Search and Discovery Article #40536 (2010) Posted June 21, 2010

Transcription

1 Modern Examples of Mass Transport Complexes, Debrite and Turbidite Associations: Geometry, Stratigraphic Relationships and Implications for Hydrocarbon Trap Development* Fabiano Gamberi 1, Marzia Rovere 2 and Michael Marani 2 Search and Discovery Article #40536 (2010) Posted June 21, 2010 *Adapted from oral presentation at AAPG Annual Convention and Exhibition, New Orleans, Louisiana, April 11-14, ISMAR CNR, Bologna, Italy (fabiano.gamberi@bo.ismar.cnr.it) 2 ISMAR CNR, Bologna, Italy Abstract Two modern mass transport deposits are present along the northeastern Sicilian margin in the Tyrrhenian Sea. They are the result of the failure of slope and channel levee complex deposits. The eastern, Villafranca MTC occurred through repeated failures that resulted in the stacking of successive mass transport deposits. The main deposit is a frontally confined landslide with a basal shear surface exhibiting ramp and flat geometry. Thus, the geometry of the landslide provides a lateral seal of pre landslide units both along the sidewalls and along the frontal region of the landslide. The headwall region of the Villafranca MTC is scoured by channels that are 1 km wide and are filled by thick deposits that are transparent in subbottom profiles. Since the shelf facing the headwall region is very narrow, they are likely the result of deposition from coarse grained sediment gravity flows fed directly from nearby rivers. The transparent deposits are also found downslope from the channel mouth where they pinch out against the relief behind the confined front of the MTC. The frontal elevated region of the MTC also serves as partial confinement to flows that are fed from a nearby actively building channel levee system. The main body of the western, Capo d Orlando MTC also possesses a ramp and flat geometry but its front was able to spread above the paleoseafloor and thus represents an example of a frontally emergent landslide. Thus the MTC can represent a lateral seal to pre landslide units along the sidewalls and a top seal in the distal toe region where it overlies basin plain turbiditic lobe units. Beside the large landslide, thick transparent layers are also present in the western part of the basin plain that can be interpreted as debrites on the basis of their blocky reflective character on the side scan sonar data. The debrites have central channalized areas that erode as much as 10 m into the underlying succession, as well as conformable, wing like margins. In the eastern area on the contrary, a turbiditic lobe is fed by an actively growing channel levee system. Therefore in large parts of the basin plain debrites and turbidites alternate in the subbottom sedimentary column. The detailed side scan sonar and subbottom data capture a high resolution image of the character of their relationships and therefore have the potential to represent a good analog to help in the prediction of hydrocarbon trap potential in areas with a similar stratigraphic setting. Copyright AAPG. Serial rights given by author. For all other rights contact author directly.

2 Modern Examples of Mass- Transport Complexes, Debrite and Turbidite Associations: Geometry, Stratigraphic Relationships and Implications for Hydrocarbon Trap Development Fabiano Gamberi, Marzia Rovere, Michael Marani ISMAR-CNR, Bologna Italy

3 Southeastern Tyrrhenian Sea Rifting due to back-arc basin opening Extensional tectonics Seismicity High rates of differential vertical movements

4 Leveed channels and mass-transport complexes Capo d Orlando basin Gioia Basin Basin plain confined by the Aeolian Islands Stromboli axial valley Aeolian Islands Sicily Data set Multibeam bathymetry and reflectivity Seismics High resolution subbottom profiles High resolution deep towed sidescan sonar

5 Leveed channels and mass-transport complexes Capo d Orlando basin Gioia Basin Basin plain confined by the Aeolian Islands Stromboli axial valley Aeolian Islands Sicily Aims of work Large scale depositional architecture of the margin Geometry of single depositional units Debrite-turbidite relationships

6 Notes by Presenter: Together with multibeam bathymetry data, also a network of seismic profiles are available, blue are depicted the old 30 KJ sparker lines acquired in the 70s by the institute for marine geology of bologna, in black the single-channel lines acquired together with the bathymetry, in red the more recent CHIRP profiles acquired during a pre-survey GEOSTAR deployment in The seimic data made possible to map two distinct events one the so called Nicotera slump an a frontally confined slide, defined as Villafranca.

7 Notes by Presenter: Together with multibeam bathymetry data, also a network of seismic profiles are available, blue are depicted the old 30 KJ sparker lines acquired in the 70s by the institute for marine geology of bologna, in black the single-channel lines acquired together with the bathymetry, in red the more recent CHIRP profiles acquired during a pre-survey GEOSTAR deployment in The seimic data made possible to map two distinct events one the so called Nicotera slump an a frontally confined slide, defined as Villafranca.

8 Notes by Presenter: Together with multibeam bathymetry data, also a network of seismic profiles are available, blue are depicted the old 30 KJ sparker lines acquired in the 70s by the institute for marine geology of bologna, in black the single-channel lines acquired together with the bathymetry, in red the more recent CHIRP profiles acquired during a pre-survey GEOSTAR deployment in The seimic data made possible to map two distinct events one the so called Nicotera slump an a frontally confined slide, defined as Villafranca.

9 Eastern Basin Repeated and on-going failures; Slope channels upslope from main failure Slope channel Levee wedge failure Western basin Turbidite leveed channel and lobe Leveed channel Slab slide Debris flow lobe Distributary channels Transpressional margin Of main landslide SE

10 Notes by Presenter: Together with multibeam bathymetry data, also a network of seismic profiles are available, blue are depicted the old 30 KJ sparker lines acquired in the 70s by the institute for marine geology of bologna, in black the single-channel lines acquired together with the bathymetry, in red the more recent CHIRP profiles acquired during a pre-survey GEOSTAR deployment in The seimic data made possible to map two distinct events one the so called Nicotera slump an a frontally confined slide, defined as Villafranca.

11 Notes by Presenter: Together with multibeam bathymetry data, also a network of seismic profiles are available, blue are depicted the old 30 KJ sparker lines acquired in the 70s by the institute for marine geology of bologna, in black the single-channel lines acquired together with the bathymetry, in red the more recent CHIRP profiles acquired during a pre-survey GEOSTAR deployment in The seimic data made possible to map two distint events one the so called Nicotera slump an a frontally confined slide, defined as Villafranca.

12 Villafranca channel mouth The relief at the eastern transpressional margin of the main landslide is onlapped by turbidites and debrites. Debrite 1 1 km 50 m

13 Sheet turbidites Debrite 1 Sheet turbidites Debrite Progressive onlap Villafranca channel mouth Debrite 1 channel Debrite 1 has an erosional basal surface that cut underlying turbidites. As a consequence, a package of turbidites with a thickness of 12 m is sandwiched between debrites and onlaps against the main landlside bolcks. The relief at the eastern transpressional margin of the main landslide is onlapped by turbidites and debrites. Debrite 1 Sheet turbidites Top of main landslide 1 km 50 m 1 km 50 m

14 Further downslope Debrite 1 has a conformable base. It is present to the east of the main depositional relief created by the distributary channels. Debrite 1 heals the topography of the lobes and seals turbidite deposits formed in the distributary channel area of the Villafranca fan. In turn, to the north, the debrite is eroded in places by successive channalized flows that, otherwise deposit sheet turbidites. Distributary channel Debrite 1 Distributary channel Distributary channel 50 m 1 km

15 Debris flow lobe Post-debris flow sediments Debris flow headwall scar Erosional steps Possible coarse grained material from slope channel Pressure ridges 500 m 25m The detachment of the debris flow lobe created a depression that is starting to be filled by confined coarse-grained deposits. Finer grained material can overspill the relief at the rear of the debris flow lobe and deposit above it 1 km 50 m Debrite 1 Debris flow lobe A further failure in the headwall of the main landslide resulted in the emplacment of a debris flow lobe with pressure ridge and high relief.

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17 Leveed channels mass-transport complexes Capo d Orlando basin: seaward confined basin plain fans

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19 Distributary channels Sediment waves Debrite lobes

20 Channels connected with the coastal areas are mainly fed by shelf derived turbidites. Channels not connected with the coastal area are mainly fed by landslides. As a consequence, turbidite and debrite fans are developed. A mixed facies occurs where levee failures is occurring adjecent to turbidite channels or where landslide can evolve into turbidites within the channels. Turbidite fan Mixed fans Debite fan

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22 Sheet turbidite lobe Debrites 1200 m 50m Coherent block landslide Turbidite channel infill Unfailed levee wedge

23 Debrite Sheet turbidites 300 m 25m Top of blocky Mass-transport deposit Sheet turbidite lobe Debrites 1200 m 50m Coherent block landslide Turbidite channel infill Unfailed levee wedge

24 600 m 20 m Sheet turbidites Basal erosion Debrites 300 m 25 m Sheet turbidite lobe Debrites 1200 m 50m Coherent block landslide Turbidite channel infill Unfailed levee wedge

25 1000 m 1200 m Sheet turbidite lobe 1200 m 25 m Debrites MTD Blocks Unfailed levee wedge Turbidite channel infill

26 MTD blocks Turbidite channels MTD blocks 1200 m 25 m 1000 m 1200 m Sheet turbidite lobe 1200 m 25 m Debrites MTD Blocks Unfailed levee wedge Turbidite channel infill

27 1200 m 25 m Sheet turbidites Debrites MTD blocks 1000 m 1200 m Sheet turbidite lobe 1200 m 25 m Debrites MTD Blocks Unfailed levee wedge Turbidite channel infill

28 600 m 25 m Sheet Debrite turbidites 1000 m 1200 m Sheet turbidite lobe Debrites 1200 m 50 m Turbidite channel infill

29 Summary and conclusions: Relatively large-scale mass-transport deposits create seafloor topography In the evacuation area negative relief is infilled by coarse-grained deposits fed by slope channels. Debris flow lobe Post-debris flow sediments Debris flow headwall scar Erosional steps Possible coarse grained material from slope channel Pressure ridges 500 m 25m The detachment of the debris flow lobe created a depression that is starting to be filled by confined coarse-grained deposits. Finer grained material can overspill the relief at the rear of the debris flow lobe and deposit above it

30 Relatively large-scale mass-transport deposits create seafloor topography In the distal area the positive relief is onlapped by packages of turbidites and by debrites. As a result, sandy lobe deposits with thickness up to 30 m and with 3 km of lateral extent are sandwiched between debrite deposits. Sheet turbidites Debrite 1 Sheet turbidites Debrite Progressive onlap Sheet turbidites Top of main landslide 50 m Debrite 1 channel 1 km

31 Debrite lobes are characterized by a variety of shape 300 m 25 m Narrow channelized portion with steep margins deeply ploughing into the underlying sediments and lateral conformable wings. 600 m 20 m Sheet turbidites Basal erosion Debrites Gently dipping basal erosional surface without lateral conformable wings 600 m 25 m Sheet Debrite turbidites Gently dipping basal erosional surface and widespread lateral conformable wings

32 When conformable, debrites can seal turbidite lobe deposits due to the preexisting topography Distributary channel Debrite 1 Distributary channel Distributary channel 50 m 1 km A large variety of relationships between sand-prone turbidite units and clay-rich sealing debrites is thus to be expected.

33 General points: In tectonically active areas mass-transport processes and turbidity currents can create favourable conditions for the development of stratigraphic traps, with lobe turbidites that are sealed by thick debrite bodies. However, the large variety of geometry of the resultant depositional bodies can make reservoir characterization difficult. High resolution studies of modern examples can greatly help in deriving models. The concomitant growth of turbidites- mass transport deposits- and mixed fans demonstrate that models that predict changes in submarine fan facies on the base of sea-level cycles hardly apply to systems developed along tectonically active a margins.