Sedimentary Constraints Research Articles

Channel Profiles Reveal Fault Activity along the Longmen Shan, Eastern Tibetan Plateau

Assessing fault activity in regions lacking Quaternary sedimentary constraints remains a global challenge. In this study, we used channel slope distribution to examine variations in rock uplift along faults. By comparing channel steepness with published low-temperature thermochronology and paleo-seismic data, we identified deformation changes both perpendicular to and along the Longmen Shan at various time scales. Our data revealed distinct fault segments displaying distinct thrust activities along the Longmen Shan’s strike. In the southern segment, the Dachuan fault exhibited the highest activity, and its movement had persisted for millions of years. In the central segment, the Wenchuan fault was active during theearly Quaternary but has become dormant since the late Pleistocene. Within the past millions of years, the Yingxiu and Pengguan faults displayed significant vertical displacement. Fault activity in the northern Longmen Shan was relatively weak, with the Qingchuan fault transitioning from thrust movement during the Neogene to pure strike-slip activity since the Pleistocene. Overall, the Dachuan and Huya faults exhibited deformation patterns similar to the Yingxiu fault during the Quaternary. Similar to the Yingxiu fault, which triggered the Wenchuan earthquake, the Dachuan and Huya faults possess the capacity to produce significant earthquakes in the future. The variations in deformation perpendicular to and along the Longmen Shan fault system underscore the importance of upper crustal shortening in shaping the rock uplift patterns and topography of the eastern Tibetan Plateau margin.

Stratigraphic and sedimentary constraints on presalt carbonate reservoirs of the South Atlantic Margin, Santos Basin, offshore Brazil

Stratigraphic and sedimentary constraints on presalt carbonate reservoirs of the South Atlantic Margin, Santos Basin, offshore Brazil

Morpho-Sedimentary Constraints in the Groundwater Dynamics of Low-Lying Coastal Area: The Southern Margin of the Venice Lagoon, Italy

Complex freshwater–saltwater exchanges characterize most Holocene groundwater aquifers in low-lying coastal plains around the world, particularly in mechanically drained territories. This is due to the combination of several factors that control groundwater dynamics, including the high variability of the Holocene coastal deposits that host the shallow aquifers and the water management practices. The relationships between the stratal architecture of sedimentary deposits and the vertical changes in the salinity of the phreatic aquifer are poorly studied although they represent an issue of primary importance for a sustainable use of water resources and for agriculture. This research work is focused on the influence of sedimentary constraints, i.e., stratigraphic discontinuities and related changes in permeability in shaping salinity stratification into the unconfined aquifer at the southern margin of the Venice lagoon (Italy). Nine sites have been investigated by collecting sediment cores for facies analysis and monitoring water electrical conductivity in piezometric wells. The results show that buried channelized sandy deposits can enhance salinity mitigation of the phreatic aquifer in conjunction with precipitations and sufficient freshwater supply from nearby rivers and irrigation channels. Our analyses also reveal that the differences in stratigraphic architecture of the upper 10 m of the subsoil determine different fresh–saltwater dynamics of the phreatic aquifer. In particular, three possible behaviors can occur: (i) where the subsurface is characterized by the presence of a thick, up to 5 m, paleochannel, a freshwater lens is always present in the most surficial part of the phreatic aquifer; (ii) where the subsurface is composed by fine-grained sediments of marsh and lagoon paleo-environment, the phreatic aquifer tends to be salt-contaminated over its entire thickness; (iii) where the subsurface contains thin, up to 2–3 m, paleochannel deposits, the fresh–saltwater dynamics of the most surficial part of the phreatic aquifer varies more during the year, as a result of seasonal precipitation trend. The provided characterization of saltwater dynamics represents the basis for planning mitigation measures to improve the farmland productivity of the Venetian coastal plains.

New sedimentary constraints for the Late Devonian north-dipping Paleo-Tethys subduction and its eastern continuation on Hainan Island, South China

As a major boundary between the Simao-Indochina and South China blocks, the Jinshajiang–Ailaoshan–Song Ma suture zone preserves the remnants of a back-arc basin or a branch of the Paleo-Tethys Ocean. However, whether this suture zone extends eastward to the Hainan Island is still controversial. Here, we use detrital zircon U–Pb geochronology to explore the source-to-sink characteristics of the Lower Carboniferous-Lower Permian strata in Hainan Island and mainland southeast China (SE China). The results, combined with published data for the Devonian-Triassic sandstones from Hainan and SE China, show that the Devonian-Lower Permian samples display similar detrital zircon age populations at ∼430 Ma, ∼930–980 Ma, ∼1600–1800 Ma and ∼2400 Ma. However, the Upper Permian-Triassic sandstones have a predominant zircon population at ∼370 Ma, indicating a dramatic change in the detritus provenance for Hainan-SE China since the early Late Permian. The presence of similar 400-350 Ma detrital zircons peaked at ∼370 Ma with ϵHf(t) values from −12 to +3 in the sedimentary rocks from both Hainan-SE China and Simao-Indochina blocks indicates that these two terranes should have a similar detritus source with abundant Late Devonian magmatic rock exposure during the Late Permian-Triassic. These Late Devonian magmatic rocks were most likely formed by the north-dipping Paleotethyan subduction. This conclusion is consistent with the recent discovery of Upper Devonian arc-related tuffs, volcaniclastics, tuffaceous chert and rhyolite in the North Qiangtang, Simao-Indochina and East Malaya terranes, and possibly also in the southern Hainan. These Upper Devonian rocks could have acted as detritus source for the basins in SE China-Hainan, as well as the Youjiang Basin in SW China, after the collision between the Indochina and South China blocks. Combined with the transition from a carbonate platform to clastic facies in the early Late Permian in SE China, the Indochina-South China collision on Hainan Island may have occurred at ∼266-260 Ma, earlier than that (∼250-230 Ma) along the Jinshajiang–Ailaoshan–Song Ma suture zone. Such a temporal–spatial source-to-sink relationship between the Late Devonian arc and basins on the southern margin of South China suggests that SE China-Hainan should be located within the Paleo-Tethys rather than the Paleo-Pacific tectonic domain during the Early Carboniferous-early Late Permian.

Geochemical and sedimentary constraints on the formation of the Venta Micena early Pleistocene site (Guadix-Baza Basin, Spain)

Despite the paleontological relevance of the terrestrial Early Pleistocene Venta Micena bonebed (Baza Basin, Spain), it lacks a comprehensive geochemical/sedimentological study. Here, we demonstrate that the 1.5-m-thick Venta Micena limestone formed in a relatively small freshwater wetland/pond located at the periphery of the large saline Baza paleolake. Two microfacies are observed, with high and low contents of invertebrate fossils, and which originated in the centre and margin of the wetland, respectively. X-ray diffraction (XRD) mineralogy and paleohydrological characterization based on ostracod and bulk-rock geochemistry (δ13C and δ18O) indicate that the limestone reflects a general lowstand of the Baza lake, permitting the differentiation of freshwater wetlands that were fed by adjacent sources. Conversely, during highstands, the Baza lake flooded the Venta Micena area and the freshwater fauna was replaced by a saline one. Bulk-rock isotopic data indicate that the lower interval C1 of the limestone (bone-rich in marginal settings) displays general negative values, while the upper interval C2 (bone free) displays less negative values. The bones of predated mammals accumulated in the marginal areas, which were flooded and buried by recurring water-table fluctuations. Lake dynamics played a critical role in bone accumulation, which was previously considered as representing a hyena den.

Reconstructing environmental signals across the Permian-Triassic boundary in the SE Germanic basin: Paleodrainage modelling and quantification of sediment flux

Reconstructing sediment load in deep-time is one of the greatest challenges in the reconstruction of ancient sediment routing systems, particularly because solid statistical models are absent and paleo-climatic, paleo-tectonic, and sedimentary constraints are lacking. This study proposes a reliable workflow for the estimation of paleo-sediment fluxes (Qs) applying the BQART model to a case study from the SE Germanic Basin across the Middle Permian – Early Triassic interval. The input parameters of the simulations derive from: integrated plate modelling and structural kinematics; paleodrainage and paleogeographic reconstructions; global circulation models; and sandstone compositional signatures. We apply Monte Carlo simulation to overcome the input uncertainties for eight different scenarios obtained from the combination of two area estimates, two climate models, and two time resolutions. All the models are in general agreement and show changes in sediment flux (i) being steady or declining slightly through the Middle Permian, (ii) an increase of 31% at the beginning of the Late Permian (3.6–4.6 Mt yr−1), (iii) and a nearly 100% rise at the onset of the Early Triassic (7.4 Mt yr−1). The variation of sediment load across the PTB is coeval to the transition from meandering/sabkha to perennial braided depositional settings recorded from the well data of Obernsees-1 and Lindau-1; it results from both increased tectonism and seasonal precipitation. The Qs estimates agree with those of modern drainages under analogous environmental conditions, highlighting the reliability of the workflow included in this study for the quantification of sediment flux in deep time. Furthermore, the results of this study provide new insights on the highly debated evolution of the continental sequences across the PTB with strong implications for both past and future paleo-environmental reconstructions.

Sedimentary responses to rifting of the Upper Yangtze Block (Sichuan basin area) in the Middle-Late Permian

中-晚二叠世，上扬子（四川盆地区）碳酸盐岩台地内发育三条北西-南东走向的裂谷，它们是重要的油气储集区带，如普光和元坝气田就产于开江-梁平裂谷两侧。但是对这些裂谷的开始时代和构造成因等关键地质问题，还缺乏详细的沉积学研究，且存在较大争议。本文通过大比例露头剖面和钻井岩芯测量以及详细的沉积相分析对比，对开江-梁平裂谷的构造沉积过程进行了深入细致的研究。调查发现，在开江-梁平裂谷北缘，中二叠统栖霞组上段至茅口组2段发育大规模斜坡相碳酸盐岩滑塌堆积，揭上扬子地块四川盆地区于中二叠世栖霞晚期开始发生伸展裂解。茅口组3段至上二叠统长兴组为超覆于滑塌堆积之上的硅质岩和碳-硅质泥岩等深水盆地相沉积，表明开江-梁平裂谷从中二叠世茅口晚期开始由伸展裂解转变为区域沉降，即开江-梁平裂谷经历了伸展裂解和区域沉降两个构造沉积阶段。伸展裂解阶段，开江-梁平裂谷是一个发育于碳酸盐岩台地内的不对称海相半地堑盆地，北侧为发育大规模碳酸盐岩滑塌堆积的下盘断斜坡带，南侧为发育缓斜坡生物碎屑滩和礁灰岩的上盘缓斜坡带；区域沉降阶段，开江-梁平裂谷表现为东翘西降的不均匀沉降，发育自东向西不断进积的潮坪-潟湖相和高能浅滩相沉积等。本文研究成结果对分析和圈定四川盆地区中-晚二叠世油气储集相带的时空分布具有重要科学意义，也为研究碳酸盐岩滑塌堆积提供了一个新范例。;Three rift valleys in NW-SE strike have been outlined by the gas and oil explorations in the Upper Yangtze Block in the past 20 years. More importantly, these two rift valleys are the locations of proved gas fields in the present Sichuan Basin, such as the Puguang and Yuanba gas fields developed on both sides of the Kaijiang-Liangping (KL) rift valley. However, the initiating ages of these rift valleys and their tectono-sedimentary evolutionary processes are still unclear, mainly because of lacking the sedimentary constraints. Based on careful observations of field outcrops along three sections and a drill core, we analyzed the sequences of the KL rift valley in the Permian and reconstructed its tectonic and filling processes. The results presented in this paper show that carbonate olistostromes were highly developed in the upper section of the Qixia Formation to the second member of the Maokou Formation of the Middle Permian in the northern flank of the KL rift valley, floored by platform carbonates and overlapped by deep-water deposits, which indicates that the slope facies related to the rifting occurred in the Upper Yangtze carbonate platform in the Middle Permian. The lowest carbonate olistostromes suggest the rifting initiated at the Middle Qixia Stage (approximately the Early Wordian) and gradually developed from west to east. Overlapped deep basin deposits in the third member of the Maokou Formation to the Changhsing Formation of the Upper Permian demonstrate the change from the rifting to post-rift subsidence at the beginning of the Late Maokou Stage (approximately the Late Capitanian). In a word, the KL rift valley underwent the tectono-sedimentary processes of the rifting and then post-rift subsidence. During the rifting, the KL rift valley was a marine half-graben developed on the Upper Yangtze carbonate platform, and its northern flank was a fault-controlled slope and characterized by massive carbonate olistostromes. The drill core (Yuanba 8) shows that deeply buried southern flank of the half-graben was a gentle slope and deposited bioclastic and reef limestones. During the post-rift subsidence, the KL rift valley was characterized by cherts and cherty mudstones of the deep basin facies enriched the fossils such as Ammonites. The post-rift subsidence was highly uneven and therefore resulted in the lagoon-tidal flat facies and high-energy shoal facies progressively overlapping the deep basin sediments from east to west along the KL rift valley.

Preliminary results based on geochemical sedimentary constraints on the hydrocarbon potential and depositional environment of a Messinian sub-salt mixed siliciclastic-carbonate succession onshore Crete (Plouti section, eastern Mediterranean)

This study details new geochemical analysis from an outcrop in Crete to improve understanding of the hydrocarbon potential of the southern margin of the Hellenic Arc along the continental convergent zone of the central Mediterranean Ridge. Seventeen samples were collected from the Late Miocene sub-salt sedimentary succession of Plouti section in central Crete and were studied in terms of their organic geochemical features using Rock-Eval VI pyrolysis. Results of this investigation revealed intervals with sufficient organic material of good enough quality and quantity to be considered as potential source rocks. The obtained data generally present poor to fair and/or good in some cases hydrocarbon generation potential. The TOC values range from 0.03 to 1.99%, with an average fair (2.1 mg HC/g rock) hydrocarbon potential. A Type III kerogen was identified, indicating a terrestrial origin organic matter. T max and Production Index values suggest that the most promising parts of the section (organic-rich sediments) are immature with respect to oil generation and have not experienced high temperature during burial. Overall, the present study offers the opportunity to advance our understanding on the hydrocarbon potential onshore Crete and further investigate hydrocarbon prospectivity in the adjoining area, and particularly, the Greek part of the Mediterranean Ridge, a region with crucial economic and strategic importance.

Sedimentary constraints on the development of a narrow deep strait (São Sebastião Channel, SE Brazil)

The Sao Sebastiao Channel (SSC), which separates Sao Sebastiao Island from the continent, is a deep elongated strait on the inner shelf of the Sao Paulo Bight (SE Brazil). The aim of this study is to explain why it is presently sediment starved, instead of forming a tombolo. Wave data were obtained from both a WW3 model database and buoy records, and wave propagation patterns from the SWAN numerical model. Grain size trend analysis of 579 surficial sediment samples from the strait and the surrounding region served to estimate the residual transport directions. Bedload sediment transport was computed considering in situ currents and bottom sediment grain size. Moreover, six seismic profiles and one gravity core were obtained in the strait in order to evaluate the hickness of the sedimentary deposits. The geometry of the SSC (X/B=0.3, where B is the breakwater or island diameter and X is its cross-shore distance to the mainland) predicts that a tombolo should be formed, and wave patterns confirm that it is a zone sheltered from both S and NE waves. Previous studies have shown that the hydrodynamics of the SSC is controlled by wind-driven currents, which are more intense in the eastern and central sectors of the strait. The western sector is currently covered by sandy mud, whereas very coarse to fine sand prevails in the deeper eastern sector. Sediment patterns show a trend to deposition of fine sediment in the western sector of the SSC and two main depocentres located at the northern limit of the study area and at the southern mouth of the strait. Sandy mud in the western sector forms a 40-m-thick deposit close to the outer limit of Araca Bay, whereas the remainder of the SSC is covered by a very thin layer of sandy sediments. Dominance of mud in the depositional western sector suggests low availability of sand in the area. Therefore, despite the geometry and wave patterns of the SSC favouring the formation of a tombolo, the dominance of wind-driven currents and the low availability of sand determine that such a sedimentary feature cannot be formed, resulting in a deep strait.

Sedimentary constraints on the duration of the Marinoan Oxygen-17 Depletion (MOSD) event

The ~635 Ma Marinoan glaciation is marked by dramatic Earth system perturbations. Deposition of nonmass-dependently (17)O-depleted sulfate (SO4(2-)) in worldwide postglacial sediments is, thus far, unique to this glaciation. It is proposed that an extremely high-pCO2 atmosphere can result in highly (17)O-depleted atmospheric O2, or the Marinoan Oxygen-17 Depletion (MOSD) event. This anomalous (17)O signal was imparted to sulfate of oxidative weathering origin. However, (17)O-depleted sulfate occurs in limited sedimentary intervals, suggesting that Earth surface conditions conducive to the MOSD had a finite duration. An MOSD duration can, therefore, provide much needed constraint on modeling Earth system responses at that time. Unfortunately, the sulfate (17)O record is often sparse or lacks radiometric dates. Here, we report 11 barite layers from a post-Marinoan dolostone sequence at Wushanhu in the South China Block. The (17)O depletion fluctuates in magnitude in lower layers but is persistently absent up section, providing the most confident first and last sedimentary appearance of the anomaly. δ(13)C chemostratigraphy is used to correlate the Wushanhu section to two proximal sections on the same shallow platform that lack barite layers but have published U-Pb dates that occur in dolostone and shale. Assuming a similar pattern and rate for carbonate and shale deposition among the different sections, we estimate the MOSD duration at 0-0.99 My. This number can be further constrained by new radiometric dates from equivalent sequences worldwide, thus underpinning models on the nonsteady-state Earth system response in the immediate aftermath of the Marinoan meltdown.

Distribution and functional response of sublittoral soft bottom assemblages to sedimentary constraints

Mollusc and annelid polychaete macrofaunal assemblages were studied in a sublittoral sandy bottom of 1.8 km 2 extension, along the western Calabrian coast (low Tyrrhenian Sea). The strict coupling of the local sedimentary dynamics with the benthic assemblages was investigated on a small spatial scale (patchiness), at the mesoscale depth-related gradients and at the level of functional/trophic habits. Non-metrical correlations ( ρ), index of dispersion (Di) and dispersion weighted abundances, averaged per depth level highlighted the response of some characteristic species to the patchiness of sediments as well as to the predominant environmental gradients. Species habits and trophic guilds, that were assessed in terms of biomass (wet weight) and secondary “pseudo-production” (abundance × biomass), clarified the differential functional response of the assemblages at different depth levels. Polychaetes reached 84.86% abundance and showed a highly clumped distribution of sessile species ( Ditrupa arietina, Aponuphis brementi, Chone acustica, Spiophanes kroyeri); to a lower extent the motile species ( Hyalinoecia tubicola, Marphisa bellii, Phylo foetida) were present. Molluscs reached 15.14% abundance and only some bivalve taxa showed significant aggregated distributions ( Corbula gibba, Tellina donacina, Tellina distorta), whereas gastropod species were more evenly distributed. Total biomasses were almost equal between the two taxonomic groups (46.41 g WW on average). Biotic–environmental rank matching highlighted depth, very fine sands (60–200 μm), sorting grade, skewness index and pH as being the most influential factors in the distributions of some species, followed secondarily by coarse silts (40–60 μm) and coarser sands (200–2000 μm). Within the local context of water/sediment oligotrophy, the adaptive strategies of macrofauna to a highly seasonal supply of autochthonous phytoplanktonic seston associated with imported macro debris and terrigenous components were emphasized. Evidence of such a differential nutrient supply was the clear functional differentiation of the shallower levels from the deeper ones, and the presence of an intermediate zone which was selectively dominated, in terms of abundance and biomass, by microphagous filter/suspension feeders. Moreover, the shortage of burrowing deposit feeders as well as the prevalence of motile macrophagous omnivores beyond 20 m depth may be considered as ecologically correlated aspects.

Major geodynamic and sedimentary constraints on the chronostratigraphic correlation of the lower-middle Cambrian transition in the western Mediterranean region

The sedimentary rocks of the lower-middle Cambrian transition in the western Mediterranean region have recorded a superposition of extensive tectonic, volcanic, epeirogenic, and eustatic events that led to a complex sequence framework that, in some cases, makes detailed chronostratigraphic correlations difficult. This paper summarizes and updates the relationships between event stratigraphy, fluctuations of relative sea level, setting of major stratigraphic discontinuities, unconformities, and condensed levels, and succession of benthic community replacements displayed by outcrops located in the Iberian Peninsula (Iberian, Cantabrian and Cordoba platforms), Moroccan Atlas (Souss Basin), and the Montagne-Noire and Sardinian platforms. The resulting mosaic of inter-related geodynamic processes is correlated by trilobite, archaeocyath-and acritarch-based chronostratigraphic scales, taking as reference for the base of the Middle Cambrian in West Gondwana the immigration of paradoxidid trilobites.

ABSTRACT: Sedimentary Constraints on the Epicentral Location and Degree of Deformation for the New Madrid 12/16/1811 Dawn Earthquake, and the Role of Splays in Tectonically Driven Floodplain Aggradation

ABSTRACT: Sedimentary Constraints on the Epicentral Location and Degree of Deformation for the New Madrid 12/16/1811 Dawn Earthquake, and the Role of Splays in Tectonically Driven Floodplain Aggradation