Tectono-stratigraphic evolution of the Upper Jurassic–Neocomian rift succession,Araripe Basin,Northeast Brazil

The rift succession of the Araripe Basin can be subdivided into four depositional sequences, bounded by regional unconformities, which record different palaeogeographic and palaeoenvironmental contexts. Sequence I, equivalent to the Brejo Santo Formation, is composed of fluvial sheetflood and floodplain facies association, while Sequence II, correspondent to the lower portion of the Missão Velha Formation, is characterised by braided fluvial channel belt deposits. The fluvial deposits of Sequences I and II show palaeocurrents toward SE. The Sequence III, correspondent to the upper portion of Missão Velha Formation, is composed of fluvial sheetflood deposits, which are overlain by braided fluvial channel deposits displaying a palaeocurrent pattern predominantly toward SW to NW. Sequence IV, equivalent to the Abaiara Formation, is composed of fluvio–deltaic–lacustrine strata with polimodal paleocurrent pattern. The type of depositional systems, the palaeocurrent pattern and the comparison with general tectono-stratigraphic rift models led to the identification of different evolutionary stages of the Araripe Basin. Sequences I, II and III represent the record of a larger basin associated to an early rift stage. However, the difference of the fluvial palaeocurrent between sequences II and III marks a regional rearrangement of the drainage system related to tectonic activity that compartmentalised the large endorheic basin, defining more localised drainage basins separated by internal highs. Sequence IV is associated with the renewal of the landscape and implantation of half-graben systems. The high dispersion of palaeocurrents trends indicate that sedimentary influx occurs from different sectors of the half-grabens.     

Paleo-environment and provenance in a lacustrine shallow-water delta-meandering river sedimentary system: insights from the Middle–Upper Jurassic formations of the Fukang Sag of Junggar Basin,NW China

The Middle–Upper Jurassic Shishugou Group in the central Junggar Basin was deposited in a lacustrine shallow-water delta-meandering river sedimentary system. The integrated petrological (thin-section, granularity and heavy minerals analysis), geochemical (trace elements and rare earth elements analysis) and geophysical analyses (well logging and 3D-seismic slice analysis) are used to determine redox conditions, paleoclimate, paleosalinity, provenance and sedimentary evolution extant during deposition of the Shishugou Group: (1) the redox condition changed from a weak anoxic/oxic condition to a strongly oxic condition; (2) the climate changed from humid to hot and arid in the Middle–Late Jurassic, which may have resulted in the lake water having slight–medium salinity; (3) the relatively distant northeastern provenance from the Kelameili Mountain is the most important sediment source; and (4) the south provenance from the Tianshan Mountains (Bogeda Shan) decreases with the development of the sag piedmont, which supplies sediments to the southeastern Fukang Sag. The sedimentary environment changed from a lacustrine shallow-water delta to a meandering river during the deposition of the Shishugou Group. The shallow-water meandering river delta was characterised by pervasive mudstones with oxide colours, thin single-layer sand bodies (1–15?m, mean 3?m), relatively low sand–strata ratios (0.2–0.5) and the absence of progradation, mouth bars and reverse rhythms. The gentle slope is the primary condition necessary for the formation of a shallow-water meandering river delta. Paleo-environment (climate change from warm-humid to hot-arid) and the stable and remote Kelameili Mountain provenance played critical roles in the development and evolution of lacustrine–delta-meandering river sedimentary systems.     

Geochemistry and Sr–Nd–Pb isotopic composition of the Harrat Al-Madinah Volcanic Field,Saudi Arabia

Whole-rock geochemical and Sr, Nd and Pb isotope data are presented for the Harrat Al-Madinah volcanic field, in the north western part of the Arabian plate, aiming to understand their origin and the composition of their mantle source. This area is an active volcanic field characterized by the occurrence of two historic eruptions approximately in 641 and 1256 A.D. Field investigation of the main volcanic landforms indicates dominantly monogenetic strombolian eruptions, in addition to local phreatomagmatic eruption style. The lavas consist mainly of alkali olivine basalt, olivine transitional basalt, and hawaiite with ocean island basalt (OIB)-like characteristics. Evolved rocks, represented by mugearites, benmoreites, and trachytes, occur mainly as domes, tuff cones and occasionally as lava flows. Chemical variations in the evolved rocks indicated their evolution by low pressure crystal fractionation of olivine, plagioclase, clinopyroxene, and Fe–Ti oxides from the relatively primitive basalts. The isotopic compositions of ¹⁴³Nd/¹⁴⁴Nd (0.512954–0.512995), ⁸⁷Sr/⁸⁶Sr (0.702899 to–0.702977) and Pb (²⁰⁶Pb/²⁰⁴Pb = 18.5515–18.7446, ²⁰⁷Pb/²⁰⁴Pb = 15.5120–15.5222, ²⁰⁸Pb/²⁰⁴Pb = 38.1347–38.4468), show restricted variations suggesting only minor crustal contamination. They defined an array consistent with mixing of two geochemically distinct components of depleted MORB-mantle (DMM) and high ²³⁸U/²⁰⁴Pb ratio (HIMU). The variations in Tb/Yb, La/Yb and Sm/Yb ratios in the relatively primitive basalts (MgO > 6 wt.%) indicated garnet peridotite source. However, the positive Nb, Sr, Ba and Ti anomalies in the primitive mantle-normalized incompatible element patterns and the significant variation between Zr/Nb vs. Ce/Y and La/Yb vs. Yb suggest contribution of an amphibole-bearing spinel lherzolite source. Moreover, the negative correlations between SiO₂ vs. ⁸⁷Sr/⁸⁶Sr and Th vs. ¹⁴³Nd/¹⁴⁴Nd are interpreted as an indication of mixing melts derived from two end-members; one is garnet bearing asthenospheric source with OIB characteristic and the other is amphibole-bearing spinel lherzolite. The Harrat Al-Madinah volcanic field occurs near the Red Sea Rift System and its origin reflects a strong lithospheric control on the loci of partial melting. The dominantly NNW alignment patterns of the volcanoes, which is similar to the regional Red Sea trend, may suggest that the magmas were produced by decompression partial melting triggered by lithospheric extension related to the Red Rift.     

Lower–Middle Jurassic foraminiferal and ostracode biostratigraphy of the Barents Sea shelf

The Barents Sea shelf is an attractive target as a prospective large petroleum province. Further development of geological and geophysical exploration in the area requires high-resolution biostratigraphic constraints and update stratigraphic charts. The zonal succession of Lower and Middle Jurassic assemblages of foraminifers and ostracodes of the Barents Sea fits well the division for northern Siberia based on correlated independent Jurassic and Cretaceous zonal scales on all main microfossil groups, of which some scales were suggested as the Boreal Zonal Standard. The stratigraphic range of the Barents Sea microfossil assemblages has been updated through correlation with their counterparts from northern Siberia constrained by ammonite and bivalve data. Joint analysis of foraminiferal and ostracode biostratigraphy and lithostratigraphy of the sections allowed a revision to the stratigraphic position and extent of lithological and seismic units. The discovered similarity in the Lower and Middle Jurassic lithostratigraphy in the sections of the Barents Sea shelf and northern Siberia, along with their almost identical microfossil taxonomy, prompts similarity in the Early and Middle Jurassic deposition and geological histories of the two areas.     

Pliocene–Pleistocene stratigraphy and macrofauna of the Farasan Islands, South East Red Sea, Saudi Arabia

The stratigraphy of the Farasan Islands (Pliocene?CPleistocene deposits) is established on the basis of a detailed study of six stratigraphic sections described and sampled in the field. Detailed examinations involve the microfacies analyses and identification of macrofossils makes it possible to determine two new informal formations, namely, from the base to the top: Esbah formation of Pliocene age and Farasan formation of Pleistocene age. The detected microfacies types of the studied samples are only carbonate facies and include five major types: mudstone, wackestone, packstone, floatstone and boundstone. No grains of quartz sand or igneous mineral were found in the islands. The nomenclature of the biostratigraphic units established in the present work is not intended to define world-wide zonal standards. It is only used to subdivide the sequence into biostratigraphic zones according to 137 macrofaunal species (78 bivalves, 56 gastropods and three echinoids). These biozones, namely: Lithophaga teres zone (Early Pliocene), Clypeaster reticulates?CLaganum depressum zone and Chesapecten madisonius?CNoetia limula interval zone are assigned to the Late Pliocene; meanwhile, Noetia limuli?CAnadara ovalis interval zone and A. ovalis range zone are assigned to the Pleistocene age. The affinity of the Pliocene?CPleistocene fauna recorded from the Farasan Islands increase with time towards the Indo-Pacific realm. The identified bivalves and gastropods are dominated by the Indo-Pacific forms suggesting the connection of the Red Sea rift with the open Indian Ocean via the Gulf of Aden and Bab El Mandab in the latest Miocene and Early Pliocene.     

Sedimentogenesis and resource potential of Middle–Upper Bathonian reservoirs in the Middle Ob’ region

This study provides a comprehensive sedimentologic analysis of the J₂ prospective horizon (Middle–Late Bathonian) in the central West Siberian Basin. Based on the extensive dataset, it was established that structural complexity of this horizon is largely caused by a variety of depositional environments. Sedimentary facies of this horizon pass upward from widespread continental at the base, through deltaic or coastal-continental, to marginal-marine at the top. Change in the paleohypsometry of the study area reflects the distribution of depositional environments, in terms of the proportions of continental, transitional, and marine deposits. The study also shows that facies variability and change in depositional settings can have a significant control on reservoir quality, as well as its vertical and lateral distribution. Using a combination of detailed GDE reconstructions, structure contour mapping on the top and base of the J₂ horizon, analyses of well test data, probability of reservoir presence, distribution of average porosity and permeability within different subenvironments, a composite map showing variations in the reservoir effectiveness in the J₂ horizon was generated.     

Facies Analysis and Sequence Stratigraphy of the Qal’eh Dokhtar Formation (Middle–Upper Jurassic) in the West of Boshrouyeh, East Central Iran

The study area is located in the east Tabas Block in Central Iran. Facies analysis of the Qal’eh Dokhtar Formation (middle Callovian to late Oxfordian) was carried out on two stratigraphic sections and applied to depositional environment and sequence stratigraphy interpretation. This formation conformably overlies and underlies the marly-silty Baghamshah and the calcareous Esfandiar formations, respectively. Lateral and vertical facies changes documents low- to high energy environments, including tidal-flat, beach to intertidal, lagoon, barrier, and open-marine. According to these facies associations and absence of resedimentation deposits a depositional model of a mixed carbonate–siliciclastic ramp was proposed for the Qal’eh Dokhtar Formation. Seven third-order depositional sequences were identified in each two measured stratigraphic sections. Transgressive systems tracts (TSTs) show deepening upward trends, i.e. shallow water beach to intertidal and lagoonal facies, while highstand systems tracts (HST) show shallowing upward trends in which deep water facies are overlain by shallow water facies. All sequence boundaries (except at the base of the stratigraphic column) are of the no erosional (SB2) types. We conclude eustatic rather than tectonic factors played a dominant role in controlling carbonate depositional environments in the study area.     

Geochemistry and provenances of the Jurassic terrigenous rocks of the Upper Amur and Zeya–Dep troughs,eastern Central Asian fold belt

This paper reports the results of complex geochemical and Sm–Nd isotope-geochemical studies of terrigenous rocks of the Upper Amur and Zeya–Dep troughs, as well as U–Pb geochronological studies of detrital zircons. It is established that the studied troughs have orogenic nature, which is of key significance for understanding the geodynamic evolution of East Asia in the Mesozoic. Such interpretation is consistent with structural features of the troughs (migration of basin axis inward the continent with time, stratigraphic rejuvenation in the same direction), which are typical of foreland basins regarded as analogues of foreland (marginal) troughs. Obtained data indicate that orogenic processes responsible for the formation of the Mongol-Okhotsk fold belt began in the Early Jurassic.     

Neogene–Quaternary sedimentary and paleovegetation history of the eastern Solimões Basin,central Amazon region

Palynological and stratigraphical analyses were carried out on the outcrops of the Solimões River to present new information about freshwater paleoenvironments of a fluvial–deltaic and meandering river system, evaluate the vegetation changes in the upper Solimões and Içá Formations in the eastern Solimões Basin, and the role of the Purus Arc in the evolution of central Amazon during the upper Neogene. The upper Miocene to Pliocene Solimões Formation is related to a fluvial–deltaic system, with fine-grained sediments of the prodelta–lacustrine environment supplied by meandering distributaries and delta front environment. The lake and distributaries were surrounded by extensive deltaic and floodplains colonized by lowland freshwater forests under wet climate conditions, persisting until the Pliocene. The Içá Formation started to deposit unconformably on the Solimões Formation during the Pleistocene, following the development of extensive meandering channels surrounded by floodplains of an essentially fluvial system linked to development of the present eastward direction of the Amazon River until the Atlantic coast. These floodplains were colonized by few palm species and pteridophytes of lowland freshwater forests during the Pleistocene. Additionally, no algae and fungi were observed, which may be related to drier climate conditions and/or different morphological conditions than the upper Solimões Formation.     

Rock slope stability and design in Arafat–Muzdalifa area,Saudi Arabia

The present contribution is a complete study extending before, during, and after the excavation of the mountain side that lying north of road 7. It includes slope stability analysis, rock cut design, and rockfall modeling for natural slope and rock cut face. Neoproterozoic granodiorite and biotite granite forming the slope body have medium to very high strengths. Mineral compositions and textures of these intact rocks control the strength values. These rocks are intensively dissected by fractures that are filled with montmorillonite and chlorite. The high plasticity and slippery nature of these filling materials represent the main problem that may face a rock cut designer because they damage the mechanical properties of these fractures. The problem begins with the selection of the rock mass classification that deals with the fracture fillings and extends during the stability analysis and the suggestion of mitigation and supporting measures. The rock masses building the natural slope are suffered by plane, wedge, and toppling failures. Therefore, two rock cut designs are suggested to avoid the hazards related to these failures and considering the construction cost as well. Rockfall modeling for the natural slope and rock cut designs was done to assess the hazards related to these falling of the blocks. The kinetic energy of falling blocks is represented on the roadway by the coverage distance and block rebound amplitude. Slope height has a positive effect on the values of these distance and amplitude, whereas the steepness of berm height has a negative effect on them. Coverage distance is a function to the location of rockfall barrier and to the width of road ditch, while the amplitude controls the barrier height.     

Deposition and deformation of fluvial–lacustrine sediments of the Upper Triassic–Lower Jurassic Whitmore Point Member,Moenave Formation,northern Arizona

The stratigraphic section of the Upper Triassic–Lower Jurassic Whitmore Point Member of the Moenave Formation at Potter Canyon, Arizona, comprises c. 26 m of gray to black shales and red mudstones interbedded with mainly sheet-like siltstones and sandstones. These strata represent deposition from suspension and sheetflow processes in shallow, perennial meromictic to ephemeral lakes, and on dry mudflats of the terminal floodout of the northward-flowing Moenave stream system. The lakes were small, as indicated by the lack of shoreline features and limited evidence for deltas. Changes in base level, likely forced by climate change, drove the variations between mudflat and perennial lacustrine conditions. Lenticular sandstones that occur across the outcrop face in the same stratigraphic interval in the lower part of the sequence represent the bedload fill of channels incised into a coarsening-upward lacustrine sequence following a fall in base level. These sandstones are distinctive for the common presence of over-steepened bedding, dewatering structures, and less commonly, folding. Deformation of these sandstones is interpreted as aseismic due to the lack of features typically associated with seismicity, such as fault-graded bedding, diapirs, brecciated fabrics and clastic dikes. Rapid deposition of the sands on a fluid-rich substrate produced a reverse density gradient that destabilized, and potentially fluidized the underlying, finer-grained sediments. This destabilization allowed synsedimentary subsidence of most of the channel sands, accompanied by longitudinal rotation and/or ductile deformation of the sand bodies.     

Use of Sedimentary Structures in the Recognition of Sequence Boundaries in Upper Jurassic–Upper Cretaceous Peritidal Carbonates of the Western Taurides,Turkey

Subtidal, intertidal, and supratidal carbonate facies are recognized in the Upper Jurassic (Kimmeridgian)-Upper Cretaceous (Cenomanian) peritidal carbonates of the Fele area (Western Taurides, Turkey). Vertical stacking patterns of these facies are of a cyclical character; shallowing upward is the trend of the cyclicity in these carbonate facies. In-situ karstic breccias, collapse breccias, caliche (laminar calcrete), “Microcodium” accretion, and root casts are structures commonly indicative of third-order sequence boundaries. However, mud cracks, solution pores or vugs, sheet cracks, loferites, and birds-eye structures are commonly delineated by parasequence boundaries. In-situ or collapse breccias can be genetically derived from sheet cracks, mud cracks, solution pores or vugs, and birds-eye structures with increasing exposure time. The use of such sedimentary structures in the recognition of sequence boundaries is highly practical in the ancient carbonate platforms of the world, inasmuch as the sequence boundaries, as demonstrated in this study, correlate with the eustatic sea level curves.     

Reworked Middle Jurassic sandstones as a marker for Upper Cretaceous basin inversion in Central Europe—a case study for the U–Pb detrital zircon record of the Upper Cretaceous Schmilka section and their implication for the sedimentary cover of the Lausitz Block (Saxony,Germany)

International Journal of Earth Sciences - The Saxonian–Bohemian Cretaceous Basin (Elbsandsteingebirge, E Germany and Czech Republic, Elbtal Group) comprises Upper Cretaceous sedimentary rocks...     

Deposition in a changing paleogulf: evidence from the Pliocene–Quaternary sedimentary succession of the Nile Delta,Egypt

Sedimentary complexes of ancient gulfs provide valuable information about paleoenvironmental dynamics. The study of several Pliocene–Pleistocene sections allowed reconstruction of the regional stratigraphical framework in the southwestern fringes of the Nile Delta. The Kafr El-Shiekh, the Gar El-Muluk, and the Kom El-Shelul formations of the Zanclean Age and the Wastani Formation of the Piacenzian Age constitute the Pliocene sedimentary succession in the study area. The establishment of 11 facies types related to 5 facies associations coupled with the results of the stratigraphical study indicate the existence of a paleogulf corresponding to the modern delta and lower valley of the Nile. This Nile Paleogulf appeared and reached its maximum spatial extent in the beginning of the Pliocene. Then, it retreated gradually and disappeared before the end of this epoch when alluvial sedimentation reestablished. There was significant flux of siliciclastic material to the study area. The Zanclean Flood in the Mediterranean Sea allowed marine incursion in the study area where the river valley incised during the precedent Messinian Salinity Crisis. Regional tectonic uplift and filling of the accommodation space with siliciclastic material from the eroded land were the main controls on the paleogulf evolution. Strengthened glaciation triggered global sea level fall, and alluvial deposition dominated the study area in the late Pliocene–Pleistocene.     

Palynostratigraphy and paleobiogeography of the Jurassic – Lower Cretaceous succession in Kabrit-1 well,northeastern Egypt

Well-preserved and abundant Jurassic–Early Cretaceous palynomorph assemblages were recorded from the Kabrit-1 well, north Eastern Desert, Egypt. Thirty-one rock-cutting samples were analyzed and six rock units were differentiated. Seventy-one palynomorph species were identified from the productive samples. Six palynozones were differentiated, and they covered all the studied succession except for a palynomorph barren interval present in the uppermost part. These palynozones arranged in ascending order are as follows: two palynozones were recorded from the Middle-Upper Jurassic (Gonyaulacysta jurassica – Lithodinia jurassica Assemblage Zone and Klukisporites pseudoreticulatus- Systematophora penicillata – Escharisphaeridia pocockii Assemblage Zone) and the other four palynozones characterize the Lower Cretaceous deposits (Pilosisporites trichopapillosus – Cribroperidinium orthoceras Assemblage Zone; Dicheiropollis etruscus Interval Zone; Murospora florida – Afropollis operculatus Assemblage Zone and Afropollis jardinus Range Zone). We infer open marine conditions during deposition of the lower part of the Khalig El Ayoun Formation (Oxfordian-Kimmeridgian) and within the Kharita Formation (Albian), and shallow marine or coastal environments during deposition of the remainder of the studied succession. Paleobiogeographically, Late Jurassic index terrestrial palynomorph species documented here are in common with those previously recorded from North Africa, while marine dinocyst species are common to those documented from the West European and North American province. During the Early Cretaceous, the recorded terrestrial microfloral species were similar to those previously recorded from the West African-South American Province, while the marine dinocyst species were still related to the West European and North American marine palynofloral province.