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The heavy minerals of the Kurnub Sandstone (Early Cretaceous) of Jordan
Sedimentary Geology, 62 (1989) 101-107 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
101
The heavy minerals of the Kurnub Sandstone (Early Cretaceous) of Jordan S. N A S I R a n d W . S A D E D D I N Department of Earth and Environmental Sciences, Yarmouk University, lrbid (Jordan)
Received August 1, 1988; revised version accepted January 18, 1989
Abstract Nasir, S. and Sadeddin, W., 1989. The heavy minerals of the Kurnub Sandstone (Early Cretaceous) of Jordan. Sediment. Geol. 62: 101-107. A study of the heavy-mineral distribution in the Kurnub Sandstone (Early Cretaceous) in Jordan was carried out in vertical and lateral sections. The heavy-mineral suites of the Kurnub Sandstone in north and south Jordan are identical and comparable to those in south Israel and southwest Sinai. The suites are mainly opaques, zircon, tourmaline and rutile; garnet, staurolite, epidot, anatase, barite and hornblende are less frequent. Staurolite and hornblende are confined to the south, whereas garnet is confined to a few horizons in the north. Selective chemical decomposition played a significant role in the modification of the unstable heavy-mineral variations in the Kurnub Sandstone. The ultrastable heavy minerals indicate a source area predominantly composed of granitic and metamorphic rocks. The association of zircon, tourmaline and rutile in a pure quartz arenite indicates that the main source of the Kurnub Sandstone of Jordan must be weathered Paleozoic sediments.
Introduction
succession consists of m a t u r e s a n d s t o n e (quartz arenite) which was deposited in a fluvial e n v i r o n -
A thick clastic succession was deposited d u r i n g the Early Cretaceous in Jordan. Q u e n n e l (1951) used the term " K u r n u b S a n d s t o n e " for the Lower Cretaceous in J o r d a n a n d correlated it with the W a d i H a t i r a S a n d s t o n e (e.g. Shaw, 1947) which is exposed in the K u r n u b structure west-southwest of the s o u t h e r n edge of the D e a d Sea. The K u r n u b S a n d s t o n e is considered as a part of the N u b i a n S a n d s t o n e ( B l a n c k e n h o r n , 1914). Bender (1968) s u b d i v i d e d the K u r n u b S a n d s t o n e i n t o the massive white s a n d s t o n e u n i t a n d the varicolored s a n d s t o n e unit. These two u n i t s are equivalent to the A m i r a n d H a t i r a F o r m a t i o n s of Israel (Bender, 1968). T h e K u r n u b S a n d s t o n e is exposed in Jordan, Sinai, Israel a n d n o r t h w e s t e r n Saudi Arabia. T h e
m e n t with a few interfingering s h a l l o w - m a r i n e horizons (Bender, 1968; A b e d , 1978, 1982; Schneider et al., 1984; Amireh, 1987). T h e K u r n u b
0037-0738/89/$03.50
© 1989 Elsevier Science Publishers B.V.
S a n d s t o n e appears to represent sediments obtained through weathering a n d reworking of clastic sediments of Early Paleozoic age (Bender, 1968; Amireh, 1987). I n J o r d a n , the K u r n u b S a n d s t o n e o u t c r o p s in several deep wadis. It is exposed along the east side of the D e a d Sea where it overlies u n c o n f o r m a b l y the Triassic sediments (Schneider et al., 1984). I n n o r t h J o r d a n it overlies the Jurassic sediments, whereas in south J o r d a n it overlies u n c o n f o r m a b l y the Paleozoic sediments. The objective of this work is to establish vertical a n d lateral profiles for the K u r n u b S a n d s t o n e
102
in Jordan on the basis of its heavy-mineral content and to determine their qualitative and quantitative relationships.
along randomly chosen traverses. Opaque minerals were examined in polished sections. Lithostratigraphy
Methods Two sections of the Kurnub Sandstone in north and south Jordan were studied for their heavymineral content (Figs. 2, 3). In north Jordan, at King Talal Dam (Fig. 1), the Kurnub Sandstone overlies non-conformably Jurassic calcareous rocks and underlies Cenomanian limestone. The succession starts with a basal conglomerate up to 5 m thick, followed by medium- and coarse-grained
Heavy minerals were counted in 100 samples. 100 g of each sample were initially sieved and the sand-size fraction between 2 and 4 ~ (e.g., Friis, 1974) was utilized for heavy-mineral separation using bromoform. The heavy-mineral grains were mounted in Canada balsam and microscopically examined. About 300 grains were point counted
~so
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::."::.".:~:-':::.'.i'.:::'.::'::'"~'" ':. X
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Fig. 1. Outcrops of the Paleo-Mesozoic clastic Series and the Precambrian basement rocks in Jordan (after Bender, 1968) and location of the studied sections.
.
+
2_+ 2
Barite
.
5
0-10
0- 4
0-
.
.
8
.
.
X (20)
.
+
+
.
9-+ 6
57 _+ 16
33 _+ 17
45 _+ 15
.
.
0-
03
2
.
1-14
30-85
5-50
25-80
R
.
c W e i s s b r o d a n d N a c h m i a s (1986).
.
1_+ 2
5 _+ 5
3_+ 2
.
8_+ 5
43 -+ 10
41 _+ 12
64_+ 14
X (30)
b W S U : w h i t e s a n d s t o n e u n i t ; V C S U : v a r i c o l o r e d s a n d s t o n e unit.
X = a v e r a g e (70); R: r a n g e (70); ( ): n u m b e r o f s a m p l e s .
+
Epidote
.
Hornblende
Anatase
.
Staurolite
0-
5-20
4+
3
10_+ 5
Garnet
Rutile
15-60
25-75
35 _+ 15
48 + 13
Zircon
Tourmaline
R
15-50
(30)
27_+ 8
Opaque
.
R
-
0 .
. 5 5
0-25
0-
1-15
20-70
10-70
40-80
2_+ 2
-
-
+
7-+ 6
47 -+ 11
40_+ 13
51 _+ 16
X (20)
0-
-
0-
8
2
1 10
25-60
10-60
25-85
R
VCSU (Amir Fm.)
WSU (Hatira Fm.)
WSU b (Hatira Fm.)
VCSU b (Amir Fm.)
South Jordan (Wadi Quseib)
North Jordan (King Talal Dam)
H e a v y - m i n e r a l c o n t e n t s o f the K u r n u b S a n d s t o n e in J o r d a n , Israel a n d Sinai a
TABLE 1
-
2
7
66
25
22
R
1- 4
1-15
11-98
0-69
18-27
X
2
-
11
43
44
43
R
0-
-
8
5-26
13-86
8-72
22-84
-
8
1
51
40
77
R
4
-
7-11
0-
21-86
7-68
64-86
3
-
6
64
27
35
X
0-13
-
1-14
26-94
2-57
28-95
R
Amir Fm. c
Hatira Fm. ¢
Hatira Fm. ¢
Amir Fm. ¢
S o u t h w e s t e r n Sinai ( U r n B o g m a a r e a )
S o u t h Israel ( T i m n a a r e a )
104
white sandstones up to 140 m thick that alternate with silt and marl. Then follow up to 100 m thick varicolored fine, medium- and coarse-grained, cross-bedded sandstone. Calcareous sandstone and silts are found as intercalations. Some horizons are cemented by carbonate, iron hydroxides or barite. In general, the sandstones are mineralogically and texturally mature. In south Jordan, at Wadi Quseib (Fig. 1), the Kurnub Sandstone unconformably overlies the Ordovician. The lower part starts with a 3 m thick basal conglomerate, followed by a 140 m thick coarse white sandstones. These are overlain by multicolored medium- to coarse-grained sandstones up to 110 m thick. Sandy shales and ferruginous sandstones are intercalated. The sandstone is friable and poorly cemented. The quartz grains are mostly rounded and in some horizons they are well sorted. Feldspar and muscovite are only found in this succession. Some horizons are cemented by iron hydroxides and kaolinite.
g
g
:
~)
= •
u.~
~
gg
.'.J O O
a
o z
Non-Opaque
30=/=20 4 0 !
,., =,,
..... ::
i
60 I
80% I
. ....
_=_i=i=:=:=:NI
.JO 0 IU m
0 h-
Fig. 3. Heavy-mineralcomposition of the Kurnub Sandstone in south Jordan. Composition section at Wadi Quseib.
Heavy minerals Table 1 shows the heavy-mineral distributions in the Kurnub Sandstone of north and south Jordan in comparison to those from south Israel
0J u~
=P
_ o •= ":_
oo o.
0 i c o
Non-Opaque
"; :~ DO zloo*/.2o 40 --~ .... ) ,l!i. ] ' ' ~::;:
:::,'.
O Z:
(
f'l ~ ,~--
.JO
-,-
'
Description of the Minerals
LEGEND r mali n e
~:::;;::::: ...... ~ Z i r c 0 n ~dlliiiiii!!!::
J(
t
'Z ii i FT/Z- S,oor0.,e ~J. ..........
--7.
:::::
80%
~ ' ~ 7 ' ',I I : ',: ',i',~*~',~.~ ~ T o u
I
•::::
80
60
"s.'.,,,.,~,..,j.~;__:~,,
~t!!!!!!!iiii]iii;~/ 1 6 o r n e ,I"
~Cz
and southwest Sinai. The heavy-mineral suites of the Kurnub Sandstone in north and south Jordan are fairly comparable (Table 1, Figs. 2, 3). They are composed mainly of opaques, zircon, tourmaline, rutile with less frequent minerals like garnet, staurolite, epidote, hornblende, barite and anatase. The total content of the heavy minerals ranges between 0.05% and 0.3%.
:
.7!
~'P
~-~Hornblende
_"H H',',,?,,i'~
~
!'iiiiii~
F ~ ~
Quart
z -
Qz-Oe b hies
rTT.[T.FI c ~ o l c o r e o u s .....
~andstone Boundary
Fig. 2. Heavy-mineral composition of the Kurnub Sandstone in north Jordan. Composite section at King Talal Dam.
(1) Opaque minerals. Opaque heavy minerals are common in all the examined samples. They are mostly composed of ilmenite with lesser amount of hematite and limonite. They occur as subangular to subrounded grains with irregular outline. Their average percentage varies between 27% in the white sandstone unit and 45% in the varicolored sandstone unit of north Jordan and between 64% and 51% in the white and varicolored sandstone units of south Jordan, respectively. (2) Zircon. Zircon is abundant. It occurs in general as colorless, highly refracting prismatic crystals with rounded edges. Inclusions of opaque minerals are common.
105
(3) Tourmaline. Tourmaline is abundant and occurs in various forms, mostly as prisms and rounded grains. It shows intense pleochroism. Dominant colors are olive and pale green. Inclusions of opaque grains are widespread. (4) Rutile. Rutile is common throughout the succession. It occurs as rounded grains and prisms. Simple crystals consist of tetragonal prisms. The color is intensely dark reddish brown to yellow. (5) Anatase. Anatase is found as an accessory mineral in most of the samples. The grains are authigenic. They display an euhedral tabular habit with a bluish grey color. (6) Garnet. G a r n e t occurs in irregular, rounded, isotropic, pale pink grains. The grains show etching and dissolution features. Garnet is confirmed to two calcareous sandstone horizons in the upper part of the varicolored sandstone unit of north Jordan (Fig. 2). (7) Staurolite. Staurolite occurs as irregular yellow grains with conchoidal fractures. Pleochroism is distinct and ranges from light to deep yellow. Inclusions of quartz and opaques are very
~ Non-Opaque :E ~ o ~oo%2o .4o e o
~-,,o
~:~:
!lib i!i,
Fig.4. Heavy-mineral composition of the Kurnub Sandstone in south Israel. Composite section, Timna area (Weissbrod and Nachmias, 1986).
.~ ~ -
z
$ g 81 Nan-Opaque -Jo iqm.?0 'to ~0
ep*/.
"-'~:,i!!!
Fig. 5. Heavy-mineral composition of the Kurnub Sandstone in southwestern Sinai. Composite section, Um Bogma area (Weissbrod and Nachmias, 1986).
common. Etching and dissolution at grain boundaries are characteristic. The greatest percentage was noted from south Jordan at the lower and upper horizons. The occurrence of staurolite is comparable to those in south Israel and southwest Sinai (Figs. 4, 5) (Weissbrod and Nachmias, 1986). Staurolite is completely lacking in north Jordan. (8) Hornblende. Hornblende occurs as dark green pleochroic grains. It is distinguished from tourmaline by cleavage. Etching and dissolution features are characteristic. Hornblende is confined to one horizon of the varicolored sandstone in south Jordan. (Fig. 2). It is completely lacking in the Kurnub Sandstone of south Israel and southwest Sinai (Weissbrod and Nachmias, 1986). Its presence was first indicated by Bender (1968) in a section measured at Quweira-Mudawwara, south Jordan. (9) Epidote. Epidote occurs as yellow green grains that show etching and dissolution features at grain boundaries. It is found mostly in south Jordan associated with staurolite. In north Jordan it is associated with garnet. (10) Barite. Barite occurs as intergranular, colorless, euhedral crystals. It is mostly found in the successions in north Jordan, where it occurs mostly as a cementing material.
106
Discussion
The average percentage of the heavy-mineral distribution in the Kurnub Sandstone of Jordan, south Israel, and southwest Sinai (Table 1, Figs. 2-5) indicate some regional variability, mostly with respect to unstable heavy minerals (garnet, staurolite, epidote, and hornblende), induced most probably by chemical weathering. Two suites of unstable minerals are present: the north Jordan suite, which contains garnet and traces of epidote, and the south Jordan suite which contains staurolite, hornblende and epidote. The preservation of garnet and traces of epidote in two marine horizons from the Kurnub Sandstone of north Jordan indicates a warm and humid climate (Bender, 1968; Amireh, 1987). In south Jordan, the Kurnub Sandstone has more unstable heavy minerals, predominantly staurolite, hornblende and epidote. The proximity of this sandstone to the source area (the Arabian-Nubian Shield) probably played a role in the relative enrichment with unstable heavy minerals relative to north Jordan. The Paleo-Mesozoic clastic sequence (Nubian Sandstone; Blanckenhorn, 1914) in Jordan overlies unconformably the Precambrian igneous basement, which was the permanent area of detrital supply (Bender, 1968; Amireh, 1987). Weissbrod and Nachmias (1986) have found three heavymineral associations within the Paleo-Mesozoic clastic succession: an unstable Precambrian association, characterized by abundant hornblende, chlorite and staurolite, that appears to have been derived from the igneous basement, a mostly ultrastable Early Paleozoic association, characterized by a dominance of zircon, tourmaline, rutile, apatite and barite, that appears also to be derived from an igneous source, but to have undergone more weathering, and an ultrastable Late Paleozoic-Mesozoic association, where the zircon-tourmaline-rutile assemblage is more dominant. The gradual upward change from Late Precambrian and Early Paleozoic arkosic and subarkosic sandstones (Amireh, 1987) to Late PaleoMesozoic quartz arenite and the vertical changes in the heavy-mineral associations could be attributed primarily to changes in province and to
modifications due to weathering and transport (e.g., Friis, 1974; Morton, 1985). The Kurnub Sandstone sequence was deposited in a stable tectonic setting subsequent to epirogenic uplift in the Late Jurassic (Bender, 1968). The Kurnub Sandstone sequence consists of pure quartz arenite (Amireh, 1987) associated with an ultrastable heavy-mineral assemblage (zircontourmaline-ruffle index of 92-99; Table 1). Such a composition implies a high degree of chemical weathering (Morton, 1985). However, chemical weathering was not sufficient to dissolve all unstable heavy minerals. Intrastratal solutions cause corrosion of garnet, epidote, hornblende and staurolite, but this was not sufficient to dissolve them completely. The carbonate cement in the two marine horizons of the Kurnub Sandstone from north Jordan helped to protect unstable heavy minerals like garnet and epidote against intrastratal solutions. The occurrence of unstable heavy minerals such as staurolite, hornblende and epidote in the Kurnub Sandstone of south Jordan points to local metamorphic outcrops which provided these unstable heavy minerals to the mature Kurnub Sandstone. Post-depositional chemical processes are indicated by the presence of corrosion marks and the authigenesis of minerals such as barite and hematite. Conclusions
The heavy-mineral suites of the Kurnub Sandstone in north and south Jordan are mainly opaques, zircon, tourmaline and rutile; garnet, epidote, staurolite, anatase, barite and hornblende are less frequent. The maturity of the Kurnub Sandstone and the high zircon-tourmaline-ruffle index (92-99) indicate prolonged reworking and extensive weathering of pre-existing clastics. The main source of the Kurnub Sandstone is considered to be mainly the weathered and reworked clastic of the Paleozoic which still outcrop in south Jordan and northwestern Arabia. Local admixture of unstable heavy minerals, mainly garnet, epidote and staurolite occurs within the ultrastable heavy-mineral assemblage in north and south Jordan. These minerals were derived probably from local outcrops of igneous and metamorphic
107 rocks.
However,
selective
chemical
weathering
played a significant role in the modification of the unstable heavy mineral variations in the Kurnub Sandstone. The heavy-mineral distribution enables a good
lateral correlation
Sandstone
from north
between
and
the Kurnub
south Jordan,
Israel
and Sinai.
Acknowledgements The Yarmouk
support
of
the
Faculty
University, Grant
of
Nr. 13/88
Research, is g r a t e -
fully acknowledged.
References Abed, A., 1978. Depositional environments of the Kurnub (Lower Cretaceous) Sandstone, I. A coal horizon at the lower most Kurnub, north Jordan. Dirasat, 5: 31-44. Abed, A., 1982. Depositional environment of the Early Cretaceous Kurnub (hathir) Sandstone, North Jordan, Sediment, Geol., 31: 267-279. Amireh, B., 1987. Sedimentological and petrological interplays of the Nubian Series in Jordan with regard to paleogeogra-
phy and diagenesis. Thesis, University of Braunschweig, Braunschweig, 232 pp. Bender, F., 1968. Geologie von Jordanien, Borntr~iger, Berlin, 230 pp. Blanckenhorn, M., 1914. Syrien, Arabien und Mesopotamien. Handb. Reg. Geol. 5, Winter, Heidelberg. Friis, H., 1974. Weathered heavy-mineral associations from the Young Tertiary deposits of Juttland, Denmark. Sediment. Geol., 12: 199-213. Morion, A., 1985. Heavy minerals in provenance studies, in: G.G. Zuffa (Editor), Provenance of Arenites. Nato ASI Series. Reidel, Dordrecht, pp. 249-277. Quennel, A.M., 1951. The geology and mineral resources of Trans-Jordan. Colon. Geol. Miner. Resour., 2: 75-115. Schneider, W., Abed, A. and Salameh, E., 1984. Mineral content and diagnetic pattern. Useful tools for litho-stratigraphic subdivisions and correlation of the Nubian Series --Result of work in the Wadi Zerqa-Main area, Jordan. Geol. Jahrb. Reihe B, 53: 55-75. Shaw, S.M., 1947. Southern Palestine geological map on a scale of 1:250,000 with explanatory notes. Government of Palestine, Jerusalem, 42 pp. Weissbrod, T. and Nachmias, J., 1986. Stratigraphic significance of heavy minerals in the Late Precambrian-Mesozoic clastic sequence (Nubian Sandstone) in the Near East. Sediment. Geol. 47: 263-291.
101
The heavy minerals of the Kurnub Sandstone (Early Cretaceous) of Jordan S. N A S I R a n d W . S A D E D D I N Department of Earth and Environmental Sciences, Yarmouk University, lrbid (Jordan)
Received August 1, 1988; revised version accepted January 18, 1989
Abstract Nasir, S. and Sadeddin, W., 1989. The heavy minerals of the Kurnub Sandstone (Early Cretaceous) of Jordan. Sediment. Geol. 62: 101-107. A study of the heavy-mineral distribution in the Kurnub Sandstone (Early Cretaceous) in Jordan was carried out in vertical and lateral sections. The heavy-mineral suites of the Kurnub Sandstone in north and south Jordan are identical and comparable to those in south Israel and southwest Sinai. The suites are mainly opaques, zircon, tourmaline and rutile; garnet, staurolite, epidot, anatase, barite and hornblende are less frequent. Staurolite and hornblende are confined to the south, whereas garnet is confined to a few horizons in the north. Selective chemical decomposition played a significant role in the modification of the unstable heavy-mineral variations in the Kurnub Sandstone. The ultrastable heavy minerals indicate a source area predominantly composed of granitic and metamorphic rocks. The association of zircon, tourmaline and rutile in a pure quartz arenite indicates that the main source of the Kurnub Sandstone of Jordan must be weathered Paleozoic sediments.
Introduction
succession consists of m a t u r e s a n d s t o n e (quartz arenite) which was deposited in a fluvial e n v i r o n -
A thick clastic succession was deposited d u r i n g the Early Cretaceous in Jordan. Q u e n n e l (1951) used the term " K u r n u b S a n d s t o n e " for the Lower Cretaceous in J o r d a n a n d correlated it with the W a d i H a t i r a S a n d s t o n e (e.g. Shaw, 1947) which is exposed in the K u r n u b structure west-southwest of the s o u t h e r n edge of the D e a d Sea. The K u r n u b S a n d s t o n e is considered as a part of the N u b i a n S a n d s t o n e ( B l a n c k e n h o r n , 1914). Bender (1968) s u b d i v i d e d the K u r n u b S a n d s t o n e i n t o the massive white s a n d s t o n e u n i t a n d the varicolored s a n d s t o n e unit. These two u n i t s are equivalent to the A m i r a n d H a t i r a F o r m a t i o n s of Israel (Bender, 1968). T h e K u r n u b S a n d s t o n e is exposed in Jordan, Sinai, Israel a n d n o r t h w e s t e r n Saudi Arabia. T h e
m e n t with a few interfingering s h a l l o w - m a r i n e horizons (Bender, 1968; A b e d , 1978, 1982; Schneider et al., 1984; Amireh, 1987). T h e K u r n u b
0037-0738/89/$03.50
© 1989 Elsevier Science Publishers B.V.
S a n d s t o n e appears to represent sediments obtained through weathering a n d reworking of clastic sediments of Early Paleozoic age (Bender, 1968; Amireh, 1987). I n J o r d a n , the K u r n u b S a n d s t o n e o u t c r o p s in several deep wadis. It is exposed along the east side of the D e a d Sea where it overlies u n c o n f o r m a b l y the Triassic sediments (Schneider et al., 1984). I n n o r t h J o r d a n it overlies the Jurassic sediments, whereas in south J o r d a n it overlies u n c o n f o r m a b l y the Paleozoic sediments. The objective of this work is to establish vertical a n d lateral profiles for the K u r n u b S a n d s t o n e
102
in Jordan on the basis of its heavy-mineral content and to determine their qualitative and quantitative relationships.
along randomly chosen traverses. Opaque minerals were examined in polished sections. Lithostratigraphy
Methods Two sections of the Kurnub Sandstone in north and south Jordan were studied for their heavymineral content (Figs. 2, 3). In north Jordan, at King Talal Dam (Fig. 1), the Kurnub Sandstone overlies non-conformably Jurassic calcareous rocks and underlies Cenomanian limestone. The succession starts with a basal conglomerate up to 5 m thick, followed by medium- and coarse-grained
Heavy minerals were counted in 100 samples. 100 g of each sample were initially sieved and the sand-size fraction between 2 and 4 ~ (e.g., Friis, 1974) was utilized for heavy-mineral separation using bromoform. The heavy-mineral grains were mounted in Canada balsam and microscopically examined. About 300 grains were point counted
~so
A
\
",-~
~o S Y R I A
..-~
N .--'"'"
I
T°.o. o o .
~
~2o
#4~AMMAN ~erles ~ [ ] Basement
JERUSALE~ f /
~ -"
<-
Hatlro
"3J° ~
(~
:
, ",,
@
",
•
"\
,~ ll
/x
,~
l
"~.
x
~XX X~ ~1Xx X~.:.: IX
/ t~ /
~X i
.:'...: ,......"
,~ ~ i l i l / o d i
J
;x
x
/
Ouselb
L..".'--. • .'-.':.'-"-'.'~'---"..':
.:" "..,
x x ..::::: :::'::i:::.:.::::.".?i:.".i:::~.:i(. i..:.:"?:":::.:;' x
x x
-• _ X
X
......
t
,s
9 \
::."::.".:~:-':::.'.i'.:::'.::'::'"~'" ':. X
X
_x X x
""~::'.:?.'.'.(.'.";-. 0,...','"•
;-.:'., ;'"
Fig. 1. Outcrops of the Paleo-Mesozoic clastic Series and the Precambrian basement rocks in Jordan (after Bender, 1968) and location of the studied sections.
.
+
2_+ 2
Barite
.
5
0-10
0- 4
0-
.
.
8
.
.
X (20)
.
+
+
.
9-+ 6
57 _+ 16
33 _+ 17
45 _+ 15
.
.
0-
03
2
.
1-14
30-85
5-50
25-80
R
.
c W e i s s b r o d a n d N a c h m i a s (1986).
.
1_+ 2
5 _+ 5
3_+ 2
.
8_+ 5
43 -+ 10
41 _+ 12
64_+ 14
X (30)
b W S U : w h i t e s a n d s t o n e u n i t ; V C S U : v a r i c o l o r e d s a n d s t o n e unit.
X = a v e r a g e (70); R: r a n g e (70); ( ): n u m b e r o f s a m p l e s .
+
Epidote
.
Hornblende
Anatase
.
Staurolite
0-
5-20
4+
3
10_+ 5
Garnet
Rutile
15-60
25-75
35 _+ 15
48 + 13
Zircon
Tourmaline
R
15-50
(30)
27_+ 8
Opaque
.
R
-
0 .
. 5 5
0-25
0-
1-15
20-70
10-70
40-80
2_+ 2
-
-
+
7-+ 6
47 -+ 11
40_+ 13
51 _+ 16
X (20)
0-
-
0-
8
2
1 10
25-60
10-60
25-85
R
VCSU (Amir Fm.)
WSU (Hatira Fm.)
WSU b (Hatira Fm.)
VCSU b (Amir Fm.)
South Jordan (Wadi Quseib)
North Jordan (King Talal Dam)
H e a v y - m i n e r a l c o n t e n t s o f the K u r n u b S a n d s t o n e in J o r d a n , Israel a n d Sinai a
TABLE 1
-
2
7
66
25
22
R
1- 4
1-15
11-98
0-69
18-27
X
2
-
11
43
44
43
R
0-
-
8
5-26
13-86
8-72
22-84
-
8
1
51
40
77
R
4
-
7-11
0-
21-86
7-68
64-86
3
-
6
64
27
35
X
0-13
-
1-14
26-94
2-57
28-95
R
Amir Fm. c
Hatira Fm. ¢
Hatira Fm. ¢
Amir Fm. ¢
S o u t h w e s t e r n Sinai ( U r n B o g m a a r e a )
S o u t h Israel ( T i m n a a r e a )
104
white sandstones up to 140 m thick that alternate with silt and marl. Then follow up to 100 m thick varicolored fine, medium- and coarse-grained, cross-bedded sandstone. Calcareous sandstone and silts are found as intercalations. Some horizons are cemented by carbonate, iron hydroxides or barite. In general, the sandstones are mineralogically and texturally mature. In south Jordan, at Wadi Quseib (Fig. 1), the Kurnub Sandstone unconformably overlies the Ordovician. The lower part starts with a 3 m thick basal conglomerate, followed by a 140 m thick coarse white sandstones. These are overlain by multicolored medium- to coarse-grained sandstones up to 110 m thick. Sandy shales and ferruginous sandstones are intercalated. The sandstone is friable and poorly cemented. The quartz grains are mostly rounded and in some horizons they are well sorted. Feldspar and muscovite are only found in this succession. Some horizons are cemented by iron hydroxides and kaolinite.
g
g
:
~)
= •
u.~
~
gg
.'.J O O
a
o z
Non-Opaque
30=/=20 4 0 !
,., =,,
..... ::
i
60 I
80% I
. ....
_=_i=i=:=:=:NI
.JO 0 IU m
0 h-
Fig. 3. Heavy-mineralcomposition of the Kurnub Sandstone in south Jordan. Composition section at Wadi Quseib.
Heavy minerals Table 1 shows the heavy-mineral distributions in the Kurnub Sandstone of north and south Jordan in comparison to those from south Israel
0J u~
=P
_ o •= ":_
oo o.
0 i c o
Non-Opaque
"; :~ DO zloo*/.2o 40 --~ .... ) ,l!i. ] ' ' ~::;:
:::,'.
O Z:
(
f'l ~ ,~--
.JO
-,-
'
Description of the Minerals
LEGEND r mali n e
~:::;;::::: ...... ~ Z i r c 0 n ~dlliiiiii!!!::
J(
t
'Z ii i FT/Z- S,oor0.,e ~J. ..........
--7.
:::::
80%
~ ' ~ 7 ' ',I I : ',: ',i',~*~',~.~ ~ T o u
I
•::::
80
60
"s.'.,,,.,~,..,j.~;__:~,,
~t!!!!!!!iiii]iii;~/ 1 6 o r n e ,I"
~Cz
and southwest Sinai. The heavy-mineral suites of the Kurnub Sandstone in north and south Jordan are fairly comparable (Table 1, Figs. 2, 3). They are composed mainly of opaques, zircon, tourmaline, rutile with less frequent minerals like garnet, staurolite, epidote, hornblende, barite and anatase. The total content of the heavy minerals ranges between 0.05% and 0.3%.
:
.7!
~'P
~-~Hornblende
_"H H',',,?,,i'~
~
!'iiiiii~
F ~ ~
Quart
z -
Qz-Oe b hies
rTT.[T.FI c ~ o l c o r e o u s .....
~andstone Boundary
Fig. 2. Heavy-mineral composition of the Kurnub Sandstone in north Jordan. Composite section at King Talal Dam.
(1) Opaque minerals. Opaque heavy minerals are common in all the examined samples. They are mostly composed of ilmenite with lesser amount of hematite and limonite. They occur as subangular to subrounded grains with irregular outline. Their average percentage varies between 27% in the white sandstone unit and 45% in the varicolored sandstone unit of north Jordan and between 64% and 51% in the white and varicolored sandstone units of south Jordan, respectively. (2) Zircon. Zircon is abundant. It occurs in general as colorless, highly refracting prismatic crystals with rounded edges. Inclusions of opaque minerals are common.
105
(3) Tourmaline. Tourmaline is abundant and occurs in various forms, mostly as prisms and rounded grains. It shows intense pleochroism. Dominant colors are olive and pale green. Inclusions of opaque grains are widespread. (4) Rutile. Rutile is common throughout the succession. It occurs as rounded grains and prisms. Simple crystals consist of tetragonal prisms. The color is intensely dark reddish brown to yellow. (5) Anatase. Anatase is found as an accessory mineral in most of the samples. The grains are authigenic. They display an euhedral tabular habit with a bluish grey color. (6) Garnet. G a r n e t occurs in irregular, rounded, isotropic, pale pink grains. The grains show etching and dissolution features. Garnet is confirmed to two calcareous sandstone horizons in the upper part of the varicolored sandstone unit of north Jordan (Fig. 2). (7) Staurolite. Staurolite occurs as irregular yellow grains with conchoidal fractures. Pleochroism is distinct and ranges from light to deep yellow. Inclusions of quartz and opaques are very
~ Non-Opaque :E ~ o ~oo%2o .4o e o
~-,,o
~:~:
!lib i!i,
Fig.4. Heavy-mineral composition of the Kurnub Sandstone in south Israel. Composite section, Timna area (Weissbrod and Nachmias, 1986).
.~ ~ -
z
$ g 81 Nan-Opaque -Jo iqm.?0 'to ~0
ep*/.
"-'~:,i!!!
Fig. 5. Heavy-mineral composition of the Kurnub Sandstone in southwestern Sinai. Composite section, Um Bogma area (Weissbrod and Nachmias, 1986).
common. Etching and dissolution at grain boundaries are characteristic. The greatest percentage was noted from south Jordan at the lower and upper horizons. The occurrence of staurolite is comparable to those in south Israel and southwest Sinai (Figs. 4, 5) (Weissbrod and Nachmias, 1986). Staurolite is completely lacking in north Jordan. (8) Hornblende. Hornblende occurs as dark green pleochroic grains. It is distinguished from tourmaline by cleavage. Etching and dissolution features are characteristic. Hornblende is confined to one horizon of the varicolored sandstone in south Jordan. (Fig. 2). It is completely lacking in the Kurnub Sandstone of south Israel and southwest Sinai (Weissbrod and Nachmias, 1986). Its presence was first indicated by Bender (1968) in a section measured at Quweira-Mudawwara, south Jordan. (9) Epidote. Epidote occurs as yellow green grains that show etching and dissolution features at grain boundaries. It is found mostly in south Jordan associated with staurolite. In north Jordan it is associated with garnet. (10) Barite. Barite occurs as intergranular, colorless, euhedral crystals. It is mostly found in the successions in north Jordan, where it occurs mostly as a cementing material.
106
Discussion
The average percentage of the heavy-mineral distribution in the Kurnub Sandstone of Jordan, south Israel, and southwest Sinai (Table 1, Figs. 2-5) indicate some regional variability, mostly with respect to unstable heavy minerals (garnet, staurolite, epidote, and hornblende), induced most probably by chemical weathering. Two suites of unstable minerals are present: the north Jordan suite, which contains garnet and traces of epidote, and the south Jordan suite which contains staurolite, hornblende and epidote. The preservation of garnet and traces of epidote in two marine horizons from the Kurnub Sandstone of north Jordan indicates a warm and humid climate (Bender, 1968; Amireh, 1987). In south Jordan, the Kurnub Sandstone has more unstable heavy minerals, predominantly staurolite, hornblende and epidote. The proximity of this sandstone to the source area (the Arabian-Nubian Shield) probably played a role in the relative enrichment with unstable heavy minerals relative to north Jordan. The Paleo-Mesozoic clastic sequence (Nubian Sandstone; Blanckenhorn, 1914) in Jordan overlies unconformably the Precambrian igneous basement, which was the permanent area of detrital supply (Bender, 1968; Amireh, 1987). Weissbrod and Nachmias (1986) have found three heavymineral associations within the Paleo-Mesozoic clastic succession: an unstable Precambrian association, characterized by abundant hornblende, chlorite and staurolite, that appears to have been derived from the igneous basement, a mostly ultrastable Early Paleozoic association, characterized by a dominance of zircon, tourmaline, rutile, apatite and barite, that appears also to be derived from an igneous source, but to have undergone more weathering, and an ultrastable Late Paleozoic-Mesozoic association, where the zircon-tourmaline-rutile assemblage is more dominant. The gradual upward change from Late Precambrian and Early Paleozoic arkosic and subarkosic sandstones (Amireh, 1987) to Late PaleoMesozoic quartz arenite and the vertical changes in the heavy-mineral associations could be attributed primarily to changes in province and to
modifications due to weathering and transport (e.g., Friis, 1974; Morton, 1985). The Kurnub Sandstone sequence was deposited in a stable tectonic setting subsequent to epirogenic uplift in the Late Jurassic (Bender, 1968). The Kurnub Sandstone sequence consists of pure quartz arenite (Amireh, 1987) associated with an ultrastable heavy-mineral assemblage (zircontourmaline-ruffle index of 92-99; Table 1). Such a composition implies a high degree of chemical weathering (Morton, 1985). However, chemical weathering was not sufficient to dissolve all unstable heavy minerals. Intrastratal solutions cause corrosion of garnet, epidote, hornblende and staurolite, but this was not sufficient to dissolve them completely. The carbonate cement in the two marine horizons of the Kurnub Sandstone from north Jordan helped to protect unstable heavy minerals like garnet and epidote against intrastratal solutions. The occurrence of unstable heavy minerals such as staurolite, hornblende and epidote in the Kurnub Sandstone of south Jordan points to local metamorphic outcrops which provided these unstable heavy minerals to the mature Kurnub Sandstone. Post-depositional chemical processes are indicated by the presence of corrosion marks and the authigenesis of minerals such as barite and hematite. Conclusions
The heavy-mineral suites of the Kurnub Sandstone in north and south Jordan are mainly opaques, zircon, tourmaline and rutile; garnet, epidote, staurolite, anatase, barite and hornblende are less frequent. The maturity of the Kurnub Sandstone and the high zircon-tourmaline-ruffle index (92-99) indicate prolonged reworking and extensive weathering of pre-existing clastics. The main source of the Kurnub Sandstone is considered to be mainly the weathered and reworked clastic of the Paleozoic which still outcrop in south Jordan and northwestern Arabia. Local admixture of unstable heavy minerals, mainly garnet, epidote and staurolite occurs within the ultrastable heavy-mineral assemblage in north and south Jordan. These minerals were derived probably from local outcrops of igneous and metamorphic
107 rocks.
However,
selective
chemical
weathering
played a significant role in the modification of the unstable heavy mineral variations in the Kurnub Sandstone. The heavy-mineral distribution enables a good
lateral correlation
Sandstone
from north
between
and
the Kurnub
south Jordan,
Israel
and Sinai.
Acknowledgements The Yarmouk
support
of
the
Faculty
University, Grant
of
Nr. 13/88
Research, is g r a t e -
fully acknowledged.
References Abed, A., 1978. Depositional environments of the Kurnub (Lower Cretaceous) Sandstone, I. A coal horizon at the lower most Kurnub, north Jordan. Dirasat, 5: 31-44. Abed, A., 1982. Depositional environment of the Early Cretaceous Kurnub (hathir) Sandstone, North Jordan, Sediment, Geol., 31: 267-279. Amireh, B., 1987. Sedimentological and petrological interplays of the Nubian Series in Jordan with regard to paleogeogra-
phy and diagenesis. Thesis, University of Braunschweig, Braunschweig, 232 pp. Bender, F., 1968. Geologie von Jordanien, Borntr~iger, Berlin, 230 pp. Blanckenhorn, M., 1914. Syrien, Arabien und Mesopotamien. Handb. Reg. Geol. 5, Winter, Heidelberg. Friis, H., 1974. Weathered heavy-mineral associations from the Young Tertiary deposits of Juttland, Denmark. Sediment. Geol., 12: 199-213. Morion, A., 1985. Heavy minerals in provenance studies, in: G.G. Zuffa (Editor), Provenance of Arenites. Nato ASI Series. Reidel, Dordrecht, pp. 249-277. Quennel, A.M., 1951. The geology and mineral resources of Trans-Jordan. Colon. Geol. Miner. Resour., 2: 75-115. Schneider, W., Abed, A. and Salameh, E., 1984. Mineral content and diagnetic pattern. Useful tools for litho-stratigraphic subdivisions and correlation of the Nubian Series --Result of work in the Wadi Zerqa-Main area, Jordan. Geol. Jahrb. Reihe B, 53: 55-75. Shaw, S.M., 1947. Southern Palestine geological map on a scale of 1:250,000 with explanatory notes. Government of Palestine, Jerusalem, 42 pp. Weissbrod, T. and Nachmias, J., 1986. Stratigraphic significance of heavy minerals in the Late Precambrian-Mesozoic clastic sequence (Nubian Sandstone) in the Near East. Sediment. Geol. 47: 263-291.