Uppermost Aptian Research Articles

Unravelling the origin of reworked deposits in Aptian lacustrine carbonate reservoirs of the Santos Basin, SE Brazil

The Barra Velha Formation, representing the uppermost Aptian formation of the Santos Basin, predominantly comprises dolomudstones, intraclastic grainstones, and rudstones. Additionally, spherulitic and Mg-rich claystones suggest deposition in a shallow alkaline lacustrine environment. Despite the significance of reworked deposits within the Barra Velha Formation, limited attention has been given to understanding their origin, provenance, and their link to high well productivity. This study aims to characterize the reworked carbonate facies and establish their diverse genesis using a multi-scale approach. Through the analysis of core samples retrieved from the upper 19 m of the Upper Barra Velha Formation, we identified eight sedimentary facies, including microfacies grouped into two distinct associations: back-barrier deposits and foreshore-shoreface transition deposits. Back-barrier deposits consist of shrubstones, laminated shrubby spherulitestone, laminated mudstone, massive grainstone, and massive rudstone facies, composed of in situ facies and carbonates reworked by wave and distal hyper-concentrated flow. Foreshore-shoreface transition deposits comprise laminated grainstone, pebble grainstone, and massive rudstone. The facies analyses provide insights into swash-backwash effects, hyper-concentrated flow, and high wave reworking deposits. Detailed interpretation of seismic reflectors in the Uppermost interval of Barra Velha Formation revealed two distinct geometric patterns: high-amplitude onlapping seismic reflectors toward the basement and bidirectional high-amplitude reflectors on the platform edge. These patterns primarily consist of spherulitestones, shrubstones, and grainstones-packstones BHI facies. Gravity flow deposits of a fan-delta in the Lowermost interval of the Barra Velha Formation were interpreted as rudstones-grainstones and mixed reworked carbonates/volcanic rocks BHI facies, associated with low-amplitude sheet-like shape reflectors dipping toward the slope seismic reflectors. Based on the constructed onlap curve derived from the seismic lines in the study area and the described facies associations, it is evident that the lake margins are expanding, conducive to the formation of reworked facies mainly associated with wave action.

Carbon Isotope Stratigraphy of the Uppermost Aptian–Lower Cenomanian Strata from the Lut Block, East Iran

Carbon Isotope Stratigraphy of the Uppermost Aptian–Lower Cenomanian Strata from the Lut Block, East Iran

Aptian–Albian sequence stratigraphy, biostratigraphy, chemostratigraphy, and chronostratigraphy: Sonoran shelf and Tamaulipas Basin, Mexico

The Late Jurassic extensional Bisbee Basin in northwestern Mexico and southwestern United States lay between the Pacific magmatic arc and subduction zone and the cratonic Comanche shelf. Aptian to late Albian fluvial, deltaic, and shallow marine sediments and patch reefs of the Bisbee Group filled the basin. The upper Barremian(?)–lower Aptian Cerro de Oro Formation and its equivalent Rancho La Colgada Formation are overlain by the Morita, Mural, Cintura, and La Juana formations. The paralic Morita Formation and the marine Mural Limestone grade southeast into the marine Agua Salada and Lampazos formations, which correlate with deep-water facies in the Chihuahua trough and Tamaulipas Basin. Three late Aptian to middle Albian long-term depositional cycles were approximately 2.5 myr in duration.Foraminifers, calcareous algae, bivalves, rudists, corals, dinoflagellates and scarce ammonites compose the Mural Limestone biostratigraphy. First-occurrence datums of Aptian–Albian benthic Foraminifera are integrated with planktonic Foraminifera and rudists and define biostratigraphic zones that correlate with the Comanche shelf. In the Chihuahua trough and Tamaulipas Basin planktonic Foraminifera and nannofossils identify global zones. Stage boundaries on the Sonora shelf are correlated by a comprehensive biostratigraphic database.Carbon isotope chemozones correlate with Tethyan chemostratigraphy. The lower Aptian OAE 1a and uppermost Aptian–lowest Albian OAE1b chemozone are in the Lampazos section. The negative δ13C excursions and fossil evidence correlate with global Jacob, Kilian, Paquier, and Leenhardt levels. Low-oxygen water masses flooded the shallow shelf and even affected coral-rudist buildups.

Taxonomy, phylogeny and biostratigraphy of the upper Aptian–lower Albian ammonites of the Chott area, southern Central Tunisia

Four sections were measured and studied in the uppermost Aptian and lower Albian of the Chott Basin (southern Central Tunisia), providing an abundant, bed-by-bed collected paleontological material. The ammonite succession allows precise correlations with the ammonite biozonation established in Central Tunisia.The phylogeny of knemiceratids and acanthohoplitinids of the Chott Basin is investigated and the alleged extreme variability of knemiceratids is questioned.Five new ammonite species are herein described: Knemiceras sagetae sp. nov., Knemiceras lanceolatum sp. nov., Knemiceras multicostatum sp. nov., Knemiceras tunisiense sp. nov., Parengonoceras chottensis sp. nov., highlighting the highly endemic character of the Chott Basin ammonite faunas.

New insights into the depositional environment and stratigraphic position of the Gugu Breccia (Pădurea Craiului Mountains, Romania)

The study of the carbonate clasts and matrix of a problematic sedimentary formation (the Gugu Breccia) from the Pădurea Craiului Mountains reveals new information concerning its depositional environment and stratigraphic position. The identified microfacies and micropaleontological assemblages demonstrate that all the sampled limestone clasts from the Gugu Breccia represent remnants of a fragmented Urgonian-type carbonate platform. The Barremian age of the clasts suggests that the stratigraphic position of the Gugu Breccia at its type locality could be uppermost Barremian-lowermost Aptian, a fact demonstrated also by the absence of elements from Lower Cretaceous carbonate platforms higher in the stratigraphic column (e.g., Aptian or Albian) of the Bihor Unit. The sedimentological observations together with the matrix mineralogy bring new arguments for the recognition of terrigenous input during the formation of the Gugu Breccia.

Aptian–Albian deposits of the Ait Ourir basin (High Atlas, Morocco): New additional data on their paleoenvironment, sedimentology, and palaeogeography

AbstractThis sedimentological and palaeontological analysis of the Aptian–Albian sedimentary succession of the Ait Ourir basin in the High Atlas Mountains of Marrakesh in Morocco provides new data from a previously poorly understood basin. The palaeoenvironmental evolution is deduced based on a facies analysis allowing the restoring of depositional environments and their stratigraphic architecture. Within the Aptian–Albian succession, we distinguish two sedimentary sequences separated by a major discontinuity. The first sequence is composed of calcareous and dolomitic marls with the rudistPseudotoucasia catalaunicaof the Tadhart formation (upper Aptian in age) and of strongly dolomitized limestones with corals (Eugyrasp.,Thalamocaeniopsissp., andHolocystissp.) of the Lemgo formation (uppermost Aptian in age). These two formations were formed in an internal carbonate platform (the intertidal zone to the subtidal zone). The second sequence, Albian in age, is composed of sandy limestones of the Oued Tidzi formation and is represented by sediments showing terrigenous influence, with deposits of silt, sandstone, dolomitic sandstone, and limestone.

Ostracods as proxies for marginal marine to non-marine intervals in the mid-Cretaceous carbonate platform of the Central Tunisian Atlas (North Africa): Response to major short-term sea-level falls

Two non-marine to marginal-marine intervals have been identified by ostracod assemblages in the mid-Cretaceous carbonate platform of the Central Tunisian Atlas, the deposits of which belong to the Orbata Formation. The first non-marine interval has been recorded within member Unit 2b of the Orbata Formation which yielded the first lower Aptian ostracod fauna composed of Alicenula? leguminella, Vecticypris polita, Cypridea ventriosa, Perissocytheridea altesulcata sp. nov., Harbinia? cf. sinuata, Hourcqia aff. bateke, Ovocytheridea nuda, Bythocypris? pythagorasi sp. nov., Paracypris lusitanicus and Paracypris chekhmai sp. nov. The assemblages indicate continental to marginal-coastal environment and lower Aptian emergence of the Orbata Platform, and are interpreted as response to an earliest Aptian 3rd-order (0.5–3 myr) sea-level fall event of major amplitude. A second lowermost Albian ostracod fauna, recorded within members Unit 5b, 6 of the Orbata Formation, is composed of Candonopsis carthaginensis sp. nov., Cypridea quadrangulata, Virgatocypris kechoulaensis, Alicenula? leguminella, Vecticypris polita, Stenestroemia mosensis, Perissocytheridea kouminiensis sp. nov., Hourcqia aff. bateke, Dolocytheridea bosquetiana, Dolocytheridea donzei sp. nov., Ovocytheridea anterocompressa, Paracypris dubertreti, Paracypris mdaouerensis, Clithrocytheridea espichelensis, Bythocypris? multagracilis sp. nov. and Bythocypris dorsogibba sp. nov. The assemblages indicate another interval of non-marine to marginal-marine depositional settings as direct response to a prominent eustatic latest Aptian to earliest Albian sea-level fall event that enhanced the quasi-total emersion of the Central Tunisian Atlas palaeogeographic domain. Hence, the two studied faunas herein allow us to define two stratigraphic key surfaces of regional utility giving new insights into the chronostratigrahic subdivision of the Orbata carbonate platform, especially in supporting a previously neglected early Albian age of its upper part (Unit 5b, 6 and 7) and allow the regional stratigraphic correlation of these key surfaces in the Central Tunisian Atlas (CTA) domain. Accordingly, our results not only disprove the previous consideration of an uppermost Aptian–lower Albian hiatus but also implicate the necessity to redefine and review the previous palaeogeographic and tectono-sedimentary schemes of the CTA as suggested for almost fourty years.

Morphometric response of late Aptian planktonic foraminiferal communities to environmental changes: A case study of Paraticinella rohri at Poggio le Guaine (central Italy)

The Aptian-Albian boundary interval represents a pivotal time of pronounced climate/ocean changes associated with Oceanic Anoxic Event 1b (OAE 1b) that seriously influenced marine pelagic ecosystems. The sedimentary successions record the first and most significant species turnover in the evolutionary history of planktonic foraminifera, consisting of the selective extinction/disappearance of large Aptian species and resulting in inter-specific size reduction (the post-extinction dwarfing as in the Lilliput effect) in the earliest Albian assemblages. In this study we investigate how the planktonic foraminifera respond to crucial environmental stress and if any intra-specific decrease in test size predate the extinction (pre-extinction dwarfing). Paraticinella rohri was chosen as the most representative of the Aptian planktonic foraminiferal taxa and its test-size evolution was compared with the high-resolution record of redox and productivity geochemical proxies through the uppermost Aptian - lowermost Albian pelagic succession of Poggio le Guaine (central Italy). Our geochemical data document long-term fluctuations characteristic of a system with transitions among different states (oligotrophic-mesotrophic-eutrophic and oxic-dysoxic-anoxic). The strong correlation of the large test-size changes of Pa. rohri during its total range with higher productivity (increased Baexcess concentrations) suggests that the trophic regime was the key factor controlling robust abundance and size variability in this taxon. The progressive increase in surface water fertility during the late Aptian offered optimum ecological conditions for planktonic foraminifera, that increased in abundance, size, and specific diversity. After the transient anoxic 113/Jacob sub-event, smaller to dwarfed specimens of Pa. rohri and depauperate planktonic foraminifera assemblages faced high selective pressures due to more oligotrophic conditions. Transition to a more eutrophic ocean in the latest Aptian irreversibly eroded their resilience, and Aptian dwarfed k-strategist taxa became extinct. The planktonic foraminifera turnover has been therefore the result of an irreversible and drastic regime shift toward a more eutrophic ecosystem that promoted the thriving of small-sized opportunistic/disaster planktonic foraminiferal species and the siliceous radiolaria.

Ammonite taxonomy and biostratigraphy for the upper Aptian-lower Albian (Lower Cretaceous) of Cerro Chino, Chihuahua State, northeast Mexico

In this paper we study the ammonoid taxonomy and biostratigraphy from the upper Aptian to the lower Albian of the Cerro Chino area, with an emphasis on an accurate taxonomic characterization of the American endemic forms Kazanskyella, Quitmanites, Immunitoceras and Huastecoceras. These genera are important because they are characteristic of the unique ammonite fauna of the Central Atlantic province. In a critical taxonomic study of these endemic forms, we review numerous holotypes and other specimens that are currently housed in several collections in the United States and Mexico. Based on our analysis, we propose a local zonation from the upper Aptian to the lower Albian, with three ammonoid zones (Kazanskyella minima, Hypacanthoplites sp. and Douvilleiceras sp.), based on the Cerro Chino sections. This newly proposed zonation constitutes a step forward in the development of the standard Central Atlantic province ammonoid zonation, particularly because biostratigraphic data for this province during this time span are very scarce. In general, the uppermost Aptian ammonoid record worldwide is scarce and/or condensed, and so the fauna preserved at this location is significant, making the contribution here even more important. In this work, we are not able to pin down the position of the Aptian/Albian boundary based solely on the ammonoids from these sections.

Two new angiosperm leaf morphotypes from the Anfiteatro de Ticó Formation (mid-Aptian) Santa Cruz Province, Argentina

Floodplain deposits of the Anfiteatro de Ticó Formation (Baqueró Group, Aptian), in Patagonia (Argentina), are rich in plant remains and contain some of the oldest angiosperm records of southern Gondwana. Many gymnosperm and pteridophyte species, as well as three morphotypes of medium sized angiosperm leaves, have already been described from this unit at different fossiliferous outcrops. We report two new angiosperm morphotypes from the Bajo Tigre locality. Both morphotypes (AT1 and AT2) consist of nano- to microphyllous leaves, nearly elliptic, with untoothed margins and pinnate brochidodromous venation. These leaves mostly exhibit characteristics of a high first or low second rank vein system. This combination of characters is associated with early angiosperm evolution. Morphotype AT1 is similar to one of the brochidodromous morphotypes from the La Cantera Formation (uppermost Aptian), which could be possibly conspecific. Morphotype AT2 has gross features already observed in leaf records from the younger Kachaike Formation (Albian ̶ lower Cenomanian) though they differ in lamina shape and secondary venation features. The angiosperm leaves of the Anfiteatro de Ticó Formation suggest that the early stages of angiosperm evolution in Patagonia had included forms with more than one type of growth habit.

The neglected history of Oceanic Anoxic Event 1b: insights and new data from the Poggio le Guaine section (Umbria–Marche Basin)

The upper Aptian to lower Albian interval (~114–109 Ma) represents a crucial period during Earth’s history, with a major evolution in the nature of mid–Cretaceous tectonics, sea level, climate, and marine plankton communities. Interestingly, it also includes multiple prominent black shale horizons that are the sedimentary expression of oceanic anoxic event (OAE) 1b. However, due to a set of geological, stratigraphic, and taxonomic challenges, difficulties constraining this OAE may sometimes result in inaccurate correlation. At Poggio le Guaine (central Italy), a continuous and undisturbed section of central western Tethyan pelagic sediments deposited during the latest Aptian and earliest Albian, complete with black shale horizons that record the OAE1b carbon cycle perturbations, has provided a unique opportunity to address the shortcomings referred to above. High–resolution geochemical proxies (CaCO3, TOC, and δ13C), along with planktonic foraminifera and calcareous nannofossils, were used to establish an integrated and robust global stratigraphic framework in order to: (1) precisely correlate the prominent black shale horizons of OAE1b in different marine environments (the Vocontian Basin in southeast France, Deep Sea Drilling Project Site 545 and Ocean Drilling Program Hole 1049C in the eastern and western North Atlantic, respectively); and (2) provide an effective tool to reconstruct, in high resolution, the paleobiological, paleoceanographic and paleoclimatic changes across the upper Aptian to lower Albian interval. The Poggio le Guaine section stands out as a valuable reference section for OAE1b, its constituent subevents, and the δ13C record for the uppermost Aptian to lower Albian interval. The exceptional chemo- and biochronostratigraphic control allow direct comparison to the proposed candidate for the GSSP for the base of the Albian Stage at the Col de Pré-Guittard section in France.

Paraticinella rohri ( ) as the valid name for the latest Aptian zonal marker species of planktonic foraminifera traditionally called bejaouaensis or eubejaouaensis

The planktonic foraminiferal taxon Ticinella bejaouaensis Sigal, 1966 had long been an important zonal biomarker for the latest Aptian characterized by its large test, numerous (8–10) final-whorl chambers, and rugose test surface, usually with an umbilical cover-plate. Upon confirmation that Sigal's Madagascan holotype was actually from the upper Albian, this species was renamed as T. eubejaouaensis Randrianasolo and Anglada, 1998 using Sigal's Tunisian bejaouaensis paratype, which is late Aptian in age, as the new holotype. Following emendation of the genus, Paraticinella eubejaouaensis has recently become the standard usage. However, the validity of this species is still uncertain because the original designation was given in very obscure publication(s). Meanwhile, albeit tenuous, a presumable senior name “Paraticinella rohri (Bolli, 1959)” has recently been proposed in place of eubejaouaensis.Rigorous assessment of the original species designation of T. eubejaouaensis ascertains that the method of publication used does not comply with the criteria required in the International Code of Zoological Nomenclature, thereby making this species an invalid name, or nomen nudum. New backscattered scanning electron microscopic observations of the primary types of Praeglobotruncana rohri Bolli, 1959 reveal that this hitherto unattended species is indeed synonymous to “T. eubejaouaensis” particularly by exhibiting equatorially aligned rugosities on the wall surface, and that the holotype is sufficiently preserved and well qualified as the name-bearing type. The latest Aptian age of the rohri type level is robustly established by its co-occurrence with Pseudoplanomalina cheniourensis (Sigal, 1952) and Hedbergella trocoidea (Gandolfi, 1942) (= another rohri paratype). Upon confirmation of the absence of any potential nomenclatural acts for conservation of the junior name “[eu]bejaouaensis,” we are obliged to provide formal redescription and establish the valid, objective senior name Paraticinella rohri (Bolli, 1959), the binomen that should be of mandatory use henceforth. Accordingly, the uppermost Aptian “[eu]bejaouaensis” Zone should be referred to as the “Pt. rohri Zone.”Having reviewed the supraspecific taxonomy, herein the type species of the genus Paraticinella is redefined as Pt. rohri, and the subfamily Pseudoplanomalininae is proposed.

Sequence development influenced by intermittent cooling events in the Cretaceous Aptian greenhouse, Adriatic platform, Croatia

Depositional sequences capped by peritidal carbonates and breccias on the Aptian Adriatic carbonate platform, Croatia, were studied to evaluate evidence for glacioeustasy within an age framework constrained by carbon-isotope chemostratigraphy. Sequence Ad1 (17–60-m [56–197-ft] thick; uppermost Barremian–lower Aptian) is dominated by shallow subtidal parasequences. Sequence Ad2 (7–13-m [23–43-ft] thick; lower Aptian–lowermost upper Aptian) contains oceanic anoxic event (OAE) 1a, associated with lagoonal laminated carbonates. Sequence Ad3 (3–8-m [10–26-ft] thick) probably is lower upper Aptian and likely is separated by a major hiatus from sequence Ad4 (8–20-m [26–66-ft] thick; uppermost Aptian), which spans OAE1b. Both Ad2 and Ad3 are dominated by peritidal parasequences updip in the lower transgressive systems tract and upper highstand systems tract and by subtidal parasequences elsewhere, whereas sequence Ad4 is dominated by shallow subtidal parasequences. Low accommodation rates (4.0–6.0 cm [1.6–2.4 in.] in the earliest Aptian, decreasing to approximately 1.0 cm/k.y. [0.3 in./k.y.] later) promoted widespread breccia development during relative sea level falls, aided by tectonic warping. The sequence-capping breccias, eccentricity-dominated cyclicity, restriction of peritidal facies to late highstands, and coeval off-shelf oxygen-isotope records all suggest that sea level falls occurred during times of cooling and had a significant glacioeustatic component. These intermittent cooler periods and continental ice buildup punctuated the Aptian greenhouse climate.

Biostratigraphy and carbon-isotope stratigraphy of the uppermost Aptian to Upper Cenomanian strata of the South Palmyrides, Syria

ABSTRACT Biostratigraphic and carbon-isotope data were used to introduce a high-resolution stratigraphic reference section of the Upper Aptian to Upper Cenomanian platform carbonates of the South Palmyrides in Syria. We studied the biostratigraphic evolution of the Zbeideh to Abou-Zounnar formations in two sections, based on 42 species of benthonic foraminifera and 38 species of planktonic foraminifera. Comparisons with other Tethyan assemblages allowed determining 11 biozones; six are based on planktonic foraminifera, and five on benthonic foraminifera. Four hiatuses (earliest Albian, Middle–Late Albian, Late Albian–Early Cenomanian, and Mid Cenomanian) are marked by hardgrounds or dolomitic intervals. The planktonic biozones Ticinella bejaouaensis, T. primula, T. praeticinensis, Rotalipora subticinensis, R. globotruncanoides and R. cushmani co-occur with the following benthonic biozones: Mesorbitolina texana partial range zone, M. subconcava range zone, Neoiraqia convexa taxon-range zone, Praealveolina iberica interval zone and Pseudedomia drorimensis range zone. Within this biostratigraphic framework, a new carbon-isotope curve from the South Palmyrides was compared with δ13C records of the Tethyan Realm and England that allows identifying several biotic events and Oceanic Anoxic Events (OAE), recorded in the Upper Albian to Upper Cenomanian succession. The combination of sequence-stratigraphic interpretations and comparisons, with our results have led to an improved understanding of the Cretaceous platform architecture of the South Palmyrides that links the Arabian Platform to the east with the Levant Platform to the southwest.

Reassessment of the genus Sergipella Krömmelbein, 1967 (Ostracoda, Trachyleberididae), uppermost Aptian-Albian of Brazil and West Africa: Taxonomy and paleogeographic distribution

A revision and a redescription of the external and internal morphology of the carapace, ontogeny and sexual dimorphism of Sergipella transatlantica Krömmelbein, 1967, from the uppermost Aptian and lower Albian of Brazil and West Africa is presented. Two new species are described: S. grosdidieri nov. sp. and S. viviersae nov. sp. The three species of Sergipella are restricted to areas of the South Atlantic during the late Aptian-early Cenomanian. The present data provide detailed taxonomic criteria for the identification of the type-species of Sergipella and its closely related species. A detailed analysis of the internal and external characteristics of the valves shows that the genus Sergipella that belongs to the Family Trachyleberididae, although it possesses some characteristics close to those of Protocytheridae. This study is based on samples from Riachuelo Formation, lower Albian, Sergipe/Alagoas basin, Sergipe State, NE-Brazil and from wells in West Africa, Madiéla Formation, lower Albian, Gabon basin, east of Libreville, Gabon.

PLANKTIC FORAMINIFERAL SPECIES TURNOVER ACROSS DEEP-SEA APTIAN/ ALBIAN BOUNDARY SECTIONS

A major planktic foraminiferal species turnover accompanied by a dramatic reduction in shell size, a fundamental change in shell architecture, and a precipitous drop in the abundance of planktic relative to benthic species occurs across the Aptian/Albian boundary interval (AABI) at globally distributed deep-sea sections. Extinction of the large and distinctive planktic foraminifer Paraticinella eube-jaouaensis , used to denote a level at or near the Aptian/ Albian boundary, coincides with the extinctions of relatively long-ranging Aptian species of Hedbergella and Globiger-inelloides . At Deep Sea Drilling Project (DSDP) Site 511 (southern South Atlantic), which is the most complete and best preserved of the studied AABI sections, the Aptian assemblage is of low diversity and species are replaced by initially one and then two very small, smooth-surfaced, thin-walled species of Microhedbergella n. gen. The oldest species of this genus, Mi. miniglobularis n. sp., probably descended from Hedbergella praelippa n. sp. and is the nominate taxon for a new lowermost Albian interval zone and is considered ancestral to several small, gradually evolving microperforate species, including Mi. praeplanispira n. sp., Mi. pseudopla-nispira n.sp., and Mi. pseudodelrioensis n. sp., which range into the middle and upper Albian. The small hedbergellids that characterize the Mi. miniglobularis Interval Zone at Site 511 have also been identified from samples taken just above the Kilian black shale level in the Vocontian Basin of southeast France. The Albian record at Site 511 reveals a gradual increase in planktic foraminifera shell size and assemblage dominance, as well as the gradual evolution during the middle Albian of species characterized by a finely perforate, pustulose test. Taxa with this shell infrastructure are included in Muricohedbergella n. gen. A new “ Ticinella yezoana ” Partial Range Zone is erected at Site 511 for correlation of the middle-upper Albian at high latitudes. At Ocean Drilling Program (ODP) Site 1049 (western North Atlantic), which also yields well-preserved foraminifera across the AABI, Aptian species of Hedbergella , Globiger-inelloides , and Pseudoguembelitria blakenosensis n. gen., n. sp. are replaced by lower Albian assemblages composed only of two minute species of Microhedbergella . However, this boundary section is considered incomplete because of the absence of the Mi. miniglobularis Zone. A new upper lower Albian Ti. madecassiana Zone is defined at Site 1049 for the interval between the lowest occurrence (LO) of the nominate taxon and the LO of Ti. primula , the nominate species of the middle Albian Ti. primula Zone. The AABI at DSDP Site 545 (eastern North Atlantic) has a major unconformity spanning the uppermost Aptian through the upper Albian. A black shale sequence previously placed in the lower Albian and designated as Oceanic Anoxic Event 1b is now determined to be latest Aptian in age. The AABI at ODP Site 763 (southeast Indian Ocean) is also marked by an unconformity between the upper Aptian Pa. eubejouaensis Zone and the lower Albian Mi. rischi Zone. This site needs further study to resolve whether overlap of species from both zones is the result of downslope reworking or an exception to the pattern of abrupt species turnover observed at the other deep-sea sites. The dramatic changes in planktic foraminiferal assemblages across the AABI suggest major changes in carbonate chemistry, vertical stratification, or productivity in the surface mixed layer occurred during the last 1 myr of the Aptian. Understanding the cause or causes for these changes will require much further investigation.

PARATICINELLA N. GEN. AND TAXONOMIC REVISION OF TICINELLA BEJAOUAENSIS SIGAL, 1966

Based on examination of the type material deposited by Jacques Sigal at the Musee National d’Histoire Naturelle in Paris, we have validated the hypothesis of Randrianasolo and Anglada (1998) that the holotype and paratype of Ticinella bejaouaensis Sigal 1966 belong to two different species, the distributions of which do not overlap. Indeed, the holotype is of late Albian age and from Madagascar whilst the paratype is of a latest Aptian age and from Tunisia. Sigal’s paratype is here confirmed to be the holotype of the species eubejaouaensis Randrianasolo and Anglada, 1998. It displays a distinctive wall texture bearing perforation cones that coalesce to form irregularly arranged rugosities and ridges, which tend to parallel the periphery. In addition, flaps may cover the umbilical area. However, it lacks true umbilical supplementary apertures and therefore cannot be included in the genus Ticinella Reichel, 1950. The new genus Paraticinella , with Paraticinella eubejaouaensis as the type species, is here formalized to accommodate uppermost Aptian trochospiral individuals with a wall texture bearing perforation cones, rugosities, and ridges in patterns paralleling the margin, and possessing an umbilical cover-plate. Paraticinella eubejaouaensis evolved from Hedbergella trocoidea in the upper Aptian. The evolutionary trend is exemplified by the increasing number of chambers, by flattening of the spire height, by widening of the umbilicus with the appearance of a cover-plate, by acquisition of well-developed ridges on wall surfaces, and by the appearance of weakly developed infralaminal accessory apertures in later specimens of P. eubejaouaensis . A close study of the holotype of Ticinella bejaouaensis Sigal, 1966 reveals a substantial similarity in morphology and wall structure with Ticinella roberti and a lack of distinguishing criteria between the two species. Consequently, the species Ticinella bejaouaensis is invalidated and is considered to be a junior synonym of T. roberti . A third species was observed associated with Ticinella roberti and Biticinella breggiensis in Madagascar and Spain, and it is attributable to the genus Ticinella based on the presence of true umbilical supplementary apertures and a typical Ticinella wall structure (muricate to coarsely pustulose), while in gross morphology, it resembles Paraticinella eubejaouaensis . We have named this new taxon Ticinella moulladei . It differs from T. roberti by its thinner test, more numerous chambers, and wider umbilicus. Finally, the last zone of the uppermost Aptian must be renamed the Paraticinella eubejaouaensis Zone to replace Ticinella bejaouaensis , which is now considered to be an invalid taxon.

High-resolution carbon isotope records of the Aptian to Lower Albian from SE France and the Mazagan Plateau (DSDP Site 545): a stratigraphic tool for paleoceanographic and paleobiologic reconstruction

High-resolution carbon isotope stratigraphy is established for the Aptian to Lower Albian of the Vocontian Basin (SE France), and correlated to the carbon isotope record of the Mazagan Plateau (DSDP Site 545). The carbon isotope stratigraphy of the Vocontian Basin is proposed as a standard reference curve for the Aptian to Lower Albian, due to the completeness and high temporal resolution of the stratigraphic succession, the good biostratigraphical time control, and the frequent occurrence of regional to global black shale horizons including Oceanic Anoxic Events 1a (OAE 1a) of the Lower Aptian and OAE 1b of the Lower Albian. The carbon isotope record appears better suited for long-distance short-term correlation of different marine and terrestrial environments than biostratigraphy because of the synchroneity of carbon isotope signals in a range of sediment types. However, the combination of both biostratigraphy and carbon isotope stratigraphy provides an effective tool to reconstruct biotic change and paleoceanography, and to correlate regional to global black shale horizons in different marine environments. This combined approach allows us to ascertain the synchroneities or diachroneities of first and last appearances of biostratigraphic marker species. Based on the demonstrated diachroneity of important biostratigraphic markers of the Aptian/Albian boundary, the globally observed break point between the end of the uppermost Aptian positive carbon isotope excursion and the onset of the pronounced negative shift of δ 13C values, is an alternative criterion. The distinctive structure and amplitudes of the carbon isotope record are observed in both the inorganic and organic carbon and can therefore be recognized in all marine and terrestrial environments of the Aptian to Lower Albian.

Early Cretaceous planktonic foraminifera from the Tethys: the small, few-chambered representatives of the genus Globigerinelloides

New findings of well-preserved Early Cretaceous planktonic foraminiferal assemblages from the Cismon core (NE Italy), Calabianca (NW Sicily), Lesches en Diois (SE France) and DSDP Site 545 (off Morocco) sections allow a better understanding of the morphological features of several taxa. This paper deals with the revision of the small, planispiral individuals that several authors include in the genus Blowiella Krechmar and Gorbachik. Comparison of morphological characteristics between Blowiella and the genus Globigerinelloides Cushman and ten Dam has resulted in retention of the latter as senior synonym of Blowiella. In fact, the morphological differences (i.e. the number of chambers in the outer whorl, the width of the umbilical area, and size and spacing of pores) used to distinguish Blowiella from Globigerinelloides cannot, in our opinion, be used in discriminating genera, but can only be applied at species level. The small, few-chambered species of the genus Globigerinelloides retained here are Globigerinelloides blowi(Bolli), Globigerinelloides duboisi (Chevalier), Globigerinelloides maridalensis (Bolli), and Globigerinelloides paragottisi sp. nov. (= Globigerinelloides gottisi auctorum). Stratigraphically, in the sections studied Globigerinelloides blowi and Globigerinelloides paragottisi sp. nov. are first recorded from the mid-Upper Barremian in the Cismon core and Calabianca section, while rare individuals belonging to Globigerinelloides maridalensis and Globigerinelloide duboisi occur intermittently from the Barremian/Aptian boundary and from the Lower Aptian, respectively. All of these taxa become more frequent and abundant just above the Selli Level (OAE1a, Lower Aptian), within the Leupoldina cabri Zone (Upper Aptian). Based on the DSDP Site 545 succession, all four globigerinelloidid taxa range up to the Ticinella bejaouaensis Zone (uppermost Aptian), with Globigerinelloides maridalensis disappearing at the base of the zone, followed in close succession by the disappearance of G. blowi, G. paragottisi and finally G. duboisi.

Calcareous nannofossils from the Aptian–Lower Albian of southeast France: palaeoecological and biostratigraphic implications

The Aptian–lower Albian succession of the Vocontian Basin (SE France) consists of marine hemipelagic sediments including several black shale horizons. The latter are partly of regional and partly of global distribution. This sedimentary succession records the nannoplankton evolution of the Aptian–early Albian interval and thus provides an excellent opportunity to calibrate the calcareous nannofossil record with Tethyan ammonite and planktic foraminiferal biostratigraphy. The calcareous nannofossil biostratigraphy presented in this paper supports previous zonations, but it also provides a much higher resolution and thus improves the correlation of different black shale horizons on a supraregional scale. Up to 23 major (supraregionally significant) and minor (regionally significant) first and last occurrences of calcareous nannofossil taxa are recognized. Nannoconid abundances decrease rapidly in the upper Lower Aptian (nannoconid crisis I, NCI) and in the middle Upper Aptian (nannoconid crisis II, NCII). Both decreases correlate with carbonate–platform drowning events. The upper Lower Aptian interval above the NCI is characterized by high abundances of large specimens of Assipetra infracretacea and Rucinolithus terebrodentarius probably of supraregional significance. The uppermost Aptian–Lower Albian is characterized by high abundances of the calcareous nannoplankton taxon Repagulum parvidentatum, reflecting boreal influence on the Tethyan Realm. This suggests a temporary decrease in surface-water temperatures in the Vocontian Basin.