Sandy Sequence Research Articles

Continental Genesis of Sands of the Novolutsk Member, Sablinskaya Formation of the Middle Cambrian (Northwestern Flank of the Moscow Syneclise)

Despite the high degree of knowledge about Cambrian-Ordovician sandy sequence in the northwestern flank of the Moscow syneclise, some of its subdivisions are still poorly studied. For the first time the article provides a comprehensive lithological analysis of the textural and mineral-structural composition of the Novolutsk member sands, common in the west of the Leningrad region. This member conventionally belongs to the Sablinskaya Formation of the Middle Cambrian. Significant differences between the studied sands and the sands of other units of the formation are shown, and their analogues are found in the eastern sections of the Baltic-Ladoga glint. The lenticular occurrence, specific textural complex and coarse-medium-grained composition of the Novolutsk unit sands made it possible to prove their continental alluvial genesis and link them with the sedimentary environments of the earlier identified Putilovskaya member sands of the Sablinskaya Formation.

Кварцевые песчаники сосновской толщи палеогена Ульяновско-Сызранского Поволжья (восток Русской плиты): вещественный состав и происхождение

The Paleogene quartz sandstones of the Sosnovka formation are widely occurred in the Uljanovsk-Syzran Volga region and are used as valuable building materials. The articlecomprises an improvement for thecontinental origin of the Sosnovkasandstones based on the results of a comprehensive study of the features of the mineral composition and microstructure of quartz sandstones of the Sosnovka formation obtained by using petrographic, XRD and electron-microscopic analyses. Therelevance of thestudy is based on the debatability of the origin ofsandstones, the depletion ofthemineralresource base ofthistype ofmineralrawmaterials andthe needto develop new approachesto its prediction. Accordingto theresults ofthestudy, itwasfoundthat opokas and diatomites ofthe Lower Syzransubformation, brought uptothe denudationsurface,could be the source of free silica for the cementation of sand grains of the Sosnovka sandstones. The deficit of siliceous cement and its extremely irregular distribution among the clastic grains indicate the local and restrict occurance of the source of solutions saturated with free silica, which, most likely, was controlled by paleorelief. Electron microscopic images and microprobe analysis of individual sandstone microcomponents indicate strong bacterial activity and frequent change of the land paleoenvironments to extensive marshy ones. The formation of pyrite framboids in the cementitious mass is a sign of oxygen deficit in the continental basin and the activity of magnetotactic bacteria. Whereas the decay of framboids is associated with dissolution of organic matter inside the framboids due to oxidation of the paleobasin. The results of the study leave no doubt about the non-marine origin of the sandstones studied, hence, we should not assume the presence of extended bodies of sustained thickness when solving prognostic-mineralogical problems. The Sosnovka sandstones are of extremely irregular distribution in the sandy sequence and formation in extremely continental pedological conditions will allow us to solve the important task of improving approaches to the prediction of new objects of this valuable mineral resource in the Ulyanovsk-Syzran Volga region.

Interpretation of electrical logging data from the Hettangian-Aalenian terrigenous reservoirs in the Southeast of Western Siberia

In the southeast of Western Siberia, the most studied are the Upper Jurassic deposits, most of the oil and gas fields being confined to them. However, the probability of discovering new hydrocarbon deposits in the Upper Jurassic horizons is extremely small. Therefore, of great importance is finding new hydrocarbon deposits in less studied deep-lying complexes. The article considers the development of a criterion for determining the saturation type of the terrigenous reservoirs in the Hettangian-Aalenian deposits in the southeast of the West Siberian sedimentary basin. We use the example of the Ust-Tym megadepression, a large depression located in the central part of the Tomsk region. The Lower and Middle Jurassic sections are represented by the Urman and Togur formations, Salat formation (Peshkov formation is its isochronous analogue) and Tyumen formation, and characterized by the alternation of predominantly sandy (potential reservoirs) and argillaceous-carbonaceous (seals) sequences. In the studied interval, tests were carried out in just a few wells, for which reason the identification of deposits and promising objects is complicated. Determining the type of reservoir saturation will significantly improve the assessment of oil and gas potential. As a result of interpreting lateral logging sounding data, the geoelectric parameters of the invasion zone and undisturbed formation were reconstructed for the Lower Jurassic and Aalenian deposits. Based on the well logging data interpretation by means of numerical inversion, we obtained the criterion for the saturation type of the reservoirs (Ju11-17) in the Hettangian-Aalenian complex. The boundary resistivity values for the oil-saturated reservoirs vary from 8 to 20 ohm∙m, while for the water-saturated ones they do not exceed 5 ohm∙m.

Provenance of aeolian sands in the Hetao Plain, northwestern China

Abstract Patches of aeolian sand are distributed throughout the Hetao Plain, which pose threats to farming and agriculture. Identification of the provenance of the aeolian sands may help with efforts to alleviate ecological stress in Inner Mongolia and in the paleoenvironmental interpretation of sandy sequences. This study uses geochemical data to determine the provenance of aeolian sands from the Hetao Plain. Provenance discrimination diagrams revealed that the aeolian sands were mainly derived from mixed source felsic granites and granodiorites, which have undergone weak sedimentary recycling. The chemical index of alteration and A–CN–K data indicated that the aeolian sediments were transported over a short distance. Comparison of trace element and rare earth element (REE) ratios of the aeolian sands with rock samples from potential source areas has revealed that aeolian sand deposits in the Hetao Plain were mainly derived from Sertengshan and Yellow River sediments. The Langshan and Ordos Plateau may represent additional sand sources for the Hetao Plain.

U–Pb detrital zircon ages from the Paleozoic Marbella Conglomerate of the Malaguide Complex (Betic Cordilleras, Spain). Implications on Paleotethyan evolution

The Marbella Conglomerate (Betic Cordilleras, SW Spain) is a poorly sorted and polymictic rock of vaguely constrained Late Carboniferous age interlayered within a sandy sequence. It contains variable amounts of pebbles of quartzite, gneiss, deformed granitoid, schist, aplite, dacite and other volcanic rocks among others, which makes it a potential target for detrital zircon provenance studies. In order to decipher provenance we combined U–Pb SHRIMP and LA–ICP-MS analyses on zircons obtained from single pebbles of deformed rocks (schist, granitoids) and detrital zircons from the sandy sequence, respectively. The age spectra of the detrital zircons indicates that at least the sedimentation took place soon after the start of the Permian according to the youngest detrital zircon age (≈286Ma), and it involved the denudation of terranes with rocks bearing Paleoproterozoic, Neoproterozoic, Cambro-Ordovician, Devonian and Carboniferous zircon age clusters. In contrast with the Permian age of the detrital zircons from the sandstones, igneous (ca. 532 and 516Ma) and metamorphic (ca. 356Ma) U–Pb SHRIMP Concordia ages were obtained from the pebbles. The different age clusters observed could be correlated to igneous, metamorphic and detrital rocks from an already eroded terrane similar to the Ossa-Morena Zone of the Iberian Variscan Belt. Therefore, we propose that most of the sedimentation of the Marbella Conglomerate took place along the western border of the Paleotethys at the north margin of Gondwana during the dismantling of the Variscan orogenic edifice and/or the Neotethys ocean opening and the birth of the Cimmerian ribbon continent.

Associations de kystes de dinoflagellés des séries du Jurassique supérieur (Oxfordien–Tithonien) du Rif externe (Prérif interne et Mésorif, Maroc) et comparaisons régionales

A biostratigraphic study of dinoflagellate cysts of the Upper Jurassic series from the eastern External Rif Chain, has been achieved for the first time on four outcrop sections : the DM section (Douar Marticha), the TB section (the Tarhchenna “Sof”), the KSD section (the Kef Mallou “Sof”) and the Y section (Douar Lamriene) among which three sections (TB, KSD and Y) are well-dated by ammonites and calpionellids fauna. The DM and TB sections are complementary in terms of stratigraphy and correspond respectively to the upper part of the “Ferrysch” Formation, a thick shaly–silty and sandy sequence assigned to the Callovian-Oxfordian stages and to the El Gouzat limestones Formation (Kimmeridgian - Lower Tithonian age) and to the Tarhchenna marly limestones Formation (Upper Tithonian age) from the EL Gouzat area (Mesorif). The KSD and Y sections are also complementary and correspond to the Kimmeridgian-Lower Tithonian Msila limestones Formation and to the overlying marly limestones Massif Formation of Upper Tithonian age, outcropping in the Msila region (Internal Prerif). These four sections have shown many dinocysts rich levels, which had allowed characterizing the Middle? and Upper Oxfordian substages in the DM section. In the other sections, the dinoflagellate cyst assemblages are nearly similar to those of the Kimmeridgian–Tithonian of many sections from the Boreal, Sub-boreal and North tethyan realms, particularily from England, Russia and South-East France basin. The results of the present work confirm once again, the important value of dinoflagellate cysts, for age dating of ammonites-lacking Mesozoic sedimentary sequences and for biostratigraphic correlations.

High resolution facies analysis and sequence stratigraphy of the Siluro-Devonian succession of Al Kufrah basin (SE Libya)

New fieldwork data collected from the flanks of Al Kufrah basin, SE Libya, provide insight into the controls on Siluro-Devonian sedimentation patterns along the eastern part of the North Gondwanan platform. A stratigraphic and sequential correlation framework from the northern and eastern flanks of the basin is presented for the Tanezzuft, Akakus, Tadrart and Binem formations. Ten facies associations are recognised, classified within three process-driven groups, facilitating high-resolution sequence analysis and highlighting key regional unconformities.The basal, shaly Tanezzuft formation is organised into a regional transgressive cycle that overlies upper Ordovician glacially-related deposits of the Mamuniyat formation. The shale grade upward into the heterogeneous Akakus formation that comprises complex deltaic thin sandy strata interbedded with silty shale and siltstones, widely influenced by storm to tide related flows. In Jabal az Zalmah (northern flank), four 3rd order transgressive–regressive (T/R) depositional sequences were identified, whilst only one in Jabal ‘Asba (eastern flank), indicating significant erosion of the Akakus due to the Caledonian deformation. Depositional cycles are made of sheltered tidal flat deposits which pass upward into lower to upper offshore heterolithic deposits. They are bounded by regional disconformities interpreted as forced regression surfaces. The Silurian Tanezzuft and Akakus formations form together an overall 2nd order regressive succession.The Caledonian unconformity is interpreted as a mega-regional sequence boundary resulting from uplift and erosion during the late Silurian into the early Devonian. The thickness variability of the Akakus formation across Al Kufrah basin is strongly indicative of differential erosion which generated a complex basin physiography. Above, the Tadrart formation of lower Devonian age forms an aggrading braided-style fluvial sandy sequence of approximately constant thickness across the basin.A return to marine conditions by the mid to late Devonian resulted in deposition of the Binem formation as a series of three stacked 3rd order T/R cycles. These deposits comprise bioturbated, tide-dominated successions which preserve some evidence for periodic open marine flooding. Lying conformably on the Tadrart formation, the Binem formation forms an overall 2nd-order transgressive trend where a maximum flooding surface occurs within the uppermost bioturbated deposits.Stratigraphic correlations made on Siluro-Devonian deposits reveal a complex sequential organisation and also account for the impact of the Caledonian erosion on pre-tectonic strata. Post-Caledonian Devonian deposits develop on a smoothed topography associated with a regional uplift and can be easily correlated over the Al Kufrah basin.

Cretaceous anoxic–oxic changes in the Moldavids (Carpathians, Romania)

This study focused on the Cretaceous black shale successions, followed by red shales that crop out at the outer regions of the Romanian Carpathians, in the Moldavids. The oldest parts of the black shale units deposited in an abyssal plain during Late Valanginian–Late Barremian time; they are mainly characterized by hemipelagic and pelagic muddy siliciclastic rocks and carbonates, commonly intercalated with fine-grained turbidites. During the sedimentation of the middle part of the black shale units in the Late Barremian–Early Albian interval, the depth of the basin increased, as the carbonate hemipelagic sedimentation was replaced by a mainly siliceous one. Only a few thin turbidite intercalations are present. The youngest part (Albian pro parte) of the black shale units is characterized by a turbiditic sedimentation, with mainly sandy sequences of middle and lower deep-water fans. We may assume that the depth of the basin continuously decreased. The presence of authigenic glauconite in the Albian sandstones suggests a palaeoenvironmental change, linked to the occurrence of oxygenated turbidity current circulation. A significant shift in the sedimentation regime in the Eastern Carpathian Moldavids took place in the Late Albian, when Cretaceous Oceanic Red Beds (CORB) occurred. This type of sedimentation lasted up to the Coniacian. The lower part of the CORBs that contains radiolarites intercalated with variegated shales, pyroclastic tuffs and thin sandstones is interpreted as a hemipelagic and pelagic sedimentation in the abyssal plain environment, where rarely turbidites occurred. Upwards, there are mainly burrowed variegated red and green shales. The youngest parts of CORBs are characterized by increased thickness and frequency of the turbidites. While the main part of the CORB is carbonate free or has very low carbonate content, the upper part of these strata becomes rich in marl and mudstone strata, indicating a decrease of the basin-depth. The accumulation of black shales in the Eastern Carpathians during the Late Valanginian–Late Albian interval is linked to the existence of a small, silled basin of the Moldavian Trough, in which restricted circulation led to the density stratification of the water column, resulting in the deposition of anoxic Lower Cretaceous sediments (i.e., the black shales). Because of the tectonic deformation that took place within the Lower–Upper Cretaceous boundary interval, the restricted circulation had changed to an open circulation regime in the Moldavian Trough. Hence, the anoxic regime was progressively replaced by an oxic one, across the Albian–Cenomanian boundary interval. The beginning and the end of the CORBs in the Moldavid units depend thus on various palaeogeographic and palaeoenvironmental settings, and it was controlled by the regional tectonic activity.

Calcretes e registros de paleossolos em depósitos continentais neocretáceos (Bacia Bauru, Formação Marília)

The results presented are based on regional research of calcrete and palaeossols records in the Eastern part of the Bauru Basin, in Sao Paulo State and Triângulo Mineiro region. This basin was filled by Upper Cretaceous siliciclastic sandy sequence, in semi-arid climate on the edges, desert in the center. The most significant calcretes occurrences belong to the the Marilia Formation (Bauru Group), whichon a regional scale, are represented by two extreme types, related to the depositional context. The Ponte Alta type was formed in marginal alluvial fan deposits, the Echapora type in inner aeolian sandy deposits, of wide sand sheets and smooth depressions with temporary rivers and lakes. Three genetic contexts are proposed for the Marilia Formation calcretes: pedogenetic peripheral (Pp), pedogenetic interior (Pi) and phreatic (F). In the first two contexts the edaphic vadose and palustrine processes prevailed, as well as soil profiles poorly developed. It was noticed in them a big frequency of the beta microstructure association. They occur in the Triângulo Mineiro (MG), regions of Monte Alto, Agudos and Bauru (SP). In the phreatic context there was intense development of micritic and spar textures, which probably destroyed the original features of the beta association, generated in contexts Pp and Pi. The superimposed phreatic processes determined the predominance of the alpha microstructure association. They were probably more intense and of the last and/or the most important event in the internal calcrete formation of the basin,in Echapora type profiles. They occur in the regions of Echapora and Marilia (SP). The dendritic configuration of the long and narrow plateaux, sustained by calcified sandstones of the Marilia Formation indicates processes of landscape elaboration through the relief invertion.

Calcretes e registros de paleossolos em depósitos continentais neocretáceos

The results presented are based on regional research of calcrete and palaeossols records in the Eastern part of the Bauru Basin, in Sao Paulo State and Triângulo Mineiro region. This basin was filled by Upper Cretaceous siliciclastic sandy sequence, in semi-arid climate on the edges, desert in the center. The most significant calcretes occurrences belong to the the Marilia Formation (Bauru Group), whichon a regional scale, are represented by two extreme types, related to the depositional context. The Ponte Alta type was formed in marginal alluvial fan deposits, the Echapora type in inner aeolian sandy deposits, of wide sand sheets and smooth depressions with temporary rivers and lakes. Three genetic contexts are proposed for the Marilia Formation calcretes: pedogenetic peripheral (Pp), pedogenetic interior (Pi) and phreatic (F). In the first two contexts the edaphic vadose and palustrine processes prevailed, as well as soil profiles poorly developed. It was noticed in them a big frequency of the beta microstructure association. They occur in the Triângulo Mineiro (MG), regions of Monte Alto, Agudos and Bauru (SP). In the phreatic context there was intense development of micritic and spar textures, which probably destroyed the original features of the beta association, generated in contexts Pp and Pi. The superimposed phreatic processes determined the predominance of the alpha microstructure association. They were probably more intense and of the last and/or the most important event in the internal calcrete formation of the basin,in Echapora type profiles. They occur in the regions of Echapora and Marilia (SP). The dendritic configuration of the long and narrow plateaux, sustained by calcified sandstones of the Marilia Formation indicates processes of landscape elaboration through the relief invertion .

Stratigraphy and depositional environment of late Pleistocene Sunakothi Formation in Kathmandu Basin, central Nepal

Thick sandy sequences were recognised between the central and southern part of the basin, it was named as the Sunakothi Formation. We designate the type locality of this formation at Sunakothi, a village lying 3.0 km south of Patan. This formation is extensively distributed in the Nakhu, Kodku, and Godavari Kholas ranging in altitude from ca 1420 m in the southern margin to 1300 m in the central part. The average thickness of this formation ranges from 34 to 60 m. The sedimentary strata are gently inclined towards the north. On the basis of geological mapping this formation is located between the muddy part of the Kalimati Formation of the ancient lake and the terrace gravel deposits. It is further divided into the following four parts: (1) muddy rhythmic basal part, (2) sandy lower part, (3) muddy, sandy, and gravelly middle part, and (4) laminated silty upper part. The basal part shows a transition from the lacustrine to fluvial environment in the south and the prodeltaic environment towards the basin centre. Its lower part contains sandy fluvial to lacustrine delta front deposits whereas the middle part comprises sandy bar, muddy floodplain, and gravelly channel-fill deposits. The upper part of this formation is restricted only to the southern end of the basin and shows marginal shallow lacustrine environments. The sedimentological evidence indicates that the Palaeo-Kathmandu Lake was drained out from the south due to tectonic activities as well as late Pleistocene climatic changes.

Seismites in continental sand sea deposits of the Late Cretaceous Caiuá Desert, Bauru Basin, Brazil

Two large-scale sediment deformation structures, minor fold occurrences in cross-bedded sand dune deposits and complex convolute folds, are observed in red sandstones, in a zone about 1.5 km long in floodway cuts at the Sérgio Motta/Porto Primavera dam, São Paulo state, Brazil. The most important structures are confined to planar zones, up to 10 m thick, in undeformed dune foreset strata were they can be traced laterally for about 50–60 m. The sandstones are part of the Rio Paraná Formation, Caiuá Group, which accumulated in a great sand sea of about 100,000 km 2. The Caiuá Desert developed during the Late Cretaceous in the southern part of the Bauru Basin, an intracontinental subsiding area in the central-southern part of the South-American Platform. The basin was filled by a sandy sequence about 300 m thick. The sand sea deposits correspond to the Caiuá Group and comprise: a) deposits of dry sand sheets (Santo Anastácio Formation), b) deposits of medium-sized dunes and humid interdunes of the sand sea peripheral zones (Goio Erê Formation), and c) deposits of large-sized complex aeolian dunes and draas, that correspond to the central part of the inland sand sea (Rio Paraná Formation). The deformations in the sediments are attributed to the effects of fluidization, liquefaction and shear stress, which are interpreted as being earthquake-induced structures, mainly because: (1) the deformed horizons are confined between undeformed cross-bedded strata, (2) the complex convolute folds sometimes include nappe-like structures that overlie foreset facies, (3) during the Bauru Basin infilling there was tectonic activity associated with alkaline volcanism on the borders of the basin and related silicification in the central-southern part. The main silicification zones are aligned to regional lineaments that cross the area near the large-scale sedimentary deformation structures.

Lithology and geochemistry of Albian-Cenomanian sandy sequences of the Voronezh Anteclise and their paleogeographic implication

The paper proposes subdivision of Albian and Cenomanian monotonous sandy sequences of the Voronezh anteclise on the basis of textural-structural features and distribution of accessory minerals. Distribution of rare earth, trace, and major elements was studied in sandy rocks and early diagenetic formations (glauconites and phosphorites). Dependence of the distribution on tectonic factor is noted.

Opal content in the Ría de Vigo and Galician continental shelf: biogenic silica in the muddy fraction as an accurate paleoproductivity proxy

Biogenic silica (BSi) content was determined in both superficial marine sediments from the Ría de Vigo and gravity core samples (core CGPL00-1) from the adjacent continental shelf. Samples were processed following the alkaline leaching procedure. The standard deviation for opal-rich samples is very low (±0.2), whereas for opal-poor samples (<1.3 wt.%) the relative standard deviation can reach up to 16%. Opal percentages in superficial dry bulk sediments and gravity core samples range between 0.2–5.1 wt.% and 1.1–2.0 wt.%, respectively. Maximum opal percentages are found in the inner part of the ria around San Simón Inlet. Values of 2–3 wt.% typify the inner-central part of the ria. Throughout the ria longitudinal axis opal content is about 2 wt.%. Smaller values are found in the margins at the mouth of the ria. Opal distribution throughout the core is irregular, but there is a general tendency for higher values in upper muddy level and lower values in sandy sequence. Opal analyses were performed for the total and <63 μm fractions of both ria and core sediment samples. For the core samples, there is no correlation between opal content in the fine and bulk fractions, but opal percentage in the muddy fraction is an useful parameter to standardize results and to apply as a paleoproductivity proxy. For the ria surface sediments there is a good correlation between BSi content in both fractions ( R 2 = 0.90 ). This fact suggests that the information provided by total and fine fraction analysis is similar; as a result, the opal content analysis in the fine fraction does not supply any new information concerning diatom productivity.

Découverte des sables à Mactres de la base du Burdigalien à Martillac (Nord Aquitaine ; SW France) ; données paléontologiques

The Early Burdigalian in the type area of the stage (Gironde, South of Bordeaux) comprises marine deposits with rather various facies, often rich in molluscs. Locally, the very basal Formation of “Sables à Mactres” is present, formerly known in Léognan, but very little studied in litteris. We have discovered first at Martillac deposits allocated to this Formation, and we study their paleontological contents. The macrofauna is more diversified than it was expected from the aspect of sediment; for instance, 210 mollusc species have been inventoried in these grey fine sands, bedded and very carbonatic, where Bivalvia shells are well preserved and dominant among the whole fauna. These shells are either scattered in the layers or accumulated in small beds. Echinoids, Asteroids, Crustacea, Annelida, Scleractinia, Brachiopoda, fishes, Alga Rhodophycea, are present, as well as an abundant microbenthos. Taphonomic observations are made on the sandy sequence, and taxonomic and biostratigraphic remarks concern some mollusc species. From a paleoecologic point of view, the endobiont forms are dominant within the malacofauna, they are accompanied by several epibiont and semi-endobiont taxa, and few pelagic and endolith ones. Concerning the trophics, the suspension-feeders molluscs are dominant in specimens number, notably amongst Bivalvia, and carnivores, detritivores/deposit-feeders, herbivores and commensal/parasites are more or less well represented. On the whole, the soft-substrate species are obviously in a majority. This paleobiofacies with Mactrids – Donax – Capsa – Pitar – Loripes – Ringicula corresponds to a deposit in a coastal tidal area, rather calm, of a shallow embayment type, with very few detritics, and submitted to a moderate hydrodynamism and to a subtropical to tropical climate. The reworking is insignificant in the sequence where shells are dispersed (parautochthonous species), and the transport has been limited to the falun beds (e.g. little channels, tides action). The conditions of settlement of the earliest phases of Burdigalian transgression are thus specified in this type area.

The Early and Middle Miocene transgression at the southern border of the North Sea Basin (northern Belgium)

The Lower–Middle Miocene Berchem Formation of northern Belgium is an essentially sandy sequence with a varying glauconite content and often abundant shelly intervals. The formation was deposited in a shallow marine environment and rests unconformably on stiff Rupelian clays or Chattian sands. The lithological recognition of the four members (Edegem Sands, Kiel Sands, Antwerpen Sands and Zonderschot Sands members) of the Berchem Formation solely based on lithological criteria proved to be difficult, especially in boreholes. The geometry of the Formation in the subsurface of northern Belgium remained largely unknown. Diverse and well preserved dinoflagellate cyst associations have been recovered from the four members in seven boreholes and two outcrops, and allow a refinement of the biostratigraphy of these deposits. A Miocene biozonation defined in mid-latitude shallow marine deposits in the Atlantic Coastal Plain of the USA (Salisbury Embayment, Maryland) is readily applicable to this material, and has led to a detailed stratigraphic assessment of each member. Three detailed profiles depicting the distribution of the biozones in the subsurface of northern Belgium allow the reconstruction of the geometry and depositional history of the Berchem Formation. The oldest Miocene deposits are of early Burdigalian age and they testify to a transgression, which invaded Belgium from a north–northwestern direction. The maximum flooding took place during early Serravallian times. The upper boundary of the formation is a major erosional surface of late Serravallian or (slightly) younger age. Copyright © 2005 John Wiley & Sons, Ltd.

MAPA LITOESTRATIGRÁFICO DA PARTE ORIENTAL DA BACIA BAURU (PR, SP, MG), ESCALA 1:1.000.000

A Bacia Bauru é uma bacia continental interior do Neocretáceo (Coniaciano-Maastrichtiano), desenvolvida no centro-sul da Plataforma Sul-Americana. Acumulou uma seqüência sedimentar essencialmente arenosa, que ocorre em área de cerca de 370.000 km2. Tem por substrato rochas vulcânicas, sobretudo basaltos da Formação Serra Geral (Cretáceo Inferior). A área do mapa corresponde à parte oriental da bacia, com cerca de 180.000 km2. A seqüência neocretácea é composta por dois grupos cronocorrelatos: Caiuá (formações Rio Paraná, Goio Erê e Santo Anastácio) e Bauru (formações Uberaba, Vale do Rio do Peixe, Araçatuba, São José do Rio Preto, Presidente Prudente e Marília, incluindo os Analcimitos Taiúva). LITHOSTRATIGRAPHIC MAP OF THE BAURU BASIN EASTERN PART (PR, SP, MG), SCALE 1:1.000.000 Extended Abstract The Bauru Basin is a Late Cretaceous (Coniacian-Maastrichtian) interior continental basin developed as a result of subsidence of the central-southern part of the South-American Platform. It spreads over an area of approximately 370,000 km2 and is filled by a sandy sequence with a preserved maximum thickness of 300 meters. The substratum is made up of volcanic rocks (mainly basalts) of the Serra Geral Formation (Early Cretaceous). The map area corresponds to the eastern part of the basin, with about 180,000 km2 (west of São Paulo, southwest of Minas Gerais, northwest of Paraná), located between the coordinates 18°S to 25° S and 47° W to 54° W (Figure 1). The Upper Cretaceous sequence is composed by two partially contemporaneous groups (Figure 2): Caiuá (Rio Paraná, Goio Erê and Santo Anastácio formations) and Bauru (Uberaba, Vale do Rio do Peixe, Araçatuba, São José do Rio Preto, Presidente Prudente, and Marília formations, including the Taiúva analcimites). The intensification of the tectonic activities at the north-northeastern and eastern margins, and probably also at the northwestern margin, caused significant changes in the paleogeographic scenario, promoting progradation of alluvial fans. At the same time, climatic changes increased the humidity in the marginal zones. These changes mark the beginning of the sedimentary phase during which important fluvial systems from northeast to southwest were established between the marginal zone and the inland Caiuá Desert. During the uplift of the margins, the intrusion of several alkaline magmatic bodies cause extrusive magmatism near the eastern border (Taiúva analcimites), as well as localized silicification in the southern border. All known fossil occurrences are located in the eastern part of the basin and were paleogeographically controlled. They comprise bone remains, mainly from reptiles -crocodiles, turtles, dinossaurs -, as well as amphibians, fishes, mollusks, crustaceans, and oogones of charophytic algae. The main occurrences are from fluvial flood plain deposits and ephemeral lagoons in the interior of the basin, as well as from those of braided water flows and lagoons located in zones of marginal alluvial fans. In the interior of the basin the hot desertic condition prevailed during the two phases of sedimentation.

Paleoclimatic evolution of the Galician continental shelf (NW of Spain) during the last 3000 years: from a storm regime to present conditions

A multiproxy study of the sedimentary record carried out on gravity core CGPL00-1 retrieved from the outer Galician continental shelf (NW of Spain) has allowed us to establish the main climate fluctuations affecting the region during the Upper Holocene. Grain size, TOC, C/N ratio, biogenic opal and planktonic foraminifera are the main analysed parameters. Lithology and grain size distribution lead to identify two sedimentary sequences: a lower half mainly composed by glauconitic sand and a muddy upper half. A chronology has been established based on three AMS radiocarbon ages, 907 cal. BC, 898 cal. BC and 1399 AD, and the aforementioned sedimentary sequences. The obtained radiocarbon ages are the first dated sediment samples for the Galician continental shelf. Geochemical markers show different trends in both sequences: low and/or fluctuating values in the sandy sequence and high and relatively constant values in the upper muddy sequence. The whole sandy interval is interpreted to be a nearly instantaneous deposit from a distal storm ebb current. The muddy interval was deposited in a stable and low-energy marine environment, similar to that found on the present outer shelf. The shift from a storm-dominated shelf to a low-energy environment took place synchronous with the Subboreal/Subatlantic transition, when an increase in storminess appears related to climatic instability. Transitional planktonic foraminiferal assemblage dominates the whole record, although a change to more abundant cold water species at 1420 AD, may relate to an intense upwelling pulse, probably reinforced by colder atmospheric temperatures during the Little Ice Age (LIA). Despite the presence of an upwelling regime since 1420 AD, lesser amount of opal has accumulated in the outer shelf due to enhanced offshore transport and stronger remineralization.

DEPOSITIONAL ENVIRONMENTS AND RESERVOIR ASSESSMENT OF LATE CRETACEOUS SANDSTONES IN THE SOUTH CENTRAL KIRTHAR FOLDBELT, PAKISTAN

Sandstones of Late Cretaceous (Campanian‐Maastrichtian) age constitute much of the Pab and Mughal Kot Formations, which are well exposed in western Pakistan. In the south central part of the Kirthar foldbelt, these units attain thicknesses ranging up to 350m and are dominated by quartzose sandstones with subordinate argillites and marls, all deposited on the western continental margin of the Indo‐Pakistan Plate. Seven sedimentologic logs, measured through this sandy sequence along a strike‐wise extent of some 290 km, provide new data on the palaeoenvironments and dispersal patterns represented in these rocks and on their reservoir potential.The eight main facies were formed by a range of sand‐transporting mechanisms that includes classical turbidity flows, storm‐ and river flood‐generated underflows, high and low‐energy tractional flows, storm‐ and fair weather wave reworking, and local slope failure and remobilisation. The four facies associations comprise a Shoreface Association, a Shelfal Delta Lobe Association, a Deeper Shelf/Ramp Association (the distal equivalent of the Shelfal Delta Lobe Association), and a deep‐water Submarine Fan Lobe Association.Facies distributions and palaeoflow patterns demonstrate the existence of two depositional systems in this area during the Late Cretaceous. Sandbodies formed in a NW‐prograding submarine fan dominate a southern system, while in the north of the study area, storm‐ and river flood‐influenced shelfal sands were conveyed to the west and WNW. Here, sediment‐gravity flows evolved from east to west, following a broadly across‐shelf pattern from cross‐bedded sandstones to graded turbidites. Sandstone petrography suggests supply from the uplifting Indo‐Pakistan Shield to the east, feeding a broad, west‐facing shelf or clastic ramp characterised by Mutti‐type “shelf‐lobes”.At outcrop, these sandstones possess low porosities but other reservoir characteristics (total sand thickness, percent sand, sand‐body geometry, vertical and lateral connectivity, The authors acknowledge the financial assistance of the Pakistan Science Foundation for the fieldwork. Most of the analytical and laboratory work was carried out at Keele University under the auspices of the Commonwealth Fellowship Scheme. The principal author thanks the Association of Commonwealth Universities for financial support and the School of Earth Sciences and Geography, Keele University, for providing facilities. Special thanks are due to P. Greatbatch, D. Wilde and A. Lawrence (Keele University) for technical and drafting assistance. Andrew Brown (ENI‐Lasmo, London), John Warburton and Simon Beswetherick of Lasmo Oil (Pakistan) Ltd. were most helpful and their sponsorship of new biostratigraphical analyses is also acknowledged. Thanks are due to the Centre of Excellence in Mineralogy, University of Balochistan for granting leave to the principal author. We much appreciated helpful discussions with John Smewing (Earth Resources Ltd, Swansea, UK) and Stuart Burley (BG Group), whose perceptive comments on an earlier draft of this paper were most valuable.

Revisão estratigráfica da parte oriental da Bacia Bauru (Neocretaceo)

This paper deals with the stratigraphy of the Bauru Basin based on regional investigation. The Bauru Basin was formed in the Late Cretaceous (Coniacian- Maastrichtian) as a result of subsidence of the central-southern part of the South-American Platform.This inner continental basin spreads over an area of approximately 370,000 km2 and is filled by a sandy sequence with maximum thickness of 300 meters at present. Its substratum is constituted by volcanic rocks (mainly basalts) of the Serra Geral Formation (1K) from which it is separated by a regional erosive surface. The studied area, with about 180,000 km , corresponds to the eastern part of the basin (west of Sao Paulo, southwest of Minas Gerais, northwest of Parana), and is located between the coordinates 18°S to 25° S and 47° W to 54° W. According to the distribution and interrelations of the units a stratigraphic revision was proposed for the basin. The Upper Cretaceous sequence is now divided in two groups, partially contemporaneous: Caiua Group (Rio Parana, Goio Ere and Santo Anastacio formations) and Bauru Group (Uberaba, Vale do Rio do Peixe, Aracatuba, Sao Jose do Rio Preto, Presidente Prudente, and Marilia formations, including the Taiuva analcimites).