Umbrian Apennines Research Articles

The micrometeorite flux to Earth during the earliest Paleogene reconstructed in the Bottaccione section (Umbrian Apennines), Italy

AbstractBased on sediment‐dispersed extraterrestrial spinel grains in the Bottaccione limestone section in Italy, we reconstructed the micrometeorite flux to Earth during the early Paleocene. From a total of 843 kg of limestone, 86 extraterrestrial spinel grains (12 grains > 63 μm, and 74 in the 32–63 μm fraction) have been recovered. Our results indicate that the micrometeorite flux was not elevated during the early Paleocene. Ordinary chondrites dominated over achondritic meteorites similar to the recent flux, but H chondrites dominated over L and LL chondrites (69%, 22%, and 9%, respectively). This H‐chondrite dominance is similar to that recorded within an enigmatic 3He anomaly (70, 27, and 3%) in the Turonian, but different from just before this 3He anomaly and in the early Cretaceous, where ratios are similar to the recent flux (~45%, 45%, and 10%). The K‐Ar isotopic ages of recently fallen H chondrites indicate a small impact event on the H‐chondrite parent body ~50 to 100 Ma ago. We tentatively suggest that this event is recorded by the Turonian 3He anomaly, resulting in an H‐chondrite dominance up to the Paleocene. Our sample spanning the 20 cm above the Cretaceous–Paleogene (K–Pg) boundary did not yield any spinel grains related to the K–Pg boundary impactor.

Cytotoxicity and genotoxicity of size-fractionated particulate matter collected in underground workplaces

Road tunnel construction involves the use of explosives and diesel-powered machines in a very limited indoor space. Tunnel construction workers are thus exposed to a variety of toxic substances, including dust, asbestos, silica, concrete, diesel fumes, and oil mist. In this study, the low noise miniaturized Sioutas Cascade Impactor (SKC) has been used to collect PM samples as a function of particle size (i.e., aerodynamic diameter). Airborne particulates were sampled into a road tunnel (final length 2391 m) under construction near the village of Pale, Municipality of Foligno, Umbrian Apennines (State Highway 77 “Val di Chienti”). Three sampling sessions were performed: (i) in the West yard, during dislodging of rocks; (ii) in the East yard during drilling of rocks, and (iii) during scaling and grouting with quick-drying shotcrete. The aim of this study was to characterize size-fractionated PM samples for their cytotoxic/genotoxic potentials. Toxicological evaluation was carried out in vitro on A549 lung carcinoma cells: cytotoxicity was assessed by Trypan blue dye exclusion assay, whereas genotoxicity was assessed by comet assay (primary DNA damage) and cytokinesis-block micronucleus (CBMN) Cytome assay (cytogenetic effects). Primary DNA damage (i.e., strand breakage) was mainly caused by coarse fractions A (O > 2.5 μm) sampled in the West yard (sample i) and in the East yard (sample iii). Cytogenetic effects were mainly caused by the fine fractions AF (aerodynamic O < 0.25 μm) sampled in the East yard (sample ii). Results reported in this article show that particulate matter (PM) samples collected underground (i.e., during road tunnel construction) may trigger various cytotoxic/genotoxic effects. The recent classification of air pollution and PM itself as carcinogenic to humans (group 1) by the IARC makes indoor/outdoor air pollution a growing matter of concern. Our results highlight the need in this occupational setting for a reduction, if applicable, of PM emission (prevention), or an implementation of work practices by stressing the importance of proper use of protective equipment (protection).

Patterns of local and global redox variability during the Cenomanian–Turonian Boundary Event (Oceanic Anoxic Event 2) recorded in carbonates and shales from central Italy

AbstractCareful evaluation of the local geochemical conditions in past marine settings can provide a window to the average redox state of the global ocean during episodes of extensive organic carbon deposition. These comparisons aid in identifying the interplay between climate and biotic feedbacks contributing to and resulting from these events. Well‐documented examples are known from the Mesozoic Era, which is characterized by episodes of widespread organic carbon deposition known as Oceanic Anoxic Events. This organic carbon burial typically leads to coeval positive carbon‐isotope excursions. Geochemical data are presented here for several palaeoredox proxies (Cr/Ti, V, Mo, Zn, Mn, Fe speciation, I/Ca and sulphur isotopes) from a section exposed at Furlo in the Marche–Umbrian Apennines of Italy that spans the Cenomanian–Turonian boundary. Here, Oceanic Anoxic Event 2 is represented by a ca 1 m thick radiolarian‐rich millimetre‐laminated organic‐rich shale known locally as the Bonarelli Level. Iron speciation data for thin organic‐rich intervals observed below the Bonarelli Level imply a local redox shift going into the Oceanic Anoxic Event, with ferruginous conditions (i.e. anoxic with dissolved ferrous iron) transiently developed prior to the event and euxinia (i.e. anoxic and sulphidic bottom waters) throughout the event itself. Pre‐Oceanic Anoxic Event enrichments of elements sensitive to anoxic water columns were due to initial development of locally ferruginous bottom waters as a precursor to the event. However, the greater global expanse of dysoxic to euxinic conditions during the Oceanic Anoxic Event greatly reduced redox‐sensitive trace‐metal concentrations in seawater. Pyrite sulphur isotopes document a positive excursion during the Oceanic Anoxic Event. Carbonate I/Ca ratios were generally low, suggesting locally reduced bottom‐water oxygen conditions preceding the event and relatively increased oxygen concentrations post‐event. Combined, the Furlo geochemical data suggest a redox‐stratified water column with oxic surface waters and a shallow chemocline overlying locally ferruginous bottom waters preceding the event, globally widespread euxinic bottom waters during the Oceanic Anoxic Event, followed by chemocline shallowing but sustained local redox stratification following the event.

Geological heritage in Valcasana (southeastern Umbria): mass wasting and structural control

The physical landscape of Umbria (central Italy) has one of the highest cultural values of the region and the tourism is a fundamental economic source. Due to this fact the enhancement of the geological component in the management of the territory is the necessary starting point to: promoting the scientific research in this area, spreading the knowledge of natural contexts and promoting the geotourism. Starting from this assumption, this paper aims to identify the geological heritage of Valcasana (southeastern Umbria), a suggestive valley in the Umbrian Apennines with outstanding landforms due to the interaction between mass wasting and tectonic features.

Ichnocoenoses in the Macigno turbidite basin system, Lower Miocene,Trasimeno (Umbrian Apennines, Italy)

Facies analysis and ichnology in a foredeep system of the Lower Miocene Macigno Formation, N of Lake Trasimeno (Umbrian Apennines, Italy), show that ichnoassemblages, developed into several ichnocoenoses - typical ichnotaxa and their stratinomic position in different facies - can be diagnostic indicators for siliciclastic and carbonatic gravity flow deposits. Ichnologic analysis allows defining palaeoecological adaptations in deep-sea burrower organisms, as already applied successfully in other deep-sea environments of Cenozoic turbiditic successions of Italy and Spain.Fourteen sections of the three members of Macigno Formation, some of these revisited in this work, contain ichnocoenoses, differing among distal lobes, inter-lobes deposits (hemipelagic mud), lobe fringes and mud turbidites. The use of ichnocoenoses (e.g. the Halopoa-Spirophycus-Spirorhaphe ichnocoenosis with the fucusopsis preservation of the ichnogenus Halopoa), described here for the first time, underline, rather than classical ichnofacies (Nereites) or ichnosubfacies, the usefulness of ichnology in foredeep basin analysis.

The middle Eocene climatic optimum event in the Contessa Highway section, Umbrian Apennines, Italy

We report a high-resolution paleomagnetic investigation constrained by new qualitative and semiquantitative analyses of planktic and benthic foraminifera, nannofossil assemblages, integrated with oxygen and carbon isotope measurements, for the middle Eocene Scaglia limestones of the Contessa Highway section, central Italy. Calcareous plankton assemblages enable recognition of several biostratigraphic events from planktic foraminiferal zone P11 to the lower part of zone P15 and from calcareous nannofossil zone NP15 to the upper part of zone NP17, which results in refi nement of the magnetobiostratigraphy of the Contessa Highway section. Correlation of the paleomagnetic polarity pattern with the geomagnetic polarity time scale provides a direct age interpretation for strata around the middle Eocene Scaglia limestones of the Contessa Highway section, from chrons C21n (47 Ma) through to subchron C18n.1n (38.5 Ma). Bulk carbon isotope values indicate a distinct carbon isotopic shift at 40 Ma that is interpreted to represent the fi rst evidence in the Northern Hemisphere of the middle Eocene climatic optimum, which has recently been observed as a stable isotope anomaly in multiple records from the Indian-Atlantic sector of the Southern Ocean. This demonstrates a global response of the carbon cycle to the proposed transient increased pCO 2 levels during the late middle Eocene and consequent global CO 2 -driven climate change.

Reversed polarity characteristic magnetizations in the Albian Contessa Section, Umbrian Apennines, Italy: Implications for the existence of a Mid‐Cretaceous mixed polarity interval

Paleomagnetic and paleontologic data from the Valle della Contessa (Umbrian Apennines, Italy) span a 14 m.y. gap in previous magnetostratigraphic sections and reveal several intervals of reversed characteristic remanent magnetization (ChRM) in limestones and marls of the Albian Marne a Fucoidi. Rock magnetic data indicate that the reversed ChRM is carried by hematite having high unblocking temperatures (∼ 625–690° C). Hematite with these unblocking temperatures also carries a normal polarity ChRM in other intervals. A potential bias towards the identification of normal polarity is present since at every horizon measured a normal polarity component, carried by magnetite and hematite, is isolated at lower unblocking temperatures (∼300–600°C). Bulk magnetic properties vary throughout the measured section. In the portion containing most of the reversed ChRM intervals, hematite is the dominant carrier of natural remanent magnetization, while magnetite is the dominant carrier stratigraphically above and below. These changes correspond approximately with lithology. The zone of dominant hematite magnetization is marked by reddish bands (pigmentary hematite) which can be correlated throughout Umbria and are thought to record changes in the oxidation state of the seafloor during deposition. Two models may account for the observed magnetization directions. The reversed magnetizations may record a remagnetization which occurred at least 18 m.y. after deposition, while the beds were still flat‐lying, in reversed polarity chron 33R (83–79 Ma) or later. If the reversed ChRM represents a remagnetization, the process is potentially of great importance since it can produce magnetization patterns which resemble polarity intervals. Alternatively, the reversed magnetizations may have been acquired during intense seafloor oxidation episodes during the mid‐Albian (107–104 Ma) and may record unrecognized intervals of reversed geomagnetic field polarity. Milankovitch‐like bedding cyclicity can be used to tune the sedimentation rate and obtain estimates of the duration of the potential reversed intervals. Using these estimates, two of the potential reversed polarity intervals are of sufficient duration (&gt; 100 kyr) to be recognizable in both detailed stratigraphic sections and marine magnetic anomaly surveys. A primary magnetization model predicts that several intervals of reversed magnetization should be found near the boundary of the Biticinella breggiensis and Ticinella primula foraminiferal zones and within the Prediscosphaera cretacea nannofossil zone on a worldwide basis.

Oxygen and carbon isotope stratigraphy of the Palaeogene and Cretaceous limestones in the Bottaccione Gorge and the Contessa Highway sections, Umbria, Italy

ABSTRACTWe have made oxygen and carbon isotope measurements on limestone samples of Albian to Eocene age recovered from the Bottaccione Gorge section in the Umbrian Apennines, central Italy. Additional measurements have been made on topmost Maastrichtian and Palaeocene sediments from the adjacent Contessa Highway section. Our data from the Bottaccione Gorge show 13C maxima at the Cenomanian/Turonian boundary and during the Palaeocene, as well as a pronounced 13C minimum 7 metres above the clay layer at the K/T boundary. Our data from the Contessa Highway show a 13C minimum 9 metres above the K/T boundary clay. These minima are probably diagenetic artifacts. In the Bottaccione Gorge there is evidence for a hiatus in the early Middle Eocene. The Palaeocene of the Bottaccione Gorge appears to have been affected by slumping or faulting (in addition to the diagenetic overprinting) giving a spurious δ13C recovery after the K/T boundary, the Contessa Highway section appears to be more complete. The Coniacian‐Maastrictian is characterized by relatively stable 13C values. Our data indicate an increase in δ18O (and therefore possible cooling) across the Cretaceous/Tertiary boundary in both the Bottaccione and Contessa Highway sections.

Origin of clay minerals in the Bonarelli Horizon (Umbrian Apennines, central Italy)

AbstractChemical, thermal, X-ray and statistical analyses were carried out on the clay fraction of the Bonarelli Horizon (Umbrian region, Central Italy) in order to investigate its origin. The vertical lithological sequence (organic carbon, siliceous and clay layers of varying colour and thickness) seems to change regularly, allowing the horizon to be subdivided into five sub-horizons (A to E). Sub-horizon B is clearly distinguishable from the others on the basis of the clay fractions. The presence of organic material and authigenic sulphates, constant chemical composition within a single sub-horizon, and regular repetition of the layers, show that the Bonarelli Horizon is the result of an alternation of anoxic events in a continental margin facies. A substantial contribution of volcanoclastic material is suggested for sub-horizon B.

Agglutinated Foraminifera of Western Mediterranean Upper Cretaceous Pelagic Limestones (Umbrian Apennines, Italy, and Betic Cordillera, Southern Spain)

Agglutinated Foraminifera of Western Mediterranean Upper Cretaceous Pelagic Limestones (Umbrian Apennines, Italy, and Betic Cordillera, Southern Spain)

M-sequence reversals recorded in DSDP sediment cores from the western Mid-Pacific Mountains and Magellan Rise

New paleomagnetic and paleontologic data from Pacific DSDP Sites 463 and 167 define the magnetic reversals that predate the Cretaceous Normal Polarity Superchron (K-N). Data from Mid-Pacific Mountain Site 463 provide the first definition of polarity chron M0 in the Pacific deep-sea sedimentary record. Foraminiferal biostratigraphy suggests that polarity chron M0 is contained entirely within the lower Aptian Hedbergella similis Zone, in agreement with foraminiferal data from the Italian Southern Alps and Atlantic Ocean. Nannofossil assemblages also suggest an early Aptian age for polarity chron M0, contrary to results from the Italian Umbrian Apennines and Southern Alps, which place polarity chron M0 on the Barremian-Aptian boundary. Biostratigraphic dating discrepancies caused by the time-transgressive, preservational, or provincial nature of paleontological species might be reconciled by the use of magnetostratigraphy, specifically polarity chron M0 which lies close to the Barremian-Aptian boundary. At Magellan Rise Site 167, five reversed polarity zones are recorded in Hauterivian to Aptian sediments. Correlation with M-anomalies is complicated by synsedimentary and postsedimentary sliding about 25 m.y. after basement formation, producing gaps in, and duplications of, the stratigraphic sequence. The magnitude and timing of such sliding must be addressed when evaluating the stratigraphy of these oceanic-rise environments.

Kinematics of orocline and arc formation in thin‐skinned orogens

The regional traces of folds, faults, and foliations found in many fold‐thrust belts are bent in plan view. It proves valuable to distinguish between two types of bent orogens based on their kinematic evolution: oroclines (or rotational arcs) are bent orogens in which segments of the orogen change strike during the evolution of the bend, and nonrotational arcs are bent orogens in which segments of the orogen do not change strike during development of the bend. The kinematic evolution of a bend that forms in a thin‐skinned orogen can be described in terms of three parameters: the displacement path trajectories followed by points along the strike of the orogen, the magnitude and distribution of tangential extension along the strike of the orogen, and the change in position of the endpoints of the orogen with respect to a reference line. Only slight differences in the displacement path trajectory pattern determine whether an orogen evolves as a nonrotational arc or as an orocline; thus the distinction between these two types of bends is not always of major tectonic significance. Compressional deformation along irregular continental margins or the impact of indentors on continental margins during collisional orogenies more likely leads to formation of nonrotational arcs (as can be simulated with a sand wedge model). Interaction between a fold‐thrust wedge with obstacles in the foreland or with a wrench fault more likely leads to orocline formation. Orocline formation is also associated with noncoaxial reactivation of thrust faults. Tangential extension is a necessary consequence of certain displacement path trajectory patterns and can accompany development of either nonrotational arcs or oroclines. Two examples, one from the Umbrian Apennines and one from the Makran Range, demonstrate how movement on cross‐strike fault arrays can accommodate tangential extension in thin‐skinned bends.

Valanginian to Aptian calcareous nannofossil stratigraphy and correlation with the upper M-sequence magnetic anomalies

Calcareous nannofossil stratigraphy has been investigated in Lower Cretaceous Italian sections at Gorgo a Cerbara, Presale and Frontale (all in the Umbrian Apennines) and at Cismon (Southern Alps). A modified sample preparation technique has allowed a thorough stratigraphic study of the well-lithified Maiolica limestone and although nannofossil preservation is generally quite poor, the major Valanginian to Aptian marker species can be detected. Nine nannofossil events can be determined and correlated to magnetic stratigraphies previously established in these sections. Nannofossil stratigraphy confirms most magnetostratigraphic correlations made between sections and allows a more precise correlation of magnetic Chrons M-0 to M-11 with the Valanginian, Hauterivian, Barremian and Aptian stages. The results obtained differ considerably from previous timescales. Nannofossil events recorded in the various sections may be time-transgressive by as much as one magnetic chron, probably due to differential preservation.

Anoxic events, productivity rhythms, and the orbital signature in a Mid‐Cretaceous deep‐sea sequence from central Italy

Albian pelagic sediments from the Umbrian Apennines exhibit rhythmic bedding in outcrop. High temporal resolution (∼ 4‐kyr spacing) sampling of carbonate, Si, and Al along a 1.6‐m.y. interval of core demonstrates that changes in accumulation rate of calcareous and siliceous microorganisms were controlled by insolation cycles. Optical densitometry logging correlates variations of geochemical parameters to episodes of deep‐sea anoxia, indicated by numerous black, laminated zones (“black shales”). Harmonic analysis of data shows oscillations at three frequencies, which correspond closely in estimated duration and ratio to the modern eccentricity and precessional orbital cycles. As in Pleistocene marine sequences, the eccentricity (approximately 100 kyr) term dominates the sedimentary variance in the Umbrian cycles. Anoxic episodes occur in phase with a limestone‐marl repetition and reflect minima of the precessional (21 kyr) cycle. The covariance of carbonate and silica, with estimates of foraminiferal abundances, suggest that carbonate cycles are the result of changes in surface productivity of calcareous organisms rather than an effect of dissolution or diagenesis. Recognition of orbital cyclicity provides a tool for making quantitative estimates of these changes. Productivity during anoxic events was uniformly low (0.4– 0.5 g/cm2/kyr carbonate, 0– .05 g/cm2/kyr silica), but it rose to high levels during oxygenated periods (1– 2.5 g/cm2/kyr carbonate, 0.1– 0.3 g/cm2/kyr silica). Vertical overturning and organic carbon flux decreased during anoxic episodes, but decreased oxygenation of the deep water led to enhanced preservation of the organic matter delivered. The degree of paleoceanographic variability indicated by this study requires that accepted notions of climate stability and oceanic quiescence during nonglacial times be reassessed.

Lower Cretaceous magnetic stratigraphy in Umbrian pelagic limestone sections

The magnetic stratigraphy of the Lower Cretaceous, pelagic Maiolica limestone has been investigated in three partially correlative sections at Gorgo a Cerbara, Presale and Frontale in the northern Umbrian Apennines of central Italy. The white, well-bedded limestone has a magnetic mineralogy dominated by magnetite. Stable magnetic directions isolated by thermal demagnetization define alternating polarity zones in each section. The magnetozone patterns are distinctive and can be correlated with the geomagnetic reversal history derived from the M-sequence marine magnetic anomalies. The three new sections confirm the polarity sequence for anomalies M0 to M10N. Although the Maiolica is inadequately dated, the correlated anomalies, together with the results of other investigations, allow tentative associations of anomalies M0–M19 with individual stages in the Lower Cretaceous and Upper Tithonian. The investigations also demonstrate the usefulness of magnetic stratigraphy in basin analysis. They yield mean sedimentation rates, confirm that there is a hiatus between the base of the Presale section and the underlying Jurassic formations, and show that a large part of the Frontale section has been cut out by faulting.

Jurassic magnetic stratigraphy from Umbrian (Italian) land sections

The Umbrian Apennines were the site of pelagic sedimentation throughout most of the Jurassic. Magnetic stratigraphy from four sections spanning many of the Jurassic stages indicates that the geomagnetic field at this time was characterized by two intervals of mixed polarity, separated by an interval of predominantly normal polarity corresponding to the Jurassic “quiet-zone” in the oceanic magnetic anomaly record. Unfortunately, ammonites are poorly preserved or absent throughout most of these sections; the duration of this “quiet-interval” cannot be well defined, although it is probably restricted to the Callovian and Oxfordian stages.

Upper Cretaceous palaeomagnetic stratigraphy at Moria (Umbrian Apennines, Italy): verification of the Gubbio section

Summary. The Gubbio section, in the Umbrian Apennines, yielded a sequence of Upper Cretaceous polarity zones precisely corresponding to the sea-floor magnetic anomalies of that age; the Gubbio polarity zones have been dated with planktonic foraminifera. As a test of the validity of the Gubbio reversal sequence, we have studied the section at Moria, 16 km to the north. The polarity sequence at Moria closely agrees with the sequence at Gubbio; only the two thinnest polarity subzones were not found. Comparison of polarity zone thicknesses in the two sections gives an excellent correlation. Declinations in the upper part of the Moria section are somewhat erratic, suggesting the possibility of detachment surfaces and relative structural rotations at these levels. Remanent magnetic intensity varies in a cyclical pattern that is unmistakably the same in the Gubbio and Moria sections. The results from the Moria section provide strong confirmation of the validity of the magnetic polarity sequence established at Gubbio.

Palaeomagnetism and tectonics in Umbria, Italy

Detailed records of palaeomagnetic directions from two Upper Cretaceous Umbrian sections are compared with the composite section compiled by Van den Berg et al. [1]. In addition to these sections, fifty-one geographically distributed sites have been studied magnetically and palaeontologically. The Late Miocene-Pliocene fold belt of the Umbrian Apennines is arcuate in outcrop, being convex toward the east. The fold axes are generally tangential to the Umbrian arc, which can be divided into a northern northwestern-trending part and a southern northeastern-trending part. Sites from the north have more westerly declinations than those from the south. The differences are significant at the 95% probability level and most probably reflect the bending of originally straight fold axes or the development of fold axes with initial curvature. The palaeomagnetic directions from Umbria provide important information concerning the Umbrian tectonic deformation, but are not applicable to the Italian autochthon.

Classification of solution cleavage in pelagic limestones

Spaced cleavage formed by rock dissolution can represent major amounts of shortening parallel to bedding; much so-called fracture cleavage is of this origin. We classify the solution cleavage developed in Mesozoic pelagic limestones of the Umbrian Apennines into four intensity types ( weak, moderate, strong, very strong ) on the basis of qualitative attributes and mean spacing of cleavage surfaces. Shortening can be determined from imbricated chert beds and reaches 50% in rocks with very strong cleavage. In the Umbrian Apennines, solution cleavage is commonly associated with detachment thrusts. We describe an example in which the dissolution mechanism “damaged” the rock beneath a thrust by creating closely spaced discontinuities; fragments bounded by these discontinuities were torn up and incorporated in a nearly chaotic shear zone as the thrust sheet moved forward.

Upper Cretaceous–Paleocene magnetic stratigraphy at Gubbio, Italy I. Lithostratigraphy and sedimentology

Research Article| March 01, 1977 Upper Cretaceous–Paleocene magnetic stratigraphy at Gubbio, Italy I. Lithostratigraphy and sedimentology MICHAEL A. ARTHUR; MICHAEL A. ARTHUR 1Department of Geological and Geophysical Sciences, Princeton University, Princeton, New Jersey 08540 Search for other works by this author on: GSW Google Scholar ALFRED G. FISCHER ALFRED G. FISCHER 1Department of Geological and Geophysical Sciences, Princeton University, Princeton, New Jersey 08540 Search for other works by this author on: GSW Google Scholar Author and Article Information MICHAEL A. ARTHUR 1Department of Geological and Geophysical Sciences, Princeton University, Princeton, New Jersey 08540 ALFRED G. FISCHER 1Department of Geological and Geophysical Sciences, Princeton University, Princeton, New Jersey 08540 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1977) 88 (3): 367–371. https://doi.org/10.1130/0016-7606(1977)88<367:UCMSAG>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation MICHAEL A. ARTHUR, ALFRED G. FISCHER; Upper Cretaceous–Paleocene magnetic stratigraphy at Gubbio, Italy I. Lithostratigraphy and sedimentology. GSA Bulletin 1977;; 88 (3): 367–371. doi: https://doi.org/10.1130/0016-7606(1977)88<367:UCMSAG>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract An essentially complete section of middle Cretaceous to Paleocene, calcareous, pelagic sediments is exposed at Gubbio, in the Umbrian Apennines of Italy. This, the first of five papers, presents the lithostratigraphic and sedimentological basis for subsequent discussions of biostratigraphy and magnetic stratigraphy. Biogenic coccolith-globigerinid oozes were deposited along with a constant but low background of fine terrigenous detritus at a mean sedimentation rate (compacted) of 6.6 m/m.y. from Albian to Eocene time; individual stages deviate from this by a factor of two. Short-term variations in carbonate input yielded a sequence of limestone beds punctuated by thin shale interbeds. These shale-limestone couplets accumulated in time spans between 20,000 and 100,000 yr, and the thin shales may represent up to one-half of the total time. Modification by diagenetic solution, tectonic shear, and weathering render shale interbeds unsuitable for magnetic work. The limestone beds, first bioturbated and then compacted and cemented during diagenesis, appear likely to have recorded magnetic history at intervals on the order of 50,000 yr, sufficient to provide a good record of polarity changes. Moderate to high states of oxidation prevailed except in Aptian-Albian and a portion of Turonian to Santonian times. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.