Balearic Abyssal Plain: An example of modern basin plain deformation by salt tectonism

Marine Geology, 17 (1974) 183--200 ©Elsewer Scmntffm Pubhshmg Company, Amsterdam -- Printed m The Netherlands

BALEARIC ABYSSAL PLAIN: AN EXAMPLE OF MODERN BASIN P L A I N D E F O R M A T I O N BY S A L T T E C T O N I S M

DANIEL J STANLEY' , F L O Y D W M c C O Y '

and LISELOTTE DIESTER-HAASS2

' Dwzslon ofSedzmentology, Sm,thsonmn Institution, Washington, D C ( U S A ) 2Geological Institute o f the Klel Unwerslty, Kzel (Germany)

Accepted for pubhcahon May 22, 1974)

ABSTRACT Stanley, D J , McCoy, F V~ and Dmster-Haass, L , 1974 Belearm Abyssal Plato an example of modern basra plato deformation by salt tectomsm Mar Geol, 17 183--200 Hlgh-resoluhon sub-bottom (3 5 kHz) traverses of the southwestern portion of the Balearm Abyssal Plato between North Africa and the Balearm block show an ~rregular topography where rates of deformatmn appear to locally exceed those of sedimentation The basra is underlain by salt of Messmlan age, and dlaplrlsm has disturbed post-Mess]man sediments The 3 5 kHz records, augmented by 30,000 Joule seismic reflectmn profiles, mdmate that this dmpmsm Is continuing at present and is even now slgmfmantly deform,ng the uppermost sediment sequences A high concentration of structural features including doming and the development of rim synchnes w~thm the 35--60 m of section penetrated are associated w~th dmpmsm Over 70% of the domes have penetrated the surface m the studmd area, of these, most display a rehef of 10 m or more In some instances, domes apparently act as dams behind which sediment is ponded Non-faulted rehef averages 3--4 m/km, notable for an abyssal plato surface Frequently, the uppermost Holocene strata are offset several meters as a result of normal faults and grabens This concentrahon of sea-floor lrregulantms necessarily modffms the present-day sediment dispersal pattern and rules out the uniform flow of turbidity currents and lateral continuity of sedlmentatmn umts across th~s basra plain

INTRODUCTION T h e Balearlc A b y s s a l Plain, b y f a r t h e l a r g e s t such f e a t u r e in t h e M e d i t e r r a n e a n Sea, has b e e n d e s c r i b e d as a g e n e r a l l y f l a t s u r f a c e d u e t o s e d i m e n t a c c r e t i o n a n d s m o o t h i n g by d e p o s l t l o n a l p r o c e s s e s T h e p l a t o is t h e u p p e r m o s t s u r f a c e o f a think s e c t i o n o f P h o - Q u a t e r n a r y t u r b l d l t e a n d h e m l p e l a g m d e p o s i t s {Horn e t a l , 1 9 7 2 ) L a t e Q u a t e r n a r y s e d i m e n t a t i o n r a t e s h a v e b e e n high ( ~ 10 c m / 1 0 0 0 y r ) ( E r l k s s o n , 1 9 6 5 , R u p k e a n d S t a n l e y , 1 9 7 4 , a n d o t h e r s ) E a r h e r s u r v e y s b y o t h e r w o r k e r s ( M e n a r d et a l , 1 9 6 5 , W a t s o n a n d Johnson, 1968, Ryan et al, 1970, Auzende et al, 1971, and others) and J O I D E S L e g 13 d n l h n g ( R y a n e t a l , 1 9 7 3 ) h a v e s h o w n t h a t m u c h o f this basin is u n d e r l m n b y s a l t o f M e s s m l a n age ( U p p e r M i o c e n e ) , a n d t h a t d l a p l n s m r e l a t e d t o p l a s t i c f l o w a g e o f this salt has d i s t u r b e d t h e p o s t Messmlan sediments

184

Two cruises by the U S N S " L y n c h " m 1972 (cruises LY-I-72 and LY-II-72) over the southwestern plato (Alg6ro-Baleanc Abyssal Plato) between North Afrma and the Balearm block prowde detailed accounts of sea-floor deformatmn related to salt tectomsm through b o t t o m and subb o t t o m surveys A hlgh-resolutmn, medmm-frequency 3 5 kHz bottomsoundmg system was operated simultaneously (crmse " L y n c h I") with continuous selsmm profiling equipment (30,000 J sparker) The 3 5 kHz system theoretmally can resolve stratffmatmn differences of 1 0 m or less These techmques, used with success m the salt dome-rmh Gulf of Mexmo (Walker and Ensmmger, 1970), allow the best d e h m t m n of structures within the upper 35--60 m of the Balearlc sediment sequence, a zone generally poorly defined on most sparker profile records The relatmnshlp of these surface and near-surface structures with the deeper salt layers prowdes good d e h m t m n of dmpmsm and its consequences on sedimentary structures, processes, and dlspersmn patterns m an otherwise essentially deposltmnal environment Ship tracks m the area discussed here (I°W to 6°E long ) are shown m Fig 1 Satelhte navlgatmn was used for posltmmng A t t e n t m n has been called to isolated knolls nsmg above the abyssal plato surface m this area These have been interpreted as salt domes by earher workers (Glangeaud et al, 1967, Watson and Johnson, 1968, Bellmche and Pautot, 1968, Leenhardt,

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185

1968, 1970, Ahnat et al., 1970, Montadert et al., 1970; Wong et al., 1970) on the basis of (1) an absence of magnetm anomahes over these knolls, (2) an apparent c o n t m m t y between deeper reflective acoustm layers and d m p m c structures beneath the knolls, (3) their morpholog:cal similarity to subb o t t o m structures m the Gulf of Mexmo, (4) apparently higher sound velocltins m se:smm refractmn profiles, and (5} geochemmal charactenstms of sediments and rocks from knolls standmg m rehef on the abyssal plam surface. The recovery of evapontes m JOIDES Leg 13 cores 124, 133 and 134 m the Baleanc basm confirms this mterpretatmn. A distract band of reflectors, reflector M of Ryan et al (1970) and Blscaye et al. (1972), or reflector H of Ahnat et al. (1966), represents a group of p r o m m e n t deep acoustm layers occurring at a depth of 500 to over 1000 m below the abyssal plato surface This group of reflectors has been deformed by salt tectomsm suggesting that the " m o t h e r " salt layer hes below reflector M (as also noted by others, c f , R y a n et al, 1973) Our sparker records do n o t show the base of the salt layer (Fig 2). The overlying Phocene sediments are largely transparent acoustmally, as also shown by selsmm profiles m other sectmns of the Balearm Abyssal Plato (Alla et al., 1972, Ryan et al, 1973), the Quaternary sectmn above :t is characterized by numerous, closely-spaced, distract reflectors, the "layered sequence," or reflector G, of Leenhardt (1970) Records obtmned with the 3.5 kHz system show m a way not prevmusly d o c u m e n t e d the degree of mtense deformatmn m the upper 35--60 m of the sediment column over much of this southwestern sector of the abyssal plmn. Rim synchnes, broad antmlmes, parallel folds and normal and reverse faults are apparently assocmted with d m p m s m both within the upper portmn of the sediment column (3.5 kHz records) and at depth (selsmm profiling records) The consequences of these structures on Late Quaternary to m o d e m sediment dispersal patterns are slgmfmant SALT DOMES

The various types of dlapmc domes encountered are shown m Fig.3 They appear either as simple (single hyperbohc echo trace) or compos:te (multiple hyperbohc echo traces) Simple dlaplrs may be both symmetrmal (Fig 3B,C), or asymmetrmal (Fig 3E), composite dlaplrs appear to have an Irregular and complex surface topography (Fig 3D,F) S:mple symmetrmal dlaplrs are most common. Some occur at depth with httle or no surface expression {Flg.3B), b u t most along our profiles (> 70%) have penetrated through the surface sediments and protrude as knolls (F:g 3AC--F) Most are veneered by sed:ment Vertmal exaggeration of the 3.5 kHz records (about × 50) produced by ship's speeds of approximately 10 knots gives the Impression that these diapers are narrow features with steep flanks Broad h y p e r b o h c traces recorded while moving slowly and drifting during a detmled survey (Fig.l) indicate that the majority of these dmp:rs are broad domal features with low slopes (Fig 3A) Subsurface domes, on the other

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188 hand, are frequently marked by single h y p e r b o h c returns suggesting narrowt o p p e d features with a single acoustm point-reflector (Fig 3B), others, however, are broader (Fig 4C) Dlapmc knolls vary between 1 and 35 m in rehef above the sea-floor, most frequently being 1 0 1 0 m In cross-section, t h e y vary from 400 to 3500 m at the sea-floor, simple dyaplrs are smaller in dmmeter (400--2800 m, average 500 m) than compomte dlaplrs (600--3500 m, average 2500 m) Larger dlaplrs often show higher rehef, generally in the westernmost sector of the plato The heights of these dl apm c knolls are considerably lower than those described by Menard et al (1965), Leenhardt (1968), Watson and Johnson (1968), Mauffret (1969), Ahnat et al. (1970) and Mauffret et al (1972) m o t h e r areas of the Balearlc Plain Acoustmally transparent areas adjacent to

Fig 4 Examples of folded structures from 3 5 kHz records Think homzontal bars are 1 0 kin, thin horizontal hnes are 20 fms (36 6 m) apart in water See text for explanation of arrows

189 some faults (thin arrows, Fig 3E,F and 4C,D) could represent either d m p m c Intrusions along these fault planes or acoustm shadowing effects in the lee of high-angle faults. In plan, the domes appear to be either elhptmal or short ndges up to 1 km long with northerly and northwesterly trends, b u t control is adequate only where the tracks of LY-I and LY-II intersect and in the detmled survey area (see Fig 1 and 9). Long salt ridges (salt walls) described b y Ryan et al. (1970) are not apparent here There is no suggestion in our 3.5 kHz records of lateral salt flowage at the sediment/water interface. Cap rock over dlaplrs, as has been proposed by Alla and Leenhardt {1971) south of France, is n o t seismically distinguishable. The frequency of chapmc structures that project above the abyssal plain surface as knolls along the LY-II track-line decreases markedly east of about the 3°E mendIan. West of this, however, knolls are frequent to a b o u t the 0 ° menchan, with higher concentrations both on the basin plmn north of Algiers, and along the base of the Spanish continental rise FOLDED STRUCTURES Synchnal structures occur adjacent to virtually all dmplrs (Fig 4). They are particularly well-developed near plercement domes that project above the sea-floor, and, in this sense, they resemble rim syncllnes as discussed by Trushelm (1960). Often they are separated (arrow 1, Flg.4A) from nearby knolls by smaller bathymetrlc depressions (arrow 2, Flg.4A), which may result from later lsostatlc sinking of the dlaplrs The smaller depressions are usually adjacent to only one flank of the knolls in our records, and if lSOstatm adjustment is occurring, it would also suggest concomitant tilting of the dlaplrs. They may also represent embryonic secondary peripheral sinks (true rim synchnes according to Trushelm). The larger synchnal structures produce only a shght surface depression, b u t often have a progressive increase in dip below the surface. This would imply that either the rate of synchnal subsidence has progressively decreased with time, or that sedimentation rates have progressively Increased relative to synchnal deformatlonal rates, Enksson (1965) has noted that sedimentation rates in the Balearm Abyssal Plato have increased during the past 40,000 years In some cases, it is n o t clear if these synchnes have formed b y subsidence, as has been suggested by Hinz (1972), by a process similar to what Barton (1933) has termed "downbulldmg". In approximately one-third of the synchnes, however, distinct angular unconformities at depth separate the older dipping sediment strata from the younger flat-lying sechments forming the present-day abyssal plmn surface Here an abrupt cessation of synchne formation or a decrease in deformatIonal rates is lndmated, whereby local sedimentation rates have greatly exceeded deformatmnal rates. It should be pointed out, however, that locahzed depositlonal processes also may have partly formed some of these stratlfIcatmn features, for example, thickening of lndlwdual sedimentation units towards the center of sea-floor depressions would be typmal of deposition by turbIdltes

190 Unusual synchnal structures occur at the eastern portmn of the study area (Flg.4B) In the 3 5 kHz records, they precede any evidence of structures related to salt tectonlsm Unfortunately, seismic records are n o t available here, and any explanatmn concerning their formation is difficult Their occurrence prior to other evidence of salt tectomsm, however, might suggest a tensmnal feature marking the boundary of the salt layer where lateral salt flowage has produced a "pull apart" structure at depth Broad antmlines and domal structures also occur, often expressed on the abyssal plmn surface as broadly uplifted areas (Fig 4C) Smaller anticlines appear to be largely the result of adlacent synchnal formation, as has been noted m the northwestern Balearic basin (Mauffret, 1969) In other areas, such as near the LY-I and LY-II track crossing (see Fig 1), the abys~al plain has been intensely deformed by parallel folding (Fig 4D) FAULTS Numerous faults are clearly shown m the 3 5 kHz records, they are predominantly high-angle normal faults related to pmrcement domes (thin arrows, Flg.4C,D, F~g 5). A few occur only at a depth with no surface expression (Flg.5A,B), and, following Storm (1945), suggest faulting that is contemporaneous with deposition by an increase m throw with depth (arrows, Fig.5). Downwarplng of strata near the fault trace may result from drag or from local compaction caused by the release of interstitial fluids ( c f , Storm, 1945). Many faults, however, lndmate active faulting that has resulted m distinct displacement of the abyssal plmn surface (Fig 5B--F) In many instances, a lack of any sediment cover draped over the fault plane Indicates very recent, and perhaps continuing, movement (Flg.5C,F) Both normal (Fig 5B,C) and reverse faults (arrow, Fig 6B) occur as peripheral faults near dlaplrs Normal faulting over large dlapmc domes has produced graben and horst structures (FIg.5E,F) and are probably locally produced by doming as discussed by Currie (1956). Other grabens that occur some distance from dlapiric structures {Fig 6A) may be produced by pmrcement structures at depth Large portions of the abyssal plain surface have been displaced vertically (to > 6 m) b y both faulting (Fig 5C--F) and subsurface doming (Fig 6B--D) In some Instances, dlapirIc knolls apparently form dams behind which sediment is ponded For example, in Fig 6C,D, smoothing of sediment strata over uplifted subsurface domes mdmates that deposltlonal processes are now dominant, these processes are active on only one side of adjacent knolls standing m relief on the sea-floor, and would suggest a damming effect by these knolls RELATIONSHIP TO SUBSURFACE STRUCTURE The relationship between dlaplrs, domes, faults, folds, e t c , with the subsurface structure beneath the abyssal plain surface is illustrated m Fig 7 and 8

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It is clear t h a t m o s t of the features observed on 3 5 kHz records are surface m a m f e s t a t l o n s o f d e e p e r structural e l e m e n t s d e p m t e d on seismic r e f l e c t i o n profdes most o f the chaplrs and faults c o n t i n u e t h r o u g h r e f l e c t o r M (Fig 7A,B), individual dtaplrs and faults t h a t are p r o n o u n c e d features at the abyssal surface are also individually distract at d e p t h (Fig 7A--C, 8A,B) T h e intense folding n o t e d m Fig 4D is s o m e w h a t c o n c o r d a n t wlth the folds in r e f l e c t o r M, as s h o w n m Flg.8C Many synchnes also c o n t i n u e at d e p t h (Fig 7A, 8A,B) and m a y be related to similar structures in the basal salt layer In some cases, however, a p p a r e n t n m s y n c h n e s in 3 5 kHz records disappear at d e p t h (arrows, Fig 8A,B). Similar relationships b e t w e e n sea-floor lrregularttms and d e e p e r structural features have been n o t e d b y others (Watson and J o h n s o n , 1 9 6 8 , L e e n h a r d t , 1968, 1 9 7 0 , R y a n et a l , 1 9 7 0 , Wong et a l , 1 9 7 0 , A u z e n d e et a l , 1971). Our 3 5 kHz seismic r e f l e c t i o n profdes, however,

193

illustrate this relationship sn greater detml, parhcularly within the upper 35-60 m of the abyssal plato surface. Unconsohdated sediment thicknesses overlying reflector M vanes between 0 2 and 0.5 sec (two-way travel time; eqmvalent to about 170--430 m, assuming an interval velocity of 1.7 km/sec, c f , Ryan et al., 1973). Thicker sequences occur beneath the central portion of the abyssal plmn, t h m m n g towards the continental margin of both Spam and the Baleanc Islands where the sediments appear to be abruptly truncated (Ryan et al., 1973; Weller and Stanley, 1972). The average thickness of sediment m this study area is less than half t h a t noted m other portions of the Balearlc Abyssal Plato, particularly east and north of the Balearlc Islands Intense deformation of reflector M by plercement structures is particularly nohceable in the seismic records both in smaller areas beneath the central portion of the abyssal plato, and m a broad hnear area paralleling the base of the continental slope southeast of Spam and south of the Baleanc Rise (Fig.l,2). Deformation by salt tectonlsm of the uppermost 60 m of the sediment column on the abyssal p l a n , as noted in 3 5 kHz records, occurs pnnclpally over these zones. East of about the 5 ° meridian, for example, salt-related structures are n o t present in the 3.5 kHz records obtained d u n n g cruise LY-II To the west, however, both the number and size of dmplrs mcreases A marked Increase of these structures both at the surface and m the subsurface occurs north and west of Algiers at about 3°E longitude with the largest dlaplrlc structures occurrmg west of 1 ° 30'E longitude There is also a concomitant increase m the number and density of other structural features such as faults and folds Faults are predominantly d o w n t h r o w n to the east near the base of the Spanish contmental rise. There is thus an apparent relationship both m 3.5 kHz records and m seismic profiles between the number and size of salt-related structures, and their distance from the base of the southeastern Iberian and Baleanc Islands continental slope higher concentrations of these structures occur near this northeast-southwest trending slope/abyssal p l a n contact, as well as areas of intense folding of surflclal sediments (Flg.4D). This zone apparently delineates a major structural feature related to the f o u n d e n n g of the Balearlc Rise and adjacent margin (Stanley et a l , 1974), and is parallel to other distract regional trends m this area of the BalearlC basra, including the Emile Baudot and Mazarron escarpments bounding the southern Baleanc block and the Alboran Ridge to the west, m addition to some d o m i n a n t NE--SW structural trends on the North African margin. Auzende et al (1971) and Ryan et al (1973) have described similar concentrations of salt-related features along the southern boundary of the Baleanc Abyssal Plato. Wong et al (1970) noted a decrease in the depth of burml of dlaplrs towards the continental shelf of Sardmm, along the eastern boundary of the BalearlC basra, similar relationships are ewdent m our seismic records (Fig 2) and those of Auzende et al. (1973) These relationships between salt structures and both the major structural trends and the boundaries of the BalearlC basin might suggest that regional

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196 orogemc activity ~s a significant factor m salt movement e~ther m a direct or redirect sense, such as through ghdmg and slumping as proposed by Auzende et al (1973) On the other hand, unconsohdated sed:ment thicknesses m most of the Balearlc Abyssal Plmn are adequate to lmtiate vertical salt mlgrat:on, or halokmesls (Trushelm, 1957) There :s a close slmflamty here between the model of Hanna (1959) and Gussow (1968) for progressively younger salt diapmsm away from the margins towards deeper portions of an actively subsiding basin RATES OF DEFORMATION Ewdence cited previously from both the se:sm:c reflection and 3.5 kHz sub-bottom profiles would suggest that (1) rates of dlapmsm and deformat:on are equal to, or shghtly higher than, the average Late Quaternary sed:mentatlon rates, and (2) these processes are presently active and now affecting the modern abyssal plato surface In many areas, for example, th:s surface has been uphfted and cut by faults, some of whmh show no draping by sed:ments, others are covered by only a t h m manthng of sediments Throw along most of the faults appears to be constant with depth mdmatmg that rates of displacement are h:gher than sedlmentat:on rates, m a few cases, throw appears to increase with depth suggesting that displacement rates are less than sedimentation rates S:mllar relatlonsh:ps m faults overlying subsurface diapers also mdmate that chapmsm :s continuing at present, often at rates exceeding local sedlm e n t a t m n rates In th:s respect the sltuatmn ~s analogous to that of the Gulf of Mex:co where the effect of salt dome mtrusmn on concurrent sedlmentatmn patterns has been demonstrated (Walker and Ensmmger, 1970) Tenslonally produced horst and graben structures, for example, are not filled by modern sed:ment. Sed:ment strata adjacent to some diaplrs standing in relief on the sea-floor are thinned and uplifted In other cases, rates of intrusion have apparently been rapid enough to truncate these beds. Synchnal structures are often expressed on the sea-floor as troughs, also mchcatmg that deformatlonal rates may be exceeding sedlmentatmn rates locally. Calculated Late Quaternary sedlmentatmn rates m this portion of the abyssal piton range from 23 cm/1000 years (Rupke and Stanley, 1974) to 35 cm/1000 years (Enksson, 1965) If it is assumed that sedimentatmn and deformat:onal rates are about equal, then minimum rates of dmp~rm mtrustun can be estimated Thus the latter would range from 0 23 to 0 35 m m / y r Such rates of dmpmc mtrusmn would be m close agreement with other est:mates (0 3 m m / y r , Sanneman, 1965) and measured rates (1--2 m m / y r , Lotze, 1957, 1 m m / y r , Ewmg and Ewmg, 1962) In the Balear:c basra, however, rates of d e f o r m a t m n have not been constant during the past 40,000 years. For example, discordant surfaces within synchnes occur, on the average, about 9 m below the abyssal plato surface. Some faults also terminate at about this same depth Assuming the

197

sedimentation rates noted above, a general cessation m deformatlonal processes would be suggested at sometime between 40,000 and 26,000 years BP The use of faults in such calculatmns, however, must be interpreted with cautmn m view of Currm's (1956) experimental evidence that young faults overlying active dlaplrs m a y terminate at depth and need not produce surface traces EFFECT UPON ABYSSAL PLAIN SEDIMENTARY PROCESSES

It is clear from the 3.5 kHz records that the southwestern BalearlC Abyssal Plain differs considerably from other abyssal plains whmh are dominantly shaped by deposltlonal processes (cf., Hersey, 1965). Sea-floor deformation related to active salt tectonlsm results in structures on the abyssal plain surface that have a profound effect on both local sedlmentat:on rates and upon sediment dispersal patterns. Non-faulted relief averages 3--4 m/km, notable for an abyssal plato surface Rupke and Stanley (1974}, for example, studmd a suite of cores m the southern Balear:c Plato and found that correlation of turbldlte sequences between these cores was not possible Because deformatlonal rates of the abyssal plato surface may be in excess of those due to sedimentation, local dispersal patterns may be slgmf:cantly altered through time Structures such as low knolls, small escarpments, and depressions divert the movement of sediment, and materials are moved across a very gentle sloping but Lrregular surface somewhat similar topographmally to a broad alluvial system. Grabens and syncllnes channehze turbidity currents, and active growth of dmplrs and fault scarps produce local dams inhibiting the unldlrectmnal spread of both turbldltm and hemlpelaglc deposits. Pondlng of sediments behind dlaplrs, for example, has produced wedge-shaped fills 3--9 m think Deformatmn of the sea-floor would also form locally-rejuvenated slopes, thereby producmg local slump deposits While none of these salt structures are regionally extensive, their high concentration on the sea-floor would modify significantly sedlmentatmn patterns on the basm plam For example, south and southeast flowing turbld:ty currents originating on the continental margin off Spain and the Balearlc Platform would be confronted with an Lrregular sea-floor topography of large domes, a number of faults, and troughs produced b y syncllnal structures (Fig.9), all of which would have a profound effect upon regional dispersion and deposition These Irregularities would also provide similar constraints upon sediment dispersal by bottom-current activity Any deposltmn of c o n t o u n t e s would be locally d:scontmuous, thus complicating regmnal correlatmn of strata m cores and reflectors m 3 5 kHz profiles Closely-spaced 3 5 kHz surveys coupled with a detailed cormg program m selected sectors of this abyssal plato are needed to detail the three-dlmensmnal conflguratmn of the Late Quaternary sediment units and properly interpret provenance and depos:tlonal processes.

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199 ACKNOWLEDGEMENTS

We are indebted to the U S. Navy for prowdmg ship time and scientific data on two Mediterranean crmses of the U.S N.S "Lynch" (Jan --Feb and March--April 1972, LY-I-72 and LY-II-72, respectively) The offmers and men of the "Lynch" and members of the scmntfflc party are thanked for their help m the collection of the profiles reported upon here The fmal text benefited from useful comments by Drs O Leenhardt, Umverslty of Kml, J. A Ballard, G L Johnson and P Taylor, Naval Oceanographm Offme, Washington, and L. Butler, NOAA, Mmml Financial support for this study, part of the on-going Mediterranean Basins Project, was pro'llded by the Smlthsoman Research Foundatmn grant (D.J.S) Fy-72 and 73-430035, and by the Deutsche Forschungsgememschaft (L.D.-H.) REFERENCES Ahnat, J , Glermann, G and Leenhardt, O , 1966 Reconnaissance slsmlque des accidents de terrain en met ligure C R Acad Scl , Paris, 262 1311--1314 Ahnat, J , Bellalche, G , Giermann, G , Leenhardt, O and Pautot, G , 1970 Morphologm et s6dimentologm d'un d6me de la plalne abyssale llgure Bull Inst Oc6anogr, 69 1--22 Alia, G and Leenhardt, O , 1971 D6couverte d'un affleurement de caprock sur le sommet d'un d6me de sel (d6me TI, Sud-Toulon) avec le bathyscaphe C R Acad S c l , Paris, 272 1347--1349 Alla, {:] , Dessohn, D , Leenhardt O and Pierrot, S , 1972 DonnSes du sondage smmique contlnu concernant la s6dlmentatlon Pho-Quaternaire en M6diterran~e nordoccldentale In D J Stanley (Editor), The Mediterranean Sea A Natural Sedimentation Laboratory Dowden, Hutchinson and Ross, Stroudsburg, Pa , pp 471--488 Auzende, J M , Bonnln, J , Olivet, J L and Pautot, G , 1971 Upper Miocene salt layer in the western Mediterranean basin Nature, Phys Scl, 230 82--84 Auzende, J M , Bonnm, J and Olivet, J L , 1973 The origin of the western Mediterranean basra J Geol Soc L o n d , 129 607--620 Barton, D C , 1933 Mechanics of formation of salt domes with special reference to Gulf Coast salt domes of Texas and Louisiana Bull Am Assoc Petrol Geol , 17 1025--1083 Bellamhe, G and Pautot, G , 1968 Sur la pr6sence de nlveaux ~ pyrite au sommet d'un d6me de la plame abyssale hgure C R Acad ScI Pans, 267 991--993 Blscaye, P E , Ryan, W B F and Wezel, F C , 1972 Age and nature of the pan-Mediterranean subbottom reflector M In D J Stanley (Editor), The Mediterranean Sea A Natural Sedlmentatmn Laboratory Dowden, Hutchinson and Ross, Stroudsburg, P a, pp 83--90 Bourcart, J , 1962 La M6dlterran6e et la r~volutson du Phoc6ne Soc G6ol France, Llvre P Fallot, 1 103--116 Currle, J B , 1956 Role of concurrent deposition and deformation of sediments in development of salt-dome graben structures (Mississippi) Am Assoc Petrol G e o l , Bull, 40 1--16 Erlksson, K G , 1965 The sediment core no 210 from the western Mediterranean Sea Rep Swedmh Deep Sea E x p , 1947--1948, 8 395--594 Ewmg, M and Ewing, J I , 1962 Rate of salt-dome growth Bull Am Assoc Petrol Geol , 46 708--709 Glangeaud, L , Allnat, J , Agarate, C , Leenhardt, O and Pautot, G , 1967 Leg ph6nom6nes ponto-pho-quaternalres dans la M6dlterran~e occldentale d'apr~s les donn ~ es d e GEOMEDE I C R Acad Scl Parts, 264 208--211

200 Gussow, W C , 1968 Salt dlaplrlsm importance of temperature, and energy source of emplacement In I Braunstem and G D O'Brmn (Editors), Dlaplrlsm and Dlapirs Am Assoc Petrol Geol M e m , 8 16--52 Hanna, M A , 1959 Salt domes favomte home for oll Oil Gas J , 57 138--142 Hersey, J B , 1965 Sedlment pondmg in the deep sea Bull Geol Soc A m , 76 1251--1260 Hinz, K , 1972 Zum Dlapirmmus m westhchen Mlttelmeer Geol J h r , 90 389--396 Horn, D R , Ewmg, J I and Ewmg, M , 1972 Graded-bed sequences emplaced by turbidity currents north of 20 ° N in the Pacific, Atlantm and Mediterranean Sedlmentology, 18 247--275 Hsu, K J , Clta, M B and Ryan, W B F , 1973 The origin of the Mediterranean evaponte In Imtlal Reports of the Deep-Sea Dmlhng Project, 13 U S Government Printing Office, Washington, D C , pp 1203--1232 Leenhardt, O , 1968 Le probl~me des d f m e s de la M~dlterran~e occidentale Etude g~ophyslque d'une colhne ahyssale, la structure A Bull Soc G~ol F r , 10 497--509 Leenhardt, O , 1970 Sondages slsmlques contmus en M~dlterran~e occldentale M~m Inst Oc~anogr, Monaco, 1 120 pp Lotze, F , 1957 Stemsalz und Kahsalze, Borntrager, Berlin, 465 pp Mauffret, A , 1969 Les dSmes et les structures "antmhnales" de la M~dlterran~e occldentale au nord-est des Bal~ares Rev Inst Fr P~trole, 24 953--960 Mauffret, A , Auzende, J , Olivet, J L and Pautot, G , 1972 Le bloc continental balfiare (Espagne)--extensmn et ~volutlon Mar G e o l , 12 289--300 Menard, H W , S m i t h , S M and Pratt, R M , 1 9 6 5 The Rhone deep-sea fan In W F Whlttard and R Bradshaw (E&tors), Submarine Geology and Geophysms Proc 17th Symp Colston Res Soc , 1965 271--285 Montadert, L , Sancho, J , Fad, J -P, Debyser, J and Wmnock, E , 1970 De l'fige tertlalre de la s~rm sahf~re responsible des structures dmplrlques en M~hterran~e occldentale (Nord-est des Bal~ares) C R Acid S c l , Paris, 271 812--815 Rupke, N A and Stanley, D J , 1974 Distractive propertms of turbidltm and hem~pelagic mud layers m the Alg~ro-Balearlc basra, western Mediterranean Smlthsoman Contr Earth Scl, 13 1--40 Ryan, W B F , S t a n l e y , D J , H e r s e y , J B , F a h l q u l s t , D A and Allan, T D , 1 9 7 0 The tectomcs and geology of the Mediterranean sea In A E Maxwell (Editor), The Sea, 4 Interscmnce, New York, N Y , pp 387--492 Ryan, W B F , Hsu, K J and co-workers, 1973 Balearm Rise-Site 124 In Imtml Reports of the Deep Sea Dnlhng Project, 13 U S Government Printing Offme, Washington, D C , pp 133--162 Sannemann, D , 1965 Salt stock famihes m northwestern Germany (abs) Bull Am Assoc Petrol G e o l , 49 357 Stanley, D J , Got, H , Leenhardt, O and Weller, H , 1974 Subsidence of the Western Mediterranean Basra m Phocene--Quaternary time further evidence Geology, 2 345--350 Storm, L W,, 1945 Resum4 of facts and opinions on sedimentation in Gulf Coast regmn of Texas and Lomsmna Bull Am Assoc Petrol G e o l , 29 1304--1335 Trushelm, F , 1957 uber Haloklnese und lhre Bedeutung fur die strukturelle Entwicklung Norddeutschlands Z Dtsch Geol Ges, 109 111--158 Trushelm, F , 1960 Mechanism of salt migration in northern Germany Bull Am Assoc Petrol G e o l , 44 1519--1540 Walker, J R and Ensminger, H R , 1970 Effect of dlaplrism on sedimentation in Gulf of Mexico Bull Am Assoc Petrol G e o l , 54 2058--2069 Watson, J A and Johnson, G L , 1968 Me&terranean dmplrm structures Bull Am Assoc Petrol Geol , 52 2247--2249 Weller, Y and Stanley, D J , 1972 Foundering of the Balearm Rme (Western Mediterranean) and its tectomcally controlled sedimentation (abs) P r o c , 23 Congr -Assembl Plan Athene Comm Int Expl Scl Mer M~dit, Symp G~odyn M~dit, 2 pp Wong, H K , Zarudzkl, E F K , Knott, S T and Hays, E E , 1970 Newly discovered group of dmplric structures m the western Mediterranean Bull Am Assoc Petrol G e o l , 54 2200--2204