The morphology of Methane Derived Authigenic Carbonate (MDAC) tube in outcrops   by Jean-Philippe Blouet & Sutieng Ho

In the classification of Blouet et al. (2012), Methane Authigenic Derived Carbonate (MDAC) tubes have been classified according to their morphologies.        

In addition, MDAC tubes have various sizes, on the field they are observed to exhibit different sizes range from:

• diameter x10s cm (Fig. 1a)

• diameter 10-20 cm (Fig. 1b)

• diameter <10 cm (Fig. 1c)

Fig. 1(a-c) MDAC tubes in marl formation. Left) a fossil MDAC tube with a diameter of about 35 cm, Middle) 15 - 20 cm, Right) tubes with diameters less than 5 cm.

The length of tubes can also vary from meter to centimeter scale. In the field we observed the lengths vary from:

• > 1 meter (fig. 2, 7, 8, 9, 10)
• Tens meters (fig. 3, 5, 6)
  
• Centimeters (fig. 4)
  
  

For the more detailed morphology of MDAC tubes, they are not necessary develop along a vertical straight line, but they can also:

• grow into meandering forms (fig. 2);
• superimpose with each others (fig. 3);
• present as segments of broken tubes in cluster (fig. 4) (cf. Agirrezabala, 2009);
• grow obliquely and cut across the stratigraphy (fig. 5, 6);
• grow as a network and extend horizontally along straigrapic layers (fig. 7 -10) (see Aiello et al., 2001; Aiello, 2005).

Example of MDAC tube with meandering form

Fig. 2. A meandering form MDAC tube.

Example of MDAC tubes superimpose with each others

Fig. 3. A bloc of MDAC tubes which are superposing with each other. Left) Zoom out of the bloc. Right) Zoom in of the tubes which have length of more then 10 centimeter long.





Example of  broken tubes in cluster

Fig. 4. A big bloc of aggregation of MDAC tube segments. The length of tubes is only several centimeters long.

Upper) The zoom out of the bloc.

Right) The zoom in of the white square area in image above.

Example of MDAC tubes grow obliquely and cut through the stratigraphy 

Fig. 5. Upper) An oblique MDAC tube cut across the horizontal layers.





Fig. 6. Right) A sub-vertical MDAC tube with ramifies cut across the horizontal beds.


Example of MDAC tubes grow as horizontal network along straigrapic layers

Fig. 7. A MDAC tube with its lower part cut through the horizontal marl layers then extend horizontally along the stratigraphic layer. The tube is highlighted by yellow dots beneath it.

Fig. 8. Another example of MDAC tube developed horizontally along stratigraphy. White arrows indicate the lateral section view of the tube network which is shown in figure below.

Fig. 9. Plan view of the MDAC tube network with it's cross section shown in figure above. Notice that the tubes developed into a branching network along a horizontal plan and is indicated by white dot lines. The branching network is being dug out from a marl bloc.

Fig. 10. The branching network of MDAC tube can extend laterally into a large area.

Key words: Jean-Philippe Blouet fault Sutieng Ho methane authigenic carbonate

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