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1.
《Basin Research》2018,30(2):249-278
The Turonian‐Coniacian Smoky Hollow Member of the Straight Cliffs Formation in the Kaiparowits basin of southern Utah records a stratigraphic transition from isolated fluvial channel bodies to increasingly amalgamated channel belts capped by the Calico bed, a sheet‐like sand‐gravel unit. Characteristics of the Smoky Hollow Member are consistent with a prograding distributive fluvial system including: up‐section increases in average grain size, bed thickness, channel‐body amalgamation, a fan‐shaped planform morphology and a downstream increase in channel sinuosity. The system prograded to the northeast based on thickness and facies patterns, and palaeocurrent indicators. This basin‐axial sediment‐dispersal trend, which was approximately parallel to the fold‐thrust belt at this latitude, is supported by provenance data including detrital zircons and modal sandstone compositions indicating sediment derivation mainly from the Mogollon Highlands and Cordilleran magmatic arc to the southwest, with episodic input from the more proximal Sevier fold‐thrust belt to the west. Progradation occurred during a eustatic still‐stand, relatively stable climatic conditions, and continuous tectonic subsidence, thus suggesting increased extrabasinal sediment supply as a primary control on basin‐fill. Progradation of the Smoky Hollow Member fluvial system culminated in a ~2–3 My hiatus at the top of the lower Calico bed. Correlation with the Notom delta of the Ferron Sandstone, 80 km northeast in the Henry basin, is proposed on the basis of facies relationships and geochronology. The Calico bed unconformity is linked to regional tectonically driven tilting and erosion observed in both basins.  相似文献   

2.
ABSTRACT Fluvial megafans chronicle the evolution of large mountainous drainage networks, providing a record of erosional denudation in adjacent mountain belts. An actualistic investigation of the development of fluvial megafans is presented here by comparing active fluvial megafans in the proximal foreland basin of the central Andes to Tertiary foreland‐basin deposits exposed in the interior of the mountain belt. Modern fluvial megafans of the Chaco Plain of southern Bolivia are large (5800–22 600 km2), fan‐shaped masses of dominantly sand and mud deposited by major transverse rivers (Rio Grande, Rio Parapeti, and Rio Pilcomayo) emanating from the central Andes. The rivers exit the mountain belt and debouch onto the low‐relief Chaco Plain at fixed points along the mountain front. On each fluvial megafan, the presently active channel is straight in plan view and dominated by deposition of mid‐channel and bank‐attached sand bars. Overbank areas are characterized by crevasse‐splay and paludal deposition with minor soil development. However, overbank areas also contain numerous relicts of recently abandoned divergent channels, suggesting a long‐term distributary drainage pattern and frequent channel avulsions. The position of the primary channel on each megafan is highly unstable over short time scales. Fluvial megafans of the Chaco Plain provide a modern analogue for a coarsening‐upward, > 2‐km‐thick succession of Tertiary strata exposed along the Camargo syncline in the Eastern Cordillera of the central Andean fold‐thrust belt, about 200 km west of the modern megafans. Lithofacies of the mid‐Tertiary Camargo Formation include: (1) large channel and small channel deposits interpreted, respectively, as the main river stem on the proximal megafan and distributary channels on the distal megafan; and (2) crevasse‐splay, paludal and palaeosol deposits attributed to sedimentation in overbank areas. A reversal in palaeocurrents in the lowermost Camargo succession and an overall upward coarsening and thickening trend are best explained by progradation of a fluvial megafan during eastward advance of the fold‐thrust belt. In addition, the present‐day drainage network in this area of the Eastern Cordillera is focused into a single outlet point that coincides with the location of the coarsest and thickest strata of the Camargo succession. Thus, the modern drainage network may be inherited from an ancestral mid‐Tertiary drainage network. Persistence and expansion of Andean drainage networks provides the basis for a geometric model of the evolution of drainage networks in advancing fold‐thrust belts and the origin and development of fluvial megafans. The model suggests that fluvial megafans may only develop once a drainage network has reached a particular size, roughly 104 km2– a value based on a review of active fluvial megafans that would be affected by the tectonic, climatic and geomorphologic processes operating in a given mountain belt. Furthermore, once a drainage network has achieved this critical size, the river may have sufficient stream power to prove relatively insensitive to possible geometric changes imparted by growing frontal structures in the fold‐thrust belt.  相似文献   

3.
Lacustrine deposits of the Malanzán Formation record sedimentation in a small and narrow mountain paleovalley. Lake Malanzán was one of several water bodies formed in the Paganzo Basin during the Late Carboniferous deglaciation. Five sedimentary facies have been recognized. Facies A (Dropstones-bearing laminated mudstones) records deposition from suspension fall-out and probably underflow currents coupled with ice-rafting processes in a basin lake setting. Facies B (Ripple cross-laminated sandstones and siltstones) was deposited from low density turbidity currents in a lobe fringe environment. Facies C (Massive or graded sandstones) is thought to represent sedimentation from high and low density turbidity currents in sand lobes. Facies D (Folded sandstones and siltstones) was formed from slumping in proximal lobe environments. Facies E (Wave-rippled sandstones) records wave reworking of sands supplied by turbidity currents above wave base level.The Lake Malanzán succession is formed by stacked turbidite sand lobe deposits. These lobes were probably formed in proximal lacustrine settings, most likely relatively high gradient slopes. Paleocurrents indicate a dominant direction from cratonic areas to the WSW. Although the overall sequence shows a regressive trend from basin fine-grained deposits to deltaic and braided fluvial facies, individual lobe packages lack of definite vertical trends in bed thickness and grain size. This fact suggests aggradation from multiple-point sources, rather than progradation from single-point sources. Sedimentologic and paleoecologic evidence indicate high depositional rate and sediment supply. Deposition within the lake was largely dominated by event sedimentation. Low diversity trace fossil assemblages of opportunistic invertebrates indicate recolonization of event beds under stressed conditions.Three stages of lake evolutionary history have been distinguished. The vertical replacement of braided fluvial deposits by basinal facies indicates high subsidence and a lacustrine transgressive episode. This flooding event was probably linked to a notable base level rise during postglacial times. The second evolutionary stage was typified by the formation of sand turbidite lobes from downslope mass-movements. Lake history culminates with the progradation of deltaic and braided fluvial systems  相似文献   

4.
In this study, measured outcrop sections and geolocated photomosaics are integrated with areal mapping of channel dimensions, degree of amalgamation, calculations of channel‐to‐floodplain ratios and sedimentary facies variability to study and quantify the channel and floodplain deposits in the Sunnyside Delta Interval of the Lower Eocene Green River Formation in the Uinta Basin, Utah. Vertically, sand content and bed thickness increases, due to an increase in the channel‐to‐floodplain ratio, channel size and the degree of channel amalgamation. Laterally, the channel‐to‐floodplain ratio, channel size, the degree of channel amalgamation and the sand content in channel facies decreases in the paleo‐downstream direction. Such vertical and lateral transitions identify the Sunnyside Delta Interval as a fluvial fan (or distributive fluvial system). However, the vertical and lateral transitions occur at multiple spatial scales, demonstrating considerable stratigraphic complexity as compared to the existing facies and architectural models suggested for fluvial megafans and distributive fluvial systems. The smallest‐scale transitions are identified as avulsion‐related packages that form the building blocks of the stratigraphy, whereas the intermediate‐ and largest‐scale transitions are suggested to be related to lobe and whole fan progradation respectively. This documented complexity indicates the significance of self‐organization in building fluvial fan stratigraphy, and demonstrates that changes in the degree of channel amalgamation or in channel‐to‐floodplain ratio are not linked to accommodation changes. On facies scale, an abundance of Froude supercritical‐flow and high‐deposition‐rate facies, in‐channel mud deposits, and in‐channel bioturbation and desiccation indicate deposition in rivers with highly variable discharge. Such discharge conditions suggest seasonally and inter‐annually variable precipitation conditions in the US Western Interior in the Early Eocene.  相似文献   

5.
In order to evaluate the relationship between thrust loading and sedimentary facies evolution, we analyse the progradation of fluvial coarse‐grained deposits in the retroarc foreland basin system of the northern Andes of Colombia. We compare the observed sedimentary facies distribution with the calculated one‐dimensional (1D) Eocene to Quaternary sediment‐accumulation rates in the Medina wedge‐top basin and with a three‐dimensional (3D) sedimentary budget based on the interpretation of ～1800 km of industry‐style seismic reflection profiles and borehole data. Age constraints are derived from a new chronostratigraphic framework based on extensive fossil palynological assemblages. The sedimentological data from the Medina Basin reveal rapid accumulation of fluvial and lacustrine sediments at rates of up to ～500 m my?1 during the Miocene. Provenance data based on gravel petrography and paleocurrents reveal that these Miocene fluvial systems were sourced from Upper Cretaceous and Paleocene sedimentary units exposed to the west in the Eastern Cordillera. Peak sediment‐accumulation rates in the upper Carbonera Formation and the Guayabo Group occur during episodes of coarse‐grained facies progradation in the early and late Miocene proximal foredeep. We interpret this positive correlation between sediment accumulation and gravel deposition as the direct consequence of thrust activity along the Servitá–Lengupá faults. This contrasts with one class of models relating gravel progradation in more distal portions of foreland basin systems to episodes of tectonic quiescence.  相似文献   

6.
The Sivas Basin, located in the Central Anatolian Plateau of Turkey, is a foreland basin that records a complex interaction between sedimentation, salt tectonics and regional shortening during the Oligo‐Miocene leading to the formation of numerous mini‐basins. The Oligocene sedimentary infill of the mini‐basins consists of a thick continental succession, the Karayün Formation, comprising a vertical succession of three main sub‐environments: (i) playa‐lake, (ii) fluvial braided, and (iii) saline lacustrine. These sub‐environments are seen as forming a large Distributive Fluvial System (DFS) modified through time as a function of sediment supply and accommodation related to regional changes in climate and tectonic regime. Within neighbouring mini‐basins and despite a similar vertical stratigraphic succession, subtle variations in facies assemblages and thickness are observed in stratigraphic units of equivalent age, thus demonstrating the local control exerted by halokinesis. Stratigraphic and stratal patterns reveal in great detail the complex interaction between salt tectonics and sedimentation including different types of halokinetic structures such as hooks, wedges and halokinetic folds. The regional variations of accommodation/sediment supply led to coeval changes in the architectural patterns recorded in the mini‐basins. The type of accommodation regime produces several changes in the sedimentary record: (i) a regime dominated by regional accommodation limits the impact of halokinesis, which is recorded as very small variations in stratigraphic thickness and facies distribution within and between mini‐basins; (ii) a regime dominated by localized salt‐induced accommodation linked to the subsidence of each individual mini‐basin enhances the facies heterogeneity within the DFS, causing sharp changes in stratigraphic thickness and facies assemblages within and between mini‐basins.  相似文献   

7.
Evolution of the late Cenozoic Chaco foreland basin, Southern Bolivia   总被引：3，自引：1，他引：3  
Eastward Andean orogenic growth since the late Oligocene led to variable crustal loading, flexural subsidence and foreland basin sedimentation in the Chaco basin. To understand the interaction between Andean tectonics and contemporaneous foreland development, we analyse stratigraphic, sedimentologic and seismic data from the Subandean Belt and the Chaco Basin. The structural features provide a mechanism for transferring zones of deposition, subsidence and uplift. These can be reconstructed based on regional distribution of clastic sequences. Isopach maps, combined with sedimentary architecture analysis, establish systematic thickness variations, facies changes and depositional styles. The foreland basin consists of five stratigraphic successions controlled by Andean orogenic episodes and climate: (1) the foreland basin sequence commences between ～27 and 14 Ma with the regionally unconformable, thin, easterly sourced fluvial Petaca strata. It represents a significant time interval of low sediment accumulation in a forebulge‐backbulge depocentre. (2) The overlying ～14–7 Ma‐old Yecua Formation, deposited in marine, fluvial and lacustrine settings, represents increased subsidence rates from thrust‐belt loading outpacing sedimentation rates. It marks the onset of active deformation and the underfilled stage of the foreland basin in a distal foredeep. (3) The overlying ～7–6 Ma‐old, westerly sourced Tariquia Formation indicates a relatively high accommodation and sediment supply concomitant with the onset of deposition of Andean‐derived sediment in the medial‐foredeep depocentre on a distal fluvial megafan. Progradation of syntectonic, wedge‐shaped, westerly sourced, thickening‐ and coarsening‐upward clastics of the (4) ～6–2.1 Ma‐old Guandacay and (5) ～2.1 Ma‐to‐Recent Emborozú Formations represent the propagation of the deformation front in the present Subandean Zone, thereby indicating selective trapping of coarse sediments in the proximal foredeep and wedge‐top depocentres, respectively. Overall, the late Cenozoic stratigraphic intervals record the easterly propagation of the deformation front and foreland depocentre in response to loading and flexure by the growing Intra‐ and Subandean fold‐and‐thrust belt.  相似文献   

8.
Reconstruction of the geological history of orogenic events can be challenging where basins have limited and/or fragmentary preservation. Here, we apply understanding gained from modern analogues to the sedimentological analysis of the succession of Upper Silurian to Lower Devonian Lower Old Red Sandstone (LORS), northern Midland Valley, Scotland, in order to reconstruct the foreland to the Caledonian orogeny. A new depositional model is presented which differs significantly from current understanding. Using facies analysis, grain size distribution and palaeocurrent data a large distributive fluvial system is reconstructed. Three lithofacies and nine sublithofacies are identified, forming fluvial channel and floodplain facies associations. The system was derived from an emerging mountain range in the Caledonian foreland undergoing constant tectonic rejuvenation to produce 9 km of coarse‐grained sediment, exhibiting an overall decrease in thickness towards the west and a large‐scale downstream reduction in grain size. Conglomerate sublithofacies dominate proximal areas in the east where amalgamated fluvial channel facies association is abundant, with a downstream increase in the dominance of floodplain facies. Additionally, observed grain size cyclicity is attributed to a pulsatory tectonic influence. The LORS records the time‐period between the late phases of the Caledonian Orogeny and the onset of post‐orogenic collapse in the mid‐Devonian and the presented model allows improved understanding of the north‐Atlantic Caledonian foreland.  相似文献   

9.
《Basin Research》2018,30(1):148-166
Determining the response of fluvial systems to syn‐sedimentary halokinesis is important for reconstructing the palaeogeography of salt basins, determining the history of salt movement and predicting development and architecture of sandstone bodies for subsurface fluid extraction. To assess both the influence of salt movement on fluvial system development and the use of lithostratigraphic correlation schemes in salt basins we have analysed the Triassic Chinle Formation in the Paradox Basin, Utah. Results indicate that sandstone body development proximal to salt bodies should be considered at two scales: intra‐ (local) and inter‐ (regional) mini‐basin scale. At the intra‐mini basin or local scale, conformable packages of up to 12 m deep meandering fluvial channel deposits and associated overbank deposits are developed, which may thin, pinch‐out or become truncated towards salt highs. When traced down the axis of a mini‐basin, individual stories extend for a few hundred metres, and form part of amalgamated channel‐belt packages up to 60 m thick that can be traced for at least 25 km parallel to palaeoflow. Where salt movement outpaces sediment accumulation, progressive low angle unconformities are developed along the flanks of salt highs. Significantly, in mini‐basins with high sand supply, sandstone bodies are present across salt highs where they show increased amalgamation, decrease in thickness due to truncation and no change in internal sandstone body character. At inter mini‐basin or regional scale, spatial and temporal variations in accommodation space generated by differential salt movement strongly influence facies distributions and facies correlation lengths. Broad lithostratigraphic packages (5–50 m thick) can be correlated within mini‐basins, but correlation of these units between adjacent mini‐basins is problematic. Knowledge of fluvial system development at a regional scale is critical as, fluvial sediment distribution is focussed by topography generated by growing salt bodies, such that adjacent mini‐basins can have significant differences in sandstone body thickness, distribution and lateral extent. The observations from the Chinle Formation indicate that lithostratigraphic‐based correlation schemes can only be applied within mini‐basins and cannot be used to correlate between adjacent mini‐basins or across a salt mini‐basin province. The key to predicting sandstone body development is an understanding of the timing of salt movement and reconstructing fluvial drainage system development.  相似文献   

10.
Abstract The Devono-Carboniferous Horton Group of Cape Breton Island was mostly deposited in two fault-bounded asymmetric sub-basins which were part of a large intracontinental rift system. This system lay at a palaeolatitude of about 10–15o S–a warm, semi-arid climate. The half-graben sub-basins had opposed polarity, were approximately 100 times 50 km in size and were separated by a narrow zone of elevated Acadian basement. These features are common to the adjacent structural segments of known rifts, and are unlike those of transtensive pull-apart systems. Sedimentation occurred in four successive depositional systems which reflect a tectonic evolution of increased and then decreased extensional subsidence through the 8–12 Myr interval represented. Post-Acadian sedimentation began with System 1 bimodal volcanics and grey distal braided fluvial sediments deposited in a slowly subsiding broad linear sag basin. System 2 consists of reddened braidplain sediments near fault-bounded margins and mudflat/playa sediments in sub-basin centres, deposited in two discrete asymmetric sub-basins with a general upward-fining trend. Gradual expansion of the mudflat setting and confinement of coarse marginal fades is interpreted as a response to increasingly rapid and deep fault-bounded subsidence. Depositional System 3, is a complex of grey lacustrine offshore, shoreline and fan delta facies deposited in two adjacent half-graben segments with opposed polarity of asymmetry. An increased rate of tectonic subsidence allowed a large standing body of water to accumulate lacustrine sediments along the axis of each sub-basin during this phase of maximum subsidence. System 4 consists of reddened proximal alluvial fan, medial fluvial and distal grey meandering fluvial/floodplain sediments which accumulated in sub-basins with fault-bounded margins and asymmetry identical to those of earlier systems, indicating a continuation of tectonic style. However, an overall coarsening-upward trend indicates waning of active fault-related subsidence and consequent progradation of marginal coarse wedges to fill the sub-basins. Rapid marine transgression and deposition of Windsor Group carbonates, evaporites and elastics continued within a more extensive rift basin during renewed fault-bounded subsidence.  相似文献   

11.
The relationships between large‐scale depositional processes and the stratigraphic record of alluvial systems, e.g. the origin and distribution of channel stacking patterns, changing architecture and correlation of strata, are still relatively poorly understood, in contrast to marine systems. We present a study of the Castillian Branch of the Permo‐Triassic Central Iberian Basin, north‐eastern Spain, using chemostratigraphy and a detailed sedimentological analysis to correlate the synrift Triassic fluvial sandstones for ~80 km along the south‐eastern basin margin. This study investigates the effects of Middle Triassic (Ladinian) Tethyan marine transgression on fluvial facies and architecture. Chemostratigraphy identifies a major, single axially flowing fluvial system lasting from the Early to Middle Triassic (~10 Ma). The fluvial architecture comprises basal conglomerates, followed by amalgamated sandstones and topped by floodplain‐isolated single‐ or multi‐storey amalgamated sandstone complexes with a total thickness up to ~1 km. The Tethyan marine transgression advanced into the basin with a rate of 0.04–0.02 m/year, and is recorded by a transition from the fluvial succession to a series of maximum flooding surfaces characterised by marginal marine clastic sediments and sabkha evaporites. The continued, transgression led to widespread thick carbonate deposition infilling the basin and recording the final stage of synrift to early‐post‐rift deposition. We identify the nonmarine to marine transition characterised by significant changes in the Buntsandstein succession with a transition from a predominantly tectonic‐ to a climatically driven fluvial system. The results have important implications for the temporal and spatial prediction of fluvial architecture and their transition during a marine transgression.  相似文献   

12.
Accurate magnetostratigraphic dating of Plio-Pleistocene alluvium in the Palomas half-graben permits correlation of transverse and axial deposits, thus enabling analysis of the movement of alluvial facies belts in time and space for the first time. Northern areas show evidence for basinward progradation of footwall-sourced Matuyama-age alluvial fan deposits over axial channel belt deposits of the ancestral Rio Grande, despite both deposits having similar deposition rates. This gradual ‘forced’ westward migration of the axial belt was in opposition to ongoing eastward growth of hangingwall-sourced fans and tectonic tilt imposed by the bounding Caballo normal fault. Fan growth was coincident with a recently proposed gradual climatic shift that may have increased sediment flux out of transverse catchments. It is also possible that continuing tectonic footwall uplift and divided retreat caused catchment areas to increase, contributing to these trends. Southern areas of the Palomas half-graben feature late Gilbert/early Gauss deposits indicative of rapid westwards progradation of large low-gradient, footwall-sourced fans over axial deposits. This ‘forced’ migration of the ancestral Rio Grande may have occurred due to footwall catchment and fan growth consequent upon initiation and growth of the Red Hills Fault. Subsequent eastward movement of the axial channel belt in late Gauss and Matuyama times overwhelmed these large fans. We attribute this to continued tilting on the Red Hills Fault and to development of the Jornada Fault to the south-east, the axial river belt avulsing north and eastwards through a developing Red Hills/Jornada crossover transfer zone. We conclude generally that facies architecture of axial and transverse elements in half-graben must reflect both climatic influences and the effects of fault development. Careful field mapping, accurate dating and palaeoclimatic studies are all necessary to determine the relative importance of these controls. Although adequate as broad guides, previous purely ‘fixist’ tectonosedimentary models allow for no fault growth, decay or climatic modulation of facies trends and are thus generally inadequate to explain important aspects rift basin stratigraphy.  相似文献   

13.
The Po River Basin, where accumulation and preservation of thick sedimentary packages are enhanced by high rates of tectonic subsidence, represents an ideal site to assess the relations between vertical changes in stratigraphic architecture and sediment accumulation rates. Based on a large stratigraphic database, a markedly contrasting stratigraphy of Late Pleistocene and Holocene deposits is reconstructed from the subsurface of the modern alluvial and coastal plains. Laterally extensive fluvial channel bodies and related pedogenically modified muds of latest Pleistocene age are unconformably overlain by Holocene overbank fines, grading seaward into paralic and nearshore facies associations. In the interfluvial areas, a stiff paleosol, dating at about 12.5–10 cal ky BP, marks the Pleistocene–Holocene boundary. Across this paleosol, aggradation rates (ARs) from 16 radiocarbon‐dated cores invariably show a sharp increase, from 0.1–0.9 mm year?1 to 0.9–2.9 mm year?1. Comparatively lower Pleistocene values are inferred to reflect fluvial activity under a low‐accommodation (lowstand and early transgressive) regime, whereas higher ARs during the Holocene are related to increasing accommodation under late transgressive and highstand conditions. Holocene sediment accumulation patterns vary significantly from site to site, and do not exhibit common trends. Very high accumulation rates (20–60 mm year?1) are indicated by fluvial channel or progradational delta facies, suggesting that extremely variable spatial distribution of Holocene ARs was primarily controlled by autogenic processes, such as fluvial channel avulsion or delta lobe switching. Contrasting AR between uppermost Pleistocene and Holocene deposits also are reported from the interfluves of several coeval, alluvial‐coastal plain systems worldwide, suggesting a key control by allogenic processes. Sediment accumulation curves from adjacent incised valley fills show, instead, variable shapes as a function of the complex mechanisms of valley formation and filling.  相似文献   

14.
Mixed siliciclastic‐carbonate deep‐marine systems (mixed systems) are less documented in the geological record than pure siliciclastic systems. The similarities and differences between these systems are, therefore, poorly understood. A well‐exposed Late Cretaceous mixed system on the northern side of the Eastern Greater Caucasus, Azerbaijan, provides an opportunity to study the interaction between contemporaneous siliciclastic and carbonate deep‐marine deposition. Facies analysis reveals a Cenomanian–early Turonian siliciclastic submarine channel complex that abruptly transitions into a Mid Turonian–Maastrichtian mixed lobe‐dominated succession. The channels are entrenched in lows on the palaeo‐seafloor but are absent 10 km towards the west where an Early Cretaceous submarine landslide complex acted as a topographic barrier to deposition. By the Campanian, this topography was largely healed allowing extensive deposition of the mixed lobe‐dominated succession. Evidence for irregular bathymetry is recorded by opposing palaeoflow indicators and frequent submarine landslides. The overall sequence is interpreted to represent the abrupt transition from Cenomanian–early Turonian siliciclastic progradation to c. Mid Turonian retrogradation, followed by a gradual return to progradation in the Santonian–Maastrichtian. The siliciclastic systems periodically punctuate a more widely extensive calcareous system from the Mid Turonian onwards, resulting in a mixed deep‐marine system. Mixed lobes differ from their siliciclastic counterparts in that they contain both siliciclastic and calcareous depositional elements making determining distal and proximal environments challenging using conventional terminology and complicate palaeogeographic interpretations. Modulation and remobilisation also occur between the two contemporaneous systems making stacking patterns difficult to decipher. The results provide insight into the behaviour of multiple contemporaneous deep‐marine fans, an aspect that is challenging to decipher in non‐mixed systems. The study area is comparable in terms of facies, architectures and the presence of widespread instability to offshore The Gambia, NW Africa, and could form a suitable analogue for mixed deep‐marine systems observed elsewhere.  相似文献   

15.
This paper addresses foreland basin fragmentation through integrated detrital zircon U–Pb geochronology, sandstone petrography, facies analysis and palaeocurrent measurements from a Mesozoic–Cenozoic clastic succession preserved in the northern Andean retroarc fold‐thrust belt. Situated along the axis of the Eastern Cordillera of Colombia, the Floresta basin first received sediment from the eastern craton (Guyana shield) in the Cretaceous–early Palaeocene and then from the western magmatic arc (Central Cordillera) starting in the mid‐Palaeocene. The upper‐crustal magmatic arc was replaced by a metamorphic basement source in the middle Eocene. This, in turn, was replaced by an upper‐crustal fold‐thrust belt source in the late Eocene which persisted until Oligocene truncation of the Cenozoic section by the eastward advancing thrust front. Sedimentary facies analysis indicates minimal changes in depositional environments from shallow marine to low‐gradient fluvial and estuarine deposits. These same environments are recorded in coeval strata across the Eastern Cordillera. Throughout the Palaeogene, palaeocurrent and sediment provenance data point to a uniform western or southwestern sediment source. These data show that the Floresta basin existed as part of a laterally extensive, unbroken foreland basin connected with the proximal western (Magdalena Valley) basin from mid‐Paleocene to late Eocene time when it was isolated by uplift of the western flank of the Eastern Cordillera. The Floresta basin was also connected with the distal eastern (Llanos) basin from the Cretaceous until its late Oligocene truncation by the advancing thrust front.  相似文献   

16.
Reconstructions of grain-size trends in alluvial deposits can be used to understand the dominant controls on stratal architecture in a foreland basin. Different initial values of sediment supply, tectonic subsidence and base-level rise are investigated to constrain their influence on stratal geometry using the observed grain-size trends as a proxy of the goodness of fit of the numerical results to the observed data. Detailed measurements of grain-size trends, palaeocurrent indicators, facies and thickness trends, channel geometries and palynological analyses were compiled for the middle Campanian Castlegate Sandstone of the Book Cliffs and its conglomerate units in the Gunnison and Wasatch plateaus of central Utah. They define the initial conditions for a numerical study of the interactions between large-scale foreland basin and small-scale sediment transport processes. From previous studies, the proximal foreland deposits are interpreted as recording a middle Campanian thrusting event along the Sevier orogenic belt, while the stratal architecture in the Book Cliffs region is interpreted to be controlled by eustatic fluctuation with local tectonic influence. Model results of stratal geometry, using a subsidence curve with a maximum rate of ≈45 m Myr?1 for the northern Wasatch Plateau region predict the observed grain-size trends through the northern Book Cliffs. A subsidence curve with a maximum rate of ≈30 m Myr?1 in the Gunnison–Wasatch Plateaus best reproduces the observed grain-size trends in the southern transect through the southern Wasatch Plateau. Eustasy is commonly cited as controlling Castlegate deposition east of the Book Cliffs region. A eustatic rise of 45 m Myr?1 produces grain-size patterns that are similar to the observed, but a rate of eustatic rise based on Haq et al. (1988) will not produce the observed stratal architecture or grain-size trends. Tectonic subsidence alone, or a combined rate of tectonic subsidence and a Haq et al. (1988) eustatic rise, can explain the stratal and grain-size variations in the proximal and downstream regions.  相似文献   

17.
Megafan conglomerates of foreland basins chronicle the combined effect of palaeoclimate conditions, tectonic processes and the flux and granulometric composition of the supplied sediment. However, the architecture of these deposits is seldom uniquely compatible with a single driving force. This problem is illustrated here with a field‐based analysis of the ca. 30–20 Ma‐old Napf deposits in the north Alpine foreland basin which are coeval with a substantial global warming of ca. 6°C during the Late Oligocene. The observed larger grain sizes and a change in fluvial style from wandering to braided could be explained climatically by a shift to drier conditions with sparse vegetation, but would have resulted in less than 400 m of additional accommodation space during the 1 Ma duration of change. Accordingly, a climate scenario alone is also not compatible with rapid sediment accumulation rates of >1000 m Ma?1 recorded at Napf, or with a lack of any remarkable shifts in the Froude number, which would be expected if water discharge patterns changed substantially. Alternatively, flexural downwarping in response to a tectonic pulse could account for the increase in grain size and the change in fluvial style from wandering (more distal facies) to braided (proximal equivalent). However, a third driving force is required to explain the contemporaneous backstepping of the distal gravel front and progradation of the proximal braided facies. We suggest that the erosional hinterland steepened in response to an inferred tectonic pulse, resulting in a more widespread exposure of lithologies with higher erosional resistance, as inferred from an increasing contribution of crystalline constituents in the clast suites. Such a change would result in a larger D50 and a higher clast size variability in the supplied sediment, which in turn would contribute to the observed change from wandering to braided and the related shift in depositional systems. This study highlights the importance of tectonic processes and the role of changing surface lithologies in the source area for explaining variations in megafan construction even in the light of substantial palaeoclimate shift.  相似文献   

18.
Recent advances in our understanding of palaeovalleys are largely guided by examples from passive margins, in which accommodation increases down depositional dip. This study tests these models against a dataset from the Pennsylvanian Breathitt Group of the central Appalachian foreland basin, USA. This fluvio‐deltaic succession contains extensive erosionally based fluvio‐estuarine sand bodies that can be tracked over 80 km down depositional dip from a proximal zone of high accommodation close to the orogenic margin to a distal, lower accommodation zone close to the cratonic margin of the basin. The sand bodies are up to 25 m thick, multi‐storey and characterized in their lower parts by strongly amalgamated storeys containing sandy fluvial to estuarine bar accretion elements, and in their middle to upper parts by more fully preserved storeys up to 10 m thick and laterally extensive over 100s of metres. The upper storeys include abandonment channel‐fills of heterolithic marine or marginal marine deposits or muddy to sandy point‐bar elements. Three major regional‐scale architectures include: (i) Tabular sand bodies that everywhere incise open marine prodelta and mouth bar facies and are interpreted as palaeovalleys formed during falling stage and lowstand systems tracts, when eustatic sea‐level fall outpaced tectonic subsidence across the entire study area. (ii) Sand bodies that incise genetically related floodplain lake and/or bay‐fill minor mouth bar deposits up depositional dip and open marine prodelta and mouth bar facies down dip. These stacked distributary channel deposits map down dip into palaeovalleys and formed when up dip subsidence rate resulted in positive, but reduced rate of accommodation creation, while lower tectonic subsidence rate down‐dip resulted in incision. (iii) Sand bodies that incise genetically related floodplain, lake and/or bay‐fill minor mouth bars up dip and pass down‐dip into genetically related unconfined floodplain, prodelta and mouth bar deposits. These sand bodies represent stacked distributary channel fills and channel amalgamation was the product of high rates of lateral migration, typical of the behaviour of channels above their backwater reach. Case (2) sand bodies demonstrate that in rapidly subsiding foreland basins, cross‐shelf palaeovalleys may form down depositional dip from aggradational, distributive fluival strata. Additionally, the genetic relationship between stacked distributary channels and palaeovalleys supports recent models for palaeovalley formation that emphasize diachronous, cut‐and‐fill during falling stage and lowstands of relative sea level.  相似文献   

19.
At the Muskeg River Mine, bitumen is hosted in the clastic sediments of the lower Cretaceous McMurray Formation. Within the mine area, the McMurray Formation is divided informally into mappable units representing fluvial, continental floodplain, open estuarine, estuarine channel complex (ECC), and marine environments. Fluvial, open estuarine, and ECC deposits host more than 90% of the mineable bitumen reserves. Bitumen grade is more consistent within the fluvial and open estuarine units (12–15 mass%), whereas ECC sediments are characterized by significant lateral and vertical grade variability (0–15 mass%). In the ECC deposits, bitumen grade is controlled by significant reservoir heterogeneity. Facies assemblages including point-bar deposits (PB), abandoned channel-fills (AC), and tidal flat deposits (TF), create complex internal geometries, architectures and associated reservoir properties. Traditional facies mapping and correlation has proven to be difficult even in closely spaced wells for the ECC deposits of the McMurray Formation; thus, an alternative technique using concepts of Stratigraphic Dip Analysis (SDA) was developed to assess bitumen grade for the deposits at the Muskeg River Mine. This approach involves three main steps: (l) juxtaposing azimuth maps (rose diagrams) over horizon slice facies maps for selected stratigraphic intervals to identify major channel trends (paleo-current directions); (2) comparison of dips, with corresponding sedimentary structures allows for a better prediction and geometries of point bars and abandoned channel-fills; and (3) comparison of dip trends with dominant lithology of facies assemblages and available bitumen grades provides a base for accurate delineation of architectural elements. A detailed case study is presented and shows that this approach provides a base for accurate delineation of architectural elements and confirms that bitumen grade decreases laterally with inferred maturity of point bar successions.  相似文献   

20.
Results from analyses of the Arles‐Piton sediment core, retrieved from the apex of the Rhône Delta, highlight processes of Holocene deltaic construction controlled mainly by hydrosedimentary variability and channel avulsions. The alluvial suite was investigated for grain size, sedimentary structures, CaCO3, organic matter, heavy minerals and chrono‐stratigraphy (14C and archaeological/historical dates). The study shows the succession of six facies associations: a distributary channel (before 6157‐5843 BC), a swamp (5719‐5530/4796‐4463 BC), a distal flood plain (5719‐5530/4796‐4463 BC), a distributary channel (4796‐4463/2900‐2503 BC), a proximal flood plain (2900‐2503 BC/AD 270‐290), and a crevasse splay (after AD 270‐290). Substantial changes in hydrodynamics are strongly linked to three channel avulsions (before 6157‐5843 BC, after 4796‐4463 BC and after 2900‐2503 BC). A correlation with the whole channel avulsion history of the Rhône Delta allowed us to propose an average rhythm of channel avulsion of c. 1450 years. From 5719‐5530 BC to AD 270‐290, the flood plain aggraded at the average rate of 2.5 mm/a. The aggradation rates were higher both in the proximal and distal flood plains, where sedimentation process is continuous. They were lower both in the active distributary channels, because of frequent truncation of the alluvial suite, and the abandoned channels where detritic inputs are minimum. The sediment supply arriving to the upper Rhône Delta was derived mainly from proximal source areas (Massif Central, Southern Alps) during the last 8000 years, except during the hydrological changes of Roman antiquity during which detritic inputs were derived firstly from the Northern Alps and Southern Alps, and secondly from the Massif Central.  相似文献   

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