Rivers are the principal transport pathways along which sediment and nutrients are moved from sediment source areas (above base level) to depositional settings and the marine system (below base level). Reconstructing how these pathways have changed through time is essential for predicting and understanding clastic reservoir, seal and source facies distribution and character.
At Getech, we use a suite of geomorphological and geological tools to analyse the Present Day landscape and drainage networks, in order to unravel the history of changes in an evolving landscape. These methods include, but are not limited to: network analysis (using Horton plots, Horton Laws, hypsometric analysis, long profile analysis, river patterns, morphometric statistics – this is done using the hydrological toolsets in ArcGIS™ and Rivertools software), landscape analysis (surface analysis, including high- and low-pass topographic filters to analyse incision patterns, enveloping surfaces to calculate and identify pre-existing landscape surfaces). These analyses give us hypotheses about former landscape changes that can then be tested against the Geological Record in order to assign cause and timing. This is constrained by an array of analyses including the following: provenance, sedimentology, mass balance, tectonic modelling, published data and literature, Getech’s Global Palaeogeographies, Getech’s Structure and Tectonics databases, and fish DNA.
Once timings have been assigned we then build up the palaeodrainage maps that are fully integrated with the mapped Gross Depositional Environments (areas below contemporary base level) and tectonophysopgraphic terrains (areas above base-level sourcing sediment) for each stratigraphic Stage.
Getech’s drainage networks are calculated in ArcGIS™ using detailed DEMs in order to identify all potential transport pathways, independent of currently available water. This gives a more systematic and uniform drainage network to analyse compared with using blue lines from published maps. This follows many of the methods developed by the USGS (Hydro 1k and derivatives).
Once the palaeodrainage reconstructions have been built, these are then used with the results of climate models (weathering, erosion, and transport) to model sediment composition (in conjunction with palaeogeology bedrock maps), and sediment flux.
The palaeodrainage definitions themselves are an explicit boundary condition for the Earth System Models.