viseras & arribas (2009) - visit to fonelas p-1 site-print

8/7/2019 VISERAS & ARRIBAS (2009) - Visit to Fonelas P-1 Site-print

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2009 SEQS CONFERENCE, ORCE AND LUCENA, SPAIN

VISIT TO FONELAS P-1 SITE

César VISER AS, Departam ento de Estratigrafía y Paleontología, Facultad de Ciencias,Universidad de Granada, 18071 GranadaAlfonso ARRIBAS, Área de Investigación en Patrimonio Geológico, Departamento de

Investigación en Recursos Geo lógicos, Instituto Geológico y Minero de E spaña, 28003Madrid

THE GUADIX BASINGeological general features

The G uadix Basin is located in the central sector of the Betic Cord illera and o ccupiessome 4600 km 2 on the contact between the Internal and External Zones. The basin‘ssedimentary filling has been divided into six genetic units whose bo undaryunconform ities are related to both tectonic events and eustatic changes. The two lower

units (Units I and II) are Late Tortonian, correspond ing to a stage of m arinesedi mentation, the thi rd (Unit III) i ncl udes sedi me nts deposited duri ng sea retreat fromthe central sector of the Betic Cordillera at the end of the Tortonian and the three m ostmode rn (Units IV, V and VI) cover the L ate Turolian to the Late Pleistocene, which w asa period of exclusively continental sedimentation in an endorheic (a basi n w ith internaldrainage, where no surface drainage reaching the ocean can be detected) basin context.

This sedimentary stage was interrupted in the Late Pleistocene, when ageom orphological i nversion of the basi n took place and it was captured in its enti rety bythe drainage network of the Guad alquivir River, becomi ng an exorheic domain m ai nlysubjected to erosion. The Fonelas P-1 large mam mals site is dated to 2,000,000 yearB.P. and forms part of the continental sediments of Unit V (Upp er Pliocene).

Palaeogeography and local sedi mentary contextUsing both the origin of the sediment supply and analysis of sedimentary facies duringthe continental filling of the basi n, two sectors with different depositional characteristicshave bee n differenti ated: the eastern sector, mostly occ upied by a l arge shal low lakeacti ng as base level for the who le basi n, and the western sector, dom i nated by alluvialfans and fluvial pl ains, draini ng towards the eastern l ake. Three m ain drainage system shave been disti nguished in this western sector, where the Fon elas P-1 site is located.

Lyi ng appro xi mately parallel to the axis of the basi n, the Ax ial System is represented bya broad fluvial val ley through which the mai n drainage to the eastern l ake took place. I nits proximal zone this system conn ects with alluvial fans lying at the foot of the SierraNeva da rel iefs. The rest of it consists of a flood plai n crossed by high si nuo sity channels(meanderi ng rivers) and occasionally occupied by shallow ephem eral l akes andpalustri ne areas. The Fonelas P-1 site is located pal aeogeographical ly on the flood plai nof this Axial System, near the mouth of a channel i n one of the shal low l akesThe Ax ial or Longitudinal System was fed transversal ly by two other drainage systemsmade up of coalesci ng alluvial fans and nam ed the I nternal and External TransverseSystems, as thei r source areas we re i nstal led on the rel iefs of the I nternal Zone s (SierraNevad a and Sierra de Baza) to the South, and the External Zones (Sierra Arana, Mon tes

Orientales, Sierra del Pozo an d Sierra de Ca zorl a) to the North. I n the case of the top ofUnit V (Upper P liocene) and in Unit VI (Lower P leistocene), the Axial System w as

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of flow, when fine sedi m ents settled and cl ay p l ugs developed that gradual ly fi l led andsoftened the topograph ical depression of the old channel.- Facies association D (flood plain)

This is located in gradual transition above facies association C . It is a series of cycleswith two intervals: a lower one of horizon tally l ami nated lutite (lithofacies Fl) and

calci um carbonate nodules, occasional ly begi nni ng with medi um to fine sand withri pples (lithofacies Sr); and an upper i nterval of nodulous l i me stone or marly l i m estoneand abund ant root traces (lithofacies M r). These elementary lutite-carbonate cyclesrecur four times with remarkable (tens of metres) extension. Disperse large mamm alfossils are found, although no ichnites can b e detected, unli ke the case of the l utitelayers i n facies associ ation C.Because of the si mi l arity between the se sedi ments and other exam ples described i n thel iterature, we i nterpret this facies associ ation as distal flood pl ai n deposits. Bycomp arison with other outcro ps i n the basi n, where this facies associ ation can be tracedby di rect correlation to the channel whose overflow produced it, we can esti mate adistance of around one hundred metres from the si nuous active channel .

- Facies association E (bioturbation)

This occupies the sam e stratigraphic position as facies association C (abando nedchannel) and is separated from it by a highly irregular net surface. Facies association Eis a ribbon-shaped body 25 to 40 cm thick and tens of centi metres wide mai nly orientedSW -N E. T he base has a very irregular morphology, whi le the top is fl at-horizontal .Seen in cross-section, the boundary surface of this body has vertical wal ls withscalloped morphology (sm all saw-toothed cavities) tens of centi metres thick. The mostcharacteristic lithofacies of this body are sub-angu lar, very irregularly sized fragmentsof l utite strata from assoc iation C held in a m atrix of sand, cl ay and si lt. It has nointernal organization (massive or chaotic structure) and there are some rather narrowlevels of sand not more than 3 cm thick with ri pples similar to the sandy i ntervals infacies association C (Sr). It should be pointed out that there is often lateral coincidencebetween the lutite levels of association C and stratiform lutite fragments in faciesassociation E. The importance of association E is that it contains the large mamm alfossil concentration with most elemen ts and highest diversity of species at the FonelasP-1 site (Trench B).

W e interpret this facies to be the result of animal bioturbation of the sedi m ents ofassociation C (abandoned chann el) exposed to weathering and who se original featureswere com pletely destroyed by the effects of mam mal passage, si nce we take the site,li nked with facies association E, to be a hyena den w here these ani mals w ere active. The

excavating action of these animals‘

feet on a soft substratum (clay plugs) was the maincause of the massive or ch aotic structure of association E. This i nterpretation issupported by two m ain pieces of evidence: 1) the presence of large mam mal ichnites inthe l utite i nterval of facies association C, i mm ediately prior to association E and onwhich the latter l ies at several places of the site and 2) the conc entration of the m ostabundant accumul ation of bones i n the bioturbated lithofacies, as there is a di rectrel ation between this lithofacies and the fossil record. Similar examples of deform ationof soft sedi ments by passage of large vertebrates have been described i n both modernand ancient fluvial and marginal lacustri ne flood pl ai n environments.

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Sedimentological/taphonomical production of the siteThe largest concentrations of bone rem ains at the Fonelas P-1 site (Trench B ) appear inwha t we have de scribed as facies associ ation E, l ocated in a very specific position inone of the characteristic cycles of the succession in Unit V of this sector of the basi n.The simple lithofacies making u p associations A to D, as w ell as the spatial relation

between facies associ ations were expl a i ned in 2006. The sedi mentological evidencei ndicates that the area was crossed by a si nuous fluvial channel flowi ng north-eastwardswhich at this poi nt made a conve x curve towa rds the East. The reconstruction of thischanne l i n the area excav ated sugges ts its si nuous na ture, as is corroborated by theconti nuation of the sedi mentary body to the North, where, several hundred m etres fromthe site, another curve of the same chann el can be reconstructed, i n this case convextowards the West.

Unfortunately, neither the base of the channel nor the accretion margi n duri ngmaxim um fluvial activity outcrop sufficiently well for observation. Howev er, the grainsize of the sediment and the size of the bars and other bedform s suggest that this was

not the mai n channel of the A xial System, but rather one of the m any meanderi ngsecondary channels crossi ng the distal plai n of the system and connected to the mai nchannel . Taki ng the data avai lable from the outcroppi ng part of this channel and bycom parison with other well exposed exam ples in this sector of the basin, we canesti mate a size for this channel i n bankful l state of 6-8 m wide and around 1.5 m deep.The rem arkable facies associ ation E (bioturbated) is clearly unl inked to this evol ution ofpurely fluvial processes. Moreov er, it does not appear i n the other cycles of thesuccession. The fact that it is coetaneous with association C (aban doned ch annel) mean swe can genetical ly link the animal bioturbation with the last stages of the chan nel‘sevolution. Thus, the slight depression form ed by the residual chan nel in the stage ofabandonment (ox-bow lake), occasionally ponded by both rainwater and overflow fromthe nearby active channel, would have been a rel atively protected area, with easy accessto water for the ani mals, probably used by some (carnivorous scavengers) as feedingplace and den. This hypothesis of a hyena d en is also based on da ta, which showi ntensive feedi ng on bones by scavengi ng carnivores, as well as the fact that the ani malsdid not die at the site (with the possible exception of Pachycrocuta brevirostris cubs).Passage of ani mals over such a depression w ith a very soft substratum w ould havecaused a very dense pattern of tracks, creati ng narrow corridors with an i ntenselybioturbated bottom, coinciding approx i mately in orientation with the abandonedchanne l). After complete fi ll i ng of this residual channel, the topograph y wou ld havebeen ho mog enized at the level of the flood plain. This is why the particular location of

the site ceased to be a preferenti al occupation zone for the ani m als, j ust at the begi nni ngof the developm ent of facies associ ation D (flood plain). At this poi nt, the main animaloccupation m ust have transferred to another place providing the topographicalconditions described above (proba bly to Fonelas SCC-1 p aleontological site, onekilometre to the N orth). The high sedi m entation rate in the abandoned channel, resultingfrom bo th the local concentration of sediment from rainfall and detrital supply fromoverflow of the active chann el in its new position (about a hundred m etres from itsprevious position), and from chemical preci pitation of the flood pl ai n, led to the buri alof the fossil accum ulations. This genetic contex t characterizi ng the site remainedoutside the erosive i nfl uence of fluvial channels, which were d isplaced tens or hundredsof metres from the abandon ed channel. Consequ ently, the position of this site in the

context of the local evol ution of an alluvial channel abandoned by avulsion coincideswith that of other vertebrate sites described in the literature.

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The m ain results of the stratigraphic and sedime ntological study are the following:- On the scale of the general pal aeogeography of the b asi n, the Fonelas P-1 site islocated on the distal stretch of the axial drainage system of the G uadix Basi n, near itsconnection to a sha llow lake, occupying a pa laeogeographic situation similar to that ofmany other vertebrate sites.

- The site is located in a sedi m entary cycle typical of a m eanderi ng fluvial system. Thiscycle consists of four fac ies associations related to fluvial processes: (A) gravel and/orsand in layers with sigmoidal geom etry, caused by the lateral accretion natural to thefi ll i ng of a si nuous channel, (B) sand and l utite i n wedge-sha ped bodies abutti ng on tothe erosion bank o f the channel, i nterpreted as levee depos its, (C) fine sand an d l utite i nsigmoidal laminae, gradual ly overlying the A facies and representing progressivechannel aband onm ent deposits, (D) lutite and carbonate in extensive horizontal layerslying directly on the C facies and record i ng typical flood plain sedi mentation.- The m ain accumu lation of large mamm al fossils (Trench B) is found in a faciesgenetically independent of those described above, as it is unconne cted with purelyfluvial processes. This facies (E) consists of very angular fragm ents of lutite of the C

facies (channel abandon ment) w ith no internal organization, held in a matrix of sand,silt and cl ay and is interpreted as the result of bioturbation of a soft substratum byconti nuous passage of l arge m amma ls (carnivorous scavengers, specifical ly hyaenids) i nan occupation space.-- The detai led palaeogeographic context i nferred for facies E is that of an abandonedmeand er. This would have described a slight topographic depression that wasperiodical ly flooded, either by rai nfal l or by smal l overflow from the distant activechannel, and occupied by large mammals.-- The type of facies represented by association E has never be fore been identified anddescribed in continental basi n fi l l i ng. Its sedi mentological and pal aeobiologicali mportance is du e to the fact that these are biogenetic facies characteristic of thebiological activity of large scaven gi ng carnivores on fluvial substrata. Whether theypresent fossi l content or not, they are predictive, as they i ndicate sedimentaryinterruption, subaerial exposure and biological occupation whe rever they ma y beidentified in the geological record. Reco gnition of this facies association can be used asa sedimentological criterion for prospecting large mam mal activity in futurepalaeontological research.

FOSSIL RECORD A T FONELA S P-1 (Trench B)The Fo nelas P-1 site contains a vertebrate fossil assemb lage consisting mainly of largemamm al fossi l remai ns -- as wel l as smal l m i nority of amphi bi ans, reptiles, smal l

mam mals and birds - by which it can be dated to the Late U pper Pliocene (in the top ofUnit V of the Guad ix Basin), near the Pleistocene bound ary (Late Villafranchian, ca 2,0Ma).In four seasons of systematic excavation, al most three thousand bone fragm ents wererecovered. Man y are anatomically complete to a high degree (allowing their taxonom icclassification), which leads us to consider this as the most imp ortant large mam mals sitefrom the end of the Pl i ocene i n the enti re I berian Peni nsul a.

A nalysis of fi rst and l ast appearance data (FA D and LA D) of the species identified todate, and new pal aeomagnetic results, corroborates the hypothesis of the ti me-scalebei ng on the Late Upper Pl iocene (2,0 Ma) in zone MN Q18.

The faun al assemblage to date identified at this site consists of 32 species of mam mals(Mam malia). Four groups of large mamm als have been identified according to their

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paleobiogeographic origin and the ti m e-scale of thei r i ncorporation i nto the I beri anpaleomastocenosis: i) a group of ani mals typical of the Late Pl iocene i n Europe, someof which extended from A sia i nto these ecosystems around 2,6-2,5 Ma; i i) a secondmam mal association of Asian origin reaching these latitudes during the Late UpperPliocene; iii) a third group na tive to Africa which also reached the Iberian Peninsula

during the La te Upper P liocene; iv) a fourth set of endem ic taxa. There is also a fifthgroup of anim als at Fonelas P-1 of uncertain origin (either Asian or African) thatreached Atl antic Europe in the same brief i nterval . Thanks to the qual ity of thepaleontological remains, their extraordinary state of preservation and the abunda nce ofskeletal elemen ts, advanced taxonom ic study has led to verification of the presence ofnew species or subspecies of the genera Meles, Canis, Megantereon, Gazellospira,

Croizetoceros, Capra and Potamochoerus.

As this is the only known paleontological record with such a v ariety of species of suchdiverse origin, the large mam mals assemblage at Fon elas P-1 holds extremelyinteresting information for the reconstruction of the m ain migratory routes and theinterrelations betwe en A frican and E urasian species. In addition, the high scientific

i nterest i n this site is due to the fact that, because of the time -scale and com bi nedpresence of A frican and Caucasi an species, it is the only site i n w estern Europe similarto the Cauc asian site at Dmanisi. Fonelas P-1 is, therefore, the first evidence in Europeto al low defi nition of the paleoenvi ronmental framework of the L ate Upper Pl iocene,when the fi rst humans spread be yond A frica. As such, therefore, attention should bedrawn to the enorm ous si mi l arities between the sedi mentary envi ronme nt of Fonelas P-1 and the recently recon structed context of the sites of the earl iest stone tool makers i nthe Awa sh River Basi n, Ethiopi a.The provisional assembl age of this site is heterogeneous as regards thepal aeobiogeographic significance of the identified taxa and also thei r biochronologicalsignificance. In view o f the foregoing, the taxonom ic study of Fonelas P-1 w ill lead tointeresting paleon tological discoveries regarding faunal turnover and d istribution intime of different groups across the Europea n Pliocene-Pleistocene boundary.

Out of al l the new sites located by our team si nce 2001 in this area of the Gu adix basi n(62 locations with large mamm al records), the Fonelas P-1 site has proved to beespecially rich in num ber and d iversity of large m amm al remains. It is significant thatmost of the taxa identified at this location are represented by bo th cranial elements(mainly com plete crania, half maxillas and half lower jaws) and parts of the p ostcranialskeleton (bone s of the spi ne and l i mbs) that in many cases ca n be identified asbelonging to the sam e individual. Isolated teeth are rare in this record. They represent

only 10% of the total sample and often appear either fragme nted with traces of gastricdissol ution (teeth belongi ng to grazi ng ani ma ls such as Equus, Gazellospira orLeptobos), or com plete, in a site position vertical to the alveolar reg ion of theircorrespondi ng crani a (belongi ng to carnivores such as Canis and Hyaena).

Vertebrate association of Fonelas P-1 (Trench B ).REPTILIAL acertidae gen. indet.A nguidae gen. indet.Rhinechis scalaris (Schi nz, 1822)

V i peridae gen. indet.

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AVES

Aves gen. indet.MAMMALS (LAGOMORPHA)Prolagus cf . calpensis Maj or, 1905

* * Oryctolagus sp.MAM MALS (INSECTIVORA)* * Eri naceidae gen. indet.MAMMALS (RODENTIA)Eliomys sp.Mimomys sp.Apodemus cf . atavus Heller, 1936Castillomys sp. gr. C. crusafonti Michaux, 1969- C. rivas Martín Suárez y M ein, 1991Stephanomys sp .MAMMALS (CARNIVORA)* Meles ibericaArribas y Garrido, 2007V ulpes alopecoides (Forsyth-Major, 1877)* Canis accitanus Garrido y Arribas, 2008Canis etruscus Forsyth-Major, 1877

Canis cf. falconeri Forsyth-Major, 1877Pachycrocuta brevirostris (Aymard, 1846)Hyaena brunnea Thunberg, 1820Lynx issiodorensis valdarnensis Werdelin, 1981A cinonyx pardinensis (Croizet y Jobert, 1828)* Megantereon cultridens roderici Arribas y Garrido, 2008Homotherium latidens (Owen, 1846)MAMMALS (ARTIODACTYLA)* Potamochoerus magnus Arribas y Garrido, 2008* Croizetoceros ram osus fone lensis Garrido, 2008Metacervoceros rhenanus philisi (Schaub, 1941)Eucladoceros sp.* * Mitilanotherium sp .* Gazellospira torticornis hispanica Garrido, 2008* Capra baetica Arribas y Garrido, 2008* * Praeovibos sp .Leptobos etruscus (Falconer, 1868)MA MMA L S (PERISSODA CTY LA)

Equus cf . major Depéret, 1893Stephanorhinus etruscus (Falconer, 1859)MAMM ALS (PROBOSCI DEA)Mammuthus meridionalis (Nesti, 1825)

(*) singular taxa at Fonelas P-1.(* * ) in study.

Other taxa (unpub lished):Eurotestudo sp. (fossils).Hystrix sp. (taphonomical evidence: toothmarks).

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viseras & arribas (2009) - visit to fonelas p-1 site-print

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