Late Bathonian Research Articles

Mode of origin of dispersed clasts in Jurassic shales, southern part of the Yana-Kolyma fold belt, North East Asia

In an effort to estimate climatic conditions in high latitudes, we undertook field studies of Middle to Late Jurassic clast-bearing mudrocks in northeastern Russia. Most of the enclosed clasts, previously attributed to seasonal ice rafting, consist of rip-up shale clasts associated with turbidites and blocks and slabs of intrabasinal sediments. The emplacement processes for these materials are here considered to have been gravity driven mass movements. Evidence of ice rafting, not of the best quality but including penetration structures in adjacent shale, is restricted to one locality in mudrocks of the Kolyma River area, which are tentatively assigned to the middle to late Bathonian. Marked seasonality with freezing winters therefore may have characterized this time, in accord with GCM results suggesting strong seasonality in the Jurassic high latitudes. The evolution of Jurassic climate is still to be defined, however, as other reports of clasts in Bajocian-Tithonian mudrocks in the region remain unevaluated.

Bathonian ammonites from CantonAargau, Northern Switzerland: Stratigraphy, taxonomy, and biogeography

Abstract The first Bathonian ammonites found in measured sections in Canton Aargau (Switzerland) are described and figured: they are mainly tulitids, some oppeliids, rare perisphinctids and stephanoceratids. A comparative study of the ontogeny of the tulitids has allowed the number of genera to be reduced to three: Tulites Buckman , 1921 , Bullatimorphites Buckman , 1921 and Morrisiceras Buckman , 1920 . The dimorphism is expressed by the subgenera. Among the oppeliids, Trimarginia Arkell , 1952 , a genus proposed for the Late Bajocian ammonites of the Sinai Peninsula in Egypt, is represented by T. sylviae nov. sp. of Late Bathonian age. These ammonites date from the Middle and Late Bathonian in thin condensed iron oolitic beds that were previously assumed to belong to the Callovian or even Oxfordian ages due to a lack of dating elements. Trimarginia is found for the first time in what are undoubtedly Upper Bathonian beds. This enlarges its previously known biogeographic and stratigraphic range.

Chapter 19 Jurassic-Cretaceous history

Jurassic-Cretaceous follows Triassic history with minor change. It was an interval dominated by deposition of marine muds, silts and sands, with occasional non-marine environments on advancing deltas (Parker 1967; Harland 1973a; Kelly 1988). Subdued topography contrasted with Triassic and Paleogene terrains. But there was also Late Jurassic and Early Cretaceous intrusion of basic sills and volcanism in eastern Svalbard. Figure 19.1 shows the distribution of Jurassic and Cretaceous deposits in Svalbard. The two periods (208-65 Ma) span 143 million years but the stratal record for this interval totals only 1700 m of which more than half was deposited in Albian time. The Jurassic-Cretaceous rocks of the eastern platform, presently cropping out on some islands, represent a relict of a once continuous sheet of strata, which is still preserved extensively across much of the Barents Shelf. The Triassic-Jurassic boundary is marked by seemingly continuous facies from Rhaetian to Toarcian; but then follows a contrast between the main Spitsbergen Basin (which hardly subsided) and the Eastern Platform. The contrasting areas of east and west Svalbard were divided by the continuing activity along the Billefjorden lineament. To the east, subsidence permitted a complex and variable sequence resulting from deltas from the east (marine and non-marine) through Liassic to mid-Bathonian time. To the west there was little evident subsidence and only condensed deposits of the uppermost Wilhelmoya Formation were washed by shallow seas. This part of the story concluded the history of the Kapp Toscana Group. A Late Bathonian marine transgression transformed east and

Stratigraphic record of the structural evolution of the western extensional margin of the Subalpine Basin during the Triassic and Jurassic, Ardeche, France

The nature and the geometry of Mesozoic deposits in the Ardeche region reflect the different stages of structural evolution of the western extensional margin of the Subalpine Basin. Through stratigraphic analysis of a broad transect passing from the Uzer block, through the GPF (“Géologie Profonde de la France”) borehole Balazuc 1 and two petroleum exploration wells on the different blocks of the margin, it has been possible to integrate data from borehole BAI in a sequential stratigraphic and regional dynamic framework, and to attempt to specify the modes of tectonic control on the organization of the deposits along a profile of this extensional palaeomargin. The Triassic and Jurassic deposits are composed of six major transgressive-regressive cycles for which the geometric and stratigraphic characteristics indicate that they were controlled by the tectonic evolution of the basin, and more specifically by variations in the type and rate of subsidence. The first two cycles, Anisian-early Sinemurian in age, correspond to the initial structural creation of the margin with a west-east sedimentary polarity. Extensional tectonism, which affected the Palaeozoic basement, in part controlled the duration and intensity of the transgressive phases, with the regressive phases reflecting a decrease in regional subsidence. The third and fourth cycles, early Sinemurian-middle Bathonian in age, were contemporaneous with the Tethyan rifting. In particular, they record evidence of decreasing regional subsidence, and even uplift, associated with block faulting. This caused strong tectonic decoupling and highly variable subsidence along the margin profile; episodes that are represented by that part of each sedimentary cycles deposited around the maximum regression, i.e. end of the regressive phase and beginning of the transgressive phase (Sinemurian and Aalenian). A regional phase of subsidence followed which allowed maximum expansion of the transgression (Toarcian and Bajocian transgressive peaks). The fifth and sixth cycles, middle Bath on ian-Kimmeridgian in age, were deposited during a period of widespread subsidence of the margin that was synchronous with the onset of Tethyain oceanic spreading. They preferentially record episodes of accelerated subsidence giving rise to transgressive phases generally associated with a synsedimentary tectonic activity that incurred relatively heterogeneous subsidence across the entire palaeomargin (late Bathonian and early Oxfordian). The regressive phases are subsequently marked by a decreased, but uniform subsidence with no evidence of uplift. The sediments of these last two cycles were deposited in a post-rift context and are liable to record effects of geodynamic events outside the basin. Characterization of the different stages in the evolution of the Ardeche palaeomargin by their stratigraphic expression provides geological constraints for modelling fluid migration throughout this extensional margin, the objective of the 'GPF Ardeche' project.

The Ardèche palaeomargin of the South-East Basin of France: Mesozoic evolution of a part of the Tethyan continental margin (Géologie Profonde de la France programme)

This paper incorporates the results of seismic and gravity investigations, borehole data and studies of sedimentology, biostratigraphy, sequence stratigraphy and structural geology, carried out in the framework of the Deep Geology of France programme. The main purpose of the paper is to define the structure and to reconstruct the evolution of the Ardèche palaeomargin of the South-East Basin of France from the Stephanian to the end of the Mesozoic. The acquisition and processing of three seismic reflection profiles, the drilling of two scientific boreholes (BA1 and MM1), and subsequent structural modelling, with the use of cross-section balancing techniques applied to both the depth-migrated seismic and geological sections, provide new geometrical constraints which lead to the following hypothesis of the geodynamic evolution of the margin: 1. (1) Late Palaeozoic extension with the development of high-angle basement faults, asymmetrical Permian half-grabens, (pre-extension) sedimentary cover. 2. (2) During the Middle Triassic, a pre-rift stage with the creation of small fault blocks and, in the Late Triassic, the formation of an E-W flexure. 3. (3) End-Lias (Early Jurassic) to Middle Jurassic formation of a major detachment in the Carboniferous coal measures, leading to complete decoupling of the Mesozoic sedimentary cover from the basement. This episode of extension, coeval with the opening of Tethys, can be related to a phase of episodic rifting between the late Sinemurian and the late Bathonian (i.e. during 30 Ma). 4. (4) Late Jurassic to Early Cretaceous thermal subsidence, with regional downwarping of the basement towards the east. 5. (5) After the Late Cretaceous (the period of maximum burial), Pyrenean and Alpine deformation in the south and east, causing progressive uplift of the Ardeche palaeomargin, as much as two kilometres of Mesozoic deposits subsequently being eroded from the section during the Tertiary.

On the earliest known occurrence of the Middle Jurassic ammonite genusReineckeia in the Upper Bathonian of Jumara, Kachchh, western India

Two specimens of the Middle Jurassic ammonite genusReineckeia (sensu lato) have been found in the lowest beds of the Pachchham (Patcham) Limestones exposed in the core of the Jumara Dome, Kachchh (Kutch), Gujarat, western India. The stratigraphy is described in detail and the age bracketed to lie between latest Late Bathonian and Middle Bathonian, older than any previously described examples of this genus, either in India or in Europe (middle Early Callovian). The new finds are compared with other known pre-Callovian Reineckeiidae, notably those of the eastern borders of the Pacific, but the relationships are not close. The phylogenetic consequences are briefly discussed. The roots of the Reineckeiidae continue to lie hidden.

Les brachiopodes du Bathonienet du Callovien inférieur de Thakkhola (Népal central): Paléontologie et biostratigraphie

This article describes and figures the brachiopod faunas collected in the Bathonian and in the EarlyCallovian from Thakkhola (Central Nepal). The faunas are located in the chronostratigraphical framework based on the standard ammonite scale. Three brachiopod communities are evidenced, two in the Bathonian and another one in the Early Callovian. The first appearance nowadays known of the terebratulid genera Aromasithyris and Dorsoplicathyris occurs in Thakkhola where A. damodarkundensis nov. sp. and D. nepalensis nov. sp. are issued to the Retrocostatum Zone of the Late Bathonian. Then, the representatives of these genera have migrated along continental shelves towards the Western North-Tethyan realm and towards the Mid-European platforms where they are represented by abundant specimens in the Early and Middle Callovian.

Découverte d'une association à Ataxella Occitanica Peybernes, grand foraminifère du jurassique moyen, dans Le Sud du Bassin Parisien

Microfaunas with conical-shaped Foraminifera Ataxella occitanica (Peybernes) 1974 associated with primitive Kurnubia, Kilianina sp. and Chablaisia chablaisensis, were discovered in platform limestones attributed to Late Bathonian, in the South of the Parisian Basin near the town of Le Blanc (Indre, France). A Late Bathonian or Early Callovian age is suggested for this species, formerly considered as restricted to the Pyreneo-lusitanian domain.

L'“oolithe de Balin” (Pologne méridionale).Nouvelles observations et interprétations stratigraphiques

The unusualness and provisional outcropings of the “Balin Oolithe” (Krakow area) have led authors to propose, either a Late Bathonian, or an Early Callovian age for this formation. More than 120 years later than the monographs of Laube, Neumayr, Szajanocha, Teisseyre and Siemiradzki, new collected faunas owe to precise that the sandstones, underlaying the ferrugineous deposits, begin in the Middle Bathonian and reach the Upper Bathonian (Retrocostatum Zone). The famous “Balin Oolithe” is dated from Late Bathonian (Retrocostatum (=Hodsoni pars.. sup.-Orbis) and Discus Zones) to Early (Macrocephalus/Bullatus (=Herveyi pars)) and Gracilis (=Koenigi-Calloviense Zones) and Middle Callovian (Jason Zone). considering the special conditions of sedimentation of this ferruginous facies corresponding to a transgressive period and the subsequently action of cryoturbation and solifluxion during the Quaternary, it is obvious that the use of this formation, to specify the biostratigraphy of the Bathonian-Callovian boundary, should lead to confusion and unfruitfull discussions. The sedimentation is reduced, discontinuous and the fauna is different in each profile, even if the typical ferruginous facies is widespread; one can notice that, in the new section, no Callovian Proplanulites have been collected within the ammonite fauna, although Teisseyre have created his genera on specimens coming from neighbouring sections showing this formation. In comparison with other European areas, these faunas, collected in thin and lenticular sediments, typical of the global transgressive Late Bathonian-Lower/Middle Callovian, must be considered only for fundamental problems in paleontology (variability, systematic, biogegraphy, etc…) but not as reliable data for a refined biozonation to a better understanding of the boundary between these two Middle Jurassic stages.

Dinoflagellates cysts of the Bathonian/Callovian boundary beds in Southern Germany

The Bathonian/Callovian boundary beds in Swabia contain diverse and mostly well preserved dinoflagellate assemblages, including 58 species assigned to 29 different genera. Lowest diversity of 29 species is recorded in the uppermost Bathonian, while highest diversity of 45 species is found in a sample from the Koenigi Zone (Early Callovian). Most of the recorded species range through the latest Bathonian and Early Callovian. None of the species appear to be restricted to the latest Bathonian. Species not found below the Bathonian/Callovian boundary include Atopodinium haromense, Mendicodinium groenlandicum, Fromea torantilis, Lagenadinium callovianum and Valvaeodinium groenlandicum.. The most frequent species in the latest Bathonian and the earliest Callovian (i.e. Keppleri Subzone) is Ctenidodinium combazii.. Representatives of the genera Sentusidinium and Chlamydophorella are, together with micrhystrid acritarchs, relatively common in both the Late Bathonian and Early Callovian. Comparable high abundances of Ctenidodinium combazii at the Bathonian/Callovian boundary are also described from southern France, Normandy and the Bathonian type area in southern England.

Lepidosauromorph reptiles from the Middle Jurassic of Skye

Abstract The Middle Jurassic Kilmaluag Formation (previously known as the Ostracod Limestones) of the Great Estuarine Group in Skye, Scotland, has yielded an assemblage of Bathonian terrestrial vertebrates including mammals, tritylodonts, crocodiles and turtles. This paper presents the first description of Jurassic lepidosauromorph reptiles from Scotland. Two genera are represented: a crown-group lizard referable to the late jurassic/early Cretaceous genus Paramacellodus (Squamata: Scincomorpha) and a stem-group lepidosauromorph, Marmoretta Evans, 1991, first described from the late Bathonian of Kirtlington, Oxfordshire. The Skye material of Marmoretta includes the first associated skull and postcranial remains. These confirm the original description and reconstruction, and provide further support for a hypothesis of relationship which places Marmoretta as the sister taxon of Lepidosauria.

Lepidosauromorph reptiles from the Middle Jurassic of Skye

The Middle Jurassic Kilmaluag Formation (previously known as the Ostracod Limestones) of the Great Estuarine Group in Skye, Scotland, has yielded an assemblage of Bathonian terrestrial vertebrates including mammals, tritylodonts, crocodiles and turtles. This paper presents the first description of Jurassic lepidosauromorph reptiles from Scotland. Two genera are represented: a crown-group lizard referable to the late jurassic/early Cretaceous genus Paramacellodus (Squamata: Scincomorpha) and a stem-group lepidosauromorph, Marmoretta Evans, 1991, first described from the late Bathonian of Kirtlington, Oxfordshire. The Skye material of Marmoretta includes the first associated skull and postcranial remains. These confirm the original description and reconstruction, and provide further support for a hypothesis of relationship which places Marmoretta as the sister taxon of Lepidosauria.

Paleogeographic and paleotectonic implications of clay mineral distribution in late Jurassic-early Cretaceous sediments of the Pindos-Olonos and Beotian Basins, Greece

A new method is proposed for solving the controversial problem of the location of oceanic areas from which the Pindos and Othrys ophiolites originated. Assuming that clay fractions, quickly disseminated over large areas, may be reliable markers of erosional processes, we studied these fractions in sediments from two “external” basins (Pindos-Olonos and Beotian) located between the main carbonate platforms of the Greek Hellenids. Chronologically, two different clay associations can be distinguished in the sedimentary sequences of the basins. The lower one is dominated by illite and subregular illite-smectite mixed-layers and poor in Mg, Ni and Cr; this association is consistent with common continental sources. The upper one, appearing in late Tithonian synchroneously in both basins, consists of trioctahedral smectite (saponite type) enriched in Fe, Mg, Ni and Cr; they are considered to be derived from weathered ophiolites. Thus, the beginning of the ophiolite detrital sedimentation, accepted as being middle to late Bathonian in the basinal sequences of the Maliac or Othrys zone from Hydra or lower-middle Oxfordian in all the internal units in the Argolis Peninsula, is much younger (late Tithonian) in the external basins. Such a diachronism is not consistent with a model postulating initial ophiolite displacements within the Pindos-Olonos basin by late Jurassic time. It suggests that a platform was acting as a barrier between the site of the ophiolite first intra-oceanic deformation and the “external” basins. This barrier cannot be the Parnassus platform that kept subsiding in neritic environments until late Cretaceous inside the “external” basins; it is likely to be the Pelagonian platform, positively known to have been submerged during the Tithonian. Consequently, we conclude that there was no genetic relationships between the “external” basins (Pindos-Olonos basin in a broad sense) and the “Pindos ophiolites” of which the zone of origin is to be located on the opposite eastern “internal” side of the Pelagonian platform.

Microfaunes, microflores etpaléoenvironnements successifs dans la formation d'El Mers (Bathonien-?Callovien) du synclinal de Skoura (Moyen-Atlas, Maroc)

In the Middle-Atlas (Morocco), the lower part of the “Red beds” (El Mers Formation), Middle Jurassic in age,contains various microfossils which permit to reconstruct the palaeoenvironmental evolution of this area for this period. Populations of abundant charophytes, collected at the base of the formation, are assigned to a new species: Porochara hiansFeist & Grambast-Fessard. Species of ostracods are generally different than the European synchronous ones. The first ostracods appearing at the base of the formation are monospecific and euryhaline (continental or brackish). They are more diversified above and correspond to a typical marine depositional environment. Marine incursions occur up to the top of the formation where they are represented by limestones bearing dasycladales and benthonic foraminifera, Late Bathonian to Early Callovian in age. The transgressive trend observed at the top of the “El Mers Formation” can be correlated to the deepening-upward trend of the Transgressive Systems Tract from the Depositional Sequence DS 158,5 (3rd order eustatic cycle LZA 3-1) which corresponds to a general transgression of the sea over the palaeostructures of the Jurassic Tethyan Basin.

Biogeography of Bathonian to Oxfordian (Jurassic) dinoflagellates: Arctic, NW Europe and circum-Mediterranean regions

Calculations of the Koch Index of biotal dispersity suggests that the range of dinoflagellate cyst diversity in the Arctic, NW Europe and circum-Mediterranean regions was relatively high in the studied Late Bathonian to earliest Callovian, Early to Middle Callovian, Late Callovian and Early Oxfordian time intervals. Although there are no great differences, the dispersity values increase from Late Bathonian to Early Oxfordian. The Simpson Coefficient of biotal similarity (Simpson, 1960), which has been applied to quantify the variations between the dinoflagellate floras within the different regions, suggests that the differences in composition of the dinoflagellate assemblages became less prominent during Late Callovian-Early Oxfordian time compared to the Late Bathonian-Middle Callovian. During the Late Bathonian to Early Oxfordian the true Boreal dinoflagellages assemblages (Sverdrup Basin-Svalbard/Franz Josef Land) show a southwardly decreasing similarity to the contemporaneousassemblages approaching the Tethyan region. Similarly, assemblages in the southernmost Tethyan region (Middle East-Iberian Penninsula) show decreasing similarity to the assemblages approaching the Boreal areas. The dinoflagellate assemblages in the Yorkshire/East Midlands area appear to be intermediate between the true Boreal and Tethyan marine microfloras, altjough they may show a slightly closer similarity to the Tethyan than the Boreal assemblages. This distribution patterns found among the dinoflagellate cysts appears similar to that observed for the ammonities, with distinct differences between Boreal (Arctic) and the Tethyan (Mediterranian) Provinces and with a mixing of elements within the Sub Boreal Province. From late Early Callovian times the previous faunal barriers were disrupted and it is possible to make correlations at the ammonite zonal level among the Arctic, NW central European and Sub-Mediterranean regions. The dinoflagellate assemblages are profoundly different between the Boreal assemblages (i.e. in the Sverdrup Basin, Svalbard and Franz Josef Land) and those of the Sub-Mediterranean province (southern Germany, France, Switzerland) and this continued through the Middle Callovian. The Late Callovian was a period of distinct diversification among the Boreal and Sub Boreal dinoflagellate cyst floras, as shown by an increase in number of species compared to the older Callovian assemblages observed within the Sverdrup Basin, Barents Sea Region, the North Sea area and the British Jurassic. Similar to Late Bathonian-Early Callovia time, the West European Sub Boreal Province in Late Callovian time also represented an area of mixing of Boreal and Tethyan marine microfloras. As evident within the Late Bathonian-Early Callovian interval, a transition between two distinctive dinoflagellate cyst provinces appears as a generally fluctuating line transversing the Britain-North Sea region. In overall character, the Early Oxfordian dinoflagellate cyst assemblages are very similar to those of the Late Callovian time. The Simpson Coefficients for the Early Oxfordian dinoflagellate assemblages display latitudinally decreasing similarity trends comparable to the older middle Jurassic time intervals. It is evident from the present study that the increase in the dispersity values and the decreased differences in composition among the dinoflagellate assemblages from Late Bathonian to Early Oxfordian times coincided with the disappearance of important land-barriers and the establishment of new open marine sea-ways between the Boreal and Tethyan basins. These changes in the provinciality of the dinoflagellates also coincide with a period when southward migration of boreal faunas into the Paris and Lusitania Basins and a migration of Mediterranean faunas into Eastern Greenland took place.

Potential reservoir and source rocks in relation to Upper Triassic to Middle Jurassic sequence stratigraphy, Atlantic margin basins of the British Isles

Atlantic margin basins from the Celtic Sea to the Hebrides and North Minch, west of the British Isles, and in the Northern North Sea, have the same major genetic sequences ( sensu Morton 1989 ) in the Upper Triassic to Middle Jurassic. The basins were tectonically related, and six major sequences can be recognized throughout. The tectono-stratigraphic evolution of the basins was through two episodes of extension comprising: syn-rift phases (1) Late Triassic to Early Sinemurian and (4) Latest Toarcian to Late Bajocian; thermal and loading sag phases (2) Mid Sinemurian to earliest Toarcian and (5) Late Bajocian to Late Bathonian (except North Sea ?); and stabilization phases (3) Toarcian and (6) Late Bathonian and Callovian. Potential and proven reservoirs (sandstones) occur in the syn-rift sequences (e.g. Statfjord, Bearreraig, Brent) and in the upper parts of sag sequences (e.g. Cook, Scalpa, Elgol, Valtos). Several organic-rich shales (potential source rocks) occur: in the basal parts of sag sequences (e.g. Heather, Cullaidh, Pabba); in stabilization sequences after eustatic sea-level rises (e.g. Drake, Portree); and locally at the base of syn-rift sequences (e.g. Dun Caan).

Bathonian and Valanginian fossils from Honduras

The Agua Fria Formation of Honduras, Chortis Block, consists approximately of 200 or more meters of beds of gray, quartzose sandstone alternating with beds of gray and/or black shale. From this formation Mark Gordon has collected Choffatia s.l. sp. juv. (or a leptosphinctine) and Iniskinites (?) cf. andinus ( Burckhardt 1903). Their age is most likely Late Bathonian. The Cantarranas Formation consists of tens of meters of thin-bedded (1 cm to 6 cm thick), platy beds of limestone separated by even thinner partings of shale. The known fossils from the Cantarranas Formation are flattened specimens of filose species of Olcostephanus, which are most likely Valanginian.

Middle to Late Jurassic basin evolution and sandstone reservoir distribution in the Danish Central Trough

During the Mid- to Late Jurassic, long-term eustatic sea-level rise and half-graben subsidence in the Danish Central Trough resulted in a major transgression. Deposition of widespread alluvial plain sediments in the Søgne Basin and Tail End Graben was terminated in the Late Bathonian due to bypass and erosion following a short-term relative sea-level fall. The sea-level fall was followed by a relative sea-level rise during the Callovian which caused the development of a transgressive succession of coastal plain and shallow marine deposits. The transgressive succession consists of several prograding sediment wedges commonly terminated by a coal bed and a flooding surface. As transgression continued during the Late Jurassic, the shoreline shifted westwards. Transgressive Oxfordian shoreface to back-barrier sandstones were deposited. Another short-term relative sea-level fall occurred during the Kimmeridgian during which regressive shoreface to beach sandstones were deposited. During the Late Kimmeridgian and Volgian, the long-term relative sea-level rise resulted in deposition of thick Volgian offshore claystones in the central part of the Central Trough (Heno Plateau, Gertrud Graben and Feda Graben). During the Volgian and Early Cretaceous, the transgression continued towards the west and shallow marine sandstones may have been deposited along the western margin of the Central Trough fringing the Mid North Sea High (Grensen Nose Basin and Outer Rough Basin). Along the Ringkøbing Fyn High in the easternmost part of the Central Trough, Volgian and Early Cretaceous fan-delta sandstones and basin floor turbidite sandstones are interstratified with offshore claystones.

On the age of the Upper Ostrea Member, Staffin Bay Formation (Middle Jurassic) of north-west Skye

Synopsis The precise age, late Bathonian or early Callovian, of the Middle Jurassic Upper Ostrea Member (Staffin Bay Formation) of NW Skye, Inner Hebrides has proved controversial. Twelve samples from the type section at Dunans, Staffin Bay, Skye yielded palynofloras rich in miospores with subordinate proportions of marine microplankton. All the samples produced low diversity dinoflagellate cyst florules which include Meiourogonyaulax caytonensis, M. planoseptata, Mendicodinium groenlandicum and Rhynchodiniopsis cladophora and thus indicate an early Callovian age. The Upper Ostrea Member represents, therefore, the oldest Callovian strata in Scotland and is coeval with the Fleet Member of England. The Staffin Bay Formation, with marine macrofauna and microplankton, overlies the regressive Skudiburgh Formation (Great Estuarine Group) and this boundary has been deemed to be a genetic sequence boundary. This interpretation is consistent with current assessments of global eustasy.

On <i>Trochamijiella gollesstanehi</i>, gen. nov et sp. nov. (Foraminiferida, Loftusiacea), an index for the Middle Eastern marine Late Bathonian

Abstract. The new taxon Trochamijiella gollesstanehi is described; it is morphologically similar to, but phylogenetically distinct from, Amijiella, and is initially trochospiral; it is known from Iran, the United Arab Emirates and Oman, and is believed to characterise the Late Bathonian. Primary type specimens of Amijiella amiji and Haurania deserta are refigured for comparison and are believed to characterise Early Bathonian and older Jurassic strata. All three genera are reclassified and all are placed in the Biokovinidae Gušić, 1977.