Molecular Indicators of Sources and Biodegradation of Organic Matter in Sediments of Fluid Discharge Zones of Lake Baikal

Inna Morgunova,Anna Kursheva,Petr Semenov,Olga Pavlova,Tamara Zemskaya,Oleg Khlystov,Alexey A. Krylov,Sergey Malyshev,Ivan Litvinenko,Sergey Bukin

doi:10.3390/geosciences12020072

Abstract

This paper performs a detailed study of a wide set of organic-geochemical proxies in 15 sediment cores collected from the main basins of Lake Baikal (the northern, the central and the southern) where processes of focused fluid discharge were detected. A variety of studied zones includes sites with gas and hydrothermal seepage, mud volcanoes with or without gas-oil fluid discharge, gas hydrates and authigenic carbonates. The composition of the dispersed organic matter and individual hydrocarbon molecular markers (n-alkanes, dimethyl alkanes, isoprenoids, steranes, terpanes and polycyclic aromatic hydrocarbons) testify to the input from predominantly allochthonous terrestrial and autochthonous microbial and algal sources. The studied sources, maturity and biodegradation parameters of organic matter vary significantly for areas with different fluid discharge. The composition of specific biomarkers including isoprenoids and immature hopanoids reflects the lateral and vertical changes of microbial activity in sediments associated with various environmental conditions. The identified types of terpanes distribution (mature, mixed and immature) correlate well with types of fluid discharge and attest to the development of various methanogenic and methanotrophic microbial communities in sediments. Moreover, the revealed specificity of microbial molecular markers distribution allowed us to suggest the fluid discharge processes in zones where they were not previously detected.

Highlights

We present the results of the distribution of a wide set of organicgeochemical proxies in the bottom sediments of all the geographic zones of Lake Baikal
The cores collected from zones where fluid discharge was not detected we have considered as a background
Special attention should be paid to the sediment cores with oil inclusions, authigenic carbonates and gas hydrates collected from the zones with focused fluid discharge

Summary

Introduction

Introduction published maps and institutional affilLake Baikal is a unique ultra-deep freshwater inland reservoir characterized by a variety of liquid and gas fluid discharge zones detected in the main deep basins (the northern, the central and the southern), submarine elevations and shallow water areas [1,2,3,4,5].Discharge processes include hydrothermal venting (HTh), oil (OS) and gas (GS) seepage, mud volcanism (MV) and associated gas hydrate (GH) and authigenic carbonates (Carb) that form due to various diagenetic, catagenetic, endogenous and circulation processes in sediments of the Baikal Rift Zone [3,6,7,8,9,10]. Lake Baikal is a unique ultra-deep freshwater inland reservoir characterized by a variety of liquid and gas fluid discharge zones detected in the main deep basins (the northern, the central and the southern), submarine elevations and shallow water areas [1,2,3,4,5]. It is important to note that microorganisms play a key role in sedimentary biochemical processes. They are involved in the generation of hydrocarbons (HCs) and the active biological transformation of their dispersed and concentrated forms [13,16,17,18,19].

Methods

Results

Conclusion