Umbria-Marche Basin Research Articles

Cretaceous planktonic foraminiferal biostratigraphy of the Umbria–Marche Basin (Central Italy)

Abstract The Umbria–Marche Basin of central Italy includes some of the most studied, continuous and well-exposed sequences of Cretaceous pelagic sediments known from the Tethyan Realm. A complete and well-preserved Cretaceous pelagic composite succession of this area is here presented. It has been constructed through the integration of the well-established magnetostratigraphy with the planktonic foraminiferal biostratigraphy based on previous and newly identified events from six key sections and one drill core. The recovery of planktonic foraminifera successfully disaggregated from the hard lithologies allows the identification and precise placement of several primary and secondary bioevents. In particular, the record of the identified bioevents counts 35 primary biohorizons, which allow the subdivision of the studied succession into 34 zones and 4 subzones. Following this study and previous findings on Cretaceous planktonic foraminifera, an updated planktonic foraminiferal zonation for the Cretaceous Period is proposed. This refined magnetobiostratigraphical framework, which in this study is integrated with the Cretaceous inoceramid, anoxic and carbon-isotope events recognized in the Umbria–Marche Basin, may provide an invaluable tool for improving Cretaceous correlations at low to middle latitudes, as well as palaeoenvironmental, palaeoclimatic and palaeoceanographical interpretations.

Calcareous nannofossils from the Poggio le Guaine core (Umbria-Marche Basin, central Italy): Biostratigraphy and discussion of Aptian–Albian bioevents.

Calcareous nannofossils from the Poggio le Guaine core (Umbria-Marche Basin, central Italy): Biostratigraphy and discussion of Aptian–Albian bioevents.

Environmental magnetic characterization for the Pialli Level and the Cretaceous Oceanic Red Bed 7 (late Albian, Poggio le Guaine core, central Italy)

The mid-Cretaceous is known as the most extreme greenhouse period in the last 150 Myr and was punctuated by repeated environmental perturbations. The mid-Cretaceous was also characterized by the emplacement of major Large Igneous Provinces and the deposition of organic-rich layers known as Oceanic Anoxic Events. Here, we present a high-resolution environmental magnetic and stable isotopic records of the western Tethyan pelagic interval in the Poggio le Guaine (PLG, Italy) core, deposited during the late Albian. Environmental magnetic data are here applied to detect redox and paleoproductivity variations across the OAE 1d and CORB 7 events. Combing the magnetic data and geochemical data from carbon (δ13C) and oxygen (δ18O) isotopic records, we document changes in the paleoenvironmental conditions across the Pialli Level and CORB 7 events in the Tethyan realm. The magnetic properties of the 10-m-thick pelagic marine sediments of the PLG core record the onset between upper part of Cretaceous Oceanic Red Bed 7 (CORB 7) and the Pialli Level that is a part of the Oceanic Anoxic Event (OAE) 1d. An increase in the magnetic mineral concentrations with hematite and goethite as the main magnetic carrier characterizes the upper CORB 7 sediments. Variations in “hard” isothermal remanent magnetization and the S-ratio during the upper CORB 7 are interpreted as changes in aeolian dust input into the Umbria-Marche Basin. During the interval between the upper part of CORB 7 and OAE 1d (Pialli Level), the magnetic mineral concentration decreases, and the magnetic mineralogy changes from hematite to magnetite, suggesting a change in the oceanic system. This change might be associated to an increase in orbital forcing capable of modulating the monsoon activity at the onset of the Pialli Level. First-order reversal curves for all samples from the PLG core are similar and indicate a dominance of detrital magnetite. The absence of magnetically non-interacting single domain biogenic particles suggests that an increase in primary productivity was not significant or variation of the anoxic-oxic boundary could have also occurred. Finally, our records show cyclic alterations that reflect changes in the terrigenous input that was triggered by a period of enhanced orbital forcing paced by monsoonal systems.

Benthic foraminifera across the Albian–Cenomanian transition and their paleoceanographic significance during OAE1d in the western Tethys (Umbria–Marche Basin, Italy)

The benthic foraminiferal assemblages from the upper Albian-lower Cenomanian interval of the Scaglia Bianca Formation in the Monte Petrano (MP) and Le Brecce (LB) sections (Umbria–Marche Basin; Italy) provide a detailed record of the faunal changes across the Oceanic Anoxic Event 1d (OAE 1d). Fluctuations in abundance, diversity, and species composition reflect variations in bottom-water oxygenation and organic carbon fluxes. Benthic foraminifera are integrated with planktonic foraminifera, calcareous nannofossils, and geochemical proxies to reconstruct the bottom and surface water conditions across the OAE 1d in the Umbria–Marche Basin.The pre-OAE 1d interval was characterized by benthic foraminifera that thrived under stable mesotrophic condition in bottom waters. In surface waters, planktonic foraminifera indicate dominant mesotrophic conditions in agreement with calcareous nannofossil assemblages suggesting a regime of higher fertility under cooler conditions.During the OAE 1d interval, benthic foraminifera display an increase in the abundance of infaunal taxa, suggesting mesotrophic conditions in bottom waters. Nevertheless, within the Pialli Level, the six laminated black-to-dark grey shale horizons (MP1/LB1 to MP6/LB6), benthic foraminifera are absent or highly impoverished (MP1, MP2, MP4, MP6, LB5, LB6), suggesting hypoxic/anoxic conditions in bottom waters. Planktonic foraminifera in this interval reflect mesotrophic to oligotrophic conditions under the presence of an expanded mixed layer and deeper thermocline in the surface waters. Calcareous nannofossils record warm conditions and lower fertility starting just prior to and across the OAE 1d. However, higher values of fertility are recorded in the black-to-dark grey shales MP3/LB3, MP4/LB4 and MP5/LB5 of the Pialli Level.The post-OAE 1d interval is marked by an increase in the diversity of benthic foraminifera, indicating a restoration of the oxygen conditions in a continuous mesotrophic regime in bottom waters. The surface waters experienced oligotrophic conditions based on the planktonic and calcareous nannofossils.A minor discrepancy between benthic foraminifera and geochemical reconstruction of oxygenation levels of bottom waters was recorded, especially in the Pialli Level. The benthic microfaunas appear to be very sensitive to very short-term oxygen depletion at the seafloor when geochemical proxies suggest temporary suboxia. This might indicate that very rapid redox changes are not resolved by bulk elemental data. Otherwise, benthic foraminifera might be much more responsive to very low concentrations of oxygen in bottom waters and temporarily disappear under strong suboxia before reaching fully anoxic conditions.

Cosmogenic 3He anomaly K1 vs. the early Campanian isotopic event (ECE) as recorded in pelagic limestones of the Umbria-Marche succession (Italy)

In this paper, we report on a biostratigraphic, magnetostratigraphic, and stable isotope (δ13C and 3He) analysis across three pelagic limestone sections of the Campanian Scaglia Rossa Formation exposed in the classic Bottaccione Gorge at Gubbio (Umbria region), near the village of Furlo, and near the town of Apiro (both in the Marche region), all located in the Umbria-Marche basin of the northeastern Apennines of central Italy. These sections record the coincidental occurrence of an extraterrestrial 3He (3HeET) anomaly known as K1 and a negative shift in the δ13C record known as the early Campanian event. Cyclostratigraphic spectral analysis of the Furlo section based on a high-resolution magnetic susceptibility record in these pelagic limestones revealed that the regular orbitally forced Milankovitch cycles are somewhat disturbed or blurred through the interval of the coincident 3HeET K1 anomaly and the early Campanian event isotopic anomaly, suggesting a causal effect resulting from the enhanced influx of extraterrestrial material (i.e., interplanetary dust particles and a myriad of small meteorite impacts). This would have altered the transparency of the atmosphere, causing a short-lived climate change event.

Calcareous nannofossils from the Poggio le Guaine core (Umbria-Marche Basin, central Italy): Biostratigraphy and discussions on the bioevents of the Aptian–Albian interval

The calcareous nannofossil biostratigraphy of the Aptian–Albian interval has been continuously applied and developed along the last decades. The shortage of complete and continuous outcropping marine sections and even marine subsurface sections is one of the challenges of the stratigraphic studies of this interval. Taxonomic ambiguities, diachronism and reworking are constantly pointed as challenging aspects for the calcareous nannofossil biostratigraphic studies of this interval. Amid this scenario, the Poggio le Guaine section of the Umbria-Marche Basin (central Italy) stands out by presenting a complete and undisturbed pelagic to hemipelagic marine sedimentary succession of the Aptian–Albian interval. The present work is aimed to provide a detailed biostratigraphic zonation based on calcareous nannofossils, to calibrate the results to other stratigraphic tools of previous published works and to discuss some important bioevents of the Aptian–Albian interval along the PLG core. The following biozones of the calcareous nannofossil reference zonation for the Aptian–Albian interval were recognized: the Chiastozygus litterarius Zone (NC6 Zone), the Rhagodiscus angustus Zone (NC7 Zone), the Prediscosphaera columnata Zone (NC8∗ and NC8 zones), the Axopodorhabdus albianus Zone (NC9 Zone) and the Eiffellithus turriseiffelii Zone (NC10 Zone). The PLG core encompasses the chronostratigraphic interval from the Barremian/Aptian through the Albian/Cenomanian boundaries. Finally, detailed discussions on some important calcareous nannofossil bioevents of this interval were performed, among them: the first occurrence (FO) of Hayesites irregularis, the FO of Hayesites albiensis, the last occurrence (LO) of Conusphaera rothii, the LO of Micrantholithus hoschulzii/Micrantholithus obtusus, the FO of Rhagodiscus achlyostaurion, the FO of Prediscosphaera columnata, the FO of Tranolithus orionatus and the LOs of Assipetra spp.

LOWER PALEOCENE DEEP-WATER AGGLUTINATED FORAMINIFERA FROM THE CONTESSA HIGHWAY SECTION (UMBRIA-MARCHE BASIN, ITALY): TAXONOMY, STRATIGRAPHIC DISTRIBUTION AND ASSEMBLAGE TURNOVER ACROSS THE CRETACEOUS/PALEOGENE BOUNDARY

Deep-water agglutinated foraminifera (DWAF) are investigated from the lower Paleocene of the Contessa Highway Paleocene (CHP) section in the Umbria-Marche Basin in Italy. In the lowermost part of the Paleocene corresponding to the P0–Pα interval and lowermost P1 planktonic foraminifera zones, a total of 46 species of DWAF are identified. A comparison with the uppermost Maastrichtian DWAF assemblages documented by Cetean (2009) results in a combined total of 94 DWAF species over the Cretaceous/Paleogene boundary interval at Contessa Highway. Of these, 49 species are listed as extinction taxa, nine are survivor taxa, 19 are Lazarus taxa, and 17 taxa display first occurrences in the Paleocene. The record of DWAF in the Contessa Highway Paleocene section displays a moderate decrease in diversity across the K/Pg boundary, followed by a gradual recovery in the first meter of the Paleocene. The lower Paleocene record is characterized by blooms of opportunistic species belonging to the genera Reophax, Subreophax, Repmanina, and Spiroplectinella. The K/Pg boundary interval records a major change in the proportions of DWAF morphogroups, from a suspension-feeding community in the Maastrichtian to one dominated by epifaunal detritivores in the lower Paleocene, reflecting a fundamental change in marine primary productivity following the bolide impact.

Paleobiogeographic significance of Tethyan Lower Cretaceous Cecrops septemporatus Zone radiolarian faunas

The Cecrops septemporatus Zone is widely applied in correlation of Valanginian to lower Hauterivian successions, but paleobiogeographic distributions of radiolarian fauna from this zone remain ambiguous. To address this issue this study compares radiolarian faunas from the Vispi Quarry section, Umbria–Marche Basin, central Italy with the Guigong section, southern Tibet. Similarity between these C. septemporatus Zone faunas suggests a close marine connection may have existed between western and eastern Tethys during Early Cretaceous time. Lithologies, depositional setting, associated fossil records, and paleomagnetic data from contemporaneous radiolarian occurrences in different areas globally are also assessed. The paleobiogeographic distribution of the C. septemporatus Zone fauna was mainly restricted to low latitudes in the Tethyan and Pacific regions, but also shows a significant migration from low latitudes in the Tethyan Realm to mid latitudes in the Boreal and Austral realms. Climatic and oceanographic conditions during the Weissert Event may have played important roles in the development of the paleobiogeographic distribution patterns observed for the C. septemporatus Zone faunas.

A new agglutinated foraminiferal species (Arenoturrispirillina waskowskae sp. nov.) from the Danian of Contessa, Italy

This paper describes a new Paleogene deep-water agglutinated foraminifera from the Contessa Highway Section, Umbria-Marche Basin, Italy. The new species Arenoturrispirillina waskowskae is characterised by its predominently high trochospiral coiling, which distinguishes it from the genus Glomospira. The new species is also found in the Polish Carpathians.

Post-rift extensional tectonics at the edge of a carbonate platform: insights from the Middle Jurassic-Early Cretaceous Monte Giano stratigraphic record (central Apennines, Italy)

A new interpretation of the Middle Jurassic-Early Cretaceous paleogeographic evolution of the NW sector of the Latium-Abruzzi carbonate platform facing the Umbria-Marche Basin is proposed, based on Monte Giano area (central Apennines, Italy). During Late Triassic-early Bajocian time, the area was characterized by shallow water sedimentation. Inner and marginal carbonate platform deposits are overlain by pelagic deposits (Posidonia level), early Bajocian p.p. in age. This unconformity testifying the sudden drowning of the Monte Giano area, while shallow water sedimentation persisted in the remaining sectors of the carbonate platform. The Posidonia level is paraconformably overlain by distal slope deposits of the Velino Gorge limestones Formation, Kimmeridgian p.p.-Tithonian p.p. in age. Therefore, a 12Ma gap is recorded as in the Umbria-Marche Basin pelagic carbonate platforms. An extensional Bajocian tectonic phase, possibly related to the Piemont-Ligurian Ocean opening coupled with rheologic differences at the basin/platform boundary, drastically changed the regional paleogeography causing the breakup and the drowning of the NW sector of the Latium-Abruzzi carbonate platform and the creation of a large flat-topped pelagic carbonate platform. The estimate offset of the early Bajocian fault is around 300-350m. The Velino Gorge limestones fm. pass laterally and vertically to the Upper Tithonian platform-margin reef complex of the Ellipsactinia limestones fm.; these units constitute a shallowing and coarsening upward sequence and levelled the paleobathymetric gradient created by the Bajocian extension. The progradation of the Latium-Abruzzi carbonate platform continued during Early Cretaceous time. These results have strong implications on the tectonic and paleogeographic evolution of the major domains of the central Apennines.

Long-term Aptian marine osmium isotopic record of Ontong Java Nui activity

AbstractThe early to mid-Aptian was punctuated by episodic phases of organic-carbon burial in various oceanographic settings, which are possibly related to massive volcanism associated with the emplacement of the Ontong Java, Manihiki, and Hikurangi oceanic plateaus in the southwestern Pacific Ocean, inferred to have formed a single plateau called Ontong Java Nui. Sedimentary osmium (Os) isotopic compositions are one of the best proxies for determining the timing of voluminous submarine volcanic episodes. However, available Os isotopic records during the age are limited to a narrow interval in the earliest Aptian, which is insufficient for the reconstruction of long-term hydrothermal activity. We document the early to mid-Aptian Os isotopic record using pelagic Tethyan sediments deposited in the Poggio le Guaine (Umbria-Marche Basin, Italy) to precisely constrain the timing of massive volcanic episodes and to assess their impact on the marine environment. Our new Os isotopic data reveal three shifts to unradiogenic values, two of which correspond to black shale horizons in the lower to mid-Aptian, namely the Wezel (herein named) and Fallot Levels. These Os isotopic excursions are ascribed to massive inputs of unradiogenic Os to the ocean through hydrothermal activity. Combining the new Os isotopic record with published data from the lowermost Aptian organic-rich interval in the Gorgo a Cerbara section of the Umbria-Marche Basin, it can be inferred that Ontong Java Nui volcanic eruptions persisted for ∼5 m.y. during the early to mid-Aptian.

Late Cenomanian-Turonian isotopic stratigraphy in the chalk of the Paris Basin (France): a reference section between the Tethyan and Boreal realms

A chemostratigraphic study (δ13C and δ18O) of the Late Cenomanian and Turonian chalk succession from the “Craie 701” Poigny borehole (near Provins in the Paris Basin, France) provides new high-resolution stable carbon and oxygen isotope data. Correlation of the bentonite horizons and the isotopic trends from Poigny with its English Chalk equivalent allows the development of a precise stratigraphic framework. δ13C and δ18O variations are synchronous and widespread throughout the European epicontinental seas and Tethyan Ocean. In the Poigny borehole, the Oceanic Anoxic Event 2 (OAE 2) is marked by a large and brief positive excursion of carbon isotopes (a carbon isotope excursions: CIE of 3‰ amplitude) without any apparent anoxia in the Late Cenomanian Chalk. Comparisons between different key sections on a North-South transect from the Anglo-Paris Basin to the Umbria-Marche Basin (Gubbio Section, Italy) and the Vocontian Basin (South-East France), suggests that the OAE 2 is linked to an increase in marine organic matter production, modulated by a regional effect on the organic carbon burial rate. Thus, the large positive carbon isotope increase spanning the Middle Cenomanian through to the Middle Turonian, including the salient CIE associated with the OAE 2, reflects a global scale increase in marine productivity that would be concomitant with a major long-term sea level rise. The stratigraphic position of the Turonian-Coniacian boundary can also be better defined by this isotopic study. A comparison of δ18O data between the Anglo-Paris Basin and Tethyan Basin shows high-amplitude, long-term synchronous variations reflecting primary paleo-environmental changes which are independent of local facies, sediment thickness and diagenesis. In particular, a negative shift (−1‰ of amplitude) reflects a warmer climate regime, marking the onset of OAE 2. Two colder phases (+1‰ amplitude each) occurred in the Early Turonian and the beginning of the Late Turonian.

Major and trace element characterization of Oceanic Anoxic Event 1d (OAE 1d): Insight from the Umbria-Marche Basin, central Italy

The Pialli Level in the Umbria-Marche Basin (central Italy) correlates with the lowermost part of the positive carbon isotopic excursion characterizing the late Albian–early Cenomanian Oceanic Anoxic Event 1d (OAE 1d). High-resolution litho-, bio- and chemostratigraphic data from the Monte Petrano and Le Brecce sections allow for a bed-by-bed comparison of the two successions, and discriminate local from basin-scale signals. We present new X-ray fluorescence, ICP-MS and TOC data for both the limestones and the Pialli Level shales integrated with available carbonate carbon isotopes and nannofossil temperature and nutrient indices. Data indicate a homogenous background sedimentation dominated by pelagic carbonates, biogenic silica with little contribution by clays. The limited variation in lithogenic elements points to an essentially homogeneous detrital source area with limited fluvial terrigenous input. Higher Mn concentrations coupled with low enrichments in redox-sensitive elements, such as U, Fe, S, Re, Mo, Ag, suggest that the Pialli Level shales represent temporary suboxia without reaching anoxia. Furthermore, P, authigenic Ba, Cd and Ni enrichments, together with nannofossil nutrient index indicate generally low primary productivity conditions along the entire succession, with only minor increases for some of the black-to-dark grey shales of the Pialli Level. The nannofossil temperature index highlights a warm climate during the OAE 1d, with the warmest conditions experienced during the deposition of the Pialli Level shales. During the late Albian, the warm and humid climate was interrupted by brief episodes of relatively warmer and less saline surface waters ensuring slower rates of bottom water renewal and producing temporary suboxic conditions. Such paleoceanographic dynamics would be the continuation of episodic warmer and humid pulses characterizing the late Albian interval in the Umbria-Marche Basin. As such, the Pialli Level can be considered the result of a last episode closing a cycle before the establishment of a steadier climate during the early Cenomanian.

Similarity analysis of Ostracoda faunas in the Western Tethys during the Late Pliensbachian-Early Toarcian (Early Jurassic)

The present study is focused on the biogeographic dynamic quantification tested on ostracods of Upper Pliensbachian-Lower Toarcian. The calculation of similarity and distance indices made it possible to compare the contents of nine regions belonging to the palaeobiogeographic province of Western Tethys. The generic comparison realized for each chronological interval (Emaciatum Zone of the Late Pliensbachian and Polymorphum and Levisoni zones of the Early Toarcian) shows the presence of two subprovinces of ostracods during this time interval, the most stable in the westernmost part of the Tethys composed by the Traras (Algeria) and Lusitanian (Portugal) basins. This was probably facilitated by the presence of communication seaways. The other subprovince for ostracod is located in the eastern regions mainly composed by the Aquitanian Basin (France) and southern Germany. In regions such as the Iberian Cordillera (eastern Spain), the composition of the ostracod assemblages changed with more affinity to the eastern subprovince during the Late Pliensbachian and to the western subprovince during the Early Toarcian. Other regions such as the Central High Atlas (Morocco) and Umbria Marche Basin (Italy) show a remoteness of the ostracod assemblages during the studied interval. Otherwise, the Pielou criterion calculation confirms the absence of a geographical or chronological gradient among the studied regions probably related to oceanographic changes (the sea-level rise, the global warming and the development of oxygen depleted conditions in north central Europe).

Foraminiferal assemblages, extinctions and appearances associated with the Early Toarcian Oceanic Anoxic Event in the Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, United Kingdom

The uppermost Pliensbachian-Lower Toarcian sediments recovered from Llanbedr (Mochras Farm) Borehole (North Wales, UK) were deposited in the Cardigan Bay Basin and mainly consist of alternating marls and marly limestones. The current study analyses the foraminiferal assemblages from the cored interval (143 m) that has been assigned to the Spinatum Zone (Upper Pliensbachian) to the lower part of the Bifrons Zone (Middle Toarcian). The foraminiferal assemblages are dominated by the suborders Lagenina and Robertinina. Four main ecostratigraphic intervals have been identified, based on changes in the foraminiferal assemblages that occurred before, during and after the Toarcian Oceanic Anoxic Event (T-OAE). Ecostratigraphic interval I (upper part of the Spinatum Zone) is characterized by a diverse assemblage with specialist, opportunist and intermediate forms. This assemblage is interpreted to represent a phase that pre-dates the biotic crisis. The ecostratigraphic interval II (Tenuicostatum Zone) shows an abrupt increase in opportunist forms such as the genus Reinholdella, and a facultative opportunist such as Paralingulina tenera, which was tolerant to oxygen depleted conditions. This second interval represents the initial biotic crisis phase, in response to decreasing oxygenation. The ecostratigraphic interval III is considered the peak of the biotic crisis, coincident with the negative carbon isotopic excursion (at the base of the Serpentinum Zone) and characterized by the dominance of the opportunist Reinholdella (87–97% of the assemblage) and low diversity. The ecostratigraphic interval IV (upper part of Serpentinum Zone and lower part of Bifrons Zone) is characterized by an increase of diversity and an abrupt decrease in Reinholdella. This assemblage is interpreted to reflect the increased availability of oxygen from deep-infaunal to epifaunal microhabitats and the return to normal conditions at the sea bottom. Ecostratigraphic fluctuations in the Mochras foraminiferal assemblages across the T-OAE event are comparable with those from other parts of the UK, the Lusitanian Basin (Portugal), the Umbria Marche Basin (Italy) and the Atlassic Basin (North Africa). In addition, a foraminiferal turnover is evident across the Pliensbachian-Toarcian boundary and the T-OAE, and reflects the effects of the Early Jurassic biotic crisis on benthic foraminifera. Controlling factors of the biotic crisis are discussed, regarding that anoxic conditions do not necessarily have a lethal effect on all foraminiferal species and other oceanographic and environmental factors need consideration (fragmentation of epicontinental platforms, sea-level changes, crisis of carbonate productivity and temperature changes).

First report of Sclerobiont Bryozoans in the Maiolica Fm. of the Umbria-Marche Basin (Northern Apennines, Italy)

We describe the first evidence of sclerobiont bryozoans found loose in the pelagic Maiolica Fm. of the Umbria-Marche Basin (Monte Acuto Massif, Northern Apennines, Italy). The material is represented by three small sub-circular colonies with tube-shaped zooecia radially developing from the centre. These characters are not enough for generic or specific classification, consequently, these cyclostomes have been only identified as belonging to the Suborder Tubuliporina.Calpionellid assemblages allow to constrain the bryozoan-bearing rock sample to the early Berriasian. The occurrence of isolated bryozoans in the Maiolica Fm. enriches the knowledge about the fauna of this unit in pure basinal settings, composed by radiolarians, calpionellids, dinoflagellate cysts and rare macrofossils (ammonites and aptychi), including very rare benthic organisms (gastropods, brachiopods and bivalves). Up to date, no sclerobiont organisms in ‘normal’ pelagicMaiolica facies were known, due to the lack of suitable substrates to be colonised. Encrustation of a planktonic or nektonic hard-shelled organism seems the most parsimonious hypothesis based on our material.

Accuracy and precision of the late Eocene–early Oligocene geomagnetic polarity time scale

AbstractAn accurate and precise geomagnetic polarity time scale is crucial to the development of a chronologic framework in which to test paleoclimatic and paleoenvironmental interpretations of marine and terrestrial records of the Eocene–Oligocene transition (EOT). The magnetic polarity patterns of relatively continuous marine and terrestrial records of the EOT have been dated using both radio-isotopic techniques and astronomical tuning, both of which can achieve a precision approaching ±30 k.y. for much of the Paleogene. However, the age of magnetic reversals between chrons C12n and C16n.2n has proved difficult to calibrate, with discrepancies of up to 250 k.y. between radio-isotopically dated and astronomically tuned marine successions, rising to 600 k.y. for comparisons with the 206Pb/238U-dated terrestrial record of the White River Group in North America. In this study, we reevaluate the magnetic polarity pattern of the Flagstaff Rim and Toadstool Geologic Park records of the White River Group (C12n–C16n.2n). Our interpretation of the Flagstaff Rim polarity record differs significantly from earlier studies, identifying a previously unreported normal polarity zone correlated to C15n, which eliminates discrepancies between the WRG and the 206Pb/238U-dated marine record of the Rupelian Global Stratotype Section and Point in the Italian Umbria-Marche basin. However, residual discrepancies persist between U-Pb–dated and astronomically tuned records of the EOT even when stratigraphic and systematic uncertainties associated with each locality and dating method are taken into account, which suggests that the uncertainties associated with astronomically tuned records of the EOT may have been underestimated.

Orbital forcing of carbonate versus siliceous productivity in the late Albian–late Cenomanian (Umbria-Marche Basin, central Italy)

Orbital forcing of carbonate versus siliceous productivity in the late Albian–late Cenomanian (Umbria-Marche Basin, central Italy)

Correlation of Early Cretaceous radiolarian assemblages from southern Tibet and central Italy

Comparison of radiolarian assemblages from marls in the Gorgo a Cerbara section in the Umbria–Marche Basin in central Italy and a siliceous sequence (BB1 section) near Babazhadong in southern Tibet indicates similar faunas comparable to those in the Aurisaturnalis carinatus zone and the Turbocapsula costata zone. Several significant species, Archaeodictyomitra lacrimula (Foreman), A. excellens (Tan Sin Hok), Dictyomitra communis (Squinabol), and Aurisaturnalis carinatus perforatus Dumitrica and Dumitrica-Jud, which are common in older strata, make their last occurrences near the base of the Turbocapsula costata zone in these two areas. Comparison with the Gorgo a Cerbara section provides an accurate age constraint for the siliceous succession in southern Tibet, which contains no fossils other than radiolarians. The comparison indicates a close connection between the western and eastern Tethys during the Barremian to early Aptian. The correlation testifies that the radiolarian zonation in southern Tibet is applicable for the whole Tethys. The siliceous succession in BB1 section encompasses the early Aptian Oceanic Anoxic Event 1a (OAE 1a). The early Aptian OAE 1a is located in the upper part of the Aurisaturnalis carinatus perforatus subzone. The first occurrence biohorizon of the genus Turbocapsula and the evolutionary first appearance biohorizon of T. costata costata (Wu) are useful markers for constraining the OAE 1a in the Tethys.

A 9 million-year-long astrochronological record of the early–middle Eocene corroborated by seafloor spreading rates

The early-middle Eocene (ca. 56-41 Ma) is recorded in the pelagic Scaglia Rossa and Variegata Formations of the Umbria-Marche Basin (central Italy). Geochemical and magnetostratigraphic alignment between the Bottaccione section (Gubbio, central Italy) and the Smirra core (Cagli, central Italy) allows us to generate a continuous and wellpreserved new record that, combined with previously published data from the same area, creates a continuous high-resolution record from the Paleocene-Eocene thermal maximum (ca. 56 Ma) to the lower part of chron C21n. Comparison with carbon isotope records from Ocean Drilling Program Sites 1258 and 1263 reveals a satisfactory match, providing further evidence of the global significance of the long-term trend and superposed perturbations captured by the δ13C records. The identification of astronomically forced geochemical cycles allows us to develop a 405 k.y. tuned age model, thereby extending the astrochronology from ca. 56.0 to ca. 47.5 Ma. Marine magnetic anomaly profiles from major oceanic basins characterized by high seafloor spreading rates were used to independently test the astronomical polarity time scale associated with our tuning, as well as other polarity time scales. Our age model suggests the existence of periods of relatively constant seafloor spreading rates separated by rapid changes, while the other time scales generate more gradual variations and also include large and short-term deviations in spreading rates that occur simultaneously in different oceanic basins, implying errors in polarity reversal ages. The Umbria- Marche age model further contributes to the closure of the middle Eocene gap in the astronomical time scale.