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Map of the eastern Mediterranean Sea with the positions of the cores discussed in the text. Contours are at 1000 m.
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High relative concentrations of the lower photic zone nannofossil Florisphaera profunda have been reported in all recent eastern Mediterranean sapropels. In the most recent sapropel (S1), high bulk sediment Sr/Ca ratios occur along with high F. profunda contents toward the base of the unit, exemplified here in four cores from 1.5–3.5 km water depth...
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... The positions and water depths of the investigated cores in the eastern Mediterranean basin are specified in Table 1 and displayed in Figure 1. For calcareous nanno- fossil analyses, a small amount of sediment was moistened with distilled water, smeared homogeneously on a slide, and permanently mounted with optical adhesive. ...
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... turbidite is formed from sediments from shallow (photic zone) waters in the Gulf of Sirte and has an aragonite content of up to 15% ascribed to the green alga Halimeda out of a total carbonate content of 50-60% [Hieke and Werner, 2000]. Although the Augias turbidite is >12 m thick on the Ionian Plain floor [Hieke and Werner, 2000], it is only $14 cm thick in core T87-19B [Rasmussen, 1991;Troelstra et al., 1991], which was retrieved 500 m shallower in the northeastern part of the plain (Figure 1). The S1 sapropel is also present in this core at 30-44 cm (Figure 7), and like the cores in Figure 2, the Sr/Ca profile exhibits values of >0.005 between 29 and 45 cm with a maximum value of 0.007 at 43 cm. ...
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... In samples from the S1 sapropel in cores LC25 and T87-19B, the dominant forms identified on morphological grounds as aragonite by SEM were aggregates of needles or ''rods,'' typically 1 -5 Â $0.2 mm in dimension and very small (0.5 mm) equant crystals ( Figure 10). Ion microprobe determination of Sr and Ca in particles on stubs that had also been examined by SEM confirmed that all biogenic nannoplankton consistently analyzed with a Sr/Ca mass ratio in the range 0.001 -0.003, whereas the rod aggregates had Sr/Ca mass ratios in the range 0.02 -0.03. ...
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... Both well-separated and more fused rods were observed in the different aggregates (Figures 10a-10d and 10f ). In those aggregates with a loose open framework of randomly oriented rods, the rods commonly had smooth surfaces and rounded terminations (Figures 10a and 10b) and resembled the original aragonitic skeletal needles of the calcareous alga Halimeda reported by Macintyre and Reid [1995, Figures 2b and 2c]. ...
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... Both well-separated and more fused rods were observed in the different aggregates (Figures 10a-10d and 10f ). In those aggregates with a loose open framework of randomly oriented rods, the rods commonly had smooth surfaces and rounded terminations (Figures 10a and 10b) and resembled the original aragonitic skeletal needles of the calcareous alga Halimeda reported by Macintyre and Reid [1995, Figures 2b and 2c]. The thicker rods in these aggregates did not, however, exhibit the blunt crystal terminations and well-developed crystal faces typical of needles of living Halimeda [Hover et al., 2001, Figure 6c]. ...
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... thicker rods in these aggregates did not, however, exhibit the blunt crystal terminations and well-developed crystal faces typical of needles of living Halimeda [Hover et al., 2001, Figure 6c]. The second type of aggregate, in which the rod framework appears more fused, is more common (Figures 10c and 10d), and in this type the rods have more irregular surfaces, rounded terminations, and some cementation between them. The surfaces of these rods appear better preserved than the etched surface of bioneedles illustrated by Macintyre and Reid [1995, Figure 7b]. ...
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... third type of aggregate with a loose framework, character- ized by well-spaced elongate crystals (typically 1-5 m long  0.07 m thick) was also observed. This form was commonly surrounded by what appeared to be amorphous organic matter (Figure 10f), and the crystals vaguely resemble the inorganic precipitates reported by Robbins and Blackwelder [1992, Figure 3b] and aragonitic needles from living calcareous algae [Reid and Macintyre, 1998, Figure 1e]. In addition to aggregates, randomly spaced single rods were also common, and subcircular anhedral microcrystals (0.5 m) were occasionally present (Figure 10e) that are similar to the nanograins produced by progressive micritization of original skeletal needles documented by Macintyre and Reid [1995, Figures 3c, 3e, 6b, 6e] and to the crystal form of many calcareous algae [Macintyre and Reid, 1992, Figure 2]. ...
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... form was commonly surrounded by what appeared to be amorphous organic matter (Figure 10f), and the crystals vaguely resemble the inorganic precipitates reported by Robbins and Blackwelder [1992, Figure 3b] and aragonitic needles from living calcareous algae [Reid and Macintyre, 1998, Figure 1e]. In addition to aggregates, randomly spaced single rods were also common, and subcircular anhedral microcrystals (0.5 m) were occasionally present (Figure 10e) that are similar to the nanograins produced by progressive micritization of original skeletal needles documented by Macintyre and Reid [1995, Figures 3c, 3e, 6b, 6e] and to the crystal form of many calcareous algae [Macintyre and Reid, 1992, Figure 2]. ...
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... The sapropel S1 aggregates are typically smaller (rarely >20 mm with an average of all types of $8 mm) and more irregular in shape than those from the Augias turbidite (Figures 10g and 10h) that were referred to Halimeda sp. by Hieke and Werner [2000]. Some larger aggregates were subcircular to elliptical in shape, 5 -10 m in length (Figure 10g), and resembled faecal pellets [e.g., Wassmann et al., 2000]. ...
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... The sapropel S1 aggregates are typically smaller (rarely >20 mm with an average of all types of $8 mm) and more irregular in shape than those from the Augias turbidite (Figures 10g and 10h) that were referred to Halimeda sp. by Hieke and Werner [2000]. Some larger aggregates were subcircular to elliptical in shape, 5 -10 m in length (Figure 10g), and resembled faecal pellets [e.g., Wassmann et al., 2000]. Although the individual needles comprising the different aggregates appear similar, the degree of compaction and fusion always appears less in the sapropel S1 aggregates than in the Augias turbidite grain illustrated by Hieke and Werner [2000, Figure 2]. ...
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... A few irregular small particles with much higher Sr/Ca mass ratios in the range 0.12 -0.15 were also observed in ion microprobe analysis (Figure 10i), and the fact that one of these particles appears to have grown around a Syracosphaera coccolith (Figure 10j) suggests that they are likely to be diagenetic. While it was not possible to identify the nature of these high Sr particles further, their occasional presence may contribute to the aragonite end- member that has a Sr/Ca mass ratio higher than that anticipated for biogenic aragonite ( Figure 6). ...
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... A few irregular small particles with much higher Sr/Ca mass ratios in the range 0.12 -0.15 were also observed in ion microprobe analysis (Figure 10i), and the fact that one of these particles appears to have grown around a Syracosphaera coccolith (Figure 10j) suggests that they are likely to be diagenetic. While it was not possible to identify the nature of these high Sr particles further, their occasional presence may contribute to the aragonite end- member that has a Sr/Ca mass ratio higher than that anticipated for biogenic aragonite ( Figure 6). ...
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... contrast, the increased C org contents and high Ba/Al ratio values used to indicate sapropel thickness do not increase above their low baseline (S1 sapropel at 43 cm in core T87-19B.) (d) Aggregate of compacted rods in which most rods are slightly longer than those in Figure 10c but have the same irregular surface. There are distal views of etched E. huxleyi coccoliths to the upper right and upper left, and a proximal view of a well-preserved E. huxleyi to the bottom left (S1 sapropel at 43 cm in core T87-19B). ...
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Citations
... The literature suggests that these bands are a deoxygenation-reoxygenation phenomenon [52][53][54][55] . The most pronounced increase in deep water oxygen levels should occur at the deglaciations, providing an opportunity for a rst order test of reoxygenation hypothesis. ...
... Low oxygen conditions there permit the burial of these organic rich layers, and they occur in phase with precession variability in Northern Hemisphere insolation 60, [95][96][97] . Most sapropels have lost some of their original thickness due to the "burn-down" of organic matter from their tops after oxygenated water returns to the depths of the Mediterranean Sea 54,55 . However, there are long intervals in the Mediterranean barren of sapropels. ...
... Later, Froelich 58 described the typical cascading series of diagenetic reactions in pore waters, where organic material acts as a key catalyst and donor of electrons in the reduction of nitrate, manganese, iron, and sulfate. Wilson 52,53 then described how the emplacement of an organic rich layer in sediment could disrupt the typical reaction series, producing steep redox gradients above it that are capable of immobilizing dissolved Fe 2+ from porewaters below and concentrating it into a thin layer.The best-known example of this phenomenon is the geochemical and color anomalies above organic-rich sapropel layers from the Mediterranean that have been "burned down" by oxic bottom waters and indicate their original thickness54,55 . Indeed, there are extended intervals of Mediterranean sediment where the rhythmic reappearance of the sapropels is replaced with sapropel "ghosts" -color-banded sediment indicating the complete burndown of the organic material in the layer 60 . ...
Ocean ventilation of "young" surface waters, which have recently been in contact with the atmosphere, in the high-latitude North Atlantic Ocean, serves as a major source of oxygen-rich deep waters (> 2.5 km) to the world's oceans 1,2 . Both models and observations suggest deep water production and the oxygenation of deep water are declining, threatening valuable marine ecosystems and the crucial role the ocean plays in carbon storage 3–6 . Widely observed diagenetic banding in marine sediments is believed to be connected to the availability of oxygen in pore waters and the remineralization of buried organic matter. This study combines a comprehensive spatial survey of distinctive green banding in near-surface sediments with an analysis of the temporal variability in banding at International Ocean Discovery Program (IODP) Sites U1313 and U1474 to document fluctuations in bottom water oxygen across the mid-late Pleistocene (1 million years to present). The survey of near surface sediments (core-tops) indicates that the green bands have their origin in the post-glacial resurgence in the production of oxygen-rich North Atlantic Deep Water (NADW). The stratigraphic survey shows the synchronous development of banding numerous times during the glacial marine isotope stages (MIS) of the Pleistocene, indicating the timing of regional deoxygenation events as a consequence of Northern Component Water (NCW; the glacial equivalent of NADW) slowdowns. This glacial-interglacial pattern in band abundance is superimposed on a lower-frequency cycle corresponding to the 400-thousand-year (ka) band in orbital eccentricity and a globally prevailing pattern in benthic carbon isotopes. We link green band formation and benthic carbon isotopes to sapropel barren intervals from the Mediterranean Sea and productivity records from the Southern Ocean and propose that long eccentricity cycles influenced bottom water oxygen across the Late Pleistocene.
... Looking in more details at the patterns of three key calcareous nannofossil taxa, which are shown individually in Fig. 6, a visual correlation with insolation/precession is clearly observed. As expected, this is evident for the pattern of F. profunda, as a result of its well-known relation with stratified surface waters and DCM development (Rohling and Gieskes, 1989;Castradori, 1992;Kemp et al., 1999;Negri et al., 1999;Negri and Giunta, 2001;Corselli et al., 2002;Thomson et al., 2004;Triantaphyllou et al., 2010;Incarbona et al., 2011;Grelaud et al., 2012;Incarbona and Di Stefano, 2019;Maiorano et al., 2019), occurring during precession minima/insolation maxima (Hilgen, 1991a;Lourens et al., 1996) and due to intensified monsoon freshwater release especially via the Nile River (Rossignol-Strick et al., 1982;Rohling et al., 2002;Marino et al., 2009;Weldeab et al., 2014;Hennekam et al., 2015). Interestingly, new evidence is here observed for H. sellii and C. pelagicus ssp. ...
We present the first high-resolution results on planktonic foraminiferal stable oxygen isotopes and calcareous plankton assemblages at the Monte San Nicola GSSP section (near Gela, Sicily), the type-section for the Lower Pleistocene Gelasian Stage. The oxygen isotope profile is remarkably similar to the Eastern Mediterranean oxygen isotope record and indicates that the studied section, extending from marine isotope stage (MIS) G4 to MIS 103, clearly records glacial-interglacial variability. Cyclic changes of calcareous plankton assemblages (calcareous nannofossils and foraminifera) indicate that warmer and stratified surface waters occurred during interglacials, while cooler and unstable conditions developed during glacial phases. Signatures of further increase in surface water stratification are also captured by our surface water proxies and are coeval with enhanced monsoon run-off, developed during precession minima/insolation maxima. The surface water changes recorded at the Monte San Nicola section are in phase with North Atlantic climate variability, even at suborbital scale, and
reveal evidence of the first significant southward migration of the Subarctic Front in the mid-latitudes during MIS 104, slightly below the GSSP. The overall dataset provides precise alignment of the Gelasian GSSP within MIS 103 as well as new climatostratigraphic constraints, close to the GSSP, thus improving its correlation potential outside the type-area.
... The Sr/Ca ratio, confronts two elements from the carbonate fraction. Higher values in the Sr/Ca ratio in sediments from the Mediterranean usually indicate a higher percentage of aragonite in the sediment, as it is enriched in Sr (Reitz and De Lange, 2006;Thomson et al., 2004). Aragonite is typically abundant in shallow marine environments, because deep waters are undersaturated in Sr and it is commonly dissolved in the water column or in the sediment after its deposition (Fabry & Deuse, 1991;Reitz and De Lange, 2006). ...
... Aragonite is typically abundant in shallow marine environments, because deep waters are undersaturated in Sr and it is commonly dissolved in the water column or in the sediment after its deposition (Fabry & Deuse, 1991;Reitz and De Lange, 2006). Nonetheless, several processes can trigger Sr enrichment in deep sediments, such as (1) authigenic formation as consequence of sulphate reduction during diagenesis, (2) in situ productivity of Sr rich organisms (i.e., pteropods), or (3) shallow-dwelling organisms transported basinward by density fluxes during enhanced precipitation events (Reitz and De Lange, 2006;Thomson et al., 2004). Therefore, a correct interpretation of this proxy has to be done in comparison with other geochemical data. ...
... On the other hand, high Sr/Ca ratio triggered by in situ productivity of Sr rich organisms should increase from the shelf to the deep and open marine settings. Conversely, high Sr/ Ca ratio triggered by sediment input from shallow depths should decrease toward deep marine settings (see Reitz and De Lange, 2006;Thomson et al., 2004, for a review). ...
We present a high-resolution analysis of seven marine sediment records from the western Mediterranean in a transect from the Algero-Balearic basin to the Alboran Sea, spanning the last 20 ka, to decipher the paleoenvironmental and paleoceanographic evolution of the Western Mediterranean Sea. To do so, diverse elemental ratios have been used for reconstructing sediment input variations and paleo-oxygen conditions. In particular, the Ti/Ca ratio has been used to reconstruct variations in the terrigenous and carbonate fractions. However, the specific sedimentary processes controlling this ratio are still poorly understood thus, we also provide new insights for appropriate interpretations, in the studied zone. Our results suggest that the Ti/Ca ratio at the suborbital scale is mostly controlled by bottom current intensity, and less influenced by marine productivity, sea level variations, and the fluvial and eolian inputs. Comparison of diverse records within the western Mediterranean reveals that the Ti/Ca ratio depicted a similar trend in both regions, except during the Heinrich Stadial 1 (HS1) and the Middle Holocene. The HS1 is recorded as a single-phase event in the Algero-Balearic basin, whereas three phases are recognized in the Alboran Sea basin, with a relative minimum in the Ti/Ca ratio. Conversely, during the Middle Holocene, an increase in the Ti/Ca ratio is recorded in the Alboran Sea and the Atlantic Iberian margin, but not in the Algero-Balearic basin, which could be related to the establishment of the Alboran gyres. Redox sensitive proxies, in particular the Mo/Al, U/Al and Mn/Al ratios, point to different phases within the Organic Rich Layer 1 (ORL1): the ORL1a (15-11.7 ka cal BP), characterized by more reducing conditions in the Alboran Sea sediments, and the ORL1b (11.7- ~9 ka cal BP) characterized by suboxic-ferruginous conditions. The sea level transgression, the enhanced fluvial input and the shelf flooding played a key role during the ORL1 onset and demise, increasing the sedimentation rate in the basin and preventing the organic matter oxidation. During the last 2 ka cal BP, an unprecedented common response is recognized in all the studied regions, showing an overall increase in the Ti/Ca ratio, which may be related to intensified human activity in the Mediterranean area, promoting a greater terrigenous input.
... This is likewise observed in the bi-gradational negatively loaded C-PC1 at these intervals, which represents the accumulation of carbonates with respect to the terrigenous fraction (Fig. 9A). Enhanced Sr may indicate the presence of high-Sr aragonite, which usually requires a shallow-water source (Thomson et al., 2004;Rothwell et al., 2006). Biogenic aragonite often contains much more Sr than biogenic calcite in foraminifers (Thomson et al., 2004). ...
... Enhanced Sr may indicate the presence of high-Sr aragonite, which usually requires a shallow-water source (Thomson et al., 2004;Rothwell et al., 2006). Biogenic aragonite often contains much more Sr than biogenic calcite in foraminifers (Thomson et al., 2004). Hence, the Sr/Ca proxy may reflect an enrichment in shallow-marine bioclasts over foraminifers (Table 4, Fig. 12). ...
The purpose of this study is to differentiate and characterise contouritic sands in two different locations with variable sediment compositions (siliciclastic and bioclastic) based on a multiproxy approach that includes the analysis of sedimentary texture, semi-quantitative geochemistry, microfacies and ichnological information, as well as a Principal Component Analysis (PCA) applied to geochemical and sedimentary data on sediment cores. The integration of sedimentological analyses and the PCA permits also to the differentiation between fine-grained deep-water deposits such as hemipelagites, muddy contourites and hyperpycnites. A depositional model is proposed here, based on geochemical and sedimentological characteristics of the Holocene-highstand Mozambique Channel upper slope sands, and glacial-lowstand Corsica Contourite Depositional System middle slope sands. The upper continental slope of the Mozambican margin is characterised by siliciclastic sandy contourites, muddy contourites and muddy hyperpycnites. Mozambique siliciclastic sandy contourites constitute large accumulations of well-sorted very fine to coarse sand with evidences of strong winnowing and reworking under high-energy conditions. The sedimentary facies represents highstand contourite sands and shows a reversely-graded trend. The contourite drift on the Pianosa ridge (eastern flank of the Corsica Trough) consists of bioclastic sandy and muddy contourites and hemipelagites. Bioclastic sandy contourites are made up of shallow-marine winnowed bioclasts with a reversely- and normally-graded trend and represent lowstand contourite sands. The PCA in the two environments —showing a distinctive geochemical signal— allows for differentiation of the contourite deposits. In siliciclastic sands, reworking is marked by an accumulation of Si, Zr, and Sr in fine- to medium-grained sands. In bioclastic sands, reworking is less evident but it is characterised by accumulations of Ca and Sr. The reworking and winnowing bottom current effects are also observed at the microfacies scale. Both types of contourite deposits show evidences of intermittent depositional conditions depending on the ichnodiversity, distribution and abundance of trace fossils. This work is useful to discriminate similar fine-grained deposits in different continental margins which would contribute to a better understanding of sedimentary deposits and processes in deep-marine environments.
... The sandy deposits within the contourite channels are richer in bioclasts than the other studied facies. Enhanced Sr may indicate the presence of high-Sr aragonite, which is common in shallow-water sediments with bivalves, gastropods and corals (Thomson et al., 2004;Rothwell et al., 2006). Hence, the Sr/Ca proxy may reflect a shallow-marine provenance and a more proximal shelf source. ...
Despite numerous efforts to properly differentiate between contourites and other deep-water deposits in cores and outcrops, reliable diagnostic criteria are still lacking. The co-occurrence of downslope and along-slope sedimen-tary processes makes it particularly difficult to differentiate these relatively homogeneous deposits. The main aim of this paper is to identify differences in deep-water sediments based on Principal Component Analysis of grain size and geochemistry, sedimentary facies, and reinforced by microfacies and ichnofacies. The sediments studied were obtained from two International Ocean Drilling Program Expedition 339 sites in mounded and sheeted drifts in the Gulf of Cadiz. The statistical approach led to the discernment of hemipelagites, silty contourites, sandy contourites, bottom current reworked sands, fine-grained turbidites and debrites over a range of depositional and physiographic elements. These elements are linked to contourite drifts, the drift-channel transition, the contourite channel and distal upper slope. When bottom currents or gravity-driven flows are not the dominant deposi-tional process, marine productivity and continental input settling forms the main depositional mechanism in deep-water environments. This is reflected by a high variability of the first principal component in hemipelagic deposits. The stacked principal component variability of these deposits evidences that the contourite drift and the adjacent contourite channel were influenced by the interrelation of hemipelagic, gravitational and bottom current induced depositional processes. This interrelation questions the paradigm that a drift is made up solely of muddy sediments. The interrelation of sedimentary processes is a consequence of the precession-driven changes in the intensity of the Mediterranean Outflow Water related to Mediterranean climate variability , which are punctuated by millennial-scale variability. Associated vertical and lateral shifts of the Mediterranean Outflow Water, and therefore of its interface with the East North Atlantic Central Water, controlled sediment input and favoured turbulent sediment transport in the middle slope. During 1 the interglacial precession maxima/insolation minima, a more vigorous upper core of the Mediterranean Outflow Water and the enhanced impact of the East North Atlantic Central Water-Mediterranean Outflow Water interface allowed for the development of the sandier contourite deposits.
... Ratios of ln Ca/Ti can be used to detect variation in biogenic (Ca) and detrital (Ti) sediment supply (Hodell et al., 2013). Strong correlations between Ca and Sr support the use of ln Ca/Sr as a proxy for changes in carbonate (foraminifera/shallow-marine bioclast) assemblages (Thomson et al., 1999(Thomson et al., , 2004Ritcher et al., 2006;Rothwell et al., 2006;Keul et al., 2017). ...
The differentiation of pure turbidites and contourites from mixed deposits —as the bottom current reworked sands (BCRS) — in sedimentary cores and outcrops from the modern or ancient records is still challenging. An accurate evaluation of facies associations calls for detailed understanding of processes controlling these deep-water systems and how they record interactions of along- and down-slope processes. Connecting features to processes is of particularly relevant in the study of contouritic drifts that include sandy deposits. This research describes and interprets BCRS within a Pleistocene contouritic drift located along the middle continental slope of the Gulf of Cadiz. Seismic, wireline, and sedimentological analyses of sediment samples were applied to core material representing a muddy drift that hosts sandy deposits. A sedimentary sequence, comprising five facies (F1 to F5) is defined here; it records background sedimentation influenced by the initial deposition of a gravity-driven flow followed by bottom current reworking. It is moderately bioturbated and contains distinctive trace fossil assemblages, often dominated by ichnofabrics of the Planolites and Thalassinoides. These assemblages represent intermittent deposition between down-slope and along-slope processes during relatively short time scales. The sequence is defined as a partial bi-gradational contourite sequence including BCRS reworked from underlying turbiditic deposits due to the interaction of down- and along- slope processes within the contouritic drift and its adjacent contouritic channel. Longer-term trends include an increase and subsequent decrease in both sediment supply and bottom currents. The sedimentary facies model presented here represents a new end member for a mixed turbiditic-contouritic system in which turbiditic flows influence a contourite drift. As such, it may support basic sedimentological interpretation and petroleum exploration strategies.
... Climate change is a likely control on creating failure-prone lithological contrasts Down-core changes in Ca/Sr ratios have been successfully related to variations in sea-level and water temperature (through integration with oxygen isotope curves and biostratigraphy), wherein high Ca/Sr ratios are indicative of ice-rafted debris and changes from colder to warmer conditions (e.g. Smith et al. 1979;Thomson et al. 2004;Hodell et al. 2008). High Fe/K ratios and low Ca/Fe, on the other hand, have been related to colder periods (Kuijpers et al. 2003;Perez et al. 2016). ...
Contourite drifts are sediment deposits formed by ocean bottom currents on continental slopes worldwide. Although it has become increasingly apparent that contourites are often prone to slope failure, the physical controls on slope instability remain unclear. This study presents high-resolution sedimentological, geochemical and geotechnical analyses of sediments to better understand the physical controls on slope failure that occurred within a sheeted contourite drift within the Faroe–Shetland Channel. We aim to identify and characterize the failure plane of the late Quaternary landslide (the AFEN Slide), and explain its location within the sheeted drift stratigraphy. The analyses reveal abrupt lithological contrasts characterized by distinct changes in physical, geochemical and geotechnical properties. Our findings indicate that the AFEN Slide likely initiated along a distinct lithological interface, between overlying sandy contouritic sediments and softer underlying mud-rich sediments. These lithological contrasts are interpreted to relate to climatically controlled variations in sediment input and bottom current intensity. Similar lithological contrasts are likely to be common within contourite drifts at many other oceanic gateways worldwide; hence our findings are likely to apply more widely. As we demonstrate here, recognition of such contrasts requires multi-disciplinary data over the depth range of stratigraphy that is potentially prone to slope failure.
... This study aims to assess paleoenvironmental changes across the eastern Mediterranean transect during Sapropel S1 deposition. We pay special attention to coccolith preservation and selective dissolution of holococcoliths, because coccoliths produced during the holococcolithophore life stage seem to be especially prone to dissolution during early diagenesis (Crudeli et al., 2006;Incarbona & Di Stefano, 2018;Thomson et al., 2004). Different processes that occurred during S1 deposition may have altered the calcite saturation state, which at present is at supersaturated levels throughout the Mediterranean Sea (Schneider et al., 2007): These include: (1) increased primary productivity and water column oxygen shortage affecting the extent and the strength of dissolution and thus the lysocline (Barker, 2016;Paulmier et al., 2011); (2) anoxic remineralization of Corg by sulfate reduction establishes an alkaline environment in interstitial pore waters, below the water/sediment interface (Ten Haven et al., 1987;Thomson et al., 2004); and (3) gypsum precipitation from Ca released by dissolving biogenic carbonate and SO4 released from pyrite oxidation (Calvert, 1983;Cita et al., 1977;Ten Haven et al., 1987) upon postdepositional diffusion of oxygen into the sediment (De Lange et al., 2008;Thomson et al., 1999;Van Santvoort et al., 1996). ...
... We pay special attention to coccolith preservation and selective dissolution of holococcoliths, because coccoliths produced during the holococcolithophore life stage seem to be especially prone to dissolution during early diagenesis (Crudeli et al., 2006;Incarbona & Di Stefano, 2018;Thomson et al., 2004). Different processes that occurred during S1 deposition may have altered the calcite saturation state, which at present is at supersaturated levels throughout the Mediterranean Sea (Schneider et al., 2007): These include: (1) increased primary productivity and water column oxygen shortage affecting the extent and the strength of dissolution and thus the lysocline (Barker, 2016;Paulmier et al., 2011); (2) anoxic remineralization of Corg by sulfate reduction establishes an alkaline environment in interstitial pore waters, below the water/sediment interface (Ten Haven et al., 1987;Thomson et al., 2004); and (3) gypsum precipitation from Ca released by dissolving biogenic carbonate and SO4 released from pyrite oxidation (Calvert, 1983;Cita et al., 1977;Ten Haven et al., 1987) upon postdepositional diffusion of oxygen into the sediment (De Lange et al., 2008;Thomson et al., 1999;Van Santvoort et al., 1996). ...
... Late Quaternary sapropels are associated with high concentrations of aragonite, alternating with high-Mg calcite in underlying and overlying marls, both thought to be early diagenetic products (Calvert & Fontugne, 2001;Thomson et al., 2004). During S1 deposition, anoxic remineralization of C org by sulfate reduction would have enhanced sediment pore water alkalinity and thus enhanced diagenetic aragonite precipitation (Thomson et al., 2004). ...
Organic‐rich layers (sapropels), preserved in eastern Mediterranean marine sediment records, represent pronounced perturbations to thermohaline circulation and environmental conditions in the basin, in response to enhanced African monsoon activity and subsequent massive freshwater discharge. During the most recent event, Sapropel S1 formed between 10.8 and 6.1 ka, when freshwater‐driven stratification caused seafloor anoxia below ~1,800‐m depth, as a result of both failure of deep water formation and enhanced productivity. Here we analyze coccolith assemblages from the open eastern Mediterranean that form a west‐east transect across the basin and provide insights on past environmental changes. We focus on holococcoliths, which are specifically produced by coccolithophores as part of their life cycle during the haploid phase. Since holococcolith calcification is characterized by nanocrystals highly susceptible to dissolution, we are testing their potential preservation under different bottom environmental conditions, including the effect of postdepositional oxidation. A comparison with benthic foraminifera assemblages in a core recovered close to Lybia reveals that holococcolith preservation is enhanced during seafloor reventilation and benthic foraminiferal repopulation in the middle to upper part of the record, before the actual sapropel termination. There are two such events of improved deep‐water oxygenation in the Aegean and Adriatic Seas at 8.2 and 7.4 ka. The latter episode marks the onset of the transition to restored circulation in the eastern Mediterranean Sea, due to resumption of deep‐water formation in the southern Aegean Sea and the conclusion of enhanced biogenic productivity.
... This trend is also better expressed in core C40. The decrease in the Mg-calcite content in sapropel S1 has been reported in the central and eastern Aegean (Aksu et al., 1995b), and eastern Mediterranean (Thomson et al., 2004) based on semi-quantitative estimations in the b2 μm clay fractions, and seems to be a universal feature of the Aegean sediments. Also the average concentrations of quartz, plagioclase and K-feldspar is comparable in the two cores (Table 2). ...
Sediments from two deep-sea bottom cores from the Myrtoon basin in the SW Aegean Sea and Eastern Cretan Sea were examined by quantitative mineralogical and geochemical analysis to infer sediment provenance and its possible role in models of climatic conditions and palaeo-environmental control on sediment deposition. Both cores contain calcareous muds and silts with dark olive-grey organic rich intervals corresponding to the sapropel S1 horizon. The presence of a few tephra layers documents volcanic activity in the southern part of the Aegean Sea. The bulk sediments contain abundant carbonate minerals (mainly calcite and Mg-calcite) and clay minerals (mainly illite and smectite) and accessory serpentine, talc and hornblende, which attest to contributions from ultrabasic sources. There is a sharp decrease of the Mg-calcite content and the Mg/Ca ratio of the carbonate fraction in sapropelic sediments followed by an increase of the average grain size. A well expressed negative relationship between illite and smectite was observed in the clay fraction in full accordance with previous studies. However, this trend is absent from the bulk sediments, because smectite is significantly overestimated in the oriented clay fractions. Clay mineral distribution is controlled mainly by sediment sorting, with deposition in the sapropelic sediments being also affected by climatic changes. The different types of smectite in the cores and the presence of smectite with high dehydroxylation temperature in the SE Aegean, suggests that the sediment supply from SE Mediterranean sources should be limited.
... This trend is also better expressed in core C40. The decrease in the Mg-calcite content in sapropel S1 has been reported in the central and eastern Aegean (Aksu et al., 1995b), and eastern Mediterranean (Thomson et al., 2004) based on semi-quantitative estimations in the b2 μm clay fractions, and seems to be a universal feature of the Aegean sediments. Also the average concentrations of quartz, plagioclase and K-feldspar is comparable in the two cores (Table 2). ...
