Basin Research - Volume 33, Issue 3, 2021

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Quartz overgrowth textures and fluid inclusions can be used as a fingerprint for basin‐scale sedimentary recycling.

, Abstract

Sedimentary recycling has the potential to obscure source‐to‐sink relationships, provenance interpretations, burial history reconstructions and robust reservoir quality predictions in siliciclastic sedimentary basins. Here, we integrate petrographic and cathodoluminescence microtextures with fluid inclusion thermometry in quartz overgrowths to identify sedimentary recycling and to constrain the potential provenance candidate for recycled grains in Lower Mesozoic sandstone of the western Barents Sea basin. Four diagenetic imprints were recognized as proof of sediment recycling: (a) microtextural surface properties of overgrowths, (b) the presence of overgrowths at sutured grain contacts, (c) reversed diagenetic sequences and (d) fluid inclusions within quartz overgrowths. The diagenetic imprints confirm delivery of recycled sediments across the western Barents Sea basin. Their widespread distribution across the basin suggest that the recycled grains were derived from a drainage basin with regional‐scale sediment dispersal potential during the latest Triassic. Furthermore, the drainage basin must have contained sedimentary rocks. Prior to surface exposure, the precursor sedimentary basin was subjected to burial temperatures exceeding 130°C, whereby syntaxial quartz overgrowths precipitated. This temperature indicates an uplift of around 3–4 km, which represents a significant tectonic event. Recycled quartz grains can provide insights on their provenance as they retain direct temperature records. The geothermal signatures and geographically widespread distribution of recycled quartz exclude spatially restricted intrabasinal highs and higher‐temperature crystalline rocks as provenance candidates for the recycled grain portion. Our data support the contemporaneous Novaya Zemlya Fold and Thrust Belt as the most likely provenance candidate in the region. The integrated approach demonstrated herein can be used to constrain sediment recycling and partly eroded provenance candidates in sedimentary basins of equivalent setting worldwide, particularly in quartz‐rich strata susceptible to sediment supply from older uplifted sedimentary basins.

]

[Abstract

Lateral spread and submarine creep are processes that occur near the headwalls of both terrestrial landslides and submarine mass‐transport complexes (MTCs). Both submarine creep and spread deposits may contain giant (km‐scale) coherent blocks, but their transport processes remain poorly constrained. Here we use seismic reflection data to determine the geometry, scale, and origin of a Late Miocene mass‐transport complex (MTC) located in the Kangaroo Syncline, offshore NW Australia. We show that this large remobilised mass of carbonate ooze is ca. 170–300 m thick and covers an area of at least 1,050 km². The deposit is defined internally by two distinct seismic facies: (a) large, upward‐tapering blocks (210–300 m thick, 170–210 m wide and 800–1,200 m long) with negligible internal deformation, which decrease in height and spacing along the transport direction (identical, but in situ, seismic facies forms undeformed slope material immediately updip of the deposit headwall); and (b) troughs (160–260 m thick, 190–230 m wide and 800–1,200 m long) comprising moderately deformed strata, which contain ‘v’‐shaped, pipe‐like structures that extend upwards from the inferred basal shear surface to the top surface. The lack of deformation within the blocks, and their correlation to adjacent in situ deposits, suggests they underwent limited transport (ca. 50 m–70 m). The relatively high degree of deformation within the intervening troughs is attributed to the vertical expulsion of fluids and sediment during hydraulic failure of the sediment mass. We present a hydraulic failure model that invokes evacuation of the lower slope by a precursor MTC and which formed the space to trigger the lateral spread. Our study also provides new insights into the genesis and rheology of subaqueous lateral spreads. The genetic links identified between mass wasting and spatially focused fluid flow, as well as disturbing the deep seafloor, indicate that submarine landslides may also create important deep‐sea biodiversity hotspots.

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Our study present a hydraulic failure model that accounts for the styles of intra‐MTC deformation process. The genetic links identified between MTC and spatially‐focused fluid flow indicate that, as well as disturbing the deep seafloor, MTC may also create important deep‐sea biodiversity hotspots.

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Detrital apatite fission track analysis on synorogenic sediments in the northern Qaidam Basin indicate that Cenozoic tectonic deformation began

in the Qilian Shan in the late Paleocene‐early Eocene.

, Abstract

The evolution of the tectonic deformation of the northeastern Tibetan Plateau (TP) in the Cenozoic is significant for understanding plateau growth during India‐Asia convergence. However, when deformation began and how it has developed in this pivotal region remain controversial. We focus on the temporal progress of Cenozoic deformation in the Qilian Shan, a major tectonic belt of the northeastern TP. In the present study, detrital apatite fission‐track (AFT) thermochronological analysis was performed on Oligocene‐Quaternary synorogenic sediments in the northern Qaidam Basin, where detritus is sourced from the Qilian Shan. Age components of buried but unannealed detrital AFT samples reveal two static peaks (i.e., peak ages that are consistent upsection) at ca. 60–50 Ma and ca. 40–36 Ma and a moving peak (i.e., peak ages that are younger upsection) with increased lag time during ca. 30–8 Ma. These new detrital AFT ages, integrated with the analysis of sedimentary provenance and data from previously published studies, indicate that Cenozoic tectonic deformation began in the Qilian Shan in the late Paleocene‐early Eocene. Furthermore, the Qilian Shan experienced a subsequent episodic deformation event in the late Eocene and the deformation or erosion of some terranes in the Qilian Shan decelerated during the Oligocene‐Miocene. Our results suggest that the northeastern TP responded to the India‐Asia collision almost instantaneously.

]

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Two strikingly different models indicate a Palaeocene initiation of either an India‐Asia collision or an India‐intra‐oceanic island arc collision

, Abstract

Upper Cretaceous to Eocene marine sedimentary sequences of the Yarlung‐Tsangpo Suture Zone (YTSZ) provide critical constraints on the initial process of the India–Asia continental collision and the closure time of the Neo‐Tethyan Ocean. New sedimentological, petrographic, biochronological and detrital zircon age data of Cretaceous–Palaeogene strata from the southern margin of the YTSZ are reported in this study. Detrital zircons from the Lower Cretaceous Gyabula Formation are dominated by Archean to Cambrian U–Pb ages, indicating a likely source originating from the Indian continent. In contrast, zircon ages from the Palaeogene Jiachala Formation are predominantly younger than 200 Ma, with a major peak of ca. 76–187 Ma, which is consistent with a source from either an intra‐oceanic island arc system or the Asian continent. Sixty species of radiolarian fossils obtained from the Gyabula, Zongzhuo and Jiachala Formations provide a regional correlation with the Cretaceous Tethyan realm and Palaeogene low‐latitude biozonation schemes based on the Unitary Association method. The Palaeogene radiolarian zonation UAZ JP10 identified in the Jiachala Formation, when combined with existing absolute age models derived from the Deep Sea Drilling Project and Ocean Drilling Program, indicates an age of ca. 61.8–61.1 Ma. Integration of the biochronological and detrital zircon age data suggests that major changes in provenance occurred at the Indian continental margin, allowing an important timing constraint on the onset of collision to be placed no later than the Danian at ca, 61.8 Ma. This study highlights the significance of focusing on distinct sedimentary sequences in collisional orogens to reconstruct the timing and processes of continental collision events.

]

[Abstract

The Porcupine Basin is a large underexplored sedimentary basin located offshore west of Ireland within the structurally complex European North Atlantic Margin. The basin has evolved through multiple Jurassic–Recent phases of deformation and although the overall plate tectonic context of the margin is well‐documented, there are still uncertainties regarding the phases of tectonic activity, and their associated strain distribution and fault kinematics. Based on the analysis of large volumes of 2D and 3D seismic data from the Porcupine Basin, we provide an overview of the nature and origin of multiple fault systems, both tectonic and nontectonic, with links to regional tectonic events where possible. Three distinct basin‐wide phases of tectonically induced extensional faulting are recognized: (a) Late Jurassic N‐S to NE‐SW trending rift faults, (b) Late Cretaceous E‐W to ENE‐WSW trending normal faults and (c) Mid Eocene N‐S trending faults. The Jurassic faults were active over a period of 11.5 Myr between the Oxfordian and Kimmeridgian but with an intervening 4.5 Myr period of quiescence providing a two‐stage rift evolution. The Late Cretaceous faulting in the Porcupine Basin broadly correlates with extension in the Celtic Sea basins and is tentatively attributed to the rotational spreading of the Bay of Biscay in the south. The Mid Eocene phase of extension, which coincides with the onset of spreading between Europe and Greenland (Atlantic spreading), resulted in partial reactivation of the Jurassic faults. A series of non‐tectonic fault systems occur within specific stratigraphic intervals suggesting a compactional or gravitationally driven origin, including basinward dipping normal faults within a Palaeocene–early Eocene deltaic sequence, and multiple tiers of polygonal faults within Cretaceous, late Eocene and Neogene strata.

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Schematic illuration of tectonic deformations in the Porcupine Basin.

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[Abstract

Despite salt being regarded as an extremely efficient, low‐permeability hydraulic seal, an increasing number of cross‐evaporite fluid escape features have been documented in salt‐bearing sedimentary basins. Because of this, it is clear that our understanding of how thick salt deposits impact fluid flow in sedimentary basins is incomplete. We here examine the causes and evolution of cross‐evaporite fluid escape in the northern Levant Basin, Eastern Mediterranean. High‐quality 3D seismic data offshore Lebanon image hundreds of supra‐salt fluid escape pipes distributed widely along the margin. The pipes consistently originate at the crest of prominent sub‐salt anticlines, where overlying salt is relatively thin. The fact the pipes crosscut the salt suggests that hydrofracturing occurred, permitting focused fluid flow. Sequential pipes from unique emission points are organized along trails that are several kilometres long, and which are progressively deformed due to basinward gravity gliding of salt and its overburden. Correlation of pipes in 12 trails suggests margin‐wide fluid escape started in the Late Pliocene/Early Pleistocene, coincident with a major phase of uplift of the Levant margin. We interpret that the consequent transfer of overpressure from the central basin area, in addition to gas exsolution from hydrocarbons already trapped in sub‐salt anticlines, triggered seal failure and cross‐evaporite fluid flow. We infer that other causes of fluid escape in the Eastern Mediterranean, such as subsurface pressure changes driven by sea‐level variations and salt deposition associated with the Messinian Salinity Crisis, played only a minor role in triggering cross‐evaporite fluid flow in the northern Levant Basin. Further phases of fluid escape are unique to each anticline and cannot be easily correlated across the margin. Therefore, despite a common initial cause, long‐term fluid escape proceeded according to structure‐specific characteristics, such as local dynamics of fluid migration and anticline geometry. Our work shows that the mechanisms triggering cross‐evaporite fluid flow in salt basins vary in time and space.

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In the northern Levant Basin, hundreds of fluid escape pipes are organized in linear trails, documenting widespread cross‐evaporite fluid migration since the Late Pliocene/Early Pleistocene. Major uplift of the basin margin is inferred to have caused lateral overpressure transfer and the resulting seal failure above prominent sub‐salt anticlines. This study shows that cross‐evaporite fluid escape in the Eastern Mediterranean can have multiple causes, which vary over time, act in synergy, and have different impacts in the various areas of this salt giant basins.

]

[Abstract

Many sedimentary basins host thick evaporite (salt) deposits. Some of these basins also host extensive igneous intrusion networks. It thus seems inevitable that, in some locations, magma will interact with salt. Yet how interaction between these materials may influence salt tectonics or magma emplacement, particularly at the basin‐scale, remains poorly understood. We use 3D seismic reflection data from the Santos Basin, offshore Brazil to image 38 igneous intrusions spatially related to thick Aptian salt. Based on identified seismic–stratigraphic relationships, we suggest sill emplacement likely occurred during the late Albian‐to‐Santonian. We show intra‐salt sills are geometrically similar to but laterally offset from supra‐salt sills. We suggest ascending magma was arrested by the salt in some areas, but not others, perhaps due to differences in evaporite lithology. Our mapping also reveals most sills occur within and above the presalt Merluza Graben, an area characterized by Albian‐to‐Neogene, salt‐detached extension. In adjacent areas, where there are few intrusions, salt deformation was driven by post‐Santonian diapir rise. We suggest emplacement of hot magma within evaporites above the Merluza Graben enhanced Albian‐to‐Santonian salt movement, but that crystallization of the intrusion network restricted post‐Santonian diapirism. Our work indicates salt–magma interaction can influence salt tectonics, as well as the distribution of magma plumbing systems, and thus could impact basin evolution.

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Here we use 3D seismic reflection from the Santos Basin, offshore Brazil, to map igneous sills below, within, and above a salt layer characterised by the development of salt diapirs and rollers. By mapping these features, as well as the surrounding stratigraphic and structural architecture, we are able to reconstruct the evolution of salt‐magma interactions. In particular, we suggest magma emplacement may have locally facilitated salt movement, but that solidification of the intrusions may have produced a rigid framework that inhibited later salt movement.

]

[Abstract

Structurally controlled bathymetry in rifts has a significant influence on sediment routing pathways and depositional architecture of sediment gravity flow deposits. In contrast to rift segments characterized by crustal‐scale half‐grabens, the tectono‐stratigraphic evolution of deep‐water rift domains characterised by distributed faulting on narrow fault terraces has received little attention. We use 3D broadband seismic data, calibrated by boreholes, from the Lomre and Uer terraces in the northern North Sea rift to investigate Late Jurassic syn‐rift sediment gravity flow systems on fault‐terraced slopes. The sediment gravity flow fairways were sourced from hinterland drainages via basin margin deltaic systems on the Horda Platform to the southeast. The deep‐water sedimentary systems evolve from initial, widespread submarine channelized lobe complexes, through submarine channels, to incised submarine canyons. This progressive confinement of the sediment gravity flow system was concomitant with progressive localization of strain onto the main terrace‐bounding faults. Although the normal fault network on the terraces has local impact on deep‐water sediment transport and the architecture of gravity flow deposits, it is the regional basin margin to rift axis gradient that dominantly controls deep‐water sediment routing. Furthermore, the gravity flow deposits on the Lomre and Uer terraces were predominantly sourced by rift margin deltaic systems, not from erosion of local uplifted footwall crests, emphasising the significance of hinterland catchments in the development of volumetrically significant deep‐water syn‐rift depositional systems.

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This study uses novel 3D seismic data together with an extensive selection of boreholes to investigate Late Jurassic syn‐rift gravity flow systems on fault‐terraced slopes from the northern North Sea rift system. Our results show how the structurally controlled bathymetry can influence sediment routing pathways and gravity flow depositional architecture in such rift settings.

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Salt flow and overburden across various base‐salt reliefs can influence deformations. In the mid‐slope domain of the Outer Kwanza Basin, salt detached contractions are resulted from the salt flow and overburden across various base‐salt reliefs and encounter a primary salt weld. Serial section restorations on selected 2D cross‐sections illustrate that the salt‐detached contractions have undergone multiphase extension and contraction and spatially translated 12.6‐22 km since Albian.

, Abstract

It is now well‐established that base‐salt relief drives complex deformation patterns in the mid‐slope domain of salt‐bearing passive margins, in a location classically thought to be dominated by simple horizontal translation. However, due to a lack of detailed studies drawing on high‐quality, 3D seismic reflection data, our understanding of how base‐salt relief controls four‐dimensional patterns of salt‐related deformation in natural systems remains poor. We here use 3D seismic reflection data from, and structural restorations of the Outer Kwanza Basin, offshore Angola to examine the controls on the evolution of variably oriented salt anticlines, rollers, and walls, and related normal and reverse faults. We show that the complex geometries and kinematics of predominantly contractional salt structures reflect up to 22 km of seaward flow of salt and its overburden across prominent base‐salt relief. More specifically, this contractional deformation occurs where the seaward flow of salt is inhibited due to: (a) it flowing being forced to flow up, landward‐dipping ramps; (b) it encountering thicker, slower‐moving salt near the base of seaward‐dipping ramps; or (c) the formation of primary salt welds at the upper hinge of seaward‐dipping ramps. The rate at which salt and its overburden translates seaward varies along strike due to corresponding variations in the magnitude of base‐salt relief and, at a larger, more regional scale, primary salt thickness. As a result of these along‐strike changes in translation rate, overburden rotation accompanies bulk contraction. Our study improves our understanding of salt‐related deformation on passive margins, highlighting the key role of base‐salt relief, and showing contraction, extension and rotation are fundamental processes controlling the structural style of the mid‐slope translational domains of salt basins.

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3D seismic survey and novel wellbore data were used to describe the basement geology and its controls in the nucleation and growth of faults during the Early Cretaceous rifting in the northern of Campos Basin (Brazil).

, Abstract

The rift phase of the Campos Basin developed during the Early Cretaceous on a heterogeneous crust comprising structures inherited from the Brasiliano‐Pan African tectonic events, mostly generated during the Neoproterozoic‐Cambrian amalgamation of western Gondwana blocks. The main rifting episode took place from the Hauterivian to the Barremian, then was succeeded by the transition and post‐rift (SAG) phases during the Aptian. Rift faults developed as a result of a progressive rotation of extension from E‐W to NW‐SE. The role of pre‐existing intra‐basement structures on the style and evolution of the rift faults was investigated using 3D high‐resolution seismic data, borehole logs and sidewall samples. Three seismic facies (SF1, SF2 and SF3) and three types of intra‐basement structures (Surfaces, Geobodies and Internal Reflections) were identified and mapped. They represent, respectively, contrasting levels of seismic anisotropy, interpreted as metamorphic foliation, and ductile shear zones that bound rock units with particular seismic facies signatures. Sidewall cores show that banded biotite‐gneiss is the predominant rock type in the eastern half of the study area, while more homogeneous granitoid is the dominant lithology on the west. Such a binary division of lithotypes is consistent with the distribution of mapped intra‐basement seismic facies and features. The contrasting basement heterogeneity across the study area is the major control in the strain distribution during rifting. Where the basement is highly heterogeneous, the pre‐existing fabric was selectively reactivated whenever its orientation was favourable, resulting in faults forming progressively as the extension direction rotates, whilst shallower low to very low angle basement fabric were cross‐cut by rift faults. Where the basement is homogeneous, only early formed faults remain active throughout the rifting.

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Onshore fault illite dates indicate that the North Sea rifting evolved from an initial phase of widely distributed extension that reached far into its margins, followed by the formation of large‐displacement rift faults. This pattern was repeated during the second phase of rifting, and we suspect that a similar pattern may exist for other rifts.

, Abstract

Although seismic and stratigraphic well information put tight constraints on rift basin evolution, eroded rift shoulders commonly expose polydeformed prerift basement whose deformation history may be difficult to constrain. In this work, we apply K‐Ar dating of fault gouge samples from 18 faults to explore the brittle deformation of the well‐exposed eastern rift margin to the northern North Sea rift. We find evidence of clay gouge formation since the Late Devonian, with distinct Permian and Jurassic fault activity peaks that closely match early stages of the two well‐established North Sea rift phases. A marked decay in fault density away from the rift margin confirms a close relationship between rifting and onshore faulting. The results show that initial rift‐related extension affected a much wider area than the resulting offshore rift. Hence our data support a rift model where strain is initially distributed over a several 100 km wide region, as a prelude to the development of the ~150–200 km wide Permo‐Triassic northern North Sea rift as defined by large marginal faults. Towards the end of the second rift phase, strain localises even more strongly to the 25–50 km wide Viking Graben. Interestingly, a period of early widespread extension is seen for both phases of North Sea rifting and may be a general characteristic of continental rifting. The documented prerift faulting and fracturing of the basement since the Devonian weakened the basement and probably facilitated the widespread initial extension that subsequently localised to form the northern North Sea rift, with further localisation to its relatively narrow central part (Viking Graben).

]

[Abstract

Delineating sediment source areas is critical for source‐to‐sink analysis and energy exploration because it can reveal sediment pathways and their associated reservoir rocks. We developed a methodology that integrates stratigraphic forward modelling and inversion analysis to provide a first‐order provenance estimate. By employing a large number of modelling runs, and then applying a neighbourhood algorithm we are able to efficiently identify the best source‐to‐sink reconstruction(s). This methodology only requires shelf‐margin records to calibrate the modelling results, therefore, it can be applied in frontier basins with relatively poor data coverage. We test this methodology on a synthetic example with predetermined parameters, and then apply it to deposits of the Colville Basin of northern Alaska, which is known for its remote location and high cost of data collection. The best‐fit reconstructions from our modelling show that Cretaceous Colville Basin sediments deposited from 120 to 97 My were mainly sourced from the Herald Arch, Chukchi Platform, and western Brooks Range Orogenic Belt, consistent with the interpretations of previous provenance studies. The proposed method provides quantitative constraints for analysing deposits of large, remote, or ultra‐deep basins, particularly those with sparse datasets or where sandstone detrital modes are largely unknown.

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We developed a methodology that integrates stratigraphic forward modelling and inversion analysis to provide a first‐order provenance estimate. By employing a large number of modelling runs, and then applying a neighborhood algorithm we are able to efficiently identify the best source‐to‐sink reconstruction(s). This methodology only requires shelf‐margin records to calibrate the modelling results, therefore, it can be applied in

frontier basins with relatively poor data coverage.

]

[Abstract

Isolated, Miocene continental basins scattered over Israel and Jordan represent the remnants of a continental‐wide fluvial system, which originated in Arabia and transported siliciclastic sediments westward to the deep Levant Basin. These basins define two geographically separated sedimentary provinces. The detrital zircon age spectra in both provinces are dominated by Neoproterozoic U‐Pb ages (550–1,000 Ma), resembling those of Paleozoic‐Mesozoic sandstones exposed along the uplifted Red Sea Rift flank. However, while the southern province exhibits two prominent peaks at ~600 and ~1,000 Ma, similar to those seen in Cambrian‐Ordovician sandstones in southern Israel and Jordan, the northern province shows an additional significant age peak at ~800 Ma and its overall spectrum resembles that of Devonian sandstones in northern Saudi Arabia. These variations distinguish the two Miocene clastic outliers as pertaining to two separate, NW‐directed transport systems delivering siliciclastic sediments from Arabia towards the deep Levant Basin. The detrital zircon U‐Pb‐Hf signal of the Israeli Miocene clastic units differs from that of the River Nile, particularly in the lack of Cenozoic‐Mesozoic‐aged zircons in the former. This allows us to distinguish the properties of the fluvial system that existed in Arabia, on the eastern side of the Red Sea, from that of the River Nile that drained its western flanks. While it is commonly accepted that the (proto‐)Nile River played a key role in the Levant Basin fill, the eastern fluvial system that prevailed on the Arabian side may have been also important.

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Paleogeographic reconstruction of the Levant area in the Early Miocene (15–20 Ma) highlighting the main sediment routing systems into the deep Levant Basin and their detrital zircon and rutile U‐Pb age spectra and a non metric multi‐dimensional scaling map (MDS) of detrital zircon U‐Pb ages of studied Israeli Miocene samples and Miocene Nile Delta samples. ASG, Azrqa Sirhan Graben; DST, Dead Sea Transform.

]

[Abstract

Upscaling Carbon Capture and Storage requires identification of suitable storage sites, with robust reservoir seals. The Utsira Formation in the northern North Sea has been flagged as a target for further storage. However, there are no regional studies of seal variability addressing heterogeneities that could facilitate seal bypass. This study aims to: (a) identify, assess and map the elements that promote or restrict fluid migration, (b) develop a matrix to regionally map containment confidence (CC) and (c) rank the different areas for CO2 containment across the Utsira Formation. The seal and overburden were mapped using a high‐resolution, pre‐stack depth‐migrated 3D broadband seismic reflection dataset and 141 exploration wells. Seal geometry, sandstone presence and sandstone connectivity in the seal and overburden were assigned relative CC scores, which were summed to map overall CC of the Utsira Fm. Indicators for shallow gas and migration were mapped and correlated with the other elements. Areas with the lowest CC are in the west of the Utsira Fm. Here, sandstones within the Seal Interval are connected through the overburden via sandy submarine fans. In the southeast, dipping stratigraphy downlaps onto the Utsira Fm., increasing the potential for connection with glacially‐derived channel‐lobe systems in the overburden. The areas with the highest CC are the central and northeast parts of the Utsira Fm., where the Seal Interval is mudstone‐dominated and parallel to the reservoir, and channel‐lobe systems identified in the Overburden Interval are disconnected from the reservoir. This area coincides with a thick depocentre of the northern Utsira Fm. These results can be used to inform CO2 storage site selection and constrain future CO2 plume simulation analyses for the Utsira Fm. The CC matrix outlined here can also be adapted and applied to regionally assess the containment of other potential CO2 storage reservoirs in any setting.

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Containment Confidence (CC) analysis of the seal and overburden, applied to the northern Utsira Fm. (a) Workflow followed to provide a regional CC summary. (b) Schematic scenarios of seal ond overburden bypass that could result in migration out of the Utsira Fm. and through the overburden. (c) Well data tied to seismic showing the typical seismic response of the sandstone and mudstone interfaces. URU, Upper Regional Unconformity; sandst., sandstone; int., interval

]

[Abstract

In contrast to much of the European Atlantic margin, the influence of salt on basin evolution has received little attention to date in the basins west of Ireland, despite salt being proven in several boreholes. Using an extensive seismic reflection database coupled with data from exploration wells and shallow boreholes, this study maps the distribution and composition of salt layers and investigates their role in the structural evolution of the Slyne and Erris basins offshore west of Ireland. Two salt‐prone intervals have been proven. The Upper Permian Zechstein Group is present throughout the Slyne and Erris basins, whereas the Upper Triassic Uilleann Halite Member is only developed in the Northern Slyne and Southern Erris sub‐basins. Both sedimentary units mechanically detach pre‐, post‐ and intra‐salt stratigraphy. Both salt layers underwent halokinesis during basin development, creating a variety of salt‐related structures. Salt pillows and salt rollers formed in the Zechstein Group, causing folding and rafting in the overlying Mesozoic section, driven by active faulting within the pre‐salt basement. Halokinesis in the Uilleann Halite Member caused thin‐skinned crestal collapse of the overlying Jurassic section above anticlines cored by Zechstein salt. Where both Triassic and Permian salt are present, unique structural geometries are formed when two stratigraphically discrete but kinematically linked halokinetic structures develop. The most common structural configuration consists of a Zechstein salt pillow and an Uilleann Halite salt wall separated by Lower Triassic sandstones. The fold axis of the salt pillow trends parallel to the strike of the salt wall. The results of this study provide a framework for the evolution of halokinetic structures in other basins on the Irish Atlantic margin, give a greater insight into the Permian and Triassic palaeogeography of the region and have more general implications for the evolution of salt‐related structures in rift basins with multiple stratigraphically discrete salt layers.

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Schematic evolutionary model for the formation of different salt‐related structures discussed in this study highlighting their multiphase structural evolution. Seismic lines through the structures illustrated in the Southern, Central and Northern Slyne sub‐basins are shown in Figures 6, 7a and 8b respectively. NAIP, North Atlantic Igneous Province.

]

[

The present study uses data coming from a sequential kinematic restoration to constrain an evolutionary geomechanical model for the Tarfaya basin. The resulting geomechanical model provides more realistic results that are in accordance with seismic information. Further sensitivity analysis of the evolutionary geomechanical model identifies the sedimentation rates as the key driver for the basin system evolution.

, Abstract

We systematically incorporate burial history, sea floor geometry and tectonic loads from a sequential kinematic restoration model into a 2D evolutionary geomechanical model that simulates the formation of the Sandia salt diapir, Tarfaya basin, NW African Coast. We use a poro‐elastoplastic description for the sediment behaviour and a viscoplastic description for the salt. Sedimentation is coupled with salt flow and regional shortening to determine the sediment porosity and strength and to capture the interaction between salt and sediments. We find that temporal and spatial variation in sedimentation rate is a key control on the kinematic evolution of the salt system. Incorporation of sedimentation rates from the kinematic restoration at a location east of Sandia leads to a final geomechanical model geometry very similar to that observed in seismic reflection data. We also find that changes in the variation of shortening rates can significantly affect the present‐day stress state above salt. Overall, incorporating kinematic restoration data into evolutionary models provides insights into the key parameters that control the evolution of geologic systems. Furthermore, it enables more realistic evolutionary geomechanical models, which, in turn, provide insights into sediment stress and porosity.

]

[

The garnet trace is the smoking gun. Pearl River and rivers of coastal SE China carry only a few grossular and andradite garnets, in stark contrast with Neogene sandstones of western Taiwan and modern river sands derived from them, which, like Yangtze sand, are much richer in pyralspite garnet. Garnet geochemical fingerprints concur with zircon geochronological fingerprints to indicate that sand supplied by the paleo‐Yangtze River since the Miocene was transported for ~1000 km by prevailing south‐directed longshore currents, fostering the growth of the Chinese passive margin eventually incorporated in the Taiwan fold‐thrust belt during the Plio‐Pleistocene.

, Abstract

In this study, we use provenance analysis to shed light on the Neogene evolution of river drainage and sediment dispersal in eastern Asia as a consequence of the Himalayan orogeny and topographic rise of the Tibetan Plateau. As an attempt to envisage how sediment‐routing systems operated in the past, and to identify the ultimate source of siliciclastic detritus originally generated in mainland China and now incorporated in, and recycled from, the western Taiwan accretionary prism, we have used Raman spectroscopy of detrital garnet in modern river sands and upper Neogene sandstones, complemented by detrital‐zircon geochronology and by petrographic and heavy‐mineral analysis. Garnet grains are relatively abundant and largely represented by almandine with various percentages of pyrope molecules in Yangtze sand as in western Taiwan sandstones and modern river sand derived from them. Instead, they are rare and largely represented by grossular or andradite in the sand of the Pearl River and of coastal rivers of SE China facing the Taiwan Strait. This finding supports the result of detrital geochronology, which documents a sharp difference between U‐Pb age spectra of Pearl River and coastal SE China zircons (characterised by a Paleozoic‐Mesozoic triple peak) and Yangtze and western Taiwan zircons (characterised by prominent Neoproterozoic, Paleoproterozoic, and latest Archean clusters). The Pearl River and minor rivers facing the Taiwan Strait are thus ruled out as ultimate sources of upper Neogene sandstones exposed today along the western front of the Taiwan fold‐thrust belt. In the envisaged scenario, sand mostly supplied by the paleo‐Yangtze River was entrained for ~ca.1,000 km southward by longshore currents and deposited on the Chinese passive margin before being accreted along the front of the Taiwan orogen since ~6 Ma. Littoral sand drift represents a major factor of long‐distance sediment transport in modern shelves and needs to be taken into full account in source‐to‐sink studies and paleogeographic reconstructions.

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3‐D conceptual block model synthesising the structural styles and processes that occur in isolated‐minibasin provinces at low regional shortening strain.

, Abstract

Shortening styles in salt‐influenced basins can vary markedly, with the volume and distribution of salt prior to shortening being a key control. Here, we use a suite of physical models to examine styles of thin‐skinned regional shortening in settings where the preshortening structure comprised minibasins surrounded by salt (‘isolated‐minibasin’ provinces). Our models show that the high volume of mechanically weak salt localizes lateral regional shortening, with shortening inducing salt flow towards the foreland that subsequently contributes to three key processes – translation, tilting and rotation of minibasins. First, we demonstrate that the flowing salt pushes against minibasins, propelling them in the regional shortening direction. Minibasin translation is enhanced by fast‐flowing salt streams and impeded by basal friction due to welding and base‐salt buttresses. Second, we show how minibasin tilt directions and magnitudes vary spatially and temporally during regional shortening. Minibasins tilt away from zones of pressurized salt, the locations of which may shift due to changes in salt flow regimes. Tilt directions may also change as minibasins pivot on primary welds, or due to forces associated with minibasin collision. Third, minibasins can rotate around sub‐vertical axes during regional shortening. We speculate that this rotation is caused by a combination of: (a) traction imparted on the minibasin boundary by differential horizontal flow of adjacent salt; and (b) pivoting on primary and secondary welds. We synthesize our results in a series of 3‐D conceptual models, before we compare and contrast regional shortening styles and processes in salt‐influenced basins with different preshortening salt configurations. Our findings contribute to the understanding of the geometry and kinematics of shortened salt basins, as well as a deeper understanding of the tectono‐stratigraphic evolution of minibasins.

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The Fucino is an overall dual polarity half‐graben, built around two border fault systems: the northern one lies along the east‐northeast striking Avezzano‐Bussi regional fault‐zone; the other, south‐eastern trending, bounds the basin to the east. Two separate fault‐driven depocentres of fluvio‐lacustrine sequences (maximum thicknesses of ~1,750 m) are present. The northern border fault showed mainly a Late Pliocene activity; the eastern border‐faults reveal a stepwise Pleistocene‐Recent activity. Tectonic depocentres have migrated clockwise through time, and new‐born fault systems have developed at the south‐eastern basin periphery (Gioia dei Marsi area). This, together with the progressive accumulation of throw in time without significant fault lengthening, suggests that the model of fault growth by segment linkage is not the best explanation for this basin.

, Abstract

Normal faults grow either by radial propagation and segment linkage or by accruing displacement without a proportional increase in fault length. To test these competing models of fault growth, a novel 2D seismic stratigraphic interpretation of the recent Fucino Basin of the central Apennines (Italy) has been performed. The Fucino is a major Pliocene‐Quaternary non‐marine ‘extensional collapse basins’, developed immediately after the Apenninic compressional strain had locally abated, and bounded by seismogenic faults that generate strong (Mw = 6–7) and destructive earthquakes. The Fucino is an overall dual polarity half‐graben, built around two border fault systems: the northern one lies along the east‐northeast striking Avezzano‐Bussi regional fault‐zone; the other, south‐eastern trending, bounds the basin to the east. Two separate fault‐driven depocentres of fluvio‐lacustrine sequences (maximum thicknesses of ~1,750 m) are present. One is associated to the northern border faults, with mainly Late Pliocene activity; the second is to the hanging‐wall of the eastern border‐faults and reveals a stepwise Pleistocene‐Recent activity. Tectonic depocentres have migrated clockwise through time, and new‐born fault systems have developed at the south‐eastern basin periphery (Gioia dei Marsi area). This, together with the progressive accumulation of throw in time without significant fault lengthening, suggests that the model of fault growth by segment linkage is not the best explanation for this basin. Instead, the stepwise onset and growth of the Fucino extensional collapse faulting, and its ongoing earthquake hazard, may have been promoted by polyphase inversion tectonics of inherited deep‐seated zones of weaknesses (e.g. Avezzano‐Bussi Line).

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