Il’ya Zakiryanov, a specialist from the Laboratory of Sedimentology IPGG SB RAS, told us about the importance of these research works.
According to him, bioherms (i.e. ancient organic reef of moundlike form, or sea-(lake)floor features) have unabatingly been of interest to scientists. Gorny Altai whose area is reported to have been a basin favorable for the formation and evolution of organic reefs due to its suitable conditions for bioherm growth, with calcareous algae actively participating in the processes, nowadays represent an excellent testing ground for extensive research into ancient reefs conducted by IPGG SB RAS staff.
Barrier reefs are widespread among coral reefs as forms of ‘biogenic structures’. The world’s most extensive coral reef ecosystem, the Great Barrier Reef near Australia, represents an example of such an organogenic structure. Due to the algal nature of bioherms, they are often associated with significant reserves of both hydrocarbon raw materials, and solid minerals.
Scientists from Novosibirsk – the IPGG SB RAS researchers in partnership with colleagues from NSU – have completed a number of research works to define structural features and distribution of calcareous algae, as well as their applications to paleogeographic reconstructions.
On the way to the study area in Gorny Altai
Among other things, the researchers have investigated the biogenic origin and structural features of dome-shaped microstructures (aka “calyptras”, smallest biogenic structures) from Upper Ordovician limestones in the central part of the Altai Mountains, with deposits dating more than 445 million years ago.
Using materials from the Chakyr-Azratkan cross-section located near Ust-Kan settlement, Altai Republic, researchers revealed that cyanobacterial communities participated in the formation of calyptras.
Scientists also identified abundant calcareous algae - the Hedstroemia Halimedoidea Rothpletz type species - in the studied rocks. Representatives of this genus are also known as Early Paleozoic reef-builders (over 485 million years old), i.e. algae bodies formed shrubby thallus structures.
а) the appearance of a single calyptra; b) its cross-section; c) mass concentrations of calyptras
Besides, researchers from the Sedimentology Laboratory and the Laboratory of Paleozoic Paleontology and Stratigraphy of IPGG SB RAS studied other sections, as follows: Tachalov (western Gorny Altai), Lebed’ and Bura (northeastern Gorny Altai). Results of the petrographic analysis showed calcareous algae (represented by both cyanobacteria and green and red algae) to be present in all studied sections.
Field works on the Tachalov section conducted by researchers from the Laboratory of the Paleozoic Paleontology and Stratigraphy. From left to right: N.V. Sennikov, O.T. Obut, E.V. Lykova
According to the researchers, the Tachalov section is of particular interest in the context of these studies, since its upper part is represented by a reef-like carbonate buildup consisting of numerous coalesced small bioherms which are up to 1-1.5 m thick. The discovered complex of calcareous algoflora was studied in great detail at IPGG SB RAS and NSU.
In addition, we investigated the Late Ordovician algae buildups in the cis-Teletskoye Altai region. Optical petrography studies were carried out on the material from the Verkhny Turochak section. The research results revealed calcified red algae (the genus Solenopora Dybowski) whose abundance reaches 50-60% against the backdrop of other organogenic fossils. Contributions of these lower plants to the growth of oncolith-like buildups are found to be measurable.
Further work will be aimed at a profound analysis of the prospects of fossil calcareous algae with respect to (i) paleogeographic reconstructions, (ii) identification of new species /genera, (iii) the role of calcareous algae as framework builders and sediment producers, or their contribution to biogenic deposits and buildups of carbonate materials.
Polished surface of sample with large oncoliths-rhodoids
For reference
The research works were conducted within the state task of the Russian Academy of Sciences for Fundamental Scientific Research (projects FW ZZ2022-0003, FWZ-2022-0007).
Photos/ illustrations courtesy of I.G. Zakiryanov
Published by the IPGG Press Service