勿 D enis Vaslet U pper O rdovician glacial deposits in S a u d i A rab ia

K ingdom . N ew data have been published by D G M R on the early O ne of the niaJor results of the geologic m ap- Paleozoic lithostratigraphy resulting from this w ork as 1:250 ,000- scale geologic m aps and explanatory notes (V aslet and others, 1985: M anivit and others, 1986} W illiam s and others, 1986: Ekren and oth- ers, 1987; V aslet and others, 1987), and these data have been sum - m arized in a D G M R Professional Paper (V aslet, 1989). B efore 1985, the stratigraphy ot low er Paleozoic ro c k s of Saudi A rabia w as based m ostly on the international stratigraphic lexicon (Pow ers, 1968), w hich form alized the earlier w ork ot Thralls and H asson （1956), Steineke and others （1958), and Pow ers and others (1966). In th e schem e proposed by Pow ers （1968), the early Paleozoic succession of central S aud i A rab ia w as sub divided in to tw o form a- tions (fig. 2):（I）the C am brian(?) to E arly O rdovician (A renigian) Saq Sandstone. unconform ably overlying Proterozoic Shield rocks 卷not*thive,vtern Arabia. G rap浪tolite Z,0110tiO17 ifRhU lteS and com posed of conglom eratic and coarse- to fi ne-grained sandstone th at m a n ne and siltstone; and (2) the T abuk Form ation, conform able on the Saq cla-v sedimentation began (ilier ihe ice- Sandstone, consisting of shale and sandstone and subdivided into COP M elted : bY m iddle Llundoveriun time in central seven inform al units considered to range in age from Early O rdovi- A ra b ia a nd 脚 ea吻 Llandoverian tinte in nol-th- cian (A renigian) to E arly D evonian (G edinnian). H elal（1964 , 1965) w estern A rabia . used a different term inology and restricted the Tabuk Form ation to O rdovician deposits. H e defi ned a new form ation for the Tabuk re- Updated paleofacies inaps have been inte- gion Silurian rocks, that is, the Sharaw ra form ation . H elal（1964) also con sidered th e base of the T abuk F orm atio n to b e L lanv irm an B ahafzallah and others (198 1）and A l-Laboun (1982, 1986) proposed the am putation of the upper, the D evonian, part of the Tabuk Form a- tion, that is, the Taw il M em ber of Pow ers （1968). M cC lure 门978) and Y oung (1981）w ere the f ir s t to describe glacial deposits of early Paleozoic age from central Saudi A rabia (Jal as Saqiyah). T hese deposits w ere (partly) m apped by Bram kam p and others (1963) as "brow n to tan sandstone Ithat] transgresses the low er and m iddle parts of the [Tabuk I forination, ' although they w ere not interpreted as such at that tim e. 拼萝 In 1978, M cC lure tentatively referre d t o the L ate O rdovician glaciation previously described in the Sahara (Beuf and others. 1971）although he concluded that insu什icient data w ere available. In tro d u c tio n The existence of Late O rdovician glacial environm ents w as corrobo- rated by a sedim entologic study by C lark-Low es (1980) in the Q asim E arly Paleozoic rocks in Saudi Arabia crop out in three areas。、。 region . This latter author proposed the nom enclature of the "Sarah discontinuous fringe around the Proterozoic A rabian Shield (fig. 1): m em ber" for glacial deposits that form ed part of the "T abuk Form a- (1) in the northw estern (T abuk) area extending w est from the G reat tion" defi ned by Pow ers (1968). N afud (A n N afud) to Jordan, (2) in the central area including the D etailed study of the stratig ra p h ic succession that includes these H a'il and Q asim regions in central A rabia. and (3) in the southern glacial deposits led V aslet（1987a, b. c: 1989) to recognize tw o m a- area extending from Jabal W ajid to N orth Y em en. T hese outcrops jor glacial erosional surfaces that underlie the glacial to periglacial are bounded to the north by the erosional surface beneath the U pper deposits w ithin the "T abuk Form ation" of Pow ers （1968). L ithostrati- C retaceous W asia Form ation and to the northeast and cast by the graphic evidence clearly dem onstrates the need for revision of the erosional surface beneath the U pper Perm ian K huff Form ation. U p- l ab u k F orm atio n . w hich m u st be con sidered an o bsolete u nit in view per Perm ian deposits directly overlie the eastern part of the Shield. of the internationally accepted rules of stratigraphic nom enclature. In southern A rabia, the K huff Form ation is m issing and the Paleozo- N ew I ithostratig raphic units replacing the form er "T abuk Forin a - ic is overlain directly by Jurassic deposits. tion" w ere defined and featured on the D G M R G eoscience M aps P aleozo ic ro cks of cen tral S aud i A rab ia h a ve b een stu d ied in published for the H a'il and Q asim regions, and a synthesis of the detail by the French B ureau de Recherches G 6ologiques et M inj}res currently available lithostratig raphic, sedim entologic, and biostrati- (B RG M ) as part of the Saudi A rabian D irectorate G eneral of M ineral graphic data has been sum m arized in a D G M R Professional P aper R esources' (D G M R ’s ) system atic geologic m apping program of the (V aslet, 1989 ).

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F igure I一 S im plified geologic m ap of the A rabian P eninsula. 一 E X P LA N A T IO 国N O m an A llochthonous front Late Perm iant o Early Cretaceous 翌 O m an o phiolites 一Ero sion surface pre-Khuf Form ation (Late Perm ian) A 四 O m a n A uto c h tho n o u s P ale o zo ic P re - L a te P e rm ian F ig ure 2 . - H istory oj'lith ostratigraphic ＊ 囚 classification w ithin the Paleozoic 口 P ro te ro zo ic S h ie ld ro c ks succession oj Saudi A rabia and Jordan. Q u atern a ry A bbreviations: conglom ., conglom erate; 姗 J., jacies; fm ., form ation; gr., grained; Tertiary to Q uatern ary v olcanism M a in o il fie ld s in S a u d i A ra b ia 圈 夕 H am m ., H am m annyat; lim est., Ist., Late C retaceo us to Tertiary lim estone; Llandov., L landoverian; m b., 2 0 0 旧 0 O 2 0 0 月0 0 砚而 m em ber;尸recam b., P recam brian; sh., Erosion surface pre-W asia Form ation shale; sst., sandstone; Trans., (Late C retaceo us) ｝ T r a n sitio n .

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nadir M em ber show s a clearly transgressive character and a possible L ow er Paleozoic preglacial deposits hiatus of early Llanvirnian deposition betw een the tw o units. The next oldest m em ber of the Q asim Form ation is the K a h fah B efore the first glacial episode of Late Ordovician age, and hence M em ber （104 m ), defi ned near A l K ahfah by V aslet and others below the earliest unconform ity, deposits ranging in age from C am - (1987 ). This m em ber is divided into tw o assem blages. T he low er brian(?) to Late O rdovician are represented by three form ations, assem blage (40 ni) consists of fine-grained , feldspathic sandstone w hich are assigned to the new ly nam ed Taym a group. T hese form a- interspersed w ith graptolite- and trilobite-bearing claystone of possi- tions are, from bottom to top (fig . 3), the Y atib form ation, the Saq ble L landedian age. L ocally , it contains coarse bioclastic sandstone. Sandstone. and the Q asirn Form ation. T he upper assem blage (64 m ) is undated and is com posed of fi ne- grained , tigillite-bearing sandstone that probably w as deposited in a Y atib form ation m arine, prodeltaic environm ent, 1 he R a'an M em ber (43 ni) f o ll ow s, defined at A r R a'an by T he o ldest o f the th ree fo rm ation s is the Y atib fo rm atio n o f C am bri- W illiam s and others (1986). It consists m ainly of claystone deposited an(?) age (nam ed after Jabal Y atib, E kren and others, 1987), w hich in an outer-shelf environm ent, and it contains a basal graptolite overlies the Proterozoic basem ent w ith an angular unconform ity and (diplograptids) and trilobite (dalm anitids) fauna of possible late C ara- is found only w est of long 42'15' E . This form ation occupies depres- docian age. sions in the palcosur几ce of the Shield rocks and is overlain discon- T he yo u n g est inem ber of the Q asim Form ation is the Q uw arah form ably by the Saq Sandstone. It is com posed of polym ictic con- M em ber (87.5 m ), defined by W illiam s and others （1986) near A l .1om erate. the rounded clasts of w hich include typical Shield rocks, Q uw arah. It consists of alternating fine-grained (in places bioclastic) quartz pebbles of undeterm ined origin, coarse-gram ed sandstone, and sandstone, m icaceous siltstone, and claystone. T his m em ber, w hich siltston e . all set in an aren itic m atrix . m akes up the upper part of the Q asim Form ation, is truncated every- w here by the first glacial erosional surface (base of the Z arqa Form a- tion) and is considered to be C aradociam ?) to A shgillian('?) in age. Saq Sandstone T he m iddle of the three form ations of the T aym a group is the Saq Sandstone of C am brian(") to Early O rdovician (A renigian) age. a form ation defined in central Saudi A rabia (Steineke and others, U pper O rdovician glacial deposits 1958: Pow ers and others. 19W Pow ers, 1968). A revision of the type section is provided by W illiam s and others （1986) in the vicin- U pper Ordovician glacial deposits are subdivided，。central Arabia itV of Jabal Saq, w here the total thickness is 663 m . T he Saq Sand- into tw o form ations, each underlain by strong glacial unconform ities: stone is subdivided into tw o m em bers by V aslet and others （ 1985), the Zarqa Form ation (V aslet and others. 1987) below and the Sarah a s fo llo w s . Form ation (W illiam s and others, 1986) above. In both form ations, T he lo w e r part of the Saq Sandstone is the R isha M em ber (308 the glacial deposits are continental (tillite), fl uvial glacial (tillite. ru), nam ed aft er W adi at R isha. T he m em ber lies unconfortriably on sandstone), and glacial m arine and (or) lacustrine (boulder clay , re- rocks of the Proterozoic Shield east of long 42'15 ' E . T he base of w orked tillite, slum ped fine-grained sandstone). T hese deposits lie the R isha M em ber consists of conglom erate of centim eter-sized unconform ably on rocks of the Q asim Form ation, but the palcoero- sion surface cuts dow n as far as the Saq Sandstone (fig. 4). w ell-rounded. w hite quartz pebbles in a sandstone m atrix. A bove the conglom erate, the R isha M em ber consists of coarse- to fine-grained sandstone. T his m em ber is interpreted as representing a braided allu- Z arqa Form ation via] system that evolved upw ard into a deltaic system . I he Z arqa Form ation crops out in central Saudi A rabia betw een A SD- The Sajir M em ber (355 rn) is the upper part of th e S a q Sand- yah d at 27'55' N ., long 42'07' E .) and A l Q ara (lat 26'23' N ., long stone and is nam ed after W adi Sajir. It consists of m edium - to fine- 43'50' E .) (fig . 5). T he unit unconform ably overlies the Q asirn For- grained sandstone interspersed w ith m icaceous siltstone beds bearing m ation, w hich it erodes to a varied extent. T he Zarqa Form ation it- C ruziana trails. I he Sa}jir M em ber represents a prodeltaic (shallow - self is channeled everyw here by the erosional surface that preceded w ater) environm ent and contains tidal-flat deposits in its upper part. deposition of the Sarah Form ation. L ocated betw een tw o erosional T igillite-bearing (Scolithus) sandstone occurs discontinuously in the surfaces, outcrops of the Z arqa Form ation are discontinuous. and topm ost part of the m em ber. consequently the form ation is now here fully preserved . O utcrops of the Z arqa Form ation that are preserved indicate that the deposits are Q asim F orm ation located in the low -lying zones of a paleotopography notched into the Q asim Form ation (fig. 4 ). Locally, they correspond to the filling of Fhe youngest of the three form ations of the T aym a group is the paleovalleys, the traces of w hich rem ain visible (for exam ple, the Q asim Form ation, w hich is nam ed after the A ] Q asim region and is Ilb , R ada'if, K uhayfi, K ahfah. and T urm us paleovalleys} see fig. 5). of L lanvirm an to C aradocian (or A shgillian')) age. D efined by The type section of the Z arqa Form ation, as detined by V aslet W illiam s and others （1986 ), it lies conform ably on the Saq Sand- and others （1987). is 115 rn thick and is located near Jal az Z arqa stone. T he form ation, w hich has a total thickness of 261 m , is sub- (fig. 5). It com prises com plex interbeds of siltstone or clayey silt- divided into four m em bers, as follow s, from bottom to top. stone containing dropstones (boulder clay), fine-grained m icaceous The oldest m cm ber of the Q asim Form ation is the H an a d ir sandstone that com m only is slum ped, and fillite. A nalysis of the type M e m ber (26 .5 rn ). nam ed aft er the cuesta of A l H anad ir in the section (V aslet and others, 1987, and V aslet, 1989) show s that the Q asini region. M ainly argillaceous. the m em ber is 48 m thick in a form ation is m ade up of three m ain facies. new reference section defined at A t 'I m iyat by V aslet and others （1987). It contains a graptolite, trilobite, and conodont fauna of rnid- T illite fa c ies die to late Llanvirnian a-e (D idv}no gr upt its m urchisom Zone). Lo- cally, a phosphatic. bioclastic (fish debris) conglom erate occurs at T illite 2 to 9 m thick k located at the bottom of the Z arqa Form ation the base of the m em ber. C om pared w ith the Saq Sandstone, the Fla- and is channeled into the underlying Q asim Form ation (fig. 4). The

Sep tem ber 1990 1 5 1

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F ig ure 3. - T he pre-L ate P erm ian depositional succession in central A rabia. A bbreviations: fin ., fi n-m ation; V andov., L landoverian; Ist., lim estone; in , m eter; m b., m em ber. See fig ure 4 for explanation of sym bols.

Episodes, 认4. 13, no. 3 1＿52

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E X P LA N A T IO N

II I I T igillites 盛A & 石Ilite 、 只“ Q u saib a M b . n o w H aw b an M b . % / B ioclasts G la c ia l b o u ld e rs so 多 zo S a rah F orm atio n ．协 Intraclasts Striations, groove m arks Qw Zarqa Form ation 目 Ra Q u w a ra h M b . E) Ferruginous ooliths 了V a rv e s Kos R a'an M b . Kai 2 Graptolites S lum ping Ho 黑 〕Kahfah Mb 夕 S H a n a d ir M b . M M 717- Ferruginized surface B u rro w s Saq Sandstone -- V --ir- B io lu rb ated su rface 目 卜喇 二！lite 国C layey sandstone 巨到 昌S andy or silty claystone 区 图3.61 Conglomerate C laystone 皿 ～ lo o m 医 习 Coarse-grained sandstone 巨二］ Tigillite-bearinc s口 。 巨二口

F igure 4. - Stratigraphic relationships of glacial dep osits in central A rabia. A bbreviations:户n., form ation; m b., m em ber.

Sep tem ber 1990 之

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A ：H A 'IL Q U A D RA 刀U L F ＿2 7 E 日 B A Q A QU A D R A N G LE · 2 7 F C : B U RA YD A H C UA D R A N G } E 一26 百 D } JA B A L H A B A S H I Q U A D R A N G L E - 26 F 2 6 - N

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F ig ure 5. - L ate O rdov ician glacial features in central A rabia.

注 15 4

tillite is com posed typically of heterogenous m aterial that includes stone interpreted to be intertidal deposits. The Zarqa Form ation de- com ponents both from the Shield and from the sedim entary "cover" posits can be interpreted, respectively, as rem nants of glacial m o- rocks that surround the Shield and that range in size from gravel to raines in the case of the continental deposits and as subglacial or boulders up to 1 ni in diam eter (see fig. 6). N um erous pebbles and proglacial subaquatic deposits into w N ch erratic com ponents w ere cobbles show polyhedral shapes and striated surfaces. The m atrix is released by drift ice in front of the glacier. Th e ice also m ay have coarse- to fine-grained sandstone or clayey siltstone in places; it is been responsible for the intense plastic deform ation (slum ps) that com m only brow n or is blackened by iron oxides. In places like the occurred w hile these sedim ents w ere saturated w ith w ater. A ddition- type section, the fine-grained boulder clay and the substratum have ally, w ells in the Z arqa Form ation have yielded an O rdovician fro st crack s that a re filled w ith co arse tillite . m icrofl ora sim ilar to that encountered in the underlying Q asim F o rm ation . Boulder-clay facies S arah F orm ation The boulder-clay facies com prises a very constantly dark-green, clay- ey, m icaceous siltstone (rock flour of Beuf and others, 1971) that O utcrops of the Sarah Form ation in central Saudi A rabia (fig. 5) are contains a varied proportion of pebbles, cobbles, or boulders. The located betw een the southeast edge of the G reat N afud (A n N afud) clasts, in places faceted, are derived from Shield and cover rocks and W 56 ar R im ah, the m ain tributary to W 56 al B atin near B uray- and represent dropstones in a m udstone facies. The faceted drop- dah (fig. 1). They form a northwest-trending belt of irregular width, stones com m only show striated faces and range in diam eter from I and they take one of the follow ing tw o form s. (1) A t the north and cm to I in. Thickness variations of the facies are abrupt, such as northeast edges of the belt, the outcrops appear to be continuous, ranging from 2 to 20 in thick in less than 10 ni laterally. V ariations although they are interrupted by substantial T ertiary and Q uaternary also occur in the proportion of dropstones, w hich are absent in cover, particularly around the large consequent w adis. (2) A t the places, and in the proportion of clay and silt. south and southw est edges of the belt, the Sarah F orm ation crops ou in the form of elongate, bar-type relief features that are oriented per- S a n d sto n e fa c ie s pendicular to the general alignm ent of the fori-nation. T hese bars, in places up 50 kni long and betw een several hundred m eters and sev- Beige, fine-grained sandstone, in places m icaceous, is present as I- era] kilom eters w ide, represent the fi lling of paleovalleys, so the to 3-m -thick beds that locally are lam inated and alternate w ith, and original low relief is now reversed. A total of 19 m ain paleovalleys in places channel, the boulder clay. T he beds m ay have a coarse- has been distinguished and nam ed aft er local features (the Sarah pa- grained or conglom eratic base blackened by iron oxides. Plastic de- leovalley, the T urm us paleovalley, and so on, fi g. 5). form ation, such as slum ping, is nearly ubiquitous, com prising 1一to T he fl ow direction of the paleovalleys ranges from e a stw ard to 10-m -thick beds of sandstone slum ped into the boulder clay or northw ard, the preferential average flow being northeastw ard. T he centim eter-sized m icroslum ping w ithin the sandstone itself. O ther paleovalleys system atically broaden dow nstream (that is, roughly structures, such as frost w edges and polygonal ground typical of gla- northeastw ard) and becom e coalescent, so that they form a continu- cial environm ents (B euf and others, 1971), are also present in the ous outcrop belt. T he Sarah Form ation is bounded at the base by a san d sto ne . m ajor unconform ity and lies on an erosional surface cut deeply into the Saq Sandstone, the Q asim Form ation, and the Z arqa Form ation. H istory of deposition T he upper boundary of the Sarah Form ation is m arked by a discon- form ity w ith the overlying m arine claystone of the Q usaiba M em ber The Z arqa Form ation consists of glacial features and continental de- of the Q alibah (Tayyarat) Form ation (fi g. 4). posits succeeded by subaquatic deposits that are either lacustrine or T he Sarah Form ation , defi ned at K hanas ir S arah by W illiam s shallow m arine in origin. T he topm ost part of the form ation displays and others (1986), is essentially sandy and relatively uncem ented , predom inantly a m arine character, as in the case of lam inated sand- except in the low er part of paleovalleys w here tillite is preserved locally. T o the north betw een A ] A jfar and B aq'a, a local facies of glacial to m arine origin, know n as the H aw ban M em ber (V aslet and 拭轰 others, 1987), gives rise to a cuesta in the upper part of the fornia- tion (figs. 3-5). 奢 A lthough th e re sidual thickness of the Sarah Form ation is only 27 m in the type section at Sarah, the unit is locally over 300 in thick in the dow nstream axial part of the paleovalleys (V aslet, 1987a, b, and c). T he form ation show s a m inim um of 90 m of sedi- m entary rock w here the form ation crops out continuously outside the paleovalleys. T he Sarah Form ation is com posed m ainly of m edium - to fine-grained sandstone accom panied at the edges and at the bottom of the paleovalleys by tillitic rocks very sim ilar to those of the Z arqa Form ation. In the new reference section described by V aslet and oth- ers (1987) and V aslet (1989), w hich is above the type section of the Zarqa Form ation in the B aq'a area, the form ation is 139 in thick and includes the type section of the H aw ban M em ber (54 m ).

M orphologic features 笋塔 尤夕器蒙菠多攀I 户洲 A s in the case of the Z arqa Form ation, a num ber of structures, F igure ‘一 Tillite at the base of the Z arqa F orm ation near A t shapes, and facies that are characten stic of a glacial or periglacial T iniyat showing a boulder of s triated sandstone (a) and a environm ent m ark the Sarah Form ation. T he follow ing are the m ost polyhedral, faceted basem ent cobble (b). significant of those m orphologic features.

S O n te m b e r 1 9 9 0 1 5 5

gos 100 to in diam eter w ere discovered by the author in the low er part of the Sarah Form ation near T aym a in northw estern A rabia (fig . 1). A l ar g e (300 m in diam eter), perfectly fossilized paleopingo rests on the Q asim Form ation in central A rabia (fig. 9). It is a circu- lar depression 户at is 100 m w ide and surrounds a central, steep- sided, and uplifted center. The core of this feature contains rocks of the low er unit of the K ahfah M em ber of the Q asim Form ation. T hese rocks, consisting of argillite and bioclastic sandstone that contain fi sh debris, have been affected by intense plastic deform ation. T his pa- leopingo, located close to a paleovalley in the Sarah Form ation , is thought to be related to a later glacial event.

H istory of deposition

The developm ent of the Sarah Form ation paleoenvironm ent is inter- preted as follow s. Initially, the low er part of the Sarah Form ation , w hich channels the Zarqa Form ation and its substratum , w as depos- F igure 7. - Tillite at the base of the Sarah F orm ation on ited in very deeply cut paleovalleys that had fl at bottom s and slightly tigillite-bearing sandstone of the Qasim F orm ation near R awd al inclined sides. T he sides of these paleovalleys locally show roches 协un show ing a polyhedral basem ent cobble (a) and a boulder of m outonn6es, grooves, and pockets in w hich tillite is preserved, and Ugillite sandstone 彻 ． the paleovalleys are interpreted to be glacial in origin . B ecause of the strong secondary cem entation that affected the porous m aterial at the bottom of the paleovalleys and in the substratum , these paleoval- (1) Tillite (fig . 7) i s p resent locally at the base of the paleoval- leys are now in reverse relief. leys, particularly at the present-day m argins rather than at the bot- The filling in the paleova ll e ys is very hom ogeneous (m edium - tom , w here it appears to have been eroded during the deposition of grained , crossbedded sandstone) and is fl uviatile or fl uvial m arine in sedim entary fill. T his tillite displays all stages of evolution from con- character. Layers of rew orked tillite locally alternate w ith the sand- tinental tillite (at R aw d al U yun and A l Q uw arah) to tillite rew orked stone, and a striated glacial fl oor occurs in the low est few m eters of in a subaquatic environm ent (at R aw d al U yun and Silm an; see loca- sedim entary rocks in som e paleovalleys. These factors indicate the tions in fi g. 5). Polyphase episodes, such as the alternation of tillite presence and activity of ice, tem porarily anyw ay , w hen the paleoval- an d sand ston e in th e lo w er 10 m o f the fo rm ation near R aw d a] leys began to be filled. T herefore, at least som e of the fill sedim ents U yun, m ay represent stages of seasonal advance and retreat of the are proglacial in character. Such fluvial-glacial sedim ents channeled ic e . the earliest tillite, and probably also the earliest glacial deposits, that ( 2 ) G lacial fl oors (fi g. 8A ) appear in the low er part of the Sarah is preserved only in pockets on the fl anks and bottom of the paleo- paleovalley, as at K hanasir Sarah. H ere, a grooved fl oor has been valleys. spared from further erosion over a distance of 26 m because of later T he u p per part of the Sarah Form ation overflow ed the paleoval- ferruginous cem entation and the very recent rem oval of overlyingm a- leys and covered m uch of central Saudi A rabia w ith sandstone that terial. A t this locality, parallel striations and grooves are oriented N . w as no longer directly glacial in origin . H ow ever, it represents suba- 75* E . and occur over the entire length of the grooved fl oor. In addi- quatic sedim entation in w hich the traces of a periglacial lacustrine environm ent (varves) persist locally and in w hich a m arine character tion, concave pluck structures, crescent-shaped fractures, and a sinu- is increasingly predom inant. This thick and volum inous detrital sedi- ous ice groove (fig. 8B) are seen. Sim ilar ice groove structures de- m entation m ay have resulted from an episode of a general thaw ing scribed by D ionne (1985) in present-day C anadian periglacial facies indicate the relative plasticity of m aterial during passage of that liberated the huge am ount of sandy m aterial stored in the ice. T his sandy m aterial resulted from the cutting of paleovalleys in es- the ice . sentially sandy form ations such as the Saq Sandstone and the Q asim (3) S tr iated and grooved roches m outonn6es protrude over the F orm atio n . Saq Sandstone and the Z arqa Form ation or rem ain w ithin the Sarah The H aw b an M em ber of the S arah Form ation is locally (be- Form ation itself, either in the low er part of the paleovalleys or in the H aw ban M em ber. tw een A l A jfar and B aq'a; see fi g. 5) indicative of a new glacial environm ent at the top of the Sarah Form ation. It is characterized by (4) R ock slid e s a re evident. For instance, large parts of the H a- roches m outom ides and grooved glacial surfaces, tillite, boulder clay, nadir M em ber of the Q asim Form ation slid to the bottom of the pale- and bedded sandstone, w hich becam e m arine at the top . The m em ber ovalleys, w here they are preserved as distorted m asses. m ay represent a final advance of the ice over central Saudi A rabia (5) Slum ps of sandy m aterial are found in the Sara h F orm ation, after deposition of the Sarah F orm ation and before (or, in the case of such as th e san dsto ne o f th e H aw ban M em b er. the upper part of the m em ber, sim ultaneously w ith) a return to true (6) The presence of erratic blocks in the H a w ban M em ber indi- m arine conditions. T hese m arine conditions are represented by the cates that they w ere dropped into the boulder clay of the m em ber. clays at the base of the overlying Q usaiba M em ber of the Q alibab (7) Lam inated, varvelike rocks occur in the upper part of the (T ayyarat) Form ation, w hich contain Silurian graptolites. T he pas- Sarah F o rm ation . sage of the ice w ould have been responsible for the deform ation that (8) H ydrolac c o li ths, or pingos, are know n in present-day peri- is observed at the top of the Sarah Form ation (glaciotectonic defor- glacial areas of the A rctic (M aarleveld, 1965). These features are m ation). caused by the elevation and deform ation of upper layers of frozen T h e m i c r o flo ra enco un tered in w ells that cro ss the S arah F o rm a- ground (perm afrost) due to the pressure of an underlying w ater tion in the Q asim region indicates the appearance of an E arly Siluri- pocket that has been transform ed into a lens of ice. Several paleopin- an association of acritarchs and chitinozoans tow ard the upper part of

P,)isodes, Vol. 13, no. 3 1 5 6

the form ation. This evidence suggests that the O rdovician-Silurian boundary is possibly located w ithin the form ation.

梦照 L ow er Paleozoic postglacial deposits 臀蔓T he lower Paleozoic glacial deposits in central and northwestern 遗笠互 妻黔 Arabia are overlain disconform ably by Llandoverian transgressive m arine deposits (figs. 2, 3, and 4). Previously described as the "T ay yarat Form ation" by V aslet and others (1987), this Llandoverian unit 廖鲜； w ill be redefined as the "Q alibah Form ation" (D . M ahm oud, D . V as 01-犷二_ 绪 A," let, and M .I. H usseini, unpublished data) on the basis of new sub- su rface and su rface refere nce sectio n s. 卿沉 The Q alibah Form ation (alias Tay ya r a t Form ation) includes tw o 狄蒸 砂八 、 漏 m em bers. T he low er m em ber is the Q usaiba M em ber, as redefined 擎}2 by M anivit and others (1986). It is predom inantly clayey , w hich in- 蒸 纂 淤 dicates deposition in an outer-shelf environm ent, and it is inter- 鑫黔馨纂 妒 spersed w ith siltstone and m icaceous, fi ne-grained sandstone layers 犷 in its upper part. In central A rabia, the basal part of the Q usaiba 黔翼 M em ber contains a rich graptolite fauna of m iddle L landoverian age 蟒 (M onograptusfi m briatus Subzone, M onograptus convolutus Z one) (V aslet and others, 1987, aft er P . L egrand, w ritten com m un., 1984; E l-K hayal, 1985, 1987; M cC lure, 1988). H ow ever, prelim inary in- I 蓦 vestigations in northw estern A rabia dem onstrate an early Llandoveri- 撇豢黔 髓 an graptolite association (P . Legrand , w ritten com m un., 1989) from 黔 翼 the clayey basal part of the Q usaiba M em ber that directly overlies 群翼黔 黑象 the sandy facies of the Sarah Form ation. A sim ilar diachronism of 纂 transgressive m arine rocks has been dem onstrated by Legrand (1985) 潺 缎葬 in the basal Silurian rocks of southern A lgeria (H oggar M ountains). 黔 蒸 T he upper part of the Q alibah Form ation is the Sharaw ra M em - 彭攀 her (V aslet and others, 1987), w hich m ainly consists of sandy m a- rine strand deposits containing surface-type sequences and thin con- 参娜 薪毅 glom erate layers at the base. D evoid of characteristic fossils, this t 掣 m em ber is assum ed to be late Llandoverian in age on the basis of com parison w ith surface data (A l-L aboun , 1982, 1986). A The Liandoverian rocks of the Q alibah (alias T ayya r a t) Form a- tion are, in turn, overlain disconform ably by a braided-stream , allu- vial sandstone unit (T aw il Form ation) of probable Early D evonian age (B ahafzallah and others, 1981; A l-L aboun, 1982, 1986). C onse- quently, U pper Silurian deposits are unknow n in central A rabian out- cm p s .

D istribution of low er Paleozoic glacial deposits in Saudi A rabian outcrops R econnaissance work in northwestern Arabia (D. Vasiet, A. Berthi- aux, and Y .-M . Le N indre, unpublished data) has show n that glacial deposits, including both the Z arqa and Sarah Form ations, are also w ell represented throughout the T abuk area (fig. 1) as far north as the Jordanian border. H ere, the glacial unconform ities show the sam e features as those in central A rabia and com prise long and narrow paleovalleys cut deeply into the Q asim Form ation and Saq Sandstone B equivalents. The paleovalleys indicate fl ow directions to the north and northeast (fig . 10). B elow the glacial f o r m ations, the sam e four m em bers of the F ig ure 8. - G lacialf eatures in the Sarah F orm ation. A , G rooved Q asim Form ation can be distinguished in northw estern A rabia. They and striated glacial p avem ent in the lower part of the Sarah show sim ilar rock types and thicknesses, except for the Q uw arah F orm ation at K hanasir Sarah . B , Sinuous ice groove and th e M em ber, w hich is slightly thicker here than it is farther southeast. surrounding ridge, a detail from th e glacial p avem ent pictured A bove the glacial form ations, L ow er Silurian deposits are also sim i- in A . lar to those in central A rabia, even though thev are considerablv

Sep tem ber 199( 15 7

(B ellini and M assa, 1980; K litzsch , 1981); in D jado , L ibya (D ey- noux and others, 1985); and on the w est and east (Jabal A w aynat) flanks of the K ufra basin of L ibya (B ellini and M assa, 1980). The presence of glacial deposits at the south edge of the K ufra basin (at EDDedi and Erdis in C had) is not dem onstrated. In E gypt, Issaw i and Jux (1982) described possible fl uvial-glacial deposits, including drop- stones, in the Sinai, the N ortheastern D esert, and the Southeastern D esert. N o evidence of glacial episodes is described in Jordan (B ender, 1975; W olfart, 1981) but possibly should be sought in the Conularia Sandstone, the upper part of w hich contains A shgillian trilobite faunas (W olfart and others, 1986). N onetheless, it appears probable that this glaciation affected at least the south of Jordan, such deposits having been recognized by the present authors as far as the border betw een Saudi A rabia and Jordan. T he presence of U pper O rdovician glacial deposits is also cited in Ethiopia by Saxena and A ssefa (1983), but this area is still under controversy ow ing to the presence of both early and late Paleozoic glacial events. T he early Paleozoic geodynam ic evolution of A rabi a c l early F ig ure 9. - A erial view of p aleop ingo approxim ately 300 m in belongs to the broader paleogeographic context of the G ondw ana diam eterf ound south of W adt al N akhrim in central A rabia. paleocontinent and its m argins. G iven the am plitude of the continen- tal ice sheet in relation to the G ondw ana paleocontinent as a w hole, the A rabian and south L ibyan ice sheets probably should be assigned thicker. T his area h as be en retained for the n ew referen ce sectio n o f to the sam e L ate O rdovician glacial events. This concept is not con- the Q alibah Form ation (D . M ahm oud, D . V aslet, and M .I. H usseini, tradicted by the paleolatitudes indicated by Sm ith and others (1981), unpublished data). w ho position central A rabia betw een lat 55' and 60* S. (that is, by T he presence o f lo w er Paleozoic glacial deposits in southern com parison w ith present-day geography, betw een T ierra del Fuego Saudi A rabia (Jabal W ajid area, fi g. 1) is less w ell docum ented than and R oss Island in the Southern H em isphere). N or is this concept in the central part of the K ingdom . In the south, M cC lure (1980) contradicted by the hypothesis of an ice pole located to the south of assigned a C am brian to L ate O rdovician age to the exposed part of the Sahara (B euf and others, 1971; D eynoux , 1980), central A rabia the W ajid Sandstone, described as "Low er Perm ian and ?older" by being positioned tow ard lat 50' S Pow ers (1968). T o the north and northeast of A r abia, a G ondw anian m arine The north p ar t of the W ajid Sandstone w as m apped m ore re- fringe is represented by A shgilhan, fairly uniform m arine sedim enta- cently by K ellog a叫 others (1986), w ho subdivided it into four tion, including coarse- to fine-grained sandstone, siltstone, and argil- m em bers. The second and fourth (upperm ost) m em bers, the S anam ah lite, in T urkey (B rinkm ann, 1976), in Iran (Stbcklin, 1972; W olfart, and Juw ayl M em bers, respectively, show strong erosion at their 1981), in northern Syria (B rinkm ann, 1976; Fontaine, 1981), and in bases, as w ell as sedim entary features that m ight indicate deposition the O m an m ountains (L ovelock and others, 1981; L e M 6tour, 1988). in a periglacial environm ent. V aslet (1989; fi g. 3) proposed correlat- A s in Saudi A rabia, the glacial event in the H oggar M ountains ing this upperm ost m em ber w ith the Sarah Form ation. H ow ever, region of southern A lgeria (B euf and others, 197 1) is dated from late m ore recent field investigations by the author and an A ram co team C aradocian onw ard. T hese authors proposed a depositional zonation. of geologists dem onstrated that the Sanam ah M em ber cropping out at They show ed that the continental glacial deposits w ere centered on Jabal W ajid is strictly equivalent to the Sarah Form ation of central the present-day H oggar m assif and its im m ediate periphery, w hereas A rabia and indicates (glacial pavem ents, paleovalleys) a northw ard continental or m arine periglacial deposits w ere distributed further direction of ice m ovem ent during Late O rdovician tim e. In this north in H onrra, Tripolitania. A zonation of this type cannot be de- southern area, the O rdovician glacial deposits are directly overlain by fined on the basis of outcrops in Saudi A rabia, but m arine glacial fish-bearing D evonian sandstone, and the top unit (Juw ayl M em ber) deposits nonetheless predom inate over continental glacial deposits represents Perroian-C arboniferous glacial deposits. th ere. A p o lar projection of the Southern H em isphere during L ate O r- dovician tim e (fi g. 11) show s the direction of glacial m ovem ents according to previous w ork in northern and w estern A frica (B euf and C o rrela tio n s b etw een A r a b ia a n d others, 197 1; D estom bes and others, 1985; D eynoux and others, 1985) and in southern A frica (R ust, 1981; Spjeldnaes, 1981). T aken neighboring regions during L ate in conjunction w ith new data from Saudi A rabia, this w ork indicates O rdovician glaciation the approxim ate boundaries of the Late O rdovician icecap that cov- ered a large part of the G ondw ana paleocontm ent. Furtherm ore, the average northeast-flow directions of the ice in Saudi A rabia support T races of the Late Ordovician glaciation were first described in the the hypothesis of an ice pole located at that tim e in central A frica. H oggar M ountains region of southern A lgeria by B euf and others (1966, 197 1), R ognon and others (1972), and B iju-D uval (1974), and they w ere described subsequently in w estern A frica by D eynoux (1980, 1985). M any other studies undertaken since then in northern C on clu sion s and w estern A frica are included in com pilations by D eynoux and others (1985), D estom beg and others (1985), and Legrand (1985). B etw een the H oggar region and A rabia, evidence of glacial o r In Saudi Arabia, the Late Ordovician glaciation is marked by sev- periglacial sequences of Late Ordovician age is recorded (fig. 10) in eral episodes of advance and retreat of the icecap that developed on the Fezzan region and in the M urzuk and H om ra basins of L ibya the G ondw ana paleocontinent. T w o m ajor extensions of the ice over

即isodes, Vol. 13, no. 3 L 至

、

、 理 'N go M A } -100, 0 10h...... C H A D K O ADC F iN dSOC OTRAPALEOFACIE S OF THE MIDDLE EASTDURING LATE OR DOVICIAN GLAC IATION f AdA DIRECTIONS rulfEmerged or eroded are a GIL CIAL FLOW %y(Tortior to Quater ary sro.ion) (Poleovalleys, striations, grooves)Eroded area ( Permian Northern boundary of glacial 010 d,frid operiglocialid depo Its,, :r'INOA/ SALTAf r Bouf nd others,1971)s RANGCONTINENTAL GLACIAL AND 4% Trilobite faunal Addis Abo P AXiSTAPERIGLACIAL DEPOSITSGraptolile faunas A Asligillian $OKATillits , boulder clay , sandstone LO EarlyGLACIO - MARINE DEPOSITSConodont faunas LiandovorlonSandstone , cloystons with rare dropstorolsOGADEMARINE (NON-GLACIAL) DEPOSITSSandstone HE Thickness In motors K.-hiClayslon* , ollistoneLimestone , sandy [at., clayey Ist. -411 PALEOLATITUDE during LATEORDOVICIAN I - 440 my) 飞 气 芯 心 乙 %-Zc0}Tb7,U. 71 A1, NIAstI 4SCT LZIROAl.U1

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权：：．水 长，． ，．1．，．，．，． t L"-J * _1 份：和A 拼之 f -IJ R 决 又常登令必 姗 丫今、拭冲 馨 N O RT H A M ER IC A 之：： _v 'A*'*""-'.N. .. .".Y......

口 EX PLA N A TIO N Em erged land 一D irection of glacial m ovem ent 圆 ︸(striae, paleovalleys) Epicontinental seas 徽N ew data from the A rabian peninsula 口 娜Central ice-cap area O ceans (deep seas) 。 Presum ed glacial pole (PG ) F igure IL - P olar projection of the Southern H em isp here during the L ate O rdovician at approxim ately 430 M o. The p ositions of t he continents and m agnetic p ole are interpreted and m odified from Scotese and others (1979), Sm ith and others (1981), and C rowell (1981). G eologic data from outside the A rabian Peninsula are from B euf and others (1971), D estom bes and others (198.5), D eynoux and others (1985), C aputo and C row ell (198习，and Spjeldnaes (1981). A bbreviations: PM , m agnetic pole; M a, M ega-annum , 1 0 6 y ea rs.

Episodes, Vol. 月，爪，．3 j 6 门

the A rabian Peninsula are recorded by tw o inaJor erosional surfaces Deynoux. M ., Sougy, J., and Trom pette, R ，1985一Low er Paleozoic of west and subsequent glacial and periglacial, continental to subaquatic de- A frica and the western part of central Africa, in H olland, C .H ., ed二 L ow er Palaeozoic of north-w estcrn and w est-central A frica , v . 4 。厂 posits. as w ell as by typical features that indicate an average ice-flow L o w e r P a lae o zo ic rocks of the w orld: Chichester, Frigland, John W iley, direction tow ard the northeast. Secondary glacial phases took place p . 3 37-495 . w ithin each m ajor episode. A fter the trelting of the ice, w hich prob- D ionne, J,C ., 1985, Forines, fiLures, et faci}s s6dirrientaires glacials des ably retreated in a single but oscillating process. the E arly Silurian estrans vaseux des r6gions froides: Palaeogeography. 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Science et Techniqu e d u G eoscience M ap G M - 103 A , scale 1:250,000. M role. no. 18, 464 p. Klitzsch, E ，1981，Low er Palaeozoic rocks of Libya, Egypt, and Sudan, in Bcuf, S., B ijLI-Duval, B ．SteVaLIX, J.. and K ulbicki. G .. 1966, A m pleur des H o lland , C .H .. ed., Lo w er Palaeozoic of the M iddle East, eastern and glaciations "siluriennes*' an Sahara, leurs in门uences et tents consequences Southern A frica, and A ntarctica, v . 3 （，／Lo w er P alaeo zoic rock s of the s ur la s6 d im e ntatio n R evue de l'Institut Fran}ai} d u P 6trole, v . X X I world: Chichester, England, John W iley, p. 131一163. p . 363- 38 1． Legrand. P ，1985, R611exions sur la trans2ression silurienne an Sahara Bi,ju-D u%al. B ．19/4一Exernples dc d6p6ts fluvic-glaciaires dans FO rdovicien alg& ien: Congres N ational des Soci6tes Savantes一I 10}m e, M ontpe ll ie r . SUp6rieur et le Precam brien SL甲ericur dLI Sahara central: Societe Nationale France, 1985. Section Sciences, Actes, v. 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southern A frica, and A ntarctica, v. 3 of Low er Palaeozoic rocks of the V aslet, D ., B erthiaux, A ., Le Strat, P., Kellogg, K .S., and Vincent, P.L., w orld: Chichester, England, John W iley, p. 165- 187. 1987, G eologic m ap of the B aq'a quadrangle, sheet 27F, K ingdom of Saxena,, G .N ., and A ssefa, G ., 1983, New evidence on the age of the glacial Saudi A rabia: Saudi A rabian D eputy M inistry for M ineral R esources ro ck s o f n o rth e rn G eological M agazine, v. 6,p. 549-554. G eoscience M ap G M -1 16 A , scale 1:250,000. Scotese, C .R ., B am b B arton, C ., V an D en V oo R ., and Ziegler, V aslet, D ., B eurrier, M ，V illey, M ., M anivit, J., Le Strat, P., Le N indre, A｛M ., 1979, Paleozoic base maps: Journal of Geology,v. 87, p. 217- Y .-M ., Brosse, J.M ., Berthiaux, A ., and Foum iguet, J., 1985, Geologi c 2 7 7 . m ap of the A l Faydah quadrangle, sheet 25G , K ingdom of Saudi A rabia: Sm ith, A .G ., H urley, A .M ., and Briden, J.C ., 1981, Phanerozoic paleocon- Saudi A rabian D eputy M inistry for M ineral Resources G eoscience M ap tinental w orld m aps: C am bridge, England, Cam bridge U niversity Press, G M - 10 2 A , scale 1:250 ,000 . 102 p. W illiam s, P .L ., V aslet, D ., Joh nson, P .R ., B erthiaux, A ., Le Strat, P ., and Spjeldnaes, N ., 1981, Low er Palaeozoic palaeoclim atology, in H olland, Foum iguet, J., 1986, G eologic m ap of the Jabal H abashi quadrangle, C .H ., ed ., L ow er P alaeozoic of the M iddle E ast, eastern and southe rn sheet 26F , K ingdom of Saudi A rabia: Saudi A rabian D eputy M inistry f o r Africa, and A ntarctica, v. 3 of Lower Palaeozoic rocks of the w orld: M ineral R esources Geoscience M ap-GM -98 A , scale 1:250,000. W olfart, R ，198 1, L ow er Palaeozo ic rocks of the M iddle E ast, in H olland , Chichester, England, John W iley, p. 199-256. C .H ，ed., Low er P alaeozoic of the M iddle E ast, eastern and southern Steineke, M ., B ram kam p, R .A ，and Sander, N .J., 1958, Stratigraphic A frica, and A ntarctica, v. 3 of Low er Palaeozoic rocks of the world: relations of A rabian Jurassic oil, in W eeks, L.G ., ed., H abitat of O i l一 C hichester, England, John W iley, p. 5-30. A Sym posium , Tulsa, O klahom a, U SA , 1958: A m erican A ssociation of W olfart, R ., Bender, F., and Stein, V ., 1968, Stratigraphie und fauna des Petroleum G eologists, p. 1294-1329. O ber-O rdovizium s (Caradoc-A shgill) und U nter-Silurs (U nter-Llandove r y ) 3tbcklin, J., 1972, Lexique stratigraphique international, A sie, v. III, von Sudjordam en: G eologisches Jarhbuch, v. 85, p. 517-564. 华scicule 9bl, Iran central, septentrional et oriental: Paris, Centre Y oung, G .M ., 1981, Early Palaeozoic tillites of the northern A rabian N ational de la Recherche Scientifique, p. 5-283. FhraIls-, W .H ., and H asson, R .C ., 1956, Geology and oil resources of Peninsula, in H am brey, M T , ana H arland, W .B ., eds ，Earth's pre-Pleistocene glacial record: Cam bridge, England, Cam bridge eastern Saudi A rabia: International Geological Congress, 20th, M ex i c o C ity, 1956, Sym posium sobre yacim ientos de petroleo y gas, v. 2, U niversity Press, p. 338-340．口 p. 9-32. Vaslet, D ., 1987a, Early Paleozoic glacial deposits in Saudi Arabia, a D r. D enis Vaslet (B ureau de R echer- lithostratigraphic revision: Saudi Arabian D irectorate General for M in e ral ches G iologiques et M im }res, B P Resources Technical R ecord B RG M -TR-07-1, 24 p. 6009, O rlians-la-Source, F rance) is - 1987b, The Paleozoic (pre-Late Perm ian) of central A rabia and correlations w ith neighbonng regions: Saudi A rabian D irectorate G e n eral responsiblefor the cover rocks map- for M ineral Resources Technical R ecord B RG M -TR -07-2, 167 p. p ing project of the Saudi A rabian D i- _ 1987c, Gdologic du PaldozoYque Perm ien Sup6rieur, Trias, rectorate G eneral of M ineral R esour- Jurassique; lithostratigraphie, in Le N indre, Y .-M ., M anivit, J. , a n d ces. D uring the last 10 years, he has V aslet, D ., H istoire g6ologique de la bordure occidentale de la been involved in revising the P hanero- plate-form e arabe du Pal6ozo项ue m f6rieur an Jurassique sup6rie u r : Paris, zoic stratigrap hy of Saudi A rabia. H e University of Paris V I, D .Sc. thesis, v. 1, 4 13 p. has specialized in the low er Paleozoic - 1989, Late O rdorvician glacial deposits in Saudi Arabia: A rocks, and comp lete lithostratigrap hic lithostratigraphic revision of the early Paleozoic succession: Sa u d i revision of t hese has been carried out A rabian D eputy M inistry for M ineral Resources Professional Paper 3, p . 13一 4. as a result of his w ork.

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