Sequence stratigraphic interpretation of the Chilga basin sediments, Northwest Ethiopia

Abstract

Sequence stratigraphic interpretation of passive margins and marine environments reveal stratigraphic records that result from the influence of long-term change in eustatic sea level, tectonic subsidence, and climate. On the other hand, sequence stratigraphic interpretation of continental rift basin sediments reveal stratigraphic records that are dominantly controlled by short-term local tectonic conditions and climatic fluctuations. The Chilga co ntinental rift basin, located in northwest Ethiopia, consisting of sediments composed of claystones, siltstones and silty sandstones, volcanic ashes, lignite beds, and vertebrate and plant fossil-rich sandstones provides ample information for such a sequence stratigraphic interpretation. This paper presents a sequence stratigraphic interpretation of the Chilga basin sediments using integrated approaches such as regional stratigraphic correlation and interpretation of depositional environment derived from petrography, x-ray diffraction analysis, and lithologic associations. Results indicate that the Chilga basin preserves three 4 th order sedimentary cycles within 1.0 Ma. Sequence stratigraphic analysis of the Chilga continental rift basin is a working model for the many unstudied Ethiopian rift and non-rift basin sediments, which are dominantly composed of fine-grained sediments. Key words/phrases : Basin, Chilga, continental rift, Ethiopia, sequence stratigraphy SINET: Ethiopian Journal of Science Vol. 28 (1) 2005: 75-92