High-resolution record reveals climate-driven environmental and sedimentary changes in an active rift

Abstract

Young rifts are shaped by combined tectonic and surface processes and climate, yet few records exist to evaluate the interplay of these processes over an extended period of early rift-basin development. Here, we present the longest and highest resolution record of sediment flux and paleoenvironmental changes when a young rift connects to the global oceans. New results from International Ocean Discovery Program (IODP) Expedition 381 in the Corinth Rift show 10s–100s of kyr cyclic variations in basin paleoenvironment as eustatic sea level fluctuated with respect to sills bounding this semi-isolated basin, and reveal substantial corresponding changes in the volume and character of sediment delivered into the rift. During interglacials, when the basin was marine, sedimentation rates were lower (excepting the Holocene), and bioturbation and organic carbon concentration higher. During glacials, the basin was isolated from the ocean, and sedimentation rates were higher (~2–7 times those in interglacials). We infer that reduced vegetation cover during glacials drove higher sediment flux from the rift flanks. These orbital-timescale changes in rate and type of basin infill will likely influence early rift sedimentary and faulting processes, potentially including syn-rift stratigraphy, sediment burial rates, and organic carbon flux and preservation on deep continental margins worldwide.

A new crustal fault formed the modern Corinth Rift

“…Models of mechanics and evolution in the Corinth Rift are diverse, despite an impressive volume of research that spans from the fifth century BC philosophical arguments on mythological attributions given to karstic features in the mountains south of the Corinth Gulf (Herodotus "History"; e.g., Clendenon, 2009) to present-day results of the IODP Expedition 381 in the gulf itself (McNeill et al, 2019). Models lack a coherent view on growth history, kinematics and mechanics of the latest, currently active, rift border fault system and its significance for the Corinth Rift and for generic rift growth processes.…”

Straight from the source's mouth: Controls on field‐constrained sediment export across the entire active Corinth Rift, central Greece

“…In contrast, medium and fine sand, silt and mud may be readily mobilized and transported predominantly as suspended load for the same flow conditions, suggesting disparate timescales of transit for fine and coarse fraction of sediment being supplied to the basin. This observation provides a mechanistic explanation for the facies partitioning seen in the modern Corinth Rift basin architecture where large relatively coarse‐grained Gilbert‐type deltas fringe much of the Gulf and fine sediments dominate the basin fill (McNeill et al, 2019; Moretti et al, 2004). The bedload sediment budget of the rift is primarily composed of pebble grade and coarser sediment, and we infer that this sediment budget corresponds to the Gilbert‐type deltas that fringe much of the Gulf of Corinth with the suspended sediment load primarily contributing to the sediment budget of the main basin depocentre. Together, our results demonstrate how the interplay between bedrock lithology, tectonics, climate and fluvial morphodynamics may manifest in the grain‐size export signal at the rift scale with implications for controls on basin architecture and for inferring paleoenvironmental changes from the sedimentary record.…”

“…The resulting bedload sediment budget, the first for any rift system, shows that 79% of the bedload is pebble grade and coarser (Figure 12) and the remaining 21% is coarse sand to granule grade (Figure 12). The presence of Gilbert‐type deltas, that fringe much of the coast, coupled with new borehole data indicating that the main basin is predominantly composed of muds and silts (McNeill et al, 2019), suggests that (a) the constrained bedload sediment budget is deposited at the coast and does not reach the main basin floor, and for many source catchments this sediment may be entirely sequestered in the their Holocene Gilbert delta or associated proximal turbidite systems (cf. Cullen, Collier, Gawthorpe, Hodgson, & Barrett, 2019); (b) for rivers that do not have large deltas, the bedload is likely mostly trapped on the shelf.…”

“…Using seismic reflection data, Watkins et al (2018) determined that the volume of Holocene‐aged sediment within the Corinth basin (the Gulf of Corinth) is 35 km 3 . This is likely the suspended fraction of the budget as long‐piston cores (Moretti et al, 2004) and IODP drilling results (McNeill et al, 2019) suggest that Holocene sediment is predominantly silts and sands. To quantify the total Holocene sediment budget averaged over the Holocene, we estimated the bedload sediment budget using a range of ratios.…”

“…The presence of the Rion‐Antirion Sill at 60 m depth at the basin's western end (Perissoratis, Piper, & Lykousis, 2000) implies that the basin is isolated during lowstands and effectively closed during highstands with respect to sediment export from the rift (Perissoratis et al, 2000). The modern depositional facies of the Gulf comprise highstand Gilbert deltas that fringe large parts of the Gulf, particularly in the south‐central and eastern portion of the Gulf, and offshore drilling has revealed that the Holocene deposits in the main basin are predominantly mud/silt‐grade sediments (McNeill et al, 2019; Moretti et al, 2004).…”