Active faulting at the western tip of the Gulf of Corinth, Greece, from high-resolution seismic data

peer reviewedThe Gulf of Corinth is one of the fastest-spreading intra-continental rifts on Earth. GPS data indicate that the rift is currently opening in a NNE-SSW direction, with a rate of extension reaching up to 16 mm yr-1 in its westernmost part. Although the rest of the offshore rift has been well studied, the western tip of the rift is still poorly explored. We present an accurate map of submarine faults in this area based on two high-resolution seismic reflection surveys (single channel sparker). In the eastern part of the studied area, the sedimentary infill is affected by the known North Eratini, South Eratini and West Channel faults. Further to the west, the seafloor is mostly flat, and is bounded to the north by the normal, south-dipping, Trizonia fault. To the north, the shallower part of the Gulf shows to the east a diffuse pattern of normal and strike-slip deformation which is replaced to the west by a 7.5 km long SE striking strike-slip fault zone, called the Managouli fault zone. To the westernmost tip of the Gulf, in the Nafpaktos Basin, two fault sets with different strikes are encountered; the one with aNE-SW strike exhibits a clear strike-slip component. The western tip of the Gulf of Corinth is the only part of the Corinth Rift where convincing evidence for strike-slip movement has been found. This fault pattern is likely related to the complex deformation occurring at the diffuse junction at the western tip of the Rift between three crustal blocks: Continental Greece, Peloponnese, and the Ionian Island-Akarnia block

Influence of bottom currents on the sedimentary processes at the western tip of the Gulf of Corinth, Greece

We investigated the sedimentary processes that were active during the Holocene in the Gulf of Corinth, using high-resolution seismic reflection profiles and gravity cores. Seismic reflection data clearly show the presence of shallow-water sediment drifts at the western end of the Gulf, close to the Rion Sill that links the gulf to the Ionian Sea. Short cores indicate that drifts are composed of homogenous bioturbated mud in their upper part. The drift deposits flank a wide central area where the sea floor is eroded and where pre-Holocene deposits locally outcrop. The sea floor morphology in this area is marked by furrows oriented in different directions and by a depression attributed to the action of bottom-currents. The magnetic fabric of sediment samples from the drift, shelves, sub-basins and from the basin floor show a significant anisotropy and a similar orientation of Kmax axes along core. The largest anisotropy (P = 1.043 ± 0.007) is observed in the drift and is interpreted as resulting from the action of bottom currents. The similar orientation of Kmax axes in the other cores, collected from areas East of the drifts, suggests that bottom currents also affect sediment deposition in the rest of the study area, even if seismic profiles and core analyses demonstrate that gravitational processes such as submarine landslides and turbidity currents exert the main control on sediment transport and deposition. Average Kmax axes for four cores were reoriented using the declination of the characteristic remanent magnetization. Kmax axes show variable orientations relatively to the slope of the sea floor, between along-slope and roughly parallel to the contour lines.SISCO

Investigations on the Peach 4 Debrite, a Late Pleistocene Mass Movement on the Northwest British Continental Margin

The Peach 4 debrite is the most recent in a series of large scale Pleistocene MTDs within the Barra fan on the northwest British continental margin. Geophysical data indicate that Peach 4 was formed through a combination of blocky and muddy debris flows and affects an area of ~ 700 km2. BGS core sample 56 -10 36, located directly over the Peach 4 debrite, provides a minimum age of 14.68 ka cal BP for the last major failure. An upwards fining turbidite sequence in BGS core sample 56 -10 239 is associ-ated with increased As and S concentrations, indicators of diagenetic pyrite which forms under anoxic conditions. It is proposed that As and S concentrations may pro-vide a method of distinguishing between contourite and turbidite sedimentation, though further research is required

Evolution of depositional and slope instability processes on Bryant Canyon area, Northwest Gulf of Mexico

Bryant and Eastern Canyon systems are located on the northwest Gulf of Mexico, and they are characterized by a very complex sedimentological history related to glacioeustatic cycles, river discharges, and interactions of depositional and halokinetic processes. Both canyon systems were active during the low sea-level stand of Oxygen Isotope Stage 6, and provided the pathways for the transport of enormous amounts of sediments on the continental slope and abyssal plain of the northwest Gulf of Mexico. Right after their abandonment, at the beginning of Stage 5, salt diapirs encroached into the canyons, and resulted in their transformation into a network of intraslope basins. The transformation of the canyons resulted in the generation of massive sediment failures. The mid-shelf (Stages 4 and 3) to shelf edge (Stage 2) lowering of the sea-level during the last glacial episode resulted in: 1) extensive river-sourced deposits on the outer shelf and/or upper continental slope that contributed in a seaward mobilization of the underlying salt masses, and 2) the generation of numerous gravity flows and turbidity currents on the outer shelf/upper continental slope. The seaward mobilization of the salt masses resulted in the oversteepening of the flanks of the basins, and consequently in the generation of numerous and massive sediment failures. The turbidity currents were confined on the intraslope basins of the upper continental slope, depositing their coarsest material. However, their most diluted upper and end members were able to continue their downslope propagation depositing characteristic fine-grained turbidites. The frequency of the turbidity currents was highly increased during the last glacial maximum (Stage 2), and three short melt-water pulses centered at 30.5, 36, and 52 ky B.P. The last deglaciation event is characterized by the development of a major melt water event that resulted in the deposition of distinct organic rich sediments, similar to the sapropels of the Eastern Mediterranean. At about 11 ky B.P. the melt water discharges of the North America switched from Mississippi River to St Lawrence Seaway, causing the domination of hemipelagic sedimentation on the continental slope of the northwest Gulf of Mexico

A DEBATE ON THE SIMILARITY OF PARTICLE SIZING RESULTS DERIVED FROM THE ANALYSIS OF FINEGRAINED SEDIMENTS BY TWO DIFFERENT INSTRUMENTATIONS

Δύο ενόργανες μέθοδοι κοκκομετρικής ανάλυσης εφαρμόζονται για την ανάλυση θαλάσσιων λεπτόκοκκων ιζημάτων συλλεγμένων από τον πυθμένα του Κορινθιακού κόλπου, για την σύγκριση των αποτελεσμάτων τους. Οι τεχνικές που χρησιμοποιούνται είναι η μέθοδος της περίθλασης της ακτίνας λείζερ (Laser diffraction ή LS) και κοκκομετρική ανάλυση με τη μέθοδο της ηλεκτροαντίστασης (Electroresistance particle counting ή CC). Αν και ικανός αριθμός εργασιών έχουν δημοσιευθεί ως αναφορά στη σύγκριση μεταξύ των ενόργανων και των κλασσικών (κόσκινα-πιπέτα) μεθόδων κοκκομετρικής ανάλυσης, λίγα στοιχεία είναι διαθέσιμα σχετικά με τη σύγκριση των αποτελεσμάτων των ενόργανων μεθόδων και ιδιαίτερος αυτών της παρούσας εργασίας. Η σύγκριση των στατιστικών παραμέτρων με τη μέθοδο των ροπών έδειξε ότι η LS μέτρησε μικρότερες τιμές μέσου μεγέθους (αδρομερέστερα δείγματα) από ότι η CC. Η συσχέτιση των ποσοστών των κλάσεων πηλού και αργίλου κρίνεται ικανοποιητική (R=0.69). Η απόκλιση των μετρήσεων των αδρομερεστέρων κλασμάτων των δειγμάτων είναι αποτέλεσμα του γεγονότος ότι οι δύο μέθοδοι μετρούν το μέγεθος των κόκκων με βάση διαφορετικές ιδιότητες τους (σχήμα, πυκνότητα). Η απόκλιση των aπoτεL·σμάτωv μεταξύ των δυο μεθόδων αυξάνεται σε δείγματα που χαρακτηρίζονται από την παρουσία ενός κυριάρχου τύπου (mode) με ποσοστό συμμετοχής συνήθως άνω του 6 %.A set of grab-sample sediments collected from the basin floor of the Corinth Gulf, Greece, was analysed using two different techniques; LS 230 laser system and Coulter Counter TA II. The present study presents the results derived from the comparison between the two techniques. The correlation between the mean size and the sorting values obtained from the two methods is moderate. Also moderate are the correlations estimated for the fractions of clay and silt obtained from the two methods Furthermore the analysis showed that the Laser Coulter determines coarser grain sizes than the Coulter. The analysis of variation/residuals within individual size intervals showed a higher variability of residuals for the coarser fractions (7-6 and 5-4 phi)

Morphology of late Quaternary submarine landslides along the U.S. Atlantic continental margin

This paper is not subject to U.S. copyright. The definitive version was published in Marine Geology 264 (2009): 4-15, doi:10.1016/j.margeo.2009.01.009.The nearly complete coverage of the U.S. Atlantic continental slope and rise by multibeam bathymetry and backscatter imagery provides an opportunity to reevaluate the distribution of submarine landslides along the margin and reassess the controls on their formation. Landslides can be divided into two categories based on their source areas: those sourced in submarine canyons and those sourced on the open continental slope and rise. Landslide distribution is in part controlled by the Quaternary history of the margin. They cover 33% of the continental slope and rise of the glacially influenced New England margin, 16% of the sea floor offshore of the fluvially dominated Middle Atlantic margin, and 13% of the sea floor south of Cape Hatteras. The headwall scarps of open-slope sourced landslides occur mostly on the lower slope and upper rise while they occur mostly on the upper slope in the canyon-sourced ones. The deposits from both landslide categories are generally thin (mostly 20–40 m thick) and comprised primarily of Quaternary material, but the volumes of the open-slope sourced landslide deposits can be larger (1–392 km3) than the canyon-sourced ones (1–10 km3). The largest failures are located seaward of shelf-edge deltas along the southern New England margin and near salt domes that breach the sea floor south of Cape Hatteras. The spatial distribution of landslides indicates that earthquakes associated with rebound of the glaciated part of the margin or earthquakes associated with salt domes were probably the primary triggering mechanism although other processes may have pre-conditioned sediments for failure. The largest failures and those that have the potential to generate the largest tsunamis are the open-slope sourced landslides.The U.S. Nuclear Regulatory Commission and the U.S. Geological Survey are acknowledged for their support of this research.Work was funded by US Nuclear Regulatory Commission grant N6480 Physical study of tsunami sources

True volumes of slope failure estimated from a Quaternary mass-transport deposit in the northern South China Sea

Submarine slope failure can mobilize large amounts of seafloor sediment, as shown in varied offshore locations around the world. Submarine landslide volumes are usually estimated by mapping their tops and bases on seismic data. However, two essential components of the total volume of failed sediments are overlooked in most estimates: a) the volume of sub-seismic turbidites generated during slope failure and b) the volume of shear compaction occurring during the emplacement of failed sediment. In this study, the true volume of a large submarine landslide in the northern South China Sea is estimated using seismic, multibeam bathymetry and ODP/IODP well data. The submarine landslide was evacuated on the continental slope and deposited in an ocean basin connected to the slope through a narrow moat. This particular character of the sea floor provides an opportunity to estimate the amount of strata remobilized by slope instability. The imaged volume of the studied landslide is ~1035±64 km3, ~406±28 km3 on the slope and ~629±36 km3 in the ocean basin. The volume of sub-seismic turbidites is ~86 km3 (median value) and the volume of shear compaction is ~100 km3, which are ~8.6% and ~9.7% of the landslide volume imaged on seismic data, respectively. This study highlights that the original volume of the failed sediments is significantly larger than that estimated using seismic and bathymetric data. Volume loss related to the generation of landslide-related turbidites and shear compaction must be considered when estimating the total volume of failed strata in the submarine realm

Eco-biostratigraphic advances in late quaternary geochronology and palaeoclimate : the marginal Gulf of Mexico analogue

This study combines high-resolution planktonic foraminiferal eco-biostratigraphy and palaeoclimatic data from the high-sedimentation-rate core JPC-26 from the northwestern margin of the Gulf of Mexico (GoM). The eco-biozones recognized (GOMPFE1-12) being correlated with published Mg/Ca-based sea surface temperatures. This updated palaeoclimatic and stratigraphic reference record facilitates correlations with the Greenland ice core events and their climatic relationships, and also provides a solid stratigraphic framework for correlations with other palaeoclimatic and palaeoceanographic records in the circum-GOM/Caribbean region. This multidisciplinary approach underlines the utility of supporting conventional dating methodologies with different constraints, and further reveals a powerful tool for reliably correlating marine records between comparable deep-sea marginal settings and coeval sequences of this region

Lateral variability in strain along a mass-transport deposit (MTD) toewall: a case study from the Makassar Strait, offshore Indonesia

Contractional features characterise the toe domain of mass-transport deposits (MTDs). Their frontal geometry is typically classified as frontally-confined or frontally-emergent. However, it remains unclear how frontal emplacement style and contractional strain within an MTD can vary along strike. We use bathymetry and 3D seismic reflection data to investigate lateral variability of frontal emplacement and strain within the toe domain of the Haya Slide in the Makassar Strait. The slide originated from an anticline flank collapse, and the toe domain is characterised by a radial fold-and-thrust belt that reflects southwestwards emplacement. The frontal geometry of the slide changes laterally. In the S, it is frontally-confined, associated with a deep, c. 200 mbsf, and planar basal shear surface. The frontal geometry gradually changes to frontally-emergent in the W, associated with a shallow, c. 120 mbsf, and NE-dipping, c. 3o, basal shear surface. Strain analysis shows c. 8-14% shortening, with cumulative throw of the thrusts that increases along strike westwards from c. 20-40 to c. 40-80 m. We show that even minor horizontal translation of MTDs (c. 1 km) can result in marked lateral variability in frontal geometry and strain within the failed body, which may influence their seal potential in petroleum systems