Late Glacial and holocene aeolian deposits and geomorphological features near Roccaraso (Abruzzo — Central Italy)

QuaternaryInternational,Vol. 5, pp. 89-95,1990. Printed in Great Britain. All rights reserved.

1040-6182/90 $0.00 + .50 © 1991 INQUA/Pergamon Press plc

LATE GLACIAL AND HOLOCENE AEOLIAN DEPOSITS AND GEOMORPHOLOGICAL FEATURES NEAR ROCCARASO (ABRUZZO m CENTRAL ITALY)

Massimo Frezzotti and Carlo Giraudi

ENEA C.R.E. Casaccia, C.P. 2400, 00100 Rome A.D., Italy Aeolian deposits and geomorphological features due to wind erosion have been recorded in the Aremogna plain, near Roccaraso (Central Apennines). A t this site, three different aeolian deposits can be distinguished: 1 - - silty loess deposits, composed mainly of quartz; 2 - - aeolian sand deriving from the reworking of tephra which lies on a peat level dated to 12,850 + 200 BP; and 3 - - aeolian silt coming from the deflation of the deposits 2, which is associated to deflation geomorphological features in part still active. The onset of these processes is more recent than 4690 + 200 BP. The first and the second aeolian deposits are related to cold and dry phases of the Late Glacial period. The third set of aeolian deposits and deflation features corresponds to wind erosion on a denudated landscape as a consequence of a dry climatic phase the effect of which was amplified by winter freezing-thawing activity.

2 km in width, at the altitude of 1400-1500 m and surrounded by limestone slopes which exceed an altitude of 2000 m (Mt. Toppe del Tesoro, 2140 m) (Fig. 1). The plain is constituted of Late Pleistocene moraines, of outwash deposits which originated during the glacier retreat, of alluvial fans, and of alluvial, lacustrine and aeolian deposits which accumulated from late Upper Pleistocene to the present (Fig. 2) (Giraudi, 1987). Climatic data have been deduced from the records of the closest meteorological station situated 7 km north from the Aremogna plain near Pescocostanzo (1395 m). The mean yearly temperature is 7.2 °C with a below zero mean in January and February (-2.0 and - 1 . 9 °C) and highest temperature in July and August (16.6 and 16.7 °C) (Mennella, 1973). The mean precipitation is 1088 mm per year with a minimum in summer (Mennella, 1973). There is, in general, snow for five months from NovemberDecember to March-April (Naviglio, 1975).

INTRODUCTION While at comparable latitudes loess deposits are well known both in Spain and in Greece (see Coud6Gaussen, this issue) and aeolian dust has been recorded on islands of the Tyrrhenian Sea (Sevink and Kummer, 1984), in Central Italy, within the Apennine range, aeolian deposits have been only sporadically recorded (Demangeot, 1965). However, a recent field survey in the Abruzzo province led to the identification of thin but widespread aeolian deposits and of geomorphological features due to wind activity Late Glacial to Holocene in age. This paper deals with the Aremogna plain in which these deposits and landforms were observed in detail and dated by means of radiocarbon technique. METHODS

The area has been studied by means of detailed geomorphological mapping. Several drillings and trenches were excavated in crucial sites. Major exposures were carefully described and sampled for further analyses. Mineralogical analysis was performed by X-ray diffractometer (Philips PW 1710) and petrographical study on thin sections. The grain size analysis was carried out by sieving, and by Micromeritics Sedigraph particle size analyser. The specific gravity and porosity of pumice granules were measured by pycnometer procedure and Macropores Unit 20 Carlo Erba analyser. The soil analyses (pH, organic matter and bulk density) were performed according to procedures of FAO--UNESCO (1988).

DESCRIPTION OF THE SEQUENCE

GENERAL INFORMATION

In the sequence of the Aremogna plain the following stratigraphic units have been observed from bottom to top (Figs 2 and 3): FL: outwash sandy gravel. EOI: brown (7.5 YR 4/6) massive, poorly sorted silt, mainly composed of quartz, calcite, muscovite and kaolinite (Fig. 4); up to 50 cm thick; including small clasts at the top, slightly calcareous at the base. LA: thin peat layer covered by tephra, colluviated at the top; the peat has been dated by radiocarbon to 12,850 + 200 BP (UD - - 318). Pollen content, determined by FoUieri, M., Magri, D. and Sadori, L. (unpublished data) consists of Pinus and Cyperaceae,

The Aremogna plain, located in the Central Apennines, is a flat valley of about 6 km in length and up to

Artemisia, Juniperus, Chichorioideae, Asteroideae, Rubicaceae, Graminae, Plantago, Chenopodiaceae, _Sparganium, _Myriop__hyllum. 89

90

M. Frezzotti and C. Giraudi

0 I

I00

ZOO

~

400

500

Dz D3

600

?O0

900

IOO0 m

7-16

FIG. 1. Geologicalmap of the southern Aremogna Plain. 1 -- Holocene alluvial deposits; 2 - - lacustrine and aeolian deposits; 3 - - outwash fan deposits; 4 - - till; 5 - - talus slope deposits; 6 - - bedrock; 7 - - fluvial scarps; 8 - - fault scarps; 9 - - fans.

The peat is covered in linear conformity by normal grading poorly sorted fall-tephra, 20 cm thick, silty sand in size lacking stratification, the sand fraction of which is composed of abundant whitish and grey pumices, K-feldspar, plagioclase, rare pyroxenes and biotite. Stratified tuffites follows, 20-40 cm thick, which is composed of alternating medium sorted sandy loam layers and well sorted sand layers (Fig. 4). Fragments of weathered pumice are present. At the top of the unit colluvial deposits, 10 cm thick, reddish (7.5 Y R 4/4) in colour occur, which are composed of volcanic material and decalcified limestone gravel. EO2: The whole unit has been affected by soil

forming processes which have led to the development in it of a pedological profile (Table 1) constituted, from the top, by: - - A horizon, 30-50 cm thick, black (5 Y R 1.7/1) silt loam, friable and soft when dry, granular poorly developed, outstanding thixotropic properties, clear transition to: - - Bw horizon, 10-30 cm thick, dark yellowish brown (10 Y R 4/6) fine sand, gradual transition to - - C horizon, 30--40 cm thick, massive medium sorted sand (Fig. 4), constituted of pumice and volcanic mineral. The pumice granules have a specific density of 2.54 g/crn3, 46% of voids and therefore a bulk density of 1.35 g/cm 3. The bulk density of the whole sediment is 0.66 g/cm 3, the voids reach

91

Late Glacial and H o l o c e n e Aeolian Deposits

......... ' . : ~ ' . : : : : : : - . : : : ; . - : . : : . ' : . . : : ~ : : ; . ' . : : : : ..... "J ~ , 7 " - - ' ( , . L I ' U

,,,

.

~ ,;

~,

....

.

. ,-'.-~']q

' o'"--",':'.'~,0.'-'.i".;

,....:-,¢~..('~.',,-:..,::.q;~."

:i-! "-'.~:.';:i.

:,...." ".. ~ , . . . , ~ ' , ' ~ . . .

F I G . 2. Stratigraphic sketch of the main stratigraphic units of the A r e m o g n a Plain. 1 - - Aeolian deposits ( E O 3 ) ; 2 - - alluvialcolluvial deposits (AL2); 3 - - soil horizon in dissolution pit; 4 - - alluvial deposits ( A L l ) ; 5 - - aeolian deposits ( E O 2 ) ; 6 - palustrine-lacustrine deposits ( L A ) ; 7 - - loess ( E O 1 ) ; 8 - - o u t w a s h fan deposits (FL).

1 mO

2

3 Om

ljO0

Z,O0

2,00

3,00

3,00

F I G . 3. Detailed stratigraphic sections o f ' t h e deposits o n the A r e m o g n a Plain. 1 - - Aeolian deposits ( E O 3 ) ; 2 - - alluvialcolluvial deposits (AL2); 3 - - soil horizon in dissolution pit; 4 - - alluvial deposits ( A L l ) ; 5 - - aeolian deposits ( E O 2 ) ; 6 - colluvial deposits; 7 - - tuffites; 8 - - tephra; 9 - - peat; 10 - - loess ( E O 1 ) ; 11 - - o u t w a s h fan deposits (FL); 12 - A1-A2-Bw-C-IIC-soil horizons.

92

M. Frezzoni and C. Giraudi

100~

f S/ ;

../ /,

/ /; / /

80

i;

i t

•

6o

I I

t

~,'~

~

/""

! ,

40

i/

]

/

! ; t

!/

20

/

I

/

/

/ l/ /'~¢ ~

J

J

-1

2

3

5

6

7

8

9

10

11

12

phi

FIG. 4. Grain size cumulative curves: (1) EO2 aeolian deposit; (2) tuffite; (3) tephra; (4) EO1 loess.

TABLE 1. NaFpH

Organic

Bulk

sand

Grain size silt

clay

Water pH

2 rain.

matter

density gr/cm3

her, A

14%

81%

4%

4.7

11.2

13.55%

0.65

her, (B)

56%

44%

0%

6.6

11.0

her. C

90%

100

0%

7.4

__

her, A 1

9%

83%

7%

5.4

11.3

6.~'/o

069

her. A 2

4%

82%

14%

5.1

11.4

7.0%

0.76

20%

67=/0 130

5.4

9.2

about 50% and water content ranges from 25 to 50% in weight. The unit lies on the deposits of the LA unit, in the profile in Fig. 2, as well as on the FL deposits. EO3: volcanic silty sand from 70 to 150 cm in thickness, also including chert fragments. The soil developed at the top of this unit consists of the A1 and A2 horizons (Table 1), dark brown (7.5 YR 2/2-7.5 YR 3/3) loamy silt, subangular blocky poorly developed, which lacks thixotropic properties and has a rather higher pH than the soil at the top of the EO2 unit. A trench excavated across one of the larger accumulations (Figs 2 and 3) uncovered 1.2 m thick colluvial silt-loamy deposits (AL 2). These cover gravelly deposits (AL 1) (Figs 2 and 3) at the top of which a discontinuous organic A horizon is preserved in a small dissolution pit. The organic matter of this A horizon has been dated to 4690 + 220 BP (UD - - 356) by radiocarbon dating. The surface morphology of the unit EO3 is constituted by levees bordering semicircular, circular or elliptical depressions the diameter of which (or longest axis) ranges from a few to 80 metres (Figs 5 and 6). DISCUSSION

E1

E2

Silt loam her. IIC colluvium

0.66

The FL unit at the base of the sequence is an outwash fan deposited as a consequence of the retreat of the local glaciers during the last Pleniglacial period of the Upper Pleistocene (Giraudi, 1987). The arguments for the aeolian origin of the EO1 unit are (1) - - the grain size which displays a sigmoidal,

FIG. 5. Depression and levee of an active blow-out feature.

Late Glacial and Holocene Aeolian Deposits

93

FIG. 6. Inactive blowout feature. unimodal curve, with a large peak in the coarse silt fraction which is typical of loess deposit; (2) - - the mineralogical composition of the silt fraction, mainly quartz, which is of non-local origin - - the reliefs surrounding the Aremogna plain being constituted of limestone. These loess deposits are older than 12,850 + 200 BP and younger than the outwash deposits (FL unit) deposited in the retreat of the local glacier during the last Pleniglacial. It could be correlated with the older cold climatic phase of the Late Glacial (Older Dryas?) which corresponds to the first Apennine glaciers advance of the Late Glacial (the so called 'II stadio Apenninico' according to Federici, 1979). The LA unit was deposited at the beginning in a shallow peat bog in which tuffites sedimented on several times. The pollen content at the base of the unit indicates a steppe environment with sparse boreal trees. The tephra which is younger than 12,850 + 200 BP, lies upon the peat, and therefore can be correlated to the eruption of the Phlegraean Fields volcano responsible for the Neapolitan Yellow Tuff dispersion (Di Girolamo et al., 1984). Because of the grain-size distribution, the EO2 sand, lying both on the LA tuffites and on older deposits can be interpreted as an aeolian deposit. It was originated by wind reworking of older tuffite during a dry and probably cold phase of the Late Glacial period (Younger Dryas?). The EO2 unit has been affected by soil forming processes which led to the development of a humic andosol, according to the FAO-UNESCO classification (1988), or to a Distrandepts according to the Soil Survey Staff (1987). The andosols develop in volcanic

glasses and consist essentially of allophane-humus complexes, which maintain the mineral gels in an amorphous state, preventing all neoformation of clay. This type of pedogenesis occurs if the soil is constantly wet; if the dry periods are long or frequent, amorphous material is irreversibly changed into other types of soil (Duchaufour, 1982). Therefore, the development of the soil is attributed to a fairly wet period during the Early Holocene. The deposition of EO3 and the formation of its top morphology is to be related to aeolian processes which induced blowout deflative effects. The formation of wind-blown deposits can be easily explained by the fact that when the A horizon of the andosol dries, it becomes extremely powdery: as the grains of powder are so fine, they can be carried by the wind and then fixed, a short distance away, by the vegetation. The onset of the third aeolian phase occurred after the development of the organic soil in a decalcification pit dated to 4690 + 220 BP. Today deflation is still an active process, but it involves the described features only locally, where pipkrakes due to quick freezing-thawing process and local causes have uncovered the soil. Where the features are entirely protected by vegetation cover, the process is completely inactive. These observations are in agreement with Troll's (1973) statements. Present deflation activity is in evidence where road excavations removed the vegetation cover and cut the soil. The original width of artificial excavations may be extended as much as 2-3 times (Fig. 7). The shape of the depressions (direction of the long

94

M. Frezzotti and C. Giraudi

FIG. 7. Ancient road excavation extended by deflation.

axes) and the position of aeolian deposits provide indications as to the direction of the winds which have produced depressions and accumulations. The inactive features have been produced by wind blowing to the north and N 30° E, while the active ones are shaped by winds blowing mainly towards the north and N 30° W (Fig. 8). The winds are presumed to be dry and also warm because they are blowing from the south and drying the soil. Wind direction has changed, shifting from the northeast to the northwest quadrant.

CONCLUSION

-

Geological research in the Aremogna plain yielded the first identification in the Abruzzo Apennines of aeolian deposits and geomorphological features which can be dated to the Late Pleistocene and to the Holocene. In particular, three phases in which aeolian processes were active have been identified: the first phase is younger than the last Pleniglacial -

ACTIVE DEFLATION FEATURES

INACTIVE DEFLATION FEATURES

NORTH

NORTH

90

270

T80

270

90

180

FIG. 8. Comparison between the directions of dry and warm winds shown by the analysis of active and inactive deflation features.

Late Glacial and Holocene Aeolian Deposits and older than 12,850 _ 200 BP, and could be correlated with the first cold phase of Late Glacial period (Older D r y a s ? ) ; it led to the deposition of quartz silty loess (CO1). - - the second phase is m o r e recent than 12,850 _+ 200 BP, older than the H o l o c e n e climatic amelioration which led to the f o r m a t i o n of the andosol. It is to be referred to a cold phase of the Late Glacial ( Y o u n g e r Dryas?). It caused the aeolian reworking of tuffite ( E O 2 ) which must, in fact, have taken place during a dry period, characterized by very p o o r vegetation cover. - - the third phase is m o r e recent than 4690 + 220 B P and partially still active; it has led to the accumulation of r e w o r k e d tuffite ( E O 3 ) and to the d e v e l o p m e n t of clear b l o w o u t deflation features. T h e onset of this aeolian phase is p r o b a b l y c o n n e c t e d to a progressive decrease in precipitation. This d r o p has g r a d u a l l y b r o u g h t about the disappearance of arboreal plants cover of the A r e m o g n a Plain and the f o r m a t i o n of a steppe-like e n v i r o n m e n t . F a v o u r a b l e conditions for the beginning of the d e n u d a t i o n p h e n o m e n a were caused by f r e e z e - t h a w cycles which disrupted the grass cover. A t the same time, local desiccation of andosol during s u m m e r f a v o u r e d the aeolian forms of deflation and accumulation. H e n c e , the aeolian p h e n o m e n a seem to have a definite climatic significance: in the first case (CO1), the loess is related to a climatic cold phase during which the local glaciers advanced. In the second case (CO2), the mobilization of volcanic material by wind o c c u r r e d during an arid period, in which the lake dried out and the vegetation cover disappeared. T h e third (CO3) also indicates the onset of a relatively drier climate, probably with brief, alternating f r e e z e - t h a w cycles, linked to wide daily t e m p e r a t u r e shifts during the late-autumn and spring periods. T h e hypothesis of a dry climate phase m o r e recent than 4690 + ' 2 2 0 B P fits with the shifts of the Fucino L a k e level, which is situated a b o u t 40 km N W of the

95

Plain of A r e m o g n a . D u r i n g the period f r o m 5 to 2.8 ka BP, the lake level decreased and r e a c h e d its m i n i m u m depth, p e r h a p s never r e a c h e d before, during the H o l o c e n e time (Giraudi, 1989).

ACKNOWLEDGEMENTS We wish to thank Prof. A. Pissart for suggestions and stimulating discussion and Prof. M. Follieri, dr. D. Magri and dr. L. Sadori for pollen analysis.

REFERENCES Demangeot, J. (1965). G~omorphologie des Abruzzes Adriatiques. Centre Recherche et Documentation Cartographiques M6moires et Documents, Num6ro hors series, Paris, 403 p. Di Girolamo, F., Ghiara, M. R., Liter, L., Munno, R., Rolandi, G. and Stanzione, D. (1984). Vulcanologia e petrologia dei Campi Flegrei. Bollettino Societgl Geologica Italiana, 103, 349-413. Duchaufour, Ph. (1982). Pedology. Translated by G. Paton. Allen and Unwin. London, 448 p. FAO-UNESCO (1988). Soil Map of the World. Revised Legend. World Soil Resources Report 60, Rome, 119 p. Federici, P. R. (1979). Una ipotesi di cronologia Wurmiana, tardo e post-Wurmiana nell' Appennino Centrale. Geografia Fisica e Dinamica Quaternaria, 2, 196--202. Giraudi, C. (1987). Segnalazione di fagliazioni superfieiali legate ad eventi sismici nella zona del Piani di Aremogna - - Piano delle Cinquemiglia (Roecaraso - - Abruzzo). Atti del Convegno "Geofisica della terra solida", l, 111-116, Roma. Giraudi, C. (1989). Lake level and climate for the last 30,000 years in the Fucino area (Abruzzo - - Central Italy): a review. Palaeogeography, Palaeoclimatology, Palaeoecology, 70 (1-3), 249-260. Mennella, C. (1973). II Clima d'Italia nelle sue earatteristiche e variet~ e quale fattore dinamico del paesaggio. I climi compartimentali della regione Italiana, Vol. I1. Fratelli Conte, Napoli. Naviglio, L. (1975). Researches on beech forest ecosystem: III - Description of the three beech forests studied in the Abruzzo National Park (Monti Marsicani, Abruzzo). Annali di Botanica, vi, XXXIV, 201-222. Soil Survey Staff (1987). Keys to Soil Taxonomy, (third printing). SMSS technical monograph no. 6. Ithaca, New York, 280 p. Sevink, J. and Kummer, E. A. (1984). Eolian dust deposition on the Giare di Gesturi basalt plateau, Sardinia. Earth Surfaces Processes and Landform, 9, 357-364. Troll, C. (1973). Rasenabschalung (Turf exfoliation) als periglaziales Phanomen der subpolaren Zonen und der Hochgebirge. Zeitschrift fiir Geomorphologie N.F., Suppl. Bd. 17, 1-32, Berlin, Stuttgart.