The Turonian (93.5 to 89.3 million years ago) was one of the warmest periods of the Phanerozoic eon, with tropical sea surface temperatures over 35°C. High-amplitude sea-level changes and positive ...δ¹⁸O excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth. New δ¹⁸O data from the tropical Atlantic show synchronous shifts ~91.2 million years ago for both the surface and deep ocean that are consistent with an approximately 200,000-year period of glaciation, with ice sheets of about half the size of the modern Antarctic ice cap. Even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets, calling into question the common assumption that the poles were always ice-free during past periods of intense global warming.
The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative ...importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing. We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change. Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from postextinction volcanism.
The Niveau Breistroffer black shale succession in the Vocontian Basin (SE France) is the regional equivalent of the widely distributed Late Albian Oceanic Anoxic Event 1d. The studied black ...shale-rich interval at the Col de Palluel section is 6.28 m thick and comprises four black shale units with up to 2.5 wt% total organic carbon (TOC) intercalated with marlstones. Calcareous nannofossil, palynomorph, planktic Foraminifera and stable isotopic data from the Niveau Breistroffer succession suggest that short-term climate changes influenced its deposition, with relatively warm and humid climate during black shale formation in comparison with relatively cool and dry climatic conditions during marlstone deposition. An increase in the terrigenous/marine ratio of palynomorphs indicates enhanced humidity and higher runoff during black shale formation. A nutrient index based on calcareous nannofossils and the abundance pattern of small (63-125 µm) hedbergellid Foraminifera show short-term changes in the productivity of the surface water. Surface-water productivity was reduced during black shale formation and increased during marlstone deposition. A calcareous nannofossil temperature index and bulk-rock oxygen isotope data indicate relative temperature changes, with warmer surface waters for black shale samples. At these times, warm-humid climate and reduced surface-water productivity were accompanied by greater abundances of "subsurface"-dwelling calcareous nannofossils (nannoconids) and planktic Foraminifera (rotaliporids). These taxa presumably indicate more stratified surface-water conditions. We suggest that the formation of the Niveau Breistroffer black shales occurred during orbitally induced increase in monsoonal activity that led to increasing humidity during periods of black shale formation. This, in turn, caused a decrease in low-latitude deep-water formation and probably an increase in surface-water stratification. The combination of these two mechanisms caused depleted O2 concentrations in the bottom water that increased the preservation potential of organic matter.
We present new quantitative calcareous nannofossil data from a Barremian (Early Cretaceous) black shale interval of the Boreal Realm. Thirty samples from two sections in northern Germany have been ...investigated. The current study aims to understand the genesis of the Barremian black shales, so far only described from the Boreal Realm, in a supraregional to global context by assessing the diversity patterns, relative abundances and biometry of calcareous nannofossils from a distinctive late early Barremian black shale horizon. For morphometric size measurements, three common taxa, Biscutum constans, Rhagodiscus asper and Watznaueria barnesiae have been investigated.
The results show a decrease in size and abundance of the high fertility indicator B. constans for the main black shale horizon (Hauptblätterton), while abundances of the warm water species R. asper and Watznaueria spp. increase. Deep dwelling nannoconids only flourished during black shale deposition. This indicates warm, oligotrophic surface waters and an expanded photic zone during the formation of the Hauptblätterton black shales. Similar observations have been made for the Oceanic Anoxic Event 1d (OAE 1d, Albian) in the Vocontian Basin (Southern France) and for the OAE 2 (Cenomanian) in the Western Interior Seaway and southern England. For W. barnesiae our data confirm a high ecological tolerance and we assume a response in size if a certain limit is exceeded towards more extreme conditions. Nutrients therefore likely play a larger role than water temperature. From our results, it seems likely that nutrient availability controls both, size and abundance patterns of B. constans.
•First calcareous nannofossil morphometry data for mid Barremian black shales from the Boreal Realm.•Warm and oligotrophic surface waters are assumed during black shale deposition.•OAE 1d and OAE 2 black shales seem to have been formed regionally under comparable conditions.•Nutrients seem to have controlled size and abundance patterns of calcareous nannofossils.
The marine ecosystem has been severely disturbed by several transient paleoenvironmental events (<200 kyr duration) during the early Paleogene, of which the Paleocene-Eocene Thermal Maximum (PETM, ...~56 Ma) was the most prominent. Over the last decade a number of similar events of Paleocene and Eocene age have been discovered. However, relatively little attention has been paid to pre-PETM events, such as the "Latest Danian Event" ("LDE", ~62.18 Ma), specifically from an open ocean perspective. Here we present new foraminiferal isotope (δ13C, δ18O) and faunal data from Ocean Drilling Program (ODP) Site 1210 at Shatsky Rise (Pacific Ocean) in order to reconstruct the prevailing paleoceanographic conditions. The studied five-meter-thick succession covers ~900 kyr and includes the 200-kyr-lasting LDE. All groups surface dwelling, subsurface dwelling and benthic foraminifera show a negative δ13C excursion of >0.6‰, similar in magnitude to the one previously reported from neighboring Site 1209 for benthic foraminifera. δ18O-inferred warming by 1.6 to 2.8°C (0.4-0.7‰ δ18O measured on benthic and planktic foraminiferal tests) of the entire water column accompanies the negative δ13C excursion. A well stratified upper ocean directly before and during the LDE is proposed based on the stable isotope gradients between surface and subsurface dwellers. The gradient is less well developed, but still enhanced after the event. Isotope data are supplemented by comprehensive planktic foraminiferal faunal analyses revealing a dominance of Morozovella species together with Parasubbotina species. Subsurface-dwelling Parasubbotina shows high abundances during the LDE tracing changes in the strength of the isotope gradients and, thus, may indicate optimal living conditions within a well stratified surface ocean for this taxon. In addition, distinct faunal changes are reported like the disappearance of Praemurica species right at the base of the LDE and the continuous replacement of M. praeangulata with M. angulata across the LDE.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Quaternary volcanogenic landscape and the volcanogenic sediments of the Netherlands Antilles (NA) (Aruba, Bonaire, Curaçao) reflect the most recent stage of the evolution of the Cretaceous to ...early Cenozoic Great Arc of the Caribbean Plate. They provide a “geoscientific keyhole” to look at its geodynamic and lithological evolution at different scales. This sedimentological, micropaleontological, geomorphological/geo-morphometrical, litho-chemical and mineralogical approach, holistic in essence and focused as to the target, can also be taken to better understand other volcanic arcs or facies zones, e.g., in Colombia. It allows for a climatic-geomorphological zonation governed by uplift and erosion of the volcanic arc in time and space. The host rock quality of landforms for volcanogenic sediments abundant in heavy minerals (HM) that are known as the most suitable markers for provenance and geodynamics can be arranged in decreasing order of significance as follows: coastal-marine volcaniclastic > fluvial–marine (deltaic) > aeolian-coastal-marine > mass wasting > residual > coastal-marine calcareous. The coastal sediments facing towards the plate margin contain Cr–Fe–Ti–Nb–Th–U–Zr-bearing HM which derived from off-shore ophiolites, Precambrian shelf sediments of the South-American Plate, volcanic–subvolcanic units, and mantle source rocks. The Quaternary hydrography evolved on different erosion levels and exposes different basement lithologies of volcanic and subvolcanic type. The drainage system is controlled by faulting (tecto-variance) and the volcanic lithologies (litho-variance) both of which indicate different phases of tectonic and magmatic activity during arc emplacement. This in-active volcanic arc of the Netherlands Antilles has been shaped during the Cenozoic by the climate change and modern tectonics on a deeper level of erosion than the active volcanic arc of the Lesser Antilles.
The Latest Danian Event (LDE, ~ 62.2 Ma) is characterized by global changes in the carbon cycle as indicated by two negative δ
13
C excursions of up to ~ 1‰. These δ
13
C shifts are accompanied by a ...2–3 °C warming of both surface and deep waters based on benthic and planktic foraminiferal δ
18
O measurements, and the LDE has, thus, been considered as a so-called hyperthermal event. The event lasted for 200 kyr and has been identified in various ocean basins and shallow marine settings. Here, we present a compilation of data from three deep-sea cores covering the Pacific, North and South Atlantic oceans as well as a southern Tethyan shelf section to document the response of planktic foraminifera assemblages to ocean warming. In all studied successions, we observe the disappearance of the planktic foraminifer genus
Praemurica
on a global scale that took place close to the onset of the LDE. Moreover, on the long run, praemuricids were contemporaneously replaced by morozovellids. Both the decline of
Praemurica
and a temperature increase started between 200 and 260 kyr before the LDE onset and were punctuated by the LDE itself. In this paper, we propose two mechanisms that have controlled the environmental changes associated with this event, (1) increased activity of the North Atlantic Igneous Province acting on long time-scales, and (2) changes of orbital parameters resulting in insolation changes on shorter time-scales.
In contrast to a proposed muted benthic foraminiferal response, the planktic community has been substantially impacted by the LDE as indicated by changes in planktic foraminifera faunas and calcareous nannofossils. Finally, our quantitative and conventional approaches identifying stratigraphically important planktic foraminifera datum levels justify a revision of the upper Danian to lower Selandian planktic foraminifera biozonation.
Strata of Valanginian age (Early Cretaceous, 139.8–132.9 Ma) record a 1.5‰ positive carbon isotope excursion (CIE), the Weissert Event. It coincides with volcanic activity of the Paraná-Etendeka ...large igneous province. Unlike the Mesozoic Oceanic Anoxic Events (OAEs), no organic-rich deposits documenting widespread perturbation of the marine carbon-cycle are associated with the Weissert Event. To study the impact of paleoceanographic changes in the Valanginian on calcareous nannofossils, this study analyzes coccolith size data of three species (Biscutum constans, Watznaueria barnesiae, Zeugrhabdotus erectus) from northern Germany and the western North Atlantic. Further it presents a new Valanginian carbon isotope record of organic material (δ13Corg) from northern Germany. The dataset records the Weissert Event CIE in the late Valanginian.
At both locations biometric analyses reveal size decreases of B. constans coccoliths during the Weissert Event. A size reduction of ~1 μm has been observed for northern Germany (37°N) and of 0.4 μm for the North Atlantic (23°N). The different magnitudes of size decrease possibly reflect the different paleogeographic positions of the sites and the paleoceanographic response to the late Valanginian climate variations. Proxy data support a link between a humid climate with increased weathering, and the observed coccolith size variations. This impacted nannoplankton communities either through the availability of light or by eutrophication and, possibly, nutrient limitation. In addition to increased terrigenous input, emissions of the Paraná-Etendeka volcanism possibly acted fertilizing. Furthermore, widely dispersed volcanic emissions possibly caused increased concentrations of toxic trace metals in the surface ocean which affected marine primary producers.
•Morphometric analyzes reveal nannofossil size decrease during Weissert Event.•Size variations may be linked to increased humidity and weathering in the Valanginian.•New δ13Corg data record the Weissert Event in northern Germany.
High-amplitude changes in sedimentary δ
13
C characterize the Cretaceous system and have been proven useful for supra-regional chemostratigraphic correlation. In the Cretaceous, these δ
13
C ...perturbations indicate large shifts between the global carbon reservoirs that are usually caused by volcanic activity of large igneous provinces, the widespread deposition of thick organic carbon-rich sequences and/or changes in orbital parameters. Here, we present an upper Berriasian to lower Coniacian (c. 142–88 Ma) composite carbon isotope record based on 14 drill cores, 2 outcrops, and almost 5,000 samples. The total record comprises a composite thickness of more than 1,500 m. All cores and successions are located in the larger Hanover area, which represents the depocenter of the North German Lower Saxony Basin in Early to mid-Cretaceous times. In Northern Germany, Boreal Lower Cretaceous sediments are predominantly represented by CaCO
3
-poor mud and siltstones of up to 2,000 m thickness, which become more carbonate-rich during the Albian–Cenomanian transition and even chalkier in the upper Cenomanian to Coniacian interval. The carbon isotope record reveals a number of global key events, including the Valanginian Weissert Event, the Oceanic Anoxic Events (OAEs) 1a and d, and the Kilian Event (Aptian–Albian boundary, part of OAE 1b). For the early Late Cretaceous, the Mid-Cenomanian Event, the OAE 2 (Cenomanian–Turonian Boundary Event), and the Navigation Event, among others, have been identified. The Kilian Event represents the Aptian–Albian boundary and has been identified herein for the first time in Northern Europe. Based on the evaluation of its relative position to the Vöhrum boundary tuff, we tentatively propose a slightly older age for the Aptian–Albian boundary of c. 113.65 Ma instead of 113.2 Ma. The observed chemostratigraphic events enable a detailed stratigraphic comparison with Tethyan and other Boreal records and associated paleoenvironmental data. Thus, this new detailed chemostratigraphy provides a unique opportunity to potentially overcome many still existing Boreal–Tethyan correlation issues. The presented record can be considered almost complete, albeit a 2-Myr gap during the early Albian is likely, and condensed intervals occur specifically during the lower Aptian.
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