Relative Sea-level Fluctuations Research Articles

Changes in organic matter composition during the Toarcian Oceanic Anoxic Event (T-OAE) in the Posidonia Shale Formation from Dormettingen (SW-Germany)

During the Early Toarcian, deposition of organic carbon-rich-shales occurred throughout the epicontinental sea across Europe. Climate instability and high extinction rates in the marine realm were associated with profound environmental changes. The Toarcian Oceanic Anoxic Event (T-OAE) has been linked to the injection of greenhouse gases (e.g. oceanic methane) into the atmosphere triggered by the emplacement of the Karoo-Ferrar large igneous province (LIP) volcanism. The data presented are obtained from the Posidonia Shale Formation in Dormettingen (southwestern Germany), ~2 km from the well-known Dotternhausen section. Despite the intense palaeontological and geochemical research, studies on the particulate organic matter (POM) across the T-OAE are scarce. Here, we provide a detailed study of POM of the Dormettingen section as a tool to evaluate changes in the depositional environment. Integrated POM (i.e. amorphous organic matter, marine and terrestrial palynomorphs) and geochemical (i.e. carbon isotope δ13C) analyses reveal different episodes of palaeoecological upheavals during the studied time interval. In this study, we will integrate new palynofacies data and combine it with the existing sedimentological and palaeoecological data of Dotternhausen in order to interpret relative sea-level fluctuations and climatic changes at the local palaeogeographic setting.

Sequence stratigraphy, paleogeography, and coal accumulation in a lowland alluvial plain, coastal plain, and shallow-marine setting: Upper Carboniferous–Permian of the Anyang–Hebi coalfield, Henan Province, North China

To study the stratal stacking patterns and controls on coal accumulation in a lowland alluvial plain, coastal plain, and shallow-marine setting, the depositional facies, sequence stratigraphy, and paleogeography of the Carboniferous–Permian strata in the Anyang-Hebi (Anhe) coalfield, Henan Province, northern China were analyzed based on borehole cores. Ten facies were grouped into four facies associations, which represent alluvial plain, delta plain, delta front and prodelta, and offshore marine depositional environments. Ten sequences (S1 to S10, in ascending order) were defined on the basis of vertical facies stacking patterns. Sequences S1–S3, of Moscovian to early Asselian age, are composed mainly of offshore marine carbonate and mudstone, prodelta and delta front mudstone and sandstone, and delta plain sandstone, mudstone and coal. Sequences S4–S9, late Asselian to Wuchiapingian in age, consist of delta plain sandstone, mudstone and coal. Sequence S10, corresponding to the Changhsingian stage, is composed mainly of alluvial plain sandstone and mudstone. From S1 to S10, the Anhe coalfield experienced an environmental evolution from offshore marine, prodelta and delta front through delta plain to alluvial plain environments, an evolution from a low-accommodation to a high-accommodation setting, and a paleoclimatic change from humid to semi-arid conditions. Coal accumulation was controlled by a combination of relative sea-level fluctuation, paleoclimate and paleogeography. The cyclothemic nature of S2, including presence of parasequences, and the significant sea-level fall interpreted at the base of S4 may be related to Gondwanan ice dynamics in the late Carboniferous–early Permian. The thick coals are concentrated in the transgressive systems tracts of S2 and S4. The results of this study provide new insights into the environmental evolution of Carboniferous–Permian lowland alluvial plain, coastal plain and shallow-marine successions of the northern subtropical paleolatitudes and the controls on coal deposits in North China.

Major, trace-elemental and sedimentological characterization of the upper Ordovician Wufeng-lower Silurian Longmaxi formations, Sichuan Basin, south China: Insights into the effect of relative sea-level fluctuations on organic matter accumulation in shales

The relative sea-level fluctuations play a vital role in the organic matter enrichment of black shales across the world. The Wufeng-Lower Longmaxi shales deposited during the Late Ordovician to Early Silurian stage are accompanied by the global transgression and regression, whereas the role of relative sea-level changes on organic matter accumulation has been rarely discussed. In this study, we integrated TOC content, X-ray diffraction (XRD) mineralogical composition, thin section and scanning electron microscope (SEM) images, elemental geochemical data, and petrographic features of pyrite framboids to investigate the varying paleoenvironmental conditions and the effect of relative sea-level changes on organic matter accumulation under a robust sequence stratigraphic framework.Based on detailed petrographic observations and mineralogical analysis, six major lithofacies are identified in the Wufeng-Lower Longmaxi formations, including siliceous mudstone, clay-rich siliceous mudstone, siliceous-argillaceous mixed shale, silty mudstone, siltstone, and bentonite. TOC content is generally higher in the transgressive systems tracts (relative sea-level rise stage) than in the highstand systems tracts and falling stage systems tract (relative sea-level fall stage). Multiple geochemical proxies indicate contrasting paleoenvironmental changes between relative sea-level rise and fall stage. Relative sea-level rise resulted in elevated productivity, predominantly anoxic conditions, low detrital flux, and moderate water mass restriction, as indicated by high biogenic Si content, high Mo-EF (enrichment factor of element Mo), small-sized pyrite framboids, low Al content and moderate Mo/TOC ratio. On the contrary, relative sea-level fall generally resulted in decreased productivity, dysoxic conditions, increased detrital flux, and strongly restricted conditions. The correlations between TOC content and geochemical proxies suggest that organic matter accumulation was a combined effect of paleoproductivity, paleoredox conditions, detrital influx, and water mass restriction. The variation of these factors was strongly influenced by relative sea-level fluctuations related to Hirnantian glaciation and regional tectonic movements during the Late Ordovician-Early Silurian transitional stage.

Mass-transport deposits and the onset of wedge-top basin development: An example from the Dinaric Foreland Basin, Croatia

ABSTRACTMass-transport deposits (MTDs) represent resedimentation phenomena triggered by the combined effect of seismic shocks of regional scale, structural tilting, basin-floor gradient, relative sea-level fluctuations, and/or excess pore-water pressure and can be useful in the reconstruction of basin development dynamics. The present study from the Dinaric Foreland Basin in Croatia documents several limestone blocks (olistoliths), carbonate debris, and associated bipartite carbonate megabeds as MTDs of exotic origin encased in deep neritic hyperpycnites, referred to as host deposits. Detailed facies and micropaleontological analyses indicate that host deposits were sourced from a fluvio-deltaic system located in the proximity of the uplifting orogen, while the MTDs originated from gravitational collapses of late Ypresian and early Lutetian limestones that were uplifted on blind-thrust anticline ridges on the opposite side of the basin. Mass wasting-produced carbonate blocks, debris, and gravity flows were probably triggered concurrently during the middle to late Eocene, but the blocks could have travelled faster downslope due to the lubricating effect of the underlying water “cushion,” overpressured mud, and the pull of gravity. Debrisflows and co-genetic turbidity currents that contributed to the formation of bipartite megabeds were likely mobilized deeper and moved slower than the carbonate blocks and could have been partly deflected by the previously emplaced olistoliths, resulting in megabed thinning along the olistoliths' down-dip edges. Those collapses were most likely triggered by the combined effect of relative sea-level changes associated with tectonic activity and seismic shocks of regional scale. The study suggests that progressive uplift of the frontal blind-thrust anticline ridge resulted in episodic emergence and collapses of progressively older limestone units, and marked the onset of development of the wedge-top basin. Conceptual models of olistolith emplacement and onset of basin development are suggested and may be applicable to both ancient and recent settings. The insights obtained from the integration of detailed facies analysis and micropaleontology may be useful in similar areas where such a level of detail cannot be obtained by conventional field methods.

Forward numerical modelling constraining environmental parameters (Aptian carbonate system, E Iberia)

The facies distribution in time and space of sedimentary successions is controlled by a complex interplay between physical, chemical and biological processes, which are nowadays difficult to construe from the geological record. Numerical models constitute a valuable tool to identify and quantify such controlling factors permitting a reliable 3D extrapolation and prediction of stratigraphic and facies architectures beyond outcropping rock strata. This study assesses the roles of three controlling parameters being carbonate production rate, relative sea-level changes and terrigenous clastic sediment supply, on the evolution of an Aptian carbonate system. The SIMSAFADIM-CLASTIC, a 3D process-based sedimentary-stratigraphic forward model, was used for this evaluation. The carbonate succession modelled crops out in the western Maestrat Basin (E Iberia), and corresponded to a platform-to-basin transition comprising three depositional environment-related facies assemblages: platform top, slope and basin. Testing of geological parameters in forward modelling results in a wide range of possible 3D geological scenarios. The documented distribution of facies and sequence-stratigraphic framework combined with a virtual outcrop model were used as a reference to perform geometric (quantitative) and architectural and stacking pattern (qualitative) research by model-data comparison. The time interval modelled spans 1450 ky. The best-fit simulation run characterizes and quantifies (1) relative sea-level fluctuations recording five different genetic types of deposit (systems tracts) belonging to two depositional sequences as expected from field-data analysis, (2) a rate of terrigenous clastic sediment input ranging between 0.5 and 2.5 gr/s, and (3) a mean autochthonous carbonate production maximum rate of 0.08 m/ky. Furthermore, the quantitative and qualitative sensitivity tests carried out highlight that the fluctuation of relative sea level exerted the main control on the resulting stratigraphic and facies architectures, whereas the effect of inflowing terrigenous clastic sediment is less pronounced. Facies assemblages show different sensitivities to each parameter, being the slope carbonates more sensitive than the platform top facies to inflowing fine terrigenous sediments. On slope depositional settings, siliciclastic input also controls stratal stacking patterns and the dimensions of the carbonate bodies formed. The final 3D model allows to spot architectural features such as stacking patterns that can be misinterpreted by looking at the resulting record in the outcrop or by using other 2D approaches, and facilitates the comprehension of reservoir connectivity highlighting the occurrence of initial disconnected regressive platforms, which were later connected during a transgressive stage.

Salt marsh palynological assemblages as modern analogue tools for interpreting past vegetation zones and environmental conditions in the NE coastal plain of Argentina

In this study we examine the distribution patterns of modern palynological assemblages from different salt marsh zones and microenvironments in order to generate reference data for the north-central sector of Bahía Samborombón, to be used as analogues for interpreting fossil palynological assemblages. For the modern palynological analysis, 23 surface sediment samples were taken from different tidal environments in the coastal zone, including intertidal, low, middle and high salt marsh. The results allowed to differentiate and characterize the tidal environments from the palynological point of view. Small changes in the microrelief such as tidal channels, cheniers, and depressions areas, modify the local vegetation and therefore determine the final palynological assemblage. Fossil data from the central zone of Bahía Samborombón (PM 1 stratigraphic sequence) was compared with the modern pollen data to interpret vegetation and paleoenvironmental changes; which demonstrated that salinity, mainly related to the tidal influence, drove the paleoenvironmental changes. This study provides new modern palynological data for Bahía Samborombón and may constitute an important tool to interpret Holocene fossil sediment sequences. This data could be used in future paleoenvironmental reconstructions in coastal plain deposits whose evolution are linked to relative sea-level fluctuations.

The stratigraphy of latest Devonian and earliest Carboniferous rocks in Ireland

Thick successions of latest Devonian and early Carboniferous siliciclastic rocks of fluviatile and shallow marine origin are well exposed in numerous coastal sections in the south of Ireland. Correlations based on palynostratigraphy demonstrate that an overall northward transgression, in detail consisting of several fluctuations of relative sea level, resulted in the replacement of fluvial coastal plain environments by shallow marine conditions. The most conspicuous lithological record of transgression occurred at or close to the base of the Carboniferous, when a regionally distributed mudstone deposited in a shallow sea, replaced the generally sandy strata that had prevailed in the latest Devonian. There is no evidence for very large glacioeustatic changes of sea level related to the coeval western Gondwanan glaciation. Of the three horizons for a new GSSP for the base of the Carboniferous currently under review, the base of the Protognathodus kuehni Zone/basal Siphonodella sulcata Zone and coastal plant extinction is the most easily applied in Ireland and can be identified using palynology and corresponds to an easily recognised, extensively developed lithological change in the south of the country.

Geoarchaeology as a tool to understand ancient navigation in the northern Persian Gulf and the harbour history of Siraf

Historical texts and archaeological studies attest to the maritime and trade importance of the Persian Gulf since the Sassanid Empires. Nonetheless, there is a paucity of data regarding ancient navigation and the reasons for a shift in maritime trade from the western (e.g. Shatt-al-Arab) to eastern (Siraf) Persian Gulf by the Abbasid dynasty. For some scholars, Siraf was occupied between 360 and 977 CE, after which time an earthquake entrained the demise of the city. However, it is unclear when Siraf was founded and how natural navigation conditions changed for ocean-going vessels in harbours of the NW Persian Gulf. To address this knowledge gap, we here present new geoarchaeological data from Siraf. Two anthropogenic facies were detected in drilled cores. They suggest that Siraf dates back to 2 BC-317 CE. After a hiatus, a second occupation phase began during the reign of Shapur II. Relative Sea-Level (RSL) fluctuations, climate change and Persian Gulf bathymetry all affected the possible nautical accessibility of this ancient Persian harbour. A fall in RSL, leading to a shortening of navigable water columns and amplified summer-time Shamal wind from 550 CE onwards possibly led to a loss in the importance of Shatt-al-Arab and other ports in the western Persian Gulf. It appears to have made Siraf the best alternative for seafarers. According to the wind regimes, the best time for arrival and departure from Siraf was August and October, respectively. RSL rise and increasing coastal erosion during the winter-time Shamal winds led to the degradation of harbour potentialities and was possibly at the origin of economic decline and poorly adapted harbour works at Siraf during a 150-year period between 850 and 1000 CE.

Sea level, biotic and carbon-isotope response to the Paleocene–Eocene thermal maximum in Tibetan Himalayan platform carbonates

Abstract During the Paleocene–Eocene Thermal Maximum (PETM, ~56 Ma), a large, negative carbon-isotope excursion (CIE) testifies to a massive perturbation of the global carbon cycle. Shallow-marine settings are crucial to understand the environmental and ecological changes associated with the PETM and the connection between continental and open-marine environments. Detailed sedimentological, paleontological, and geochemical analysis of a quasi-continuous succession of shallow-marine carbonates in the Tethys Himalaya of southern Tibet indicates that a relative rise in sea level coincided with PETM onset, continued through PETM core, and terminated with a regression at PETM recovery. At PETM onset, corresponding to the SBZ4/SBZ5 boundary, no obvious impact on biota and specifically on larger benthic foraminifera (LBF) is observed. The major biotic change occurs later on at PETM recovery, corresponding to the SBZ5/SBZ6 boundary. Our data suggest that relative sea level, rather than temperature, exerted the main control on benthic biota during the PETM. Although the δ13Corg values of organic matter are similar in the deep sea and shallow-marine continental margins, the δ13Ccarb value of bulk carbonates are significantly 13C-depleted, which we attribute to environmental change driven by relative sea-level fluctuations.

Mid to Late-Holocene relative sea-level fluctuations and palaeoenvironment: Evidences from the southern Saurashtra coast, western India

Around 2 m thick relict mudflat, stabilized coastal dune and marine notches are used to estimate the relative sea level (RSL) changes during the mid-Holocene along the part of southern Saurashtra coast. The study identifies two events of high RSL which are dated to 7.3 cal yr BP to 5.1 cal yr BP (Mid-Holocene) and ~1 ka BP (Late-Holocene). Based on the geochemical proxies, the Mid-Holocene high RSL is ascribed to the combined contribution of global ice melt and the strengthened Indian Summer Monsoon (ISM), whereas, the Late-Holocene high RSL is attributed to the Medieval Climate Anomaly. A decline in the ISM is observed at ~4.2 ka which also corresponds with the declining trend in the RSL. However, after 4 ka, a sustained ISM is inferred which continued till 1 ka. The uplift estimated based on the tectonic overprinting of the raised intertidal platforms and marine notches shows ~1.5–2 m uplift after the Mid-Holocene. This implies that the net RSL component during the Mid to Late-Holocene was marginally high (above the present high-tide mark). Further, the notch morphology and empirically driven erosion rate estimates indicate that the coastal uplifts occurred at ≤ 4 ka and was probably responsible for the present-day coastal configuration.

Seismic stratigraphy of late Neogene - Quaternary units and evolutionary model in the inner sector of Bahia Blanca estuary (Argentina)

The Quaternary sedimentary deposit of the inner sector of Bahía Blanca estuary (BBE), Argentina, was studied using high-resolution seismic profiles, core samples and correlation with continental – marine units outcropping in the continent. We interpreted four prominent seismic reflection surfaces and the acoustic basement which together defined five seismic stratigraphic units (S0, S1, S2, S3, S4) and four related systems tracts. Studying those units, we proposed a fourth Stage deposition evolutionary model that took place in a relative sea-level fluctuation context after the Miocene in the BBE area. The first stage contained the deposition of the regressive seismic units S0 and S1. The S0 was determined as an acoustic basement. The top of the S0 erosional surface (SU) was determined and it was formed by subaerial processes during the Late Pleistocene fall in sea-level and the following marine reworking during transgression. The unit was correlated with the oldest continental Miocene loess deposit and was associated with an Early Lowstand Systems Tract (ELST). Unit S1 was associated with a Late Lowstand Systems Tract (LLST). An irregular stratigraphic surface was observed above it. It was inferred as a Maximum Regressive Surface and the Ravinement Surface (RS/MRS) which are related to a maximum regression and subsequent transgression. The S1 unit was correlated with Pliocene-Pleistocene continental deposits. The Miocene - Pleistocene coastline movement in this sector would be associated with both Neogene Andean dynamics and the Last Maximum Glacial. After that, during the second Stage in the Late Pleistocene - middle Holocene the sea-level on the Bahia Blanca coast rose and unit S2 was formed. We interpreted unit S2 as a Transgressive System Tract which developed until the maximum sea-level of the Mid-Holocene. The coastline extension on the continent conformed the Maximum Flooding Surface. After a stabilization period to the mid Holocene, the sea-level started falling, offering conditions for the deposition of the High Stand System Tract (S3 – S4). Following stabilization, the third Stage took place and a progradation unit S3 was deposited overlying the MFS and a minor stratigraphic surface Bedset Boundary (BsB) separated this unit from S4. During the fourth phase, the sea-level continued to fall until the present level and the last HST (S4) was interpreted, which is interpreted as an aggradational – progradational deposit formed in the Middle Holocene to the present day by a change in the rate of sediment supply or energy flux.

Hydrocarbon reservoir development in reef and shoal complexes of the Lower Ordovician carbonate successions in the Tazhong Uplift in central Tarim basin, NW China: constraints from microfacies characteristics and sequence stratigraphy

The analyses of hydrocarbon reservoirs in the high-frequency reef and shoal facies of the Lower Ordovician carbonate successions in the Penglaiba Formation (O1P) and Yingshan Formation (O1–2Y) in the Tazhong (Katake) Uplift in central Tarim basin showed three types of hydrocarbon reservoirs: type 1 associated with synsedimentary facies, type 2 developed by hot active basinal dissolution fluids [mesogenetic fluids, geothermal/hydrothermal fluids and thermochemical sulfate reduction-related fluids] and tectonic activity, and type 3 are hypogenic–epigenetic karst reservoirs formed by meteoric and mesogenetic dissolution fluids. Porosity and permeability development in the reef and shoal facies in the highstand system tracts (HST) of the third-order sequence cycles (SQ1–SQ3) correlates well with regression peaks in O1P and O1–2Y, mostly related to multiphase tectonic activity, long-term exposure, denudation and dissolution in near-surface to shallow burial settings. The carbonate successions in the O1P and O1–2Y are composed of seventeen microfacies (MF-1 to MF-17) deposited on a shallow marine platform. Six main groups of microfacies associations (MFA-1 to MFA-6) were recognized, with each microfacies association corresponding to the transgressive system tracts and HST of SQ1–SQ4 in O1P and O1–2Y. The microfacies represent specific sedimentary environment including platform interior and platform margin deposited under particular hydrodynamic conditions. Tectonics and frequent relative sea-level fluctuation associated with rapid transgression and slow regression favored the deposition of the large-scale vertical stacking, high-frequency reef and shoal facies across the carbonate platforms in this uplift. The hydrocarbon reservoirs in this study have relatively moderate porosity and low permeability, and are somewhat potential reservoirs for hydrocarbon exploration in the Tazhong Uplift.

Senonian platform-to-slope evolution in the tectonically-influenced Syrian Arc sedimentary belt: Beni Suef Basin, Egypt

The Beni Suef Basin is a rift basin that was formed in the Early Cretaceous in response to the break-up of the Gondwana. The infill consists of a thick Mesozoic–Paleogene succession deposited during two main tectonic phases; the Early Cretaceous syn-rift phase and the Late Cretaceous post-rift phase. The post-rift phase was subsequently subjected to an intense compressional tectonic regime related to late Cretaceous Syrian arc tectonics. Within the basin-fill succession, the Senonian deposits, which are composed of carbonates and mixed siliciclastic/carbonate rocks of the “B” and “A” members of the Abu Roash Formation, was formed as a marine platform developed under fluctuated shelfal conditions. These deposits were overlain by chalk of the Khoman Formation that is interpreted to have formed in an outer shelf–middle slope setting. The Senonian succession is subdivided into two 3rd order depositional sequences (Latest Turonian–Early Coniacian SQ-1 and Coniacian–Santonian SQ-2) and one 2nd order depositional sequence (Campanian–Maastrichtian SQ-3). The depositional history of the Senonian in the Beni Suef Basin is interpreted to have been controlled by variable sedimentation accompanied by progradation and retrogradation of carbonate platform between inner and outer shelf environments during the Coniacian–Santonian, and between inner shelf and upper slope environments during the Campanian–Maastrichtian to the end of Senonian. The changes in depositional environments and relative sea-level fluctuations were a factor of the variations in accommodation and sedimentation likely controlled primarily by the Syrian Arc tectonic pulses, which may also have affected basin development and that of the surrounding areas over the northern Western Desert of Egypt particularly during Senonian.

Tectonic controls on late Cambrian-Early Ordovician deposition in Cordillera oriental (Northwest Argentina)

The western Gondwana margin underwent a complex geodynamic history during the early Paleozoic, and major uncertainties remain as to the role of tectonism in sedimentary dynamics. This study focuses on the lower part Santa Rosita Formation and the coeval Guayoc Chico Group (Cordillera Oriental; Northwest Argentina), ranging from the late Cambrian (Furongian; Age 10) to Early Ordovician (early Tremadocian; Tr1). This stratigraphic interval has been previously interpreted as deposited in an extensional basin to a retro-arc basin without major regional tectonic-induced deformation during its deposition, only recording long-term relative sea-level fluctuations. Four areas (Sierra de Cajas, Angosto del Moreno, Quebrada de Trancas, and Quebrada de Moya) were chosen because they host the most complete and temporally well-constrained stratigraphic sections of the Cordillera Oriental. Throughout the stratigraphic sections, four main facies zones are described and attributed to deposition in estuarine, foreshore-shoreface, delta-front, and offshore environments. Trilobite biozones are used as the biostratigraphic framework. By integrating sedimentary facies analysis, biostratigraphy, and sequence stratigraphy from the four selected sections, a new scenario showcasing the evolution of the basin is proposed. This scenario interprets a tectonically induced deformation during the deposition of the Santa Rosita Formation and the coeval Guayoc Chico Group. The newly acquired sedimentological data show that physiographical changes took place during the Cambrian-Ordovician transition and are expressed in various localities. This major change is recorded in the stratigraphic architecture, where extensive wave-ravinement surfaces and sedimentary hiatus are the result of local, syn-depositional basement uplifts. The initiation of the Puna-Famatinian volcanic arc during the Early Ordovician on the western margin was likely responsible for deformation in the retro-arc basin and the proposed scenario is consistent with the stratigraphic evolution in other areas of the Cordillera Oriental (e.g., Sierra de Mojotoro) and the Sierra de Famatina. Therefore, this study helps to constrain the evolution of the western Gondwana margin during the early Paleozoic, showing changes in the stratigraphic architecture and basin evolution from an extensional to a retro-arc style.

Facies patterns and depositional processes in two Frasnian mixed siliciclastic-carbonate systems in the Cantabrian Mountains, northwest Spain

Abstract Relative sea level fluctuations during the Frasnian generated two shallow-marine, mixed siliciclastic-carbonate successions in the Devonian Asturo-Leonese Basin. Each system represents a third-order sequence-stratigraphical unit deposited in the same basin during comparable extreme greenhouse conditions without nearby fluvial entry points. Depositional control on the siliciclastic and carbonate distribution was driven by relative sea level fluctuations, basin geometry, availability of sand and the way sediment was distributed by shelf currents. Early Variscan flexural bending of the continental crust changed the basin shape from a shelf with a gradual profile and low dip (early Frasnian) towards a shelf with a steep depositional dip (late Frasnian). Shelf distribution changed from along-shelf transport (early Frasnian) towards offshore-directed gravity flows (late Frasnian). As a consequence, siliciclastic-carbonate distribution changed from a predominance of skeletal carbonate in the proximal shoreface – foreshore area and siliciclastic predominance distally (early Frasnian), to a distribution pattern with proximal shoreface skeletal carbonates, offshore muddy carbonates and a siliciclastic zone in between where gravity flows distributed the siliciclastic sediment down dip (late Frasnian).

Sea Level Change Controlled the Sedimentary Processes at the Makran Continental Margin Over the Past 13,000 yr

AbstractClimate change, sea level fluctuations, and tectonic uplift play key roles in the evolution of sedimentary systems on continental margins. In the Arabian Sea, the Makran continental margin is suitable for studying these processes during the Holocene due to its high sedimentation rate and continuous sequence of Holocene sediments. Here, high‐resolution clay mineral and grain size analyses have been conducted to better understand the sedimentary process and controlling factors over the past 13,000 yr. The results show that the influence of Indus‐derived sediments on the Makran continent margin is negligible. Holocene relative sea level fluctuations can strongly control the shelf accommodation space due to the narrow shelf, which in turn affects the deposition process at the Makran continental margin. The sediment records at the central Makran continental margin are more suitable for studying ancient earthquakes or tsunamis.

EPR dating of shells from Malhada Marsh, Rio de Janeiro, Brazil

The formation of the coastal plain of the Brazilian sea is mainly due to the fluctuation of relative sea level in the past. Armacao dos Buzios or simply Buzios is a municipality in the microregion of lakes, in the state of Rio de Janeiro. In this region there is a lowland area about two meters above current sea level. This lowland area is also known as coastal plain of Una River. It is expected that during the Holocene period the sea level reached a maximum about 2.5 meters above the current level. During that time billions of mollusks lived and proliferated in the shallow waters around the coastal plain of the Una River. As they died their shells formed a layer in the soil including Malhada Marsh that belongs to the Una River plain. In this study, shells were collected from this region and dated using the techniques of Electronic Paramagnetic Resonance (EPR). Ages from 2480±130 to 4490±270 years were obtained. Radiocarbon dating were performed at the Beta Analytic Lab, USA for comparison with the EPR results. Shells ages obtained are compatible with geological data from the Holocene period relative to past sea level fluctuations.

Sea-level fluctuations in the late Middle Permian estimated from palaeosols of the Sichuan Basin, SW China

AbstractTwo upper Middle Permian palaeosols, consisting of coal and pyrite intercalated with a 20 cm thick limestone, were found near Mount Emei in the SW Sichuan Basin, China. The macro- and micromorphology and physico-chemical properties, in conjunction with the mineralogical composition of the palaeosol horizons were investigated. This type of palaeosol is common within the Permian intertidal facies of the Upper Yangtze Craton. The section reflects fluctuations within the range of 0–25 m in relative sea-level, with the depositional environment changing from shallow-marine to littoral, followed by tidal-flat to littoral, and finally to continental volcanic rocks, based on a combination of palaeopedological and carbonate microfacies analyses. Such short-term relative sea-level fluctuations in late Middle Permian times in the SW Sichuan Basin of South China are consistent with the long-term falling trend on a global scale in late Middle Permian times, and may be related to regionally variable subsidence and global cooling. The combination of coastal palaeosol and carbonate microfacies analyses is proposed as an additional tool for estimating the amplitude of sea-level changes.

Late Quaternary sedimentological history of a submerged gravel barrier beach complex, southern Namibia

Through comprehensive seismic, stratigraphic, and sedimentological analysis, this paper describes the stratigraphic architecture of the late Quaternary sediments and depositional dynamics in a region ~ 3.5 km offshore of the current south-west Namibian coastline. The landscape evolution model of this area is based on 2D seismic reflection profiles calibrated to approximately 500 boreholes, which yielded sedimentary and seismic facies data of exceptionally high resolution. The data permitted the characterization of four sedimentary facies units and the reconstruction of the submerged landscape dominated by a barrier complex. We compare this barrier complex with the sediment bodies preserved along the adjacent coastline, and account for their geological evolution in response to late Quaternary relative sea-level fluctuations along the West Coast. The most noteworthy depositional units in the study area are the normal regressive coarse gravel beaches trending shore parallel, with the primary gravel barrier and its preserved coeval back-barrier deposits that exceed 7 km in length along the coast. Based on the radiocarbon dates from the rarely preserved early flooding facies (14.0 and 13.3 ka BP), the primary barrier complex formed during a stage of slowing rising relative sea-level subsequent to Meltwater Pulse 1A. Moreover, the barrier beach complex formed on a low-gradient palaeo-bathymetry slope that is punctuated by a break on its landward side (i.e., a regional knick point), which promoted the local accommodation of sediments. The preservation of the barrier beach complex and back-barrier deposits is attributed to rapid relative sea-level rise, linked to the early Holocene Meltwater Pulse 1B between ~ 11.5 and 11.2 ka BP, and an increase in back-barrier accommodation facilitated by the antecedent topography.

The characteristics and controlling factors of facies-controlled coastal eogenetic karst: insights from the Fourth Member of Neoproterozoic Dengying Formation, Central Sichuan Basin, China

Karst porosity system is widely developed in the Fourth Member of Neoproterozoic Dengying Formation in Central Sichuan Basin of China. The result of the previous exploration in this area based on the theory of telogenetic karst, which mainly focused on the fracture/fault belt especially in the karst slope, leaves much to be desired. Though a systematically geological research in this study, it is found that the dissolution holes are mainly concentrated on the mud mound deposits and granular rocks. Both of them have a greater primitive porosity and permeability than the micrite that originally formed in low-energy environments, which is facies controlled. On the basis of the above and the fact that a tectonic movement has caused a massive subaerial exposure of the formation that only experienced a shallow burial, it is proposed that the paleokarst porosity system is the product of eogenetic karst. Two-stage eogenetic karsts have been interpreted: the syngenetic exposure caused by the short-term relative sea-level fluctuation and the exposure caused by the uplift of the second phase of Tongwan tectonic movement. The meteoric alteration in syngenetic period is commonly marked by the development of intergranular pores but on a small scale. It is believed to be important for providing a good pore-permeability foundation for the later eogenetic karst. The later exposure occurs immediately at the end of the deposition of the Fourth Member of Dengying Formation that only experienced a shallow burial. Since the effect of compaction and cementation in this shallow burial before uplift is relatively weak, only the micrite has been densified and retaining the majority of original pores in the carbonate mounds and grain shoals as paths for karst flow. Moreover, combined with the geological background and seismic profile, it can be ascertained that the karst occurs in a coastal environment. Twelve meteoric lenses have been interpreted after recovering the karst palaeogeomorphology. The scale of the meteoric lens and the reservoir performance have shown a decreasing tendency from the coastal to the inland area, which also confirms this view. The results of this research have put emphasis on the lithologic differentiation in eogenetic karst and the geographical location of karst development thus might provide a reference for further reservoir prediction in this area and other similar places.