Basin‐Fill Incision, Rio Grande and Gulf of Corinth Rifts: Convergent Response to Climatic and Tectonic Drivers

Abstract

The influence of tectonics and climate on basin-fill erosion and incision in the Gulf of Corinth rift, central Greece, and Rio Grande rift, southwest USA, is examined. Overall, it is suggested that climate change controls the downstream water:sediment ratio and sediment transport capacity, via operation of the continuity equation. Tectonics, specifically the rapid growth and propagation of structures, sets up gradient contrasts and upstream-migrating changes in transport capacity via operation of the diffusivity equation. A steady-state aggradational mode operated in the southern Rio Grande rift between ~5 and 0.8 Ma, causing preservation of ancestral axial-channel and floodplain deposits due to relatively slow, long-term active rift subsidence. The onset of major climatic change around 0.8 Ma resulted in the axial river periodically incising to a total extent of ~150 m, removing about 25% by volume of previously accumulated sediment, despite continued active faulting and fault-induced subsidence. This climatic mode is interpreted to be a periodic response to positive downstream gradients in sediment transport rate during glacial and glacial-transition periods, caused by low-level external sediment sourcing and a dominance of large magnitude spring snowmelt floods from northern mountain valleys. Tectonic drivers are spectacularly demonstrated in the Gulf of Corinth, where a new theory of 'piggy-back' basin abandonment and regional uplift is proposed, as formerly active rift-margin faults are progressively dragged above the flat slab of underriding African lithosphere. Basin abandonment occurred across newly propagating faults, with erosion and basin-fill incision of up to 800 m depth, as discontinuities in drainage channel slope have migrated rapidly upstream. In both rifts, sediment relaxation time, T s = l 2 /κ, where l is a length scale and κ is sediment diffusivity, is probably short, since relevant length scales are small and diffusivities large. Thus in the Rio Grande rift, despite the great length of the river system as a whole, it is the balance between hydrological and sediment input from the many lateral tributaries that controls non-uniform transport capacity of the axial channel. In the case of the Gulf of Corinth rift, it is the high strain rate that causes diffusivity to be large in drainages cutting across rapidly vertically-growing normal faults.

Late Neogene rift-basin evolution and its relation to normal fault history and climate change along the southwestern margin of the Gerania Range, central Greece

“…Regional uplift independent of movement on individual faults has also been suggested for the Perachora Peninsula and Isthmus of Corinth between the eastern Gulf of Corinth and Saronic Gulf ( Fig. 1; Leeder et al, 2003;Leeder and Mack, 2007).…”

“…Climate change can cause incision in previously aggrading fl uvial systems, as is well documented from Quaternary examples far from coastal sites and areas of tectonic activity (Begin, 1988;Hereford, 1993;Blum and Tornqvist, 2000;Dethier, 2001;Mack et al, 2006;Leeder and Mack, 2007). Such incision arises because of changes in sediment:water discharge ratios as precipitation and vegetation change in catchments.…”

“…About 400 m of footwall uplift over the past 1 Ma is recorded by the backtilted sediments in the northwestern part of the extinct Megara basin (Leeder et al, , 2005. (3) The southwestern and western margin of the Gerania Range is bordered by inactive south-and southwest-dipping normal faults and complexly faulted, Pliocene-Pleistocene basin sediment (Collier and Dart, 1991), both of which are currently being uplifted in response to regional rise of the Perachora Peninsula and Isthmus of Corinth between the southeastern Gulf of Corinth and northwestern Saronic Gulf (Leeder et al, 2003;Leeder and Mack, 2007). (4) Toward the southeast, the impressive topographic ridge of the Gerania Range ends in a coastal escarpment known since preclassical times as the Skironian Cliffs.…”

“…Given the history of late Quaternary sealevel change and its known effect upon fl uvial systems (Begin, 1988;Leeder and Stewart, 1996;Blum and Tornqvist, 2000;Paola, 2000;Leeder and Mack, 2007), channel incision during lowstands and aggradation during highstands are to be expected. Channel cutting and subsequent sediment backfi lling are indeed seen in the younger basin fi ll at the landfi ll site and along the Skironian Cliffs.…”

“…In this model, active faulting occurs above the infl ection point of the subducting slab, while formerly active faults and their complementary basins become inactive and are uplifted as they move above the buoyant fl at slab (Leeder et al, 2003;Leeder and Mack, 2007).…”