Controls on Sediment Distribution From Source-to-Sink in an Active Extensional Setting: The Sperchios Rift, Central Greece

Abstract

Inversion of grain-size trends from fluvial successions can provide quantitative insights into the dynamics and functioning of sediment routing systems. This study presents an integrated analysis of the grain size distribution from source-to-sink in an active rift setting. We study the downstream variation in sediment caliber along the Sperchios routing system in order to investigate its response to forcing mechanisms such as tectonic subsidence and sediment supply. The Sperchios rift is located in central Greece and forms an asymmetric half-graben basin, bounded to the south by NW–SE-striking normal faults. The source-to-sink system is characterized by a major axial river approximately 80 km long, which drains the upland basin from west to east and supplies sediment to a fine-grained deltaic succession. Coarse sediment is supplied to the axial river by catchments draining across the basin bounding faults. We quantify the present-day grain-size distribution along the axial system using scaled photos of active gravel bars and in-situ sieving. We calculate downstream fining rates and we implement a two-dimensional self-similarity model to predict grain size fining as a function of sediment flux and selective deposition due to tectonic subsidence. Furthermore, we explore the relative importance of abrasion in modifying the observed grain-size distribution. Our analysis demonstrates that the down-system increase in tectonic subsidence along the Sperchios rift is the first-order controlling factor in the extraction of the coarse sediment fraction into the stratigraphy, and this process can explain the downstream transitions from a braided to a meandering fluvial depositional system and ultimately to fine-grained deltaic deposition. The study has implications for grain-size and sedimentary facies development in transverse and axial depositional systems in rifts and prediction of reservoir quality in fluvio-deltaic syn-rift reservoirs.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016