Stratigraphy of the Late Proterozoic Murdama Group, Saudi Arabia

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Stratigraphy of the Late Proterozoic
Murdama Group, Saudi Arabia
U.S. GEOLOGICAL SURVEY BULLETIN 1976

Stratigraphy of the Late Proterozoic
Murdama Group, Saudi Arabia
By ROBERT C. GREENE
U.S. GEOLOGICAL SURVEY BULLETIN 1976
U.S. DEPARTMENT OF THE INTERIOR
BRUCE BABBITT, Secretary
U.S. GEOLOGICAL SURVEY
Dallas L. Peck, Director
Any use of trade, product, or firm names
in this publication is for descriptive purposes only
and does not imply endorsement by the U.S. Government
Illustrations and plates edited by Dale Russell
Illustrations prepared by Fred Garrido, plates by Sara Boore
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1993
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Library of Congress Cataloging-in-Publication Data
Greene, Robert C.
Stratigraphy of the late Proterozoic Murdama Group, Saudi Arabia I by
Robert C. Greene.
p. em. - (U.S. Geological Survey bulletin ; 1976)
Includes bibliographical references.
1. Geology, Stratigraphic-Proterozoic. 2. Geology-Saudi Arabia. 3.
Murdama Group (Saudi Arabia). I. Title. II. Series.
QE75.89 no. 1976
[QE653.5]
557.3 s-dc20
[551.7'15'09538] 93-1837
CIP
CONTENTS
Abstract 1
Introduction 2
General geology of the Arabian shield 2
Murdama formation and group 3
General description of the Murdama 3
Field study 5
Open-file reports 6
Rock nomenclature and metamorphism 6
Arabic names 6
Acknowledgments 6
South part of the Afif belt 6
Previ9us work 6
Underlying rocks 7
Structure 7
Sections on the west limb of the Maslum synclinorium 7
Jabal Murdama section 7
Jabal Raqabah section 8
As Sawadah sections 9
Sections on the east limb of the Maslum synclinorium 9
Jabal Zaydi section 9
Jabal Farida section 10
Jabal Damkh section 11
Jabal Qatar section 12
Wadi Sirrah section 12
North part of the Afif belt 13
Previous work 13
Underlying rocks 15
Structure 15
Sections and other locality descriptions 16
WadiJarirsections 16
Jabal Ajam section 19
Uqlat as Suqur quadrangle 19
An Najady area 20
Jabal umm Sammah section 20
Jabal as Silsilah and Jabal Saq quadrangles 20
Buqaya formation 21
Conglomerate 21
Qarnayn formation 21
Jabal al Muwashsham sections 21
Maraghan formation 21
Section east of Jabal as Silsilah 21
Hibshi formation 21
Jabal Hibshi sections 22
Jabal Khidar section 22
Nonconglomeratic basal Hibshi 22
Contents Ill
Afif belt depositional basin and sediment sources 22
South part 22
North part 23
Triangular diagrams 24
Environment of deposition 25
Rate of sedimentation 26
Sources and deposition of volcanic rocks 27
Jabal Hadhah belt 27
Previous work 27
Topography and structure 27
Sketch section 27
Discussion 29
Mistahjed belt 29
Previous work 29
Underlying rocks 33
Structure 33
Traverses and sections 34
Jabal Hashishiyah sections 34
Section A 35
Section B 35
Correlation with Afif belt 36
Jabal Yafikh-Bir Zain area 36
Wadi Mistahjed section 36
Correlation with the Afif belt 36
Jabal Y afikh 36
Ya fikh northeast traverse 36
Wadi al Farshah and Jabal Ibna Quirban 38
Traverses to Bir Zain and Wadi Rafiyah 38
Correlation 40
Bir J arir area 40
Jabal Jasl section 40
Traverse northeast of Jabal Jasl 40
Traverse north of Jabal Bijad 40
Section north of Jabal Jarir 42
Jabal Jara traverse 42
Stratigraphic order and correlation 44
Sources of sediment and depositional history 44
Origin of the volcanic rocks and the J arir formation 45
Junaynah belt 45
Previous work 45
Structure and underlying rocks 45
Murdama(?) group 45
Depositional basin 47
Correlation 47
Lithologic unity of the Murdama group 47
Geochronology 48
Radiometric ages from the Afif belt and adjacent areas 48
Discussion 50
Radiometric ages from the Mistahjed belt and adjacent areas 51
Radiometric ages from the Junaynah area 52
Interpretation 52
Plate-tectonic interpretation 52
References cited 55
IV Contents
PLATES
[Plates are in pocket]
1. Geologic map and columnar sections of the Murdama group in south part of the Afif
belt.
2. Geologic map and columnar sections of the Murdama group in north part of the Afif
belt.
FIGURES
1. Index map showing location of Saudi Arabia 2
2. Map of part of Arabian Shield showing Murdama group and gabbro and
ultramafic rocks associated with Nabitah and Jabal Burqah belts 4
3--6. Photographs showing:
3. Jabal Zaydi, looking northwest along strike from line of measured section at
unit 26 10
4. Jabal Farida from the southwest 11
5. Wadi Jarir section B 17
6. Wadi Jarir section A 18
7-10. Triangular diagrams showing estimated modes of framework grains:
7. South part of Afifbelt, Q-F-L system 24
8. North part of Afif belt and Mistahjed belt, Q-F-L system 24
9. South part of Afifbelt, Qm-P-K system 25
10. North part of the Afif belt and the Mistahjed belt, Qm-P-K system 25
11. Geologic map of Jabal Hadhah belt 28
12. Geologic map of Mistahjed belt, showing locations of sections and traverses 30
13. Photograph showing Jabal Y afikh 38
14. Geologic map of Junaynah belt 46
15. Diagram showing radiometric ages and speculative age ranges of units 50
16. Palinspastic map of part of Arabian Shield showing 255 km of displacement on
three major Najd faults removed 54
TABLES
1. Selected major layered rock units appearing in quadrangle maps of the Arabian
Shield 3
2. Estimated modes of some volcanic rocks from the Wadi Sirrah section 13
3. Estimated modes of some igneous cobbles from conglomerate in the Wadi Sirrah
section 14
4. Summary of group and formation names utilized by authors of quadrangle maps
in the northern shield for the Murdama and some underlying and overlying
layered rock units 16
5. Summary of informal unit names utilized for the Murdama group and some
underlying units in quadrangle maps covering parts of the Mistahjed belt 32
6. Jabal Hashishiyah section A of the Murdama group 34
7. Jabal Hashishiyah section B of the Murdama group 35
8. Wadi Mistahjed section of the Murdama group 37
9. Descriptions of the Murdama group at the Yafikh northeast traverse 39
10. Jabal Jasl section of the Jarir formation 41
11. Section of the Murdama group north of Jabal Jarir 43
12. Radiometric ages from the Afif, Mistahjed, and Junaynah belts and adjacent
areas 49
Contents V

STRATIGRAPHY OF THE LATE PROTEROZOIC
MURDAMA GROUP, SAUDI ARABIA
By Robert C. Greene
Abstract
Sections in the north part of the Afif belt have appar
The Murdama group is in the upper part of the se ent thickness of about 3,300 and 7,600 m at Wadi Jarir,
quence of Proterozoic layered rocks in the Precambrian 840 m at Jabal Ajam, 534 and 1,833 m at Jabal
shield of Saudi Arabia. It consists of clastic sedimentary Muwasham, about 3,800 m adjusted for folding east of
rocks and small amounts of limestone and volcanic rocks. jabal Silsillah, 4,900 m at Jabal Khidar, and 8,400 m at
The Murdama crops out in the eastern part of the exposed jabal umm Sammah. The Wadi Jarir section consists of
part of the shield, within 200 km of its margin. The princi sandstone very similar to that at Jabal Murdama, with thin
pal outcrop area, herein designated the Afif belt, is 600 km basal conglomerate and local ash tuff. The other sections
long and has a maximum width of 80 km. Two other sig consist of conglomerate, sandstone, and siltstone.
nificant outcrop areas lying to the south are designated the The predominance of silicic volcanic lithic grains in
Jabal Hadhah and the Mistahjed belts. Murdama sandstones of the Afif belt indicates a source in
The Murdama group unconformably overlies older a silicic volcanic belt, and discontinuous belts of such
plutonic rocks that range in composition from diorite to rocks lie to the southwest. Paleocurrent indicators also
granite and volcanic rocks ranging from basalt to rhyolite. suggest a source from the southwest. In the north part of
It is unconformably overlain in the north part of the Afif the belt, the lower part of the Murdama is probably a sub
belt by sedimentary and volcanic rocks of the Jurdhawiyah aerial mass-movement or fluvial deposit. The strata in the
group, and in many areas is intruded by younger granite. rest of the belt were probably deposited at a prograding
In the south part of the Afif belt the Murdama group lacustrine or marine strandline. Near the northwest edge of
lies in the Maslum synclinorium, a structure characterized the basin, particularly from Jabal Farida north, locally de
by tight folding near its northwest margin and open folding rived conglomerate was deposited and carbonate bank
elsewhere. To the north, the synclinorium is much broken deposition prevailed for a time.
up by faulting, particularly by left-lateral faults of the Najd In the jabal Hadhah belt, limestone is identical to
system. that at Jabal Farida. It is apparently overlain by conglomer
Sections on the west flank of the Mast urn ate that fines upward to sandstone and may be part of the
synclinorium in the south part of the Afif belt have appar Murdama.
ent thicknesses of about 5,300 m at Jabal Murdama, 5,700 Structure in the Mistahjed belt is more complex and
m at Jabal Raqabah, and 1 ,400 and 4,000 m at As the stratigraphic sequence is less certain than in the Afif
Sawadah. The strata in these sections consist mostly of belt. Murdama rocks have been assigned to a number of
greenish-gray, very fine to coarse-grained volcanic arenite formations, and traverses were made across most units.
that is poorly sorted and consists of angular grains. Basal The rocks include sandstone, siltstone, limestone, con
conglomerates are thin and inconspicuous, but coarse glomerate, and volcanic rock; much of the volcanic rock
arenite, locally pebbly, predominates in the jabal Raqabah may not be part of the Murdama group.
section. A prominent air-fall ash tuff caps Jabal Murdama, The source of sedimentary materials in the Mistahjed
and an ash-flow tuff caps Jabal Raqabah. belt, as in the Afif belt, appears to be a belt of volcanic
Sections on the east flank of the synclinorium have rocks lying to the southwest.
apparent thicknesses of about 2,500 m at Jabal Farida, The junaynah belt of sedimentary rocks lies to the
3,600 m at Jabal Damkh, 12,400 m at Jabal Zaydi, and west of the Mistahjed belt. The rocks consist of basal
16,800 m, adjusted for folding, at Wadi Sirrah. Jabal Farida cobble conglomerate grading up to coarse- and fine
and Jabal Damkh are underlain principally by limestone of grained sandstone. These rocks have been assigned to the
distinctive tan- and gray-weathering types, which has been Murdama group in the past, but I conclude that they
named the Farida marble. Limestones of these and other col should be restricted from it, because their tectonic setting
ors occur in all the belts composing the Murdama and form and age appear to be different.
a unifying element. The other sections consist mostly of Radiometric ages suggest an age range of 650 to 615
sandstone similar to that at Jabal Murdama. Ma for the Murdama group, the laterally equivalent Hibshi
formation, and the overlying Jurdhawiyah group in the Afif
belt. Ages from the Mistahjed belt suggest that the
Manuscript approved for publication, February 15, 1991. Murdama rocks there are younger than 650 Ma and ages
Abstract
from the junaynah area suggest that the sedimentary sec ping has also contributed to mineral exploration pro
tion is younger than 61 0 Ma. grams conducted by these agencies and by the Riofinex
The Murdama group probably was deposited in a Geological Mission, Ltd.
back-arc basin on a continental platform bounded on the A general stratigraphic column for the layered
west by an active volcanic arc above an east-dipping sub
rocks of the southern part of the shield (table 1) was
duction zone. The position of the subduction zone, which
compiled early in the USGS mapping program and has
was active during most of the deposition in the Afif belt, is
provided a framework for the map units utilized on
marked by a belt of gabbro and ultramafic rocks herein
many quadrangle maps. A similar column was utilized
named the jabal Burqah belt. The subduction zone later
by BRGM in the north-central .part of the shield. How
stepped out to the southwest to the Nabitah belt, and
Murdama strata were deposited in the Jabal Hadhah, ever, the thickness, age, and mutual relations of the lay
Mistahjed, and smaller basins. ered rocks are in fact not well known, and many units
were extended from quadrangle to quadrangle or into
distant areas without adequate justification.
INTRODUCTION During the mapping program, the need to make a
compilation of the stratigraphic names in use, establish
standards for naming units, and undertake systematic
Understanding of the complex geology of the Pre stratigraphic studies was recognized. Names in published
cambrian shield in Saudi Arabia (fig. 1) has progressed and open-file reports were compiled in the Saudi Ara
rapidly in recent years owing principally to mapping bian Stratigraphic Lexicon (Fitch, 1980), a volume that
programs conducted by the Saudi Arabian Directorate contains over 1,500 entries. To guide future work, the
General of Mineral Resources (DGMR), the U.S. Geo Saudi Arabian Code of Stratigraphic Nomenclature
logical Survey (USGS), and the French Bureau de (Stratigraphic Committee, 1979; 2d edition 1984) was
Recherches Geologiques et Minieres (BRGM). The map- established. An interagency group was set up to carry
out stratigraphic studies.
The Murdama group is stratigraphically high in the
sequence of layered rocks, its structure is simpler than
that of older units, and exposures are locally excellent.
Therefore, a study of the Murdama was undertaken, an
ticipating that a fairly detailed picture of the group was
obtainable and might form a good basis for future work
on lower units.
General Geology of the Arabian Shield
The Arabian shield is shown on the Geologic Map
of the Arabian Peninsula, compiled by the U.S. Geologi
cal Survey and the Arabian American Oil Company or
ARAMCO (1963). Although much of the information on
this map has been superseded by more recent work, it
still is an excellent general guide to the geology.
The Arabian shield (figs. 1, 2) consists of sedimen
tary, volcanic, and plutonic rocks of Late Proterozoic
age, 900 to approximately 570 Ma. The bulk of the rocks
may be classified into five main types: (1) layered sedi
mentary and volcanic assemblages, variously metamor
phosed, and forming strike belts many kilometers long;
(2) plutonic rocks ranging in composition from diorite to
tonalite, commonly foliate, and commonly intruding
sedimentary-volcanic assemblages of similar composi
tion; (3) voluminous foliate plutonic rocks ranging from
0 1000 2000 3000 KILOMETERS
tonalite to granite, and commonly forming plutonic belts
separating major belts of layered rocks; (4 ) nonfoliate
Figure 1. Index map showing location of Saudi Arabia and plutonic rocks consisting mostly of granite, some in
area of figure 2. subcircular masses, which locally intrude cogenetic vol-
2 Stratigraphy of the Late Proterozoic Murdama Group, Saudi Arabia