Late Neogene and Quaternary Vertical Movements in Eastern Crete and Their Regional Significance

J. geol. Soc. London, Vol. 142, 1985, pp. 501-513, 8 figs. Printed in Northern Ireland

Late Neogene and Quaternary vertical movements in eastern Crete and their regional significance

J.M. Peters, S. R. Troelstra" & D. vanHarten

Geologisch Instituut, Universiteit van Amsterdam, Nieuwe Prinsengracht 130, 1018 VZ Amsterdam,The Netherlands;* Instituutvoor Aardwetenschappen, Vrije Universiteit, Postbus 7161, 1007 MC Amsterdam, The Netherlands

SUMMARY: Geological and geomorphological investigations along the E Cretan coast allow us to set up a model for the genesis of a staircase-morphology formed by a series of wave-cut platforms. Field observationsindicate that the early Pliocene period was characterized by stepwise subsidence. The area stabilized in the middle Pliocene and subsequently underwent Quaternary uplift. The character of late Cenozoicsedimentation is closely related to this Plio-Quaternary inversion of vertical movements. The discovery in early Pliocene mark of the psychrospheric ostracod Agrenocythere pliocenica, which was known before almost exclusively from the western Mediterranean, shows thatdeep marinecirculation extended as far as the Levantine basin during this period.In addition, itsubstantiates the postulated relatively deep marinedepositional environment in easternCrete during the earlyPliocene, as opposed to continental-shallow marine late Messinian conditions. Reversal of vertical movements around the Pliocene-Quaternary boundary is not only found on eastern Crete. Data from other Cretan districts and adjacent islands support the proposed model, which thereforeappears to be significant for the S Hellenic arc. Its timing is concurrent with an important geodynamical revolution in the Aegean region.

Along the coast of the island of Crete (eastern Coastal morphology Mediterranean) marine terraces, abrasion platforms and raised shorelines are presentat numerous loca- The study area (Fig. 1) comprises a relatively straight tions (e.g. Bonnefont 1972; Dermitzakis 1973; Ange- NNE-SSW orientated coastalstrip from Karoubes lier 1979; Pirazzoli et d. 1982). Reconstruction of Bay in the N up to the deserted hamlet of Ayia Irini in successive stages of uplift andlor subsidence is, the south. In this area the Cretan pre-Neogene alpine however, frequently hampered by subaerial erosion of 'basement' is mainly represented by dark Mesozoic- the terraces and denudation of the platform deposits. early Tertiary shallow marine carbonates, the Tripolit- Moreover, the marine structures are displaced along za limestones. In various places thesepre-Neogene active normal fault systems which are related to the rocks are unconformably overlain by Neogeneand current extensionalstress regime in the S Aegean Quaternary sediments. region. The most striking phenomenon along this stretch of The present investigations, which form an integral coast is the presence of numerous platforms cut into part of a regional study of the Neogene and Quater- the Tripolitza limestones. The platforms producea nary tectonostratigraphic development, focus on ver- typical staircase-morphology (Fig. 2) which is de- tical movements in eastern Crete (Sitia district) where veloped over the whole length of the study area (c. late Cenozoicabrasion platforms are extensively 18 km).The good preservation of the staircase- developed and well preserved. As opposed to other morphology is remarkable because once a platform is parts of Crete, significant recentnormal faulting is elevatedabove sea level, either by uplift or glacio- absent in the study area. In addition, information on eustatic drop of sea level, it is subject to weathering the Neogene and Quaternary sedimentary history of andsubaerial erosion and will eventually be de- the region can be obtained from fairly complete stroyed. sedimentary successions along the S coast and on the The staircase morphology has been interpreted by island of Koufonisi, which is located several some authors to result from a system of normal faults kilometres S of the study area. These factors allow a cutting the Tripolitzalimestones (Ziros geological quantitative analysis of late Cenozoic vertical move- map, I.G.S.R. 1959; Bonnefont 1972). More recently, ments in this segment of the Hellenic outer arc. Kelletat (1979) considered the platforms to result from

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Kat0 Zakros

(30- 9

-8

I 6

FIG. 1. Simplified geological map of the southeast coast of Crete (Sitia district).Pre-Neogene rocks: (1) Phyllite-Quartzite unit; (2) Tripolitza nappe, Mesozoic-early Tertiary limestones; (3) Tripolitza nappe, ‘flysch’. Late Cenozoicdeposits: (4) ?middleMiocene clastic sediments; (5) late Mioceneterrestrial conglomerates and sandstones; (6) late Miocene shallow marine deposits; (7) Pliocene sediments, in the Xerokambos plain also comprising Quaternarymarine terraces. Arrows indicateminor exposures of early-late Pliocene deposits. The numerous small occurrences of Quaternary marine and aeolian sediments are not indicated on this map. (8) young canyon (‘pharangi’); (9) contour line, 100 m interval; (10) bedding; (11) normal fault.

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FIG. 2. Characteristic morphology of wave-cut platforms on massive Tripolitza limestones. Well-developed platforms are situated at 1OC-110, 145-155 and 17G180m. Location: north of Ayia Irini.

marinecorrosion, which encompasses physical and massive pre-Neogene limestones. In detail, platforms chemical processes and biogenic degradation. Finding have a rugged topography with crevices and holes. Quaternary sediments onthe lowerplatforms, he These features are due to recent subaerial karstifica- dated them as Pleistocene. However, Angelier (1979) tion of primary irregularities in the wave-cut surfaces. reported early Pliocene mark ona platfoml in the area The width of platforms ranges between several tens of SE of Zakros. He concluded thatthe platform metres and more than 200m. Usually the platforms morphology was the result of a more complex are terminated by abrupt, near-vertical walls usually geological history, with Pliocene surfaces overprinted not morethan 25m high. The ancient cliffs are by Quaternary platforms at lower altitudes.This characterized by steep slopes which resulted from less configuration suggests that the well established Qua- intensive marine corrosion during a period of rapidly ternary uplift of easternCrete (Angelier & Gigout changing sea level. Their hyperbolic lower slopes 1974; Fortuin 1978) was preceded by it period of represent gradualtransitions to the next lower plat- stepwise, probablytectonically-induced, relative sea form (Fig. 2). Locally, lithophaga borings andsea level changes (Peters 1984). caves can be observed inthe cliffs, a feature suggesting The apparently complex pattern of vertical move- that subaerialerosion of thecarbonates has been ments is also reflected in the geomorphology. For limited. instance, on the southern slope of Mount Traosalos Individual platforms can be traced over considerable (Fig. 1) platforms can be traced continuously from the distances; observations from offshore show that they frontal cliffs towards the interior of Kat0 Zakros bay. may be continuously developed over more than 3 km. Thus, the bay already existed prior to the formation of On thebasis of geometry, altitude and vertical spacing the platforms and consequently the presentcoastal of successive platforms,correlations were made be- indentation is largely an inherited palaeorelief. tween different locations. There are several limitations to this procedure: (1) One may be tempted to infer from the relatively Description of wave-cut homogeneous nature of the carbonate substrate that platforms the moreextensive platforms represent longera period of stable sea level. However, platform extent is The platforms are subhorizontal or gently seaward not only time dependent. Slopedifferences in the dipping, irrespective of the layering in the substrate of initial topography may also have played an important

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/142/3/501/4888754/gsjgs.142.3.0501.pdf by guest on 27 September 2021 504 J. M. Peters et al. role. In addition, platforms may or may not have been primary dips occur in mark overlying a steep palaeo- formed simultaneouslyalong the whole coastalstrip relief, e.g. in the vicinity of ancient cliffs. The primary during a particular time interval, depending on local dip was probably partly enhanced by post-sedimentary conditions.A sheltered positionrelative tothe compaction. prevailing wind direction,for instance along an Nomajor vertical lithological variations were embayedshoreline, will causea decrease in wave observed in the up to 15 m thick marly successions. energy and result in less intensivemarine abrasion. The lowermostsediments locally containfragments The observed platforms therefore laterally change in and pebbles of pre-Neogene rocks (Figs 3 & 4a); these width or even disappear. deposits represent remnants of in situ initial platform (2) The availabletopographic maps of thearea, cover. Generally such transgressive basal clastic sedi- which have a contour interval of 20 m, areof little help ments are absentbecause they have beenstripped in determining the elevation of the platforms along the away by concurrent mass-flows (see below). mountain slopes, so independent altimetric data were The bulk of the sediments consists of well bedded needed. The level of the platforms between present mark with awhite or yellowish colour (Fig. 4b). sea level and 50 m could beestablished accurately Bedding is defined by grainsize differences: fine- while repeated series of measurements with a Thom- grained mark, frequently with abundant Orbulina menaltimeter allowed the elevation of platforms spp.,alternate with coarser, sometimes positively between 50 and 200 m tobe determined with a gradedintervals containing displaced faunas and precision of 5 m. The accuracy for the platforms above terrigenouscomponents. Thelatter include poorly 200m is about 10m. This latter figure is of the same roundedpebbles of Tripolitzalimestone, minor order of magnitude as the vertical distances between quantities of sand and reworkedfragments of sand- some of the platforms. stone. In a lateral sense, the character of the sediments Despite these limitations some correlation is possi- is clearly dependenton the position of the deposits ble. For example, both at the location of Ayia Irini with respect tothe palaeorelief. Mark filling up and in the area N of Xerokambos aseries of eight topographic features predating the staircase- platforms is visible between sea level and an altitude morphology are coarserthan the sediments on the of220111. Especially well developed abrasion surfaces platforms. This feature will be discussed later. occur at altitudes of 10&110,145-155, 17C-180 and Micropalaeontological analyses (planktonic forami- 200-210 m. Higher elevated platforms, reaching up to nifera, calcareous nannoplankton) of the marly plat- at least 450 m, are developed on Mount Traosalos, W form sediments and coeval deposits on the island of of Ambelos Bay and near Ayia Irini. Koufonisi indicate an early-late Pliocene age. Based Unfortunately, data on the level of the lowermost onthe presence of characteristicplanktonic forami- platforms aremore difficult toobtain. At several niferal marker species, the sediments can be assigned locations the platformmorphology can betraced to various intervals of the biozonal schemes of Cita below sea level, as was ascertained by a short survey (1975) and Spaak (1983). Samples of the stratigraphi- with a small boat carryinga shallow water echo- cally lowermost mark contain fair quantities of sounder. Along thestretch of coast near Ayia Irini, flat Sphaeroidinellopsissubdehiscens (Blow) associated surfaceswere visible between 25 and30m on with Globigerinanepenthes Toddand G. bulloides echo-sounder recordings; the lowermost detected well d’Orbigny and, in the absence of other marker species, defined horizontalsegment of the submarineslope havetentatively been assigned to the basal Pliocene occurs at a depth of c. 50 m. Sphaeroidinellopsis-Acme zone (MP1 1, Cita 1975). Because the initial platform cover hasoften been incorporated in early Pliocene mass-flows, the age of Pliocene andQuaternary the basal sediments may differ laterally on a particular platform sediments platform. Thus, the lowermost mark also yield slightly younger early Pliocene assemblages containing Many of the platforms, especially the higher elevated Sphaeroidinellopsissubdehiscens, Globorotalia rnar- ones,are barren dueto rapid denudation of the garitae Bolli & Bermudez and/orrare Globorotalia relatively soft sedimentary cover. Despite the denuda- puncticulata (Deshayes) (MP12/3-?4, Cita 1975; tion, light-coloured pelagic mark unconformably over- Interval 2/3-?4, Spaak 1983). Similar assemblages lying massive Tripolitzalimestones were found at dominate in highersamples from completestrati- more than 10 localities (Fig. 1). At all these sites there graphic sections, which can be foundnear Ambelos is ample evidence that the sediments were deposited Bay (Fig. 4b), along the coast near Xerokambos and after the formation of the platform on which they rest. on Koufonisi. In the upper part of these sections high The mark covera distinct palaeorelief of platforms abundances of sinistral Globorotaliacrassaformis and cliffs (Figs 3 & 4a) and fill up small-scale (Galloway & Wissler) occur; othermarker species irregularities in the limestones (furrows, lithophaga). such as Globorotalia rnargaritae andlor G. puncticulata The sediments are usually horizontally stratified but are absent in thesesamples. Atentative middle

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FIG.3. Coastal exposure in a small bay north of Xerokambos showing poorly bedded early Pliocene mark (Pl) with abundant pre-Neogene clastics. The sedimentscover an ancient, near-vertical ancient cliff wallin Tripolitza limestones (Tr) and fill up holes and furrows in the pre-Neogene substrate. Note the indurated shallow marine Quaternary sediments (Q) which cap the Pliocene mark.

Plioceneage (Globorotalia crassaformis-zone, Spaak Benthonic ostracods and foraminifera were studied 1983) has been given to these sediments. The youngest to get an insight in the Pliocene depositional environ- fine-grained mark containcalcareous nannoplankton ment and to obtaininformation on palaeobathymetw. assemblages indicative of late Pliocene age (Angelier The ostracod faunas include Bythocypris lucida et al. 1979a; C. Miiller, pers. comm.) (Seguenza), B. obtusata (Sars), Henryhowella asperri-

Platforms on pre-NeogeneTripolitza limestones

Abrasion plot form

3 . .. m4

FIG. 4. (a) Schematic cross-section of a series of platforms illustrating the present configuration along the coast in the vicinity of Xerokambos. No vertical exaggeration. (1) substrate of massive Tripolitza limestones; (2) stratified Pliocene marly sediments. Basal beds may show primary dips and locally contain coarse pre-Neogene clastics; (3) unconformable lithified terrace-deposits of Quaternaryage, consisting of littoralcoarse clastics with abundant macrofauna; (4) Quaternary continental deposits, comprising red-coloured slope breccias and aeolian sandstones.

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FIG.4. (b) Succession of early-middle Pliocene mark with distinctly bedded and laminated intervals. Coarser beds containing admixed terrigenous material are intercalated in fine-grained pelagic mark. Location west of Ambelos Bay, altitude 50 m.

ma (Reus), Krithe spp., Parakrithe sp. and Cytherella latter species indicates a depositional depth of more spp. This association suggests a fairly deep palaeoen- than 200 m(Benson 1978). Samples containing Glo- vironment(i.e. several hundredmeters), which is borotalia margaritae yielded the psychrospheric ostra- supported by the find in several samples of numerous cod species Agrenocythere pliocenica (Seguenza) (Fig. Oblitacythereismediterranea Benson (Fig. 5). The 5), indicating a depth of more than 500m (Benson

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/142/3/501/4888754/gsjgs.142.3.0501.pdf by guest on 27 September 2021 Vertical movementsCrete in eastern 507 water depths exceeding 300-400 m. Benthonicforaminifera are generally rare in samples from the basal Pliocene Sphaeroidinellopsis-Acme zone; species include Cassidulina spp., Bolivina spp., Cibicides spp. and Siphonina sp. Deeper water forms in sediments of this age are rare to absent. Quaternarysediments unconformably overlie the platforms andtheir Neogenesedimentary cover at different altitudes. The Pliocene marls are frequently capped by marine terraces which consist of miliolid- limestones, fine-grained calcareoussandstones and conglomerates. Fossils are abundant in these shallow marinesediments and includeechinoids, gastropods and pelecypods. In turn, platforms and both Pliocene and Quaternary marine sediments may be covered by continental breccias and lithified bioclastic sands of aeolian origin (Fig. 4a). Interpretation of field data Our field observations confirm Angelier’s (1979) conclusion thatnot all platforms are of Quaternary age. In fact we havefound isolatedoutcrops of Pliocene markon variousplatforms between 0 and 200 m and thus many, if not all, of these surfaces are older than the Quaternary. Clearly, the presence of Quaternarymarine sediments covering aplatform does not necessarily imply that the abrasion surface is a Quaternary structure. Although positive identification of true Quaternary platforms appears to be difficult, the existence of Quaternary platforms should be kept in mind since the observed spacing betweenplatforms could partlybe the result of superposition of abrasionsurfaces of FIG. 5. Top: Agrenocyfhere pliocenica (Seguenza), Pliocene and Quaternary age. In addition, one should psychrospheric ostracod from the east Cretan early becautious in assigning a Pliocene age tothe Pliocene(left valve). Bottom: Oblitncyfhereis subhorizontal surfaces detected offshore because simi- mediterranea Benson (left valve). larstructures may have beenformed during a low Quaternarysea level stand. Nevertheless,north of 1972; Van Harten, 1984). The occurrence of this Xerokambosa submerged vertical cliff wall, which ostracod is especially important from a palaeoecologic- reachesa depth of 15 m, is partially covered by a1 point of view because it evidences early Pliocene Pliocene marls. Therefore, this site proves that at least oceanic circulation in the eastern Mediterranean (Van a part of the subhorizontal structures below present Harten, 1984). sea level is of pre-Quaternary age. The deep ostracod fauna is usually attended with Angelier & Gigout (1974) havedescribed raised shallow water taxa such as Aurila spp., Bairdia spp., Quaternary terracesalong the southeasterncoast of Loxoconcha spp., Quadracythere spp., Urocythereis Crete which have an elevation of up to 200 m. Recent spp. and Xestoleberis spp. This is interpreted asa investigations in thesame area show that small secondaryadmixture from shallow coastalenviron- outcrops of shallow marinecalcareous sediments, ments, owing to down-slope contamination along the which are lithologically and faunistically similar to steep palaeorelief. The same feature is evident from deposits dated as Quaternary, occur at a level of over the presence of shallow water benthonic foraminifera 400m (J. M. Peters, unpubl. data). This figure (e.g. Elphidium spp. and epiphytic discorbids) associ- corresponds well with the maximum height of the ated with characteristic deeper waterforms such as platformsin the study area (approximately 450 m). Sphaeroidinabulloides d’orbigny, Planulinaari- Rapid uplift of the E Cretan fault block during the minensis d’Orbigny, Eggerellabradyi (Cushman) and Quaternary is also indicated by thenarrow, deeply Pullenia bulloides d’orbigny. The latterforms point to incised canyons in the limestone massifs (‘pharangis’,

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PLIO-QUATERNARY VERTICAL MOVEMENTS E.CRETE

-__....____hrE PUOCENE - CALABRIAN ------,

_1y__ ~~IDDLE REGRESSION:PROGRESSIVE UPLIFT, WITH PLIOCENE SUPERIMPOSEDGLACIO-EUSTATIC SEALEVEL CHANGES ‘N:Q ‘N;X 1 I ’k DEPOSITIONSTONES AND OFCONGLOMERATES MARINE SIND- l DEPOSITION OF g (BlOCLASTlC) MARLS I3I

l &IN&, &IN&, RECENT - .. . - . . MASSIFS(STAIRCASE MORPHOLOGY) /T t 11 / FIG.6. Diagrammatic representation of Plio-Quaternary vertical movements and contemporaneous sedimentation. Abbreviations along left vertical axis indicate successive higher positions-of sea level during the lower part of the Pliocene. Quaternary sea level stands along right vertical axis are hypothetical since no data are available on their exact positions. Further explanation in text. -

Fig. 1) andthe goodpreservation of the platforms. late Pliocene time (e.g. van Gorse1 & Troelstra 1981; Consequently, the highest relative sea level stand Suc 1984), the position of successive Quaternary sea probablyoccurred in late Pliocene-early Quaternary level stands with respect to the E Cretan margin was times.This viewis supported by theopen marine controlled by glacio-eustatic sea level oscillations Pliocene sedimentation which lasted till the end of this superimposed on uplift. This fluctuation of base-level epoch (see previous section). and associated erosionuncovered the Plioceneplat- Mostplatforms must actually predatethe Quater- forms and had a profound influence on the character nary because theyare locally covered by Pliocene mark. of marine sedimentation. Considering the timing of the highest relative position Due to lack of data we cannot evaluate whether the of sea level, it is logical to suggest that the platform Quaternary emergence of the region had a stepwise morphology was mainly formed by progressive relative character, which seems to be the case in other parts of rise of sea level during the early to middle Pliocene. the island (Angelier 1979). The existence of a still Since no significant eustatic sea level rise is known to submerged cliffwall covered by Pliocene mark (see have occurred during this time interval, we postulate above) illustrates that the amountof Quaternary uplift an early Pliocene stepwise foundering of eastern Crete has not yet equalled Pliocene subsidence. Adopting an and the simultaneous formation of a series of wave-cut age of approximately -2.0m.y. for the Pliocene- platforms by the shifting littoral zone. Current inves- Quaternary boundary and excluding netsea level tigationsin adjacentareas on Crete indicate that changes, the average rate of uplift can be estimated subsidence may have been initiated at the end of the roughly atabout 25 cd1000 y. This rate correlates Messinian . wellwith the mean value of vertical movements on Subsidence must have been rapid because the basal Crete during the last 110,000 y, which was estimated at strata of platform deposits between 0 and 200 m are of 10-30 cm/1000 y by Angelier (1979). earlyPliocene age. As spasmodicsubsidence pro- ceeded,the platformsbecame moreand more sub- Discussion merged and were covered by open marine mark (Fig. 6). The differencein elevation between the highest The proposedmodel of platformformation can be and lowest knownplatforms (more than 450m) is a tested by studying the Pliocenelithostratigraphic minimum value forthe amount of Pliocene subsi- development of southeastCrete. Up to 20 m thick dence. This value corresponds well with the estimated mass-flows formthe lowest stratigraphicunit in depositional depth deduced from the study of benthic Pliocene sections along the coast and on the island of faunas in the platform sediments. Koufonisi (see also Angelier et al. 19796). The Therate of foundering progressively decreased mass-flows comprisepre-Neogene rocks, reworked during the middlePliocene; this attenuation of Miocenedeposits and basalPliocene sediments in a tectonic activity and associated vertical movements matrix of earlyPliocene mark (Fig. 7a). The resulted in a stabilization of the area. Thus, sea level componentshave a local provenance; there- did not fluctuate significantly for some time during the sedimented basal Pliocene marly sediments and pre- late Pliocene-early Quaternary (‘Calabrian’). This Neogene clastics represent initial platform cover. The periodmarks an inversion of verticalmovements, mass-flows are succeeded upwards by an alternation of resultingin Quaternary uplift (Fig. 6). Because the mass-flows and early Pliocene mark (Fig. 7b) belong- modern type of climatic fluctuations was established in ing tothe Globorotaliamargaritae-zone. The strati-

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iCOMPOSITE PLIO-QUATERNARY STRATIGRAPHIC COLUMN E. CRETE 1 CONTINENTALBRECCIAS

SEDIMENTATION CONTROLLED BY GLACIO-EUSTATICSEALEVEL CHANGES

LITTORAL COARSE CLASTICSEDIMENTS

INITIATION OF LIPLIFT

(LAMINATED) MARLS, YY PALAEO-WATERDEPTH * 400 M MI DDLE I PLIOCENE 30 M ALTERNATION OF MASS-FLOWS WITHPELAGIC MARLS

EXTENSIVE MASS-FLOWS WITH A MATRI> OF EARLY PLIOCENEPELAGIC MARLS

POST-MESSINIAN TRANSGRESSION ---_.---0 ---lM IOCENE I- l I I I

FIG. 7. (a) Synthetic sedimentary log illustrating the Pliocene andQuaternary lithostratigraphic development of eastern Crete. (b) Two distinct mass-flows, consisting predominantly of resedimented blocks of late Miocene bioclastic limestones and basal Pliocene sediments in a marly matrix. The mass-flows are intercalated in laminated, partly slumped early Pliocene maris. Location: northern coast of the island of Koufonisi.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/142/3/501/4888754/gsjgs.142.3.0501.pdf by guest on 27 September 2021 510 J. M. Peters et al. graphicsections end with aseries of usually undis- bryozoa, corals and shallow water benthonic forami- turbed middle-late Pliocene mark (Dermitzakis & nifera such as Ammonia spp., Elphidium spp.and Theodoridis 1978; C. Miiller pers. comm.). Thus, the small discorbids. Cross-bedding, scour-and-fill struc- sedimentation pattern clearly reflects tectonic instabil- tures and positively graded beds are common. This ity during the lower part of the Pliocene. The distinct sedimentaryunit fits very well the sketched mass-flows wereprobably triggered by intermittent palaeoenvironmentalmodel of a steep, dissected seismic activity, associated with en-bloc vertical move- submarine slope with drowned platforms. The litholo- ments in the area. gical propertiesand sedimentary structures, together Inthe description of the coastal morphology we with the position of these deposits, indicate that the have shown that the coastal indentation is older than calcirudites represent the remainder of an offlapping the platforms. From the outlinedpalaeogeographical submarine fan (Fig. 8). The sediments accumulated on evolution of thearea it seems plausible thatthe a break in the submarine slope and partially eroded topographic lows wereformed or enlarged by sub- the underlying pelagic marls. aerialerosion during thelate Messinian desiccation Even though the postulated model (Fig. 6) is stage. During the earlyPliocene foundering these supported by the Pliocene sedimentaryhistory, one depressionsbecame submerged and frequentlyacted might argue that not all platforms supporting Pliocene as wide submarine canyons through which bioclastics marls necessarily have to be of the same age. Several and coarse detritus were channelled to deeper deposi- lines of evidenceindicate that formation of the tional environments. This is substantiated by the fact platforms during an earlier period is improbable. For thatat thesesites reworked (?late Messinian) con- instance, it is unlikely that they were formed during tinentaldeposits were found along the base ofthe regression at the beginning of thelate Messinian Pliocene successions. Moreover, most of the Pliocene desiccation stage in the Mediterranean because: sediments in theseformer bathymetric lows are (1) There is no evidence of subaerial erosion of the coarser than their platform equivalents. platformsprior tothe deposition of early Pliocene Down-slope mass transport through submarine can- marls, even though the whole desiccation stage must yons appearsto havebeen considerable. In a cliff represent aperiod of some 300,00~500,000y(Cita section on the small cape forming the north side of 1979;Langereis et al. 1984). Moreover,the initial Ambelos Bay (Fig. l), analternation of middle regression must have taken place during only a minor Pliocene pelagic and bioclastic marls is erosively part of this timespan. Although there are no specific overlain by a thick succession of calcirudites with data available on the rate of development of abrasion marly intercalations. The deposits show giant foresets platforms onthe Tripolitzalimestones, observations indicating E to SE directed sediment transport. Indi- on Holocene shorelines developed in similar rocks on vidual beds consist predominantly of coarse-grained the island of Antikythira by Pirazzoli etal. (1982) bioclastic debris of shallow marine origin mixed with show that erosion may not exceed 0.3 mm/y. Thus, the Tripolitzalimestone pebbles. Fossils include algae, regression period appears to be too short to encom-

200

FIG. 8. Schematicblock-diagram of the middle-late Pliocene palaeogeographic configuration of the SE Cretan coast.Wave-cut platforms in Tripolitzalimestones (A) become gradually indistinct towards the interior of the submerged bay. An inactive N-S trending normal fault separates the limestones from flyschoid rocks (B) which belong to the same pre-Neogene rock unit. Sediment gravity flows (C) were initiated in the nearshore canyon head by wave action andior earthquakes and travelled down-slope, partly eroding marly sediments (D) on a segment of the submarine slope with a low gradient.

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pass the generation of numerous platforms; Furthermore, ostracod associations from the upper (2) No late Miocene marine or terrestrial deposits part of theZounaki section, which consists of werefound onthe platforms. Onthe contrary, mass-flow intercalations in homogeneousmarls, are platforms are also developed on the highest elevated directly comparable tothe above described assemb- (300 m) late Miocene reefal limestones (Zakros area). lages since they also contain Agrenocythere pliocenica Thiselevation also indicates thatthe reconstructed and Oblitacythereismediterranea (V. Tsapralis, pers. relative position of sea level prior to the Messinian comm.). salinity crisisis too low to explain the platforms Thus, even though it has not been possible up till presently situated above 300 m. now to date a large number of platforms on Crete with (3) Messinian depositsexposed in nearby coastal certainty, it is clear thatimportant early Pliocene sections do not contain limestone clastics which should vertical movementswere not confined to eastern have been produced during the marine corrosion. Crete. Our data suggest that the reported mass-flows The basal Pliocene transgression in the Mediterra- weregenerated by spasmodicsubsidence of fault nean can also be excluded as a possible mechanism blocks, which is at variance with Meulenkamp et al. because this process must have been far too rapid to (1977) who considered them to result from erosion of cause theintermittent formation of seriesa of early Pliocene sediments on rising fault blocks. platforms (e.g. Cita 1982). Conclusions Regional significance Although the behaviour of different fault blocks and A similar platformmorphology, although usually of related sedimentation patterns may not be completely smaller extension andmore degraded, hasbeen identical all overthe island, the above evidence reported by Bonnefont (1972) and Angelier (1979) suggests that large segments of the S Aegean region fromvarious districts of the island.Platforms are werecharacterized by rapid subsidence during the developed in Tripolitza limestonesat several sites early Pliocene. Thereported Plio-Quaternary inver- along the N coast, e.g. the Irakliondistrict, the sion of vertical movements is not restricted to Crete; Gramvousa and Rhodope peninsulas in western Crete Keraudren (1970) described a rather similar pattern (Chania district), and also on the small islands of Ayii from Rhodos. The platform sediments on this island Theodoriand Dia.Dating the platforms is usually are coarse clastic and late Pliocene in age. However, impossible because of totaldenudation. However,a subsidence may have been initiated somewhat earlier reconnaissance survey yielded someinteresting new since the lowermostplatforms are situatedbeneath data.One of the higher abrasion surfaces east of present sea level. Iraklion(Kakon Oros, 300m) is pre-Quaternaryon Consequently, the geodynamic model of Le Pichon the basis of Plioceneplatform cover. Along the S & Angelier (1981), Angelier (1981) and Angelier et al. coast, near the villages of Tsoutsouras and Arvi, west (1982) for vertical movements in the S Hellenic arc has of Ierapetra, Pliocene sediments directly comparable to be modified. This model assumes that accumulation to the successions in eastern Crete are exposed at the of underthrusted sediments along the Hellenic conver- foot of alimestone massif showing degraded plat- gent boundary caused progressive uplift of the outer forms. This area may represent an identical but more arc since theend of the middle Miocene. Early eroded andfaulted disposition. Clearabrasion sur- Pliocene founderingdoes not fit this postulated faces covered by weathered Pliocene marls were also pattern of vertical motion. found in the Goudouras area, just west of our study The kinematics of convergence along the Hellenic area. plate boundary appear to have undergone an impor- The postulatedgenetic relationship between early tant change during the early Pliocene. The timing of Pliocene subsidenceand contemporaneous gravity early Pliocene subsidence coincides with the onset of sliding appearsto be animportant one. Like the compressional tectonics androtation in the western platforms,early Pliocene mass-flows are present at Hellenic arc (Sore1 1976; Laj et al. 1982) and can also many different locations all over the island (Gradstein be correlated with important vertical movements along 1973; Fortuin 1977; Meulenkamp et al. 1977), and the S Cretan continental margin (Peters & Huson have recently also beenreported fromadjoining 1985). Rapid subsidence of fault blocks along the offshore areas (Peters & Troelstra 1984). In addition, Hellenic arc may havebeen related to different the significance of the proposedmodel of early tectonic processes. The westernenlargement of the Pliocene founderingfor other parts of Crete iswell Hellenic convergent boundary in early Pliocene times illustrated by data from Pliocene stratigraphic sections modified the geometry of the plate margin and in the Chania district (Zounaki, Kaloudhiana).A facilitated ongoing extensionaldeformation of the recent lithological and fauna1 study of these sediments Aegean continentallithosphere, causing augmented (Spaak 1981) showed a progressive deepening of the strain rates along the preexisting dense normal fault sedimentary facies in the course of the early Pliocene. pattern in the Aegean region. Furthermore, this event

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may have been associated with a (temporary) higher sions in the field. A. R. Fortuin and D. Beets critically read rate of subductionwhich, in turn, led to tectonic the manuscript. C. Miiller kindly provided thedata on erosion of previously accreted sediments alongthe calcareous nannoplankton. Scanning electron micrographs base of the continental lithosphere and induced overall were Prepared by L. J. Witte in co-operation with the subsidence along the Hellenic arc. ‘WerkgroepSEM’ of the University of Amsterdam. Field- work was carried out with permission of I.G.M.E. (Athens), which is gratefully acknowledged. This paper is a contribu- ACKNOWLEDGEMENTS.A. R. Fortuin is thankedfor discus- tion ofthe UvA/VU Werkgroep Mariene Geologic.

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Received 5 April 1984; revised typescript accepted 9 October 1984.

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