Sediment Supply

The type of sediment found on carbonate slopes can have several origins:

1)Pelagic: particles typically less than a few micrometers which primarily consists of calcareous and siliceous skeletal remains of marine phytoplankton and zooplankton.

2)Platform: Platform carbonates result from the off-platform transport of varying proportions of mud-sized algal and inorganically precipitated aragonite needles, mud to sand sized skeletal and nonskeletal debris, lithoclasts and bioeroded particles.Coarser sediments such as gravel and bolder sized lithoclasts may originate from shallow-water facies or weathered carbonate bedrock.

3)Hemipelagic: These sediments are fine-grained terrigenous materials that enter the marine system as a result of coastal erosion or fluvial transport across the shelf and are deposited on the slope where they are thoroughly mixed with carbonate sediment.

4)Autochthonous carbonates: These sediments include carbonates that are formed in-situ, e.g., fecal pellets of epifauna and infauna, seafloor Mg-calcite cement, peloidal Mg-calcite in foraminifera tests, and skeletal debris associated with the fauna of the slope environment.
 

The relative proportions of different sediments vary spatially according to different controlling factors, such as:

1)proximity to continent

2)productivity of shallow water carbonate organisms

3)latitudinal changes in tectonic plates which may effect carbonate production

4)evolution of reef- building organisms

5)locus of deposition of platform-derived sediments

6)oceanographic setting
 
 

Sedimentary Structures

There are several types of sedimentary structures associated with the different areas of a carbonate slope.Among them are:

1)Bouma Sequences:

This sequence is an ideal succession of five intervals, characteristic of a turbidite deposit, from top to bottom this sequence includes:

a)pelitic or mud layer

b)parallel laminations

c)ripple laminations

d)parallel laminations

e)graded coarse sediment
 
 

                  Bottom 4 intervals of an ideal bouma sequence:

(Coniglio and Dix, 1992)
 
 

2)Debris Flows

Boulders and blocks up to 10 feet in diameter surrounded by mud flow material.
 
 

           Conglomerate with calcareous matrix:

(Coniglio and Dix, 1992)
 
 
 

(Scholle et al., 1983)
 
 

3)Flute Casts 

These structures are formed by the filling of an erosional scour.Flutes are somewhat spoon-shaped; the up-current end is bulbous and flares in the down-current direction.
 

             Flute Cast:

              http://www.geo.duke.edu/ss/ss.htm
 
 

4)Groove casts or Tool Markings:

These are sole markings with rounded ridges, which form from the filling of grooves.Shells, grains, pebbles and logs swept over firm muddy bottoms by currents, may produce grooves.They are preserved as casts on overlying beds.

         Groove cast:

          http://www.geo.duke.edu/ss/ss.htm
 

           Sole Markings:

          http://www.geo.duke.edu/ss/ss.htm
 

          Load casts:

                 http://www.geo.duke.edu/ss/ss.htm
 
 

5)Glide surfaces:

These erosional features are observed within thinly bedded muds, and form as a result of large-scale slides or slumps without much internal deformation.They are normally recognized by their sharp contacts.
 
 

Glide plane identified in outcrop:

(Brown and Loucks, 1993)
 

6)Mud Mounds:

Mounds of skeletal debris and lime mud enclosed in beds of dark laminated sandy beds, or shales.

7)Medium-scale cross-bedding:

Cross beds up to ½ mm thick, caused by scour and fill of megaripples formed by moderately strong currents.
 
 

           Cross bedding:

              http://www.geo.duke.edu/ss/ss.htm
 

8)Injection Dikes:

Beds which cut vertically through massive or normally bedded strata, filled by material squeezed up from below through loading of the substrate by the carbonate mass.

9)Filled fissures

Discordant sediment filling fissures, which cut across normally, bedded strata.These fissures may have opened by slumping or tectonic activity, and the sediment fill is normally sand or coarser material.

10)Nodular bedding:

Layers that consist of fine beds grading to loosely packed nodular bodies of rock in matrix of like or unlike character.
 
 

             Nodular Chert:

              http://www.geo.duke.edu/ss/ss.htm
 
 

11)Sedimentary Boudinage:

This feature results from differential compaction of patchy deposits of shale and carbonate.These deposits form irregular, closely spaced structure caused by a disruption of layers by stretching and flowage.
 
 

         Boudin Structure: