Axial Sediments 



BoHom samples representing axial sediments are from the relatively flat area 

 located at the base of the flanks of the channel in the narrow, elongated portion of 

 the TOTO north of the cul-de-sac (Fig 6). Compared to near-flank sediments, axial 

 sediments are characterized by lighter, more varied color, a wider range of particle 

 grain size, higher density, lower water and organic carbon content, and many abrupt 

 changes in lithology with depth in the sediment. Cores 62-60 through 62-63, which 

 are from Northeast Providence Channel, are included herein because of their similarity 

 to axial sediments. 



Cores included within the axial category are: 



62-2 



62-22 



62-50 



61-6 



62-3 



62-23 



62-51 



61-7 



62-5 



62-27 



62-52 



61-8 



62-7 



62-29 



62-60 



61-21 



62-8 



62-30 



62-61 



61-22 



62-13 



62-31 



62-62 





62-16 



62-47 



62-63 





62-17 



62-48 



61-2 





62-18 



62-49 



61-4 





Samples from the central reaches of the channel show frequent, abrupt changes in 

 sediment color with depth in the core (Fig 8). Colors range from dark yellowish brown 

 (10YR6/6) to a pure white (N9), and, in the majority of instances, the color changes 

 do not appear related to a change in any particular sedimentary property. Colors in 

 the orange hue are prevalent and are believed to represent oxidation of the ferrous ions 

 present in the sediment. As opposed to the near-flank sediments, no H2S odor was de- 

 tected in the axial sediments, and the few pH measurements taken were always in excess 

 of 7.0. Superimposed on the colors recorded in Figure 8 are occasional bluish-black 

 mottles and streaks throughout the majority of the cores which are probably due to de- 

 composition of plant debris incorporated in the sediment. Plate I compares a typical 

 core from the axial and near-flank area. 



Almost all axial cores contain relatively coarse-grained layers oriented normal to 

 the core axis. These layers are in sharp contrast with the underlying material, grade 

 gradually into the overlying material, and show a gradation from coarse to fine sedi- 

 ments upward in the core. Plate II is an example of this type deposit, and core 61-21 

 In Figure 8 shows the decrease in median grain size diameter upwards In one of the 

 graded beds. In a few of the cores the coarse layers are only slightly coarser than the 

 surrounding material, and, as a result. In a freshly split core the upper portion of the 

 graded sequences are difficult to recognize. However, on drying, the decrease in 

 particle size upwards becomes conspicuous, and, as discussed by Ericson et_al (1961), 

 the shrinkage of such sediment on drying is proportional to the ratio of lutite particles 

 to larger grains. In effect, the differential shrinkage of the sediment when thoroughly 

 dry produces a smoothly tapered Increment where the base of the sequence (due to less 

 contraction) Is wider than the upper portion of the layer where it makes contact with the 

 overlying sediment. 



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