The Miocene Pakhna Formation, southern Cyprus and its relationship to the Neogene tectonic evolution of the Eastern Mediterranean

Sedimentary Geology, 86 (1993) 273-296

273

Elsevier Science Publishers B.V., Amsterdam

The Miocene Pakhna Formation, southern Cyprus and its relationship to the Neogene tectonic evolution of the Eastern Mediterranean Simon E a t o n

a, Alastair R o b e r t s o n

b

a Brunei Shell Petroleum Co., Seria 7082, Darussalam, Sultanate of Brunei b Department of Geology and Geophysics, West Mains Road, Edinburgh EH9 3J~, Scotland, UK Received November 5, 1991; revised version accepted November 23, 1992

ABSTRACT Eaton, S. and Robertson, A.H.F., 1993. The Miocene Pakhna Formation, southern Cyprus and its relationship to the Neogene tectonic evolution of the Eastern Mediterranean. Sediment. Geol., 86: 273-296. The Miocene Pakhna Formation is interpreted as relating to onset of the present northward subduction of the African plate beneath Cyprus and is, thus, critical to understanding of the Neogene evolution of the Eastern Mediterranean basin. Following a period of deep-water pelagic chalk deposition in the Late Eocene and Oligocene (Upper Lefkara Fm.), the Pakhna Formation records heterogeneous, mainly carbonate, sedimentation. The Pakhna Formation is bounded by the Limassol Forest Block, an uplifted ophiolitic terrain to the north, and by the Akrotiri High, a ridge of exotic Mesozoic lithoiogies to the south. Two sub-basins, Maroni in the E and Khalassa in the W, within the Pakhna Formation were separated by the WNW-ESE-trending Yerasa lineament, located near the S margin of the ophiolite. In most areas, the Pakhna Formation overlies the Lefkara Formation disconformably. The succession begins with deep-water pelagic carbonates and shows increased input of shallow-water bioclastic and terrigenous sediment upward. During the Early to mid-Miocene, the ophiolitic terrain to the N was uplifted, deformed and eroded, followed by marine transgression and patch-reef development in the Tortonian (Late Miocene). Ophiolite-derived clastics were mixed with shallow-water bioclastic sediment, reworked in a high-energy coastal setting and transported downslope within channels into the basin, accumulating as massive sands, debris flows and calciturbidites. In the Maroni sub-basin, localised debris aprons prograded into a pelagic carbonate environment to the SE. Further west, in the Khalassa sub-basin, little uplift occurred along the basin margins and redeposited sediment was mainly bioclastic. Contrasting sediment, including chert, was derived from the allochthonous Mamonia Complex, exposed on the Akrotiri High to the S and its possible offshore extension. Bioclastic sediment, including reef talus, was also derived from an intrabasinal high in the Khalassa sub-basin. Eventually, normal marine deposition was ended by the Messinian salinity crisis.

Introduction

Miocene sedimentary rocks of southern Cyprus, known as the Pakhna Formation, include a range of shallow- to deeper-water carbonates and subordinate terrigenous sediments, that were mainly deposited by pelagic and gravity-con-

Correspondence to: A.H.F. Robertson, Department of Geology and Geophysics, West Mains Road, Edinburgh EH9 3JW, Scotland, UK.

trolled processes. Southern Cyprus is currently located on the upper plate of a northward-dipping, acti~,e subduction zone (Jackson and McKenzie, 1984; Kempler and Ben Avraham, 1987; Fig. 1), but the earlier history of this subduction zone, particularly its time of initiation is poorly constrained, although critical to understanding of the Neogene tectonic evolution of the Eastern Mediterranean. In southern Cyprus Early Tertiary deep-water pelagic carbonate sedimentation of the Lefkara Formation gave way to much more variable, tectonically controlled deposition

0037-0738/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved

274

S. E A T O N A N D A. R O B E R T S O N

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in the Early Miocene. It is probable that this change was related to onset of the present cycle of northward subduction beneath Cyprus (Robertson, 1990). The purpose of this paper is to document and interpret the palaeoenvironments and local tectonic setting of southern Cyprus in the Miocene.

Regional structural setting The present-day Cyprus active margin forms the northern margin of the African plate, extending westward along the Hellenic trench system, into the Western Mediterranean (Fig. 1, inset; McKenzie, 1978; Jackson and McKenzie, 1984).

Sedimentological and structural evidence from southeastern Crete (Iapetra area) shows that a compressional regime dominated, at least during Late Serravallian-Early Tortonian time, and this may be related to Mid Miocene activation of the Hellenic trench system (Monogiou, 1989; Drinia, 1989). Also, in the Western Mediterranean, the Tyrrhenian Sea began to rift as a marginal basin above a northwestward-dipping subduction zone in Tortonian time (Late Miocene) (Kastens et al., 1988; Robertson et al., 1990). In Cyprus, Late Cretaceous ophiolite genesis and initial covering by deep-sea sediments (lower part of the Perapedhi Formation), was followed by rotation of the Troodos microplate, although

THE

MIOCENE

PAKHNA

FORMATION,

SOUTHERN

275

CYPRUS

to the north of a prominent east-west-trending fossil oceanic transform fault zone (Simonian and Gass, 1978), now termed the South Troodos Transform Fault Zone (MacLeod, 1990; Fig. 3C). To the south of this fault zone is the Limassol Forest Block, which may have originated at a separate spreading axis ("anti-Troodos plate"; Fig. 4). It is important to recognise the distinction between various basement ophiolite blocks, because older lineaments were tectonically reactivated during the Miocene (Fig. 3D). During the Early-Middle Miocene, the ophiolitic terrain of the Limassol Forest Block was deformed and thrust southward over the Early Tertiary sedimentary cover, giving rise to the "Yerasa fold and thrust belt" (Morel, 1960; Figs. 5, 6). Four WNW-ESE-trending structural lineaments are recognised (Eaton, 1987; Robertson et al., 1991), comprising from west to east: the Akrotiri lineament, the Yerasa lineament, the Ayia Mavri lineament (Fig. 2), and, further east the Petounda lineament (Fig. 3B). Emergence and

this had ended by Early Eocene time (Clube et al., 1985; Clube and Robertson, 1986). During the Late Eocene and Oligocene, deposition of deepwater chalks of the Upper Lefkara Formation covered a relict sea-floor topography in a relatively quiescent tectonic setting, with no regional evidence of contemporaneous subduction (Robertson, 1976). However, an abrupt change to more localised, tectonically controlled deposition took place in the Early Miocene, initiating deposition of the Pakhna Formation. We suggest that this change corresponds to onset of the present cycle of northward subduction beneath southern Cyprus. The Pakhna Formation crops out widely throughout southern Cyprus and is bounded by the Troodos ophiolitic terrain to the north and by the Akrotiri Peninsula and the Mediterranean Sea to the south (Figs. 2, 3A, 3B; Robertson et al., 1991). The ophiolitic terrain is divided into two parts. In the north and west is the main outcrop of the Troodos ophiolite. This is located

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Fig. 2. Major structural elements and geological units of Cyprus. This paper focusses on the central southern Cyprus area. Note the location of the depositional sub-basins and the position of structural lineaments.

276

S. E A T O N A N D A. R O B E R T S O N

erosion of the Yerasa lineament, and probably also of the Akrotiri High to the south, was followed by marine transgression in the Tortonian. By this time the Yerasa lineament had stabilised, but faulting continued along the Ayia Mavri lineament into the Messinian and Early Pliocene (McCallum, 1989; Fig. 2). During the Miocene, the Yerasa lineament divided the overall Pakhna \ \ \ \

basin of southern Cyprus into two linked subbasins, the Maroni sub-basin in the east and the Khalassa sub-basin in the west. Along the northern and eastern margins of the Troodos ophiolite, the Pakhna Formation is underlain by complete successions of Late Cretaceous to Oligocene deep-water pelagic limestones and calciturbidites of the Lefkara Formation (Ro-

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Fig. 3. Tectonic setting of the Pakhna Formation. (A) Regional plate tectonic setting (modified after McCallum and Robertson, 1990). (B) Miocene active tectonic lineaments of Cyprus. (C) Inferred structure of southern Cyprus during Late Cretaceous ophiolite genesis and juxtaposition with Mesozoic allochthonous units (Mamonia Complex and Moni melange) (modified after Clube and Robertson, 1986). (D) Miocene tectonic setting of southern Cyprus during deposition of the Pakhna Formation.

THE MIOCENEPAKHNAFORMATION,SOUTHERNCYPRUS FACIES ASSOCIATIONS PERIPHERAL SANDS GULLIED SLOPE :~

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Fig. 4. Outline geological map showing the main features of the geology of southern Cyprus and the distribution of facies associations.

bertson and Hudson, 1974; Robertson, 1976). These deep-water carbonates overlie Late Cretaceous metalliferous mudstones, radiolarites and volcanogenic clays of the Perapedhi Formation, which, in turn, rest depositionally on the highest

extrusives of the Troodos ophiolite. By contrast, in the study area to the south of the ophiolitic terrain, the Lefkara Formation and, in places the Pakhna Formation unconformably overlie the Moni melange (Fig. 4), which is composed of

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278

S. E A T O N A N D A. R O B E R T S O N

~ ]

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Fig. 6. Thinning of the Late Miocene Koronia Member southward away from the Yerasa lineament in the western part of the Khalassa sub-basin.

Late Cretaceous volcanogenic clays, with exotic blocks of Mesozoic rocks (Robertson, 1977c; Fig. 2). Further south still, allochthonous Mesozoic rocks, similar to the Mamonia Complex of SW Cyprus (Lapierre, 1975; Swarbrick, 1980), crop out below the southern cliffs of the Akrotiri Peninsula (Morel, 1960; Fig. 4). Borehole data also reveal a marked unconformity between Pliocene sediments and underlying, exotic Mesozoic lithologies (Hadjistavrinou and Constantinou, 1977). The Mamonia Complex probably formed the basement of the Pakhna Formation in southern coastal Cyprus and offshore areas.

et al., 1991). Limited data for southern Cyprus indicate ages ranging from Burdigalian (N 6) to Langhian (N 9), implying that the base of the formation is diachronous. Sedimentation appears to have persisted through the Langhian, Serravallian and Tortonian. Near the top of the succession, a prominent lithified chalk, containing Discospirina has been dated as lower Messinian (Baroz and Bizon, 1977; Orszag-Sperber et al., 1980, 1989). The overlying evaporites of the Kalavasos Formation are similar to the Messinian evaporites elsewhere in the Mediterranean (Hsii, 1973; Hsii et al., 1978).

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Stratigraphy •

Two members are recognised regionally within the Pakhna Formation: the Early Miocene Terra Member and the Late Miocene Koronia Member. The Pakhna Formation is overlain by the evaporitic Kalavasos Formation (Follows and Robertson, 1990)• The Terra Member is, however, absent from the study area in central southern Cyprus. The biostratigraphy of the Pakhna Formation (Fig. 7) is based mainly on published planktonic and benthic foraminifera, calcareous nannoplankton and shelly fossils (Adams, 1959; Bagnall, 1960; Mantis, 1970a, b; Hadjistavrinou, 1974, 1975; Greitzer and Constantinou, 1977), supplemented by unpublished studies (Herguera, 1982; Ortiz, 1982; Haskett, 1984; Philpott, 1984; Urquhart, 1984; H. Stowe, pers. commun, to S. Eaton, 1987)• Details are summarised in Eaton (1987). In northern and southeastern Cyprus, the base of the Pakhna Formation appears to be of Aquitanian age (N 4) (Follows, 1990; Robertson

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Fig. 7. Stratigraphy and age o f the Miocene successions o f southern Cyprus.

THE MIOCENE PAKHNA FORMATION, S O U T H E R N CYPRUS

279

terrain. However, north-directed palaeocurrents were also noted, locally, in the south of the area. Slump data were reported from southern Cyprus by Farrell and Eaton (1987; Fig. 9) and indicate a Miocene palaeoslope directed toward the south, away from the ophiolitic terrain during the Miocene. However, there are two exceptions. First, at Ayia Phyla, northwest of Limassol, interpreted as a basin-margin setting, slumps within massive calcarenites are intimately associated with debris flows (Fig. 10). Toward the north, the slumps show increasing rotation and break-up and then pass into disorganised matrix-supported debris-flows. These features are interpreted as a single depositional event, related to transport on a northward-dipping palaeoslope. Secondly, near the top of the Happy Valley road section (Fig. 8), small-scale shear planes in bedded calcarenites beneath a prominent debris flow indicate displacement towards the north (Fig. 11). This is interpreted as the result of frictional drag on a northward-dipping palaeoslope. Small-scale softsediment folds in associated bedded sediment also verge toward the north in this succession. In summary, most data indicate a palaeoslope dipping inward, into a basin sited between the ophiolitic terrain in the north and the Akrotiri High in the south, within both the Maroni and Khalassa sub-basins.

Morphology of the basin

The three-dimensional morphology and sedimentation of the Pakhna Formation can be inferred from evidence of regional thickness variations, palaeocurrent data, slump orientations and provenance studies, combined with facies analysis, which is discussed later. Bagnall (1960) constructed an isopach map for the Pakhna Formation to the east of Limassol. This revealed an elongate, NE-SW-trending basin with a depocentre towards the SE, near Ayios Theodoros (Fig. 8). The evaporites of the Kalavasos Formation, which are also considered to have precipitated within the Maroni sub-basin, show further thickening to the southeast and thus it is probable that the true depocentre lies in the vicinity of Maroni, or offshore (Fig. 8). Insufficient thickness data are available to construct an isopach map for the westerly outcrop areas (north and northwest of Limassol). Palaeocurrent directions in the calciturbidites are rare, due to limited exposure of bed soles, lack of three-dimensional outcrop, destruction of structures by burrowing and the original rarity of bottom structures and micro-cross-lamination in calciturbidites. Available palaeocurrent data are, however, shown in Fig. 9, mainly ripple-crosslamination, and some clast imbrication. Sole marks could be measured at only one locality. In some places, it was only possible to measure an approximate palaeocurrent direction. The palaeocurrent data collected indicate transport dominantly from the north, away from the ophiolitic ,/ /

Facies associations

Four facies associations are recognised within the Pakhna Formation (Fig. 12). From proximal

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Fig. 8. Outline map of southern Cyprus showing the places mentioned in the text.

280

s . E A T O N A N D A. R O B E R T S O N

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Fig. 9. Sediment trans)ort indicators. Palaeocurrent determinations are from: 1 = Ay. Therapon, 2 = Kandou, 3 = Ypsonas, 4 = Ayia Phyla, 5 = Yermasoyia, 6 = Moutayiaka, 7 = Parekklisha, 8 = A m a t h u s (Pliocene), 9 = Tokhni, 10 = Khirokitia (Pliocene), l ! = Kophinou, 12 = Psematismenos. Determinations from cross-lamination except (2) from flutes, and (10), (11) from clast imbrication. Large arrows show the best constrained data. Measured in Miocene successions, except where indicated. Slumps are shown (thin arrows) from a n u m b e r of the above-listed localities, also from Happy Valley ( 1 3 ) , Ayios Theodhoros ( 1 4 ) and Petounda Point ( 1 5 ) . Note the opposing slope directions.

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Fig. 11. Line drawing of the toe of a debris flow at Happy Valley (see Fig. 4 for location). Note the south to north sense of displacement.

281

THE MIOCENE PAKHNA FORMATION, SOUTHERN CYPRUS

S

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PRESENT DAY EROSIONALSURFACE

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Fig. 12. Sketch section showing the inferred spatial relationships of the five facies associations, to the south of the Yerasa lineament (Maroni sub-basin). Note the shallowing-upward sequence and presence of margin facies, both to the north and south. Not to scale.

to distal, these are: (i) the Peripheral Sands Association; (ii) the Gullied-slope Association; (iii) the Channel-fill Association; (iv) the Basin-margin Association and (v) the Basin-plain Association. Peripheral Sands Association The Peripheral Sands Association is poorly developed, due to uplift and non-deposition along the northern margin of the Maroni sub-basin in the Early-Middle Miocene and is represented only by the Late Miocene Koronia Member (Follows, 1990). Exposures are mainly located along the south margin of the Yerasa lineament, south of the ophiolitic terrain (Fig. 2). The Peripheral Sands Association consists of amalgamated, massive calcarenites in local successions up to 12 m thick. Bedding, where visible, is 50-100 cm thick. In general, the deposits are homogeneous, coarse-grained bioclastic grainstones (Figs. 13c, 13d). Locally, graded calcarenites occur in laterally continuous, parallel beds, 30-50 cm thick. Thalassinoides burrows are occasionally seen. Provenance studies indicate three sources for the clastic sediment: (i) from marginal shallowwater areas; (ii) from the Troodos ophiolitic terrain to the north; and (iii) from the allochthonous Mamonia Complex to the south. Shallow-water bioclastic sediment was largely derived from patch-reefs and benthic foramini-

feral sands, sited along the southern flank of the ophiolitic terrain (Robertson, 1977a; Eaton, 1987; Follows, 1990; Follows, 1992; Follows et al., 1992). However, coarse shallow-water bioclastic sediment was also derived from the south, from evidence of the southerly outcrops of the Pakhna Formation. Ophiolite-derived sediment is present in the Peripheral Sands Association along the margin of the ophiolitic terrain and within redeposited units further south, in the Maroni sub-basin, but is rare, or absent in successions further east, in the Khalassa sub-basin (e.g. Kouris River, Fig. 8). Pebble- to cobble-sized clasts of weathered basalt, diabase (dolerite), rare metalliferous chert, chalk (partly chertified) and poritid coral are present. The non-carbonate component of associated sandstones contains feldspar aggregates, clinopyroxene crystals and rare, clear quartz (sometimes with inclusions of epidote and reddish chert), interlava ferruginous chert ("jasper"; Boyle, 1984), silicified metalliferous sediment (umber), radiolarite of the Perapedhi Formation (Robertson and Hudson, 1974) and replacement chert of the Middle Lefkara Formation (Robertson, 1977b). In addition, less resistant lithologies from higher in the sequence are well represented, particularly unsilicified chalks from the Upper Lefkara Formation (Robertson, 1976) and the Pakhna Formation. Gabbro and ultramafic rocks (e.g. serpentinite) are absent, indicating that deep erosion of the ophiolitic terrain to the north did not take place in the Miocene. In summary, clastic material found mainly along the north margin of the Maroni sub-basin was derived from the upper levels of the ophiolite and its sedimentary cover. Contrasting clastic material was derived from the south. Seven types of siliceous pebble were extracted from redeposited, graded calcarenites, as follows. (i) Very common, well-rounded pebbles of yellowish, translucent microcrystalline quartz, up to 10 mm across. (ii) Very common, angular, to well-rounded grains of unstrained monocrystalline quartz, up to 3 mm across. (iii) Common, well-rounded pebbles of translucent, yellow radiolarian chert, up to 10 mm across. (iv) Common, well-rounded argillaceous quartzose

282

S E A T O N A N D A. R O B E R T S O N

siltstone, up to 10 mm across, with sub-angular silt grains. (v) Rare, mature quartzitic intraclasts, up to 5 mm across, with well compacted sub-angular, to rounded, to angular quartz grains and a silica cement. (vi) Rare, rounded aggregates of strained and sutured micro- and mega-quartz, up to 3 mm across, sometimes showing preferred grain orientation. (vii) Very rare, sub-angular to

well-rounded chert, with relict peloidal texture, preserved as micro-quartz and chalcedonic quartz. These pebble types are dissimilar to lithologies of the sedimentary cover of the ophiolite to the north, but can be matched with lithologies in the allochthonous Mamonia Complex. This is widely exposed in SW Cyprus (e.g. Lapierre, 1975; Swarbrick, 1980), more locally in SE Cyprus (Para-

k

i iii '

Fig. 13. Field photographs and photomicrographs.(a) N-dipping thrust in the Limassol Forest Block,juxtaposing microgabbrosover pillow breccias; east of Apsiou village. (b) View west showing Miocene unconformityon the Yerasa lineament. Shallow-dipping Pakhna Formation sediments overstep steeper-dipping Lefkara sediments to the north (right-hand side of the photo). (c) Bioclastic calciturbidite-containing grains of coralline algae, benthic foraminifera and echinoderms; plane polarised light. (d) Laminated pelsparite from the top of the Pakhna Formation, near Kalavasos; Maroni sub-basin. Plane polarised light.

283

THE MIOCENE PAKHNA FORMATION, SOUTHERN CYPRUS

Fig. 13 (continued) limni Melange; Follows and Robertson, 1990) and as small exposures of radiolarian Chert along the south coast of the Akrotiri Peninsula (Morel, 1960). Mamonia Complex-type exotic rocks were also cored in boreholes near Akrotiri village (Hadjistavrinou and Constantinou, 1977); this area is the obvious source of southerly derived clastic material in the Pakhna Formation.

Gullied-slope Association Mapping has shown that dominantly hemipelagic successions pass laterally (i.e. along

palaeoslope) into coarser-grained channelised units (Eaton, 1987), as follows. (i) Fine-grained successions. Fine-grained successions are mainly bioturbated foraminiferal chalks, silty marlstones and laminated calcilutites, which become more abundant toward the top of the Pakhna Formation (Fig. 14a). Successions are thin (up to 100 m), relative to the more basinal successions described below. Rare, graded calcarenites, containing reworked neritic and pelagic components are also present. Successions commonly pass gradationally downward into chalks of

284

s. EATON AND A. ROBERTSON

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the "Lefkara Formation and pass upward into laminated, basinal gypsum of the Kalavasos Formation. Toward the top of the fine-grained succession, bioturbation diminishes and laminated calcilutites predominate. (ii) Channel-fill successions. Channel-fill successions of two ages are present in the Pakhna Formation. The larger and more spectacular channels (i.e. at Khirokitia and Amathus, Fig. 8) include terrigenous muds with calcareous nanno-

plankton of Late Pliocene age (Houghton et al., 1990), incised into Miocene successions. A number of other channelised units, however, are undoubtedly within the Pakhna Formation. One of the best examples of such Miocene channels is exposed at Tokhni quarry (Figs. 15a, 15b), where a c. 30 m-thick vertical succession (Fig. 14b) comprises massive calcarenites, clastsupported polymict conglomerates and minor, thin marlstones (Fig. 15c). Although channel mar-

THE MIOCENE PAKHNA FORMATION, SOUTHERN CYPRUS

285

7ig. 15. Field photographs. (a) Thinning-upward channel-fill sequence of massive calcarenites at Tokhni (quarry face, foreground). Scarp slope in the distance is Pakhna Formation marlstones and laminated calcilutites capped conformably by gypsum of the Kalavasos Formation. Note the inclined surfaces in the lower part of the unit. (b) Inverse grading in a conglomerate of reworked carbonate clasts, including Miocene coral and igneous clasts derived from ophiolitic basement to the north. Near Tokhni, Maroni sub-basin. (c) Massive channelised calcarenites at Tokhni.

Dominates lower part of Pakhna Fro., above Lefkara Fm., often near exposed ophiolite.

Becomes more abundant upwards in all areas and includes dark organic-rich mudstones, brown-yellow where weathered, and thus only easily recognisable in fresh outcrops.

Restricted to the uppermost part of the Pakhna Fm. and continuing up to the base of the overlying evaporitic Kalavasos Fm.

Lime mudstone

Marlstone

Laminated calcilutite

Occurrence

Poorly exposed, millimetre-scale, parallel lamination; brown or grey fissile, with fossil plant material and fish scales; sponge spicule and foraminifera also present; little or no bioturbation.

Thin- to medium-thick (550 cm), laterally continuous beds of marls and silty marls; argillaceous content leads to recessive weathering; Planolites- and Chon'drites-type trace fossils; fine-grained plant material and rare carbonised wood.

Light grey, grey brown homogeneous lime mudstones. Beds laterally continuous (20-50 cm), with Planolites, Chondrites and Zoophycos and Teichichnus trace fossils; bioturbation extensive.

Field character

Summary of the main facies of the Pakhna Formation

TABLE 1

Microcrystalline argillaceous carbonate, with silt-grade forum tests (benthic and pelagic), sponge spicules, minor detrital quartz and feldspar grains. The lamination reflects marly/silty compositional variation, or preferential partings along surfaces rich in detrital plant material.

Similar to lime mudstones, but with greater argillaceous content. Planktonic forum tests are generally uncemented, either hollow, or infilled with mud or calcite cement. Other minerals present: quartz, kaolinite, smectite, palygorskite and traces of chlorite/illite.

Globigerinid wackestones and mudstones with a micritic matrix; traces of kaolinite, smectire, palygorskite; calcareous nannoplankton abundant; forums well preserved, mud-filled or with internal calcite cement.

Petrology

Relatively deep-water setting; lamination suggests deposition in quiet, protected waters above storm base; plant material is well preserved; the argillaceous component was introduced by dilute turbidity currents.

Biogenic carbonate content is diluted by silicate material; marl-filled burrows penetrate lime mudstone and highlight facies differences. Burial diagenesis leads to stylolitic pressure solution seams.

Dominantly planktonic foram assemblage, with deep-water trace fossils; mud-filled forums in more burrowed intervals; bedding-parallel solution seams relate to burial diagenesis (more than 300 m).

Comments

Deposited in a shallowingupward, quiet marine setting, with pelagic and terrigenous inputs; oxygen-deficient bottom waters with suppressed benthic activity; transitional upwards to Messi nian evaporites.

Deep-sea deposition similar to the lime mudstone, but with a higher proportion of silicate minerals and redeposited plant material; the difference reflects local tectonism a n d / o r global eustatic sea-level change.

Open marine pelagic deposition in an outer shelf, to bathyal setting; minor fine-grained detrital input; more than 1 km burial leading to pressure solution seams.

Interpretation

Throughout sequences in most areas, but becoming more common higher up, especially close to ophiolitic basement in the north.

Mostly restricted to the uppermost sequences of the Pakhna Fm.; however, matrix-supported rudites also occur sporadically throughout the whole formation, especially to the E of the Limassol Forest Block.

Calcarenites

Rudites

Carbonate grainstones, with sparry calcite cement, or mud matrix, with some globigerinid sands, with minor sand-grade quartz grains near the base; up-sequence, large benthic forams and neritic bioclastic material become more abundant; a siliciclastic component appears near the top of the succession.

Two types: (i) generally micrite, with planktonic forams (e.g. Happy Valley); (ii) terrigenous pebbles and granules (e.g. basalt), with neritic skeletal material. Mouldic porosity created by dissolution of aragonite.

Thin (2-10 cm), mediumbedded (10-50 cm); also thick-bedded ( > 50 cm); thin-bedded facies often very burrowed; medium-bedded facies has many rip-up clasts, Thalassinoides-type trace fossils and occasional infaunal escape burrows.

Two types are present. (i) Clast-supported conglomerates, largely channelised, or as laterally extensive sheets, with planar bases. Clasts are well-rounded, mainly less than 30 cm in size, either carbonate dominated, or polymict. (ii) Matrix-supported conglomerates, often in channel-fill sequences, cut into marls and chalks. Clasts are usually of the same composition as the local substrate. Two types; (i) with similar matrix and substrate composition; (ii) different matrices (i.e. terrigenous, or neritic), deposited in deep er-water pelagic dominated setting; debris flows were commonly developed by break-up of sedimentary slides; great variation in rounding related to variable transport distances.

Thin-bedded calcilutites are interbedded with thickbedded calciturbidites, consistent with a deep-water setting; classic Bouma-type structures are largely absent from medium-bedded calciturbidites; massive beds have sharp base and tops, and occasional escape burrows, that are restricted to channels.

Massive, planar or channelfill deposits, with gravitycontrolled depositional mechanisms, dominated by high-density turbidity currents with significant grain interaction; the clasts were derived from uplifted basement and sedimentary cover units, mixed with reefal and neritic carbonate material.

Thin-bedded calcilutites deposited by dilute turbidity currents, some quite 'proximal'; medium-bedded carbonates deposited by turbidity currents; massive carbonates deposited as high-density turbidites, transitional to mass flow deposits, mainly channelised. Shallow-water carbonate reworked into deeper water. -] -r rn z ¢3

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288

gins are not observed, sections along strike to the northeast (towards Khirokitia) and southwest (towards Tokhni) are dominantly fine-grained, as described above. At Tokhni, the east face of the old quarry (Fig. 15a) exhibits a single thinningupward succession of massive, coarse-grained calcarenites, interbedded with silty marls. Above, discontinuous marlstones are cut by a second, smaller channel sequence, with a basal clast-supported rudite composed of chalk cobbles and boulders in a bioclastic matrix. Toward the south, the base of the channel is incised up to 5 m down into underlying lithologies, for a distance of 20 m. At Tokhni, the top of the channel-fill succession is capped by a clastic deposit (mapped as Koronia Limestone by Bagnall, 1960), containing fossil serpulids, bryozoan fragments, coralline algae and coral clasts. The matrix is micritic, with numerous peloids. Aragonitic components are dissolved, resulting in widespread mouldic porosity. The following main facies are present (Table 1). Thick-bedded calcarenites exhibit sharp bases and tops, weakly expressed parallel lamination, vague normal-size grading in the upper parts of beds, occasional dish-structures (Robertson, 1977a), de-watering pipes and escape burrows. Chalk lithoclasts, tens of centimetres across, are common near the base of individual depositional beds. Subordinate amounts of thinner-bedded calcarenites are also present, as described below. Both matrix-supported conglomerates (Type 1) and clast-supported conglomerates (Type 2) are present. Three types of matrix-supported conglomerates are observed (Table 1). Type la conglomerates as commonly monomict, the clasts reflecting the composition of the underlying sediment. Clasts show plastic deformation, indicating erosion prior to complete consolidation. Type lb conglomerates contain angular platy limestone clasts, up to 50 cm long, mainly of irregularly laminated pelsparite in a micritic matrix, with scattered pelagic foraminifera, or rarer admixed bioclastic debris. Some clasts have been encrusted with serpulids, indicating seafloor exposure. Type lc conglomerates contain rounded cobbles and boulders of finely crystalline limestone, compound corals, chalk and lithified muddy calcarenites with shallow-water debris. The ma-

S. E A T O N A N D A. R O B E R T S O N

trix is chalky and contains pelagic foraminifera. Bed-thicknesses of the matrix-supported conglomerates, as a whole, range from 0.5 to 4 m, but vary greatly on the outcrop scale. Bed bases are mostly unscoured and planar, except where loading has occurred. Channelling of these deposits is locally evident, with beds overlapping the channel margins. Bed tops are usually planar, with occasional upward projecting blocks. Two types of clast-supported conglomerates are also present. Type 2a conglomerates have a globigerinid chalk matrix, which contains echinoid and coral fragments, chalk and marl, recrystallised limestone and carbonate lithoclasts of shallow-water origin. The Type 2b conglomerates contain cobbles and boulders of chalk, poorly preserved corals and ophiolite-derived material. The matrix is sand- to pebble-grade grainstone, including corals, vermetid gastropods, bivalve fragments, coralline algae, large benthic foraminifera and echinoid debris, mixed with chert and altered igneous pebbles. The fabric of both the clast-supported conglomerate types varies from well organised, with grading, imbrication and stratification, to completely disorganised. Where imbrication is present, long (a-) axis of the clasts dip up-current and the intermediate (b-) axes lie transverse to flow, as in the "resedimented conglomerate" model of Walker (1975).

Basin-margin Association The Basin-margin Association is characterised by massive, graded and medium- to thin-bedded calcarenites, interbedded with chalks and marls. There are also local occurrences of slumps, matrix-supported conglomerates and clast-supported conglomerates, as described above (Fig. 14c). Some channelling of the clastic lithofacies is observed, but this is generally of a broad, shallow nature. Beds tend to occur as lenticular, or sheet-like bodies in amalgamated packets. This is in marked contrast to the discrete, channelised clastic bodies of the Gullied-slope Association. In between clastic packets, the sequences comprise bioturbated marls and chalks, with sporadic, thinto medium-bedded, fine-grained, graded calcarenites. Thicker beds tend to occur in amalga-

289

THE MIOCENE PAKI-INA FORMATION, SOUTHERN CYPRUS

mated packets, separated by more thinly bedded intervals, but there is little evidence of thinning/fining- or coarsening-upward within this facies association. Well-sorted globigerinid grainstones/packstones dominate the lower part of the succession, with minor silt-sized quartz. Large shallow-water benthic foraminifera (mostly discorbaceans, orbitiloids and rotaliaceans) become increasingly common upward, at the expense of planktic varieties. Shallow-water bioclastic material (Fig. 15c) includes bivalve fragments (especially pectinids and oysters), coralline algae (branching and encrusting varieties), coral fragments, sponge spicules, echinoids, serpulid worm tubes and large foraminifera. Additional clasts of chert pebbles, chalk lithoclasts, peloids and rare ooids are present (Follows, 1990; Follows et al., 1992). Toward the top of the succession, there is a significant siliciclastic component, made up of detrital feldspars, pyroxene, quartz, and fragments of chert, globigerinid chalk, micritic limestone and basalt. The lava fragments are usually highly altered, with common limonite and chlorite. Thalassinoides-type trace fossils are locally present toward the top of the succession. Thin-bedded calcarenites occur as laterally extensive, 2-10 cm-thick, parallel beds of silt- to sand-grade grainstones and packstones, or more rarely, as thin, to lenticular pebbly beds. Where not obscured by burrowing, beds are graded, with sharp bases and intraclastic lags. The bed-tops comprise marl, commonly burrowed. Pebbly, thinbedded calcarenites occur at the top of the Pakhna Formation at some localities and contain angular, to well-rounded chert, and coarse, to granular bioclastic material. These sediments grade laterally into medium-bedded calcarenites. Medium-bedded calcarenites (10-50 cm thick) are commonly pebbly at the base and fine upward to coarse, medium, or fine grain sizes. Bedding is mostly parallel, but the bases of some beds are channelised. Sorting is generally good, except where large (to 20 cm) marl clasts occur at the base of some beds. Flutes, grooves, parallel and low-angle cross-lamination, load and flame structures are common, suggesting turbidity deposition. Ideal Bouma sequences are, however, rarely

developed (Bouma, 1962). Thin-bedded calcarenites are also present, as described below.

Basin-plain Association Sequences of the Basin-plain Association (Table 1) are dominated by planktonic foraminiferal, nannofossil chalk and marl (Fig. 14d). The sediments are off-white in colour, in contrast to the underlying, less argillaceous Lefkara Formation. The proportion of planktic foraminifera greatly exceeds that of benthic ones (i.e. 85-95% planktics; Herguera, 1982; Ortiz, 1982), as noted in the modem Eastern Mediterranean at mid-bathyal depths (700-1100 m; Parker, 1958). Bioturbation is extensive, mainly of Zoophycos, Chondrites and Planolites type and indicates deep-water deposition (e.g. Ekdale, 1978). Macrofossils are restricted to thin-shelled epi-pelagic bivalves, echinoids and rare fish teeth. Burrow fills contain a high proportion of globigerinid tests, commonly as grain-supported foraminiferal sands. Sub-horizontal, anastomosing pressure seams, composed of muddy carbonate are common. Such features, elsewhere have been attributed to concentration of clay minerals upon pressure solution within unlithified chalk, resulting from burial to more than 300 m (Garrison and Kennedy, 1977b; Einsele, 1982; Ricken and Hemelben, 1982). Scanning electron microscopy indicates extensive solution welding of adjacent grains, suggesting lithification at burial depths of more than 1000 m (Neugebauer, 1974; Schlager and Douglas, 1974). Pure indurated, medium-bedded, white chalks near the top of the Pakhna Formation contain small bivalves and the large benthic foraminifera, Discospirina (Adams, 1959), marking the "Discospirina band" (Bagnall, 1960; Pantazis, 1967). Although generally structureless, one occurrence, at Moutayiaka (Fig. 8), shows fine parallel lamination and contains well preserved fossil fish. Modern discospirids range well down into the bathyal zone (Sturani, 1978). A marlstone facies is also present mainly toward the overlying, evaporitic Kalavasos Formation and comprises bioturbated globigerinid mudstone, fine-grained, terrigenous clay, mud and

290

S. E A T O N

plant material. Fresh exposures are black and rich in organic matter, mostly finely divided plant material. X-ray diffraction shows quartz, kaolinite, smectite, palygorskite and trace quantities of chlorite and illite, as significant minor components. Pyrite framboids are distributed widely in the sediment. Near the top of the Pakhna Formation is a laterally continuous, 1.5 m-thick layer of red and pink globigerinid mudstone, exposed between Ayia Mavri and the Kalavasos road section (Fig. 8). X-ray diffraction shows minor contents of limonite, muscovite, kaolinite, quartz and feldspar. One other succession, known only at Happy Valley, west of Limassol (Fig. 8), shows features of both the Basin-margin Association and the Basin-plain Association (Fig. 14e). These successions include Late Miocene reef limestones of the Koronia Member. Recent work indicates that some of this material comprises in-situ patch reefs, in addition to reworked talus (Follows, 1990; Follows et al., 1992). In the Happy Valley road section, the lower part of the succession is dominated by homogeneous pelagic chalk, while the upper part of the succession contains calcirudites, calcarenites and slumps. The calcirudites

comprise cobble and boulder conglomerates, as irregular thick sheets, with loaded bases. Clasts include coral debris of shelf derivation, in a matrix of lime, mud with comminuted echinoid and bivalve debris. Frictional coupling between debris flows and the substratum is evident from drag folding along the base, and thrusting beneath the toe of redeposited units (Farrell and Eaton, 1987).

Discussion and interpretation The facies and provenance information indicate that the Pakhna Formation of southern Cyprus accumulated in two sub-basins, the Maroni sub-basin in the east and the larger Khalassa sub-basin in the west (Fig. 16). The two sub-basins were separated by the Yerasa lineament. Erosion products of the ophiolite and its pre-Miocene sedimentary cover are mixed with shallow-water bioclastic sediment, including coral, in facies of the Peripheral Sands Association. These sediments mostly accumulated as sheet-like bodies in a high-energy, shallow-marine, transgressive setting, within the Tortonian Koronia Member. Mixing of terrigenous and bioclastic sediment was consequent upon uplift and erosion, then transgression and reworking during the Tortonian. UPLIF TE U LIMASSOI F O[~[ S f BLOCK

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THE MIOCENE PAKHNA FORMATION, SOUTHERN CYPRUS

291

Depositional processes

for example, from the gullied slope of the Tongue of the Ocean in the Bahamas (Schlager and Chermak, 1979). Also, the facies associations are distributed in roughly concentric belts, similar to those found in small off-platform basins in the Bahamas (Mullins et al., 1984), suggesting an essentially linear source (i.e. coastal areas), rather than isolated point sources (i.e. canyons). The scale of the basin was insufficient in any case to have allowed large-scale submarine fans to develop (see Walker, 1978; Shanmugam et al., 1985). Along the northwest margin of the Maroni sub-basin the Tortonian Koronia Member is underlain by channels cut into the underlying sediments. At Tokhni, mainly calcarenites and conglomerates infilled one such submarine channel. This channel is compound, showing repeated downcutting and partial filling, whereas adjacent areas continued to undergo hemipelagic deposition. Such channels are envisaged as feeders of successions exposed further down palaeoslope. At Tokhni, ophiolite-derived material disappears at the highest levels, possibly reflecting late-stage peneplanation of the ophiolitic terrain to the north. Calcirudites are also present further west, in slope facies of the Khalassa sub-basin. These conglomerates, however, are planar sheet de-

The fine-grained facies between channels of the Gullied-slope Association accumulated in a sediment-starved slope setting. These sediments are mainly hemipelagic and accumulated during up to 10 Ma, equivalent to a relatively low sedimentation rate of ca. 1 cm/1000 years (cf. Scholle et al., 1983). The preferred explanation of the low sedimentation rates is by-passing of the submarine slope. There is, however, little evidence of hiatuses in deposition, which would probably have given rise to hardgrounds a n d / o r nodular cementation (Schlager and James, 1978). The dominant mode of coarse-grained sedimentation within the Maroni sub-basin involved the infilling of submarine channels and development of debris flows aprons at their mouths (Fig. 17; cf. Cook, 1982; Cook and Mullins, 1983). There is an absence of obvious small-scale thickening- or thinning-upward trends in the basinplain, or basin-margin successions, typical of ideal submarine fans. Also, the locations of the channel-fill sequences indicate that the basin was fed by a series of small gullies, rather than by rare, larger submarine canyons. The spacing of the gullies (i.e. 3-10 km) is similar to that reported,

1 2 3 4

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sub-basin at Tokhni. See text for further explanation.

292

posits a n d / o r broadly lenticular. They probably reflect basinal transport from line sources in areas where only limited uplift took place; erosional gullies are not well developed in contrast to the Maroni sub-basin in the east. However, local channelised conglomerates were encountered while excavating water-supply tunnels near the northwestern margin of the Khalassa sub-basin (C. Xenophontos, pers. commun., 1990). The deposition of the various conglomerate types was gravity-controlled, dominated by highdensity turbidity currents, with a significant amount of grain interaction. Internal organisation, in the light of theoretical models, suggests that deposition was influenced by an interplay of traction, suspension, friction and cohesive "freezing" processes. Specifically, the Type la matrixsupported conglomerates were deposited by high-density turbidity currents, in which the final grain-support mechanism was the upward flow of pore fluid (Lowe, 1976a, b). By contrast, the Type lb matrix-supported conglomerates are interpreted as the result of localised erosion and reworking by turbulent mixing during transport, with enhanced buoyancy and cohesion of semilithified rudite clasts (Lowe, 1982). The internal organisation of the Type 2a clast-supported conglomerates is suggestive of deposition by high-density turbidity currents (Walker, 1975). Inverse grading, where present, is interpreted to represent "freezing" of a highly concentrated traction carpet, following a drop in the flow velocity below that necessary to maintain upward dispersive pressure. The Type 2b, disorganised grain-supported conglomerates, probably resulted from cohesive flow processes (Lowe, 1982), in which the matrix/water mixture provided buoyant lift and lubricated grains, preventing frictional locking (Rodine and Johnson, 1976). These deposits resemble debris flows, except that clast support during transport was by lubricating intergranular dispersion, combined with rolling, sliding and bouncing in a buoyant matrix/water mixture. Where a more cohesive, more dense matrix was present, the clasts were fully supported, and a true debris flow resulted (Lowe, 1982). This latter facies is structureless except in the lower boundary layer, where simple shear

S E A T O N A N D A. R O B E R T S O N

developed due to frictional resistance with the substrate, having the effect of imbricating clasts with short axes perpendicular to the base. The Basin-slope facies and basinal facies of the Khakassa sub-basin in the west include numerous medium- to thick-bedded calciturbidites, mainly composed of shallow-water-derived carbonate, redeposited from line sources to the north (e.g. Kouris River). In this area, tectonic uplift and erosion was much reduced relative to the Maroni sub-basin further east (Fig. 16). However, intraformational sediment, including reef talus was shed into the Khalassa sub-basin from an isolated fault-controlled high, in the Happy Valley area. In addition, small volumes of bioclastic and terrigenous sediment were derived from the basement of the allochthonous, Mesozoic Mamonia Complex. Chert pebbles were rounded in a highenergy marginal setting, on the east-west-trending Akrotiri High, mixed with less texturally mature shallow-water-derived bioclastic material and then gravity reworked, northward into the basin. The facies of the Basin-plain Association accumulated in a deep marine basin. In many areas the slope-to-basin transition exhibits a ramp-like morphology (Read, 1984). The transition was marked by decreasing overall bed-thickness, grain-size, abundance and frequency of bioclastics (e.g. Crevello and Schlager, 1980) and by a rapid increase in the scale and frequency of slumps, slides and debris-flows basinward of the slope (e.g. Cook and Mullins, 1983). Interbedded thin- to medium-bedded calciturbidites within the basin comprise mainly shallow-water bioclastic carbonates, mainly derived from the north. Deep-water-type burrowing commonly obscures primary sedimentary structures. The basinal facies of the Maroni sub-basin, locally also contain large clasts of white pelagic chalk, up to 1 m in size, which were derived from the underlying Pakhna and Upper Lefkara Formations. These clasts are often plastically deformed, due to reworking prior to complete lithification and reflect localised gravity reworking from active submarine faults. Lastly, the finely laminated calcilutites near the highest levels of the Pakhna Formation indi-

293

THE MIOCENE PAKHNA FORMATION, SOUTHERN CYPRUS

cate increased stratification and development of anoxia, immediately prior to desiccation of the Mediterranean basin in the Messinian (Hsti et al., 1978).

Evolution of the basin through time The Pakhna basin was created by tectonic movements at the beginning of the Miocene. The appearance of shallow-water-derived carbonate sediment a short distance above the base of the Pakhna Formation is attributed to tectonic uplift of marginal areas, both to the north and to the south, giving rise, after transgression, to substantial areas of shallow-water carbonate production, including coral patch-reefs. The spatial distribution of facies associations remained virtually unchanged during the Miocene, suggesting that palaeoslopes remained relatively constant during this time. Local tectonic effects (Robertson et al., 1991), rather than global eustatic sea-level change (Vail et al., 1984) are seen as the main controls of sequence boundaries, prior to the Messinian. Alternations of thinner- and thicker-bedded calciturbidites may reflect cycles of relative sea-level change, whereby transgressions increased the area of shallow-water bioclastic production and, hence augmented detrital carbonate input into the basin. However, overall shallowing took place, mainly in the Late Miocene. In most areas, especially within the more proximal facies associations, the uppermost Pakhna Formation sediments contain s!gnificant quantities of calcirudites a n d / o r coarse calcarenites (e.g. Kouris River valley to Ayia Phyla transect; Fig. 8). Ophiolite-derived sediment also increases in abundance in the uppermost levels of the Pakhna Formation in most northerly marginal areas (e.g. at Tokhni). Microfossil populations extracted from the Pakhna Formation show that the ratio of pelagic to benthic forms decreases rapidly up-section (Eaton, 1987). Of the trace fossils, Zoophycos, Planolites and Chondrites characterise the lower levels of the Pakhna Formation, while the shallower-water f o r m Thalassinoides predominates up-sequence, mainly in calcarenites. However, bioturbation disappears from the highest levels of

the Pakhna Formation beneath the evaporitic Kalavasos Formation, notably in the distal Basinplain settings. The marlstone facies high in the Pakhna Formation Basin-plain Association marks an increased influx of fine-grained terrigenous sediment, in response to marginal emergence and erosion, following a relative drop in sea-level, probably in advance of the Messinian salinity crisis. The presence of kaolinite is indicative of tropical weathering, while the smectite and palygorskite reflect erosion of the ophiolitic terrain to the north a n d / o r soil-forming processes (e.g. Chamley, 1979). Upward shallowing is also supported by the relative increase of benthic foraminifera and changes in trace fossil type. Finally, during the Messinian, the Mediterranean sea-level fell, resulting in isolation of the south Cyprus Pakhna basin from the open Mediterranean Sea to the south. Conclusions

The Pakhna basin is subdivided into two, linked sub-basins by the WNW-ESE-trending Yerasa lineament, delineating the Maroni sub-basin in the east and the Khalassa sub-basin in the west. The tectonic movements that produced these sub-basins are thought to relate to initiation of the present northward-dipping subduction zone beneath southern Cyprus. During the Early-Middle Miocene, the ophiolitic terrain (Limassol Forest Block) in the north was strongly uplifted, deformed and eroded, followed by transgression and the growth of patch-reefs, preserved as talus within the Tortonian Koronia Member. Large volumes of mixed, ophiolite-derived and bioclastic sediment were gravitationally transported into the basin within channels, as massive debris flows and calciturbidites. Deep-water carbonate sediment was gravitationally reworked from slope areas by turbidity currents and mass flow processes. Deep-water, mainly hemipelagic sediments accumulated on. the basin plains. Detached blocks of basinal facies were also shed from submarine faults within the Maroni sub-basin and shallowwater carbonates, including reef debris, were redeposited from an isolated tectonically controlled

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high within the Khalassa sub-basin (at Happy Valley). The southern margin of the Pakhna basin as a whole, was delineated by the east-westtrending Akrotiri High, which can be traced offshore on shallow seismic data (McCallum, 1989). Any lower Tertiary chalk sediment there was removed, exposing Mamonia basement rocks, which were eroded, and reworked, along with coeval shallow-water carbonate, including reef limestone. This material was then redeposited northward into the basin, mainly by mass flow and turbidity currents. During the Messinian, sea-level progressively fell in the Mediterranean, creating silled basins within the Maroni and Khalassa sub-basins, in which stratified anoxic sediments accumulated, then gypsum facies.

Acknowledgements The present paper is based on a Ph.D. thesis by S. Eaton funded by a N.E.R.C. research studentship. A.H.F. Robertson's fieldwork was funded by Edinburgh University. For discussions in the field we thank John Boyle, Tristan Clube, the late Steve Farrell, Ed Follows, Bramley Murton and Chris MacLeod. Drs. Andreas Panayiotou and Costas Xenophontos of the Cyprus Geological Survey Department gave welcome support. The manuscript benefitted from reviews by N. G6riir and an anonymous reviewer.

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