Sedimentary Package Research Articles

Latitudinal variability in the Quaternary development of the Eurasian ice sheets—Evidence from the marine domain

Abstract Here we present the first compilation of sediment volumes, sedimentation rates, and chronology of Quaternary sediment packages along the entire marine margin of the Eurasian ice sheets (EurIS; British–Irish, Kara–Barents Sea–Svalbard, and Fennoscandian). This compilation allows for a subdivision of the EurIS development into three phases (2.6–1.5 Ma, 1.5–0.78 Ma, and 0.78–0 Ma). At the start of the Quaternary, sedimentation rates increased, relative to pre-Quaternary rates, by an order of magnitude. This abruptness in rate change excludes tectonic raising of landmasses as the main factor, but more likely reflects climate change through increased glacial erosion. The sediment distribution data suggest that the Kara–Barents Sea–Svalbard Ice Sheet (KBSIS) already was quite large at the beginning of the Quaternary, and well before 1.5 Ma it extended to the shelf edge and coalesced with the Fennoscandian Ice Sheet (FIS), which prior to 1.5 Ma most likely was located near the coast. Large ice streams and intense glacial erosion characterized the KBSIS in the 1.5–0.78 Ma time period, whereas the FIS at that time extended farther out on the continental shelf. After 0.78 Ma, a north-south change in EurIS development occurred. In the FIS and the British–Irish Ice Sheet (BIIS), large ice streams developed and shelf-edge glaciations occurred nearly 1 m.y. later compared to the KBSIS. The FIS and BIIS also repetitively coalesced in the North Sea. A significant drop in sediment input along the KBSIS marine margin, to the lowest Quaternary level, suggests a less erosive KBSIS.

Sediment Deposition Following Construction of a Breakwater Harbor: Point Judith Harbor of Refuge, Rhode Island, USA

Breakwaters are a common shoreline protection structure, often trapping sediment as the incoming wave energy is reduced. Quantifying the dynamics and volume of these sediment sinks within a coastal system is an important step toward understanding the sediment budget for a particular coastal area. This study examines the volume of sediment deposited within the breakwater enclosed Point Judith Harbor of Refuge (Rhode Island, United States of America (USA)) in the late 19th century using seismic reflection profiles, bathymetric mapping, and isotopic analysis of core sediment. Geophysical profiles show a district seismic facies up to 4 m thick above the ravinement surface, particularly in the western and central portion of the harbor. Century-scale bathymetric changes revealed shoaling of a similar magnitude, and isotopic data support the deposition of this sediment package within the 20th century. The total volume of sediment within the harbor exceeds 5.0 × 106 m3, with an estimated sand volume of 3.6 × 106 m3. The results show that the harbor is a substantial sediment sink for the Rhode Island South Shore and provide the basis for future studies of the sediment budget for this shoreline.

Basal Accretion Along the South Central Chilean Margin and Its Relationship to Great Earthquakes

AbstractThe south central Chilean margin regularly produces many of the world's largest earthquakes and tsunami, including the 2010 Mw 8.8 Maule and 1960 Mw 9.5 Valdivia events. In 2017, we acquired seismic reflection data along ~1,000 km of the margin using the R/V Langseth's 15 km long receiver array and 108.2 l (6,600 in3) seismic source to image structures associated with these ruptures. We focus on the Valdivia segment with the largest coseismic slip (~40 m). The outer 40 km of the forearc is an accretionary wedge constructed primarily of stacked sedimentary packages with irregular lengths and thicknesses and little along‐strike continuity. Forearc structures indicate that the accretionary wedge grows primarily through basal accretion of the downgoing trench fill. The décollement propagates along a weak boundary near the top of the trench fill but occasionally branches downward into the underthrust sediment along bedding horizons, peeling off slices that are underplated to the forearc. The shallow décollement level and the rarity of underplating events allow most of the trench sediment to subduct. As a result, only ~30% of the incoming sediment has been accreted since the Early Pliocene. This implies that, on average, ~1 km of sediment must subduct beyond the outer forearc, an inference that is supported by our seismic images. We propose that the thickness and great downdip and along‐strike extent of the underthrust layer, which separates the megathrust from the underlying roughness of the igneous ocean crust, ensures a smooth broad zone of strong coupling that generates the world's largest earthquakes and tsunami.

Halokinetic analysis of the Frade field area, Campos Basin, Brazil: Salt tectonics within an offshore strike-slip setting

The Frade field, located within the Campos Basin in the southeastern Brazilian margin, is a key oil field that produces from Oligo-Miocene turbidite reservoirs that derived their structural positioning due to the presence of an underlying salt diapir. The evolution of the Frade salt structure was examined using well data, selected 2D lines, and a 3D volume that were interpreted in detail focusing on the Aptian evaporite interval and its influence on the overburden. Analysis of the salt-sediment interaction indicated a complex deformation history that included five main stages of deformation, some assisted by tectonic reactivation episodes. (1) Post-Albian reactivation of a nearby north–northwest-south–southeast basement fault caused the Albian carbonate interval to fault, forming a west–northwest-east–southeast shear zone with a dextral strike-slip component. This movement initiated thin-skinned tectonics that offset the Albian carbonates and formed a pull-apart basin that accommodated a thick Late Cretaceous interval, which weakened the overburden and allowed for the initial formation of the Frade salt diapir. (2) Renewed diapir growth thickened and redistributed the Cenomanian-Maastrichtian sedimentary package proximal to the Frade salt anticline. (3) An initial and localized collapse of the Frade salt anticline occurred during early Paleogene extension. (4) Paleogene shortening caused the salt to flow, resulting in salt withdrawal in the southeast and diapir rejuvenation near its present-day apex, forming several inversion structures. In addition, the Paleogene shortening resulted in a low-relief anticlinal structure that rotated the turbidites into geometries favoring hydrocarbon accumulation. (5) A return to an extensional regime occurred during the late Oligocene/early Miocene. The results of this study provide a new insight into the development of strike-slip salt tectonic structures and show for the first time within the Campos Basin an Albian-level pull-apart basin that formed in association with salt tectonics.

Evolution assessment of structurally-controlled differential subsidence using SBAS and PS interferometry in an emblematic case in Central Mexico

ABSTRACT The city of Morelia has been affected by Structurally-Controlled Differential Subsidence (SCDS) since at least 1983, modifying civil structures and infrastructure through the appearance of ground failures and differential ground subsidence. The resulting damage to streets, homes, hydraulic lines, and government facilities has caused economic losses worth millions of dollars. An increase in population has led to the overexploitation of groundwater, which is the main trigger for SCDS, while the subsoil's geology and bedrock configuration are considered conditioning factors of this phenomenon. This paper offers an analysis of the SCDS evolution over the last fourteen years and its relationship with groundwater extraction and thickness of unconsolidated sediments. The former was carried out through SAR Interferometry techniques to detect and monitor land subsidence, using Small Baseline Subset (SBAS) from 2003 to 2010 and Persistent Scatterer Interferometry (PSI) from 2014 to 2017. Additionally, groundwater pumping well data and lithological information from boreholes enabled a spatial analysis to evaluate the role of these factors in the development and acceleration of SCDS. The SBAS results show maximum sinking rates of 2.2 cm/yr. with a spatial distribution that is clearly controlled by buried geological structures. In this period, the maximum sinking rates were induced by high groundwater extraction rates in focused areas, while intermediate rates were linked to notable depletion cones. The PSI results indicate a maximum sinking rate of 2.74 cm/yr. and an accelerated subsidence migration to the west, owing to the construction of new wells and persistent high groundwater extraction rates. For both periods, the larger compressible sediment package reveals a good correlation with high subsidence rates, mainly in the hanging wall blocks of the buried faults. The identification of differential subsidence accompanied by high sinking rates in novel areas of Morelia, as well as the detection of the subsidence migration, will provide scientific support to decision-makers for the proposal of engineering solutions and urban planning capable of reducing hydrogeological hazards associated with SCDS.

The magma-poor Somalian continental margin: Lower crustal boudinage and mantle exhumation

Combined interpretation of 2D reflection seismic data and 2D gravity modelling reveals an Iberian-type magma-poor margin across the Obbia Basin in offshore central Somalia. The configuration of the syn-rift and post-rift sediments as well as the upper crust, the lower crust and the Moho delineates four distinct marginal domains. The proximal domain is characterized by thickest crust and narrow underfilled basins, bounded by normal faults piercing the low-reflective upper crust. On top of the upper crust, there is a thick package of Karoo-aged pre-rift sediments (>2 s two-way time (TWT)). A major normal fault, with a throw of 4 s (TWT) dissects the sediments, the crystalline crust and likely also the Moho and represents the necking point, the oceanward limit of the proximal domain and the transition to the necking domain. The necking domain hosts deep half-grabens filled with wedge-shaped syn-rift sediments of likely Early Jurassic age. Crustal thinning was predominantly accommodated by ductile extension of the high-reflective lower crust, resulting locally in lower crustal boudins. With ongoing extension, the upper crust may have become completely detached from the lower crust and rests on the upper mantle at present-day. Within the subsequent hyperextended domain, the Moho shallows significantly and reaches the top basement level in the seaward portion of the line. Normal faults commonly penetrate through the entire crust and bound minor isolated syn-rift deposits. The termination of the hyperextended domain is marked by a major, shallow-dipping, concave downward fault that apparently connects the Moho with the top basement further seaward. Several small continental blocks, so-called extensional allochthones may be present in the transitional area between the coupling point and the exhumation point. The absence of Moho reflections in the east of the profile indicates that crust may be absent and the upper mantle is exhumed.

Triassic faunal successions of the Paraná Basin, southern Brazil

The Paraná Basin was filled by a sedimentary package deposited in successive sedimentation episodes related to the tectonic events that hit the SW portion of the Gondwana. The Triassic portion of this package, known worldwide for its continental tetrapod fauna, occurs only in the southern portion of the basin and is represented by 2 s-order sequences: the Sanga do Cabral Supersequence (SCS - Early Triassic) and the Santa Maria Supersequence (SMS - Middle-Late Triassic). The SCS fauna, including temnospondyls, parareptiles (mainly Procolophon), archosauromorphs, putative synapsids, and a number of indeterminate specimens, is traditionally considered Early Triassic and corresponds to the “Procolophon abundant zone” of the Karoo Basin (the upper levels of the Lystrosaurus AZ), in the upper Katberg Formation, which is Induan to early Olenekian in age. The sedimentary environment of the SCS is thought to be a wide alluvial plain, in which small and shallow channels spread northwards into a vast semiarid environment. By its turn, the Middle-Upper Triassic Santa Maria Supersequence is divided into four third-order sequences, from base to top: Pinheiros-Chiniquá, Santa Cruz, Candelária and Mata. Each of these sequences begins with fluvial deposition (low sinuosity rivers) that is overlain by transgressive shallow lacustrine deposits. The first three of these sequences present a very rich record of fossil tetrapods, including four successive faunal associations: Dinodontosaurus Assemblage Zone (Ladinian, within the Pinheiros-Chiniquá Sequence), Santacruzodon AZ (Ladinian/Carnian, in the Santa Cruz Sequence), Hyperodapedon AZ (Carnian) and the Riograndia AZ (early Norian), the latter two respectively at the base and top of the Candelária Sequence. In general, the lower portion of the package (Pinheiros-Chiniquá and Santa Cruz Sequences) was deposited under more basic and dried environmental conditions and are dominated by synapsids, while the top of the section (Candelária Sequence) is characterized by more acid and humid conditions and by a shift in the faunal content, with diapsids as dominating forms and presenting an increase of diversity compared to the lower biozones.

The Late Pleistocene-Holocene sedimentary evolution of the Sines Contourite Drift (SW Portuguese Margin): A multiproxy approach

The Sines Contourite Drift (SCD), located in the Alentejo margin, southwest Iberian continental margin, has been through many depositional phases in result of climatic variations and bottom current oscillations, which determined a variable depositional pattern and an irregular sedimentary evolution since the Late Pleistocene. The SCD, being in the main path of the Mediterranean Outflow Water (MOW), which greatly constrains the sedimentary building of this drift, constitutes the distal part of the Gulf of Cadiz Contourite Depositional System and its sedimentary evolution therefore reflects the history of MOW variations.In order to investigate this, we report on a multiproxy analysis of grain-size, carbon content and physical, geochemical, and environmental-magnetic properties on the AMS 14C dated 350-cm long gravity core CO14-GC-07, retrieved in the SCD, at 1425 meters water depth (mwd). The main objective is to reconstruct the evolution of the sedimentary package of the SCD from >43 cal kyr BP to Present and bring new insights about the impact of bottom currents' activity on the morphosedimentary evolution of the margin. Results show the existence of four distinct depositional phases in response to climate variations and bottom current oscillations during the Late Pleistocene-Holocene. Phase 1 (350–322 cm: >42.9 cal kyr BP) occurred in Marine Isotope Stage (MIS) 3 and presents silty-muddy sediments with presence of shell fragments and moderate bioturbation. Phase 2 (322–176 cm: >42.9–~30.5 cal kyr BP), which lasted from middle MIS 3 to the onset of MIS 2, reveals sediment coarsening towards the top limit, suggesting climate cooling and strong bottom current winnowing. Phase 3 (176–144 cm: ~30.5–17.1 cal kyr BP) covers most of MIS 2 prior to the last deglaciation and shows the sharpest variations on all sediment properties and the coarsest sediment facies, with Fe-rich layers associated with the increase of terrigenous input and sea-level regression that coincide with the enhancement of MOW. Phase 4 (144–0 cm: <17.1 cal kyr BP) is associated with the deglacial sea-level rise and represents a calmer depositional environment with finer sediments and increasing contributions of biogenic material. The MOW is the most prominent bottom current and the most active seabed shaping agent in the study area, whose vertical shifting during glacial (~800–2200 mwd) and interglacial (600–1500 mwd) periods is coincident with the most active morphosedimentary sector of the area, contributing to the development of landslide scars and sediment waves.

An Early Paleozoic Tectonic Mélange at the Western Margin of West Cathaysia: Constraints from Organic‐walled Microfossils

AbstractThe Jiangshan‐Shaoxing‐Pingxiang Fault (JSP Fault) is traditionally considered as the boundary between the Yangtze and Cathaysia blocks in South China. Whether the previously defined Shenshan and Kuli formations located along the JSP fault and near the Xinyu City, Jiangxi Province, are continuous strata or parts of a tectonic mélange is important for understanding the geological history of South China. A carbonaceous phyllite from the area, previously considered as part of the Neoproterozoic Shenshan and Kuli formations, is analyzed palynologically in this study. The Asteridium‐Comasphaeridium acritarch assemblage found in the slate can be correlated with the basal Cambrian Asteridium‐Heliosphaeridium‐Comasphaeridium (AHC) acritarch assemblage in Tarim and the Yangtze Block. The early Cambrian biostratigraphical age assignment for the carbonaceous phyllite indicates the presence of both Neoproterozoic and Cambrian rocks in the sedimentary package, and supports that the package is a part of tectonic mélange rather than a continuous Neoproterozoic strata. The Cambrian slate is the youngest known lithology in the mélange at present.

Basin analysis using seismic interpretation as a tool to examine the extent of a basin ore ‘play’

Stratiform and stratabound base metal ores typically form in sedimentary basins during the overall rifting process with mineralising fluids transported along the growing normal faults. Understanding the detailed structural evolution, i.e. the timing, the growth and the extent of the faults, and the distribution and thickness of the syn-faulting sedimentary packages, is critical for focusing exploration efforts. In this paper, we describe how seismic interpretation and basin analysis techniques can help to do this. We assess the potential for Pb-Zn mineralisation within the Northumberland Trough, northern England, in the context of the wider Early Carboniferous basin evolution and the associated base metal ores. Through structural interpretation of seismic reflection data, we consider the detailed evolution of the fault geometries and sedimentation in time and space, to show the extent and distribution of the Early Carboniferous faulting and growth packages at depth in the study area. We conclude that basin evolution and structural framework in northern England is very similar to that associated with the significant Pb-Zn mineralisation in Ireland. We suggest a refined model for the Carboniferous evolution of this part of the basin. The study demonstrates how the techniques of basin analysis can be a used in ore exploration to establish whether the basic structural and sedimentary framework exists to enable mineralisation. In addition to assessing the general potential of base metal mineralisation, a more precise identification of potentially suitable areas for further investigation can be made. The seismic data and basin analysis approach used in this paper and exemplified through the Northumberland case should be directly applicable to any basin ore 'play' associated with rifting and/or sedimentation. The added, significant advantage of this method is the ability to assess the 3D fault geometries, including fault linkage and growth in space and time, and the associated sedimentation – an unachievable outcome if relying solely on other geophysical and geological data traditionally used in regional ore exploration.

Using Ambient Noise Seismic Interferometry and Local and Teleseismic Earthquakes to Determine Crustal Thickness and Moho Structure of the Northwestern Gulf of Mexico Margin

AbstractThe northwestern part of the Gulf of Mexico has undergone two episodes of continental rifting and collision and produced structural artifacts that are now buried under many kilometers of sediments, complicating investigations of the region. The deep sedimentary package precludes outcrops and points to a need for the application of seismic techniques, but low rates of seismicity in the region and sparse seismic monitoring limit the utility of traditional seismic methods. We therefore use diverse data to perform two‐dimensional seismic tomography across the dry land portion of the margin. Data are gleaned from teleseismic and regional earthquakes, postcritical SsPmp arrivals, and direct P wave energy identified with seismic interferometry that were recorded by a broadband, three‐component array and partially overlapping short‐period, vertical‐component array. The Pn and postcritical SsPmp phase help constrain the Moho discontinuity, which a previous receiver function study suggested was absent beneath the seaward portion of this transect. A high‐velocity body is observed in the crust at the same location as the Houston Magnetic Anomaly, possibly marking rocks from the Alleghenian continental assembly. The crust thins from NW to SE, indicating that extension occurred mostly to the south of the Ouachita orogeny. Our model indicates that the margin's sediment package reaches a maximum thickness of ~15 km at the coast and becomes unresolvably thin near the Llano Uplift.

The Norwegian–Danish Basin: a dynamic setting for subsurface sand remobilization – established concepts on distribution and controlling factors

Abstract The Norwegian–Danish Basin is characterized by a depositional environment governed by incised valleys, localized sand deposition and rapid progradation of thick sediment packages during the Paleogene and Neogene. Subsurface sand injectites occur at five locations, with distinctive geometries and injection styles. Such vary from short-distance injectites where injected dykes and sills are in direct contact with the parent sand, to a long-distance sand extrudite &gt;1 km vertically above the proposed parent sand. These endmembers establish the Norwegian–Danish Basin as a dynamic environment for subsurface sand remobilization. Although formation models exist for the injectites at each of the five locations, general considerations of sand injection mechanisms in the Norwegian–Danish Basin remain untested. This study presents a synthesis of geometrical characteristics, sand injection style and controlling factors for sand injection in the Norwegian–Danish Basin. By reviewing the existing literature and including new data, the study qualitatively addresses the effects of parent-sand distribution on injection style at the five locations, the overpressure generating mechanisms and the importance of faulting as a trigger mechanism. The results show that short-distance injectites typically occur in areas with a confined parent sand and that salt-related faulting is locally important as a trigger mechanism for sand remobilization. The main overpressure generating mechanism is differential loading and lateral transfer of pressure. The case studies also show a trend between larger depocentres required for remobilization of more distal parent sands relative to the depocentre. The results confirm the prevailing consensus that local conditions related to parent sand distribution and burial depth partly control injection geometry and style.

Paleomagnetic Constraint of the Brunhes Age Sedimentary Record From Lake Junín, Peru

Normalized remanence, a proxy for relative geomagnetic paleointensity, along with radiocarbon and U-Th dates, facilitates the generation of a well-constrained chronology for sediments recovered during International Continental Scientific Drilling Program (ICDP) coring of Lake Junín, Peru. The paleomagnetic record of the ~88 meter stratigraphic section from Lake Junín was studied, and rock magnetic variability constrained, through analysis of 109 u-channel samples and 56 discrete samples. Downcore variations in sediment lithology reflect climate and hydrological processes over glacial-interglacial time frames and these changes are strongly reflected in the bulk magnetic properties. Glacial sediments are characterized by higher detrital silt content, higher magnetic susceptibility and magnetic remanence values, and a magnetic coercivity that is characteristic of ferrimagnetic (titano)magnetite and/or maghemite. Interglacial sediments and low lake-level facies are dominated by carbonate lithologies and/or peat horizons that result in lower magnetic concentration values. Sediments with moderately high NRM intensity (>1 x 10-3 A/m) have well-resolved component directions and inclination values that vary around geocentric axial dipole expectations. This remanence value can be used as a threshold to filter the lowest quality paleomagnetic data from the record. Normalized NRM intensity values are also sensitive to lithologic variability, but following NRM remanence filtering, only the highest quality ferrimagnetic dominated data are retained which then show no coherence with bulk magnetic properties. Constrained by the existing radiocarbon based chronology over the last 50 kyrs and 18 U-Th ages that are restricted to five interglacial sediment packages, filtered normalized remanence parameters compare well with global relative paleointensity stacks, suggesting relative variations in geomagnetic intensity are preserved. By adjusting the existing age-depth model we improve the correlation between the Junín normalized intensity record and a well-dated RPI stack and RPI model. We then incorporate these paleomagnetic tie points with the existing radiometric dates using a modeling approach to assess uncertainty and refine the age-depth model for Lake Junín. In combining relative and radiometric dating, the new age-depth model captures glacial-interglacial variations in sedimentation rate and improves the orbital-scale age model for the sediments accumulated in Lake Junín basin over most of the Brunhes.

Towards an understanding of the Ca isotopic signal related to ocean acidification and alkalinity overshoots in the rock record

In this contribution, we explore the idea that the Ca isotope proxy has utility as an indicator of carbonate authigenesis (i.e., post-depositional precipitation of CaCO3 within the sedimentary package). Given the strong contrast in isotopic fractionation factor between the formational and diagenetic environments, Ca isotopes have the potential to fingerprint carbonate authigenesis when it occurs close to the seawater-sediment interface. We demonstrate that Ca isotopes are particularly applicable to exploring ocean acidification events, and potentially ocean anoxic events, and focus our attention on ocean acidification related to the Paleocene-Eocene Thermal Maximum (PETM). We present three scenarios that vary in the magnitude and duration of the carbon fluxes that are simulated using an Earth System model of intermediate complexity (cGENIE), and we use the cGENIE output to constrain the upper boundary conditions of 1-D reactive transport models of authigenesis and recrystallization in the sedimentary section. Along with simple mixing calculations, the models inform our exploration of the hypothesis that authigenic carbonate induced by a saturation state overshoot during the PETM explains recently published Ca isotope records, and perhaps bulk carbonate records over Ocean Anoxic Event (OAE) 2. Our simulations suggest that fractionation factor variability does not explain the PETM δ44Ca records, and we propose a δ44Ca-CaCO3 space framework to assist with the elucidation of authigenic additions over time scales that are short relative to the residence time of Ca in the ocean (~1 Ma). Ultimately, we find that the ‘authigenic zone’ generated in the sedimentary column may be influenced by alkalinity overshoots or redox state; the CaCO3 produced in this zone can overprint temporal signals with depth-dependent signals that reflect lithology and sedimentation rate and need not be spatially uniform, even when driven by a global event. Ultimately, we demonstrate the utility of Ca isotopes for exploring short time scale climatic events and a quantitative framework to guide interpretations.

The Rockall and the Orphan Basins of the Southern North Atlantic Ocean: Determining Continuous Basins across Conjugate Margins

Reconstructions of the opening of the North Atlantic Ocean generally result in the Orphan Basin, offshore Newfoundland, Canada, lying approximately conjugate to the rift basins on the Irish Atlantic margin at the onset of seafloor spreading toward the end of the Early Cretaceous. Most of these plate reconstructions have involved rigid plates with plate motions based solely on the interpretation of oceanic magnetic anomalies. In particular, these reconstructions often show the Rockall Basin, west of Ireland, forming a continuous Mesozoic basin with the West Orphan Basin, offshore Newfoundland. However, more recent plate reconstructions involving deformable plates have called this conjugate relationship into question. The goal of this study is to investigate the validity of this potentially continuous basin system by reconstructing and restoring present-day seismically-constrained geological models both spatially and temporally back to their original configurations pre-rift. By comparing the reconstructions in terms of sedimentary package thicknesses and crustal thicknesses in 3D, using both rigid and deformable plate reconstructions to orient the reconstructed models, we are able to test different basin connectivity scenarios using a multidisciplinary approach. Our analysis provides subsurface geophysical support for the hypothesis that the Rockall Basin was originally conjugate to and continuous with the East Orphan Basin during Jurassic rifting, later linking to the West Orphan Basin as rifting evolved during the Early Cretaceous. This complex basin evolution example highlights the need for using 3D rifting mechanism models to properly understand the fundamental driving forces during rifting and has significant implications for assessing basin prospectivity across conjugate margin pairs.

Compositional modification and trace element decoupling in rutile: Insight from the Capricorn Orogen, Western Australia

The trace element composition of rutile is widely used to constrain the temperature and timing of geological events, the provenance of detrital grains and as a potential indicator of proximal ore mineralisation. Understanding the processes of trace element mobility in rutile is therefore paramount to the successful application of rutile geochemistry to geological research. Using a combination of electron backscattered diffraction and laser-ablation split-stream ICP-MS, we studied the microtextures, trace-element contents and U–Pb isotopes of rutile from the siliciclastic rocks of the Mesoproterozoic Edmund Group, Capricorn Orogen (Western Australia). The Capricorn Orogen experienced multiple tectonothermal events during the Proterozoic under conditions spanning from low- to high-grade metamorphism. Rutile textures, U–Pb ages, trace-element variations and calculated Zr-in-rutile temperatures reveal different generations of rutile, including detrital or metamorphic-hydrothermal grains.U–Pb age data of detrital rutile indicate a wide span of ages (ca. 2.7–1.7 Ga) of the source rocks and Cr-Nb compositions point to metamafic, metapelitic and granitic origins for this rutile. The youngest detrital ages of 1.68 Ga constrain the maximum depositional age of the sedimentary package. The comparison of age spectra across the stratigraphy indicates a change in provenance, with sourcing from circa 1.7 Ga rocks during early stages of deposition, followed by unroofing of older basement during deposition of the youngest units of the Edmund Group. Partial resetting of detrital rutile is observed in the increase of 207Pb/206Pb ratios, accompanied by a decrease of Zr-in-rutile calculated temperatures. Lower-temperature metamorphic-hydrothermal rutile yielded imprecise Mesoproterozoic ages (1.3–1.1 Ga). This rutile has significant variations of Zr/Hf and Nb/Ta extending to values both lower and higher than primitive mantle, which may record crystallisation from, or interaction with hydrothermal fluids. Partial remobilisation of trace elements in metamorphic-hydrothermal rutile is demonstrated by sub-grain domains with sharp geochemical variations and by evidence of element diffusion at grain margins. Orders of magnitude differences in trace element concentrations (including Nb, Cr and Zr) in metamorphic-hydrothermal rutile grains suggest thorough investigation of rutile textures needs to be carried out prior to using the trace element concentrations in rutile for provenance and Zr-in-rutile temperature studies.

Joint Inversion of High-Frequency Receiver Functions and Surface-Wave Dispersion: Case Study in the Parnaíba Basin of Northeast Brazil

ABSTRACTWe assess the performance of the joint inversion of receiver functions (RF) and surface-wave dispersion in the characterization of the sedimentary package comprising the Parnaíba basin. This procedure is routinely utilized in passive-source crustal studies to retrieve S-wave velocity variations with depth, and has seldom been used with higher-frequency datasets to investigate fine sedimentary structure. The Parnaíba basin is a Paleozoic cratonic basin composed of five supersequences, accumulating ∼3.5 km of sedimentary rocks interbedded by Late Cretaceous diabase sills. The dataset used for this research was acquired between 2015 and 2017 through deployment of 10 short-period and one broadband seismic stations distributed along an approximately 100-kilometer-long linear array in the center of the basin. The deployment was carried out under the Parnaíba Basin Analysis Project, a multi-institutional and multidisciplinary effort funded by BP Energy do Brasil. High-frequency RFs (f&amp;lt;4.8 Hz) were calculated from deconvolution of teleseismic P waveforms (30°&amp;lt;Δ&amp;lt;90°) after rotation into the great-circle path, whereas high-frequency dispersion curves (0.25–2 Hz) were obtained through multiple filter analysis of empirical Green’s functions developed from cross-correlation (ZZ component) and stacking (six months) of time–frequency-normalized ambient seismic noise recordings. S-wave velocity–depth profiles down to ∼5 km depth were developed through an iterative, linearized joint inversion approach. Comparison to independent active-source seismic profiles overlapping with our passive-source seismic line reveals the inverted velocity models successfully retrieve sedimentary thickness (top of the Cambrian), sedimentary velocity structure, and depth to the Cenozoic sedimentary sequence. In addition, high-velocity zones at depths ranging from 1.5 to 2.5 km are observed in the inverted velocity–depth profiles, which are interpreted as due to the Late Cretaceous sills interbedding the basin’s sedimentary rocks. The relative low cost of our approach makes it ideal for basic characterization of relatively unknown sedimentary basins.

Büyük Menderes Granbeni'nin Rolling Hinge (Yuvarlanan Reze) Modelinde Supra-Detachment (Sıyrılma Üstü) Havzadan Rift Havzasına Evrimi

Two types of basins developed in the Western Anatolian extensional tectonic system during the Miocene- Quaternary interval, supra-detachment and rift basins, in the form of a rolling-hinge mechanism. In this study, stratigraphic and structural data on the presence of a rolling-hinge model in the area between Buharkent-Buldan on the northern edge of the Buyuk Menderes Graben are presented for the first time and the geological evolution of the graben is discussed. In the light of obtained field data, the Miocene-Quaternary sequences deposited on the northern edge of the Buyuk Menderes Graben were evaluated under 4 main sedimentary packages, which are separated from each other by angular and/or intrabasinal unconformities. These are the Lower-Middle Miocene (1st Package) and the Middle-Upper Miocene (2nd Package) which were deposited in the supra-detachment basin, and the Plio- Quaternary 3rd and 4th packages formed in the rift basin. The structural elements that provide the basin formation and deformation of the region are the Miocene Buyuk Menderes Detachment Fault, the Pio-Quaternary Gokdere Fault, and the Holocene Buharkent Fault Segment that cuts the youngest graben basin-fill located in the most eastern part of the Buyuk Menderes Fault System. The main fault contacts of the supra-detachment basins characterizing the Miocene period are represented by a structural boundary of gneisses and schists belonging to the Menderes Massif, which is a relict of the effective compressional tectonic products of the Eocene–Oligocene interval. Due to the effectiveness of low-angle faults in the Menderes Massif until the end of Pliocene, a high rate of extension occurred; because of this, the crust thickness was reduced. As a result of cooling of the crust during Quaternary, the supra-detachment basin system was replaced by a rift system and the Menderes Massif was divided into blocks along the high-angle boundary faults of the rift basin. Field observations and kinematic analysis reveal that tectonic structures on the northern margin of the Buyuk Menderes Graben evolved from low-angle to high-angle normal faulting, and were rejuvenated southward parallel to the basin propagation in a rolling-hinge model. Thus, the basin formation also evolved from being supra-detachment to the rift type.

Aspectos texturais dos sedimentos quaternários da planície costeira do sul do estado de Santa Catarina, Brasil: região das lagoas dos Esteves, Faxinal e Mãe Luzia

As planícies costeiras se constituem de ambientes extremamente dinâmicos que comportam pacotes sedimentares de relevância para os estudos costeiros. Estes pacotes sedimentares denotam características dos agentes de transporte e dos ambientes de deposição, sendo estas características de fundamental importância para o conhecimento da história geológica local. Portanto, o objetivo deste trabalho é caracterizar, através da análise textural, os sedimentos quaternários e os ambientes deposicionais da planície costeira que representa o sistema deposicional laguna-barreira IV na região das lagoas dos Esteves, Faxinal e Mãe Luzia, sul do estado de Santa Catarina, Brasil. A poligonal de estudo compõe-se de uma área de barreira e uma área de retro barreira. Sendo a área de barreira composta por sedimentos arenosos oriunda de ambientes eólicos e marinhos, e a área de retro-barreira por sedimentos areno-lamosos de ambientes lagunares.

New U[sbnd]Pb, Hf and O isotope constraints on the provenance of sediments from the Adelaide Rift Complex – Documenting the key Neoproterozoic to early Cambrian succession

The Adelaide Rift Complex is arguably one of the most complete and best studied Neoproterozoic to early Cambrian successions worldwide, preserving evidence of the breakup of Rodinia, two Cryogenian glaciations and the interglacial phase, and one of the best documented Ediacaran to early Cambrian biotic transitions. However, the complex and protracted tectono-sedimentary history of this 0.8–0.5 Ga province is still being debated. We present new and published UPb ages and Hf and O isotope data for detrital zircons from the Adelaide Rift Complex, representing the most complete assembly of such data for this succession. Deposition during initial mid-Tonia extension was largely sourced locally from rift shoulders. As the basin evolved from rift- to sag-phase following continental breakup in the Cryogenian the provenance regions extended to more distal late Mesoproterozoic terranes to west and northwest. New data from Sturtian Glacial Epoch deposits are consistent with termination of this event at 0.66 Ga, with most deposition during deglaciation. Uplift of the Musgrave region during the Ediacaran to early Cambrian Petermann Orogeny led to dominant sediment supply from that terrane at that time in the north. In the south, earliest Cambrian deposition followed local tectonism, initially revitalising local proximal basement sources. An abrupt change in provenance occurred at the base of the Cambrian Kanmantoo Group, the youngest sediment package in the south. Paleocurrent data indicates transports from the south, probably from formerly contiguous Antarctica, possibly reflecting the onset of convergent tectonics and deposition in a foreland basin, consistent with the near depositional age of the dominant detrital zircon population. Whilst several episodes of significant crustal reworking are identified in the Hf and O isotope data, many of the zircon TDM ages lie within 0.5 Ga of the UPb ages indicating that new additions from the mantle were common in the provenance regions.