High Siliciclastic Input Research Articles

Carbonate factories and their critical control on the geometry of carbonate platforms (mid-Cretaceous, southern Iran)

Tropical rimmed platforms represent a much more efficient protection from coastal erosion than carbonate ramps. Understanding the controlling factors of platform geometry is therefore crucial to predict the fate of rimmed platforms under global-warming conditions. Here, we present detailed biostratigraphic, sedimentological, geochemical, and high-resolution carbon-isotope analyses of mid-Cretaceous (Albian-Cenomanian) carbonate rocks well exposed in the Khormoj section located in the Zagros Mountains of southern Iran. Sixteen microfacies were identified, allowing us to define the superposition of different platform geometries, a carbonate ramp in the Albian and a rimmed platform in the Cenomanian. Biostratigraphic and carbon-isotope analyses allowed us to identify the OAE1b, OAE1d, and Middle Cenomanian events in the Khormoj section. The paleodepth changes documented by carbonate microfacies testify to two transgressive events that can be correlated with long-term eustatic curves during the ramp stage. The Albian ramp was formed by orbitolinids under high siliciclastic input whereas the Cenomanian rimmed platform was built by rudists during clear water conditions. These two carbonate factories have drastic different carbonate sedimentation modes. The orbitolinid factory is characterized by a low carbonate production rate and fine carbonate grains resulting in ramp geometry, whereas the rudist factory is characterized by a high carbonate production rate and coarse carbonate grains leading to a rimmed platform geometry.

Sedimentological Characteristics And Paleoenvironmental Implication Of Triassic Vertebrate Localities In Villány (Villány Hills, Southern Hungary)

Abstract There are two Triassic vertebrate sites in Villány Hills (Southern Hungary), where productive and continuous excavations have been carried out in the last six years resulting in a rich and diversified assemblage of shallow marine to coastal animals. The studied formations belong to the Villány–Bihor Unit of the Tisza Megaunit, which was located at the passive margin of the European Plate during the Triassic. The relatively diverse vertebrate assemblage was collected from a Road-cut on Templom Hill and a newly discovered site at a construction zone located on the Somssich Hill. Four main lithofacies were identified and interpreted in the newly discovered Construction vertebrate site consisting of dolomite (deposited in a shallow, restricted lagoon environment), dolomarl (shallow marine sediments with enhanced terrigenous input), reddish silty claystone (paleosol) and sandstone (terrigenous provenance) indicating that the sediments of the Construction vertebrate site were formed in a subtidal to peritidal zone of the inner ramp environment, where the main controlling factor of the alternating sedimentation was the climate change. However, the recurring paleosol formation in the middle part of the section also indicates a rapid sea-level fall when the marine sediments were repeatedly exposed to subaerial conditions. In the Road-cut site the siliciclastic sediments of the Mészhegy Sandstone Formation are exposed, representing a nearshore, shallow marine environment characterized by high siliciclastic input from the mainland.

Holocene glacier fluctuations and environmental changes in subantarctic South Georgia inferred from a sediment record from a coastal inlet

AbstractThe subantarctic island of South Georgia provides terrestrial and coastal marine records of climate variability, which are crucial for the understanding of the drivers of Holocene climate changes in the subantarctic region. Here we investigate a sediment core (Co1305) from a coastal inlet on South Georgia using elemental, lipid biomarker, diatom, and stable isotope data to infer changes in environmental conditions and to constrain the timing of late-glacial and Holocene glacier fluctuations. Because of the scarcity of terrestrial macrofossils and the presence of redeposited and relict organic matter in the sediments, age control for the record was obtained by compound-specific radiocarbon dating of mostly marine-derivedn-C16fatty acids. A basal till layer recovered in Little Jason Lagoon was likely deposited during an advance of local glaciers during the Antarctic cold reversal. After glacier retreat, an oligotrophic lake occupied the site, which transitioned to a marine inlet around 8.0±0.9 ka because of relative sea-level rise. From 7.0±0.6 to 4.0±0.4 ka, reduced vegetation coverage in the catchment, as well as high siliciclastic input and deposition of ice-rafted debris, indicates glacier advances in the terrestrial catchment and likely in the adjacent fjord. A second, less extensive period of glacier advances occurred in the late Holocene, after 1.8±0.3 ka.

Influence of regional environment in guiding the spatial distribution of marine bivalves along the Indian coast

Tropical coastal areas are amongst the most diverse ecosystems in the world. However, there are quite a few coasts that have rarely been studied for their macro-benthic diversity. The Indian coastline presents one such gap area. Two sub-parallel coastlines of India have a wide latitudinal span (8–23°N) and strikingly different physiographic environments. While the east coast receives a high siliciclastic input from large river systems flowing to the Bay of Bengal with fluctuating salinity, the west coast has a large shelf area and high productivity of the Arabian Sea. Such difference enables us to evaluate the effect of regional environmental parameters on marine molluscan diversity and distribution in an intra-tropical setting. Because of the wide latitudinal range, it is also possible to assess if spatial difference in species richness in such a regional scale follows the large-scale biodiversity pattern such as Latitudinal Biodiversity Gradient (LBG) despite inherent environmental variation. We used species distribution of marine bivalves, compiled using bioSearch and the Ocean Productivity database, to address this question. Our results show that intra-tropical species richness of marine bivalves is guided primarily by regional environmental parameters. Even with identical latitudinal extent, higher nutrient availability and larger shelf area, the west coast has significantly lower richness than the east coast; among environmental variables, productivity, salinity and coastline length emerged as significant predictors of species diversity. Moreover, a positive influence of a South Asian biodiversity hotspot on east coast fauna and a negative impact of the oxygen-depleted condition of Arabian Sea on west coast fauna, may have a significant contribution in developing such coastal variation in species richness. The latitudinal variation in species richness did not follow LBG. In contrast to the coast-specific diversity difference, species composition is not found to be dictated by coastal affiliation. The composition corresponds primarily to physiographic conditions. We identified three distinct eco-regions (north-western, southern, north-eastern) with characteristic species composition corresponding to unique physiography and productivity mechanism. The NW region has low siliciclastic input and high productivity associated with upwelling during winter cooling. The NE region has a distinctly high riverine input and salinity fluctuation. The southern region, in contrast, has well developed reefal system with moderate variation in salinity. Such correspondence underscores the importance of the regional environment in dictating the species diversity and distribution in the shallow marine realm.

Paleoenvironmental distribution patterns of orbitolinids in the Lower Cretaceous deposits of eastern Rafsanjan, Central Iran

Abstract The Lower Cretaceous orbitolinid-rich deposits in eastern Rafsanjan, Central Iran were studied for analysis and interpretation of paleoenvironmental distribution patterns of orbitolinids. Based on detailed studies, a total of seven microfacies were determined. From the microfacies and paleontological studies the continental shelf (with a relative water depth of 0 to 20 m) can be separated into supralittoral, littoral–sublittoral transitional and sublittoral (includes proximal and distal sublittoral) paleoenvironmental zones. Orbitolinids with diverse test shapes were the main inhabitants of the sublittoral zone. The orbitolinids in this zone commonly represent nutrient-rich shallow warm waters of the photic zone with normal marine salinity (ca 30–40 psu) in a depth range of approximately 10 to 20 m. The general abundance or richness of orbitolinids in the sublittoral zone resulted from a nutrient-driven transgression. The studies showed that the conical orbitolinids were the most abundant forms in the sublittoral zone reflecting their better adaptation to different water depths, turbulence, light levels and substrate stability. However, the almost discoidal and discoidal orbitolinids were dominant in the middle part of the proximal sublittoral zone with a muddy substrate, deeper depth, lower water energy and decreased light intensity. All discoidal orbitolinids (slightly discoidal, almost discoidal and discoidal) were very rare and sparsely distributed in the distal sublittoral zone and the middle–outer part of the proximal sublittoral zone and generally reflect the highest sea-level rise or transgression, deepening, maximum nutrient enrichment and increased water cloudiness that can be correlated with a transgressive systems tract (TST) and probably maximum flooding surface (MFS). The lowest diversity and abundance of orbitolinids in the outer part of the proximal sublittoral zone commonly co-occurred with the presence of algal and sparse coral associations reflecting increased water temperature. Also, the absence of in situ orbitolinids in the littoral–sublittoral transitional zone resulted from high siliciclastic input and very high wave energy.

A DIVERSE PATCH REEF FROM TURBID HABITATS IN THE MIDDLE MIOCENE (EAST KALIMANTAN, INDONESIA)

The Kutai Basin (East Kalimantan, Indonesia) contains a rich and well-preserved Miocene fossil record of small patch reefs that developed under the influence of high siliciclastic input associated with the progradation of the Mahakam Delta. In this study, we reconstruct the biodiversity and paleoenvironments on one of these delta-front, mixed carbonate-siliciclastic systems that developed at the Serravallian–Tortonian boundary near the city of Samarinda. In two newly exposed sections, we analyzed the sedimentology and distribution of the main fossil biota including corals, foraminifers, coralline algae, and bryozoans. Seven facies are herein defined, including two dominated by platy corals and two by larger benthic foraminifera. Facies distributions were driven by changes in depth and variations in terrigenous input within a range of delta-front habitats. Despite the turbid conditions, fossil assemblages are highly diverse, including 69 coral species and 28 bryozoan species that occur in coral-dominated facies. Crustose coralline algae were mainly associated with the coral-dominated facies. Larger benthic foraminifera showed broader ecological tolerance within the range represented in the studied sections and thus are common in most facies. These diverse patch reef ecosystems were able to cope with high siliciclastic input during the early development of the Miocene coral reef biota.

Recovery dynamics of benthic marine communities from the Lower Triassic Werfen Formation, northern Italy

The Lower Triassic Werfen Formation of northern Italy represents an important archive for Early Triassic ecosystems. Based on quantitative community analysis using species level identifications, we reconstruct the recovery of benthic ecosystems after the end-Permian mass extinction throughout this unit. The analysis of benthic macrofossil communities shows that incipient recovery has taken place during the Griesbachian and the Griesbachian–Dienerian transition. A probable deterioration in environmental conditions is observed towards the end of the Dienerian. The Smithian part of the Werfen Formation is characterized by high siliciclastic input, which ceases around the Smithian-Spathian boundary. The Spathian marks the definitive phase of recovery in the Werfen Formation. The comparison of this pattern with other palaoegeographical regions suggests that both the Griesbachian recovery and the Dienerian decline were of inter-regional if not global extent, whereas the Smithian diversity low in the Werfen Formation is a local signal. In contrast to the recovery dynamics of ammonoids and conodonts, the Smithian–Spathian boundary interval was no caesura for benthic ecosystems. The Spathian recovery pulse is possibly also an inter-regional event, at least in the palaeotropics. These results are in contrast with the previously proposed scenario of persistent hostile conditions during the Griesbachian time interval and highlight an initial recovery phase restricted to Griesbachian times. Instead, the apparently sluggish recovery of benthic ecosystems was at least partly shaped by set-backs due to short-term environmental perturbations during the Dienerian.

The Mianwali and Tredian Formations: An Example of the Triassic Progradational Deltaic System in the Low-Latitude Western Salt Range, Pakistan

The Nammal Gorge, Salt Range, Pakistan, preserves a record of the interacting Triassic open-marine carbonate sedimentation, cyclic siliciclastics progradation and fluctuating relative sea level. The sediments at the bottom in the Mianwali Formation, show bivalves and ammonoids rich wacke- to packestone lithofacies (i.e. ML 1 and ML 2), which indicates an open-marine depositional setting. The overlying shale of the Mianwali Formation (i.e. ML 3), has ammonoids and gastropods, the lower part of which indicates a relatively deep-marine depositional setting. Upwards, the ML 3 grades into the sandstones and shales (i.e. ML 4), which show ripple marks, mudcracks, bioturbation, graded, and cross bedding and syndepositional deformation. These features indicate deposition in delta lobe/shoreline sub-environments, with a high siliciclastic input. The lower part of the overlying Tredian Formation contains interbedded shale and sandstone (i.e. TL 1), having large scale slumps, which indicate deposition in cyclic, proximally located varied sub-environments of the delta topsets/channels and in the flood plain environments. The overlying thick, coarse, conglomeratic sandstone (i.e. TL 2) has planar, trough cross bedding and lenticular channelized bedding, which indicates a fluvial to continental environment. Further up, in the Tredian Formation, the presence of dolomite (i.e. TL 3) represents marine transgression. The facies association in the Mianwali and Tredian formation indicates many coarsening upward cycles representing the progradation of individual delta lobes. This study therefore proposes that, subsequent to the Permian-Triassic paraconformity, an open-marine depositional setting established in this area that gradually built up into a progradational deltaic system.

Stable carbon isotope stratigraphy in the Ordovician of South China

About 500 samples from 11 Ordovician sections in South China have been analysed for their δ 13C carb composition. Four sections are located in the Yangtze platform region, the remaining seven sections in the Jiangnan slope region. The sections span more or less the entire Ordovician, but the sample resolution in its lower part (Tremadocian to Dapingian) is lower than in its upper part (Darriwilian to Hirnantian). Overall, the data show a good correlation with the published global isotope curve. At the Cambrian–Ordovician boundary positive values are observed. In the succeeding Tremadocian the values decrease and remain negative into the early Floian. In the late Floian, the values increase to slightly positive. The correlation of Dapingian rocks between the Yangtze and the Jiangnan regions is somewhat problematic which might be due to high siliciclastic input in the Yangtze section. In the Darriwilian a small positive excursion is observed in the Yangtze platform area, however, it is missing in the Jiangnan slope area. This excursion probably correlates with the mid-Darriwilian excursion (MDICE) reported from Baltoscandia. Both chemostratigraphy and conodont biostratigraphy indicate a possible gap between the Shihtzupu Formation and the Pagoda Formation, i.e. most of the Sandbian is probably not represented in the Upper Yangtze region. The earliest Katian is characterised by a pronounced positive excursion correlating with the well-known global Guttenberg excursion (GICE). In the late Katian at least one additional positive excursion was determined. The precise biostratigraphy, however, is not clear, and therefore it is not known which of the known four to five remaining Katian δ 13C excursions identified in Baltica correlate(s) with the one(s) observed in the present study, and further biostratigraphic study is required. The lower part of the Hirnantian excursion (HICE) is probably not preserved, with only small remnants of the HICE observed near the base of the Kuanyinchiao Bed.

Microfacies Analysis of Upper Eocene Shallow-water Carbonates from the Rodnei Mountains (N Romania)

A Priabonian carbonate ramp developed in the NW Rodnei Mountains as a part of a Paleogene sedimentary cover that overlies the metamorphic basement of the Eastern Carpathians (N Romania). Two sections, namely Iza Valley and Btrâna Spring, were sampled at different locations along the carbonate ramp. The deposits accumulated in a shallow environment, in which relative sea level change is seen as the main controlling factor of facies distribution. A shore facemiddle rampinner ramp transition was recorded in both sections. Associations of large benthic foraminifers and high siliciclastic input are the dominant features in the northern part of the ramp, while in the south corals and coralline algae thrived in an environment characterized by low hydrodynamic energy and clastic input. A 4-5 m thick intercalation identified in the middle ramp deposits of both studied sections shows a temporary change in fossil assemblages, with foraminifers almost completely replaced by red algae and rhodoliths, and extensive bioturbation caused by ostracods and gastropods. Towards the top of the carbonate deposits, large bivalve colonies and an increase in clastic input indicate a relative sea-level fall, which ultimately led to the cessation of carbonate sedimentation and the deposition of black shales on a basin-wide scale during the Lower Oligocene.

Three‐hundred‐year hydrological changes in a subtropical estuary, Rookery Bay (Florida): Human impact versus natural variability

The coastal wetland ecosystems in Florida are highly sensitive to changes in freshwater budget, which is driven by regional sea surface temperature, tropical storm activity, and the El Niño–Southern Oscillation (ENSO). Although studying Florida wetlands is pivotal to the understanding of these interacting climate systems, wetland dynamics have been severely altered by recent land use and drainage activities. To gather insights into the natural variability of the coastal ecosystems in Florida versus the effects of anthropogenic impact in the area, we present a 300‐year record of changes in the hydrological cycle from a shallow subtropical estuary (Rookery Bay) on the western shelf of Florida, Gulf of Mexico. Palynological (pollen and organic‐walled dinoflagellate cysts), diatom, and sedimentological analyses of a sediment core reveal significant changes in past runoff and wetland development. The onset and development of human impact in Florida are evident from high influx of Ambrosia pollen at about A.D. 1900, indicative of land clearance and disturbed conditions. To date, this is the southernmost record of Ambrosia increase related to human impact in the United States. Wetland drainage and deforestation since A.D. 1900 are evident from the reduced freshwater wetland and pine vegetation, and lower abundances of phytoplankton species indicative of lagoonal and brackish conditions. High runoff after A.D. 1900 relates to increased erosion and may correspondingly reflect higher impact from hurricane landfalls in SW Florida. Several phases with high siliciclastic input and greater wetland pollen abundance occur that predate the human impact period. These phases are interpreted as periods with higher runoff and are likely related to regional longer‐term climate variability.

Faunal turnover and changing oceanography: Late Palaeozoic warm-to-cool water carbonates, Sverdrup Basin, Canadian Arctic Archipelago

Carbonate sedimentary rocks in the Fosheim–Hamilton sub-basin at the eastern end of the Sverdrup Basin contain a particularly sensitive record of changing palaeoceanography and faunal turnover during the northward movement of Pangaea through the Late Palaeozoic. Carboniferous and earliest Permian inner ramp carbonates are a photozoan association of colonial corals, fusulinids, algae and ooids, with sparse heterozoan elements (crinoids, brachiopods and bryozoans). Based on modern analogues these biotic components reflect warm-water oligotrophic marine environments. Contemporaneous mid-ramp and basin biotas are dominated by a heterozoan fauna (solitary corals, crinoids, bryozoans and brachiopods) that grew in cooler deeper waters that may have been beneath a thermocline. Initial cooling began in the latest Sakmarian with an influx of cool deep water and climatic deterioration allowing cool and warm waters to mix, disrupting the thermocline, and producing a sub-tropical marine biota whose remains were reworked by storms and re-deposited as tempestites. Faunas are heterozoan (crinoids, bryozoans, brachiopods and sponges) with photozoan elements (colonial corals and symbiont bearing fusulinids) prominent only in inner ramp facies. By late Artinskian these photozoan components are only present in shallowest basin-margin environments. Artinskian subtropical waters contained somewhat elevated trophic resources that together with mixing of photozoan and heterozoan elements in the subtropical inner ramp produced the greatest faunal diversity seen in the Sverdrup Basin. The biota was completely boreal in nature, and warm shallow waters with a warm refuge biota, were now supplemented by cool waters derived from the Panthalassa Ocean. Profound change took place in the Kungurian, coincident with localised uplift during the Melville Disturbance and increased siliciclastic input. Neritic, storm-dominated sediments are wholly heterozoan (brachiopods, bryozoans, crinoids and sponges) with no remaining photozoan elements. Nutrient levels are elevated (but not eutrophic) as indicated by phosphate and glauconite, extensive bioerosion, numerous infaunal foraminifers, and an impressive and diverse shelly biota, that during times of high siliciclastic input was replaced by a profuse Zoophycos infauna. Brachiopod and bryozoan faunas are distinctly boreal. Continued cooling, relatively high nutrients, as indicated by abundant glauconite and phosphate, and decreased siliciclastic input eventually resulted in an abundant heterozoan biota (brachiopods, bryozoans, crinoids and sponges) with local gigantism, but reduced brachiopod and bryozoan diversity. These Middle Permian rocks may be the coolest water deposits in the Sverdrup Basin. The faunas are still part of a boreal Arctic province, with strong ties to cool water faunas of Uralian basin. The succession ends with Late Permian biosiliceous spiculitic cherts containing accessory heterozoan components (brachiopods, bryozoans and few crinoids). These sediments, in part coeval with evaporites and terrestrial red beds on the Eastern European Platform, are interpreted to reflect a combination of cool waters, elevated nutrients, and mid-latitude storminess.

Development of Equatorial Delta-Front Patch Reefs During the Neogene, Borneo

Abstract Miocene patch reefs formed in turbid waters associated with high siliciclastic input at the seaward margin of the equatorial Mahakam Delta in eastern Borneo, SE Asia. Patch reefs were initiated on unstable substrates on localized low-relief bathymetric highs associated with delta-front channels or distributary mouthbars in the process of abandonment. Patch reefs developed only in shallow waters, formed low-relief buildups, lacked rigid frameworks, and had gently sloping margins. Although the biodiversity of the patch reefs may be comparable with that of clear-water systems, all the organisms present were adapted to turbid-water areas associated with siliciclastic, and sometimes nutrient, influx. The patch reefs were transient features, and their demise was influenced by increased siliciclastic and nutrient input, perhaps at times associated with deepening. Carbonate production and bioherm or patch-reef development can occur in turbid-water delta-front areas as localized or more regionally extensive units during any phases of eustatic sea level. However, development and preservation of turbid-water carbonates is most likely during relative transgression or perhaps late lowstand periods. This is in contrast with common highstand carbonates from clear-water shelves, where nearly pure carbonates interdigitate with siliciclastics. It is the interplay between factors such as tectonics, eustasy, delta lobe switching, shelf currents, and amount and size fraction of siliciclastic influx that ultimately controlled carbonate development and preservation.

Stromatolitic and Trace Fossils Community of the Cerro Victoria Formation, Arroyo del Soldado Group (Lowermost Cambrian, Uruguay)

The Cerro Victoria Formation of the Arroyo del Soldado Group (Uruguay) comprises 400 m of mainly stromatolitic, micritic and oolitic limestones. In this low-diversity stromatolite paleocommunity, moundlike and planar laminites dominate, but columnar forms, ooids and pisoids occur as well. Stromatolites played a major role in the construction of the carbonate ramp, which developed onto a passive (eastern) margin of the Río de la Plata Craton. A paleobiological reconstruction of the stomatolite community, which includes subtidal, intertidal and supratidal environments, is presented. A low-diversity trace fossil association, dessignated as “Thalassinoides-Gyrolithes-Palaeophycus” assemblage, is preserved in syngenetic concretions. The stromatolite community, ichnofossil assemblage and ichnofabrics are typical for the lowermost Cambrian, corroborating earlier age estimations. The unit represents a shallowing-upward sequence deposited under predominantly subtidal, normal marine, high energy conditions. Tropical climate prevailed, as shown by thick carbonate deposits, evaporitic minerals (halite, gypsum) and abundance of ooids. The Cambrian of western Gondwana is characterized by scarcity of carbonate ramps. This was mainly determined by high siliciclastic input related to erosion of the Pan African-Rio Doce orogenic belts. Carbonate ramps developed in blocks located at tropical paleolatitudes and characterized by low clastic input, such as the Nico Pérez Terrane and Argentine Precordillera.