Episodic Sedimentation Events Research Articles

Pulse sediment event does not impact the metabolism of a mixed coral reef community

Sedimentation can bury corals, cause physical abrasion, and alter both spectral intensity and quality; however, few studies have quantified the effects of sedimentation on coral reef metabolism in the context of episodic sedimentation events. Here, we present the first study to measure coral community metabolism - calcification and photosynthesis - in a manipulative mesocosm experiment simulating a pulse sediment event. We exposed a mixed benthic community composed of 75% live carbonate rubble cover and 25% Montipora capitata coral cover to an approximately 275 mg cm−1 (sediment accumulation) acute pulse sediment loading event. No differences were found in net calcification or net photosynthesis between the control and treated mesocosms 48 h and 25 d following exposure to pulse sediment input. Results from this community experiment indicate the ability of Montipora capitata, a common reef coral, to persist under these acute sediment levels, demonstrating resistance to episodic sediment events.

Are early plants significant as paleogeographic indicators of past coastlines? Insights from the taphonomy and sedimentology of a Devonian taphoflora of Paraná Basin, Brazil

The continental colonization process by plants is an underexplored theme in Brazil, especially concerning taphonomic studies of plants that existed during this age. This study aims to interpret the taphonomic and paleoenvironmental settings that best represent the fossil plant assemblages preserved in the upper strata of the Furnas Formation (Lower Devonian of Paraná Basin), at Jackson de Figueiredo county, municipality of Jaguariaíva (Paraná), clarifying the potential of these fossil plant assemblages for paleogeographic reconstructions. Taphonomic and sedimentological signatures were analyzed and submitted to multivariate statistical analyses (cluster and correspondence analyses). Two taphonomic groups were identified (Taphofacies A and B). The interpretation of the two groups allowed the visualization of: Taphofacies A, which consists of samples with a dispersed degree of packing, fragmented plant fossils, 40% mica with sizes between 0.5 and 1 mm and no trace fossils, is representative of relatively high-energy conditions; and Taphofacies B, which consists of densely packed plants with partial degree of fragmentation, 10% mica with sizes under 0.5 mm and both horizontal and vertical trace fossils, is representative of relatively low-energy conditions. Our taphonomic data are consistent with previous facies interpretations of a lagoon/interdistributary bay environment. In this context, taphofacies A represents episodic sedimentation events influenced by fluvial dynamics, yielding assemblages that are not suitable for paleogeographic interpretations, while Taphofacies B represents fossil assemblages originated in a low-energy sedimentary regime, with utility for paleogeographic reconstructions.

Carbon isotope (δ13Ccarb) heterogeneity in deep-water Cambro-Ordovician carbonates, western Newfoundland

Carbonates of western Newfoundland span the Cambro-Ordovician interval and preserve a record of slope-basinal deposition in the Cow Head Group near Cow Head. This unit consists of conglomerates and ribbon and laminated limestone interbedded with shale that is well exposed in sea cliffs at Cow Head Peninsula. These conglomerates, although prevalent throughout the section, vary in thickness and abundance stratigraphically and record both local disruption and large-scale episodic sedimentation events. Microfacies drilled for carbon isotope (δ13Ccarb) analysis of conglomerates reveal isotopic heterogeneity within individual samples, in some cases more than 1‰. While this might be an expected outcome of drilling multiple areas of a heterogeneous conglomerate hand sample, permil-level variability was observed both between individual clasts in a sample, between different parts of the same matrix, and between a clast and its surrounding matrix. No associated variation in δ18Ocarb or trace element distributions exists to suggest that this δ13Ccarb variability is the result of later-stage meteoric diagenesis. The δ13Ccarb variability suggests multiple sources of dissolved inorganic carbon (DIC) associated with carbonate precipitation for phases within these individual samples. These data indicate that processes such as local organic matter remineralization and early authigenic carbonate precipitation during lithification at the sediment–water interface (SWI) are either contributing to or controlling δ13Ccarb values in Cambrian carbonates, perhaps more so than at other intervals in Earth history.

Effects of mass sedimentation events after the 2011 off the Pacific coast of Tohoku Earthquake on benthic prokaryotes and meiofauna inhabiting the upper bathyal sediments

We examined the effects of mass sedimentation events caused by the 2011 off the Pacific coast of Tohoku Earthquake on abundances and vertical distributions of prokaryotes and metazoan meiofauna in sediments, using sediment cores collected from eight bathyal stations off Tohoku 1 year after the M9.0 earthquake. Event deposits 1–7 cm thick were observed at the topmost part of the sediment cores at all sampling stations. At some stations, prokaryotic cell abundances were lower in the surface event-deposit layers compared to those in deeper sediments. These variations were explained by environmental parameters such as a dimensionless sorting factor and mean grain size, suggesting that turbidite sedimentation affected prokaryotic cell abundances. Nematodes had anomalously higher subsurface abundances at the stations where subsurface peak prokaryotic cell numbers were observed, whereas copepods always showed peak densities in the sediment surface layer. Although there are no available data for prokaryotic cell abundances and meiofaunal densities before the earthquake from the same sites, it is likely that the subsurface peaks in prokaryotic cell numbers and nematode densities resulted from the sedimentation events. The effects of sedimentation events on the organisms were observed 1 year after the earthquake, indicating that episodic sedimentation events on scales of several centimeters have a large effect on small organisms inhabiting sediments.

Post-depositional alteration and preservation of sedimentary event layers on continental margins, I. The role of episodic sedimentation

The degree of post-depositional alteration and hence the preservation potential of sedimentary event beds and transient signals is determined by the outcome of a ‘race’ between biological (and to a lesser extent physical) processes that conspire to destroy a signal and sediment accumulation which advects the layer or signal out of the surface mixing zone. Preservation potential specifically depends on the relative magnitudes of the (1) biological mixing intensity (sometimes parameterized as a biodiffusivity, D b), (2) mixing-layer thickness, (3) layer or signal thickness, and (4) sediment accumulation rate. These terms control the dissipation time (i.e. time required to destroy a signal) and the transit time (i.e. time necessary to advect a signal through the surface mixing layer). On fine-grained, upper continental margins in general, and the Eel River shelf (northern California) in particular, biological mixing intensity is high (i.e. D b ranges from 10 to 100 cm 2/yr), mixing-layer thickness is large (>10 cm), and sediment accumulation rates are rapid (0.1–1 cm/yr). Despite the high sediment accumulation rates, transit times through the surface mixing-layer range from decades to a century. Signal dissipation times are considerably shorter: (1) <3 yr for beds up to 6 cm thick imaged in X-radiographs, and (2) <15 yr for the grain-size signature of beds up to 8 cm thick. Therefore event layers and their corresponding grain-size signature have a low probability of preservation. However, short-lived episodic sedimentation events (e.g. oceanic floods) can instantaneously advect material through the surface mixing layer, thereby preserving event beds and transient signals. On the Eel River shelf the sequential timing of episodic sedimentation events has exerted a first-order control on the resultant stratigraphic record (presence/absence of layers and grain-size fluctuations). Episodic sedimentation – a hallmark of continental shelf settings – is key to understanding strata formation and preservation on margins.

Accumulation of algal pigments and live planktonic diatoms in aphotic sediments during the spring bloom in the transition zone of the North and Baltic Seas

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 248:41-54 (2003) - doi:10.3354/meps248041 Accumulation of algal pigments and live planktonic diatoms in aphotic sediments during the spring bloom in the transition zone of the North and Baltic Seas Jørgen L. S. Hansen*, Alf B. Josefson National Environmental Research Institute, 4000 Roskilde, Denmark *Email: joh@dmu.dk ABSTRACT: The sediment contents of algal pigments and live planktonic diatoms were measured in cores sampled at 6 stations with aphotic sediments at depths between 27 and 55 m located in the transition zone between the Baltic Sea and the Skagerrak. Five of the stations were sampled before and after the spring phytoplankton bloom in 2001. Within the area, there was a highly significant increase after the bloom in the sediment content of viable planktonic diatoms, quantified by the dilution extinction method, and in the sediment content of the pigments chlorophyll a and fucoxanthin. The composition of algal pigments as well as the number of germinable diatoms suggested that live pelagic diatoms were the source of almost the entire pool of chlorophyll a in the sediment both before and after the spring bloom. In the northern Kattegat, Great Belt, Femer Belt and in the Arkona Sea, the pools of diatoms increased 10- to 100-fold during the spring bloom. In total, the sediment received between 0.3 and 4 million germinable units of pelagic diatoms cm-2. In terms of organic nitrogen, the enrichment of live diatoms in the sediment corresponded to on average 202% of the total spring bloom production, calculated from the pool of nitrate consumed in the water column during the spring bloom. A similar calculation based on the enrichment of the pigments chlorophyll a and fucoxanthin indicated input corresponding to 24 and 64% respectively of the potential production during the spring bloom. There was considerable variation among stations; in the central Kattegat there was no detectable sedimentation of diatoms or pigments. Here, the pools of pigments and diatoms decreased during the spring bloom and the shape of the pigment profiles also indicated that these pools did not originate from a recent input. Other stations received twice as much diatom biomass than could be produced from the pool of inorganic nitrogen in the mixed layer before the bloom. It is hypothesized that the unequal distribution of the spring bloom sedimentation is a result of episodic sedimentation events in combination with advection of the water masses. The potentials of using sediment profiles of pigments to quantify spring bloom sedimentation are discussed. KEY WORDS: Diatoms · Spring bloom · Benthic-pelagic coupling · Sediment · Chlorophyll a · Fucoxanthin Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 248. Online publication date: February 20, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Modern tropical analogs for Carboniferous standing forests: Comparison of extinct Mesocalamites with extant Montrichardia

Assemblages of in situ upright stem casts, or fossil standing forests, provide information on the composition and spatial arrangement of the original plant communities they record, with minimal taphonomic bias. Stands of calamites and lycopsids are found repeatedly as fossil forests in the Late Carboniferous, while other major groups of plants are only rarely preserved in this way. The Carboniferous coal measures of Europe and North America were formed in low‐latitude, tropical environments. The ancient plant communities of these settings can be interpreted by comparison of their taxa with specific, modern tropical analogs. Here, ancient standing forests of the extinct sphenopsid Mesocalamites suckowii are compared with modern stands of the monocot Montrichardia arborescens. These modern analogs occur in the Orinoco Delta of Venezuela and the mouth of the Amazon. Montrichardia and its ancient counterparts occur in comparable clastic facies of fluvio‐deltaic and estuarine depositional systems. Although Mesocalamites and Montrichardia are very different anatomically and taxonomically, they exhibit some intriguing morphological similarities that can be linked to a common ecology. These modern and ancient taxa have evolved convergent forms of vegetative propagation that enable the plants to colonize and survive in environments characterized by very high rates of sedimentation, or episodic sedimentation events. Such environments have an unusually high potential to preserve standing forests.

Sedimentary environments and facies in an arctic basin, Itirbilung Fiord, Baffin Island, Canada

Itirbilung Fiord typifies a deep arctic basin that experiences episodic sedimentation events, cycled principally by aeolian transport, nival and glacier melt, with punctuations by mass-sediment failures. A Quaternary sedimentary fill exceeding 150 m is found in two of the fjord's four sub-basins. Basin circulation is associated with meltwater influx during the summer, wind-generated drift during the fall accompanied by deep-water exchanges, winter isohaline-generated circulation, and tidal currents which operate over the entire year. Sediment accumulation decreases down the basin; this general trend is interrupted by side-entry fan deltas that locally contribute large volumes of sediment. Basin deposits are largely ponded between the fjord walls, although two of the fjord's sills are mantled by hemipelagic deposits. Five seismo-stratigraphic units are identified and may represent sedimentary deposits associated with a single phase of ice sheet advance and retreat. The upper three seismic units were cored and contain seven sedimentary facies that show little correlation between sub-basins: pebbly-sandy-mud, from the melt of debris-laden ice; burrowed /mottled mud, reflecting the bioturbation of hemipelagic deposits; wispy laminated /mottled mud, from low-velocity currents and/or melt-out of seasonal sea ice cover, and bioturbation; laminated sand and mud, from the hypopycnal flows from rivers; graded-coarse sand/gravel, and pebbly sand and sand, reflecting very rapid deposition from high-concentration turbidity currents or from sandy debris flows; and cross-bedded sands, that may relate to the reworking of turbidity current deposited sands, possibly by reverse flow mechanisms.

Recent geochemical history of flood deposits in the northern Chesapeake Bay

210 Pb and 137 Cs dating of sediment cores from the extreme northern Chesapeake Bay has revealed that episodic sedimentation events associated with Susquehanna River floods in 1936 and 1972 have contributed half of all sediment deposited in this area since 1900. Much of this sediment is derived from resuspension of sediment trapped along the riverbed during years of normal riverflow. The normal 210 Pb determined sedimentation rate in this region, excluding flood events, is 0·45 cm year −1 which is in good agreement with rates previously estimated from sediment budget models. The long term sedimentation rate is probably twice this value which is in agreement with drainage basin sediment yield and denudation rate studies.

Abyssal traces and megafauna: comparison of productivity, diversity and density in the Arctic and Antarctic

The megafauna and associated behavioral traces of two deep-sea benthic environments, the central Arctic and Antarctic, with a surface primary productivity differential of 104 were compared to assess the role of food availability in foraging strategy and community structure. Bottom photographs, analyzed for megafauna and trace density and diversity at comparable depths in the Arctic Canada Basin and the Antarctic Bellingshausen Basin, indicated that trace frequency was inversely proportional to organism density but that trace diversity directly reflected organism diversity. Those traces identified in the fossil record to represent efficient foraging strategies, i.e., the Nereites facies, were conspicuously absent at all depths in the Arctic and present at all depths in the Antarctic, in contradiction of the paradigm of increasing behavioral complexity and sediment exploitation as food availability decreases. Presence or absence of surface-grazing organisms seems to exert a greater influence on trace diversity than depth or nutrient supply. Trace density, however, may reflect episodic sedimentation events which intermittently influence the deep-sea trophic regime.

Morphological variability and temporal change in a Paleocene lucinid bivalve mollusk

Analysis of morphological variability, using six characters, in four stratigraphically successive popula­tions of the lucinid bivalve mollusk Myrtea (Gonimyrtea) uhleri shows a unidirectional trend toward decreasing mean size. Differences in mean length for stratigraphically adjacent populations are significant at the 5% level of probability. Chronoclinal trends toward decreased magnitude of apical angle meas- urements and of increased magnitude of two form ratios associated with apical angularity can be ex­plained by a tendency toward increase with growth in the quadrateness of the shell. Thus, populations of smaller mean size are also on average more trigonal. The observed decrease in mean size is associated with marine regression in the study area (Paleocene Brightseat and Aquia Formations of Maryland and Virginia, U.S.A.). Earlier representatives of the species are more common in an offshore facies, and later ones are more common in a nearer-shore but still subtidal one. Comparing specimens from nearshore and offshore facies without regard to stratigraphic position shows a statistically significant difference in size; the nearshore specimens are nearly 20% smaller, on average, than the offshore ones. Possible contributors to the size decrease may have been a slowdown of growth rate in the physically more· rigorous nearshore facies; an increased probability of mortality at earlier ages in episodic sedimentation events, expected to occur more frequently nearer shore; or selection for accelerated maturation in more rigorous and unpredictable environments.