BRUNO ACCORDI - ANGIOLA M. MACCAGNO

Istituto di Geologia e Paleontologia - Università di Roma

RESEARCHES IN THE PLEISTOCENE OF RIANO (ROME)

The results of studies and excavations in the diatomitic basin of Riano Romano during the years 1960 /62 are exposed; some stratigraphical data on the Pleistocene tufaceous series from " Vulcano Sabatino " and on fresh water diatomites are discussed too.

Afterwards we inform about numerous very interesting paleontological discoveries consist­ing in elephants, deer, leaves and fishes remains.

A reconstruction of environment by means of diatoms and pollen analysis is tentatively proposed.

Laboratory and field researches where carried out with a grant of the "Wenner Gren Foundation for Anthropological Research" an d of the "Consiglio Nazionale delle Ricerche".

During the period between 1960-62 some strati­graphical and paleontological researches bave been accomplished by the Institute of Geology, Rome University, on the Quaternary of Riano (a village situated 20 km north of Rome, between Flaminia and Tiberina state roads), under the leadership of Prof. B. Accordi, and with the assistance of Prof. A.M. Maccagno and Doctors Affricano, Ambrosetti, Bonadonna, Gasparini, Menasci, Praturlon, as cow­orkers. Only the main and preliminary results of tbe researches, which are very promising, will be exposed in the present work. Further data will be obtained from the study of the wbole collected materia!.

The hills neighbouring Riano bave been investig­ated partially in the past. They are of the utmost interest, since it is possible to reconstruct from them a stratigraphy, and also to undertake tenta­tively a paleogeographical reconstruction and to make some paleontological considerations of the highest interest.

The base (Plio-Pleistocenic clays, sands and gravels)

The formations we are concerned wbitb (pyroc­lastics an d diatomites) are lying on a bed once assigned to Pliocene. Quite likely clays and sands

with marine fossils, wbicb constitute the oldest soil of tbe area, are to be referred partially to Pliocene and partially to Pleistoccnc, and namcly to Calabrian and to marine Sicilian. The outcrops of clays and sandy-clays, appearing in several points, contain numerous fossils, presently under investigation. In the marine sandy clays, contain­ing Turritella tricarinata BR. s.I., from the locality called " Il Crocifisso ", tbe abundant microfauna of neritic environment indicates, in our opinion, the passage to the inferior Pleistocene, as confirmed by the presence of fossils such as: Bolivina catanensis, Cassidulina laevigata var. carinata, Cibicides loba­tulus, Nonion cfr. citai, Elphidium advenum, E. decipiens and Valvulineria bradyana.

In another outcrop quite near the above men­tioned, we bave found in a very high percentage (77 %) the left-hand form of Rotalia beccari, which demonstrates an uneasy condition of the population, which can be related to a drop in the temperature.

Proceeding upwards the materia! becomes less and less clayey, meanwhile increases the sand con­tent. The sands contain here and there some levels of crusts, more or less cemented and consolidated, which gradually assume tbe form of a conglomerate. The gravel, usually loose and containing mainly elements of small size, does not appear everywbere in tbe region. Actually it is represented generally outside the real Riano area. Near Rome it con-

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Fig. 1 - "Pian dell'Olmo", Km 7,5 of Tiberina road. In the center is evident the edge of the diatomitic formation (layered and white) and his connections with the bank

of " yellow vacuolized tuff ".

- Nel centro della figura è visibile la parte terminale della formazione diatomitica (bianca e stratificata) appoggiata su un grosso banco di tufo «giallo vacuolare >>.

tains some layers in the bottom rich with oysters and beach molluscs.

Pyroclastics (lower and rniddle Pleistocene)

Our series of volcanic tuff and diatomites lies in an area of erosion, composed of clays, sands or gravels.

The '' yellow vacuolized tuff " is the thickest and the more characteristic of these formations. Under this in the Prima Porta area, where this formation presents some noticeable complications, a '' grey pisolitic tuff" appears, meanwhile, in the zone of Riano, it lies directly over the base sandy day. As much as the upper formations are concerned, the " yellow vacuolized tuff " is followed by a complex of " stratified tuff" containing diato­mites, which represents the formation that has given us the most interesting fossil remains collected in the area.

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On the north side of the zone the series is more complicated because of the presence of two levels of '' pisolitic tuff ", one underlying the '' yellow vacuolized tuff " (" inferior p isoli tic tuff ") and the other immediately above ('' superior pisolitic tuff "). Therefore where i t is present, the '' supe­rior pisolitic tuff" is interposed between the " yellow vacuolized tuff " and the " stratified diatomitic tuff ".

The '' yellow vacuolized tuff " appears in large an d big banks; i t is exploited for building purposes and we can see various details from the diggings made very frequently in these years in the area of Riano. This lithic tuff forms a series of hills, generally about 50 meters high and not very wide. The hills appear round-shaped, parted by small valleys normally narrow, a geomorphic process which began by stopping of the ejection of pyroclastic materials.

On the contrary, other incisions (it is not too easy to distinguish them in every case) can be

FIG. 2- "Valle dell'Inferno " (Riano), Km 3,8 Rianese road. The ancient lake bottom, partly exposed, is bounded by round­ed - shaped hills of the "yellow vacuolized tuff". Low on the right the diatomite quarry.

- L'alveo dell'antico lago, in parte denudato, è delimitato dalle colline rotondeggianti del " tufo giallo vacuolare ". In basso a destra la cava di farina fossile.

referred to roman and medioeval diggings, and, like the natura! ones, are modelled and covered by vegetation.

The large banks of " yellow vacuolized tuff " are covcred by the '' tufaceous-diatomitic form­ation ", widely extended in the neighbouring regio n. Occasionally (" Il Crocifisso ") the "yellow vacuo­lized tuff " is missing and the " tufaceous-diatomitic formation " lies on the marine sandy days of the base.

In the district of Riano, the '' tufaceous-diatomitic formation " is the last of the series. It consists of incoherent stratified tuff with various colours ranging from yellow to dark gray, and strata of pumice and numerous diatomitic episodes inter­posed, which sometimes present a noticeable thick­ness (more than 40 m. in the "Valle dell'Inferno"). The diatomitic materia!, very pure in the more important episodes, indicates a deposit in very dean waters. On the contrary it is very impure in the narrowest basins.

In the fresh cuts it is easy to detect the contact between the " tufaceous-diatomitic formation " and the " yellow vacuolized lithic tuff ". This contact is very dear when the same diatomitic episodes are leaning directly over the lithic tuff (fig. l).

Diatom.ites

The diatomites lie in narrow basins, the edges of which mount and lean over the erosion surfaces,

very irregular, of the lithic tuff. They are white or very white in colour and varvate.

Thc numbering of the varves, which appear dearly because of the purity of the materia!, is rather difficult, due to the extreme slenderness of the layers. From the large number of sections examined, we have found an average thickness of half a millimeter for the single varve.

Consistently we numbered 22-26 varves per centimeter.

The slender layers of very pure and perfectly white diatomite are regularly alternated with the greenish and darker ones (rich in organic substances). Sometimes they are interrupted by day or tuff levels of various thickness.

In the main basin of "Valle dell'Inferno" (Riano) the layers are perfectly horizontal. Only in the edges of the basin, which are preserved in the N and the S, the clip of the layers indicates the proximity of the shore line.

In a diatomite quarry of this basin, we per­formed a detailed sampling of the set, and numerous '' lack-films " of the most interesting levels.

Considering the varves as an indication of the seasonal variation, and taking in account that the exposed thickness of the diatomite is about 38 meters, from which we must withdraw on the whole about two meters for the pyrodastic and day materials interbedded here and there, we can

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conclude that the lenght of sedimentation phase of the "Valle dell'Inferno " basin is around 45,000 years.

In the adiacent basin of " V alle di Pianaperina ", in which the thickness of the laky sediments is slender, we. made some explorative drilling with a hand drill, which confirmed the presence of the tuff at the base of the diatomite.

In the center of the basin we were concerned with, exactly 500 meters eastward from Riano

FIG. 4 - " Valle dell'Inferno " quarry (q. 47 a.s.l.). Levels of the first and second deer fìndings. Observe the slender layers of tuffs interposed to diatomite beds and the folded layers, half a meter of thick­ness, between the levels where the two deer skeletons were found; on the photo is evident the rippling surface of the high­est of the folded beds.

- Cava «Valle dell'Inferno>> (quota metri 74 s.l.m.). In cor­rispondenza del livello più basso (dove vi sono le persone) venne raccolto il secondo cervo, men­tre sul ripiano più alto fu scavato il primo cervo da noi recuperato. Sono visibili alcuni straterelli di tufo intercalati alla dia tomi te; fra i livelli ai quali si sono trovati i primi due cervi, vi sono due strati (di circa mezzo metro di spessore) che mostrano un forte turba­mento nella stratifìcazione. È visi· bile la superficie increspata del più alto degli strati piegati.

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-l i

FIG. 3 - Sight of the "Valle dell'Inferno " quarry. The ex­posed beds present a thickness

of 40 meters about.

- Veduta della cava di « Valle dell'Inferno >>. Lo spessore visi­bile è di 40 metri circa.

(fig. 4), the varvated complex (which outcrops, as we said, with a thickness of about 40 meters), is intercalated here and there by black coloured tufa­ceous banks, composed of coarse material. Some layers of diatomaceous earth contain leaves or fossil fishes, which we collected in a fair quantity. The lcaves have been studied by Dr. Follieri, who also performed some palinologic investigations on the set.

The results of these studies, which have been

published, show the presence in lower levels of a rich colchic-type forest, which testtfìes a climate clearly oceanic.

In the lower and middle parts of the basin (till 72 meters a.s.l.) the leaves and pollens association is composed mainly by Pterocarya (more than 50%), which indicates a more expressly oceanic and warmer climate, as confirmed by the contemporary lessening of the oak-wood.

In the upper levels (79-8lm. a.s.l.), there is a more accentuateci characterization towards the oceanic colder type, as is testified by the decrease of the Pterocarya and the large increase of the beechtree.

Layers, with fresh-water fishes, which we have a good collection of, have been found during our investigations. Besides these fishes, we also found some batrachian specimens.

A detailed sampling in the whole series was made (a sample every 0,5 m.), for a thorough study of the diatoms, which constitute the main element. To date we have made a preliminary exploration of the levels containing fossils (fishes, leaves, deer). They showed a monotone flora, containing almost exclusively Cyclotelìa kiitzingiana var. planetophora FRICKE, with a percentage ranging from 80-90 to l 00%. This associati o n indicates laky deposition in clean, fresh waters.

A preliminary investigation has been made on the seasonal variations and on the changes of the population over long periods. This investigation was based o n the ratios of the two prevailing species: Cyclotella kiitzingiana var. planetophora FRICKE an d C. meneghiniana KZ., between them and with the other species represented.

We can say that in a sample of the lower p::trt of the series, a single individuai perhaps to ascribe to Rhopalodia gibberula var. minuens o.M. (which at present lives in some non-salted parts of Baltic Gulf) was noticed.

As an introduction to the generai study of thc diatoms of the region, the genus Cyclotella, whicb is represented by six different forms, is illustrateci by A.M. Maccagno, in the present volume.

Ma m malia

The most important paleontological discoveries were not made in the center of the basin, but on the boundaries ; we like to note that just over the cross­road through Rianese and Tiberina roads, which is about 3 km. south of the diatomitic outcrop, at

80 m. a.s.l., an elephant skeleton, referable to E. antiquus FALC. and CAUTL., very young in age, and almost complete, was found. Only the pelvis and t:he posterior part of the vertebra! column was missing (figs. 5, 6). The skeleton, studied and published in another work of the present volume by A.M. Maccagno, was restored in our laboratory and will be mounted in the Paleontological Museum of our Institute.

In the basin of " ~lle di Pianaperina ", in the uppermost layers of Qe diatomite in correspond­ence to pyroclastic- ·~pisodes, recently one tusk of E. antiquus FALC.,and CAUTL. was discovered, which, for the good -state of preservation, allowed us to obtain the projection line of the curve, accord­ing to Trevisan's method (1942). In the same piace, some years ago, a young specimen of E. antiquus FALC. and CAUTL., presently at Genoa for restoration and study, was found.

Another superb elephant skull was discovered in a place called " Pian dell'Olmo" (a. 56 m.). It

(Foto Bucciarelli)

FIG. 5 - Locality " Il Crocifisso "; Rianese road, 5th Km. The diatomitic formation where the skeleton of a young specimen of Elephas antiquus was found.

- Località « Il Crocifìsw >>, Km 5 della Via Rianese. La formazione diatomitica dove fu trovato lo scheletro

di un giovane esemplare di Elephas antiquus.

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is a very large skull, belonging to an old specimen of E. antiquus FALC. and CAUTL., which was lying on a sm-all layer of earthy tuff. Unfortunately, the molars, fans and occipital condyles are missing from the skull, meanwhile the preservation of the parieto-occipital regio n, of the frontal '' toro " (transverse frontal crest) and of temporal fossa is perfect. The cerebral cavitv and the internai and external nasal ones where also well preserved. This allowed a very profitar~ ·. study.

f Ì -~

FIG. 6 - Drawing out the elephant skeleton. The scapula and the anterior limbs are partly visible. In

the center one can see the mandible appearing.

- Una fase dello scavo dell'elefante di cui alla fig. 5. Sono parzialmente visibili la scapola e gli arti anteriori.

Nel centro si vede affiorare la mandibola.

The lucky discovery made last september of two skeletons of deer which soon will be removed from the chalk envelope, restored and studied, must be not overlooked. Last spring, in the same locality, and about at the same level, an interesting head and a good and complete skeleton of deer were found. These discoveries too were located in the "Valle dell'Inferno", between 72 and 74,50 m. altitude, always in correspondence to tuff levels. The layers containing the second of such deer are included in perturbed levels (fig. 4).

At the present we are examining such perturba­!lOns, which are repeated in severa! levels of the diatomitic formation.

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Subsequent formations

As we said before, as much as Riano zone is conce m ed, the w ho le seri es stops with the '' diato­miferous stratified tuff ". In neighbouring p laces (f. i. La Storta) the series continues with a brown earthy tuff, rich in leucitic materia!, in which sometimes we can notice some pumice layers inter­posed. Such earthy tuffs dose as a rule the series we are concerned with. By the way we can re­member two facts. The first is related to the presence in the surrounding zone of materials over­lying the diatomitic complex, and that appear as a reddish tuff with big black slags an d day fragments. According to the researches of Dr. Menasci, this tuff has been originated from a supposed neck, which was discovered near Grotte. The second is related to the presence on the top of the hills, where the earthy brown tuff which closes the series is placed, of some modest atypic artifacts which have been detected long time ago, not only by Blanc and Cardini, but also by other students and researchers. These modest and rare chips have been found always scattered in the fields, notwithstanding that the countrymen affirm to ha ve seen them cropping out of the tuff. W e believe therefore that they are subsequent to the series we illustrateci.

As a conclusion we can state that in the period covering the years 1960-62, we acquired a lot of new data that certainly will contribute to a strati­graphical and paleogeographical knowledge of the region during the Quaternary.

Till now we are not able to refer this succession of events to a chronological interval exactly deter­mined; in fact w e must wait for the studi es o n the malacofauna and microfauna of the base materials (sands and clays) to be completed. We must conclude too the sedimentological studies started on the various materials and we wait the possibility to proceed at further studies of the fossil findings, and in the first piace of the deer, to the recovery of new samples of which we are attending at present (fig. 8), and of ali other fossils we are collecting in the zone, with the purpose to obtain the set of paleontological and paleobotanic data which we need absolutely for a detailed dating.

At present the significant arguments for the age of the tufaceous-diatomitic formation, which is the most interesting of the zone, are:

l) Its stratigraphical position subsequent to the big ejection of the "yellow vacuolized tuff ".

This important phase of volcanic activity is sub­sequent to the pebbly alluvions of the Sicilian, and preceding to the terraces attributed to the Tyrrhenian (Trevisan and Blanc, 1948; Blanc, Trevisan and Tongiorgi, 1953). The existence itself of lakes and small lakes can be related both to the counter-pendencies due to the intense vol­vanic activity (Trevisan, 1947 e 1948; Blanc, Tre­visan and Tongiorgi, 1953) and to the barrage ma de by tuff to the rivers ( see the lake ma de by Tiber river immediately south of Rome) (Blanc, Trevisan, Tongiorgi, 1953).

2) The presence of the listed fossils, particu­larly the conspicuous remains of Elephas antiquus, referable to a mutational stage corresponding to the typical of this species, which is therefore more evoluted than the archaic forms of the Giinz-Mindel (E. antiquus of the Bufalotta; Trevisan, 1948, p. 62), but less evoluted than E. antiquus italicus OSB.,

subspecies differentiating itself in the big inter­glacial Mindel-Riss and flourishing till the Riss­Wiirm. The floristic associations and the palino­logic investigations, cannot be neglected, which give some rather exact indications in the same direction, with some archaic elements such as the prevalence of Pterocarya (see Follieri, VI Congress INQUA,

Varsavia, 1961 ). The tufaceous- diatomitic formation is referred

by Authors to the Mindel-Riss or to the Pre-Riss (Blanc, 1957; Follieri, 1959). According to our observations we can attribute it to a rather cool phase of Mindel II-Riss, phase that would prelude to the further hardening of climate.

FIG. 7 - The deer found on the lower leve! of fig. 4.

- Il cervo rinvenuto sul livello inferiore indicato in fig. 4.

Fra. 8 - The latest discovery. A supe1·b specimen of deer lying in the diatomitic beds (73 meters a.s.l.) of

the "Valle dell'Inferno" quarry.

- La più recente scoperta. Un superbo esemplare di cervo giacente negli strati diatomitici della cava di <<Valle dell'Inferno>>, alla quota di 73 metri sul livello

del mare.

About at 72 m. a.s.l. we note a warmer variation, as indicated by the prevailing of Pterocarya in floristic association.

RIASSUNTO

Si espongono i risultati delle ricerche e degli scavi nel bacino diatomitico di Riano Romano, effettuati dal 1960 ad oggi. Ai dati stratigrafici sulla serie, costituita da tufi del vulcanismo sabatino e da depositi lacustri poggianti in trasgressione su argille e sabbie marine del Pleistocene inferiore, seguono i dati sui numerosi reperti paleontologici. Sono stati recuperati infatti importanti resti di elefanti e di cervi e si è provveduto al recupero di collezioni di filliti e di pesci. Le ricerche sulle diatomee e i dati di analisi polliniche completano il quadro paleogeografico della zona.

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