Grain-Size Analysis of the Late Pleistocene Sediments in the Corinth Rift: Insights into Strait Influenced Hydrodynamics and Provenance of an Active Rift Basin

Under embargo until: 2023-12-08Grain-size analysis of the sediments in borehole M0079A, which is located in the Corinth Rift, was used to explore hydrodynamic conditions and provenance in the Late Pleistcene Corinth Rift. Grain-size populations that were sensitive to the sedimentary environments were characterized by frequency distribution, particle size-standard deviation, and probability cumulative curves. Our results indicate the grain-size population component in the range 0.15-0.25 μm may be used as a sensitive proxy for hyperpycnal flows, which have commonly been triggered by river floods from the southern margin of the rift since ca. 0.593-0.613 Ma. The high-density plumes derived from the longer rivers of the southern rift that were prevalent before ca. 0.593-0.613 Ma. When sediment is supplied as hemipelagic deposition, the proportion of the total grain-size population that is in the 0.3-0.5 μm range becomes an index for suspension fall-out deposits. The core shows coarser sediments during the marine periods and this may be linked to the current circulation related to the Ishtmia Strait opening. The study thus illustrates how the establishment of interbasinal straits can influence the details of sedimentary hydrodynamics in the deep- water axis of an adjacent depocenter.acceptedVersio

Tectono-sedimentary evolution of the Plio-Pleistocene Corinth rift, Greece

The onshore central Corinth rift contains a syn-rift succession >3 km thick deposited in 5–15 km-wide tilt blocks, all now inactive, uplifted and deeply incised. This part of the rift records upward deepening from fluviatile to lake-margin conditions and finally to sub-lacustrine turbidite channel and lobe complexes, and deep-water lacustrine conditions (Lake Corinth) were established over most of the rift by 3.6 Ma. This succession represents the first of two phases of rift development – Rift 1 from 5.0–3.6 to 2.2–1.8 Ma and Rift 2 from 2.2–1.8 Ma to present. Rift 1 developed as a 30 km-wide zone of distributed normal faulting. The lake was fed by four major N- to NE-flowing antecedent drainages along the southern rift flank. These sourced an axial fluvial system, Gilbert fan deltas and deep lacustrine turbidite channel and lobe complexes. The onset of Rift 2 and abandonment of Rift 1 involved a 30 km northward shift in the locus of rifting. In the west, giant Gilbert deltas built into a deepening lake depocentre in the hanging wall of the newly developing southern border fault system. Footwall and regional uplift progressively destroyed Lake Corinth in the central and eastern parts of the rift, producing a staircase of deltaic and, following drainage reversal, shallow marine terraces descending from >1000 m to present-day sea level. The growth, linkage and death of normal faults during the two phases of rifting is interpreted to reflect self-organisation and strain localisation along co-linear border faults. In the west, interaction with the Patras rift occurred along the major Patras dextral strike-slip fault. This led to enhanced migration of fault activity, uplift and incision of some early Rift 2 fan deltas, and opening of the Rion Straits at c. 400–600 ka. The landscape and stratigraphic evolution of the rift was strongly influenced by regional palaeotopographic variations and local antecedent drainage, both inherited from the Hellenide fold and thrust belt

Expedition 381 Summary

The primary objective of International Ocean Discovery Program Expedition 381 was to retrieve a record of early continental rifting and basin evolution from the Corinth rift, central Greece. Continental rifting is fundamental for the formation of ocean basins, and active rift zones are dynamic regions of high geohazard potential. However, the detailed spatial and temporal evolution of a complete rift system needed to understand rift development from the fault to plate scale is poorly resolved. In the active Corinth rift, deformation rates are high, the recent synrift succession is preserved and complete offshore, and earlier rift phases are preserved onshore. Additionally, a dense seismic database provides high-resolution imaging of the fault network and seismic stratigraphy around the basin. As the basin has subsided, its depositional environment has been affected by fluctuating global sea level and its absolute position relative to sea level, and the basin sediments record this changing environment through time. In Corinth, we can therefore achieve an unprecedented precision of timing and spatial complexity of rift-fault system development, rift-controlled drainage system evolution, and basin fill in the first few million years of rift history. The following are the expedition themes: High-resolution fault slip and rift evolution history, Surface processes in active rifts, High-resolution late Quaternary Eastern Mediterranean paleoclimate and paleoenvironment of a developing rift basin, and Geohazard assessment in an active rift. These objectives were and will be accomplished as a result of successful drilling, coring, and logging at three sites in the Gulf of Corinth, which collectively yielded 1645 m of recovered core over a 1905 m cored interval. Together, these cores provide (1) a long rift history (Sites M0078 and M0080), (2) a high-resolution record of the most recent phase of rifting (Site M0079), and (3) the spatial variation of rift evolution (comparison of sites in the central and eastern rift). The sediments contain a rich and complex record of changing sedimentation, sediment and pore water geochemistry, and environmental conditions from micropaleontological assemblages. The preliminary chronology developed by shipboard analyses will be refined and improved during postexpedition research, providing a high-resolution chronostratigraphy down to the orbital timescale for a range of tectonic, sedimentological, and paleoenvironmental studies. This chronology will provide absolute timing of key rift events, rates of fault movement, rift extension and subsidence, and the spatial variations of these parameters. The core data will also allow us to investigate the relative roles of and feedbacks between tectonics, climate, and eustasy in sediment flux, basin evolution, and basin environment. Finally, the Corinth rift boreholes will provide the first long Quaternary record of Mediterranean-type climate in the region. The potential range of scientific applications for this unique data set is very large, encompassing tectonics, sedimentary processes, paleoenvironment, paleoclimate, paleoecology, geochemistry, and geohazards

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

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

Rapid spatiotemporal variations in rift structure during development of the Corinth Rift, central Greece

The Corinth Rift, central Greece, enables analysis of early rift development as it is young (<5Ma) and highly active and its full history is recorded at high resolution by sedimentary systems. A complete compilation of marine geophysical data, complemented by onshore data, is used to develop a high-resolution chronostratigraphy and detailed fault history for the offshore Corinth Rift, integrating interpretations and reconciling previous discrepancies. Rift migration and localization of deformation have been significant within the rift since inception. Over the last circa 2Myr the rift transitioned from a spatially complex rift to a uniform asymmetric rift, but this transition did not occur synchronously along strike. Isochore maps at circa 100kyr intervals illustrate a change in fault polarity within the short interval circa 620-340ka, characterized by progressive transfer of activity from major south dipping faults to north dipping faults and southward migration of discrete depocenters at ~30m/kyr. Since circa 340ka there has been localization and linkage of the dominant north dipping border fault system along the southern rift margin, demonstrated by lateral growth of discrete depocenters at ~40m/kyr. A single central depocenter formed by circa 130ka, indicating full fault linkage. These results indicate that rift localization is progressive (not instantaneous) and can be synchronous once a rift border fault system is established. This study illustrates that development processes within young rifts occur at 100kyr timescales, including rapid changes in rift symmetry and growth and linkage of major rift faults