ten Haaf, Ernst

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   University of GroningenGraded beds of the northern Apenninesten Haaf, ErnstIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1959Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):ten Haaf, E. (1959). Graded beds of the northern Apennines: Sedimentary structures and directions ofsupply. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 01-02-20249 3SUMMARYObject of ihe present investigation were the syngeneticstructures of  graded beds (" turbidi tes) of  the Apennines,their interpretation in the l ight of the turbidity currenthypothesis, and their orientation. A regional mapping of theseor ientat ions has disclosed a s ingle persistent t rend of  currentf low, f rom which conclusions can be drawn regarding thesource of the clastics, the mechanism and environment ofsedimentation, and even the subsequent tectonics.Ch.I .  Three major Tert iary turbidi te format ions:  macigno,marnoso-arenacea, and Picene f lysch, have been surveyedin detai l .  These format ions represent s imi lar ,  successivestages of orogenic development, and their sedimentaryphenomena are very much the same.Ch.I I .  Strat i f icat ion is extremely regular.  The turbidi te beds arecommonly graded; but, as the grain síze rarely exceeds thatof medium sand, grading in thick beds is not very markedexcept near the top.These top levels,  and separate f ine-grained beds, aregeneral ly laminated and rnay reveal  character ist ic structures:r ipples ( t ransversal ,  per ic l inal ,  or  longi tudinal) ,  current-laminat ion,  convolut ion.  Some laminat ionplanes are var ious-ly str iated. Coarse, elongate grai .ns tend to be al igned.Ch.I I I .  Among sole markings f lute casts are the most common. On afew bedding planes, minute terraces record the laminat ion ofthe eroded underJ,y ing mud. Frondescent casts are a noveltype of erosional marking.-  Groove casts intersect,-on many'  soles,  at  angles up to 30o;the directions usually constitute two distinct systems of whichone is parallel to the principal orientation. The oblique systemsare probably due to offshoots advancing in fron of the maincurrent.  The major i ty of  grooves is supposed to have beenmade by benthonic animals, dislodged and swept along passi-vely at high speed by the turbidity current.Sl ide marks and f i l led erosion channels occur.Ch. IV.  Many load casts evident ly developed from erosionalmarkings. Some other soles are wrinkled in variegated andmore or less random patterns. A few recurrent and distinctivefornrs (striations, squamiform and syndromous load casts)have been recognized.Slump structures are rare; they constitute zones of differen-tial sl ip parallel to the bedding. To judge from the orientationof these slump foldings, many are due to posterior tectonicsrather than to the primary depositional slope. One instanceof injected sand dykes has been found.Ch. V. Fossi ls are very scarce. Reworked plant f ragments occurin turbidites, but not in the intervening pelites. The situationof echinid remains suggests burial in situ by turbidite sedimen-tation. Antecedent tracks and burrows in the mud floor arepreserved as casts on turbidi te soles.  Post-deposi t ional ,  sand-filleeco lCh.  V I .  Aoriebed,visihavrCh. VII .  Ftectdon'wit.meIhasCh. VII I .  TpanDeFfiorApeI1maltecla n .PlarIo f lThthYrturro:tecdelthederev:f" !t r ttotr(l irapth,C h . I X .A1C istthe syngeneticle Apennines,bidi ty currentnapping ofthesetrend of  currentt regarding theenvironment ofr ic s.ons: macigno,been surveyedàf,  successiveir  sedimentary'b id i te beds arely exceeds thatof very markedned beds, arest ic structures:inal) ,  current-)s are var ious-:  a l igned.;common.  On ae lamination ofls are a novelg ies  up  to  30o;stems of  whichbl ique systemsn of the mainI  to have beenrt  a long passi-r ,)m erosional'ariegated andmd distinctives  load cas ts )rs of differen-he orientation:ior tectonic sOne instancements occurThe situationl i te sedimen-rud floor are.tional, sand-94fil led burrows through and below thick turbidite beds pose anecological  problem.Ch. VI.  A s ingle constantcurrent direct ioncan be i .nferredfrom theorientation of the various syngenetic structures of one turbiditebed. In each outcrop the current direct ions of  near ly al l  thevis ib le beds correspond closely to a s ingle t rend; these trendshave been mapped.Ch.VI I .  For  the  measurement  o f  sed imentary  d i rec t ions ,  the  pre-tectonic s i tuat ion of  the strata must be reconstructed; th is isdone most easi ly by the use of  a special ly deslgned compass.With steep dips,  axial  p i tch mustbe al lowed for;  and measure-ments on overturned beds are inval id unlesr;  the tectonic axishas been careful ly ascertained.Ch, VII I .  The observed current t rends are recorded on the accom-panyingmap: their  uni formity and paral le l ism are remarkable.Deposi t ion of  the turbidi tes was apparent ly f rom currents thatflowed lengthwise from the northwestern extrernity of theApennine range, paral le l  to the tectonic str ike.I t  is  a lso revealed that large root less s labs of  macigno andmarnoso-arenacea have been var iously rotated from their  pre-tectonic or ientat ion,  wi thout di .s integrat ing.  This const i tutesan independent neïv proof of allochthony, as well as of em-placement by indiv idual  s l id ing as opposed to nappe tectonics.Turbidi ty currents must have f lowed down the general  s lopeof the basin;  def lexion by the Cor io l is ef fect  was very s l ight .The uni form, longi tudinal  current t rend thus necessi tates twohypotheses: an axial  s lope of  the successive foredeeps whereturbidi tes were deposi ted,  and a source of  c last ics to thenorthwest.The f i rst  hypothesis is in harmonywith what is knownof thetectonic development of  the northern Apennines; moreover,deposi t ion i tsel f  would tend to bui ld a gradual  s lope away fromthe source area. Such long slopes imply deposi t lon at  bathyaidepth,  which is conf i rmed by the avai lable paleontologicalevidence and by the complete absence of  shal low-waterfeature s.Locat ion of  the source areaof sand at  the northwestern ex-tremity of  the chain gets r id of  a long-standing di f f icul ty:howto account for  the suddencopious suppiy of  sand to an Ol igocenetrough, f lanked by tectonic r idges that consj .sted of  marls andl imestones only.  In the area where turbldi ty currents nowappear to have or ig inated (Ligur ia and adjacent regions),  onthe contrary,  arenaceous sediments prevai led.Ch.IX. Observat ions on a number of  minor turbidi te ser ies of  theApennines serve toconf i rm and ampl i fy some of these points.Calcareous turbidi tes exhibi t ,  as far  as observed, the samestructural  phenomena as sandstones.

Graded beds of the northern Apennines:Sedimentary structures and directions of supply

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Graded beds of the northern Apennines:Sedimentary structures and directions of supply

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