Geochemical evidence for the link between sulfate reduction, sulfide oxidation and phosphate accumulation in a late cretaceous upwelling system

Background: On Late Cretaceous Tethyan upwelling sediments from the Mishash/Ghareb Formation (Negev, Israel),bulk geochemical and biomarker analyses were performed to explain the high proportion of phosphates in thelower part and of organic matter (OM) preserved in upper parts of the studied section. The profile is composed ofthree facies types; the underlying Phosphate Member (PM), the Oil Shale Member (OSM) and the overlying MarlMember (MM). Results: Total organic carbon (TOC) contents are highly variable over the whole profile reaching from 0.6% in theMM, to 24.5% in the OSM. Total iron (TFe) varies from 0.1% in the PM to 3.3% in the OSM. Total sulfur (TS) rangesbetween 0.1% in the MM and 3.4% in the OSM, resulting in a high C/S ratio of 6.5 in the OSM section. A meanproportion of 11.5% total phosphorus (TP) in the PM changed abruptly with the facies to a mean value of only 0.9% in the OSM and the MM. The TOC/TOC$_{OR}$ ratios argue for a high bacterial sulfate reduction activity and in addition, results from fatty acidanalyses indicate that the activity of sulfide-oxidizing activity of bacteria was high during deposition of the PM,while decreasing during the deposition of the OSM. Conclusions: The upwelling conditions effected a high primary productivity and consequently the presence of abundant OM. This, in combination with high sulfate availability in the sediments of the PM resulted in a higher sulfide production due to the activity of sulfate-reducing bacteria. Iron availability was a limiting factor during the deposition of the whole section, affecting the incorporation of S into OM. This resulted in the preservation of a substantial part of OM against microbial degradation due to naturally-occurring sulfurization processes expressed by the high C/S ratio of 6.5 in the OSM. Further, the abundant sulfide in the pore water supported the growth of sulfide-oxidizing bacteria promoting the deposition of P, which amounted to as much as 15% in the PM. These conditions changed drastically from the PM to the OSM, resulting in a significant reduction of the apatite precipitation and a high concentration of reactive S species reacting with the OM

Chronology with a pinch of salt:Integrated stratigraphy of Messinian evaporites in the deep Eastern Mediterranean reveals long-lasting halite deposition during Atlantic connectivity

The Messinian Salinity Crisis (MSC; 5.97–5.33 Ma) is considered an extreme environmental event driven by changes in climate and tectonics, which affected global ocean salinity and shaped the biogeochemical composition of the Mediterranean Sea. Yet, after more than 50 years of research, MSC stratigraphy remains controversial. Recent studies agree that the transition from the underlying pre-evaporite sediments to thick halite deposits is conformal in the deep Eastern Mediterranean Basin. However, the age of the base and the duration of halite deposition are still unclear. Also disputed is the nature of the intermediate and upper MSC units, which are characterized as periods of increased clastic deposition into the Eastern Mediterranean based on marginal outcrops and seismic data. We provide a multidisciplinary study of sedimentary, geochemical, and geophysical data from industrial offshore wells in the Levant Basin, which recovered a sedimentary record of deep-basin Mediterranean evaporites deposited during the MSC. In combination with previous observations of the MSC throughout the Mediterranean Basin, our results promote the need for a new chronological model. Remarkably, the one-kilometer-thick lower part of the evaporitic unit is composed of essentially pure halite, except for a thin transitional anhydrite layer at its base. The halite is undisturbed and homogeneous, lacking diverse features apparent in more proximal sections, indicating a deep-sea depositional environment. We find that distinct, meters-thick non-evaporitic intervals interbedded with the halite, previously thought to be clastic layers, are diatomites. While XRD analysis confirms an increase in clastic components in these sediments, they are composed primarily of well-preserved marine and freshwater planktonic diatoms. The occurrence of marine planktonic diatoms in these intervals indicates the input of Atlantic waters into the Mediterranean Basin during the deposition of the massive halite unit. Seismic stratigraphy and well-log cyclostratigraphy further support deep basin halite deposition, which started about 300 kyr earlier than widely assumed (~5.97 Ma). We propose that halite deposition in the deep Mediterranean took place during stage 1 of the MSC, rather than being limited to the short 50 kyr MSC acme when sea level was presumably at its lowest. Thus, brine formation, salt precipitation, and faunal extinction occurred at least in part in a deep, non-desiccated basin, with a restricted yet open Mediterranean-Atlantic connection that allowed inflow of oceanic water. We observe an increase in heavy minerals and reworked fauna within the clastic-evaporitic, Interbedded Evaporites of the basinal MSC section, and argue that these settings correspond in the deep basins with a significant sea-level drawdown during stage 2 of the MSC, as observed in the marginal sections. This correlation is corroborated by astrochronology and chemostratigraphic markers, such as the distribution of n-alkanes and biomarker-based thermal maturity indices. The Levant deposits indicate that high sea level and partial connectivity with global oceans promoted the deposition of deep-basin deep-water halite, while sea-level drawdown promoted deposition of reworked and transported material from the margins into deep Mediterranean basins. This study modifies the current understanding of the mechanisms governing salt deposition throughout the MSC with implications for other evaporitic events in the geologic record

Deep-basin evidence resolves a 50-year-old debate and demonstrates synchronous onset of Messinian evaporite deposition in a non-desiccated Mediterranean

The Messinian salinity crisis (MSC) is perceived as an environmental crisis governed by climatic and tectonic controls, affecting global oceans' salinity and shaping the Mediterranean Sea's biochemical composition. Recently drilled offshore wells in the Levant Basin retrieved a sedimentary record of the deep-basin Mediterranean MSC salt deposits and the underlying pre-evaporite unit. In this study, we have concentrated on the pre-evaporite interval and its transition into the overlying evaporites. Analysis of this data set changes the way these deposits have been perceived since the 1970s, when they were first penetrated in their uppermost part during Deep Sea Drilling Project expeditions. Using sedimentology, seismic interpretation, biostratigraphy, and astronomical tuning, we show that Messinian salt deposition in the Eastern Mediterranean began during stage 1 of the MSC. In contrast to the present paradigm, salt was deposited synchronously with gypsum in the marginal and intermediate-depth basins significantly before the 50 k.y. interval coined as the "MSC acme event", ~400 k.y. after the crisis began. Thus salt precipitation took place in a non-desiccated deep basin, having a restricted but often open connection with the Atlantic Ocean, substantially altering our understanding of the mechanisms governing the deposition of salt giants. A coeval onset of basinal halite and marginal gypsum precipitation calls for a revaluation of global-scale climatic and oceanographic models of the MSC, taking into account a much older age for the beginning of halite deposition

Deep-basin evidence resolves a 50-year-old debate and demonstrates synchronous onset of Messinian evaporite deposition in a non-desiccated Mediterranean

The Messinian salinity crisis (MSC) is perceived as an environmental crisis governed by climatic and tectonic controls, affecting global oceans' salinity and shaping the Mediterranean Sea's biochemical composition. Recently drilled offshore wells in the Levant Basin retrieved a sedimentary record of the deep-basin Mediterranean MSC salt deposits and the underlying pre-evaporite unit. In this study, we have concentrated on the pre-evaporite interval and its transition into the overlying evaporites. Analysis of this data set changes the way these deposits have been perceived since the 1970s, when they were first penetrated in their uppermost part during Deep Sea Drilling Project expeditions. Using sedimentology, seismic interpretation, biostratigraphy, and astronomical tuning, we show that Messinian salt deposition in the Eastern Mediterranean began during stage 1 of the MSC. In contrast to the present paradigm, salt was deposited synchronously with gypsum in the marginal and intermediate-depth basins significantly before the 50 k.y. interval coined as the "MSC acme event", ~400 k.y. after the crisis began. Thus salt precipitation took place in a non-desiccated deep basin, having a restricted but often open connection with the Atlantic Ocean, substantially altering our understanding of the mechanisms governing the deposition of salt giants. A coeval onset of basinal halite and marginal gypsum precipitation calls for a revaluation of global-scale climatic and oceanographic models of the MSC, taking into account a much older age for the beginning of halite deposition

Short-lived early Cenomanian volcanic atolls of Mt. Carmel, northern Israel

Volcanic atolls host exceptionally important marine ecosystems in the modern oceans. Yet, due to limited exposures, fossil atolls are poorly constrained. Multiple drowned Cretaceous volcanic atolls have been reported in the Pacific, but less information exists regarding those in the Tethys. Here we report on two early Cenomanian age volcanic atolls outcropping in Mt. Carmel (northern Israel), along the eastern Levant margin. These atolls are a few kilometers in diameter and differ significantly in facies from their surroundings, which are dominated by chalky calcareous mudstone and wackestone. The atolls are composed of grainstone, floatstone, rudstone and bafflestone facies, which are dominated by molluscans, notably gastropods, rudists, oysters and other bivalves. Corals and green algae are absent throughout these atolls. The studied sections of these atolls display a full succession, beginning with aggradation and ending with drowning. Age constraints for the volcanic phases suggest that deposition occurred within a relatively short time interval (<1 Myr) and the sequence represents a keep-up to give-up transition, within rising global and local sea-level trends. The inability of these atolls to keep up with rising sea level is attributed here to a suppressed carbonate factory, either due to drowning, turbidity and/or nutrient excess. Our study sheds new light on the dynamics of carbonate buildups during the Late Cretaceous and their ability to persist

Evidence for specific adaptations of fossil benthic foraminifera to anoxic-dysoxic environments

It has generally been argued that the majority 8 of fossil benthic foraminifera, the most common proxy for paleo bottom oceanic conditions, could not tolerate anoxia. Here we present evidence that fossil foraminifera were able to successfully colonize anoxic–dysoxic bottom waters, by using adaptations similar to those found in living species. Our study is based on a multi-proxy micropaleontological and geochemical investigation of the Upper Cretaceous sediments from the Levant upwelling regime. A shift from buliminid to diverse trochospiral dominated assemblages was recorded in an interval with a distinct anoxic geochemical signature coinciding with a regional change in lithology. This change was triggered by an alteration in the type of primary producers from diatoms to calcareous nannoplankton, possibly causing modifications in benthic foraminiferal morphological and physiological adaptations to life in the absence of oxygen. Our data show that massive blooms of triserial (buliminid) benthic foraminifera with distinct apertural and test morphologies during the Campanian were enabled by their ability to sequester diatom chloroplasts and associate with bacteria, in a similar manner as their modern analogs. Diverse trochospiral forms existed during the Maastrichtian by using nitrate instead of oxygen for their respiratory pathways in a denitrifying environment. Species belonging to the Stilostomellidae and Nodosariidae families might have been affected by the change in food type arriving to the seafloor after the phytoplankton turnover at the Campanian/Maastrichtian boundary, in a similar manner as their mid-Pleistocene descendants prior to their extinction. This study promotes the need for a re-evaluation of the current models used for interpreting paleoceanographic data and demonstrates that the identification of adaptations and mechanisms involved in promoting sustained life under anoxic-dysoxic conditions should become a standard in faunal paleoceanographic studies.status: publishe

Chronostratigraphy of the Upper Cretaceous high productivity sequence of the southern Tethys, Israel

The Levantine high productivity sequence is a product of an extensive upwelling system that operated in the Late Cretaceous along the SE Tethyan margin. This system resulted in the deposition of a unique sequence of carbonate, chert, porcellanite, phosphorite and organic-rich (oil shale) sediments in a series of basins located proximally and marginally to the upwelling center. This study presents a detailed and updated chronostratigraphic framework for the high productivity sequence in Israel based on eight sections covering a NeS cross section of w90 km. The Shefela Basin (central Israel) represents the thickest and the most complete penetrated stratigraphic interval of the oil shale deposits in Israel. The newly drilled Aderet borehole in the Shefela Basin provided a continuous core record coupled with high quality geophysical well logs and was used in this study as a ‘type-section’ for the detailed chronostratigraphic scheme of the high productivity sequence. A total of 23 datum levels were recognized using planktic and benthic foraminiferal biostratigraphy, lithostratigraphy and gamma ray well log markers. The varying lithostratigraphic units (containing chert, phosphate, porcellanite and organic-rich carbonates) of the more proximal basins of southern Israel (Negev) were individually correlated to specific horizons within the monotonous organic-rich carbonates of the distal setting of the Shefela Basin. The first occurrence of the Late Cretaceous organic-rich carbonates in Israel is documented in the Negev during the late Coniacian, within the upper Dicarinella concavata Zone, and corresponds chronologically to the upper part of the lower Menuha Formation. The regional unconformity around the Santonian/Campanian boundary was found to be less substantial at the distal localities in comparison to the proximal ones. The distinct appearance of the ‘Mishash Tongue’ chert in the Shefela was correlated to the massive Chert Member (Mishash Formation) in the Negev, and assigned to the middle Campanian. Deposition of the overlying phosphate series spans from the lower Contusotruncana plummerae to the base of the Pseudoguembelina palpebra Zones (78.3e71.7 Ma) and co-occurs in both proximal and deeper distal areas, although in a much lesser magnitude in the latter. The top of the phosphatic unit is marked by a regional unconformity. The oil shale deposits in southern Israel coincide with the 100 m richest TOC interval (average of 15.2 wt.% TOC) in the Shefela. The diminishing phase of organic-rich deposition occurred in a diachronous step-wise manner across Israel, from the top of the P. palpebra Zone to the upper part of the Abathomphalus mayaroensis Zone in southern and central Israel, respectively. This indicates that the full duration of the high productivity sequence in Israel spans approximately 19 myr.publisher: Elsevier articletitle: Chronostratigraphy of the Upper Cretaceous high productivity sequence of the southern Tethys, Israel journaltitle: Cretaceous Research articlelink: http://dx.doi.org/10.1016/j.cretres.2014.04.006 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.status: publishe

Chronology with a pinch of salt : Integrated stratigraphy of Messinian evaporites in the deep Eastern Mediterranean reveals long-lasting halite deposition during Atlantic connectivity

The Messinian Salinity Crisis (MSC; 5.97–5.33 Ma) is considered an extreme environmental event driven by changes in climate and tectonics, which affected global ocean salinity and shaped the biogeochemical composition of the Mediterranean Sea. Yet, after more than 50 years of research, MSC stratigraphy remains controversial. Recent studies agree that the transition from the underlying pre-evaporite sediments to thick halite deposits is conformal in the deep Eastern Mediterranean Basin. However, the age of the base and the duration of halite deposition are still unclear. Also disputed is the nature of the intermediate and upper MSC units, which are characterized as periods of increased clastic deposition into the Eastern Mediterranean based on marginal outcrops and seismic data. We provide a multidisciplinary study of sedimentary, geochemical, and geophysical data from industrial offshore wells in the Levant Basin, which recovered a sedimentary record of deep-basin Mediterranean evaporites deposited during the MSC. In combination with previous observations of the MSC throughout the Mediterranean Basin, our results promote the need for a new chronological model. Remarkably, the one-kilometer-thick lower part of the evaporitic unit is composed of essentially pure halite, except for a thin transitional anhydrite layer at its base. The halite is undisturbed and homogeneous, lacking diverse features apparent in more proximal sections, indicating a deep-sea depositional environment. We find that distinct, meters-thick non-evaporitic intervals interbedded with the halite, previously thought to be clastic layers, are diatomites. While XRD analysis confirms an increase in clastic components in these sediments, they are composed primarily of well-preserved marine and freshwater planktonic diatoms. The occurrence of marine planktonic diatoms in these intervals indicates the input of Atlantic waters into the Mediterranean Basin during the deposition of the massive halite unit. Seismic stratigraphy and well-log cyclostratigraphy further support deep basin halite deposition, which started about 300 kyr earlier than widely assumed (~5.97 Ma). We propose that halite deposition in the deep Mediterranean took place during stage 1 of the MSC, rather than being limited to the short 50 kyr MSC acme when sea level was presumably at its lowest. Thus, brine formation, salt precipitation, and faunal extinction occurred at least in part in a deep, non-desiccated basin, with a restricted yet open Mediterranean-Atlantic connection that allowed inflow of oceanic water. We observe an increase in heavy minerals and reworked fauna within the clastic-evaporitic, Interbedded Evaporites of the basinal MSC section, and argue that these settings correspond in the deep basins with a significant sea-level drawdown during stage 2 of the MSC, as observed in the marginal sections. This correlation is corroborated by astrochronology and chemostratigraphic markers, such as the distribution of n-alkanes and biomarker-based thermal maturity indices. The Levant deposits indicate that high sea level and partial connectivity with global oceans promoted the deposition of deep-basin deep-water halite, while sea-level drawdown promoted deposition of reworked and transported material from the margins into deep Mediterranean basins. This study modifies the current understanding of the mechanisms governing salt deposition throughout the MSC with implications for other evaporitic events in the geologic record