Ruprecht Schleyer

Basins and Channel Network

We digitized the topographic map 1: 25000 using a 250·m geomatrix and quantified nearly all geomorphological properties of the area which comprises 103 basins and interfluves. We subdivided three main physiographic provinces, Aspromonte, Zomaroand SerreProvinces; 19 larger rivers were investigated more closely.

Rock Units and Their Regional Distribution

We digitized the Carta Geologica Della Calabria (CGDC) 1: 25000 using the 250-m geomatrix. Granitic rocks cover 24% of the basins 01 — 19, metamorphic rocks yield 37%, and 39% are made up by sedimentary rocks. We condensed the 55 lithological rock units of the CGDC to eight source rock types to which the provenance discussion of this book refers: granite (24% area), gneiss (7%), schist (30%), limestone (1%), conglomerate (9%), sandstone (9%), siltstone (12%) and argillite (8%). It goes without saying that source area geology is by far the most important variable controlling the composition of river-mouth sediments.

Erosion and Predicted Sediment Composition

The mean erosion rate, calculated as long-term (1 Ma) erosional budget instead of sediment yield, is 178mm/ka for the total area and 206 mm/ka if only the 19 basins are calculated, maximum values being 850 mm/ka. During the reference time of 1 Ma the entire area would have been able to produce a sedimentary deposit of 100 x 100 km, 55 m thick, with a calculated pore volume of 50%.

Water Budget and Dissolved Load

The mean effective precipitation in the 50-year period between 1921 and 1970 is 698 mm/a, the mean evaporation rate 48.6%. This results in an average annual runoff of 1278x 106 m3. The mean mineralization of the river waters is 322.6 ppm after the summer period and 221.4 ppm in late winter, 250 ppm being a reliable mean. About 47% of this dissolved load is regarded as being recycledor from atmospheric and anthropogenic input. The composition of the Calabrian river water corresponds fairly well to the worldwide mean of river water. Compared to the long-term (1 Ma) mean erosion rates of the 19 basins (206 mm/ka) the proportion of the present–day dissolved load is 16.3%; compared to mean actual effective erosion rates of 1527mm/ka consequently it is only 2.2%. Today the 19 basins release 319425 metric tons of dissolved load per year into the Ionian Sea, of which 169295 tons (53%) are geogenetic. This corresponds to a solid-rock cube of about 40 m side length.

Composition of Rocks and Soils

The igneous rocks of the Serre are mostly granodiorites. The majorityof the metamorphic rocks belong to the transition from greenschist to amphibolites facies, sometimes retrograde. Among the sediments the conglomerates are a distinct but controllable source of misleading results due to recycled gravels. The sandstones are mainly arkosic. The siltstone or olisthostrome complex contains only 20% sand (40% silt, 40% clay). The soils are dystric and eutric cambisols, orthic luvisols, calcaric regosols; we measureda mean of 71% sand, 19% silt and only 10% clay. Soils of granite and feldspathic sandstone show an arkosic composition (F/Rf and F/L> 1), while the samples from gneiss and schist show a lithic composition (F/Rf and F/L< 1). ZTR values of soil vary greatly; soils from metamorphic rocks contain 12% of ZTR and from granitic or sedimentary ones only 4%.

Development of the Chemical Composition of Sand

The chemical composition of the single types of source rocks and the sand fraction 63 — 500 μm of the soils, of the effective composition of the source rocks and soils, of the river-mouth sediments and of the longshore bar is compared. Gain and loss and constant-AI2O3 calculations reveal that the composition of the river-mouth sands comes closer to the source rocks than to the soils. Attrition during fluvial transport is the most important source of sand at this active plate margin, chemical weathering and soil formation being less effective.The chemical composition of the average Calabrian river-mouth sand fits almost perfectly that of active-margin sandstones; single rivers, however, deviate greatly from this mean and it may be hazardous to draw conclusions from only one or even a limited number of rivers.

Mass Balances in the Marine Realm

The central part of the research area is bordered by the 5-km-wide Bianco shelf and the 2-km-wide Bovalino shelf, separated by the head of the Buonamico-Careri Canyon. The shelf break is between 100 and 120 m water depth;we mapped the slope to a depth of about 900 m. The comparison of our 1974 map with soundings from 1877 reveals negative deviations or erosion in the dimension of 100 m and positive deviationsor accumulationup to 30 m. Loci of enhanced sedimentation are the canyon head and the outer shelf, where also the major slump scars occur.The conversion of only accumulation values on the shelf into erosion rates of the respective hinterland yields 7500 mm/ka. This huge value surmounts the 1-Ma average of the entire area (206 mm/ka) by factor 35 and the 50-year average of the Buonamico [08] basin (1527 mm/ka) by factor 5.

Development of Gravel Sphericity

The axes of more than 40000 pebbles were measured. Sphericity is strongly dependent on lithology and increases with grain size. It increases from the jointed and weathered source rocks towards the river-mouth sediments and decreases along the beach, seen as a whole, that is, the sphericity distribution of the coast returns exactly to its starting pattern or joint block origin. So sphericity fails to be a useful provenance signal.

Altitude and Slopes

The altitude standard deviation, the measure of relief, varies considerably between the single basins (213 to 481 m), as does the altitude skewness, the measure of dissection (-0.144 to 1.156). However, both variables exert no influence on properties of the river-mouth sediments such as uni–or bimodality of grain-size distributions.

Comparison of Source and Sediment: a Multivariate Approach

The Euclidian distances between the basins in a kdimensional space defined by k variables were used as a measure of similarity. According to this procedure, based on both source and sediment properties, the subdivision of Calabria into Aspromonte, Zomaro and Serre Provinces has to be modified. The Aspromonte basins have to be regrouped into two subprovinces, one whose rivers reach the main divide, the large Aspromonte Province, and one whose short rivers do not, the small Aspromonte Province. Novito [13] and Torbido [14] prove to be special cases which fit neither the Zomaro Province nor the Serre Province. A t-test of the distances between different provinces and with in provinces yields the following rank of source area properties: geology and altitude separate the provinces with more than 99% significance;gradient and precipitation yield between 95 and 99% significance, and erosion rates finally separate the provinces with only less than 95% significance.The same procedure ranks the sediment properties: heavy minerals, the mineralogy of the clay fraction and gravel petrography with more than 99% significance, silt minerals and geochemistry between 95 and 99% significance and, the least, grain sizes and light minerals with less than 95% significance.It is the first time a quantitative rank and evaluation of the commonly used provenance signals has been established.