From grain size to tectonics

Abstract

[1] Regional grain size trends in fluvial successions can reveal important information regarding the dynamics of sediment routing systems. Self-similar solutions for downsystem grain size fining have recently been proposed to explore how key variables, such as the spatial distribution of deposition, sediment discharge, and sediment supply characteristics, control spatial distribution of grain size in fluvial successions over time scales of 10 4 -10 6 years. We explore the sensitivity of these solutions to changes in key variables and assess their applicability to ancient fluvial successions. Several sensitivity analyses are presented to investigate the relative control of the key model variables on the spatial pattern of down-system grain size fining in fluvial successions. Sensitivity analyses demonstrate that (1) an increase in the initial value of sediment discharge to a basin causes a decrease in the rate of grain size fining in fluvial successions, an effect that becomes nonlinear for large values of initial sediment discharge; (2) a short-wavelength/ high-amplitude subsidence regime generates a greater rate of down-system grain size fining and a long-wavelength/lower-amplitude subsidence regime generates a lesser rate of down-system grain size fining in fluvial successions; and (3) an increase in the spread of grain sizes in the sediment supply generates a greater rate of down-system grain size fining. We apply this modeling technique to grain size data sets collected from two time surfaces within conglomerates of the Upper Eocene Montsor Fan Succession of the Pobla Basin, Spanish Pyrenees. These data sets exhibit approximately self-similar grain size distributions; further, the observed increase in down-system grain size fining associated with smaller depositional system lengths provides support for the application of self-similar solutions to fluvial successions. By applying these solutions to carefully collected grain size data from fluvial successions, we are able to relate explicitly the initial grain size supplied to the system, the spatial distribution of subsidence and the sediment discharge into the basin to the rate of grain size fining in fluvial successions. This method thus offers a powerful means of elucidating sediment routing system dynamics over time.

Abrupt landscape change post–6 Ma on the central Great Plains, USA

“…Time-averaged grain size distributions were collected from sites within the RRB and AHF (locations in Fig. 1A), using several in-situ and photographic Wolman point counts to give averages per 10 m 2 areas (see Duller et al, 2010;Whittaker et al, 2011). Present-day slope values of the base of variously aged Ogallala paleochannels, and the base of the RRB, were each constructed from an exponential fi t to scattered well and outcrop data (Swinehart et al, 1985;Diffendal, 1995, 1997).…”

Towards a sequence stratigraphic solution set for autogenic processes and allogenic controls: Upper Cretaceous strata, Book Cliffs, Utah, USA

“…However, recent outcrop studies demonstrate that the construction of sediment volume or mass budgets within the source-to-sink context of a sediment routing system can provide a powerful tool to quantitatively estimate the volume and grain size of sediment supply (e.g. Duller et al 2010;Whittaker et al 2011;Carvajal & Steel 2012;Michael et al 2013). The results are particularly useful if analysed in a mass-balance framework, in which the cumulative deposited volume of sediment in the downsystem direction is normalized by the total sediment volume (e.g.…”

The distribution of rivers to terrestrial sinks: Implications for sediment routing systems

“…For instance, an increase in initial sediment discharge decreases the rate of initial grain size fining (Duller et al, 2010). Tectonic uplift in the source catchment will initially increase grain size at the proximal fan while increased precipitation will increase in the lateral extent of a coarse grained fan (Armitage et al, 2011).…”

“…This is particularly relevant to extensional, strike-slip and foreland tectonic settings where the terrestrial sink is typically bounded by numerous but smaller high relief source catchment regions. The use of grain size in defining spatial trends, sediment supply characteristics and controls on fluvial successions over different spatial and temporal scales (Duller et al, 2010) is thereby complicated by the along strike variability observed in sediment discharge of the contributing source catchments. Grain size profiles in these systems may then represent a lateral coalescence of variability in source catchment discharge that contribute over different spatial and temporal scales.…”