Cretaceous Calcareous Nannofossils Research Articles

Morphometric changes in two Late Cretaceous calcareous nannofossil lineages support diversification fueled by long-term climate change

Morphometric changes have been investigated in the two groups of calcareous nannofossils, Cribrosphaerella ehrenbergii and Microrhabdulus undosus across the Campanian to Maastrichtian of the Zagros Basin of Iran. Results reveal a common episode of size increase at c. 76 Ma, with a sudden increase in the size of C. ehrenbergii and with the emergence of a newly defined, larger species Microrhabdulus zagrosensis n.sp. An even larger species emerges at c. 69 Ma within the Microrhabdulus lineage, Microrhabdulus sinuosus n.sp. The timing of these size changes and origination events matches global changes in nannoplankton diversity and/or in diversity of other planktonic organisms and marine invertebrates. Comparison with long-term global climate change supports that these two distinct episodes of morphological change coincide respectively with the late Campanian carbon isotope event and acceleration of cooling and with climatic instability across the mid-Maastrichtian event.

Insights into mechanisms of coccolithophore speciation: How useful is cell size in delineating species?

A recommendation of: Mohammad Javad Razmjooei, Nicolas Thibault Morphometric changes in two Late Cretaceous calcareous nannofossil lineages support diversification fueled by long-term climate change https://doi.org/10.31233/osf.io/nfyc9

Lower Cretaceous calcareous nannofossils and their biostratigraphic and paleoceanographic implications in Southern Tibet

Lower Cretaceous marine strata are widely distributed and well exposed in the Tingri area of Southern Tibet, which includes the Gucuocun and the overlying Gambacunkou Formations. However, the age of the boundary between these two lithologic formations is poorly constrained due to a scarcity of macrofossils. A detailed biostratigraphic study was carried out on the abundant, moderately preserved calcareous nannofossil assemblages obtained from the lower part of the Gambacunkou Formation and the underlying Gucuocun Formation in the Kangsha Section, Tingri. The first occurrence of the marker species Tranolithus orionatus (110.73 Ma) constrains the Gucuocun/Gambacunkou boundary to slightly below the lower boundary of Subzone NC8c (early Albian age), which correlates with Ocean Anoxic Event (OAE) 1b. The absence of Axopodorhabdus albianus and Eiffellithus turriseiffelii throughout the section suggests that the lower part of the Gambacunkou Formation mostly falls within nannofossil Subzone NC8c (110.73–109.94 Ma; early Albian), with a mean sedimentation rate of 12.7 cm/kyr, which is higher than that typical of the open ocean. The consistently high total organic carbon (TOC) and CaCO3 contents in Interval I (Gucuocun Fm.) indicate that productivity was higher during OAE1b, possibly due to increased terrigenous input (as evidenced by elevated C/N and nutrient/fertility indices) that carried nutrients to promote productivity during this event. Nannofossil assemblages and geochemical proxies, including TOC and elemental ratios (Ti/Al, Zr/Al, K/Al), reveal a parallel upsection increase in surface water fertility and continental weathering intensity from Interval II-1 (0–60 m) to the overlying Interval II-2 (60–102 m) in the Gambacunkou Fm., suggesting that enhanced continental weathering contributed to increase the surface water fertility and dilute the sediment carbonate content. These data also indicate that the depositional environment in the Tingri area was aerobic to hypoxic during the early Albian. Our result confirms the presence of OAE1b at the top of the Gucuocun Formation.

Early Jurassic–Early Cretaceous Calcareous Nannofossil Biostratigraphy and Geochemistry, Northeastern Iraqi Kurdistan: Implications for Paleoclimate and Paleoecological Conditions

Early Jurassic- to Early Cretaceous-age calcareous nannofossils from the Sarki, Sehkanyian, Sargelu, Naokelekan, Barsarin and Chia Gara formations are investigated for the first time from the Warte area, northeastern Iraqi Kurdistan. A range of isotopic and inorganic geochemical analyses are carried out in order to reconstruct the paleoecological and paleoclimatic conditions during which the Sarki, Sehkanyian, Sargelu, Naokelekan, Barsarin and Chia Gara formations were deposited. The age of the Sargelu Formation was determined as Bajocian–Callovian based on the first occurrence of Cyclagelosphaera margerelii, Watznaueria britannica, W. fossacincta, W. manivitiae, Watznaueria barnesiae and Watznaueria ovata. Geochemical proxies (Sr, Ca, Al, Rb/Sr, Sr/Cu and Sr/Ba) for paleoclimate and paleoecological conditions, along with oxygen isotopes (δ18O) data, suggest that warm and arid climatic conditions were predominant during the Early Jurassic–Early Cretaceous period.

Integrated bio- and chemostratigraphy of the Cretaceous – Paleogene boundary interval in the Zagros Basin (Iran, central Tethys)

An expanded Upper Cretaceous – Lower Paleocene succession, which encompasses the Cretaceous – Paleogene boundary (K – Pg), was studied in detail from the Zagros Basin (southwest Iran, central Tethys). In order to characterize the K – Pg transition, high resolution sampling was performed in the upper part of the Gurpi Formation. The studied interval consists of dark grey marly shales and marls with interbedded limestones. Based on calcareous nannofossils, the studied section is attributed to calcareous nannofossil zones CC26b to NP3 (latest Maastrichtian – early Paleogene). High relative abundances of the nannofossil species Micula staurophora (= Micula decussata) in the Maastrichtian part (CC26) might delineate cool surface water conditions, which are followed by an increase in abundance of Micula murus about 2 m below the K – Pg boundary. Reworked Cretaceous taxa were found at the K – Pg boundary and in the overlying Danian (NP 1–3). These findings hamper a reliable determination of the last occurrence of Cretaceous calcareous nannofossil taxa at the K – Pg boundary. The K – Pg boundary is located in the uppermost part of a positive carbon isotope excursion. Diversity and absolute abundances of calcareous nannofossils show a significant decrease at the K – Pg boundary. A bloom of the dinoflagellate cyst Cervisiella operculata (formerly Thoracosphaera operculata), which is indicating environmental stress, is recorded slightly below the boundary. Throughout the lowermost Danian (NP1), the assemblages are dominated by a bloom of small species like Neobiscutum romeinii, Neobiscutum parvulum, Futyania petalosa and small Cruciplacolithus primus. These taxa indicate stressful, and eutrophic surface water conditions throughout the initial recovery phase. The Dan-C2 and Lower C29n events, recorded in the lower Danian NP1 and lower NP2 biozones, are marked by negative carbon isotope excursions. High relative abundances of Prinsius dimorphosus followed by a Coccolithus pelagicus bloom in the full recovery phase (middle Danian, NP 3), are attributed to a short term cooling phase followed by warm surface water environments recorded along with the highest absolute abundance of calcareous nannofossils.

Primary deposition and early diagenetic effects on the high saturation accumulation of gas hydrate in a silt dominated reservoir in the Gulf of Mexico

On continental margins, high saturation gas hydrate systems (>60% pore volume) are common in canyon and channel environments within the gas hydrate stability zone, where reservoirs are dominated by coarse-grained, high porosity sand deposits. Recent studies, including the results presented here, suggest that rapidly deposited, silt-dominated channel-levee environments can also host high saturation gas hydrate accumulations. Here we present several sedimentological data sets, including sediment composition, biostratigraphic age from calcareous nannofossils, grain size, total organic carbon (TOC), C/N elemental ratio, δ13C-TOC, CaCO3, total sulfur (TS), and δ34S-TS from sediments collected with pressure cores from a gas hydrate rich, turbidite channel-levee system in the Gulf of Mexico during the 2017 UT-GOM2-1 Hydrate Pressure Coring Expedition. Our results indicate the reservoir is composed of three main lithofacies, which have distinct sediment grain size distributions (type A-silty clay to clayey silt, type B-clayey silt, and type C-sandy silt to silty sand) that are characteristic of variable turbidity current energy regimes within a Pleistocene (< 0.91 Ma) channel-levee environment. We document that the TOC in the sediments of the reservoir is terrestrial in origin and contained within the fine fraction of each lithofacies, while the CaCO3 fraction is composed of primarily reworked grains, including Cretaceous calcareous nannofossils, and part of the detrital load. The lack of biogenic grains within the finest grained sediment intervals throughout the reservoir suggests interevent hemipelagic sediments are not preserved, resulting in a reservoir sequence of silt dominated, stacked turbidites. We observe two zones of enhanced TS at the top and bottom of the reservoir that correspond with enriched bulk sediment δ34S, indicating stalled or slowly advancing paleo-sulfate-methane transition zone (SMTZ) positions likely driven by relative decreases in sedimentation rate. Despite these two diagenetic zones, the low abundance of diagenetic precipitates throughout the reservoir allowed the primary porosity to remain largely intact, thus better preserving primary porosity for subsequent pore-filling gas hydrate. In canyon, channel, and levee environments, early diagenesis may be regulated via sedimentation rates, where high rates result in rapid progression through the SMTZ and minimal diagenetic mineralization and low rates result in the stalling of the SMTZ, enhancing diagenetic mineralization. Here, we observed some enhanced pyritization to implicate potential sedimentation rate changes, but not enough to consume primary porosity, resulting in a high saturation gas hydrate reservoir. These results emphasize the important implications of sedimentary processes, sedimentation rates, and early diagenesis on the distribution of gas hydrate in marine sediments along continental margins.

Early Cretaceous calcareous nannofossils and foraminifera from the Huitrín Formation (La Tosca Member), Neuquén Basin, Argentina, and their biostratigraphic and paleoecological implications

The limestones, marlstones and gypsiferous shales of the La Tosca Member of the Huitrín Formation record the end of the last Pacific marine transgression in the Neuquén Basin. Since before this contribution, the presence of microfossils from this unit was restricted to unpublished reports or brief mentions; thus this study aims to present and illustrate for the first time the calcareous nannofossils and foraminifera found at Quebrada del Gastrópodo (S 36°32′14.00′′; W 69°36′47.30′′) and Ranquil 1 (S 36°36′36.80′′; W 69°45′46.50′′) sections, both located in southern Mendoza province, west-central Argentina. The recovered calcareous nannofossils were scarce and of low diversity, nevertheless, the presence of Diloma galiciense constrains the age of the La Tosca Member of the Huitrín Formation to the lower Barremian. In addition to nannofossils, a single sample of marlstones from Quebrada del Gastrópodo provided a relatively rare assemblage of foraminifera that includes calcareous benthic species distributed in three suborders (Spirillinina, Lagenina and Miliolina) corresponding to an inner-middle ramp paleoenvironment. The studied nannofossils and foraminifera indicate partial connections with an open marine environment. Furthermore, the recovered calcareous nannofossils at the La Tosca Member confirm a Barremian age for these deposits and the persistence of the Paleo-Pacific-Tethyan connection through a Tethys-Caribbean seaway (Hispanic Corridor) at this time.

Calcareous nannofossil biostratigraphy of the Late Cretaceous‒early Paleocene interval in the Zagros basin (southeastern Tethys), Iran

Calcareous nannofossil biostratigraphy reveals a continuous depositional record through the Upper Cretaceous‒Paleocene succession in the Zagros Basin; southwest Iran (southeastern part of the Neo-Tethys), especially through the Cretaceous‒Paleogene and the Danian‒Selandian boundaries. The upper part of the Gurpi Formation and the lower part of the Pabdeh Formation were investigated. Calcareous nannofossil assemblages from these formations are characterized by abundant, diverse and moderate- to well-preserved forms with Tethyan affinities. This study concentrates on two sections (the Gurpi and Kabir-Kuh sections) in the west and southwest of Iran in the Zagros Basin, which span biozones CC25c/UC20bTP to NP6/NTp10B in the Kabir-Kuh and CC25b/UC20aTP to NP5/NTp9 in the Gurpi section. Late Maastrichtian nannofossil abundance and diversity in the studied intervals is high with a sharp decrease slightly above the K/Pg boundary. The K/Pg boundary interval is marked by the FO of Biantholithus sparsus, an acme of the dinoflagellate cyst Thoracosphaera operculata, a notable decrease in Cretaceous calcareous nannofossil abundance and diversity, and the appearance of new Paleocene taxa. An increased abundance of Thoracosphaera is recorded similar to that in the El Kef (Global Stratotype Section and Point, GSSP, for the K/Pg boundary), Ellés (auxiliary section), Egypt, Atlantic Ocean and sections elsewhere in the world. Reworked Cretaceous calcareous nannofossils are recorded from the base of the Danian along with the new Paleocene species. The Danian‒Selandian boundary is marked by the appearance of Lithoptychius ulii, Lithoptychius pileatus and Lithoptychius janii at the base of NTp8C; this level is also marked by the second radiation of Fasciculithus. Azam Mahanipour [a_mahanipour@uk.ac.ir], Department of Geology, Faculty of Science, Shahid Bahonar University of Kerman, Kerman, Iran; Mohammad Parandavar [parandavar.m@gmail.com], Paleontological Research Department, Exploration Directorate of Oil and Gas, NIOC, Tehran; Mohamed Youssef [myousefgeology@gmail.com], Department of Geology, Faculty of Science, South Valley University, 83523 Qena, Egypt.

Cretaceous (Albian-Turonian) calcareous nannofossil biostratigraphy of the onshore Cauvery Basin, southeastern India

A suite of outcrop samples from the Cauvery Basin belonging to the mudrock-claystone dominated Karai Formation were analysed for nannofossil biostratigraphy in two newly measured sections at Karai and Garudamangalam. The age of the Karai Section is interpreted as early Albian to early Turonian, whereas the Garudamangalam Section is interpreted as late Albian to late Cenomanian. The Albian ‘BC’ zones of Bown et al. (1998) are applicable in both sections, whereas the Cenomanian and Turonian ‘UC’ zones of Burnett (1998), are only partially applicable, due to some problematic primary and secondary markers. The Albian-Cenomanian boundary appears to be continuous and is approximated in both sections using the FO of lower Cenomanian ammonites of the M. mantelli Zone. The Cenomanian-Turonian boundary interval is incomplete in the two sections, with a hiatus of ~0.66 myr, indicated by the absence of the upper Cenomanian Nannofossil Zone UC5. The nannoplankton assemblages are composed of broadly cosmopolitan taxa, despite the relatively high-latitude setting of SE India during the Albian (~45°S), which is reflected in the common occurrence of biogeographically bipolar taxa such as Repagulum parvidentatum and Seribiscutum primitivum. The palaeobiogeographic affinity of the nannoplankton, however, does not bear a distinct Austral stamp, as typical Austral taxa, such as Sollasites falklandensis and Zeugrhabdotus kerguelenensis are very rare in the studied sections. The early appearance of Crucibiscutum hayi in the lower Albian, and Gartnerago segmentatum in the upper Albian in the Cauvery Basin suggests that these two species may have originated in southern high latitudes before migrating to the northern Boreal regions. Four new calcareous nannofossil species, Calculites karaiensis, Loxolithus bicyclus, Manivitella fibrosa and Tranolithus simplex are described.

New biostratigraphic framework for the Triassic–Paleogene in the Neo-Tethys realm of southern Xizang (Tibet), China

Abstract Multifaceted biostratigraphic work on Triassic to Paleogene strata in southern Xizang (Tibet), western China, in the last decades allows a new, refined biochronostratigraphic framework in the Qinghai–Xizang plateau region. Synthesis of the latest biostratigraphic progress is carried out in this paper to build a new integrated biostratigraphic scheme comparable to the international Geological Time Scale. The scheme incorporates key fossils as many of each system, such as ammonites, calcareous nannofossils, conodonts and foraminifers. Other fossil groups that are helpful for stratigraphic division and interregional correlation are also contained. These include bivalves, miospores and radiolarians, some of which, e.g. radiolarians and miospores, not previously well explored, are now utilised for new zones. Biostratigraphic zones of this new integrative system, especially the Lower Triassic conodonts and ammonites, uppermost Triassic–Lower Jurassic ammonites, Upper Cretaceous planktonic foraminifers and calcareous nannofossils, correlate well with the international standards. The results are tabulated as four new comprehensive biostratigraphic charts, which, we hope, will provide a new and more reliable chronostratigraphic foundation for study of Neo-Tethys.

Calcareous nannofossil assemblages of the Late Cretaceous Fiqa Formation, north Oman

Abstract. This study presents the first detailed calcareous nannofossil assemblage data from the Late Cretaceous succession of the subsurface Aruma Basin, north Oman. The taxonomic description and documentation of assemblage composition are based on extensive quantitative analysis of ditch cuttings and side-wall samples from eight hydrocarbon exploration wells across north Oman. The samples studied from those wells cover the Coniacian to earliest Maastrichtian deep marine shales and marls of the subsurface Fiqa Formation. These fine-grained siliciclastic deposits often yield moderately to well-preserved nannofossil assemblages, especially in the Campanian intervals. Consequently, diverse assemblages have been recorded from the Fiqa Formation, with a total diversity of ∼200 species, including two new species, Staurolithites ormae sp. nov. and Chiastozygus fahudensis sp. nov., which are illustrated and described. Extensive imaging of this diversity is provided here, as are stratigraphic distributions of the main components from a key reference well in north Oman, W-4. Poorly described groups such as Staurolithites are closely investigated and their utility for stratigraphic applications is highlighted. Relative abundances of nannofossil taxa with strong palaeoenvironmental preferences have revealed new insights into the palaeo-productivity of the basin. High-fertility species like Discorhabdus ignotus, Biscutum constans and Zeugrhabdotus erectus show substantial variations in abundance throughout the Fiqa Formation, reflecting long-term shifts in the productivity conditions of the basin. This is supported by abundance patterns of Watznaueria barnesiae and Micula staurophora that show a broadly inverse correlation with the high-fertility species. The Fiqa Formation represents a key regional seal unit for the Cretaceous hydrocarbon reservoirs of Oman, as well as being a productive unit elsewhere in the Arabian Peninsula. Beyond the Aruma Basin of Oman, this study will provide a key reference point for future biostratigraphic or palaeoenvironmental analyses of the Late Cretaceous calcareous nannofossil assemblages across the Middle East and other southern Tethyan areas.

A story told by calcareous nannofossils—the timing and course of an Eocene meteorite impact in central Jordan

A circular structure, 5.5 km in diameter, in central eastern Jordan has been interpreted as a large meteorite impact structure. The age of the Waqf As Suwwan impact is poorly constrained. By examining calcareous nannofossils from the sediments exposed in this structure, an age model of the timing of the event has been obtained. A total of 81 smear slides from two cores (BH-1, BH-2) penetrating the sediments of the central structure were prepared in order to obtain a biostratigraphic age for the post-impact sediments. The calcareous nannofossils assign sediments below the breccias of the core BH-1 an age of late Campanian to late Maastrichtian and a mixture of late Maastrichtian to early Eocene ages in the breccia horizon, while core BH-2 is of early Maastrichtian to late Maastrichtian age. The upper part of the sediments, removed in from adjacent area, consists of breccia components. The presences of calcareous nannofossil marker assemblages suggest that these components were derived from two different sources: a Cretaceous and a Paleocene-Early Eocene one. The deposition of the breccia resulted from gravitational collapse of water-saturated sediments in two stages; the earlier of these was more intensive than the latter. The stratigraphic framework and the presence of reworked Cretaceous and Paleocene calcareous nannofossils within Paleogene nannofossil Zone NP12/NP13 suggests an early Eocene age for the impact. The upper part of the Cretaceous sediments was thermally altered by the impact causing partial or complete dissolution of the calcareous nannofossils. This caused overgrowth for the more resistant species, while others were dissolved.

Cretaceous calcareous nannofossils from Tanot #1, Jaisalmer Basin, Rajasthan, Western India: morphotaxonomy and biostratigraphy

The present paper deals with the record of rich and highly diversified calcareous nannofossil assemblage of Late Albian to Early Maastrichtian age from the subsurface sediments of Jaisalmer Basin, western India. The nannofossil assemblage include, 222 species belonging to 86 genera and 22 families including 6 nannolith families which are Braarudosphaeraceae, Ceratolithaceae, Lapideacassaceae, Microrhabdulaceae, Nannoconaceae, Polycyclolithaceae and one holococcolith family Calyptrosphaeraceae. An alpha–numeric zonal scheme has been proposed in the present study which will be useful for shallow shelf areas of low latitude. 17 Zones are assigned on the presence of last occurrence (LO) of zonal markers and 5 subzones of basal most zone (TA1) are demarcated on the basis of first occurrence (FO) of subzonal markers with due nomenclature procedures.

Physical behaviour of Cretaceous calcareous nannofossil ooze: Insight from flume studies of disaggregated chalk

AbstractGeomorphic features such as drifts, sediment waves and channels have been documented in the Upper Cretaceous of north‐west Europe. These features are interpreted to result from bottom currents and have been used to refine chalk depositional models and quantify palaeocirculation patterns. Chalk was first deposited as calcareous nannofossil ooze and geomorphic features are the result of sediment reworking after deposition. There is limited knowledge on the processes that govern nannofossil ooze mobility, thus forcing uncertainty onto numerical models based on sedimentological observations. This article provides an extensive view of the erosional and depositional behaviour of calcareous nannofossil ooze based on experimental work using annular flumes. A fundamental observation of this study is the significant decrease of nannofossil ooze mobility with decreasing bed porosity. Erosion characteristics, labelled as erosion types, vary with total bed porosity (φ) and applied shear stress (τ0). High‐porosity ooze (φ &gt;80%) is characterized by constant erosion rates (Em). At φ &lt;77%, however, erosion characteristics showed greater variance. Surface erosion was typically followed by transitional erosion (with asymptotically decreasing Em), and stages of erosion with constant, and exponential erosion rates. The estimated erosion thresholds (τc) vary from ca 0·05 to 0·08 Pa for the onset of surface erosion and up to ca 0·19 Pa for the onset of constant erosion (φ of 60 to 85%). Variability of deposition thresholds (τcd) from ca 0·04 to 0·13 Pa reflects the influence of variable suspended sediment concentration and τ0 on settling particle size due to the identified potential for chalk ooze aggregation and flocculation. Additionally, deposition thresholds seem to be affected by the size of eroded aggregates whose size correlates with bed porosity. Lastly, slow sediment transport without resuspension occurred in high‐porosity ooze as surface creep, forming low‐relief sedimentary features resembling ripples. This process represents a previously undescribed mode of fine‐grained nannofossil ooze transport.

Late Cretaceous Calcareous Nannofossil Biostratigraphy and Paleoecology in the Northwestern Desert, Egypt

The Upper Cretaceous succession of the northwestern desert in Egypt comprises two distinctive formations distributed throughout the studied subsurface succession. These formations are the Abu Roash and the Khoman from base to top, respectively. The examination of the studied samples resulted in the identification of thirty-six calcareous nannoplankton species belonging to twenty-three genera. Based on calcareous nannoplankton assemblages, the studied El-Noor-1 borehole succession was subdivided into seven calcareous nannoplankton biozones. These biozones were correlated with those recorded in Egypt and in other parts of the world. The analyses of calcareous nannofossils revealed the presence of hiatuses between the Late Santonian and Late Campanian. Abundance, diversity, preservation, fertility indices and temperature indices of the Late Cretaceous calcareous nannofossils were analyzed to determine the paleoecology of the studied succession. According to the calcareous nannoplankton content, the studied successions are subdivided into five ecozones. The environment of each ecozone is interpreted. The environmental indicators point to warmer climate oligotrophic environments for the Lucianorhabdus cayeuxii, Reinhardtites levis, Arkhangelskiella cymbiformisand Micula murus zones and cooler climate eutrophic environments for the Quadrum trifidum, Tranolithus orionatus and Lithraphidites quadratus zones.

BOREAL EARLY TURONIAN CALCAREOUS NANNOFOSSILS FROM NEARSHORE SETTINGS—IMPLICATIONS FOR PALEOECOLOGY

Abstract Nutrients and sea-surface temperature were likely the most important paleoecological parameters that controlled the composition of Late Cretaceous calcareous nannofossil assemblages. The extinct nannofossil taxa Biscutum spp., Tranolithus orionatus and Zeugrhabdotus spp. are commonly thought to have preferred nutrient-rich surface waters. In order to test this hypothesis, calcareous nannofossils from two lower Turonian nearshore sections (Bochum, Herne; northwest Germany) were studied. These sections, which reflect a mesotrophic and perhaps cool paleoenvironment, contain well-preserved and highly diverse calcareous nannofossil assemblages yielding 92 species. Based on the first occurrences of Eprolithus eptapetalus, Quadrum gartneri, and Eiffellithus eximius, both sections have been assigned an early Turonian age. The most common taxa are Watznaueria barnesiae, Zeugrhabdotus spp., Biscutum constans, Prediscosphaera cretacea, and Tranolithus orionatus. In combination with previously published data...

Nannostratigraphy and investigation of sedimentation conditions of the lower boundary and the upper boundary of the Aitamir Formation in the east and west Kopet Dagh, northeast of Iran

By attention to the stratigraphic value of calcareous nannoplanktons for the age determination of sedimentary beds, for the first time Late Cretaceous calcareous nannofossil taxa, their distributions and relative abundances were recorded from the lower and the upper boundary of Aitamir Formation located in northeast Iran. In the present study, biostratigraphy and paleoecological conditions were reconstructed. The Aitamir Formation comprises glauconitic sandstones and olive-green shales. In this work, samples were prepared with smear slides, and nannofossils of these boundaries are listed and figured. They were photographed under a light microscope. Based on nannoplanktons and as a result of biostratigraphic studies, the age of the lower boundary of the Aitamir Formation in the east Kopet Dagh is Early/Middle Turonian, the age of the lower boundary in the west Kopet Dagh is Late Turonian/Early Coniacian, the age of the upper boundary of the Aitamir Formation in the east Kopet Dagh is Late Santonian, and the age of the upper boundary of this Formation in the west Kopet Dagh is Early Campanian. Based on paleoecological interpretation, the Aitamir Formation was deposited in a shallow marine environment, at relatively low latitude. A deepening trend of the sedimentary basin is recognized passing from Aitamir Formation to the overlying Abderaz Formation while in the lower boundary from Sanganeh to Aitamir Formation depth decreased.

Nanofósiles Calcáreos y Bioestratigrafía del Cretácico del Sudeste de la Cuenca Austral, Patagonia, Argentina

Abstract CRETACEOUS CALCAREOUS NANNOFOSSILS AND BIOSTRATIGRAPHY OF SOUTHEASTERN AUSTRAL BASIN, PATAGONIA, ARGENTINA. This study presents the results of a quantitative analysis of the calcareous nannofossils recovered in five localities in the southeastern sector of the Austral Basin. On the basis of the assemblages recovered and its comparison with previous biozonations for the Austral Atlantic Ocean, it was possible to identify Valanginian—early Hauterivian, early Albian—middle Albian, late Albian—Cenomanian, Coniacian/Santonian—Campanian and late Maastrichtian assemblages. Two discontinuities evidenced by biostratigraphical hiatuses for the Cretaceous sequence were deduced: one for the late Hauterivian—Barremian and the other for at least the Turonian. The Early Cretaceous assemblages are comparable to those of the Falkland Plateau and they would be developed on an external platform having cold surface waters and high availability of nutrients. The Late Cretaceous assemblages are similar to those found ...

Two new Cretaceous calcareous nannofossils from SE Spain and Tunisia.

Two new Cretaceous calcareous nannofossils from SE Spain and Tunisia.

Cretaceous calcareous nannofossils from Pelotas Basin, Brazil: Biostratigraphic and paleoecological inferences

Abstract Biostratigraphic and paleoecological inferences are made on the distribution of calcareous nannofossils in three wells drilled in the Pelotas Basin, southern Brazil. The succession is composed mainly of siliciclastic rocks sampled by cutting and short core intervals. Eleven biozones were recognized, comprised the late Albian and the Maastrichtian. The frequency and relative abundance of some Cretaceous calcareous nannofossils species suggest a prevalence of warm-water conditions, with cooling events during the late Turonian, late Turonian/early Coniacian, late Coniacian and late Santonian/early Campanian.