Downfan Transformation from Turbidity Currents to Debris Flows at a Channel-to-Lobe Transitional Zone: The Lower Pleistocene Otadai Formation, Boso Peninsula, Japan

Transformation of turbidity currents into debris flows across a channel-to-lobe transition zone was recognized on the basis of lateral mapping of a falling-stage-systems-tract deposit in the lower Pleistocene Otadai Formation submarine-fan sequence on the Boso Peninsula, Japan. The most proximal outcrops comprise 1 to 4 m thick turbidites, which are laterally equivalent to debrites encased in turbidites in outcrops farther down flow. Such turbidites and encased debrites were deposited from single flow events. The most distal outcrops comprise only thinner (2 to 40 cm thick) turbidites. Debrites contain many siltstone clasts and finer-grained sediments, which are characterized by deep-water faunas and clay-mineral composition similar to those of interbedded hemipelagites. Therefore, the transformation of turbidity currents into debris flows is interpreted to have occurred in response to the incorporation of many siltstone clasts and finer-grained sediment particles into the precursor turbidity currents through erosion of muddy substrates. Subsequently, turbulence in the precursor turbidity currents was suppressed and near-bed flow with higher sediment concentration developed. Intense erosion of muddy substrates is interpreted to have occurred in response to the increase in intensity of turbulence in the precursor turbidity currents at the mouths of middle-fan channels. The precursor turbidity currents (or turbidity currents generated by dilution of debris flows) produced a turbidite deposit, which was subsequently overrun by the debris flow in a proximal lobe environment. The debris flows are interpreted to have subsequently been transformed into turbidity currents, which are recorded by turbidite deposition in the more distal-lobe environment. Debrites can characterize the proximal portion of an attached-lobe deposit in a channel-to-lobe transition zone. Such debrites can be significant heterogeneities for fluid flows in sand-prone successions from middle-fan channel to attached-lobe deposits.

[1]  R. Schiebel,et al.  Onset of submarine debris flow deposition far from original giant landslide , 2007, Nature.

[2]  B. Xia,et al.  Geochemical and Nd isotope composition of detrital sediments on the north margin of the South China Sea: provenance and tectonic implications , 2007 .

[3]  Makoto Ito,et al.  Gravel Waves in an Ancient Canyon: Analogous Features and Formative Processes of Coarse-Grained Bedforms in a Submarine-Fan System, the Lower Pleistocene of the Boso Peninsula, Japan , 2006 .

[4]  E. Sumner,et al.  An experimental investigation of sand–mud suspension settling behaviour: implications for bimodal mud contents of submarine flow deposits , 2006 .

[5]  P. Talling,et al.  Anatomy of turbidites and linked debrites based on long distance (120 × 30 km) bed correlation, Marnoso Arenacea Formation, Northern Apennines, Italy , 2006 .

[6]  Jeff Peakall,et al.  Transformation of debris flows into turbidity currents: mechanisms inferred from laboratory experiments , 2006 .

[7]  J. Alexander,et al.  Quantifying velocity and turbulence structure in depositing sustained turbidity currents across breaks in slope , 2005 .

[8]  Makoto Ito,et al.  Sequence-stratigraphic signatures of hemipelagic siltstones in deep-water successions: the Lower Pleistocene Kiwada and Otadai Formations, Boso Peninsula, Japan , 2004 .

[9]  Makoto Ito,et al.  Long-term ENSO-like events represented in the Middle Pleistocene shelf successions, Boso Peninsula, Japan , 2004 .

[10]  R. Wynn,et al.  Beds comprising debrite sandwiched within co‐genetic turbidite: origin and widespread occurrence in distal depositional environments , 2004 .

[11]  D. Waltham.  Flow Transformations in Particulate Gravity Currents , 2004 .

[12]  P. Haughton,et al.  ‘Linked’ debrites in sand‐rich turbidite systems – origin and significance , 2003 .

[13]  Jeffrey G. Marr,et al.  Constraining the efficiency of turbidity current generation from submarine debris flows and slides using laboratory experiments , 2003 .

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

[15]  T. Mulder,et al.  Reply to discussion by Shanmugam on Mulder et al. (2001, Geo-Marine Letters 21: 86–93) Inversely graded turbidite sequences in the deep Mediterranean. A record of deposits from flood-generated turbidity currents? , 2002 .

[16]  A. Hogg,et al.  Occurrence and origin of submarine plunge pools at the base of the US continental slope , 2002 .

[17]  J. Best,et al.  Turbulence Modulation in Clay-Rich Sediment-Laden Flows and Some Implications for Sediment Deposition , 2002 .

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

[19]  B. Kneller,et al.  Process controls on the development of stratigraphic trap potential on the margins of confined turbidite systems and aids to reservoir evaluation , 2001 .

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

[21]  Y. Sohn.  Depositional Processes of Submarine Debris Flows in the Miocene Fan Deltas, Pohang Basin, SE Korea with Special Reference to Flow Transformation , 2000 .

[22]  Allen,et al.  The Saharan debris flow: an insight into the mechanics of long runout submarine debris flows , 1999 .

[23]  Normark,et al.  Outcrop‐scale acoustic facies analysis and latest Quaternary development of Hueneme and Dume submarine fans, offshore California , 1999 .

[24]  Makoto Ito.  Submarine fan sequences of the lower Kazusa Group, a Plio-Pleistocene forearc basin fill in the Boso Peninsula, Japan , 1998 .

[25]  Makoto Ito.  Contemporaneity of component units of the lowstand systems tract: An example from the Pleistocene Kazusa forearc basin, Boso Peninsula, Japan , 1998 .

[26]  Morris,et al.  Downstream changes of large‐scale bedforms in turbidites around the Valencia channel mouth, north‐west Mediterranean: implications for palaeoflow reconstruction , 1998 .

[27]  H. Kitazato.  Paleogeographic changes in central Honshu, Japan, during the late Cenozoic in relation to the collision of the Izu‐Ogasawara Arc with the Honshu Arc , 1997 .

[28]  N. Kenyon,et al.  Erosional and depositional patterns in the Valencia Channel mouth: An example of a modern channel-lobe transition zone , 1996 .

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

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

[31]  Marcelo Horacio Garcia,et al.  Hydraulic Jumps in Sediment‐Driven Bottom Currents , 1993 .

[32]  Makoto Ito,et al.  Inferred glacio-eustatic control for high-frequency depositional sequences of the Plio-Pleistocene Kazusa Group, a forearc basin fill in Boso Peninsula, Japan , 1992 .

[33]  H. Kitazato,et al.  Late Cenozoic paleobathymetric indices based on benthic foraminifers in Japan , 1989 .

[34]  W. Nemec,et al.  Large floating clasts in turbidites: a mechanism for their emplacement , 1988 .

[35]  Y. Katsura.  Depositional environments of the Plio-Pleistocene Kazusa Group, Boso Peninsula, Japan , 1984 .

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

[37]  G. Shanmugam,et al.  Sequence of structures in fine-grained turbidites: Comparison of recent deep-sea and ancient flysch sediments , 1980 .

[38]  Rex Britter,et al.  The dynamics of the head of a gravity current advancing over a horizontal surface , 1979, Journal of Fluid Mechanics.

[39]  R. Walker.  Deep-Water Sandstone Facies and Ancient Submarine Fans: Models for Exploration for Stratigraphic Traps , 1979 .

[40]  T. Nakajima,et al.  Analytical study of turbidites, Otadai Formation, Boso Peninsula, Japan , 1977 .

[41]  M. Hampton,et al.  The Role of Subaqueous Debris Flow in Generating Turbidity Currents , 1972 .

[42]  P. Komar.  Hydraulic Jumps in Turbidity Currents , 1971 .

[43]  P. Gingerich.  Markov analysis of cyclic alluvial sediments , 1969 .