Sedimentation in Proval Bay (Lake Baikal) after earthquake-induced subsidence of part of the Selenga River delta

Abstract

The paper presents the results of a comprehensive investigation into the recent sediments of Proval Bay. This bay formed during catastrophic flooding of a big block of land as a result of an earthquake in 1862. Comparison of the sketch map of the bay for 1862 with its modern map shows that the boundary of the Selenga River delta has shifted considerably eastward. The sediments of Proval Bay are sands, silty pelite, and pelitic silt. Terrigenous material is predominant and consists of mineral grains and land plant remains, admixed with diatom frustules and sponge spicules. In the southwestern part of the bay, turbidites and a soil layer have been found. The latter was buried when the water level in Lake Baikal rose after the construction of the Irkutsk dam in 1959–1964. In the northeastern part of the bay, a peatlike layer has been found in the bottom sediment core. It formed in Lake Beloe, which existed in the Tsagan steppe before the 1862 earthquake. According to diatom analysis, this lake was shallow and eutrophic. The sedimentation rates in different parts of Proval Bay differ greatly and directly depend on proximity to the Selenga River. Variations in the geochemical indicators which reflect the ratio of organic to clastic components in the bottom sediments of the bay are controlled by temperature and water level variations in Lake Baikal.

Controls on gravel termination in seven distributary channels of the Selenga River Delta, Baikal Rift basin, Russia

“…8B), and the highest-order channels tend to be concentrated on the eastern portion of the delta, which also presently receives the largest proportion of Selenga River water discharge (Il'icheva et al, 2014). In addition, this region of the delta empties into Proval Bay, which was produced by the instantaneous subsidence of ~200 km 2 of delta by ~3 m during a 7.5 magnitude earthquake event in 1862 (Vologina et al, 2010). This produced an increase in local channel slope, which attracted distributary channels from the central sector of the Selenga River, therefore increasing the contribution of water and sediment to the eastern portion of the delta.…”

“…In the Baikal basin, tectonically driven earthquakes induce subsidence on the delta topset with a recurrence time of 350-500 yr and with an average of ~3 m of vertical (downward) movement per event (Shchetnikov et al, 2012). This magnitude and frequency produce subsidence rates of 6-8 mm/yr over time scales of centuries to millennia (Vologina et al, 2010), and this is a minimum estimate of subsidence rate because it does not consider sediment compaction. The tectonic time scale (T t ), which captures the time scale required for the signal of tectonically driven subsidence to propagate across the landscape and to preserve topset sediment to basin stratigraphy, was estimated using the formulation by Kim et al (2010):…”

When does faulting-induced subsidence drive distributary network reorganization?

“…Situated along the margin of rift-basin bound Lake Baikal (Russia), the Selenga River delta is tectonically active (Figure 1a; ). An earthquake in 1862 induced up to 9 m of vertical displacement along the eastern delta edge , lowering >230 km 2 of land below the water surface and creating Proval Bay (Figure 1a; Vologina et al, 2010;. As a result, the shortest path from delta apex to lake level was available via Proval Bay (i.e., eastern deltaic lobe).…”

“…An earthquake in 1862 induced up to 9 m of vertical land subsidence along the eastern delta edge , lowering more than 230 km 2 of land below the water surface and creating Proval Bay (Figure 1a; Vologina et al, 2010;; lowered land comprised unconsolidated Quaternary and older Tsagan Steppe deposits . As a result, the shortest path from delta apex to lake level was available via Proval Bay (i.e., the eastern delta lobe).…”

Seismically-triggered organic-rich layers in recent sediments from Göllüköy Lake (North Anatolian Fault, Turkey)

“…Effects of co-seismic subsidence on sedimentation can be further investigated through taxonomical and biogeochemical analyses on diatom, foraminifera, pollen and organic matter contents. For example, proportional changes in benthic versus planktonic species and terrestrial versus lacustrine origin of organic matter can provide valuable information to trace evidences of tectonic subsidence in lake basins (e.g., Mirecki, 1996;Leroy et al, 2009;Vologina et al, 2010;Bertrand et al, 2011).…”