The Bajocian of the region located at South-East of Digne is characterized by a thick limestone-marl sequence, in which the rhythmical alternation of marls and of limestones, more or less marly, the abundance of fossils, especially Ammonites, and the vast outcrops supply the best conditions for detailed biostratigraphic subdivisions.

In this report we have described the Ammonite assemblages and the subzone subdivision of the Upper Bajocian. These have been updated on the basis of recent collections of fossils, made after we had published a preliminary account on the Bajocian series of the Digne area (Pavia & Sturani 1968). The faunas of the Lower Bajocian will be illustrated in another publication, at present in preparation.
As far as the Upper Bajocian is concerned we are describing two stratigraphic sections, meausured in places which were already known in the literature (Garnier 1872; Haug 1891): Ravin du Feston section, measured from the Humpbhriesianum zone to the basal part of the Parkinsoni zone; Ravin de la Coueste section, on the outskirts of Chaudon, where the sequence is continuous from the Humpbriesianum zone to the basal part of the Bathonian (Sturani 1967).
For both sections we are supplying the stratigraphic column and the vertical distribution (see tables 1 and 2) of the Ammonites species which have been identified. The Chaudon section is particularly suitable for carrying out the biostratigraphic study of the strata at the junction between the Humphriesianum and the Subfurcatum zones.
The study of the rich Ammonites faunas (more than 1500 specimens for the Upper Bajocian), although sometimes hindered by the plastic deformations of the limestone-marly moulds of the Ammonites, has allowed to distinguish subsequent faunal horizons with subzone value, in accordance with a scheme that reproduces that discussed by Pavia & Sturani (1968) and by Sturani (1971).
Just considering the Ammonites species of greater stratigraphic value, the subdivision in zones and in subzones, as illustrated on table 3, can be summarised as follows:
Subfurcatum zone. In the sections of Ravin du Feston and of Chaudon the lower limit of the zone is established by the appearence of the genus Caumontisphinctes, evidently derived from Leptosphinctes, which were already present at the top of the Humphriesianum zone, Blagdeni subzone, underneath (L. festonensis n.sp. and L. garnieri n.sp.).
Banksi subzone: it is characterized by the presence of Caumontisphinctes aplous (along with the subspecies diniensis n. ssp. in the lower half of the subzone and the nominate subspecies in the upper one) and of its corresponding dimorphic partner C. (Infraparkinsonia) debilis. Other characteristic elements of the fauna are: Patrulia aenigmatica and some species of Stephanoceratidae of the Humpbhriesianum zone (Teloceras coronatum, Cadomites lissajousi, Normannites orbignyi), which persist in the lower third of the Banksi subzone; to these lasts we can add Normannites aff. orbignyi latiumbilicatus, which is present only at the bottom of the subzone, at least in the Chaudon section.
Polygyralis subzone: it is characterized by two dimorphic couples Caumontisphinctes polygyralis – C. (I.) phaulus and, only in the upper half of the subzone, C. bifurcus – C. (I.) inferior. Orthogarantiana haugi n.sp. and O. cfr. bifurcata equally characterize this horizon, but continue
in the subzone next above. At this level Strenoceras makes its first appearence.
Baculatum subzone: it is the more fossiliferous horizon of the whole Upper Bajocian of Digne. This subzone is characterized by the appearance of Garantiana s.s. and Spiroceras. Orthogarantiana densicostata, Garantiana baculata and Strenoceras subfurcatum are quantitatively the most
characteristic species; their appearance establishes the lower limit of the Baculatum subzone in the section of Chaudon. Spiroceras bifurcati is equally usual in the subzone. Except O. densicostata, the other mentioned species range up to the top of the Subfurcatum zone. Spiroceras baculatum is exclusively characteristic of this horizon and has been chosen as subzone index. Numerous species of Leptosphinctes l.s. seem to be limited to this subzone; among these the dimorphic couple L.? subcoronatus n.sp., L.? (Cleistosphinctes?) interruptus n.sp. is exclusively characteristic of the basal part of the subzone.
Schroederi subzone: fossils are scarce in both section of Ravin du Feston and of Chaudon. The available paleontologic data do not allow either to confirm or to deny the validity of this subzone, suggested by Westermann (1967) for the Bajocian of Bielefeld.
Garantiana zone. At Digne the lower limit of the zone is marked by the appearance of Pseudogarantiana dichotoma. Although scarcely fossiliferous in both sections, the strata relevant to the Garantiana zone have supplied a limited number of species, which are nonetheless sufficient to recognize three horizons with subzonal value: Pseudogarantiana dichotoma subzone, G. (Hlawiceras) trauthi subzone, G. (Hlawiceras) tetragona subzone. The Trauthi subzone is characterized by the appearance of the subgenus G. (Hlawiceras) with G. (H.) trauthi. The Tetragona subzone is characterized by the great development of G. (Hlawiceras) and, at the same time, by the rapid decrease of Garantiana s.s.; in addition some species of Bigotites are confined to this horizon.

Parkinsoni zone. This zone, very rich of fossils only in its upper half, in the section of Chaudon, is characterized by the appearance and by the fast development of Parkinsonia, and at the same time by the decrease of G. (Hlawiceras).
Acris subzone: scarcely fossiliferous in both sections, it has supplied a limited number of Species, among others Parkinsonia acris and P. rarecostata, which are establishing the lower limit; but the latter continues up to the top of the zone.
Densicosta subzone: a first datum is given by the appearance of Nannolytoceras tripartitum, that replaces in the upper part of the subzone N. (Eurystomiceras) polyhelictum. This horizon is characterized by: Parkinsonia parkinsoni and P. (Durotrigensia?) densicosta, which, however, range up into the basal part of the Bomfordi subzone. Several other species, among which Cadomites extinctus and Parkinsonia (Durotrigensia?) pseudoferruginea, continue upward.
Bomfordi subzone: at Chaudon the characteristic species of the subzone are: Cadomites psilacanthus, Parkinsonia bomfordi, Procerites costulatosus, P. (Lobosphinctes) aff. intersertus, Planisphinctes tenuissimus. Parkinsonia (Gonolkites?) subplanulata, exclusively characteristic of this subzone at Bas Auran (Sturani 1967), has not been found in the section of Chaudon. Apart from the species present also at the levels that are above and/or below, many of which have a limited stratigraphic value, several Ammonites (see table 2) are confined to this horizon, but they do not supply important information at a subzone level, due to the scarcity of material.
In the systematic part of this report we have described over sixty species (nine are proposed as new, two however in open nomenclature) and two subspecies (both new). Some of the new forms belonging to the genus Leptosphinctes, up to the present still almost unknown for the Subfurcatum zone, have allowed to support by documentary evidence, on a stratigraphic and paleontologic basis, the connections of filetic derivation existing between Caumontisphinctes and Leptosphinctes, through the development line: L. festonensis n.sp. – L. garnieri n.sp. – C. aplous diniensis n.ssp. – C. aplous aplous – C. polygyralis.
Moreover it is evident the strict morphologic relationship existing between the more primitive Cadomites and Orthogarantiana associated in the middle-lower part of the Subfurcatum zone. Orthogarantiana would seem to be derived from Cadomites of the lower part of the Banksi subzone through two forms, filetically connected one another, C. lissajousi n.ssp. ind. and O. haugi n.sp.

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