Unitary Association Method Research Articles

Global correlation of the Guadalupian–Lopingian transition and associated events using a quantitative conodont-based biostratigraphic scheme

The Guadalupian–Lopingian boundary (GLB) interval contains global-scale changes in biota and environment. The establishment of a uniform time scale and a robust system of global correlation are critical in order to unravel the tempo of these events. Conodonts are key biostratigraphic tools; however, major discrepancies exist in conodont taxonomy and correlation in this interval. In this paper, we compile conodont data from 17 well-studied sections in South China, Japan, Oman and North America, comprising 206 occurrences and 100 species, based on previous publications and our own revisions, to test the reproducibility and correlation value of formerly established interval zones. The Unitary Association method (UAM), a quantitative stratigraphic method for the construction of biozones, is applied to construct a robust conodont biozonation for the GLB. Eleven unitary associations (UAs) and eight unitary association zones (UAZs) are recognized to establish biozones and the GLB was constrained within the UAZ5. According to the reproducibility of these UAZs, the correlation of the Lopingian is generally better than the Guadalupian. Apparent contradictions revealed by the UAZs suggest that biostratigraphic and/or taxonomic issues are present within the Clarkina liangshanensis, C. leveni, C. transcaucasica interval zones. The interval between UAZ4 and UAZ5 records the conodont turnover event from Jinogondolella to Clarkina in the paleoequatorial region. Our results suggest that the UAZs are more reliable for correlation. By contrast, some taxonomic and phylogenetic issues are present in the interval zones based on the conodont succession around the GLB. Although at a coarser stratigraphic resolution, removing all the contradictions enables UAZs to better correlate global sections compared with interval zones. The newly established UAZs indicate that the previously reported isotope excursions around the GLB in different regions may be temporally inconsistent.

A Unitary Association-based conodont biozonation of the Smithian–Spathian boundary (Early Triassic) and associated biotic crisis from South China

The Smithian–Spathian boundary (SSB) crisis played a prominent role in resetting the evolution and diversity of the nekton (ammonoids and conodonts) during the Early Triassic recovery. The late Smithian nektonic crisis culminated at the SSB, ca. 2.7 Myr after the Permian–Triassic boundary mass extinction. An accurate and high-resolution biochronological frame is needed for establishing patterns of extinction and re-diversification of this crisis. Here, we propose a new biochronological frame for conodonts that is based on the Unitary Associations Method (UAM). In this new time frame, the SSB can thus be placed between the climax of the extinction and the onset of the re-diversification. Based on the study of new and rich conodont collections obtained from five sections (of which four are newly described here) in the Nanpanjiang Basin, South China, we have performed a thorough taxonomical revision and described one new genus and 21 new species. Additionally, we have critically reassessed the published conodont data from 16 other sections from South China, and we have used this new, standardized dataset to construct the most accurate, highly resolved, and laterally reproducible biozonation of the Smithian to early Spathian interval for South China. The resulting 11 Unitary Association Zones (UAZ) are intercalibrated with lithological and chemostratigraphical (δ13Ccarb) markers, as well as with ammonoid zones, thus providing a firm basis for an evolutionary meaningful and laterally consistent definition of the SSB. Our UAZ8, which is characterized by the occurrence of Icriospathodus ex gr. crassatus, Triassospathodus symmetricus and Novispathodus brevissimus, is marked by a new evolutionary radiation of both conodonts and ammonoids and is within a positive peak in the carbon isotope record. Consequently, we propose to place the SSB within the separation interval intercalated between UAZ7 and UAZ8 thus leaving some flexibility for future refinement and updating.

Unitary Associations of the Aptian-Albian calcareous nannofossils of the Essaouira-Agadir Basin (NW Africa)

Although the Essaouira-Agadir Basin (EAB) in Morocco is one of the most complete successions of the Lower Cretaceous in Northern Africa, recent investigations have indicated major basinal-scale hiatuses, which may hinder interregional correlation. To test the quality of the existing stratigraphic scheme and provide a robust biozonation, nannofossil occurrence data from four sections were processed using the Unitary Association (UA) method. Based on critical evaluation of the singletons, which are all of a very important stratigraphic value, they were included in the analyses. The UA range chart of the studied time interval indicates six distinct segments, which are all comparable to the Standard Tethys Zones. The Aptian/Albian contact is also well defined. The results demonstrated that empirical index nannofossil zones have different quality depending mainly on their vulnerability to dissolution. In addition, some secondary marker species (i.e., their appearance/disappearance is located within a specific nannofossil zone), which exclusively occur in only one UA, can substitute the zonal index species. Although marker nannofossil species are different from section to section due to poor preservation, the UA method still provides a robust stratigraphic scheme at considerable resolution. The Aptian/Albian boundary was marked by a dramatic increase in the extinction rates and decrease in the species richness, whereas the Early Albian interval was characterized by relatively low diversity and high turnover rates.

Impact of the late Cenomanian sea-level rise on the south Tethyan coastal ecosystem in the Middle East (Jordan, Egypt, and Tunisia): A quantitative eco-biostratigraphy approach

Sea-level rise can cause changes in coastal ecosystems. To understand the link between sea-level rise and the coastal ecosystems during the late Cenomanian of the southern Tethys, five exposed sections from three Middle East countries were quantitatively analyzed. The Unitary Association (UA) method allowed a two-fold increase in the resolution of zones compared to the Oppel method. Five UAs were obtained from analyses of both ammonite and benthic fauna. However, they were grouped into 3 UA Zones (UAZ) to enable basin-wide correlation. These zones were linked to one and half 3rd-order depositional cycles. During the Neolobites vibrayeanus/ Calycoceras guerangeri ammonite zone (95.5–94.4 Ma), high-energy shallow subtidal environments were formed by the transgression that followed the global sequence boundary ‘KCe 4’. They were dominated by stationary epifauna and suspension-feeders (mainly oyster bivalves). During highstand, a restricted lagoonal environment prevailed, where oyster bivalves, which have well-known adaptive strategies, were still dominant. No ammonites were recorded in this zone. Upward, the fauna has underwent a major shift, which documents the beginning of a new depositional sequence above a regional sequence boundary ‘KCe 5’ with a gradual increase of hemipelagic organic-rich sediments and planktic/nektic fauna in addition to infaunal deposit-feeders and mobile benthos, which have lived in a deeper subtidal environment (Vascoceras cauvini/Pseudospidoceras pseudonodosides ammonite zone; 94.4–93.8 Ma). This dramatic change in the character of the macrofauna at the Cenomanian/Turonian boundary (maximum flooding of KCe 5) can be attributed to the hydrodynamic changes associated with the eustatic sea-level rise. Therefore, the sea-level-based faunal changes can be integrated in sequence stratigraphic analyses. The geographic reproducibility of the UA mirrors the delay of the transgressive onlap in proximal sections, and thus, can be used to define transgressive and maximum flooding surfaces. This eco-biostratigraphic scheme can be implemented in reliable large-scale correlations.

Biostratigraphy and provenance analysis of the Cretaceous to Palaeogene deposits in southern Tibet: Implications for the India‐Asia collision

AbstractUpper Cretaceous to Eocene marine sedimentary sequences of the Yarlung‐Tsangpo Suture Zone (YTSZ) provide critical constraints on the initial process of the India–Asia continental collision and the closure time of the Neo‐Tethyan Ocean. New sedimentological, petrographic, biochronological and detrital zircon age data of Cretaceous–Palaeogene strata from the southern margin of the YTSZ are reported in this study. Detrital zircons from the Lower Cretaceous Gyabula Formation are dominated by Archean to Cambrian U–Pb ages, indicating a likely source originating from the Indian continent. In contrast, zircon ages from the Palaeogene Jiachala Formation are predominantly younger than 200 Ma, with a major peak of ca. 76–187 Ma, which is consistent with a source from either an intra‐oceanic island arc system or the Asian continent. Sixty species of radiolarian fossils obtained from the Gyabula, Zongzhuo and Jiachala Formations provide a regional correlation with the Cretaceous Tethyan realm and Palaeogene low‐latitude biozonation schemes based on the Unitary Association method. The Palaeogene radiolarian zonation UAZ JP10 identified in the Jiachala Formation, when combined with existing absolute age models derived from the Deep Sea Drilling Project and Ocean Drilling Program, indicates an age of ca. 61.8–61.1 Ma. Integration of the biochronological and detrital zircon age data suggests that major changes in provenance occurred at the Indian continental margin, allowing an important timing constraint on the onset of collision to be placed no later than the Danian at ca, 61.8 Ma. This study highlights the significance of focusing on distinct sedimentary sequences in collisional orogens to reconstruct the timing and processes of continental collision events.

Cenomanian (early Late Cretaceous) ammonoid faunas of western Europe. Part I: Biochronology (unitary associations) and diachronism of datums

Biochronological data of Cenomanian ammonoid faunas of Western Europe are analyzed for three well-documented basins: the Vocontian Basin in southeastern France, the Mnster Basin in Germany, and the Anglo-Paris Basin. A taxonomically standardized data set is constructed for these three basins and includes more than one hundred species and is analyzed with the deterministic Unitary Association Method. Data for each basin are first processed separately, thus yielding three regional biochronological zonations. Then, the three regional sequences are processed together as a three- section data set for the construction of the inter-basin sequence. The latter comprises 24 unitary associations grouped in eight zones for the Cenomanian Stage. These results take into account species that co-occur in time and space (real coexistence), those that only co-occur in time (virtual coexistence), and those that do not co-occur in space nor in time (exclusion of chronological significance). At the paleogeographical scale of Western Europe, this new zonation is in good agreement with the widely used standard zonation, but its resolution is three times higher. This demonstrates the benefits of applying the Unitary Association Method, even to a taxonomic group which is traditionally acknowledged as one of the leading group in dating Mesozoic marine rocks. It also highlights the variable completeness and resolution of the faunal record through space and time, and reveals that a substantial number of the taxa (47%, inclusive of some indexes) have a diachronous distribution across these three Cenomanian basins. However, even with such an enhanced time resolution, no preferred orientation of the diachronous taxa emerges, suggesting that none of these basins seemed to have functioned as a paleobiogeographical source or sink. The absence of any preferred direction of the diachronism of the datums is most likely explained by two, non-mutually exclusive causes: either a random distribution of the incompleteness of the faunal record and/or a common paleobiogeographical history of the faunas in the three basins.

The Unitary Association method in biochronology and its potential stratigraphic power between benthic and planktic organisms: A case study on foraminifers from Paleocene–Eocene strata of southern Egypt

Although foraminifers have been extensively used for biochronology, no quantitative evaluation of the quality of their application is available. In this work we apply a quantitative approach – the Unitary Association (UA) method – to evaluate the relative quality of planktic and benthic foraminifers in biostratigraphy. Based on 12,321 specimens belonging to 65 planktic and 132 benthic foraminifer species in 117 samples from the Paleocene–Eocene strata of the Kharga-Baris Oases (Western Desert, Egypt), the potential stratigraphic resolution power of benthic foraminifers is quantitatively assessed and compared to planktic foraminifers. The UA method accounts for superpositional contradictions between sets of coexisting taxa and generates unitary associations, which are conceptually similar to Oppel zones. The analysis produced fifteen unitary associations for the Paleocene–Eocene benthic Foraminifera of the studied sections, instead of three classical zones; most of these unitary associations are easily identified by the restricted occurrence of a single species. Although planktic Foraminifera have a higher seriation reality leading to a more robust biozonation, benthic Foraminifera have a higher stratigraphic resolution, at least at such regional scale. Furthermore, there was a significant positive correlation between the number of unitary associations and the number of species (R=0.78 for planktic and 0.70 for benthic foraminifers; both with p<0.001). These results corroborate that quantitative techniques may lead to a higher resolution in biochronology, even when applied to poor biochronological markers. Moreover, in contrast to simple spatiotemporal analyses, the Unitary Association method can accurately assess the stratigraphic potential of a given taxonomic group.

Smithian ammonoid faunas from northeastern Nevada: implications for Early Triassic biostratigraphy and correlation within the western USA basin

Intensive sampling of the lower portion of the Thaynes Group within the Palomino Ridge area (northeastern Nevada) yielded abundant and well-preserved Smithian (Early Triassic) ammonoid faunas. Ammonoid taxonomy and a detailed biostratigraphy for this locality are reported herein. One new genus (Palominoceras) and one new species (?Pseudosageceras bullatum) are described. Additionally, based on new data from Palomino Ridge and previous data from neighboring localities in Utah, we porvide here the first quantitative Smithian ammonoid biochronological scheme for the western US basin. This new zonation is based on the Unitary Associations (UA) method. The biochronical sequence comprises five unitary association zones that can be correlated with other localities from the Northern Indian Margin (Salt Range, Pakistan, Spiti, northern India and Tulong, South Tibet). Three unitary association zone (UAZ1, UAZ2 and UAZ3) are defined for the early Smithian, one (UAZ4) spans the entire middle Smithian and one (UAZ5) signifies the first part of the late Smithian. Finally, a hypothetical UAZ6 would represent the second part of the late Smithian.

Reply to the Comment on “Quantitative biochronology of the Permian–Triassic boundary in South China based on conodont unitary associations”

1. Introduction In their Comment, Jiang et al. (2016) claim that the discordance between our zonation (Brosse et al., 2016) and the interval zones does not rest on the use of the Unitary Association method (Guex, 1991 and Guex et al., 2015) per se but on our “failure to use the most recent published conodont ranges from some key Chinese sections”. They add that our analysis is based on “unreliable taxonomic data sets with unjustified taxonomic re-assessments”, and hence, that we did not demonstrate that the Unitary Association method performs better than traditional interval zones. Additionally, the Comment by Jiang et al. (2016) contains misunderstandings pertaining to the method used in our study (Brosse et al., 2016). Our goal was to apply the Unitary Association Method on a dataset of conodont distributions from South China around the Permian–Triassic boundary (PTB) in order to reassess the quality of the corresponding data and to provide a discrete and robust alternative zonation to the continuous, First-Occurrence-based interval zones. Such interval zones are routinely utilized in Permian and Triassic conodont biostratigraphy, regardless of their abundant internal contradictions. Three categories of points of contention can be extracted from the Comment of Jiang et al. (2016): method, selection of data and taxonomy, and illustrations. Each of these is addressed separately below. 2. Method Fig. 1 complies with the recommendation of Jiang et al. (2016) and takes into account all the recent literature, summarizing the most recent published conodont ranges from the relevant sections. The reader will immediately observe that the sequences of First Occurrences (FOs) used in the most recently published interval zones occupy contradictory positions between the different sections. This is precisely the main criticism expressed in our work. This problem cannot be solved by simply standardizing the taxonomy of the considered taxa. Many contradictions do persist after taxonomic homogenization. As conceded by Jiang et al. (2016), FOs are prone to diachronism. But contrary to what Jiang et al. (2016) suggest, sampling effort is not the only nor the main reason for such diachronism and PTB sections from South China are no exceptions in this respect. Fig. 9 of Brosse et al. (2016) demonstrates the contrary. Ironically enough, Jiang et al. (2016) acknowledge that Last Occurrences (LOs) can be diachronous because of local, ecological differences, but they exclude that FOs can be affected. In reality, these authors unduly equate every local FO with an alleged instantaneous spreading of a species across all sections. Incidentally, such an unwarranted assumption also deliberately ignores that speciation is an intrinsically space-restricted evolutionary process.

High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: The Dienerian faunas of the Northern Indian Margin

A new high resolution biozonation based on the Unitary Association (UA) method is constructed for the Dienerian ammonoid succession of the Northern Indian Margin. It includes 12 UA-zones and leads to the subdivision of the Dienerian into three parts (early, middle and late). The corresponding diversity analyses, coupled with results previously obtained for the early Smithian ammonoids of the same regions, highlight the four following phases: (1) a first modest peak of diversity in the early Dienerian; (2) a very low diversity persisting throughout the middle Dienerian; (3) a slow increase of diversity during the late Dienerian, and (4) a marked diversification in the early Smithian. Turnover rates are very high during this entire time interval, and the boundaries between early–middle and middle–late Dienerian are emphasised by complete renewals of the ammonoid faunas. The low diversity values in the middle and early late Dienerian are concomitant with an anoxic event on outer continental shelves and coincide with warmer temperatures than those of the early Dienerian and early Smithian. This diversity pattern stands in strong contrast with the credo of a protracted or stepwise recovery following the end-Permian mass extinction. Together with the end-Smithian extinction, the middle and early late Dienerian diversity crises were likely both radical setbacks in the recovery of Early Triassic ammonoids. However, these two diversity crises do not necessarily imply identical environmental triggers that ultimately led to anoxic bottom waters on outer continental platforms in both cases.

Guadalupian (Permian) brachiopods from the Ruteh Limestone, North Iran

ABSTRACTThirty-three brachiopod species from the Guadalupian Ruteh Limestone of North Iran are here systematically described and illustrated. Brachiopods have been collected bed-by-bed along five stratigraphic sections and in one fossiliferous locality in the region between Dorud and Shirinibad in the Alborz Mountains. Four new species and one new genus are erected in the present paper: Haydenella eminens n. sp. Perigeyerella rutehiana n. sp., Martinia bassa n. sp. and Bisolcatelasma iraniana n. gen. n. sp.Quantitative biostratigraphic analysis of the brachiopod data based on the Unitary Association method (Guex, 1991) has lead to the construction of a local sequence of three discrete biozones: the Squamularia sp. B-M. bassa Biozone at the base of the formation, the H. kiangsiensis-N. (N.) asseretoi Biozone in its middle part and the R. exile-R. gemmellaroi Biozone at its top. The latter however has been recognized only in the Shirinabad section.As already envisaged for the Carboniferous and Lower Permian brachiopod faunas from North Iran, the Guadalupian fauna is comprised mostly of cosmopolitan taxa, confirming the role of the Iranian microplate as a staging-post for most of the late Palaeozoic. When compared to the younger Lopingian faunas collected in the same regions of North Iran, the Ruteh brachiopods appear significantly different, indicating a marked biotic change in the brachiopod communities across the end-Guadalupian biotic crisis.

Some recent ‘refinements’ of the Unitary Association Method: a short discussion

In a recent Lethaia paper,Monnet et al. (2011) elaborated an excel-lentanalysis ofthe Devonianammonoid biochronology fromMor-occo. In their paper, they proposed a series of refinementsintended to ameliorate the performances of the Unitary Associa-tion Method (UAM) and of the UAgraph program. Their mainproposals and criticisms are welcome, but need to be evaluated.UAM is a graph theoretical model designed for the constructionof concurrent range zones using a fully deterministic approach.The basic idea is to construct a discrete sequence of coexistenceintervals of species. Each interval, corresponding to one UA, is ofminimal duration while consisting of a maximal set of intersectingranges. Each UA is characterized by a set of species allowing itsidentification in the stratigraphical sections. The chronological sig-nificance of the units generated by the UA software (UAgraph byHammer Guex Savary, http://folk.uio.no/ohammer/uagraph)depends on two important parameters: (1) Their lateral traceability(what we call ‘reproducibility’); and (2) The superpositional con-trol between two adjacent units. The major difficulties related tothe construction of such units are related to the conflicting inter-taxa relationships (=cycles in the biostratigraphical graph G*) andthe inter-maximal cliques contradictions (strongly connected com-ponents in the maximal clique graph Gk). Such contradictions aregenerally eliminated by adding virtual coexistences (=edges) in theG* graph. The goal of the method is not to reduce the number ofvirtual coexistences at all cost, but to produce a robust solutionthat reflects the quality of the data, i.e. a solution optimizing thereproducibility andinter-unitssuperpositional control. UAs shouldbe considered as intervals of uncertainty on which we have estab-lished an order relation: the UA sequences represent units whichare ordered as older, sub-contemporaneous, or younger. The orderof the event within a single particular unit is not known (details inGuex & Davaud 1984; Guex 1991; see also Mailliot et al. 2006 foran application) because the virtual coexistences between some taxarepresent intertaxa exclusions, which cannot be solved by means ofstatistical techniques; they can only be solved by the constructionof composite stratigraphicalsections, whenever possible. For exam-ple: if you tell a neutral observer that three different sectionscontain, respectively, an ammonite, trilobite and nummulite inter-calated between Precambrian and Quaternary sediments, theobserver will be unable to tell you that the true order is trilobite->ammonite-> nummulite, because there is no superpositional con-trol between the three taxa. The observer can only enumerate thenine possible sequences, which is an useless exercise. The presenceof any one of the three taxa just indicates that the sedimentis post-Precambrian and pre-Quaternary.Monnet et al. (2011) were first to suggest the use of the statisti-cal technique known as ‘bootstrapping’ to evaluate the robustnessofthe UAgraphsolutions by meansof ‘confidence intervals’.‘Boot-strapping’ is a well-known technique of re-sampling using itera-tions resulting from the application of a Monte-Carlo method.Monnet et al. propose to use that technique, but they do not sayhow the re-sampling should be done: for instance, should onebootstrap the occurrencesof the taxa,the samples andthe sections?The identity and ordering of the UAs will of course partially breakdown in the bootstrap replicates – how should the ‘confidenceintervals’then be reported? Inourview, the use of such a techniquewould add nothing to current results of the UAs: the robustness ofthe solutions, as mentioned before, depends strictly on the repro-ducibility and inter-units superpositional control. They are theonly criteria allowing a serious evaluation of the internal coherenceof the UAresults.Concerning the strongly connected components of the Gkgraph, Monnet et al. (p. 15) write : ‘UA-graph currently solvesthese contradictions by using the ‘weakest link’ rule (i.e. the cliquesuperposition supported by the fewest inter-taxon relationships isdestroyed; see Guex 1991, p. 82). Given the uncertainties related tothis type of resolution, the unique result produced by the UAM islikely to be partly wrong. Figure 9 reports an imaginary example(Fig. 9A) containing cycles between its maximal cliques, where theautomatic resolution by the software UA-graph yields a result(Fig. 9B), which is clearly not the most parsimonious comparedwith what can be found empirically (Fig. 9C). This example clearlyillustrates and demonstrates that the ‘weakest link’ rule is not ade-quate in such cases.’ Figure 9A of Monnet et al. (2011) is redrawn

Quantitative biochronology of Devonian ammonoids from Morocco and proposals for a refined unitary association method

Monnet, C., Klug, C., Goudemand, N., De Baets, K. & Bucher, H. 2011: Quantitative biochronology of Devonian ammonoids from Morocco and proposals for a refined unitary association method. Lethaia, Vol. 44, pp. 469–489. Based on a rich dataset, the biostratigraphy of the late Emsian and the Eifelian (Early–Middle Devonian) ammonoids from the Moroccan Tafilalt is re-evaluated. We processed this dataset (comprising 53 species from 15 sections) with the unitary association method (UAM), by means of the UA-graph freeware. This led to the construction of a sequence of 17 UAs (maximal sets of actually or virtually coexisting taxa), which are grouped into 10 laterally reproducible association zones. This biostratigraphical subdivision of this interval is in some parts finer than the classically used empirical stratigraphical scheme and than a previous graphic correlation analysis. It enabled us to measure regional ammonoid diversity of this interval in detail. The UAM is a powerful biochronological method, which benefits from complementary tools to analyse conflicting inter-taxon stratigraphical relationships inherent to complex biostratigraphical datasets. In cases of under-constrained superpositional relationships between the taxa, the UAM can yield results, which are not parsimonious in terms of reconstructed virtual coexistences. We suggest several additions to complement the algorithmic steps of the method. The most important is the exhaustive or heuristic reconstruction of possible solutions resolving the observed biostratigraphical contradictions (conflicting inter-taxon superpositional relationships and cycles between maximal cliques) and the selection among the solutions of the most-parsimonious one(s) in terms of reconstructed virtual coexistences. Multiple equivalent results may then be processed with standard consensus techniques. Finally, the robustness of the results can be tested by bootstrapping methods to provide confidence estimates on the ranges and associations of studied taxa. □Ammonites, Anti-Atlas, biostratigraphy, correlation, zonation, diversity.

High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: The Smithian faunas of the Northern Indian Margin

Based on new collections of abundant and well preserved material from the Salt Range (Pakistan), Spiti (Northern India) and Tulong (South Tibet), several recent studies focused on the taxonomic revision and detailed biostratigraphy of Smithian ammonoids. In this work, biochronological data for these three well-documented basins are analyzed by means of the Unitary Associations method, resulting in a biochronological scheme of unprecedented high-resolution for the Smithian of the Northern Indian Margin (NIM). Data for each basin are first processed separately, thus yielding three local biochronological zonations. Then, the three sequences are processed together as a regional three-section data set for the construction of an inter-basin sequence at the NIM level. The latter zonation comprises 16 Unitary Associations grouped into 13 zones for the entire Smithian. Analysis of ammonoid diversity dynamics based on this new highly resolved time frame highlights (i) a marked diversification during the early Smithian, (ii) a severe extinction during the late Smithian, and (iii) an overall very high turnover throughout the Smithian. At a global spatial scale and stage resolution, the diversity of Smithian ammonoid genera appears surprisingly high, as highlighted by a previous study. It is shown that at a smaller geographic scale and with the most highly resolved time frame, Smithian ammonoids of the NIM reached their explosive diversity peak essentially through extremely high turnover rates rather than through a classic diversification process of high origination rates coupled with low extinction rates. Based on recently published U/Pb ages, regional apparent total rates of origination and extinction of more than 100 species per My can be inferred for the Smithian ammonoids of the NIM.

A new low-latitude late Paleocene-early Eocene radiolarian biozonation based on unitary associations: applications for accreted terranes

The late Paleocene – early Eocene sequences of DSDP Leg 10 Sites 86, 94, 95, and 96, Leg 43 Site 384 and ODP Leg 171B Hole 1051A have been re-sampled and re-examined for radiolarians. A new late Paleocene to early Eocene low-latitude radiolarian zonation suited for the correlation of accreted terranes is established by using the Unitary Association (UA) method. This method has the property of attributing equal weight to each species occurrence, which has the advantage of not being dependant on a limited set of key datums. Twenty-two UAs have been erected and correlated to the existing age models (given by nannofossils, planktonic foraminifera and radiolarians) for each site. The 22 UAs have been united into seven Unitary Associations Zones (UA Zones) (JP10- JE4) to increase lateral traceability. Herein we present the resulting composite range chart and correlation between the studied cores. The position of the UA Zones in the Paleogene timescale of Berggren et al. (1995) have been estimated using a general consensus correlation with calcareous microfossil groups and the existing radiolarian zonation. Reproducible radiolarian events identifi ed in the present work are bound to directly tied and compiled absolute ages given by Nigrini et al. (2006) and Sanfi lippo and Nigrini (1998a). The RP zones (Sanfi lippo and Nigrini 1998a) and the UA Zones are consistent. Unitary Associations permit to distinguish supplementary zonal subdivisions within RP7 and RP6. Topotypes from DSDP Leg 10 have been illustrated using mainly SEM imaging to facilitate the identifi cation of re-crystallized forms.

Ammonite-based correlations in the Cenomanian-lower Turonian of north-west Europe, central Tunisia and the Western Interior (North America)

The biochronology of Cenomanian-early Turonian ammonite faunas from three key stratotype areas (north-west Europe, central Tunisia and the Western Interior of North America) has been analysed and revised by utilizing the unitary association method. This review is prompted by the huge amount of biostratigraphic data published during recent decades and by a taxonomic homogenisation of the ammonite faunas from these key areas. The Cenomanian and lower Turonian of Tunisia comprise twenty-four Unitary Association zones and the middle Cenomanian-lower Turonian of the Western Interior Basin twenty-three such zones. The unitary association method means a two-fold increase in resolution of these ammonite zonations compared to the standard, empirical schemes. Central Tunisia and the Western Interior are correlated with north-west Europe by constructing a zonation including all taxa common to these areas. These correlations highlight the variable completeness and resolution of the faunal record through space and time, and reveal a significant number of diachronous taxa between the three areas. These correlations enable the designation of a new global marker for the middle/upper Cenomanian boundary, which is characterised by the disappearance of the genera Turrilites, Acanthoceras and Cunningtoniceras and by the appearance of Eucalycoceras, Pseudocalycoceras and Euomphaloceras. The only synchronous datum known is the last occurrence of Turrilites acutus, which may thus be used as a marker for the middle/upper Cenomanian boundary, provided that it does not turn out to be diachronous in the light of any new data.

Anisian (Middle Triassic) ammonoids from North America: quantitative biochronology and biodiversity

This study synthesizes and revises the ammonoid zonations as well as their correlationwith each other for westernNevada (USA), British Columbia (Canada), and the Sverdrup Basin (Canada) by utilizing the unitary association method. Based on a standardized taxonomy, the Anisian in the studied areas contains 13, 10, and 3 zones and a total of 174, 90, and 7 species, respectively. The zonations are correlated bymeans of a ‘common taxa zonation’, which includes all taxa common to the studied basins. This leads to new andmore precise correlations,which are at slight variancewith those of the literature.Hence, the Buddhaites hagei Zone (Canada) correlates only with the Intornites mctaggarti Subzone (Nevada) and not with the entire Acrochordiceras hyatti Zone (Nevada). The Tetsaoceras hayesi Zone (Canada) appears to correlate with the Unionvillites hadleyi Subzone (Nevada) of the hyatti Zone and not with the Nevadisculites taylori Zone. The Hollandites minor Zone (Canada) more than likely correlates with the taylori Zone (Nevada) rather than the Balatonites shoshonensis Zone as is usually acknowledged. The unitary association method enables us to quantify the diachronism of the studied taxa,which affects about 67% of the genera and 18% of the species common toNevada and British Columbia. Therefore, this diachronism is significant and its value for correlation should not be overlooked. Finally, a diversity analysis based on the revised zonations is performed. This analysis reveals that the major event occurred during the Nevada hadleyi Subzone (early Middle Anisian), which in Nevada and British Columbia, records the highest species richness of the Anisian as well as enhanced exchanges between usually latitudinally restricted faunas. This event may reflect significant changes in climate or oceanic circulation at that time.

UPPER JURASSIC RADIOLARIANS FROM INICI MOUNTAIN AREA (NORTHWESTERN SICILY, ITALY): BIOCHRONOLOGY AND CALIBRATION BY AMMONITES

This research is devoted to the biostratigraphic analysis of radiolarian assemblages of the Upper Jurassic intermediate siliceous member of the Rosso Ammonitico Formation in the Inici Mountain area (Northwestern Sicily, Italy). The aims of this paper are to give the first description of this radiolarian associations, to establish a direct biochronostratigraphy by means of radiolarians, and to calibrate radiolarian biozones by ammonite zones. During Late Jurassic time, Inici Mt. area was part of a submerged pelagic plateau characterized by deposition of Rosso Ammonitico condensed facies (Rosso Ammonitico Inferiore -RAI- and Rosso Ammonitico Superiore -RAS-) and basinal facies (Rosso Ammonitico Medio -RAM-). Four stratigraphical sections from the RAM have been studied: Fornazzo Strada, Fornazzo Cava, Castello Inici and Balada di Baida. In all sections RAM consists of siliceous nodular limestone alternating with marly limestone, and moderately preserved radiolarians. Biostratigraphic correlation has been made using the Unitary Associations (UAs) method: 11 UAs have been identified and grouped in 5 biozones (Unitary Associations Zones: UAZs) whose age is calibrated by ammonites found in the same successions and/or in the under- and overlying formations. Ammonite assemblages assign the top of RAI to mid Oxfordian and the top of RAM to upper Kimmeridgian. The ranges of Eucyrtidiellum unumaense (Yao) s.l. and Williriedellum (?) marcucciae Cortese have been extended with respect to those stated in Baumgartner et al. 1995a. Syring ocapsidae family is extraordinarily abundant and new morphogroups are presented here: Podobursa sp. A, Podobursa sp. B, Syring ocapsa sp. A, Syring ocapsa sp. B. Other new morphogroups are: Fultacapsa sphaerica (Ozvoldova) ssp. A, Loopus sp. A, transitional forms between Emiluvia orea Baumgartner and Emiluvia ultima Baumgartner & Dumitrica, transitional forms between Tetratrabs bulbosa Baumgartner and Tetratrabs zealis (Ozvoldova).

Radiolarite ages in Alpine-Mediterranean ophiolites: Constraints on the oceanic spreading and the Tethys-Atlantic connection

The history of continental breakup and oceanic spreading of the Alpine Tethys is defined by a revision of isotopic and biochronologic ages of 65 stratigraphic sections located in the Alps, Apennines, Betic Cordillera, Rif, and central Atlantic and a reinterpretation of the stratigraphic sequences of surpraophiolitic radiolarites. The biochronology of radiolarites is revised by using the deterministic approach known as the unitary association method. During the early Bajocian (unitary association zone, UAZ 3) radiolarite sedimentation began at the continental margin. Biochronologic ages determined in the lowermost radiolarites in basinal sequences of Tethyan margins are synchronous and mark a regional change in sedimentation regime in the Alpine Tethys. The onset of oceanic spreading of the Alpine Tethys is dated by isotopic methods as Bajocian, and is consistent with the timing of the structural evolution of the continental margins. The earliest fragments of Tethyan oceanic crust are characterized by the associations of ophiolites with deep-sea sediments, and coarse reworked sediments including platform and continental basement fragments. The earliest ophiolites also show geochemical affinities with synrift and transitional mid-oceanic-ridge basalts. The oldest radiolarites on oceanic crust are so far dated as Bathonian (UAZ 6) and are located in the Gets nappe (western Alps), in the Balagne nappe (Corsica), and in the central Atlantic (Deep Sea Drilling Project [DSDP] Site 534A). The oldest remnants of Alpine Tethyan crust have been identified in weakly metamorphosed cover nappes that occupy an external tectonic position in the Alpine orogenic belts, as compared to the main ophiolitic sutures. Thus, the older relics of oceanic lithosphere were the first to be accreted and transported onto the foreland during the collision. Siliceous sedimentation during the early Bajocian is correlated with westward deep-water circulation in the Alpine Tethys related to the opening of deep seaways between Laurasia and Gondwana. In the central Atlantic no radiolarites, but thin radiolarian-rich layers, were deposited during the earliest Bathonian (UAZ 6). The similarity between radiolarian faunal assemblages and ages in the Northern Alps, Gets nappe, Betic Cordillera, and Site 534 (DSDP Leg 76) suggest a Middle Jurassic connection between the Alpine Tethys and central Atlantic. Biochronologic and isotopic ages currently indicate that oceanic spreading of the Alpine Tethys began during the Bajocian and continued until the Kimmeridgian.

Taxonomy and quantitativebiochronology of Guadalupian brachiopods from the Khuff Formation, Southeastern Oman

The Guadalupian Khuff Formation of the Huqf area (Sultanate of Oman) is composed of marine marls and bioclastic limestones which yield a rich brachiopod fauna associated with conodonts, foraminifers, ostracods, bivalves, gastropods, and cephalopods. The brachiopod fauna of the Khuff Fm. includes Perigeyerella raffaellae nov. sp., Derbyia sp. cf. D. diversa Reed, 1944 , Neochonetes (Sommeriella) arabicus ( Hudson & Sudbury, 1959) , Celebetes manarollai nov. sp., Haydenella sp., Chonetellini? gen. and sp. indet., Dyschrestia rugosa nov. sp., Kozlowskia tescorum ( Hudson & Sudbury, 1959) , Calliprotonia sp., Juresania omanensis Hudson & Sudbury, 1959, Bilotina yanagidai nov. sp., Linoproductus sp. aff. L. kaseti Grant, 1976, Grandaurispina ghabaensis nov. sp., Magniplicatina sp., Cyclacantharia sp., Acritosia sp., Orthotichia sp. cf. O. bistriata Reed, 1944, Cleiothyridina sp. cf. C. seriata Grant, 1976, Pennospiriferinoidea genus and species undetermined, Dielasma sp. A, Dielasma sp. B, Dielasma sp. C, D. sp. aff. D. minor Waagen, 1882 and Hemiptychina sp. This fauna shows strong affinities with that of the Amb Fm. (Salt Range, Pakistan) and that of the Rat Buri Limenstone of southern Thailand. Analysis of the brachiopod data of the Khuff Fm by means of the Unitary Association method (Guex 1991) leads to the construction of a local biochronological sequence of eight faunal associations. Strictly based on a bed rock-controlled sampling, this result provides a firm basis and a first step for future correlations with other Guadalupian brachiopod sequences. It also suggests that species diversity and rates of faunal turnovers are only partly controlled by the vertical succession of depositional environments, which reflects an intra-Khuff asymmetric transgressive-regressive cycle. A full evaluation of the biochronologic component of the Guadalupian brachiopod faunas still requires further tests against other similarly well-documented sequences.