Emileia

Abstract: Ammonites from the pillow basalt associations of the Siquisique ophiolites located in west-central Venezuela indicate a minimum Bajocian to early Bathonian age for emplacement of the complex. The ammonites have been identified as ? Stephanoceras ( Skirroceras ) cf. macrum (Quenstedt), ? Emileia ex gr. multiformis (Gottsche) et quenstedti Westermann, and ? Parkinsonia sp. This association of cosmopolitan Pacific and Tethyan elements aids in the location of the western end of the Middle Jurassic seaway set between the Tethys and the Pacific Oceans (Hispanic Corridor). The apparent age of the ammonites indicates that some of the Siquisique sediments, pillow basalts, and serpentines are the oceanic remnants of an arrested early phase of rifting between North and South America.

Abstract: Early and middle Bajocian (Middle Jurassic) ammonites have been found in six areas in southern Alaska over a distance of about 500 mi (800 km) from the Wrangell Mountains on the east to the Wide Bay area of the Alaska Peninsula on the west. In the Wrangell Mountains, some float obtained near the base of the Nizina Mountain Formation has furnished the ammonites Chondrocerax, Normatniitex, and Tehccras, which constitute good evidence for a late middle Bajocian age not older than the upper part of theS^Mawocerax hnmphriexiannm zone. In the Nelchina area of the Talkeetna Mountains northeast of Anchorage, the Tuxedni Group has furnished ammonites ranging in age from latest early Bajocian to early late Bajocian. These ammonites from the base upward include (1) Eri/citoides howelli (White), representing the Graphoce rax concarum zone; (2) Sonninia (Enhoploccrax) bifurcata Westermann, representing the lower part of the S hinctex, and Chondrocerax, representing the Stephanoceras humphriexiannni zone; and (5) Megasphrieroeerax, Sphaeroceran, Cadom itcx, and Nornta n n itex, representing the topmost Strenocerax xubfurcataw zone of early late Bajocian age. An even more complete ammonite succession of early to middle Bajocian age has been found on the west side of Cook Inlet between Tuxedni Bay and the eastern part of thelniskin Peninsula just west of Chinitna Bay. Basally that succession differs from the succession in the Talkeetna Mountains by the presence of Tmetocerax xcixxnm (Benecke) both below and along with occurrences of Eri/citoidex hoici'Ui (White) and by the presence of Emileia, Sonninia, and S. (Papilliccrax) between the underlying beds containing Parabigotitex and the overlying beds containing Teloeerax, Norman n itex, and Chondrocerax. The presence of Tmetoceras below the occurrences of Erijcitoidex favors an age slightly older than the Graphocerax conearn m zone of latest early Bajocian age. The presence of Sonninia and Em ileia is evidence of an age not younger than the zone of Otoitex xaiizei. The Bajocian ammonite succession at Wide Bay is essentially the same as that on the west side of Cook Inlet as high as the bed containing Sonninia tii.rednienxix Imlay. The succession at Wide Bay, however, has furnished more genera and species and has made possible a threefold faunule division of the beds characterized by Docidocerax (Pxeiidocidocerax) iridebayenxe. INTRODUCTION Most of the early and middle Bajocian (Middle Jurassic) ammonite taxa present in southern Alaska were described by the writer in 1964 and by Gerd Westerman in 1964 and 1969 (figs. 1-7). The writer at that time dealt mainly with ammonites collected either northwest of Cook Inlet between Tuxedni Bay and Iniskin Bay or in the eastern part of the Nelchina area of the Talkeetna Mountains. Gerd Westermann at those times dealt mainly with ammonites of late early to early middle Bajocian age that had been collected near Wide Bay on the Alaska Peninsula. Most of those collections had been made by field geologists working for the U.S. Geological Survey, as listed by Imlay (1964, p. Bl), who also made extensive collections from Bajocian sedimentary rocks in southern Alaska, in 1948, 1952, 1962, 1972, 1974, and 1977. The stratigraphic occurrences of the ammonites (figs. 8-13) are based mainly on studies by R. L. Detterman (1963) and by J. K. Hartsock (1966, p. 20-34) in the area west of Cook Inlet; by Arthur Grantz (1965) in the Nelchina area of the Talkeetna Mountains; by E. M. MacKevett, Jr. (1971, p. 16,17), in the Wrangell Mountains; and by R. L. Detterman and associates (1977, 1980, and 1981) in the Paule Bay and Wide Bay areas of the Alaska Peninsula. Only those taxa are described herein that have not previously been identified or described, or for which new biologic, stratigraphic, or geographic data are now available. BIOLOGICAL ANALYSIS The U.S. Geological Survey's fossil collections from southern Alaska contain at least 1,224 ammonite specimens of early and middle Bajocian age. Their distribution by genus, subgenus, subfamily, and family is shown in table 1. Among the families, the Hammatoceratidae comprise about 28% percent of the total number of specimens; the Stephaneroceratidae, nearly 19 percent; the Sonniniidae, 8% percent; the Sphaeroceratidae and Perisphinctidae, each a little more than 8 percent; the Oppeliidae, 7% percent; the Otoitidae, 6% percent; the Phylloceratidae and Hildoceratidae, each EARLY AND MIDDLE BAJOCIAN AMMONITES FROM SOUTHERN ALASKA

Abstract: A new section opened on the site of the former South Main Road Quarry, Dundry, Avon, is described. The biostratigraphy of the ammonite succession has been revised through careful bed-by-bed collecting and is presented in a range chart. It is recast in the form of a sequence of discrete ammonite fauna! horizons as has become customary in the classical areas of Somerset and Dorset first described in this way by Buckman. One new ammonite faunal horizon has been identified in the Lower Bajocian: Bj-10b, Sonninia micracanthica (Buckman). This carries several of what have been regarded in the past as leading guide-fossils of the Sauzei Zone. But it is now seen to be also the type horizon of the index of the Laeviuscula Zone, Witchellia laeviuscula. It is therefore retained in the Laeviuscula Zone as its youngest horizon on grounds of nomenclatural stability. The basal boundary of the overlying Sauzei Zone is drawn above it and its lowest ammonite horizon renamed, Bj-11a, Stephanoceras kalum (Buckman). The systematics of some important species based on types from Dundry are reviewed briefly and the origins and phylogeny of some important ammonite genera of the Ovale to Sauzei Zones are discussed. The succession of forms of Witchellia is now separated as a phyletic subfamily Witchelliinae subf. nov. within the polyphyletic clade of the Sonniniidae. A new species of Emileia, E. dundriensis, is described from the Laeviuscula Zone. The nautiloids are also reviewed briefly.

Abstract: The Middle Jurassic of west-central Argentina comprises several stratigraphic sequences characterized on thebasis of ammonoids, bivalves, brachiopods, foraminifers and ostracods. Aalenian and Bajocian ammonoids belong in the Bredyia manflasensis, “Zurcheria” groeberi Puchenquia malarguensis, Pseudotoites singularis, Emileia giebeli, Stephanoceras humphriesianum and Megasphaeroceras rotundum Zones. Three independent series of four biozonal units each, respectively based on bivalves, brachiopods and microfauna, are recognized in this interval. Bathonian and Callovian ammonoids are allocated to the Cadomites--Tulitidae, Lilloettia steinmanni, Eurycephalites vergarensis, Neuqueniceras (Frickites) bodenbenderi, Hecticoceras proximum Zones and Rehmannia (Loczyceras) patagoniensis Horizon. At the same time, further biostratigraphic subdivisions are distinguished by other taxa, totalling two for bivalves, three for brachiopods and one for calcareous microfossils. Diversity trends of the different faunal groups and sequence distribution are explained by changes in relative extension of platform and basinal areas.

Abstract: Seven species of ammonites are described from the Lungma (Langma) limestone of Mekyigunru, eight miles south of Kampadzong, Tibet. The genera Sonninia, Witchella, Dorsetensia, and Emileia are represented; two species are new--Witchella tibetica and Dorsetensia? haydeni. The age is middle Bajocian (Jurassic), with only the Sowerbyi and Sauzei zones present, from which it is inferred that the formation here represents a condensed deposit.