The early Matuyama Diatom Maximum off SW Africa: a conceptual model

An important discovery during Ocean Drilling Program Leg 175, when investigating the record of upwelling off Namibia, was the finding of a distinct Late Pliocene diatom maximum spanning the lower half of the Matuyama reversed polarity chron (MDM, Matuyama Diatom Maximum) and centered around 2.6–2.0 Ma. This maximum was observed at all sites off southwestern Africa between 20°S and 30°S, and is most strongly represented in sediments of Site 1084, off Lüderitz, Namibia. The MDM is characterized by high biogenic opal content, high numbers of diatom valves, and a diatom flora rich in Southern Ocean representatives (with Thalassiothrix antarctica forming diatom mats) as well as coastal upwelling components. Before MDM time, diatoms are rare until ca. 3.6 Ma. After the MDM, in the Pleistocene, the composition of the diatom flora points to increased importance of coastal upwelling toward the present, but is accompanied by a general decrease in opal and diatom deposition. Here we present a simple conceptual model as a first step in formalizing a possible forcing mechanism responsible for the record of opal deposition in the upwelling system off Namibia. The model takes into account Southern Ocean oceanography, and a link with deepwater circulation and deepwater nutrient chemistry which, in turn, are coupled to the evolution of North Atlantic Deep Water (NADW). The model proposes that between the MDM and the Mid-Pleistocene climate revolution, opal deposition off Namibia is not directly tied to glacial–interglacial fluctuations (as seen in the global δ¹⁸O record), but that, instead, a strong deepwater link exists with increased NADW production (as seen in the deepwater δ¹³C record) accounting for higher supply of silicate to the thermocline waters that feed the upwelling process. The opal record of Site 1084 shows affinity to eccentricity on the 400-kyr scale but not for the 100-kyr scale. This points toward long-term geologic processes for delivery of silica to the ocean.     

The occurrence and significance of Pleistocene and Upper Pliocene sapropels in the Tyrrhenian Sea

Numerous sapropels and sapropelic strata from Upper Pliocene and Pleistocene hemipelagic sediments of the Tyrrhenian Sea show that intermittent anoxia, possibly related to strongly increased biological productivity, was not restricted to the eastern Mediterranean basins and may be a basin-wide result of Late Pliocene-Pleistocene climatic variability. Even though the sapropel assemblage of the Tyrrhenian Sea clearly originates from multiple processes such as deposition under anoxic conditions or during spikes in surface water productivity and lateral transport of organic-rich suspensates, many “pelagic sapropels” have been recognized. Stratigraphic ages calculated for the organic-rich strata recovered during ODP Leg 107 indicate that the frequency of sapropel formation increased from the lowermost Pleistocene to the base of the Jaramillo magnetic event, coinciding with a period when stable isotope records of planktonic foraminifera indicate the onset of climatic cooling in the Mediterranean. A second, very pronounced peak in sapropel formation occurred in the Middle to Late Pleistocene (0.73-0.26 Ma). Formainifers studied in three high-resolution sample sets suggest that changes in surface-water temperature may have been responsible for establishing anoxic conditions, while salinity differences were not noted in the faunal assemblage. However, comparison of sapropel occurrence at Site 653 with the oxygen isotopic record of planktonic foraminifers established by Thunell et al. (Proc. ODP, Sci. Results 107, 1990) indicates that sapropel occurrences coincide with negative δ¹⁸O excursions in planktonic foraminifers in thirteen of eighteen sapropels recognized in Hole 653A. A variant of the meltwater hypothesis accepted for sapropel formation in the Late Pleistocene eastern Mediterranean may thus be the cause of several “anoxic events” in the Tyrrhenian as well. Model calculations indicate that the amount of oxygen advection from Western Mediterranean Deep Water exerts the dominant control on the oxygen content in deep water of the Tyrrhenian Sea. Inhibition of deep-water formation in the northern Adriatic and the Balearic Basin by increased meltwater discharge and changing storm patterns during climatic amelioration may thus be responsible for sapropel formation in the Tyrrhenian Sea.     

Lago Mare and the Messinian Salinity Crisis: Evidence from the Alboran Sea (S. Spain)

This paper provides a new environmental, sedimentological and stratigraphic context of the Lago Mare deposits from the North Alboran region and clarifies their chronologic location with respect to the Messinian Salinity Crisis. We present new micropalaeontological data (dinoflagellate cysts, calcareous nannoplankton, planktonic foraminifers), correlated with field observations and offshore seismic interpretations. We show that the Lago Mare event known in three onshore localities (Río Mendelín near Malaga, Zorreras near Sorbas, Gafares near Níjar) follows the marine reflooding of the Mediterranean Basin which ended the Messinian Salinity Crisis. Chronologically, these Lago Mare deposits last from the latest Messinian to the early Zanclean. In fact, the first influx of Paratethyan organisms is revealed by the dinoflagellate cyst record from near Malaga within a Gilbert-type fan delta overlying the Messinian Erosional Surface. Invading molluscs and/or ostracods may have persisted in lagoonal coastal areas more or less affected by discontinuous marine influxes (Sorbas and Níjar). The Malaga area is convenient for a palaeogeographic and sedimentary reconstruction which shows the prevalent forcing of sea-level changes during the time-interval 5.600–5.332 Ma at the difference of the usually solicited prevalent tectonics. The studied Lago Mare event is the third episode resulting in such a palaeobiological assemblage in the Mediterranean region and corresponds to the final two-way water exchange at high sea level between the Mediterranean and the former Paratethys. It documents the onset of the modern marine circulation in the Mediterranean after the reflooding ending the Messinian Salinity Crisis.     

The Messinian event in the Paratethys: Astronomical tuning of the Black Sea Pontian

This study presents new data on the orbitally calibrated Maeotian/Pontian and Pontian record of the Black Sea Basin (Paratethys) obtained by time-series analysis of magnetic susceptibility (MS) data from relatively deep-water Upper Miocene sediments exposed in the Zheleznyi Rog section (Taman Peninsula, Russia). In the studied interval, a ∼145-m-long sedimentary sequence, spectral analysis revealed statistically significant signals with 6.1–8.2 m and 3.0–4.0 m wavelength. These signals correspond to the obliquity and precession cycles, respectively. This study correlates the main steps of Messinian Salinity Crisis (MSC) of the Mediterranean to the Black Sea Pontian record based on astronomical tuning of the study sequence and evaluation of integrated biostratigraphic, paleomagnetic and sedimentological data. Based on cyclostratigraphic results, Maeotian/Pontian beds with Actinocyclus octonarius accumulated from ∼6.3 to 6.1 Ma. Most of the Novorossian sediments correspond to the first MSC step. The TG 22 (5.79 Ma) and TG 20 (5.75 Ma) glacial events occur in the uppermost Novorossian record and are marked by extraordinary high values of MS. The Portaferian, dated at the base as ∼5.65 Ma and the top as ∼5.45 Ma, corresponds to the second MSC step. The Novorossian/Portaferian transition is marked by the hiatus of approximately 150–160 kyr, which agrees well with the concept of the intra-Pontian unconformity in the Black Sea Basin and a sea-level drop in the Mediterranean from 5.6 to 5.46 Ma. The ages for the base and the top of the Bosphorian were estimated as ∼5.45 Ma and ∼5.27 Ma, respectively. The base of the Bosphorian corresponds to the third Lago Mare episode caused by the high sea-level connection between the Mediterranean and Eastern Paratethys.     

Stable isotope evidence for a marine origin of ophicalcites from the north-central Apennines (Italy)

Carbon and oxygen isotope ratios of 59 samples of Mesozoic ophicalcites from the north-central Apennines were measured. Strontium content and isotope ratios were only determined for selected samples.

The data obtained (−4.1 ≤ δ ¹³C ≤ + 3.0; 16.5 ≤ δ ¹⁸O ≤ 30.1; 0.7076 ≤ ⁸⁷Sr/⁸⁶Sr ≤ 0.7086; 60 ≤ Sr ppm ≤ 1140) suggest that the carbonate cement of the Apennines ophicalcites had a marine origin.

The ¹⁸O/¹⁶O values of most of the carbonates studied, however, indicate that the rocks have interacted with hydrothermal fluids, dominantly represented by sea water. In particular, the rocks from the northern section of the Apennines apparently reequilibrated their δ ¹⁸O content at higher temperature than those from the central zone.

Strontium isotope ratios, close to the Cretaceous—Cenozoic ocean water values, are well in agreement with such a kind of sea water/ophicalcites interaction, even if the carbonate cement formed earlier during the Jurassic period.     

Deep-water circulation in the Northeast Atlantic and climatic changes during the Late Neogene (DSDP Site 141)

Oxygen and carbon stable isotope data of Pyrgo murrhina and flux rates of calcium carbonate in the bio- and magnetostratigraphically dated sediment sequence at DSDP Site 141 were used for a reconstruction of the deep-water circulation in the Northeast Atlantic during Late Miocene and Pliocene times. A distinct change towards reduced advection of deep water recorded near 5.4 Ma is contemporaneous with the cessation of the outflow of the saline Mediterranean water into the Atlantic. During the Pliocene, between 4.5 and 2.75 Ma and between 2.1 and 1.8 Ma, North Atlantic Deep Water (NADW) circulation was sluggish and Site 141 possibly influenced by Antarctic Bottom Water (AABW). Near 2.75 Ma, the advection of well-oxidized NADW was strongly intensified. This change is related to an onset of major Arctic ice growth and/or a major cooling of NADW.     

Carbon and oxygen isotope composition of foraminifera in two cores from the Bannock Basin area, eastern Mediterranean

Two cores from the Bannock Basin in the eastern Mediterranean have been analysed for δ¹⁸0 and the δ¹³C in planktonic foraminifera. One core (02-PC) was extracted from the anoxic brine, the other (08-GC) from a plateau east of the brine.

The absence of sapropelic muds in Core 08-GC from the two Holsteinian euxinic cycles, together with the presence of isotopic spikes, suggests that the plateau has risen during the last ca. 200,000 years by ca. 2.5 mm/yr.

The δ¹⁸0 amplitude of Globigerinoides ruber in eastern Mediterranean cores is only ca. 0.5%. larger than for this species in North Atlantic cores. This suggests that the surface oxygen isotopic composition of both bodies of water followed each other fairly closely during the Late Pleistocene, except during the stagnant phases.     

4个代表站点的珊瑚δ18O数据对热带印度洋气候变率的反演能力分析*

珊瑚中的δ¹⁸O含量可以高精度地记录热带海洋中的气候变率及气候变化信息, 从而弥补器测观测时间长度有限的缺陷, 为反演过去长期的气候状况提供了可能。热带印度洋的气候模态通过海气相互作用影响周边区域甚至全球的气候, 具有重要的研究意义。本文对比分析了1880—1999年间热带印度洋4个站点(肯尼亚、坦桑尼亚、塞舌尔、明打威)的珊瑚δ¹⁸O数据, 研究了其对热带印度洋气候的反演情况。结果显示, 珊瑚δ¹⁸O对海表温度(sea surface temperature, SST)的长期变化趋势反演良好, 珊瑚δ¹⁸O与局地SST在季节循环中保持一致, 且在低温季节对SST的变化更为敏感。此外, 4个站点的珊瑚δ¹⁸O对印度洋海盆模态(Indian Ocean Basin Mode, IOBM)和印度洋偶极子模态(Indian Ocean Dipple Mode, IODM)有一定的表征能力, 并且δ¹⁸O记录的热带印度洋年际变率受年代际变率调制。本文的研究结果表明, 珊瑚δ¹⁸O数据对于了解古气候时期热带印度洋气候变率具有重要的指示意义, 但同时也需要综合考虑不同站点的信息来完整地反映印度洋在历史时期的气候变化情况。     

Clay mineral assemblages,siliciclastic input and paleoproductivity at ODP Site 1085 off Southwest Africa: A late Miocene–early Pliocene history of Orange river discharges and Benguela current activity,and their relation to global sea level change

A late Miocene to early Pliocene sequence drilled on the continental slope of southwest Africa off the Orange river mouth (ODP Site 1085) has been investigated. Clay mineral assemblages, coarse siliciclastics and benthic foraminifer accumulation rates (BFAR) unravel a step by step evolution of marine and continental environments closely related to sea level variations, ocean circulation and global climate: (1) smectite is a typical tracer of the Orange river load, whereas illite is mostly transported by the Benguela current (like chlorite) and winds, and kaolinite is derived from low latitudes by the poleward undercurrent and the North Atlantic Deep Water (NADW); (2) increased erosion and influence of the Orange river after 9.6 Ma is linked to a sea level drop at a time of Antarctic ice-growth. This has been followed by an increased seasonality of precipitation and high productivity, but low oxygen content and associated dissolution of carbonates; (3) increased productivity and dissolution of carbonates, and coeval increase of continental aridity after 8.9 Ma express a further development of the Benguela current and upwelling; (4) better preservation of carbonates and increased contribution of terrigenous material from northern sources at 6.9 Ma are related to increased circulation of NADW after an early stage of northern hemisphere glaciation; (5) increased erosion and contribution from the Orange river and westward shift of the area of higher productivity from 5.9–5.8 Ma to 5.3–5.2 Ma are related to a significant fall of sea level, and encompass the time of the entire Mediterranean salinity crisis; (6) short-term variations of the smectite/illite ratio (S/I) and BFAR suggest a major control of productivity by wind and current activities (and related upwelling), but may express brief variations of sea level in specific intervals before 8.9 Ma and during the late Messinian especially.     

南海北部冷泉区深水珊瑚的发现及其特征

冷水珊瑚也称为深水珊瑚, 在生物多样性、生态资源和科研价值等方面具有重要意义。文章对采自南海北部冷泉区的冷水珊瑚骨骼碎屑进行测定, 鉴定出冷水珊瑚2个种(Crispatotrochus sp.1和Crispatotrochus sp.2), 以及4个属[Balanophyllia (Balanophyllia)、Balanophyllia (Eupsammia)、Lochmaeotrochus和Enallopsammia]。测定的冷水珊瑚的δ¹³C为-7.36‰~-1.15‰, δ¹⁸O为-1.38‰~3.67‰, 与全球冷水珊瑚碳氧同位素组成相似, 但明显不同于南海暖水珊瑚、冷泉碳酸盐岩及低温热液成因碳酸盐岩的碳氧同位素组成。     

Neogene oceanographic variations recorded in manganese nodules from the Somali Basin

A detailed study of a nodule from the Somali Basin dated by ²³⁰Th_excess was correlated with the paleoceanographic events recorded in Site 236 (Leg 24) Deep Sea Drilling Project (DSDP) cores. Tentative indications are that the phase of nodule accretion starting with the development of pillar structure at a depth of 20 mm in the nodule around 13 Ma coincides with increased Antarctic Bottom Water (AABW) flow and an elevated calciumcarbonate compensation depth (CCD).

The Late Miocene lowering of the CCD is represented by the mottled zones between 8 and 18 mm in the nodule is characterised by an abundant silicate component (>20%) of aeolian origin. The Miocene/Pliocene boundary (5 Ma) occurs at a depth of about 8 mm and is represented by the development of pillar structure and a minimum of aeolian dust (10.3%).

The increased biological productivity of the Somali surface water since the Middle Miocene is demonstrated by the increasing C_org content of the nodule (from 0.11 to 0.19%) towards its surface.     

Environmental changes in the neogene and the biotic response

Among the abiotic factors that determined via the paleoceanographic processes development and evolution of the oceanic biota in the Neogene, noteworthy are the tectonic, volcanic, climatic and extraterrestrial events. The most important tectonic events of such kind include the subsidence of the Faroe-Iceland Threshold 14–13 Ma ago, the closure of the Tethys Ocean in the east 19–12 Ma ago, the orogenesis in the western Mediterranean region and closure of the Mediterranean Sea (Messinian Crisis) 5.59–5.33 Ma ago, the formation of the Central American Isthmus 6.0–3.5 Ma ago, and the opening of the Bering Strait that occurred (according to different data) in the period of 7.4 to 3.1 Ma ago. The most significant climatic consequence resulted from the formation of the Circum-Antarctic Current, the irregular growth of the Antarctic ice shield, the cooling in the Arctic region 3.2–3.1 Ma ago, and the development of continental glaciations in the Northern Hemisphere approximately 2.5 Ma ago. The variations in the atmospheric CO₂ content are correlative with the climatic fluctuations. The entire Cenozoic climatic record reflects the influence of the orbital parameters of the Earth. The Neogene was marked by several significant extraterrestrial events: the fireball falling in southwestern Germany in the middle Miocene 14.8–14.5 Ma ago probably accompanied by enhanced volcanic activity particularly in the rift valley of eastern Africa; the drastically increased influx of interplanetary dust due to the disruption caused by a large asteroid in the late Miocene 8.3 ± 0.5 Ma ago, the fall of a large (>1 km in diameter) asteroid in the Eltanin Fault zone of the Southern Ocean in the terminal Pliocene 2.15 Ma ago; and the explosion of a supernova star, which was probably responsible for the partial extinction of marine organisms at the Pliocene-Pleistocene transition approximately 2 Ma ago.     

Glacial–interglacial variations in Quaternary production of marine organic matter at DSDP Site 594, Chatham Rise, southeastern New Zealand margin

CaCO₃ and total organic carbon concentrations, organic matter C/N and carbon isotope ratios, and sediment accumulation rates in late Quaternary sediments from DSDP Site 594 provide information about glacial–interglacial variations in the delivery of organic matter to the Chatham Rise offshore of southeastern New Zealand. Low C/N ratios and nearly constant organic δ¹³C values of −23‰ indicate that marine production dominates organic matter supply in both glacial and interglacial times during oxygen isotope stages 1 through 6 (0–140 ka) and 17 through 19 (660–790 ka). Increased organic carbon mass accumulation rates in isotope stages 2, 4, 6, and 18 record enhanced marine productivity during glacial maxima. Excursions of organic δ¹³C values to ca. −29‰ in portions of isotope stage 2 suggest that the local concentration of dissolved CO₂ was occasionally elevated during the last glacial maximum, probably as a result of short periods of lowered sea-surface temperature. Dilution of carbonates by clastic continental sediment generally increases at this location during glacial maxima, but enhanced delivery of land-derived organic matter does not accompany the increased accumulation of clastic sediments.     

A late Pliocene diatom Ge/Si record from the Southeast Atlantic

As a result of both culture and sediment core studies, the ratio of germanium (Ge) to silicon (Si) in diatom shells has been proposed as a proxy for monitoring whole-ocean changes in seawater Ge/Si, a ratio affected by changes in continental weathering. However, because of the difficulties of extracting and cleaning diatom frustules from deep-sea sediments, only samples from highly pure diatom oozes in the Antarctic region have been previously analyzed. Here we present data on diatom Ge/Si ratios, (Ge/Si)_opal, for the time interval between 3.1 and 1.9 Ma from a mid-latitude, coastal upwelling area where significant terrigenous sediment input complicated the sample processing and analyses. In general, our (Ge/Si)_opal values show the same decreasing trend after 2.6 Ma than previously measured in Antarctic sediments (Shemesh et al., 1989. Paleoceanography 4, 221–231), but with a noisier background that may reflect the local imprint of proximal continental input superimposed upon global changes in the ocean reservoir. The time of initiation of large-scale North Hemisphere glaciation at 2.6 Ma is characterized by a declining pattern of diatom Ge/Si ratios, which could have resulted from a global increase in the input of riverine Si due to enhanced silica weathering and/or equatorward (northward) intrusions of subantarctic waters enriched in silica. High (Ge/Si)_opal ratios are associated with high opal contents from the same sediment samples and with warm climate as indicated by depleted benthic foraminiferal δ¹⁸O values from the North and Equatorial Atlantic. Cold periods signified by enriched benthic δ¹⁸O values, on the contrary, are associated with lower (Ge/Si)_opal ratios. We interpret diatom Ge/Si values to reflect the prevailing weathering state on the continents, with greater chemical weathering during warm and wet periods of the Pliocene and less during cooler and drier intervals.     

Carbon and nitrogen isotope excursions in mid-Pleistocene sapropels from the Tyrrhenian Basin: Evidence for climate-induced increases in microbial primary production

The modern Mediterranean Sea is oligotrophic, yet its sediment record contains layers of organic-carbon-rich sapropels at 21 ky (precessional) spacing that imply periods of elevated paleoproductivity that approached the high productivities of modern upwelling systems. Resolution to this paradox is provided by lines of evidence suggesting that the mode of primary productivity changed from one dominated by algae to one during times of sapropel deposition in which photosynthetic bacteria were important. We have made a high-resolution comparison of the organic carbon and nitrogen isotopic compositions of three sapropels and their background sediments in a 3-m sequence that corresponds to 1001 to 946 ka. Organic δ¹³C values systematically increase from − 26‰ to − 21‰ and δ¹⁵N values systematically decrease from 4‰ to < 0‰ as organic carbon mass accumulation rates increase in the sapropel layers. The increase in carbon isotope values mirrors the increases in primary productivity and associated organic matter export indicated by the increased mass accumulation rates. The decrease in nitrogen isotope values implies major contributions of nitrogen-fixing cyanobacteria to the total marine productivity. The precessional minima with which sapropels coincide were times of wetter climate that stratified the surface Mediterranean Sea, increased delivery of soil-derived phosphorus, and evidently amplified microbial primary production. Our high-resolution study reveals several relatively rapid excursions into and out of the high-productivity mode that suggest that sapropel deposition was a climate-sensitive surface-driven phenomenon that was not accompanied by basin-wide stagnation.     

The late Miocene onset of high productivity in the Benguela Current upwelling system as part of a global pattern

We have examined the history of the elevated primary productivity associated with the Benguela Current upwelling system off southwest Africa using sediments from 7.5 to 4.8 Ma at Ocean Drilling Program Site 1085 in the middle Cape Basin. Sedimentation rates are low until 6.9 Ma. Low accumulation rates of benthic foraminifers and organic carbon indicate that biological productivity was also low. Paleoproductivity dramatically increased at 6.7–6.5 Ma and was highly variable until 4.8 Ma with productivity maxima during cooler periods. The presence of radiolarian opal only between 5.8 and 5.2 Ma suggests an interlude of silica-rich intermediate water in the Cape Basin. The onset of heightened productivity under the Benguela Current is mirrored by similar increases reported between 6.9 and 6.7 Ma in the tropical eastern Pacific, the western and northern Pacific, and the Indian Ocean. The similarity between the patterns at Site 1085 and in the Pacific and Indian Oceans suggests that the dramatic productivity increase off southwest Africa is part of a global response to paleoceanographic changes.     

A 33 Ma lithostratigraphic record of tectonic and paleoceanographic evolution of the South China Sea

The 853 m thick sediment sequence recovered at ODP Site 1148 provides an unprecedented record of tectonic and paleoceanographic evolution in the South China Sea over the past 33 Ma. Litho-, bio-, and chemo-stratigraphic studies helped identify six periods of changes marking the major steps of the South China Sea geohistory. Rapid deposition with sedimentation rates of 60 m/Ma or more characterized the early Oligocene rifting. Several unconformities from the slumped unit between 457 and 495 mcd together erased about 3 Ma late Oligocene record, providing solid evidence of tectonic transition from rifting/slow spreading to rapid spreading in the South China Sea. Slow sedimentation of 20–30 m/Ma signifies stable seafloor spreading in the early Miocene. Dissolution may have affected the completeness of Miocene–Pleistocene succession with short-term hiatuses beyond current biostratigraphical resolution. Five major dissolution events, D-1 to D-5, characterize the stepwise development of deep water masses in close association to post-Oligocene South China Sea basin transformation. The concurrence of local and global dissolution events in the Miocene and Pliocene suggests climatic forcing as the main mechanism causing deep water circulation changes concomitantly in world oceans and in marginal seas. A return of high sedimentation rate of 60 m/Ma to the late Pliocene and Pleistocene South China Sea was caused by intensified down-slope transport due to frequent sea level fluctuations and exposure of a large shelf area during sea level low-stands. The six paleoceanographic stages, respectively corresponding to rifting (33–28.5 Ma), changing spreading southward (28.5–23 Ma), stable spreading to end of spreading (23–15 Ma), post-spreading balance (15–9 Ma), further modification and monsoon influence (9–5 Ma), and glacial prevalence (5–0 Ma), had transformed the South China Sea from a series of deep grabens to a rapidly expanding open gulf and finally to a semi-enclosed marginal sea in the past 33 Ma.     

The structural evolution of the Messinian evaporites in the Levantine Basin

The Levantine Basin in the South-eastern Mediterranean Sea is a world class site for studying the initial stages of salt tectonics driven by differential sediment load, because the Messinian evaporites are comparatively young, the sediment load varies along the basin margin, they are hardly tectonically overprinted, and the geometry of the basin and the overburden is well-defined. In this study we analyse depositional phases of the evaporites and their structural evolution by means of high-resolution multi-channel seismic data. The basinal evaporites have a maximum thickness of about 2 km, precipitated during the Messinian Salinity Crisis, 5.3–5.9 Ma ago. The evaporite body is characterized by 5 transparent layers sequenced by four internal reflections. We suggest that each of the internal reflection bands indicate a change of evaporite facies, possibly interbedded clastic sediments, which were deposited during temporal sea level rises. All of these internal reflections are differently folded and distorted, proving that the deformation was syn-depositional. Thrust angles up to 14° are observed. Backstripping of the Pliocene–Quaternary reveals that salt tectonic is mainly driven by the sediment load of the Nile Cone. The direction of lateral salt displacement is mainly SSW–NNE and parallel to the bathymetric trend. Apparent rollback anticlines off Israel result rather from differential subsidence than from lateral salt displacement. In the south-eastern basin margin the deposition of the Isreali Slump Complex (ISC) is coeval with the onset of salt tectonic faulting, suggesting a causal link between slumping processes and salt tectonics.

The superposition of ‘thin-skinned’ tectonics and ‘thick-skinned’ tectonics becomes apparent in several locations: The fold belt off the Israeli Mediterranean slope mainly results from active strike-slip tectonics, which becomes evident in faults which reach from the seafloor well below the base of the evaporites. Owing to the wrenching of the crustal segments which are bounded by deep-rooted fault lines like the Damietta–Latakia, Pelusium and Shelf Edge Hinge line the setting is transpressional south of 32°N, where the fault lines bend further towards the west. This adds a component of ‘thick-skinned’ transpression to the generally ‘thin-skinned’ compressional regime in the basin. Above 1.5 km of evaporites, a mud volcano is observed with the mud source seemingly within the evaporite layer. At the eastern Cyprus Arc, the convergence zone of the African and the Anatolian plates, deep-rooted compression heavily deformed the base of the evaporites, whereas at the Eratosthenes Seamount mainly superficial compression affecting the Post-Messinian sediments and the top of the evaporites is observed.     

Erosion of continental margins in the Western Mediterranean due to sea-level stagnancy during the Messinian Salinity Crisis

High-resolution multi-channel seismic data from continental slopes with minor sediment input off southwest Mallorca Island, the Bay of Oran (Algeria) and the Alboran Ridge reveal evidence that the Messinian erosional surface is terraced at an almost constant depth interval between 320 and 380 m below present-day sea level. It is proposed that these several hundred- to 2,000-m-wide terraces were eroded contemporaneously and essentially at the same depth. Present-day differences in these depths result from subsidence or uplift in the individual realms. The terraces are thought to have evolved during one or multiple periods of sea-level stagnancy in the Western Mediterranean Basin. According to several published scenarios, a single or multiple periods of relative sea-level stillstand occurred during the Messinian desiccation event, generally known as the Messinian Salinity Crisis. Some authors suggest that the stagnancy started during the refilling phase of the Mediterranean basins. When the rising sea level reached the height of the Sicily Sill, the water spilled over this swell into the eastern basin. The stagnancy persisted until sea level in the eastern basin caught up with the western Mediterranean water level. Other authors assigned periods of sea-level stagnancy to drawdown phases, when inflowing waters from the Atlantic kept the western sea level constant at the depth of the Sicily Sill. Our findings corroborate all those Messinian sea-level reconstructions, forwarding that a single or multiple sea-level stagnancies at the depth of the Sicily Sill lasted long enough to significantly erode the upper slope. Our data also have implications for the ongoing debate of the palaeo-depth of the Sicily Sill. Since the Mallorcan plateau experienced the least vertical movement, the observed terrace depth of 380 m there is inferred to be close to the Messinian depth of this swell.     

Pliocene export production and terrigenous provenance of the Southern Cape Basin, southwest African margin

We have analyzed 33 Pliocene bulk sediment samples from Ocean Drilling Program Site 1085 in the Cape Basin, located offshore of western Africa in the Angola–Benguela Current system, for 17 major and trace elements, and interpreted their associations and temporal variations in the context of an allied data set of CaCO₃, opal, and C_org. We base our interpretations on elemental ratios, accumulation rates, inter-element correlations, and several multi-element statistical techniques. On the basis of qualitative assessment of downhole changes in the distributions of P and Ba, utilized as proxies of export production, we conclude that highs in bulk and biogenic accumulation that occur at 3.2 Ma, 3.0 Ma, 2.4 Ma, and 2.25 Ma were caused by increases in export production as well as terrigenous flux, and record a greater sequestering of organic matter during these time periods. Studies of refractory elements and other indicator proxies (SiO₂, Al₂O₃, TiO₂, Fe₂O₃, MgO, V, Cr, Sr, and Zr) strongly suggest that the terrigenous component of the bulk sediment is composed of two compositional end-members, one being ‘basaltic’ in composition and the other similar to an ‘average shale’. The basaltic end-member comprises approximately 10–15% of the total bulk sediment and its presence is consistent with the local geology of source material in the drainage basin of the nearby Orange River. The increase in bulk accumulation at 2.4 Ma appears to reflect a greater relative increase in basaltic input than the relative increase in shale-type input. Although studies such as this cannot precisely identify the transport mechanisms of the different terrigenous components, these results are most consistent with variations in sea level (and associated changes in shelf geometry and fluvial input) being responsible for the changing depositional conditions along the Angolan Margin during this time period.