Biozones Research Articles

Biostratigraphy and Paleoecology of the Sinjar Formation (Late Paleocene-Early Eocene) in the Dokan and Sinjar Areas, Iraq

Biostratigraphy of the Sinjar Formation is investigated in two sections (Dokan and Sinjar) from northeastern and northwestern Iraq, respectively. Two hundred samples from all the limestones and marl that form the main lithological components of the studied sections were collected. The studied limestones and marl are rich in microfossils. Through thin sections, we were able to identify thirty species of benthic foraminifera and fifteen species of other microfossils (coral, algae, mollusca, bryozoa, and echinoids) at Dokan section, and fifty-one species of benthic foraminifera and thirty species of other microfossils at Sinjar section. 3 biozones were distinguished from both sections 1-Biozone A: Kathina sp.- Lockhartia hunti Assemblage zone (SBZ 5) (Dokan section); (Kathina pemavuti - Lockhartia hunti Assemblage zone (Sinjar section), 2- Biozone B: Idalina sinjarica Total Range zone (SBZ 6-7) and 3-Biozone C: Alveolina globosa- Alveolina pasitisilata Concurrent Range Zone (SBZ8-10). These zones indicate the Late Paleocene –Early Eocene age of the Sinjar formation. The biostratigraphic correlations in the studied sections are based on benthic foraminiferal zonations. Showed the correlation comparison between the biostratigraphic zones of the commonly used benthic zonal scheme around the Late Paleocene -Early Eocene in and outside of Iraq. paleoecological studies suggest that the carbonate sedimentation of the Sinjar Formation thrived in 18-25oC, with mesophotic to oligophobic light, under an oligotrophic to mesotrophic middle ramp environment with normal marine to slightly saline and at water depths from 40 - 80 m. Stable isotopic carbon (δ13C) and oxygen (δ18O) data revealed generally hot conditions with high productivity during the deposition of the Sinjar Formation accompanied by an abrupt change in paleoenvironmental conditions across the Paleocene-Eocene contact.

Biostratigraphy and Microfacies of the Mauddud Formation (Late Albian – Early Cenomanian) in Musaiyib Well No.1, Central Iraq

Upper Albian and Lower Cenomanian biostratigraphy and microfacies types of the Mauddud Formation from Musaiyib well No.1, Central Iraq are described and examined, which consists of thick to medium bedded limestone, marly limestone rich in argillaceous material, green shale, and dolomitic limestone beds. Thirty-six species from twenty-two genera of benthic foraminifera in addition to calcareous algae, coral, bivalves, gastropods, rudist fragments, brachiopods, bryozoan, and echinoid fragments are recognized from the Mauddud Formation of the studied well. On the basis of the recognized benthic foraminifera three biozones were determined: Mesorbitolina texana - Orbitolina qatarica Concurrent Range zone- Orbitolina sefini-Total R. Zone and Orbtolina concava Total R. Zone. Both suggest the Late Albian – Early Cenomanian age. The results of this study are compared with the work of others inside and outside Iraq. Based on the petrographical analyses, four major microfacies (Mudstone, wackestone, wackestone to packstone, and packstone), and nine sub-microfacies were identified. The Mauddud Formation was formed in a marine environment that was composed of the following three sub-environments: the inner ramp and the middle to the outer ramp.

Paleoclimate and Paleoenvironment Reconstructions from Middle Eocene Successions at Beni-Suef, Egypt: Foraminiferal Assemblages and Geochemical Approaches

The Eocene deposits of Egypt provide a wide variety of shallow marine facies and fossil assemblages, allowing paleoenvironmental reconstructions in this warmhouse climate interval. Forty-three rock samples have been collected from two middle Eocene sections, exposed at southeast Beni-Suef area in northern Egypt. The studied outcrops are lithologicsally subdivided into two rock units named from base to top as follows: (1) the Qarara Formation (Lutetian) and (2) the El Fashn Formation (Bartonian). Most investigated rock samples showed richness in benthic foraminiferal assemblages and only rare occurrences of index planktonic foraminifera. They yielded 160 foraminifera species which belong to 4 suborders, 19 superfamilies, 34 families, and 59 genera. The stratigraphic distribution of the identified species allowed us to define four local benthic bio-ecozones: (1) Bolivina carinata Lowest Occurrence Zone (Lutetian), (2) Cibicides mabahethi/Cancris auriculus primitivus Concurrent-Range Zone, (3) Nonion scaphum Lowest Occurrence Zone, and (4) Brizalina cookei/Nonionella insecta Concurrent-Range Zone (Bartonian). These biozones are described and discussed in detail and correlated to stratigraphic equivalents in Egypt. The rareness of index planktonic foraminifera through the studied sections does not allow a precise biostratigraphic and chronostratigraphic correlation. The shale samples show low TOC values, which may be related to low productivity, high sediment influx, and/or prevailing oxic conditions. Bulk rock geochemistry, consistent with the benthic foraminifera ecological preferences, indicated that the studied sections were deposited in moderate to high oxygen levels and warm climatic conditions in a typical shelf marine setting. The identified species showed strong similarities with nearby southern Tethys areas, reflecting migration via the trans-Sahara seaway, and minor similarities with those identified from the northwestern Tethys and the North Atlantic province attributed to the change in the environmental and climatic conditions, such as cooler, latitudinal zoned climatic conditions along the northwestern Tethys, which was unsuitable for their biological demands. The warming trend identified from Lutetian to Bartonian intervals corresponds to the onset of the Middle Eocene Climatic Optimum (MECO).

Biostratigraphyand Paleoenvironments of Benthic Foraminifera From Lower Part of the Damlouk Member, Western Desert, Iraq

Age and paleoenvironment of part of the Damlouk Member, Ratga Formation from a surface section in the Iraqi Western Desert are investigated. Twenty-nine species of Larger Benthic Foraminifera (LBF) belonging to 13 genera are recognized from the studied section. The LBF assemblage is dominated by the following groups, Nummulites, Alveolina, Rotalia, and Lockhartia. Two species of corals with fragments of bryozoan, red algae and mollusca had also been identified. The palaeontological investigation aimed at identification of LBF assemblages to evaluate their abundance and distribution with respect to sedimentary environment and to determine its age. Based on the recognized Larger Benthic Foraminifera of the studied part of the Damlouk Member, it is subdivided into two biozones: Nummulites gizhensis -Nummulites moculatus Assemblage Zone and Assilina spira- Lokharatia hunti Concurrent Range Zone. Both biozones suggest a Middle - Late Lutetian to Early Bartonian age. The LBF are concentrated around shallow marine carbonate bank-controlled limestone unit and the associated ramp facies. Two basic environmentally significant assemblages were recognized based on the vertical distribution and the relative abundance of the LBF. The Nummulite bank assemblage is characterized by lensoidal and robust Nummulites of different species. The other group is the fore-bank assemblage which shows relatively higher diversity, including flat LBF such as: Nummulite, Assilina, Lockhartia, Heterostigina and Operculina. The third back-bank assemblage is not well presented in the studied section, shows the limited distribution, and is considered part of the back-bank lagoon facies. This group is characterized by the occurrence of Alveolina and other imperforated forams. The recognized assemblages represent the transition from inner to middle ramp facies with a water depth not exceeding 50m in relatively low energy conditions.

Dinoflagellate cyst biostratigraphy of the Bathonian, Callovian, and the Upper Jurassic in North Bulgaria

Forty-four selected organic-walled dinoflagellate cyst species have been used for biozonation of the Bathonian, Callovian, and the Upper Jurassic in North Bulgaria. The dinocysts were collected from 49 borehole sections and two exposures. The following dinocyst zones are herein introduced and described: Lithodinium valensii–Gongylodinium erymnoteichos Concurrent-range Zone (lower–middle Bathonian); Ellipsoidictyon reticulatum Assemblage Zone (upper Bathonian–lower Callovian); Dingodinium harsveldtii Taxon-range Zone (middle–upper Callovian); Lambodinium absidatum Assemblage Zone (lower Oxfordian); Scriniodinium dictyotum papillatum–Caddasphaera halosa Concurrent-range Zone (middle–upper Oxfordian); Rhyncodiniopsis gongylos Assemblage Zone (lower Kimmeridgian); Systematophora varispinosa–Gonyaulacysta? crassicornuta Concurrent-range Zone (middle–upper Kimmeridgian); Edmontodinium polyplacophorum Assemblage Zone (lower Tithonian); and Leptodinium? plagatum–Prolixosphaeridium perforospineum Concurrent-range Zone (middle–upper Tithonian). Some of the zones were partly or completely subdivided in subzones. The dinocyst zones and subzones were correlated with the Bulgarian ammonite and calpionellid zones and subzones.

Late Cretaceous Diatoms (Bacillariophyta) from the Teshio-Nakagawa Area, Hokkaido, Northern Japan: Significance for Their Origin and Biostratigraphy

Well-preserved marine diatoms are documented for the first time from authigenic carbonate rocks induced by cold methane (hydrocarbon) seepage in the Omagari Formation (latest Santonian to earliest Campanian in age, Late Cretaceous Epoch; around 83.6 Ma) of the upper part of the Yezo Group in the Teshio-Nakagawa area, northern Hokkaido (northern Japan). The diatom flora is rich in species of Hemiaulus and Triceratium, associated with a few other extinct diatom genera. An araphid genus (Sceptroneis) was also observed; this is one of the earliest fossil records of “pennate” (Bacillariophyceae) diatoms. Although valve ultrastructures have been mostly dissolved, the preservation of these diatoms is much better than that in the few previous reports of Cretaceous siliceous photosynthetic organisms from Japan and adjacent regions in the northwestern Pacific Ocean. Because of their common generic composition in the mid- to high-latitude regions in both hemispheres, diatoms are suggested to have experienced a global radiation by early Campanian time. Thus, our diatom records provide insights into the Late Cretaceous floral adaptive radiation around the northwestern Pacific margin, where the radiation history of diatoms is yet unclear. As Gladius antiquus was confirmed but Basilicostephanus species were absent from the present material, the flora from the Teshio-Nakagawa area is tentatively regarded as belonging to the G. antiquus Concurrent Range Zone, an interval extending from an undetermined Late Cretaceous Epoch to the latest Santonian Age. However, this floral correlation is inaccurate because our materials are latest Santonian to earliest Campanian in age, as dated by the molluscan (ammonoids and inoceramids) biostratigraphy. Hence, further research is required to clarify the sensitivity of different chronological proxies and the stratigraphic ranges of age-diagnostic diatoms in different geographic provinces.

Foraminiferal patterns and palaeoenvironmental inferences from DEL-1 well, offshore Niger Delta

The Miocene Epoch (23.3–5.3 Ma) represents a remarkable time in the Earth's geological history with significant palaeoclimatic and palaeoenvironmental relevance. In this study, microfossils recovered from the DEL-1 (4600–9460 ft) well in the western Detachment Fold Zone, offshore Niger Delta in the Gulf of Guinea were used to construe the age, palaeoenvironment, and palaeoecology of the penetrated successions. Standard foraminiferal analyses were carried out on one hundred and forty-eight (148) ditch cuttings retrieved from the studied interval following standard laboratory and identification procedures. Globigerinatella spp./Catapsydrax dissimilis Concurrent-range Zone (M3/N6), Fohsella birnageae Lowest Occurrence Subzone (M4b/N7), and Orbulina suturalis Lowest Occurrence Zone (M6/N9) of early to middle Miocene were identified. An overall progradational coastal and shelfal facies dominated by argillaceous and arenaceous sediment in the early and middle Miocene is construed, whereas interpreted palaeoenvironment of deposition indicates fluctuation between coastal deltaic, inner, middle, and outer neritic system with some fluvio-marine incursions between 4600 and 9460 ft intervals. The identified early Miocene succession is characterised by significantly high ecological parameters (diversity, evenness, richness), low salinity, and relatively high occurrence of foraminifera faunas compared to the middle Miocene. The relationships between the foraminiferal faunas and environmental factors suggest the local ecologic niche exhibits environmental heterogeneity that might have influenced even distribution of different microhabitat faunal preferences. Whereas the contributing influence of arenaceous sediment on the general dearth of microfossils in the upper section of the well cannot be neglected, the foraminiferal signatures reflect the ubiquitous middle Miocene carbonate crash event, and thus confirm its occurrence in the Gulf of Guinea.

UPPER KIMMERIDGIAN AND TITHONIAN AMMONITES FROM THE TUNISIAN "DORSALE" (NE TUNISIA): UPDATED BIOSTRATIGRAPHY FROM THE JEBEL OUST

In the context of updating biostratigraphic analysis in the Upper Kimmeridgian-lowermost Berriasian from the whole of the Tunisian Dorsale (NE Tunisia), new results obtained from the Jebel Oust reference section are presented. The bed-by-bed-sampling of a rather rich ammonite fauna gathered in the two most favourable profiles in the area allowed to propose, for the first time, a biozonation for Upper Kimmeridgian to Tithonian limestones. Calpionellids relayed or completed ammonite assemblages, and were also useful for biostratigraphy in beds close to the Jurassic-Cretaceous boundary. The composition of ammonite assemblages, as well as the known ranges for genera and species, is in accordance with the available information from epioceanic areas in West-Mediterranean Tethys. The recognized biozones fit the standard proposal given by Groupe Francais D'Etude du Jurassique in 1997. Age-interpretation for turbiditic horizons in the Jebel Oust is made for the first time. In spite of some limitations, the biostratigraphic results obtained in Jebel Oust sections provide a valuable tool for potential correlations with poorly known sections in northern Tunisia, as well as with other Tethyan areas.

Stratigraphy of the Oligocene-Early Miocene successions, Sangaw area, Kurdistan Region, NE- Iraq

Lithostratigraphy and biostratigraphy of the Darzila section from Low Folded Zone, Ashdagh Mountain, Sangaw area, Kurdistan Region, Northeastern Iraq, is investigated. Forty-three species from twenty-nine genera of large benthic foraminifera (LBF) in addition to non-foraminifera fossils such as echinoid fragments, bryozoan, red algae, green algae, bivalve, and coral are recognized from the studied section. Based on the recognized large benthic foraminifera, it is subdivided into six biozones: Nummulites vascus - Nummulites fichteli Assemblage Zone, Eulepidina dilatata - Nephrolepidina marginata Concurrent-Range Zone, Praerhapydionina delicata- Peneroplis evolutus- Concurrent Range Zone, Meandrospina anahensis - Austrotrillin asmariensis Interval Zone, Ammonia beccarii –Austrotrillina howchini Assemblage Zone, and Dendritina rangi- Rotalia viennoti Assemblage Zone. Both suggest an Oligocene to Early Miocene age. Each of these biozones represents certain lithostratigraphic units, which are Sheikh Alas, Baba, Bajwan, Anah, Jeribe, and Fatha formations. The recognized biozones were correlated with comparatively well-known biozones from other parts of the tethys region which showed a good comparison between the biostratigraphic zones established in this study with other studies.

Planktonic foraminiferal biostratigraphy of the Limboto Limestone, Gorontalo Province, Indonesia

The limestone research within the Limboto Basin of Gorontalo Province becomes a new challenge, particularly for the study of planktonic foraminiferal biostratigraphy. This study uses the data obtained from the measured section in the north-western part of Limboto Lake. The purpose of this study is to determine the planktonic foraminiferal biozonation and the relative age of Limboto limestones. The analyzed planktonic foraminiferal fossils can be classified as well to moderately preserved of various species, in the context of abundance, categorized as frequent to abundant. There are three recognized planktonic foraminiferal biozones, i.e., two biozones for Miocene age (M13b and M14) and one biozone for Pliocene age (PL1). The Miocene biozones are named as Globorotalia plesiotumida partial range zone (M13b) and Pulleniatina primalis-Globoquadrina dehiscens concurrent range zone (M14), while the name of Pliocene biozone is Globorotalia acostaensis partial range zone (PL1). The results of this study can be a reference to propose an age of Limboto Limestone Formation. Identification and demarcation of the Limboto Limestone Formation are based on the time interval and relative age of the formation based on planktonic foraminifera.

The palaeontology and dating of the ‘Weybourne Crag’, an important marker horizon in the Early Pleistocene of the southern North Sea basin

In the North Sea basin the marine bivalve Macoma balthica first appears within the Early Pleistocene ‘Weybourne Crag’, which forms an important biostratigraphical datum. Here we review the fossil assemblages from sites of this age, prompted by new discoveries from Sidestrand, Norfolk, UK. The molluscan assemblages from this horizon are dominated by intertidal species with some colder/deeper water taxa and a few temperate non-marine species. A high boreal/low arctic marine environment with reduced salinities is indicated. An extensive assemblage of small mammals dominated by voles includes two species (Mimomys hordijki and Ungaromys dehmi) previously unknown from the British Pleistocene. The assemblage can be assigned to Tesakov’s Mammal Biozone MNR1 (=MN17, Middle Villafranchian), which according to current estimates corresponds to a date of ∼2.2-2.1 Ma (MIS 84-79). It matches another assemblage from -61 m to -65 m in the Zuurland-2 borehole in The Netherlands, and is similar to that from the Dutch Tiglian type site at Tegelen, although this has more temperate elements. A late Tiglian age is consistent with the co-occurrence of the marine bivalves Macoma balthica, Mya arenaria and the freshwater gastropod Viviparus glacialis in the Zuurland-2 borehole and in a North Sea borehole (BGS 52-02-472). A Macoma balthica – Mya arenaria Concurrent Range Zone is defined for this assemblage, which can be traced across the North Sea basin. Amino acid dating provides strong independent support for these correlations and indicates that the Baventian cold stage post-dates the Bramertonian (Norwich Crag). It also confirms that Early Pleistocene molluscan assemblages with M. balthica are younger than those without it. The correlation of this marine marker horizon with Mammal Biozone MNR1 provides a secure link between continental and marine sequences during the Early Pleistocene. It also provides a basis for dating events in the pre-glacial fluvial drainage history and linking it to the East European mammal zonation.

Planktonic foraminiferal biostratigraphy and paleoenvironments at the Santonian-Campanian boundary of Northern Tunisia

The Santonian-Campanian boundary in Northern Tunisia has been studied in Oued el Khannga section, based on biostratigraphic and paleoecological analysis. The detailed biostratigraphic analysis allows us to define the stratigraphic distribution of diverse planktonic foraminifera and to establish a continuous biozonation. Sixty-six planktonic foraminiferal species belonging to 13 genera have been identified and two Tethyan planktonic foraminiferal zones have been organized, indicating the upper Santonian - lower Campanian age. These zones are: Dicarinella asymetrica (Total Range Zone) and Globotruncanita elevata/Globotruncana arca (Concurrent range zone). A major turn over event was recorded in this interval including the extinction of several species characterized by complex morphotypes with a double keel such as the genera of Dicarinella, Marginotruncana. In fact, the extinction of the index species D. asymetrica is the most important event which defines the Santonian-Campanian boundary. Many representative species of the genera Globotruncanita and Globotruncana occurred, for the first time, in the uppermost of the Santonian and thrived close to the Santonian-Campanian boundary. In addition some surviving species with a simple morphotype, which are considered like opportunistic taxa, crossed the boundary. This various responses of planktonic foraminifera and the fluctuation in diversity and in the number of species may be related to an increase in temperature and a deep outer shelf upper bathyal environment deposit.

Benthic foraminiferal communities of the Eocene platform, north Eastern Desert, Egypt

The Eocene successions on Beni Suef – El Zaafarana road at north Eastern Desert of Egypt have been examined for their benthic foraminiferal contents from three rock units: El Fashn, Beni Suef and Maadi formations. The studied material of this work allowed us to identify 153 benthic foraminiferal species. The Eocene age of the studied successions is defined by the co-occurrence of the planktonic and benthic foraminiferal species. The studied succession could be subdivided into five benthic foraminifera biozones from the late Middle to Late Eocene age. These zones are Palmula ansaryi Range Zone (late Middle Eocene), Bulimina jacksonensis - Uvigerina mediterranea Concurrent-Range Zone, Cancris auricula Lowest Occurrence Zone, Pararotalia audouini Concurrent-Range Zone and Pyrgo elongata Concurrent-Range Zone (Late Eocene). The identified benthic foraminiferal species were analyzed using R- and Q-mode cluster analysis in order to better understand the linkage between the benthic foraminiferal assemblages and paleoenvironmental conditions. The cluster analysis revealed that the benthic foraminifera could be grouped into 7 assemblages and 7 biofacies in the measured sections. The recorded benthic foraminiferal biofacies suggest that the environments are deep outer ramp setting with meso-to moderately eutrophic conditions, and minimum to moderate oxygenation level on El Fashn Formation. The environment of Beni Suef and Maadi formations is inner to middle ramp with high oxygen level and oligotrophic conditions.

MIDDLE JURASSIC FLORA FROM THE HOJEDK FORMATION OF TABAS, CENTRAL EAST IRAN: BIOSTRATIGRAPHY AND PALAEOCLIMATE IMPLICATIONS

The Middle Jurassic deposits of the Shemshak Group and Hojedk Formation are widespread in North, Central, and Central East Iran. In this paper, the Hojedk Formation in South Kouchekali, southwestern Tabas city, east-central Iran was studied for palaeobotany and stratigraphy. This formation contains well preserved plant macrofossils belonging to 43 species assigned to 24 genera of various orders such as Equisetales, Filicales, Bennettitales, Cycadales, Caytoniales, Ginkgoales and Pinales. One biozone and four subzones are recognized. The lower and the upper boundaries of this assemblage biozone are identified by the first and the last observed occurrences of Coniopteris hymenophylloides (Brongniart) Seward 1900 and Klukia exilis (Phillips) Raciborski 1890, respectively. According to the occurrences of these index species and Ptilophyllum harrisianum Kilpper 1968 and Nilssonia macrophylla Jacob & Shukla 1955, an early Middle Jurassic (Aalenian-Bajocian) age is considered for this assemblage biozone. Moreover, a comparative biostratigraphy for the Middle Jurassic of Iran is suggested. As a result, the Coniopteris hymenophylloides-Klukia exilis Assemblage biozone is proposed as a biozone widespread through the whole Iranian Plate. On the basis of the relative abundance of Filicales, Pinales, Cycadales, and Equisetales and of the high diversity and abundance of macrophyllous cycadophytes (eight species), a humid sub-tropical climate is suggested for this locality. In addition, floral gradient, correspondence analysis and similarity index were considered. Therefore, it is confirmed that a uniform palaeoclimate and vegetation cover occurred in Iran during the Middle Jurassic and that Iran was located within Vakhrameev's Euro-Sinian Region.

Upper Ordovician conodont biostratigraphy and revised lithostratigraphy and geological map, Akpatok Island, Ungava Bay, Nunavut

Stratigraphic units exposed on Akpatok Island, Ungava Bay, Nunavut, were previously recognized as Boas River and Akpatok formations; their biostratigraphic ages and correlations, in particular the stratigraphic position and age of the organic rich “Boas River” Formation, were largely based on limited data. New detailed field observations have recognized three stratigraphic units, namely the Amadjuak, Akpatok, and Foster Bay formations, in which extensive microfossil sampling recovered over 22 000 conodont elements from 66 productive samples from both outcrops and rubble at over 20 localities in four areas. Four Upper Ordovician conodont zones and one unzoned interval are established for the three redefined formations: Belodina confluens and Oulodus velicuspis Interval zones are confined to the exposed Amadjuak Formation and correlated to Edenian and Maysvillian; Amorphognathus ordovicicus – Plegagnathus dartoni Concurrent-range Zone occurs with the Akpatok Formation and correlated to lower Richmondian; Rhipidognathus symmetricus Taxon-range Zone is retained in the Foster Bay Formation and correlated to upper Richmondian; and an “Unzoned Interval” is defined between the last two zones in the lower Foster Bay Formation. The conodont Amorphognathus ordovicicus occurs in both Akpatok and lower Foster Bay formations, and it is also recovered from the bituminous, argillaceous limestone rubble, based on which the stratigraphic position of the previously named “Boas River” Formation is most likely positioned within the lower Foster Bay Formation. The biostratigraphy and lithostratigraphy are combined with geographic information systems (GIS) to establish the thicknesses of the three formations and revise the geologic map of the island.

Growth of the Ballena fan delta on the Gulf of California (Mexico) at the close of the Pliocene Warm Period

Tectonic uplift on the shores of Bahia San Rafael in Mexico’s upper Gulf of California exposed a Pliocene delta system that covers a map area of 4 km2. Subaerial dissection by arroyos entrenched during Pleistocene and post-Pleistocene time carved cross-sectional slices through the delta, showing its dominant construction resulting from massive transfers of siliciclastic sand derived from the breakdown of igneous rocks (tonolite) in a well-defined terrestrial basin. Restoration of the sedimentary structure by elimination of Pleistocene arroyos and linkage of former topographic lines reveals a triangular shape recognizable as a classic fan delta. The complex includes an alluvial fan that emerges from a small opening in the landscape connected to a semi-circular, high-walled basin with a map area of 2.6 km2. Through a strictly longitudinal sequence, estimates of the excavated basin’s volume and the delta’s sedimentary volume were conducted as a mass-balance exercise that yielded a strong match. The lower central part of the delta features dense concentrations of sand dollars (Dendraster granti) that form a distinct limestone coquina not previously recognized elsewhere in Baja California. Through the regional biostratigraphy of concurrent range zones supplemented by absolute age dates from inter-bedded volcanics in other places, a later Pliocene age around 3–2 Ma is suggested for the sand dollars and the delta complex in which they are buried. Such timing corresponds to the close of the Pliocene Warm Period, during which a persistent El Nino climate brought tropical storms and excessive rainfall to the upper Gulf of California. Comparisons with other Pliocene deltas throughout the Gulf of California underscore the unique status of the complex named the Ballena fan delta.

The stratigraphic architecture and depositional environments of non-marine carbonates from barremian-aptian pre-salt strata of the Brazilian continental margin

The stratigraphic architecture and depositional environments of non-marine carbonates from barremian-aptian pre-salt strata of the Brazilian continental margin

CONODONTS FROM THE WA’ERGANG SECTION, CHINA, A POTENTIAL GSSP FOR THE UPPERMOST STAGE OF THE CAMBRIAN

Furongian (upper Cambrian) conodonts from the Shenjiawan Formation, Wa’ergang section, Taoyuan County, Hunan Province, South China are described. The Wa’ergang section has been proposed as a potential GSSP for the base of the uppermost stage of the Cambrian System, at the first appearance of the agnostoid trilobite Lotagnostus americanus . The Shenjiawan Formation consists of limestone with intercalations of marlstone and shale. The conodont yielding is low and the preservation is moderate. The conodont fauna includes proto-, para- and euconodonts. Conodont taxa characteristic of North China, South China and Korea occur together with cosmopolitan taxa. The biostratigraphic distribution of conodonts is directly correlated with the agnostoid trilobite biozones, with the base of the Proconodontus posterocostatus Zone very close to the base of the Lotagnostus americanus trilobite Zone.

STRONTIUM ISOTOPE STRATIGRAPHY AS A CONTRIBUTION FOR DATING MIOCENE SHELF CARBONATES (S. MARINO FM., NORTHERN APENNINES)

This paper provides new data on strontium isotope stratigraphy applied to the Miocene heterozoan shelfal carbonates of the S. Marino Fm. (Marecchia Valley, northern Apennines). Sr isotopic analyses were carried out on oyster shells, bryozoans and bulk-rocks from the lower-middle carbonate portion of the section. In the upper part of the succession that shows evidence of detrital influx, 87 Sr/ 86 Sr analyses were performed on foraminifera tests, separating planktonic and benthic forms. Results were compared with calcareous nannofossil biostratigraphic data from the same levels, in order to test the reliability of Sr dating in mixed carbonate-siliciclastic sediments. Mean ages obtained from oysters range between 16.9 Ma and 16.3 Ma. Very similar results are obtained using bryozoans (16.5 Ma to 16.1 Ma) and bulk-rocks (16.8 Ma to 16.2 Ma). These results allow to better constrain the age of the massive carbonate shelf, referable to the upper Burdigalian. In the upper carbonate-siliciclastic portion of the shelf, numerical ages obtained from planktonic and benthic foraminifera are in good agreement with nannofossil biozones (mean ages respectively around 15.3 Ma and 14.5 Ma) although they display wide confidence intervals. These wide age uncertainties depend on the slow rate of change of marine 87 Sr/ 86 Sr through time that characterizes the interval between ~15 and ~13.5 Ma.

Lithostratigraphy and Microbiostratigraphy of Gadvan and Darian Formations in South Semirom, East of Zagros Basin, South-Central Iran

This research focuses on the lithostratigraphy and microbiostratigraphy implications of the Gadvan and Darian Formations in a part of Zagros sedimentary basin. The Gadvan and Darian Formations in the study area with a thick-ness of 520 meters consist of gray to green marls and shales, dark-grey limestones and Orbitolina limestone with Late Barremian-Aptian age. According to the lithostratigraphic investigations, the Gadvan and Darian Formations in the study area are subdivided into eleven units. The upper boundary of the Darian Formation with the Kazhdomi Formation and the lower boundary of Gadvan Formation with the Fahliyan Formation are in the form of disconformity. Micropaleontological study of the Gadvan and Dariyan Formations has led to the recognition 20 families, 45 genera, 35 species of benthic foraminifera, 2 genera of pelagic foraminifera and 8 genera and species of the calcareous algae. In this research, three biozones have been recognized by distribution of the larger benthic foraminifera in the Gadvan and Dariyan Formations of the South Semirom, including: 1) Palorbitolina lenticularis-Choffatella decipiens Concurrent Range Zone (middle Late Barremian to early Early Aptian); 2) Praeorbitolina cormyi-Orbitolina (Mesorbitolina) lotzei Assemblage Zone (late Early Aptian); 3): Orbitolina (Mesorbitolina) texanae-Orbitolina (Mesorbitolina) parva Assemblage Zone (Middle to Late Aptian). Based on the identified foraminifera, the age of the Gadvan and Darian Formations in the study area is assigned to Late Barremian to Aptian.