Atlas of Sedimentary Structures

Reduction halo

The lighter coloured band is yellowish brown (10YR 6/4) and contrasts with the much darker yellowish brown (10YR 4/3) pelagic clayey nannofossil ooze below. The lighter coloured halo is 22 cm thick.  The dark yellowish brown colour of the pelagic sediment is due to pervasive staining by hydrothermally-derived iron and manganese oxyhydroxides.  The haloes are attributed to the burial of labile surficial organic carbon by turbidites, followed by remineralisation of this organic carbon with Mn and Fe oxyhydroxides as electron acceptors.  The colour alteration of the halo is ascribed to the removal of Mn oxyhydroxides and their migration out of the halo section.  Similar reduction haloes have also been noted in Atlantic brown clays (Thomson et al., 1989).

Reduction halo under volcaniclastic turbidite in the Lau Basin (SW Pacific)

(20º13.307'S, 176º49.360'W)  DSDP 135-837A-8H-2

Thin reduction halo, 2-3 cm thick, under vitric silt turbidite in the Lau Basin (SW Pacific)

(20º41.531'S, 176º46.492'W)  DSDP 135-839A-5H-3

 

References:
Thomson, J., Higgs, N.C. and Colley S. 1989. A geochemical investigation of reduction haloes developed under turbidites in brown clay.  Marine Geology, 89, 167-178.
Thomson, J., Rothwell, R.G. and Higgs, N.C. 1994.  Development of reduction haloes under calcareous and volcaniclastic turbidites in the Lau Basin (Southwest Pacific).  In Hawkins, J., Parson, L., Allan, J. et al., Proceedings of the Ocean Drilling Program, Scientific Results, 135, 151-162.