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Jurassic ammonites of early and middle Callovian Age occur in southern Alaska in the Chinitna and Shelikof Formations. Ranges of the ammonite genera and subgenera present, on the basis of the stratigraphic distribution of these fossils in Eurasia and East Greenland, show that these formations should be equivalent te at least the European zones of Sigaloceras calloviense, Kosmoceras jason, and Erymnoceras coronatum. Whether the basal few hundred feet of these formations is equivalent to the earliest Callovian or to the highest Bathonian, or both, cannot be demonstrated for certain. Two ammonite zones are recognizable. The upper zone, named after Cadoceras (Stenocadoceras) stenoloboide (Pompeckj), is characterized by an abundance of the subgenus Stenocadoceras. It has been recognized west of Cook Inlet in the Paveloff Siltstone Member of the Chinitna Formation and in the upper one-sixth of the underlying Tonnie Siltstone Member. In the Talkeetna Mountains it is represented locally near the top of the Chinitna Formation. In the Alaska Peninsula it occurs in the middle member of the Shelikof Formation and in the upper fifth of the lower member. The lower ammonite zone, named after Cadoceras catostoma Pompeckj, is characterized also by the presence of C. glabrum Imlay, all species of C. (Paracadoceras), and all species of Lilloettia except L. stantoni Imlay. These ammonites range through the entire lower part of the Chinitna Formation below the beds characterized by C. (Stenocadoceras) stenoloboide (Pompeckj) and C. (S.) multicostatum Imlay. The lower part of the C. catostoma Zone is herein recognized as a subzone and is named after the most common species, Iniskinites intermedius (Imlay). This subzone marks the top of the range of Parareineckeia, of the new genus Iniskinites, and also of Xenocephalites, except for one spscimen. Its lower part includes also all known specimens of evolute Kepplerites. Characteristic ammonites of the subzone occur in the lower 500 feet of the Chinitna Formation west of Cook Inlet and in the lower half of the lower member of the Shelikof Formation on the Alaska Peninsula. The Callovian ammonites of southern Alaska include some genera characteristic of the Boreal realm, such as Kepplerites, Cadoceras, and Pseudocadoceras, and other genera characteristic of the Pacific realm, such as Xenocephalites, Lilloettia, and Parareineckeia. On the specific level, however, nearly all relationships are southward with Callovian ammonites in British Columbia, Oregon, and northern California. Evidently, southern Alaska during Callovian time was part of a Pacific Coast faunal province. INTRODUCTION The Callovian ammonites of southern Alaska described by the writer in 1953 have been restudied in order to revaluate the stratigraphic distribution of the genera and species, to establish ammonite zones for regional and continental correlations, and to date the formations and zones more precisely in terms of the standard Jurassic zones of western Europe. This study is based on biostratigraphic data compiled by Detterman and Hartsock (1966, p. 38, 39, 44-46, 48) for the Chinitna Formation west of Cook Inlet and by Arthur Grantz (written commun., Apr. 1972) for the Chinitna Formation in the Talkeetna Mountains. These data are much more accurate than those available to the writer in 1950. Likewise, study of the many fossil collections made by Arthur Grantz and associates in the Talkeetna Mountains between 1952 and 1963 has provided a check on conclusions based on data from other areas concerning ammonite associations, generic and specific variations, and stratigraphic distribution. The study includes descriptions of two new genera, Iniskinites and Chinitnites, that succeed and are closely related to Cranocephalites, a genus of late Bajocian(?) to early or middle Bathonian Age. Also, two specimens of Parareineckeia are illustrated to show the characteristics of the small septate whorls and of the body chamber of a genus hitherto represented only by four specimens (Imlay, 1953b, p. 101, pi. 55, fig. 1, 2, 5-8; 1962, p. C25, C26, pi. 7, figs. 1-7). The biological distribution of the described species is shown in table 1. STRATIGRAPHIC SUMMARY On the west side of Cook Inlet between Iniskin Bay and Tuxedni Bay the Callovian is represented by the Chinitna Formation which, as described by Detterman and Hartsock, 1966, p. 40-47), consists of two siltstone members separated by a sandstone unit 30-200 feet thick. The lower member, named JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA TABLE 1. Some Callovian ammonite genera and species described herein, showing biological relationships and relative numbers available for study. Famiy Genus and species Number of specimens Kosmoceratidae -Kepplerites chisikensis Imlay, n. sp _ 2 Cardioceratidae -Chinitnites chinitnaensis Imlay, n. gen., n. sp 102 parviformis (Imlay) __ _ 22 Iniskinites magniformis (Imlay) 7 abruptus (Imlay)  9 martini (Imlay)  3 intermedius (Imlay)  12 Reineckeiidae _Parareineckeia shelikofana (Imlay) _ 2 the Tonnie Siltstone Member, is roughly equivalent to the lower two-thirds of the Chinitna Formation, as classified by Imlay (1953b, p. 51). It thins northward from 1,300 to 800 feet, rests sharply on the Bowser Formation, and north of Chinitna Bay is marked basally by pebbles or by channel conglomerates that locally cut as much as 200 feet into the Bowser Formation. The upper member, named the Paveloff Siltstone Member, ranges in thickness from 900 to 1,350 feet, is thickest in the central part of the area, is generally marked basally by a sandstone unit, and is overlain unconformably by the Naknek Formation. This unconformity is most conspicuous where the Paveloff Siltstone Member is thinnest. The Shelikof Formation on the Alaska Peninsula between Wide Bay and Puale Bay consists of three members, as originally described by Capps (1923, p. 97-101) and later summarized by Martin (1926, p. 192-199), Imlay (1953b, p. 48, 49), and Burk (1965, p. 27). The lower member consists of 800 to 1,800 feet of siltstone and sandy siltstone, contains limestone concretions throughout, and in its lower part has many thin beds of volcanic ash. These ash beds, plus associated fossils, serve to differentiate the basal beds of the lower member from similar siltstone beds in the underlying Kialagvik Formation. The middle member consists of 1,000 to 3,500 feet of massive gray sandstone interbedded with some siltstone and conglomerate. Its upper part grades laterally and vertically into the adjoining siltstone members. The upper member consists of 900 to 1,500 feet of siltstone, contains some beds oi sandstone and limestone, and is overlain unconformably by conglomerate at the base of the Naknek Formation. The Chinitna Formation in the Nelchina area is overlain by the Naknek Formation with a marked unconformity that becomes angular to the north. At some places the Chinitna Formation rests concordantly but disconformably on Cranocephalitesbearing beds which are older than Callovian and which correlate faunally with the lower part of the Bowser Formation west of Cook Inlet (Imlay, 1962, p. C2; Detterman and Hartsock, 1966, p. 35-40). At many other places in the Talkeetna Mountains, the Chinitna Formation rests directly and unconformably on beds of middle to late Bajocian Age (Grantz, written commun., 1959). The Chinitna Formation crops out extensively in the southern Talkeetna Mountains but has been mapped in detail only in the southeasternmost part of those mountains, known as the Nelchina area (Grantz, 1960a, b; 1965). North of Horn Mountains in the Nelchina area the formation has been divided into two unnamed members, whereas south of the mountains it has been mapped as a single undivided unit of siltstone and shale that contains limestone concretions and thin sandstone beds. The lower member north of the mountains comprises two facies: (1) a northern facies that consists of cobble conglomerate and conglomeratic sand siltstone, contains many fossil wood and coal fragments, attains a thickness of 100 feet, and lies in channels cut in the underlying rocks and (2) a southern facies that consists of sandstone and siltstone, contains marine mollusks, and attains a thickness of as much as 1,500 feet. The upper member north of Horn Mountains consists of siltstone and shale, contains limestone concretions and thin sandstone beds, thickens southward from 0 to 800 feet or more, and is similar in appearance to the entire Chinitna Formation south of Horn Mountains (Grantz, 1965; written commun., 1972). CALLOVIAN AMMONITE SUCCESSION

Stratigraphic distribution and zonation of Jurassic (Callovian) ammonites in southern Alaska