Eocene Planktonic Foraminifera Research Articles

Upper Eocene planktonic foraminifera from northern Saudi Arabia: implications for stratigraphic ranges

Abstract. The Rashrashiyah Formation of the Sirhan Basin in northern Saudi Arabia contains diverse assemblages of planktonic foraminifera. We examined the biostratigraphy, stratigraphic range and preservation of upper Eocene planktonic foraminifera. Assemblages are well-preserved and diverse, with 40 species and 11 genera. All samples are assigned to the Priabonian Globigerinatheka semiinvoluta Highest Occurrence Zone (E14), consistent with calcareous nannofossil biostratigraphy indicating Zone CNE17. Well-preserved planktonic foraminifera assemblages from the lower part of the upper Eocene are rare worldwide. Our study provides new insights into the stratigraphic ranges of many species. We find older (Zone E14) stratigraphic occurrences of several species of Globoturborotalita previously thought to have evolved in the latest Eocene (Zone E15, E16) or Oligocene; these include G. barbula, G. cancellata, G. gnaucki, G. pseudopraebulloides, and G. paracancellata. Older stratigraphic occurrences for Dentoglobigerina taci and Subbotina projecta are also found, and Globigerinatheka kugleri occurs at a younger stratigraphic level than previously proposed. Our revisions to stratigraphic ranges indicate that the late Eocene had a higher tropical–subtropical diversity of planktonic foraminifera than hitherto reported.

Eocene planktonic foraminifera from the north Eastern Desert, Egypt: Biostratigraphic, paleoenvironmental and sequence stratigraphy implications

Eocene planktonic foraminifera from the north Eastern Desert, Egypt: Biostratigraphic, paleoenvironmental and sequence stratigraphy implications

Біостратиграфія палеоцен-еоценових відкладів Українських Карпат за планктонними форамініферами

Paleogene deposits are the main reservoir of hydrocarbon resources in the Carpathians and creation of the modern stratigraphic scheme of these deposits is the basis for improving the efficiency of geological search works. The reliable stratification is a necessary precondition for the preparation of geological maps. Stratification of the Paleocene–Eocene sediments is provided by foraminifera, nannoplankton, dinocysts, radiolarians, sponge spicules, palynoflora. Planktonic foraminifera is the main stratigraphic group of the Paleogene fauna. In the predominantly non-calcareous flysch of the Paleocene–Eocene of the Carpathians, mainly agglutinated benthic foraminifera of siliceous composition are developed. Planktonic foraminifera are distributed locally – in calcareous facies. The most complete sequence of Paleocene–Eocene planktonic foraminifera is represented in the Metova Formation (the Vezhany nappe of the Inner Carpathians). The results of own researches of natural sections of sediments distributed within the Magursky, Monastyretsky and Vezhany nappes of the Ukrainian Carpathians together with the analysis of literature sources are used. The article presents a generalized biozonal division of the Paleocene–Eocene of the Ukrainian Carpathians by planktonic foraminifera. On the basis of certain correlation levels, a comparison with the Geological Time Scale was made. The Parvularugoglobigerina eugubina Zone (lowermost Danian), Globoconusa daubjergensis Zone (middle Danian), Praemurica inconstans Zone (upper Danian); Morozovella angulata Zone (lower Selandian); Globanomalina pseudomenardii Zone fnd Acarinina acarinata Zone (upper Selandian–Thanetian); Morozovella subbotinae Zone (lower Ypresian), Morozovella aragonensis Zone (upper Ypresian); Acarinina bullbrooki Zone (lower Lutetian), Acarinina rotundimarginata Zone (upper Lutetian); Hantkenina alabamensis Zone (Bartonian); Globigerinatheka tropicalis Zone (lower Priabonian) and Subbotina corpulenta Zone (upper Priabonian) based on planktonic foraminifera are characterized in studied deposits.

Eocene Planktonic Foraminifera and the Age of the Youngest Marine Sediments in Tüna, Yadong, Southern Tibet

Eocene Planktonic Foraminifera and the Age of the Youngest Marine Sediments in Tüna, Yadong, Southern Tibet

Early Eocene planktonic and benthic foraminifera from the Khangiran formation (northeast of Iran)

The Kopet-Dagh sedimentary basin is located in northeast of Iran and southeast of Turkmenistan in the Middle East. The Khangiran formation represents the last marine deposition in the Kopet-Dagh sedimentary basin. The early Eocene planktonic and benthic foraminifera from the Khangiran formation which belongs to the lower 376 m thickness of this formation are identified and biostratigraphically evaluated. Due to rarity of Morozovella species, planktonic foraminiferal zonation was difficult to determine in this formation. The determination of upper part of the late Paleocene for the lower 124 m of this formation is according to the lowest occurrence of Acarinina sibaiyaensis species. From E5 to near middle of E7 biozone, increasing trend of Acarinina frequency and a peak in Morozovella species and decreasing trend of frequency of Subbotina and Pseudohastigerina species indicate the warm and oligotrophic condition of the seawater during sedimentation of the studied interval. Toward the Ypresian-Lutetian boundary, the increasing trend of Pseudohastigerina and Subbotina species and decreasing in frequency of Acarinina species suggest the low-oxygen level, eutrophic and intermediate condition of the seawater. In this formation, the high abundance of the epifaunal taxa such as Anomalinoides spp., Cibicidoides spp., Gyroidinoides spp., and Lenticulina spp. from the base (late Paleocene sediments) up to E6 biozone reflects oligotrophic and oxic shallow water conditions. The occurrence of several peaks in abundance of Bulimina and Uvigerina species at the Ypresian/Lutetian boundary suggests eutrophic condition. These paleoecological conditions could be correlated with fluctuations in the numbers of the planktonic foraminifera.

Algorithmic approaches to aid species' delimitation in multidimensional morphospace

BackgroundThe species is a fundamental unit of biological pattern and process, but its delimitation has proven a ready source of argument and disagreement. Here, we discuss four key steps that utilize statistical thresholds to describe the morphological variability within a sample and hence assess whether there is evidence for one or multiple species. Once the initial set of biologically relevant traits on comparable individuals has been identified, there is no need for the investigator to hypothesise how specimens might be divided among groups, nor the traits on which groups might be separated.ResultsPrincipal components are obtained using robust covariance estimates and retained only if they exceed threshold amounts of explanatory power, before model-based clustering is performed on the dimension-reduced space. We apply these steps in an attempt to resolve ongoing debates among taxonomists working on the extinct Eocene planktonic foraminifera Turborotalia, providing statistical evidence for two species shortly before the lineage's extinction near the Eocene/Oligocene boundary.ConclusionBy estimating variance robustly (samples containing incipient species are unlikely to be scaled optimally by means and standard deviations) and identifying thresholds relevant to a particular system rather than universal standards, the steps of the framework aim to optimize the chances of delineation without imposing pre-conceived patterns onto estimates of species limits.

Loftusia persica: an Eocene Lazarus occurrence?

A specimen of Loftusia persica Brady is described that contains as a part of its inner test a specimen of Turborotalia pomeroli (Toumarkine and Bolli), which is a very distinctive Middle to Late Eocene planktonic foraminifera. Although originally described as a "Tertiary" form, more recently Loftusia persica has been considered to be restricted to theMaastrichtian. Anumber of scenarios that could have led to the inclusion of an Eocene planktonic foraminifera deep within the test of a specimen of Loftusia are discussed, and it is concluded that the most probable interpretation is that Loftusia persica reappeared as a "Lazarus" species in the Eocene having survived the Cretaceous-Paleocene mass extinction, but was eventually driven to extinction by the orogeny that led to the formation of the Zagros Mountains.

Nuovi dati litostratigrafici e biostratigrafici sulla Scaglia Toscana nella Toscana meridionale (area di Rapolano Terme)

Nuovi dati litostratigrafici e biostratigrafici sulla Scaglia Toscana nella Toscana meridionale (area di Rapolano Terme)

Recent advances in the study of Eocene planktonic foraminifera

Abstract

Tectonostratigraphy of the Khoy Complex, northwestern Iran

Previous studies suggested that only one ophiolite, the “Khoy ophiolite", existed near Khoy, northwestern Iran. This thesis is no longer tenable. Combined investigations (biostratigraphic, chronostratigraphic, geochonometric, geochronologic, and geochemical) demonstrate that there are at least two and perhaps three ophiolite remnants in the Khoy area: (1) A Late Jurassic (early to middle Oxfordian: 156 Ma to 159 Ma 40Ar-39Ar on gabbro) remnant; (2) A Late Cretaceous (early Coniacian: Radiolaria) remnant (~N-MORB geochemistry); and, possibly, (3) A Late Cretaceous (latest Campanian) remnant (E-MORB geochemistry). Because it is impossible to use the term “Khoy ophiolite" in this report, we refer the ophiolitic rocks in the Khoy area to the “Khoy Complex” (sensu International Stratigraphic Guide). The sedimentary contact between Late Cretaceous (early Coniacian) red manganiferous ribbon chert lacking calc-alkaline volcanic contributions and overlying pyroclastics (tuff and tuff breccia) in the far northwestern part of the Khoy complex is of great tectonostratigraphic significance. This interface represents a sudden change from pelagic to pyroclastic sedimentation. Field evidence indicates that the contact is disconformable and is associated with a hiatus of unknown magnitude. Red ribbon chert (lacking calcalkaline contributions) in the same area overlies and is interbedded with N-MORB pillow basalt; early Coniacian Radiolaria were recovered from interpillow siliceous mudstone. We postulate that by the early Coniacian oceanic crust (covered with a veneer of Radiolarian ooze) had moved close enough to an island arc system to receive calc-alkaline pyroclastics. Tectonic melange in the Khoy Complex represents a subduction complex probably associated with the island arc noted above. Micrite (pelagic limestone) knockers in the tectonic melange belt contain Early Cretaceous (late Albian: Vraconian) planktonic foraminifera; Late Cretaceous (early Cenomanian) Radiolaria; Late Cretaceous (early Campanian to early Maastrichtian) planktonic foraminifera; Late Cretaceous (late Maastrichtian) planktonic foraminifera; and early Middle Eocene planktonic foraminifera. The age of the micrite knockers in the tectonic melange, suggests that subduction associated with island arc volcanism continued from the Early Cretaceous (latest Albian) to the Early Tertiary (early middle Eocene).

Biostratigraphic zonation and 40Ar– 39Ar ages for the Neotethyan Khoy ophiolite of NW Iran

The Khoy ophiolite in northwestern Iran represents a piece of oceanic lithosphere formed in the Mesozoic Neotethys. This ophiolite consists from bottom to top of well-defined basal metamorphic rocks, peridotites, gabbros and a variety of upper to lower Cretaceous deep-marine rocks. These include pelagic fossiliferous carbonates and basalts as interlayers or exotic blocks. Four hornblende separates from gabbros and amphibolites give values from 108 to 111 Ma. The results from microfossil studies show the presence of late Cretaceous (e.g. Marginotruncana, Globotruncana) and middle to late Eocene (e.g. Globorotalia, Orbulonoides) planktonic foraminifera. The data suggest that although the initial rifting and crystallization of the oceanic crust of the Khoy ophiolite began in the late Albian, the volcanic activities continued through to the late Eocene time. Another possibility for such variation of lithofacies and biofacies and disturbances in the fossil record may be the result of bioturbation and transportation and rapid changes of depositional conditions during eruption of the basaltic lava flows. Pelagic sediments alone have been listed and of the foraminiferas the first three are planktonic, as would be expected. Only Orbulonoides is a benthic form and aberrant. The third possibility is that the Khoy ophiolite may represent a classic supra-subduction-type ophiolite where volcanic members of the different parts of oceanic environment (e.g. MORB, volcanic arc, ocean island) are now juxtaposed.

Hantkeninid depth adaptation: An evolving life strategy in a changing ocean

The interplay between evolution, paleoecology, and environmental change is examined in a geochemical study of a group of Eocene planktonic foraminifera. The hantkeninids, which are well-known biostratigraphic inde × fossils, underwent spectacular long-term evolution in the middle and upper Eocene (49.0–33.7 Ma), a time when major global climate and oceanic changes were occurring. We use oxygen and carbon isotope analysis of their shell calcite to investigate how their habitat changed as they evolved. The hantkeninids originated in a deep-water oxygen-minimum environment, but migrated into fully oxygenated near-surface waters as global temperatures decreased and water-column stratification declined. This change in depth ecology coincided with pronounced morphological evolution, involving changes in chamber shape and degree of inflation, and modification of the primary aperture. These developments are considered to be adaptations to a near-surface habitat.

New evidence for subtropical warming during the Late Paleocene thermal maximum: Stable isotopes from Deep Sea Drilling Project Site 527, Walvis Ridge

The late Paleocene thermal maximum (LPTM) was a dramatic, short‐term global warming event that occurred ∼55 Ma. Warming of high‐latitude surface waters and global deep waters during the LPTM has been well documented; however, current data suggest that subtropical and tropical sea surface temperatures (SSTs) did not change during the event. Conventional paradigms of global climate change, such as CO2‐induced greenhouse warming, predict greater warming in the high latitudes than in the tropics or subtropics but, nonetheless, cannot account for the stable tropical/subtropical SSTs. We measured the stable isotope values of well‐preserved late Paleocene to early Eocene planktonic foraminifera from South Atlantic Deep Sea Drilling Project (DSDP) Site 527 to evaluate the subtropical response to the climatic and environmental changes of the LPTM. Planktonic foraminiferal δ18O values at Site 527 decrease by ∼0.94‰ from pre‐LPTM to excursion values, providing the first evidence for subtropical warming during the LPTM. We estimate that subtropical South Atlantic SSTs warmed by at least ∼1°–4°C, on the basis of possible changes in evaporation and precipitation. The new evidence for subtropical SST warming supports a greenhouse mechanism for global warming involving elevated atmospheric CO2 levels.

A field of volcanoes on the Manihiki Plateau: Mud or lava?

A field of about 100 cones surrounding a 1900 m high seamount was discovered on the northeastern edge of Manihiki Plateau (10° 18.5′S, 161°27.5′W) during a February 1987 cruise of the R.V. Moana Wave in the territorial waters of the Cook Islands. The cones appear as acoustically transparent piercements on single-channel seismic reflection profiles collected during this and earlier expeditions to the area. SeaMARC II sidescan images typically reveal nearly conical, steep-sided peaks of about 1 km diameter rising several hundred meters above the smooth and featureless plateau surface. Many of the cones appear to be formed by multiple flow units. A few have summit depressions, and moats partially surround some of the cones. Distributed like holes on a dart board, individual cones become more densely spaced about a bulls eye located near the eastern edge of the Manihiki Plateau, 50 km southwest of Rakahanga Island. At that location, about 40 cones coalesce to form the seamount, which is about 25 km in diameter and rises from a plateau depth of 3200 m to a summit at a depth of 1310 m. Sidescan images show that incised channels trend away from the seamount toward the east, where the irregular seafloor in the area truncates tilted, E-dipping sub-bottom reflectors. To the south and west, the seafloor and sub-bottom reflectors are smooth and dip gently to the southwest. Recent foraminiferal ooze was cored from a satellite cone. Dredging of the seamount summit recovered middle Eocene planktonic foraminifera embedded in burrowed limestone. Some of the limestone cobbles had manganese crusts; coralline fragments and Recent foraminifera were also recovered in the same dredge. Despite the apparent absence of igneous rocks, geopotential modelling indicates a basement high at this location. If fluid escape rather than magma flow is involved in the genesis of these cones, it is localized by faulting associated with basement uplift or the presence of an older igneous intrusion. At this time we cannot say with certainty whether the cones are igneous or sedimentary features.

Productivity change as a control on planktonic foraminiferal evolution after the cretaceous/tertiary boundary

The rate of evolution of Palaeocene and Early Eocene planktonic Foraminifera is examined using taxonomic data from two distant sites. The two million years immediately following the Cretaceous/Tertiary boundary was characterised by low rates of evolution within the group. Peaks in the rate of species turnover at 62.5 and 57.5 Ma suggest a close relationship between the evolution of this group and changes in ocean productivity and therefore the intensity of the sub‐surface oxygen minimum zone. A model for the evolution of the early Palaeogene planktonic Foraminifera is proposed.

Wall-Hispidity and -Perforation in Eocene Planktonic Foraminifera

SEM (Scanning Electron-Microscope) studies of Eocene planktonic foraminifera from Israel show that the hispidity of test surfaces is due to the presence of protuberances (tubercles, pustules, pseudospines) of the same type as those found in many other Cenozoic species which do not possess true spines and spine-bases. Relatively raised interpore areas may be due to flaring pore-funnel walls (residual ridges) or to externally protruding inflational features (built-up ridges). Pore size and especially the ratio between pore-diameter and interpore distance, together with type and distribution of wall surface features, facilitate the recognition of species groups and genera, as well as of evolutionary lineages. Wall-hispidity and -perforation in Eocene planktonic foraminifera

The development of planktonic biogeography in the Southern Ocean during the Cenozoic

The development of planktonic biogeography in the Southern Ocean during the Cenozoic

Sea water weathering effect on K-Ar age of submarine basalts

K-Ar dating and 40Ar- 39Ar step heating experiments have been done for successive zones from the surface to the interior in two, altered dredged submarine basalts (16-2-6 and Aries V-23). The K contents show a systematic decrease (surface to the interior), whereas the K-Ar ages show a similar decrease in one sample (16-2-6) and almost no change in the other (Aries V-23). A simple diffusion model suggests that the K content decreases systematically from the surface to the interior, whereas the K-Ar age decreases or remains almost constant, depending on whether the times of solidification and of commencement of K-diffusion are close to each other or differ significantly. Comparison of the observed K content and K-Ar age variations within the rocks with the theoretical model then suggests that the solidification age of the sample Aries V-23 is much older than the commencement of the potassium-diffusion, the latter age perhaps being represented by the Eocene planktonic foraminifera on this sample. The 40Ar- 39Ar isochron age obtained for the freshest specimen of Aries V-23 is 86.6 ± 3.7 m. y., supporting the above conclusion. The mathematical simulation indicates that an apparent concordance of the K-Ar age observed in some submarine basalts may be an artifact, only reflecting the significant gap between the solidification age and the time of the commencement of the K-diffusion in the rocks. Microprobe examination reveals that the potassium enrichment in the outer margin, is mainly due to K feldspar, which is an alteration product of plagioclase.

Eocene and miocene rocks off the northeastern coast of the United States

A grab sample from a depth of 1675 m at a point south of Cape Cod contains early Eocene planktonic Foraminifera and is correlated with the Globorotalia rex zone of Trinidad. The assemblage indicates a depth comparable to that existing today. Regional relations suggest that the Cretaceous and Eocene deposits deepen to the west toward New Jersey.Two mollusk-bearing blocks dredged from the northern side of Georges Bank are correlative with the Miocene Yorktown Formation. Rocks from two other stations are probably Miocene. Benthonic Foraminifera in one sample indicate deposition in cool temperate waters of less than 60 m depth.

Stratigraphy and Foraminifera of Lower Tertiary Vidono Shale, Near Puerto La Cruz, Venezuela

The mid to upper Vidono shales in northeastern Venezuela contain an abundant foraminiferal fauna. Of the 86 species recorded in this paper, 31 are new to the formation. A characteristic low-oxygen Haplophragmoides-Trochammina-Cyclammina-Glomospira faunule is restricted to the lower black shales of a Vidono outcrop southwest of Puerto la Cruz. The overlying sediments of this section are different and contain benthonic forms indicating that the density stratified waters of a partly restricted basin were overturned by an incursion of the sea. The benthonic Foraminifera give the Vidono shale its Upper Cretaceous aspect but study of the planktonic species, recognized over wider geographical areas, indicates more precise Paleocene (Landenian) to lower Eocene (Ypresian) age for the mid to upper shales and siltstones of the Vidono formation. Two zones are recognized: a Globorotalia velascoensis-Globorotalia pseudomenardii zone and a younger Globorotalia rex zone. The Upper Cretaceous to lower Eocene planktonic Foraminifera of the Vidono shales offer a more precise means of studying the Cretaceous-Tertiary boundary problems in the Caribbean area.