Paolo Monaco

Hummocky cross-stratified deposits and turbidites in some sequences of the Umbria-Marche area (central Italy) during the Toarcian

Abstract Some sections of the Umbria-Marche basin (central Italy) were characterized during the Toarcian by alternately thicker and thinner organic-rich marls and well-oxygenated, red and nodular marly limestones. These sequences exhibit sharp-based hummocky cross-stratified (HCS) deposits and turbidites, ranging in thickness from several centimetres to 200 cm. Palaeocurrent measurements of HCS beds and turbidites indicate the same SE-NW direction. HCS deposits, that show wavelengths mostly from 70 to 140 cm, are grainstones and matrix-poor packstones. A complete sequence consists of three divisions. (a) A lower, coarse-grained bivalve and echinoderm lag, from 0.5 to 40 cm thick. The lag is generally erosive and discontinuous and probably represents a proximal material deposited during a high-energy phase of a storm event. (b) A middle, well-sorted calcarenite/calcisiltite division (from 20 to 100 cm thick), that exhibits well preserved hummocky cross-stratification. Bioclastic calcareous sands transported by offshore currents from storm surges were organized into HCS beds under an oscillatory/unidirectional flow regime near the bottom. (c) An upper, oscillatory ripple-bedded calcisiltite division from 0.5 to 25 cm thickness. Ripples were probably formed during a dominant oscillatory regime (wave action?) after the sand sedimentation had stopped. Locally a pervasive bioturbation is common in the upper part of this bed. Turbidites (10–200 cm thick) are packstones and rudstones with abundant muddy matrix and generally show the classical Bouma BC sequence. The lower and middle interval of the studied sequences, from the late Domerian to the early Toarcian, is dominated by fining-upward turbidites. On the contrary, the upper part of the sequence, middle/late Toarcian in age, is dominated by sharp-based HCS beds. The vertical transition from turbidites to sharp-based HCS deposits is indicative of a general regressive trend. The causes of the sea-bottom depth changes can be related respectively to a sea-level rise documented for the early Toarcian and to the sea-level fall of the middle Toarcian. Lateral and vertical distribution, frequency, grain size, structures and composition of detritic beds and microfaunal assemblages confirm the differentiated topography of the Umbria-Marche basin during Toarcian time.

The Eocene-Oligocene Boundary in the Umbrian Pelagic Sequences, Italy

Publisher Summary Detailed biostratigraphic and paleomagnetic studies on Eocene–Oligocene pelagic sequences from Umbria (Central Italy) revealed that deposition across the Eocene–Oligocene boundary was continuous and undisturbed in that area. This chapter presents the data from eight stratigraphic sequences spanning the interval from the Early to Middle Eocene boundary through the Early Oligocene with specific emphasis on the events at the Eocene–Oligocene boundary. To have a complete biostratigraphic and paleomagnetic record, the Contessa highway section was sampled upwards into the northwestern quarry—that mirrors the Contessa quarry of Lowrie—where the Eocene–Oligocene boundary is undisturbed. Lithologically, the scaglia formation is very monotonous except for the major color changes. Visual correlations among sections are limited to minor changes that are not easily detected. Some of these changes, however, appear to be of larger (not local) significance.

Three-dimensional burrow systems and taphofacies in shallowing-upward parasequences, lower Jurassic carbonate platform (Calcari Grigi, Southern Alps, Italy)

SummaryAnalysis of parasequences of carbonate platform origin from the Calcari Grigi Formation (Rotzo Member, Lower Jurassic) in the Venetian Pre-Alps of Northern Italy reveals intense burrowing affecting warm lagoonal and protected shelf environments of the Trento carbonate platform. The trace fossil pattern suggests a strong biogenic activity by many unknown organisms (episodic surficial bioturbation) and by decapod crustaceans (deep burrowing) during the Sinemurian—Pliensbachian. Burrow networks ofThalassinoides (T. suevicus, type I to IV) andOphiomorpha form three-dimensional systems (3DBS), up to 150 cm in thickness, that reveal well developed taphonomic characteristics. Occasionally, also rare body fossil remains (exuvia) ofPhlyctisoma (Erymidae) are preserved, although it is very difficult to attribute to this decapod crustacean a real tracemaker activity. In a total of 18 shallowing-upward taphosequences, each 2.3–2.6 m in thickness, the lower, subtidal part (BOP: base of parasequence), is invariably characterized by 3DBS. Three parts of a 3DBS are taphonomically relevant: a) the enlargement at bifurcation points (the so-called turning chambers) with related tunnel sections in horizontal networks; b) the distribution of vertical tunnels and their openings, locally associated with biogenic mounds; and c) the infilling with coarse-grained skeletal debris of abandoned burrows (tubular tempestites). Case (a), although well known in the literature, is nevertheless peculiar because of the exceptional diameter (up to 22 cm) and shape of bifurcations ofThalassinoides suevicus. Therefore their taphonomic analysis helps to refine shallowing-upward taphosequences. Case (b) and (c), instead, are exceptional because traces of the activity of decapod crustaceans at the sea-floor are very rare in the geologic record. The 3DBS involve taphofacies that are peculiar of the upper part of the Calcari Grigi across western Venetian Prealps. The analysis of 3DBS in all Lower Jurassic para-sequences will aid sequence stratigraphy and the paleoenvironmental reconstruction of the carbonate platform setting.

Eocene and early oligocene micropaleontology and paleoenvironments in SE Umbria, Italy

A detailed study, based on calcareous nannofossils and planktonic and benthic Foraminifera, has been carried out on five sections in the “Scaglia” Group of the Umbrian region (Visso and Cascia areas, Central Italy). These sections are characterized by continuous pelagic sedimentation and are constituted mainly of marls, marly limestones and limestones of Early Eocene to Early Oligocene age. Calcareous turbidites, with shallow-water skeletal debris, discharged from the Latium-Abruzzi carbonate platform, are interbedded within the pelagic sequences. The biostratigraphic study, based on calcareous nannofossils and planktonic Foraminifera, confirmed the continuous succession of standard events and revealed some new ones. These results allow us to refine the biostratigraphic resolution, with a very good correlation between calcareous nannofossil and planktonic foraminiferal zonations. The major features and events recognized are: • The Early-Middle Eocene boundary (Zones P9–P10) is characterized by the first occurrence (FO) of hantkeninids, by abundant thick-walled Globigerinatheka (G. senni) and by spinose acarininids. A decrease has been noted in planoconvex morozovellids and an increase of low-spired subbotinids. • The benthic assemblage shows a great variability, with an increase in the Zone P11 of the large Heterolepa and Cibicidoides. This is an event of worldwide significance. • In the calcareous nannofossils, the FO of Nannotetrina sp. was used to define the lower boundary of Zone CP13 instead of N. fulgens, because poor preservation prevented identification at the specific level. • The FO of Reticulofenestra umbilica, marking the lower boundary of Zone CP14, occurs in the upper part of Zone P11. • The Zone P13 was recognized indirectly because of the absence of the index species Orbulinoides beckmanni. The base of the zone is close to the FO of Turborotalia cerroazulensis, and is defined by an increase of Catapsydrax sp. and by the last occurrence (LO) of Acarinina bullbrooki. The top of the zone is defined by an increase of the high-spired subbotinids of the S. corpulenta group and the disappearance of Morozovella spinulosa • The Middle/Late Eocene boundary (Zones P14/P15) is characterized by the extinction of the spinose acarininids and of the smooth-walled Planorotalites. From Zone P13 to Zone P15 there is a replacement in the benthic assemblages. In fact, Pleurostomella, Heterolepa and Anomalinoides capitata characterize these zones, bolivinids become abundant and uvigerinids appear around the P14/P15 boundary. • The Late Eocene is characterized by an increase of subbotinids with abortive chambers and of the Turborotalia cerroazulensis lineage. Hantkeninids and cribohantkeninids are rare, particularly C. inflata. The FO of Istmolithus recurvus has been noted at the base of Zone P16. Within this zone, Globigerinatheka index and Turborotalia cunialensis coexist. The LO of G. index is associated with a strong decrease of representatives of the genus Globigerinatheka. At the same level of the LO of G. index, the coeval extinctions of Discoaster barbadiensis and Discoaster saipanensis are noted. Just above this level, within Zone P17, the LO of T. cerroazulensis lineage (T. cocoaensis and T. cunialensis) has been recognized. The Eocene/Oligocene boundary is defined by planktonic Foraminifera at the extinction level of hantkeninids and cribrohantkeninids, shortly following that of the T. cerroazulensis group.

Ichnological Analysis of Lateral Environmental Heterogeneity Within the Bonarelli Level (Uppermost Cenomanian) in the Classical Localities Near Gubbio, Central Apennines, Italy

ABSTRACT Dark, pelagic sediments of the uppermost Cenomanian Bonarelli Level (OAE2 event) interval, in two classical sections Contessa and Bottaccione in the Central Apennines, contain unbioturbated and bioturbated beds suggesting fluctuations in pore water oxygenation from anoxic to oxic or dysoxic conditions. The oxic and dysoxic improvement events prior to, during, and after the event are marked by biogenic structures showing an increase in the diversity of the trace fossils (Chondrites, Planolites, Thalassinoides, Trichichnus, and Zoophycos) from none to five ichnotaxa in individual beds. The number of anoxic events differs in the Contessa and Bottaccione sections, even though they are only 2.5 km apart. Comparison with sections from the Carpathians (Poland) and the Betic Cordillera (Spain), reveals that minor anoxic events below and above the Bonarelli Level are absent in the studied Apennine sections. Moreover, the diversity and density of trace fossils in the Apennine sections are lower than those from other studied sections in the Tethys, most likely indicating a comparatively lower availability of food in the Gubbio area as a result of its paleogeographic location. The preservation of trace fossils, controlled by the consistency of sediments and diagenetic processes, can mask diversity and density in some beds.

Stratigraphy and geochemical anomalies of the early Toarcian oxygen-poor interval in the Umbria-Marche Apennines (Italy)

Abstract A multidisciplinary approach is used to demonstrate the occurrence of oxygen-poor sediments in theTenuicostatum Zone (Early Toarcian) within the clayey-marly pelagic sediments of Marne del Monte Serrone Formation (Umbria-Marche basin). This approach involves examination of some geochemical anomalies (trace elements), measurement of Total Organic Carbon and observation of benthic foraminifera and trace fossils. A distinction between “ black shale facies ” (BSF1) and “ black shale-like sediments ” (BSF2) allows better identification of the variable anoxic conditions present within the same basin. A high degree of organic matter preservation and major anoxia extensions occur in the middle-upper part of the Tenuicostatum Zone (Early Toarcian) probably related to maximum flooding-high stand of the global Early Toarcian sea-level rise. Several subenvironments showing pelagic conditions and high primary productivity of planktonic organisms (mainly radiolarians and calcareous nannofossils), have been defined on the basis of organic matter content and positive geochemical anomalies. The diversified physiography of the Umbria-Marche basin, related to synsedimentary tectonic activity and circulation patterns, probably determined different intensities of ventilation conditions on the sea-floor.

Taphonomic Features of Paleodictyon and Other Graphoglyptid Trace Fossils in Oligo-Miocene Thin-Bedded Turbidites, Northern Apennines, Italy

Abstract Taphonomic features of 156 graphoglyptids and other trace fossils preserved as hypichnia of thin-bedded turbidites in Oligo-Miocene flysch of the northern Apennines (central Italy) were analyzed. Two biogenic taphonomic categories—deformation and elongation—were produced in hemipelagic mud by the behavior of endobenthic organisms. Deformation includes such features typical of bulldozing and burrowing as twisting, squeezing, tilting, thickening, and widening. Elongation is considered a primary biogenic character controlled directly by the tracemaker. Taphonomic features induced by such physical agents as currents and creep usually developed unidirectionally and include stretching, straightening, smoothing, bending, tapering, thickening, and thinning. These features, associated with hundreds of microgrooves (5–10 per 0.01 m2) interpreted as mud-current lineations, suggest that currents were active and produced deformational structures of fluting before, during, and after the biogenic activity. Preservation of such delicate structures recognizable at different levels is particularly noticeable when a thin layer of fine material settled by suspension, molding all structures and producing a cemented film. Deformational structures may be particularly well preserved in thin-bedded (3–6-cm-thick) and fine-grained calcarenitic turbidites as in diluted turbulent flow deposits that fringed the isolated Verghereto High. Activities of epi- and infaunal communities in this area are also exceptionally well preserved. Physical taphocharacters of graphoglyptids are interpreted in two ways: (1) as true tool marks produced in mud by a tractive water mass preceding sand deposition by turbidite flows, or (2) as structures inherited from preturbidite phases. Taphonomic analysis in deep-sea deposits, therefore, is a promising methodology to resolve the preservational state of trace fossils above and below the soles of turbidites.

Relationships between trace-fossil communities and substrate characteristics in some Jurassic pelagic deposits in the Umbria-Marche basin, Central Italy

Abstract The study of trace fossil assemblages is a very useful tool for defining depositional palaeoenvironments, such asthose of some early Jurassic pelagic sequences in the Umbria-Marche basin (late Carixian to early Aalenian). These sequences - Valdorbia and Fiuminata Colle Corno- are represented by thick bioturbated marls and limestones which alternate locally with poorly-bioturbated shales. Clay and silty-sandy deposits representing turbidites and storm beds (HCS = hummocky cross-stratified deposits) are very common, especially in the Toarcian interval. A comparison between trace fossil assemblages and sedimentologic/stratigraphic features permits an accurate paleoecologic and palaeoenvironmental analysis of sediments deposited in regressive conditions such as, for instance, the sequences studied. Trace fossil communities provide evidence of periods of non sedimentation or erosion during the Jurassic, when firm- or hardgrounds were commonly developed on muddy or sandy substrates. Penetration depth, burrow diameter, trace fossil density and species diversity emphasize the relationships with substrate characteristics and oxygen variations on the seafloor or in the sediment column. Consequently, analysis of different types of substrate and of substrate-controlled ichnofacies permits an evaluation of the paleoecologic strategies of the endobenthos in low to high-stress environmental conditions.

Paleoenvironmental changes during the late Miocene (Messinian)–Pliocene transition (Bajo Segura Basin, southeastern Spain): Sedimentological and ichnological evidence

ABSTRACT A detailed sedimentological and paleontological analysis of the uppermost Miocene (Messinian)–Pliocene boundary at the northern border of the Bajo Segura Basin, southeastern Spain, was carried out in order to describe the evolution of the regional paleocoastline during the Pliocene reflooding of the Mediterranean immediately after the sea-level fall related to the Messinian Salinity Crisis. Multiple trace fossils typical of firm- and hardgrounds were recognized, allowing identification of Glossifungites (two different types), Entobia, and Gnathichnus ichnofacies. Trace-fossil analysis showed that lithology and media consistency exerted considerable control on the development of the different ichnocoenoses and that there was a clear decrease in hydrodynamic energy from a coastal to a shallow-water shelf environment related to progressive sea-level rise. Ichnological and sedimentological data provide evidence that the definitive flooding of the Mediterranean was rapid and synchronous throughout the northern margin of the Bajo Segura Basin. The following model for the Pliocene transgression in the study area is therefore proposed: (1) the marine ingression penetrated along the incised paleovalleys carved as a consequence of the fall in sea level, where the first two Pliocene systems were deposited (P0–P1); (2) during the maximum flooding surface of the transgression, the sea overflowed the margins of the paleovalleys and extended throughout the entire northern margin of the basin; and (3) the third Pliocene system was deposited, forming the lower part of a highstand systems tract (P2).

Burrows and body fossil of decapod crustaceans in the Calcari Grigi, lower Jurassic, Trento platform (Italy)

Crustacean burrows are largely known and well described in the literature but a concurrence of abundant burrows and fossil remains of decapods represents an exceptional circumstance in the geological record. Well-preserved burrows of decapod crustaceans in the Pliensbachian of the Trento carbonate platform, northern Italy, reveal several ichnoassemblages of Thalassinoides and Ophiomorpha from 2 to 16 cm in diameter forming complex burrow systems in the lagoonal facies of the Rotzo Member. These burrows have been found both in the lower surface of beds and within shallowing-upwards cycles of fossiliferous limestones (Lithiotis facies), which reveal peculiar taphonomic characteristics. The abundant concentration of decapod crustacean burrows suggests intense burrowing activity of such organisms during the Early Jurassic as indicated also by an exuvia of Phlyctisoma (Erymidae), although we do not know if it was an active tracemaker. Many shallowing-upward parasequences occur and burrow systems were concentrated mainly in their lower part suggesting intense biological activity in deeper and quiet subtidal conditions; conversely, biologic activity was interactive with physical agents in the middle part of cycles and progressively replaced by wave or tidal-induced physical agents in the upper part where intertidal/supratidal conditions were formed.