Time lag of syntectonic sedimentation across an alluvial basin: theory and example from the Ebro Basin, Spain

Abstract

We propose and test a conceptual framework for evaluating the relative timing of different types of sedimentary indicators of tectonism in alluvial foreland basin settings. We take the first occurrence of a detrital grain from a newly exposed source‐area lithology to provide the best indicator of the onset of tectonic uplift in the source area. Source‐area unroofing may lag behind initial uplift because of the type, thickness and structure of rocks in the uplifted mountain block, drainage patterns and climate. However, once exposed, advective transport disperses grains quickly throughout fluvial systems. Because of increased subsidence rate from thrust belt loading, an increase in sedimentation rate begins coincident with tectonic load emplacement within the flexural half‐width of the basin. However, farther out into the basin increased sedimentation rates lag behind the composition signal because of time lags associated with propagation of the thrust load and attendant sediment loads into the basin. The progradation of syntectonic gravel lags behind all of these signals as a direct function of the relative proportion of gravel fraction within transported sediment and rates and geometry of subsidence, which selectively traps the coarsest grain‐size fractions in the most proximal parts of the basin. We demonstrate this signal attenuation in the syntectonic Horta–Gandesa alluvial system (late Eocene–Oligocene), exposed along the southeast margin of the Ebro Basin, Spain. The results demonstrate that: (1) the time spans between the compositional signal and the progradation of the gravel front can be geologically significant, on the order of more than a million years within as little as 20 km of the thrust front; and (2) time lags between the signals increase with distance away from the deformation front. No lag time was observed between the first appearance of a new clast composition and the arrival of gravel front when the thrust front was within a few tens of metres from the depositional site. In contrast, the time lag was 0.5–1 Myr when the thrust front was about 5–6 km away and it increased to >1 Myr when the deformation front was about 8 km away. At the most extreme position, when the thrust front was 15–20 km away, the gravel front never reached the study area.

Distinguishing allogenic from autogenic causes of bed elevation change in late Quaternary alluvial stratigraphic records

“…1. Nevertheless, numerous examples from the rock record provide evidence in support of the basic conclusion that tectonic influence is the dominant control on bed elevation change (and the resulting sedimentary record) over long (geologic) timescales Miall, 1997;Jones et al, 2004;Leckie et al, 2004;Gibling, 2006;Bishop, 2007).…”

20 Myr of eccentricity paced lacustrine cycles in the Cenozoic Ebro Basin

“…The first expansion includes the coal-bearing carbonate sequences of the lower Mequinenza Fm, dated to within chron C9n (Gomis et al, 1997). At this time, lacustrine facies spread to nearly reach the basin margins in the Gandesa area (Barberà et al, 2001;Jones et al, 2004). The second lacustrine expansion within the Mequinenza Fm is traced along the Cinca River valley, where lacustrine limestones spread northwards over more than 10 km on top of distal alluvial red mudstones of Pyrenean source (Fig.…”

Field test of autogenic control on alluvial stratigraphy (Ferris Formation, Upper Cretaceous-Paleogene, Wyoming)

“…For example, tectonic tilting may result in changes in grain size and/or water depth of attendant rivers (e.g., Heller et al, 2003), potentially changing the grain size and bar clinoform thickness within deposited sand bodies. Likewise, drainages could be reset or diverted by fault movements (e.g., Schumm et al, 2000) and manifested as changes in paleocurrent directions and possibly composition in the proximal basin (e.g., Jones et al, 2004). Additionally, uplift resulting in channel incision could produce prominent scour surfaces within a fl uvial succession (e.g., Holbrook et al, 2006).…”

“…Building on provenance work in the Ferris Formation by Ryan (1977), and following the methods of Jones et al (2004), compositions of 100+ coarse (~10 mm and larger) clasts were recorded for channels with substantial gravel content. Gravel-composition surveys were conducted along bedding planes exposed at the base of sand bodies (Fig.…”