A Sequence Stratigraphic Reference Section for the Tithonian of Lebanon
Published:January 01, 2000
- PDF LinkChapter PDF
Christopher Toland, 2000. "A Sequence Stratigraphic Reference Section for the Tithonian of Lebanon", Middle East Models of Jurassic/Cretaceous Carbonate Systems, Abdulrahman S. Alsharhan, Robert W. Scott
Download citation file:
Central Lebanon provides some of the best exposed and most readily accessible Upper Jurassic (Kimmeridgian-Tithonian) sections in the Middle East, and is one of the few places where lateral equivalents of the prolific Arab Formation (Kimmeridgian-Tithonian) reservoirs of Peninsular Arabia can be studied at outcrop.
At the Bikfaya outcrop section (35 km ENE of Beirut), the uppermost Jurassic comprises at least two disconformity-bounded third-order depositional sequences. Sequence 1 (“Falaise de Bikfaya”) is 61 m+ thick and comprises a progradational succession (highstand systems tract) of foreshoal micropeloid packstones, shoal-crest stromatoporoid floatstones, back-shoal Permocalculus wackestones, and (?attached mainland-) shoreface facies culminating in tidal-flat deposits. This interval is of Early to Middle Tithonian age.
Sequence 2 (“Calcaire de Salima”) is ca. 63 m thick, and commences with an abrupt transgressive surface and an associated influx of calcareous dinocysts. The lower part of this sequence comprises strongly argillaceous micropeloidal packstones and occasional peloid-intraclast packstones, interpreted as an offshore transition zone facies association. The initial marine flooding event is of late Middle Tithonian (upper fallauxi-ponti Zone) age. A candidate maximum flooding surface (MFS) is recognized within the late Middle Tithonian ponti Zone, coincident with calcareous dinocyst species and abundance maximum. (A ponti Zone MFS has also been identified elsewhere in the Middle East.) The recessive middle part of Sequence 2 is largely unexposed, whereas the upper cliff-forming part comprises ca. 22 m of Upper Tithonian ooid-skeletal grainstones that coarsen and thicken up-section. These grainstones are characterized by pronounced planar cross-stratification with set heights of up to 3.6 m, and are interpreted as a wave-dominated shoal complex culminating in emergent foreshore facies. Sequence 2 is terminated by a prominent paleo-karst (Type 1 sequence boundary) corresponding to the Jurassic-Cretaceous boundary, and is overlain by basal Cretaceous wacke-ironstones that form the lower part of the Chouf Sandstone Formation.
The lower part of the Chouf Sandstone Formation lacks age-diagnostic fossils. The timing of initial Cretaceous onlap is thus only poorly constrained by the presence of Late Tithonian taxa in the underlying “Calcaire de Salima” and the presence of Barremian spores in the upper part of the Chouf Sandstone Formation.
The Bikfaya reference section is located in central Lebanon, ca. 35 km due ENE of Beirut, at 33°55’20”N, 35°42’40”E (Fig. 1). The section is reached by traveling from Beirut to Antilyas on the Beirut-Juniyah coast road, and then eastward on the Antilyas-Bikfaya road. The base of section is located ca. 2 km east of Bikfaya town center, in the floor of a partially infilled roadside quarry on the south side of the Bikfaya-Zahle road, a short distance east of the Hamlaya turnoff. The top of the section is located directly below the hilltop monastery of Mar Elias (Figs. 1, 2A).
There have been relatively few recent studies of the Upper Jurassic in Lebanon. Given that the succession is well exposed and more accessible than almost any other in the Middle East, Lebanon may be an ideal place to establish a sequence stratigraphic reference section for the Oxfordian-Tithonian succession, which hosts vast petroleum resources across the adjacent Arabian Peninsula.
The macropaleontology of the Upper Jurassic succession has attracted most previous attention, with early studies by Felix (1904), Krumbeck (1905), Renz (1930), Pfender (1937), Delpey (1940), and Hudson (1954). The micropaleontology is less well documented, with significant publications by Bischoff (1964) and Basson and Edgell (1971).
Summaries of the Upper Jurassic stratigraphy of Lebanon are provided by Zumoffen (1926), Heybroek (1942), Renouard (1951), and Dubertret (1950a, 1963, 1966, 1975), and Picard and Hirsch (1987) present an excellent up-to-date review and synthesis of previous work. The stratigraphy of the basal Cretaceous has been formalized by Walley (1983). The study area is represented by the 1:50,000 Beirut geological map sheet and accompanying explanatory memoir (Dubertret, 1951), and adjacent Upper Jurassic outcrops in the northern Anti-Lebanon (Zebdani-Rayak region) and Israeli-occupied Syria (Mount Hermon) have been described by Dubertret (1949, 1950b), Ponikarov (1967), and Toland (1998).
Details of Lebanese Upper Jurassic subsurface sections are provided in Renouard (1955) and Beydoun (1977, 1981). The paleogeographic reconstructions of May (1991) suggest a mid-shelf to outer-shelf paleo-position for the Bikfaya area, ca.10 km east (i.e., landward) of a N-S trending Jurassic shelf break. The correlation of Tethyan and Boreal Tithonian biozones as used in this study is based on Geyssant (1997) (Fig. 3).
The measured section at Bikfaya comprises at least two uppermost Jurassic depositional sequences and the lower part of a basal Cretaceous sequence (Fig. 4):
Sequence 3: basal Cretaceous (123.85–151.1 m)
Sequence 2: upper Middle-Upper Tithonian (61.1–123.85 m)
Sequence 1: Lower to lower Middle Tithonian [pre-Chitinoidella Zone] (0–61.1 m)
Sequence 1 corresponds to the “Falaise de Bikfaya” of Dubertret (1951), the “Falaise de Djisr el Qadi” of Heybroek (1942) and the “Niveau 7” of Renouard (1951). Sequence 2 corresponds to the “Calcaire de Salima” of Dubertret (1951), the “Couches Jaunes Superieur” of Heybroek (1942), and the “Niveau 8” of Renouard (1951). Sequence 3 corresponds to the lower part of the basal Cretaceous “Grés de Base” of earlier authors, and the “Chouf Sandstone Formation” of Walley (1983). In the present study thin-section biostratigraphic analysis (benthic forams, calcareous algae, calcareous dinocysts, and stromatoporoids) was undertaken at ca. 2 m intervals (Fig. 5).
Sequence 1:Lower to lower Middle Tithonian “Falaise de Bikfaya”
Sequence 1 comprises three informal members (0–61.1 m) (Fig. 4): the cliff-forming “lower member” (0–32 m), comprises medium-bedded, silt-grade peloidal packstones and stromatoporoid floatstones; a distinct 2-m-thick coral-stromatoporoid rudstone unit occurs at 15.8–17.8 m. Discrete beds of coalesced decimeter-scale chert nodules occur sporadically throughout. The sparse, moderately diverse biota recorded in this study (Fig. 5) is dominated by agglutinated foraminifera (Ammobaculites sp., Pfenderina neocomiensis-trochoidea, Pseudocyclammina lituus Yokoyama) and stromatoporoids (Actinostromarianina lecompti Hudson, Burgundia trinorchii Dehorne, Parastromatopora libani Hudson, Shuqraia zuffardi Wells), with sparse calcareous algae (Actinoporella podolica Alth, Permocalculus sp. cf. P. inopinatus Elliott, Salpingoporella annulata Carozzi, Rajkaella (=Likanella) bartheli Bernier, Campbeliella (= “Vaginella”) striata Carozzi, Lithocodium aggregatum Elliott, Terquemella sp.) and gastropods (Nerinea salinensis d’Orbigny = N. maroni Krumbeck). The associated coral assemblage described by Felix (1904) includes Actinarea sponginoides Blanckenhorn, Baryhelia hexaconena Felix, Centrastrea leptomeres Felix, C. polystila Felix, Diplocoenia punica Blanckenhorn, Latimaeandra zumoffeni Felix, L. amphitrites Felix, L. sulcata Fromentel, Metatsrea cf. delmontana Koby, Stephanocoenia pentagonalis Becker, S. helmopotis Felix, S. trochiformis d’Orbigny, Stylina girodi Etallon, and S. bullosa Blanckenhorn. The mollus-can fauna recorded by Krumbeck (1905), Delpey (1940), Heybroek (1942), and Renouard (1951) includes Ampullina vautriniDelpey, “Cardium” corallium Leymerie, Harpagodes oceani Brogniart, Lima acutorostris Krumbeck, L. densistriata Krumbeck, L. libanensis Krumbeck, Natica (= Ampullina) dido Krumbeck, N. (= Ampullina) mulitta Krumbeck, N. sp. (= Ampullina krumbecki Delpey), Nerinea maroni Krumbeck (= N. salinensis d’Orbigny), N. desvoidyi pauciplicata Krumbeck, N. sesostris (?= N. contorta var. sesostris Krumbeck), Nerinella sp. cf. N. elatior d’Orbigny, Nerita littoralis Krumbeck, Ostrea sp. cf. O. expansa Sowerby, O. matronensis De Loriol, Pachyerosma blanckenhorni Krumbeck, Pecten palmyrensis Krumbeck, and Phylobrissus thevenini Etallon.
The “lower member” is interpreted as a lower-shoreface succession, with the stromatoporoid floatstone units representing episodic storm deposits. The 2-m-thick coral-stromatoporoid rudstone unit at 15.8–17.8 m is interpreted as a subtidal biostrome. The co-occurrence of stromatoporoids and the codiacean alga L. aggregatum at 16.5 m suggests paleo-water depths on the order of 10–15 m (Banner and Simmons, 1994; Toland, 1994).
The “lower member” is conformably overlain by a “middle member” (32–47.5 m), comprising recessive, slightly argillaceous lime mudstones (grading to silt-grade peloidal packstones) and peloid-algal wackestones/packstones. This interval is characterized by abundant ramifying Thalassinoides burrows, which result in a distinct pseudo-nodular weathering fabric. The low-diversity biota is dominated by calcareous algae (Permocalculus sp. cf. P. inopinatus in flood abundance, Cylindroporella arabica Elliott, and Actinoporella podalica), ostracodes, and indeterminate exaragonitic molluscan debris. There is no precise indication of paleo-water depth, Permocalculus having a wide depth range of ca. 5–50 m (Banner and Simmons, 1994). Elsewhere in the Middle East Permocalculus is known to form important backshoal “la-goonal” buildups, as in the Rumailah Field of Southern Iraq (Gaddo, 1971). It may, thus, have occupied a niche similar to present-day halimedid-form algae, which form extensive lagoonal buildups leeward of the Great Barrier Reef (e.g., Orme and Salama, 1988).
The base of the “upper member” (47.5–61.1 m) is marked by a 0.25 m skeletal packstone rib with prominent Rhizocorallium burrows, yielding abundant P. inopinatus and occasional Rectocyclammina chouberti Hottinger. This is overlain by interbedded recessive lime mudstones and cortoid-ooid-dasyclad packstones. The lime mudstones are characterized by Thalassinoides burrow systems, and become increasingly argillaceous upsection, grading to calcareous claystones above 58.5 m. The uppermost part of this interval (58.5–61.1 m) is characterized by fine, millimeter-scale (?tidal) parallel laminae. The “upper member” biota is dominated by abundant Everticyclammina praekelleri Banner and Highton (1960) and Permocalculus inopinatus. The presence of . praekelleri in the lower part of the “upper member” suggests a shallow neritic (?upper shoreface) paleoenvironment (Banner and Highton, 1990). The strongly argillaceous upper part of the “upper member” is tentatively interpreted as a (?brackish) intertidal mudflat facies, based on the millimeter-scale (?tidal) lamination, the absence of bioturbation, the restricted biota (ostracodes and bivalves), and the complete absence of stenohaline faunal elements.
Sequence 1 is dated as no older than Early Tithonian, on the basis of the presence of P. inopinatus and A. podolica (Simmons and Al-Thour, 1994; Bassoullet, 1997). This is consistent with the presence of N. salinensis (= N. maroni) in the “lower member”, a species known from the basal Tithonian gigas Zone in Europe (Delpey, 1940). The upper part of the sequence is no younger than lowermost Upper Tithonian on the basis of a single specimen of Chitinoidella insueta Rehanek in the basal part of the overlying interval. The range of C. insueta is uppermost fallauxi to lower microcanthum Zone (Geyssant, 1997; Remane, 1997).
The interval 0–61.1 m is tentatively interpreted as a single, large-scale shoaling-up cycle, commencing with storm-influenced lower-shoreface facies (“lower member”), passing upward through subtidal Permocalculus algal-bank facies (“middle member”), culminating in intertidal facies (“upper member”). This is consistent with an aggradational-progradational highstand systems tract (HST) interpretation. The implication is that the measured section represents only the HST and not a complete depositional sequence. The TST and basal bounding surface are presumed to occur below base of section.
Sequence 2: Upper Middle to Upper Tithonian “Calcaire de Salima”
Sequence 2 (61.1–123.85 m) commences with an abrupt marine flooding surface and an associated influx of calcareous dinocysts, including Colomisphaera lapidosa Vogler, C. tenuis Nagy, Crustocadosina semiradiata Wanner, C. semiradiata olzae Nowak, Stomiosphaera sp. cf. S. moluccana Wanner, S. echinata Nowak, Cadosina fusca Wanner, C. fusca cieszynica Nowak, and Commitosphaera sublapidosa Vogler (Figs. 4, 5). This is the first record of calcareous dinocysts from Lebanon, though a very similar dinocyst assemblage occurs at about the same stratigraphic level in southern Yemen (Toland et al., 1995; Toland, unpublished data.).
The lower part of Sequence 2 (61.1–85 m) comprises recessive, strongly argillaceous silt-grade peloidal packstones and lime mudstones, with local resistant decimeter-scale interbeds of peloid-intraclast-superficial ooid packstone (Fig. 6A). The recessive silt-grade peloidal packstones and lime mudstones are characterized by local simple horizontal burrows (Planolites sp). The peloid-intraclast-ooid packstone interbeds are, in contrast, intensely bioturbated with abundant, small vertical and oblique escape burrows, and with bed tops heavily reworked by Thalassinoides networks. This is interpreted as an offshore transition zone facies association, with the resistant interbeds representing episodic storm deposits that have been biogenically reworked during fair-weather interludes. In addition to the rich dinocyst assemblage noted above, this interval has yielded agglutinated foraminifera (Everticyclammina ?praekelleri Banner and Highton, E. ?virguliana Koechlin, ?Ammobaculites sp) and, at 78 m above base of measured section, a single specimen of Chitinoidella insueta Rehánek (Fig. 5) (Bischoff, 1964) also records the ostracodes Cytherelloidea bikfayaensis Bischoff and C. salimaensis Bischoff from this interval. The age of this lower interval (61.1–85 m) can be constrained to the upper Middle Tithonian (ponti Zone)-lowermost Upper Tithonian (lower microcanthum Zone), based on the presence of C. tenuis (ponti-lower microcanthum Zone), C. sublapidosa (upper darwini to lower microcanthum Zone), and C. insueta (uppermost fallauxi-lower microcanthum Zone).
The middle part of Sequence 2 (85–100 m) is poorly exposed at this locality, being covered by scree and scrub vegetation. This recessive (?marly) unit may be the source of rare cephalopods (Phylloceras salima Krumbeck, Nautilus turcicus Krumbeck, Aspidoceras sp., Berriasella richteri Oppel) described by Felix (1904), Krumbeck (1905), and Zumoffen (1926). Dr. Michael Howarth of the Natural History Museum (London) (personal communication, 1994). has suggested that the specimen referred to as “B. richteri” may, in fact, belong to the Upper Tithonian genus, Pseudosubplanites (Zumoffen’s specimens were removed from St. Joseph’s University to the Ecole Superieure d’Ingenieure de Beyrouth (ESIB) during the recent civil war, but an attempt to trace them there in 1994 proved unsuccessful and they may now be lost.)
The upper part of Sequence 2 (100–123.85 m) is, in contrast, well exposed in the low cliffs and abandoned quarries below Mar Elias, where it comprises medium- to thick-bedded, ooid-skeletal grainstones (Fig. 6B) which coarsen and thicken upsection. These grainstones are characterized by decimeter-scale unidirectional trough and tabular-planar cross-stratification, with foreset laminae dipping consistently towards the ESE (90–130°), i.e., onshore-directed. A prominent 3.6-m-thick tabular planar cross-set at 116.1–119.7 m can be traced laterally for almost 1 km along the quarry face and adjacent hillside (Fig. 2B). This cross-set represents a straight-crested subtidal sandwave, with the set height of 3.6 m, indicating minimum paleo-water depth. This sandwave has its long axis oriented NNE-SSW, i.e., normal to the foreset dip azimuth and broadly parallel to the regional platform-margin trend. This orientation suggests a wave-dominated setting (in a tide-dominated setting, by contrast, the major bedforms would tend to be oriented normal to the margin).
Directly overlying the sandwave unit at 116.1–119.7 m above base of section is a 3.2-m-thick interval characterized by indistinct, very-low-angle, planar bedding, with high-angle trough cross-sets (119.7–122.9 m). This is very tentatively interpreted as a ridge-and-runnell foreshore facies association, with the low-angle sets perhaps representing swash laminae. Diagnostic foreshore criteria such as keystone vugs were, however, not observed. This (?)foreshore member is overlain by a thin, recessive paleosol at 122.9–123.0 m (Fig. 6C), and a thin, terminal, trough cross-stratified oolitic grainstone unit (123.0–123.85 m). The sequence is abruptly terminated at 123.85 m by a prominent, irregular paleokarst surface with up to 0.2 m vertical relief (Fig. 6C). This former exposure surface was colonized to a depth of 5 mm by iron-stained, fossil endolithic lichen colonies, representing a proto-paleosol (Fig. 6D).
The sparse microfauna in the upper part of Sequence 2 (100–123.85 m) is dominated by calcareous benthic foraminifera (Conicospirillina sp; Lenticulina sp.). An abundant and diverse macrofauna includes bivalves (Ostrea matronensis), terebratulid brachiopods, corals, crinoids, and echinoids (Fig. 6B). Krumbeck (1905) records Terebratula asiatica Krumbeck, T. beyroutiana Krumbeck, T. curtirostris Krumbeck, T. logistimata Krumbeck, T. bauhini Etallon, T. bisuffaricimta Schloth., Kingenia gutta Quenstedt, K. cubica Quenstedt, K. latifrons Krumbeck, Rhynchonella drusorum Krumbeck, Alectryonia hastellata Schloth, Mytilus alatus Krumbeck, Ceratomya excentrica Agas., Pecten lycosensis Krumbeck, Lima (= Plagiostoma) sublaeviuscula Krumbeck, Lithodomus zumoffeni Krumbeck, Turbo (Chilodonta) antonini Krumbeck, Hemipedina eliasensis Krumbeck, and Trigonia libanensis Krumbeck from this interval. The associated coral assemblage, described by Felix (1904), includes Dimorphastrea kobyi Felix, Protoseris cf. foliosa Beckmann, Stephanocoenia trochiformis d’Orbigny, Centrastrea blanckenhorni Felix, and Actinarea cf. granulata d’Orbigny. Delpey (1940) records the Tithonian gastropod Nerinea cf. zeuschneri Peters from the terminal part of the Jurassic at Bikfaya.
The significant flooding surface at 61.1 m, which marks the base of Sequence 2, is interpreted as a cryptic “shale-on-shale” sequence boundary, with open-marine transgressive mudstones resting directly on paleontologically barren (?intertidal) mud-stones of the underlying sequence. This initial marine flooding event is of inferred upper Middle Tithonian age (upper fallauxi-ponti Zone) given the presence of C. insueta 0.9 m up section. Inferred maximum flooding occurs within the Chitinoidella Zone at ca. 62 m, coincident with calcareous dinocyst species and abundance maxima. This suggests a potential correlation with a ponti Zone MFS, which has been identified at about this same stratigraphic level elsewhere in the Middle East (Toland, 1998), and a broadly coincident pectinatus Zone MFS is recognized in the northern North Sea (Partington et al., 1993). The interval 62–85 m is interpreted as a sediment-starved distal early HST with sedimentation occurring in the offshore transition zone, above storm wave base but below fair-weather wave base.
The overlying recessive unexposed unit at 85–100 m above base of section may be the source of previous ammonite finds. Alternatively, at least some of the ammonites may originate from the basal Cretaceous. Further fieldwork is required to resolve this uncertainty.
The ooid grainstones that comprise the uppermost part of the Jurassic section (100–122.9 m) could be interpreted as an aggradational HST, genetically linked to the underlying interval. Alternatively they could represent a forced regressive wedge systems tract, bounded below by a basal surface of forced regression and above by a sequence boundary. Further examination of the poorly exposed lower bounding surface is required to determine which of these two interpretations is most likely.
Sequence 3: Lower Cretaceous “Chouf Sandstone Formation” [pars]
Sequence 3 (123.85–151.1m) commences with a thin vadoid gravel (123.85–124.0 m) that infills solution hollows, pipes, and cavities in the underlying paleokarst surface; this is perhaps the same “pisolite bed” as documented by Ponikarov (1967) from the “Upper Tithonian” of Jebel Sheikh Mansour, NW Syria. This vadoid gravel represents a paleosol that may have supported conifer stands, judging by the presence of coniferous wood fragments a short distance upsection.
The basal vadoid gravel is overlain by a recessive, strongly argillaceous, oolitic wacke-ironstone bed (124–126.35 m), yielding a sparse, non-age-diagnostic biota including echinoid debris, coniferous wood fragments (Dadoxylon (= Araucarioxylon) sp.), and calcareous benthic foraminifera (“Spirillina sp.”). These wacke-ironstones may represent transgressive reworking of contemporaneous lateritic iron-rich paleosols. Basalt lava flows, which are locally present directly beneath the Chouf Sandstone at Bhannes ca. 3 km WSW of the measured section, are a potential source of iron. The Bhannes basalt has recently yielded a late Midd le to Late Tithonian radiometric age of 146.2 ± 2.5 Ma (Mike Simmons, personal communication), i.e., significantly older than the 139 ± 3 Ma Late Berriasian age recorded previously by Saint-Marc (1980).
The overlying interval 126.35–140 m is not exposed at this locality, though its recessive weathering profile suggests that it is continuous with the underlying argillaceous wacke-ironstone facies.
The uppermost part of the measured section (140–151.1 m) comprises cliff-forming, medium- to thick-bedded, sandy–ooid–peloid grainstones (Fig. 7A, B). Content of detrital quartz increases progressively upsection to a maximum of 24% bulk volume at the top of measured section. Glauconitized and phosphatized grains are also moderately common, accounting for up to 5% and 1% of bulk volume, respectively. This interval is characterized by prominent tabular-planar and trough cross-stratification, with unidirectional foresets dipping towards the east (60–110°). This is only slightly different from the ENE mean dip azimuth recorded in the underlying sequence. The presence of reactivation surfaces, clay-draped foreset laminae, and a Skolithos–Ophiomorpha–Diplocraterion ichnofauna all suggest a tide-influenced setting, with the unidirectional landward-facing foresets indicating a flood tide-dominated regime. The strong tidal signature is consistent with minimal frictional damping on a relatively narrow shelf, and supports the full separation of Apulia from the Levant by Early Cretaceous times, as suggested by Dercourt et al. (1986).
The sparse, non-age-diagnostic biota in the upper part of Sequence 3 (140–151.1 m) is dominated by echinoid debris and lituolid foraminifera (?Ammobaculites sp.), together with minor bivalve, bryozoan, and calcareous sponge debris. This is perhaps the same fauna of Haplophragmoides sp., Ammobaculites subaequalis, Pseudocyclammina sp., and Globulina sp. documented by Ponikarov (1967) from a 6-m-thick “Upper Tithonian” black marl unit at Ain Qaya, northern Anti-Lebanon. In the absence of an age-diagnostic biota, perhaps the best way of dating this interval would be Ar-Ar single-grain laser ablation radiometric dating of the glauconite and phosphate grains and/or single-grain laser ablation Sr/Sr dating of low-Mg calcite bivalve fragments.
Dubertret (1951) records a total thickness of 100–220 m for the “Grès de Base” and implies a Berriasian-Barremian age, on the basis of definitive Early Aptian echinoids and orbitolinid foraminifera in the directly overlying “Couches Orbitolina”. Heybroek (1942) assigns an Early Cretaceous age to the “Grès de Base”, and notes the occurrence of the Aptian bivalve, Trigonia syriaca, in the overlying succession cited previously by Fraas (1878) and Zumoffen (1926). A pre-Aptian Early Cretaceous age is further substantiated by the presence of the Early Aptian charophyte Atopochara trivolvis Peck in the overlying interval (Grambast and Lorsch, 1968; Tixier, 1972). The only fossils recorded previously from the “Grès de Base” itself are wood fragments (Dubertret, 1975), the Early Cretaceous (?Barremian) pteridophyte taxon Weichselia reticulata Stokes and Webb (Koert, 1924), and Barremian spores (Mroueh, 1980).
The karstified upper surface of the “Calcaire de Salima” (Sequence 2) is an abrupt, disconformable, Type 1 sequence boundary. The contact with the overlying “Grès de Base” is clearly not gradational, as has been suggested previously by numerous authors. The mature paleokarst at 123.85 m represents a prolonged period of subaerial exposure, i.e., a relative sea-level lowstand. The timing and duration of this lowstand event are poorly constrained, though it is clearly no older than (late?) Late Tithonian, and probably spans the Jurassic-Cretaceous boundary. A broadly co-incident end-Jurassic erosional hiatus is evident across much of the Arabian Plate (Toland, 1998), with the Upper Tithonian being generally absent except in some of the intra-shelf grabens of Yemen and at Chia Gara in northern Iraq (Howarth, 1992).
The thin vadoid gravel at 123.85–124.0 m represents transgressive reworking of a paleosol developed on the karstified upper surface of the “Calcaire de Salima”. This basal lag is overlain by an argillaceous oolitic wacke-ironstone bed which represents a sediment-starved drowned shelf in “catch-up” mode. The winnowing and concentration of ooids to form packstone ribs suggests water depths above storm wave base during inferred maximum flooding at ca. 124 m. The inferred relatively shallow water depths are consistent with May’s (1991) paleogeo-graphic reconstruction for the Early Cretaceous of the Eastern Mediterranean, which depicts a paleoshoreline located a short distance east of Bikfaya.
The timing of base-Cretaceous onlap is only poorly constrained by the presence of Late Tithonian taxa in the underlying section and the presence of Barremian spores in the upper part of the Chouf Sandstone Formation. Onlap may be broadly coincident with a pronounced lower Middle Berriasian (subalpina Subzone in the upper part of Calpionella Zone B) transgression evident throughout much of Arabia (Toland, 1998; Toland et al., 1993) and farther afield in NW Europe (Jan du Chene et al., 1993; Coe, 1996), though there is at present no hard evidence to substantiate this possibility.
The stacked tidal facies that form the uppermost part of the Bikfaya section (140–151.1 m) are tentatively interpreted as an Early Cretaceous HST, with the presence of glauconite and phosphate suggesting starved sedimentation. This condensed interval may represent sediment bypassing during a relative stillstand, with abundant sediment supply but no accommodation space creation. The upper sequence boundary was not observed at this locality, and is assumed to occur some distance upsection.
The upper part of the “Falaise de Bikfaya” extends into the Lower (and perhaps lower Middle) Tithonian, i.e., considerably younger than the Kimmeridgian age suggested previously.
The lower part of the “Calcaire de Salima” is precisely dated for the first time as upper Middle Tithonian (ponti Zone) on the basis of a previously undescribed, rich assemblage of calcareous dinocysts.
The Tithonian of the Bikfaya section comprises parts of at least two third-order depositional sequences and their component systems tracts.
The upper part of the “Falaise de Bikfaya” is interpreted as an aggradational-progradational highstand systems tract.
The base of the overlying “Calcaire de Salima” is a significant flooding surface of inferred upper Middle Tithonian age (upper fallauxi-ponti Zone).
A candidate maximum flooding surface (MFS) occurs ca. 1 m above the base of the “Calcaire de Salima”, coincident with planktic species and abundance maximum; this MFS is of upper Middle Tithonian ponti Zone age, i.e., broadly coincident with a ponti Zone MFS recognized elsewhere in the Middle East.
The top of the “Calcaire de Salima” is marked by a prominent paleokarst (sequence boundary) and superimposed transgressive surface corresponding to the Jurassic-Cretaceous boundary.
The timing of base-Cretaceous onlap is uncertain; it may be broadly coincident with a pronounced lowermost Middle Berriasian (subalpina Zone in the upper Calpionella Zone B) transgression evident throughout much of Arabia, though there is no hard evidence to substantiate this at present.
It is my pleasure to thank Dr. Mike Simmons (Aberdeen University) and Dr. Bruno Granier (Total) for assistance with foram and algal identifications. The late Dr. Ziad Beydoun provided generous logistical assistance in the field. Financial and logistical support for this study was provided by Halliburton Reservoir Description Services and Oolithica Geoscience.
Figures & Tables
Middle East Models of Jurassic/Cretaceous Carbonate Systems
This volume will interest tectonic modelers, stratigraphers, sedimentologists, and explorationists. It is the product of the international conference of “Jurassic/Cretaceous Carbonate Platform-Basin Systems, Middle East Models” that was convened in December 1997 jointly by SEPM (Society for Sedimentary Geology) and the United Arab Emirates University in Al Ain, United Arab Emirates. The twenty-three papers present new data and interpretations arranged in three sections: 1) sequence stratigraphy, cyclostratigraphy, chronostratigraphy, and tectonic influences, 2) depositional and diagenetic models of carbonate platforms, and 3) hydrocarbon habitat and exploration/development case studies. New tectonic models of the Arabian Basin, new stratigraphic and sequence stratigraphic reference sections, new geochemical and source rock data, and new reservoir data are presented. New geologic models make this set of papers relevant to geoscientists working outside of Arabia also.