Changes In Sedimentary Processes Research Articles

Sedimentary Processes and the Temporal Resolution of Sedimentary Strata

AbstractAn appealing strategy for reconstructing the timing and tempo of paleoenvironmental change from sedimentary strata is to linearly interpolate between marker beds of known age. This method requires significant assumptions, but more advanced age modeling methods are usually not feasible. We used experiments to explore how changes in sedimentary processes invalidate these assumptions and affect estimates of time from the strata. When sedimentary processes changed to favor widespread deposition, we found that measuring time linearly systematically overestimated time duration from the resulting strata (time dilation) and misestimated the beginning and end of geologic intervals (phase shifting). When simple age models must be used for sedimentary strata, geologic evidence for transient changes in spatial sediment dispersal may help identify sections of dilated and shifted time, and better resolve time in sedimentary strata.

The Far-Field imprint of the late Paleozoic Ice Age, its demise, and the onset of a dust-house climate across the Eastern Shelf of the Midland Basin, Texas

The late Paleozoic is a period of pronounced climatic and tectonic change, characterized by the onset and disappearance of continental-scale glaciers across polar Gondwana, the formation of Pangea, and widespread large igneous province volcanism. The low-latitude equatorial tropics are assumed to be places of persistent warm and wet climatic conditions throughout the Phanerozoic, which through intense silicate weathering, exert a major influence on Earth’s climate via the consumption of atmospheric carbon through carbonic hydrolytic weathering, formation of clay minerals and deliverability of alkalinity to ocean basins. Here we investigate the late Paleozoic sedimentary record of the Eastern Shelf of the Midland Basin in order to refine the climatic and provenance record of this region. The Eastern Shelf of the Midland Basin was situated within the equatorial tropics throughout the late Paleozoic and was connected to the open ocean through a network of fluvial systems that drained into the marine Midland Basin. We present new U-Pb zircon geochronology (19 samples, 2591 analyses) and sedimentary petrography (11 samples, 5800 grain counts), which we integrate with previously published paleobotany, paleosol chemistry and clay mineralogy to provide a holistic climate and tectonic record from this region. We observe major changes in sedimentary processes that we attribute to the formation of Pangea, eustatic changes linked to a dynamic high-latitude glaciation and teleconnections with low latitude hydrology, and a long-term shift in the Earth climate system all of which result in a dynamic sediment provenance history. Late Pennsylvanian and earliest Permian deposits are enriched in zircons with local affinity and interpreted to reflect local uplift and repeat incision across the basin margin, the latter a result of glacioeustatic forcing during an “everwet” climate. A major paleoenvironmental shift occurs in the late early Permian, which is reflected by the transition from fluvial to mixed fluvial-aeolian and ultimately aeolian dominant sedimentation by the late Permian. The transition from fluvial to aeolian dominant sedimentation is accompanied by a change in clay chemistry, sedimentary rock textual maturity, paleosol morphology and a threefold increase in Paleozoic zircons in the mid to late Permian strata. Widespread loess deposits across equatorial Pangea during the Permian have been used to argue for the possibility of equatorial glaciers situated in highland settings during the early Permian. Conversely, our data suggest initiation of a substantial component of aeolian deposition across the field areas, which is coincident with widespread ice loss across high latitude Gondwana, and ultimately highlights the teleconnections between high latitude glaciation and the low latitude hydrologic cycle.

The interplay of fluvial, lacustrine and aeolian deposition and erosion along the Neales Cliffs and its relevance to the evolution of Kati Thanda-Lake Eyre, central Australia, during the Quaternary

ABSTRACT A high-resolution record of fluvial, aeolian and lacustrine deposits of Late Pleistocene age is exposed along the Neales Cliff in the lower reaches of the Nappamurra-Neales River, western Kati Thanda-Lake Eyre (KT-LE). Five major stratigraphic units reflect a variety of changes in sedimentary processes, depositional environments and hence palaeo-lake level fluctuations. This detailed record of a dryland terrestrial sedimentary succession in the northern part of KT-LE enables comparison to contemporaneous sequences in the southern part of KT-LE. The sedimentary record from the Neales Cliff area is placed into a continental stratigraphic framework, in which changes in sediment accumulation and depositional style are linked to climatically driven palaeo-lake level fluctuations independent of eustatic sea-level changes. Following the ~200 ka interglacial maximum, a drying-up systems tract is represented by a fluvial fining-upward trend, capped by palaeosols. A wettening-up systems tract followed, when lake level rose to +10 m AHD during the last interglacial, resulting in a lacustrine succession but punctuated by regular desiccation events. During the following drying-up systems tract, progressive lake-level fall resulted in deep incision around 100 ka, followed by enhanced fluvial deposition of fine-grained sediments. A brief rise in base level resulted in a wettening-up systems tract comprising a thin veneer of fluvial/alluvial sediments followed by extensive dune build-up and desert pavement development during the Last Glacial Maximum. Subsequent lake level fall to the present lake level of −15 m AHD, resulted in deep incision of up to 10 m by the modern day Nappamurra-Neales River.

Grain-size characteristics in lake Fuxian sediments: Implication for dry-humid transformation of Indian summer monsoon over the past 150 years

Polymodal distributions and end-member modeling of grain-size in lacustrine sediments can reveal the changes in sedimentary processes, transportation mechanisms, and climatic changes. The temporal and spatial variation characteristics of grain-size were investigated in six sediment cores of the plateau deep-lake Fuxian, in southwest China, where the climate was driven by Indian Summer Monsoon (ISM). Results indicated that the size of the dominant grain-size exponentially decreased with the declining hydrodynamic condition towards the deep-water zones, with an exception of the maximum grain-size near the outlet of the lake. Measured grain-size distributions were classified into four end-members (EMs) with a basic end-member model algorithm (BasEMMA), of which could be linked to a distinct transport mechanism and source: EM1 (long-term suspended load from atmospheric dust) with the modal size of 0.3–11.2 µm, EM2 (off-shore suspended load from fine riverine input) with 7.9–14.2 µm, EM3 ((near-shore suspended load from coarse riverine input) with 15.9–31.7 µm, and EM4 (near-shore riverbed load from extremely coarse riverine input) with 35.6–70.9 µm, respectively. Temporal variation of EM2 + EM3 components of grain-size in Core F5 are responses to the changes in instrumentally recorded precipitation in Chengjiang (1961–2008) and ISM (1860–2006), which indicates that changes in river flow in response to changes in precipitation is the primary driver of clastic sediment deposition especially in the narrow section of the lake. Our findings indicate grain-size distribution and sediment compositions are significant tools for improving the understanding of the spatiotemporal heterogeneity in dry-humid transformation of ISM over the past 150 years.

Changes in Sedimentary Processes in Macrotidal Flats in Garolim Bay, West Coast of Korea

Changes in Sedimentary Processes in Macrotidal Flats in Garolim Bay, West Coast of Korea

Spatio-temporal variations of sedimentary metals in a large suburban lake in southwest China and the implications for anthropogenic processes

Environment quality of suburban and urban lakes receives special attention due to their great impacted by human perturbations and important roles in ecosystem services. Herein, the spatio-temporal variations of 10 metal and metalloid elements in 13 sediment cores from a large suburban lake (Dianchi) were studied to explore the changes in sedimentary environment and pollution and their associations with human activities since the last century. Concentrations of each element were largely varied at spatial scales, but showed similar vertical trends among the profiles, suggesting comparable changes in sedimentary processes in each lake region. Cluster analysis showed two groups of elements: group I includes Al, Ti, Cu, Cr and Ni, and group II includes As, Cd, Hg, Pb and Zn. Temporally, concentrations of all elements were generally constant until the 1950s. Thereafter, group I elements along with the clay percentage started to decrease, indicating accelerated input of coarser soils due to strengthening human perturbation and changing land use. However, group II elements showed increasing values of concentrations, particularly the enrichment factors (EF = 1.0–10.8), which peaked between mid-1990s and 2000, indicating continued pollutants input with watershed economic development. With the implementation of environment management measures, pollution was initially restrained or reduced in recent decades as indicated by the stable EFs and sedimentary fluxes of Cd, Hg, Pb and Zn and decreasing values of As. Spatially, the stocks of anthropogenic As, Cd, Hg, Pb and Zn were higher in the northern while lower in the southern lake area. This spatial difference was mainly due to the large input of industrial and domestic wastewaters in the northern compared to the area in the southern that receives runoff from agricultural and forested land. Overall, the spatio-temporal patterns in accumulation of metal and metalloid elements in the lake reliably reflected the impacts of watershed human activities.

Climate variability and sea level change during the Holocene: Insights from an inorganic multi-proxy approach in the SE Brazilian continental shelf

Two sediment cores collected in the shelf off Rio de Janeiro (RJ13-01B: 10.8 cal kyr BP, and RJ13-02B: 4.7 cal kyr BP) were investigated in high-resolution to evaluate changes in sedimentary processes and paleoclimatic and paleoceanographic variability during the Holocene in the Southeastern Brazil. Information from inorganic proxies of continental input (Al/Ca and Fe/Ca), redox-sensitive elements (Fe/Al, V/Al and Mn/Al), paleoproductivity (Sr/Al, Cd/Al and Ba/Al), as well as data for grain size, geophysical properties (p-wave velocity, gamma-ray density, acoustic impedance, magnetic susceptibility and porosity), Si, total organic carbon and calcium carbonate were considered. The data revealed three main periods of sediment accumulation: (i) from 10.8 cal kyr BP to 7.6 cal kyr BP the sediment was coarse, Si content was high (27%), the magnetic susceptibility was low and the presence of shell fragments all suggest a period of low continental input and the deposition site was shallow (i.e, lower sea level); (ii) from 7.5 cal kyr BP to 4.6 cal kyr BP the elevated ratios of Al/Ca (0.69 ± 0.08), Fe/Ca (0.27 ± 0.04), Sr/Al (31.57 ± 4.47) ×10−4, Cd/Al (0.09 ± 0.03) ×10−5 and Ba/Al (0.70 ± 0.16) ×10−4 are consistent with a period of maximum sea transgression and elevated influence of the nutrient-rich South Atlantic Central Water (SACW); (iii) from 4.5 cal kyr BP to the present, events of higher fluxes of TOC, Ni, Cu and Zn were observed from ca 3.2 cal kyr BP to 3.4 cal kyr BP, in both cores, related to humid climate. Overall, the multi-proxy approach shed light on the effects of climate and oceanographic variability on sediment input and accumulation in a less-studied portion of the Brazilian shelf, which are consistent with other shelf areas and with changes in regional climate systems like the Intertropical Convergence Zone (ITCZ), South American Monsoon Systems (SAMS) and South Atlantic Convergence Zone (SACZ).

Neogene to Quaternary stratigraphic evolution of the Antarctic Peninsula, Pacific Margin offshore of Adelaide Island: Transitions from a non-glacial, through glacially-influenced to a fully glacial state

A detailed morphologic and seismic stratigraphic analysis of the continental margin offshore of Adelaide Island on the Pacific Margin of the Antarctic Peninsula (PMAP) is described based on the study of a regular network of reflection multichannel seismic profiles and swath bathymetry. We present an integrated study of the margin spanning the shelf to the continental rise, establish novel chronologic constraints and offer new interpretations on tectonic evolution and environmental changes affecting the PMAP. The stratigraphic stacking patterns record major shifts in the depositional style of the margin that outline three intervals in its evolution. The first non-glacial interval (Early Cretaceous to middle Miocene) encompasses a transition from an active to a passive margin (early Miocene). The second glacially-influenced interval (middle to late Miocene) is marked by pronounced aggradational sedimentary stacking and subsidence. Ice sheets advanced over the middle shelf of the margin at the end of this second interval, while the outer shelf experienced rare progradational events. The third, fully glaciated interval shows clear evidence of glacially dominated conditions on the margin. This interval divides into three minor stages. During the first stage (late Miocene to the beginning of the Pliocene), frequent grounded ice advances to the shelf break began, depositing an initial progradational unit. A major truncation surface marked the end of this stage, which coincided with extensive mass transport deposits at the base of the slope. During the second progradational glacial margin stage (early Pliocene to middle Pleistocene), stacking patterns record clearly prograding glacial sequences. The beginning of the third aggradational glacial margin stage (middle Pleistocene to present) corresponded to an important shift in global climate during the Mid-Pleistocene Transition. Morphosedimentary characteristics observed along the margin today began to develop during the latest Miocene but did not become fully established until sometime during the interval between the end of the Pliocene and middle Pleistocene. Between these two time intervals, the northeastward lateral migration of the Marguerite Trough also played a critical role in margin evolution, as it controlled ice sheet drainage pathways across the shelf, which in turn influenced development of slope and rise morphologies. Areas offshore from Adelaide Island differ from other areas of the PMAP due to changes in sedimentary processes that resulted from migration of the trough. This study confirms that the PMAP represents an exceptional locality for decoding, reconstructing and linking past tectonic and climatic changes. The study area specifically records not only the most relevant changes in depositional style, but also the relative importance of persistent along- and down-slope sedimentary processes. Our study approach can be extended to other areas and integrated with additional techniques to understand the evolution and the global linkages of the entire Antarctic continental margin and the ice sheets.

Sea-level control on turbidite activity in the Rhone canyon and the upper fan during the Last Glacial Maximum and Early deglacial

The timing, routing, and processes of sediment transfer from the continents to the oceans at millennial time-scale are still largely unknown. The potential of turbidite systems (dominantly deposited during sea-level lowstands) to record global or regional environmental fluctuations is usually under-exploited because of the difficulty to obtain robust chronostratigraphic constraints in turbiditic deposits, and therefore to tie changes in sedimentary processes to environmental fluctuations. We were able to obtain a millennial-scale chronostratigraphy based on oxygen isotopes of the scarce foraminifera preserved in turbiditic deposits of the Rhone Turbidite System within the Western Mediterranean. Our results show that 1) objective criteria can be defined for the selection of foraminifera preserved within the pelagic intervals between the turbiditic sequences, in order to obtain a reliable isotope stratigraphy; 2) turbidites triggered by hyperpycnal currents are described for the first time within the Rhone Turbidite System. They are related to the periods of direct fluvial connection with the canyon head (during the sea-level lowstand and early rise), and to a period of high sediment flux in relation to the massive recession of the Rhone glaciers in the Alps; 3) the lithofacies change passing from hyperpycnal to “Bouma-type” is dated at ca 19cal.ka BP, which might correspond to an acceleration of sea-level rise (19-ka Meltwater Pulse).

Sedimentation and seafloor mound formation in the southern slope of the Ulleung Basin, East Sea, Korea, since the Last Glacial Maximum

Detailed analysis of core sediments and acoustic characteristics of Chirp sub-bottom profiles from a submarine ridge in the southern slope of the Ulleung Basin, East Sea, Korea, reveals changes in sedimentary processes and deformation of sedimentary sequence induced by seafloor mound formation since the Last Glacial Maximum (LGM). The core sediments consist generally of four sedimentary facies which represent hemipelagic sedimentation under a poorly-oxygenated bottom-water condition during the LGM (crudely laminated mud), shoreface erosion and seaward transport off the shelf break during the post-glacial transgression (bioturbated sandy mud or muddy sand), hemipelagic sedimentation under generally well-oxygenated bottom-water condition after the sea-level rise (bioturbated mud), and episodic precipitation of authigenic carbonates by methane venting since the LGM (authigenic carbonate-bearing mud), respectively. The formation of authigenic carbonate-bearing mud facies and associated accumulation of near-seafloor gas hydrates might have led to up-warping of the sediment cover since the LGM that resulted in the seafloor mounds protruding along the crest line of the ridge. The effects of up-warping by expansion of the subsurface gas hydrates are firstly manifested in this paper by the abrupt lateral changes in the sedimentary facies distribution and uplifted acoustic reflectors between the mounds and the background seafloor.

Climatic influences on sediment deposition and turbidite frequency in the Nitinat Fan, British Columbia

Continental margins in regions influenced by temperate ice sheets experience climate-dependent changes in sedimentary processes. A new stratigraphy is presented for Ocean Drilling Program Hole 888B, from the Nitinat Fan, on the Vancouver Margin, in which we examine the relationship between fluctuations in glacial-sourced sediment delivered to the continental shelf and turbidite character and frequency. Glacial/interglacial episodes are determined based on: (1) core lithology, where sandy/coarse-grained sediment and fine-grained clay/silty clay represents glacial and interglacial intervals, respectively; (2) δ 18O of planktonic foraminifera G. bulloides, in which higher values indicate warmer sea surface temperatures and lower global ice volume; (3) magnetic susceptibility, in which higher values indicate coarser grain sizes deposited during glacials; and (4) ratios of sinistral N. pachyderma to dextral N. incompta, in which higher proportions of N. pachyderma are a sign of cooler sea surface temperatures. Finally, using radiocarbon 14C dates, specific Marine Isotope Stages (MIS) within the top 240 m of core are assigned: MIS 2–4 (2–118 mbsf), MIS 5 (118–157 mbsf), and MIS 6 (213–240 mbsf). Using this chronology, sedimentation rates for the Nitinat Fan were greater (187 cm/kyr) during glacial MIS 2–4 than interglacial MIS 5 (69 cm/kyr). Additionally, during glacial MIS 2–4 thicker turbidites (upwards of ~ 150 cm) were deposited relatively frequently (~ 75 year periodicity) compared with those from MIS 5, which are relatively thin (up to 27 cm) and deposited more rarely (~ 130 year periodicity). These results indicate that turbidite frequency and thickness are linked to climate through ice sheet extent, since transport of glacimarine sediment to the continental slope promotes turbidity currents that are responsible for the most significant amount of offshore sedimentation. This study shows that geological processes influencing turbidite deposition can fluctuate over time and may not necessarily be represented by ongoing processes within the modern depositional setting.

Late Quaternary sedimentary processes and variations in bottom-current activity in the Ulleung Interplain Gap, East Sea (Korea)

A detailed facies analysis of core sediments from the Ulleung Interplain Gap (UIG) reveals ten sedimentary facies which reflect a variety of sedimentary processes: volcaniclastic high-concentration sediment gravity flows, low-density turbidity currents, pelagic settling under either well or poorly oxygenated bottom-water conditions, marine fallout of tephra, hampered sedimentation by bottom currents, top-truncation of turbidites by bottom-current reworking, and Mn-carbonate precipitation under changing bottom-water oxygenation states. Distribution of the facies in the cores, integrated with echo characters of high-resolution subbottom profiles, delineates spatial and temporal changes in sedimentary processes, influenced by variations in bottom-current activity during the late Quaternary. The glacial (> ∼15 ka) sediment units from the Ulleung Interplain Channel (UIC), an erosional axial channel system in the UIG, consist mainly of manganiferous and muddy contourites, interbedded with coarse-grained volcaniclastic turbidites or debrites and non-bioturbated pelagites. This indicates prevalent activity of bottom currents, rarely interrupted by volcaniclastic high-concentration sediment gravity flows and deep-water stagnations which resulted in anoxic bottom-water conditions. On the other hand, the glacial units of the southeastern margin of the UIC, where upslope migrating sediment waves developed, are generally dominated by alternating fine-grained turbidites and bioturbated or non-bioturbated pelagites. This suggests that frequent turbidity currents derived from upslope mass wasting were responsible for the generation of the sediment waves. The post-glacial (< ∼15 ka) units from both the UIC and its southeastern margin consist mostly of muddy contourites or bioturbated pelagites with basal manganiferous contourites. They correspond to an acoustically transparent layer which occurs as an elongate mound parallel to the UIC in the southeastern margin. These features are suggestive of bottom-current-controlled sedimentation, hampered sedimentation in the UIC axis by stronger bottom-current activity and focused accumulation of resuspended sediments in the southeastern margin. The post-glacial bottom-current activity was initiated by renewed circulation with open ocean at ∼ 15 ka, probably more vigorous than that of the present. The bottom-current activity seems to have been augmented by enhanced bottom-water formation by colder sea-surface temperature.

Spatial and Temporal Changes in Sedimentary Processes at Proglacial Bear Lake, Devon Island, Nunavut, Canada

Spatial and Temporal Changes in Sedimentary Processes at Proglacial Bear Lake, Devon Island, Nunavut, Canada

Spatial and Temporal Changes in Sedimentary Processes at Proglacial Bear Lake, Devon Island, Nunavut, Canada

Lacustrine sedimentary processes are identified on an intra-annual scale at proglacial Bear Lake, Devon Island. Stage recorders, recording thermistors, sediment traps, and underflow monitoring equipment were deployed during the 1999 melt season. Episodic proximal turbidity currents were measured as positive near-bottom temperature anomalies and currents. The timing of individual positive temperature anomalies was clearly associated with diurnal peaks of discharge into the lake. During the period of 23 to 25 July, continuous underflow occurred, which preceded a large discharge event by about 24 h. Sediment traps placed throughout the lake recorded sediment accumulation rates from 16 June to 4 August. An extremely large precipitation event occurred on 29 June, when coarse, carbonate-rich sediment was deposited in front of a secondary tributary by spatially limited turbidity currents. A niveo-eolian deposit was observed on the lake ice, and sediment traps were deployed under this area. Mass accumulation rates in these traps locally overwhelmed fluvially generated sedimentation. This sediment was dominantly sand, which quickly melted through the lake ice and hastened the date of localized break-up.

A long lacustrine record from the Piànico-Sèllere Basin (Middle-Late Pleistocene, Northern Italy)

Abstract The stratigraphical succession of the Pianico-Sellere Basin (Northern Italy) represents an exceptionally well preserved sedimentary assemblage which formed in a closed lake basin during the Middle–Upper Pleistocene. These deposits are grouped into the hereby proposed “Pianico Formation”. This includes four lacustrine, fine-grained, laminated lithostratigraphical units containing a 10.5 m thick interval of well preserved varved carbonates. The lacustrine units are coeval, and laterally heteropic to lake-marginal, talus cone/fan delta debris flow deposits accumulated within the lake. The stratigraphical study and sedimentary facies analysis throughout the lacustrine succession, combined with a preliminary pollen and microstratigraphical investigation, provide evidence of a complex environmental and climatic evolution which occurred during the lacustrine deposition. The Pianico Formation shows multiple changes in sedimentary processes which indicate a transition from a peri/proglacial to a temperate lacustrine environment. Within forested phases a complex evolution is evident. Main changes in vegetational patterns from conifer to broad-leaved, warm temperate forests correspond to changes in sediment composition from distal sand silt turbidites to a regular continuous succession of endogenic calcite-rich annual varves. An increased rate of erosional processes on the surrounding slopes is also indicated by debris flow deposits. Stratigraphically, their frequency within the fine-grained basinal sediments increases upwards which would indicate increasing subaerial erosion processes at the end of the sedimentation of the Pianico Formation. These data highlight the sensitivity of the Pianico-Sellere Basin sedimentation in recording minor climatic fluctuations and related environmental changes which occurred before the Last Glacial Maximum probably during oxygen isotope stage 5, 7 or 9.

Significance of lamination in Toarcian (Lower Jurassic) shales from Yorkshire, Great Britain

Lamination in shales is an important feature useful in providing clues to ancient sedimentary environments and processes. Variations in types of lamination in Toarcian (Lower Jurassic) shales of Yorkshire, Great Britain are related to changes in sedimentary processes. X-radiography, petrography, and scanning electron microscopy techniques reveal three lamination types in the dark grey (Grey Shales) and black (Jet Rock and Bituminous Shales) Jurassic shales. Fine lamination is produced in deeper, more offshore anaerobic conditions in which suspension settling dominates. Thick lamination indicates the influence of bottom flowing currents in shallow water. Wavy lamination is produced by benthic microbial mats. The Toarcian transgressive shale sequence shows a progressive change from thick to wavy to fine lamination relating to progressive changes in the sedimentary processes operating in the environment. The examples of various unique macro- and microfabrics associated with lamination type offer a useful frame of reference for interpretation of conditions of shale formation.