Shallow Marine Environment Research Articles

Devonian stratiform ironstone deposits in South China formed in a shallow marine environment of a passive continental margin

Devonian ironstone deposits in South China are widely distributed and are major Fe resources of China. They are spatially associated with coeval SEDEX sulfide and Mn deposits. Stratiform orebodies of these ironstone deposits are part of the middle and late Devonian shallow marine sedimentary sequences. The main ironstone layers are interlayered with silty or muddy shales and limestones. The majority of these deposits contain hematite ores and some deposits contain siderite ores. Hematite ores display ooidal textures with Fe-rich ooids and they have Hg isotopic compositions indicative of multiple sources of metals, but trace elemental concentrations are supportive of sources of Fe from seafloor hydrothermal fluids. The Devonian ironstone deposits in South China were formed in a passive continental margin under shallow water conditions. These deposits and coeval SEDEX sulfide and Mn deposits were formed in the same continental shelf but in different sub-basins when the South China Block drifted northward after it was separated from Gondwana.

Diagenetic effect on reservoir quality of siliciclastic and volcaniclastic sandstones from a Paleogene volcanic rifted margin, East Greenland

ABSTRACT Siliciclastic and volcaniclastic sediments in a volcanic rifted-margin succession may experience a complex diagenetic history during burial that can have a large impact on sandstone reservoir properties. To understand such changes, variations in initial sediment composition and succeeding diagenetic changes have been studied for a Paleogene outcrop analogue in the Kangerlussuaq area, East Greenland. The nature of the mafic volcanics-bearing succession, which consists of intra-volcanic sandstones, accommodated over quartz-rich pre-volcanic fluvial sandstones, are comparable to the settings of recently discovered hydrocarbon-producing sandstones in the Faroe–Shetland Basin on the conjugate Atlantic margin. Our petrographic and provenance investigations of the pre- and intra-volcanic sandstones are supported by geochemical and X-ray diffraction analyses. The intra-volcanic sandstones were deposited in shallow marine environments with mixed siliciclastic and volcaniclastic input, the latter rich in felsic to mafic volcanic rock fragments and feldspar grains. Similar zircon age distributions of pre- and intra-volcanic sandstones support a continued supply from the same siliciclastic sediment source after the onset of volcanism. Variations in initial detrital grain and pore-fluid (fresh to marine) compositions resulted in different diagenetic changes in the pre- and intra-volcanic sandstones. However, where siliciclastic sandstones were overlain by volcaniclastic rocks rather than massive lava flows, the diagenetic changes resemble those of the intra-volcanic sandstones. The cementing phases are typically quartz, illite (probably illitized kaolinite), and rare anatase in the pre-volcanic sandstones. Chlorite, calcite, zeolite/feldspar, opal/quartz, and titanite are characteristic authigenic phases in the intra-volcanic sandstones. Precipitation of different minerals in the pre- and intra-volcanic sandstones show that the detrital composition (and to a lesser extent depositional environment) played a major role during early and late diagenesis after deep burial (up to 6–8 km). Inter-eruptive siliciclastic units may prove to form highly valuable reservoirs when they are composed of mixed siliciclastic and volcaniclastic material. In the stratigraphically youngest intra-volcanic sandstones and pre-volcanic sandstones overlain by hyaloclastite or tuff, there is a high potential for preservation of interparticle porosity during burial (< 5 km) due to early chlorite rims and the generation of secondary porosity after the dissolution of early zeolite cement.

Early Eocene biotic assemblage from the sedimentary deposits of the Tarkeshwar Lignite Mine, Gujarat and its palaeoenvironmental implications

The Palaeogene biota and the palaeoenvironmental history from the low latitudes are remarkably well–preserved in theopen–cast lignite deposits from Western India. Lignite sequences of the Cambay Shale Formation (Gujarat) have been a majorsource to understand the concept of early evolution of fossils including flora, arthropods, vertebrates fauna, and several aquaticforms during the Early Eocene. The study deals with an extensive record of amber inclusions and extracted pollen, vertebratefragments, dinoflagellate cysts and Carbon isotopes from the lignite and associated sediments from the Tarkeshwar Lignite Mineto add insights into the palaeoenvironment and depositional conditions of the Cambay Basin during the Early Eocene period. Thecurrent study demonstrates that throughout the late Palaeocene and early Eocene epoch, the palaeoenvironment changed fromlow land, marshy (lower portion), to shallow marine environment, presumably due to hyperthermal event PETM (middle part).Age diagnostic taxa, viz. Auxiodinium longispinosum, Apectodinium parvum and early wetzelielloid (Vallodinium? sp.) excursionprovide late Palaeocene–early Eocene period (~56–53 Ma) for the dinocyst interval in the middle part of the section. A pronouncednegative Carbon Isotope Excursion (CIE) in the middle part is correlated to the second Eocene Thermal maximum (53.7 Ma),which is a globally recorded hyperthermal event. During the ETM–2 warming, the rise in pCO2 caused warm, humid conditionsas well as a rise in sea level, which may have contributed to the establishment of constrained shallow marine environments in theexamined middle unit sedimentary succession. Floral (spore–pollens, leaf, wood, seed, fruits) and faunal assemblages (Crocodiles,fish remains, amber insects) revealed the prevalence of a dense tropical luxurious rain forest (floral and faunal) near shore duringthe ETM–2 in the Tarkeshwar Lignite Mines, Cambay Basin.

Increasing terrigenous input into the continental margin seawater during the late Ediacaran, North China

The late Ediacaran period encompasses widespread glacial deposits and early animal radiation. The temporal and spatial context of these events is not well established. The possible links between the glacial deposits and late Ediacaran fossils are critical for understanding the co-evolution of early animals and marine environments. This study presents a detailed geochemical reconstruction from the Tuerkeng Formation on the western margin and the Dongpo Formation on the southern margin along the North China Craton (NCC). The two fossiliferous late Ediacaran formations cover a critical interval between the end of the Zhengmuguan-Luoquan glaciation and the occurrence of late Ediacaran tubular fossils (e.g., Shaanxilithes). The two formations' similar and intermediate CIA values indicate moderate weathering under a warm and humid climate. Stratigraphic covariation of water-insoluble elements in samples from Tuerkeng and Dongpo formations suggest a rapid input of terrestrial materials at the beginning of deglaciation, and these terrestrial materials continued to be input into the shallow marine environment along the western and southern margins of NCC during the deposition of the two formations. Accompanied by the continental weathering and erosion of fresh rocks during the postglacial period of late Ediacaran, abundant nutrients as well as the terrigenous materials would be continuously transported into the continental margin seawater, which may ultimately lead to the rise of the Ediacaran biota. Our results provide new insights into paleoenvironment conditions along the continental margin of NCC and highlight the critical role of the postglacial terrigenous input in the evolution of early animals.

Facies architecture and sequence stratigraphy of Kungurian Amb Formation, western Salt Range, Pakistan

The Amb Formation of the Permian age is exposed in the Salt Range in the upper Indus basin of Pakistan. This rock unit is mainly composed of sandstone and shale in which three facies (named AF1, AF2, AF3) and five microfacies were distinguished based on field and petrographic study, respectively. Porosity and permeability have changed and exhibit various diagenetic processes. Sequence stratigraphy identifies the zones of all upward concaving cycles and HST. The petrophysical study indicates good reservoir characteristics for the Amb Formation and this can act as reservoir rock in the petroleum system. Fossil assemblages, including Fusulina spp., identified during petrographic analysis indicate an Early Permian age of the Amb Formation in the study area. The multidisciplinary study carried out in the study area allowed us to reconstruct the depositional model for the Amb Formation which occurred in the middle to inner shelf and in a shallow marine environment. Interpretation of well logs of the Dhermund well show good reservoir properties of the Amb Formation including total porosity (13%), effective porosity (9.04%), volume of shale (14.54%), water saturation (34%), hydrocarbon saturation (65%), permeability (121.92 mD), total thickness of the formation (107 m) and net reservoir thickness (13.12m). This research approach of combined field and laboratory stratigraphy and biostratigraphy would be applied in other areas of exposure of the Amb Formation to unravel the age and depositional environment of this formation.

Rare earth elements as tracers of iron ore tailings on the Brazilian eastern continental shelf.

Iron ore tailings are stored in large dams and pose risks to the environment around the world. In Brazil, the rupture of these dams has become frequent and has generated environmental and social concern. Rare earth elements are good tracers of sediment sources and our results indicated chronic contamination of the seabed sediment from the marine region affected by the Fundão Dam tailings since 2015, including areas of environmental protection. This research, carried out between November 2018 and September 2021, with a database of 575 samples, showed a greater amount of contaminated material in the marine region adjacent to the Doce River mouth. Although data suggest prior mining contamination of the Doce River basin, the Fundão episode was an empirical and massive example of the environmental damage caused by these human activities over the centuries, showing that the impact remains in the shallow marine environments for years. Integr Environ Assess Manag 2024;20:179-188. © 2023 SETAC.

Serpulid microbialitic bioherms from the upper Sarmatian (Middle Miocene) of the central Paratethys Sea (NW Hungary) – witnesses of a microbial sea

Abstract. We present previously unknown stacked bowl-shaped bioherms reaching a size of 45 cm in diameter and 40 cm in height from weakly solidified peloidal sand from the upper Sarmatian of the Paratethys Sea. The bioherms were mostly embedded in sediment, and the “growth stages” reflect a reaction on sediment accretion and sinking into the soft sediment. The bioherms are spirorbid–microclot–acicular cement boundstones with densely packed Janua tubes surrounded by microclots and acicular cement solidifying the bioherm. The surrounding sediment is a thrombolite made of peloids and polylobate particles (mesoclots) which are solidified synsedimentarily by micrite cement and dog-tooth cement in a later stage. The shape of the bioherms reflects a series of growth stages with an initial stage (“start-up stage”) followed by a more massive “keep-up stage” which grades into a structure with a collar-like outer rim and a central protrusion and finally by a termination of growth (“give-up stage”). The setting was a shallow subtidal environment with normal marine or elevated saline, probably oligotrophic, conditions with an elevated alkalinity. The stacked bowl-shaped microbialites are a unique feature that has so far been undescribed. Modern and Neogene microbialite occurrences are not direct analogues to the described structures, but the marine examples, like in The Bahamas, Shark Bay and the Persian Gulf, offer insight into their microbial composition and environmental parameters. The microbialites and the surrounding sediment document a predominance of microbial activity in the shallow marine environments of the Paratethys Sea during the late Middle Miocene, which was characterized by a warm, arid climate.

The trace fossil Thalassinoides paradoxicus Kennedy, 1967 revisited from its type locality (Albian-Cenomanian chalk, SE England)

The trace fossil Thalassinoides includes ichnospecies that have been recognised for a long time and widely used in the interpretation of depositional systems. Despite its broad occurrence, the ichnotaxonomic status of this important ichnogenus is far from being unmistakable, which in turn hampers its application in palaeoenvironmental reconstructions. One of the most common ichnospecies is Thalassinoides paradoxicus, originally described from the Paradoxica Bed of the Lower Chalk in the Hunstanton Cliff in SE England. To demarcate this characteristic form from similar ichnospecies, T. paradoxicus is reexamined and described from its type locality. It is characterised by an ‘irregular, very extensive horizontal burrow network, occurring at several levels, connected by vertical shafts’ (Kennedy), but its morphological variability also includes a range of significant architectural elements as well as burrow portions with a laminated wall, scratches and pellets. A series of colonisation events along omission surfaces can be reconstructed based on the occurrence of several burrow generations. T. paradoxicus is an important constituent of shallow-marine environments and subtle variations in morphology may help to constrain facies interpretations. Based on modern analogues and finds of body fossils within their burrows, decapod crustaceans (foremost callianassid shrimp) are known producers of T. paradoxicus from the Mesozoic onwards, whereas older records can be attributed to other malacostracans but also trilobites.

Petrographic analysis of Oligocene carbonates of Kachchh basin

The Kachchh basin is located on the northwestern margin of India. The basin consists of a relatively continuous sequence of sediments from the Mesozoic, followed by the Deccan Traps and finally a complete sequence of the Cenozoic sediments. The Cenozoic sediments of Kachchh basin are mainly shallow marine deposits characterised by five formations viz. Matanomadh, Naredi, Harudi, Fulra Limestone and Maniyara Fort Formation. The Maniyara Fort Formation belongs to the Oligocene age. The field and petrographic characteristics of the Oligocene limestones from the Golay river section were studied in order to understand the depositional environment. The petrographic investigation of the carbonate rocks of three members of the Maniyara Fort Formation, namely Lumpy Clay Member, Coral Limestone Member and Bermoti Member provides important information for understanding the depositional facies and diagenetic signatures. The Lumpy Clay Member has shale-siltstones with interbedded limestones, characteristically composed of a significant proportion of detrital grains of quartz and some lithic fragments. The lithic fragments are sub-angular to rounded, which indicates substantial transport. They are also worn down and broken, bear small cracks which are filled by micritic matrix or mud. The presence of stylolitic seams within the limestone (though not significant) along with mud filling is also noticed. The dissolution is not prominent, pointing towards shallow burial of the sediments. Paucity of marine fossils as well as the rarity of foraminifera in the Lumpy Clay Member indicate a restricted to semi-restricted shallow marine environment. The limestones of the Coral Limestone Member are petrographically classified as packstone, wackestone and mudstone. Thus, the environment of deposition seems to have varied from restricted lagoonal to shallow marine environment. The Bermoti Member is characterised by a lens of claystone, which consists of both greyish to yellow coloured claystones interbedded with limestones. The Bermoti limestones are petrographically classified as packstone, wackestone and mudstone assemblage. The limestones were observed to be highly micritised, which indicates open, shallow marine settings. The Maniyara Fort Formation, thus characterised by wackestone-packstone-mudstone facies of carbonates, is interpreted to be part of a carbonate ramp system. The limestones from Maniyara Fort Formation exhibit signatures of marine as well as meteoric diagenesis.

Rock Typing and Characterization of the Late Cretaceous Abu Roash "G" Reservoirs at East Alam El-Shawish Field, Western Desert, Egypt

Rock typing and petrophysical characterization play a vital role in constructing reservoir models for petroleum exploration and development. This study focuses on evaluating the petrophysical characteristics of the Late Cretaceous Abu Roash "G" Reservoirs at the East Alam El Shawish field in Egypt's Western Desert. The study involved five vertical wells and employed various techniques and analyses to investigate the reservoir. Lithology determination utilizing well logs and core analysis helps identify the lithology types and corresponding porosity of the Abu Roash "G" reservoirs. Sandstone and limestone lithologies with varying porosity ranges were identified, along with the influence of shale on neutron porosity values. Facies analysis of the Abu Roash "G" Member identified seven lithofacies types, categorized into shallow marine and deeper marine depositional environments. The petrophysical analysis involves evaluating gamma-ray logs, porosity, permeability, flow zone indicator (FZI), and reservoir quality index (RQI) values for each lithofacies type. This analysis classifies the core samples into seven reservoir rock types (RRT1 to RRT7) based on petrophysical attributes, providing a clear classification of the Abu Roash "G" reservoir interval. RRT1, RRT2, and RRT3 exhibit the highest reservoir quality, while RRT4 and RRT5 indicate moderate reservoir quality. RRT6 and RRT7 exhibit low reservoir quality due to unfavorable petrophysical behavior. The findings of this study provide valuable insights into the Abu Roash "G" reservoir, including its lithofacies, reservoir properties, and depositional environments. This knowledge is crucial for reservoir characterization and optimizing oil production strategies in the region.

Carbonate Ramp Facies and Porosity Recognition: Case Study of the Late Albian-Early Cenomanian Mauddud Formation in Ratawi Oilfield, Southern Iraq

The carbonate ramp facies of the Late Albian-Early Cenomanian Mauddud Formation were studied in the Ratawi Oilfield, Basra Governorate, south of Iraq using integrated borehole data set that included, core and cutting samples in three drilled wells to analyze the petrography of the Mauddud Formation, two hundred and eighty-one (281) thin sections were prepared and examined for the three selected wells. The results show that the formation is composed of light grey dolomitized limestone and pseudo-oolitic creamy limestone with green to bluish shale. The petrographic observations results show four facies’ associations in the Mauddud Formation. These include: Mid–Ramp environment which is represented by Argillaceous mudstone microfacies, Argillaceous wackestone microfacies and orbitolinid wackestone microfacies; the shallow open marine environment which is assimilated by foraminiferal wackestone microfacies and foraminiferal packstone microfacies; a restricted marine environment that represented by bioclastic fossiliferous wackestone microfacies and miliolid wackestone microfacies and Shoal environment is represented by bioclastic packstone microfacies, bioclastic grainstone microfacies, peloidal foraminiferal pack-grainstone microfacies, and peloidal packstone-grainstone microfacies with diverse skeletal grains. The porosity includes Vuggy, Interparticle, Intraparticle and Fracture porosity.

Is there a link between carbon isotopes and sea level in epicontinental carbonate settings?

A presumed link between carbon isotopic trends and sea level change features prominently in many studies of epicontinental carbonates. In these shallow marine environments, a combination of basin restriction, burial/oxidation of organic carbon, proximity to terrestrial carbon sources, carbonate mineralogy, and/or meteoric influence can result in δ13Ccarb records that are distinct from that of the open ocean. Because many of these processes are linked to sea level change, it has been argued that sea level might exert a significant and systematic control on the δ13Ccarb records from epicontinental settings. Multiple studies have attempted to document sea level's influence on carbon isotopic trends, but they do so with only limited constraints on sea level change and without objective evaluations of interpreted trends and relationships. We argue that the complex and complicated set of processes influencing carbon isotopic values in epicontinental settings requires a systematic approach to truly address the question of sea level's influence on δ13Ccarb. Only by integrating carbon isotopic records with a detailed sedimentological and sequence stratigraphic framework can we properly track changes in depositional environments and reconstruct the transgressive-regressive history of the rocks. Trends and relationships in these robust datasets can be evaluated with rank correlation tests specifically designed and empirically tested to deal with noisy datasets. In short, we map a possible path forward for systematic testing of the relationship between sea level and δ13Ccarb.

Dispersion inversion for P- and S-wave velocities based on guided P and Scholte waves

Inversion based on dispersion curves is widely used for the estimation of subsurface velocity structures. However, conventional surface-wave dispersion inversion usually uses normal modes, and only the S-wave velocities are retrieved. To retrieve P-wave velocities, the dispersion of guided P waves should be considered. We develop an inversion scheme that uses the guided-P-wave and Scholte-wave modes to implement an integrated inversion for P- and S-wave velocity structures of shallow marine sediments. The forward modeling of dispersion curves is based on the spectral-element method and the perfectly matched layer technique. A quantitative sensitivity analysis of guided P modes is then carried out, which not only confirms the capability of guided P modes for estimating the P-wave velocity but also indicates that guided P modes can be combined with Scholte modes to better constrain the S-wave velocity. Based on the Levenberg-Marquardt algorithm, a joint inversion scheme that uses guided P and Scholte modes is developed. The validity of the inversion scheme is assessed by testing synthetic and field ocean-bottom seismometer data obtained in shallow marine environments. The results demonstrate the effectiveness of the joint inversion for retrieving the P- and S-wave velocity structures of shallow marine sediments.

FIRST DATA ON PALEOGEOGRAPHICAL SETTINGS AND CHRONOLOGY OF THE LAST INTERGLACIAL ON ZIMNII COAST OF THE WHITE SEA

Field lithostratigraphic studies, microfaunistic and palynological analyses, as well as optically stimulated luminescence (OSL) dating revealed for the first time that the lower part of Quaternary sediment sequences exposed along Zimnii Coast of the White Sea accumulated in marine and nearshore environments during the Boreal transgression at the beginning of the Last Interglacial and thus form the Upper Pleistocene Mikulinian Horizon. This is confirmed by lithology of sediment beds; species composition of foraminifers, ostracods and aquatic palynomorphs; and OSL dates in the range of 118–104 ka. The composition of benthic microfossils indicates that during the early Boreal transgression the entire Zimnii Coast was occupied by an coastal arctic ice-covered basin with water depths of 50 m, high sedimentation rates, and water stratification induced by melt/river water inflow. At the stage of regression, sedimentation in shallow marine environments was dominant along Zimnii Coast.

Persistent late Tonian shallow marine anoxia and euxinia

The increase in the complexity of eukaryotic life during the Tonian Period (ca. 1000 to 720 Ma) is commonly associated with the oxygenation of the Earth’s ocean–atmosphere system, yet the timing and duration of these redox changes remain uncertain. In particular, it is unclear how shallow marine environments, which were likely crucial habitats for early eukaryotic organisms, responded to Neoproterozoic oxygenation. This study uses trace and rare earth element geochemistry to determine shallow marine redox conditions during the deposition of the late Tonian (ca. 760 Ma) Devede Formation, northern Namibia. In this unit, although carbonate phases (microbialite, former aragonite and high Mg calcite marine cements, and primary dolomite marine cements) generally exhibit no Ce/Ce* anomaly, rare negative values (up to 0.55) are consistent with short-lived periods of oxygenation. In contrast, the dominantly positive Eu/Eu* anomalies of the same phases suggest that basinal conditions were anoxic. These phases also exhibit low concentrations of redox-sensitive (U, V, Mo) and chalcophile (Co, Cu, Cd, Zn, Pb) elements, suggesting that euxinic conditions were predominant during the deposition of the Devede Formation. Integration of this data (Ce/Ce* and Eu/Eu*) with that of analogous late Tonian (ca. 840 to 731 Ma) carbonate strata reveals that shallow marine settings were characterised by persistent anoxia and euxinia, suggesting that any potential increase in atmospheric O2 ca. 800 Ma (e.g. the Bitter Springs Anomaly) was insufficient to facilitate resilient ocean oxygenation. These findings suggest that the late Tonian oceans were likely challenging environments for complex (e.g. eukaryotic) life, and add to a growing body of evidence that the spatially variable redox conditions of late Proterozoic shallow marine settings likely reflect the complex nature of the Neoproterozoic Oxygenation Event.

Sound pressure and particle motion calculations considering pile skin friction

Modelling sound propagation over seabeds where the seabed cannot be approximated as an equivalent fluid due to limestone layers with high shear wave speeds is a common underwater acoustic propagation modelling problem for Australian shallow marine environments. With the increase in prospective areas for offshore windfarm development across Australia, construction operations across large regions of the continental shelf area are set to increase. Windfarm construction will require the installation of a large number of foundation piles near potentially sensitive marine habitat areas. Predicting the underwater noise from these activities requires suitable models. This paper investigates the modelling approaches for including a full elastic parameterisation of the seabed when conducting numerical predictions of pile driving sound emissions. The approach considers buried sources and the excitation of shear waves via a skin friction model for the stress–strain relation at the pile-seabed boundary. Shear waves are considered in the source model and in the propagation model. Sound pressure level metrics and particle motion metrics are considered as part of the numerical predictions.

Lithofacies Interpretation Of Sediment Rocks In The Cipamingkis River Outcrop, Jonggol Area, Bogor District, West Java

This research aims to study sedimentary structures and determine the depositional environment of the outcrop in the Cipamingkis River, Jonggol area, Bogor Regency, West Java. The method in this study includes literature studies, field surveys, data interpretation, and facies analysis. The result shows the outcrop in the Cimangkis River can be divided into four (4) sedimentation sequences unit: Claystone Unit (Sequence 1), Limestone/Calsirudit Unit (Sequence 2), Limestone/calcarenite-Calcilutite Unit (Sequence 3), Mudstone/ Calsilutite Unit (Sequence 4). Based on the depositional environment analysis, this outcrop displays characteristics of a shallow marine environment. The Interpretation of facies from outcrops can be used as a reservoir analog and can support subsurface interpretation in the Northwest Java Basin

Initial cyclostratigraphy of the middle Nama Group (Schwarzrand Subgroup) in southern Namibia

The Ediacaran Period includes critical evolutionary trends of early complex life as well as climatic variations associated with ocean oxygenation, glaciations, and carbon cycling, which are still poorly understood in terms of astronomical climate forcing. The middle Nama Group in southern Namibia was deposited during the late Ediacaran in mainly shallow marine environments within a foreland basin and consists of hierarchically arranged depositional sequences. Here, we test a possible astronomical origin of these sedimentary variations by developing an initial cyclostratigraphic framework based on satellite images integrated with recently published high-precision U-Pb zircon ages. Regular sedimentary alternations occur dominantly on scales of several tens of meters, accompanied by smaller- and larger-scale variations, and are correlatable over distances of ∼50 km. Throughout the studied succession, 35 to 39 alternations are recognized on this dominant scale, which have an average duration of ∼120–180 k.y. This duration corresponds well with the period of short eccentricity (∼100 k.y.), given the likely presence of hiatuses, or alternatively, the period of obliquity amplitude modulation (∼173 k.y.), which would imply no time is missing on this scale. The dominant alternations are consistent with previously identified medium-scale sequences in this succession, which have been interpreted to record fluctuations in relative or eustatic sea level. We hypothesize that astronomically-forced fluctuations in eustatic sea level modulated deposition of the middle Nama Group. Geochemical studies suggested a relation between fossil distribution, redox variability and sea level, implying that astronomical forcing may have played a role in the distribution of early complex life.

The myth of the Highland Cretaceous revealed by the art of palaeogeographic mapping

Abstract Since the term was coined in 1873, palaeogeography has provided a powerful map-based tool for synthesizing, visualizing, and testing diverse regional data and hypotheses, but there are problems in deducing the palaeogeography of areas with few data points. As an example, the Scottish Highlands are better mapped and more studied than almost any other ancient orogen, yet questions remain on the persistence of topography since the Caledonian orogeny and the possibility of Cretaceous marine inundation. This paper reviews the data available on Scottish Cretaceous outcrops using published geological maps and memoirs to extract data: outcrop length, stratigraphic thickness and component units, elevation range of the outcrop and subcrop formations. All Cretaceous rocks in western Scotland were deposited in shallow marine and shoreline environments; deposits thin northwards and appear to be close to a feather edge. Elevation data are used to construct a Cretaceous surface which intersects present-day topography at low to intermediate altitudes. It is concluded that the Scottish Highlands were largely emergent during the Late Cretaceous, confirming previous palaeogeographic studies.

Ecological risk assessment on nutrient over-enrichment in water quality: A case study of the Kenyan Coral Reef ecosystems

The natural (seasonality) and anthropogenic drivers (e.g., coastal developments and change in land-use practices), continue to threaten the lives of organisms in shallow marine environments by compromising water quality. A case study was conducted to assess the impact of these drivers on nutrient over-enrichments using water and sediment samples that were collected from healthy live Porites spp. colonies from three Kenyan coral reef ecosystems: Tana Delta, Watamu, and Shimoni Mupunguti Reef. The evaluated nutrient over-enrichment levels were above the universal reference background concentrations of 0.01 and 0.003 mg/L for (N-(NO3- + NO2-)) and (P-PO43-) respectively. Ecological risk exposure to nutrient over-enrichments was evaluated using Renfield (N/P) ratio and nitrogen-phosphorous pollution index. Results on N/P ratios were < the Renfield ratio (N/P = 16 ratios), implying that phosphorous was in surplus in water columns in all the three reefs investigated. The nitrogen pollution indices were between > 0.85 to ˂ 2.45, while that of phosphorous, the pollution indices were < 0.5. The nutrient over-enrichment followed the order; Watamu > Tana Delta > Shimoni Mupunguti coral reef ecosystem. To identify the possible sources of the nutrient influx in the investigated coral reef ecosystems, a principal component analysis was carried out, and results revealed that anthropogenic activities e.g., tourism, coastal cities urbanization and change in land use practices accounted for 36.26%, while seasonality accounted for 17.82% of the total nutrients influx in the investigated coral reefs.