Variations In Terrigenous Input Research Articles

A magnetic and geochemical approach to the changing sedimentation accumulation on the upper slope of the great barrier reef, northeastern Australian margin

The Great Barrier Reef (GBR) located along the northeastern margin of Australia is the largest coral reef system in the world. Modern climatic alterations are quickly changing the GBR ecosystem. To understand the implications of these changes it is important to reconstruct the geological history of GBR. Here we use geochemical and magnetic proxies to evaluate past climatic fluctuations and their consequences on sediment deposition along the GBR margin. IODP Expedition 325 – Hole M0058A, drilled on the uppermost slope at ca. 170 m water depth, reveals the depositional history of the GBR margin during the interval of MIS 7 to 5 and MIS 1. Magnetic and geochemical variations along the core section reveal detailed information on sediment accumulation and on the variations in terrigenous input in relation to sea-level fluctuations and climate change. Sea-level variations influenced margin deposition between MIS 7 and 6 impacting shoreline progradation/retrogradation and siliciclastic redistribution, resulting in a mixture of finer to coarser magnetic assemblages with no significant changes in terrigenous input. At the end of MIS 6 a decline in the deposition of carbonate sediments concomitant with the deposition of fine-grained magnetite-rich terrigenous sediments suggests an intensification of the monsoon in response to global warming trends. Arid periods over NE Australia were established after the glacial/interglacial transition (the MIS 6-5e) and at the middle Holocene (after the MIS 2–1 transition at ca. 7 ka), which favored dust deposition over the region. Enhanced dust fertilization subsequently promoted primary productivity at these intervals resulting in the presence of biogenic magnetite at Hole M0058A produced by magnetotactic bacteria.

Hydroclimate reconstruction during the last 1000 years inferred from the mineralogical and geochemical composition of a sediment core from Lake-Azuei (Haiti)

This study aims to reconstruct the hydro-climatic variations over the last 1000 years in Haiti using mineralogical and geochemical composition of well dated lacustrine sediment core retrieved from Lake Azuei. The results show changes in sedimentological processes linked to environmental and climatic variations. The general pattern suggests a wetter Medieval Climate Anomaly (MCA), drier Little Ice Age (LIA), high climate variability during the MCA-LIA transition and more anthropogenic impacts that dominate natural climate during the Current Warm Period (CWP). The MCA period (~1000–1100 CE) thus appears marked by increase sedimentation rate supported by higher terrigenous input linked to erosive events particularly increases in precipitation. During the LIA, particularly from ~1450 to 1600 CE, there is a great variation toward a decrease of terrigenous input, which is related to a decrease on sedimentation rate and increase Mg-calcite precipitation, suggesting less precipitation and high evaporation respectively during dry climate conditions. The MCA-LIA transition (~1200–1400 CE) is characterized by variations between terrigenous input, Mg-calcite formation and organic matter deposition, which indicate succession of dry and humid conditions. The CWP (1800–2000 CE) shows a progressive increase on sedimentation rate and decrease of gray level, which indicate more organic matter sedimentation as consequence of anthropogenic activities in the surrounding basin of the lake. High-resolution gray level analysis, which reflects principally variations in terrigenous input, carbonate mineral formation and organic matter deposition, shows that the AMO, NAO, PDO and ENSO are the principal modes affecting the hydro-climatic changes in Haiti during the last millennium. In addition, temporal correlation of other Caribbean paleoclimate records with our geochemical and mineralogical data, suggests that trends observed in Lake Azuei were controlled by regional climate, likely associated with shifts in the position of the ITCZ.

Chemo- and cyclostratigraphic records of the Albian from the Tethyan Himalaya of southern Tibet, China

The Albian Age is characterized by frequent short-lived perturbations of the global carbon cycle, including a series of Oceanic Anoxic Events (OAEs). Carbon Isotope Excursions (CIEs) document these OAEs in detail. A strong influence of orbital forcing on oceanographic and climatic conditions in the Albian has been documented, but the relationship between orbital changes and the carbon cycle is still unclear. The Albian CIEs are well recorded globally, except in the eastern Tethys. The major forcing mechanisms of Mesozoic carbon cycling have long remained a conundrum. Here, we present bulk carbon (δ 13 C carb ) and oxygen (δ 18 O carb ) isotope data, magnetic susceptibility (MS) and total organic carbon (TOC) data from the Nirang Section in the Tethyan Himalaya of southern Tibet, China. The δ 13 C carb record for the first time documents the long-term secular variations in δ 13 C during the Albian in the Tethyan Himalaya in high resolution. The δ 13 C curve obtained in Nirang can be correlated well with reference sections in other basins. OAE1b and 1c were identified as troughs in the δ 13 C profile in the lowermost and upper part of the section. Cyclostratigraphic analysis of MS, δ 13 C carb and TOC content from the Nirang Section reveals the imprint of the orbital cycles of eccentricity (∼100 kyr and ∼ 405 kyr) and a long-term amplitude modulation of either obliquity or eccentricity (∼1.2 Myr). The band-pass filters of the ∼100 kyr periodicity in MS provide the estimation of 563 kyr for the duration of OAE 1c and 677 kyr for that of the negative shift between OAE 1b and 1c. A detected ∼1.1 Myr periodicity is the most significant cycle, providing strong evidence for astronomically paced climate change in the eastern Tethys during the Albian. The band-pass filters of the ∼1.1 Myr periodicity in MS and TOC display a close correspondence, suggesting that the productivity and/or preservation potential of organic matter was likely controlled by orbitally forced changes in terrigenous input. Increasing δ 13 C values correspond to higher values of MS and TOC content and vice versa, indicating that the δ 13 C values of the eastern Tethys during the Albian were influenced by the intensity of the terrigenous flux and the subsequent burial of organic matter paced by orbital change. This work implies that cyclic changes in carbon reservoirs in the low latitudes of the Southern Hemisphere during the Albian were controlled by seasonal variations in terrigenous input driven by the influence of orbital cycles on regional hydrological processes. • A high-resolution δ 13 C curve of the Albian in the eastern Tethys. • A floating ATS built to estimate the duration of Albian CIEs. • The Albian carbon cycle in the eastern Tethys is paced by a ∼ 1.1 Myr cyclicity. • Terrigenous inputs and organic matter burial are responsible for δ 13 C changes in Tibet.

Seismic sequence stratigraphy and depositional evolution of the Cretaceous-Paleogene sedimentary successions in the offshore Taranaki Basin, New Zealand: implications for hydrocarbon exploration

The seismic stratigraphy and sedimentary facies of the Cretaceous and Paleogene sedimentary successions in north-eastern offshore part of Taranaki Basin, New Zealand have been investigated in order to unravel their depositional evolution and identify the potential hydrocarbon plays. Interpretation of regional seismic lines covering the entire shelf-slope and deepwater regions as well as integrating seismic and sedimentary facies allows the identification of several seismic-stratigraphic sequences within the studied successions. Early Cretaceous syn-rift successions (C1 sequence) were deposited in the structural lows near the present-day slope as swamp and marsh facies changing basinwards into turbidites and marine shales. The post-rift Cretaceous sequences (C2, C3 sequences) started with the progradation of the Taranaki delta (C2A-C2D units) followed by sedimentation of the transgressive C3A-E facies accumulated in response to thermal subsidence and high-rates of clastic supply. Extensive shelf conditions prevailed during the deposition of C2 and C3 Cretaceous sequences continued during the Paleogene with deposition of uniform marine shales throughout the basin. Rates of sediment supply substantially decreased during Oligocene prompting the deposition of marine micrite-rich carbonate. Variation in fossil content confirms the occurrence of several cycles of sea level fluctuations and episodic variations in terrigenous input. Organic-rich facies could be associated with the prograding clinoforms of the C2B unit and probably contain, basinward, large amount of gas and oil prone kerogen. The transgressive facies of C2D unit may also contain organic-rich shales basinward and coal near the present day Taranaki shelf. Potential reservoirs are hosted on the C3 transgressive estuarine sandstones. Paleogene mudstones are excellent regional seals for the hydrocarbons generated and trapped in the underlying Late Cretaceous facies.

Variation in magnetic susceptibility in the Bellingshausen Sea continental rise since the last glacial period and implications for terrigenous material input mechanisms

Magnetic susceptibility (MS) is routinely used as a proxy for terrigenous material input to Antarctic continental margin sediments. Variations in terrigenous input on glacial-interglacial timescales in this setting are related to a range of environmental changes; including to the cryosphere, atmosphere, and hydrosphere. However, the exact environmental factors and depositional processes that control MS values in sedimentary cores from the Antarctic continental margin remains unresolved. Here, we explore in detail sedimentary physical characteristics and MS values of core BS17-GC01 collected from Bellingshausen Sea continental rise, to understand how depositional process have varied during the late Quaternary. We found that input of terrigenous material increased markedly during Marine Isotope Stages (MIS) 2 and 4, compared to deposition during the adjacent interstadial and Holocene times. Variation in the bulk MS values were associated with changes in grain size. Size specific mass-normalized MS measurements show the fine fraction (<16 μm) has the highest MS values, followed by the coarse silt fraction (16–63 μm). However, because coarse silt is the predominant grain size, the increased bulk MS during MIS 2 and 4 are mainly driven by changes in this fraction. We propose that the coarse silt with high bulk MS values observed in glacial sediments were transported to the site as iceberg rafted debris, originating from the Bellingshausen Sea shelf region. In contrast, grains >1 mm – a commonly applied proxy for glacial transport in this setting – were observed during MIS 1 and 3 only. We conclude these contrasting signatures of iceberg rafted debris in this Bellingshausen Sea core arise from changes in the to the erosive dynamics of the adjacent ice shelf and continental shelf on glacial/interglacial timescales. • The MS in the Bellingshausen Sea co-varied with Antarctic ice core dust record. • The correlations of MS and dust record can be used for obtaining chronological points. • The MS is controlled by source/transport mechanism changes resulting in grain size change. • MS increases during MIS 2 and 4 are ascribed to increased coarse silt having high MS. • The coarse silt fraction during glacial periods was transported by icebergs.

Source of silica and its implications for organic matter enrichment in the Upper Ordovician-Lower Silurian black shale in western Hubei Province, China: Insights from geochemical and petrological analysis

To improve the understanding of the relationship between silica source and organic matter accumulation, the origin of silica and its implications for organic matter enrichment in the Upper Ordovician-Lower Silurian (O 3 w -S 1 l ) black shale in western Hubei Province in the middle Yangtze area, were investigated through geochemical and petrological analyses. The results show that the O 3 w -S 1 l black shale is mainly composed of five lithofacies with varying graptolite abundance, total organic carbon (TOC), and silica contents. Biogenic silica and terrigenous siliciclastic input constitute the main silica sources in O 3 w -S 1 l black shale and they exhibit an upward inverse variation trend interpreted to be related to sea-level changes. Moreover, with the increase in biogenic silica content or decrease in terrigenous siliciclastic input, TOC values in black shale initially rise and then fall, which is different from originally expected simple linear relationship. We infer that organic matter enrichment and the distribution of silica from different origins are controlled by sea-level changes and variations in terrigenous input in a continental shelf with little hydrothermal influence. An environment with appropriate sea level and terrigenous input should be most favorable for organic matter accumulation, rather than one with excessive high sea level and less terrigenous input.

Eocene (46–44 Ma) Onset of Australia‐Pacific Plate Motion in the Southwest Pacific Inferred From Stratigraphy in New Caledonia and New Zealand

AbstractThe Pacific plate circuit went through a complex reorganization during the early to middle Eocene, approximately coinciding with the onset of subduction along the western Pacific margin. However, the timing and dynamics of this change in the southwest Pacific and evolution of subduction beneath the Tonga‐Kermadec Arc are not fully resolved. We present magneto‐biostratigraphic data from an early to middle Eocene sedimentary section exposed in the Koumac‐Gomen area, New Caledonia, which is an emerged portion of the Norfolk Ridge. The 260 m‐thick succession contains a transition from pelagic micrite to terrigenous‐rich calciturbidite that is observed regionally in New Caledonia and which is interpreted to represent a shift from sedimentation on a stable submarine plateau to slope formation developed under a convergent tectonic regime. The stratigraphic contact between pelagic micrite and overlying calciturbidite is not exposed, but our magnetic polarity‐based chronology constrains the age of transition to 46–44 Ma, in agreement with the 45.3 Ma age recently obtained from the Noumea area in southern New Caledonia. We integrate records from New Caledonia with recent magnetostratigraphic data from South Island, New Zealand, where marked variations in terrigenous input occurred during the early and middle Eocene. Synchronous sedimentary changes in the southwest Pacific occurred at the same time as onset of rapid seafloor spreading south of Australia and New Zealand. We infer that the underlying cause of stratigraphic change was inception of slip at a new configuration of the Australia‐Pacific plate boundary, which evolved into the Tonga‐Kermadec subduction system.

Variations in terrigenous input into the eastern Equatorial Atlantic over 120ka: Implications on Atlantic ITCZ migration

Variation in the location of the Intertropical Convergence Zone (ITCZ) in eastern equatorial Atlantic (EEA) drastically affects rainfall in equatorial Africa and hence sedimentation on the African margin. Sediment core DY26III-Nig-S60-GC2 taken from the slope of the EEA offshore Nigeria (4°28′56′′.388′E, 3°33′10′′.764′N; water depth: 2946 m) was studied to decode the climatological response to the ITCZ migration in the past 120 ka. Based on oxygen isotope stratigraphy and radiocarbon dating, the sedimentation rates of this core range from 0.64 to 6.90 cm/ka and average of 3.17 cm/ka. The periods MIS 2, MIS 4 and MIS 5b from our studied core are characterized by Minima of Fe/K and maxima of K/Al, Ti/Al and magnetic susceptibility along with more kaolinite. This reflects a period when the region supposedly dominated by less precipitation and strong trade winds which suggest southward position of the ITCZ. Conversely, the periods MIS 1, MIS 3 and MIS 5a exhibit an opposite trend; these wet periods are of weak trade winds and northerly ITCZ excursion.Fluctuations in Fe/K, K/Al and Ti/Al records reflect changes in the low-latitude insolation cycle (23 kyr) and thus indicate a close coupling between terrigenous input and climate changes. This work thus highlights the importance of the terrigenous input as a prerequisite for the interpretation of ITCZ position in the EEA.

Evidence for sea level and monsoonally driven variations in terrigenous input to the northern East China Sea during the last 24.3 ka

AbstractGeochemical and sedimentological analyses of core PC‐1 recovered from the northern East China Sea (ECS) provide insights into variations in terrigenous input associated with sea level and climate changes over the past 24.3 ka. Based on high‐resolution multiproxy records, our results suggest that the competing processes of sea level and monsoonally driven precipitation determined terrigenous input to the northern ECS. Dominance of terrigenous material, along with relatively light Globigerinoides ruber δ18O, indicates that the Last Glacial Maximum (LGM) lowstand of sea level has occurred during the period 21.5–19.6 ka, not suggesting an early slow rise but supporting the conventional LGM age of 21 ka. This LGM lowstand was terminated by the rapid sea level rise of 19 ka meltwater pulse (MWP), which is well expressed by the nearly synchronous decreases in both terrigenous detritus and mean grain size from 19.6 to 18.9 ka. MWP‐1A is clearly marked in our records by a sharp reduction in terrigenous input and pronounced maxima of G. ruber δ18O at 15.3–14.8 ka, given the considerable age uncertainties of deglacial marine radiocarbon samples. A slightly increasing input of terrigenous matter is noted after 13.4 ka, potentially pointing to a sea level fall following the Inter‐Allerød Cooling Period, which was seldom reported previously. Although MWP‐1B did not leave robust signatures in terrigenous input, it is explicitly captured by the heavy δ18O of G. ruber and decline in mean grain size at 11.5–10.9 ka. MWP‐1c probably occurred in a broad millennial interval with multiple peaks, which are robustly marked by the abrupt variations in terrigenous input and marine organic matter at 9.7–9.3 and 9.1 ka, respectively. During the late Holocene, the effect of continuously weakening monsoon precipitation overwhelmed that of stable sea level resulting in a uniform increase in the proportion of marine‐derived organic matter after 5.5 ka.

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.

Terrigenous n-alkane input in the South China Sea: high-resolution records and surface sediments

Molecular abundances of n-nonacosane are reported for a suite of 44 surface sediments and four deep sea cores distributed throughout the South China Sea (SCS), covering the last 220 ky at different time resolutions. The patterns of glacial to interglacial variability of the concentrations of this terrigenous marker are parallel for all cores, taking values linearly inversely correlated to the U 37 K′ index sea surface temperatures (SST), with high concentrations during cold-glacial intervals and low concentrations during warm-interglacial periods. The oscillations of this terrigenous marker likely result from the emergence and flooding of the shelves caused by sea-level variations which, together with SCS SSTs, have a clear dependency on the Northern Hemisphere climate evolution. Calculation of accumulation rates for the northernmost core together with the modern distribution of n-nonacosane concentrations in surface sediments evidences the complexity of sedimentation patterns in the northern SCS. In particular, and in agreement with recent studies, terrigenous materials deposited there might originate from areas different than the highly loaded Pearl River. For paleoceanographic purposes, the noticeable general pattern of the n-alkane concentration down-core profiles for the four cores studied, a parameter apparently unaffected by changes in sedimentation rates, prompts its use as a tracer of variations in terrigenous input into this basin over glacial to interglacial times.

Late Quaternary high‐resolution biomarker and other sedimentary climate proxies in a Northeast Atlantic Core

We studied variations in terrigenous input and sea surface temperature over the last 208 ka using a multiproxy approach, involving direct comparison of terrigenous and marine molecular biomarker, foraminiferal abundance, and other sedimentological data for the same horizons in a single northeast Atlantic core (core T88‐9P; 48°23′N, 25°05′W, 3193 m water depth, 790 cm core length) with a well‐resolved δ18O stratigraphy. The abundances of three land‐derived, long‐chain compound classes, the n‐alkanes (C27, C29, and C31), the n‐alkanoic acids (C24, C26, and C28), and the n‐alkanols (C24, C26, and C28) show glacial/interglacial related changes in the past 208 ka which generally parallel the weight percent noncarbonate. The abundances of these three compound classes are higher in glacial than in interglacial sediments. Such changes are consistent with the expected higher dust inputs during glaciations as well as enhanced advection of particulate matter in current systems. Ice‐rafted debris (Heinrich events) may also contribute to the terrigenous biomarker record. The sea surface temperature (SST) signals derived from the alkenone unsaturation index (UK′37) give an average SST during interglacial periods of 13°C, which is about 3–4°C higher than the average glacial SST estimate. The UK′37− derived SST values dropped markedly in some Heinrich layers, while sometimes leading the onset of the layer; the percent Neogloboquadrina pachyderma(s), which is another frequently used qualitative temperature proxy, generally shows maxima coinciding with the layers. Our results show that most Heinrich layers were produced during times of intensely cold waters in the eastern North Atlantic. They demonstrate that sufficient alkenones are present in the sediments for alkenone stratigraphy to be used as a tool for the assessment of short‐term variations in sea surface temperatures even in these oligotrophic North Atlantic waters.

Ostracode paleoecology of the Bangor-Pennington transition (Chesterian, Mississippian) in northeastern Alabama

The Pennington Formation (Chesterian, Mississippian) of northeastern Alabama is a regressive, distal lobe of the Pennington/Lee clastic wedge, located on the western flank of the Appalachians in the Tennessee structural salient. The clastic units of the Pennington include sandstone, siltstone, mudstone, clay shale and coal and are genetically related to the effects of progradation. The presence of limestones and dolostones within the southwestwardly prograding and thinning Pennington is due to the lateral equivalency and interfingering relationships of the Pennington with the upper part of the adjacent Bangor Limestone shelf.A highly diverse ostracode fauna as been collected from outcrops along the Pennington-Bangor transition in northeastern Alabama. The most common assemblage of ostracodes is dominated by kirkbyaceans and includes species of Amphissites, Polytylites, Kirkbyella, Kirkbya and Reviya. Bairdiaceans are noteably absent from this assemblage. The Kirkbyacean Assemblage is only found in middle to outer shelf palaeoenvironments where clastic input is high, but where salinity conditions are thought to have been typically marine. In middle to outer shelf limestone-producing palaeoenvironments, a Bairdiacean Assemblage is dominant, although kirkbyaceans are still present.A Sansabellid Assemblage, consisting of kloedenellaceans such as Sansabella, Geisina, Geffenina, Nufferella and Glyptopleura appears to be produced under rapidly changing nearshore, inner shelf conditions, where terrigenous input was often high and palaeosalinities may have been variable or less than normal marine. The Sansabellid Assemblage contains occasional kirkbyaceans, however bairdiaceans are noteably absent. Intermediate assemblages contain elements of the three main assemblages and reflect the transition from the inner to outer shelf.In summary, the ostracode assemblages of the Pennington-Bangor transition in northeast Alabama provide indicators of palaeoenvironmental change during the southwestward progradation of the Pennington deltaic wedge onto the Bangor Limestone shelf. The prime factors resulting in palaeoecological response appear to have been variations in terrigenous input and palaeosalinity.

Variations in Terrigenous Input into the Deep Equatorial Atlantic During the Past 24,000 Years

Estimates of terrigenous fluxes at three different water depths at two sites in the equatorial Atlantic by normalization against excess (230)Th flux indicate that the flux of terrigenous material to the seafloor was significantly higher during the last glacial period than it is today. Fluxes started to decrease during deglaciation and reached minimal values in the middle of the Holocene. From 15,000 to 5,000 years ago, there was a substantial increase in flux with increasing water depth below 2,800 meters; this increase may reflect resuspension and lateral transport of slope and rise sediment, possibly because of intensification of deepwater circulation during that period.