High-resolution Seismic Reflection Data Research Articles

A review of sinuous channel avulsion patterns in some major deep-sea fans and factors controlling them

This paper reviews side-scan sonar, multi- and single-beam echo-sounder, and high-resolution seismic reflection data, and discusses the anatomy and patterns of the most recent sinuous channel avulsions in the Amazon, Zaire, Indus and Bengal Fans, all located along passive continental margins and all fed by major river systems. Channel patterns formed by fore- (seaward) or back- (landward) stepping avulsions are common in the western Amazon Fan and in the Northern and Axial Zaire Fan. However, channels in the Indus and Bengal Fans, and in the Southern Zaire Fan, appear to form radial patterns, with most of the main avulsions having occurred in relatively restricted areas (avulsion nodes). High degrees of development of channel instabilities or avulsion-threshold conditions (e.g. channel sinuosity increase and lengthening, channel thalweg aggradation, differential channel fill and decrease in channel relief, slumping and channel plugging, bank cohesion), and increased peak volumes and speeds of turbidity currents, determined where avulsions occurred in the fan channels. During the Late Quaternary intervals considered here, several global sea-level falls and rises occurred and these, along with climatic changes, are likely to have influenced sediment-gravity flows and may have thus timed many, if not all, significant avulsions. However, available data do not allow documentation of this timing in many cases. The main differences between fan areas with (1) fore-and back-stepping and (2) radial channel avulsion patterns are that, in the former case, fan gradients are steeper with frequent slope breaks, and channel thalweg aggradation occurs along much of the depositional profile. In the latter case, downdip of avulsion nodes, fan gradients are either flat or possibly have no breaks, and channels are incised below the fan surface with no thalweg aggradation in the middle and lower fan regions. These characteristics may have caused differences in avulsion-triggering turbidity flow volumes and avulsion threshold conditions that, in turn, may have resulted in different channel avulsion patterns.

Seismostratigraphic analysis of the Transkei Basin: A history of deep sea current controlled sedimentation

The Earth's climate is controlled by various factors, with large scale ocean currents playing a significant role. In particular, the global thermohaline circulation of water masses like the Antarctic Bottom Water (AABW), or the North Atlantic Deep Water (NADW), is a global motor for maintaining the exchange of water masses. The AABW and NADW have met and interacted off South Africa since Oligocene times. Here, the narrow deep Agulhas Passage gateway, located between South Africa and the submarine Agulhas Plateau, constrains bottom water exchange between the southeast Atlantic and the southwest Indian Ocean. A seismostratigraphic analysis of sedimentary structures in the Transkei Basin, which opens up at the eastern end of the Agulhas Passage, was carried out, to reconstruct the palaeocurrents off South Africa. The analysis of newly collected high resolution seismic reflection data showed the effect of large scale current deposition. There are at least 5 major sedimentary phases to observe, some of which seem to be influenced by NADW and AABW. The first stage represents ongoing deep sea sedimentation from middle Cretaceous to middle Tertiary times. Later stages are separated by discordances, which represent the onset of AABW and NADW, among others, triggered by the opening of the Drake Passage gateway (∼ 35 Ma) and the closure of the Isthmus of Panama (∼ 3 Ma). We found two large drift bodies located one above the other. Corresponding to their shape and position, the older drift is inferred to have been deposited by currents flowing in a north–southerly direction, whereas the younger drift lies perpendicular to it and seems to be built up by west–east flowing currents.

Marine Isotope Stage 6 Canyon and Spillover Deposits of the Bryant and Eastern Canyon Systems, Northwest Gulf of Mexico: Importance of Fine-Grained Turbidites on a Delta-Fed Prograding Slope

Abstract A large set of long sediment cores and high-resolution seismic-reflection data were used to study the sedimentology of the delta-fed prograding slope of the northwest Gulf of Mexico, during Marine Isotope Stage (MIS) 6 (125–180 ka). Bryant and Eastern canyon systems were the main pathways during this period through which Mississippi River sediment was delivered down the continental slope. Two MIS 6 sedimentary environments have been defined on the slope of the northwest Gulf of Mexico: intracanyon and overbank environments. The erosional action of turbidity currents in Bryant and Eastern canyons was focused mainly on the thalweg, whereas, on the rest of the canyon floors, the flows acquired a mainly depositional character, resulting in the formation of inner levees and terraces. MIS 6 deposits in overbank environments consist entirely of thick (> 50 m), widespread (> 15–20 km), and continuous successions of mud turbidites, which indicate that spillover processes were dominant along Bryant and Eastern canyons. The total absence of bioturbation structures and hemipelagic sediments in MIS 6 overbank deposits indicate high sedimentation rates exceeding 200–600 cm/ky. The majority of the overbank deposits are normally graded, indicating that most of the turbidity currents during MIS 6 resulted from sediment failures on the outer shelf and upper continental slope. Sedimentological observations indicate that a complete mud turbidite sequence (T0–8 sequence in the nomenclature of Stow and Shanmugam 1980) results from a waning low-density turbidity current consisting of four successive flow-regime stages: (1) an initial erosional stage (≥ 30 cm/s), (2) deposition of the coarsest, noncohesive fraction (silt) of the suspended sediment in the flows (30–100 cm/s), (3) cyclic deposition of cohesive (mud) and noncohesive (silt) laminae due to fluctuations in the shear stress in the boundary layer of the flow (12–30 cm/s), and (4) deposition from a silt-depleted and slowly moving (≤ 15 cm/s) sediment cloud.

Shallow stratigraphy and sedimentation history during high-frequency sea-level changes on the central California shelf

Analyses of high-resolution seismic-reflection data and sediment cores indicate that an extensive sediment deposit on the central California continental shelf is comprised of several late-Pleistocene to Holocene age facies. Offshore of the littoral zone, in water depths of 30–90 m, a 3–6 m thick veneer of fine sediment referred to as the mid-shelf mudbelt has formed along 50–100 km of the coast. The mudbelt drapes a parasequence characterized by prograding clinoforms that in places overlies a 1–3 m thick basal transgressive lag deposit. These facies overlie a prominent erosional unconformity that extends from the shore to the outer shelf. Eighteen calibrated 14C AMS ages of marine molluscs and terrestrial wood detritus sampled in cores range 15,800 yr BP to modern indicating a postglacial age for these sediments (one >55,000 yr BP represents relict sand). We model accumulation of these facies using (1) the topography of the underlying erosional unconformity interpreted from seismic reflection profiles, (2) observed sediment facies (grain size) distribution across the shelf (a proxy for wave/current sediment partitioning), and published estimates of (3) eustatic sea-level history, and (4) regional tectonics. Our model and data indicate that deposition of the transgressive lag began during early, slow postglacial sea-level rise and that a notable change in depositional environment occurred across an area of more than 200 km 2 of the outer shelf likely in response to abrupt drowning during Meltwater Pulse 1B (11,500 yr BP). We propose that rapid progradation of clinoforms may have occurred during transgression because of the unique interaction of modest rates of sediment input and tectonic uplift, variable rates of eustatic sea-level rise and a complex stepped antecedent topography.

Late Quaternary (marine isotope stages 6-1) seismic sequence stratigraphic evolution of the Otago continental shelf, New Zealand

A proposed chronostratigraphic model for the Late Quaternary evolution of the Otago continental shelf, New Zealand, includes fluvially incised sequence boundaries eroded during marine isotope stages 2, 4 and 6, bounding three sequences subdivided into lowstand, transgressive and highstand/regressive systems tracts. Datable material is limited to the uppermost 1 m of the sequence, and consequently the model is based on correlation of new high-resolution seismic reflection data (Geopulse™) to a compilation of independent global sea-level curves. A second chronostratigraphic model that lacks a stage 4 sequence boundary and distinct stage 3 highstand/forced regressive deposit is discounted because its subsidence-corrected paleoshoreline depths do not match lowstands in the eustatic curves or temporally constrained sequences at other far-field locations. In the preferred chronostratigraphic model, sea-level lowstands during stages 2, 4 and 6 reached maximum depths of 126–131 m, 101–111 m and 116–135 m, respectively, producing sequence boundaries, landward-pinching deltaic wedges on the outer Otago shelf, and submarine canyon incision. Lowstand paleoshoreline depths have been corrected for subsidence from thermal cooling, sediment compaction and loading, but may be erroneously deep owing to erosion of paleoshoreline indicators. Clastic, shallow marine wedges and back-barrier valley-fill deposits accumulated during the stage 6–5, 4–3 and 2–1 marine transgressions. Contrary to the traditional sequence stratigraphic model, deltaic and strandline units deposited during highstand through falling sea level (stages 5–4, 3–2, 1) volumetrically dominate Otago Late Quaternary sequences. Discrete units and minor marine erosion surfaces within the transgressive and regressive systems tract deposits are interpreted as strong evidence for seventh- (∼ 20 ka) or higher-order sea-level fluctuations influencing sedimentation on the Otago shelf.

Migration of the Pee Dee River system inferred from ancestral paleochannels underlying the South Carolina Grand Strand and Long Bay inner shelf

Several generations of the ancestral Pee Dee River system have been mapped beneath the South Carolina Grand Strand coastline and adjacent Long Bay inner shelf. Deep boreholes onshore and high-resolution seismic-reflection data offshore allow for reconstruction of these paleochannels, which formed during glacial lowstands, when the Pee Dee River system incised subaerially exposed coastal-plain and continental-shelf strata. Paleochannel groups, representing different generations of the system, decrease in age to the southwest, where the modern Pee Dee River merges with several coastal-plain tributaries at Winyah Bay, the southern terminus of Long Bay. Positions of the successive generational groups record a regional, southwestward migration of the river system that may have initiated during the late Pliocene. The migration was primarily driven by barrier-island deposition, resulting from the interaction of fluvial and shoreline processes during eustatic highstands. Structurally driven, subsurface paleotopography associated with the Mid-Carolina Platform High has also indirectly assisted in forcing this migration. These results provide a better understanding of the evolution of the region and help explain the lack of mobile sediment on the Long Bay inner shelf. Migration of the river system caused a profound change in sediment supply during the late Pleistocene. The abundant fluvial source that once fed sand-rich barrier islands was cut off and replaced with a limited source, supplied by erosion and reworking of former coastal deposits exposed at the shore and on the inner shelf.

Multiple bottom-simulating reflections in the Black Sea: Potential proxies of past climate conditions

A previously unknown pattern of multiple bottom-simulating reflections (BSRs) occurs on high-resolution reflection seismic data in the Danube deep-sea fan, associated with acoustic features indicating free gas. Our study provides evidence that this pattern is developed in relation with the architecture of distinct channel–levee systems of the Danube fan. Channel–levee systems hosting multiple BSRs act as relatively sealed gas-bearing systems whose top is situated above the base of the gas hydrate stability zone (BGHSZ). Inside these systems, free gas accumulates below the BGHSZ under a combined lithological, structural and stratigraphical control. The uppermost BSR marks the current equilibrium BGHSZ, for a gas composition of more than 99% methane. Model-derived depths of the BGHSZ for different gas compositions and pressure–temperature conditions show that multiple BSRs would correspond to the BGHSZ either for (1) layers of gas hydrates with high contents of heavy hydrocarbons or hydrogen sulphide, or (2) stable climatic episodes with temperatures between glacial values and the present-day conditions. As the gas hydrate compositions required by hypothesis (1) are in sharp contradiction with the general background of the gas composition in the study area, we suggest that multiple BSRs are most probably relics of former positions of the BGHSZ, corresponding to successive steps of climate warming. In this case, they can provide sea-bottom paleotemperature values for these episodes, and hence they are potential new proxies for deciphering past climate conditions.

Shallow high-resolution seismics and reprocessing of industry profiles in southern Bavaria: The Molasse and the northern Alpine front

The purpose of this seismic investigation in the Upper Bavarian Miesbach area, as part of the international TRANSALP project, was to study the tectonic contact between the autochthonous Foreland Molasse and the allochthonous Folded Molasse marking the tectonic front of the Alpine orogen. Another specific target was the dip of the frontal emerging main thrust of the tectonic units Helveticum/Ultrahelveticum and Rhenodanubian Flysch overriding the Folded Molasse. Twelve seismic profiles obtained from the hydrocarbon industry were reprocessed. From the Foreland Molasse southward to the Autochthonous Molasse in the subsurface of the overthrust Folded Molasse conspicuous features such as steep normal faults at the Molasse base, S-directed thickening of Molasse sediments or sedimentary discordant base of Upper Marine Molasse can be recognized. Shallow high-resolution seismic measurements were conducted along two profiles across the tectonic contact between Foreland Molasse and Folded Molasse, as well as along a profile across the frontal emerging main thrust of the Helveticum/Ultrahelveticum and the Rhenodanubian Flysch. Geological structures could be identified in the top 300–500 ms two-way traveltime interval, which is hardly possible with the usual deep-seismic method. The method thus provides a bridge between deep-reflection seismics and surface geology. In contrast to the western Bavarian Molasse zone, the tectonic boundary between the Foreland Molasse and the Folded Molasse in the investigated area is not characterized by a large blind-thrust triangle zone but by a simple south-dipping thrust plane. Adjacent to the S follow several steeply south-dipping inverse Molasse thrust slices and the Miesbach syncline. The inverse thrust slices are interpreted as the overturned and sheared northern limb of a fault propagation fold, which linked the Folded Molasse to the Foreland Molasse during a final orogenic phase. The main thrust of the Helveticum/Ultrahelveticum and the Rhenodanubian Flysch are well imaged in the near-surface interval of the high-resolution reflection seismic data. In contrast to previously published results, these thrust planes show a gentle dip to the S from the surface down to at least 500–1000 m depth.

Shelf stratigraphy and the influence of antecedent substrate on Holocene reef development, south Oahu, Hawaii

Paired analyses of drill cores and high-resolution seismic reflection data show that development of Holocene framework reefs on the Oahu (Hawaii) shelf is limited to settings of low wave energy and to the period 8000 to 3000 yr BP. A prominent bounding surface that is mapped across much of the Oahu shelf is an erosion surface cut into Marine Isotope Stages 5 and 7 limestones that show extensive loss of primary porosity, aragonite, and MgCO 3 owing to meteoric and vadose-zone diagenesis. This acoustic reflector is found exposed at the surface where wave energy is high or in the shallow subsurface below Holocene reef and sand sheet deposits where energy is low. Ship-towed video along 30 km of the shelf reveals a steady decrease in limestone accumulation from offshore of Honolulu southeast to Koko Head where the seafloor is characterized by volcanic pavement and/or thin sand deposits. This may reflect the build-up of late Pleistocene volcanics associated with the Hanauma Bay eruption (30,000–7000 yr BP) that now comprise the substrate in depths shallow enough to limit reef accretion. The absence of significant Holocene reef build-up on the south Oahu shelf is consistent with observations from north-facing coasts that lack Holocene reefs, indicating that Holocene reef formation in Hawaii is complex and patchy.

The Fugløy Reef at 70°N; acoustic signature, geologic, geomorphologic and oceanographic setting

This is the first in-depth study of a cluster of cold-water coral reefs, the Fugloy Reefs, found at 70°N on the Norwegian margin. Combining high-resolution seismic reflection data, side-scan sonar, video-images, and oceanographic measurements reveals the geologic, geomorphologic and oceanographic setting in which the reefs occur. The reefs consist mainly of the scleractinian ahermatypic Lophelia pertusa, and exist below the thermocline at water depths between 140 m and 190 m. The reefs appear as cone-shaped, acoustically transparent features on seismic reflection data, consistently located in places characterized by the availability of hard substrate, high relief, and periodical exposure to high tidal currents (>30 cm/s). These currents transport water of the Norwegian Atlantic Current to the reefs from an area with fluid expulsion-related pockmarks. The spatial relationship between reef, pockmark locations, and current directions suggests that seepage of biogenic gas might be a catalyst to reef growth. With a height of more than 40 m some of the Fugloy reefs are among the highest reported from the Norwegian Margin. This indicates highly favourable growth conditions, and conservative estimates indicate a net growth rate for the reefs of ~5 mm/year. We expect that cold-water reefs will be found further north along the Barents Sea margin as general awareness on the geophysical signature and appearance of the reefs increases, because all known factors involved in reef establishment and growth are within the required intervals also further north.

Imaging of Buried Archaeological Materials: The Reflection Properties of Archaeological Wood

Effective marine archaeological site management demands detailed information on not only the spatial distribution of artefacts but also the degradation state of the materials present. Although sonar methods have frequently been used in an attempt to detect buried wooden shipwrecks they are currently unable to indicate their degradation state. To assess the sensitivity of acoustic measurements to changes in the degradation state of such material, and hence the potential for sonars to quantify degradation, laboratory measurements of compressional wave velocity, as well as bulk density for oak and pine samples, in varying states of decay, were undertaken. These data enabled the calculation of theoretical reflection coefficients for such materials buried in various marine sediments. As wood degrades, the reflection coefficients become more negative, resulting in the hypothesis that the more degraded wood becomes, the easier it should be to detect. Typical reflection coefficients of the order of −0.43 and −0.52 for the most degraded oak and pine samples in sand are predicted. Conversely, for wood exposed to seawater the predicted reflection coefficients are large and positive for undegraded material (0.35 for oak, 0.18 for pine) and decrease to zero or slightly below for the most degraded samples. This indicates that exposed timbers, when heavily degraded, can be acoustically transparent and so undetectable by acoustic methods. Corroboration of these experimental results was provided through comparison with high resolution seismic reflection data that has been acquired over two shipwrecks.

Integration of High and Very High-resolution Seismic Reflection Profiles to Study Upper Quaternary Deposits of a Coastal Area in the Western Gulf of Lions, SW France

High resolution (HR – sparker) and very high resolution (VHR – boomer) seismic reflection data acquired in shallow water environments of the Roussillon coastal area are integrated to provide an accurate image of the stratigraphic architecture of the Quaternary deposits. The complementary use of the two systems is shown to be of benefit for studies of shallow water environments. The HR sparker data improved the landward part of a general model of Quaternary stratigraphy previously established offshore. They document an incised valley complex interpreted as the record of successive late Quaternary relative sea-level cycles. The complex is capped by a polygenetic erosional surface developed during the last glacial period (>18 ky) and variably reworked by wave ravinement during the subsequent post-glacial transgression. The overlying transgressive systems tract is partly preserved and presents a varying configuration along the Roussillon coastal plain. The VHR boomer data provide information on the architecture of the uppermost deposits, both in the near-shore area and in the lagoon. These deposits overlie a maximum flooding surface at the top of the transgressive systems tract and constitute a highstand systems tract composed of two different architectural elements. In the near-shore area, a sandy coastal wedge is subdivided into a lower unit and an upper unit in equilibrium with present day dynamics. In the Salses-Leucate lagoon area, the sedimentary architecture is highly complex due to the closure of a former embayment and the formation of the present beach barrier.

Sedimentary sequences in the Gulf of Lion: A record of 100,000 years climatic cycles

The wide continental shelf of the Gulf of Lion (up to 70 km) has been the object of numerous investigations since the early days of oceanography. Yet, the question of sequences duration, the mechanisms of deposition and factors implied remained unanswered. A study of a very dense grid of Very High Resolution (VHR) seismic reflection (Sparker) data associated with surficial cores both, collected by IFREMER between 1992 and 2001 on the outer shelf and upper slope offshore of Sète in the Languedoc region gives a new insight into these issues. Analysis of the 3D geometry of the sedimentary record reveals a basic depositional pattern consisting of a pair of horizontally juxtaposed and downlapping prisms. Prism PI with low angle clinoforms (<1°) lies on the upper part of the shelf and is interpreted to be prodeltaic-offshore deposits. Prism PII with steeply dipping clinoforms (∼4°) lies on the outer shelf between 40 and 70 km from the present day coastline and is interpreted to be littoral deposits. Results obtained from integrating lithology, palynology, micropaleontology, seismic stratigraphy, stratigraphic simulation, support the hypothesis that the basic depositional pattern records a 100 000-years glacioeustatic (interglacial/glacial) cycle. As previously suggested by Aloïsi [Aloïsi, J.C., 1986. Sur un modèle de sédimentation deltaïque: contribution à la connaissance des marges passive, Thèse de Doctorat d'Etat. Université de Perpignan, 162 pp], prisms PI corresponds to deposition at high sea level and prisms PII to deposition during low sea level at glacial maxima. Five sequences of paired prisms capped by five major erosion surfaces have been identified and modelled showing that the corresponding glacioeustatic cycles (the last five cycles at least) are recorded on the shelf of the western part of the Gulf of Lion.

Salt tectonics off northern Israel

The Messinian evaporites in the Eastern Mediterranean represent a world class site to study thin-skinned salt tectonic processes like gravity gliding or gravity spreading. In contrast to the Mesozoic evaporites in the Atlantic the related structures are just slightly overprinted by additional tectonic events. New high-resolution reflection seismic data image for the first time the entire lateral succession of gravity gliding-related features as they were suggested by analog models and demonstrate therewith the validity of those models for the Messinian evaporites. All three regimes of extension, translation and compression are present within the range of the seismic profiles. However, additional observations lead to an adapted and improved model. The generation of a critical slope angle caused by subsidence of the Levantine Basin is considered to be the main driving force for the thin-skinned salt tectonics and the lateral basinward creep of the basinal Messinian evaporites. In the extensional section beneath or near to the continental slope, where the basinal evaporites have been withdrawn, listric and antithetic listric growth faults, rollovers and keystone grabens form asymmetric turtleback structures above salt welds and salt rollers. Further basinwards an area with little or no deformation of the evaporites defines the translational segment. In the compressional region the lower and thickest part of the evaporites show ductile deformation (buckle folds), and the upper evaporites reveal brittle deformation (reverse faults and pop-up structures). Here the basinal evaporites have a maximum thickness of about 1500 m. The extensional zone shows continuous synsedimentary tectonic activity until recent times, whereas the compressional structures have developed later in a rather sudden event. There is clear evidence for neotectonics off the Israeli coast which is not related to salt dynamics. Faults cut through the entire pile of evaporites and the Post-Messinian overburden. Where the faults pierce the sea floor, mud escape structures have been observed. Deep rooted faults have been interpreted at the base of the Messinian paleo-slope, suggesting a shear zone off Israel and parallel to the Dead Sea Transform.

Recent Deformation along the Offshore Malibu Coast, Dume, and Related Faults West of Point Dume, Southern California

Offshore faults west of Point Dume, southern California, are part of an important regional fault system that extends for about 200 km, from near the city of Los Angeles westward along the south flank of the Santa Monica Mountains and through the northern Channel Islands. This boundary fault system separates the western Transverse Ranges, on the north, from the California Continental Borderland, on the south. Previous research showed that the fault system includes many active fault strands; consequently, the entire system is considered a serious potential earthquake hazard to nearby Los Angeles. We present an integrated analysis of multichannel seismic- and high-resolution seismic-reflection data and multibeam-bathymetric information to focus on the central part of the fault system that lies west of Point Dume. We show that some of the main offshore faults have cumulative displacements of 3–5 km, and many faults are currently active because they deform the seafloor or very shallow sediment layers. The main offshore fault is the Dume fault, a large north-dipping reverse fault. In the eastern part of the study area, this fault offsets the seafloor, showing Holocene displacement. Onshore, the Malibu Coast fault dips steeply north, is active, and shows left-oblique slip. The probable offshore extension of this fault is a large fault that dips steeply in its upper part but flattens at depth. High-resolution seismic data show that this fault deforms shallow sediment making up the Hueneme fan complex, indicating Holocene activity. A structure near Sycamore knoll strikes transversely to the main faults and could be important to the analysis of the regional earthquake hazard because the structure might form a boundary between earthquake-rupture segments.

Active faulting within the offshore western Gulf of Corinth, Greece: Implications for models of continental rift deformation

Research Article| April 01, 2005 Active faulting within the offshore western Gulf of Corinth, Greece: Implications for models of continental rift deformation L.C. McNeill; L.C. McNeill 1Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar C.J. Cotterill; C.J. Cotterill 1Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar T.J. Henstock; T.J. Henstock 1Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar J.M. Bull; J.M. Bull 1Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar A. Stefatos; A. Stefatos 2Laboratory of Marine Geology and Physical Oceanography, University of Patras, Patras 26500, Greece Search for other works by this author on: GSW Google Scholar R.E.Ll. Collier; R.E.Ll. Collier 3School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar G. Papatheoderou; G. Papatheoderou 4Laboratory of Marine Geology and Physical Oceanography, University of Patras, Patras 26500, Greece Search for other works by this author on: GSW Google Scholar G. Ferentinos; G. Ferentinos 4Laboratory of Marine Geology and Physical Oceanography, University of Patras, Patras 26500, Greece Search for other works by this author on: GSW Google Scholar S.E. Hicks S.E. Hicks 5Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar Geology (2005) 33 (4): 241–244. https://doi.org/10.1130/G21127.1 Article history received: 14 Sep 2004 rev-recd: 06 Dec 2004 accepted: 07 Dec 2004 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation L.C. McNeill, C.J. Cotterill, T.J. Henstock, J.M. Bull, A. Stefatos, R.E.Ll. Collier, G. Papatheoderou, G. Ferentinos, S.E. Hicks; Active faulting within the offshore western Gulf of Corinth, Greece: Implications for models of continental rift deformation. Geology 2005;; 33 (4): 241–244. doi: https://doi.org/10.1130/G21127.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Discrimination between different lithospheric extension models focusing on the roles of low-angle vs. high-angle faulting, and how strain is distributed, requires high-fidelity imaging of brittle deformation. High-resolution seismic reflection and multibeam bathymetric data in the western Gulf of Corinth continental rift were collected to establish the contribution of offshore faults to extension. Onshore fault slip here is significantly less than expected from geodetic strain rates. The rift at this location is a half-graben tilted to the north by S-dipping faults within the uppermost crust. A basement horst on the northern margin is uplifted by the North and South Eratini faults, and the axial channel is fault controlled. Subsided lowstand shorelines in the hanging wall of the North Eratini and the well-studied Aigion fault suggest that the faults have similar displacements. Summed extension from the four major faults across this part of the rift (Eliki, Subchannel, South Eratini, North Eratini) is ∼8–16 mm/yr, thereby reconciling geologic and geodetic data sets. Distributed deformation across isolated multiple faults can model this part of the rift without recourse to, and potentially incompatible with, an underlying low-angle detachment. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Estrutura e Evolução dos Cordões Arenosos Pleistocênicos no Canal de Acesso à Laguna dos Patos-RS, Brasil

This work presents the results of a high-resolution seismic reflection data survey carried out in the Patos lagoon inlet, near Rio Grande the southernmost harbor of Brazil. The analysis of the reflection patterns reveals the presence of transgressive/regressive barrier structures and beach/foredune-ridges. The mapping of these barrier structures allows a better understanding of the geological evolution of the Patos lagoon system during the Quaternary period and also helps to understand the evolution and migration of the actual lagoonal inlet between the Patos lagoon and Atlantic Ocean.

The Offshore Palos Verdes Fault Zone near San Pedro, Southern California

High-resolution seismic-reflection data are combined with a variety of other geophysical and geological data to interpret the offshore structure and earthquake hazards of the San Pedro shelf, near Los Angeles, California. Prominent structures investigated include the Wilmington graben, the Palos Verdes fault zone, various faults below the west part of the San Pedro shelf and slope, and the deep-water San Pedro basin. The structure of the Palos Verdes fault zone changes markedly along strike southeastward across the San Pedro shelf and slope. Under the north part of the shelf, this fault zone includes several strands, with the main strand dipping west. Under the slope, the main fault strands exhibit normal separation and mostly dip east. To the southeast near Lasuen Knoll, the Palos Verdes fault zone locally is low angle, but elsewhere near this knoll, the fault dips steeply. Fresh seafloor scarps near Lasuen Knoll indicate recent fault movement. We explain the observed structural variation along the Palos Verdes fault zone as the result of changes in strike and fault geometry along a master right-lateral strike-slip fault at depth. Complicated movement along this deep fault zone is suggested by the possible wave-cut terraces on Lasuen Knoll, which indicate subaerial exposure during the last sea level lowstand and subsequent subsidence of the knoll. Modeling of aeromagnetic data indicates a large magnetic body under the west part of the San Pedro shelf and upper slope. We interpret this body to be thick basalt of probable Miocene age. This basalt mass appears to have affected the pattern of rock deformation, perhaps because the basalt was more competent during deformation than the sedimentary rocks that encased the basalt. West of the Palos Verdes fault zone, other northwest-striking faults deform the outer shelf and slope. Evidence for recent movement along these faults is equivocal, because we lack age dates on deformed or offset sediment. Manuscript received 26 February 2003.

The Effect of Sea Level, Climate, and Shelf Physiography on the Development of Incised-Valley Complexes: A Modern Example From the East China Sea

ABSTRACT Analysis of high-resolution seismic reflection and sonar data from the East China Sea (ECS) continental shelf reveals the presence of an extremely broad (> 330 km) and deep (maximum incision of 72 m) incised-valley complex whose development and subsequent fill is constrained to the end of the last glacial cycle ( 20,000 yr BP to present). Results from this study indicate that sea-level change, climate-controlled discharge and sediment supply, and shelf physiography were important factors in the development and subsequent fill of the ECS incised- valley complex. For example, wet climatic conditions during the initial Marine Oxygen Isotope Stage (MIS) 2 fall of sea level promoted fluvial erosion of the exposed shelf. However, the trend toward drier conditions during the MIS 2 fall of sea level slowed the overall development of the incised-valley complex to the point where only minor incision occurred during the maximum lowstand. Furthermore, the low-gradient morphology of the exposed outer shelf diminished the ability of fluvial systems to incise. Instead, fluvial systems migrated laterally, creating a shallow ( 300 km) incised-valley system on the outer shelf. During the late MIS 2 rise of sea level, accommodation was generated within the flooded reaches of the valley complex. However, arid climatic conditions that prevailed at this time resulted in minor sediment delivery to the transgressive shoreline via the incised-valley complex. Thus, the upper part of the drowned lowstand fluvial deposits were exposed at the sea floor and reworked into a valley-wide tidal-bar and tidal sheet complex. Wetter climatic conditions during middle to late MIS 1 resulted in abundant sediment delivery to the drowned parts of the valley complex (estuary) and buried lowstand fluvial deposits below the depth of tidal ravinement, where they remained undisturbed. Current sequence stratigraphic models can be applied to the late Quaternary stratigraphic secession of the ECS. However, these models are too simplistic because they rely largely on rates and directions of sea-level change to explain stratal architectures. Although the extent and rate of sea-level change is extremely important, this study shows that high-frequency climate change and shelf physiography also play important roles in the development of stratigraphic architectures. These factors are particularly important for the development of incised valleys, where they directly influence incised-valley morphology and facies distributions.

The Golo submarine turbidite system (east Corsica margin): morphology and processes of terrace formation from high-resolution seismic reflection profiles

New high-resolution seismic reflection data collected along the eastern margin of Corsica have been analysed to describe the morphology of the turbidite systems located seaward of the Golo River mouth. The boomer data reveal that there is not only one turbidite system directly associated with the river, but four additional, non-coalescing systems which grew simultaneously. In the south, the system has the typical morphology of a turbidite deposit rich in mud and sand with a well-developed meandering canyon and channel morphology. In the north, they have the morphology of sand-rich turbidite systems with shorter straight channels. The southernmost deposits are interpreted to represent a more advanced stage of turbidite system development. Terraces, recognised by their particular seismic facies on boomer profiles which clearly differs from the surrounding levee facies, are observed in the channel meanders. They are interpreted as confined levees built by vertical accretion due to deposition from low-energy flows. Despite limited penetration, boomer seismics are demonstrated to be a useful complement to lower-resolution sparker data. The boomer data are superior (1) for the characterisation of fine-grained turbidite deposits by extending seawards the limits of the turbidite systems commonly defined by the acoustic response of sands, (2) in demonstrating the persistence of turbiditic processes farther towards the basin, and (3) for proposing conceptual models for the formation of terraces in fan valleys.