The Yam Suf and Negev groups were also identified in Sinai. The Infracambrian Group is known in the Negev from the subsurface and contains only one ...
ISRAEL JOURNAL OF EARTH-SCIENCES, Vol. 22, 1973, pp. 157-164
THE CLAY MINERALOGY OF PALEOZOIC SEDIMENTS FROM SOUTHERN ISRAEL L. HELLER-KALLAl
Departme1ll of Geology, The Hebrew University of Jerusalem, Jerusalem, Israel Y. NATHAN
Geochemistry Department, Geological Survey of Israel, Jerusalem, Israel and
T. WEISSBROD Mineral Resources Department, Geological Survey of Israel, Jerusalem, Israel ABSTRACT The principal clay minerals throughout the Paleozoic section in southern Israel are kaolinite and illite, associated with minor amounts of chlorite and two types of illitesmectite interstratified material. Since most of the Paleozoic clays were derived from a similar assemblage of rocks, the Arabo-Nubic Precambrian massif, differences in clay mineralogy must be related either to changes in weathering (relief and climate) or to diagenesis (environment of deposition). INTRODUCTION AND GEOLOGICAL BACKGROUND
Weissbrod (1969a) subdivided Paleozoic sediments in southern Israel and Sinai into three groups: the Infracambrian or Precambrian, the Yam Suf and the Negev groups. The Yam Suf and Negev groups were also identified in Sinai. The Infracambrian Group is known in the Negev from the subsurface and contains only one formation, the Zenifim Formation (Weissbrod, 1969a). The Yam Suf Group comprises the PNS or 'Amudei Shelomo (Karcz, Weiler and Key, 1971), Hakhlil, Nimra, Nehushtan, Mikhrot (Bartura, 1966), Shehoret and Netafim (Weissbrod, 1969b) formations. Sediments outcrop in the Timna'-Elat region and in southwest Sinai (Fig. 1). In the subsurface they have been encountered only in the Sinaf 1 well. In the more northern wells these formations do not exist, probably due to truncation. The Shehoret Formation at Nahal Shehoret can be subdivided into three members: the lowest (multicoloured), the intermediate (white) and the uppermost (variegated). At Timna' the formation is undifferentiated, multicoloured or variegated. The entire Yam SufGroup is believed to be of Cambrian age. Received December 11, 1972 and in revised form April 12, 1973 157
158
L. HELLER-KALLAl ET AL.
Isr. J. Earth-Sci.,
,.. e
Well and secllon locoloon
BE'ER
SHE~
o
e
MAKHTESH OATAN Z )
i
,i
i
I
JORDAN
J
I I )Co
i TIMN'
I
!
el
NAHAL SHEHORET ej ELAT .
SAUDI ARABIA
l8"
Fig. 1. Location map.
The Negev Group comprises the Sa'ad, 'Arqov, Yamin and Zafir formations (Weissbrod, 19690), known in the Negev only in the subsurface. In Sinai this group is represented by the Umm Bogma and Ataqa formations. The group is of Permo-Carboniferous age. Clay is a minor constituent of the sediments in the P2leozoic section. Some formations (Hakhlil, Mikhrot, 'Arqov and Zafir) are richer in clays than the others, but even their clay content does not exceed 10%. The only continental source area for the Paleozoic clay sediments is the Precambrian massif. Differences in clay mineralogy must, therefore, be related to weathering due to changes in relief and climate or to diagenesis produced by differences in environment of deposition. A reconnaissance survey of the clay mineralogy of the Negev clays has been carried
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PALEOZOIC CLAYS FROM SOUTHERN ISRAEL
159
out by Bentor, Bodenheimer and Heller (1963). In the present study samples from the various type sections in the Negev were investigated in greater detail and, for comparison, some samples from Umm Bogma (Sinai) were also examined. PROCEDURE
"
Samples were ground in a ball mill for 15 min and aliquots of the approx. < 2/l size fraction were withdrawn from aqueous suspensions of the sieved material. About 150 samples were examined from the cores and outcrops. Carbonate-rich samples were treated with cold 1:6 HCI, care being taken to maintain the pH above 5.6. X-ray diffraction patterns were prepared of oriented specimens in an air-dried and glycolated state and, as required, after heating at various temperatures. RESULTS AND DISCUSSION
Clay Mineral Composition The principal clay minerals throughout the Paleozoic section are kaolinite and illite, with occasional minor amounts of chlorite and some interstratified illite-smectite. The diffraction maximum at about lOA, which characterizes micas, degraded micas or illites was frequently found to be very asymmetrical, fa1ling off more slowly on the low angle side. On glycol treatment there was a sometimes almost imperceptible shift of the peak maximum to higher angles, associated with a considerable increase in symmetry. A more detailed study (Heller-Kallai and Kalman, 1972) showed that this effect may be attributed to the presence of a mixture of illite and randomly interstratified material, itself composed of illite and a small proportion (of the order of magnitude of 20%) of expandable layers. The diffraction effect is due to the superposition of the original lOA peak with the 00217 /00 110 maximum of the interstratified material. If the proportion of expanded layers does not exceed 20-30% and the interstratification is completely random, no maximum occurs at lower 8 angles (Reynolds and Hower, 1970). If the interlayering is partially ordered, however, such a maximum does occur. With some of the samples it was indeed observed that the broad lOA peak of the air-dried sample is replaced by two maxima on glycolation, at about lOA and at a lower value of O. Two types of illite-expandable layers are thus differentiated: completely random (r) and partially ordered (0). In the sections studied both types are invariably associated with loA material.
The Infracambrian Group (Fig. 2)* The dominant clay mineral present in the Zenifun Formation is a well-crystallized illite, which is either little altered micaceous material or has been regenerated, possibly by mild metamorphism. A completely randomly mixed-layer mineral occurs in almost all the samples and some kaolinite occurs near the top of the formation. The small amounts of chlorite detected in the upper part of the Zenifim Formation may have been derived from sills and dykes, composed of basic to intermediate igneous rocks. The *Figures 2-4 are in cover pocket
160
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L. HELLER-KALLAl ET AL.
presence of chlorite may be the result of diagenesis. However, in the complete absence of fossils there is no field evidence to support such a hypothesis.
The Yam SufGroup (Tables I, II; Figs. 3,4) The clays of these sediments are composed predominantly of illite and kaolinite in various proportions. In the Hakhlil to Mikhrot formations outcropping at Timna' (Table I) the clay fraction is predominantly illite. The proportion of kaolinite increases towards the top, possibly indicating a gradual change in environmental conditions. The two samples available from the Hakhlil Formation, Umm Bogma (Table II), were found to contain more kaolinite than samples from equivalent stratigraphic levels at Timna'. This difference in clay composition probably reflects differences in weathering (climate) between the Negev and Sinai areas. The three members of the Shehoret Formation (Fig. 3) are characterized by a different clay mineralogy. The dominant clay mineral in the lowermost, multicoloured member is a relatively well-crystallized illite, associated with minor amounts of partially ordered interstratified material. Some samples differ from the others in their vicinity in containing randomly interstratified material. No corresponding difference in lithology could be detected. In the white member, above, the symmetry of the lOA peak decreases, but illite is the dominant clay mineral for the first 27 m. It is associated with minor amounts of mixed-layer material, the nature of which changes from partially ordered to random TABLE I Oay Mineral Composition of Samples from Timna' (Yam Suf Group)
Mixed layer
Fonnation
Sample no.
Kaolinite
Illite
63/4-5
D
C
Mikhrot
63/4-2
D
C
Mikhrot
63/3-8
A
F
Nehushtan
63/3-1
A
E
A,o
Nehushtan
63/3-5
B
D
A,d,o
Nehushtan
63/1-21
A
E
A,r
Hakhlil
63/1-16
A
F
Hakhlil
63/1-8
A
F
Hakhlil
63/1-2
A
E
90% F
Only clay mineral detectable G
, TABLE II Clay Mineral Composition of Samples from Umm Bogma
Sample no.
Kaolinite
Illite
TW 1375
E
B
1378
F
1382
Smectite
Mixed layer
Formation
~
Coordinates·
Group
P.N.S.
8448/7008
Yam sur
A
P.N.S.
8448/7008
Yam sur
D
C
Hakhlil
8448/7008
Yam sur
1384
D
C
Hakhlil
8448/7008
Yam sur
1398
C
D
Mikhrot
8448/7008
Yam sur
> t"'"
1402
C
D
Shehoret, multicoloured member
8448/7008
Yam Suf
1404
B
E
Shehoret, white member
8448/1008
Yam sur
0 N 0
1417
C
C
Shehoret, variegated member
8448/1008
Yam Suf
1424
F
A
Netafim
8448/7008
Yam sur
1428
G
Netafim
8448/7008
Yam sur
t-.l
-
~
\0
-:I
w
"'C:I
A,r
t"r:I
n
n
t"'"
> -< CIl 'TJ ~
0
1310
B
D
A,r
Ataqa
8455/7017
Negev
s::
1312
D
B
A,o
Ataqa
8455/7017
Negev
g
1326
F
A
Ataqa
8455/7017
Negev
s:!t"r:I
1331
F
A
Ataqa
8455/7017
Negev
Z
1337
F
A
Ataqa
8455/7017
Negev
Ataqa
8455/7017
Negev
Ataqa
8455/7017
Negev
A
Ataqa
8455/7017
Negev
F
A
Ataqa
8455/7017
Negev
F
A
Ataqa
8455/7017
Negev
Ataqa
8455/7017
Negev
1345
F
1352
G
1356
F
1357 1365 1372
A
G
• Egyptian red g~d. For expJanation of symbols see Table I.
CIl
~
en ~
> t"r:I t"'"
-0\
162
L. HELLER-KALLAl ET AL.
15r. 1. Earth-Sci.,
from the bottom to the top of the section. Towards the top of the member, kaolinite appears in appreciable amounts, but there is no field evidence to indicate a change in environment. The only associated chaI\ge in lithology is a finer particle size of the quartz grains. One notable exception is sample no. 555, where the difference in the mixed-layer material reflects the change in lithology.from arkosic sandstone to sandstone. The characteristic clay assemblage of the variegated member is a kaolinite/illite mixture, with the proportion of kaolinite increasing towards the top. The mixed-layer material is randomly interstratified. The clay fractions of the undifferentiated Shehoret Formation outcropping at Timna' (Fig. 4) is composed of illite and kaolinite in various proportions. A relationship can be seen between lithology and clay mineralogy: arkosic sandstones are richer in kaolinite, claystones or shales in illite. The mixed-layer material throughout this section is completely randomly interstratified. Three samples from the Shehoret Formation at Umm Bogma were studied for comparison. They consist of illite and kaolinite in various proportions (Table II). The clay minerals of the Shehoret Formation, with few exceptions, display a tendency for the occurrence of randomly interstratified illite-expanding clay in association with kaolinite. In the absence of kaolinite the interstratified material is partly ordered. The change in clay mineral assemblage from purely illitic to a mixture of illite and kaolinite and finally to predominantly kaolinitic, together with the associated trend in the nature of the interstratified material in the Shehoret Formation at Nahal Shehoret clearly indicate changes in \veathering. The weathering was continental and became more severe with time; this may be correlated with climatic changes. It resembles the kaolinitization of micaceous debris in the Sahara by early diagenesis (Millot, 1970). The clay mineral assemblage of the Netafun Formation in Nahal Shehoret is very similar to that at the top of the variegated member (Shehoret Formation).
The Negev Group (Fig. 2) The only clay mineral detected in the Sa'ad Formation is kaolinite which probably reflects a period of intense continental weathering and may be associated with the spread of land plants (Yaalon, 1963). This clay assemblage continues for about 12 m above the base of the 'Arqov Formation (Fig. 2). Higher in the 'Arqov Formation illite reappears, associated with kaolinite. However, the illite in part of this formation differs greatly from that in the Infracambrian or Cambrian. The peaks are very broad and remain essentially unchanged on glycolation. Further research is needed to establish whether this phenomenon has a correlative value and whether this horizon can be used as a marker. Towards the top of the formation kaolinite again becomes abundant, either as the only clay mineral present or in association with various amounts of illite and minor amounts of chlorite. The Yamin Formation is characterized by its calcareous composition. In the lower part of the formation kaolinite and illite occur in approximately equal amounts. Towards the top illite becomes more abundant, some chlorite appears and the illite/
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PALEOZOIC CLAYS FROM SOUTHERN ISRAEL
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expanding clay interlayering changes from partially ordered to completely random. The top of the section is rich in organic matter. The clay assemblage of the three samples examined from the Zafir Formation (Fig. 2) resembles that of samples from the top of the Yamin Formation except for the interstratified material which is ordered in the Zafir but disordered in the Yamin Formation. Marine ostracods and foraminifera were found in parts of the 'Arqov, Yamin and Zafir formations (Gerry, 1967; Hamaoui in Weissbrod, 1969a; Derin, personal communication). This supports the hypothesis that the chlorite found in these formations is the result of marine diagenesis. CONCLUSIONS
The dominant clay minerals in the Paleozoic in the Negev and Sinai are illite and kaolinite. Since the main source material is the Precambrian massif and the dominant and frequently only clay mineral in the lowermost Zenifim Formation is illite, it may be inferred that the kaolinite found in later formations is derived either from the parent rock or from the illite, either directly through an illite-expandable layer association or by dissolution and neoformation. All these processes require a humid, terrestrial climate but no data is available to distinguish between them. Moreover, it is possible that two or more processes occurred simultaneously. The illite in the Zenifim Formation is well crystallized, whereas in some later formations a poorly defined lOA material occurs. This degradation may be caused by either humid or arid weathering. Thus, the presence of kaolinite and poorly crystallized illite indicate intense weathering - kaolinite under a humid, continental regime and degraded illite under either marine or continental conditions. The presence of small amounts of chlorite seems to indicate a marine environment, but chlorite may also be inherited from basic igneous rocks. Many of the illites are interstratified, containing 20-30% expandable layers. Two types of interstratifications were distinguished - completely random and partially ordered. The geological evidence is insufficient to permit correlation between the type of interstratification and environmental conditions. It is possible that careful examination will reveal the presence of differently interstratified illites also in other sediments and perhaps sufficient data may eventually be accumulated to permit interpretation of the 4ifferent types of interstratification in terms of structure or weathering processes. According to Grim (1968) smectite is generally absent from Paleozoic sediments. This is 'attributed to metamorphic processes which would cause the alteration of smectite to mica type minerals. Smectite is also absent from Paleozoic sediments in southern Israel, although minor amounts of expandable layers interstratified with illite seem to persist. Detailed mineralogical studies in various areas may yield valuable indication of changes in environment during the Paleozoic era, a period for which geological data is scarce.
164
L. HELLER-KALLAl ET AL.
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ACKNOWLEDGEMENT
A research grant from the Ministry of Development is gratefully acknowledged.
REFERENCES Bartura, Y., 1966, Type sections of Paleozoic formations in the Timna area, Geol. Surv. Isr. Stratigr. Sect. No.3. Bentor, Y.K., W. Bodenheimer and L. Heller, 1963, A reconnaissance survey of the relationship between clay mineralogy and geological environment in the Negev, Southern Israel, J. Sediment. Petrol., 33, 874-903. Gerry, E., 1967, Paleozoic and Triassic ostracoda from outcrops and wells in Southern Israel, Israel Institute of Petroleum, Report No. 1/67. Grim, R., 1968, Clay Mineralogy, McGraw Hill, 551 pp. Heller-Kallai, L. and Z. Kalman, 1972, Some naturally occurring illite-smectite intcrstratifications, Clays Clay, Miner. 20, 165-168. Karcz, I., Y. Weiler and ·C.A. Key, 1971, Lithology and environment of deposition of the' Amudei Shelomo Sandstone ("NSP") in Nahal Shani, Elat, Isr. 1. Earth·Sci. 20, 119-124. Millot, G., 1970, The Geology o/Clays, Springer-Verlag, New York, 247 pp. Reynolds, R.C. and J. Hower, 1970, The nature of interlayering in mixed-layer illite-montmorillonite, Clays Clay Miner. 18, 25-36. Weissbrod, T., 19690, The Paleozoic of Israel and adjacent countries, Part I, Geol. Surv. Isr., Bull. No47,23pp. Weissbrod, T., 1969b, The Paleozoic of Israel and adjacent countries, Part II, Geol. Surv. Isr., Bull. No. 48,32 pp. Yaalon, D.H., 1963, Weathering and soil development through geologic time, BulL Res. Counc. Isr., llG, 149-150 (abstract).
