Late Tithonian Research Articles

Microdinium avocetianum sr nov., a dinoflagellate cyst from the latest Jurassic (tithonian) of Australia

The new species Microdinium avocetianum from the Tithonian (Upper Jurassic) of Australia is described. It is a small partiform gonyaulacalean cyst with a distinctive paratabulation style, dark autophragm and low, irregularly denticulate crests. The species may be relatively prominent in the late Tithonian (Pseudoceratium iehiense Range Zone) of the Timor Sea, offshore northwestern Australia and the Carnarvon Basin, offshore Western Australia.

Patterns of biotic change in Middle Jurassic to Early Cretaceous Tethyan radiolaria

The rate of taxic turnover of nearly 400 radiolarian species/subspecies is analyzed in order to document long term biotic change of plankton during the Middle Jurassic to Early Cretaceous (Aalenian to Aptian). The pattern and dynamic of diversity change is described using four indices: rate of species first and last occurrence, rate of diversification and rate of turnover. Plots of cumulative sampling effort suggest that the analyzed data represent an adequate sample of total standing diversity for most examined stages. Rates of species first occurrence exceed rates of last occurrence for most of the Middle Jurassic, except for the middle Bajocian. In contrast, the Late Jurassic was a time of decreasing radiolarian diversity and the Kimmeridgian records the lowest rate of diversification. It is followed by a dramatic increase in first occurrences near the Jurassic–Cretaceous boundary with as a result the highest rate of diversification recorded in the late Tithonian. Regional radiolarian diversity was stable throughout most of the Early Cretaceous. A stratigraphic permutation test was performed to assess the influence of uneven sampling on the observed pattern of taxic turnover and identified the intervals for which randomly obtained patterns are significantly different from the observed pattern. The Kimmeridgian and late Tithonian events coincide with substantial climate-derived perturbations in water cycling, nutrient supply and oceanic productivity. They point to a negative relationship between radiolarian macroevolution and changes in the state of nutrient availability, although further work is needed to refine the temporal resolution of this relationship and to explore ecological aspects of its causal link with respect to radiolarian evolution.

MICRODINIUM AVOCETIANUM SP. NOV., A DINOFLAGELLATE CYST FROM THE LATEST JURASSIC (TITHONIAN) OF AUSTRALIA

Abstract The new species Microdinium avocetianum from the Tithonian (Upper Jurassic) of Australia is described. It is a small partiform gonyaulacalean cyst with a distinctive paratabulation style, dark autophragm and low, irregularly denticulate crests. The species may be relatively prominent in the late Tithonian (Pseudoceratium iehiense Range Zone) of the Timor Sea, offshore northwestern Australia and the Carnarvon Basin, offshore Western Australia.

Occurrence of proteinaceous moieties in S- and O-rich Late Tithonian kerogen (Kashpir oil Shales, Russia)

The polar fraction, isolated from the off-line pyrolysate at 400°C of a Late Tithonian, sulphur- and oxygen-rich, kerogen was examined via Raney Nickel desulphurization and TMAH thermochemolysis. Important information on this kerogen, not accessible via conventional pyrolysis, was thus obtained: (i) its structure is not simply based on alkyl skeletons cross-linked by ether and (poly)sulphide bridges, (ii) TMAH thermochemolysis afforded direct evidence of the survival of proteinaceous moieties in this 140 million years old kerogen and (iii) encapsulation within an aliphatic organic matrix was probably the main pathway reponsible for such a conspicuous preservation, also possibly favoured by the presence of numerous sulphur links.

High-resolution magnetostratigraphy and micropalaeontology across the J/K boundary strata at Brodno near Žilina, western Slovakia: summary of results

This study summarizes the final results of magnetostratigraphic and micropalaeontological investigations of the Tithonian/Berriasian boundary (J/K) limestones at the locality of Brodno near Žilina, Western Carpathians, West Slovakia. The aim is to prepare the background for correlation of a Late Tithonian and Early Berriasian biostratigraphic zonation with global magnetoevents (manifested in detailed magnetostratigraphic profiles) between the Tethyan realm and other regions, particularly the Boreal and Pacific realms. Suitable physical properties of the limestones studied, a favourable geological setting and rich microfossil assemblages (calpionellids) at Brodno (magnetozones M21r to M18r) allowed a systematic collection of new data on the original synoptic section, which now has the character of a high-resolution profile across the J/K boundary. Two reverse subzones detected within magnetozones M20n and M19n are named ‘Kysuca Subzone’ and ‘Brodno Subzone’, respectively. Both can be correlated with analogous subzones in the M-sequence of marine anomalies. Their existence can also be confirmed in the Bosso Valley section in Umbria, central Italy. A detailed study of the interval between magnetozones M20n and M17r in the Bosso Valley profile is presently in its final stage. Both magnetostratigraphic profiles, from the Brodno and Bosso Valley localities, were thoroughly investigated in the intervals close to the J/K boundary and are still unique among continent-based profiles in the detection and precise definition of both reverse subzones within M20n and M19n. Samples collected from the boundary strata of the reverse Kysuca Subzone at Brodno indicated a transition from N (R) to R (N) polarity of the Earth's palaeomagnetic field within a time interval of c.±5ka. Limestone samples (total number n=368) were subjected to progressive thermal demagnetization in 10–12 thermal fields and to subsequent multi-component analysis of remanence. The C-component, as the carrier of palaeomagnetic directions, was determined in the temperature interval of 300° to 540°, or possibly 580°C. Magnetomineralogical analyses of pilot samples and unblocking temperatures determined for all samples showed that magnetite is the carrier of remanent magnetization. The positions of the individual events of calpionellid stratigraphy relative to the global magnetic polarity timescale are precisely defined. The base of the Calpionella Standard Zone, which is considered a provisional J/K boundary indicator in ammonite-free sections in the Tethyan realm, lies within magnetozone M19n at the level of 35% of its local thickness. None of the boundaries in the calpionellid zonation coincides precisely with any of those in the palaeomagnetic zonation, but the first appearance ofCalpionella grandalpina , indicating the base of the Intermedia Subzone, lies in close proximity to the base of magnetozone M19r.

Palynological dating of the Neocomian–Aptian succession in the Indian Peninsula

Patterns of occurrences of spore-pollen species in Neocomian–Aptian palynological assemblages are significant for characterizing Lower Cretaceous palynofloras. Using palaeofloristic differentiation, emphasis has been placed on first appearance datums (FADs) of key species in the palynological zonation scheme presented in this paper. The basic data that have been analysed are from the subsurface Lower Cretaceous Rajmahal Formation in the Panagarh area, West Bengal. The successive first appearances of the following taxa are the main criteria for identifying palynological zones: Cicatricosisporites australiensis, Crybelosporites stylosus and Aequitriradites spinulosus followed by Foraminisporis wonthaggiensis. The next phase in species change-over, which is characteristic of the Neocomian–Aptian palynoflora, is indicated by the appearances of Coptospora microgranulosa, Triporoletes simplex, Foraminisporis asymmetricus andCrybelosporites striatus . By Barremian–Aptian times maximum diversity of the palynomorph assemblages was attained, reflecting provincialism from west to east in India. Varied environments of deposition are also reflected by the Neocomian–Aptian assemblages. The palynozones recognized in the Rajmahal Formation are: (1) Cicatricosisporites australiensis (Late Tithonian–Berriasian), (2) Foraminisporis wonthaggiensis (Valanginian–Hauterivian), (3) Foraminisporis asymmetricus (Barremian–Early Aptian). These have been recognized in other Mesozoic basins on the Indian Peninsula, enabling more precise dating of assemblages that have previously been referred to merely as Microcachryidites antarcticus or Neocomian–Aptian assemblages.

Late Jurassic (Tithonian) radiolarians from a clastic unit of the Khabarovsk complex (Russian Far East): Significance for subduction accretion timing and terrane correlation

A well‐preserved radiolarian fauna from a clastic unit of the Khabarovsk accretionary complex (southern part of the Badzhal accretionary wedge terrane in the Russian Far East) is assigned to the basal part of the Pseudodictyomitra carpatica zone. The age of the fauna is most likely late Tithonian. This is the first reliable dating of the clastic unit and makes it possible to constrain the timing of subduction accretion in the Badzhal terrane. The Khabarovsk complex is correlated chronologically with the Bikin and Samarka terranes (Russian Far East), Mino, Southern Chichibu and North Kitakami terranes (Japan), and Nadanhada terrane (northeast China).

Palaeobiogeography of Tethyan ammonites during the Tithonian (latest Jurassic)

This study deals with the palaeobiogeographic distribution of Tethyan ammonites in the Tithonian. In particular, the relationships between ammonites of the Mediterranean Tethys, East Africa, Caribbean and Southeast Pacific areas are discussed. The study of palaeobiogeographical raw data allows one to recognize palaeobiogeographic patterns and delimit provinces and to infer palaeobiogeographical processes and, in some cases, palaeogeographical (geological) processes. Biological and physical factors affecting the palaeobiogeographic distribution of the ammonites are reviewed prior to a discussion of the distributional patterns. The analysis is constrained by different factors such as taxonomy, sample size, accuracy of the biostratigraphic information, etc. The highly problematic taxonomy of the family Ataxioceratidae hampers the use of quantitative analyses, only allowing `phenetic' definitions of provinces. Some of the Tethyan palaeobiogeographic provinces already known in the literature are dealt with further. In particular the subdivision into Mediterranean and Sub-Mediterranean provinces (or sub-provinces), that is quite clear at the scale of the entire Jurassic period, is rejected in the Tithonian though a phase of faunal separation is recorded during the transition between the early and late Tithonian. The ammonite assemblages in the shelves were less diverse and different from those of the distal, pelagic areas. Dispersal is recognized as an important process in ammonite palaeobiogeography although objective location of centres of origin is impossible. Vicariant phenomena certainly occurred but in marine environments barriers that separate areas of distribution instead of portions of space cannot be delimited objectively. The `barrier' is certainly represented by the different palaeoenvironmental contexts (shelf or pelagic habitats). The palaeobiogeographic distributions observed were produced by a complex of concurrent biogeographic processes.

A probable theropod bone from the latest Jurassic of New Zealand

A small bone found in the Huriwai Measures (Late Tithonian) south of the Waikato River, North Island, represents the first terrestrial tetrapod bone from the Jurassic of New Zealand. The bone, a phalanx, is hollow and is probably from a small theropod. Phalanges are not all uniform in form, and this one has a characteristic distal expansion that should permit identification should more complete specimens be found. Plant fossils from the Huriwai Measures suggest a forested environment. The specimen indicates that dinosaurs probably continuously inhabited what is now New Zealand at least from the Late Jurassic to the end of the Cretaceous.

JURASSIC PALAEOGEOGRAPHY OF THE TRANSDANUBIAN CENTRAL RANGE (HUNGARY)

The Transdanubian Central Range (TCR) is a flattened range of hills in northern Transdanubia (Hungary), formed mainly by Mesozoic carbonate rocks showing strong facies similarities with the Southern Alps and the Austroalpine domain. The Jurassic system is divided into several formations of predominantly pelagic limestones. Ammonoids are frequent and were collected bed-by-bed in numerous sections, providing an excellent biostratigraphic resolution. The thickness of the Jurassic system is usually small but changes along the strike of the TCR. It reaches a maximum thickness of 500 m in the western part; is very variable (10-400 m) in the central segment (Bakony Mts.) and rather low (less than 100 m) in the east (Gerecse). In the Bakony segment, the thickness variation reflects the strongly dissected topography of the Jurassic sea-floor. Synsedimentary tectonics is dominated by normal faults; tilted blocks and listric faults may be inferred only in the east. Five main steps were identified in the palaeogeographic evolution: 1) Late Hettangian: carbonate oolitic shoals prevail, except for a few sites where non-deposition or neritic sediments occur. 2) Sinemurian and Pliensbachian: tectonic disintegration resulted in an intricate pattern of submarine horsts and intervening basins, with condensed sedimentation or non-deposition on the horsts and thicker, continuous sedimentary sequences in the basins. The submarine topographic highs are surrounded by aprons of redeposited material (scarp breccias, brachiopod coquinas, crinoidal calcarenites, spiculitic cherty limestones), while pure or argillaceous limestones (Rosso Ammonitico) prevail in the distal areas. 3) Early Toarcian: the Tethys-wide anoxic event is superimposed on the previous submarine bottom topography; the resulting black shales and sedimentary Mn-ores are concentrated on the western sides of some horsts. 4) Dogger to Early Malm: radiolarites with heterochronous lower and upper boundaries (Aalenian to Kimmeridgian) prevail, except for the top of some submarine topographic highs. The absence of uppermost Bathonian to Lower Oxfordian carbonates suggests that the whole TCR sunk below the CCD in those times. 5) Latest Jurassic: the uniform deposition of Rosso Ammonitico and Biancone in the Late Kimmeridgian and Tithonian is interrupted only in the Early Tithonian by local intercalations of scarp breccias and coarse biodetrital limestones. This is interpreted as the last manifestation of synsedimentary tectonic movements along the faults bordering the submarine horsts. Based on palaeogeographic similarities and analogies in Jurassic times, the TCR is visualized as the northern foreground of the Trento platform/plateau (lying north of the later Insubric lineament), where the block-tectonic disintegration and differential subsidence started earlier and resulted in a bottom morphology more dissected than in the South Alpine part of this west Tethyan passive margin.

Geochemical Study of Upper Jurassic (Volgian) Black Shales from the Russian Platform

A geochemical study of Upper Jurassic black shales from the Russian Platform is presented. Samples were collected from Gorodische section, which is the type-section of the Russian 'Volgian' stage, located near Ulyanovsk along the Volga river. This section displays a 6 m thick series of black shales of Middle Volgian age (= Late Tithonian) which is a lateral equivalent of the so-called Bazhenova Formation, the main source rock of the West Siberian giant oil fields. Firstly, a bulk study by Rock-Eval pyrolysis of these black shales was performed, indicating TOC values ranging from 1 to 45% and HI between 25 and 700 mg HC/g TOC (Fig. 1) with slightly higher TOC and HI values in the higher part of the series. Such a

Le Crétacé inférieur dans le Massif de lʼOuarsenis et les Monts de Tiaret (Algérie du Nord)

The Lower Cretaceous sediments in the Monts de Tiaret (Oranian High Plains) (Tlemcenian Palaeogeographic Domain) and the Western Ouarsenis (Tellian Palaeogeographic Domain) are subdivided in lithostratigraphic units which differ for the Tlemcenian and the Tellian Domains. In the first one, a specific feature is the development of shalow, and in the second – of deep water sediments. The following formal lithostratigraphic units are distinguished in the Tlemcenian Domain: (1) Remaïlia Carbonate Formation – limestones, marls and dolomites (Berriasian – Early Hauterivian (p.p.); (2) Berthelot Sandstone Formation (Early Hauterivien (p.p.) – Aptian); (3) Djebel Tenfeld Carbonate Formation – alternation of marls and limestones, rich in shallow water molluscs. Within the Tellian Atlas (Tell ian Domain) are distinguished: (l) Oued Fodda Carbonate Formation (Late Tithonian – Early Aptian); (2) El Melaab Turbiditic Formation (new unit of Aptian (p.p.) – Early Albian age) subdivided in 2 new Members: (a) Oued Sidi Mohamed Member (Aptian) – marls with turbiditic sandstones – distal flysch; (b) Oued Mezdar Member (Early Albian) – sandstones with intercalations of marls – proximal flysch; (3) Rhedadoua Marls Formation (Middle – Late (p.p.) Albian; (4) Hassi ben Ziane Carbonate Formation – marls and limestones (Late Albian (p.p.) – Early Cenomanian). In the Chouala region crop out the allochtonous sediments of the Sidi Seba Achir Limestones-Marls Formation (new unit of Berriasian-Middle Aptian Age) subdivided in 3 new members: (a) Oued el Ouakal Member – alternation of marls and limestones (Berriasian – Valanginian); (b) Oued Malah Member - marls (Hauterivian); (c) Sidi Ounes Member – marls and limestones (Barremian – Middle Aptian). The region of the High Plains (Monts de Tiaret) was uplifted at the end of the Jurassic, and the Berriasian sea transgressed over it. The subsidence of the Tellian Domain continued since the Late Jurassic and became an area of turbiditic sedimentation during the Aptian-Early Albian. The sedimentation in the Tlemcenian and Tellian Domains continued without interruption into the Cenomanian.

Jurassic-Cretaceous boundary:Portland-Purbeck magnetostratigraphy and possible correlation to the Tethyan faunal realm

A composite magnetic polarity pattern of the Portland and Purbeck Beds (Portlandian to Berriasian age) is constructed from nine sections in the Dorset and Wiltshire regions of southern England. This pattern is tentatively correlated to the Tithonian-Berriasian magnetic polarity time scale of the Tethyan faunal realm. The shallow-marine Portland Beds began deposition during polarity chron M21r (mid-Tithonian), contain a transgressive hiatus encompassing chron M20r, and were terminated by emergence during chron M19r (Late Tithonian), corresponding to the base of the Durangites ammonite Zone in the Tethyan realm. The terrestrial to marginal-marine Purbeck Beds encompass polarity chrons M19r through M14r, implying deposition from latest Tithonian (Late Portlandian) to the beginning of the Valanginian stage. The Cinder Bed transgression of the middle Purbeck Beds occurred at the beginning of chron M17n, corresponding to the Berriasella privasensis ammonite Subzone in the Tethyan realm. The mean paleomagnetic pole of the Purbeck Beds is at 71.2°N, 207.8°E (dp/dm=3.6°/5.1°), implying a paleolatitude of 34°N.

El tránsito Jurásico-Cretácico en la Cordillera Ibérica: relación tectónica-sedimentación y evolución paleogeográfica

Stratigraphycal and sedimentologycal analysis carried out in the so-called Tithonian-Eerriasian Sequence in the Iberian Cliain (northeast Spain), resulted in further information about the origin and evolution of the accommodation in the basin at this time span. The lower boundary of 4w sequence has been related to the uplift of the western marginal arcas (i.e., Meseta Massif), which also involved an important coastal sift basinwards. During Middle and Late Tithonian a low angle and homogeneous carbonate ramp developed in the central areas of the Chain. During Early and Middle Berriasian the ramp evolved into a mixed ramp, showing clastie units in southwestern areas of Ihe basin which grade to the East into carbonate facies. This increase of the ciastic input along with the coastal sift basinwards at 4w Jurassic-Cretaceous boundary are evidences for the tectonie uplift of the marginal arcas of the basin at this time span. The generation of some subsident sedimentary furrows developed in the central part of the basin at tlie onset of the Berriasian, are the result of an increase of the tectonic extensional deformation at this time span. Tcctonics extension from the Kimmeridgian and from the Tithonian onwards also involved the genesis of the Maestrat (to the East) and Cameros (to the Northwest) basinso- respectively. To this tectonic effect, may be superimposed a long term eustatic fali, as proposed by Haq et al. (1987). However, none of the intermediate third order cycles proposed in the Exxon curve at this time span were evidenced in the Iberian basin.

Transgressive–regressive (T–R) sequence analysis of the Jurassic succession of the Sverdrup Basin, Canadian Arctic Archipelago

Transgressive–regressive (T–R) sequence analysis has been applied to the Jurassic succession of the Sverdrup Basin with sequence boundaries drawn at subaerial unconformities or the correlative transgressive surfaces. A hierarchal system of sequence order that reflects the different nature of the boundaries has been formulated on the basis of boundary characteristics. Second- through fifth-order sequences have been recognized in the Jurassic succession, which itself is part of a first-order sequence of mid-Permian – Early Cretaceous age.The Jurassic strata occur within four second-order sequences. The boundaries of these sequences are characterized by widespread subaerial unconformities across which major changes in depositional and subsidence regimes occur. These boundaries are earliest Rhaetian, earliest Pliensbachian, earliest Bajocian, earliest Oxfordian, and Hauterivian in age.Each second-order sequence is divisible into a number of third-order sequences bounded mainly by basin-wide transgressive surfaces with subaerial unconformities present on the basin margins. The ages of the 10 Jurassic third-order sequences are Rhaetian – Hettangian, Sinemurian, Pliensbachian – Toarcian, late Toarcian – Aalenian, Bajocian, Bathonian, Callovian, Oxfordian – early Kimmeridgian, late Kimmeridgian – early Tithonian, and late Tithonian. The third-order sequences commonly contain three to six fourth-order sequences. These sequences are bound entirely by transgressive surfaces that can be correlated only over a portion of the basin.A good correlation between the second- and third-order transgressive events of the Sverdrup Basin and proposed global events is observed. This worldwide occurrence suggests that the events in part reflect eustatic sea-level changes. The characteristics of the second- and third-order boundaries also indicate that each had a tectonic influence that resulted in a rapid relative sea-level fall (uplift) followed by a rapid rise (subsidence). Given the apparent combination of tectonic and eustatic influence on the generation of the second- and third-order sequence boundaries, they are interpreted to reflect significant plate-tectonic reorganizations that affected the intraplate stress regimes of the oceanic (eustatic) and continental (tectonic) portions of each lithospheric plate.

Late Jurassic Paleoclimate Simulation: Paleoecological Implications for Ammonoid Provinciality

During the Kimmeridgian and Tithonian stages (154.7-145.6 Ma) of the Late Jurassic, the Late Permian-early Mesozoic megacontinent Pangea was progressiuely fragmented by two rift systems that propagated westward out of the Tethys Sea and a third more persistent rift system that connected the Boreal and Tethys seas. By the late Tithonian, these major rift systems produced interconnected oceanic seaways that divided Pangea into four continental segments: North America, Eur-Asia, and northern and southern Gondwana

THE JURASSIC HUASTECA SERIES IN THE SUBSURFACE OF POZA RICA, EASTERN MEXICO

The Author has studied 120 cores containing ammonites and lamellibranchs of Middle and Late Jurassic ages selected from the 230 wells drilled in the Poze Rica district, eastern Mexico. The wells are spread over an area of 8,000 sq. km.The Huasteca Series is a marine sedimentary sequence that ranges in age from Bathonian to late Tithonian, and is about 1,000‐m thick. This unit is subdivided into ammonite zones and substages which have previously been established by the Author. These zones are: Wagnericeras, Kepplerites, Reineckeia, Discosphinctes, Ataxioceras, Idoceras, Virgatosphinctes, Mazapilites, Suarites, and Parodontoceras‐Salinites.The restricted vertical distribution of these fossils and the general availability of gamma‐ray logs from the wells has made it possible for the first time to delimit the lateral facies changes that took place, especially in the late Bathonian—middle Callovian (calcarenite‐shale‐silstone) and in the early Tithonian (calcarenite‐argillaceous limestone). Structural and isopach maps for each interval show the presence in the northern half of the study area of the NW‐SE striking La Mesa syncline, and, in the southern half of the area, the east‐dipping Sultepec homocline.The transgressive phase of Huasteca Series sedimentation began during Bathonian time in the NW part of this region. Evaporites and calcarenites were deposited above rocks of continental origin. This transgression advanced progressively during Callovian to Kimmeridgian time towards the central and eastern parts of the area, where the initial marine deposits overlie igneous, metamorphic, and continental sedimentary rocks. The last phase of this transgression took place during early Tithonian time in the SE part of the Poza Rica district. It is represented here by the San Andrés was deposited on the same types of rocks—igneous, metamorphic, and continental‐sedimentary. Remnants of this late transgressive phase, characterized by calcarenites and deposited on continental sediments, are preserved in very limited areas NE of the Poza Rica district.Beginning in Kimmeridgian time, two well‐defined depocentres developed. The Huizotate Basin, with argillaceous limestones and shales of the Tamán Formation, formed in the central part of the district, while the Papantla Platform with calcarenite units of the San Andrés Member (Tamán Formation) formed around the northern, eastern, and SE margins. These depocentres are named here for the first timeAn important result of this study is that it explains the presence in structural traps of hydrocarbons of Middle and Late Jurassic ages

Middle to Late Jurassic radiolarians from Sicily (Italy)

Middle and Upper Jurassic radiolarian faunas from two sections of Sicily are compared with the previously proposed zonations. The ages of the faunas are estimated by correlation with these zonations and by concurrent range zone. The faunas could be assigned to the Bathonian or earlier late Tithonian or early Berriasian. Two new spumellarian species ( Bernoullius furcospinus and Bernoullius rectispinus) from Middle Jurassic are described.

Sedimentary aspects of the Eo-Alpine cycle on the northeast edge of the Arabian Platform (Oman Mountains)

Abstract The northeast edge of the Arabian Platform in the Oman Mountains is represented by the autochthonous unit that crops out in the two windows of Jabal Akhdar and Saih Hatat, beneath and in front of the Hawasina and Samail nappes. The Eo-Alpine orogenic cycle began in the Late Permian with extension on the margin of Gondwana and ended in the Campanian with the formation of a subduction-obduction-type mountain range, the Oman Mountains of the Late Cretaceous. During this cycle, long periods of stable shelf sedimentation were interrupted by tensional tectonic episodes, often accompanied by volcanism and subsidence of the platform, passing into the bathyal domain. Deposition during the Permian to Campanian occurred during five main sedimentary cycles. In the Late Permian (Murghabian), a widespread marine transgression covered the edge of Gondwana in a tensional setting. The ‘Fusulinid Sea’ transgression was followed by the deposition, lasting until the Triassic, of a thick regressive sequence, the Akhdar Group, which was terminated by emergence and weathering in a continental environment. The next sedimentary cycle, represented by the Sahtan Group, began in the Pliensbachian, when the Oman Mountains area formed an inner carbonate shelf, and ended in the early Tithonian. The entire margin of the platform was profoundly affected, in the late Tithonian, by extension, listric faulting and foundering into the bathyal domain, with deposition of the Kahmah Group (Maiolica-type deposits: calpionellid-bearing micrite), and rapid retreat of the continental slope by about 250 km. Renewed carbonate shelf deposition then prograded SSW-NNE across the foundered part, though this was still incomplete when the latest Aptian-Albian transgression took place. At the Cenomanian-Turonian boundary, the shelf underwent profound reorganization with the development of the Muti (intrashelf) Basin, in which the Aruma Group was deposited, and the Masqat-Musandam High which provided the detritus filling the Muti Basin on the continentward side and the Hawasina Basin on the oceanic side. Fragments from the advancing nappe were redeposited in the Muti Basin only from the Campanian on, and it was only during this period that a flysch trough became superimposed on part of the Muti Basin. The closure of the Muti Basin was affected with the emplacement of the nappes on the platform and the subsequent deposition of cover formations over both nappes and the autochthon from the late Maastrichtian onward.

Tethyan carbonate carbon isotope stratigraphy across the Jurassic‐Cretaceous boundary: An indicator of decelerated global carbon cycling?

The carbon isotope record in four pelagic carbonate sections from the Southern Alps (northern Italy) across the Jurassic‐Cretaceous boundary has been correlated to biostratigraphy and magnetostratigraphy. The carbon isotope curve from bulk carbonates shows a decrease from Kimmeridgian to Early Tithonian (CM24–CM22) values of δ13C=+2.07 (± 0.14)‰ to Late Tithonian and Berriasian (CM18–CM14) values of δ13C=+1.26 (± 0.16)‰. The change in the carbon isotope record coincides with changes in Tethyan calcite and silica accumulation rates, with a drop in the calcite compensation depth in the Atlantic and Tethys oceans and with changes in organic carbon burial along the Eurasian margin of the Tethys. Reduced surface water productivity due to diminished transfer rates of biolimiting elements into the Atlantic and Tethys oceans can explain these observations. The decreased transfer rates of elements such as silica or phosphorus from continents into the oceans resulted from drier climatic conditions and decreased water runoff on continents bordering the Tethys and Atlantic oceans. The proposed changes in Tithonian ‐ Berriasian ocean chemistry and paleoclimate suggest that variations in the global carbon cycle were coupled with changes in the global hydrological cycle and in associated material cycles.