Sedimentary processes of the lower Monterey Fan channel and channel-mouth lobe

The distribution of deposits, sediment transport pathways and processes on the lower Monterey Fan channel and channel-mouth lobe (CML) are studied through the integration of GLORIA and TOBI sidescan sonar data with 7-kHz subbottom profiler records and sediment cores for ground-truthing. The lower Monterey channel is characterised by an up to 30-m-deep channel with poorly developed levees and alternating muddy and silty muddy overbank deposits. The channel is discontinuous, disappearing where gradients are less than about 1:350. Ground-truthing of the large CML shows that the entire CML is characterised by widespread deposits of generally fine sand, with coarser sand at the base of turbidites. Sand is particularly concentrated in finger-like areas of low-backscatter intensity and is interpreted as the result of non-turbulent sediment-gravity flows depositing metres thick massive, fine sand. TOBI sidescan sonar data reveal recent erosional features in the form of scours, secondary channels, large flow slides, and trains of blocks at the distal end of the CML. Erosion is probably related to increasing gradient as the CML approaches Murray Fracture zone and to differential loading of sandy submarine fan deposits onto pelagic clays. Reworking of older flow slides by sediment transport processes on the lobe produces trains of blocks that are several metres in diameter and aligned parallel to the flow direction.

[1]  K. Pickering.  Atlas of deep water environments : architectural style in turbidite systems , 1995 .

[2]  J. Bull,et al.  Channels, echo character mapping and tectonics from 3.5 kHz profiles, distal Bengal Fan , 1993 .

[3]  Jeffrey G. Marr,et al.  Experiments on subaqueous sandy gravity flows: The role of clay and water content in flow dynamics and depositional structures , 2001 .

[4]  R. Hiscott,et al.  Basin-Floor Fans in the North Sea: Sequence Stratigraphic Models vs. Sedimentary Facies: Discussion , 1997 .

[5]  J. Damuth.  Use of high-frequency (3.5–12 kHz) echograms in the study of near-bottom sedimentation processes in the deep-sea: A review☆ , 1980 .

[6]  J. Alexander,et al.  The physical character of subaqueous sedimentary density flows and their deposits , 2001 .

[7]  D. Mcculloch.  Evolution of the offshore central California margin , 1989 .

[8]  Kelin X. Whipple,et al.  Hydroplaning of subaqueous debris flows , 1995 .

[9]  N. Kenyon.  Speculations on the geological causes of backscatter variation on GLORIA sonographs from the Mississippi and De Soto fans, Gulf of Mexico , 1992 .

[10]  Neil H. Kenyon,et al.  Sediment mass-flow processes on a depositional lobe, outer Mississippi Fan , 1996 .

[11]  D. Lowe.  Sediment Gravity Flows: II Depositional Models with Special Reference to the Deposits of High-Density Turbidity Currents , 1982 .

[12]  G. Shanmugam,et al.  Types of submarine fan lobes; models and implications , 1991 .

[13]  R. Wynn,et al.  Characterization and recognition of deep-water channel-lobe transition zones , 2002 .

[14]  Jan Alexander,et al.  Observations on Experimental, Nonchannelized, High-Concentration Turbidity Currents and Variations in Deposits Around Obstacles , 1994 .

[15]  E. Mutti.  Distinctive thin‐bedded turbidite facies and related depositional environments in the Eocene Hecho Group (South‐central Pyrenees, Spain) , 1977 .

[16]  P. Malin,et al.  Evolution of the southern San Joaquin basin and mid-Tertiary , 1992 .

[17]  W. Normark,et al.  Monterey Fan: Growth pattern control by basin morphology and changing sea levels , 1983 .

[18]  M. Field,et al.  Ground‐truthing 6.5‐kHz side scan sonographs: What are we really imaging? , 1991 .

[19]  John P. Grotzinger,et al.  A Preliminary Experimental Study of Turbidite Fan Deposits , 2002 .

[20]  Xavier Lurton,et al.  Contribution of the multibeam acoustic imagery to the exploration of the sea-bottom , 1996 .

[21]  M. Link,et al.  Seismic facies and sedimentary processes of submarine fans and turbidite systems , 1991 .

[22]  D. Brunsden,et al.  The surface texture of the Saharan Debris Flow deposit and some speculations on submarine debris flow processes , 1993 .

[23]  M. Field,et al.  Monterey Fan: channel and overbank morphology , 1995 .

[24]  P. Cochonat,et al.  Acoustic data ground truthing through in-situ measurements of physical properties , 1998 .

[25]  Eez-Scan Scientific Staff.  Atlas of the Exclusive Economic Zone, western conterminous United States , 1986 .

[26]  T. Garlan,et al.  Physiography and recent sediment distribution of the Celtic Deep-Sea Fan, Bay of Biscay , 2000 .

[27]  J. Millington,et al.  Sandy submarine canyon-mouth lobes on the western margin of Corsica and Sardinia, Mediterranean Sea , 2002 .

[28]  M. Field,et al.  Geology of the United States' seafloor : the view from GLORIA , 1996 .

[29]  D. Piper,et al.  Initiation Processes and Flow Evolution of Turbidity Currents: Implications for the Depositional Record , 1991, From Shoreline to Abyss: Contributions in Marine Geology in Honor of Francis Parker Shepard.

[30]  W. Normark.  Late Pleistocene channel–levee development on Monterey submarine fan, central California , 1998 .

[31]  G. Shanmugam.  High-Density Turbidity Currents: Are They Sandy Debris Flows?: PERSPECTIVES , 1996 .

[32]  N. Kenyon,et al.  A `braided' distributary system on the Orinoco Deep-Sea Fan , 1984 .

[33]  Homa J. Lee,et al.  Upper Pleistocene turbidite sand beds and chaotic silt beds in the channelized, distal, outer-fan lobes of the Mississippi fan , 1992 .

[34]  D. Piper,et al.  Sandy fans--from Amazon to Hueneme and beyond , 2001 .

[35]  Homa J. Lee,et al.  Characteristics of a sandy depositional lobe on the outer Mississippi fan from SeaMARC IA sidescan sonar images , 1992 .

[36]  J. M. Coleman,et al.  Morphology of a submarine slide, Kitimat Arm, British Columbia , 1982 .