The buried Afiq Canyon (eastern Mediterranean, Israel): a case study of a Tertiary submarine canyon exposed in Late Messinian times

ELSEVIER

Marine

Geology

123 (1995) 167-185

The buried Afiq Canyon (eastern Mediterranean, Israel): a case study of a Tertiary submarine canyon exposed in Late Messinian times Y. Druckman a, B. Buchbinder a, G.M. Martinotti a, R. Siman Tov a, P. Aharon b ’ Geological Survey of Israel, 30 Malkhe Yisrael Street, 95501 Jerusalem, Israel b Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803-4101, USA Received 23 March 1994; revision accepted 15 December 1994

Abstract

The Afiq submarine canyon was one of a series of canyons initially incised in a drowned shelf edge and slope of the eastern Mediterranean margins in early Oligocene times (PI9 zone). During most of the Early Miocene submarine erosion or non-deposition prevailed. This was followed by deposition of pelagic marls and debris flows in early Middle Miocene (NS) times. Large-scale sliding in late Middle Miocene times (N14) resulted in the collapse of the slope, the removal of most of the middle Miocene sequence and the formation of a box-shaped scar. Back-cutting incision ultimately resulted in the incision of the shelf in Late Miocene times. A sea-level fall ranging between 50 and 800 m below the canyon’s rim resulted in the deposition of the Messinian Lower Evaporites (Mavqiim Formation) within the canyon. A subsequent rise of a similar extent led to the deposition of the Upper Evaporites (Be’eri Gypsum) which are found on the canyon’s southern shoulder. The final Messinian sea-level drop, below the canyon’s floor resulted in a subaerial environment in the canyon, the erosion of the upper evaporites and the subsequent deposition of fluvial and brackish sediments (Afiq Formation). The latter correspond to the Lago-Mare sediments known throughout the Mediterranean, The rapidly rising sea level during the Pliocene along with the high rate of Nilotic elastic sedimentation resulted in the final burial of the Afiq Canyon, and a pronounced seaward progradation (20-30 km) of the shelf edge.

1. Introduction The Messinian desiccation event in the Mediterranean involved pronounced subaerial erosion that resulted in the incision of valleys and canyons along the basin’s margins (Barber, 198 1; Barr and Walker, 1973; Chumakov, 1973; Clauzon, 1979; Escutia and Maldonado, 1992; Groupe Estocade, 1978; Gvirtzrnan and Buchbinder, 1978; Rizzini et al., 1978). Little or no attention has been paid, however, to pre-Messinian incision events, their possible submarine origin and the possibility that they were reactivated as subaerial 002%3227/95/$9.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0025-3227(94)00127-8

channels during the Messinian lowstands. Certain paleobathymetric and paleogeographic aspects of the pre-Messinian history of the Mediterranean margins have been overlooked, consequently, the prevailing interpretation of the depositional and erosional history of the drainage systems along the periphery of the Mediterranean during the Messinian may have been misconceived. A thick sedimentary wedge (up to 2000 m) of fine grained elastic sediments was deposited along the coastal plain (Fig. 1) and the Mediterranean offshore areas of Israel beginning in Oligocene times. These sediments aggraded and prograded

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enabled evaluating the characteristics of erosional processes responsible for the creation of the Afiq canyon, as well as putting constraints on the range of sea-level fluctuations during the Messinian. This study demonstrates that the Afiq Canyon was formed as a result of submarine erosion. This started in Early Oligocene times and culminated in late Middle Miocene times when the slope collapsed as a result of large-scale sliding, ultimately resulting in the incision of the shelf in Late Miocene times. It also shows that the sea level fluctuated several hundred meters during the Messinian, resulting in a short period of subaerial erosion.

2. Geological background

I

%‘-,_

Fig. 1. Location map of the study area, showing the Oligocene to Miocene shelf edge and slope incised by the Afiq and Ashdod canyons.

within the region of the shelf break and continental slope. The ancient shelf-edge area is cut by a major canyon-the Afiq Channel (Neev, 1960; Gvirtzman, 1970; Gvirtzman and Buchbinder, 1978) which is filled by Oligocene to Pliocene sediments. The upper Tertiary section in the area was studied. The lithology and biostratigraphy of this section in the numerous boreholes around the Afiq Canyon and the seismic lines crossing it were examined. The carbon and strontium isotopic composition of the Messinian evaporites and of their calcitized products was also measured and interpreted. The absence of significant tectonic displacement other than subsidence and minor westward tilting across the ancient shelf edge and slope areas

The Afiq Canyon is located in the northwestern margin of the Arabian Craton (Fig. 1). This margin was marked by a distinct shelf edge throughout most of the Cretaceous, located a few kilometers inland from the present shoreline, separating shallow platform carbonates in the east from deeper-water carbonates of slope and basin origin in the west (Bein and Gvirtzman, 1977). In Senonian times the platform was drowned and pelagic chalky sedimentation prevailed in the platform area, conditions that continued until Oligocene times. Subcrop maps (Gvirtzman, 1969b) indicate that Senonian to Eocene sediments are largely missing along the slope area. It is assumed that during this period the drowned shelf edge and upper slope areas were swept by strong currents, preventing continuous accumulation of Senonian to Eocene sediments (Fig. 2). Why the platform was drowned is not clear. It is possible that the convergence of the Arabian plate with the Eurasian plate in early Senonian times caused flexure and subsidence of the platform below the photic zone. It is also possible that the onset of an upwelling system along the southern Tethys margin in Senonian times, which entailed anoxic conditions (Almogi-Labin et al., 1993) speeded the demise of benthic platform-constructing organisms. The plates’ convergence was also accompanied by Senonian to Early Oligocene folding phases

Y. Druckman et allh4arine Geology 123 (1995) 167-185

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A

A

NW

SE

NAHAL-

02 1

SAA0 1

SHUVA

1

YAFO FM. (PLIOCENE)

TELAMIM

r

FM.

El U4CONFOFMll-V

Fig. 2. A cross section perpendicular to the paleo-shelf break north of the Afiq Canyon. The 1500 m difference between the Oligocene and Middle Miocene sediments in the Saad 1 and Nahal-Oz 1 boreholes represents the Early Oligocene paleoslope. The Jurassic and Cretaceous formations between the two boreholes are not tectonically displaced. Lithologic symbols: 1 = limestone; 2 = dolostone; 3 = marlstone; 4 = conglomerate; 5 = sandstone; 6 = shale; 7= anhydrite or gypsum. N. S. = no samples.

which resulted in the formation of the Syrian Arc fold system (Krenkel, 1924; Gvirtzman, 1970). The regional picture changed during Oligocene times. Emergence of the Arabian-African Craton occurred due to an updoming phase prior to the rifting of the Red Sea. This caused a distinct change in the elastic/carbonate sedimentation ratio. The denudation of the distally elevated landmass increased the supply of elastic sediments to the depositional basins, a condition which has been continuing until present times. Sediments began to accumulate, starting in the Early Oligocene on the drowned shelf edge and slope areas after a long period of non-deposition and erosion. The occurrence of the same Early and

Late Oligocene biozones (P19/20-P22) both on the drowned shelf and on the slope indicates a difference in water depth of more than 1500 m between the Saad 1 and Nahal-Oz 1 boreholes (Fig. 2). The slope underlying the Oligocene sediments, between these two wells, reaches 15”, and even more in some other locations. The Early Cretaceous and Jurassic strata are not down faulted in the Nahal-Oz 1 borehole, thus indicating that the difference in elevation of the Oligocene sediments between the two wells reflects an erosional slope and not a younger tectonic displacement. Based on planktic foraminiferal assemblages (Pomerancblum et al., 1962), a 100-300 m water depth was interpreted for the Oligocene sediments

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canyon walls is 12” along its upper reaches and 18”-24” along its lower reaches. Northwest of the Nahal-Oz 1 borehole (Fig. 3), the morphological shape of the canyon changes significantly, from a narrow gorge into a wide ( 15 km) box-shaped valley with a flat bottom, dipping 1.8” basinwards. Compared to the upper stream profile, the height of the canyon’s walls is significantly reduced to 400-500 m, and their inclination is reduced to 9”- 14”.

in the Beeri Sulfur borehole, which is located on the southern elevated shoulder of the canyon (Fig. 3). This, in addition to the 1500 m difference in the elevation between the Oligocene sediments on the drowned shelf and slope, indicates a water depth of 1600-1800 m in the Nahal-Oz 1 borehole during Early Oligocene times. Tibor et al. (1992) who studied the subsidence history of the southern Levant margin, also interpreted the eastern Mediterranean as deep basin at in Early Miocene times. The deep water conditions combined with a steep slope and ample sediment supply set the stage for erosion processes as a result of slumping, sliding and turbidity currents, eventually resulting in the incision of submarine canyons.

3.2 The SedimentaryJill Early Oligocene-Early Miocene succession

The oldest sediments filling the canyon are of the Globigerina ampliapertura Zone (P19/20) of Early Oligocene age, thus indicating that the incision occurred prior to this age (Figs. 4, 9 and 10). These sediments unconformably overlie Early Cretaceous to Late Eocene rock units. At the point of maximum truncation it overlies the Early Cretaceous Talme Yafe Formation, whereas further downslope, along the distal portion it overlies Eocene chalks and marls (Figs. 8 and 9). The Early OligoceneEarly Miocene section seen in boreholes along the present Mediterranean coastal plain of Israel (Fig. 8) consists of pelagic marls and includes the following biozones (from bottom to top, Fig. 4): Globigerina ampliapertura

3. The Afiq Canyon 3.1 Physiography The buried Afiq Canyon trends northwest from Beer Sheva to Gaza and the offshore area (Figs. 1 and 3). The canyon is entrenched in rocks of the Eocene Avedat Group, Senonian-Paleocene Mt. Scopus Group, Cretaceous Judea Group and Talme Yafe Formation (Figs. 5-10). It ranges in width between 2 and 4 km throughout its upper course and widens abruptly to about 15 km some 4 km inland from the present Mediterranean shoreline (Figs. 3, 5-7). The canyon is filled to its rims by Oligocene to Pleistocene sediments (the Saqiye and Kurkar groups). The topographic difference between shoulders and bottom changes abruptly downstream, from 250-500 m (along its upper 20 km), to 500-1500 m (along its lower 10 km). The average slope along the upper 20 km is 0.7”, whereas along its lower 10 km it steepens to an average of 4”. The average inclination of the

(P19/20), Globorotalia opima opima (P21), Globigerina ciperoensis ciperoensis (P22), Globorotalia kugleri (N4), Globigerinita dissimilis (N5), Globigerinita stainforthi (N6) and Globigerinatella insueta (N7) (Martinotti, 1981). Reworked fora-

minifera of Cretaceous and Tertiary age and occasional pebble-sized lithoclasts are also present. A study of cutting samples from the Nahal-Oz 1 borehole (Fig. 9), revealed Oligocene hemipelagic sediments of P19-P20 zones interbedded with pebbles of Cretaceous limestones and dolostones

Fig. 3. The morphology of the Afiq submarine canyon as expressed by contours near the base of the Pliocene Yafo Formation (isopach contours are given in meters southeast of the heavy dashed line, and isochron contours, in seconds northwest of it, modified after Gelberman and Grossowicz, 1990; Gvirtzman, 1969a). Note the difference between the narrow gorge morphology in the southeast versus the rectangular box-shaped valley, representing a large-scale slump scar, basinwards. The three seismic lines (DS-307; DS-3597 and EM-83-01, Figs. 5-7) are marked with dotted lines. The locations of cross sections A-A’ (Fig. 2), D-D’ (Fig. 8), B-B’ (Fig. 9) and C-C (Fig. 10) are also shown.

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INCISION & SLUMP EVENTS SERIES

STAGES

z! i= O-

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I SHELF

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4.3 4.2 4.1

SLUMP

Fig. 4. Incision and slumping events recorded in the Afiq Canyon as related to Haq et al.% (1988) biostratigraphy, chronostratigraphy and eustatic curve. The large-scale slumping event (box-shaped heavy line) took place in late Middle Miocene time. Note that the upstream (shelf) portion of the canyon was incised only in Late Miocene times (incision # 3). The lithostratigraphic names in parenthesis refer to the equivalent formations in the Nile delta (Egypt).

(Martinotti et al., 1984). These sediments overlie the Albian-Early Cenomanian Talme Yafe Formation at the bottom of the canyon and are interpreted as debris flows. These debris flows are

directly overlain by the marls of the early Middle Miocene Praeorbulina glomerosa (N8 ) Zone (Martinotti et al., 1984), whereas earlier Miocene zones are missing thus indicating an erosive phase

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D

D ssw

NNE

NEZARIM 1

SHIQMA 1

GAZA 1

UURKAR FM.

ma

2000

*a00

-I-*-I

0

Skm

Fig. 8. D-D shore-parallel geological cross section from the Nezarim I to Gaza 1 and Shiqma 1 boreholes (for location see Fig. 3), showing the truncation of Middle Miocene biozones caused by the large-scale slumping event in late Middle Miocene times (see also Fig. 6). Datum is sea level. Lithologic symbols: I = limestone; 2 = dolostone; 3 = marlstone; 4 = conglomerate; 5 = sandstone; 6 = shale; 7 = anhydrite or gypsum. N. S. = no samples.

predating the N8 biozone (2nd erosion phase, Buchbinder et al., 1993; Fig. 4). In the Afiq-1 borehole, which is located some 9 km upstream from Nahal-Oz 1, pelagic marls of the P19/P20 biozone (Siman-Tov, 1984) directly overlie the Cenomanian Yagur Formation (Fig. 9). Upstream of the Afiq 1 borehole, however, the oldest fill includes marls and evaporites of Late Miocene age (Fig. 9). The Middle Miocene succession

Along the present shoreline of the Mediterranean, Middle Miocene sediments (biozones

N8-N14) are found on the canyon’s shoulders in the Nezarim 1 borehole (Fig. 8). However, in the Gaza 1 and Shiqma 1 drillholes (which are located on the canyon’s floor), sediments of zone N14 of late Middle Miocene age directly overlie sediments of zone N8, while zones N9-N13 are missing [except for a 10 m remnant of zone NlO-N13 reported by Martinotti (1981) in the Shiqma 1 borehole]. A sharp erosional feature, probably corresponding to the missing Middle Miocene sections is expressed on a seismic profile running along the present shoreline (Fig. 6) and on a parallel seismic section further offshore (Fig. 7).

Y. Druckman et al./MarineGeologyI23 (1995) 167-185

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500

loo0

1500

0 --

12

3

4

5lrn iziamElm[Zl~m UNCONFORMITY 1

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Fig. 9. Cross section B-B’ along the Afiq Canyon (for location see Fig. 3). The oldest fill of Early Oligocene age is found in the Afiq 1, Nahal-Oz 1 and Shiqma 1 boreholes. The Early Miocene channeling phase was followed by the deposition of debris flows in the Nahal-Oz 1 borehole. The upstream portion (to the right) is onlapped by Late Miocene sediments. The evaporites (Mavqiim Formation) correspond to the Messinian Lower Evaporites of the Mediterranean. i3C depleted carbonates replace the anhydrites in Nahal-Oz 1, Afiq 1, Afiq 2 and Shoqeda 1 (see text). The fluvio-lacustrine Afiq Formation overlies the anhydrite. It is correlated with the Lago Mare sequence in the Mediterranean. Lithologic symbols: 1 = limestone; 2 = dolostone; 3 = marlstone; 4 = conglomerate; 5 = sandstone; 6 = shale; 7= anhydrite or gypsum. N. S. = no samples.

This feature is interpreted as a large-scale slide scar which was left after the entire Middle Miocene section was removed. Sediments of biozone N8 (of earliest Middle Miocene age) were found in boreholes located in the lower reaches of the canyon, (i.e. Nahal-Oz 1, Afiq 1 and Afiq 2). They consist of pelagic marls with reworked Tertiary and Cretaceous microfossils. In the Nahal-Oz 1 borehole (Figs. 2 and 9) however, the zone also includes a 250 m thick section of conglomerates consisting of various Cretaceous and Tertiary lithoclasts which were

interpreted as debris flows because they are interbedded with pelagic marls. The lack of core samples prevents a detailed sedimentological analysis of this coarse elastic section. However, no evidence for Middle Miocene biozones younger than N8 has been recorded in the canyon. A 90-200 m thick section, without indicative microfossils, overlies biozone N8 and underlies the Late Miocene Globorotalia menardii, Globorotalia acostaensis and Globorotalia humerosa (N15, N16 and N17) zones in the Nahal-Oz 1 and Afiq 2 boreholes. This barren sequence consists of thinly

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C’

c

NE

SW BEERI 1 BEERI 2

BEERI

CANUSA 8

SHUVAl

AFIQ 1

YAFO

FM.

2000

Fig. 10. Cross section C-C across the canyon (for location see Fig. 3), showing the incised Cretaceous and Tertiary formations and the fill in the thalweg and shoulders. Datum is sea level. See Fig. 11 for detailed relations between the fill on the canyon’s floor and its shoulders. Lithologic symbols: I= limestone; 2 = dolostone; 3 = marlstone; 4 = conglomerate; 5 = sandstone; 6 = shale; 7 = anhydrite; 8 = gypsum.

bedded silty and sandy marls with fine to medium sandstone layers ranging in thickness from a decimeter to a few meters. Farther upstream in the Ahq 1 borehole, late Miocene (N17) sediments directly overlie 16 m of marls of early Middle Miocene (N8). Upstream from Afiq 1, only Late Miocene sediments are found onlapping the canyon’s floor (Siman-Tov, 1984). The Late Miocene succession

The

Late

Miocene

is represented

by

the

Globorotalia menardii, Globorotalia acostaensis and Globorotalia humerosa (N15, N16 and N17) zones

(Martinotti,

1981; Martinotti

et al., 1984; Siman-

Tov, 1984). In the canyon the sediments are 120-300 m thick consisting of silty marls overlain either by anhydrites of the Mavqiim Formation, or by diagenetic carbonates replacing Ca-sulfate (carbonates of very light carbon isotopic composition). The Mavqiim Formation was cored in the Ahq 1 borehole, where it is 115 m thick and consists of thin interbeds (l-3 cm thick) of compacted nodular anhydrite with clayey dolomite partitions; these are overlain by 3 m thick massive anhydrite, showing densely interlocked nodules with clayey dolomite partitions. Individual nodules consist of anhydrite laths, locally arranged in a semi-concentric pattern. The latter is overlain by 8 m of clotty, micritic limestone. Similar limestones

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also occur immediately below the anhydrite in the Afiq 1 and Afiq 2 boreholes, and replace the anhydrites in the Nahal-Oz 1 borehole (Fig. 9). These carbonates are significantly depleted in 13C (Table 1) and are interpreted as a bacterial sulfatereduction product of the Mavqiim sulfates. They cannot be interpreted as representing a prelude to the salinity crisis, such as the “Calcare di Base” in Sicily (McKenzie et al., 1979; Decima et al., 1988; Rouchy and Saint Martin, 1992). since they occur also above the evaporites and unlike the latter, they show no lamination. Late Miocene sediments are usually not preserved on the canyon shoulders. However, a few patches of reefal sediments were preserved in the Beeri 1, and Beeri Sulfur boreholes, while gypsum deposits of the Be’eri Gypsum Formation have been encountered on the canyon shoulders (Fig. 11) in the Be’eri SH-1, SH-4 and SH-7 boreholes (Gvirtzman, 1969b). Samples both from the anhydrite at the bottom of the canyon and from the gypsum on the southern shoulder of the canyon were analyzed for their s7Sr/s6Sr ratios (Table 2). Overlying the Mavqiim anhydrites or the carbonates which replace them, and terminating the marine succession of the Miocene, are the fluvial to brackish conglomerates, sandstones and marls

179

of the Afiq Formation. These are about 90 m thick in the Afiq 1 borehole. Further downstream the thickness of the coarse elastics is reduced and reaches about 30 m in the Nahal-Oz 1 borehole. In the Afiq 1 borehole this section consists of several cycles of upward-fining channel deposits. Each of the cycles comprises conglomerates, sandstones, shales and marls. The conglomerates consist of rounded limestone and chert pebbles in a calcareous matrix. The pebbles represent erosion products of Cretaceous and Eocene formations, which were exposed during the Neogene. The sandstone beds are cross stratified, in places showing cut-and-fill structures. The siltstones and marlstones contain some Cretaceous and Eocene carbonate lithoclasts together with quartz and chert grains with occasional lignite (Buchbinder and Sneh, 1980). The upper part of the Afiq Formation is characterized by the euryhaline ostracode Cyprideis torosa (Rosenfeld, 1977 ). The Pliocene$ll

The Pliocene Yafo Formation overlies the Afiq Formation almost filling the canyon to its rims. It consists of pelagic marls and clays. These clays were transported to the eastern Mediterranean by the Nile River, which evolved during the Late

Table 1 Carbon and oxygen isotopic composition of Late Miocene carbonates which are interpreted as a bacterial sulfate-reduction product of the Mavqiim evaporites in the Afiq canyon

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180

S Weri Sulfur

N Elderi-1 B. SH-4

B. SH-1

Bdeti-2

B. SH- 7

Canusa- 8

Afiq-1

B. SH-5

csl +lfm. 0 -100

-zoo -300 400 -500 -600 -700 Lower Evaporltes 400

I

-----

-!300 -1000’

e 1.‘

sandstone 8 conglomerate

Fig. 11. A cross section showing the relations between the Late Miocene units on the canyon’s floor and on its southern shoulder (partly modified after Gvirtzman, 1969b). Datum is sea level. The Pattish Reef (N17) on the canyon’s shoulder predates the Mavqiim Anhydrite (= the Lower Evaporites, based on their Sr isotopic ratio: 87Sr,@6Sr=0.708900-0.708915) on the canyon’s floor. These relations indicate a sea-level drop somewhere between 50 and 800 m. The position of the Be’eri Gypsum (=the Upper Evaporites, based on its Sr isotopic ratio: 87Sr/86Sr=0.708820-0.708845), on the canyon’s shoulder, indicates a subsequent rise of sea level. The fluvio-lacustrine Afiq Formation on the canyon’s floor represents the final Messinian sea-level drop, which exceeded 662 m.

Miocene and Pliocene (Chumakov, 1973; Said, 1981). The Yafo Formation exhibits a gradual thickening westward followed by an abrupt thickening across the drowned Mesozoic continental shelf. The high sedimentation rates of Nile-derived sediments exceeded both the accommodation space created due to the Pliocene sea-level rise and the subsidence rate since the Pliocene, thus resulting in a rapid basinward progradation of ca. 20 km, burying both the Afiq canyon and the preexisting slope. With the rapid Pliocene and Pleistocene sedimentation, submarine erosion along the

canyon ceased and today it is barely manifested by a very shallow morphological depression.

4. Discussion 4.1 Submarine

incision and slope failure

The Afiq Canyon was first interpreted by Neev (1960) as a pre-Neogene subaerial channel, which drained greater parts of the southern coastal plain and northern Negev. Gvirtzman (1970) and

Y. Druckman et al./Marine Geology 123 (1995) 167-185

181

Table 2 Strontium isotopic composition of Messinian anhydrites and gypsum from the Afiq Canyon

Gvirtzman and Buchbinder (1978) also related the incision of the canyon to subaerial processes, however, they interpreted its age as Middle Miocene. The present study does not support the model of repetitive uplifting and downfaulting (yo-yo tectonics) in the range of 1000 m, as proposed by Gvirtzman and Buchbinder ( 1978) to account for the deep subaerial incision of the canyon and its subsequent filling by pelagic sediments. Inferred coast-parallel faults along which such vertical movements should have taken place have neither been detected on any shore perpendicular seismic section, nor have they been expressed on sections based on borehole data (Fig. 2). The morphological setting and the relatively deep water paleobathymetry of the Oligocene sediments point to submarine erosional processes in a continental slope setting rather than to subaerial incision of an elevated plateau. The presence of Early Oligocene sediments of zone P19 on the canyon’s floor indicates that the incision predated these sediments. The age of the youngest bed rock of the canyon’s floor is Late Eocene (Globorotalia cerroazulensis, P16-P17 Zone) in the Gaza 1 and Shiqma 1 boreholes. The earliest Oligocene Zone (Cassigerinella chipolensis/ Pseudohastigerina micra, P18) is missing in the Gaza area, and is scarcely present in Israel as a whole (Martinotti, 1986). The absence of this zone indicates a pronounced erosion phase which is ultimately expressed by the formation of the Afiq submarine canyon (first erosion, Fig. 4).

Gvirtzman (1970) however, related this erosion to an Early Oligocene folding phase of the Syrian Arc system. On the other hand, Buchbinder and Martinotti (1993) assigned the oldest fill in the Ashdod canyon north of Afiq (Fig. 1) to the Globorotalia opima opima zone (P2O/P21) which span the time range of 28-34 ma, thus the time of the incision of the Ashdod canyon may correspond with Haq et al.‘s (1988) 30 ma lowstand. It should be noted, however, that the biostratigraphic dating of the canyons’ fill may be inconsistent because of the considerable reworking and redepositional processes affecting the sedimentary fill in the canyons. The stratigraphic gap between the Oligocene sediments and the Middle Miocene sediments of zone N8 indicates another submarine erosion event (2nd erosion, Fig. 4). The occurrence of debris flows (of NS Zone) in the Nahal-Oz 1, borehole supports this interpretation. The absence of Middle Miocene sediments of zones N9-N13 in the outer reaches of the canyon points to a Middle Miocene (pre N14) slumping event which resulted in the box shape of the canyon in the offshore area (Fig. 8). The eastward onlap of Late Miocene (N15-N17) sediments on the canyon’s floor indicates a strong landward incision prior to Late Miocene, eventually resulting in the capture of the shelf (3rd erosion, Fig. 4). This event signifies the maximum landward extension after ca. 30 Myr years of active canyon-life centered around the continental slope area,

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The canyon probably originated as a failure of the slope and gradually developed through mass movement processes, analogous to those proposed by Farre et al. (1983) for the Oceanographer and Baltimore canyons on the Atlantic coast of North America. Like the Atlantic canyons, the Afiq canyon also reaches its maximum relief at the paleo shelf break (Figs. l-3), supporting the possibility of a similar genesis. Similar slope-failure processes were proposed for recently active submarine canyons off northern Israel by Almagor (1993). The abrupt change in the morphology of the Afiq canyon from a narrow gorge to a wide boxshaped valley downstream (Fig. 4) is interpreted as a large-scale slump-scar from which the entire mass of sediments has been evacuated downslope. A box-shaped mega slump, remarkably similar in shape and dimensions to the Afiq canyon has been described by Garfunkel et al. (1979) from the present continental slope of Israel. Similar slump scars, though of much greater dimensions, have been observed and documented off the Mississippi Delta by Coleman et al. (1983). The Ahq slumping event is dated as pre-N14 zone because sediments of the N14 zone pave the slump scar (Fig. 8). Following Haq et al.‘s (1988) cycle chart, it places this slumping event around the boundary between super cycles TB2 and TB3. The relief resulting from this slumping event was gradually reduced by the Late Miocene sediments paving the valley’s floor, however, the ultimate filling of the valley occurred with the onset of the overwhelming Nilotic prodelta sedimentation during the Pliocene and the Pleistocene. 4.2 The Messinian sea-level_fkxtuations The relations between the various Messinian units in the Be’eri area is clearly exhibited along a cross section perpendicular to the canyon from the canyon’s floor to its southern shoulder (Fig. 11). The units involved include the Pattish reef (Buchbinder et al., 1993) and the Be’eri Gypsum (Gvirtzman, 1970) on the south shoulder of the canyon, and the Mavqiim anhydrites and the Afiq elastics on the canyon’s floor. Although the canyon is entrenched on the flank of the Be’eri anticlinal

structure in this area (a burried fold structure of the Syrian Arc system), there is no significant vertical displacement between the canyon’s floor and its shoulder (Figs. 5, 10 and 11). The section on Fig. 11, therefore, expresses a genuine erosion feature and the elevation differences between the Late Miocene units on the floor and the shoulder can be used as a dip-stick for sea-level reconstruction. The Pattish reef in the Be’eri Sulfur borehole consists of 32 m of dolomitized poritid corals and coralline algae of Late Miocene-N17 age (Buchbinder, 1975; Buchbinder et al., 1993). Between the Be’eri Sulfur and Be’eri 1 boreholes the reef downsteps towards the canyon, indicating a sea-level drop of at least 50 m. It is assumed that the continuation of this drop eventually led, to the deposition of the Mavqiim anhydrite on the canyon’s floor. The total drop could not have exceeded 813 m, i.e., the difference in elevation between the Pattish Reef and the top of the Mavqiim anhydrites in the canyon. Assuming that the Mavqiim anhydrites were deposited under submarine conditions (Neev, 1979; Cohen, 1987; Buchbinder et al., 1993) though of unknown depth, the drop must have been greater than 50 m (the drop reflected by down-stepped reef in Be’eri 1) and smaller than 813 m. On the other hand, assuming a subaerial origin for the evaporites (Sabkha model, Buchbinder and Gvirtzman, 1978) the drop would then have to be some 813 m. The coalesced nodules (in the cores of the Atiq 1 borehole) solely, cannot be taken as an unequivocal argument in favour of a sabkha origin. Cohen ( 1987) indicated the association of coalesced nodules together with sedimentary features indicating a subaqueous origin for the Mavqiim anhydrites in the Ashdod canyon. The 87Sr/86Sr results for the Mavqiim anhydrite on the canyon’s floor (0.708900-0.708915, Table 2) are in good agreement with the Sr isotopic data obtained for the Messinian Lower Evaporites (the lower gypsum and main salt) from Sicily and the DSDP Sites 374 and 376 in the eastern Mediterranean basin (Muller and Mueller, 1991). The Sr isotopic ratio of the Be’eri Gypsum on the canyon’s shoulder (0.708820-0.708845, Table 2), however, is consistent with values obtained for the

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Upper Evaporites (Muller and Mueller 1991) in Sicily. Since the Mavqiim anhydrite on the canyon’s floor represents the Mediterranean Lower Evaporite, it implies that the sea-level drop did not exceed 813 m during the deposition of the Lower Evaporites in the canyon. The location of the Upper Evaporites (Fig. 11) on the canyon’s shoulder in Be’eri S.H-1, 662 m above the evaporites in the canyon’s floor implies, however, that during their deposition sea level rose 662 m or more, above the canyon’s floor. The fact that the Be’eri Gypsum rests directly uppon an eroded surface may indicate a syn-Mavqiim erosion (4th erosion, Fig. 4) strengthening the possibility of a significant down-drop during the Mavqiim deposition. Similar relations between sea-level fluctuations and the Lower and Upper Evaporites were interpreted by Rouchy and Saint Martin ( 1992) based on their observations in the western Mediterranean. The Lower Evaporites within the canyon are directly overlain by the fluvial and lacustrine deposits of the Afiq Formation (Buchbinder and Sneh, 1980) thus indicating, for the first time, a non-marine environment within the Afiq canyon. The Afiq elastics postdate the Be’eri Gypsum deposited on the canyon’s shoulders (Fig. 1I), indicating a substantial sea-level drop after the deposition of the Upper Evaporites (Be’eri Gypsum). The erosion resulting from this drop (5th erosion, Fig. 4) was probably responsible for the absence of an Upper Evaporite section on the canyon’s floor. Because the Afiq elastics on the canyon’s floor are terrestrial, sea level must have dropped at least 662 m below the level of the Upper Evaporite. However, it could not have been much more, because a lower base level (below the canyon’s floor) would have resulted in either erosion or non deposition, rather than fluvial accretion. The absence of erosional channeling features immediately below the base of the Pliocene Yafo Formation in the canyon (on the seismic lines crossing the canyon, Figs. 6 and 7) supports this assumption. The fine elastics containing the euryhaline ostracods of the Afiq Formation correspond to the Lago-Mare deposits known throughout the entire Mediterranean (e.g. Hsii et al., 1978; McCulloch

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and De Deckker, 1989) which predate the establishment of the Pliocene normal, deep marine conditions. Deep erosion channels cut into the latest Messinian evaporites and filled with conglomerates overlain by marine Pliocene marls have been reported from Crete (Delrieu et al., 1993). Likewise, a fluvial channeling pattern cutting into the Messinian evaporites was observed on seismic lines in the northern Tyrrhenian Sea (Millot, 1979). The fluvial nature of part of the Afiq Formation clearly implies a subaerial drainage system capable of transporting coarse elastics (sands and gravels) over great distances, thus indicating a dramatic change from an arid climate during the deposition of the evaporites to more humid conditions. The increase in the quantity of runoff caused the dilution of the Late Messinian brines, resulting in the deposition of the euryhaline Lago-Mare sediments in the Mediterranean (see also Rouchy and Saint Martin, 1992). These sediments were deposited during lowstand conditions in the Mediterranean, which was completely isolated from the Atlantic Ocean at that time (Rouchy and Saint Martin, 1992). This short-lived euryhaline event terminated with the rapidly rising Pliocene sea level.

5. Conclusions ( 1) The Cenomanian-Turonian shelf edge, located 5-10 km inland from the present Mediterranean coastline, was drowned in Senonian times and remained drowned throughout most the Tertiary. (2) The Afiq submarine canyon was incised into the drowned shelf edge and slope during the Early Oligocene (P 19 Zone). (3) Large-scale sliding across the slope in the late Middle Miocene (N14) left a box-shaped scar. (4) Back-cut incision in Late Miocene times resulted in capture of the shelf. (5) The deposition of the Messinian Lower Evaporites (Mavqi’im Formation) on the canyon’s floor is interpreted as a result of a sea-level fall to below the canyon’s shoulders not exceeding 813 m, and the deposition of the Upper Evaporite

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(Be’eri Gypsum) on the canyon shoulders, as a result of a subsequent rise of 662 m or more. (6) Fluvial sediments (the Atiq Formation) which overlie the Messinian evaporites indicate a sea-level drop of at least 662 m after the deposition of the Upper Evaporites. (7) The fluvial deposition marks a considerable increase in runoff, eventually resulting in the deposition of the euryhaline Lago-Mare sequence throughout the Mediterranean. (8) A Pliocene sea-level rise and high rate of Nilotic elastic sedimentation caused the final burial of the Afiq Canyon, and a 20-30 km seaward progradation of the shelf edge.

Acknowledgements The authors greatfuly appreciate J.M. Rouchy and S.B. Schreiber for the painful task of critically reading the manuscript. Their knowledgeable remarks and comments helped us improve the manuscript. We also thank A. Peer and N. Shragai who have drafted the figures, and B. Katz for editing the manuscript. The Israel Ministry of Energy and Infrastructure is acknowledged for the permission to publish the seismic lines, and the Israel National Oil Company is appreciated for granting us permission to use the data from the Shiqma 1 well. This study was carried out at the Geological Survey of Israel project no. 21982.

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