Retroarc Foreland Basin Research Articles

Detrital zircon geochronology of the Speewah Group, Kimberley region, Western Australia: evidence for intracratonic development of the Paleoproterozoic Speewah Basin

ABSTRACTField observations integrated with new petrographic and sensitive high-resolution ion microprobe (SHRIMP) U–Pb age data for detrital zircons from the Paleoproterozoic Speewah Group of northern Western Australia provide evidence of depositional conditions, source of detritus, timing and evolution of the sedimentary rocks in the Speewah Basin. The Speewah Group is a 1.5 km-thick succession of poorly outcropping, predominantly siliciclastic rocks that preserve a fluviatile to marine, transgressive and regressive event. The Speewah Group unconformably overlies crystalline rocks of the Lamboo Province that were stabilised by the 1870–1850 Ma Hooper Orogeny, then accreted as the Kimberley region onto the North Australian Craton during the 1835–1810 Ma Halls Creek Orogeny. Unconformably overlying the Speewah Group is about 4 km of predominantly siliciclastic marine sedimentary rocks of the Kimberley Group in the Kimberley Basin. This study has detected a detrital zircon component within the Speewah Basin at 1814 ± 10 Ma, with a youngest zircon at 1803 ± 12 Ma (1σ) in fluviatile sandstones located beneath a volcaniclastic rock with magmatic zircons that have been dated at ca 1835 Ma. Previous studies proposed that the Speewah Basin developed as a retro-arc foreland basin during accretion of the North Australian Craton. We interpret the ca 1835 Ma zircons in the volcaniclastic rocks to be xenocrystic in origin. This new 20 million years younger maximum depositional age indicates that the Speewah Group in the Speewah Basin, similarly to the overlying Kimberley Group in the Kimberley Basin, developed in a post-orogenic setting on the North Australian Craton rather than in a syn-orogenic setting associated with the 1835–1810 Ma Halls Creek Orogeny.

Tectono-stratigraphy of the Orhaniye Basin, Turkey: Implications for collision chronology and Paleogene biogeography of central Anatolia

Located along the İzmir-Ankara-Erzincan Suture (IAES), the Maastrichtian - Paleogene Orhaniye Basin has yielded a highly enigmatic -yet poorly dated- Paleogene mammal fauna, the endemic character of which has suggested high faunal provincialism associated with paleogeographic isolation of the Anatolian landmass during the early Cenozoic. Despite its biogeographic significance, the tectono-stratigraphic history of the Orhaniye Basin has been poorly documented. Here, we combine sedimentary, magnetostratigraphic, and geochronological data to infer the chronology and depositional history of the Orhaniye Basin. We then assess how our new data and interpretations for the Orhaniye Basin impact (1) the timing and mechanisms of seaway closure along the IAES and (2) the biogeographic evolution of Anatolia.Our results show that the Orhaniye Basin initially developed as a forearc basin during the Maastrichtian, before shifting to a retroarc foreland basin setting sometime between the early Paleocene and 44Ma. This chronology supports a two-step scenario for the assemblage of the central Anatolian landmass, with incipient collision during the Paleocene – Early Eocene and final seaway retreat along the IAES during the earliest Late Eocene after the last marine incursion into the foreland basin. Our dating for the Orhaniye mammal fauna (44–43Ma) indicates the persistence of faunal endemism in northern Anatolia until at least the late Lutetian despite the advanced stage of IAES closure. The tectonic evolution of dispersal corridors linking northern Anatolia with adjacent parts of Eurasia was not directly associated with IAES closure and consecutive uplifts, but rather with the build-up of continental bridges on the margins of Anatolia, in the Alpine and Tibetan-Himalayan orogens.

Structural Characteristics and Formation Dynamics: A Review of the Main Sedimentary Basins in the Continent of China

AbstractThe formation and evolution of basins in the China continent are closely related to the collages of many blocks and orogenic belts. Based on a large amount of the geological, geophysical, petroleum exploration data and a large number of published research results, the basement constitutions and evolutions of tectonic–sedimentary of sedimentary basins, the main border fault belts and the orogenesis of their peripheries of the basins are analyzed. Especially, the main typical basins in the eight divisions in the continent of China are analyzed in detail, including the Tarim, Ordos, Sichuan, Songliao, Bohai Bay, Junggar, Qiadam and Qiangtang basins. The main five stages of superimposed evolutions processes of basins revealed, which accompanied with the tectonic processes of the Paleo–Asian Ocean, Tethyan and Western Pacific domains. They contained the formations of main Cratons (1850–800 Ma), developments of marine basins (800–386 Ma), developments of Marine–continental transition basins and super mantle plumes (386–252 Ma), amalgamation of China Continent and developments of continental basins (252–205 Ma) and development of the foreland basins in the western and extensional faulted basin in the eastern of China (205–0 Ma). Therefore, large scale marine sedimentary basins existed in the relatively stable continental blocks of the Proterozoic, developed during the Neoproterozoic to Paleozoic, with the property of the intracontinental cratons and peripheral foreland basins, the multistage superimposing and late reformations of basins. The continental basins developed on the weak or preexisting divisional basements, or the remnant and reformed marine basins in the Meso–Cenozoic, are mainly the continental margins, back–arc basins, retroarc foreland basins, intracontinental rifts and pull–apart basins. The styles and intensity deformation containing the faults, folds and the structural architecture of regional unconformities of the basins, responded to the openings, subductions, closures of oceans, the continent–continent collisions and reactivation of orogenies near the basins in different periods. The evolutions of the Tianshan–Mongol–Hinggan, Kunlun–Qilian–Qinling–Dabie–Sulu, Jiangshao–Shiwandashan, Helanshan–Longmengshan, Taihang–Wuling orogenic belts, the Tibet Plateau and the Altun and Tan–Lu Fault belts have importantly influenced on the tectonic–sedimentary developments, mineralization and hydrocarbon reservoir conditions of their adjacent basins in different times. The evolutions of basins also rely on the deep structures of lithosphère and the rheological properties of the mantle. The mosaic and mirroring geological structures of the deep lithosphère reflect the pre–existed divisions and hot mantle upwelling, constrain to the origins and transforms dynamics of the basins. The leading edges of the basin tectonic dynamics will focus on the basin and mountain coupling, reconstruction of the paleotectonic–paleogeography, establishing relationship between the structural deformations of shallow surface to the deep lithosphère or asthenosphere, as well as the restoring proto–basin and depicting residual basin of the Paleozoic basin, the effects of multiple stages of volcanism and paleo–earthquake events in China.

Andean stratigraphic record of the transition from backarc extension to orogenic shortening: A case study from the northern Neuquén Basin, Argentina

The temporal transition from backarc extension to retroarc shortening is a fundamental process in the evolution of many Andean-type convergent margins. This switch in tectonic regime is preserved in the 5–7 km thick Mesozoic-Cenozoic stratigraphic record of west-central Argentina at 34–36°S, where the northern Neuquén Basin and succeeding Cenozoic foreland succession chronicle a long history of fluctuating depositional systems and diverse sediment source regions during Andean orogenesis. New findings from sediment provenance and facies analyses are integrated with detrital zircon U-Pb geochronological results from 16 samples of Jurassic through Miocene clastic deposits to delineate the progressive exhumation of the evolving Andean magmatic arc, retroarc fold-thrust belt, and foreland province. Abrupt changes in provenance and depositional conditions can be reconciled with a complex Mesozoic-Cenozoic history of extension, postextensional thermal subsidence, punctuated tectonic inversion, thick- and thin-skinned shortening, overlapping igneous activity, and alternating phases of basin accumulation, sediment bypass, and erosion.U-Pb age distributions constrain the depositional ages of Cenozoic units and reveal a prolonged late middle Eocene to earliest Miocene (roughly 40–20 Ma) hiatus in the retroarc foreland basin. This stratigraphic gap is expressed as a regional disconformity that marks a pronounced shift in depositional conditions and sediment sources, from (i) slow Paleocene–middle Eocene accumulation of distal fluviolacustrine sediments (Pircala and Coihueco Formations) contributed from far western magmatic arc sources (Cretaceous–Paleogene volcanic rocks) and subordinate eastern basement rocks (Permian-Triassic Choiyoi igneous complex) to (ii) rapid Miocene–Quaternary accumulation of proximal fluvial to megafan sediments (Agua de la Piedra, Loma Fiera, and Tristeza Formations) recycled from emerging western thrust-belt sources of Mesozoic basin fill originally derived from basement and magmatic arc sources. The mid-Cenozoic stratigraphic gap signified ∼20 Myr of nondeposition, potentially during passage of a flexural forebulge or during neutral to extensional conditions driven by mechanical decoupling and a possible retreating-slab configuration along the Nazca-South America plate boundary. Neogene eastward propagation of the Malargüe fold-thrust belt involved basement inversion with geometrically and kinematically linked thin-skinned shortening at shallow foreland levels, including late Miocene deposition of accurately dated 10.5–7.5 Ma growth strata and ensuing displacement along the frontal emergent and blind thrust structures. Subsequent partitioning and exhumation of Cenozoic clastic fill of the Malargüe foreland basin has been driven by inboard advance of arc magmatism and Pliocene-Quaternary uplift of the San Rafael basement block farther east.

Using detrital zircon U‐Pb ages to calculate Late Cretaceous sedimentation rates in the Magallanes‐Austral basin, Patagonia

AbstractDetermining 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.

Cretaceous evolution of the Andean margin between 36°S and 40°S latitude through a multi‐proxy provenance analysis of Neuquén Basin strata (Argentina)

AbstractDuring 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.

Characterisation and diachronous initiation of coarse clastic deposition in the Magallanes–Austral foreland basin, Patagonian Andes

AbstractMagallanes–Austral Basin (MAB) fill is preserved along a >1000 km north–south trending outcrop belt in the southern Patagonia region of Argentina and Chile. Although the stratigraphic evolution of the MAB has been well documented in the Chilean sector (referred to as the Magallanes Basin), its northern terminus in southern Argentina (Austral Basin) is poorly constrained. We present new stratigraphic and geochronologic analyses of the early basin fill (Aptian–Turonian) from the Argentine sector (49–51°S) of the MAB to document spatial variability in stratigraphy and timing of deposition during the initial stages of basin evolution. The initiation of the retroarc foreland basin fill is marked by the transition from mudstone to coarse‐clastic deposition, which is characterised by the consistent presence of sandstone beds > ca. 20 cm thick interpreted to represent sediment gravity flows deposited in a submarine fan system. Depositional environments within the early fill of the basin range from lower to upper deep‐water fan settings as well as previously undocumented slope deposits. These facies are present as far north as El Chalten, Argentina (ca. 49°S), indicating that facies‐equivalent rocks can be traced along‐strike for at least 5 degrees of latitude, based on correlation with strata as far south as the Cordillera Darwin (ca. 54°S). Eight new U‐Pb zircon ages from ash beds reveal an overall southward younging trend in the initiation of coarse clastic deposition. Inferred depositional ages range from ca. 115 ± 1.9 Ma in the northernmost study area to not older than 92 ± 1 Ma and 89 ± 1.5 Ma in the central and southern sectors respectively. The apparent diachronous delivery of coarse detritus into the basin may reflect (1) gradual southward progradation of a deep‐water fan system from a northerly point source and/or (2) orogen‐parallel variations in the timing and magnitude of thrust‐belt deformation and erosion that provided more local sources for sediment delivery.

Geology reviewed for the Falkland Islands and their offshore sedimentary basins, South Atlantic Ocean

ABSTRACTThe position of the Falkland Islands adjacent to the South American continental margin belies the close association of their geology with that of South Africa. A Mesoproterozoic basement is unconformably overlain by a Silurian to Devonian succession of fluvial to neritic and shallow marine, siliciclastic strata. This is disconformably succeeded by a largely Permian succession that, near its base, includes a glacigenic diamictite and, thence, passes upwards into a succession of deltaic and lacustrine strata. The lithological succession and the character of its deformation bear striking similarities to the Cape Fold Belt and Karoo retroarc foreland basin. Swarms of Early Jurassic dykes were coeval with the Karoo magmatism and the initial break-up of Gondwana; Early Cretaceous dykes were intruded during the opening of the South Atlantic Ocean. Offshore sedimentary basins surrounding the archipelago contain Late Jurassic to Palaeogene successions and are currently the focus of hydrocarbon exploration. Best known is the North Falkland Basin, a classic failed rift. To the SE, the passive margin, Falkland Plateau Basin may also be rift-controlled, whilst the South Falkland Basin is a foreland basin created at the boundary of the South American and Scotia plates. The role of the Falkland Islands during the breakup of Gondwana remains controversial. Compelling evidence from the onshore geology favours rotation of an independent microplate from an original position adjacent to the Eastern Cape, South Africa. Alternative interpretations, justified largely from offshore geology, favour extension of the Falkland Plateau as a fixed promontory from the South American margin.

Late Paleozoic to Early Mesozoic provenance record of Paleo‐Pacific subduction beneath South China

AbstractNortheast trending Yong'an Basin, southeast South China Craton, preserves a Permian‐Jurassic, marine to continental, siliciclastic‐dominated, retroarc foreland basin succession. Modal and detrital zircon data, along with published paleocurrent data, sedimentary facies, and euhedral to subhedral detrital zircon shapes, indicate derivation from multicomponent, nearby sources with input from both the interior of the craton to the northwest and from an inferred arc accretionary complex to the southeast. The detrital zircon U‐Pb age spectra range in age from Archean to early Mesozoic, with major age groups at 2000–1700 Ma, 1200–900 Ma, 400–340 Ma, and 300–240 Ma. In addition, Early Jurassic strata include zircon detritus with ages of 200–170 Ma. Regional geological relations suggest that Precambrian and Early Paleozoic detritus was derived from the inland Wuyi Mountain region and Yunkai Massif of the South China Craton. Sources for Middle Paleozoic to early Mesozoic detrital zircons include input from beyond the currently exposed China mainland. Paleogeographic reconstruction in East Asia suggests derivation from an active convergent plate margin along the southeastern rim of the craton that incorporated part of Southwest Japan and is related to the subduction of the Paleo‐Pacific Ocean. Integration of the geologic and provenance records of the Yong'an Basin with the time equivalent Yongjiang and Shiwandashan basins that lie to the southwest and south, respectively, provides an integrated record of the subduction of the Paleo‐Pacific Ocean along the southeast margin of the South China Craton and termination of subduction of the Paleo‐Tethys beneath its southwest margin in Permo‐Triassic.

Detrital zircon U–Pb ages of the Proterozoic metaclastic-sedimentary rocks in Hainan Province of South China: New constraints on the depositional time, source area, and tectonic setting of the Shilu Fe–Co–Cu ore district

The Shilu Fe–Co–Cu ore district, located at Hainan Province of South China, is well known for high-grade hematite-rich Fe ores and also two Precambrian host successions, i.e. the Shilu Group and the overlying Shihuiding Formation. This district has been interpreted as a banded iron formation (BIF) deposit-type, but its depositional time, source area and depositional setting have been in debate due to poor geochronological work. Detrital zircon U–Pb dating aided by cathodoluminescence imaging has been carried out on both the Shilu Group and Shihuiding Formation. Most of the zircon grains from both the successions are subrounded to rounded in morphology and have age spectra between 2000Ma and 900Ma with two predominant peaks at ca. 1460–1340Ma and 1070Ma, and three subordinate peaks at ca. 1740–1660Ma, 1220Ma and 970Ma. The similar age distribution suggests the same depositional system for both successions. Linked to the geological and paleontological signatures, the Shihuiding Formation is better re-interpreted as the top, i.e. Seventh member of the Shilu Group, rather than a distinct Formation. The youngest statistical zircon age peaks for both successions, i.e. ca. 1070–970Ma may define the maximum depositional time of the Shilu Group and interbedded BIFs. At least two erosional sources are required for deposition of the studied detrital zircons, with one proximal to provide the least abraded zircons and the other distal or recycled to offer the largely abraded zircons. The predominance of rounded or subrounded zircons over angular zircons probably implies a relatively stable tectonic setting during deposition. Given the Precambrian tectonics of Hainan Island, a retro-arc foreland basin is proposed for the deposition of the Shilu Group and interbedded BIFs. In comparison with those from the South China and other typical Grenvillian orogens, the detrital zircon age populations reveal that Hainan Island had crystalline basement similar to neither the Yangtze nor the Cathaysia Blocks. Combined with the tectonothermal events, we propose that Hainan Island was independent of South China at least before the late Ordovician and most likely attached or close to northwestern Laurentia before the breakup of Rodinia.

Paleozoic accretionary orogenesis in the Paleo-Asian Ocean: Insights from detrital zircons from Silurian to Carboniferous strata at the northwestern margin of the Tarim Craton

A detrital zircon U-Pb and Lu-Hf isotopic study was carried out in the Middle Silurian to Late Carboniferous sedimentary strata of the northwestern Tarim Craton in order to understand accretionary processes in the southern part of the Central Asian Orogenic Belt. Detrital zircons from these strata yielded U-Pb ages clustering around 2.8–2.3 Ga, 2.0–1.7 Ga, 1.3–0.9 Ga, 880–600 Ma, and 500–400 Ma, with age populations and Hf isotopic signatures matching those of magmatic rocks in the Tarim Craton and the Central Tianshan Block. Abundant 500–400 Ma detrital zircons most likely reflect deposition in a retroarc foreland basin inboard of an Andean-type magmatic arc to the north, supporting the northern Tarim-Central Tianshan connection during early Paleozoic time. The absence of 380–310 Ma zircon population in the Carboniferous siliciclastic rocks suggests that the Central Tianshan Block may have been separated from the Tarim Craton in the Early Devonian, caused by the interarc/back-arc opening of the South Tianshan Ocean. We propose an accretionary orogenic model switching from advancing to retreating mode during Paleozoic time in the southwestern part of the Paleo-Asian Ocean. This transition most likely occurred coevally with the rifting of Southeast Asian blocks from the northeastern margin of Gondwana.

Punctuated shortening and subsidence in the Altiplano Plateau of southern Peru: Implications for early Andean mountain building

Sedimentologic, provenance, geochronologic, and magnetostratigraphic results from clastic nonmarine deposits in the northern Altiplano Plateau of southern Peru (14–15°S) demonstrate late Eocene–Oligocene (37–26 Ma) accumulation of the >4-km-thick San Jerónimo (Puno) Group within a retroarc foreland basin related to early Andean shortening and crustal thickening. Punctuated Oligocene (29–26 Ma) displacement along deep-seated contractional structures, as revealed by growth stratal relationships, abruptly partitioned this regional flexural basin and established the structural boundaries of the smaller intermontane Ayaviri Basin, which continued to evolve in a hinterland setting during late Oligocene–Miocene shortening. This brief episode of shortening along the Altiplano–Eastern Cordillera boundary is correlated with exceptionally rapid sediment accumulation (>1100–1800 m/m.y.), tightly constrained to 30–28 Ma on the basis of U-Pb geochronology and magnetic polarity stratigraphy. Provenance data from detrital zircon U-Pb age populations and sandstone compositions indicate derivation from a complex belt of Paleogene shortening and probable basin inversion in the Western Cordillera that was subsequently overprinted by Andean arc magmatism. This early Andean zone is interpreted as the along-strike continuation of the better-exposed Marañon fold-thrust belt to the north (5–13°S) and a proposed belt of shortening to the south along the Chilean Precordillera and Western Cordillera of Bolivia and northern Argentina (17–25°S). Subsequent focusing of late Oligocene shortening along the Eastern Cordillera–Altiplano boundary may have been linked to shallowing of the subducting slab and potential reactivation of crustal anisotropies.

Basin-scale stratigraphic architecture and potential Paleocene distributive fluvial systems of the Cordilleran Foreland Basin, Alberta, Canada

The Paleocene Paskapoo Formation in western Canada is composed of several hundred meters of fluvial strata that were deposited in an actively subsiding retro-arc foreland basin adjacent to the southern Canadian Cordillera. Here, we utilize newly available subsurface data from down-hole gamma-ray well logs to reconstruct the large-scale fluvial stratigraphy and depositional history of the Paskapoo Formation in the central portion of the Cordilleran foreland basin in Alberta. Paleocene fluvial strata in this region contain several notable characteristics, including variable degrees of channel sandstone amalgamation, regionally-variable stratigraphic architecture, and a large fan-shaped sandstone unit that emanated from the adjacent fold-thrust belt. Fluvial channel sandstone bodies are abundant and amalgamated near the base of the formation in the southern portion of the basin, but become less apparent in the northernmost 100km of the basin. The middle interval of the Paskapoo Formation, characterized by abundant mudstone with isolated channel sandstone bodies, is prevalent across the entire study area. The upper portion of Paskapoo Formation is dominated by a large (5000km2), north-northwest trending, laterally continuous sandstone in the northern portion of the basin that abuts against the fold-thrust belt and fans outward into the basin. This feature is interpreted as either a distributive fluvial system or a fixed-outlet river system that experienced repeated avulsions. This area of the fold-thrust belt may be the site of a long-lived fluvial outlet. The variable degree of sandstone amalgamation in the Paskapoo Formation suggests two different modes in the relative ratio of accommodation to sediment supply. Periods of rapid subsidence, likely associated with thrust emplacement in the adjacent fold-thrust belt, resulted in mudstone-dominated successions with isolated sandstone bodies, whereas tectonically inactive periods, associated with less subsidence, resulted in amalgamated sandstone units. The principal stratigraphic features reconstructed from the data in this area can be used to better understand and predict fluvial stratigraphy within other foreland basins.

Influence of attenuated lithosphere and sediment loading on flexure of the deep-water Magallanes retroarc foreland basin, Southern Andes

Flexural subsidence in foreland basins is controlled by applied loads—such as topography, water/sediment, and subcrustal forces—and the mechanical properties of the lithosphere. We investigate the controls on subsidence observed within the Upper Cretaceous Magallanes retroarc foreland basin of southern South America to evaluate the impact of lateral variations in flexural rigidity due to Late Jurassic extension. Conventional elastic models cannot explain the observed basin deflection and thick accumulation of deep-water Cenomanian-Turonian basin strata. However, models in which the lithosphere has been previously thinned and deflects under topographic and sedimentary loads successfully reproduce regional subsidence patterns. Results satisfy paleobathymetric observations in the Magallanes Basin and suggest that lithospheric thinning is necessary to produce both long-wavelength and deep subsidence during Late Cretaceous basin evolution. Results indicate that elastic thickness decreases westward from ~45–25 km in the distal foreland to ~37–15 km beneath the foredeep. These findings are consistent with a westward reduction in crustal thickness associated with the Jurassic extensional history of the Patagonian lithosphere. Our results also show that sediment loading exerts an important control on regional deflection patterns and promotes a wider region of subsidence and reduced forebulge uplift. We propose that lateral variations in mechanical properties and large sediment loads restrict depocenter migration and may cause the foredeep to remain fixed for prolonged periods of time. These findings confirm that loading of thinned lithosphere imposes different mechanical controls on the flexural profile and have potential implications for other retroarc foreland basins characterized by earlier extensional histories.

Detrital thermochronologic record of burial heating and sediment recycling in the Magallanes foreland basin, Patagonian Andes

AbstractThe Patagonian Magallanes retroarc foreland basin affords an excellent case study of sediment burial recycling within a thrust belt setting. We report combined detrital zircon U–Pb geochronology and (U–Th)/He thermochronology data and thermal modelling results that confirm delivery of both rapidly cooled, first‐cycle volcanogenic sediments from the Patagonian magmatic arc and recycled sediment from deeply buried and exhumed Cretaceous foredeep strata to the Cenozoic depocentre of the Patagonian Magallanes basin. We have quantified the magnitude of Eocene heating with thermal models that simultaneously forward model detrital zircon (U–Th)/He dates for best‐fit thermal histories. Our results indicate that 54–45 Ma burial of the Maastrichtian Dorotea Formation produced 164–180 °C conditions and heating to within the zircon He partial retention zone. Such deep burial is unusual for Andean foreland basins and may have resulted from combined effects of high basal heat flow and high sediment accumulation within a rapidly subsiding foredeep that was floored by basement weakened by previous Late Jurassic rifting. In this interpretation, Cenozoic thrust‐related deformation deeply eroded the Dorotea Formation fromca. 5 km burial depths and may be responsible for the development of a basin‐wide Palaeogene unconformity. Results from the Cenozoic Río Turbio and Santa Cruz formations confirm that they contain both Cenozoic first‐cycle zircon from the Patagonian magmatic arc and highly outgassed zircon recycled from older basin strata that experienced burial histories similar to those of the Dorotea Formation.

Deltaic deposits formed under spatially and temporally variable accommodation regimes: A plausible alternative explanation for isolated shallow-marine sandstone bodies

Sequence-stratigraphic concepts and nomenclature are predicated on the assumption that at any time, accommodation conditions are in phase across a depositional basin. In certain situations, however, such as in evolving retroarc foreland basins, the sense of accommodation may be spatially variable because of the growth of intrabasinal structures. Herein, we present evidence for the accumulation of a fluvially dominated deltaic sandstone under strong forcing from spatially and temporally variable low accommodation within the Cretaceous western Cordilleran foreland basin of North America. The Peay Sandstone Member is a coarsening-upward sandstone body ( [] thick) that is extensive across much of the eastern half of the present-day Bighorn Basin of Wyoming. It is remarkable for its elongate planform geometry, extending many tens of kilometers across the basin, and for distal thickening patterns that are, at face value, difficult to reconcile with conventional facies models for deltaic systems. The sandstone shows some of the characteristics of falling-stage and lowstand deltas (extending far into the basin from the contemporary shoreline to the west, lack of a preserved delta-plain topset) but is not incised into its substrate and does not show a descending regressive trajectory with respect to underlying strata. We submit that the Peay Sandstone Member was formed under a regime of both temporally and spatially variable accommodation forced by the heterogeneous growth of the forebulge within the western Cordilleran foreland basin and suggest that the origin of some other apparently isolated sandstone bodies in this and other basins might also be explained in a similar manner.

Geochemical zonation across a Neoproterozoic orogenic belt: Isotopic evidence from granitoids and metasedimentary rocks of the Jiangnan orogen, China

In order to understand how Late Mesoproterozoic to Early Neoproterozoic orogenic belts evolved during the assembly and rifting of the supercontinent Rodinia, we have carried out detailed studies on the geochemical compositions of Early Neoproterozoic crust across the Jiangnan orogen (JO) which connects the Yangtze and Cathaysia blocks on the northwestern margin of Rodinia. A gradual geochemical variation is recognized from east to west, based on comparisons of whole-rock Nd isotopes, U–Pb age spectra of detrital zircons, and Hf isotopes in magmatic zircons and detrital zircons from the Neoproterozoic granitoids and metasedimentary basement sequences in the JO. LA-ICP-MS U–Pb dating of detrital zircons from the sediments and magmatic zircons from interlayered volcanic rocks suggests that the folded basement sequences formed within the span 860–825Ma, implying the final amalgamation of the Yangtze and Cathaysia blocks occurred no older than ca 825Ma. The 950–820Ma detrital zircons strongly dominate in the eastern basement sequences, and most of them show moderately to highly positive ɛHf(t). In contrast, many of the Early Neoproterozoic detrital zircons in the western JO have moderately negative ɛHf(t) and more older (>1.0Ga) detrital zircons were found in this area. We suggest that the metasedimentary basement sequences in the JO were deposited in retro-arc foreland basins which originally evolved from back-arc basins, and the change of provenance controlled the variation in crustal geochemistry of crust across the JO. Sediments in the eastern basement sequences have been sourced mainly from the juvenile subduction-related igneous rocks to the east, with a few from the central Yangtze Block, whereas those in the western JO may have been located far from arc terranes to the east and thus received more older recycled detritus from the southern part of the South China Block. Moreover, the Hf isotopes of the detrital zircons imply episodic crustal growth in the provenance of the JO metasedimentary basement sequences, with age peaks at 1.0–0.8Ga, 1.75–1.50Ga and 2.60–2.45Ga. The early crust in South China may have been formed mainly at around 3.8Ga ago, and contains some Hadean components (ca 4.1Ga).

A pericratonic model for the Pearya terrane as an extension of the Franklinian margin of Laurentia, Canadian Arctic

Research Article| January 01, 2014 A pericratonic model for the Pearya terrane as an extension of the Franklinian margin of Laurentia, Canadian Arctic T. Hadlari; T. Hadlari † 1Geological Survey of Canada, 3303 33rd Street NW, Calgary, Alberta T2L 2A7, Canada †E-mails: thomas.hadlari@nrcan.gc.ca; bill.davis@nrcan.gc.ca; keith.dewing@nrcan.gc.ca. Search for other works by this author on: GSW Google Scholar W.J. Davis; W.J. Davis † 2Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada †E-mails: thomas.hadlari@nrcan.gc.ca; bill.davis@nrcan.gc.ca; keith.dewing@nrcan.gc.ca. Search for other works by this author on: GSW Google Scholar K. Dewing K. Dewing † 1Geological Survey of Canada, 3303 33rd Street NW, Calgary, Alberta T2L 2A7, Canada †E-mails: thomas.hadlari@nrcan.gc.ca; bill.davis@nrcan.gc.ca; keith.dewing@nrcan.gc.ca. Search for other works by this author on: GSW Google Scholar GSA Bulletin (2014) 126 (1-2): 182–200. https://doi.org/10.1130/B30843.1 Article history received: 19 Dec 2012 rev-recd: 17 Jul 2013 accepted: 17 Aug 2013 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation T. Hadlari, W.J. Davis, K. Dewing; A pericratonic model for the Pearya terrane as an extension of the Franklinian margin of Laurentia, Canadian Arctic. GSA Bulletin 2014;; 126 (1-2): 182–200. doi: https://doi.org/10.1130/B30843.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract New detrital zircon sensitive high-resolution ion microprobe (SHRIMP) geochronology and published framework geology of Neoproterozoic to Silurian strata are integrated to reexamine tectonic models of the Pearya terrane and the Franklinian margin at Ellesmere Island, Arctic Canada. Compared to Cambrian detrital zircon reference spectra, Neoproterozoic sandstones from the Pearya terrane contain Laurentian detrital zircon ages. In fact, they compare very well with Neoproterozoic strata of Greenland. Ultramafic, tholeiitic, and andesitic basalts of the Maskell Inlet complex, inferred to have an age of ca. 481 Ma, predate the M’Clintock orogeny at ca. 475 Ma. Ordovician granitoid ages within the Pearya terrane span ca. 475–463 Ma. A K-Ar cooling age of 452 Ma records post-tectonic exhumation. Deposited at ca. 450 Ma, new data show that the Cape Discovery Formation contains mainly ca. 500–450 Ma detrital zircon ages, but also older ages of 660–620 Ma. Upper Ordovician sandstones indicate that the Pearya terrane platform continued to receive near-syndepositional zircon. The Pearya terrane platform was submerged at ca. 435 Ma and overlain by Silurian flysch fed by sources similar to detrital zircon within Proterozoic to Ordovician strata of the Pearya terrane. Ties between the Pearya terrane and the Franklinian shelf include: similar Proterozoic-Cambrian stratigraphy; detrital zircon ages from the Lower Cambrian Grantland Formation that appear to be a combination of recycled Marinoan strata of Pearya terrane and Franklinian shelf strata; and profound unconformities on the Franklinian shelf that correlate temporally to the M’Clintock orogeny.A pericratonic model is a straightforward solution to the tectonic history of the Pearya terrane and the Franklinian shelf. We hypothesize that the Pearya terrane was part of the Franklinian margin in the Neoproterozoic and that the intervening deep water basin, or Hazen Trough, originated as a failed rift. The Maskell Inlet complex records ca. 481 Ma volcanism as a response to mantle upwelling beneath a subducting slab, shortly before or as the continent-ocean transition zone of the Franklinian margin was over-ridden. Continued convergence and crustal thickening during arc-continent collision drove the M’Clintock orogeny at ca. 475 Ma and resulted in the unconformities on the Franklinian shelf. After arc-continent collision, magmatism between ca. 475 and 438 Ma was related to subduction on the outboard margin, and the Pearya terrane was overlain by a low-accommodation retroarc foreland basin. A subsequent collisional event led to progressive drowning of the Pearya terrane and Franklinian platforms between 435 and 425 Ma. Silurian flysch then blanketed the Pearya terrane and entered the axis of the foreland basin, which also received sediment from cratonic sources of the flexural basin margin. Limited deformation at northern Axel Heiberg Island was associated with a ca. 390 Ma granitoid within the Pearya terrane. After a Devonian pulse of subsidence, infilling of the basin to form the Devonian clastic wedge overlapped in age with small ca. 368 Ma granitic intrusions within the Pearya terrane and was followed by extensive foreland deformation of the Late Devonian–Mississippian Ellesmerian orogeny. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Flexural versus dynamic processes of subsidence in the North American Cordillera foreland basin

Dynamic subsidence related to subduction is an important process in retroarc foreland basin systems. Dynamic subsidence in the North American retroarc foreland has been proposed as dominant in the Late Cretaceous; however, questions remain about the nature of the subcrustal load and the basin response to such processes. We present new isopach data using 130 data points covering a large portion of the U.S. and a revised flexural analysis of the Sevier foreland. Higher rigidity associated with the Wyoming craton can best model flexural subsidence directly prior to ~81 Ma. We constrain the transition from flexural to nonflexural subsidence to ~81 Ma and correlate this with large Late Cretaceous progradation. The locus of subsidence and the location of the subducted Shatsky oceanic plateau suggest that dynamic loading from viscous flow above the subducting plate is the mechanism driving dynamic subsidence in the retroarc foreland basin of the North American Cordillera.

Geochemistry, provenance and tectonic setting of the Late Cambrian–Early Ordovician Seydişehir Formation in the Çaltepe and Fele areas, SE Turkey

The major, trace and rare earth element (REE) contents of metapelite (MPL), metapsammite (MPS) and metamarl (MM) samples from the Cambro-Ordovician Seydişehir Formation were analyzed to investigate their provenance and tectonic setting. The MPS, MPL, and MM samples have variable SiO2 concentrations, with average values of 72.36, 55.54, and 20.95wt%, moderate SiO2/Al2O3 ratios (means of 6.88, 3.23, and 3.80), moderate to high Fe2O3+MgO contents (means of 5.14, 9.55, 3.56wt%), and high K2O/Na2O ratios (means of 3.26, 3.64, 2.90), respectively. On average, the chemical index of alteration (CIA) values of the MPS and the MPL are 65.87 and 71.96, respectively, while the chemical index of weathering (CIW) values are 74.54 and 85.09, respectively. These data record an intermediate to high degree of alteration (weathering) of plagioclase to illite/kaolinite in the samples’ provenance. The chondrite-normalized REE patterns of all the sample groups are similar and are characterized by subparallel light rare earth elements (LREE)-enriched, relatively flat heavy rare earth elements (HREE) patterns with pronounced Eu anomalies (mean of 0.69) and moderate fractionation [average (La/Yb)N=8.7]. Plots of sediments in ternary diagrams of La, Th, Sc and elemental ratios (La/Sc, Th/Sc, Cr/Th, Eu/Eu*, La/Lu, Co/Th, La/Sc and Sc/Th), which are critical for determining provenance, and REE patterns indicate that the metaclastic units of the Seydişehir Formation were derived dominantly from felsic to intermediate magmatic rocks and not from a mafic source. The La–Sc–Th and Th–Sc–Zr/10 ternary diagrams of the Seydişehir Formation are typical of continental island arc/active continental margin tectonic settings. The geologic location and geochemistry of the Seydişehir Formation suggest that it was deposited in an Andean-type retroarc foreland basin during the Late Cambrian–Early Ordovician period. The Neoproterozoic intermediate to felsic magmatic rocks and metaclastic sediments with felsic origins of the Sandıklı–Afyon Basement Complex (SBC) and their equivalent units, which are thought to be overlain by the younger units in the study area, may be the dominant source rocks for the Seydişehir Formation.