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1.
An integrated provenance analysis of the Upper Cretaceous Magallanes retroarc foreland basin of southern Chile (50°30′–52°S) provides new constraints on source area evolution, regional patterns of sediment dispersal and depositional age. Over 450 new single‐grain detrital‐zircon U‐Pb ages, which are integrated with sandstone petrographic and mudstone geochemical data, provide a comprehensive detrital record of the northern Magallanes foreland basin‐filling succession (>4000‐m‐thick). Prominent peaks in detrital‐zircon age distribution among the Punta Barrosa, Cerro Toro, Tres Pasos and Dorotea Formations indicate that the incorporation and exhumation of Upper Jurassic igneous rocks (ca. 147–155 Ma) into the Andean fold‐thrust belt was established in the Santonian (ca. 85 Ma) and was a significant source of detritus to the basin by the Maastrichtian (ca. 70 Ma). Sandstone compositional trends indicate an increase in volcanic and volcaniclastic grains upward through the basin fill corroborating the interpretation of an unroofing sequence. Detrital‐zircon ages indicate that the Magallanes foredeep received young arc‐derived detritus throughout its ca. 20 m.y. filling history, constraining the timing of basin‐filling phases previously based only on biostratigraphy. Additionally, spatial patterns of detrital‐zircon ages in the Tres Pasos and Dorotea Formations support interpretations that they are genetically linked depositional systems, thus demonstrating the utility of provenance indicators for evaluating stratigraphic relationships of diachronous lithostratigraphic units. This integrated provenance dataset highlights how the sedimentary fill of the Magallanes basin is unique among other retroarc foreland basins and from the well‐studied Andean foreland basins farther north, which is attributed to nature of the predecessor rift and backarc basin.  相似文献   

2.
Determining both short‐ and long‐term sedimentation rates is becoming increasingly important in geomorphic (exhumation and sediment flux), structural (subsidence/flexure) and natural resource (predictive modelling) studies. Determining sedimentation rates for ancient sedimentary sequences is often hampered by poor understanding of stratigraphic architecture, long‐term variability in large‐scale sediment dispersal patterns and inconsistent availability of absolute age data. Uranium–Lead (U‐Pb) detrital zircon (DZ) geochronology is not only a popular method to determine the provenance of siliciclastic sedimentary rocks but also helps delimit the age of sedimentary sequences, especially in basins associated with protracted volcanism. This study assesses the reliability of U‐Pb DZ ages as proxies for depositional ages of Upper Cretaceous strata in the Magallanes‐Austral retroarc foreland basin of Patagonia. Progressive younging of maximum depositional ages (MDAs) calculated from young zircon populations in the Upper Cretaceous Dorotea Formation suggests that the MDAs are potential proxies for absolute age, and constrain the age of the Dorotea Formation to be ca. 82–69 Ma. Even if the MDAs do not truly represent ages of contemporaneous volcanic eruptions in the arc, they may still indicate progressive‐but‐lagged delivery of increasingly younger volcanogenic zircon to the basin. In this case, MDAs may still be a means to determine long‐term (≥1–2 Myr) average sedimentation rates. Burial history models built using the MDAs reveal high aggradation rates during an initial, deep‐marine phase of the basin. As the basin shoaled to shelfal depths, aggradation rates decreased significantly and were outpaced by progradation of the deposystem. This transition is likely linked to eastward propagation of the Magallanes fold‐thrust belt during Campanian‐Maastrichtian time, and demonstrates the influence of predecessor basin history on foreland basin dynamics.  相似文献   

3.
The Andean Orogen is the type‐example of an active Cordilleran style margin with a long‐lived retroarc fold‐and‐thrust belt and foreland basin. Timing of initial shortening and foreland basin development in Argentina is diachronous along‐strike, with ages varying by 20–30 Myr. The Neuquén Basin (32°S to 40°S) contains a thick sedimentary sequence ranging in age from late Triassic to Cenozoic, which preserves a record of rift, back arc and foreland basin environments. As much of the primary evidence for initial uplift has been overprinted or covered by younger shortening and volcanic activity, basin strata provide the most complete record of early mountain building. Detailed sedimentology and new maximum depositional ages obtained from detrital zircon U–Pb analyses from the Malargüe fold‐and‐thrust belt (35°S) record a facies change between the marine evaporites of the Huitrín Formation (ca. 122 Ma) and the fluvial sandstones and conglomerates of the Diamante Formation (ca. 95 Ma). A 25–30 Myr unconformity between the Huitrín and Diamante formations represents the transition from post‐rift thermal subsidence to forebulge erosion during initial flexural loading related to crustal shortening and uplift along the magmatic arc to the west by at least 97 ± 2 Ma. This change in basin style is not marked by any significant difference in provenance and detrital zircon signature. A distinct change in detrital zircons, sandstone composition and palaeocurrent direction from west‐directed to east‐directed occurs instead in the middle Diamante Formation and may reflect the Late Cretaceous transition from forebulge derived sediment in the distal foredeep to proximal foredeep material derived from the thrust belt to the west. This change in palaeoflow represents the migration of the forebulge, and therefore, of the foreland basin system between 80 and 90 Ma in the Malargüe area.  相似文献   

4.
The Ericson Formation was deposited in the distal foredeep of the Cordilleran foreland basin during Campanian time. Isopach data show that it records early dynamic subsidence and the onset of basin partitioning by Laramide uplifts. The Ericson Formation is well exposed around the Rock Springs uplift, a Laramide structural dome in southwestern Wyoming; the formation is thin, regionally extensive, and does not display the wedge‐shaped geometry typical of foredeep deposits. Sedimentation in this area was controlled both by activity in the thrust belt and by intraforeland tectonics. The Ericson Formation is ideally situated both spatially and temporally to study the transition from Sevier to Laramide (thin‐ to thick‐skinned) deformation which corresponded to the shift from flexural to dynamic subsidence and the demise of the Cretaceous foreland basin system. We establish the depositional age of the Ericson Formation as ca. 74 Ma through detrital zircon U–Pb analysis. Palaeocurrent data show a generally southeastward transport direction, but northward indicators near Flaming Gorge Reservoir suggest that the intraforeland Uinta uplift was rising and shedding sediment northward by late Campanian time. Petrographic data and detrital zircon U–Pb ages indicate that Ericson sediment was derived from erosion of Proterozoic quartzites and Palaeozoic and Mesozoic quartzose sandstones in the Sevier thrust belt to the west. The new data place temporal and geographic constraints on attempts to produce geodynamic models linking flat‐slab subduction of the oceanic Farallon plate to the onset of the Laramide orogenic event.  相似文献   

5.
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   

6.
《Basin Research》2018,30(4):708-729
The north–south trending, Late Cretaceous to modern Magallanes–Austral foreland basin of southernmost Patagonia lacks a unified, radiometric, age‐controlled stratigraphic framework. By simplifying the sedimentary fill of the basin to deep‐marine, shallow‐marine and terrestrial deposits, and combining 13 new U‐Pb detrital zircon maximum depositional ages (DZ MDAs) with published DZ MDAs and U‐Pb ash ages, we provide the first attempt at a unified, longitudinal stratigraphic framework constrained by radiometric age controls. We divide the foreland basin history into two phases, including (1) an initial Late Cretaceous shoaling upward phase and (2) a Cenozoic phase that overlies a Palaeogene unconformity. New DZ samples from the shallow‐marine La Anita Formation, the terrestrial Cerro Fortaleza Formation and several previously unrecognized Cenozoic units provide necessary radiometric age controls for the end of the Late Cretaceous foreland phase and the magnitude of the Palaeogene unconformity in the Austral sector of the basin. These samples show that the La Anita and Cerro Fortaleza Formations have Campanian DZ MDAs, and that overlying Cenozoic strata have Eocene to Miocene DZ MDAs. By filling this data gap, we are able to provide a first attempt at constructing a basinwide, age‐controlled stratigraphic framework for the Magallanes–Austral foreland basin. Results show southward progradation of shallow marine and terrestrial environments from the Santonian through the Maastrichtian, as well as a northward increase in the magnitude of the Palaeogene unconformity. Furthermore, our new age data significantly impact the chronology of fossil flora and dinosaur faunas in Patagonia.  相似文献   

7.
《Basin Research》2018,30(3):426-447
Integration of detrital zircon geochronology and three‐dimensional (3D) seismic‐reflection data from the Molasse basin of Austria yields new insight into Oligocene‐early Miocene palaeogeography and patterns of sediment routing within the Alpine foreland of central Europe. Three‐dimensional seismic‐reflection data show a network of deep‐water tributaries and a long‐lived (>8 Ma) foredeep‐axial channel belt that transported Alpine detritus greater than 100 km from west to east. We present 793 new detrital zircon ages from 10 sandstone samples collected from subsurface cores located within the seismically mapped network of deep‐water tributaries and the axial channel belt. Grain age populations correspond with major pre‐Alpine orogenic cycles: the Cadomian (750–530 Ma), the Caledonian (490–380 Ma) and the Variscan (350–250 Ma). Additional age populations correspond with Eocene‐Oligocene Periadriatic magmatism (40–30 Ma) and pre‐Alpine, Precambrian sources (>750 Ma). Although many samples share the same age populations, the abundances of these populations vary significantly. Sediment that entered the deep‐water axial channel belt from the west (Freshwater Molasse) and southwest (Inntal fault zone) is characterized by statistically indistinguishable age distributions that include populations of Variscan, Caledonian and Cadomian zircon at modest abundances (15–32% each). Sandstone from a shallow marine unit proximal to the northern basin margin consists of >75% Variscan (350–300 Ma) zircon, which originated from the adjacent Bohemian Massif. Mixing calculations based on the Kolmogorov–Smirnoff statistic suggest that the Alpine fold‐thrust belt south of the foreland was also an important source of detritus to the deep‐water Molasse basin. We interpret evolving detrital zircon age distributions within the axial foredeep to reflect a progressive increase in longitudinal sediment input from the west (Freshwater Molasse) and/or southwest (Inntal fault zone) relative to transverse sediment input from the fold‐thrust belt to the south. We infer that these changes reflect a major reorganization of catchment boundaries and denudation rates in the Alpine Orogen that resulted in the Alpine foreland evolving to dominantly longitudinal sediment dispersal. This change was most notably marked by the development of a submarine canyon during deposition of the Upper Puchkirchen Formation that promoted sediment bypass eastward from Freshwater Molasse depozones to the Molasse basin deep‐water axial channel belt. The integration of 3D seismic‐reflection data with detrital zircon geochronology illustrates sediment dispersal patterns within a continental‐scale orogen, with implications for the relative role of longitudinal vs. transverse sediment delivery in peripheral foreland basins.  相似文献   

8.
The Cenozoic geodynamics of the north‐eastern Mediterranean Basin have been dominated by the subduction of the African Plate under Eurasia. A trench‐parallel crustal‐scale thrust system (Misis–Kyrenia Thrust System) dissects the southern margin of the overriding plate and forms the structural grain and surface expression of northern Cyprus. Late Eocene to Miocene flysch of the Kythrea (De?irmenlik) Group is exposed throughout northern Cyprus, both at the hanging‐wall and foot‐wall of the thrust system, permitting access to an extensive Cenozoic sedimentary record of the basin. We report the results of a combined examination of detrital zircon and rutile U–Pb geochronology (572 concordant ages), coupled with Th/U ratios, Hf isotopic data and quantitative assessment of grain morphology of detrital zircon from four formations (5 samples) from the Kythrea flysch. These data provide a line of independent evidence for the existence of two different sediment transportation systems that discharged detritus into the basin between the late Eocene and late Miocene. Unique characteristics of each transport system are defined and a sediment unmixing calculation is demonstrated and explained. The first system transported almost exclusively North Gondwana‐type, Precambrian‐aged detrital zircon sourced from siliciclastic rock units in southern Anatolia. A different drainage system is revealed by the middle to late Miocene flysch sequence that is dominated by Late Cretaceous–Cenozoic‐aged detrital zircon, whose age range is consistent with the magmatic episodicity of southeast Anatolia, along the Arabia–Eurasia suture zone. Deposition of these late Miocene strata took place thereupon closure of the Tethyan Seaway and African–Eurasian faunal exchange, and overlap in time with a pronounced uplift of eastern Anatolia. Our analytical data indicate the onset of prominent suture‐parallel sediment transport from the collision zone of south‐eastern Anatolia into the Kyrenia Range of northern Cyprus, marking the drainage response to the continental collision between Arabia and Eurasia.  相似文献   

9.
Important aspects of the Andean foreland basin in Argentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones Cenozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U‐Pb geochronological data from Eocene–Pliocene sedimentary strata in the Eastern Cordillera of northwestern Argentina (Pucará–Angastaco and La Viña areas) provide an Eocene (ca. 38 Ma) maximum depositional age for the Quebrada de los Colorados Formation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Quebrada de los Colorados Formation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca. 14 Ma and the coarse‐grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge‐top depozone. Axial drainage during deposition of the Palo Pintado Formation (upper Miocene) suggests a fluvial‐lacustrine intramontane setting. By ca. 4 Ma, during deposition of the San Felipe Formation, the Angastaco area had become structurally isolated by the uplift of the Sierra de los Colorados Range to the east. Overall, the Eastern Cordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late Eocene through middle Miocene time. By middle Miocene time, the region lay within the topographically complex wedge‐top depozone, influenced by thick‐skinned deformation and re‐activation of Cretaceous rift structures. The association of the Eocene Quebrada del los Colorados Formation with a foredeep depozone implies that more distal foreland deposits should be represented by pre‐Eocene strata (Santa Barbara Subgroup) within the region.  相似文献   

10.
This study constrains the sediment provenance for the Late Cretaceous–Eocene strata of the Ager Basin, Spain, and reconstructs the interplay between foreland basin subsidence and sediment routing within the south-central Pyrenean foreland basin during the early phases of crustal shortening using detrital zircon (DZ) U-Pb-He double dating. Here we present and interpret 837 new DZ U-Pb ages, 113 of which are new DZ (U-Th)/He double-dated zircons. U-Pb-He double dating results allow for a clear differentiation between different foreland and hinterland sources of Variscan zircons (280–350 Ma) by leveraging the contrasting thermal histories of the Ebro Massif and Pyrenean orogen, recorded by the zircon (U-Th)/He (ZHe) ages, despite their indistinguishable U-Pb age signatures. Cretaceous–Paleocene sedimentary rocks, dominated by Variscan DZ U-Pb age components with Permian–Triassic (200–300 Ma) ZHe cooling ages, were sourced from the Ebro Massif south of the Ager Basin. A provenance shift occurred at the base of the Early Eocene Baronia Formation (ca. 53 Ma) to an eastern Pyrenean source (north-east of the Ager Basin) as evidenced by an abrupt change in paleocurrents, a change in DZ U-Pb signatures to age distributions dominated by Cambro-Silurian (420–520 Ma), Cadomian (520–700 Ma), and Proterozoic–Archean (>700 Ma) age components, and the prominent emergence of Cretaceous–Paleogene (<90 Ma) ZHe cooling ages. The Eocene Corçà Formation (ca. 50 Ma), characterized by the arrival of fully reset ZHe ages with very short lag times, signals the accumulation of sediment derived from the rapidly exhuming Pyrenean thrust sheets. While ZHe ages from the Corçà Formation are fully reset, zircon fission track (ZFT) ages preserve older inherited cooling ages, bracketing the exhumation level within the thrust sheets to ca. 6–8 km in the Early Eocene. These DZ ZHe ages yield exhumation rate estimates of ca. 0.03 km/Myr during the Late Cretaceous–Paleocene for the Ebro Massif and ca. 0.2–0.4 km/Myr during the Eocene for the eastern Pyrenees.  相似文献   

11.
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   

12.
The tectonic evolution of the Tian Shan, as for most ranges in continental Asia is dominated by north‐south compression since the Cenozoic India‐Asia collision. However, precollision governing tectonic processes remain enigmatic. An excellent record is provided by thick Palaeozoic – Cenozoic lacustrine to fluvial depositional sequences that are well preserved in the southern margin of the Junggar Basin and exposed along a foreland basin associated to the Late Cenozoic rejuvenation of the Tian Shan ranges. U/Pb (LA‐ICP‐MS) dating of detrital zircons from 14 sandstone samples from a continuous series ranging in age from latest Palaeozoic to Quaternary is used to investigate changes in sediment provenance through time and to correlate them with major tectonic phases in the range. Samples were systematically collected along two nearby sections in the foreland basin. The results show that the detrital zircons are mostly magmatic in origin, with some minor input from metamorphic zircons. The U‐Pb detrital zircon ages range widely from 127 to 2856 Ma and can be divided into four main groups: 127–197 (sub‐peak at 159 Ma), 250–379 (sub‐peak at 318 Ma), 381–538 (sub‐peak at 406 Ma) and 543–2856 Ma (sub‐peak at 912 Ma). These groups indicate that the zircons were largely derived from the Tian Shan area to the south since a Late Carboniferous basin initiation. The provenance and basin‐range pattern evolution of the southern margin of Junggar Basin can be generally divided into four stages: (1) Late Carboniferous – Early Triassic basin evolution in a half‐graben or post‐orogenic extensional context; (2) From Middle Triassic to Upper Jurassic times, the southern Junggar became a passively subsiding basin until (3) being inverted during Lower Cretaceous – Palaeogene; (4) During the Neogene, a piedmont developed along the northern margin of the North Tian Shan block and Junggar Basin became a true foreland basin.  相似文献   

13.
We present field and seismic evidence for the existence of Coniacian–Campanian syntectonic angular unconformities within basal foreland basin sequences of the Austral or Magallanes Basin, with implications for the understanding of deformation and sedimentation in the southern Patagonian Andes. The studied sequences belong to the mainly turbiditic Upper Cretaceous Cerro Toro Formation that includes a world‐class example of conglomerate‐filled deep‐water channel bodies deposited in an axial foredeep depocentre. We present multiple evidence of syntectonic deposition showing that the present internal domain of the fold‐thrust belt was an active Coniacian–Campanian wedge‐top depozone where deposition of turbidites and conglomerate channels of Cerro Toro took place. Cretaceous synsedimentary deformation was dominated by positive inversion of Jurassic extensional structures that produced elongated axial submarine trenches separated by structural highs controlling the development and distribution of axial channels. The position of Coniacian‐Campanian unconformities indicates a ca. 50–80 km advance of the orogenic front throughout the internal domain, implying that Late Cretaceous deformation was more significant in terms of widening the orogenic wedge than all subsequent Andean deformation stages. This south Patagonian orogenic event can be related to compressional stresses generated by the combination of both the collision of the western margin of Rocas Verdes Basin during its closure, and Atlantic ridge push forces due to its accelerated opening, during a global‐scale plate reorganization event.  相似文献   

14.
Unravelling early Cenozoic basin development in northern Tibetan Plateau remains crucial to understanding continental deformation mechanisms and to assessing models of plateau growth. We target coarse-grained red beds from the Cenozoic basal Lulehe Formation in the Qaidam basin by combining conglomerate clast compositions, paleocurrent determinations, sandstone petrography, heavy mineral analysis and detrital zircon U–Pb geochronology to characterize sediment provenance and the relationship between deformation and deposition. The red beds are dominated by matrix-supported, poorly sorted clastic rocks, implying low compositional and textural maturity and short transport distances. Although most sandstones have high (meta)sedimentary lithic fragment contents and abundant heavy minerals of metamorphic origin (e.g., garnet, epidote and chlorite), spatiotemporal differences in detrital compositions are evident. Detrital zircon grains mainly have Phanerozoic ages (210–280 Ma and 390–480 Ma), but Proterozoic ages (750–1000 Ma, 1700–2000 Ma and 2300–2500 Ma) are also prominent in some samples. Analysed strata display dissimilar (including south-, north- and west-directed) paleocurrent orientations. These results demonstrate that the Cenozoic basal deposits were derived from localized, spatially diverse sources with small drainage networks. We advocate that initial sedimentary filling in the northern Qaidam basin was fed by parent-rocks from the North Qaidam-South Qilian belts and the pre-Cenozoic basement within the Qaidam terrane interior, rather than southern distant Eastern Kunlun regions. Seismic and drilling well stratigraphic data indicate the presence of paleohighs and syn-sedimentary reverse faults and noteworthy diversity in sediment thickness of the Lulehe Formation, revealing that the Qaidam terrane exhibited as several isolated depocenters, rather than a coherent basin, in the early stage of the Cenozoic deposition. We suggest the Cenozoic Qaidam basin to have developed in a contractional deformation regime, which supports models with synchronous deformation throughout most of Tibet shortly after the India-Eurasia collision.  相似文献   

15.
Laser ablation‐multi collector‐inductively coupled mass spectrometry U‐Pb geochronology, detailed field mapping and stratigraphic data offer improved insights into the timing and style of Laramide deformation and basin development in the Little Hatchet Mountains, southwestern New Mexico, USA, a key locality in the ‘southern Laramide province.’ The Laramide synorogenic section in the northern Little Hatchet Mountains comprises upper Campanian to Maastrichtian strata consisting of the Ringbone and Skunk Ranch formations, with a preserved maximum thickness of >2400 m, and the correlative Hidalgo Formation with a total thickness >1700 m. The Ringbone Formation and superjacent Skunk Ranch Formation are each generally composed of (1) a basal conglomerate member; (2) a middle member consisting of lacustrine shale, limestone, sandstone, and interbedded ash‐fall tuffs; and (3) an upper sandstone and conglomerate member. Basaltic andesite flows are intercalated with the upper member of the Ringbone Formation and the middle member of the Skunk Ranch Formation. The Hidalgo Formation, which crops out in the northern part of the range, is dominantly composed of basaltic andesite breccias and flows equivalent to those of the Ringbone and Skunk Ranch formations. The Laramide section was deposited in an intermontane basin partitioned across intrabasinal thrust structures, which controlled growth‐stratal development. U‐Pb zircon ages from five tuffs indicate that the age range of the Laramide sedimentary succession is ca. 75–70 Ma. U‐Pb detrital‐zircon age data (n = 356 analyses) from the Ringbone Formation and a Lower Cretaceous unit indicate sediment contribution from uplifted Lower and Upper Cretaceous rocks adjacent to the basin and the contemporary Tarahumara magmatic arc in nearby northern Sonora, Mexico. The new ages, combined with published data, indicate that uplift, basin development, and magmatism in the region proceeded diachronously northeastwards as the subducting Farallon slab flattened under northern Mexico and southern New Mexico from Campanian to Palaeogene time.  相似文献   

16.
During the Cretaceous, the Neuquén Basin transitioned from an extensional back‐arc to a retroarc foreland basin. We present a multi‐proxy provenance study of Aptian to Santonian (125–84 Ma) continental sedimentary rocks preserved in the Neuquén Basin used to resolve changes of sediment drainage pattern in response to the change in tectonic regime. Sandstone petrology and U–Pb detrital zircon geochronology constrain the source units delivering detritus to the basin; apatite U–Pb and fission track dating further resolve provenance and determine the age and patterns of exhumation of the source rocks. Sandstone provenance records a sharp change from a mixed orogenic source during Aptian time (ca. 125 Ma), to a magmatic arc provenance in the Cenomanian (ca. 100 Ma). We interpret this provenance change as the result of the drainage pattern reorganisation from divergent to convergent caused by tectonic basin inversion. During this inversion and early stages of contraction, a transient phase of uplift and basin erosion, possibly due to continental buckling, caused the pre‐Cenomanian unconformity dividing the Lower from Upper Cretaceous strata in the Neuquén Basin. This phase was followed by the development of a retroarc foreland basin characterised by a volcanic arc sediment provenance progressively shifting to a mixed continental basement provenance during Turonian‐Santonian (90–84). According to multi‐proxy provenance data and lag times derived from apatite fission track analysis, this trend is the result of a rapidly exhuming source within the Cordillera to the west, in response to active compressional tectonics along the western margin of South America, coupled with the increasing contribution of material from the stable craton to the east; this contribution is thought to be the result of the weak uplift and exhumation of the foreland due to eastward migration of the forebulge.  相似文献   

17.
The details of how narrow, orogen‐parallel ocean basins are filled with sediment by large axial submarine channels is important to understand because these depositional systems commonly form in through‐like basins in various tectonic settings. The Magallanes foreland basin is an excellent location to study an orogen‐parallel deep‐marine system. Conglomerate lenses of the Upper Cretaceous Cerro Toro Formation have been previously interpreted to represent the fill of a single submarine channel (4–8 km wide, >100 km long) that funneled coarse detritus southward along the basin axis. This interpretation was based on lithologic correlations. New U/Pb dating of zircons from volcanic ashes and sandstones, coupled with strontium isotope stratigraphy, refine the controls on depositional ages and provenance. Results demonstrate that north‐south oriented conglomerate lenses are contemporaneous within error limits (ca. 84–82 Ma) supporting that they represent parts of an axial channel belt. Channel deposits 20 km west of the axial location are 87–82 Ma in age. These channels are partly contemporaneous with the ones within the axial channel belt, making it likely that they represent feeders to the axial channel system. The northern Cerro Toro Formation spans a Turonian to Campanian interval (ca. 90–82 Ma) whereas the formation top, 70 km to the south, is as young as ca. 76 Ma. Kolmogorov–Smirnoff statistical analysis on detrital zircon age distributions shows that the northern uppermost Cerro Toro Formation yields a statistically different age distribution than other samples from the same formation but shows no difference relative to the overlying Tres Pasos Formation. These results suggest the partly coeval deposition of both formations. Integration of previously acquired geochronologic and stratigraphic data with new data show a pronounced southward younging pattern in all four marine formations in the Magallanes Basin. Highly diachronous infilling may be an important depositional pattern for narrow, orogen‐parallel ocean basins.  相似文献   

18.
Detrital zircon (DZ) geochronology has become a popular tool in provenance studies during the past two decades. However, similar zircon crystallization ages from different source regions greatly hamper the interpretation of sediment dispersal and recycling processes. The Alleghenian–Ouachita–Marathon (AOM) foreland and vicinity in North America is a region where some dominant DZ age groups could come from both the southern Appalachians in the eastern United States and the Gondwanan terranes in Mexico. In this study, we present 1045 new DZ U–Pb ages and 81 DZ core–rim age pairs in lower Permian sandstone in the Permian Basin and Miocene sandstone in the eastern Gulf of Mexico (GOM). These new data were integrated with published DZ single U–Pb age and core–rim ages from syn- to post-orogenic strata in the Permian Basin, Marathon foldbelt, southern Appalachian foreland basin and eastern GOM to interpret the sediment-dispersal models in the AOM foreland and eastern GOM. Our models show that during the Leonardian Stage, sediments derived from the Appalachians were first delivered to the US midcontinent and then recycled to the Permian Basin; during the Miocene, sediment from the Appalachians fluxed to the eastern GOM, with no longshore mixing from the western GOM. These models based on the integration of single U–Pb and core–rim ages are consistent with published results that used other methods, including zircon single U–Pb age, zircon Hf isotopic data, zircon (U–Th)/He age, sedimentology and stratigraphy. Our results demonstrate that although some limitations exist, zircon core–rim age is a powerful tool, adding an extra constraint on the interpretation of sediment-dispersal systems. This tool is particularly applicable to the post-orogenic stage, during which the sediment pathways are more complicated because of the dominant input from distal sources. Insights gained in this study imply that this novel strategy of using core and rim ages could be integrated with other methods to better understand sediment dispersal.  相似文献   

19.
The Sichuan Basin and the Songpan‐Ganze terrane, separated by the Longmen Shan fold‐and‐thrust belt (the eastern margin of the Tibetan Plateau), are two main Triassic depositional centres, south of the Qinling‐Dabie orogen. During the Middle–Late Triassic closure of the Paleo‐Tethys Ocean, the Sichuan Basin region, located at the western margin of the Yangtze Block, transitioned from a passive continental margin into a foreland basin. In the meantime, the Songpan‐Granze terrane evolved from a marine turbidite basin into a fold‐and‐thrust belt. To understand if and how the regional sediment routing system adjusted to these tectonic changes, we monitored sediment provenance primarily by using detrital zircon U‐Pb analyses of representative stratigraphic samples from the south‐western edge of the Sichuan Basin. Integration of the results with paleocurrent, sandstone petrology and published detrital zircon data from other parts of the basin identified a marked change in provenance. Early–Middle Triassic samples were dominated by Neoproterozoic (~700–900 Ma) zircons sourced mainly from the northern Kangdian basement, whereas Late Triassic sandstones that contain a more diverse range of zircon ages sourced from the Qinling, Longmen Shan and Songpan‐Ganze terrane. This change reflects a major drainage adjustment in response to the Late Triassic closure of the Paleo‐Tethys Ocean and significant shortening in the Longmen Shan thrust belt and the eastern Songpan‐Ganze terrane. Furthermore, by Late Triassic time, the uplifted northern Kangdian basement had subsided. Considering the eastward paleocurrent and depocenter geometry of the Upper Triassic deposits, subsidence of the northern Kangdian basement probably resulted from eastward shortening and loading of the Songpan‐Ganze terrane over the western margin of the Yangtze Block in response to the Late Triassic collision among Yangtze Block, Yidun arc and Qiangtang terrane along the Ganze‐Litang and Jinshajiang sutures.  相似文献   

20.
Located on the southern margin of the Lhasa terrane in southern Tibet, the Xigaze forearc basin records Cretaceous to lower Eocene sedimentation along the southern margin of Asia, prior to and during the initial stages of continental collision with the Tethyan Himalaya in the Early Eocene. We present new measured stratigraphic sections, totalling 4.5 km stratigraphic thickness, from a 60 km E–W segment of the western portion of the Xigaze forearc basin, northeast of the Lopu Kangri Range (29.8007° N, 84.91827° E). In addition, we apply U–Pb detrital zircon geochronology to constrain the provenance and maximum depositional ages of investigated strata. Stratigraphic ages range between ca. 88 and ca. 54 Ma and sedimentary facies indicate a shoaling‐upward trend from deep‐marine turbidites to fluvial deposits. Depositional environments of coeval Cretaceous strata along strike include deep‐marine distal turbidites, slope‐apron debris‐flow deposits and marginal marine carbonates. This along‐strike variability in facies suggests an irregular paleogeography of the Asian margin prior to collision. Paleocene–Eocene strata are composed of shallow marine carbonates with abundant foraminifera such as Nummulites‐Discocyclina and Miscellanea‐Daviesina and transition into fluvial deposits dated at ca. 54 Ma. Sandstone modal analyses, conglomerate clast compositions and detrital zircon U–Pb geochronology indicate that forearc detritus in this region was derived solely from the Gangdese magmatic arc to the north. In addition, U–Pb detrital zircon age spectra within the upper Xigaze forearc stratigraphy are similar to those from Eocene foreland basin strata south of the Indus‐Yarlung suture near Sangdanlin, suggesting that the Xigaze forearc was a possible source of Sangdanlin detritus by ca. 55 Ma. We propose a model in which the Xigaze forearc prograded south over the accretionary prism and onto the advancing Tethyan Himalayan passive margin between 58 and 54 Ma, during late stage evolution of the forearc basin and the beginning of collision with the Tethyan Himalaya. The lack of documented forearc strata younger than ca. 51 Ma suggests that sedimentation in the forearc basin ceased at this time owing to uplift resulting from continued continental collision.  相似文献   

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