Depositional controls on sediment properties in dryland rivers: influence on near-surface diagenesis

Sandy braided dryland rivers, deposited under arid to semi-arid conditions, constitute important clastic reservoirs worldwide whose reservoir quality reflects the effect of primary sediment properties on near-surface diagenetic processes. A literature review is presented of existing facies models, mainly based on geomorphological analysis of modern perennial braided rivers, which is further illustrated with own outcrop and subsurface examples of dryland river deposits in: (a) Argana Basin (Triassic, Morocco), (b) Iberian Meseta (Triassic, Central SE Spain), (c) Huesca Fluvial Fan (Miocene, Spain) and (d) Rotliegend hydrocarbon reservoirs in the Southern Permian Basin (The Netherlands). The facies models combined with the analyses of the rock record provide a comprehensive depositional framework where investigated for the influence of depositional characteristics, such as grain-size and sorting variations, interstitial clay distribution and composition and amount of intrabasinal components, on the extent and pathway of near-surface mechanical and chemical processes. The particular dryland setting is characterized by prolonged periods of inactivity and short, episodic periods of peak discharge which lead to the transport and deposition of poorly-sorted, clay-rich extra- and intraformational conglomeratic sediments upstream. Downstream, channels, mid-channel and bank attached bars develop with conspicuous anisotropic trough and tabular cross-stratified sandstones. The most common near-surface diagenetic processes that alter the textural properties of these deposits are the rapid decrease of porosity and permeability due to grain-rearrangements and mechanical compaction of mud intraclasts along with pervasive early carbonate cementation. The results of this study will help to better configure the boundary conditions (e.g., external versus local supply for carbonates cements) in state-of-the-art reservoir quality forward models for ancient dryland river sandstones, which are especially prominent in Devonian, Permian, Triassic and Jurassic reservoir settings.

Jaar van publicatie:2020

BOF-keylabel:ja

IOF-keylabel:ja

BOF-publication weight:10

CSS-citation score:1

Auteurs:International

Authors from:Higher Education

Toegankelijkheid:Open