Volumetric budget and grain-size fractionation of a geological sediment routing system: Eocene Escanilla Formation, south-central Pyrenees

Abstract

The supply of sediment and its characteristic grain-size mix are key controls on depositional facies and stratigraphic architectures in sedimentary basins. Consequently, constraints on sediment caliber, budgets, and fl uxes are a prerequisite for effective stratigraphic prediction. Here, we investigate a mid-to late Eocene (41.6-33.9 Ma) sediment routing system in the Spanish Pyrenees. We derive a full volumetric sediment budget, weighted for grain-size fractions, partitioned between terrestrial and marine depositional sectors, and we quantify sediment fl uxes between depocenters. The paleo-sediment routing system was controlled by syndepositional thrust tectonics and consisted of two major feeder systems eroding the high Pyre nees that supplied a river system draining parallel to the regional tectonic strike and that ultimately exported sediment to coastal, shallow-marine and deep-marine depo centers. We show signifi cant changes in both the volume and grain-size distribution of sediment eroded from the Pyrenean mountain belt during three different time intervals in the mid-to late Eocene, which controlled the characteristics of stratigraphy preserved in a series of wedge-top basins.The time-averaged sediment discharge from source areas increased from ~250 km 3 /m.y. to 700 km 3 /m.y. over the 7.7 m.y. interval investigated. This temporal increase in sediment supply caused major westward progradation of facies belts and led to substantial sediment bypass through the terrestrial routing system to the (initially) marine Jaca Basin. The grain-size mix, measured as size fractions of gravel, sand, and fi ner than sand, also changed over the three time intervals. Integration of volumetric and grain-size information from source to sink provides an estimate of the long-term grain-size distribution of the sediment supply, comprising 9% gravel, 24% sand, and 67% fi ner than sand.The techniques and concepts used in the Escanilla study can profi tably be applied to paleo-sediment routing systems in other tectonic and climatic settings and to catchments with a range of bedrock lithology and vegetation. This will promote a better generic understanding of the dynamics of source-tosink systems and provide a powerful tool for forward stratigraphic modeling. The sediment routing system approach has the potential to contribute strongly to new models of sequence stratigraphy.

Numerical modelling of landscape and sediment flux response to precipitation rate change

“…This issue is pertinent because within sedimentary basins, a change in the erosional dynamics upstream could be recorded by changes in the total sediment volumes stored in sedimentary basins (e.g. Allen et al, 2013;Michael et al, 2014), in sediment delivery or sediment accumulation rates linked to landscape response times (Foreman et al, 2012;Armitage et al, 2015), and/or in the grain sizes deposited as a function of sediment flux output (Paola et al, 1992;Armitage et al, 2011;Whittaker et al, 2011;D'Arcy et al, 2016).…”

Numerical modelling landscape and sediment flux response to precipitation rate change

“…Allen et al, 2013;Michael et al, 2014); in sediment delivery or sediment accumulation rates linked to landscape response times (Foreman et al, 2012;Armitage et al, 2015) and/or in the grain-sizes deposited as a function of sediment flux output (Paola et al, 1992;Armitage et al, 2011;5 Whittaker et al, 2011;D'Arcy et al, 2016). Furthermore, laboratory scale experiments have demonstrated that within a physical system of erosion dirven by the surface flow of water, there is a clear response time for the system to recover to steady state after a perturbation Crave, 2003, 2006;Singh et al, 2015).…”

Erosion rates in the source region of an ancient sediment routing system: comparison of depositional volumes with thermochronometric estimates

“…Sediment was transported westwards through the Pyrenean pro-wedge-top region towards an ocean in the Biscay area, and the routing system is therefore distinct from coeval sediment routing systems sourced in the eastern Pyrenees that dispersed sediment into the northeastern Ebro pro-foreland basin (Michael et al 2013). Although there are substantial thicknesses of mid-to upper Eocene sedimentary rocks in the eastern Ebro Basin (Sinclair et al 2005), this region was part of a different, though coeval, sediment routing system to the Escanilla, and was supplied with sediment from feeder systems in the eastern Pyrenees, Catalanides and Iberian chain (Michael et al 2013(Michael et al , 2014.…”

“…2), occupying a total time span of 7.7 myr. The recognition and mapping of these time intervals is based on bio-and magnetostratigraphy (Beamud et al 2003(Beamud et al , 2010Beamud 2013) backed up by changes in provenance data and sedimentology (Michael 2013), and has been explained in greater detail elsewhere (Michael et al 2013(Michael et al , 2014.…”

“…The linkage of the Escanilla Formation and age-equivalents within one source-to-sink system is based on a range of provenance tools (clast lithologies, heavy minerals, U-Pb geochronology of detrital zircons, apatite fission-track analysis, palaeocurrent analysis, magneto-and biostratigraphy), which have been described in detail elsewhere (Michael 2013;Michael et al 2014). A summary of key data is provided here, and the results used to delimit catchment regions acting as sediment source areas are given in the 'results' section.…”