- Home
- A-Z Publications
- Basin Research
- Previous Issues
- Volume 20, Issue 4, 2008
Basin Research - 4, Thu Nov 27 00:00:00 UTC 2008
4, Thu Nov 27 00:00:00 UTC 2008
-
-
Gas seeps linked to salt structures in the Central Adriatic Sea
Authors Riccardo Geletti, Anna Del Ben, Martina Busetti, Riccardo Ramella and Valentina VolpiABSTRACTThe analyses of about 800 km of Chirp sub‐bottom profilers and 600 km2 of Multibeam data acquired during the 2005 and 2007 surveys of the R/V OGS Explora, and their correlation with one new, and several public, multichannel seismic profiles, allow us to propose a relation between the distribution of gas seepages, fracture systems and deep salt features present in the Central Adriatic Sea. Gas seepage is evident from pockmarks on the seabed and in the shallow sub‐bottom, where acoustic chimneys and bright spots have been highlighted and analyzed. The Mid‐Adriatic Depression (MAD) is a distinct morphological feature in the Central Adriatic Sea elongated in a NE–SW direction. The area is affected by salt doming of Triassic evaporites which cause the two main alignments of the Mid‐Adriatic Ridge as far as the Palagruza High and the Jabuka Ridge. These salt tectonics have existed since, at least, Paleogene times and are still active: they characterize sectors with less resistance to deformation produced by successive regional compressive regimes that have affected the area differently during the different geodynamic phases. Gas‐seep features are distributed preferentially above and along the fracture systems produced above and around the salt mounds.
-
-
-
Submarine and subaerial erosion of volcanic landscapes: comparing Pacific Ocean seamounts with Valencia Seamount, exposed during the Messinian Salinity Crisis
Authors Neil C. Mitchell and Johanna LofiABSTRACTSimilarity of form between subaerial and submarine landscapes affected by erosion could suggest similarities in the process of erosion, such as by runoff and sedimentary flows, respectively. On the other hand, if aspects of form vary, its characteristics may be used to identify the environmental origin of erosion. Towards these goals, this contribution addresses the morphology of submarine volcanoes (seamounts) with widely differing histories of erosion. One set from the Pacific Ocean never exposed above sea level includes Cretaceous‐age seamounts near Hawai'i (including Apu'upu'u Seamount), two seamounts of <3 Ma in age near a mid‐ocean ridge and the 11–4 Ma Jasper Seamount. These seamounts are all isolated from continents and hence from any erosion associated with mass wasting of unstable terrigenous deposits. In such isolated submarine environments, surfaces erode slowly from in situ weathering, mass wasting and scouring by sedimentary flows initiated by slope failure in pelagic or bedrock materials. The Pacific seamounts are compared with Valencia Seamount in the western Mediterranean, exposed subaerially for 100–400 k.y. during the Messinian Salinity Crisis before 5 Ma. Multibeam and deeply towed sidescan sonar data of Valencia Seamount reveal features typical of subaerial erosion of volcanic islands, such as canyons and relatively uneroded sectors (planezes) between them. Using a simple topographical reconstruction, the apparent erosion depth typically reaches 100 m within canyons and up to 180 m in places. Whereas the younger Pacific seamounts do not show these erosional features, the much older Cretaceous seamounts do have channels, which in one example suggests up to 200 m of incision. Both Valencia and Apu'upu'u seamounts have channel longitudinal profiles that are steep and typically linear to concave upwards. The erosion depth of Apu'upu'u Seamount is significant, despite the seamount's persistent submarine environment, because of its greater age, steeper flanks and greater contributing areas to channels compared with Valencia Seamount. These results illustrate that the channel morphology resulting from submarine erosion can become similar to that produced by subaerial erosion given sufficient time.
-
-
-
Comparison of sedimentary processes on adjacent passive and active continental margins offshore of SW Taiwan based on echo character studies
Authors J.‐K. Chiu and C.‐S. LiuABSTRACTEcho character recorded on Chirp sub‐bottom sonar data from offshore of SW Taiwan was analysed to examine and compare the sedimentary processes of adjacent passive and active continental margin settings. Seafloor echoes in the study area are classified into four types: (1) distinct echoes, (2) indistinct echoes, (3) hyperbolic echoes and (4) irregular echoes. Based on the mapped distribution of the echo types, the sedimentary processes offshore of SW Taiwan are different in the two tectonic settings. On the passive South China Sea (SCS) margin, slope failure is the main process on the upper continental slope, whereas turbidite deposits accumulate in the lower continental slope. In contrast, the submarine Taiwan orogenic wedge is characterized by fill‐and‐spill processes in intraslope basins on the upper slope, and mass‐transport deposits are observed in the canyons and on the lower Kaoping slope. This difference is largely caused by the huge influx of terrigenous sediments into the submarine Taiwan orogenic wedge compared with the passive SCS continental margin. In the latter, loading and movement of the Taiwan orogenic wedge has had a significant effect on the seafloor morphology and has triggered retrogressive failures. Gas hydrate dissociation may have enhanced the slope failure processes at some locations.
-
-
-
Lower slope morphology of the Sumatra trench system
ABSTRACTAt convergent margins, the structure of the subducting oceanic plate is one of the key factors controlling the morphology of the upper plate. We use high‐resolution seafloor mapping and multichannel seismic reflection data along the accretionary Sumatra trench system to investigate the morphotectonic response of the upper plate to the subduction of lower plate fabric. Upper plate segmentation is reflected in varying modes of mass transfer. The deformation front in the southern Enggano segment is characterized by neotectonic formation of a broad and shallow fold‐and‐thrust belt consistent with the resumption of frontal sediment accretion in the wake of oceanic relief subduction. Conversely, surface erosion increasingly shapes the morphology of the lower slope and accretionary prism towards the north where significant oceanic relief is subducted. Subduction of the Investigator Fracture Zone and the fossil Wharton spreading centre in the Siberut segment exemplifies this. Such features also correlate with an irregularly trending deformation front suggesting active frontal erosion of the upper plate. Lower plate fabric extensively modulates upper plate morphology and the large‐scale morphotectonic segmentation of the Sumatra trench system is linked to the subduction of reactivated fracture zones and aseismic ridges of the Wharton Basin. In general, increasing intensity of mass‐wasting processes, from south to north, correlates with the extent of oversteepening of the lower slope (lower slope angle of 3.8° in the south compared with 7.6° in the north), probably in response to alternating phases of frontal accretion and sediment underthrusting. Accretionary mechanics thus pose a second‐order factor in shaping upper plate morphology near the trench.
-
-
-
Quantifying geomorphology associated with large subduction zone earthquakes
Authors Eugene C. Morgan, Brian G. McAdoo and Laurie G. BaiseABSTRACTFor 30 large‐earthquake generating subduction zones, we quantify forearc basin size and subducting seafloor roughness to see if the size and shape of geomorphologic features determine earthquake magnitude. The subduction of geomorphologic features, such as ridges and seamounts, not only influences seismicity, but increases basal erosion and subsidence of the accretionary wedge, resulting in the formation of forearc basins. Many subduction zone ruptures have been associated with these basins, where a great portion of the ruptures' asperities collocate with the basins. First, we attempt to discern a relationship between forearc and subducting geomorphology by quantifying along‐strike variations in the bathymetry associated with 30 different rupture zones and the sections of subducting seafloor adjacent to those rupture zones. Two parameters, determined from theoretical models fit to empirical semivariograms, characterize areas of bathymetry: the sill, which estimates the degree of relief in the terrain, and the range, which is the horizontal scale associated with the sill. The ratio of sill to range provides us with a measure of seafloor roughness at a scale relevant to the mechanics of subduction. We investigate the control that forearc basins and subducting bathymetric highs may have on the occurrence of large thrust earthquakes by separately comparing our rupture zone and subducting seafloor roughness measurements to the moment magnitudes of the 30 events. The trench‐parallel dimension of bathymetrically high features on the subducting seafloor appears to correlate with moment magnitude. Also, we observe in the ratio of sill to range measurements that geomorphology on the subducting seafloor and forearc constrain the earthquake size at a margin.
-
-
-
Seamounts, knolls and petit‐spot monogenetic volcanoes on the subducting Pacific Plate
More LessABSTRACTOn the western part of the Pacific Plate most seamounts formed during the Cretaceous period in the so‐called West Pacific Seamount Province (WPSP). On the northwestern part of the same plate, the Joban and Japanese Seamount Trail (JJST) are also composed of Early Cretaceous seamounts. However, two new groups of knolls were recently discovered during multibeam surveys on the Pacific Plate along the Japan Trench. One group consists of circular knolls that are flat‐topped in shape and correspond to eruptive ages of approximately 75 Ma. The other group consists of irregularly shaped knolls, also called petit‐spot volcanoes, that are found on the outer‐rise systems of the subducting Pacific Plate. These petit‐spots seem much younger and available age data suggest that they only formed in the last few million years. Acoustic reflective data, which are simultaneously obtained with bathymetrical data, are a most powerful tool to distinguish the petit‐spots from the Cretaceous edifices in the WPSP and JJST. In this paper, we present the results of an exploratory search for these new kind of petit‐spot volcanoes along the trenches in the Pacific Ocean, with an emphasis on the Japan and Tonga trenches. The sizes of these irregularly shaped petit‐spot volcanoes are several orders of magnitude less than the Cretaceous seamounts and circular knolls, yet they appear to be ubiquitous on the ocean floor, in particular, where incipient melts in the asthenosphere can be squeezed out by tectonic forces.
-
-
-
Seamount detection and isolation with a modified wavelet transform
More LessABSTRACTThe size, shape and number of seamounts, once detected and isolated from other features such as oceanic plateaus or trenches, have the potential to provide valuable constraints on important solid Earth processes, e.g. oceanic volcanism. The variability of seamount size and morphology, however, presents problems for computational approaches to seamount isolation. This paper develops a novel and efficient wavelet‐based seamount detection routine ‘Spatial Wavelet Transform (SWT)’; the first use of multiple scales of analysis to directly isolate edifices from bathymetric data. Only weak shape‐related criteria are used and no a priori knowledge of the scale and location of the seamounts is required. For a bathymetric profile collected on cruise v3312 SWT matches, to within 25%, the dimensions of five times the number of the features determined by manual inspection than does the best statistically based (e.g. mean, median or mode) sliding window filter. The size–frequency distribution, a key descriptor of seamount populations, is also much better estimated by the SWT method. As such, the SWT represents a step towards the goal of objective and robust quantification and classification of seamounts.
-
-
-
Do ridge–ridge–fault triple junctions exist on Earth? Evidence from the Aden–Owen–Carlsberg junction in the NW Indian Ocean
Authors M. Fournier, C. Petit, N. Chamot‐Rooke, O. Fabbri, P. Huchon, B. Maillot and C. LepvrierABSTRACTThe triple junctions predicted to be ridge–ridge–fault (RRF) types on the basis of large‐scale plate motions are the Azores triple junction between the Gloria Fault and the Mid‐Atlantic Ridge, the Juan Fernandez triple junction between the Chile Transform and the East Pacific Rise and the Aden–Owen–Carlsberg (AOC) triple junction between the Owen fracture zone (OFZ) and the Carlsberg and Sheba ridges. In the first two cases, the expected RRF triple junction does not exist because the transform fault arm of the triple junction has evolved into a divergent boundary before connecting to the ridges. Here, we report the results of a marine geophysical survey of the AOC triple junction, which took place in 2006 aboard the R/V Beautemps‐Beaupré. We show that a rift basin currently forms at the southern end of the OFZ, indicating that a divergent plate boundary between Arabia and India is developing at the triple junction. The connection of this boundary with the Carlsberg and Sheba ridges is not clearly delineated and the triple junction presently corresponds to a widespread zone of distributed deformation. The AOC triple junction appears to be in a transient stage between a former triple junction of the ridge–fault–fault type and a future triple junction of the ridge–ridge–ridge (RRR) type. Consequently, the known three examples of potential RRF triple junctions are actually of the RRR type, and RRF triple junctions do not presently exist on Earth.
-
Volumes & issues
-
Volume 36 (2024)
-
Volume 35 (2023)
-
Volume 34 (2022)
-
Volume 33 (2021)
-
Volume 32 (2020)
-
Volume 31 (2019)
-
Volume 30 (2018)
-
Volume 29 (2017)
-
Volume 28 (2016)
-
Volume 27 (2015)
-
Volume 26 (2014)
-
Volume 25 (2013)
-
Volume 24 (2012)
-
Volume 23 (2011)
-
Volume 22 (2010)
-
Volume 21 (2009)
-
Volume 20 (2008)
-
Volume 19 (2007)
-
Volume 18 (2006)
-
Volume 17 (2005)
-
Volume 16 (2004)
-
Volume 15 (2003)
-
Volume 14 (2002)
-
Volume 13 (2001)
-
Volume 12 (2000)
-
Volume 11 (1999)
-
Volume 10 (1998)
-
Volume 9 (1997)
-
Volume 8 (1996)
-
Volume 7 (1994)
-
Volume 6 (1994)
-
Volume 5 (1993)
-
Volume 4 (1992)
-
Volume 3 (1991)
-
Volume 2 (1989)
-
Volume 1 (1988)