High-Resolution Studies of Mass Transport Deposits: Outcrop Perspective for Understanding Modern Submarine Slope Failure and Associated Natural Hazards N
MT5 unit, Division I Burgui section
S
B
9
N
Slide/slump
1 mm
2.5 Lens
0.1 mm
10 Lens
E
0.1 mm
10 Lens
BDP
Pre-slide succession
I
Matrix
S
33°
A
Blocky-flow
B
Blocky/debris-flow 2 MTD1
MTD2
00
20
136°E
137°
138°
139°
SE Hole C0018A
MTD O
cm
MTD
C
MTD
MTD
G
Section 333-C0018A-15H-3
Section 333-C0018A-16H-2
cm
90
90
95
95
100
100
MTD
N
B debrite with slide blocks (7 meters)
A
5-80 m
H
1
500 m VE ~ 4.75x
B
C 3
3
3
1
blocky flow interval
2
debris flow interval
3
slide-slump interval
E
D
2 I 105
H
I
105
A. Bathymetric map, with 2-D MCS profile locations, NanTroSEIZE Stage 1 and 2 drill sites (white circles), and Expedition 333 drill sites (red circles). White barbed line = position of deformation front of accretionary prism, yellow arrow = estimated far-field vectors between Philippine Sea plate and Japan (Seno et al. 1993; Heki, 2007). B. Lithology of Site C0018 on seismic profile. IL=in-line, VE=vertical exaggeration. Key seismic horizons are labeled B, G, N, and O, MTD=mass transport deposit. Figure modified after Strasser et al. (2011). C. Detailed log and explanation of the thickest MTD shown in B (MTD 6). From Pini et al., 2013. D. Example of ductile-plastic shear zone observed in the debris flow part of the MTD 6. E. Example of ductile-plastic shear zone observed in the slump/slide part of the MTD 6. F. Three steps axial rotation of the CT scan data of the shear zone shown in D. Data visualization: volume rendering, first level = raw X-ray mode, all CT numbers are shown; right = shaded mode, windows =high CT numbers only (highest CT values shown). G. Four steps axial rotation of the shear zone shown in E. Data visualization: volume rendering, shaded mode, windows =high CT numbers only (highest CT values shown). These shear zones are loci of concentrated deformation enabling the differential movements of discrete masses inside the body, and correspond to CT numbers higher than the surrounding sediments, but lower (darker) than mineralized “lineations”and bioturbations. H and I. Examples of fluidal structures observed within the matrix of the blocky flow and debris flow intervals of the MTD 6, respectively. Location shown in C. Note the similarity with fig. K of the Epiligurian Specchio MTC case study
Poverty MTC
A Poverty MTC
Offshore wedge-top basin, Hikurangi Margin, northeastern New Zealand
Deformed seafloor (pressure ridges)
C
A. Compilation of geographic, schematic geological and composite multibeam maps showing the location of the investigated Inner Isfjorden MTDs. B. Multibeam seafloor map of the Inner Isfjorden area with labeling of the main MTDs and their morphological-anatomical features. C. Close up of B showing in detail the interaction zone between MTD 1 and MTD2 and their accumulation zones.
Conclusions
Liquefaction, fluidization and hydro-plastic deformation are common processes in the internal structural evolution of MTCs and are interpreted as a critical process controlling the mobility of seafloor mass transport. Meso- and micro-structural and sedimentologic analyses suggest a deformation mechanism controlled by un-drained simple shearing of water-saturated, poorly-consolidated to loose sediments due to the dragging forces acting at high strain rates along boundaries of internal elements (i.e. internal differential movements) and at the basal slide interval (i.e. general down-slope movement). Most of the shearing achieved during the slide movement is likely accommodated within the basal interval, resulting in a sort of “overpressured carpet” that mechanically separates the slide mass from the substrate due to hampered hydraulic diffusivity (Ogata et al. 2012b). Frictional heating is another possible mechanism able to increase pore pressure up to liquefaction (Goren and Aharonov 2007). When the mechanical coupling becomes strong enough (e.g. during slide mass deceleration and freezing, and/or impacts against topographic highs), the momentum can then be partly transferred downward into the substratum, with the consequent involvement of the underlying sediments. This deformation is likely caused by dynamic/static overloading and rear push of the sliding mass, causing substrate deformation and incorporation (i.e. erosion in sedimentological meaning). Compressional stress is mainly located at the front of the slide mass and then, transferred to the surrounding sediments, causing folding and thrusting at various scales. During the early post-depositional compaction, the internal fluid overpressure may be dissipated through developing of fluid-escape structures, sometimes reaching the slide surface as mud/sand volcanoes (Strachan 2008; Moernaut et al. 2009), or can be retained for a relatively long time interval, favouring slow differential movements of the entire mass (Major 2000). The diagnostic product of mass transport-related liquefaction, fluidization and soft-sediment deformation processes can be found in outcrop (or drill cores) as a sedimentary matrix represented by an unsorted, hyper-concentrated mixture of loose and poorly consolidated fine-grained sediments. Shear zones with concentrated fluid excess pore pressure can be visualized in seismic reflection profiles and drill cores, especially at the very base of the unit where horizons of trapped high fluid pressure may induce high amplitude reflectivity and even negative polarity. Such reflectors can be observed also within the slide mass, and depending on their lateral continuity, may indicate the amalgamation surface/interval between two subsequent bodies, therefore representing a powerful tool to distinguish single depositional units (MTDs) from composite, multiple accumulation complexes (MTCs). Fluidized sediment is a fundamental component of a slide body along with other discrete parts that behave coherently (e.g. slide blocks, undissociated masses, etc.), and it typically occurs with the internal and basal shear zones as cm- to m-sized elongated lenses and bands. In this framework the relative amount of composing sedimentary matrix may indicate the catastrophic or episodic/periodic character of the slide event (Fig. 2). The systematic integration of the large amount of available geophysical data with detailed, high-resolution outcrop studies represents the most reliable method for the study of submarine landslides. This synergic approach permits observations covering all the scales, overcoming the intrinsic resolution limits of the single methods. This is particularly so for fine scale, shearzone mechanical processes that exert a major influence on the mobility of extremely large continental margin mass transport processes, representing the key concepts for forecasting and mitigation of submarine landslide-related geohazards. Debris Flow
Matrix amount 80-100% vol
Debris Flow internal shear zones
GRAIN TO TURBULENT FLOW
Flow transformation
Hydroplaning (?) paleo-transport direction
basal shear zone
Block-dominated portion
Blocky Flow
B
paleo-transport direction shear zones
internal shear zones
D
Isolated blocks
basal shear zone
C
C
Matrix (mixed intra- and extra-slide)
Slide/Slump
~2m
Matrix-dominated portion
paleo-transport direction
internal shear zones
Matrix amount 30-70% vol
Blocky Flow
Matrix (extra-slide)
Matrix (intra-slide)
Matrix-dominated portion
Slide/Slump
Block-dominated portion
detached slump folds and bedded slide blocks Flow transformation
substrate-eroded intraclsts
Hydroplaning (?)
Matrix amount 0-20% vol
U1
Slide/slump
B
NE Perunk unit
Shikoku Basin (Philippine Sea plate)
~4-6 cm/y
C
Ductile shear zones
BASAL CONTACT (not exposed)
F E
SW
Carbonate debris flow unit
Perunk 2 unit
4000
NW
B
ca. 300 m
N
U2
F
0
400
3.0
N
U3-4-5
300 Km
4000
Paleocene-Eocene basin plain foredeep succession, SE Alps-NW Dinarides, Italy-Slovenia
Associated grain flow-turbidite
ROOF CONTACT
Site C0018
2000
0
C
Eastern foreland province
Slide scar 1
Consolidated
A
00
40
400
A. Panoramic photo-mosaic showing the main Specchio MTC internal subdivisions (single MTDs). See schematic log in B for comparison. B. Simplified stratigraphic column of the Specchio MTC in the type locality in the Pessola Valley outlier. The component MTDs and the relative thickness ranges are indicated. C. Photo-mosaic and line drawing representing a shear zone underlined by a matrix horizon, which separates two block portions (intra-block thrust), and correspondent conceptual block diagram representing structural associations (inspired from Bradley and Hanson, 1998), which characterize block-dominated portions (BDP). D. Photo-mosaic and interpretation of a meso-scale folding system involving a single thick, coarse-grained sandstone bed, enclosed within a matrix-dominated portion. Asymmetries and relative vergences are roughly uniform (apart from few minor backthrusts), and correspondent conceptual block diagram representing structural associations (inspired from Bradley and Hanson, 1998). E. Medium- to coarse-grained sand particles with mud infillings within inter-granular spaces. Elongated patches of fine-grained material, sharing the same characteristics of the muddy component are aligned to the overall oblique banding (from the upper-left to the lower-right), expressed by iso-orientation of grains' long axes and by elongated clustering of particles sharing similar dimensions. Close-up: detail of the transitional border of the fine-grained elongated patches with the surrounding matrix material. The fine-grained lithology is the same of that filling inter-granular spaces and sustaining sandy particles. Note the “fluidal” appearance of the fine-grained material and the development of faint planar discontinuity (e.g. pseudo-foliation) marked by the preferential alignment of elongated/platy grains. F. Matrix showing a thinly banded appearance. Note the fine-grained material arranged in “ribbon”-like patches. Lineations are also highlighted by the preferential alignment of particles, along their long axis. Close-up: boundary be- tween two relatively fine- and coarse-grained elongated clusters. These structures suggest overall simple shear conditions achieved through an independent particulate flow without cataclasis (i.e. grain breakage) and, are here defined as pseudo-deformation/disaggregation bands. G. Basal surface of the Specchio MTC showing a ramp geometry roughly toward the W, cutting the underlying strata. H. Same basal surface shown in D, further to the north, showing the same ramp geometry. Here it is possible to observe dragging-related recumbent synclines. I. Photo-mosaic and interpretation of a meso-scale injection-like structure observed within the upper part of the Specchio MTC. These kinds of structures dissect the block integrity; probably joining different matrix-rich shear zones through vertical and oblique pathways. The infilling matrix intrudes along weak zones (e.g. stratification surfaces), as observable along the margins (secondary lateral injections). Note also the occurrence of sand- stone intraclasts within the infilling matrix, ripped up from structure margins. Encircled hammer for scale. J. Example of box-like fold in thin-bedded sandstones, characterized by vertical axial plane, slightly curving axis, limbs parallelization, and expulsion of the core zone (over- pressured conditions into the hinge zone). The axial zone of the fold is injected by a matrix with the same characteristics of the surrounding one (arrow). Encircled hammer for scale. K. Upward matrix injections (e.g. fluid escape) offshooting from a shear zone. Note the fluidal structures defined by extremely plastically deformed marly intraclasts within the pebbly mudstone.
Friuli basin MTCs
0
00
prevailing debrite (7 meters)
matrix
covered
300
40
00
30
D
not to scale
BDP stratific ation (amalga surfaces mations )
vertical primary injection
2000
4000 4000
G
MDP
slide block
lateral secondary injection
0
200
2000
00
80-230 m
BDP
200-300 m
~2m
0 20
30
from 40 m
K
~N
Specchio unit (MTD A)
H
3000 0
3.5
J
~ ESE
~ WNW
00
00
20-80 m
Pre-slide succession
20-
34°
MDP ~S
150°
MDP
F
G
Specchio unit (MTD A)
140°
TRANSPORT DIRECTION
NOT TO SCALE
1 mm
2.5 Lens
E
D
20
00
slide-slump interval (48 meters)
NOT TO SCALE
~1m
D
TRANSPORT DIRECTION
130°E
00
10
10
MDP
DRAG SYN- AND ANTI-FORMAL FOLD
Izu Izu
30°
00
Depth (km)
EXTRA-BLOCK DRAG SYN- AND ANTIFORMAL FOLD
up to 400 m
Kii Peninsula
80-140 m
SHEATH FOLD LONG AXIS
up to 450 m
shear zone
~3m
BDP
Matrix-Dominated Part (MDP)
SHEATH FOLD LONG AXIS
EXTRA-BLOCK THRUSTS
Tokai
200-
INTRA-BLOCK THRUSTS
~ NE
50
40° N
~ NE
block
(deformed)
block
(less deformed)
C
km 0
4000
SYN-DEPOSITIONAL THRUST
35° N
Offshore outer fore-arc, wedge-top slope basin, southern Japan
0
~ SW
A
SØRKAPP
B
Blocky/debris-flow 1
slide block
matrix
10
0-30 m
Thin-skinned fold-thrust belt
~N
100
INTRA-BLOCK DRAG SYN- AND ANTI-FORMAL FOLD
~S
A. Panoramic view of the verticalized MT5 “Megaturbidite”, recognizable in the landscape due to erosional relief (Fago section, South-central Pyrenees, Spain); internal subdivisions and boundaries are labeled. In the inset: Conceptual cartoon showing the main internal subdivisions of the “megabreccia” bodies (see text for explanation). Modified from Seguret et al. (1984). B. Base of the MT5 unit in the Burgui section (lower Esca valley). Here it is possible to observe the diffused upward fluid-escape features (e.g. sub-vertical foliation seams) and the deformed (folded) sandstone elements ripped off from the substrate, characterizing the basal shear interval. C. Meso-scale impact-related, soft sediment folding (dragging syncline) of the underlying basin-plain turbidites (location is about 5 m in the direction labeled in A). Encircled hammer for scale. D. Photo-mosaic and interpretation of a largescale, fluid escape-related “mushroom”-like structure, observed at the base of a slide block in the MT5 “megaturbidite” (U I). This structure roots in the basal shear interval where the bulk of the matrix occurs.
Nankai MTCs
Basement-involved fold-thrust complex
HORNSUND
Interaction zone
D
20
A
Western hinterland
Slide scar 2
SANDSTONE ELEMENTS
covered
C
N 50 km
BELLSUND
bypassed debris-flow 1
00
Blocks-Dominated Part (BDP)
~ SW
MT5 unit, UI Roncal section
BASIN PLAIN TURBIDITES
EN
ORD
ISFJ
SWEDEN
U2
not to scale
D
Single MTDs
U3
A
1944
MDP
le
Barents Sea NORWAY RUSSIA
ca. 1 km
U1
20
Specchio
C
m MTC ca.350
BASAL CONTACT
eL
A
BASAL SHEAR HORIZON
U4
Lin
C
C
00
300 Km
D B
shear zone
N
Upward fluid escape structures
Arctic Circ
U5
10
NNE
D
ca. 300 m
6
ROOF CONTACT
B
BASAL CONTACT
5
Oligocene wedge-top succession, Northern Apennines, Italy
SSW C
4
ROOFCONTACT
3000
present-day examples fossil examples
3
Fjord seafloor, central Spitsbergen, Svalbard archipelago, Arctic Norway
SLIDE BLOCK
Associated grain flow-turbidite
2
2
Epiligurian Specchio MTC
Blocky-flow
Svalbard NORWAY
ICELAND
B
Novaya Zemlya RUSSIA
Increasing degree of internal disaggregation
thickness (m)
3
0
8
100
7
6
00
5
Greenland Sea
LFZ
2
4
Franz Josef Land RUSSIA Greenland DENMARK
Increasing velocity and run-out distance
Jaca
Sevemaya Zemlya RUSSIA
Arctic Ocean
BFZ
Our inability to directly observe and monitor cross sectional area (m ) submarine landslide mass emplacement is 10 10 10 10 10 10 a major impediment to understanding landpresent-day examples 10 slide mechanics. Deformation mechanisms Poverty Jaca basin MTCs acting within a submarine landslide during MTC Specchio MTC 10 Friuli basin MTCs its downslope evolution can be better unPoverty MTC Locations of the studied Inner Isfjorden 10 examples, and diagram derstood by combining submarine geoMTCs showing relative sizes of physical observations and detailed outcrop Kumano basin MTCs ancient (dashed line 1 ancient examples envelope) and presentstudies on modern and exhumed continenday (solid line envelope) MTDs and MTCs. The tal margins, respectively. Modern seafloor 10 10 10 10 10 relative dimensions of width (m) the studied examples are and subsurface imaging techniques proplotted. Modified from Outcrop data data from Woodcock, 1979 vide the gross morphology, areal extent Geophysical data Lucente and Pini (2003). data from Macdonald et al., 1993 and internal character of single mass transport deposits (MTDs) and composite mass transport complex (MTCs). However, even where single-point ground-truthing of geophysical data by coring exists, marine geological data cannot resolve internal details and lateral complexity to any fine scale. Conversely, outcrop studies allow analyses from the microscopic scale up to the cartographic/map scale (comparable with the geophysical scale), but rarely preserve complete, source-to-deposit examples of large MTCs. Nonetheless the different boundary conditions and scales, also on-land studies on subaerial landslides would benefit of the knowledge acquired on submarine failures through this integrated approach. In this study we integrate geophysical, drill core and outcrop data in order to characterize the deformation processes critical to the emplacement of submarine landslides through a continuity of observation across scales. Two key datasets are used to bridge the outcrop detail to the seismic scale: 1) observations and analytical data from large-scale (10s-100s of m-thick and > 100 m2extensive) MTD/MTCs exhumed in the Early Oligocene Epiligurian succession (Northern Apennines, Italy; Ogata et al. 2012a), the Eocene Jaca Basin (central Pyrenees, Spain; Labaume et al. 1987), and the Paleogene Friuli basin of the northwestern Dinarides (Italy and Slovenia; Tunis and Venturini 1992), and 2) published and unpublished multichannel seismic reflection and drill core data from MTD/MTCs on the Hikurangi margin of New Zealand (Mountjoy and Micallef 2012), the Nankai wedge in Japan (Strasser et al. 2011) and the inner Isfjorden, Svalbard (Arctic Norway) (Fig. 1). We synthesize observations from these data sets to develop a scale-independent model representing the mechanical process, which control the mobility of large-scale submarine mass movements. Epiligurian Specchio MTC
Jaca basin MTCs
Unconsolidated
Kumano basin MTCs
Inner Isfjorden MTCs
North Pole
CANADA
LFZ
Jaca basin Friuli basin MTCs MTCs
Eocene basin plain foredeep succession, south-central Pyrenees, Spain
[email protected] BFZ
Introduction
Inner Isfjorden MTCs
K. Ogata, G.A. Pini, A. Festa, Ž. Pogačnik, G. Tunis, J. J. Mountjoy, K. Senger, and M. Strasser
Transformation into flow Matrix (intra-slide) basal shear zone
Coherent slide part
Hydroplaning (?)
~1m NOT TO SCALE
Mass transport facies associations and interpreted processes. All photos are from the Early Rupelian Specchio unit of the Epiligurian succession, Northern Apennines (Ogata et al. 2012a; 2012b)
U5
not to scale
U4
Isolated olistolith
D
U3
U4
U2 U1
D
N
N
Plastically folded siliciclastic (intra)clasts
Cretaceous carbonate olistolith
E
300 Km Basal matrix injections
U2
E
Rodez unit
U3
U4
U5
Podbrdo unit
S
D
G
Carbonate debris flow unit
C
E
Particle
Matrix
pseudo-matrix intra-clasts
micro-injections
A, B and C. Overview of the Vernasso (A) and Anhovo quarries (B, C), with line drawing of the main MTDs and their internal subdivisions. In the inset: Conceptual cartoon showing the main internal subdivisions of the “megabreccia” bodies (see text for explanation). D. Large silicoclastic slide block deformed into a meso-scale sheath-type fold showing an arcuate axis (dashed line). Location in C. E. Radial distribution of U3 breccia matrix injections (white arrows) around a folded rip-up olistolith belonging to the underlying U2 (Rodež unit, location in C). F. Thin section microphotographs (left) and interpretations (right) of the breccia matrix that constitutes a bended injection in a marly olistolith. G. Thin section microphotographs of the basal breccia immediately below a marly olistolith. Thin sections are oriented accordingly to the strike and dip of the lenticular breccia layer, respectively. Bed polarity (i.e. stratigraphic up), scale bar and sample ID. See A, B and C inset for locations. Modified from Ogata et al. (2014).
- Goren, L., Aharonov, E. 2007. Long run-out landslides: the role of frictional heating and hydraulic diffusivity. Geophysical Research Letters 34, 1-7. - Labaume, P., Mutti, E., Seguret, M., 1987. Megaturbidites: a depositional model from the Eocene of the SW-Pyrenean Foreland Basin, Spain. Geo-Marine Letters 7, 91–101. - Lucente, C.C., Pini, G.A. 2003. Anatomy and emplacement mechanism of a large submarine slide within a Miocene foredeep in the Northern Apennines, Italy: a field perspective. American Journal of Science 303, 565-602. - Major, J.J., 2000. Gravity-driven consolidation of granular slurries: implications for debris-flow deposition and deposit characteristics. Journal of Sedimentary Research 70/1, 64-83. - Moernaut, J., De Batist, M., Heirman, K., Van Daele, M., Pino, M., Brümmer, R., Urrutia, R., 2009. Fluidization of buried mass-wasting deposits in lake sediments and its relevance for paleoseismology: results from a reflection seismic study of lakes Villarrica and Calafquén (South-Central Chile). Sedimentary Geology 213, 121–135. - Mountjoy, J.J., Micallef, A., 2012. Polyphase Emplacement of a 30 km3 Blocky Debris Avalanche and Its Role in Slope-Gully Development. In: Y. Yamada, K. Kawamura, K. Ikehara, Y. Ogawa, R. Urgeles, D. Mosher, J. Chaytor, M. Strasser (Eds.), Submarine Mass Movements and Their Consequences. Advances in Natural and Technological Hazards Research. Springer, Netherlands, pp. 213-222. - Ogata, K., Tinterri, R., Pini, G.A., Mutti, E., 2012a. The Specchio Unit (Northern Apennines, Italy): an ancient mass transport complex originated from near coastal areas in an intra-slope setting. In: Yamada, Y., Kawamura, K., Ikehara, K., Ogawa, Y., Urgeles, R., Mosher, D., Chaytor, J., Strasser, M. (Eds.), Submarine Mass Movements and Their Consequences. Advances in Natural and Technological Hazards Research. Springer, Netherlands, 595-605. - Ogata, K., Mutti, E., Pini G.A., Tinterri, R., 2012b. Mass transport-related stratal disruption within sedimentary mélanges. Tectonophysics 568-569, 185-199. - Pini, G.A., Strasser, M., Boschetti, A., di Blasi, F., Ogata, K., Panieri, G., Festa, A. (2013) Structural characterization of a large-scale Mass Transport Deposit: origin of the internal features and possible depositional mechanism. IODP Exp. 333 second post-cruise meeting. Plaza-Faverola, A., Bünz, S., and Mienert, J., 2010, Fluid distributions inferred from P-wave velocity and reflection seismic amplitude anomalies beneath the Nyegga pockmark field of the mid-Norwegian margin: Marine and Petroleum Geology, v. 27, no. 1, p. 46-60. - Strachan, L.J., 2008. Flow transformations in slumps: a case study from the Waitemata Basin, New Zealand. Sedimentology 55, 1311–1332. - Strasser, M., Moore, G.F., Kimura, G., Kopf, A.J., Underwood, M.B,; Guo, J., Screaton, E.J. (2011) Slumping and mass transport deposition in the Nankai fore arc: Evidence from IODP drilling and 3-D reflection seismic data. Geochemistry Geophysics Geosystems (G3), 9, Q0AD13. - Tunis, G., Venturini, S. (1992) Evolution of the southern margin of the Julian Basin with emphasis on the megabeds and turbidites sequence of the Southern Julian Prealps (NE Italy). Geologia Croatica, 45, 127-150.
References
U5
Sub-angular and sub-rounded carbonate clasts
A. Bird's eye view of the northeastern continental margin of New Zealand (looking toward the SW; location of the area in the inset). Plate boundaries and position of the investigated Poverty MTC are labeled. B. Shaded relief map showing the location of the MCS profiles represented in (C, D and E), extent of the landslide deposits (dotted line) and the interpreted source area. Inferred directions of transport (black arrows) and main thrust fault traces (red toothed lines) are also labeled. C. MCS profile of the Poverty MTC (light and dark blue overlays represent the two main component bodies) showing its internal reflections and the host stratigraphy characterized by buried MTDs (gray overlay). In the inset is represented an enlargement of the MCS profile in the distal part of the MTC, showing the amalgamation between at least two MTDs (weak continuous reflector) and the basal shear zone (strong discontinuous reflector). D. MCS profile of the Poverty MTC roughly parallel to the line represented in C with inclusion of the most proximal zone and part of the headwall slide scar. The same features observed in B are labeled. The inset represents a close-up of the MCS profile in the proximal part of the MTC characterized by the thickest accumulation and overall compressional regime, as testified by the dominance of thrust faults. E. Slice and interpretation of part of the MCS profile of C with indication of the main recognizable features. Note the structurally confined depositional patterns of the sedimentary cover. The weak, discontinuous reflectors characterizing the slide blocks and the strong, coherent reflector representing the main basal shear zone and the flat part of a ramping thrust fault cutting the entire deposit. Modified from Ogata et al. (2014b), after Mountjoy and Micallef (2012).
Acknowledgments: Norwegian Hydrographic Survey provided multibeam data from Svalbard. Joshu Mountjoy supported by NIWA under Coasts and Oceans Research Programme 1 (2013/14 SCI). This work is part of the MIUR-PRIN n. 2010AZR98L_002 program. University of Trieste, project FRA2013 (G.A. Pini grants).
