Biostratigraphic Markers Research Articles

Fissumella motolae n. gen. n. sp., a new soritoidean (Foraminifera) from the lowermost Albian carbonate platform facies of central and southern Italy

The Soritoidea (Foraminifera) represent an important component of Cenomanian microfossil assemblages of the central and southern Tethyan carbonate platforms and are widely used as biostratigraphic markers. In this paper a new taxon, Fissumella motolae n. gen. n. sp., is described from the Cretaceous carbonate platform facies of central and southern Italy. It is characterized by its small size, planispiral-involute arrangement of chambers, fissure-shaped single aperture and few and short radial septula subdividing the marginal lumen of the chambers. Fissumella motolae n. gen. n. sp. represents the first soritoidean in the fossil record showing internal subdivisions of the chamber lumen. Carbon isotope stratigraphy supports an earliest Albian age for this significant step in the evolution of the superfamily Soritoidea. The new subfamily Fissumellinae is established for soritoidean foraminifera with planispiral-involute lens-shaped shells, single aperture and chamber lumen subdivided by few and short septula.

First faunal insights from biozone Db (middle Miocene, middle Aragonian) of the Madrid Basin (Spain)

Palaeontological excavations following public works around the Manzanares River in the metropolitan area of Madrid yielded new small mammal fossil remains from two locations. We present here a description of their rodent assemblages, and a biostratigraphical and palaeoecological context of them. A comparison of these levels to the contemporaneous fossil localities of the Calatayud-Montalban Basin and to other middle Aragonian sites from Madrid is also shown. A total of 371 dental elements have been studied from the five levels of the two locations (Puente de Praga site and Madrid Rio2 site). The rodent associations from the five new levels are similar and comprise eight taxa: Megacricetodon primitivus, Megacricetodon vandermeuleni, Democricetodon moralesi, Democricetodon sp., Armantomys aragonensis, Microdyromys koenigswaldi, Pseudodryomys ibericus and Heteroxerus rubricati. It represents a low equitable rodent community characterized by the predominance of the genus Megacricetodon and a poorly-represented fauna of glirids and sciurids. The fossil association and its biostratigraphical markers indicate a correlation of the levels to the upper part of biozone Db, this being the first time that the rodent assemblages of this biozone are described in the Madrid Basin. Based on the rodent content we suggest more humid or/and more closed environments in biozone Db than in biozones Dc and Dd. The Calatayud-Montalban record shows more diverse rodent assemblages in biozone Db, with taxa not recorded in Madrid that are indicative of more humid or structured environments. Therefore, the Madrid associations would represent dryer or/and more open environments than the Calatayud-Montalban associations.

A lithostratigraphic and palaeoenvironmental framework for the late Miocene El Caracolar section (Granada Basin, Betic Cordillera, Spain) and description of decapod crustaceans

The locality of El Caracolar in the Granada Basin (Central Betic Cordillera, southern Spain) has yielded a rich late Miocene assemblages composed of marine invertebrates and vertebrates, accompanied by microfossils, macroflora and trace fossils. Exposed strata consisting of sands, sandy siltstones, silty sandstones, siltstones and calcirudites are divided into four local units. Lithostratigraphically, the studied section is placed between the top of the La Peza Formation and the Quéntar Formation. Based on foraminifers, the age of units 2 and 3 is estimated to be early Tortonian (11.0–9.9 Ma), whereas units 1 and 4 do not yield any reliable biostratigraphic markers. The diverse biotic association suggests that deposition took place in a near-shore outer neritic zone of a narrow to open seaway in a mesotrophic regime, responsible for the establishment of a chemosynthetic community under (sub)tropical conditions. The palaeo-depth of the depositional setting is estimated between 70 and 130 m. We further focused on decapod crustaceans that represent the first formally reported fossil decapod assemblage from the Granada province. The faunule consists of eight genera from two assemblages representing different palaeoenvironments. The assemblage of units 1 and 4 is dominated by the ghost shrimp “Callianassa” cf. almerai and accompanied by the hermit crab Petrochirus, whereas the assemblage from unit 3 includes the ghost shrimp Ctenocheles and the brachyuran crabs Raninoides, Calappa, Goneplax, Styrioplax, and Typilobus. Unit 2 does not yield any identifiable decapod remains. Styrioplax sp. represents the first occurrence of the genus outside the Central Paratethys, substantially expanding its palaeogeographical distribution. The decapod faunule from El Caracolar shows affinities with assemblages from the Proto-Mediterranean and Paratethys. This study provides a lithostratigraphic and palaeoenvironmental framework for further palaeontological studies in this unique Western Mediterranean outcrop.

The Neogene genus Streptochilus (Brönnimann and Resig, 1971) from the Gulf of California

Abstract Four species of the planktonic foraminiferal genus Streptochilus from key Neogene marine localities are documented in relation to the evolution of the Gulf of California: S. globigerus, S. latus, S. macdougallae sp. nov., and S. inglei sp. nov. Planktonic foraminiferal bioevents and strontium isotopes in the Bouse, Tirabuzon, Carmen and Ojo de Buey lithostratigraphic units constrain the local distribution range between 6 and 5.3 Ma for the last three species, whereas S. globigerus appears locally at 5.5 Ma and disappears between 3.79 and 3.46 Ma in the Imperial and Trinidad Formations. The last occurrence of Streptochilus latus, and the first and last occurrences of S. globigerus in the ancient Gulf of California are correlated with bioevents calibrated in the equatorial Pacific; therefore, they can be used as reliable local biostratigraphic markers. The presence of Streptochilus in the ancient Gulf of California seems to correlate with upwelling, in a pattern similar to that observed in the modern oceans.

Clay mineralogy of altered tephra beds and facies correlation between the Permian-Triassic boundary stratigraphic sets, Guizhou, south China

The Permian-Triassic boundary (PTB) successions in south China contain numerous altered volcanic ash (tephra) beds (K-bentonites), which presents the opportunity to correlate the PTB position in both marine and non-marine sections, especially when no feasible biostratigraphic markers are available in the profiles. Clay mineralogical and geochemical studies of two altered ash beds in the Zhongzai (ZZ) and Tucheng (TC) sections, in Guizhou Province, south China, deposited in littoral and interactive marine-terrestrial environments, respectively, permit an investigation of the alteration of ash and correlation of ash beds between disparate facies. The results show that the two ZZ altered ashes consist of mainly R1 I/Sm and minor R0 I/Sm. Sample ZZ-1 has slightly more R1 I/Sm but less R0 I/Sm relative to sample ZZ-2. The TC ash samples contain mainly kaolinite and mixed-layer kaolinite/smectite (K/Sm). The poorly-crystallized kaolinite is present in pseudo-hexagonal plates, and the well-crystallized kaolinite occurs in book-like aggregates in veins or cavities. K/Sm minerals are derived from the transformation of smectite to kaolinite. Obviously, the TC ashes experienced terrestrial weathering and resedimentation prior to final burial and preservation, and local microenvironmental conditions control the formation of clay minerals. The ZZ ash samples have markedly higher 87Sr/86Sr values than those of the TC samples. The notable difference in 87Sr/86Sr value of ash beds between the sections is attributed to variations in RbSr partitioning during the chemical weathering process in different environments. The ZZ ash samples have notably higher 143Nd/144Nd ratios than those of the TC samples, suggesting that the ZZ ashes are likely derived from eruptions involving continental crust and the TC ashes originate from eruptions involving new continental island arcs, in agreement with the REE distributions and the Ti vs. Zr, TiO2 vs. Al2O3, and Zr/TiO2 vs. Nb/Y discrimination plots. The occurrence of tephras from such markedly different volcanic source materials different in PTB stratigraphic sets previously believed to be synchronous, Guizhou, south China, suggests that correlation between disparate facies by an ash marker requires geochemical fingerprinting of the materials to confirm correlations or otherwise.

Paleogene Nummulitid biostratigraphy of the Kohat and Potwar Basins in north-western Pakistan with implications for the timing of the closure of eastern Tethys and uplift of the western Himalayas

The Paleogene larger benthic foraminifera (LBF) of the Kohat and Potwar basins, Pakistan are very useful in dating shallow marine sediments and cessation of marine sedimentation that provides constraint for crucial information on the initial age of India-Asia collision. We record important Paleogene LBF species in multiple sections of the two basins. We performed the biometric analysis of the nummulitid species useful for taxonomic purposes. We recognize six Larger Benthic Foraminiferal Zone (BFZ Zone 1-6) in the Kohat Basin. Among these Zones the first three (BFZ Zone 1-3) occur also in the Potwar Basin and the adjoining Trans Indus Ranges (TIR). The correlation of BFZ 1-6 Zones with the previous local and regional LBF biostratigraphic schemes in the Eastern Tethys (Pakistan-India) and Western Tethys (European Basins) resulted in recognition of useful index taxa for developing a regional stratigraphic framework during Paleogene. In the BFZ 1 Zone, The last occurrence (LO) of Miscellanea miscella and first occurrence (FO) of Assilina dandotica in the BFZ 2 Zone mark the Late Paleocene (Late Thenetian) Early Eocene (Lower Illerdiuan1) Boundary. The co-occurrence of A. pustulosa, Al. vredenburgi, Al. globula and Al. pasticillata in the BFZ 2 Zone characterizes the Early Eocene (Lower IlIerdian 1-Middle Illerdian 1) sediments. The synchronous FO of N. atacicus and N. globulus is an excellent global biostratigraphic marker of the Early Eocene (Middle Illerdian 1 Middle Illerdian 2) Boundary and the FO of O. complanatus is a useful biostratigraphic marker for the Early Eocene (Lower Cuisian 2-Middle Cuisian) Boundary in the BFZ 3 Zone. Mammalian bones found at the base of Koldana Formation in the Kohat Basin represent Early Eocene (Upper Cuisian), which is in agreement with the LBF biostratigraphy of the underlying Middle Cuisian strata. The FO of A. exponens in the BFZ 4 Zone record the Middle Eocene (Middle Lutetian 1) sediments while FO of N. beaumonti in the BFZ 5 Zone marks the Middle Lutetian 1Middle Lutetian 2 Boundary. The FO of A. cancellata in the BFZ 6 Zone marks Middle Lutetian 2Upper Lutetian Boundary. The implications of our LBF study are that cessation of marine sedimentation in both Pakistani basins occurred in Early Eocene (Middle Cuisian ≈BFZ 3) around 50-49.5 Ma. Notably, marine conditions returned in the Kohat Basin in Middle Eocene (Middle Lutetian 1 ≈ BFZ 4) due to an eustatic sea level rise. The final cessation of marine sedimentation, causing closure of the Eastern Tethys seaway in the Kohat Basin occurred in Middle Eocene (Upper Lutetian ≈BFZ 6) around 41.2 Ma, probably a result of some form of post-collisional stress.

The Albian–Cenomanian transition and Oceanic Anoxic Event 1d – an example from the Boreal Realm

AbstractThe upper Albian to lower Cenomanian interval in the Hanover area (Germany) is characterized by a well‐developed lithological transition from upper Albian monotonous (marly) claystones of several hundred metres thickness, which become enriched in biosilica in the topmost Albian, to increasingly CaCO3‐rich marls and limestones in the lower and middle Cenomanian. This study presents a new 165 m thick composite record spanning the latest Albian to mid‐early Cenomanian (ca 103·0 to 97·5 Ma) based on two core drillings at Anderten in the central Lower Saxony Basin (east of Hanover), which is a sub‐basin of the North German Basin. Due to the lack or delayed occurrences of Tethyan biostratigraphic markers for the late Albian and early Cenomanian in the Boreal Realm, the definition of the Albian–Cenomanian boundary, as based on the lowest occurrence of Thalmanninella globotruncanoides, is not applicable. In order to overcome this issue, an integrated biostratigraphic–chemostratigraphic approach has been employed. In addition to biostratigraphy (calcareous nannofossils, ostracods, planktonic foraminifera and inoceramids), the Anderten succession has been studied using sedimentary geochemistry (CaCO3, total organic carbon, δ13C and δ18O), γ‐ray logging and X‐ray fluorescence core scanning. This approach enabled successful correlation of the composite Anderten record to European reference sections in England, south‐east France and Italy, as well as to further low‐resolution records from the Lower Saxony Basin (Wunstorf and Konrad 101 core). This work has made it possible to identify the δ13Ccarb expression of: (i) the Oceanic Anoxic Event 1d; (ii) the Albian–Cenomanian boundary interval; and (iii) potentially the Lower Cenomanian Event(s). Chemostratigraphic age assignments are supported by biostratigraphic results. Calcareous nannofossils indicate an extended Upper Cretaceous 0 (UC0) zone (upper Albian) up to Upper Cretaceous 2 (UC2; upper lower Cenomanian), and the occurrence of the ostracod Physocythere steghausi supports an early Cenomanian age for most of the upper part of the composite record. Notably, influxes of the planktonic foraminifer Thalmanninella aff. reicheli have previously been described from this area and the first appearance of this taxon is usually used to define the base of the middle Cenomanian Substage. However, findings from the Anderten cores and elsewhere suggest that this taxon has an apparently earlier first appearance, questioning previous age assignments from the Boreal Realm solely based on planktonic foraminifera. Due to both moderately well‐preserved microfossils and high sedimentation rates, the drilled succession of Anderten is considered as a potential Boreal reference section for the Albian–Cenomanian transition.

Sinemurian–Pliensbachian calcareous nannofossil biostratigraphy and organic carbon isotope stratigraphy in the Paris Basin: Calibration to the ammonite biozonation of NW Europe

The biostratigraphy of Sinemurian to lower Toarcian calcareous nannofossils has been investigated in the Sancerre-Couy core (Paris Basin), which contains a mixed assemblage of species with affinities to the northern and southern areas of the peri-tethyan realm, thus allowing for the use and calibration of the Mediterranean Province (Italy/S France) and NW Europe (UK) biozonation schemes. This study is based on semi-quantitative analyses of the calcareous nannofossil assemblage performed on 145 samples and the recorded bioevents are calibrated to the NW European Ammonite Zonation and to a new organic carbon isotope curve based on 385 data points. The main bioevents, i.e. the first occurrences of Parhabdolithus liasicus, Crepidolithus pliensbachensis, Crepidolithus crassus, Mitrolithus lenticularis, Similiscutum cruciulus sensu lato, Lotharingius hauffii, Crepidolithus cavus and Lotharingius sigillatus as well as the last occurrence of Parhabdolithus robustus, have been identified. However, we show that a large number of standard biostratigraphic markers show inconsistent occurrences at the base and top of their range, possibly accounting for some of the significant discrepancies observed between the different domains. In addition to the nine main bioevents used for the biozonation of the core, we document an additional 50 distinct bioevents, evaluate their reliability and discuss their potential significance by comparison to previous studies. A total of five significant negative organic carbon isotope excursions are identified and defined in the Paris Basin including the well-documented Sinemurian–Pliensbachian boundary event. One positive excursion is further defined in the Pliensbachian interval. Our calibration of high-resolution calcareous nannofossil biostratigraphy to ammonite biostratigraphy and organic carbon isotopes represents a new stratigraphic reference for the Lower Jurassic series.

Permian smaller foraminifers: taxonomy, biostratigraphy and biogeography

Abstract This review has been undertaken in order to present some interpretations about the biostratigraphy of the smaller foraminifers belonging to four classes present during the Permian: Fusulinata, Miliolata, Nodosariata and Textulariata. Biostratigraphic markers of these classes are principally known in the orders and superfamilies of Lasiodiscoidea, Bradyinoidea and Globivalvulinoidea (Fusulinata), Cornuspirida (Miliolata), and in the entire class Nodosariata. The class Textulariata is too little known during the Permian to play a significant biostratigraphical role: nevertheless, the appearance of the order Verneulinida is probably an important bioevent. The main genera among the lasiodiscids are Mesolasiodiscus , Lasiodiscus , Lasiotrochus , Asselodiscus , Pseudovidalina , Xingshandiscus and Altineria ; the bradyinoids Bradyina and Postendothyra ; the globivalvulinoids Globivalvulina , Septoglobivalvulina , Labioglobivalvulina , Paraglobivalvulina , Sengoerina , Dagmarita , Danielita , Louisettita , Paradagmarita , Paradagmaritopsis and Paremiratella ; the miliolates Rectogordius , Okimuraites , Neodiscus , Multidiscus , Hemigordiopsis , Lysites , Shanita and Glomomidiellopsis , and the tubiphytids and ellesmerellids, which might be specialized miliolate and cyanobacterium consortia, with reference to microstructures and phylogenies of these groups. The Nodosariata markers belong to Nodosinelloides , Tezaquina , Polarisella , Geinitzina , Pachyphloia , Rectoglandulina , first true Nodosaria , Langella , Pseudolangella , Calvezina , Cryptoseptida , Cylindrocolaniella , Colaniella , Frondina and Ichthyofrondina , but their lineages are too poorly understood to permit an accurate biostratigraphic use at the present time. The superfamily Geinitzinoidea is emended. Finally, palaeobiogeographical implications based on Shanita , Colaniella and Altineria are given.

Towards an Ediacaran Time Scale: Problems, Protocols, and Prospects

Shuhai Xiao, Guy M. Narbonne, Chuanming Zhou, Marc Laflamme, Dmitriy V. Grazhdankin, Malgorzata Moczydlowska-Vidal, Huan Cui. Episodes 2016;39:540-55. https://doi.org/10.18814/epiiugs/2016/v39i4/103886

Revised stratigraphic range of the Toarcian ammonite genusPorpocerasBuckman, 1911

The Toarcian ammonite genus Porpoceras Buckman, 1911 is a cosmopolitan taxon with an uncertain stratigraphic range. The oldest known occurrence of the genus was reported from the Falciferum Subzone (Early Toarcian) in Morocco, although based on a unique specimen whose taxonomic assignment to the genus Porpoceras remains doubtful. The youngest occurrence was a simple mention of Porpoceras sp. from the Variabilis Subzone (Middle Toarcian) of the Thouars area (Western France), but it was later regarded as doubtful because no specimen was figured. We here provide the first robust evidence for the youngest known occurrence of the genus Porpoceras, from the Variabilis Subzone of the Thouars area. The known revised stratigraphic range of the genus therefore extends from the Falciferum Subzone to the Variabilis Subzone. In turn, the genus Porpoceras likely went extinct in the Illustris Subzone together with the genera Catacoeloceras Buckman, 1923 and Mucrodactylites Buckman, 1928, coinciding with the drastic loss of diversity observed between the Bifrons and Variabilis Zones in northwestern Europe (also known as the Bifrons-Variabilis extinction). Finally, in the light of our new data and of previous reports, the genus Porpoceras is not a foolproof biostratigraphic marker of the NW European Bifrons Horizon, although it remains an important taxon for identifying this biostratigraphic unit.

Ontogeny of the articulated yiliangellinine trilobite Zhangshania typica from the lower Cambrian (Series 2, Stage 3) of southern China

AbstractNew discoveries of the early Cambrian yiliangellinine trilobite Zhangshania typica Li and Zhang in Kunming preserve almost all instars from early postembryonic (protaspid) to mature (holaspid) phases in articulated state, in addition to mature specimens with antennae bearing paired spines on the basal articles. The ontogenetic series shows protarthrous development with some, but likely not all, early holaspid instars expressing additional pygidial segments, gradual rearward migration of the location of the longest pleural spines on the trunk segments, and striking positive allometry of the genal spines. It also reveals Parazhangshania sichuanensis Li and Zhang, 1990 to be the holaspid stage 3 of Z. typica, and therefore its junior synonym. This new find in the Hongjingshao Formation provides species-based regional correlation across the South China block and Z. typica may provide an important biostratigraphic marker for the base of the traditional Tsanglangpuan Stage.

The effects of the inception of Amazonian transcontinental drainage during the Neogene on the landscape and vegetation of the Solimões Basin, Brazil

ABSTRACTAmazonia covers nearly 50% of Brazil. The history of this biome is marked by many changes in the landscape caused mainly by the Central and Northern Andes uplift. This event has influenced the palaeogeography of the Amazon and therefore its biogeography and possibly biodiversity. Herein we present palynological and lithostratigraphical results from the Solimões Formation in the well 1AS-33-AM. It was drilled in the Solimões Basin, Amazonas State, Brazil, reaching 405 m in depth. We identified 152 palynomorphs, in 32 samples, among them some biostratigraphical markers, such as Crassoretitriletes vanraadshoovenii, Fenestrites spinosus, Cichoreacidites longispinosus, Ladakhipollenites? caribbiensis and Echitricolporites mcneillyi, allowing us to recognise four biozones sensu Lorente (1986): Crassoretitriletes Interval Zone (399.10–276.70 m), Asteraceae Interval Zone (276.70–262.00 m), Psilatricolporites caribbiensis Interval Subzone (239.90–70.00 m) and Echitricolporites–Alnipollenites Interval Subzone (70–32 m). The palynological and lithostratigraphical results indicate two environmental phases. The palynomorph association presents a change marked by the sudden appearance and predominance of Grimsdalea magnaclavata from 239.90 m upwards and a general increase in the number of species. The lithostratigraphy shows from approximately the same depth greater amounts of sandstones towards the top of the well, suggesting a change from a paralic to a fluvial environment of higher energy. The first phase can be associated with the Pebas/Acre depositional systems, wetlands composed by lakes and swamps with seasonal floods that existed from 23 to 7–5 Ma. The second phase indicates a fluvial system that may be interpreted as a record of the modern Amazon transcontinental fluvial system, which was already established in the Pliocene.

The barren Messinian Tripoli in Sicily and its palaeoenvironmental evolution: suggestions on the exploration potential

New observations on the Sicily Messinian Tripoli have yielded a variably thick diatomitic, calcareous and shaly rock interval marked by an upwards disappearance of calcareous and siliceous plankton (barren lithosome), coexisting with a variability in vegetal remains and significant amounts of amorphous organic matter (AOM). Facies analysis associated with biostratigraphy and palaeoecology of the several field and borehole sections has been framed in a well-accepted chronological scheme that points to this barren interval coinciding with the stratigraphic upper and younger part of some Tripoli sections (bituminous Tripoli) located in the northern part of the study area. Biostratigraphically, the barren lithosome falls within the Non-Distinctive Zone (NDZ) and is generally younger than the First Common Occurrence (FCO) of T . multiloba . The age of its diachronous base appears older than the Messinian salinity crisis (MSC) deposits, because is well constrained by the calcareous plankton biostratigraphic markers along the underlying portions of the Tripoli. The top boundary of the barren rock interval, that is not always identifiable, could be age dated, following the proposed stratigraphic criteria. We infer that the Tripoli initial open-marine environment became, in more inner areas, progressively confined, with freshwater floodings alternating with short marine-water incursions in a shallow-water to continental domain. The collected information appears useful in addressing further exploration.

Late Miocene–early Pliocene planktonic foraminifer event-stratigraphy of the Bajo Segura basin: A complete record of the western Mediterranean

The Bajo Segura basin (eastern Betic Cordillera) has one of the most complete late Miocene–early Pliocene marine records of the western Mediterranean. An updated planktonic foraminifer zonal scheme based on recent astronomically tuned biozones is presented for this interval, documenting a complete succession of biostratigraphic markers, from biozone MMi9 (earliest Tortonian) to MPl3 (latest early Pliocene), of likely significance for regional-scale correlation throughout the Mediterranean. The findings reveal a series of intrazonal events (some unreported until now in the Mediterranean Neogene basin), including the particularly interesting two influxes of the Globorotalia miotumida group during the Tortonian. These biostratigraphic findings are the basis for a framework of the major allostratigraphic units in the basin based on planktonic foraminifer event-stratigraphy: synthems Tortonian I, Tortonian II, Tortonian-Messinian I, Messinian II, and Pliocene. In addition, the timing of the main tectono-sedimentary and palaeogeographic events throughout the basin's evolution has been further constrained. Our results suggest that, at least in the Bajo Segura basin, the late-Messinian barren interval (non-distinctive zone) can be considered an ecobiostratigraphic zone (cenozone) characterized by dwarf fauna of planktonic foraminifera. Consequently, the Bajo Segura composite section can be regarded as a biostratigraphic reference section for Neogene basins in the Betic Cordillera and hence also in the Western Mediterranean.

Giantism in Oligocene planktonic foraminifera Paragloborotalia opima: Morphometric constraints from the equatorial Pacific Ocean

The extinction of Oligocene planktonic foraminifera Paragloborotalia opima is an important biostratigraphic marker for the upper Oligocene (base Zone O6 [P22]), however the taxonomy of the morphospecies is unclear and therefore its biostratigraphic use is compromised. We conducted morphometric and scanning electron microscope analyses on the Paragloborotalia opima-nana plexus and investigated whether the two morphospecies P. opima (Bolli) and P. nana (Bolli) could be quantitatively separated or formed a continuous morphocline. These two morphospecies have previously been classified by their diameter, with P. opima defined as the larger morphospecies (0.39–0.55 mm) and P. nana confined to 0.32 mm. The problem with this classification is that many specimens fall between 0.32 and 0.39 mm. We measured the maximum size of 1215 specimens of Paragloborotalia from equatorial Pacific Ocean Integrated Ocean Drilling Program Site U1334, corresponding to planktonic foraminiferal Biozones O6–O2 and Chrons C8r to C11r (26.3 to 30.8 Ma). We found that the number of chambers and shape outline could not be used to determine these two morphotypes of Paragloborotalia, but size is a suitable delimiting character. We therefore reassess the taxonomy of the opima-nana plexus. Our data confirm that the 'transition' forms are consistent with P. opima and that the 0.32 mm criterion is valid for the identification of P. nana. Through the studied interval the maximum size of P. opima increases from 0.44 mm to 0.68 mm, with the largest specimens in the upper Oligocene in the lower part of Chron C9n. We propose that the progressive giantism of P. opima through the mid-late Oligocene in the equatorial Pacific Ocean is in response to high productivity.

Dinoflagellate cyst zonation for the middle to upper Eocene in the Austral Basin, southwestern Atlantic Ocean: implications for regional and global correlation

AbstractThe well-exposed marine Eocene units from southwestern Patagonia, Argentina, contain useful information for reconstructing regional climate and oceanographic patterns in an area adjacent to the Drake Passage. The aim of this paper is to integrate dinoflagellate cyst data from three sections of the southwestern Austral Basin (Río Turbio Formation) to propose a zonation scheme, which can be applied to other southwestern Atlantic Ocean sites. Assemblages of organic walled dinoflagellate cysts have been analysed in different cropping-out sections and cores, showing the high potential of this fossil group as biostratigraphic markers. Comparison of dinoflagellate cyst events of the upper member of the Río Turbio Formation with calibrated biostratigraphic ranges in the Palaeogene South Pacific Ocean allowed us to date and correlate these sedimentary sections. The resulting zonation consists of four dinoflagellate cyst zones labelled RTF 1 to RTF 4, between the middle Lutetian and late Priabonian. As a final point, we applied dinoflagellate cyst species with importance as palaeoenvironmental markers to assess long-term climatic and oceanographic evolution for the area. This study shows that the endemic–Antarctic dinoflagellate cyst assemblage is dominant during the middle to late Eocene (RTF 1 to RTF 3), while a significant replacement of these taxa by cosmopolitan species characterizes the upper part of the upper member of the Río Turbio Formation (RTF 4). This turnover seems to be a consequence of changes in the ocean circulation patterns forced by deepening of the southern Atlantic gateways (the Drake Passage and the Tasman Gateway).

Howchinia Cushman, 1927 (Foraminifera) from the Mississippian Bei’an Formation and its distribution in South China

Shen, Y. & Wang, X.L., July 2016. Howchinia Cushman, 1927 (Foraminifera) from the Mississippian Bei’an Formation and its distribution in South China. Alcheringa 40, xxx–xxx. ISSN 0311-5518.Howchinia Cushman is a useful biostratigraphic marker for Mississippian rocks. In South China, Howchinia has been reported from four sections: the Bei’an, Baping, Naqing and Yashui sections; with high species diversity in the Bei’an section. Ten species from the Mississippian Bei’an Formation in the Bei’an section are described in this paper: Howchinia bradyana, H. beleutensis, H. gibba, H. plana, H. convexa, H. subconica, H. subplana, Howchinia sp. A, Howchinia sp. B. and Howchinia beianensis sp. nov. Howchinia ranges from late Visean to early Bashkirian in South China. Howchinia species inhabited both shallow-water and relatively deep-water environments.Yang Shen [shenybj@126.com] and Xun-Lian Wang [wxl@cugb.edu.cn], State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 29 Xueyuan Road, Beijing 100083, PR China.

A note on diatom stratigraphic markers in upper Miocene sediments of the Pisco Formation, Peru, and description of Delphineis urbinai sp. nov.

With the aim of preparing the ground for a comprehensive stratigraphic work on the Mio-Pliocene Pisco Formation, Peru, diatom marker species from the upper Miocene sites of Cerro Colorado (CC) and Cerro Los Quesos (CLQ) were investigated. Samples were collected along two composite stratigraphic sections and prepared for microscope analysis. Marker species are listed and described; their ranges and taxonomy are discussed in the light of recent works on Pacific diatom biostratigraphy and compared to findings in previous works from the 1980s on the Pisco Formation. Subsequently, marker species ranges and taxonomy have been significantly revised, suggesting that age-attributions based on sediments of the Pisco Formation should also be corrected. Examples are: (1) Koizumia tatsunokuchiensis, which was known as a Pliocene marker, but is now known to first appear in the late Miocene; (2) Thalassiosira cf. flexuosa, which was reported in early works on the Pisco Formation biostratigraphy as Coscinodiscus plicatus; (3) Thalassiora antiqua, which is found both at CC and CLQ, although typical of cold waters. The need to build a specific diatom biozonation for this Pacific region is thus highlighted. In addition, a new species, Delphineis urbinai, is described. This species is not a biostratigraphic marker but its sporadic presence may help with the correlation of stratigraphic sections within the Pisco Formation.

RE-EXAMINATION OF THE USE OFCASSIDULINA NEOTERETISAS A PLEISTOCENE BIOSTRATIGRAPHIC MARKER IN THE ARCTIC OCEAN

Foraminiferal tests from two sediment cores from the western Arctic Ocean were investigated for evidence of an evolutionary transition from Cassidulina teretis Tappan to Cassidulina neoteretis Seidenkrantz during the Pleistocene. Previous results based on core material from the North Atlantic and the Nordic Seas suggested minute differences between these test types and resulted in the emendation of C. neoteretis , as well as its designation as a Pleistocene biostratigraphic marker. This study identifies both species throughout most of the western Arctic foraminiferal record, without a clear pattern of evolution from one to another, except for the uppermost part of the stratigraphy (late Pleistocene). These results indicate that the C. teretis/C. neoteretis transition was more time-transgressive than previously believed and that these foraminifers may be ecophenotypes rather than different species. The stratigraphic use of C. neoteretis is likely to be site-specific and caution should be taken in its application across the entire Polar region.