Stratigraphic Unconformities Research Articles

The Yanshan orogeny and late Mesozoic multi-plate convergence in East Asia—Commemorating 90th years of the “Yanshan Orogeny”

The Yanshan movement/orogeny has been proposed for 90 years, which is of special significance in the history of geological research in China. This study conducted a review by synthesizing major achievements regarding episodic deformation features, sedimentary and magmatic records of the Yanshan orogeny in China, and clarified the episodic tectono-magmatism and its geodynamic origins. The tectonic implications of the Yanshan orogeny are discussed in the context of global plate tectonics and supercontinent reconstruction. Lines of evidence from structural, sedimentary and magmatic data suggest that the Yanshan orogeny represents a regional-scale tectonic event that affected the entire China continent in late Mesozoic period. Numerous age and structural constraints consistently indicate that the Yanshan orogeny was initiated in the Jurassic (at ∼170±5 Ma). and was characterized by alternating stages of crustal shortening at ∼170–136 Ma, crustal extension at ∼135–90 Ma, and weak shortening at ∼80 Ma. The 170–136 Ma crustal shortening was reflected in the generation of two regional stratigraphic unconformities (the Tiaojishan and Zhangjiakou unconformities), which were initially named the A and B episodes of “the Yanshan Orogeny” by Mr. Wong Wenhao in 1928. Geodynamically, the Yanshan orogeny in East Asia was associated with nearly coeval oceanic subduction and continental convergence in the Paleo-Pacific, Neo-Tethys, and Mongol-Okhotsk tectonic domains. As a consequence, three giant accretionary-collisional tectonic systems were formed along the continental margins of East Asia, i.e., the Mongol-Okhotsk, Bangonghu-Nujiang, and SE China subduction- and collision-related accretionary systems. The Yanshan orogeny induced widespread crustal-scale folding and thrusting, tectonic reactivation of long-lived zones of crustal weakness, and extensive magmatism and mineralization in intraplate regions. Based on the time principle of supercontinent assembly and break-up, we propose that the mid-Late Jurassic multi-plate convergence in East Asia might represent the initiation of the assembly of the Amasia supercontinent, and the Yanshan orogeny might be the first “stirrings” that is a prerequisite for the birth of the Amasia supercontinent.

Permafrost Terrain Dynamics and Infrastructure Impacts Revealed by UAV Photogrammetry and Thermal Imaging

Unmanned Aerial Vehicle (UAV) systems, sensors, and photogrammetric processing techniques have enabled timely and highly detailed three-dimensional surface reconstructions at a scale that bridges the gap between conventional remote-sensing and field-scale observations. In this work 29 rotary and fixed-wing UAV surveys were conducted during multiple field campaigns, totaling 47 flights and over 14.3 km2, to document permafrost thaw subsidence impacts on or close to road infrastructure in the Northwest Territories, Canada. This paper provides four case studies: (1) terrain models and orthomosaic time series revealed the morphology and daily to annual dynamics of thaw-driven mass wasting phenomenon (retrogressive thaw slumps; RTS). Scar zone cut volume estimates ranged between 3.2 × 103 and 5.9 × 106 m3. The annual net erosion of RTS surveyed ranged between 0.35 × 103 and 0.39 × 106 m3. The largest RTS produced a long debris tongue with an estimated volume of 1.9 × 106 m3. Downslope transport of scar zone and embankment fill materials was visualized using flow vectors, while thermal imaging revealed areas of exposed ground ice and mobile lobes of saturated, thawed materials. (2) Stratigraphic models were developed for RTS headwalls, delineating ground-ice bodies and stratigraphic unconformities. (3) In poorly drained areas along road embankments, UAV surveys detected seasonal terrain uplift and settlement of up to 0.5 m (>1700 m2 in extent) as a result of injection ice development. (4) Time series of terrain models highlighted the thaw-driven evolution of a borrow pit (6.4 × 105 m3 cut volume) constructed in permafrost terrain, whereby fluvial and thaw-driven sediment transfer (1.1 and 3.9 × 103 m3 a−1 respectively) was observed and annual slope profile reconfiguration was monitored to gain management insights concerning site stabilization. Elevation model vertical accuracies were also assessed as part of the case studies and ranged between 0.02 and 0.13 m Root Mean Square Error. Photogrammetric models processed with Post-processed Kinematic image solutions achieved similar accuracies without ground control points over much larger and complex areas than previously reported. The high resolution of UAV surveys, and the capacity to derive quantitative time series provides novel insights into permafrost processes that are otherwise challenging to study. The timely emergence of these tools bridges field-based research and applied studies with broad-scale remote-sensing approaches during a period when climate change is transforming permafrost environments.

Geology of the Curone and Staffora Valleys (NW Italy): field constraints for the Late Cretaceous – Pliocene tectono-stratigraphic evolution of Northern Apennines

ABSTRACTIn the northwestern part of Northern Apennines, between Curone and Staffora Valleys, the tectonic superposition between the External Ligurian Units (i.e. the ophiolitic-bearing chaotic complex of the Groppallo Unit and the non-ophiolitic Cassio Unit), the Middle Eocene – Miocene wedge-top basin Epiligurian Units succession, and the Late Messinian – Pliocene Po Plain succession, records the multistage tectono-stratigraphic evolution from subduction to continental collision. Our geological map, at the 1:20,000 scale, allows us to define 6 main tectonic stages on the basis of (i) the crosscutting relationships between main faults and local to regional stratigraphic unconformities and (ii) the differentiation among different types of chaotic rock unit (olistostromes and broken formations) deposited since Late Cretaceous to late Messinian. This approach provides a new understanding on the tectono-stratigraphic evolution of this sector, and its meaning in the evolution of the northwestern part of Northern Apennines.

Vertical tectonic movements and sedimentary filling of basins during syn-rift and post-rift stages of lithosphere development

One-dimensional numerical modeling of isostatic response of lithosphere to thermal uplift of its bottom (active rifting) and interconnected formally independent thinning of the crust has been fulfilled. Evolution curves of vertical movements and interfaces displacements velocities have been examined. Depending on the introduced index of thinning of the crust velocity n =0,1¸3 spectrum of surface expression has been segregated: from the arc rift via annectent forms ( n =0,8¸1,5) to deep water depressions. In relation to a set of problems of paleo-tectonic reconstructions of sedimentary basins modeling of vertical movements accompanied by sedimentation was conducted. Situations have been examined when syn-rift sedimentation and dipping are much less than post-rift ones. Possibilities of establishment of conditions and evolution of continental and marine sedimentation within the limits of different regimes of riftogenesis have been investigated. In order to overcome limitations specific to methods of modern back-stripping an expanded variant of direct modeling has been tested based on the principle of «free sedimentation», taking into account facial vertical heterogeneity of the section and stratigraphic unconformities. In the model which explains formation of the Permian-Triassic sedimentary column of the Ebro depression (Iberia) paleo-geographic features of sedimentation are replicated: it was the continental one in the Permian and early Triassic with transition to marine in the end of Middle Triassic, uncertainty of stratigraphic unconformities of the Late Permian is also revealed. Accordingly, the complicated character of active riftogenesis consisting of two stages is predicted; for the second (Late Permian) variation of regime as three phases with different indices of thinning the crust is provided. Sedimentation and dipping of southeastern part of DDD which is characterized by abnormally high thicknesses of Carboniferous deposits are replicated at first approximation within the limits of a model including riftogenic dipping in the Late Devonian and the post-rift thermal one in the Carboniferous. The obtained changes of the sea depths are correlated with formational subdivisions of the Carboniferous cover and the intensity of coal accumulation.

Age and conditions of formation of sedimentary cover of the Ulleung Plateau of the Sea of Japan according to micropaleontological data

The paper reports on the micropaleontologcal (diatoms, silicoflagellates, radiolarians, and pollen flora) data substantiating the age and conditions of sedimentary cover formation of the submarine Ulleung Plateau (Krishtofovich Rise) in the Sea of Japan. Five rock complexes with different age and origin were distinguished on the basis of micropaleontological and petrographic data. Complex 1 (tuffites, tuffogenous siltstones) with numerous freshwater diatoms and pollen flora that prove the lacustrine genesis and the Early Miocene age occurs at the base of the sedimentary cover. Complexes 2–5 are composed of marine tuffogenous sedimentary deposits of end of Early Miocene–Pleistocene age. Stratigraphic unconformity between continental and marine deposits involves a short-time interval in the end of the Early Miocene and points to rather fast tectonic submersion of the Ulleung Plateau. Marine sedimentation in bathyal conditions dominated from the end of the Early Miocene. In the Late Miocene, in the northern part of the plateau, the region of the large rise was characterized by shallow-water conditions, indicating supposed existence of an island territory in this place.

The Jan Mayen microcontinent: an update of its architecture, structural development and role during the transition from the Ægir Ridge to the mid-oceanic Kolbeinsey Ridge

Abstract We present a revised tectonostratigraphy of the Jan Mayen microcontinent (JMMC) and its southern extent, with the focus on its relationship to the Greenland–Iceland–Faroe Ridge area and the Faroe–Iceland Fracture Zone. The microcontinent's Cenozoic evolution consists of six main phases corresponding to regional stratigraphic unconformities. Emplacement of Early Eocene plateau basalts at pre-break-up time (56–55 Ma), preceded the continental break-up (55 Ma) and the formation of seawards-dipping reflectors (SDRs) along the eastern and SE flanks of the JMMC. Simultaneously with SDR formation, orthogonal seafloor spreading initiated along the Ægir Ridge (Norway Basin) during the Early Eocene (C24n2r, 53.36 Ma to C22n, 49.3 Ma). Changes in plate motions at C21n (47.33 Ma) led to oblique seafloor spreading offset by transform faults and uplift along the microcontinent's southern flank. At C13n (33.2 Ma), spreading rates along the Ægir Ridge started to decrease, first south and then in the north. This was probably complemented by intra-continental extension within the JMMC, as indicated by the opening of the Jan Mayen Basin – a series of small pull-apart basins along the microcontinent's NW flank. JMMC was completely isolated when the mid-oceanic Kolbeinsey Ridge became fully established and the Ægir Ridge was abandoned between C7 and C6b (24–21.56 Ma).

The stratigraphic evolution of a large back-barrier lagoon system with a non-migrating barrier

Lake St Lucia, the largest estuarine system in Africa, is enclosed by a 120m-high compound Quaternary barrier-dune system in northern KwaZulu-Natal, South Africa. It comprises several discrete sedimentary basins within a single shallow back-barrier water body. This paper reports the first very-high-resolution seismic study of the system. Seven seismic units (A–G) are identified and interpreted based on their geometry, acoustic properties and a sediment coring programme. The units are bounded by regionally developed sequence boundaries and lower order unconformity surfaces corresponding to bay and tidal ravinement and hiatus surfaces. The lowermost subaerial unconformity formed during regression related to late-Pliocene hinterland uplift. Initial infilling of this surface in the proximal areas reflects estuarine sedimentation in a mixed wave- and tide-dominated system during the subsequent lowstand and early transgressive systems tracts, overlain by prograding highstand deltaic deposits that developed as sea-levels began to stabilise. Distally, this cycle of sedimentation is initially reflected by the infilling of a similar estuarine system that gradually transitioned to a back-barrier lagoon. Superimposed stillstands drove imbalances in the rate of sediment supply and accommodation space, and this, coupled with the development of an early barrier complex, caused lagoon aggradation and shallowing. A second similar trend is repeated for the recent postglacial sea-level cycle. There appears to be no preservation of the intervening Pleistocene cycles of erosion and deposition. The system is capped by estuarine-lacustrine deposits. The onset of lower energy estuarine-lake conditions began ~6235cal BP in North Lake and started earlier in the proximal False Bay owing to sheltering by the antecedent barrier of a rocky peninsula. This study reveals a markedly different evolutionary history in adjacent basins of the same back-barrier system during two full sea-level cycles. These are attributed to a long established, non-migrating barrier, and to the influence of antecedent conditions on the system response to transgression. Unlike the US Atlantic margin, where migrating barriers truncate the infilling sequences, the main stratigraphic unconformities within each fill sequence correspond to tidal and bay ravinement surfaces.

The Epiligurian wedge-top succession in the Enza Valley (Northern Apennines): evidence of a syn-depositional transpressive system

We here discuss the Early Oligocene–Middle Miocene evolution of the Epiligurian wedge-top basin system cropping out in the middle Enza Valley (Northern Apennines, Italy). Newly acquired stratigraphic and structural data, backed up by literature review, highlight that during the Rupelian to Serravallian time span, sedimentation was controlled by a left-lateral transpressive system. This system, here named as the Enza Valley Deformation Zone (EVDZ), is SW–NE directed and trends obliquely to the main regional NW–SE-directed structural axis characterizing this part of the Northern Apennines nowadays. The syn-sedimentary activity is testified by: (1) local to regional stratigraphic unconformities, (2) lateral variations of sedimentary facies associations, (3) thickness changes of the stratigraphic units and (4) the occurrence of mass transport deposits. This study suggests that structural lineaments like the EVDZ, transversal to the main regional tectonic trends, may have played a long-term control on the syn-orogenic sedimentation atop the evolving Apennine orogen.

Applications of 3D seismic attribute analysis in hydrocarbon prospect identification and evaluation: Verification and validation based on fluvial palaeochannel cross-sectional geometry and sinuosity, Ness County, Kansas, USA

Due to their high resolution and established success rates, the analysis of geometrical and stratigraphic 3D seismic reflection data attributes have become one of the most important tools in many hydrocarbon exploration and development programs. In areas with high drilling risk as a result of the lack of spatial continuity and lithological variation of potential prospects, analysis of relevant seismic attributes is essential to successful placement of wells. This study of the York field, Ness County, Kansas, presents a corroborative finding, based on the analysis of a set of 3D seismic attributes, revealing a meandering fluvial channel system incised on the Mississippian stratigraphic unconformity north east of a previously interpreted Weirman field palaeoshoreline and submarine channels. The York field prospect identification and appraisal program targeted the Cherokee sands where reservoir properties are favorable and where it was thought that thick Cherokee sands correlate with structural Mississippian highs. We produce evidence that Cherokee sand-prone fluvial facies is mappable based on synergistic analysis of seismic arrival time, amplitude, spectral decomposition, acoustic impedance, and waveform attributes. Seismic amplitude highs and relative acoustic impedance lows showed moderate conformance with Mississippian-horizon time lows. Controls exerted by channel post-confluence water and sediments supply provide corroborating hydraulic geometry aspects for the interpreted fluvial system.Time-structural maps, in addition to time and horizon slices of several 3D seismic attributes including amplitude, spectral decomposition components, and relative acoustic impedance all seem to indicate that five previously drilled dry wells within the study area were outside the boundary of a meandering, Cherokee fluvial system of potential reservoir quality. Additionally, comparisons of the results of this research to previous studies conducted in the south west of Ness County have provided an opportunity to support and contribute to, interpreted paleodepositional setting established by Raef et al, 2015 where a palaeoshorline was interpreted. The results of this study support a broadly NE–SW trending meandering channel system with SE flow direction.

Paired carbonate and organic carbon isotope variations of the Ediacaran Doushantuo Formation from an upper slope section at Siduping, South China

Intensive carbon isotope analyses from the Doushantuo Formation (ca. 635–551 Ma) in South China reveal decoupled carbonate and organic carbon isotopes (δ13Ccarb and δ13Corg) that have been interpreted as recording a large dissolved organic carbon (DOC) reservoir in the Ediacaran ocean or chemoautotrophic-methanotrophic recycling/modification of organic matter in a redox-stratified ocean. Existing paired δ13Ccarb–δ13Corg data, however, are mostly from sections of an intrashelf lagoon near the Yangtze Gorges area where basin restriction may have resulted in local isotope departure from the open ocean. To better understand the spatial and temporal variations of the Ediacaran δ13C excursions, we have conducted high-resolution, paired δ13Ccarb–δ13Corg analyses of the Doushantuo Formation from an upper-slope section at Siduping, Hunan Province, South China. The data reveal three negative δ13Ccarb excursions at the basal, middle, and upper Doushantuo Formation. Two prominent negative δ13Corg anomalies are also observed in black shales and shaly dolostones at the base and top of the Doushantuo Formation. For the majority of the Doushantuo Formation, however, δ13Ccarb and δ13Corg values are decoupled, similar to those observed in the Yangtze Gorges area. Both δ13Ccarb and δ13Corg show large (up to 10‰) variations among shallow- and deep-water sections that are consistent with a large carbon isotope gradient in a stratified Ediacaran ocean. The large δ13Ccarb gradient between shallow- and deep-water sections implies the availability of sulfate in deep-water environments where the addition of authigenic carbonate films/cements into surface-ocean-derived carbonate particles in anoxic water column or pore-water led to more negative δ13Ccarb values. Significant spatial δ13Corg variations suggest that the decoupled δ13Ccarb–δ13Corg may not have been resulted from direct buffering of a large DOC reservoir but from recycling of organic matter by chemoautotrophs and methanotrophs. Compilation of available paired δ13Ccarb–δ13Corg data from the Yangtze platform reveals alternating intervals of coupled and decoupled δ13Ccarb–δ13Corg values up to the early Cambrian (≤520 Ma). Intervals with coupled δ13Ccarb and δ13Corg coincide with evidence for ocean oxygenation events. This phenomenon may be explained by episodic growth and oxidation of a moderate DOC reservoir 6–12 times of the modern ocean. The upper Doushantuo δ13Ccarb anomaly temporally crosses a major stratigraphic unconformity, indicating that part of the upper Doushantuo-Shuram δ13Ccarb excursion was formed during sea-level regression. Large spatial and temporal variations of the upper Doushantuo δ13Ccarb excursion may record a mixed signature of open-ocean seawater overprinted by facies-dependent isotope variation, stratigraphic truncation and authigenic/diagenetic modification along the unconformity. The real primary δ13Ccarb excursion may be shorter-lived than previously thought.

Revised Neoproterozoic and Terreneuvian stratigraphy of the Lena-Anabar Basin and north-western slope of the Olenek Uplift, Siberian Platform

The early to mid-Neoproterozoic (pre-glacial) sedimentary succession of the Lena-Anabar Basin, northeast Siberian Platform, records protracted faulting and subsidence, possibly as part of the widespread continental rifting and the break-up of Rodinia. There is a significant stratigraphic unconformity separating the pre-glacial Neoproterozoic strata and the overlying upper Ediacaran succession in the Lena-Anabar Basin, with the Terreneuvian strata most likely to be deposited in a foreland of the Central Taimyr accretionary belt. The Cryogenian sensu strictum (i.e., younger than 720Ma) and lower Ediacaran deposits are missing in the area. In this study, we assess the palaeontological content of the Precambrian and Terreneuvian strata of the Lena-Anabar Basin and the adjacent north-western slope of the Olenek Uplift and revise the chronostratigraphy of the region, with special emphasis to biostratigraphic index taxa. For the pre-glacial Neoproterozoic section, we establish the new Tukulan, Kulady, Taimylyr formations and redefine the Khastakh Formation. We also refine the Ediacaran and Terreneuvian stratigraphy by formalising the Maastakh, Khatyspyt, and Turkut formations of the Khorbusuonka Group, whereas the Kessyusa Formation is raised to group rank and subdivided into the Syhargalakh, Oppokun, Mattaia, and Chuskuna formations. The proposed stratigraphic correlation scheme is based upon depositional unity and is consistent both lithologically and biostratigraphically, providing a robust framework for future stratigraphic, sedimentological and palaeobiological studies.

Erosion of a paleo-tsunami record by the 2011 Tohoku-oki tsunami along the southern Sendai Plain

Erosion of sediment beneath a coastal lake by the 2011 Tohoku-oki tsunami largely removed up to 1100years of the geologic record of tsunami and tephra deposition. That lost geologic record included the 1611 Keicho tsunami deposit and the 915 To-a tephra, amounting to ca. 1.4m of lake-bottom sediment, as judged from comparison of stratigraphy at four locations examined before and after the 2011 tsunami. The tsunami replaced the eroded sediment with a 7–15-cm-thick sand sheet and an overlying 20–60-cm-thick layer of black mud. Both 2011 deposit components were likely derived from sediment eroded along the tsunami flow path, including granite rock fragments downstream of the lake basin and mainly reworked lake-floor sediment. Erosion and redeposition of lake floor sediment by tsunami inundation can introduce uncertainty to sandy tsunami deposit age estimation. The 2011 tsunami sand might be dated a few hundred years older than the actual age if one overlooks the reworked muddy tsunami deposit. In its facies, the mud closely resembles mud deposited from the usual environment but is mixed with sediments of various ages. Therefore, it is important to identify the reworked muddy tsunami deposit based on geochemistry and micropaleontology, to avoid misinterpretation of the depositional age of tsunami deposits. Erosion of deposits beneath the lake floor also erases evidence, leaving an incomplete paleo-tsunami history. Reconstructing geological records of tsunamis in coastal lakes requires careful evaluation of the possible effects of tsunami erosion. Identifying sediment sources, mapping stratigraphic unconformities, and constructing detailed age-depth models to test for gaps in sedimentation can produce important insights.

Characteristics of the Paleozoic slope break system and its control on stratigraphic-lithologic traps: An example from the Tarim Basin, western China

Based on comprehensive analyses of seismic and log data, this study indicates that mainly four widespread angular to minor angular unconformities (Tg8, Tg51, Tg5 and Tg3) were formed during the Paleozoic. Through the interpretation of structural unconformities, calculation of eroded thickness, correction of palaeo-water depth and compaction and compilation of the Early Paleozoic structural maps, the Early Paleozoic slope break belt (geomorphologic unit) of the Tarim Basin is subdivided into uplift area, subaqueous uplift area, rift slope break belt, flexure slope break belt (slope belt), depression area and deep basin area. Palaeogeomorphology of the Cambrian-Early Ordovician was approximately in EW trend within which three tectonic units including the Tabei Palaeo-uplift, the northern Depressional Belt and the southern Palaeo-uplift developed respectively and are grouped into two slope break systems namely as the Tabei Palaeo-uplift and the southern Palaeo-uplift. These tectonic units obviously control the deposition of isolated platform, open platform, restricted platform and deep basin. Influenced by extrusion in the Mid-Late Ordovician, the southern and northern subaqueous uplifts gradually elevated and then were eroded. Resultantly two slope break systems developed, namely as the northern and central Palaeo-uplifts which obviously controlled the deposition of provenance area, isolated platform, mixed continental shelf, slope and basin facies. The intensive extrusion of the Mid-Late Ordovician leads to significant tectonic deformation of the Tarim Basin: large area of uplifting and erosion and development of EW trending anticline and syncline. Deposition of shore, tidal flat, delta, shallow marine clastics and deep marine facies is obviously controlled by the Tabei, the southern and the Tadong Palaeo-uplifts. Slope break systems control development of stratigraphic unconformity and thus truncation and onlap unconformity zones become favorable areas in a palaeo-uplift and at a palaeo-slope belt for forming important unconformity traps; Whereas slope (slope break) belt along a palaeo-uplift margin is a geomorphologic unit where high-energy sedimentary facies widely develops, such as reef, oolitic sandy clastics or bioclastic limestone beach bar facies, thus litho-structural composite hydrocarbon accumulations usually develop when tectonic condition is suitable. In addition, large-scale palaeo-uplifts are the most favourable areas for hydrocarbon accumulation development

Distribution of Palaeozoic tectonic superimposed unconformities in the Tarim Basin, NW China: significance for the evolution of palaeogeomorphology and sedimentary response

Seismic and drilling well data were used to examine the occurrence of multiple stratigraphic unconformities in the Tarim Basin, NW China. The Early Cambrian, the Late Ordovician and the late Middle Devonian unconformities constitute three important tectonic sequence boundaries within the Palaeozoic succession. In the Tazhong, Tabei, Tadong uplifts and the southwestern Tarim palaeo‐uplift, unconformities obviously belong to superimposed unconformities. A superimposed unconformity is formed by superimposition of unconformities of multiple periods. Areas where superimposed unconformities develop are shown as composite belts of multiple tectonic unconformities, and as higher uplift areas of palaeo‐uplifts in palaeogeomorphologic units. The contact relationship of unconformities in the lower uplift areas is indicative of truncation‐overlap. A slope belt is located below the uplift areas, and the main and secondary unconformities are characterized by local onlap reflection on seismic profiles. The regional dynamics controlled the palaeotectonic setting of the Palaeozoic rocks in the Tarim Basin and the origin and evolution of the basin constrained deposition. From the Sinian to the Cambrian, the Tarim landmass and its surrounding areas belonged to an extensional tectonic setting. Since the Late Ordovician, the neighbouring north Kunlun Ocean and Altyn Ocean was transformed from a spreading ocean basin to a closed compressional setting. The maximum compression was attained in the Late Ordovician. The formation of a tectonic palaeogeomorphologic evolution succession from a cratonic margin aulacogen depression to a peripheral foreland basin in the Early Caledonian cycle controlled the deposition of platform, platform margin, and deep‐water basin. Tectonic uplift during the Late Ordovician resulted in a shallower basin which was followed by substantial erosion. Subsequently, a cratonic depression and peripheral or back‐arc foreland basin began their development in the Silurian to Early–Middle Devonian interval. In this period, the Tabei Uplift, the Northern Depression and the southern Tarim palaeo‐uplift showed obvious control on depositional systems, including onshore slope, shelf and deep‐water basin. The southern Tarim Plate was in a continuous continental compressional setting after collision, whereas the southern Tianshan Ocean began to close in the Early Ordovician and was completely closed by the Middle Devonian. At the same time, further compression from peripheral tectonic units in the eastern and southern parts of the Tarim Basin led to the expansion of palaeo‐uplift in the Late Devonian–Early Carboniferous interval, and the connection of the Tabei Uplift and Tadong Uplift, thus controlling onshore, fluvial delta, clastic coast, lagoon‐bay and shallow marine deposition. Copyright © 2015 John Wiley & Sons, Ltd.

Geology of the Villalvernia – Varzi Line Between Scrivia and Curone valleys (NW Italy)

The External Ligurian and Epiligurian Units in the Northern Apennines of Italy are tectonically juxtaposed with the Tertiary Piedmont Basin along the Villalvernia – Varzi Line, which represents a regional scale fault zone, E-striking. Our map, at the 1:20,000 scale, describes the tectono-stratigraphic evolution of this sector that resulted from multistage faulting along that fault zone. Four main tectonic stages are defined on the basis of the crosscutting relationships between mapped faults and stratigraphic unconformities: late Priabonian – Rupelian, Chattian – early Miocene, late Serravallian – Tortonian, and late Messinian – early Pliocene. Our results demonstrate that since the late Burdigalian, the Villalvernia – Varzi Line was sealed by the gravitational emplacement of a chaotic rock body. The deposition of the late Serravallian – early Messinian succession is controlled by NW-striking strike-slip faults that crosscut to the west the Villalvernia – Varzi Line. Extensional tectonics related to regional scale N-dipping tilting characterized the late Messinian – early Pliocene time interval.

The Middle–Upper Pleistocene Fronte Section (Taranto, Italy): An exceptionally preserved marine record of the Last Interglacial

The Fronte Section, a well-exposed stratigraphic succession from southern Italy (Taranto area), provides an uninterrupted marine sedimentary record of MIS 5e. At this location, a highly expanded (8.5m thick) stratigraphic succession, unconformably overlying Middle Pleistocene marine clay deposits, provides evidence for sea-level fluctuations during the Last Interglacial. An integrated study of Fronte Section, including facies analysis, detailed macrofaunal and meiofaunal characterization, and sequence stratigraphy, is presented. The occurrence of Persististrombus latus (=Strombus bubonius) and other warm-water indicators (“Senegalaise” – “Senegalian” – guests of Gignoux, 1913), together with the presence of the dinocyst Polysphaeridium zoharyi and ten U-series dates on Cladocora caespitosa samples, permit an unequivocal MIS 5e age assignment to the upper part of the study succession. Above a stratigraphic unconformity marked by the boring coastal-lagoonal bivalve Pholas dactylus, the MIS 5e succession displays a first transgressive suite of brackish to shallow-marine deposits. These latter include highly fossiliferous muds rich in C. caespitosa, overlain by a fossil-rich calcarenite, 2m-thick, yielding warm-water “Senegalian” mollusks. Above this prominent stratigraphic marker (regionally called panchina), which is interpreted to represent a short-lived phase of sea-level stillstand or gentle fall during MIS 5e, renewed transgression took place, leading to the accumulation of middle-outer shelf muds, about 5m thick. The maximum flooding zone is clearly identified on the basis of the turnaround from a deepening-up to a shallowing-up trend. The upper part of Fronte Section records a second fossil-rich, sublittoral calcarenite containing warm-water mollusks, which is interpreted to reflect the subsequent phase of sea-level highstand, likely correlative with the MIS 5e plateau.

Geology of the Aventino River Valley (eastern Majella, central Italy)

The Apenninic fold-and-thrust belt in Italy represents one of several interconnected circum-Mediterranean orogens developed after the Late Cretaceous – early Cenozoic closure of Tethys and convergence between the European and African plates. The Geological Map of the Aventino River Valley, at 1:25,000 scale, provides original mapping of the outermost sector of Central Apennines in the Abruzzi region. Focusing on detailed mapping of the crosscutting relationships between the main regional thrust faults and tectonically driven stratigraphic unconformities, the map describes the complex structural and stratigraphic relationships between the Outer Abruzzi units (i.e. Porrara Unit), Apulia – Adriatic deformed units (i.e. Majella and Casoli Units), and the allochthonous Molise and Sicilide units. These tectono-stratigraphic relationships result from four main tectonic stages that occurred sequentially over a short time interval from late Messinian to early Pliocene.

U–Pb LA-ICP-MS geochronology of detrital zircon grains from low-grade metasedimentary rocks (Neoproterozoic – Cambrian) of the Mojotoro Range, northwest Argentina

The first results of U–Pb detrital zircons were obtained in three lithostratigraphic units of the Puncoviscana Complex in NW Argentina: Chachapoyas, Alto de la Sierra and Guachos Formations. The Chachapoyas Formation has a maximum sedimentation age of 569 Ma and a minimum age of 533 Ma, based on the U–Pb age of an intrusive porphyry granitic. The Alto de la Sierra Formation, composed by sandstones and volcaniclastic rocks, has a maximum age of 543 Ma. A maximum age of 517 Ma is here reported for the deposition of the Guachos Formation, the youngest unit. The contact between the Chachapoyas and Guachos formations is by a tectonic relation, and it's probably coincident with a stratigraphic unconformity between them (unconformity Tilcara I). The Lizoite Formation is overlying by an unconformity (Tilcara II unconformity) the Puncoviscana Complex, and represents the basal unit of the Mesón Group. The provenance zircon data for that formation indicate a maximum depositional age of 513 Ma.

Genesis Analysis of High Gamma Ray (GR) Sandstone Reservoir: Taking Toutunhe Formation of Junggar Basin, Northwest China, as an Example

On the basis of GR log analysis alone, the high GR sandstone reservoirs would probably have been regarded as mudstone and interpreted to be non-reservoir, which has greatly affected the exploration and exploitation of oil and gas reservoir to some extent. Therefore, the principles and standards to distinguish high GR sandstone reservoir from conventional sandstone reservoir, genesis of high GR sandstone reservoir have been systematically studied. Studies show that sandstone reservoir with apparent shale content calculated by GR log value greater than 50%, can be regarded as high GR sandstone reservoir. In the study area, the specific criterion of GR log value for high GR sandstone reservoir is 110API. The high GR characteristic of sandstone reservoir is mainly and directly caused by an abnormally high uranium enrichment, but not the tuff, feldspar or clay mineral. The study area has favorable conditions of abundant uranium source, favorable paleoclimate, and favorable lithology and lithofacies combination for uranium enrichment. In the process of oxygen bearing formation water migrating and leaching uranium bearing tuff, the U+4 can be oxidized to U+6, and uranium element transports in the form of UO2+2. In permeable sandstone reservoir saturated with uranium bearing formation water, the U+6 can be deoxidized into U+4 by oil and gas migrating through faults and stratigraphic unconformities, and accumulates in the form of UO2 in sandstones.

The role that plate tectonics, inferred stress changes and stratigraphic unconformities have on the evolution of the West and Central African Rift System and the Atlantic continental margins

The Muglad rift basin of Sudan, is a good example of polyphase rifting, with at least three major phases of basin development. Each phase has resulted in the generation of source rock, reservoir and seal geology with structural traps often closely linked to basement highs. In this paper we investigate on a regional scale the tectonic processes that have contributed to rift basin development.On a regional scale, the evolution of the Africa-wide Mesozoic rift system is intimately linked to relative movements of African sub-plates and to global plate tectonic processes and plate interactions. Changes in plate interactions are observed in the oceanic crust as azimuth changes of fracture zone geometries and by inference have caused significant modifications to both the orientation and magnitude of the motions of the African sub-plates. Such plate motion processes have controlled the polyphase development of the West and Central African Rift System. On the basinal scale, changes of sub-plate motions have resulted in changes in the stress field which have had a clear impact on the deformation and fault geometries of rift basins and on the resulting stratigraphy. The construction of the first unified stratigraphic chart for the West and Central African Rift System shows a close correlation in the timing of the major unconformities with the timing of changes in relative plate motion as observed in the changes of the azimuthal geometry of the oceanic fracture zones in the Central Atlantic. Since similarly timed unconformities exist along the continental margins of Africa and South America, we propose that the causative mechanism is change in relative plate motion which leads to an increase or decrease in the tension on the plate and thus controls the strength or effective elastic thickness, Te, of the crust/plate beneath the margins. This results in a focused change in isostatic response of the margin during short-period changes in relative plate motion; i.e. more tension will mean that loads are not compensated locally resulting in local uplift of the margin.