Tmetoceratidae (Ammonitina) fauna from the Gerecse Mts (Hungary)

Abstract Taxonomic and stratigraphic problems of the family Tmetoceratidae and the genera Dumortieria, Catulloceras, Cotteswoldia, Pleydellia and Tmetoceras included in it are briefly discussed. Fifteen species of Tmetoceratidae are described and illustrated from the Upper Toarcian-Aalenian ammonite assemblages of the Gerecse Mts (NE Transdanubian Range, Hungary). The fauna described here is closely allied to the Mediterranean Province of the Mediterranean-Caucasian Realm

The ammonites of the Middle Jurassic Cranocephalites beds of East Greenland, pages 01-86

Thick successions of marine Middle Jurassic deposits rich in ammonites occur in the Jameson Land Basin in central East Greenland. The fauna of the so-called Cranocephalites beds of this basin, comprising the Borealis–Pompeckji Standard Zones, was until now largely represented by a single collection. This was made by T.M. Harris during a 1927 excursion up the valley of Ugleelv to Katedralen, the type area of Cranocephalites pompeckji, which is the oldest named species of this genus. Revisits to this area in 1994 and 1996 by JHC resulted in a large bed-by-bed collection of Cranocephalites. The number of faunal horizons that could be distinguished grew from the nine previously recognised to thirty-four today. The zonal stratigraphy of the Cranocephalites beds encompasses the Borealis, Indistinctus and Pompeckji Standard Zones. The Pompeckji Zone is subdivided into four new subzones, reflecting four successive basic morphologies of Cranocephalites that should be recognisable more widely and are thus useful for subzonal correlations. The detailed zonation that serves as the secondary standard zonation for the Boreal Province in the Middle Jurassic is thus highly improved. The biostratigraphic resolution obtained here is near the achievable limits. It allows a high-resolution study of the evolution of the ammonites which on this timescale appears to be continuous. Three new species are described: Cranocephalites carolae sp. nov., Cranocephalites intermissus sp. nov. and Cranocephalites episcopalis sp. nov. An additional new species, Cranocephalites tvaerdalensis sp. nov., is described in the appendix by P. Alsen based on collections from Tværdal on Geographical Society Ø, North-East Greenland. This species is also recorded in Jameson Land

Numerical paleoceanographic study of the Early Jurassic transcontinental Laurasian Seaway

The forces governing marine circulation of a meridional transcontinental seaway is explored with the Princeton Ocean Model. The Jurassic Laurasian Seaway, which connected the low-latitude Tethys Ocean with the Arctic Sea is modeled quantitatively. The global ocean is found to have a profound influence on seaway dynamics. A north-south density difference and hence sea level difference of the global ocean was probably the main factor in forcing the seaway flow. When the Tethys waters were the denser water, the net seaway flow was southward, and conversely, it was northward for denser Arctic waters. Marine bioprovincial boundaries and sediment data indicate that the seaway probably was dominated by Boreal faunal groups and reduced salinities several times in the Jurassic. The model results suggest that this can be explained by southward flowing seaway currents, which may have been related to an oceanic thermohaline circulation where no northern high-latitude deep convection occurred

The stratigraphy of the Inferior Oolite at South Main Road Quarry, Dundry, Avon

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

Dimorphism and evolution of Albarracinites (Ammonoidea, Lower Bajocian) from the Iberian Range (Spain)

Several tens of specimens of Lower Bajocian Albarracinites (type species A. albarraciniensis Fernandez-Lopez, 1985), including microconchs and macroconchs from the Iberian Range, have been studied. This ammonite genus ranges in the Iberian Range from at least the Ovale Zone to the uppermost Laeviuscula Zone of the Lower Bajocian (Middle Jurassic). The macroconch counterpart is thought to be a group of stephanoceratids previously attributed to Mollistephanus, Riccardiceras and other new forms described in this paper. Two chronologically successive species of Albarracinites have been identified: A. albarraciniensis and A. submediterraneus sp. nov. The evolution of the Albarracinites lineage represents a hypermorphic peramorphocline starting from depressed, small and slender serpenticones of A. westermanni, to larger planorbicones with more cadiconic phragmocones and body chamber of subcircular cross section belonging to A. submediterraneus sp. nov., through A. albarraciniensis Fernandez-Lopez. In contrast, Mollistephanus planulatus (Buckman), M. cockroadensis Chandler & Dietze and M. mollis Buckman represent a peramorphocline by acceleration, producing adults of similar size but more compressed and with increasing ontogenic variation of shell ornament. Albarracinites and Mollistephanus subsequently developed two opposite peramorphoclines or gradational series of morphological changes undergoing greater development and ontogenic variation. These two genera show diverse palaeobiogeographical distributions too. Albarracinites is rarely recorded in the Mediterranean and Submediterranean from the Discites to the Laeviuscula Zone, whereas Mollistephanus is more common in north-western Europe and other biochoremas of the western Tethys from the Discites Zone to the Sauzei Zone. Albarracinites seems to be the earliest stephanoceratid lineage in western Tethys, branching off from the otoitid Riccardiceras by proterogenetic change and resulting in paedomorphosis at the Aalenian/Bajocian boundary