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Depositional environments of the early cretaceous Kurnub (Hathira) sandstones, North Jordan
Sedimentary Geology, 31 (1982) 267--279
267
Elsevier Scientific Publishing Company, Amsterdam - - Printed in The Netherlands
DEPOSITIONAL ENVIRONMENTS OF THE EARLY CRETACEOUS KURNUB (HATHIRA) SANDSTONES, NORTH JORDAN
ABDULKADER M. ABED
Department of Geology and Mineralogy, The University of Jordan, Amman (Jordan) (Received May 6, 1981;revised and accepted October 14; 1981L)
ABSTRACT Abed, A.M., 1982. Depositional environments of the Early Cretaceous Kurnub (Hathira) sandstones, north Jordan. Sediment. Geol., 31: 267--279. The Kurnub (Hathira) sandstones in north Jordan, which are most probably of Early Cretaceous age, are about 300 m thick varicoloured, friable quartz-arenitic sandstones. Based on grain-size analysis, sedimentary structures, palaeocurrent, fossil content and petrography, these sandstones are postulated to be dominantly of fluvial origin with a few interfingering shallow marine horizons. A southward displacement of Jordan by at least 100 km would bring these sandstones opposite to similar rocks west of the Jordan--Araba rift, with Jordan being higher during the Early Cretaceous.
INTRODUCTION
A thick sequence of varicoloured sandstones outcrops in several deep wadis in northern Jordan. Shaw (1947, p. 21) gave the name "Wadi Hathira Sandstone" to similar rocks of Early Cretaceous age in the Kurnub structure located in the Negev, WSW of the Dead Sea. Quennell (1951) used the term "Kurnub Sandstones" to describe andcorrelate similar rocks in Jordan, especiaUy those here under discussion. Bender (1974, 1975) prefered to use the term "Lower Cretaceous Sandstones" for the same sequence. This was due to the fact that this age was given to similar rocks west of the Jordan--Araba rift (e.g., Shaw, 1947; Aharoni, 1964). Wetzel and Morton (1959, pp. 134-138) had assigned an Albian--Aptian (Early Cretaceous)age to certain marine horizons in the Kurnub sandstones in north Jordan. These sandstones are, also, situated between the Jurassic dolomites and Cenomanian (Late Cretaceous} limestones in the same area. Due to the popularity of the term "Kurnub", it is maintained in this study. The "Gr~s de Base" or "Basal Cretaceous sandstone" in Syria and Lebanon seems to correlate with the Kurnub sandstones in Jordan. It is situated, as is the Kurnub, in Jordan and Hathira in Palestine, between the Jurassic and Cenomanian limestones (Kana'an, 1966; Wakim, 1968; Massaad, 1976). 0037-0738/82/0000--0000/$02.75 © 1982 Elsevier Scientific Publishing Company
268
These sandstones were postulated by those authors to be deposited in a fluvial environment. In southern Jordan the story is not as clear. These sandstones are considered as a part of the Nubian sandstones, whose age and environment is problematic. Blake and Ionides (1939) gave a Early Cretaceous age for all the sandstones in southern Jordan, while Bender (1963) was able to subdivide these rocks into Paleozoic and Lower Cretaceous units. Selley (1972) talked about a braided river system in the Palaeozoic sandstones in southern Jordan. However, the present study is confined to north Jordan. It is the aim of this article to study the depositional environments of these sandstones, previous knowledge of which restricted to marine and nonmarine environment. Thus enabling comparison with nearby countries. GEOLOGY AND LOCATION
Several sections of the Kurnub sandstones were measured in north Jordan. They are made up of about a 300 m thickness of varicoloured sandstones. 20O
- 30~ Ras ;n I~aqb
220
240
* Esh. $hidya SAUDI ARABIA
"~ulf of 29o Aqaba BOO
Fig. I. Location map.
0
50
9001
100 km
290. S00
269
The whole sequence could be seen in Wadi Huni in the Zerqa river canyon and some 10 km to the W and SW in the Arda' and Khunaizir (Fig. 1). In both localities they overlie the Jurassic dolomites and sandstones and underlie the Cenomanian Nodular limestone. The upper third is exposed in other localities such as Baqa', Na'ur and Mahis. A few metres of the basal part of the Kurnub is preserved on top of the uplifted Jurassic, 4 km, west of Mahis. PETROGRAPHY
Most of the sandstones in the study area are friable uncemented quartzarenites. These were studied for grain size by sieving (see below). The consolidated parts were thin sectioned; they are also quartz~renites. Feldspars are almost completely absent. Cement, when present, consists of iron oxide of different colours, which make these rocks varicoloured. The colours of the Kurnub sandstone (red, yellow-violet) become weaker with depth. It is believed that oxidation and downward leaching of the glau-
*30
x
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•
Baq a'a
khunaizir
/x
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Na'ur
•
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Fig. 2. Skewness vs standard deviation for the Kurnub Sandstones using ~0 units.
270
conites which exist in the uppermost few metres was the source of this iron colouration. Quartz grains are rounded to subrounded, and in the same horizon they are rather well sorted. It is thus believed that these sandstones are mineralogically and texturally mature. The source of these quartz grains is most probably formed by the Palaeozoic Nubian sandstones and not directly by the basement. G R A I N SIZE
More than one hundred friable sandstone samples were investigated for grain size. Coloured samples were treated by oxalic acid prior to sieving (Ingram, 1971); the sieves were arranged at 1 phi intervals throughout. The four m o m e n t s were then manually computed; i.e. mean, standard deviation, skewness and kurtosis (McBride, 1971). In addition, "mean cubed deviation" and "cubed standard deviation" (Friedman, 1967) were also computed. The
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1961)
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Fig. 3. S k e w n e s s vs standard deviation using ~ units.
271
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KURTOSIS
Fig. 4. Skewness vs kurtosis in ~ units.
data are plotted in Figs. 2, 3, 4, 5, 6 and 7 (c.f. Friedmann, 1961, 1967; Moiola and Weiser, 1968). The plots suggest that the studied samples are dominantly of fluvial origin. Sedimentologists are in general disagreement in this respect; whereas the general trend is the failure o f this technique to predict the palaeoenvironment (Pettijohn, 1975; Tucker and Vacher, 1980), certain authors are still using it (Moshrif, 1980). However, the studied sediments plotted well within the fluvial field. This is taken as an indication rather than as a final proof. A detailed investigation of the sedimentary structures supports such an interpretation (see below). LITHOFACIES The following is a subdivision of the Kumub sandstones according to their sedimentary structures:
Conglomerate facies These facies have no regional extent, rather they are restricted to certain parts of the lower contact o f the Kurnub. In the Ain Khunaizir section, a
272
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1968)
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Fig. 5. Mean vs standard deviation using ~ units.
thin bed of about 20 cm thick of extraformational chert and quartz cobbles is found in only one wadi of this area (see also Wetzel and Morton, 1959). These conglomerates are not believed to originate from the underlying Jurassic rocks, which are dominantly carbonates and sandstones. However, their roundness and lithology would suggest a long transportation history. Thirty kilometres to the south, and about 4 km to the west of Mahis, the conglomerates are rather intraformational and are made up of the Kurnub sandstone itself (Fig. 8). Once more they are restricted to a certain area. These facies resemble the basal conglomerates but without their regional distribution and they are best interpreted as channel deposits (Allen, 1970).
Rippled glauconitic sandstone facies These facies interfinger with the lignite facies and overlie the conglomerates when present, otherwise they overlie the Jurassic dolomites. These sandstones are characterised by herringbone cross-bedding with the upper part of
273 1..r
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Fig. 6. Standard deviation vs mean cubed deviation using ~0 units.
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1967)
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Fig. 7. Cube standard d e v i a t i o n ~ns mean cubed d e v i a t i o n using ~0 units.
274
Fig. 8. Basal conglomerates in the Mahis area (see text).
the facies made up of rippled glauconitic sandstones. Trace fossils (bilobites) are present. The sandstone bodies are fining-upwards and were interpreted as being deposited on a retreating tidal flat of the regressive Jurassic sea (Abed, 1978).
Lignite sandstone facies A low
Lenticular-channelled sandstone facies This is the major facies which dominates the whole sequence. It is more than 200 m thick in the study area. The samples for grain-size analysis were taken from this facies. The Kurnub sandstones are characterised o r distinguished by this type of sandstone which is widespread in Jordan over more than 300 km in a north--south direction.
275
Fig. 9. Channell in the upper Kurnub sandstones along the Ard~i highway 1 km above Ain
Khunaizir. These facies consist o f t w o rock types: varicoloured sandstones and grey siltstones to claystones. The t w o rock types are arranged in such a w a y as to give repeated cycles of thick sandstone bodies (up to 20 m) followed b y relatively thin clay~ilt horizons. Lenticular bedding dominates throughout. Sandstones are more than 90% cross-bedded. Planar cross-bedding is the main type, with minor tangential cross-bedding and very rare trough bedding. The sandstone lenses are finingupwards. Quartz pebbles up to 1 cm in diameter start at the b o t t o m , associated with cross-bedding. Both grain-size and cross-bedding sets fine upwards until a siltstone or claystone terminates the cycle. In many cases, smaller cycles are n o t e d within the larger cycle (see Allen, 1970). Channels are noted only in the upper third of this facies (e.g. Baqa', Arda'; Fig. 9). They are 50 to 100 m wide and 1--3 m deep. Channel-fill sediments start with quartz pebbles ( 2 1 cm) and m u d pebbles as channel-lag deposits on an erosional surface. Sediments then fine upward and terminate which siltstones and/or claystones. Channels trend in a north--south general direction (Leopold and Wolman, 1957). Neither fossils nor trace fossils were f o u n d in these facies, though plant remnants were encountered, especially in the finer sediments. The absence of fossils and trace fossils and the association of channels, fining-upwards cycles and the unidirectional cross-bedding suggest a fluvial origin for these facies.
276
Yellow glauconitic sandstones and dolomite facies There are t w o horizons of such facies. An upper horizon, which marks the contact with the overlying Cenomanian (Upper Cretaceous) limestones and a lower horizon 20--30 m below. The thickness of the t w o horizons decreases southwards. The upper one continues as far south as Ras En Naqb (about 300 kin), while the lower horizon disappears south of Baqa'. They are made up of fossfliferous sandstones and dolomites with various amounts of glauconites. Large zoned dolomite rhombs formed at the expense of glauconites and quartz. Ghosts of the original fine-grained dolomites are still preserved. Gastropods, bivalves and ammonites (Wetzel and Morton, 1959) are present. Trace fossils are encountered, especially in the glauconite beds. Based on these data, these facies are interpreted as shallow marine. Thus, there is a clear interaction of shallow marine deposits interfingering with the fluvial facies. PALAEOCURRENT
Several hundreds of cross-bedding directions and dip angles were measured in each locality studied. The results are shown in Fig. 10, which clearly shows a general northwards trend. This is easily understood by the existence of the Arabian--Nubian continent further south. Most of the cross-bedding
G0
E
W,
$ Fig. 10. Rose diagram for cross-bedding in the Kurnub Sandstones in north Jordan, including 1982 readings from Bag~i, Mahis, Air Khunaizir and Jarash. Numbers indicate readings in each directional unit.
277 dip angles fall within 10--25 °, with a small fraction in the upper twenties. Very rare angles are in the lower thirties. The direction and amount of dip of cross-bedding might indicate a fluvial regime rather than an eolian or a beach regime. DISCUSSIONS A N D C O N C L U S I O N S (1) The foregoing data on grain size, sedimentary structures and paiaeocurrents, together with the lack of fossils and trace fossils would favour fluvial deposits (Allen, 1965, 1970) interfingering with a few relatively thin shallow marine horizons. Such a conclusion is in general agreement with the palaeoenvironments of the same group in Lebanon (Massaad, 1976) and West of the Jordan--Araba rift (Karcz, 1965), with more marine influence than in Jordan. (2) The petrography of the studied Kurnub quartz-arenitic sandstones shows a rather mature texture. Lutites (siltstones and claystones) are relatively scarce compared with the sandstones. This is contrary to most recent fluvial deposits (Pettijohn et al., 1972, p. 461), where the sediments contain more clays, feldspars and rock fragments, depending on the source area. The absence of these components, while the granitic basement is less than 300 km south, could be explained by the source material being the Palaeozoic quartz~xenitic Nubian sandstones. Recycling of those sandstone would also explain the roundness of the Kurnub sandstones. (3) Comparison of these rocks with the Early Cretaceous rocks west of the Jordan--Axaba rift, would show that the latter are more marine and much thicker. The Early Cretaceous rocks to the west of the study area (e.g. Wadi Faria) are completely different, being dominantly marine limestone (Blake and Goldschmidt, 1947, p. 135). Similar rocks could be found further south, i.e. west and southwest of the Dead Sea. Even there, the Kurnub group is much thicker and more marine (e.g. 408 m, with several marine horizons in the Kurnub structure itself; Greenberg, 1968) and the thickness increases towards the NW (Tsiah 480 m, Beer Sheva 575 m, Halutsa 604 m; Aharoni, 1964). Such dissimilarities could be explained by: (1) Jordan being higher during Early Cretaceous times, thereby more continental sandy facies having accumulated (Wetzel and Morton, 1959; Bender, 1974); (2) a southward horizontal displacement of Jordan relative to Palestine of at least 100 km (Burdon, 1959). A displacement of 70--80 km (Freund, 1965; Jarrar, 1979) such as is generally accepted, cannot explain the present data.
REFERENCES Abed, A.M., 1978. Depositional environments of the Kurnub (Lower Cretaceous). I-A coal horizon at the lowermost Kurnub in northern Jordan. Dirasat, 5: 31---44.
278 Aharoni, E., 1964. Lithoelectric correlation of the Kurnub group (Lower Cretaceous) in the northern Negev. Israel J. Earth Sci., 13: 63--78. Allen, J.R.L., 1965. A review of the origin and characteristics of Recent alluvial sediments. Sedimentology, 5: 89--191. Allen, J.R.L., 1970. Studies in fluvial sedimentation: composition of fining-upwards cyclothemes with special reference to coarse m e m b e r composition and interpretation. J. Sediment. Petrol., 40: 298--323. Bender, F., 1963. Stratigraphie des "Nubischen Sandsteine" in Sud-Jordanien. Geol. Jahrb., 81: 237--276. Bender, F., 1974. Geology of Jordan, Borntraeger, Berlin, 196 pp. Bender, F., 1975. Geology of the Arabian Peninsula, Jordan. U.S. Geol. Surv., Prof. Pap., 560-I, 136 pp. Blake, G.S. and Goldschmidt, M.J., 1947. Geology and Water Resources of Palestine. Govt. of Palestine, Jerusalem, 113 pp. Blake, G.S. and Ionides, M.G., 1939. Report on the Water Resources of Transjordan and Their Development. Crown Agents for the Colonies, London, 372 pp. Burdon, D.J., 1959. Handbook of the geology of Jordan. Govt. of Jordan, Amman. Friedman, G.M., 1961. Distribution between dune, Beach and River Sands from Their Textural Characteristics. J. Sediment. Petrol., 31: 514--529. Friedman, G.M., 1967. Dynamic processes and statistical parameters compared for size frequency distribution of beach and river sands. J. Sediment. Petrol., 37: 327--354. Freund, R., 1965. A model of the structural development of Israel and Adjacent areas since Upper Cretaceous times. Geol. Mag., 102: 189--205. Greenberg, M., 1968. The section of Lower Cretaceous Hathira Formation in Hamakhtesh Hagadol, Northern Negev. Geol. Surv. Israel, Stratigr. Section, 5, 6 pp. Ingrain, R.L., 1971. Sieve Analysis. In: R.E. Carver (Editor), Procedures in Sedimentary Petrology. Wiley, New York, N.Y., pp. 49--69. Jarrar, G., 1979. Petrology and Geochemistry of Wadi Um-Saiyala, Wadi Araba, Jordan. M.S. Thesis, Univ. of Jordan, Amman (unpubl.). Kana'an, F.M., 1966. Sedimentary Structures, Thickness and Facies Variation in the Basal Cretaceous Sandstones of Central Lebanon. M.Sc. Thesis, American University of Beirut, Lebanon (unpublished). Karcz, I., 1965. Lower Cretaceous fluviatites in the Levant. Nature, 207: 1145--1146. Leopold, L.B. and Wolman, M.G., 1957. River channel patterns; braided, meandering and straight. U.S. Geol. Surv., Prof. Pap., 282-B: 39--85. Massaad, M., 1976. Origin and environment of deposition of the Lebanon Basal Sandstones. Eclogae Geol. Helv., 69: 85--91. McBride, E.F., 1971. Mathematical treatment of size distribution data. In: R.E. Carver (Editor), Procedures in Sedimentary Petrology. Wiley, New York, N.Y., pp. 109--129. Moiola Jr., R. and Weiser, D., 1968. Textural parameters: an evaluation. J. Sediment. Petrol., 38: 45--53. Moshrif, M.A., 1980. Recognition of fluvial environments in the Riyadh--Wasia Sandstones (Lower--Middle Cretaceous) as observed by textural analysis. J. Sediment. Petrol., 50: 603--612. Pettijohn, F.J., 1975. Sedimentary Rocks. (3rd Ed.) Harper and Row, New York, N.Y. 628 pp. Pettijohn, F.J., Potter, P.E. and Siever, R., 1972. Sand and Sandstones. Springer, New York, N.Y., 618 pp. Quennell, A.M., 1951. The geology and mineral resources of Trans-Jordan. Colon. Geol: Miner. Resour., 2: 85--115. Selley, R.C., 1972. Diagnosis of Marine and Non-Marine Environments from CambroOrdovician Sandstones of Jordan. J. Geol. Soc., 128: 135--150. Shaw, S.M., 1947. Southern Palestine geological map on a Scale 1 : 250,000 with explanatory notes. Palestine Geol. Soc. Publ., Jerusalem, Works Dept., 42 pp.
279 Tucker, R.W. and Vacher, H.L., 1980. Effectiveness of discriminating beach, dune and river sands by moments and the cumulative weight frequencies. J. Sediment. Petrol., 50: 165--172. Wakim, S., 1968. Petrography Basal Cretaceous Sandstones, of Central Lebanon. M.Sc. Thesis. The American University of Beirut, Lebanon (unpubl.). Wetzel, R. and Morton, D.M., 1959. Contribution ~i la g~ologie de la Transjordanie. Notes Mere. Moyen-Orient, 7: 95--191.
267
Elsevier Scientific Publishing Company, Amsterdam - - Printed in The Netherlands
DEPOSITIONAL ENVIRONMENTS OF THE EARLY CRETACEOUS KURNUB (HATHIRA) SANDSTONES, NORTH JORDAN
ABDULKADER M. ABED
Department of Geology and Mineralogy, The University of Jordan, Amman (Jordan) (Received May 6, 1981;revised and accepted October 14; 1981L)
ABSTRACT Abed, A.M., 1982. Depositional environments of the Early Cretaceous Kurnub (Hathira) sandstones, north Jordan. Sediment. Geol., 31: 267--279. The Kurnub (Hathira) sandstones in north Jordan, which are most probably of Early Cretaceous age, are about 300 m thick varicoloured, friable quartz-arenitic sandstones. Based on grain-size analysis, sedimentary structures, palaeocurrent, fossil content and petrography, these sandstones are postulated to be dominantly of fluvial origin with a few interfingering shallow marine horizons. A southward displacement of Jordan by at least 100 km would bring these sandstones opposite to similar rocks west of the Jordan--Araba rift, with Jordan being higher during the Early Cretaceous.
INTRODUCTION
A thick sequence of varicoloured sandstones outcrops in several deep wadis in northern Jordan. Shaw (1947, p. 21) gave the name "Wadi Hathira Sandstone" to similar rocks of Early Cretaceous age in the Kurnub structure located in the Negev, WSW of the Dead Sea. Quennell (1951) used the term "Kurnub Sandstones" to describe andcorrelate similar rocks in Jordan, especiaUy those here under discussion. Bender (1974, 1975) prefered to use the term "Lower Cretaceous Sandstones" for the same sequence. This was due to the fact that this age was given to similar rocks west of the Jordan--Araba rift (e.g., Shaw, 1947; Aharoni, 1964). Wetzel and Morton (1959, pp. 134-138) had assigned an Albian--Aptian (Early Cretaceous)age to certain marine horizons in the Kurnub sandstones in north Jordan. These sandstones are, also, situated between the Jurassic dolomites and Cenomanian (Late Cretaceous} limestones in the same area. Due to the popularity of the term "Kurnub", it is maintained in this study. The "Gr~s de Base" or "Basal Cretaceous sandstone" in Syria and Lebanon seems to correlate with the Kurnub sandstones in Jordan. It is situated, as is the Kurnub, in Jordan and Hathira in Palestine, between the Jurassic and Cenomanian limestones (Kana'an, 1966; Wakim, 1968; Massaad, 1976). 0037-0738/82/0000--0000/$02.75 © 1982 Elsevier Scientific Publishing Company
268
These sandstones were postulated by those authors to be deposited in a fluvial environment. In southern Jordan the story is not as clear. These sandstones are considered as a part of the Nubian sandstones, whose age and environment is problematic. Blake and Ionides (1939) gave a Early Cretaceous age for all the sandstones in southern Jordan, while Bender (1963) was able to subdivide these rocks into Paleozoic and Lower Cretaceous units. Selley (1972) talked about a braided river system in the Palaeozoic sandstones in southern Jordan. However, the present study is confined to north Jordan. It is the aim of this article to study the depositional environments of these sandstones, previous knowledge of which restricted to marine and nonmarine environment. Thus enabling comparison with nearby countries. GEOLOGY AND LOCATION
Several sections of the Kurnub sandstones were measured in north Jordan. They are made up of about a 300 m thickness of varicoloured sandstones. 20O
- 30~ Ras ;n I~aqb
220
240
* Esh. $hidya SAUDI ARABIA
"~ulf of 29o Aqaba BOO
Fig. I. Location map.
0
50
9001
100 km
290. S00
269
The whole sequence could be seen in Wadi Huni in the Zerqa river canyon and some 10 km to the W and SW in the Arda' and Khunaizir (Fig. 1). In both localities they overlie the Jurassic dolomites and sandstones and underlie the Cenomanian Nodular limestone. The upper third is exposed in other localities such as Baqa', Na'ur and Mahis. A few metres of the basal part of the Kurnub is preserved on top of the uplifted Jurassic, 4 km, west of Mahis. PETROGRAPHY
Most of the sandstones in the study area are friable uncemented quartzarenites. These were studied for grain size by sieving (see below). The consolidated parts were thin sectioned; they are also quartz~renites. Feldspars are almost completely absent. Cement, when present, consists of iron oxide of different colours, which make these rocks varicoloured. The colours of the Kurnub sandstone (red, yellow-violet) become weaker with depth. It is believed that oxidation and downward leaching of the glau-
*30
x
Ain
•
Baq a'a
khunaizir
/x
West
Na'ur
•
Wczdi
Huni
a
King
Ta~al d a m
o
ivla hi s
area
Ma'in x
*2.0
u~
• 1.0
c ~0.0
ix
( FRIEDMAN~
X
•
•
onxxl: ~Q
/x
o V
~llX x
V
_t -0
-2.0
-3.0
o'.s Standard
-
1.0
1.5
Deviation
Fig. 2. Skewness vs standard deviation for the Kurnub Sandstones using ~0 units.
270
conites which exist in the uppermost few metres was the source of this iron colouration. Quartz grains are rounded to subrounded, and in the same horizon they are rather well sorted. It is thus believed that these sandstones are mineralogically and texturally mature. The source of these quartz grains is most probably formed by the Palaeozoic Nubian sandstones and not directly by the basement. G R A I N SIZE
More than one hundred friable sandstone samples were investigated for grain size. Coloured samples were treated by oxalic acid prior to sieving (Ingram, 1971); the sieves were arranged at 1 phi intervals throughout. The four m o m e n t s were then manually computed; i.e. mean, standard deviation, skewness and kurtosis (McBride, 1971). In addition, "mean cubed deviation" and "cubed standard deviation" (Friedman, 1967) were also computed. The
x •
Ain Khunaizir Boqa' West
area Na'ur
• [3
Wadi Huni King Talat Dam
o
Mahis
9
Ma'in
*3.( x
°Z.I
•
x x x•
A 6
"° 6
*~
.I.(
o
~o.~
!
.to ul
X
-1.0
-Z.C
BEACH
•
\o
RIVER
Friedman
3.0 I 0.5
STANDARD
1961)
1
I
1,0
1.5 DEVIATION
Fig. 3. S k e w n e s s vs standard deviation using ~ units.
271
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x
•
I
a x
ox~
Baqa'
/%
West
Na'ur
•
Wadi
Huni
o
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o
.~
. RIVER
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,,,
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19
KURTOSIS
Fig. 4. Skewness vs kurtosis in ~ units.
data are plotted in Figs. 2, 3, 4, 5, 6 and 7 (c.f. Friedmann, 1961, 1967; Moiola and Weiser, 1968). The plots suggest that the studied samples are dominantly of fluvial origin. Sedimentologists are in general disagreement in this respect; whereas the general trend is the failure o f this technique to predict the palaeoenvironment (Pettijohn, 1975; Tucker and Vacher, 1980), certain authors are still using it (Moshrif, 1980). However, the studied sediments plotted well within the fluvial field. This is taken as an indication rather than as a final proof. A detailed investigation of the sedimentary structures supports such an interpretation (see below). LITHOFACIES The following is a subdivision of the Kumub sandstones according to their sedimentary structures:
Conglomerate facies These facies have no regional extent, rather they are restricted to certain parts of the lower contact o f the Kurnub. In the Ain Khunaizir section, a
272
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1968)
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DEVIATION
Fig. 5. Mean vs standard deviation using ~ units.
thin bed of about 20 cm thick of extraformational chert and quartz cobbles is found in only one wadi of this area (see also Wetzel and Morton, 1959). These conglomerates are not believed to originate from the underlying Jurassic rocks, which are dominantly carbonates and sandstones. However, their roundness and lithology would suggest a long transportation history. Thirty kilometres to the south, and about 4 km to the west of Mahis, the conglomerates are rather intraformational and are made up of the Kurnub sandstone itself (Fig. 8). Once more they are restricted to a certain area. These facies resemble the basal conglomerates but without their regional distribution and they are best interpreted as channel deposits (Allen, 1970).
Rippled glauconitic sandstone facies These facies interfinger with the lignite facies and overlie the conglomerates when present, otherwise they overlie the Jurassic dolomites. These sandstones are characterised by herringbone cross-bedding with the upper part of
273 1..r
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bJ r~
O LU
m_0. (.3 Z
:E
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1.0 1.2 l.& 1.6 1.8 2.0 DEVIATION
Fig. 6. Standard deviation vs mean cubed deviation using ~0 units.
x
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STANDARD
1967)
DEVIATION
Fig. 7. Cube standard d e v i a t i o n ~ns mean cubed d e v i a t i o n using ~0 units.
274
Fig. 8. Basal conglomerates in the Mahis area (see text).
the facies made up of rippled glauconitic sandstones. Trace fossils (bilobites) are present. The sandstone bodies are fining-upwards and were interpreted as being deposited on a retreating tidal flat of the regressive Jurassic sea (Abed, 1978).
Lignite sandstone facies A low
Lenticular-channelled sandstone facies This is the major facies which dominates the whole sequence. It is more than 200 m thick in the study area. The samples for grain-size analysis were taken from this facies. The Kurnub sandstones are characterised o r distinguished by this type of sandstone which is widespread in Jordan over more than 300 km in a north--south direction.
275
Fig. 9. Channell in the upper Kurnub sandstones along the Ard~i highway 1 km above Ain
Khunaizir. These facies consist o f t w o rock types: varicoloured sandstones and grey siltstones to claystones. The t w o rock types are arranged in such a w a y as to give repeated cycles of thick sandstone bodies (up to 20 m) followed b y relatively thin clay~ilt horizons. Lenticular bedding dominates throughout. Sandstones are more than 90% cross-bedded. Planar cross-bedding is the main type, with minor tangential cross-bedding and very rare trough bedding. The sandstone lenses are finingupwards. Quartz pebbles up to 1 cm in diameter start at the b o t t o m , associated with cross-bedding. Both grain-size and cross-bedding sets fine upwards until a siltstone or claystone terminates the cycle. In many cases, smaller cycles are n o t e d within the larger cycle (see Allen, 1970). Channels are noted only in the upper third of this facies (e.g. Baqa', Arda'; Fig. 9). They are 50 to 100 m wide and 1--3 m deep. Channel-fill sediments start with quartz pebbles ( 2 1 cm) and m u d pebbles as channel-lag deposits on an erosional surface. Sediments then fine upward and terminate which siltstones and/or claystones. Channels trend in a north--south general direction (Leopold and Wolman, 1957). Neither fossils nor trace fossils were f o u n d in these facies, though plant remnants were encountered, especially in the finer sediments. The absence of fossils and trace fossils and the association of channels, fining-upwards cycles and the unidirectional cross-bedding suggest a fluvial origin for these facies.
276
Yellow glauconitic sandstones and dolomite facies There are t w o horizons of such facies. An upper horizon, which marks the contact with the overlying Cenomanian (Upper Cretaceous) limestones and a lower horizon 20--30 m below. The thickness of the t w o horizons decreases southwards. The upper one continues as far south as Ras En Naqb (about 300 kin), while the lower horizon disappears south of Baqa'. They are made up of fossfliferous sandstones and dolomites with various amounts of glauconites. Large zoned dolomite rhombs formed at the expense of glauconites and quartz. Ghosts of the original fine-grained dolomites are still preserved. Gastropods, bivalves and ammonites (Wetzel and Morton, 1959) are present. Trace fossils are encountered, especially in the glauconite beds. Based on these data, these facies are interpreted as shallow marine. Thus, there is a clear interaction of shallow marine deposits interfingering with the fluvial facies. PALAEOCURRENT
Several hundreds of cross-bedding directions and dip angles were measured in each locality studied. The results are shown in Fig. 10, which clearly shows a general northwards trend. This is easily understood by the existence of the Arabian--Nubian continent further south. Most of the cross-bedding
G0
E
W,
$ Fig. 10. Rose diagram for cross-bedding in the Kurnub Sandstones in north Jordan, including 1982 readings from Bag~i, Mahis, Air Khunaizir and Jarash. Numbers indicate readings in each directional unit.
277 dip angles fall within 10--25 °, with a small fraction in the upper twenties. Very rare angles are in the lower thirties. The direction and amount of dip of cross-bedding might indicate a fluvial regime rather than an eolian or a beach regime. DISCUSSIONS A N D C O N C L U S I O N S (1) The foregoing data on grain size, sedimentary structures and paiaeocurrents, together with the lack of fossils and trace fossils would favour fluvial deposits (Allen, 1965, 1970) interfingering with a few relatively thin shallow marine horizons. Such a conclusion is in general agreement with the palaeoenvironments of the same group in Lebanon (Massaad, 1976) and West of the Jordan--Araba rift (Karcz, 1965), with more marine influence than in Jordan. (2) The petrography of the studied Kurnub quartz-arenitic sandstones shows a rather mature texture. Lutites (siltstones and claystones) are relatively scarce compared with the sandstones. This is contrary to most recent fluvial deposits (Pettijohn et al., 1972, p. 461), where the sediments contain more clays, feldspars and rock fragments, depending on the source area. The absence of these components, while the granitic basement is less than 300 km south, could be explained by the source material being the Palaeozoic quartz~xenitic Nubian sandstones. Recycling of those sandstone would also explain the roundness of the Kurnub sandstones. (3) Comparison of these rocks with the Early Cretaceous rocks west of the Jordan--Axaba rift, would show that the latter are more marine and much thicker. The Early Cretaceous rocks to the west of the study area (e.g. Wadi Faria) are completely different, being dominantly marine limestone (Blake and Goldschmidt, 1947, p. 135). Similar rocks could be found further south, i.e. west and southwest of the Dead Sea. Even there, the Kurnub group is much thicker and more marine (e.g. 408 m, with several marine horizons in the Kurnub structure itself; Greenberg, 1968) and the thickness increases towards the NW (Tsiah 480 m, Beer Sheva 575 m, Halutsa 604 m; Aharoni, 1964). Such dissimilarities could be explained by: (1) Jordan being higher during Early Cretaceous times, thereby more continental sandy facies having accumulated (Wetzel and Morton, 1959; Bender, 1974); (2) a southward horizontal displacement of Jordan relative to Palestine of at least 100 km (Burdon, 1959). A displacement of 70--80 km (Freund, 1965; Jarrar, 1979) such as is generally accepted, cannot explain the present data.
REFERENCES Abed, A.M., 1978. Depositional environments of the Kurnub (Lower Cretaceous). I-A coal horizon at the lowermost Kurnub in northern Jordan. Dirasat, 5: 31---44.
278 Aharoni, E., 1964. Lithoelectric correlation of the Kurnub group (Lower Cretaceous) in the northern Negev. Israel J. Earth Sci., 13: 63--78. Allen, J.R.L., 1965. A review of the origin and characteristics of Recent alluvial sediments. Sedimentology, 5: 89--191. Allen, J.R.L., 1970. Studies in fluvial sedimentation: composition of fining-upwards cyclothemes with special reference to coarse m e m b e r composition and interpretation. J. Sediment. Petrol., 40: 298--323. Bender, F., 1963. Stratigraphie des "Nubischen Sandsteine" in Sud-Jordanien. Geol. Jahrb., 81: 237--276. Bender, F., 1974. Geology of Jordan, Borntraeger, Berlin, 196 pp. Bender, F., 1975. Geology of the Arabian Peninsula, Jordan. U.S. Geol. Surv., Prof. Pap., 560-I, 136 pp. Blake, G.S. and Goldschmidt, M.J., 1947. Geology and Water Resources of Palestine. Govt. of Palestine, Jerusalem, 113 pp. Blake, G.S. and Ionides, M.G., 1939. Report on the Water Resources of Transjordan and Their Development. Crown Agents for the Colonies, London, 372 pp. Burdon, D.J., 1959. Handbook of the geology of Jordan. Govt. of Jordan, Amman. Friedman, G.M., 1961. Distribution between dune, Beach and River Sands from Their Textural Characteristics. J. Sediment. Petrol., 31: 514--529. Friedman, G.M., 1967. Dynamic processes and statistical parameters compared for size frequency distribution of beach and river sands. J. Sediment. Petrol., 37: 327--354. Freund, R., 1965. A model of the structural development of Israel and Adjacent areas since Upper Cretaceous times. Geol. Mag., 102: 189--205. Greenberg, M., 1968. The section of Lower Cretaceous Hathira Formation in Hamakhtesh Hagadol, Northern Negev. Geol. Surv. Israel, Stratigr. Section, 5, 6 pp. Ingrain, R.L., 1971. Sieve Analysis. In: R.E. Carver (Editor), Procedures in Sedimentary Petrology. Wiley, New York, N.Y., pp. 49--69. Jarrar, G., 1979. Petrology and Geochemistry of Wadi Um-Saiyala, Wadi Araba, Jordan. M.S. Thesis, Univ. of Jordan, Amman (unpubl.). Kana'an, F.M., 1966. Sedimentary Structures, Thickness and Facies Variation in the Basal Cretaceous Sandstones of Central Lebanon. M.Sc. Thesis, American University of Beirut, Lebanon (unpublished). Karcz, I., 1965. Lower Cretaceous fluviatites in the Levant. Nature, 207: 1145--1146. Leopold, L.B. and Wolman, M.G., 1957. River channel patterns; braided, meandering and straight. U.S. Geol. Surv., Prof. Pap., 282-B: 39--85. Massaad, M., 1976. Origin and environment of deposition of the Lebanon Basal Sandstones. Eclogae Geol. Helv., 69: 85--91. McBride, E.F., 1971. Mathematical treatment of size distribution data. In: R.E. Carver (Editor), Procedures in Sedimentary Petrology. Wiley, New York, N.Y., pp. 109--129. Moiola Jr., R. and Weiser, D., 1968. Textural parameters: an evaluation. J. Sediment. Petrol., 38: 45--53. Moshrif, M.A., 1980. Recognition of fluvial environments in the Riyadh--Wasia Sandstones (Lower--Middle Cretaceous) as observed by textural analysis. J. Sediment. Petrol., 50: 603--612. Pettijohn, F.J., 1975. Sedimentary Rocks. (3rd Ed.) Harper and Row, New York, N.Y. 628 pp. Pettijohn, F.J., Potter, P.E. and Siever, R., 1972. Sand and Sandstones. Springer, New York, N.Y., 618 pp. Quennell, A.M., 1951. The geology and mineral resources of Trans-Jordan. Colon. Geol: Miner. Resour., 2: 85--115. Selley, R.C., 1972. Diagnosis of Marine and Non-Marine Environments from CambroOrdovician Sandstones of Jordan. J. Geol. Soc., 128: 135--150. Shaw, S.M., 1947. Southern Palestine geological map on a Scale 1 : 250,000 with explanatory notes. Palestine Geol. Soc. Publ., Jerusalem, Works Dept., 42 pp.
279 Tucker, R.W. and Vacher, H.L., 1980. Effectiveness of discriminating beach, dune and river sands by moments and the cumulative weight frequencies. J. Sediment. Petrol., 50: 165--172. Wakim, S., 1968. Petrography Basal Cretaceous Sandstones, of Central Lebanon. M.Sc. Thesis. The American University of Beirut, Lebanon (unpubl.). Wetzel, R. and Morton, D.M., 1959. Contribution ~i la g~ologie de la Transjordanie. Notes Mere. Moyen-Orient, 7: 95--191.