Bi oxides and Bi tellurites with low-grade gold. Hg-containing electrum and kustelite, Ag-Sb and Ag-Pb-Sb sulfosalts, stutzite, Te-Pb-containing canfieldite, freibergite, and Au and Ag sulfides are indicator minerals of the Au-Ag (Sb) assemblage. Ore formation occurred at temperatures from 90 to 340 °C, with the participation of lowly and moderately concentrated solutions with CO₂ ± CH₄ ± N₂ gas phase. A decrease in temperature from Au-quartz mineralization (200-220 °C) to the late epithermal one (160 °C) and a slight increase in the concentration of solutions (up to 10 wt.% NaCl equiv.) have been established. The deposit resulted from the intricate multistage geodynamic evolution of the South Verkhoyansk region. Ore-forming processes are associated with the evolution of magmatic objects. Dating of igneous rocks yields the following ages: diorites—130-137 Ma (Rb-Sr), spessartites—126 ± 3 Ma (Rb-Sr), and kersantites—115 ± 1.7 Ma (Ar/Ar). Early concordant Au-quartz (Au-As) mineralization of the deposit is comparable with metamorphic-related Au-quartz veins of the Yur-Bular type, and its age is taken as > 137 Ma. The time of formation of Au-quartz (Au-Pb-Zn) mineralization is estimated at 123.5 ± 1.6 Ma (Ar/Ar) and is coeval with the time of intrusion of the Early Cretaceous granitoids of the South Verkhoyansk region. The imposed low-temperature mineralization undoubtedly has a younger age. Its formation was followed by the successive deposition of Au-rare-metal mineralization at the final stage of formation of granitoid plutons (~ 120 Ma) and Au-Ag mineralization in the period 100 ± 5 Ma, i.e., the time of formation of late-stage granodiorite-granite intrusions.     

Sediment provenance of late Quaternary morainic,fluvial and loess‐like deposits in the southwestern Verkhoyansk Mountains (eastern Siberia) and implications for regional palaeoenvironmental reconstructions

A provenance analysis of late Quaternary deposits from tributaries of the Aldan and Lena rivers in Central Yakutia (eastern Siberia) was carried out using analysis of heavy minerals and clay mineralogy. Cluster analysis revealed one assemblage that is characterized by relatively high proportions of amphibole, orthopyroxene and garnet as well as pedogenic clay minerals, reflecting a sediment provenance from the wide catchment area of the Lena and Aldan rivers. In contrast, the three other clusters are dominated by stable heavy minerals with varying amounts of clinopyroxene, apatite and garnet, as well as high percentages of illite and chlorite that are indicative of source rocks of the Verkhoyansk Mountains. Glacial moraines reveal the local mountain source signal that is overprinted by the Lena‐Aldan signal in the oldest moraines by reworking processes. Alluvial sediments in the Verkhoyansk Foreland show a clear Lena source signal through intervals of the middle and late Pleistocene, related to a stream course closer to the mountains at that time. Loess‐like cover sediments are characterized by the dominant Lena provenance with increasing proportions of local mountain sources towards the mountain valleys. Aeolian sands in an alluvial terrace section at the mountain margin covering the time between 30 ka and 10 ka BP reflect temporarily dominant inputs of aeolian materials from the Lena Plains. Copyright © 2007 John Wiley & Sons, Ltd.     

Luminescence chronology from the Verkhoyansk Mountains (North-Eastern Siberia)

This study presents new dating results from the Verkhoyansk Mountains in northeastern Siberia. Pleistocene sediments of aeolian and glacial origin have been studied and dated by infrared optically stimulated luminescence (IRSL). The chronostratigraphy of this vast area is mainly based on radiocarbon dating up to now. Aeolian sediments are widespread in the foreland of the Verkhoyansk Mountains. IRSL-dating results indicate two major periods of increased accumulation between 33 and 24 ka and between 13 and 9 ka. A new stratigraphy of Pleistocene glaciations in this area has been developed. Up to five end moraines have been identified in two catchments areas. IRSL was applied to date the sandy and silty sediments covering the glacial deposits in order to get minimum ages. Furthermore, glacial and glacio-fluvial deposits were also sampled from a few locations. According to the IRSL dating results, the uppermost end moraine was deposited prior to 50 ka. The three outermost moraines might have been formed during Early Weicheslian to Saalian times. It is very likely that no major glaciers reached the foreland of the Verkhoyansk Mountains during the Last Glacial Maximum (LGM, MIS 2).