the nature and origin of authigenic smectites in some recent marine ...

246 T. G. Cole and H. F. Shaw
35 ~ 36 ~ 37 ~ 38 ~ 319~ 40 ~
I I I I I
Oceanographer Deep
Kebrit Deep
f
.Gypsum Deep
=ma Deep
Nereus Deep
41 ~ 42 o
I I
Thetis Deep ~ o //~Atlantis II Deep
Wando Basin ~ ,Chain Deeps
Valdivia Dee
P~
--ll~e/ )~Djidda
I i- ee_____~Albatross Deep
DeepJ e ~ a
Discovery j Deep
Erba Deep I |
Port Sudan ~////)
Port Sudan DeeD
Suakin Dee
9 Deeps with brine & metalliferous sediment.
9 Deeps with metalliferous sediment only.
| Deeps with brine only.
FIG. 4. Location of the Atlantis II Deep, Red Sea.
work by Bischoff (1972) showed that the nontronites from these sediments had a typical
composition of
9 . 3+ OH nH O
Cao.09Nal.ooKo.07(Fe~+aFe~+3Mno.18Zno.41Cuo llMgo.41) (S16.74Alo.48Feo.80)O20( )4. 2 ~
From the previous work of Bischoff (1972) the nontronites appeared to be poorly
crystalline. However, recent XRD analyses carried out by Cole (1982) indicate that the
nontronites are 'well crystallized' (v/p ratio 0.80-0.85).
Scanning electron microscope examination of the nontronites showed that they had a
flaky, often 'honeycombed', texture (Fig. 5a) typical of smectites (Bohor & Hughes,
1971). However, the nontronite in the sulphide/silicate/amorphous facies may also occur
with a fibrous texture (Fig. 5b). This is a relatively unusual morphology for smectites
(Kurnosov et al., 1982).
E
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