Geological Society, London, Special Publications

The Bouma Sequence (1962) and the resurgence of geological interest in the French Maritime (1980s): the influence of the Grès d'Annot in developing ideas of turbidite systems

Arnold H. Bouma and Christian Ravenne

Geological Society, London, Special Publications 2004; v. 221; p. 27-38 doi: 10.1144/GSL.SP.2004.221.01.03

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© The Geological Society of London 2004 The Bouma Sequence (1962) and the resurgence of geological interest in the French Maritime Alps (1980s): the influence of the Gr6s d'Annot in developing ideas of turbidite systems

ARNOLD H. BOUMA 1 & CHRISTIAN RAVENNE 2

1Department of Geology & Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA (e-mail: [email protected]) 2Geology & Geochemistry Division, Institut Franfais du Pgtrole, 92852 Rueil-Malmaison Cedex, (e-mail: [email protected])

Abstract: The two authors explain how and why the Gr6s d'Annot successions were chosen for their influential studies in the context of the 1960s and the 1980s. Arnold Bouma explains the origin of the Bouma Sequence in the 1960s, while Christian Ravenne focuses on the significance of the area as analogues of deep-sea fans and seismic stratigraphy in the 1980s. Ravenne recalls the main results obtained at that time: palaeogeographicat maps, inter- pretative and synthetic sections, the spectacular onlap relationships at Chalufy, the strong interaction between seismic interpretation and field data, and the importance of large failures/collapses on the continental slope for the initiation of density surges.

The French Maritime Alps with its complex turbidites were unknown to the area initially, structural development, in which several Gr~s certain relationships were difficult to unravel, d'Annot localities are scattered, has long such as the petrography of the - received interest from French geologists (see Mercantour Massif and that of the Gr&, and summary by Stanley, this volume). Because the general grain-size fining to the north rather than the south. It was during a field trip with Faure-Muret, Lanteaume, Fallot and Kuenen that those sandstones were interpreted as turbi- dites (Faure-Muret et al. 1956). A more complete contribution by Kuenen et al. was published in 1957. The initial field trip was the reason Kuenen looked for a young student to conduct more observations and measurements. This short note offers a personal view on key aspects of Gr6s d'Annot research over the years, revealing in particular: (1) the ridiculous series of events that led to the Bouma Sequence;

Arnold Bouma on the field. Christian Ravenne on the field.

From: JOSEVH, P. & LOMAS, S. A. (eds) 2004. Deep-Water Sedimentation in the Alpine Basin of SE France: New perspectives on the Grks d'Annot and related systems. Geological Society, London, Special Publications, 221, 27-38. 0305-8719/03/$15.00 © The Geological Society of London. 28 A. H. BOUMA & C. RAVENNE

(2) a summary by Ravenne of the increased in the various scattered Gr6s d'Annot occur- geological interest in this area with the renewal rences. The purpose was to demonstrate that all of Annot studies in the 1980s, conducted for these locations were erosional remnants of a seismic stratigraphic interpretation and deep- large basin fill, fed from the south. Submarine sea fan models. This interest waned in the early gravity measurements indicated that parts of 1990s when the cost of oil production became the north-central Mediterranean were subsiding too high. A second renewal of attention occurred (F. A. Vening Meinesz, pers. comm. 1958), at the end of the 1990s (and continues), mainly supporting the concept that the sediment source due to the growth of hydrocarbon discoveries area was located to the south. We were still in deep-water systems, focusing on 'reservoir' some years away from a clear idea of what style detailed characterization. would be called seafloor spreading. In 1957, Bouma cleaned his old 96cc motor bike, overloaded it and went to south-eastern The Bouma history France. That little bike had barely enough oomph to move over flat roads, requiring fre- After completing his military obligations in quent repairs by the rider. As a result, the trip December 1953, Arnold Bouma received a non- went via Marseilles and the coastal road. From salaried undergraduate assistantship from Pro- going north the bike broke down again in fessor Phillip H. Kuenen at the University of Luc~ram. Logically, that became the base of Groningen, The Netherlands. As part of that operations, and the Peira Cava area the main position, he assisted Kuenen with experiments study area. Profiles along two roads, Col de on the rounding of grains, and later on flume l'Orme-la Cabanette and Col St. Rock-la experiments of turbidity currents. The latter Cabanette, form a triangle with a base of about aroused his interest, especially when he shared 2km; the top at la Cabanette, a few hundred an office with Ernst Ten Haaf, who had started metres. Correlation seemed impossible (Bouma a Ph.D. study on Italian turbidites. Bouma was 1959a). also able to assist Ten Haaf in the field. During It was Bouma's initial idea to compare the that trip he learned that even professors are not Gr6s d'Annot characteristics with those of always the gods they pretend to be. Kuenen Tertiary fluvial deposits in Switzerland. Doeglas had mentioned several times that most turbidites advised him to present a paper on the Gr6s at were the result of the failure of an entire delta. the International Association of Sedimentology Such a failure then translated into a large turbid- meeting in Switzerland to make it easier to get ity current that would cover the entire basin with in contact with Swiss professors. The presenta- one layer. It would take 100 000 years before the tion of that paper, published the next year delta had built itself up again and was ready for (Bouma 1959b), changed everything. the next failure. Although the idea of failure After his presentation a question came from made a lot of sense, the calamity of a major the rear of the darkened room. The French was one did not agree with the young undergraduate. too fast for Bouma to understand. The repeated Kuenen's idea was that the fill of a basin would request was a similar machine-gun volley. mimic a stack of large pancakes. At the same Fortunately, the speaker was able to find time, the massive turbidity currents would Professor Doeglas, and met with the person swipe away all bottom fauna; and, therefore, who fired off the question. This happened to be no trace fossils would be found. The purpose of Madame Yvonne Gubler, Director of Geology this first stop on the trip with Ten Haaf to the and Geochemistry of the Institut Franqais du Apennines was for Bouma to see real turbidites. P6trole. Her first comment was 'you are not It did not take long for him also to discover permitted to conduct fieldwork in that area'. several types of trace fossils. Ten Haaf readily This caused considerable consternation, but agreed with the interpretation that the features after a lengthy discussion, permission was were trace fossils, and a cable was sent to granted to carry out sedimentological studies Kuenen explaining the find. A few days later only, and not to study structural nor strati- came an answer: 'impossible, look better'. graphic details because it was the study area of After having obtained his Bachelor of Science M. Lanteaume who worked on a Th6se de l'Uni- degree, Bouma moved to the University of versit6. In addition, the young student was not Utrecht in the centre of The Netherlands. His permitted to cross the River to study the new mentor, Professor Derk J. Doeglas, was Annot and other turbidite locations. No explana- persuaded by Kuenen to send the young gradu- tion was given. ate student to the French Maritime Alps to The trip to Switzerland was less exciting than measure sections and palaeocurrent directions expected, and with the field findings differing BOUMA SEQUENCE AND FRENCH MARITIME ALPS 29

1 the series. It was published in 1962. A couple of e pelitic interval years later someone coined the term 'Bouma i'.i: :::~i-i.._ i i:i.i.::::!-:!:::~i~i-.:~.-"d upper intervo, of Sequence'. Although the name was an honour, it often embarrassed the young geologist because " intervol of current too many people asked if he was the son of 'the ~-o777~'~" "~ c ripple lamination Bouma turbidite person'. Following up his 1962-1963 Fullbright post- ~~b lower interval of doctoral fellowship under F. P. Shepard at the parallel Iominotion Scripps Institution of Oceanography at La Jolla, California, the Bouma family emigrated i to the USA. Bouma started as a professor of 1,= :]~.';:i.','~..:;!i~-:~.;. a graded interval oceanography at Texas A & M University. A ..~..~) ...... busy schedule prevented visits to his old stomp- .'. 'o.e;, o.'.'6.:~'L' ing grounds. After the 96th DSDP cruise, he was able to go back to compare the Mississippi Fig. 1. Bouma sequence (after Bouma 1962). Fan cores to the Peira Cava outcrops (Bouma & Coleman 1985). from Kuenen's ideas, it became a strong attrac- The senior author can only express his grati- tion to continue in the Maritime Alps. More sec- tude to the professors he was able to study tions and palaeocurrents were measured. Later under, and the beautiful French Maritime Alps on Shell Oil provided funding to visit areas in that gave him a start in his professional life. If , Switzerland, Belgium and Germany to the Bouma Sequence helped to stimulate field identify if those areas could be interpreted as trips and new studies in the area, it would be a turbidites. Although vertical repetition of sedi- nice reward. The reality is that the area really mentary structures was noticed in the field, it found its place on the international geological took laying out the measured sections on the map in the following decades, as described floor, back in the hall of the Geological Institute below by the junior author. in Utrecht, to recognize a turbidite sequence (Fig. 1). Overwhelming incompleteness of the total sequence had prevented the recognition of Gr6s d'Annot studies and seismic a sequence while measuring sections in the field. stratigraphy Actually it was more exciting to observe major differences in the ideas promoted by Kuenen During the 1970s, four developments occurred than to find a turbidite sequence. Unfortunately, that considerably modified the perception of many of these ideas could not be put in the dis- marine deposits. sertation. At that time turbidites were considered (1) Extensive exploration of active and passive to be the only deep-water sands, rather than part margins was carried out by both academic and of the more exciting submarine fans. industrial parties. The dual purpose was to Daniel Stanley, doing a Ph.D. study in the understand better Earth's evolution (following French Maritime Alps under Madame Gubler's the new insights brought forward by the theory guidance (IFP), received the message not to of plate tectonics), and to increase oil resources. cross the River Var to the east. Bouma's publica- Hundreds of thousands of kilometres of two- tion from the IAS meeting provided Stanley with dimensional seismic data were collected, pro- an answer as to why he was not permitted to viding continuous data-sets from platform to cross that river. Only one set of letters was the deep environment. It was thus shown that exchanged; no meeting was established. Both considerable lateral and vertical variations are Stanley and Bouma defended their dissertation present in a proximal to distal sense, very similar in the same month of 1961. It took the 1963 to Gressly's (1838) observations and Walther's AAPG-SEPM meeting in Houston, Texas, for law (1894), and with unexpected dimensions. the two young doctors to meet for the first (2) Several oil reservoirs, formerly attributed time, resulting in a joint publication emphasizing to platform environments, were now recognized the different approaches, as well as the similari- as having originated in deep-sea depositional ties of some of the geological characteristics environments. (Stanley & Bouma 1964). (3) Similarly, several bathymetric and seismic In The Netherlands dissertations have to be campaigns on modern deep-sea fans increased published, a financial burden to the student. knowledge of these depositional systems. Thus, Elsevier was planning a new series and asked in France, IFP participated in the 'Comit6 Bouma if they could use his dissertation to start d'Etudes P6troli6res et Marines' (CEPM) 30 A.H. BOUMA & C. RAVENNE framework with CNEXO, Elf EP, SNPA, Total- turbidity currents conducted by Kuenen (1937, CFP, on studies of the Cap-Ferret deep-sea fan 1964), Kuenen & Migliorini (1950), Kuenen in the Bay of Biscay (Coumes et al. 1982; et al. (1956, 1957), Middleton (1966a,b, 1967, Cremer 1983; Cremer et al. 1985; Nely et al. 1970), and Middleton & Hampton (1973) 1985; Ravenne et al. 1988b), Indus (Ravenne allowed a preliminary understanding of the et al. 1988a), Bahamas (Ravenne et al. 1988c), development of gravity deposits. The studies Rh6ne, etc. that demonstrated the importance of gravity- (4) Finally, the first course on seismic strati- generated sediment collapse at sea and transport graphy was written by Vail and the Exxon to deep water were chiefly known from the school, and published by the AAPG (1976). devastating effects on telephone lines (Heezen The following text is restricted to studies in the & Ewing 1952; Heezen et al. 1954; Gennesseaux French Alpes Maritimes and parallel laboratory et al. 1980; Piper & Savoye 1993). studies as they applied to the four points The results of these marine campaigns dealt mentioned above. Thus, many other important with the complex geometry of deep-sea fans contributions are not cited where their impact and the importance of very large remobilized was peripheral to these issues. volumes (up to 50km 3 in both the Cap Ferret Ravenne was strongly involved in points 1, 3 and Bahamas areas). However, most of these and 4, participating in the acquisition and the data were indirect data (seismic, bathymetry, interpretation of several marine seismic cam- magnetism, etc.) and lacked a straightforward paigns in the large exploration programme of correspondence with outcrop data. In the the SW Pacific. He was already using some 'seis- 1970s, all the geological effort at IFP was mic facies' even if several geophysicists consid- devoted to marine exploration. This was ered the ideas to be nonsense. He was very fantastic, but also somewhat frustrating for a happy when he was sent to the first course field-trained geologist who thought about the given by Vail et al. in 1976. Techniques of seismic great effort devoted by IFP to field studies in data acquisition and processing were in constant the 1960s (Sahara exploration). To compensate, development (Cassand et al. 1970; Cholet et al. Ravenne would take his holidays in the moun- 1979; Thillaye du Boullay 1977, 1979a,b; Grau tains. Just six months after the start of the Cap 1981), providing images relatively interpretable Ferret studies in 1978, he was in the southern by geologists. At that time Ravenne was also , in the Allos-Sanguini6re area. involved in a project aimed at the better interpre- The quality and the extent of the exposures tation of seismic data. The seismic interpretation surprised him because it allowed a direct com- course by Vail--a former student of Sloss, who parison with the scale of seismic data. He made a huge contribution to the evolution of hoped that these outcrops could be relevant to sequence stratigraphy (Sloss et al. 1949; Sloss the deep-marine environment. Returning to his 1963, 1988)--was the essential factor, particu- office, he immediately searched for literature on larly because this first course discussed all the the area and found several papers on the Gr6s reservations and hesitations of the method, thus d'Annot which was termed the 'Priabonian making it a potentially very rich tool compared trilogy' (Eocene-Lower Oligocene) (Bertrand to the AAPG 26 memorandum (Vail et al. 1896, 1936, 1946), and following investigations 1977a,b; Mitchum et al. 1977), which came out (Bouma 1962; Lanteaume 1962; Lanteaume later that year, settling a major part of the et al. 1967; Stanley 1961, 1975; Stanley et al. reservations. It also served as a support for the 1978) that had demonstrated that these sand- writing of a synthetic report (Ravenne 1978) stones were deposited in a deep-sea environment and the Ph.D. work of several students. A few by turbidity current processes. The provenance years later (1979), Ravenne became involved in of the sedimentary material was clearly identified modern deep-sea fan studies, starting with the first by Gubler (1958) and later by Ivaldi (1973, Cap-Ferret area (Bay of Biscay), followed by 1974, finalized in 1989 in his 'Habilitation fi two different deep-sea fans localized at the base Diriger des Recherches'). of the Bahamas escarpment, and the Indus At this time, Ravenne was working with deep-sea fan. Deep-sea fans were relatively Cremer (an academic from CNRS) on Cap- unknown entities, except through documenta- Ferret data and he decided to extend the scope tion of inferred onshore remnants, chiefly by of the work to include a comparison with this Mutti (1974), Mutti & Ricchi Lucchi (1974, field analogue. The first field study on the Gr6s 1975), Normark (1970, 1974, 1978), Walker d'Annot by Ravenne and Cremer was carried (1967, 1978), Walker & Mutti (1973), Bouma out in 1980, with a complete month devoted to (1962), Stanley (1961, 1975) and Stanley et al. examining these outcrops at a scale compatible (1978). Experiments in analogue modelling of with seismic resolution (at that time 10-50m in BOUMA SEQUENCE AND FRENCH MARITIME ALPS 31

..... ~ ...... ~ii!~!ii!!iii~i!!ii!~ii!i ~!!!!!~ ~i!!i') !i ¸i

ii, ~i ~iiii(i~!

Fig. 2. Gravity deposits observed on seismic marine data (Cap-Ferret) and at outcrop (Annot sensu lato). (after Ravenne & Beghin 1983, in Ravenne 2002a). The field-seismic comparisons helped to propose possible interpretations of some configurations. Inset A in the seismic profile shows the terminations of the high amplitude, sub-horizontal reflections in onlap against the inclined low-amplitude reflections. The analogy with photograph A (Chalufy) suggests a deposit of sandstones against slope clays. Insets C and D on the seismic profile again show high amplitude sub-horizontal reflections which can be interpreted as relatively massive sandstone deposits by comparison with photographs C (Cime de la Blanche) and D (Montagne de l'Avalanche). Inset B shows high-amplitude, sub-horizontal reflections eroded and overlain by chaotic reflections. The latter were normally interpreted as 'high energy" deposits, and hence potentially rich in sand. The comparison with photograph B (T6te Noire) shows that it could be mainly argillaceous deposits and hence without any reservoir property. The vertical sizes of photographs and of the seismic profile are relatively comparable (about 500 m for inset A, 200 m for photographs A, C and D, 400 m for photograph B. 32 A. H. BOUMA & C. RAVENNE thickness). Many results applicable to seismic It was believed at that time (Vail 1976; Vail stratigraphy were obtained, thereby justifying et al. 1977a,b; Mitchum et al. 1977) that the an extension of this work. Three observations very continuous seismic reflections were mainly in particular validated this first mission: (1) the generated by clay deposits, and that chaotic first identification of the onlaps at Chalufy, reflections indicated high energy from predomi- described as such (Fig. 2A); (2) the very long nantly sandy deposits. This study brought a continuity of certain coarse sandstone units contrary explanation: 'granule bars' seen in the termed 'granule bars' (described below), pro- Grds d'Annot outcrops, with their great extent viding a framework of depositional bodies and thickness, could generate very continuous compatible with seismic resolution (Fig. 2); and reflections, while largely unbedded shaly sedi- (3) the possible interpretation of the 'Schistes ments of the 'Schistes fi blocs' type could gener- blocs' (described by Kerckhove 1964, 1969) as ate chaotic reflections. Hence the interpretation major collapses affecting the eastern edge of the could be completely contradicted. The results basin where these sandstones were deposited. of these observations were not published, as con- These observations emphasized the importance stituting the general rule (i.e. great continuity and potential of the Gr6s d'Annot and led to the equals sandstones and chaotic configuration broadening of the field-work programmes by equals mixture), but attention was drawn to Cremer and Ravenne (1981, 1982). Thus, Annot this possibility. Once again, the removal of the sensu lato has been the most important survey older ideas required broadening of the seismic area in terms of duration (1980 to 1985), and by survey zones to regional profiles in order to the number of students involved [supervised by make it feasible to track facies distribution and Rich~, Tr6moli~res and Ravenne: final graduate evolution. work at ENSPM of Albussaidi, Butin-Kiener, These observations compelled the junior Calatayud, Inglis, Laval, Lepvraud, Le Varlet, author and his collaborators to: Mousset, Roy, Salim and Vially (lnglis et al. (1) combine all the formations present in the 1981)] and thesis work at the Dolomieu Institute SW alpine foreland basin fill (including the by Jean (1985) and Deharveng et al. (1987). 'Flysch des Aiguilles d'Arves', the eastern part A synthesis of all these studies was published of the Champsaur Sandstone in the Dourmil- by Ravenne etal. (1987). A palaeogeographical louse and du Fournel valleys); map, interpretative sections and synthetic sections (2) make it possible to attribute very different are among the main results concerning the Gr6s sedimentological facies to the same lithostrati- d'Annot area sensu lato. graphic unit. Uncertainty surrounded the onlaps identified Another important result was the identifica- on seismic surveys: did they result from an tion of the 'granule bars' and their sequence abrupt termination of strata against a basin arrangement (Fig. 3). These 'granule bars' are slope, or a progressive thinning below seismic very similar to the high-density turbidite deposits resolution? How were they formed? Observation described by Lowe (1982), and certain character- at Chalufy offered possible answers. istics of which had previously been clarified

l flagic to pelagic l Inclined stratification Water escape tinning up

c~ "Granules" (up to pebbles) 2 Main sedimentary body

Mud.pebbles l~roslon "Homogeneous" sandstones dckening up @

Fig. 3. Annot, 'Granule bar' and typical "sequence' (after Ravenne & Beghin 1983, in Ravenne 2002a). Part A shows the complete superposition of the levels observed in a granule bar. This may be more complex in a proximal position where several bars may be amalgamated, especially in case of fragmentation of the initial sliding body: it is accordingly not rare to observe at the base superposition of several levels with pebbles and granules, and only the last bar displays the upper levels. Part B shows the typical sequence with the thickening- up zone often less developed than the thinning-up zone. BOUMA SEQUENCE AND FRENCH MARITIME ALPS 33

(Lowe 1975, 1976). The results were the subject important for the interpretation of deposits and of a film and several publications (Ravenne & erosion mechanisms. Beghin 1983; Jean et al. 1985; Ravenne et al. (1) The first is the hydraulic jump created at 1987, 1988b). Parts of these results were used in each slope break. These slope breaks are the theses by Cremer (1983) and Jean (1985). especially frequent on the flanks of the Cap- These experiments provided an explanation for Ferret depression and in the Bahamas scarp. lateral facies evolution observed on both The forces, developed from the bottom upward, marine seismic and outcrop data. are considerable. In powdery snow avalanches, such forces are responsible for the tearing out and projection of larches to heights of sometimes Laboratory experiments several tens of metres. The larches are then re- inserted into the body of the avalanche. These These experiments were conducted with Beghin are probably the only forces capable of dissociat- of the Centre National du Machinisme Agricole, ing the particles of previously consolidated units du G6nie Rural, des Eaux et For&s (CEMA- while entraining them into suspension, tearing GREF), who was conducting flume experiments out mud clasts on the slope (bearing in mind to model snow avalanches by triggering gravity the powerful cohesion of the clay that was once flows of particles or dense fluids in water. The deposited). The mud- or silt-clasts are then objectives were forerunners to those undertaken reinserted in the dense body of the surge (where recently in several laboratories in the UK, all the material has now been completely dis- Canada and the USA. Systematic and accurate sociated) and deposited nearly immediately experiments were later conducted by Laval above the base of the 'granule bar' (Fig. 3). (1988). They are superimposed on the very first layer of this bar formed of relatively well-sorted sand- stones compared to the subsequent ones. These Flume experiments basal sandstones generally lie without significant erosion on the underlying strata. They are depos- The first experiments were performed in the early ited by a density current process and originate in 1980s in the 10m long flume of the Fluid the first suspensions induced by the hydraulic Mechanics Laboratory of the University of jump(s). The rest of the hydraulic jumps can Grenoble. The original idea was to model the cause the dislocation of the initial mass into density surges that appeared to correspond to several units which supply density surges that most of the mechanisms responsible for the succeed each other in one, more or less long deep-sea fans (developed from the numerous interval (one hour, one day?), and cause the collapses upstream of these fans) and the deposition of complex bars with the amalgama- evolution of the resulting facies. Each failure tion of frequently truncated sequences. produces a finite amount of material and a den- (2) The second application is the density surge sity surge, which is specifically characterized by hydroplanes preserving the substratum from a flow of a finite quantity of heavy fluid without substantial erosion even under very massive a subsequent input of dense fluid from behind. sliding bodies. The front of the density surge is The earlier experiments by Kuenen (1937) and raised above the substratum and the surge. Kuenen & Migliorini (1950) concerned turbidity Most of the flume experiments were conducted (or density) currents, characterized by a more with perfectly calibrated silica microspheres, and continuous supply of heavy fluid. Some studies some with clay, and clearly showed the high and were published, such as those by Liithi (1980, low transport efficiency aspects proposed by 1981) and Kelts & Hsfi (1980), involving density Mutti & Ricci Lucchi (1975). Once the initial surges, but these retained the term 'turbidity mixture contains more than about 10% clay, current', creating confusion. The terms 'turbid- the surge moves along the entire length of the ity/density current' and 'density surge' are very flume and is stopped by the length of the flume. precise. Unfortunately, the use of the first term By contrast, with silica beads, the run-out dis- usually leads to wrongful attributions. Density tance of the surge is limited to a few metres, surge and density/turbidity current have very and is a function of the grain size distribution. different characteristics. They represent two The importance of the distinction between extreme types of turbiditic flows, while many density surge and density current has already intermediate cases exist (Fig. 4) (Ravenne & been emphasized. A surge can obviously function Beghin 1983). for a period as a density current, and alternations The research was strongly based on the Annot between unsteady surge and steady current sandstone and two applications are particularly may exist. A 'granule bar', with its sequential 34 A. H. BOUMA & C. RAVENNE

, i Initial material [ I ~,, ._),Turbulent layer Ambient fluid I (~) "~..--)}~ Hydraulic jump ] - "~" ~J ~ ~ I

,1® ® , ¢ Beginning of Cessation of the remaining! Transitory zone , I sliding I unsuspended mass I Decreasing of large = I iI turbulent eddies Ii Slope • 30 to 45 ° ] Slope ~---5 ° i Slope = 0 °

---" i s ,

® ® MY Mass - Flow W Water escape GF Grain" or "dtbris flow IS Inclined stratification

Fig. 4. Evolution of a surge type density flow and sedimentation associated with the different phases (after Ravenne & Beghin 1983, in Ravenne 2002a). The upper part shows the evolution of a surge type flow (characterized by the flow of a finite quantity of dense fluid). Note the formation of the hydraulic jump at the slope break of which the energy is considerable (serves to tear off pebbles from the substratum); many slope breaks generally exist in a margin or canyon profile. Note also at 5 the presence of a fluid tongue in front of the surge and under it, protecting the substratum from erosion. The lower part shows the deposits corresponding to each of the flow phases.

arrangement, corresponds to an essentially sin- Conclusions gular event, though sometimes multiphased. The duration of its emplacement is very short The beautiful French Maritime Alps have seen compared to the total duration of about 1 Ma the inception of several influential geological for the deposition of the entire Grts d'Annot. ideas and influential geological careers. The The volume of material involved in the deposi- Bouma Sequence placed the area firmly on the tion of a single one of these parts can exceed international geological map and in subsequent 15km 3, which is closely comparable to the decades, a regular stream of new discoveries and volume of many collapses along the Armorican insights have raised worldwide awareness of this margin (Ravenne et al. 1988b). spectacular array of seismic-scale exposures. The literature often displays a confusion The field studies carried out on the Grts between the two processes, for mainly historical d'Annot in the 1980s, and in South Vercors reasons, connected with the first experiments (France) and Taiwan, initially in order to and ignorance of major gravity collapses, and interpret seismic data better. It has been possible because only the fluid mechanics experts had dis- to demonstrate the value of combined efforts cerned this distinction. For Ravenne it appears dealing with both onshore and offshore studies. that many of the thick hydrocarbon reservoirs The scales of these studies are different from of deep-sea fans originated from density surges, present ones (focused on detailed reservoir given the high frequency of catastrophic characterization), but the results remain valid. collapses in the margins. Only these are appar- Ravenne firmly believes that these studies had a ently capable of mobilizing very large quantities crucial impact on the powerful development of of material. sequence stratigraphy. BOUMA SEQUENCE AND FRENCH MARITIME ALPS 35

A decisive turning point was the identification Ravenne also thanks the Oil & Gas Science and on seismic data of huge submarine scars, which Technology--Rev. IFP for authorizing the reproduc- heralded the start of density surge studies, critical tion of the figures. He wishes to thank N. Doizelet, to understanding the evolution and the resedimen- Y. Catot-Martin, P. Le Foll, D. Deldique, M. Jehl, J. Brumaud and E. Jacquet, for their essential technical ration of large volumes. A wealth of results, assistance. obtained over a 10-year period from seismic Finally, the two authors thank S. Lomas and campaigns, field studies and experiments, have P. Joseph for their invitation to write this introductory shown the importance of catastrophic events, the chapter. improvement of seismic stratigraphic concepts, some new questions for onshore geology, the importance of chaotic facies, etc. In the Gr6s d'An- Abbreviations not, studies were devoted to a better understand- ing of seismic reflections. The main points were AMCO: AMblioration de COh6rence = coherence the Chalufy onlaps, the large gravitational slides enhancement CEMAGREF: CEntre national du Machinisme of the 'Schistes/t blocs', and the sequential order- Agricole, du G~nie Rural, des Eaux et For&s ing of the 'granules bars' easily explained by CEPM: Comit6 d'6tudes P6troli6res et Marines density surge experiments. The flume and tank CFP: Compagnie Fran9aise des P6troles experiments brought insights into some turbidite CNEXO: Centre National d'EXploitation des features, demonstrating the importance of the Oc6ans different hydraulic jumps and of the water layer CNRS: Centre National de la Recherche Scientifique below the head of density surges. DHYCA: Direction des HYdroCArbures The junior author is very pleased with the EEC: European Economic Community renewal of studies on the Gr6s d'Annot sensu ENSPM: Ecole Nationale du P6trole et des Moteurs FSH: Fonds de Soutien aux Hydrocarbures lato because he considers that there is still a consid- IFREMER: Institut Franqais pour la Recherche et erable amount of work to be done in order to l'Exploitation de la Mer understand the evolution of these deposits. After IOS: Institute of Oceanographic Sciences an AAPG field trip (Ravenne & Vially 1988d), ORSTOM: Office de la Recheche Scientifique et he led a trip in the Annot-Sanguini6re area with Technique d'Outre-Mer sedimentologists. A few hours later, all the Gr6s SNEA(P): Soci&b Nationale Elf Aquitaine d'Annot sediments were interpreted by these (Production) sedimentologists as having been deposited in shal- SNPA: Soci6t6 Nationale des Pbtroles d'Aquitaine low marine environments! The only stable part TWT: Two Way Time was the interpretation of 'granule bars' as resulting from density surges. The wide diversity of the Gr6s References d'Annot, their vast dimensions, and their many unanswered questions justify the presence of sev- BERTRAND, L. 1896. Etude gbologique du Nord des eral teams from different organizations working Alpes-Maritimes. Bulletin du Service de la Carte with different approaches. gOologique de France, IX, 56. BERTRAND, L. 1936. Sur l'fige des gr6s d'Annot dans les Bouma is very thankful for the education he received Alpes-Maritimes franco-italiennes. Comptes from Kuenen, Doeglas, Shepard and all other teachers. Rendus sornmaires de la Soci~t~ G~ologique de He also thanks the many colleagues and students he France, 73, Paris. had the pleasure of meeting and/or working with. His BERTRAND, L. 1946. Histoire gOoIogique du sol franfais, studies conducted in the eastern part of the Alpes 2, Flammarion, Orl6ans. Maritimes were the real introduction to the turbidite BOUMA, A. H. 1959a. Some data on turbidites from the part of his scientific career. For him education is a Alpes Maritimes, France. Geologie en Mijnbouw, never-ending process, making life a never-ending 21,223-227. enjoyment and challenge. Those studies provided the BOUMA, A. H. 1959b. Flysch Oligoc6ne de Pei'ra-Cava base for his research in several other areas. (Alpes-Maritimes, France). Eclogae Geologica The work discussed by Ravenne was mainly made Helvetica, 51, 893-900. possible due to IFP scientific, technical and financial BOUMA, A. H. 1962. Sedimentology of Some Flysch support. Also noteworthy was the active participation Deposits. Elsevier, Amsterdam. of numerous students of the ENSPM (IFP School) BOUMA, A. H. & COLEMAN, J. M. 1985. PeYra-Cava during their final graduate courses, DEA diploma turbidite system, France. In: BOUMA, A. H., and Ph.D. dissertations. The work done at IFP was NORMAR~:, W. R. & BARNES,N. E. (eds) Submarine initiated by L. Montadert who always supported the Fans and Related Turbidite Systems. Springer, junior author. Special thanks are due to J. Perriaux New York, 217-222. and C. Kerckhove of Institut Dolomieu for their help CASSAND, J., FAIL, J. P. & MONTADERT, L. 1970. in the field and for allowing students to prepare their Seismic reflection in deep water (Flexotir). Geo- Ph.D. on the Gr6s d'Annot. physical Prospecting, 18, 600-614. 36 A. H. BOUMA & C. RAVENNE

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Les Grbs d'Annot au Nord-Ouest du (Bay of Biscay). American Association of Petro- massif de I'At\gentera-Mercantour. Th+se de leum Geologists--Memoir Studies in continental l'Universitb de Grenoble. margin geology, 34, 583-590. JEAN, S., KERCKHOVE, C., PERRIAUX, J. & RAVENNE, C. CREMER, M. 1983. Approches sOdimentologique et g~o- 1985. Un mod61e pal6og6ne de bassin ~i turbidites: logique des accumulations sOdimentaires. L'~ventail les gr+s d'Annot du NW du massif de l'Argentera- proJond du Cap-Ferret (Golfe de Gascogne). La Mercantour. GOologie Alpine, 65, 115-143. sgrie des Grbs d'Annot ( Alpes de Haute- ). KELXS, K. & HSO, K. J. 1980. Resedimented facies Th&e de Doctorat Sciences Naturelles Bordeaux. of 1875 Horgen slumps in Lake Zurich and a R&. IFP 32036, Technip, Paris. process model of longitudinal transport of turbid- CREMER, M., ORSOLINI, P. & RAVENNE, C. 1985. Cap- ity currents. Eclogae Geologicae Helvetiae, 73, Ferret fan, Atlantic ocean. In: BOUMA, A. H., 271-281. 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Sur le flysch des Alpes frangaises Jura Soleurois. Nouveaux M~moires de la Soci&~ et italiennes. Comptes Rendus de l'AcadOmie des Helv~tique de Sciences Naturelles, Neuchfitel, 2. Sciences, Paris, CCXLIII, 1697-1701. G~BLER, Y. 1958. Etude critique des sources de mat&iel KUENEN, P. H., FAURE-MURET, A., LANTEAUME, M. & constituant certaines s&ies d&ritiques dans le FALLOW, P. 1957. Observations sur les flyschs des Tertiaire des Alpes franqaises du sud: formations Alpes franqaises et italiennes. Bulletin de la SociOt~ d6tritiques de Barr6me, flysch "Gr+s d'Annot'. G~ologique de France, VII, 11 26. Eclogae Geologica Helvetica, 51,942-977. LANTEAUME, M. 1962. Contribution gt l'&ude g~ologique HEEZEN, B. C. & EWING M. 1952. Turbidity currents des Alpes Maritimes franco-italiennes. Th6se and submarine slumps and the 1929 Grand Science Naturelles, Paris, no. 4649. Banks earthquake. American Journal of Science, LANTEAUME, M., BEAUDOIN, B. & CAMPREDON, R. 1967. 250, 849-873. 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