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Origin of northern Gondwana Cambrian sandstone revealed by
detrital zircon SHRIMP dating
D. Avigad* 
 Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel
K. Kolodner* 
M. McWilliams* Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115,
USA
H. Persing* U.S. Geological Survey, Stanford, California 94305-2115, USA
T. Weissbrod* Israel Geological Survey, 30 Malchai-Israel Street, Jerusalem 95501, Israel
ABSTRACT
Voluminous Paleozoic sandstone sequences were deposited in northern Africa and Arabia following an extended Neoproterozoic orogenic cycle that culminated in the assembly
of Gondwana. We measured sensitive high-resolution ion microprobe (SHRIMP) U-Pb
ages of detrital zircons separated from several Cambrian units in the Elat area of southern
Israel in order to unravel their provenance. This sandstone forms the base of the widespread siliciclastic section now exposed on the periphery of the Arabian-Nubian shield in
northeastern Africa and Arabia. Most of the detrital zircons we analyzed yielded Neoproterozoic concordant ages with a marked concentration at 0.55–0.65 Ga. The most likely
provenance of the Neoproterozoic detritus is the Arabian-Nubian shield; 0.55–0.65 Ga was
a time of posttectonic igneous activity, rift-related volcanism, and strike-slip faulting there.
Of the zircons, 30% yielded pre-Neoproterozoic ages grouped at 0.9–1.1 Ga (Kibaran),
1.65–1.85 Ga, and 2.45–2.7 Ga. The majority of the pre-Neoproterozoic zircons underwent
Pb loss, possibly as a consequence of the Pan-African orogeny resetting their provenance.
Rocks of the Saharan metacraton and the southern Afif terrane in Saudi Arabia (;1000
km south of Elat) are plausible sources of these zircons. Kibaran basement rocks are
currently exposed more than 3000 km south of Elat (flanking the Mozambique belt), but
the shape of the detrital zircons of that age and the presence of feldspar in the host
sandstone are not fully consistent with such a long-distance transport. Reworking of Neoproteorozoic glacial detritus may explain the presence of Kibaran detrital zircons in the
Cambrian of Elat, but the possibility that the Arabian-Nubian shield contains Kibaran
rocks (hitherto not recognized) should also be explored.
Keywords: Pan-African orogeny, erosion, Cambrian sandstone, detrital zircon, U-Pb SHRIMP
dating, Gondwana.
INTRODUCTION
The 900–540 Ma Pan-African–Brasiliano
orogenic cycle ended with the assembly of
Gondwana in late Neoproterozoic time (Unrug, 1997) and was followed by the deposition
of thick siliciclastic sequences on the margins
of the supercontinent (Wolfart, 1981; Klitzsch,
1981; Courjault-Rade et al., 1999). These Paleozoic strata are the most voluminous siliciclastic sequences ever deposited on continental crust (Burke and Kraus, 2000), and cover
large parts of North Africa and Arabia (Fig.
1; Powers et al., 1966; Klitzsch, 1981; Weissbrod, 1980; Wolfart, 1981; Amireh, 1991; Alsharhan and Nairn, 1997).
Throughout North Africa and Arabia, the PanAfrican orogeny was followed by continentalscale uplift and erosion, and a vast peneplain
that can be traced from Morocco in the west
to Oman in the east developed on top of the
exhumed Precambrian basement (Powers et
*E-mail addresses: Avigad—[email protected].
il; Kolodner—[email protected]; McWilliams—
[email protected]; Persing—Harold.persing@
vsea.com; Weissbrod—[email protected].
al., 1966; Bennacef et al., 1971; Bentor, 1985;
Garfunkel, 1999). Late– to post–Pan-African
unroofing is the most logical source for the
thick Phanerozoic siliciclastic sequences of
northern Africa and Arabia. However, previous conventional U-Pb ages of detrital zircons
(multigrain samples) from Ordovician and
younger strata exposed in northern Africa
show that the siliciclastic material was derived
from Mesoproterozoic sources rather than
from Neoproterozoic crust (Gaudette and Hurley, 1979; Abdel-Monem and Hurley, 1979).
Detrital zircons of Neoproterozoic age have
since been detected in continental fragments
detached from northern Gondwana (Kröner
and Şengör, 1990; Keay and Lister, 2002; Gebauer et al., 1989; Fernández-Suárez et al.,
1999) and in Mesozoic sandstone from Israel
(Becker and Becker, 1996). Zircons from
Cambrian siliciclastic strata of North Africa
and Arabia have not yet been dated. These
rocks extend well to the south and cover a
significant part of the Neoproterozoic orogen
(Fig. 1). Thus, it is plausible that by Late
Cambrian time, the crust of northern Africa
was no longer a source for detritus, and erosion migrated to more southerly areas dominated by Mesoproterozoic crust (Niger, Chad,
and Sudan; e.g., Klitzsch, 1981; Garfunkel,
1999). We therefore reasoned that investigation of Cambrian sandstones might help us to
discover if they had a Neoproterozoic provenance. Our samples come from southern Israel, where Cambrian sandstones unconformably overlie Neoproterozoic crystalline basement
of the Arabian-Nubian shield (Fig. 2).
GEOLOGICAL SETTING
Phanerozoic sedimentary basins and platform type sequences along northern Gondwana store a huge amount of siliciclastic rocks
(Fig. 1). In North Africa, Paleozoic siliciclastics fill a number of basins, the depths of
which may reach 3–4 km (Fig. 1; Petters,
1991). In the Middle East, Paleozoic rocks are
exposed in an arcuate belt around the northern
and eastern flanks of the Arabian-Nubian
shield (Fig. 1); they are 2–3 km thick at the
eastern edge of the Arabian plate (Wolfart,
1981; Alsharhan and Nairn, 1997). During the
early Paleozoic, the sedimentary source area
generally was in the south, in the interior of
Gondwana, whereas the open sea was to the
north (Alsharhan and Nairn, 1997, and references therein).
Precambrian crystalline rocks of the ArabianNubian shield form the basement for the
Phanerozoic platform strata of Israel, Jordan,
Egypt, and Saudi Arabia (Fig. 1). The ArabianNubian shield evolved from 0.90 to 0.53 Ga
during the Neoproterozoic Pan-African orogeny (Shimron, 1980; Bentor, 1985; Vail, 1985;
Stern, 1994; Reymer and Schubert, 1984;
Stein and Goldstein, 1996), and was deeply
denuded at the cessation of tectonic activity
(Bentor, 1985; Jarrar et al., 1991; Garfunkel,
1999). Detrital zircons derived from juvenile
crust of the Arabian-Nubian shield should
yield ages in the range of 0.90–0.53 Ga. The
northern Arabian-Nubian shield in southern
Israel, underlying the Cambrian sandstone that
we sampled, is dominated by igneous and
metamorphic rocks ranging in age (U-Pb zircon) from 0.81 to 0.60 Ga (Eyal et al., 1992;
Kröner et al., 1990; Beyth et al., 1994); preNeoproterozoic rocks are not known. Base-
q 2003 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected].
Geology; March 2003; v. 31; no. 3; p. 227–230; 3 figures; Data Repository item 2003020.
227
Figure 1. Simplified geological map of North Africa and Arabia showing distribution of Precambrian basement rocks and Paleozoic
sediments. Thickness contours (in km) of subsurface Paleozoic rocks are also shown (post-Paleozoic configuration after Petters,
1991; Alsharhan and Nairn, 1997). We analyzed detrital zircons separated from Cambrian sandstone exposed in southern Israel near
Elat (arrow).
Figure 2. Columnar section of Paleozoic clastic sequence in southern Israel (after Segev, 1984). We sampled
four different levels within Cambrian
sandstone section. Sample positions are marked by circles. A. Shelomo is Amudei Shelomo Formation,
PA is Pan-African basement.
228
ment rocks exposed in Jordan have a similar
age range (Ibrahim and McCourt, 1995).
Around the edge of the Arabian-Nubian
shield (eastern Saudi Arabia, Yemen, southwestern Egypt, and northern Sudan), older
Proterozoic basement segments were remobilized during Neoproterozoic time (Stacey and
Hedge, 1984; Harms et al., 1990; Sultan et al.,
1990; Kröner et al., 1987; Schandelmeier et
al., 1988; Stern et al., 1993; Black and Liégeois, 1993; Windley et al., 1996; Abdelsalam
et al., 2002). Farther south, the Arabian-Nubian
shield merges with the Mozambique belt
(Stern, 1994), which involved Neoproterozoic
igneous activity and high-grade metamorphism alongside remobilized and intact older
Proterozoic crustal segments (Kröner, 2001,
and references therein).
that the carbonate and overlying section are
younger than 510 Ma (e.g., Landing et al.,
1998). Paleocurrent indicators in the Cambrian section generally indicate transport toward
the northern Gondwana margin (Karcz and
Key, 1966).
Heavy minerals in the Cambrian section of
southern Israel and Jordan (Weissbrod and
Nachmias, 1986; Amireh, 1991, respectively)
are characterized by the stable zircontourmaline-rutile assemblage, indicating sediment maturity and a fairly long distance transport (Weissbrod and Nachmias, 1986),
possibly 1000 km (Garfunkel, 1999). In contrast, Harlavan (1992) obtained Neoproterozoic 40Ar/39Ar ages on detrital clays in the
Cambrian section and inferred derivation from
a more proximal source.
Cambrian Sedimentary Rocks of Southern
Israel
Cambrian sandstones are exposed in southern Israel near Elat (Fig. 1; Garfunkel, 1978;
Weissbrod, 1980). The section can be correlated with the lower part of the Saq Formation
of Saudia Arabia (Powers et al., 1966). In
Elat, the Cambrian section is 300 m thick (Fig.
2), changing gradually upward from subarkose
and arkose to mature quartz arenite. Fluvial
deposits are common at the base of the section, but shallow-marine sandstones dominate
the remainder; shale and carbonate are present. Scarce Trilobites (Parnes, 1971) indicate
SAMPLING AND PROCEDURES
We separated zircons from four sandstone
samples collected at different stratigraphic
levels in the Cambrian section in the Elat area
(Fig. 2). The zircons range in size from 80 to
200 mm, are primarily pale gray, and are euhedral to slightly rounded. The majority of the
zircons exhibit oscillatory cathodoluminescence zoning characteristic of a felsic igneous
protholith, but metamorphic zircons were also
observed. U-Pb measurements were obtained
from 191 zircon grains using the Stanford–
U.S. Geological Survey sensitive highresolution ion microprobe (SHRIMP)-Reverse
GEOLOGY, March 2003
Figure 3. Histogram showing age distribution of detrital zircon from Cambrian
siliciclastic section of southern Israel. Total number of zircons 5 200. 157
grains yielded concordant ages. 206Pb/238U ages are used for zircons younger
than 0.8 Ga; 207Pb/206Pb ages are quoted for older grains. 43 discordant grains
are plotted on basis of their 207Pb/206Pb ages.
Geometry. We analyzed 200 zircons: 65 grains
from sample K-5, 46 grains from K-15, 48
from K-20, and 41 grains from sample K-2.
Analytical data were processed using the
Prawn and Lead codes written by T. Ireland.
Plotting was performed using Isoplot (Ludwig, 1994). The 204Pb was generally ,0.01%
of total Pb. The four Cambrian samples we
analyzed revealed similar age distribution patterns, allowing them to be treated collectively.
RESULTS OF ION PROBE U-Pb
ANALYSES
An age histogram of all zircons is presented
in Figure 3. It shows that the overall proportions of Neoproterozoic and pre-Neoproterozoic
detrital zircons in the Cambrian section are
70% and 30%, respectively1. Of the zircons
(157 grains), 75% gave concordant ages (e.g.,
Wetherill, 1956), i.e., 135 grains yielded Neoproterozoic ages and 22 grains yielded older
ages; 9 grains yielded 0.5–0.55 Ga (Cambrian)
ages. Of the analyzed zircons, 20% proved to
be discordant, yielding pre-Neoproterozoic
207Pb/206Pb ages.
Of the Neoproterozoic zircons, 50% con1GSA Data Repository item 2003020, U-Pb
geochronological data of detrital zircons from the
Cambrian sandstone of southern Israel, is available on request from Document Secretary, GSA,
P.O. Box 9140, Boulder, CO 80301-9140, USA,
[email protected], or at www.geosociety.
org/pubs/ft2003.htm.
GEOLOGY, March 2003
centrate at 0.55–0.65 Ga (Fig. 3). Most of the
zircons are igneous in origin, but several
metamorphic zircons also yielded late Neoproterozoic ages. The most likely source of the
Neoproterozoic zircons is the Arabian-Nubian
shield. Of the zircons, ;30% yielded preNeoproterozoic ages: ;60% of the preNeoproterozoic zircons underwent Pb loss and
are discordant on a Wetherill concordia diagram. Relying on the 207Pb/206Pb ages of preNeoproterozoic concordant and discordant
grains, we distinguish the age groups 0.9–1.1
Ga, 1.65–1.85 Ga, and 2.45–2.7 Ga (Fig. 3).
SUMMARY AND CONCLUSIONS
Cambrian sandstones exposed in Israel belong to a regionally extensive siliciclastic sequence deposited over the northern margin of
Gondwana in the aftermath of the Pan-African
orogeny. We obtained U-Pb ages from detrital
zircons separated from four samples of Cambrian sandstone of southern Israel: these are
the first zircon ages reported from the Cambrian of North Africa and Arabia. Our data
show a significant concentration of detrital zircons at 0.55–0.65 Ga; the timing of intense
calc-alkaline and alkaline igneous activity,
rift-related volcanism, and strike-slip faulting
in the Arabian-Nubian shield (e.g., Stern,
1994). The provenance of 0.65–0.55 Ga igneous zircons is probably the voluminous late
Neoproterozoic calc-alkaline granitoids (stage
III; e.g., Bentor, 1985) and the widespread
posttectonic alkaline igneous rocks (stage IV)
of the Arabian-Nubian shield. The distribution
pattern in Figure 3 is consistent with the latest
Neoproterozoic being the most intense phase
of igneous activity in the Arabian-Nubian
shield. The presence of several 0.5–0.55 Ga
detrital zircons indicates that igneous activity
in the northern Arabian-Nubian shield outlasted the Precambrian-Cambrian boundary
(e.g., Beyth and Heimann, 1999).
Pre-Neoproterozoic zircons, grouped at
0.9–1.1 Ga (Kibaran), 1.65–1.85 Ga, and
2.45–2.7 Ga, compose ;30% of the total zircons analyzed. For the 1.65–2.7 Ga zircons,
rocks from the Saharan metacraton (Fig. 1;
Abdelsalam et al., 2002; Schandelmeir et al.,
1988; Stern et al., 1993, and references therein) and the southern Afif terrane in southeastern Saudi Arabia (Stacey and Hedge, 1984)
are plausible source terranes ;1000 km south
of Elat (Fig. 1). However, the source of 0.9–
1.1 Ga (Kibaran) zircons is enigmatic. The
nearest 0.9–1.1 Ga (Kibaran) granitoids are in
central Africa (Burundi, Rwanda; Cahen et al.,
1984) and flanking the Mozambique belt in
southeastern Africa (Malawi; Kröner, 2001),
more than 3000 km south of Elat. Likewise,
detrital zircons of that age are abundant on the
Pacific margins of Gondwana (Ireland, 1992;
Williams et al., 2002). However, the Kibaran
detrital zircons that we detected are not particularly rounded, and they occur in subarkose
that still contains some feldspar, so a distal
provenance may not be indicated. Dixon
(1981) reported 1.1 Ga zircons from granitic
cobbles (as well as other cobbles ranging in age
from 1.1 to 2.3 Ga) in Neoproterozoic sections
in the Eastern Desert, and suggested derivation
from continental areas west of the ArabianNubian shield (such as Uweinat), but 1.1 Ga
U-Pb zircon ages have not been recognized
there (e.g., Abdelsalam et al., 2002). It is remarkable that the cobbles Dixon dated were
as large as 30 cm, so they couldn’t have been
transported a long distance. Thus, the possibility that the Arabian-Nubian shield contains
0.9–1.1 Ga rocks (hitherto not recognized)
should be explored. Nonetheless, Pan-African
orogeny coalesced with repeated Neoproterozoic glaciations (Hoffman et al., 1998; Jacobsen and Kaufman, 1999; for West Africa see
Trompette, 1996, and references therein). Neoproterozoic glaciers may have transported toward Gondwana margins a large quantity of
detritus that was later reworked and deposited
in the great pile of early Paleozoic siliciclastics. This may prove an alternative explanation for the presence of unrounded Kibaran
zircons in Elat, thousands of kilometers from
any known source.
ACKNOWLEDGMENTS
Our study was funded by the Israel Ministry of Energy
and Infrastructure. We are grateful to S. Feinstein, M.
229
Beyth, A. Segev, Z. Garfunkel, and J. Wooden for advice
and discussions. We thank M. Bröcker for support and advice throughout our study, and O. Navon for providing access to his Raman laboratory. Reviews by K. Burke and
R.J. Stern and an anonymous reader helped to improve this
manuscript and are greatly appreciated.
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Manuscript received 9 July 2002
Revised manuscript received 18 October 2002
Manuscript accepted 21 October 2002
Printed in USA
GEOLOGY, March 2003