Syndepositional Tectonic Activity Research Articles

KINNEYIA-TYPE WRINKLE STRUCTURES ON SANDSTONE BEDS: NOT MICROBIALLY INDUCED BUT DEFORMATION FEATURES CAUSED BY SYNSEDIMENTARY EARTHQUAKES

ABSTRACT A category of wrinkle structures, often termed Kinneyia structure or Runzel marks, comprises bedding plane features consisting typically of anastomosing, low-relief, flat-topped ridges with intervening depressions. Topographic relief is usually less than a millimeter. They are locally common on the upper surfaces of fine- to medium-grained sandstone beds interbedded with mudstone deposited in offshore settings, especially in Precambrian and lower Paleozoic strata but as young as Cretaceous. For more than the last two decades these wrinkle structures have been widely regarded as due to microbial mats, and have been taken as evidence for dominance in the Proterozoic of microbially stabilized sediment and, in the Phanerozoic, a matground marine benthic ecology which gradually gave way to a mixground ecology. The detailed morphology and cross-cutting relationships demonstrated by a range of specimens of Proterozoic, Cambrian, and Silurian age, however, cast this interpretation into doubt. The relationship between the wrinkled surface and bioclasts such as shells and both prior- and later-formed scour surfaces, and horizontal and vertical burrows show that these wrinkles did not develop due to the surface topography of microbial mats or compaction of microbial mats during burial, but instead formed at the top of a sand bed at the interface with an overlying layer of mud. Deformation is ascribed to vibration from low-magnitude earthquakes. The presence in some units of small-scale sedimentary dikelets and crack arrays that formed later after some stiffening, along with locally associated seismites and other evidence for nearby faulting, show that syndepositional tectonic activity was not unexpected and support the interpretation that this category of wrinkle structures is a type of seismite.

A revised Mississippian (Courceyan – Chadian) geology of the Clogher Valley, counties Fermanagh and Tyrone (Northern Ireland)

Following a geological research programme in 1998-2000, the Mississippian succession in the Clogher Valley has been revised and important new detail has been revealed. Immediately overlying the terrestrial Ballyness Formation, the interval originally ascribed to the Clogher Valley Formation has been subdivided into three new formations: the Clogher Valley Formation sensu stricto, the Fardross Sandstone Formation and the Moysnaght Limestone Formation. This sequence is overlain by the Ballyshannon Limestone Formation. The lithostratigraphy of these units is described and previous biostratigraphic work is reviewed and supplemented with new data. These indicate that the top of the clastic redbed Ballyness Formation is close to the Devonian-Carboniferous boundary, whilst the following marine succession ranges in age from the late Courceyan through to the Chadian. The thickness, nature and distribution of evaporite horizons in the succession is described. The provenance of various sandstones within the sequence has been assessed and lateral facies changes and thickness variations in the succession are attributed to syn-depositional tectonic activity.

Sedimentary records of paleoseismic events in the Late Pleistocene sediments of the Southern Yangtze River deltaic plain, East China, and their implications for differential subsidence of the Taihu block

Drilling cores from the Hangjiahu Coastal plain in the southwestern corner of the Southern Yangtze River deltaic plain, East China, contain a variety of soft-sediment deformation structures in the Late Pleistocene lacustrine and tidal sediments. They include load-flame structures, ball-and-pillow structures, diapir structures, liquefied sand veins, liquefied breccias, syn-sedimentary fault, seismo-cracks and brittle breccias. Sedimentary facies assessment of host deposits and development features rule out an exogenic origin of the soft-sediment deformation structures, such as gravity-flow, storm activity, wave action or flood. These soft-sediment deformation structures in the study area are interpreted as seismites, their spatial distribution suggest that the earthquakes were sourced from the intersection of the Majin-Wuzhen Fault and the Huzhou-Jiashan Fault. Seismites recognized in cores indicate three episodes of short and sudden seismicity (magnitude > 5), which are interpreted as a response to syn-depositional tectonic activity and differential subsidence of the Taihu block during the Late Pleistocene period. Systematic study of spatial and temporal distribution of these seismites improves the understanding of the tectonic context and evolutionary history of sedimentary basement.

Reativações pós-silurianas do Lineamento Transbrasiliano na porção sul da Bacia do Parnaíba

O Lineamento Transbrasiliano (LTB) apresenta direção NE-SW. Cerca de 900 km desse sistema interceptam o substrato da Bacia do Parnaíba (BPar), inferido, a partir de dados geológicos e geofísicos, como uma zona de cisalhamento plástica transcorrente dextral. Este trabalho objetivou abordar a assinatura estrutural e os marcadores estratigráficos associados às reativações do LTB na região sul da bacia, ao leste de Palmas (TO). No embasamento cristalino, um estágio tardio do LTB se expressa como uma zona dúctil-frágil também de cinemática dextral de idade ediacarana-cambriana, no NW do Ceará. Nas unidades litoestratigráficas da BPar são distinguidos eventos de reativação em regime frágil ou hidroplástico. Na região de estudo, um evento mais antigo registra cinemática transcorrente sinistral expressa principalmente como bandas de deformação e falhas com direção NE, combinadas a estruturas dilatacionais (incluindo juntas e falhas normais) ou conjugadas/antitéticas de rejeito direcional ou oblíquo, com orientações que variam de NNE a NNW, todas observadas nos litotipos das Formações Sambaíba e Pedra de Fogo, bem como nas mais antigas. Ao sudeste de Alto Parnaíba (MA) são observadas evidências de atividade tectônica sindeposicional durante o Permiano superior. Um segundo conjunto de estruturas composto por falhas normais associadas a uma distensão N/NNW, impressas nos corpos básicos de idade eojurássica da Suíte Mosquito, que, por sua vez, é capeada por depósitos com seixos das vulcânicas, correlacionados à Formação Corda. Um terceiro conjunto de estruturas, caracterizado por falhas normais ou oblíquas com direção NE, registra distensão NW, sendo associada ao evento de rifteamento da Margem Leste brasileira, durante o Cretáceo Inferior. Finalmente, um quarto evento, de ocorrência restrita, envolve distensão NE e está registrado em arenitos correlacionados ao Grupo Urucuia, implicando uma idade máxima neocretácea.

Soft-sediment deformation related to syntectonic intraformational unconformity in the early Palaeocene alluvial-fan deposits of Kuşcular Formation in the Elazığ sector of Tauride foreland, eastern Turkey

The Kuşçular Formation was deposited in the early Palaeocene in a tectonically-controlled foreland basin in front of the southwards-advancing nappes of the Tauride orogen in eastern Turkey. This lithostratigraphic unit consists of alluvial-fan deposits, including distal mudflat–playa facies association. The proximal to middle fan deposits are composed of clastic sediments, whereas the distal deposits represent both clastic and evaporitic sedimentation. Compressional synsedimentary deformation caused development of an intraformational unconformity in the distal fan deposits of the Kuşçular Formation. Slump features and overturned beds were formed as a result of the oversteepening and recumbent folding of deposits due to the orogen thrust-wedge movement. Load casts, flame structures, intrusion features, sand dykes, interpenetrative cusps and synsedimentary faults were formed as a result of sediment liquefaction and remobilization. It is suggested that such levels of soft-sediment deformation in foreland terrestrial molasse deposits should be carefully studied as they may be related to ‘hidden’ unconformities and represent an important record of syndepositional tectonic and seismic activity in the basin.

Carbonate-clastic sediments of the Dudziniec Formation in the Kościeliska Valley (High-Tatric series, Tatra Mountains, Poland): role of syndepositional tectonic activity in facies development during the Early and Middle Jurassic

Sediments of the Dudziniec Formation (Lower Jurassic – Aalenian) outcropping in the Kościeliska Valley (autochthonous unit of the High-Tatric series) are represented by a range of mixed carbonate-clastic deposits. Seven lithofacies have been distinguished based on lithology, sedimentary structures, colour and composition of intra- and extraclasts, with sandstones and crinoidal limestones as end members of a continuous spectrum of facies. The study area represents a shallower part of the sedimentary basin located in the vicinity of source areas, as compared to the Chocholowska Valley region located in the west. Facies characteristics and distribution were controlled mainly by synsedimentary tectonic activity, with sandy varieties representing periods of faulting with enhanced influx of extraclasts, and with crinoidal limestones corresponding to intervals of relative tectonic stability. Such influence of synsedimentary tectonics on the deposition in the Early Jurassic strongly resembles the Middle Jurassic development in the High-Tatric area. Neptunian dykes cutting the Dudziniec Formation, and most probably filled by Lower Jurassic sediments, are yet another indication of tectonic instability of the area in the Early Jurassic

Stratigraphic Architecture of a Transtensional Continental Basin In Low-Latitude Semiarid Conditions: The Permian Succession of the Central Orobic Basin (Southern Alps, Italy)

Abstract Continental successions in fault-controlled extensional–transtensional basins store a wide range of clastic deposits from various depositional environments, representing a challenging target for hydrocarbon exploration. Recent advances in field-based facies analysis and genetic interpretation of these sediments show that these successions are characterized by great variability in terms of volume, geometry, facies, and stacking patterns. This variability derives from a number of factors that govern the sedimentary processes, such as tectonic setting, basin size and morphology, type and amount of sediments, and climate. The study focuses on a well-exposed Early Permian continental succession (Southern Alps, northern Italy), which was deposited in an extensional–transtensional tectonic regime under a semiarid to arid climate. The study area is characterized by a thick (more than 1000 m) succession of prevailing continental clastics with intercalations of ignimbritic flows and tuffs (Pizzo del Diavolo) Formation resting on up to 800 m of prevailing pyroclastic flows (Cabianca Volcanite). These units are unconformably covered by the Upper Permian alluvial sediments of the Verrucano Lombardo. Sedimentological features reflect a proximal fan system where mass-flow phenomena dominate, a distal fan-terminal setting with prevailing sandy sheet-flow processes and a silty floodplain environment, where sheet-flood events dominate. Laterally continuous siltstones and dark shales with carbonate nodules and layers of microbial carbonates in the most depressed part of the basin indicate alternating conditions of shallow lake and desiccated floodplain. Syndepositional tectonic activity is documented in the succession by rapid vertical and lateral facies changes. In this study, we present a data-constrained reconstruction of the depositional architecture of the basin, a description of depositional processes and depositional environments, and a model of facies distribution. Outcrop data, integrated with laboratory analyses, provide a detailed understanding not only of the small-scale elements of the system (sub-seismic scale) but also of the entire basin, focusing on how those elements are interrelated. The studied succession can be considered an interesting outcrop analogue for subsurface extensional–transtensional basins, potentially useful to predict reservoir properties for similar subsurface settings.

Sedimentary record of seismic events in the Eocene Green River Formation and its implications for regional tectonics on lake evolution (Bridger Basin, Wyoming)

Outcrops and cores from the top of the lacustrine Tipton Member and the base of the Wilkins Peak Member (~51.5Ma) of the Eocene Green River Formation, Bridger Basin in southwestern Wyoming yield a wide variety of sedimentary deformation features many of which are laterally extensive for more than 50km. They include various types of folds, load structures, pinch-and-swell structures, microfaults, breccias and sedimentary dikes. In most cases deformation is represented by hybrid brittle–ductile structures exhibiting lateral variation in deformation style. These occur in low-energy, profundal organic-rich carbonate mudstones (oil shales), trona beds, tuffs, and profundal to sublittoral silty carbonate deposited in paleolake Gosiute. The deformation is not specific to the depositional environment because sedimentary units stratigraphically higher with similar facies show no deformation.The studied interval lacks any evidence for possible trigger mechanisms intrinsic to the depositional environment, such as strong wave action, rapid sediment loading, evaporite dissolution and collapse, or desiccation, so ‘endogenic’ causes are ruled out. Thus, the deformation features are interpreted as seismites, and change in deformation style and inferred increase in intensity towards the south suggest that the earthquakes were sourced from the nearby Uinta Fault System. The 22 levels exhibiting seismites recognized in cores indicate earthquakes with minimum magnitudes between 6 and 7, minimum epicentral intensity (MCS) of ~9, and varying recurrence intervals in the seismic history of the Uinta Fault System, with a mean apparent recurrence period of ~8.1k.y. using average sedimentation rates and dated tuffs; in detail, however, there are two noticeably active periods followed by relative quiescence. The stratigraphic position of these deformed intervals also marks the transition between two distinct stages in lake evolution, from the balanced-filled Tipton Member to the overlying, underfilled Wilkins Peak Member. Thus, these seismites are evidence for regional-scale changes in lacustrine sedimentation of Eocene Lake Gosiute in response to syndepositional tectonic activity. Analysis of synsedimentary deformation features is, therefore, a promising yet under-utilized tool to trace the tectonic evolution of lacustrine deposits of the Green River Formation and other tectonically active marine and non-marine basins.

The role of tidal, wave and river currents in the evolution of mixed‐energy deltas: Example from the Lajas Formation (Argentina)

AbstractMany modern deltas show complex morphologies and architectures related to the interplay of river, wave and tidal currents. However, methods for extracting the signature of the individual processes from the stratigraphic architecture are poorly developed. Through an analysis of facies, palaeocurrents and stratigraphic stacking patterns in the Jurassic Lajas Formation, this paper: (i) separates the signals of wave, tide and river currents; (ii) illustrates the result of strong tidal reworking in the distal reaches of deltaic systems; and (iii) discusses the implications of this reworking for the evolution of mixed‐energy systems and their reservoir heterogeneities. The Lajas Formation, a sand‐rich, shallow‐marine, mixed‐energy deltaic system in the Neuquén Basin of Argentina, previously defined as a tide‐dominated system, presents an exceptional example of process variability at different scales. Tidal signals are predominantly located in the delta front, the subaqueous platform and the distributary channel deposits. Tidal currents vigorously reworked the delta front during transgressions, producing intensely cross‐stratified, sheet‐like, sandstone units. In the subaqueous platform, described for the first time in an ancient outcrop example, the tidal reworking was confined within subtidal channels. The intensive tidal reworking in the distal reaches of the regressive delta front could not have been predicted from knowledge of the coeval proximal reaches of the regressive delta front. The wave signals occur mainly in the shelf or shoreface deposits. The fluvial signals increase in abundance proximally but are always mixed with the other processes. The Lajas system is an unusual clean‐water (i.e. very little mud is present in the system), sand‐rich deltaic system, very different from the majority of mud‐rich, modern tide‐influenced examples. The sand‐rich character is a combination of source proximity, syndepositional tectonic activity and strong tidal‐current reworking, which produced amalgamated sandstone bodies in the delta‐front area, and a final stratigraphic record very different from the simple coarsening‐upward trends of river‐dominated and wave‐dominated delta fronts.

The uppermost deposits of the stratigraphic succession of the Farafra Depression (Western Desert, Egypt): Evolution to a Post-Eocene continental event

This paper gives insight into continental sedimentary deposits that occur at the uppermost part of the stratigraphic succession present in the north-eastern sector of the Farafra Depression (Western Desert, Egypt). Using space imagery to complete the field work, the geology of the area has been mapped and the presence of a N–S oriented fault system is documented. The analysis of the morphotectonic features related to this fault system allows reconstructing the structural and sedimentological evolution of the area. The study indicates that the continental deposits were accumulated in alluvial systems that unconformably overlie shale and evaporitic rocks attributable to the Paleocene–Eocene Esna Formation. The deposits of the Esna Formation show soft-sediment deformation features, which include slump associated to dish and pillar sedimentary structures and provide evidence of syndepositional tectonic activity during the sedimentation of this unit. The outcrops are preserved in two areas on separated fault-bounded blocks. Proximal alluvial fan facies crop out in a dowthrown block close to the depression boundary. The proximal facies are made up mostly by polymictic conglomerates which occasionally contain boulders. The conglomerate clasts are mainly quartz, carbonate, anhydrite satin spar vein, mudrock, ironstone and nummulite fossils. The mid-fan facies consist of trough cross-bedded, rippled and cross-laminated quartzarenites with reworked glauconite grains and carbonate rock fragments, interpreted as deposited by distributary streams. The distal alluvial fan deposits consist of sandy marls that evolve toward the top of the sections into root-bioturbated lacustrine limestone beds that are locally silicified. The limestones are biomicrites containing characea, ostracods and gastropods with fenestral porosity.A number of features, including clast provenance (mainly from marine Paleocene and Eocene rocks), the observed fractural pattern (N–S direction related to the opening of the Red Sea), and the sedimentary relationships, suggests that the continental deposits were accumulated during the Oligocene–Miocene interval.

Permian outliers in Western Kentucky

Two small, down-faulted outliers of latest Pennsylvanian to Early Permian rocks occur in western Kentucky. These are the youngest Paleozoic rocks in the Illinois basin and are approximately 550 and 750km, respectively, from strata of comparable age in the Dunkard basin and Midcontinent. A continuous core, Gil 30, was drilled in the eastern (Cap Mauzy) outlier. Fusulinids (Leptotriticies beardi) from a depth of 59.4m were originally used as evidence for Permian age, although this species is now considered to be latest Pennsylvanian. Ostracods from above the fusulinids support a Permian age. The upper 103.6m of Gil 30 is assigned to the Mauzy Formation and contains intervals of bedded, micritic, nodular to brecciated limestone of probable lacustrine origin, alternating with marine to brackish-water clastic intervals that tend to coarsen upward, a single upward-fining sandstone interval, and a single 2cm thick coal layer. Older strata contain much more coal and almost no bedded non-marine limestone. The Grove Center graben, 18km west of Gil 30, is identified on the basis of an oil-test hole electric log and coal test holes. No core samples are available, but log comparison indicates that the Grove Center outlier contains at least an additional 67m of younger strata than Gil 30, and is a prime target for further study.Regional coalification and oil-maturation trends, along with lack of evidence for syndepositional tectonic activity in Gil 30, indicate that the Permian rocks preserved in Gil 30, and by extension the Grove Center graben, are likely representative of strata that once occupied much of the Illinois basin, probably in continuity with the Midcontinent. The Kentucky outliers, therefore, provide a link between the Midcontinent and Dunkard basins and may be important in addressing long-standing problems, such as the age of the Dunkard, and paleoclimate reconstructions.

Syndepositional tectonic activity in an epicontinental basin revealed by deformation of subaqueous carbonate laminites and evaporites: Seismites in Red River strata (Upper Ordovician) of southern Saskatchewan, Canada

Research Article| March 01, 2012 Syndepositional tectonic activity in an epicontinental basin revealed by deformation of subaqueous carbonate laminites and evaporites: Seismites in Red River strata (Upper Ordovician) of southern Saskatchewan, Canada Hussam El Taki; Hussam El Taki Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK S7N 5E2 Search for other works by this author on: GSW Google Scholar Brian R. Pratt Brian R. Pratt Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK S7N 5E2 Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2012) 60 (1): 37–58. https://doi.org/10.2113/gscpgbull.60.1.37 Article history received: 11 Mar 2011 accepted: 27 Apr 2012 first online: 12 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Hussam El Taki, Brian R. Pratt; Syndepositional tectonic activity in an epicontinental basin revealed by deformation of subaqueous carbonate laminites and evaporites: Seismites in Red River strata (Upper Ordovician) of southern Saskatchewan, Canada. Bulletin of Canadian Petroleum Geology 2012;; 60 (1): 37–58. doi: https://doi.org/10.2113/gscpgbull.60.1.37 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract The Yeoman and Herald formations of the Late Ordovician Red River succession of southeastern Saskatchewan comprise two carbonate–evaporite cycles in the epicontinental Williston Basin. Although these units possess an overall ‘layer-cake’ aspect across a broad area, thickness variations in the Herald Formation show that accumulation was affected by syndepositional flexure, differential subsidence, and displacement of basement faults thought to have been oriented orthogonally NE–SW and NW–SE. The dolomudstones and anhydrites of the Lake Alma and Coronach members host a variety of synsedimentary deformation features —seismites—interpreted to have been induced by earthquakes generated by movements of these faults, and the low-energy, subaqueous environmental setting was conducive to their preservation.Individual deformed intervals are <0.2 m thick. Folds and small-scale pinch-and-swell structures indicate plastic behaviour of both carbonate and evaporite sediment under compression and shear stress. Brittle failure of stiffer material from compression or extension is shown by microfaults, cracks, disrupted layers, pseudo-intraclasts, breccias and cataclastites. Dikelets in interlaminated dolomudstone and anhydrite record cyclically elevated pore pressure that caused dewatering and shrinkage with concomitant fluidization and injection of carbonate mud and primary granular gypsum. Enterolithic anhydrite exhibits compressed vertical dikes that likely represent injection of granular gypsum. Clay-filled shear-vein arrays occur rarely in dolomudstone. Seismites are absent in bioturbated limestones except for one horizon of molar-tooth structure.The different kinds of seismites are related to the varying rheology caused by the primary nature of the carbonate and evaporite sediment plus modifications due to deformation-induced dewatering, early diagenesis, and confinement under shallow burial, as well as earthquake magnitude. A minimum shaking intensity of MM=VI was probably required, meaning that events of lesser magnitude were not recorded. Some seismite-bearing horizons can be correlated across the study region. Within the limitations of core control, their geographic distribution varies, probably in relation to the basement faults. Seismites thus serve as proxy signals of syndepositional tectonic activity but also point to components of the basement structural fabric that, if reactivated later, might induce fracture porosity or influence subsurface fluid flow. Syndepositional tectonism undoubtedly had a much more profound influence on many successions than is presently thought, and its effects are more widespread than currently appreciated. You do not currently have access to this article.

The Great Atlasian Reef Complex: An early Cambrian subtropical fringing belt that bordered West Gondwana

The so-called Great Atlasian Reef Complex developed during early Cambrian time throughout the Moroccan margin (Souss Basin) of West Gondwana. According to the syndepositional tectonic activity associated with its intracratonic Ediacaran–Cambrian rift, the great reef complex can be subdivided into four major archaeocyathan-microbial reef episodes: (i) The Atdabanian episode is recorded by a SW–NE-trending, 400 km long barrier reef that extended across the western Anti-Atlas. It was controlled by large-scale reactivation of an inherited rifting branch, which resulted in the nucleation and growth of linear reef complexes located along its margin. The interplay of block tilting, sharp modifications in accommodation space, and relative sea-level rise led to a composite retrogradational–aggradational reef systems tract, characterized by archaeocyathan-microbial kalyptrate complexes (Tiout Member and Amouslek Formation) that protected stromatolite-dominated, back-barrier environments (lower member of the Igoudine Formation). (ii) The western Anti-Atlas recorded an early Botoman reactivation of the same rifting branch that triggered a lateral migration of frame-building centres of carbonate productivity. As a result, the involved grabens and half-grabens recorded the development of fringing mound complexes (lower Issafen Formation). These occupied some linear intra-platform, deeper depressions capped by marls and shales, whereas laterally equivalent shallower environments recorded the development of patch-reefs and bioherms. (iii) The western Anti-Atlas subsequently recorded a late Botoman interval of tectonic quiescence superimposed to a local interval of progradational pulses. This favoured the nucleation of dispersed archaeocyathan-microbial patch-reefs and bioherms. (iv) A distinct palaeogeographic area is recognized in the southern High Atlas, where the entire Atdabanian–Botoman interval recorded small-scale, synsedimentary block tilting and high rates of volcaniclastic input. As a result, this sector was characterized by the record of microbial and archaeocyathan-microbial patch-reefs and bioherms, preferentially developed on the uplifted parts of tilted blocks. The end of reef development and carbonate productivity in the Souss Basin is related to the progradation of siliciclastic depositional systems (Toyonian regression), considered to have caused the collapse of reef communities throughout West Gondwana.

Paleo-earthquakes in passive-margin settings, an example from the Paleocene of the Golfo San Jorge Basin, Argentina

Paleocene sedimentary rocks in the Golfo San Jorge Basin include the marine Salamanca Formation and the continental Río Chico Formation. Both units contain soft-sediment deformation features and evidence of contemporary tectonics, which include: 1) sediment-filled fissures, hosted in muddy marine sediments of the Salamanca Formation (“Fragmentosa” Section), where the sandy infill of the fissures took place from above; 2) synsedimentary normal faults in the uppermost levels of the Salamanca Formation, with vertical throws rarely exceeding 1 m; 3) fault-graded beds in the “Banco Negro Inferior” (marine–continental transition), which show a deformed sequence with small-scale normal faults at the bottom and intraformational breccias on top; and 4) liquefaction and/or fluidization pillars, “V” or funnel-shaped, with vertical extension of up to 5 m and preserved into fluvial channels of the Río Chico Formation. Deformed strata are bounded by undisturbed horizons and some of these features can be correlated along 60 km of exposures. The suite of soft-sediment deformation structures is considered a secondary evidence of synsedimentary paleo-earthquakes (seismites) in this portion of the South American passive margin. This work shows new evidence of syndepositional tectonic activity in the lowermost Paleogene of the Golfo San Jorge Basin.

(Plio-)Pleistocene alluvial-lacustrine basin infill evolution in a strike-slip active zone (Northern Andes, Western-Central Cordilleras, Colombia)

The (Plio)-Pleistocene Zarzal Formation was deposited in the Cauca Depression and Quindio-Risaralda Basin between the Western and Central Cordilleras (Northern Andes). This area is structurally located on the transcurrent Romeral Fault System (RFS). Because of the interaction between the Nazca plate and the Choco-Panama block (an active indenter), the RFS strike-slip component changes direction around the study zone (dextral in the south, senestral in the north). Zarzal sediments are the oldest ones not to have been affected by the Pliocene Andean tectonic phase. Their study aims at better understanding the subsidence of these two interandean sedimentary basins within a regional compressional regime. The two basins are separated by the the Serrania de Santa Barbara (SSB), made of Tertiary sediments thrusted during the Pliocene tectonic phase. Zarzal sediments are fluvio-lacustrine: diatomites are encountered on both sides of the SSB and are alternating with braided stream or alluvial deposits. Sedimentation was strongly influenced by volcanic processes which led to the deposition of the Quindio-Risaralda and Cartago volcaniclastic fans sourced from the Central Cordillera. These volcaniclastic mass flows mixed with the Zarzal sediments, and even dammed and infilled a lake in the Quindio-Risaralda Basin (east of the SSB). Numerous extensional features affect Zarzal sediments with a mean extensional trend subparallel to the SSW-NNE trending cordilleras. The syndepositional tectonic activity is demonstrated by numerous seismites. In the Cauca Depression, sediments are infilling the basin more rapidly than it subsides or than the relief lifts up, thereby drowning the topography. This might be related to the tectonically-induced, downstream damming of the Cauca River valley to the north by the Choco-Panama block.

Hydrothermal venting and basin evolution (Devonian, South China): Constraints from rare earth element geochemistry of chert

This paper presents rare earth element (REE) geochemistry of siliceous deposits from which hydrothermal activity and basin evolution are elucidated, in the Late Devonian, in the Yangshuo basin, South China, where siliceous deposits widely occurred as nodular chert in the deep-water limestones and bedded chert interbeded with tuffaceous chert in the early Late Devonian. Both nodular and bedded cherts are characterized by very low La abundances (avg. 2.07 and 2.49 ppm, respectively), intermediate negative Ce anomalies (Ce/Ce*: avg. 0. 69 and 0.61), slight to intermediate positive Eu anomalies (Eu/Eu*: avg. 1.33 and 1.57), and low to intermediate shale-normalized La n/Yb n values (avg. 0.86 and 0.52) and intermediate La n/Ce n values (avg. 1.61 and 1.72). These suggest both nodular and bedded cherts formed in the open marine basin of South China, rather than in the intracontinental rift basin as previously assumed, with involvement both with seawaters as indicated by intermediate negative Ce anomalies and generally LREE-depleted patterns, and hydrothermal vent fluids as indicated by convex, less LREE-depleted patterns with apparent positive Eu anomalies. In comparison with nodular and bedded chert, the tuffaceous chert has the highest La abundances (avg. 17.11 ppm), similar ranges of Ce anomalies (avg. 0.63) and La n/Ce n values (avg. 1.77), but lower La n/Yb n values (avg. 0.48) and no apparent positive Eu anomalies (avg. 0.97). This suggests that the tuffaceous fallouts were also significantly modified by the hydrothermal fluid and seawater. Rapid spatial variations of Eu/Eu* values and degree of LREE-depletions in the studied basin are recognized, characterizing a spatially differential hydothermal activity that is not well discriminated by major element features. Such a difference in hydrothermal activity is interpreted as having been related to the intensity and depth of syndepositional tectonic activity, reconciling the structural pattern unraveled by stratigraphic packages.

Deformation history of the southwestern Taiwan foreland thrust belt: insights from tectono-sedimentary analyses and balanced cross-sections

Analysis of the basin-scale and local deformation history and estimates of shortening rates are performed in the southwestern foreland thrust belt of the Plio-Pleistocene Taiwan orogen. Timing of deformational events is constrained using both syntectonic unconformities and other markers of syndepositional tectonic activity. Three cross-sections are investigated and balanced. Intermediate shortening rates are estimated based on balanced and restored cross-sections. The total amount of shortening along studied balanced sections results from superimposed thin-skinned and thick-skinned styles. A shallow aseismic thick décollement is located to depth of 6–8km at the base of thick Late Miocene shales that behaves as ductile layer. The occurrence of a deep seismic décollement to depth of 12–15km is confirmed by seismicity, fault plane solutions of focal mechanisms and a seismic reflection profile providing evidence of reactivated and inverted inherited extensional features beneath the Coastal Plain. Three major tectonic stages are recognized within the southwestern Foothills, which are correlated with local thrusting events. The first stage begins at 5Ma with the onset of the Taiwan collision and ends at 2–1.6Ma. It reflects an initial submarine accretionary stage associated with moderate tectonic activity. The second major stage occurs during Late Pliocene–Early Pleistocene. This “intermediate” collision stage sealed the evolution of the southern foreland thrust wedge from submarine to continental environment in relation with exhumation and denudation of the Central Range. The last stage of deformation begins in the Middle Pleistocene and continues until present. It is associated with high rates of sedimentation and most of the thrusts are activated or reactivated at that time and out-of-sequence thrusting occurs. The collision started synchronously near 5Ma throughout the southwestern Taiwan. Total and intermediate shortening rates are more or less constant through time in studied sections; that may suggest that long-term deformation in the Taiwan foreland thrust belt occurred more or less at steady-state. Since 5Ma, the southward decrease of rates of shortening from 3.6 to 4.8mm/year in northern sections to 2.2mm/year in southern section might be related to both influence of indentation by the Peikang High to the north and southward transition, at the scale of the southwestern Foothills, from collision to subduction setting; the effect of the obliquity of the convergence resulting in regional southward migration of the collision cannot be definitely inferred from this analysis. Our results place new kinematic and time constraints, which must be taken into account in forthcoming geodynamic models of the Taiwan collision.

Structural Implications on the Deposition of the Upper Freeport Coal Bed in Eastern Greene County, Pennsylvania

The orientation, geometry, thickness, and quality of the Upper Freeport coal bed suggests that syndepositional tectonic activity influenced the accumulation of peat and its laterally equivalent sediments. Both strike-parallel and strike-normal structures appear to influence the deposition of the Upper Freeport coal bed. Strike-parallel structures are faults that were active during the Carboniferous, but do not penetrate into the Carboniferous section. The Carboniferous rocks at the surface within the study area reflect deeper structures as a series of gentle synclines and anticlines. The Upper Freeport coal bed was deposited as a domed peat across the Belle Vernon anticline, which represents the upthrown side of a syndepositionally active deep fault. Laterally equivalent fluvial channel sediments were deposited on the downthrown side of the structure, represented at the surface by the Waynesburg syncline. The influence of syndepositionally active faults on the distribution, thickness, and quality of the Upper Freeport coal bed is similar to the previously reported influence of contemporaneous growth faults on the distribution and thickness of Carboniferous coal beds in Kentucky and Alabama. Strike-normal features also influence the position, geometry, and thickness of the Upper Freeport coal bed. The strike-normal features appear to be produced by deep strike-slip faulting. Amore » major no-coal zone within the Upper Freeport coal bed lies within and parallel to the trend of a cross-strike discontinuity within the study area.« less

THE JURASSIC SYSTEM IN NORTHERN EGYPT: II. Depositional and tectonic regimes

The results are outlined of a detailed sedimentological study made of the Jurassic succession presented in northern Egypt at surface and in the subsurface, largely on the basis of material from over 80 wells. With the benefit of a detailed stratigraphical scheme, it has become possible to map the distribution of fluvio‐deltaic, shelf and open‐marine facies belts. Changes in distribution of facies are attributed to the eustatic interaction between Nubian and Tethyan influences, and to the repeated movement of local faults. Active basins are identified on the basis of static facies. and stacked thick sequences. The pattern of syn‐depositional tectonic activity thus assembled is compatible with existing tectonic models for the Eastern Mediterranean region: indeed, it is used to improve them. The present continental margin to Egypt is shown to have formed during a period of westward‐propagating crustal rifting, over the late Pliensbachian‐Bathonian interval. Evidence is presented for a link between movements within the central/southern African craton, and the sequence of extensional and transtensional activity observed in Egypt during the Jurassic and the “Cimmerian” event. Faults accommodating this strain were mostly orientated NE‐SW, that is, contiguous with the “Syrian Arc”.

Hangfazies in pelagischen Kalken und synsedimentäre Tektonik in Beispielen aus dem Mittel-Turon (Oberkreide) von NW-Deutschland1)

Hangfazies in pelagischen Kalken und synsedimentäre Tektonik in Beispielen aus dem Mittel-Turon (Oberkreide) von NW-Deutschland1)