GSA Connects 2021 in Portland, Oregon

Paper No. 17-14
Presentation Time: 11:35 AM


PEDAN, Halyna1, KADURIN, Sergii1, ANDREEVA, Kseniya1 and DRAGOMYRETSKA, Olena2, (1)Department of Engineering Geology and Hydrogeology, Odessa I.I. Mechnikov National University, Shampanskiy per, Odessa 65058, Ukraine, Odessa, Ukraine, (2)State Institution “Hydroacoustic Branch of Institute of Geophysics S.I.Subbotin of National Academy of Sciences of Ukraine”, Odessa, Ukraine

Lithological analysis of bottom sediments of two regions on the seaside of the Ochakov mouth of the Danube delta has been carried out, which makes it possible to reveal the features of their differentiation and sedimentation. The complex of methods includes granulometric analysis, creation and analysis of histograms of fractional composition, distribution fields and cumulative curves. The influence of the outflow of the Danube and sea sediments in the formation of the sea edge of the delta is shown. 20 samples of bottom sediments were taken during field work in 2020. The granulometric features of the sediments were studied on two profiles located perpendicular to the coastline at 1470 m towards the sea at a depth of 10 m.

The first profile is located opposite the mouth of the Potapov branch, where loose sediments from the Danube River are moved by the water flow. This is the zone of interaction between the river and sea water. The second profile is located 7 km south at the sea side of the spit separating the bay from the sea.

Four zones of different grain-size composition of bottom sediments are distinguished in the first area along the profile. Medium-grained sands (94%) with an admixture of psephites are prevail near the coast. Further, to a depth of 7 m, the deposits are represented by fine-grained sand (70-90%) and silt (10-30%) with a slight admixture of psephites and pelites (less than 1%). The slope of the depths (7-8 m) is dominated by silts with an admixture of sand, 70% and 30%, respectively. Deeper, the leading faction is the sands. The field of distribution curves and cumulative curves is wide, which confirms the conclusion about the heterogeneity of deposits and a low degree of sorting of terrigenous material. These sediments are formed due to the removal of sediments by the Danube River, their differentiation in size, their mixing with sea sands at great depths.

The bottom sediments of the second profile are 99% composed of fine-grained, homogeneous, well-sorted sand (sorting coefficient 1.3). The sands are transported by the coastal sediment flow from the north and are discharged here, as the river flow from the Bystroye mouth ( located to the south) blocks the current in the south. A spit was formed that blocked the river bed. This area is characterized by marine sedimentation conditions that flatten the outer coastline of the delta.