Lithostratigraphic Units Research Articles

First occurrence in life position of two Triassic brachiopod species (Thecideida) from NE Italy: Paleoecological considerations

The San Cassiano Formation from the Dolomites, NE Italy, is a Ladinian–Carnian (Middle – Upper Triassic) lithostratigraphic unit belonging to the Western Tethys domain. In this formation numerous groups of marine invertebrates from reef communities have been reported. In particular, brachiopods are represented by different orders. Thecideids are the most abundant and diverse, with different species of the genus Thecospira. Despite the apparent abundance, only one report exists of a thecideid of the genus preserved in life position: Thecospira tyrolensis. In this study, we describe and discuss the first finding of Thecospira semseyi and Thecospira tenuistriata in life position based on the study of thin sections of Cipit boulders. Seemingly, the Th. semseyi shells were not firmly attached to the substrate by a small cementation surface; therefore, they could have lived embedded into the biogenic matrix. By contrast, Th. tenuistriata displays an umbonal region modified in a cementation area, allowing the attachment to the bio-builder. Most samples don’t show any signal of transport since all specimens are articulated and are still attached to the substrate. Besides, the commissures are partially opened, free of any encrustation of sponge or bryozoan growing. The preservation of brachiopods suggests that the samples of both species were fossilized in life position. Moreover, Th. semseyi and Th. tenuistriata continued to live although the host’s fabric was imbibing the brachiopods’ ventral valve. This shows that thecideids were important components of Tethys reef communities.

Implication of middle Eocene to early Miocene ostracodes from the N. El Faras-1X Well, Qattara Depression, Egypt, for paleobathymetry and paleobiogeographic reconstruction

The subsurface middle Eocene - early Miocene succession in the N. El Faras - 1X Well, drilled in the Qattara Depression at the northern part of the Western Desert, Egypt (Southern Tethyan Province, STP), was studied for its ostracode content to infer changes in paleobathymetry as well as paleobiogeographic reconstructions. This succession is composed mainly of three lithostratigraphic units, as the upper part of the Apollonia Formation (middle to late Eocene), the Dabaa Formation (late Eocene and Oligocene) and the lower part of the Moghra Formation (early Miocene). The stratigraphical distribution, paleoenvironmental and paleobiogeographical significance of the ostracode faunas from the Oligocene interval of the study area are documented for the first time. Fifty seven ostracode species belonging to 36 genera were identified in this succession. Among them, two new species were described. The vertical distribution of these ostracode species enabled the recognition of seven local biozones. Qualitative and quantitative statistical analysis of ostracode associations revealed a depositional depth ranging from the inner to outer neritic setting. Considering the CONISS cluster analysis, six ecozones were established. During the middle and late Eocene, the paleobiogeographical affinities of the Egyptian ostracodes from N. El Faras-1X× Well succession with that of the Southern Tethyan countries suggest a direct connection between Egypt and the countries of the Southern Tethyan Province. This connection facilitated the dispersal and exchange within this province. The low ostracode similarity between the STP and the Northern Tethyan Province (NTP) suggests a slight connection and exchange between them. The in common occurrence of these ostracodes with that of Somalia is attributed to the connection between the STP and Somalia via the Tethyan Seaway, which facilitated the dispersal and exchange of the middle Eocene ostracodes. The similarity between the Egyptian ostracodes (STP) and that of South America and the Caribbean Sub-Province indicates a direct connection between those provinces across the Gibraltar Strait and through the North Equatorial Oceanic Water Current during that time. During the Oligocene, the low ostracode similarity between the STP and the NTP may be attributed to a more or less restricted connection. Also, the low similarity indicates a continuation of the mild connection between the STP and the South America and Caribbean Sub-Province across the Gibraltar Strait and through the North Equatorial Current. During the early Miocene, the similarity of the recorded ostracodes of the STP with that of the NTP suggests a continuous connection between the two provinces. Also, there was a connection between the South America and Caribbean Sub-Province and the North American Province through the North Equatorial Current and the warm Gulf Stream within the Caribbean Sea.

An integrated sequence stratigraphic analysis of the early Marsdenian substage of the Millstone Grit Group, Central Pennines, UK

The early Marsdenian substage (Millstone Grit Group) of the Pennines comprises repeated deltaic cycles separated by ammonoid-bearing marine bands. This cyclicity, controlled by the combined forces of glacio-eustasy and modulations in sediment supply, provides an important outcrop area for the application of sequence stratigraphic principles. A new correlation framework is presented where two orders of sequence are identified: (1) a low-order sequence, within which marine bands (R 2a 1, R 2b 1, R 2b 2 and R 2b 3) represent a maximum flooding surface, and (2) high-order sequences nested within the low-order sequences. By integrating and correlating key exposures, historic well boreholes and field mapping, lateral changes in facies and facies association are observed, and palaeogeographic trends mapped. This allows the variation in sequence and systems tract stacking patterns to be interpreted. Three orders of Milankovitch cyclicity are inferred to control the sequence stacking patterns; long-duration ( c. 400 ka) eccentricity oscillation controlling maximum flooding events represented by the R 2a 1 and R 2b 2 marine bands, sub-100 ka obliquity oscillations (controlling the R 2b 1, R 2b 2 and R 2b 3 marine bands and intervening low-order sequence boundaries), and precessional frequencies ( c. 25 ka) which may control the periodicity of the high-order sequences. Supplementary material: Locality details, including lithostratigraphic units observed, gross and sand thicknesses within sequences, and palaeocurrent data measured are available at https://doi.org/10.6084/m9.figshare.c.6408203

New magnetostratigraphy constrains in the southern Paraná magmatic province (Herveiras and Gramado Xavier areas), Rio Grande do Sul state, South Brazil: Implications for the timing between volcanic sources

This paper undertakes a new paleomagnetic study of 51 lava flows that crop out in Southern Paraná Magmatic Province. The volcanic rocks are basalt of low-Ti content type (18 flows) and Palmas silicic type (33 flows) corresponding to the Caxias do Sul, Barros Cassal, and Santa Maria sub-types covering all lithostratigraphic units of the region. This study is part of a broad magnetic study in the Brazilian part of the Paraná-Etendeka LIP to understand the temporal relationship between the volcanic units of different compositions allowing the investigation of the contemporary nature of the multiple sources. The characteristic remanent magnetization (ChRM) for the lavas was obtained by alternating field (a.f.) and thermal demagnetization methods, and is interpreted as a thermo-remanent magnetization carried by stable pseudo-single domain magnetite grains, being acquired during the cooling of the lava flows. The high-quality of the ChRM results from both areas allows us to interpret that the emplacement of all volcanic rocks was geologically very fast, as verified by the symmetrical direction of both polarities (normal and reverse i.e. positive reversal test) of the geomagnetic field associated with the stratigraphy of all lava flows. The passage from pahoehoe to rubbly basalts was marked by a change of polarity of the geomagnetic field. Our results suggest that all volcanic rocks were emplaced by at least two volcanic events as shown by the polarity changes, and the sources of basaltic and silicic rocks of different compositions were active at the same time.

The exposed Mule Creek vent deposits record the structure of a volcanic conduit during a hybrid explosive–effusive eruption

Silicic volcanic eruptions commonly begin with the explosive ejection of pyroclastic material, before transitioning to gentler effusion-dominated activity. Well-exposed dissected silicic systems are scarce and poorly studied, hindering the advances in our understanding of the explosive–effusive transition needed to improve interpretations of volcanic unrest and hazard forecasting. The Mule Creek vent (New Mexico, USA) is a dissected silicic conduit that records the processes controlling conduit formation and evolution, and the role tuffisites (fractures filled with variably welded pyroclasts) play in conduit dynamics. Here, we use decimeter-scale photo-mapping of lithostratigraphic units and thin section analysis to differentiate and interpret three dominant emplacement styles during vent evolution. First, there was repeated deposition and erosion of pyroclastic material at the conduit walls, recorded by erosive surfaces in pyroclastic breccia and agglomerates at the conduit margins. Second, sub-vertical domains of dense melt-dominated magma were emplaced and preserved as glass-dominated vitrophyre and brecciated vitrophyre, with the textural hallmarks of assembly from welding of pyroclasts. Finally, the sub-horizontal fracturing of previously deposited lithologies produced laterally cross-cutting tuffisites. The vent deposits track the widening and then narrowing of the conduit through time and reflect progressive insulation and generally higher temperatures towards the conduit center as pyroclasts accumulate. Welding of pyroclastic fill and the formation of dense vitrophyres towards the conduit center lowers deposit porosity and effective wall permeability. This drives localized gas pressure increases and results in gas-driven fracturing, generating tuffisites, which act as transient outgassing pathways. The structure of the Mule Creek vent records an explosive–effusive transition, constraining the processes controlling conduit evolution and aiding our interpretation of volcanic unrest.

Recent sediments of Lake Tamda (Middle Atlas, Morocco): New insights from geochemical and sedimentary records

This work presents the sedimentological and geochemical analyses on a sedimentary sequence taken by coring from Lake Tamda, located in the Middle Atlas, Morocco. This study aims to determine the parameters controlling the sedimentary and environmental dynamics and, consequently, the climatic dynamics. Waters in the lac are calc-magnesian, relatively alkaline, and well-oxygenated. Water dilution materializes the climatic influence from the hot season (summer) to the cold season (winter). The sedimentological and geochemical studies of surface sediments provide information on detrital sedimentation dominated by the silty-clayey fraction resulting directly from the erosion of the watershed. At Tamda cores, the sedimentary record shows three lithostratigraphic units. They represent three distinct sedimentary and geochemical deposition phases, marking three stages of lake-level fluctuation. Going toward the lake's center, there is a decrease in coarse fractions and carbonates and an increase in fine particles, organic matter, and magnetic susceptibility. The reasonably high carbonate contents at the edges are related to detrital inputs. The low levels of organic matter are linked to the current lowering of the lake level, while the low sedimentation rate is connected to the decrease in terrigenous inputs by water flows. Recent sedimentation at Lake Tamda is influenced by Allochthonous production, including seasonal inputs from the watershed and sometimes wind sedimentation.

Hydrogen sulphide (H2S) migration in groundwater of the Zechstein strata in the Legnica-Głogów Copper Basin and its vicinity, SW Poland

Hydrogen sulphide (H2S) occurs in groundwater in various lithostratigraphic units of the Zechstein Basin in the Legnica-Głogów Copper Basin (SW Poland). This region is located in the Fore-Sudetic Monocline within which, several tens of kilometres NE of the study area, at greater depths, natural gas fields with hydrogen sulphide (H2S) occur. The Main Dolomite (Ca2), in which H2S-containing natural gas has accumulated, is younger than the Zechstein Limestone (Ca1), which is actively mined. The Ca2 and Ca1 formations are separated by a thick anhydrite succession including a wedge-shaped salt body. Hydrochemical analyses of 18 groundwater samples taken from different horizons within the Zechstein strata showed spatial variability ofH2S and chloride concentrations. A conceptual model of groundwater flow with dissolved H2S in the Zechstein formations was developed. H2S migration is associated with groundwater flow between the Ca2 and Ca1 aquifers through fissures in the anhydrite strata that separate them. Hydraulic contact through fissures in the anhydrite layers is the result of long-term exploitation of the underground copper deposit. Groundwater flow between the layers is influenced by a large change in the piezometric pressure of the groundwater in the depression cone caused by mining drainage.

Regional synthesis of the Ordovician geology and stratigraphy of China

Abstract China presently comprises several independent tectonic palaeoplates or terranes and parts of other blocks, which have been assembled over geological time. In the Ordovician, these blocks included South China, North China, Tarim, Qaidam, Junggar, Qiangtang-Qamdo, Lhasa and partially Himalaya, Sibumasu and Indochina, as well as the Altay-Xing'an and Songpan-Garze fold belts, which were discrete but near-adjacent. Twelve stratigraphic megaregions bounded by tectonic sutures or major fault zones can be recognized. Some of them are further differentiated into several regions according to the lithological and biotic facies or distinct stratigraphic sequences. Here, the palaeontologic features and biostratigraphic framework of these stratigraphic megaregions and regions are summarized. The unified biostratigraphic framework presented herein is supported by 33 graptolite biozones and 27 conodont biozones, together with supplementary biozones, communities or associations of brachiopods, trilobites, cephalopods, chitinozoans, acritarchs and radiolarians. With constraints of integrative chronostratigraphy, biostratigraphy, chemostratigraphy, cyclostratigraphy and magnetostratigraphy, along with some geochronologic data, our understanding of the temporal and spatial distribution of the Ordovician lithostratigraphic units on these major blocks has been significantly advanced. Vast amounts of new data accumulated in recent decades also constrain the major Ordovician geological and biotic events evident in China, such as marine anoxia, faunal turnovers and tectonic orogenies.

Lithostratigraphy and Biostratigraphy of the Shiranish Formation (Late Campanian- Maastrichtian) in Diana area, Northern Iraq

The lithostratigraphic and biostratigraphic studies of the Shiranish Formation in the Diana area, Erbil, Northern Iraq, were conducted to distinguish the main lithostratigraphic units, depositional environment and the formation age. The Shiranish Formation in the study area can be divided into three rock units. The lower and upper units consist of marly limestone, marl and limestone deposited in the outer shelf environment, while the middle unit is dominated by laminated calcareous shale and marl deposited in the upper bathyal environment. Calcareous nannofossils showed the presence of about 20 species/genera in the studied Shiranish Formation. Three biozones are identified; Misceomarginatus pleniporus biozone; Ceratolithoides aculeus biozone, and Uniplanarius sissinghii biozone. From a regional perspective, these biozones were compared with other nannobiozones, leading to the conclusion that the studied section is of Middle Campanian age.

Lithostratigraphy of a long, fossiliferous Oligocene sequence: Revisiting Saint Jacques, Nei Mongol, China

For a hundred years the Saint Jacques area has been known to produce rich Oligocene vertebrate fossils, yet only a handful of previous studies have focused on this area. Since 2010, we have conducted 12 field expeditions to Saint Jacques, and here we report findings from our paleontological excavations and stratigraphical investigations. Twenty-two fossiliferous blocks across the area are recognized and a chronostratigraphic framework has been established to aid fossil collection. Fossil-mammal materials have been recovered in situ from 1635 localities and additionally from surface sediments. Fossiliferous blocks in the area are correlated by lithological similarity and lateral tracing. Lithologically, the area is mainly composed of reddish silty mudstone and muddy siltstone, with three distinctive layers of grayish white sandstone. The measured composite stratigraphic column spans 239 meters and are divided into 12 lithostratigraphic units. Contrary to previous knowledge that Saint Jacques contains two Oligocene mammalian assemblages, our preliminary biostratigraphic analysis of small mammals shows that the area documents successive faunal transition from the Eocene to possibly the early Miocene. The hyracodontid perissodactyl Ardynia, the ctenodactyloid rodent Gobiomys, and the basal Glires Gomphos from the bottom litho-units imply the presence of the Eocene–Oligocene boundary, while small mammal assemblage of the top units is similar to Miocene faunas in northern China and Mongolia. Thus, rock strata in Saint Jacques likely span the Eocene through the early Miocene, bracketing an entire Oligocene sequence within. In sum, our re-exploration of Saint Jacques has greatly expanded the chronostratigraphic and taxonomic coverage of the mammalian fossil collection from this area. This long, successive Oligocene sequence makes an important record for studying the Eocene–Oligocene Transition. Further study in this area will contribute to a range of paleontological and paleoenvironmental questions.

Depositional setting, mineralogical and diagenetic implication on petrophysical properties of unconventional gas reservoir of the silurian qusaiba formation, northwestern arabian peninsula

The Silurian Qusaiba Formation is known for its high potential as one of the regional unconventional hydrocarbon resources. Multiple samples cropping out in Tayma Quadrangle, Northwest Saudi Arabia, were analyzed extensively. Field work and comprehensive laboratory work was conducted including geochemical and petrophysical measurements all supported by petrographic imaging. Qusaiba Formation was classified from bottom to top into five lithostratigraphic units. Lithologically, Units 1 and 3 are composed mainly of thinly laminated shales, while units 2 and 4 are characterized with interbedding shale and siliciclastics in form of siltstone and sandstone. Uppermost Unit 5 exhibits mixed lithofacies of silty-shale, muddy-siltstone and siltstone. Clay minerals constitute the main components in Units 1, 3, and 5 while quartz, feldspar, and carbonates are dominant in Units 2 and 4. Mica, pyrite and gypsum are distributed in all units in varying proportions. Inorganic geochemical indicators suggest that shale and muddy silt subunits are predominantly of mafic to intermediate parental origins, while those of sandy and silty subunits are of intermediate to felsic origins. Qusaiba sediments appear to be derived mainly from passive margin with few from continental arc settings with limited continental facies. The variant distribution is mainly attributed to the siliciclastic input to the depositional basin. The applied redox and clay types identified a warm and humid low salinity shallow marine environment. Shale and muddy-siltstones subunits appear to be moderately to highly weathered while sandstone and siltstone units are slightly to moderately weathered. Petrophysically, tested samples lithologies are reflected by the different patterns of pore size distribution and wide porosity and permeability variations giving an insight into the depositional environment and diagenesis. Samples are characterized with different pore systems including intergranular inorganic effecting considerably the petrophysical properties, intragranular organic pores with the least effect and fracture pores inducing the highest influence. Petrographic analyses by different imaging techniques confirmed the mineralogical and petrophysical findings.

Characterization and stratigraphic review of the upper Jurassic – Lower Cretaceous Mendoza Group in the Blanco river valley (∼33°SL)

The Jurassic-Cretaceous Mendoza Group is one of the most distinctive lithostratigraphic units of the widely surveyed Neuquén basin. This work focuses on its development in the Aconcagua basin, which crops out at the Aconcagua fold-and-thrust belt in the Principal Cordillera, and contrasts with its evolution in the main Neuquén basin by remarkable differences. By logging a series of stratigraphic sections, we performed a detailed revision of the Mendoza Group's stratigraphy and contact relations along the Blanco River valley (∼33°S). We reassigned several outcrops to the Mendoza Group based on our field observations and recent research, updating the current geological map of the study area. We identified an irregular development of the lower contact relation with the Auquilco Formation that denotes the existence of a paleo-topography at the time of deposition of the upper beds of the Mendoza Group. Moreover, we dismissed previous proposals of a lateral interfingering relation with the Juncal Formation, and in place, we describe an angular unconformity with an overlying Upper Miocene volcanic unit. Additional insight from the redefinition of the upper contact is brought by the characterization of an erosive surface at the top of the Mendoza Group, and the identification of a period of subaerial platform exposition and erosion. A previous paleogeographical model shows a good fit with the observed facies along the Blanco River valley and can be extended towards southern latitudes. Differences in the development of the Mendoza Group in the Aconcagua basin and the main Neuquén basin have been acknowledged, and a potential origin of this unusual behavior has been explored in the reactivation of an Early Jurassic structural high.

Stratigraphy, volcanic processes and evolution of the Martin Vaz archipelago

The volcanic Martin Vaz Archipelago consists of four Plio-Pleistocene small islands (total area of 0.37 km2) in the South Atlantic Ocean in front of Brazil's coast. Together with Trindade Island, the archipelago corresponds to the easternmost portion of the Vitória-Trindade Seamount Chain (VTC).We performed geological mapping, coupled with X-ray diffraction, petrography, scanning electron microscopy, and lithogeochemistry analyses at Martin Vaz samples. Four lithostratigraphic units were identified (i) Martin Vaz Formation records older explosive phonolitic activity. It is interpreted as resulting from hydromagmatic volcanism; (ii) Subvolcanic phonolites consist of a dome (cryptodome) and plug morphologies, which represent the most voluminous rocks at Martin Vaz Archipelago; (iii) Mirante Formation records hyper-concentrated density currents of ultrabasic rocks; and (iv) Atobá Formation is composed of ultrabasic to intermediate lavas of basanitic to phonolitic composition, interpreted as a result of Strombolian (Fountain Fed)/Hawaiian volcanism.The volcanic rocks described at Martin Vaz Archipelago and Trindade Island represent the final members of the nephelinite-phonolite series, with a significant absence of intermediate phases. Basanites of the Martin Vaz, Mirante, and Atobá formations are geochemically similar to the nephelinites of Trindade Island. In the same way, the geochemical characteristics of phonolites from subvolcanic bodies and the Bandeira Member are similar to those observed on the phonolites of Trindade Island. Geochemical and thermodynamic modeling suggest cogeneticity between ultrabasic and phonolitic magmas. Fractional crystallization about 0.5 GPa and at low water pressures explain the chemical evolution trends observed. Geochemical characteristic points to melts of a metasomatized source composed of garnet wehrlite and/or hornblendite.The new data allowed for the elaboration of a novel conceptual model for the geological evolution of the Martin Vaz Archipelago, one of the last volcanic manifestations in the Brazilian territory.

Pleistocene subtribe Terminaliinae (Combretaceae) fossils in the middle-lower Uruguay river basin, South America

The El Palmar Formation is a lithostratigraphic unit deposited by the Uruguay River and has an extensive Upper Pleistocene fossil record. The aims of this study are i. to describe in detail three new silicified wood specimens recovered in the Punta Viracho and Santa Ana fossiliferous localities that have the diagnostic features of the Combretaceae, and ii. to add new data to their significance of palaeoenvironmental and phytogeographical implications. Through the study of wood anatomy, the taxonomic identification of fossil woods is carried out. The mesomorphy and the efficiency of the water conduction system in the fossil woods are calculated. The Nearest Living Relatives (NLRs) method by Mosbrugger (1999) based on assemblage taxa is used to obtain paleoenvironmental data. This work provides three new fossil species related to Terminalia sensu lato (Combretaceae) based on fossil wood specimens. Features such as simple perforation plate, short vessel elements, density and diameter of the vessels suggest a strictly mesomorphic structure; where water conductivity efficiency was the predominant condition of these trees. The nearest living relatives of the fossils currently occur in the Atlantic forest in Brazil but are not present in the study area. We conclude that the present-day Atlantic woodland where these species coexist was more widespread in the Upper Pleistocene, reaching higher latitudes to the south (ca. 32° S).

Middle Eocene–early Miocene planktonic foraminiferal biostratigraphy, chronostratigraphy, sea‐level reconstruction and sequence biostratigraphy at N. ElFaras‐1Xwell, Qattara Depression, Western Desert, Egypt

The planktonic foraminiferal assemblages are tracked in the middle Eocene–early Miocene succession within N. El Faras‐1X Well, Qattara Depression, Egypt. This succession is composed mainly of three lithostratigraphic units the upper part of the Apollonia Formation (middle to late Eocene), Dabaa Formation (late Eocene and Oligocene) and the lower part of the Moghra Formation (early Miocene). Biostratigraphically, the recorded 77 planktonic foraminiferal species enabled the recognition of 12 planktonic foraminiferal biozones; 4 biozones belong to middle to late Eocene, 7 biozones belong to the Oligocene and 1 belongs to the early Miocene. The proposed biozones were compared with their equivalents in other Egyptian regions and other schemes. Eleven Lowest Occurrence and two Highest Occurrence planktonic foraminiferal bioevents were also recognized and correlated all over the world. The chronostratigraphy and the stage boundaries were mainly delineated according to the diagnostic planktonic foraminifera. The middle–late Eocene boundary (Bartonian–Priabonian boundary), The Eocene–Oligocene boundary (Priabonian–Rupelian boundary), the early Oligocene–late Oligocene boundary (Rupelian–Chattian boundary) and the Oligocene–Miocene boundary (Chattian–Aquitanian boundary) were accurately determined. Based on the % P, the palaeobathymetry was estimated and hence the sea‐level fluctuation. The reconstructed sea‐level curve revealed two major transgressive–regressive cycles with minor oscillation within them. These events were globally correlated and match in most parts with that of the worldwide sea‐level curves. The sequence stratigraphy framework consists mainly of two transgressive–regressive (T–R) depositional sequences (DS1 and DS2). The DS1 includes the TST1 below which is capped by mfs1 and the HST1 above. The DS2 involves the TST2 below that was capped by mfs2 and the HST2 above.

New constraints on the closure of the Betic Seaway and the western Mediterranean palaeoclimate during the Messinian Salinity Crisis from the Campo Coy Basin (SE Spain)

The Campo Coy Basin (SE Spain) exposes >1 km of sedimentary succession with a variety of rocks including a thick evaporitic succession previously associated with the Messinian time. These evaporites were supposedly deposited in a restricted Mediterranean-Atlantic seaway connecting the Lorca and Guadix-Baza basins, although no chronological or geochemical data existed. Here we use palaeomagnetism together with vertebrate and foraminifera biostratigraphy to constrain the age of the Campo Coy succession between <9 Ma and 4.7 Ma. We use geochemistry (δ34S, δ18O and 87Sr/86Sr values) of the gypsum deposits to evaluate their marine or continental origin. In addition, we describe the underlying and overlying lithostratigraphic units to reconstruct the palaeogeographic evolution of this region. Our results show that the sediments were deposited in a continental environment, indicating that the Betic Seaway was already closed in this region during the late Tortonian and that the neighbouring marine basins of Guadix-Baza and Lorca were disconnected during that time. The δ34S, δ18O and 87Sr/86Sr values of the gypsum indicate recycling from the Triassic sulphates. Sedimentary facies of the evaporites point to an environment dominated by a saline lake with continental sabkha episodes developed during the driest periods. Well-defined and laterally continuous evaporitic cyclicity suggests an orbital forcing and high sedimentation rates preceding the Messinian Salinity Crisis (MSC). Alluvial deposits are contemporaneous with the MSC indicating a dry continental environment in this region during the Mediterranean restriction. Overlaying lacustrine carbonates are rich in small vertebrate fauna including African species that migrated to Europe during the MSC. These carbonates have low δ18O and δ13C values characteristic for freshwater input in an open lake just after the Zanclean flood, suggesting that a wet climate followed the MSC.

A global view on the Ordovician stratigraphy of southeastern Europe

Abstract The Ordovician documented in southeastern Europe reflects different sedimentary environments, from shallow water to basin, belonging to diverse palaeogeographical domains. Some of these geological sectors and their palaeontological content have been well described for a long time such as the Carnic Alps, which represent one of the most continuous Paleozoic sequences in the world. For some other areas, the quality of the data is variable and the knowledge is less detailed, sometimes with lithostratigraphic units still to be formalized, which also reflects the fragmentary nature of the outcrops. The Ordovician stratigraphy of southeastern Europe with its diverse successions has been revised herein and integrated with new data in an attempt to develop a global scenario for this critical time interval in the evolution of life.

Outcrop analogy with the subsurface geology and hydrocarbon prospectivity of Jaintiapur and adjacent areas in North-East Bangladesh

The availability of hydrocarbons in the eastern part of Bangladesh indicates the presence of active petroleum systems in the Bengal basin. Although extensive research has been conducted in the Surma basin, the correlation between structural configuration, tectonostratigraphic framework, and hydrocarbon potentiality in the basin including Jaintiapur area has not yet been established. In this study, the hydrocarbon prospectivity of Jaintiapur and the adjoining Dupigaon area has been characterized through outcrop analogy with the subsurface interpretation of seismic data along L13-01, PK-SY-5, and L13-03 lines. The main three megasequences have been recognized based on sequence stratigraphy in the Sylhet region utilizing outcrop, seismic, and well-log data. The exposed Tertiary and Quaternary formations of Jaintiapur and adjoining areas can be classified into eleven litho-stratigraphic units. Detailed facies analyses indicate that these rock units were deposited in fluvial, deltaic, and shallow marine environments. The subsurface lithology of the study area has been inferred from the petrophysical data obtained from Sylhet-7, Kailashtila-4, and Jalalabad-1 wells. Jaintiapur area lies in a tectonically complex province and is controlled by the Dauki Fault System. Folding and faulting represent intense tectonic deformation in the area. Detailed analyses of surface and subsurface geology indicate that faults pass along the rivers and transverse faults segment the reservoirs. A total of seven horizons have been interpreted using Petrel software. The seismic attribute analysis identifies leads and prospects based on transverse faults and amplitude anomalies with distinct bright spots at the PK-SY-5 line. From seismic interpretation, attribute analysis, and lithofacies distribution of Sylhet-7 well and its surround area in the Dupigaon, it seems that same gas bearing sand. Gas sands of the Sylhet-7 well indicate the possibility of gas/oil in the equivalent sedimentary sequence in the Dupigaon structure as this area is located close to and more down-dip towards the kitchen area.

Evidence of upwelling on the Brazilian continental shelf of Rio Grande do Norte

This study evaluates Foraminiferal assemblages and their relation with grain size, calcium carbonate content, organic matter, and mineralogy of sediment samples collected at the sediment-water interface along a transect on the northern continental shelf of Rio Grande do Norte State, Brazil, adjacent to the city of Areia Branca. The sedimentary sequence of this shelf is represented by lithostratigraphic units of a marine regressive sequence dominated by four facies: Siliciclastic sand, Silicibioclastic Sand, carbonate mud, and Biosiliciclastic sand. The carbonate content ranged from 5.83% to 85% and the organic matter content from 1.16% to 27.05%. Mineralogical characters separated the predominant siliciclastic content (37% to 92%) from the bioclastic content (8% to 63%). We have identified 14 species out of 50 species of Foraminifera, associated to particular depths and sediment types as follows: (1)deeper-water sediments in the middle shelf contain Bolivina striatula, Bulimina marginata, Triloculina trigonula, Pyrgo ringens, Textularia gramen (2)the shallowest sediments in the inner shelf contain Ammonia tepida, Buccella peruviana, Miliolinella subrotunda, and Quinqueloculina patagonica, (3)the central parts of the transect, also in the inner shelf, provide habitats for Quinqueloculina lamarckiana, Textularia earlandi, Buliminella elegantissima, Discorbis peruvianus, and Pyrgo nasuta. The distribution of Uvigerina striata and Buccella peruviana is probably related to colder water temperatures and possibly the occurrence of an upwelling phenomenon for the deepest parts of the area rather than the sedimentological features discussed here.

The Pliocene–Pleistocene transition in the subsurface of the Dutch-Belgian border region: insights from borehole Huijbergen

Cross-border correlations of the Pliocene–Pleistocene successions in the southern Netherlands and northernmost Belgium are problematic, because biostratigraphic markers are often lacking. Correlation is further hampered by the poor age constraints of the Belgian Merksplas Formation. To address these issues, sedimentary, mollusc and dinoflagellate cyst analyses are combined to characterise the lithostratigraphic units in the Huijbergen borehole (The Netherlands) and to provide age estimates. Subsequently, the Huijbergen borehole was correlated with nearby boreholes in Essen and Kalmthout (Belgium). The Piacenzian intervals of the Dutch Oosterhout Formation can be correlated with the Belgian Lillo Formation, with the latter’s threefold borehole log signature appearing virtually continuous across the border between both countries. The Dutch Maassluis and Waalre formations are correlated with the shell-bearing lower part and the unfossiliferous higher part of the Merksplas Formation respectively. Although dinocysts are not age-diagnostic for the Maassluis and Waalre formations in borehole Huijbergen, characteristic interglacial marine shells provide a Gelasian age assessment for the Maassluis Formation. By correlation, this age estimate can also be applied to the lower part of the Merksplas Formation, thereby elucidating the Pliocene–Pleistocene transition near the Dutch-Belgian border.