Growth Synclines Research Articles

Chronostratigraphy and tectono‐sedimentary history of the Eastern South Pyrenean foreland basin (Ripoll Syncline, North‐East Spain)

AbstractThis paper contributes to an understanding of the tectono‐sedimentary evolution of the South Pyrenean foreland system by reviewing the chronostratigraphic framework of the basin infill in its eastern sector. Six sections are analysed and cross‐correlated to build a 6.5 km thick composite magnetostratigraphy that represents the complete record of the Cadí Nappe in the Ripoll Syncline. New and previous magnetostratigraphic sections are integrated with available biostratigraphy to provide a new age calibration of the sedimentary succession of the Cadí Nappe, encompassing from Palaeocene to Middle Lutetian age. The proposed correlation with the Geomagnetic Polarity Time Scale aims at best reconcile magnetostratigraphic data with the regional biochronology built on the marine Shallow Benthic Zonation (SBZ biozones), the continental mammalian biochronology (MP levels) and the newly collected charophyte data. A subsidence analysis was performed on the calibrated composite succession, resulting in two well‐defined intervals bounded by a hiatus. A Palaeocene to Early Eocene interval with low (11–21 cm/kyr) total subsidence rates, and an Early to Middle Eocene interval, characterised by high (70–75 cm/kyr) total subsidence rates. The detailed trends in both subsidence and sedimentation mark the development and evolution of the foreland depozones, from distal foreland depozones to foredeep and wedge‐top depozones, relative to the emplacement of the Pedraforca Nappe and Cadí Thrust Nappe. The most pronounced sedimentary shift in the Cadí Nappe occurred at 49 Ma, with the rapid drowning of the carbonate platforms and its transition into talus and deep basinal environments. Carbonate platforms collapsed and resedimented on the talus of the elongated trough, newly formed parallel to the orogenic front. This marked the onset of tectonic subsidence triggered by the submarine emplacement of the Lower Pedraforca Nappe. The emersion of the orogenic wedge drove the entry of siliciclastics, lagged by 1 Myr, into the Ripoll Trough. The foredeep filled rapidly (5.5 km thickness in less than 7 Myr) compared to other South Pyrenean regions, favoured by its semi‐enclosed palaeogeography. The emplacement of the Vallfogona Thrust as early as the Middle Lutetian (43 Ma) brought the Cadi Nappe into a wedge‐top setting. However, the Ripoll growth syncline continued acting as a temporary sink for alluvial sedimentation while a foredeep developed further south in the autochthonous Ebro Basin. The flexural response of the Iberian plate to the tectonic thickening of the Axial Zone counterbalanced for a period the local uplift of the Cadi Nappe, providing accommodation space for the top sediments filling the Ripoll Syncline.

Multiple phase rifting and subsequent inversion in the West Netherlands Basin: implications for geothermal reservoir characterization

Abstract. Aiming to contribute to the energy transition, this study provides an integrated picture of the geothermal system hosted in the West Netherlands Basin and shows how the reconstruction of the basin's geological history can contribute to the correct exploration and exploitation of its geothermal resources. In the West Netherlands Basin, the main geothermal targets are found in the Cretaceous and Jurassic strata that were deposited during the rifting and post-rifting stages and were deformed during the subsequent basin inversion. Despite multiple studies on the tectonic setting, the timing and tectono-stratigraphic architecture of the rift system and its overall control on the development and evolution of geothermal systems are still to be fully deciphered. In this study, a detailed seismo-stratigraphic interpretation of the syn- and post-rift intervals in the West Netherlands Basin will be given within the framework of geothermal exploration. A recently released and reprocessed 3D seismic cube is used, covering a large portion of the onshore section of the basin. We identified two major Jurassic rifting episodes and a Late Cretaceous inversion event. During the Jurassic rifting phases, the compartmentalization of the basin and the creation of accommodation space led to the deposition of the Late Jurassic Nieuwerkerk Formation, which is the main regional geothermal producing target. Within this formation, we individuate growth synclines located in the central portions of the Jurassic half-grabens as sites that show good potential for geothermal exploration.

Secondary minibasins in orogens: Examples from the Sivas Basin (Turkey) and the sub-Alpine fold-and-thrust belt (France)

Inherited and syn-compressional salt-controlled structures in orogens are difficult to distinguish from compressional features because classical salt features (halokinetic growth strata, salt welds) can be misinterpreted as shortening-related structures (syn-kinematic growth strata, tectonic unconformities). In the Sivas basin in Turkey, syn-kinematic salt diapirism entirely shaped the architecture of the foreland and allowed the development of primary and secondary minibasins. One of the most impressive, the Tuzlagözü minibasin, formed by sinking into a salt feeder while being upturned due to compression. This minibasin has been nicknamed the “Turkish Vélodrome” because of its similarity with the well-known Vélodrome structure in the French Alps which shows growth strata and successive unconformities, commonly interpreted as foreland growth syncline features. Based on structural field descriptions and geometric analogies with the Tuzlagözü minibasin, we revisit the Vélodrome as a salt-related minibasin. We argue that the Vélodrome developed as a secondary minibasin above an Oligocene aerial salt glacier: sheet of Upper Triassic evaporites extruded during Alpine orogeny. This new interpretation enables to propose a revised evolution of the sub-Alpine fold-and-thrust belt. In line with other recent works, this study emphasises once again the important role of salt tectonics in the evolution of the sub-Alpine fold-and-thrust belt.

Tectono-climatic controls of the early rift alluvial succession: Plio-Pleistocene Corinth Rift (Greece)

Proximal alluvial sediments represent a useful sedimentary archive to reconstruct the tectono-climatic history of continental rift basins. However, poor dating of coarse fluvial successions usually prevents high-resolution distinction of tectonic and climatic processes, and thus good determination of process rates. This paper presents a dating study of Plio-Pleistocene Kalavryta river system during the early history of the Corinth Rift (northern Peloponnese, Greece) based on magnetostratigraphy and palynology. This river system developed across several active normal fault blocks that are now uplifted along the southern rift margin. The detailed sedimentary record constrains alluvial architectures from the proximal basin to the river outlet where small deltas built into a shallow lake. In four magnetostratigraphy sections the correlation to the reference scale relies on the identification of the Gauss/Matuyama magnetic reversal and biostratigraphic elements. The river system developed between about 3.6 to 1.8 Ma, with sediment accumulation rates (SARs) ranging from 0.40 to 0.75 mm yr−1. SAR is lower in the alluvial fans than in the deltaic system, and higher at the centre of the normal fault depocentres than at the fault tip. By comparison with worldwide Cenozoic SARs, our values are higher but lie in the same range as those determined in coarse alluvial foreland basins. Moreover, in the context of overfilled intra-mountainous rift basins, these rates are minimum values and can be used as a proxy for accommodation rate. Therefore, early rift stratal wedges and growth synclines attest high sedimentation rates and also high rates of tectonic processes. Finally, in the distal river system, floral compositions and changes of vegetation deduced from palynological data are coherent with alternating fluvio-deltaic and shallow lacustrine deposits, which are linked to relative base level variations. Dry/cool climate is preferentially recorded during periods of low lake level, while the warm/moist climate is mainly recorded in prodelta deposits during periods of high lake level. This correlation suggests that, despite the dominant control of active faulting, climate is a key control of syn-rift stratigraphic architectures.

Reading tidal processes where their signature is cryptic: The Maastrichtian meandering channel deposits of the Tremp Formation (Southern Pyrenees, Spain)

AbstractTidal currents can propagate tens of kilometres landward from the shoreline, forming dense networks of meandering channels, which drain vegetated areas and range in width from tens to hundreds of metres. Sedimentary products of these inland tidal channels are poorly documented in the stratigraphic record, as most studies on tidal processes occurring in inland areas are focused on fluvio‐tidal interaction. The present study contributes to filling this gap, investigating Late Maastrichtian meandering‐channel deposits of the Tremp‐Graus Basin (Southern Pyrenees, Spain). These deposits accumulated in a growth syncline, which allowed the development of a 20 to 30 km wide, 80 to 100 km long, tidal embayment. Sporadic occurrence of poorly‐developed rhythmites and bidirectional currents confirms the occurrence of tidal processes, whereas their local dominance is inferred from several pieces of evidence, including: (i) disproportion between depth of the larger channels and related catchment area; (ii) landward‐accretion of point‐bar bodies; (iii) landward fining of point‐bar bodies, and (iv) reconstruction of palaeo‐flow patterns at the meander bend scale. This work shows that three‐dimensional architectural modelling and reconstruction of bar planform transformation styles can provide a critical contribution to the understanding of tidal control on sedimentation in inland areas.

Pliocene growth of the Dowlatabad syncline in Frontal Fars arc: Folding propagation across the Zagros Fold Belt, Iran

Abstract The integration of biostratigraphy, strontium isotope stratigraphy, and magnetostratigraphy allowed for the precise dating of the >3.0-km-thick marine to non-marine foreland sedimentary succession within the Dowlatabad growth syncline along the Frontal Fars arc in the Zagros Fold Belt that extends from eastern Turkey to southern Iran. This area was the missing link to complete the dating of syntectonic deposits in the Fars arc and quantify the migration of sedimentary belts as well as the propagation of folding across the entire Mesopotamian foreland basin. Both are essential for defining the interplay of basin evolution and sequence of folding. Deposition of the foreland marine marls in the Mishan Formation started at ca. 11.5 Ma. The transition to a non-marine basin infill occurred at 4.9 Ma by the progradation of thick fluvial deposits of the Aghajari Formation with a fast accumulation rate of 63 cm/k.y. The beginning of growth strata deposition and thus the onset of folding in the Dowlatabad syncline is dated at 4.65 Ma. The first appearance of carbonate conglomerates sourced from the Guri limestone at 2.8 Ma marked the progressive dismantling of the nearby growing anticlines. The tectonic deformation in the front of the Fars arc was active for at least 2.85 m.y. and ceased at 1.8 Ma before the deposition of the discordant and slightly folded Bakhtyari conglomerates characterized by a clast composition derived from the Zagros hinterland. The compilation of magnetostratigraphic ages reveals that both the migration of the Aghajari-Bakhtyari sedimentary belts and the propagation of the folding front was in-sequence toward the foreland at a rate close to 20 mm/yr in the Fars arc and 15 mm/yr in the Lurestan arc, in the last 20 m.y. These high rates of folding propagation are about one order of magnitude larger than age equivalent shortening rates (∼4 mm/yr in Fars arc and ∼2 mm/yr in Lurestan arc) and thus imply an efficient detachment level at the base of the deformed Arabian sedimentary cover. Numerical experiments on both the cover and basement sequences are designed to test the influence of inherited basement structures on the deformation propagation within the cover sequence, providing clues on the partly coeval in-sequence deformation of the Zagros Simply Folded Belt and the local out-of-sequence Mountain Frontal Fault system as illustrated by regional and local geology.

Folding style of the Jarik Anticline, NE Dezful Embayment of Zagros Belt, the role of thickness changing of the folded layers and syntectonic deposition

Detecting the style changes and folding mechanism of anticlines in the Dezful Embayment, an oil-rich area, in the SW Zagros Fold-Thrust Belt have important applications for hydrocarbon exploration. The present study, according to the field, seismic and well data, investigates the effects of multiple factors such as detachment horizon, halokinetic process, syn-tectonic sedimentation and thickness variation on the folding style through the Jarik Anticlines in the northeast of Dezful embayment. Due to the above-mentioned factors, the Jarik Anticline shows a variable folding geometry both along the anticline strike and from the surface to the depth. The Jarik Anticline, as a detachment fold, was formed in the Fars passive Group and decoupled from the deep structures by Gachsaran evaporites (as strong detachment horizon). In the northwestern termination where the Passive Group has a considerable thickness (up to 2500 m); the Jarik Anticline displays the Lift-off detachment geometry. In contrast, from the middle segment to SE termination of the anticline thickness reduction of the Passive Group led to the formation of the asymmetric faulted detachment fold. These thickness changes of the Passive Group are the result of the interaction between deposition of this group (as syn-tectonic deposits), both laterally and vertically movements of the Gachsaran evaporites and folding of the Competent Group under the detachment horizon. Based on the results of this research, the possible development of the large subsurface anticlines under the uplifted surface growth synclines must be considered in the future exploration studies.

Stratigraphic variations control deformation patterns in evaporite basins: Messinian examples, onshore and offshore Sicily (Italy)

Three-dimensional seismic data are increasingly resolving original compositional heterogeneity and structural complexity in evaporitic successions within sedimentary basins. The relationship between basin structure, evaporite composition and its influence on subsequent deformation are investigated here using Messinian examples from the Maghrebian thrust system of Sicily and applied to the adjacent Ionian sea-bed. By integrating outcrop and onshore subsurface data, we demonstrate variations in evaporite stratigraphies deposited across thrust-top basins, and how these variations have controlled subsequent deformation of these basins. Gypsum and carbonate units develop broad single-layer buckle fold trains, with wavelengths reflecting layer thickness. The development of deformation appears limited by bending resistance at fold hinges, which can be overcome by syntectonic erosion. In contrast, the thick halite and K-salt accumulations in growth synclines have deformed with short-wavelength folds and distributed strain. These structures can display rapid lateral variations (on a scale of hundreds of metres). Similar structural styles, with buckle fold trains passing laterally into more homogeneously shortened, short-wavelength folding, are evident on seismic data from the buried Messinian interval beneath the Ionian Sea. Using the Sicilian outcrop as analogues, the structural styles for the Ionian may be used to infer evaporite type in these subsurface examples.

Basin architecture and growth folding of the NW Zagros early foreland basin during the Late Cretaceous and early Tertiary

Abstract: We present and use the chronostratigraphy of 13 field logs and detailed mapping to constrain the evolution of the early Zagros foreland basin, in NW Iran. Large foraminifera, calcareous nannofossil, palynological and 87 Sr/ 86 Sr analysis supplied ages indicating a Campanian–early Eocene age of the basin infill, which is characterizd by a diachronous, southwestward migrating, shallowing upwards, mixed clastic–carbonate succession. Growth synclines and local palaeoslope variations indicate syndepositional folding from Maastrichtian to Eocene time and suggest forelandward migration of the deformation front. We also illustrate the basin architecture with a synthetic stratigraphic transect. From internal to external areas, time lines cross the formation boundaries from continental Kashkan red beds to Taleh Zang mixed clastic–carbonate platforms, Amiran slope deposits and basinal Gurpi–Pabdeh shales and marls. The foreland basin depocentres show a progressive migration from the Campanian to Eocene ( c . 83–52.7 Ma), with rates of c . 2.4 mm a −1 during the early–middle Palaeocene ( c . 65.5–58.7 Ma) increasing to c . 6 mm a −1 during the late Palaeocene–earliest Eocene ( c . 58.7–52.8 Ma). Coeval subsidence remained at c . 0.27 mm a −1 during the first 12.7 Ma and decreased to c . 0.16 mm a −1 during the last 4.2 Ma of basin filling. Finally, we integrate our results with published large-scale maps and discuss their implications in the context of the Zagros orogeny. Supplementary material: Tables with dating results are available at http://www.geolsoc.org.uk/SUP18439 .

Tectonic control on sedimentary facies pattern and sediment accumulation rates in the Miocene foreland basin of the southern Alborz mountains, northern Iran

The southern Alborz mountains of northern Iran are an integral part of the Arabia/Eurasia collision zone. A magnetostratigraphic and rock magnetic investigation of the Eyvanekey stratigraphic section in the southern Alborz mountains reveals the spatiotemporal character of sedimentary facies migration in the Alborz foreland basin. The section constitutes three coarsening upward units (units 1, 2, and 3), comprising the Upper Red and Hezardarreh formations. Our data reveal that the Upper Red Formation was deposited between 17.5 and 7.5 Ma, while the depositional age of the top of the Hezardarreh Formation can be extrapolated to ∼6.2 Ma. Slow sediment accumulation rates correlate with sedimentary facies comprising prograding, coarsening‐upward units. This is likely the result of intraforeland uplift (units 1 and 2) and basin inversion, probably associated with a growth syncline located in the proximal foreland (unit 3). In contrast, fine‐grained strata at the bottom of each cycle are associated with faster sediment accumulation rates, testifying to enhanced flexural basin subsidence in the course of thrust loading. Progradation of coarse‐grained facies also occurred during relatively fast sediment accumulation (top of unit 2), suggesting that the influx of coarse‐grained sediment outpaced the storage capacity of the proximal foreland. Thus, despite an overall southward propagation of deformation into the southern Alborz foreland, the locus of active deformation must have migrated back and forth on a time scale of circa 0.7 to 2 Ma.

Multidisciplinary approach to an extensional syncline model for the Mesozoic Cameros Basin (N Spain)

In this paper we explore the possibility of reconstructing the initial geometry of inverted basins using combined geophysical and geological methods: seismic reflection profiles, paleomagnetism, analogue modelling and 3D geometrical analysis. These techniques allow for some unknowns in the geometry and evolution of extensional sedimentary basins (mainly the normal drag–reverse drag geometrical problem) to be solved. The example chosen for checking these techniques is the Cameros Basin (northern Iberian Chain), formed during the Late Jurassic–Early Cretaceous, and inverted during the Tertiary compressional stage. According to the reconstruction proposed, the Cameros Basin can be characterised as a lens-shaped, syncline basin with maximum thickness of deposits of about 8000 m in its depocenter, gradually diminishing toward the North and South. The extensional geometry of the Cameros Basin is defined by: 1) a large-scale growth syncline over the major basement fault, with southward-dipping beds in the northern basin margin, forming a southward-opening sedimentary wedge, with upward-decreasing dip values (large-scale normal drag geometry); 2) roll-over anticlines at the contact between the pre-rift series against the normal fault limiting the basin (smaller-scale reverse drag geometry). The combined syncline–anticline syn-extensional structures were characterised by means of paleomagnetic analysis of a remagnetization acquired at the time of extension. Analogue models indicate that the development of syncline basin geometries in extensional settings, as the one interpreted for the Cameros Basin, is closely related to the presence of a detachment level in the pre-rift sequence above the main basement faults.

Stratigraphic record of translation down ramps in a passive-margin salt detachment

Ramp syncline basins filled with synkinematic sediments record the incremental translation history and translation rates of strata transported over basement ramps. On passive margins, movement of strata over a stratabound salt detachment is stratigraphically recorded as an isopach thick on the seaward side of a monoclinal ramp. This growth syncline gradually moves seaward down and then off the monocline, as if on a conveyor belt. This shift creates accommodation space for a new isopach thick to form just landward of the older one. Repetition of this cycle creates a shingled series of isopach thicks within the ramp syncline basin. Kinematic forward models and restored cross sections from the Kwanza Basin, Angola, show that the stratigraphic pattern of ramp syncline basins is most influenced by three factors. (1) The relative rates of translation and aggradation control the curvature of the axial trace of the growth synclines. (2) Bathymetric scarps above basement ramps can create spectacular seaward-dipping onlap surfaces >30 km long downdip; adjoining ramps generate stacked, interfering onlap surfaces. (3) Salt diapirs or anticlines are commonly shortened at the top of the ramp, especially where this coincides with the base of the continental slope. Diapir shortening provides a buffer to absorb sliding from its landward side and impede sliding on its seaward side. This buffering can have a major control on the entire gravity-spreading system containing the diapirs.

Tectono-sedimentary evolution of southwest Sardinia in the Paleogene: Pyrenaic or Apenninic Dynamic?

The Narcao and Cixerri basins in Southwestern Sardinia are east-west trending basins of Oligocene age. Recent geological mapping, combined with structural and stratigraphical analyses, support the proposed hypothesis that these basins were very open growth synclines confined within a structural high, delimited by northwest trending dextral strike slip faults. Previously the basins have been interpreted as fault-bounded grabens. The newer revised interpretation is consistent with the existence of NNW trending dextral strike-slip dynamic, related to a north-south shortening which has generated reverse faulting and tight folds in the underlying, pre-synclinal evolution, Eocene succession. This deformation, along with an interfering sub-orthogonal thrust and fold system which affects the Mesozoic sequence, was traditionally linked to the Pyrenean Orogenesis. The Oligocene–Aquitanian shortening, which resulted in the growth synclines and strike-slip faulting, is consistent with the structural development recognized in north-central Sardinia; there structures related to the collision between continental margins that resulted in the Northern Apennines are well documented. Therefore, the Oligocene tectonics of Southwestern Sardinia also must be related to the collision event between the Southern Europe margin (i.e. a crustal sector corresponding to the future Corsica-Sardinia block) and the Adria Plate, which generated the Northern Apennines. Conversely, the previous E-W shortening- related structures must be related to Pyrenean tectonics.

Compressional salt tectonics (Angolan margin)

We present an analysis of compressional deformation at the front of a gravity spreading system above salt using seismic data from the Angolan margin and laboratory experiments. The geological setting and structural zonation is briefly reviewed and illustrated with two cross sections parallel to the margin slope in the Kwanza Basin. Experiments are carried out using sand and silicone putty to represent sediments and salt, respectively. The silicone layer was double-wedge-shaped to simulate more precisely the initial geometry of the Aptian salt basin of the Angolan margin. Models based on the Angolan margin example display the same structural zonation consisting of an upslope domain of extension, a downslope domain of compression and an abyssal undeformed domain. We present three different models, with different input parameters, showing the lateral variability of compressional structures in the downslope compressional domain. Models show two main stages of compression, which first appears in a domain located at some distance from the toe of the ductile wedge and then propagates both downslope to the distal salt pinchout and upslope in the formerly extensional domain. The initial zone of compression evolves into a domain of strong shortening characterised by folds, thrusts and squeezed diapirs. Synclines undergo strong pinching and can become detached as pod-like structures encapsulated within the underlying ductile layer. Anticlines are also pinched, thus isolating blobs of ductile material forming compressional diapirs that can extrude up to the surface. Unfolded layers develop into pop-up-type anticlines flanked by growth synclines. The propagation of compression, both downslope and upslope, creates domains of moderate shortening on each sides. Close to the domain of strong shortening, double-wavelength folds form a transition to a domain where compression is superposed onto the lower part of the upslope extensional domain, leading to extensional diapir squeezing. In the Angolan margin, propagation of compression downslope is characterised by recent folding affecting a sedimentary sequence of constant thickness and even the seafloor. Characteristic structures identified in the models are compared with seismic examples. We tentatively apply the mechanisms of sediment incorporation within the underlying ductile layer, as demonstrated in models, to the zone of apparently thick massive salt of the Angolan margin.

Syndepositional thrust-related deformation and sedimentation in an Ancestral Rocky Mountains basin, Central Colorado trough, Colorado, USA

Pennsylvanian–Permian synorogenic deposits (Minturn and Sangre de Cristo Formations) of the Central Colorado trough record an interplay of deformation and sedimentation in an Ancestral Rocky Mountains basin. The Central Colorado trough was a north-trending basin bordered by basement-involved highlands of the Uncompahgre uplift on the west and the Ancestral Front Range and Apishapa uplift on the east. Stratigraphic data show that the Central Colorado trough was an asymmetric basin in which coarse-grained sediments were deposited adjacent to the Sand Creek–Crestone thrust fault system of the Uncompahgre uplift. These deposits pinch out eastward against the Apishapa uplift along the eastern margin of the basin. Lithofacies analysis shows that the Central Colorado trough was filled by fan-delta, fluvial-delta, and turbidite deposits of the Middle Pennsylvanian Minturn Formation and by alluvial-fan, braided-stream, and meandering-stream deposits of the Upper Pennsylvanian–Permian Sangre de Cristo Formation. Geologic mapping has identified three syndepositional structures in the strata of the Central Colorado trough that indicate Pennsylvanian–Permian shortening: (1) the Gibson Peak growth syncline in the footwall of the Crestone thrust fault, which formed by syndepositional rotation of the Crestone Conglomerate Member of the Sangre de Cristo Formation during thrust displacement; (2) the Sand Creek thrust fault, which cuts the lower part of the Crestone Conglomerate Member but is covered by younger deposits of the Crestone Conglomerate Member; and (3) an intraformational angular unconformity in the Sangre de Cristo Formation that separates folded strata from overlying less deformed strata. All three structures indicate general east-west shortening during deposition. We interpret the Central Colorado trough as a flexural basin on the basis of syndepositional thrust-related structures, basin asymmetry, and lithofacies distribution. Displacement on the east-verging Sand Creek–Crestone thrust fault system appears to have controlled uplift of the central part of the Uncompahgre uplift and also subsidence in the adjacent basin. The Apishapa uplift, located along the eastern margin of the basin, is interpreted as a possible flexural forebulge related to crustal loading of thrust sheets along the western margin of the Central Colorado trough. Geologic mapping, subsurface data, and identification of syndepositional structures has also led to a better understanding of post-Paleozoic deformation of Pennsylvanian–Permian strata of the Central Colorado trough and the structural evolution of the present Sangre de Cristo Mountains.

Quaternary deformation of the Bajo Segura blind fault (eastern Betic Cordillera, Spain) revealed by high-resolution reflection profiling

The blind reverse Bajo Segura Fault is located at the eastern extreme of the Trans-Alboran shear zone (Betic Cordillera, southeast Iberian Peninsula). The surface expression of recent activity of this blind ENE–WSW fault is represented by coseismic surface anticlines and growth synclines on both sides of the anticlines. In the synclines, the deformation of the most recent Quaternary materials is obscured by a sedimentary unit more than 30 m thick which was deposited during the later part of the Late Pleistocene and the Holocene. The present study reports three high-resolution seismic profiles made in the northern growth syncline, which was the one developed most by the Bajo Segura Fault. In these seismic profiles we recognize the boundary between pre-growth strata and growth strata. This marker, Early Pliocene in age, dates the start of the activity of this blind reverse fault. The geometry observed in the seismic profiles of the syntectonic strata, dating from the Late Pliocene and Quaternary, indicates a limb rotation folding mechanism. On seismic profile 2, the complex geometry of the Benejúzar anticline forelimb can be attributed to several splay faults close to the surface of Bajo Segura Fault.

Architecture of the tectonically influenced Sobrarbe deltaic complex in the Ainsa Basin, northern Spain

The syn-tectonic Sobrarbe deltaic complex (Eocene of the Ainsa Basin, Spanish Pyrenees) is confined by lateral thrust ramps and influenced by intra-basinal growth anticlines. Six facies associations have been distinguished within the deltaic complex: (i) slope marls and turbidite sandstones; (ii) distal delta front silty and bioturbated sandstones; (iii) proximal delta front and delta plain deposits (tidal inlet, tidal flat, mouth-bar, bay, distributary channel, and floodplain environments); (iv) biogenic deposits at flooding surfaces; (v) collapse zone sediments; and (vi) Nummulite-dominated shallow-marine carbonates. The deltaic complex comprises four composite sequences, which each contain a number of minor sequences of the genetic (maximum flooding surface bounded) type. Regressive unconformities and their correlative surfaces separate the composite sequences (CS), and each CS can be divided into lowstand, transgressive and highstand components. At the base, the Comaron CS is a WNW-prograding deltaic complex containing six minor sequences characterized by basinward-stepping sandstone wedges separated by transgressive mudstones. Double regressive unconformities are often associated with these sandstone wedges proximally in the basin. Growth of the intra-basinal Arcusa anticline caused gentle folding of the Comaron CS, and syn-growth strata at the base of the overlying Las Gorgas CS contain a prominent forced regressive sandstone wedge (the Las Gorgas sandbody) and display thinning of bedsets onto the crest of the anticline. Moreover, it can be demonstrated that relative sea-level rise took place in the growth synclines at the same time as a fall in relative sea level occurred on the growth anticlines. The tectonic deformation caused a shift in the direction of deltaic progradation towards the north-northwest, as demonstrated by the well-developed clinoforms in the highstand sequence set of the Las Gorgas CS. A second phase of tectonic activity, this time triggering large-scale collapse of the delta front, occurred at the transition between the Las Gorgas and Barranco el Solano CS. Tilting of the basin floor led to the development of coeval transgressive and regressive strata separated by a fulcrum (line of zero net-vertical movement of the shoreline). In the post-tilt phase, reduced sediment supply and accelerated subsidence led to widespread transgression and a change from clastic- to carbonate-dominated sedimentation. This phase was terminated by a gradual increase in sediment supply causing progradation of a mixed clastic–carbonate system dominated by large Nummulite banks and bioturbated shoreface marls and sandstones. Finally, a pronounced fall in relative sea level associated with the transition to the Buil CS triggered slope instabilities and eventually established fluvial conditions all over the study area. With the exception of the anticline crests, the relatively high rate of tectonic subsidence in the study area suppressed relative sea-level falls, resulting in development of discontinuous lowstand strata and bounding surfaces. The segmented nature of many regressive unconformities may be related to incremental growth of thrust-related structures, and each segment is separated from neighbouring segments by gaps of limited vertical and lateral displacement. Precursors of progressive unconformities are seen in the upper proximal part of the Comaron CS by downdip `fanning' and updip convergence of minor sequences. These differentially tilted stratal units provide reliable indicators of syn-sedimentary tectonism.

Kinematic-stratigraphic evolution of a growth syncline and its implications for tectonic development of the proximal foreland basin, southeastern Ebro basin, Catalunya, Spain

In the southeastern Ebro basin of Spain, analysis of sequential fold history in combination with stacking patterns of conglomerate deposited in a growing syncline demonstrates the impact of local uplift attendant upon fold growth on nonmarine depositional systems in a foreland basin. The Penyagalera syncline is part of a belt of asymmetric folds developed in proximal Paleogene foreland-basin deposits by foreland-directed propagation of a detachment beneath the basin. Foreland-basin strata form a progradational succession of interbedded siltstone, sandstone, and evaporite overlain by conglomerate. Stratal stacking patterns and fold history indicate that conglomerate of the syncline marks the transition within the foreland-basin succession from foredeep to wedge-top depositional zones. The conglomerate is divided into three informal members separated by unconformities. The members are divided in turn into lithosomes separated by prominent bounding surfaces. Lithosomes represent depositional elements deposited by episodic progradation of alluvial-fan lobes. Older conglomerate members are more tightly folded than younger members, demonstrating that folding accompanied conglomerate deposition. The uplift of opposing limbs of the Penyagalera syncline was diachronous. The asymmetric syncline comprises an overturned interior (southeastern) limb and a gently dipping exterior (northwestern) limb. The interior limb rotated to a steep to slightly overturned attitude before significant rotation and uplift of the exterior limb took place. Rotation of the interior fold limb was episodic and punctuated by periods of erosion of older conglomerate. Uplift rates during rotation events along the interior limb generally were more rapid than sediment-accumulation rates and caused sediment bypass to the foreland basin; however, sediment-accumulation rates overtook uplift rates during late limb rotation, causing alluvial-fan lithosomes to onlap previously formed unconformities. Offlap, signifying a slight excess of uplift over sediment-accumulation rates, is not observed in the syncline. On the exterior limb, sedimentation rates exceeded early limb-uplift rates, but the relationship of later folding and deposition is not preserved. Most synclinal closure postdated the youngest preserved lithosomes in the fold. Young lithosomes occupy a paleocanyon incised deeply into the interior limb of the syncline and Mesozoic strata of the thrust belt. The paleocanyon was backfilled during late aggradation of the Ebro basin, an event independent of local folding.

Interaction between faulting, drainage and sedimentation in extensional hanging-wall syncline basins: example of the Oligocene Matelles basin (Gulf of Lion rifted margin, SE France)

Abstract A tectono-sedimentary model for hanging-wall syncline basins emphasizing the role of erosion in the basin architecture is proposed, based on the well-exposed Matelles basin. Detailed geological mapping is the base for the analysis of the extensional double ramp-flat Matelles fault system, hanging-wall deformation and relationships between faulting/drainage/sedimentation. Displacement of the hanging-wall above the fault resulted in the formation of (a) upper and lower rollovers associated with the upper and lower rampflat couples, (b) a hanging-wall ramp syncline above the lower ramp and (c) a half graben associated with the emergent ramp and upper flat couple. Only the hanging-wall ramp syncline and the lower rollover are preserved. Ramp syncline basin-fill architecture is characterized by progressive unconformity and faultward migration of the growth synclines ‘climbing up’ the monoclinal prerift strata corresponding to the ramp-side limb of the ramp syncline. Clast composition analysis of the synrift deposits indicates that sediments were mainly supplied from the hanging-wall flat, and allows to propose palinspastic reconstructions of the hanging wall in order to establish the palaeo-drainage system and its evolution. ‘Upper hanging-wall flat catchments’ and ‘lower rollover catchments’ are proposed as main features of the drainage system in extensional hanging-wall syncline basins.

Structural and sedimentological development of footwall growth synclines along an intraforeland uplift, east-central Bighorn Mountains, Wyoming

Structural, sedimentological, and provenance data from Paleogene synorogenic deposits of the east-central flank of the Bighorn Mountains provide new information about the development of footwall growth synclines, the evolution of fault-related folds, and the erosional unroofing history of intraforeland uplifts. Three conglomerate units, the upper conglomerate member of the Fort Union Formation and the Kingsbury and Moncrief Members of the Wasatch Formation, are incorporated within an asymmetric, east-verging growth syncline in the footwall of the main range-bounding thrust system. Three stages of footwall deformation are recorded within these conglomerates. Analysis of mapped progressive unconformities, retrodeformed balanced cross sections, and conglomerate clast composition data define these stages as part of a continuum of deformation associated with the development of footwall growth synclines. Development of an anticline-syncline pair marked the earliest stage of growth syncline formation (stage I). Rotation of the shared fold limb resulted in amplification of the growth syncline. Fine-grained, synorogenic sediment derived from easily eroded Mesozoic mudstone bypassed the growth syncline during this stage. By the end of Lebo Shale deposition, an average of 12.1% of shortening and 6.46 km of uplift had occurred along the range margin. Continued growth syncline development was marked by the deposition of the Kingsbury Conglomerate. The Kingsbury Conglomerate was derived from resistant, middle and lower Paleozoic carbonate strata in the uplifted source terrane. Intraformational unconformities, recording as much as 55° of bed rotation, were developed within the Kingsbury Conglomerate as fold limb rotation occurred coeval with deposition. Cross sections indicate that during this early stage of fault-related folding, an average of 16.9% shortening and 8.12 km of uplift occurred along the eastern flank of the Bighorn Mountains (end of stage I). The intermediate stage (stage II) of footwall growth syncline development involved partial truncation of the growth syncline by the advancing thrust faults and deposition of the Moncrief Conglomerate. The lower portion of the Moncrief Conglomerate was rotated basinward in the developing growth syncline. The final stage of deformation (stage III) was dominated by the thrust faulting of middle and lower Paleozoic strata eastward over steeply dipping Mesozoic strata and rotated Eocene synorogenic conglomerate. During this stage of deformation, the Moncrief Conglomerate was deformed, as the initially blind thrusts propagated into the near-surface conglomerate deposits, truncated the entire footwall syncline, and overrode the synorogenic conglomerate package. Cross sections in areas where this final stage of deformation is well developed indicate that an average of 24.1% shortening and 9.7 km of uplift had occurred along the eastern margin of the Bighorn Mountains. The caliber of synorogenic deposition in the Powder River basin was linked directly to the lithologic composition of the Bighorn Mountains. Approximately half of the 3.6-km-thick source-stratigraphic section of the eastern Bighorn Mountains was eroded prior to accumulation of conglomerate. The majority of this eroded material was derived from Mesozoic mudstone and poorly indurated sandstone that were incapable of generating coarse detritus. The first Paleogene conglomerates deposited along the east-central Bighorn Mountains, therefore, do not represent the initiation of Laramide uplift, but instead represent the exposure of coarse-clast–forming rock types from the lower half of the hanging-wall stratigraphic section (i.e., the Mississippian Madison Limestone and Ordovician Bighorn Dolomite).