The flora of Manosque

The Oligocene flora of Manosque (South France)

Many times we have visited a site with plant fossils from the Oligocene in the south of France during the summer holidays. The place is situated not far from the city of Manosque (dept. Alpes-de-Haute-Provence). We have assembled a rather extensive collection of specimens from this spot in the course of the years. To prevent concourse, the finding place is not exactly described here.
The fossils are in marly chalk plates, which are easily split if they have been exposed to cold and heat for more than a year. Fresh material is splitting badly.
Generally the fossils are clearly outlined against the mostly light yellow chalk and they can be very fine. The nervation of the leaves is also often very clear. Thus it seems rather simple to identify the fossils, the more so as there are rather extensive publications from the 19th century about this site. Especially De Saporta has worked intensively on this flora. Yet it turned out to be rather difficult (and sometimes impossible) to find the right name for a fossil.

Problems with identification
One of the reasons for this is the fact that it is a compression flora: no organic material has remained. In other places in the world a thin coal layer from the original plant, wrapped by the cuticle, has sometimes been preserved. From this cuticle a microscopic preparation can be made which can be used to study the cell structure. In this way the identification is easier and more reliable.
A second reason is that the variation of the leaves in one species is often very large. There are, for example, leaves of the birch tree, which can easily be confused with the leaves of an elm or a hornbeam. That's why an isolated leaf often cannot be identified with certainty.
These problems are possibly the reason that after De Saporta nobody has extensively published on this flora any more.
All this means that the identifications of the plant fossils in this chapter must not be taken too absolutely.

The flora of Manosque
Below is a survey of the species we have collected and which could be identified with some certainty. The list is certainly not complete.
Keep the cursor on a photo to read the name of the fossil. Click on the photo to get an enlargement and more information.

Some remarks about the geology
De Saporta put the flora of Manosque in the Aquitanian, i.e. the lowermost formation of the Miocene. Later research, including that made on small mammalian teeth, which have been found in some strata, has proved the sediments to be from the middle part of the Oligocene (Rupelian, Stampian). A large, irregularly shaped lake with dimensions of 40 to 60 km extended at the time. The outline of this lake is approximately the same as the outline of the present Oligocene sediments.
The depth of the lake showed a strong variation, as did the quantity of precipitation in the area. In the course of the Oligocene thick layers of marl and chalk were deposited. In times of dry heat thick layers of gypse were formed through evaporation. In periods of damp heat moors came in existence in shallow places. The peat which was formed, has transformed to lignite layers (brown coal), embedded in chalk and marl layers. This lignite was exploited in mines and open coal pits till some years after the Second World War. The traces of this acitivity are almost vanished except for some old, sometimes inundated, quarries.

At certain levels in some places plant remains occur, which have been deposited in the fine silt on the bottom of the lake. They are well preserved as compression fossils. This is the flora described here. Look at the table.

Environment and climate in the Oligocene

On the one hand the fossil flora of Manosque is rich in species, but on the other hand also very incomplete. The flora must have grown under subtropical conditions. This is demonstrated by the presence of palms, Diospyros, Laurus, Caesalpinites, Cinnamomum, Glyptostrobus and many others. These are plants of which the modern relatives nowadays mainly occur in the east of Asia. Plants from the moderate regions however are also frequently found : birch, maple, alder, oak, beech, ash and other plants with descendants occurring very commonly in Europe at present. Of the herbaceous plants only water-plants like waterlily and Ceratophyllum, and plants of the banks like ferns, burreed and sedge have been preserved. Most of the plant remains have been transported over some distance before being embedded in the mud of the beach or the bottom of the lake. It is striking that branches with attached leaves are very rare.

The scenery seems to have been a large, subtropical lake with water lilies and lotus plants, bordered by banks with ferns, burreed, sedge, and so on. In the surrounding woods were laurels, some palms and many other subtropical trees. Furthermore there grew , perhaps on the slopes of mountains, oaks, birches, beeches and other trees which needed a somewhat more moderate climate. In autumn and in winter storms pulled off leaves which landed in the water. They were transported to the lake where they were embedded in the mud. Until this herbarium was opened about thirty million years later.

Hans Steur

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