Natural and anthropogenic influences on depositional architecture of the Ural Delta, Kazakhstan, northern Caspian Sea, during the past 70 years

Abstract

This paper focuses on the Ural Delta in the northern zone of the Caspian Sea, an area with particular characteristics, where intense influence from anthropogenic and natural factors exists, which acts on the fragile delta system. We built a database to integrate the data from the published sources, bathymetric survey, and recent images in the geographical information system (GIS) environment. The results were linked to the Caspian Sea level (CSL) curve, which had many variations, changing the Ural Delta system's dynamics and in its architecture. In addition, the anthropogenic changes contribute to shaping the actual Ural Delta architecture. Through the link between the results and CSL, we reconstructed an evolution model for the Ural Delta system for the last century and identified three different architectures for the Ural Delta, determined by the energy that acted on the system in the last century and by the anthropogenic changes. This work identifies six different delta phases, which are shaped by CSL changes during the last 70 years and by anthropogenic changes. The delta phases recognized are: i) a Lobate Delta phase, shaped during high CSL before 1935; ii) Natural Elongate Delta 1935–1950 formed during rapid CSL fall; iii) Anthropogenic Elongate Delta 1950–1966, formed during rapid CSL fall and after the Ural-Caspian Sea canal construction, which modified the sedimentary deposition on the delta; iv) Anthropogenic Elongate Delta 1966–1982 shaped during low CSL phase; v) Anthropogenic Elongate Delta 1982–1996 formed during a rapid CSL rise phase; and vi) Anthropogenic Elongate Delta 1996–2009 shaped during high CSL that represent the last phase and actual Ural Delta architecture.