Mesozoic Intracontinental Orogeny in the Tectonic History of the Kolyvan’– Tomsk Folded Zone (Southern Siberia): a Synthesis of Geological Data and results of Apatite Fission Track Analysis

—The Kolyvan’–Tomsk folded zone (KTFZ) is a late Permian collisional orogen in the northwestern section of the Central Asian Orogenic Belt. The Mesozoic history of the KTFZ area includes Late Triassic–Early Jurassic and Late Jurassic–Early Cretaceous orogenic events. The earlier event produced narrow deep half-ramp basins filled with Early–Middle Jurassic molasse south of the KTFZ, and the later activity rejuvenated the Tomsk thrust fault, whereby the KTFZ Paleozoic rocks were thrust over the Early–Middle Jurassic basin sediments. The Mesozoic orogenic events induced erosion and the ensuing exposure of granitoids (Barlak complex) that were emplaced in a within-plate context after the Permian collisional orogeny. Both events were most likely associated with ocean closure, i.e., the Paleothetys Ocean in the Late Triassic–Early Jurassic and the Mongol–Okhotsk Ocean in the Late Jurassic–Early Cretaceous. The apatite fission track (AFT) ages of granitoids from the Ob’ complex in the KTFZ range between ~120 and 100 Ma (the Aptian and the Albian). The rocks with Early Cretaceous AFT ages were exhumed as a result of denudation and peneplanation of the Early Cretaceous orogeny, which produced a vast Late Cretaceous–Paleogene planation surface. The tectonic pattern of the two orogenic events, although being different in details, generally inherited the late Paleozoic primary collisional structure of the Kolyvan’–Tomsk zone.

Activity-educational aspects of geological excursions

The purpose of this article is to discuss the educational tour as a form of educational process in the activity-the educational aspect of the geological excursion in the study of rock outcrops career «Borok» of Novosibirsk as a geological object of interest for educational tours and training-practical work. To write the article, we used methods of comparative analysis, generalization, field geological observations, sampling, cross-section sketches, descriptions of outcrops, including working with a mountain compass and methods of conducting a training geological-geographical and geoecological route, drawing up a map of the territory, laboratory studies of rocks. The absolute advantage of the Borok quarry is its location, as well as optimal conditions for a thorough inspection and description of rock outcrops. Branched dikes and veins are visible in the walls of the quarry, as well as the overlap of igneous Paleozoic rocks with sedimentary later deposits. Dumps of various Intrusive igneous, dike rocks and pegmatites, hydrothermal veins with ore minerals are of educational interest during excursions. The Borok quarry cooperates with schools, colleges, and Universities in Novosibirsk and is a platform for educational excursions to the production site and a place for training practices, as well as a venue for educational Olympiads in Geology and Geoecology. On the example of one of the production facilities of the city of Novosibirsk - the stone quarry «Borok», the possibilities of organizing and conducting geological excursions in order to study the geological structure of the territory, consolidate theoretical geological and geoecological knowledge, acquire skills in educational and practical work and analyze the results obtained are demonstrated.

Telling time at Grand Canyon National Park: 2020 update

Grand Canyon National Park is all about time and timescales. Time is the currency of our daily life, of history, and of biological evolution. Grand Canyon’s beauty has inspired explorers, artists, and poets. Behind it all, Grand Canyon’s geology and sense of timelessness are among its most prominent and important resources. Grand Canyon has an exceptionally complete and well-exposed rock record of Earth’s history. It is an ideal place to gain a sense of geologic (or deep) time. A visit to the South or North rims, a hike into the canyon of any length, or a trip through the 277-mile (446-km) length of Grand Canyon are awe-inspiring experiences for many reasons, and they often motivate us to look deeper to understand how our human timescales of hundreds and thousands of years overlap with Earth’s many timescales reaching back millions and billions of years. This report summarizes how geologists tell time at Grand Canyon, and the resultant “best” numeric ages for the canyon’s strata based on recent scientific research. By best, we mean the most accurate and precise ages available, given the dating techniques used, geologic constraints, the availability of datable material, and the fossil record of Grand Canyon rock units. This paper updates a previously-published compilation of best numeric ages (Mathis and Bowman 2005a; 2005b; 2007) to incorporate recent revisions in the canyon’s stratigraphic nomenclature and additional numeric age determinations published in the scientific literature. From bottom to top, Grand Canyon’s rocks can be ordered into three “sets” (or primary packages), each with an overarching story. The Vishnu Basement Rocks were once tens of miles deep as North America’s crust formed via collisions of volcanic island chains with the pre-existing continent between 1,840 and 1,375 million years ago. The Grand Canyon Supergroup contains evidence for early single-celled life and represents basins that record the assembly and breakup of an early supercontinent between 729 and 1,255 million years ago. The Layered Paleozoic Rocks encode stories, layer by layer, of dramatic geologic changes and the evolution of animal life during the Paleozoic Era (period of ancient life) between 270 and 530 million years ago. In addition to characterizing the ages and geology of the three sets of rocks, we provide numeric ages for all the groups and formations within each set. Nine tables list the best ages along with information on each unit’s tectonic or depositional environment, and specific information explaining why revisions were made to previously published numeric ages. Photographs, line drawings, and diagrams of the different rock formations are included, as well as an extensive glossary of geologic terms to help define important scientific concepts. The three sets of rocks are separated by rock contacts called unconformities formed during long periods of erosion. This report unravels the Great Unconformity, named by John Wesley Powell 150 years ago, and shows that it is made up of several distinct erosion surfaces. The Great Nonconformity is between the Vishnu Basement Rocks and the Grand Canyon Supergroup. The Great Angular Unconformity is between the Grand Canyon Supergroup and the Layered Paleozoic Rocks. Powell’s term, the Great Unconformity, is used for contacts where the Vishnu Basement Rocks are directly overlain by the Layered Paleozoic Rocks. The time missing at these and other unconformities within the sets is also summarized in this paper—a topic that can be as interesting as the time recorded. Our goal is to provide a single up-to-date reference that summarizes the main facets of when the rocks exposed in the canyon’s walls were formed and their geologic history. This authoritative and readable summary of the age of Grand Canyon rocks will hopefully be helpful to National Park Service staff including resource managers and park interpreters at many levels of geologic understandings...

CANYONS OF THE CHARYN RIVER (SOUTH-EAST KAZAKHSTAN): GEOLOGICAL HISTORY AND GEOTOURISM

The Charyn River is located in South-East Kazakhstan, 195 km east of Almaty. The river valley cuts through Paleozoic rocks and loose sandy-clay deposits of the Cenozoic and forms amazingly beautiful canyons, the so-called "Valley of Castles". This place is actively visited by tourists from all over the world. However, Charyn canyons have not only tourist but also scientific value. Deposits with fossil fauna and flora are exposed here, and there is evidence of unique tectonic processes that took place in this area. Years of research have made it possible to describe in detail the stratigraphy of the region and outline new tourism routes that open up unknown pages in the history of South-Eastern Kazakhstan.

An insight on the polyphase thermal history of the Ghomarides and Upper Sebtides in the Internal Rif (North Morocco) by means of Raman spectroscopy on organic matter

<p>The correct assessment of maximum temperatures experienced by rocks is an essential tool to unravel the evolution of the thermal structure of the crust during the main phases of an orogenesis. Given to broad P-T stability field of classical metamorphic mineralogical indicators, maximum temperatures derived from the analyses of carbonaceous material dispersed in rocks by means of Raman spectroscopy has shown to be a suitable alternative to classical geothermometer. Initially developed for high metamorphic rocks the use of this tools has recently been extended also at lower metamorphic degree and diagenesis. This allowed us to extend the analyses of paleotemperatures experienced by rocks from Ghomarides and Sebtides from the Internal Rif in North Morocco with respect to previous works. Ghomaride and Sebtides in this portion of the Rif-Betic-Tell chain, represent respectively the upper and lower plates of a metamorphic core complex  and are composed, the first, by Paleozoic rocks with a partially preserved Mesozoic-Cenozoic cover and the second by lower Paleozoic to Triassic deep-crustal mica-schists, migmatites and granulites associated with peridotites (Beni Bousera complex).</p><p>Our data suggest that the uppermost Tiszgarine Unit of the Upper Sebtides experienced warmer condition than previously observed. Moreover, we calculate the maximum temperatures experienced by the Ghomarides  during both the Eo and Late Variscan cycles showing that differences in temperature exist among the vary units that compose the complex. Finally, in the southern area our data suggest a less severe alpine heating related to the emplacement of the Beni Bousera peridotite, than previously calculated.</p>

No continuous suture between Kudi and Oytag: new evidence from geochronology and geochemistry data

<p>A lateral continuity between belts of mafic and ultramafic Paleozoic rocks found in the West Kunlun of Northern Tibet and comparable rocks, known from an outcrop in the Chinese North Pamir, has long been proposed. This led to the concept of an originally generally straight, E–W trending Oytag–Kudi suture zone. In turn, this paleogeographic model formed a key constraint for the hypothesis, that the Pamir has indented 300 km northward with respect to Tibet during the Cenozoic. We show, that the arc volcanic rocks found in the North Pamir are distinguishable from the units known from the West Kunlun.<br>The North Pamir is dominated by Paleozoic arc volcanic rocks. We present new geochemical and geochronological data to give a holistic view of an early to mid-Carboniferous arc complex. This belt was previously identified as an intraoceanic arc in the northeastern North Pamir. Our data yields evidence for a gradual lateral change towards the west into a Cordilleran-style arc in the Tajik North Pamir. Large leucocratic granitoid intrusions are hosted in part by Devonian to Carboniferous oceanic crust and the metamorphic Kurguvad basement block of Ediacaran age (maximum deposition age) in Tajikistan. LA-ICP-MS U-Pb dating of zircons, together with whole rock geochemistry derived from tonalitic to granodioritic intrusions, reveal a major Visean to Bashkirian intrusive phase between 340 and 320 Ma ago.<br>The West Kunlun experienced two major intrusive phases, connected with arc-volcanic activity — a first phase during Proto-Tethys closure in Ordovician and Silurian times and a second phase connected to the Triassic Paleo-Tethys closure. The Carboniferous arc-volcanic phase in the North Pamir clearly postdates Paleozoic arc-magmatic activity in the West Kunlun by ~100 Ma. This observation, along with geochemical evidence for a more pronounced mantle component in the Carboniferous arc-magmatic rocks of the North Pamir, disagrees with the common model of a continuous Kunlun belt from the West Kunlun into the North Pamir. Moreover, Paleozoic oceanic units younger than and west of Tarim cratonic crust challenge the idea of a continuous cratonic Tarim-Tajik continent beneath the Pamir.</p>

An expanded diversity of oomycetes in Carboniferous forests: Reinterpretation of Oochytrium lepidodendri (Renault 1894) from the Esnost chert, Massif Central, France

335–330 million-year-old cherts from the Massif Central, France, contain exceptionally well-preserved remains of an early forest ecosystem, including plants, fungi and other microorganisms. Here we reinvestigate the original material prepared by Renault and Roche from collections of the Muséum National d’Histoire Naturelle, Paris, and present a re-evaluation of Oochytrium lepidodendri (Renault 1894), originally described as a zoosporic fungus. Confocal laser scanning microscopy (CLSM) was used to study the microfossils, enabling us in software to digitally reconstruct them in three-dimensional detail. We reinterpret O. lepidodendri as a pseudofungus and favour placement within the oomycetes, a diverse clade of saprotrophs and both animal and plant parasites. Phylogenetically, O. lepidodendri appears to belong to a group of oomycetes distinct from those previously described from Paleozoic rocks and most likely related to the Peronosporales s.l. This study adds to our knowledge of Paleozoic eukaryotic diversity and reinforces the view that oomycetes were early and diverse constituents of terrestrial biotas, playing similar ecological roles to those they perform in modern ecosystems.