100 Myr record of sequences, sedimentary facies and sea level change from Ocean Drilling Program onshore coreholes, US Mid-Atlantic coastal plain

We analyzed the latest Early Cretaceous to Miocene sections (～110–7 Ma) in 11 New Jersey and Delaware onshore coreholes (Ocean Drilling Program Legs 150X and 174AX). Fifteen to seventeen Late Cretaceous and 39–40 Cenozoic sequence boundaries were identified on the basis of physical and temporal breaks. Within‐sequence changes follow predictable patterns with thin transgressive and thick regressive highstand systems tracts. The few lowstands encountered provide critical constraints on the range of sea‐level fall. We estimated paleowater depths by integrating lithofacies and biofacies analyses and determined ages using integrated biostratigraphy and strontium isotopic stratigraphy. These datasets were backstripped to provide a sea‐level estimate for the past ～100 Myr. Large river systems affected New Jersey during the Cretaceous and latest Oligocene–Miocene. Facies evolved through eight depositional phases controlled by changes in accommodation, long‐term sea level, and sediment supply: (1) the Barremian–earliest Cenomanian consisted of anastomosing riverine environments associated with warm climates, high sediment supply, and high accommodation; (2) the Cenomanian–early Turonian was dominated by marine sediments with minor deltaic influence associated with long‐term (10⁷ year) sea‐level rise; (3) the late Turonian through Coniacian was dominated by alluvial and delta plain systems associated with long‐term sea‐level fall; (4) the Santonian–Campanian consisted of marine deposition under the influence of a wave‐dominated delta associated with a long‐term sea‐level rise and increased sediment supply; (5) Maastrichtian–Eocene deposition consisted primarily of starved siliciclastic, carbonate ramp shelf environments associated with very high long‐term sea level and low sediment supply; (6) the late Eocene–Oligocene was a starved siliciclastic shelf associated with moderately high sea‐level and low sediment supply; (7) late early–middle Miocene consisted of a prograding shelf under a strong wave‐dominated deltaic influence associated with major increase in sediment supply and accommodation due to local sediment loading; and (8) over the past 10 Myr, low accommodation and eroded coastal systems were associated with low long‐term sea level and low rates of sediment supply due to bypassing.     

Late Cretaceous to Miocene sea-level estimates from the New Jersey and Delaware coastal plain coreholes: an error analysis

Sea level has been estimated for the last 108 million years through backstripping of corehole data from the New Jersey and Delaware Coastal Plains. Inherent errors due to this method of calculating sea level are discussed, including uncertainties in ages, depth of deposition and the model used for tectonic subsidence. Problems arising from the two-dimensional aspects of subsidence and response to sediment loads are also addressed. The rates and magnitudes of sea-level change are consistent with at least ephemeral ice sheets throughout the studied interval. Million-year sea-level cycles are, for the most part, consistent within the study area suggesting that they may be eustatic in origin. This conclusion is corroborated by correlation between sequence boundaries and unconformities in New Zealand. The resulting long-term curve suggests that sea level ranged from about 75–110 m in the Late Cretaceous, reached a maximum of about 150 m in the Early Eocene and fell to zero in the Miocene. The Late Cretaceous long-term (10⁷ years) magnitude is about 100–150 m less than sea level predicted from ocean volume. This discrepancy can be reconciled by assuming that dynamic topography in New Jersey was driven by North America overriding the subducted Farallon plate. However, geodynamic models of this effect do not resolve the problem in that they require Eocene sea level to be significantly higher in the New Jersey region than the global average.     

Timing of depth‐dependent lithosphere stretching on the S. Lofoten rifted margin offshore mid‐Norway: pre‐breakup or post‐breakup?

Depth‐dependent stretching, in which whole‐crustal and whole‐lithosphere extension is significantly greater than upper‐crustal extension, has been observed at both non‐volcanic and volcanic rifted continental margins. A key question is whether depth‐dependent stretching occurs during pre‐breakup rifting or during sea‐floor spreading initiation and early sea‐floor spreading. Analysis of post‐breakup thermal subsidence and upper‐crustal faulting show that depth‐dependent lithosphere stretching occurs on the outer part of the Norwegian volcanic rifted margin. For the southern Lofoten margin, large breakup lithosphere β stretching factors approaching infinity are required within 100 km of the continent–ocean boundary to restore Lower Eocene sediments and flood basalt surfaces (～54 Ma) to interpreted sub‐aerial depositional environments at sea level as indicated by well data. For the same region, the upper crust shows no significant Palaeocene and Late Cretaceous faulting preceding breakup with upper‐crustal β stretching factors <1.05. Further north on the Lofoten margin, reverse modelling of post‐breakup subsidence with a β stretching factor of infinity predicts palaeo‐bathymetries of ～1500 m to the west of the Utrøst Ridge and fails to restore Lower Eocene sediments and flood basalt tops to sea level at ～54 Ma. If these horizons were deposited in a sub‐aerial depositional environment, as indicated by well data to the south, an additional subsidence event younger than 54 Ma is required compatible with lower‐crustal thinning during sea‐floor spreading initiation. For the northern Vøring margin, breakup lithosphere β stretching factors of ～2.5 are required to restore Lower Eocene sediments and basalts to sea level at deposition, while Palaeocene and Late Cretaceous upper‐crustal β stretching factors for the same region are < 1.1. The absence of significant Palaeocene and late Cretaceous extension on the southern Lofoten and northern Vøring margins prior to continental breakup supports the hypothesis that depth‐dependent stretching of rifted margin lithosphere occurs during sea‐floor spreading initiation or early sea‐floor spreading rather than during pre‐breakup rifting.     

Fault-proximal stratigraphic record of episodic extension and oblique inversion, Bisbee basin, southwestern New Mexico, USA

Tectonic inversion models predict that stratigraphic thickening and local facies patterns adjacent to reactivated fault systems should record at least two phases of basin development: (1) initial extension‐related subsidence and (2) subsequent shortening‐induced uplift. In the central Peloncillo Mountains of southwestern New Mexico, thickness trends, distribution, and provenance of two major stratigraphic intervals on opposite sides of a northwest‐striking reverse fault preserve a record of Early Cretaceous normal displacement and latest Cretaceous–Paleogene reverse displacement along the fault. The Aptian–Albian Bisbee Group thickens by a factor of three from the footwall to the hanging‐wall block, and the Late Cretaceous?–Eocene Bobcat Hill Formation is preserved only in the footwall block. An initial episode of normal faulting resulted in thickening of upper Aptian–middle Albian, mixed siliciclastic and carbonate deposits and an up section change from coarse‐grained deltas to shallow‐marine depositional conditions. A second episode of normal faulting caused abrupt thickening of upper Albian, quartzose coastal‐plain deposits across the fault. These faulting episodes record two events of extension that affected the northern rift shoulder of the Bisbee basin. The third faulting episode was oblique‐slip, reverse reactivation of the fault and other related, former normal faults. Alluvial and pyroclastic deposits of the Bobcat Hill Formation record inversion of the Bisbee basin and development of an intermontane basin directly adjacent to the former rift basin. Inversion was coeval with latest Cretaceous–Paleogene shortening and magmatism. This offset history offers significant insight into extensional basin tectonics in the Early Cretaceous and permits rejection of models of long‐term Mesozoic shortening and orogen migration during the Cretaceous. This paper also illustrates how episodes of fault reactivation modify, in very short distances (<10 km), regional patterns of subsidence, the distribution of sediment‐source areas, and sedimentary depositional systems.     

Seismic stratigraphy and paleogeographic evolution of Fairway Basin,Northern Zealandia,Southwest Pacific: from Cretaceous Gondwana breakup to Cenozoic Tonga–Kermadec subduction

We present the first comprehensive seismic‐stratigraphic analysis of Fairway Basin, which is situated on the rifted continent of Zealandia in the Tasman Sea, southwest Pacific, between Australia and New Caledonia. The basin is 700 km long, 150 km wide, and has water depths of 500–3000 m. We describe depositional architecture and paleogeographic evolution of this basin. Basin formation was concurrent with two tectonic events: (i) Cretaceous rifting during eastern Gondwana breakup and (ii) initiation and Cenozoic evolution of Tonga–Kermadec subduction system to the east of the basin. To interpret the basin history we compiled and interpreted 2D seismic‐reflection profiles and make correlations with DSDP boreholes and the geology of New Caledonia. Five seismic‐stratigraphic units were defined. The deepest and oldest unit, FW3, folded and faulted can be correlated with volcaniclastic sediments and magmatic rocks in New Caledonia that are associated with Mesozoic Gondwana margin subduction. Alternatively, given the basin location 200–300 km west of New Caledonia and inboard of the ancient plate boundary, the unit could have formed as Gondwana intra‐continental basin with no known correlative. The overlying unit FW2b records syn‐rift deposition, probably associated with Cretaceous Gondwana breakup. Subaerial erosion supplied terrigenous sediment into the deltas in the northern part of the basin, as suggested by the truncation surfaces on the basement highs and sigmoid reflector geometries within unit FW2b respectively. Above, unit FW2a records post‐rift sedimentation and passive subsidence as the Tasman Sea opened and the Fairway Basin drifted away from Australia. Subsidence led to the flooding of the basement highs and burial of wave‐cut surfaces. Eocene compressive deformation resulted in minor folding and tilting within the Fairway Basin and was associated with the formation of many diapiric structures. The top of unit FW2 is an extensive unconformity that is associated with erosion and truncation on surrounding ridges. Above this unconformity, unit FW1b is interpreted as a turbidite system sourced from topography created during the Eocene tectonic event, which we interpret as being related to Tonga–Kermadec subduction initiation. Pelagic carbonate sedimentation is now prevalent. Unit FW1a has progressively draped the basin during Oligocene to Pleistocene subsidence. Many small volcanic cones were erupted during this final phase of subsidence, either as a delayed consequence of subduction initiation, or related to Tasmantid and Lord Howe hotspot trails. The northern Fairway Ridge remains close to sea level and its reef system continues to supply carbonate detrital sediments into the basin, most likely during sea‐level lowstands. Fairway Basin contains a nearly continuous record of tectonic and paleoclimatic events in the southwest Pacific since Cretaceous time. Its paleogeographic history is a key piece in the puzzle for understanding patterns of regional biodiversity in the southwest Pacific.     

Cainozoic heritage in the modern landscape near Bungonia,southern New South Wales

The regional topography of much of the New South Wales Southern Highlands was long attributed to Quaternary erosion, but it has been recently demonstrated that the region was, in fact, well developed by the Eocene. The hillsides at Inverary Park are mantled by the Late‐Eocene Reevesdale Basalt, thus indicating the extent of landscape development by the mid‐Tertiary. Pre‐, intra‐, and post‐basaltic alluvial and lacustrine sediments are compared with the current extent of the basalt, clearly demonstrating the age of this landscape and the paucity of modification since the Late Eocene. Stratigraphic techniques, U/Th, TL and ¹⁴C dating aid reconstruction of much of the Cainozoic history of Inverary Park. Major changes in sediment type and source have long been common, but Late Quaternary changes do not correlate well with similar observations elsewhere, suggesting that changes in hydrologic regime, notably climate change, are not necessarily responsible for changes in the stratigraphic record. This landscape development and preservation is also at odds with most models of landscape development.     

Sediment provenance and routing evolution in the Late Cretaceous–Eocene Ager Basin,south-central Pyrenees,Spain

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.     

Constraining provenance,thickness and erosion of nappes using low‐temperature thermochronology: the Northland Allochthon,New Zealand

The Northland Allochthon, an assemblage of Cretaceous–Oligocene sedimentary rocks, was emplaced during the Late Oligocene–earliest Miocene, onto the in situ Mesozoic and early Cenozoic rocks (predominantly Late Eocene–earliest Miocene) in northwestern New Zealand. Using low‐temperature thermochronology, we investigate the sedimentary provenance, burial and erosion histories of the rocks from both the hanging and footwalls of the allochthon. In central Northland (Parua Bay), both the overlying allochthon and underlying Early Miocene autochthon yield detrital zircon and partially reset apatite fission‐track ages that were sourced from the local Jurassic terrane and perhaps Late Cretaceous volcanics; the autochthon contains, additionally, material sourced from Oligocene volcanics. Thermal history modelling indicates that the lower part of the allochthon together with the autochthon was heated to ca. 55–100°C during the Late Oligocene and Early Miocene, most likely due to the burial beneath the overlying nappe sequences. From the Mesozoic basement exposed in eastern Northland, we obtained zircon fission‐track ages tightly bracketed between 153 and 149 Ma; the apatite fission‐track ages on the other hand, generally young towards the northwest, from 129 to 20.9 Ma. Basement thermochronological ages are inverted to simulate the emplacement and later erosion of the Northland Allochthon, using a thermo‐kinematic model coupled with an inversion algorithm. The results suggest that during the Late Oligocene, the nappes in eastern Northland ranged from ca. 4–6‐km thick in the north to zero in the Auckland region (over a distance >200 km). Following the allochthon emplacement, eastern Northland was uplifted and unroofed during the Early Miocene for a period of ca. 1–6 Myr at the rate of 0.1–0.8 km/Myr, leading to rapid erosion of the nappes. Since Middle Miocene, the basement uplift ceased and the erosion of the nappes and the region as a whole slowed down (ca. 0–0.2 km/Myr), implying a decay in the tectonic activity in this region.     

Refining stratigraphy and tectonic history using detrital zircon maximum depositional age: an example from the Cerro Fortaleza Formation,Austral Basin,southern Patagonia

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.     

Intraplate subsidence and basin filling adjacent to an oceanic arc–continent collision: a case from the southern Caribbean‐South America plate margin

The upper Campanian–Lower Eocene synorogenic sedimentary wedge of the Ranchería Basin was deposited in an intraplate basin resting on a tilted continental crustal block that was deformed by collision and subsequent subduction of the Caribbean Plate. Upper Cretaceous–Lower Eocene strata rest unconformably upon Jurassic igneous rocks of the Santa Marta Massif, with no major thrust faults separating the Santa Marta Massif from the Ranchería Basin. The upper Campanian–Lower Eocene succession includes, from base to top: foraminifera‐rich calcareous mudstone, mixed carbonate–siliciclastic strata and mudstone, coal and immature fluvial sandstone beds. Diachronous collision and eastward tilting of the plate margin (Santa Marta Massif and Central Cordillera) favoured the generation of accommodation space in a continuous intraplate basin (Ranchería, Cesar and western Maracaibo) during the Maastrichtian to Late Palaeocene. Terrigenous detritus from the distal colliding margin filled the western segments of the continuous intraplate basin (Ranchería and Cesar Basins); in the Late Paleocene, continental depositional systems migrated eastwards as far as the western Maracaibo Basin. In Early Eocene time, reactivation of former extensional structures fragmented the intraplate basin into the Ranchería‐Cesar Basins to the west, and the western Maracaibo Basin and Palmar High to the East. This scenario of continent–oceanic arc collision, crustal‐scale tilting, intraplate basin generation and fault reactivation may apply for Upper Cretaceous–Palaeogene syntectonic basins in western Colombia and Ecuador, and should be considered in other settings where arc–continent collision is followed by subduction.     

Subsidence and exhumation of the Mesozoic Qiangtang Basin: Implications for the growth of the Tibetan plateau

The subsidence and exhumation histories of the Qiangtang Basin and their contributions to the early evolution of the Tibetan plateau are vigorously debated. This paper reconstructs the subsidence history of the Mesozoic Qiangtang Basin with 11 selected composite stratigraphic sections and constrains the first stage of cooling using apatite fission track data. Facies analysis, biostratigraphy, palaeo‐environment interpretation and palaeo‐water depth estimation are integrated to create 11 composite sections through the basin. Backstripped subsidence calculations combined with previous work on sediment provenance and timing of deformation show that the evolution of the Mesozoic Qiangtang Basin can be divided into two stages. From Late Triassic to Early Jurassic times, the North Qiangtang was a retro‐foreland basin. In contrast, the South Qiangtang was a collisional pro‐foreland basin. During Middle Jurassic‐Early Cretaceous times, the North Qiangtang is interpreted as a hinterland basin between the Jinsha orogen and the Central Uplift; the South Qiangtang was controlled by subduction of Meso‐Tethyan Ocean lithosphere and associated dynamic topography combined with loading from the Central Uplift. Detrital apatite fission track ages from Mesozoic sandstones concentrate in late Early to Late Cretaceous (120.9–84.1 Ma) and Paleocene–Eocene (65.4–40.1 Ma). Thermal history modelling results record Early Cretaceous rapid cooling; the termination of subsidence and onset of exhumation of the Mesozoic Qiangtang Basin suggest that the accumulation of crustal thickening in central Tibet probably initiated during Late Jurassic–Early Cretaceous times (150–130 Ma), involving underthrusting of both the Lhasa and Songpan–Ganze terranes beneath the Qiangtang terrane or the collision of Amdo terrane.     

Tectonic evolution of sedimentary basins of northern Somalia

Regional seismic reflection profiles tied to lithological and biostratigraphic data from deep exploration wells have been used to determine the structure and evolution of the poorly known basins of northern Somalia. We recognize six major tectonostratigraphic sequences in the seismic profiles: Middle‐Late Jurassic syn‐rift sequences (Adigrat and Bihen Group), ?Cenomanian‐Campanian syn‐rift sequences (Gumburo Group), Campanian‐Maastrichtian syn‐rift sequences (Jesomma Sandstones), Palaeocene post‐rift sequences (Auradu Limestones), Early‐Middle Eocene post‐rift sequences (Taleh Formation) and Oligocene‐Miocene (Daban Group) syn‐rift sequences. Backstripping of well data provides new constraints on the age of rifting, the amount of crustal and mantle extension, and the development of the northern Somalia rifted basins. The tectonic subsidence and uplift history at the wells can be explained by a uniform extension model with three episodes of rifting punctuated by periods of relative tectonic quiescence and thermal subsidence. The first event initiated in the Late Jurassic (~156 Ma) and lasted for ~10 Myr and had a NW‐SE trend. We interpret the rift as a late stage event associated with the break‐up of Gondwana and the separation of Africa and Madagascar. The second event initiated in the Late Cretaceous (~80 Ma) and lasted for ~20–40 Myr. This event probably correlates with a rapid increase in spreading rate on the ridges separating the African and Indian and African and Antarctica plates and a contemporaneous slowing down of Africa's plate motion. The backstripped tectonic subsidence data can be explained by a multi‐rift extensional model with stretching factor, β, of 1.09–1.14 and 1.05–1.28 for the first and second rifting events, respectively. The model, fails, however, to completely explain the slow subsidence and uplift history of the margin during Early Cretaceous to Late Cretaceous. We attribute this slow subsidence to the combined effect of a sea‐level fall and regional uplift, which caused a major unconformity in northern Somalia. The third and most recent event occurred in the Oligocene (~32 Ma) and lasted for ~10 Myr. This rift developed along the Gulf of Aden and reactivated the Guban, Nogal and Daroor basins, and is related to the opening of the Gulf of Aden. As a result of these events the crust and upper mantle were thinned by up to a factor of two in some basins. In addition, several distinct petroleum systems developed. The principal exploration play is for Mesozoic petroleum systems with the syn‐rift Oligocene‐Miocene as a subordinate objective owing to low maturity and seal problems. The main seals for the different plays are various shales, some of which are also source rocks, but the Early Eocene evaporites of the Taleh formations can also perform a sealing role for Palaeogene or older generated hydrocarbons migrating vertically.     

Late Cretaceous‐Palaeogene stratigraphic and basin evolution in the Zhepure Mountain of southern Tibet: implications for the timing of India‐Asia initial collision

This article presents combined stratigraphic, sedimentological, subsidence and provenance data for the Cretaceous–Palaeogene succession from the Zhepure Mountain of southern Tibet. This region records the northernmost sedimentation of the Tethyan passive margin of India, and this time interval represents the transition into continental collision with Asia. The uppermost Cretaceous Zhepure Shanpo and Jidula formations record the transition from pelagic into upper slope to delta‐plain environments. The Palaeocene–lower Eocene Zongpu Formation records a carbonate ramp that is overlain by the deep‐water Enba Formation (lower Eocene). The upper part of the Enba Formation records shallowing into a storm‐influenced, outer shelf environment. Detrital zircon U–Pb and Hf isotopic data indicate that the terrigenous strata of the Enba Formation were sourced from the Lhasa terrane. Unconformably overlying the Enba Formation is the Zhaguo Formation comprising fluvial deposits with evidence of recycling from the underlying successions. Backstripped subsidence analysis indicates shallowing during latest Cretaceous‐earliest Palaeocene time (Zhepure Shanpo and Jidula formations) driven by basement uplift, followed by stability (Zongpu Formation) until early Eocene time (Enba Formation) when accelerated subsidence occurred. The provenance, subsidence and stratigraphy suggest that the Enba and Zhaguo formations record foredeep and wedge‐top sedimentation respectively within the early Himalayan foreland basin. The underlying Zongpu Formation is interpreted to record the accumulation of a carbonate ramp at the margin of a submarine forebulge. The precursor tectonic uplift during latest Cretaceous time could either record surface uplift over a mantle plume related to the Réunion hotspot, or an early signal of lithospheric flexure related to oceanic subduction, continental collision or ophiolite obduction. The results indicate that the collision of India with Asia occurred before late Danian (ca. 62 Ma) time.     

Allogenic forcing of the late Quaternary Rhine–Meuse fluvial record: the interplay of sea-level change, climate change and crustal movements

The Rhine–Meuse system in the west‐central Netherlands is a continental‐scale fluvial system bordered by an extremely wide continental shelf. Consequently, late Quaternary eustatic sea‐level changes have resulted in dramatic shoreline displacements, by as much as 800 km. In addition, changes in climate have been severe, given the latitudinal and palaeogeographic setting of the Rhine–Meuse system. We investigated the relative importance of these allogenic controls on fluvial aggradation and incision during the last two glacial–interglacial cycles. We used optical dating of quartz from ～30 samples in a cross‐section perpendicular to the palaeoflow direction, allowing us to correlate periods of aggradation and incision with independent records of sea‐level change, climate change and glacio‐isostatic crustal movements. We found the long‐term aggradation rate to be ～8 cm kyr^?1, a value similar to previous estimates of tectonic subsidence rates in the study area. Several excursions from this long‐term aggradation trend could be identified for the last glacial–interglacial cycle. Dry climatic conditions with relatively high sediment supply induced aggradation during oxygen‐isotope stages (OIS) 4 and 3. Build‐up of a glacio‐isostatic forebulge during OIS 2 is a likely cause of incision around the Last Glacial Maximum, followed by an aggradation phase during forebulge collapse. Sea‐level highstands during OIS 5 have likely resulted in the aggradation of coastal prisms, but only minor, basal estuarine deposits have been preserved because these coastal prisms were prone to erosion during ensuing sea‐level falls. Overall, the sedimentary record is dominated by strata formed during time intervals when the study area was completely unaffected by sea‐level control, and our evidence shows that the falling‐stage systems tract has the highest preservation potential. Our study highlights the importance of considering the complex interplay of both upstream and downstream controls to obtain a comprehensive understanding of the evolution of basin‐margin successions.     

Tectonic and oceanographic process interactions archived in Late Cretaceous to Present deep‐marine stratigraphy on the Exmouth Plateau,offshore NW Australia

Deep‐marine deposits provide a valuable archive of process interactions between sediment gravity flows, pelagic sedimentation and thermohaline bottom‐currents. Stratigraphic successions can also record plate‐scale tectonic processes (e.g. continental breakup and shortening) that impact long‐term ocean circulation patterns, including changes in climate and biodiversity. One such setting is the Exmouth Plateau, offshore NW Australia, which has been a relatively stable, fine‐grained carbonate‐dominated continental margin from the Late Cretaceous to Present. We combine extensive 2D (~40,000 km) and 3D (3,627 km²) seismic reflection data with lithologic and biostratigraphic information from wells to reconstruct the tectonic and oceanographic evolution of this margin. We identified three large‐scale seismic units (SUs): (a) SU‐1 (Late Cretaceous)—500 m‐thick, and characterised by NE‐SW‐trending, slope‐normal elongate depocentres (c. 200 km long and 70 km wide), with erosional surfaces at their bases and tops, which are interpreted as the result of contour‐parallel bottom‐currents, coeval with the onset of opening of the Southern Ocean; (b) SU‐2 (Palaeocene—Late Miocene)—800 m‐thick and characterised by: (a) very large (amplitude, c. 40 m and wavelength, c. 3 km), SW‐migrating, NW‐SE‐trending sediment waves, (b) large (4 km‐wide, 100 m‐deep), NE‐trending scours that flank the sediment waves and (c) NW‐trending, 4 km‐wide and 80 m‐deep turbidite channel, infilled by NE‐dipping reflectors, which together may reflect an intensification of NE‐flowing bottom currents during a relative sea‐level fall following the establishment of circumpolar‐ocean current around Antarctica; and (c) SU‐3 (Late Miocene—Present)—1,000 m‐thick and is dominated by large (up to 100 km³) mass‐transport complexes (MTCs) derived from the continental margin (to the east) and the Exmouth Plateau Arch (to the west), and accumulated mainly in the adjacent Kangaroo Syncline. This change in depositional style may be linked to tectonically‐induced seabed tilting and folding caused by collision and subduction along the northern margin of the Australian plate. Hence, the stratigraphic record of the Exmouth Plateau provides a rich archive of plate‐scale regional geological events occurring along the distant southern (2,000 km away) and northern (1,500 km away) margins of the Australian plate.     

Imaging of Stratigraphic Pinch-Out Traps Within the Lower-Cretaceous Shaly-Sandstone System,Pakistan, Using 3D Quantitative Seismic Inverted Porosity–Velocity Modeling

Incised valleys form excellent stratigraphic pinch-out traps. Traditional seismic data analysis techniques fail to predict quantitatively the porous and low-velocity sand-fills for incised valleys. The 3D quantitative seismic inverted porosity–velocity (3DQSIPV) analysis was applied in the Indus Basin, SW Pakistan. The reflection strength attribute better portrayed the reservoir sandstone and faults compared to seismic amplitude attribute. The sweetness-based continuous wavelet transform authenticated the development of the stratigraphic play. The 17 Hz amplitude delineated the non-porous seal and porous reservoirs of sand-filled incised valley and strand plain, and faults. The integrated model of seismic attributes categorizes the reservoir and seal constituents. The petrophysical modeling corroborated the gas-bearing “sweet-spots” within the stratigraphic-based dynamical system. The facies modeling predicted the for coarse-grained sandstone and fine-grained shales, depositional environments, fluctuations of sea level and their impacts on the overall development of stratigraphic plays. The predicted density and P-wave velocity for the sandstone-filled incised valley of the lowstand system tract were?~?1.4–1.75 g/cc and?~?3217–3802 m/s, respectively. The predicted density and P-wave velocity for the sealing shales facies of strand plain of transgressive system tract were?~?1.9–2.1 g/cc and 2.55–2.7 g/cc and 3900–4700 m/s, respectively. The 3DQSIPV predicted?>?25% porosity and?~?3300 m/s velocity of reservoirs in the west. The eastern zones shows?<?12% porosity and high velocity of?~?4580 m/s. Cross-plots of porosity, velocity, and thickness showed correlation coefficients of R²?>?0.90 for inverted velocity. This workflow may serve as an analogue for the remaining oil and gas fields of the Indus Basins of Pakistan and similar geological settings of divergent plate margins.

     

Burial/exhumation histories for the Cooper–Eromanga Basins and implications for hydrocarbon exploration, Eastern Australia

The Cooper–Eromanga Basins of South Australia and Queensland are not at their maximum burial depth due to Late Cretaceous–Tertiary, and Late Triassic–Early Jurassic exhumation. Apparent exhumation (maximum burial depth–present burial depth) for the Cooper Basin has been quantified using the compaction methodology. The results show that exhumation of the Cooper Basin for the majority of the wells is greater than the exhumation of the Eromanga Basin. Using the compaction methodology, apparent exhumation of Early to Middle Triassic age Arrabury and Tinchoo Formatios has been quantified. Both units yield similar results and do not support that the Arrabury/Tinchoo boundary represents the Cooper–Eromanga boundary. Hence, the Cooper Basin is believed to have reached its maximum burial depth in Late Triassic times. Sonic log data are not available for the units overlying the Late Cretaceous Winton Formation; thus, it is not possible to date exhumation beyond the Late Cretaceous–Tertiary using the compaction methodology. Tertiary sequences as are preserved are relatively thin and separated by marked unconformities and weathered surfaces; hence, exhumation rather than sedimentation dominated the Tertiary, and in exhumed areas, maximum burial depth was attained in Late Cretaceous times. The burial/exhumation history of representative wells was synthesized using sediment decompaction and establishing porosity/depth relations for the Cooper–Eromanga units. Considering the relative significance of the major periods of exhumation in the Cooper/Eromanga Basins, three broad types of burial/exhumation histories can be distinguished. Maximum burial depth of the Cooper Basin sequence was attained before the deposition of the Eromanga Basin sequence, i.e. Late Triassic–Early Jurassic times; maximum burial depth of the Cooper and Eromanga Basin sequences attained in Late Cretaceous times; and Cooper and Eromanga Basin sequences are currently at maximum burial‐depth. Incorporation of exhumation into burial history has major implications for hydrocarbon exploration.     

Thermo‐tectonic evolution of the south‐central Pyrenees from rifting to orogeny: insights from detrital zircon U/Pb and (U‐Th)/He thermochronometry

Constraining the thermal and denudational evolution of continental margins from extensional episodes to early orogenic stages is critical in the objective to better understand the sediment routing during the growth of orogenic topography. Here, we report 160 detrital zircon U/Pb ages and 73 (U‐Th)/He ages from Albian, Upper Cretaceous and Eocene sandstones from the south‐central Pyrenees. All samples show dominant zircon U/Pb age peaks at 310–320 Ma, indicating a primary contribution from Variscan granites of the central Pyrenean Axial Zone. A secondary population at 450–600 Ma documents zircon grains sourced from the eastern Pyrenees. Zircon (U‐Th)/He ages recovered from older samples document, a Triassic age peak at ca. 241 Ma, corresponding to denudation coeval with the initiation of Atlantic rifting. An Early Cretaceous cooling event at ca. 133 Ma appears consistent with rift‐related exhumation and thermal overprint on the Iberian margin. The (U‐Th)/He age peaks from ca. 80 Ma to ca. 68 Ma with decreasing depositional ages are interpreted to reflect the southward‐migrating thrust‐related exhumation on the pro‐wedge side of the Pyrenean orogen. The increase in lag times, from ca. 15 Ma in the Tremp Formation (ca. 65 Ma) to 28 Ma in the Escanilla Formation (ca. 40 Ma), suggests decreasing exhumation rates from 0.4 km Myr^–1 to 0.2 km Myr^–1. The apparent inconsistency with convergence rates is used to infer that rocks cooled at 68 Ma may have resided in the crust before final exhumation to the surface. Finally, the cooling event observed at 68 Ma provides support to the inferred acceleration of convergence, shortening and exhumation during Late Cretaceous times.     

Fluid inclusions as constraints in a three‐dimensional hydro‐thermo‐mechanical model of the Paris basin,France

Fluid inclusion homogenization temperatures and three‐dimensional hydro‐thermo‐mechanical modelling were combined to constrain fluid flow, solute and heat transport in the Paris basin, France, focusing on the two main petroleum reservoirs i.e. the Dogger and the Triassic (Keuper) formations. The average homogenization temperatures of two‐phase aqueous inclusions in different samples range from 66 °C to 88 °C in the Dogger calcite cement, from 106 °C to 118 °C in the Keuper dolomite cement and from 89 °C to 126 °C in the Keuper quartz and K‐feldspar cements. The maximum homogenization temperatures for inclusions in the Keuper quartz and K‐feldspar cements were 17–47 °C higher than present‐day temperatures in the boreholes at similar depths. Processes that might explain higher temperatures in the past were examined through numerical simulations and sensitivity tests. A warmer climate in the Late Cretaceous–Early Tertiary resulted in a temperature rise of only 8 °C. Late Cretaceous chalk had a thermal blanketing effect that resulted in simulated temperatures as high as 15–20 °C above the present day ones. An additional 300 m deposition and subsequent erosion of chalk, not taken into account so far, has to be considered to simulate the high palaeo‐temperatures recorded by fluid inclusions in both reservoirs. In view of the simulated thermal history of the basin, in the Keuper, an age of about 85 Ma is consistent with quartz/K‐feldspar temperatures and an age of about 65 Ma is in agreement with the precipitation temperature of the dolomite cement. Our models suggest an age of about 50 Ma for the Dogger calcite cementation.     

Integrated provenance record of a forearc basin modified by slab‐window magmatism: detrital‐ zircon geochronology and sandstone compositions of the Paleogene Arkose Ridge Formation,south‐central Alaska

This study presents an integrated provenance record for ancient forearc strata in southern Alaska. Paleocene–Eocene sedimentary and volcanic strata >2000 m thick in the southern Talkeetna Mountains record nonmarine sediment accumulation in a remnant forearc basin. In these strata, igneous detritus dominates conglomerate and sandstone detrital modes, including plutonic and volcanic clasts, plagioclase feldspar, and monocrystalline quartz. Volcanic detritus is more abundant and increases upsection in eastern sandstone and conglomerate. U‐Pb ages of >1600 detrital zircons from 19 sandstone samples document three main populations: 60–48 Ma (late Paleocene–Eocene; 14% of all grains), 85–60 Ma (late Cretaceous–early Paleocene; 64%) and 200–100 Ma (Jurassic–Early Cretaceous; 11%). Eastern sections exhibit the broadest distribution of detrital ages, including a principal population of late Paleocene–Eocene ages. In contrast, central and western sections yield mainly late Cretaceous–early Paleocene detrital ages. Collectively, our results permit reconstruction of individual fluvial drainages oriented transverse to a dissected arc. Specifically, new data suggest: (1) Detritus was eroded from volcanic‐plutonic sources exposed along the arcward margin of the sampled forearc basin fill, primarily Jurassic–Paleocene magmatic‐arc plutons and spatially limited late Paleocene–Eocene volcanic centers; (2) Eastern deposystems received higher proportions of juvenile volcanic detritus through time from late Paleocene–Eocene volcanic centers, consistent with emplacement of a slab window beneath the northeastern part of the basin during spreading‐ridge subduction; (3) Western deposystems transported volcanic‐plutonic detritus from Jurassic–Paleocene remnant arc plutons and local eruptive centers that flanked the northwestern part of the basin; (4) Diagnostic evidence of sediment derivation from accretionary‐prism strata exposed trenchward of the basin fill is lacking. Our results provide geologic evidence for latest Cretaceous–early Paleocene exhumation of arc plutons and marine forearc strata followed by nonmarine sediment accumulation and slab‐window magmatism. This inferred history supports models that invoke spreading‐ridge subduction beneath southern Alaska during Paleogene time, providing a framework for understanding a mature continental‐arc/forearc‐basin system modified by ridge subduction. Conventional provenance models predict reduced input of volcanic detritus to forearc basins during progressive exhumation of the volcanic edifice and increasing exposure of subvolcanic plutons. In contrast, our results show that forearc basins influenced by ridge subduction may record localized increases in juvenile volcanic detritus during late‐stage evolution in response to accumulation of volcanic sequences formed from slab‐window eruptive centers.