Fossil Content Research Articles

Latest Oligocene to middle Miocene low-latitude calcareous nannofossil biostratigraphy and paleoenvironmental interpretations of stratigraphic well 4, Sinú-San Jacinto onshore basin, northwest Colombia

Calcareous nannofossils are one of the main fossil groups used in the petroleum industry to determine the relative age and correlation of lithofacies identified in gas and oil wells. A limited number of biostratigraphic zonation schemes based on nanoplankton and paleoceanographic reconstructions have been suggested to onshore Colombian Caribbean. Most of them are compiled in several publications for the northern Colombian units (Mejía-Molina et al., 2008, 2010). In this study, a medium to high-resolution biostratigraphy study was carried out on one of the best-known Neogene sedimentary successions in the Sinú-San Jacinto onshore Basin, where the Stratigraphic Well 4 (SW4) was drilled by Ecopetrol, the Colombian state-run oil company. The nannoplankton biostratigraphic zonation proposed here constitutes the first calcareous nanoplankton research to construct a biochronologic scheme for the Neogene of northern Colombia, which has direct applications for oil exploration, global energy matrix and the transition to clean energy in the onshore areas of the Sinú-San Jacinto domain. The section studied has a thickness of ∼269 m and comprises mainly a very thick succession of claystone and mudstone with occasional intercalations of silty sandstones corresponding to the El Carmen Formation. The studied interval is assigned to the nannofossils Zones NP25 (CP19) to NN4 (CN3) of Martini (1971) and Okada and Bukry (1980), spanning from the latest Oligocene (latest Chattian) to middle Miocene (early Langhian), approximately 24 Ma to 15 Ma. Intervals without fossil content were identified in the record and could constitute hiatuses, but the nannofloral events, which define the limits of the biozones, can be identified. Global and regional climatic changes which occurred in the Caribbean region at those times are reflected in important changes in the fossil assemblages and abundance pattern of nanoplankton. These could indicate variability in environmental conditions linked to temperature and increased nutrients within the nannofossil communities in this part of the San Jacinto folded belt (SJFB), northwest Colombia. Middle Miocene Climate Optimum (MMCO) episodes of “blooming” intervals of Sphenolithus were identified, accompanied with a drastic reduction in total nannofossil abundance and CaCO3 content. Since the Caribbean geology is framed in a very complex scenario, the data acquired and presented in this research has a potential application to improve the current stratigraphy in the area, targeted to hydrocarbon exploration and studies related to the global energy matrix and the transition to clean energy. It also strengthens the paleoceanographic reconstructions based on these organisms at low latitudes.

First record of Pridolian graptolites from South America: Biostratigraphic and paleogeographic remarks

Graptolites were planktonic organisms that constitute one of the essential biostratigraphic tools used in Paleozoic successions worldwide. Notably, Pridolian (upper Silurian) graptolites have been globally recognized in several geological units, but completely absent from South American sections until now. This study introduces the first Pridolian graptolite assemblage in this subcontinent. The Rinconada Formation, from the Eastern Precordillera of San Juan Province, Argentina, has an abundant fossil content that includes: graptolites, brachiopods, bivalves, trilobites, corals, plant remains, and microfossils. Two graptolite taxa have been identified and described, including Skalograptus parultimus (Jaeger) and cf. Enigmagraptus. Both genera are mentioned for the first time in South America. As a result, the S. parultimus Biozone is recorded from the upper outcropping levels of the Rinconada Formation at its eponymous section, indicating an early Pridolian age. This discovery represents the first mention of Pridolian graptolites for South America, and increases the knowledge about the graptolite content of the studied formation as well. In addition, the assemblage might represent the faunal recovery interval after the Kozlowskii-Lau Event, a globally recorded episode of biotic crisis. The co-occurrence of graptolites and plant remains within the same stratigraphic levels in the Rinconada Formation represents the first and oldest record in western Argentina. Finally, the age of the Rinconada Formation is reviewed, and a local, regional, and global correlation is proposed with several Pridolian sections around the globe.

New evidence for Early Miocene palaeoenvironmental changes in the North Croatian Basin: Insights implicated by microfossil assemblages

An integrated stratigraphic study has been performed of the Lower Miocene deposits of the Poljanska and Mala sections (North Croatian Basin), coupled with 40Ar/39Ar dating, geochemical and mineralogical study of tuffitic and silty sand beds. The sedimentary record evidences deposition influenced by volcaniclastic input. The presence of marine, brackish and non–marine microfossils indicates complex palaeoenvironment, palaeoecology, and palaeobiogeography. Four different units were recognized based on their fossil content and sedimentological data. At the base of the Poljanska section (Unit P1), tuffitic sediments bear common endemic brackish, and rare marine to freshwater and terrestrial microfossils. Radiometric 40Ar/39Ar dating obtained on volcanic glass shards from this layer provided an age of 22.2 ± 1.9 Ma correlating with the earliest Early Miocene and indicating the existence of older volcanic activity in the NCB pro tempore. The succession transitions into the brackish-water lacustrine environments (Unit P2). This unit has two presumed different climatic events: a maximum temperature event in the lower part of the interval and one interruption with lower temperatures recognized in the upper part of the interval. The co-occurrence of limnic and marine species in the uppermost part of the investigated sediments (Unit P3) indicates a marine inflow into the coastal lake. It marks the beginning of a salina-type lake formation in Poljanska. In the Mala section (Unit M1), biostratigraphically dated to the NN4 Zone, a transgressive sequence is documented through the presence of marine calcareous nannoplankton, planktonic and benthic foraminifera, and ostracods.

Sedimentology and palaeoenvironmental reconstruction of the late Pleistocene deposits along the Bizerte Coast, N-E Tunisia

The N–E Tunisian coast (Bizerte region) shows several Quaternary sedimentary archives of middle to late Pleistocene age. Sedimentological analyses carried out (grain size, morphoscopy, exoscopy, petrography, mineralogy, and fossil content) on 12 sections reveal a succession that begins with infratidal deposits attributed to the last Interglacial period, followed by intertidal, continental (palaeosol) and/or aeolian deposits (aeolianites). The arrangement of these deposits, their lithological characteristics and their faunal contents are the basis for a palaeoenvironment reconstruction and estimation of palaeoclimatic conditions. A warmer climate and a high sea level characterize the beginning of this interval, followed by a sea level fall accompanied by an alternation of humid and arid climate. This alternation is reflected by intercalations of the palaeosol levels between the aeolian deposits.

Fossil fauna in MIS 5e deposits of Mar Piccolo basin (Taranto, Southern Italy) suggests new palaeoclimatic constraints

A palaeoecological and palaeoclimatic study was conducted on the fossil content of Last Interglacial calcarenites (MIS 5e) in the Taranto gulf. Three bulk samples returned a rich mollusc fauna consisting of: 120 extant Mediterranean species, including 4 species that live in the tropical west Africa province (Senegalese Fauna) while they are absent from the modern Mediterranean fauna. The molluscan assemblage indicates an infralittoral soft vegetated setting characterized by lateral variations from more exposed to sheltered areas, and a climatic affinity showing similar proportions between warm and cold affinity species. The lack of a marked warm affinity character may indicate a cooler than expected palaeoclimate during the MIS 5e in the Ionian Sea, in contrast with what can be inferred from the occurrence of Senegalese species and, in particular, of Thetystrombus latus thermal constraints.

The Ordovician System in the Levant region (Middle East) and southern Turkey: review of depositional facies, fauna and stratigraphy

Abstract This contribution addresses the current state of knowledge of the mainly siliciclastic Ordovician rocks in Jordan, Syria and southern Turkey, including advances in palaeontology, stratigraphy, depositional facies analysis and supra-regional correlation. The extensive and excellent exposures of the sedimentary succession in southern Jordan represent the regional reference for the Ordovician System in the southern Levant. We discuss the sedimentological and faunal characteristics as well as the stratigraphy and correlation of the succession. For the northern Levant (especially southeastern Turkey) and the western and eastern Taurides, the Ordovician succession and an updated sedimentary architecture is explained, and a comprehensive correlation for the region is presented. Increased knowledge on the fossil content from these regions enables correlation across the southern parts of the Arabian Plate to southern Turkey, and with the greater Gondwanan regions, far field as southwestern Europe and northern Africa. The depositional environments in the southern and northern Levant and southern Turkey encompass non-marine to shallow-marine areas in the lower part of the Ordovician that are followed upsection by shelf deposits of variable proximity up to the glacial episode in the Late Ordovician that is traceable in each of the areas. Characteristic signals in the Ordovician succession are represented by the trans-regional early Darriwilian unconformity and by the base of the Hirnantian glacial-related deposits followed by lower Silurian strata, visible across the entire region. New data from zircon-based provenance analysis clearly implicate the Arabian Shield as the main source of a huge amount of the clastic detritus within the Ordovician succession. In the course of the entire Cambrian–Ordovician interval, progressive deeper erosion of the Arabian Shield occurred. Sediment sources from regions farther away indicate long time of exposure and resedimentation, and some long-distance transportation, but their sedimentary influence was only of minor extent. The excellent outcrops mainly in southern Jordan, in southeastern Turkey and in the Taurides represent potential regions for further research.

The Significance Relationship between Palynomorph Fossil Preservation and Grain Size in Rock: Case Study of Walat and Batuasih Formations, Sukabumi, West Java

Palynomorph is dust-sized material that is resistant to acids and can be preserved as fossils in sedimentary rocks. Fossil content in rocks is very diverse which is influenced by various factors, one of this factors is the texture of rock in form of grain size. The Walat and Batuasih Formations are sedimentary rock formations that have variety of grain sizes. This research aims to examine relationship or correlation between grain size and palynomorph preservation in rocks with case studies in the Walat and Batuasih Formations. 42 samples were taken from measured stratigraphic section and analyzed both grain size and palynomorph content. Statistical analysis with Normality Test using Shapiro Wilk and Liliefors; Homogeneity Test using Levene Test; and Non-Parametric Associative Test using Spearman Rank was conducted to see the relationship of these variables. Result, the Walat and Batuasih Formations have conglomerate, sandstone, mudstone and coal lithologies with quite variety of palynomorphs. Statistical results show that all variables have data that are not normally distributed with tendency to be non-homogeneous. Moreover, it was found that the grain size of rock had significant effect on the preservation of palynomorphs in the rock. Clay grains has positive correlation of 0.613 and sand grains has negative correlation of -0.653. This shows that the finer the grain size, the more effective the preservation of palynomorphs is.

New Pleistocene vertebrate assemblages from the Villány Hills (SW Hungary): Siklós and Palkonya

The Villány Hills in SW Hungary have the richest archive of Pliocene–Quaternary vertebrate faunas in the Pannonian Basin, mostly in karstic cavities. Here we present three new sites that extend the list of Pleistocene vertebrate locations for the area and add information to the evolution history of the region. In the northern part of the Siklós quarry, bone breccia was found coming from fissures in Jurassic or Cretaceous limestones. Its lithofacies and fossil content are similar to those of other well-known Plio-Pleistocene karst infills of the region. As it contained mostly snake vertebrae, its age could not be constrained precisely. In the southern part of the same quarry, two vertical shaft s were discovered, which are unusual in several respects. Th ey formed in a Middle Triassic dolomite succession, a rock type generally not prone to karstification. Th ey might have been created by gravitational deformation of the relatively steep slope, probably at diff erent times. One of them was closed from above and contained fl owstones precipitated during the late Middle Pleistocene, during the late Rissian MIS7 interglacial. The other one was filled from above with loess, rock fragments and remains of large mammals – Equus cf. ferus, Bos primigenius and Coelodonta antiquitatis –, possibly between 140–40 ka, during one of the stadials of the Weichselian or the latest Saalian. The site shows that fossil-bearing cavities could also form in lithologies not favourable for karstification, which then trapped fossils in a similar way karstic cavities do. In contrast with the previous two and with most of the other known vertebrate sites of the Villány Hills, the Palkonya outcrop is not a karst cavity fill but was deposited on the (palaeo)surface. Bison sp., possibly B. schoetensacki remains were found between the Triassic basement and Quaternary slope sediments, and within the latter succession. The Bison bones are probably Middle Pleistocene or late Early Pleistocene, older than ~300 ka. The overlying slope sediments originate from the reworking of various older deposits. Th ey were covered with loess in the Weichselian (~22 ka ago), then again with slope deposits. The abundance of bones in and around the outcrop suggests that this site acted as a fossil trap as well. Bones probably enriched in the sediments during reworking of older deposits. In cold periods, loess deposition decreased (subdued) the relief through infilling the depressions. With 21 figures and 3 tables.

Middle Eocene (Lutetian-Bartonian) larger benthic foraminifera assemblages from Batman and Siirt (Southern Neotethys, SE Turkey): a new assessment

The benthic foraminifera assemblage has been described in the limestones outcropped in Kurtalan and Eruh district of Hoya formation which is one of autochthonous units of Arabian Platform (SE Turkey). From the two measured sections, one of them has rare fossil content due to dolomitization (DH-Dodan section),while the other is fairly remarkable in terms of fossil content (EH-Eruh section). The foraminiferal assemblages are represented by Asterigerina rotula (Kaufmann), Operculina ex. gr. gomezi Colom and Bauza, Victoriella conoidea Rutten, Amphistegina sp., Elphidium sp., Peneroplis sp., Carpenteria sp., Stomatorbina sp., miliolid and rotaliid forms and echinoderms, coral fragments in the Dodan section. The foraminiferal assemblages are represented by Nummulites biedai Schaub, Nummulites maximus d’Archiac, Nummulites perforatus de Montfort, Nummulites postfossulatus Sirel and Deveciler, Nummulites praeaturicus Schaub, Assilina exponens (Sowerby), Sphaerogypsina globulus (Reuss), Asterigerina rotula (Kaufmann), Lockhartia cf. hunti Ovey, Neoratlia sp., Operculina sp., Discocyclina sp., Asterocyclina sp., Lockhartia sp., Lenticulina sp., miliolid-rotaliid forms and echinoderms in the Eruh section. The fossil assemblage described shows that the limestones are of Lutetian-Bartonian and this assemblage indicates a very shallow marine deposition environment. This study provides biostratigraphic and stratigraphic data that help to reassess the Eocene geological evolution of the region. Paleobiogeographically, larger benthic foraminiferal assemblages recorded on carbonate platforms in southeastern Turkey show an affinity to Arabian and Middle Eastern platforms.

Tidal Modulated Shoreface Facies in Eocene Agbada Formation, Niger Delta Basin, Nigeria

Tidal influence shoreface are shoreface deposit generated by wave induced tidal action. The extent of the tidal impact from lower to upper shorefaces depend mostly on the tidal range thereby controlling the impact of different shoreline wave action on sediment distribution across shorefaces. The Tidally influenced shoreface sediment display wave generated structure, however the structure are strongly associated with tidal generated structures and trace fossil consistent with tidal depositional setting. Shoreface successions in Titun well display a wide range of variability, largely restricted to the lower and middle shoreface intervals. This variation was controlled by relative wave dominance and intermittent pulsating nature of associated tidal bed deposition. The successions were subdivided into three end members, although a complete gradation between them exists. High energy shoreface consist almost entirely of erosively based amalgamated tide and wave beds with minimal bioturbation. Intermediate energy shoreface consist of stacked laminated to burrowed intervals, recording repeated erosive storm bed emplacement, followed by opportunistic colonization, and commonly overprinted by resident fairweather burrowing. Weakly storm-affected low energy shorefaces typically show intense bioturbation with minimal preservation of high energy beds. Based on the association of the facies, facies vertical build-up patterns, sedimentary structures and trace fossil content, the T1 sands in Titun well are interpreted as a prograding tidally influence shoreface deposit. This interpretation is supported by presence of tide generated structures and marine trace fossil, due to the prevalence of several tidal imprint as suggested by several mud drapes and flasers, couplets of sands and shale’s in heterolithic sequences, and bidirectional current structures (herringbone cross stratification), a tidally influence shoreface geological model is suggested for deposit.

Micropaleontological findings and absolute ages mark the termination of the Last Glacial Maximum in the Eastern Mediterranean Region: New electron spin resonance data from Gediz Delta (Western Turkey)

Sediments and fossil content of Gediz Delta (Eastern Aegean Sea-İzmir) were examined from the samples collected from three drilling cores from the west (seaward) to east (landward) of the delta. Each drilling core contains Quarternary marine deposits with a marine fauna of foraminifers, bivalves, gastropods, echinoids, and ostracods at the bottom and Quaternary continental delta deposits at the top. According to our Electron Spin Resonance (ESR) age model marine sediments of the Aegean Sea started to cover the western Gediz Delta area before 19.9 ka (thousand years). Following the Last Glacial Maximum (LGM), after the transgression due to deglaciation occurred 15.3 ka ago, the coastline progressed 15-20 km eastward and covered the entire delta area. At the end of the LGM, as a result of the overflow of Manisa Gediz Lake depending on the deglaciation in Western Anatolia, and its flow from the Emiralem Strait to the İzmir Bay, the continental deposits reaching the West Gediz Delta region are younger than 11.4 ka.

The Ordovician of Sardinia (Italy): from the ‘Sardic Phase’ to the end-Ordovician glaciation, palaeogeography and geodynamic context

Abstract This review illustrates the most important features of the Ordovician successions of the Sardinian basement. We focus on the stratigraphy and tectonic structures in the tectonic units of the External and Nappe zones of the Variscan basement. The Ordovician successions are characterized by unconformities related to tectonic events ascribed to the Sardic and Sarrabese phases. The different durations of the unconformity-related gaps in the External (17 myr) and Nappe (6 myr) zones, recent work on the trilobite fossil content, and the occurrence of a volcanic arc only in the Nappe Zone (Sarrabus and Gerrei units) highlight significant discrepancies suggesting that these domains did not share the same geodynamic setting and palaeogeographical position during the Ordovician. This implies they were amalgamated only in Variscan times. Whereas for the external and nappe zones the Ordovician features are clear, the high-grade metamorphic Inner Zone, where numerous Ordovician ortho- and para-gneiss occur, more detailed studies are needed to define a complete framework for the Ordovician evolution of Sardinia. The present revision of data for the best-preserved succession of Sardinian tectonic units suggests that at least two distinct terranes, which did not share the same Ordovician evolution, were only amalgamated during the Variscan Orogeny.

Depositional environments and transgression-regression cycles in the Mural Limestone, central Sonora, Mexico

Results of analytical studies in the Mural Limestone of the Bisbee Group exposed in northwest Mexico, carried out to determine the paleo-bathymetry of the marine depositional environment, reveal that deposition occurred in a restricted carbonate platform environment, varying from inner-neritic to shelf margin with the development of lagoon, shoal and biohermal conditions, reflecting minor transgression-regression cycles. Furthermore, the fossiliferous content and lithological characteristics support the interpretation that the studied section corresponds to the transition between Cerro La Puerta and Cerro La Espina members of the Mural Limestone.

Palynology, Paleoenvironment and Stratigraphy Relationship of Tungan Buzu Hill with Adjacent Valley Gwandu Formation, Sokoto Basin, Northwestern Nigeria

Palynological study of Tungu Buzum Hill was investigated with a view towards determining the age of the outcrop, compare its miospore content with the adjacent Tungu Buzu Valley of carbonaceous shale, their stratigraphic relationship and paleoenvironment of deposition of the litho-sequence. Field study involved litho-description and logging achieved by noting the rock type, mineralogical composition, bed thickness, texture, sorting, roundness, structure, fossil content and diagenetic effect. Palynological slide preparation involved decarbonisation, digestion, sieving, maceral separation using zinc bromide, mounting on slide and petrographic analysis. The litho-sequence is composed sequentially upward of claystone, siltstone, indurated silty claystone, mudstone and ferruginized ironstone characterized by loadcast, fracture, lithification and bioturbation. Palynologically, the litho-section exhibits few marker forms such as Belskipollis elegans, Peregrinipollis nigericus and Retibrevitricolporites obodoensis depictive of early Miocene age. The paleoenvironment was deduced based on the occurrence of peridinacean forms such as Andalusiella sp., Senegalinium sp., Lejeuncysta diversiforma and Paleocystodinium golzowense indicative of marginal marine, while deeper marginal marine forms of gonyaulacacean phytoplanktons present are Micrhystridium sp., Canningia capillata and Dinogymnium sp. There are similarities in palynomorph assemblages of this study and Tunga Buzu Valley section in terms of age and similarity to Gwandu Formation though varied in paleoenvironment in the valley litho-section, marked by continental to marginal marine settings. Field relationship suggests that the Tunga Buzu Hill is stratigraphically overlying the Tunga Buzu Valley, separated by a fault. The Tunga Buzu Hill section represents the footwall while the Tunga Buzu Valley is situated within the hanging wall of a normal fault structure.

The diversity of flora at the Late Pliocene era in the Cisubuh Formation based on palynological data

Palynological evidence on past time gives features on plant diversity. The objective of this research was to determine the flora diversity in the past based on the palynological evidence in the form of pollen and spores (palynomorphs) that stored in sediments in the Cisubuh Formation. This research consisted of two stages, field sampling, and laboratory observation. A total of 16 samples on Cisubuh Formation on Rengasdengklok area, West Java Indonesia have been identified for their fossil content. Sixty-seven palynomorphs have been identified, comprised of 53 pollen taxa and 14 type of spores. Of the 67 palynomorph taxa, 40 were arboreal pollen, 12 were non-arboreal pollen, and 15 were Pteridophytes. The geological age of Cisubuh Formation was Late Pliocene, as indicated by Dacrycarpidites australiensis and without the presence of Stenochlaenidites papuanus. Based on the palynological evidence, the flora diversity in each layer sediment of the Cisubuh Formation showed high similarity (87%).

Fossil vertebrates of the early-middle Miocene Cerro Boleadoras Formation, northwestern Santa Cruz Province, Patagonia, Argentina

The early-middle Miocene continental Cerro Boleadoras Formation (CBF) crops out in the area of Cerro Boleadoras and Cerro Plomo on the western slope of the Meseta del Lago Buenos Aires, northwestern Santa Cruz Province, Argentina. The lower levels of the CBF consist of laterally extensive medium to pebbly sandstone beds with trough cross-bedding, interpreted as fluvial channel deposits, interbedded with tabular fine-grained floodplain deposits. Recent fieldwork provided fossil vertebrates from these levels with an estimated age between ~16.5 Ma and 15.1 Ma
 (late Burdigalian-early Langhian). The studied section temporally overlaps with the middle or upper sections of the Santa Cruz Formation (SCF) in the Austral-Magallanes Basin of southern Patagonia, the Río Frías Formation in Chile, and the lower Collón Curá Formation of northern Patagonia. We compile an integrated faunal list for this locality, including specimens from previous collections, and discuss its chronological and paleoenvironmental implications. The taxa list includes most of the groups recorded in the SCF: one anuran, three birds, and at least 33 mammals (metatherians, xenarthrans, litopterns, notoungulate typotheres and caviomorph rodents), indicating a Santacrucian age sensu lato. We also recorded a testudine, which constitutes the southernmost record of tortoises in South America and worldwide. Faunal dissimilarities between the vertebrate fossil content of the CBF and the mentioned sections of the Santa Cruz, Río Frías
 and Collón Curá formations may reflect ecologic, climatic and geographic differences rather than temporal ones. The co-occurrence of arboreal or semiarboreal, browsing, frugivorous, and grazing mammals suggests the presence of both forested and open environments for the area occupied by the CBF rocks. However, it is not possible to discern whether these two environments coexisted or alternated, and whether one environment predominated over the other. Marker taxa, such as the chinchillid rodents Prolagostomus and Pliolagostomus, and the typothere Pachyrukhos indicate a trend to aridification during the Miocene in southern Patagonia, as previously reported for the upper part of the SCF along the Río Santa Cruz and south to the Río Coyle, along the Atlantic coast and the Río Gallegos.

The rise and fall of the giant stromatolites of the Lower Permian Irati Formation (Paraná Basin, Brazil): A multi-proxy based paleoenvironmental reconstruction

Giant stromatolites are meter-scale laminated carbonate biosedimentary deposits formed by the action of benthic microbiota under very specific conditions. Although occurrences of giant stromatolites are relatively common in Precambrian deposits, the Phanerozoic record is still sparse. Here, we carried out an integrated analysis of the Lower Permian Santa Rosa de Viterbo giant stromatolite field, developed in a mixed carbonate-siliciclastic depositional system within a restricted intracontinental basin (Irati Formation, Paraná Basin, Brazil). Using available and new descriptions of stromatolite morphology and associated facies, we applied a multi-proxy approach based upon sedimentological, paleontological, geochemical, and isotopic data to develop a detailed paleoenvironmental model for this particular occurrence. The NE-SW elongated giant stromatolites – of >3 m in height, > 7 m in length, and > 1 m wide – have variable external shape and internal morphology, indicating changing growth strategy due to variations in the hydrodynamic conditions, bathymetry, and terrigenous input. Increasing δ13C values towards the top of the succession are related to intense microbial activity, increased nutrient supply, and enhanced primary productivity, with the higher δ13C values matching the global Permian seawater signal. Y/Ho and La/La* ratios indicate a less restricted setting towards the top of the succession, which is consistent with the increasing water depth recorded by the stromatolite morphology. The combination of smooth lamination, exclusively coccoidal microbial community, and fossil content, point to deposition under high (possibly hyper) salinity conditions for most of the succession. Our data suggests that the existence of stressful conditions (i.e., strong currents and high salinity) protected the benthic microbial communities from predation and favored EPS production, generating the ideal conditions for the growth of giant stromatolites, a very uncommon situation in the Phanerozoic.

Stratigraphic and volcanic signatures of Miaolingian-Late Ordovician rift pulses in the Alborz Mountains, northern Iran

• The Cambrian-Ordovician succession of the eastern Alborz Mountain Range displays uplift episodes associated with erosion. • The SPICE chemostratigraphic shift marks the Miaolingian–Furongian boundary. • Alkaline to subalkaline magmatic activities are separated by quiescent intervals of up to 35 m.y. • Intraplate (continental rift) volcanism reflects OIB-type mantle sources . • Plume-related rift pulses are linked to a large igneous province about 600 km across. Recent reconnaissance geological mapping, identification of unconformities and chronostratigraphic dating of Miaolingian to Ordovician strata in the eastern Alborz Mountains have led to recognition of synsedimentary uplift episodes associated with block tilting and partial erosion of the Cambrian Mila and Ordovician Simeh Kuh, Qumes and Lashkarak formations. A chronostratigraphic revision of the Miaolingian-Late Ordovician fossil content is presented, and the Steptoean Positive Carbon Isotope Excursion (SPICE) chemostratigraphic shift, marking the Miaolingian–Furongian boundary, is constrained close to the Members 2/3 contact of the Mila Formation. Upper Ordovician basaltic lava flows embedded in the Abarsaj Formation and Devonian sills and dykes intruded in the Mila and Simeh-Kuh formations were geochemically analysed and compared with the voluminous lava eruptions recognized in the Katian-Llandovery Soltan-Maidan and Gorgan Schists formations, and in the ?Emsian-Eifelian Mighan Formation. They represent successive magmatic pulses of alkaline to subalkaline activities, separated by background (quiescent) intervals of up to 35 m.y., characterizing an intraplate field (continental rift) affinity compatible with OIB-like (ΔNb greater than 0) mantle sources. Successive Miaolingian-Mid Ordovician (volcanic-free) uplift episodes were related to lithospheric doming preceding the onset of stepwise plume-related rift pulses, which shaped a large igneous province with transects of about 600 km, linking the Damghan and Alestan domains of the eastern Alborz Mountains with South Kopet-Dagh and some blocks of Central Iran.

Microbiostratigraphy, microfacies analysis and lateral basin evolution of Lower Cretaceous deposits in the south of Kerman region, SE Iran

Detailed microbiostratigraphy and basin evolution of the Lower Cretaceous deposits in the Rayen area, south of Kerman Region, SE Iran are investigated for the first time in two sections. The section no. 1 is 324.6m in thickness and comprises five lithostratigraphic units. The section no. 2 is 218 m in thickness and includes three lithostratigraphic units. The identified fauna and flora include 41 benthic foraminifera and 11 calcareous algae species. The identified assemblage indicates that the marine strata in both sections were deposited during the Barremian to Albian. The microfacies analyses carried out on 22 carbonate and 2 clastic microfacies indicate that the deposits in the section no. 1 were deposited on a homoclinal carbonate ramp, whereas in the section no. 2 they were deposited on a rimmed carbonate shelf. Generally, the Cretaceous deposit in the two studied sections represent different sedimentary models and fossil content indicating different basin evolution histories. The paleogeographic setting of the studied area on the south eastern margin of the Central-East Iranian Microcontinent and the active tectonic history during the Mesozoic suggest that the syndepositional tectonism influenced the basement’s morphology and resulted in changes in the fossil diversity and sedimentary nature of adjacent sedimentary basins.

Stratigraphy and palaeoceanography of late Pleistocene molluscs from the northern coast of the Persian Gulf

We report an extraordinary discovery of marine Pleistocene strata from the north of the Persian Gulf. The Dayyer section contains a rich molluscan fauna including 26 bivalve species, Sr 87 /Sr 86 data showing that the succession is not older than 153 ka (late Pleistocene). These strata are time-equivalents of the Bakhtiari Formation, but have a very different fossil content and facies. Comparing the Dayyer molluscan community to the present-day fauna of the Persian Gulf shows that many fossil species are absent in the recent waters. The palaeoceanographic distribution of the identified bivalves shows the presence of many of them in the Plio-Pleistocene strata of the Mediterranean Basin. This may point to a temporary connection between the Persian Gulf and Mediterranean Basin during the late Pleistocene and the extinction of many bivalves in the past 153 ka