Unconformity-bounded Units Research Articles

Chapter 1 - Preliminary investigations on the Zard Formation at its type locality (North Khorasan Province, Iran)

This chapter presents a revision of the Zard Formation in its type area, i.e., in the North Khorasan Province (Iran), including at its type locality. It comprises a description of the sedimentological and micropaleontological criteria that permit it to be distinguished from the Mozduran Formation (below) and the Tirgan Formation (above). At its type locality, its lower boundary is a heavily bored surface. Actually, both contacts with the framing formations correspond to transgressive surfaces, which imply that this lithostratigraphic unit is an Unconformity-Bounded Unit. With respect to biostratigraphy, this formation contains a few second-order markers: Holosporella sugdeni, Kopetdagaria sphaerica, and Torinosuella peneropliformis, which are also found in the unit above, i.e., in the Tirgan Formation. Because the latter contains markers that first appear in the Barremian: Bakalovaella elitzae, Pseudoactinoporella iranica, and Balkhania balkhanica, but also Montseciella arabica, the total range of which spans the Upper Barremian, the Zard Formation (i.e., the Zardian regional stage) should partly covers the Hauterivian to Barremian interval. Finally, although it cannot be definitely excluded that the lowermost part of the Zard Formation could be Valanginian in age, this option still requires proper documentation.

Facing geological mapping at low-latitude volcanoes: The Doña Juana Volcanic Complex study-case, SW-Colombia

We present the Doña Juana Volcanic Complex (DJVC) geological map, stratigraphy, Ar/Ar-and-C14 geochronology resulting from a pilot-mapping project in Colombia, as a study-case for the application of modern, international volcano geology techniques in low-latitude environments. Lithostratigraphy and lithofacies analysis (for description of rock bodies and mapping), lithosomes (for the definition of eruptive centres) and unconformity-bounded units (for stratigraphic correlation), as well as new geochronological data and the interpretation of eruption units were successfully integrated. The geological mapping and stratigraphic analysis provided an effective representation of the volcanic edifices/vents that make up the DJVC, so that we could reconstruct the geological evolution from the time and spatial distribution of the corresponding volcanic products and the range of lithofacies associations. The geological database and the forthcoming interpretation in terms of eruption behaviour establish the basis for realistic long-term hazard assessment.The DJVC is a calc-alkaline dacitic volcanic complex within the Central Cordillera of Colombia, which started its activity about 1125.4 ± 4.4 ka ago. It comprises three spatially overlapping edifices and three adventive cones, which unconformably overlay Lower Cretaceous metasedimentary and metavolcanic rocks of oceanic origin. Each of the three overlapping edifices is truncated at the summit by a volcano-tectonic depression, without identifiable caldera-forming products. Two of these volcano-tectonic features display important proximal unconformities and, together with their correlative disconformities and paleosols, indicate significant quiescences of volcanic activity. The Holocene record has been mostly characterized by the emission of three lava-dome fields infilling the youngest volcano-tectonic depression and interrupting the corresponding unconformity. These lava domes have recurrently collapsed to originate block-and-ash flows followed by vulcanian explosions producing pyroclastic density currents and lahars. The corresponding eruptive products have drained along the present river basins to the NE and SW of DJVC, forming depositional terraces currently populated by nearly 49,000 rural and urban inhabitants.

Quaternary marine and continental unconformity-bounded stratigraphic units of the NW Sicily coastal belt

ABSTRACTIn the coastal sector of NW Sicily, the regional correlation of relevant unconformities recognised within the Quaternary sedimentary successions allowed the mapping of seven unconformity-bounded stratigraphic units (UBSUs). The regional unconformities are marine or subaerial erosional surfaces, as well as non-depositional surfaces, locally marked by paleosoils. The erosional surfaces were produced from marine abrasion, surface water overland/concentrated flow, river erosion, karst solution, mass movement, or wind erosion. The main lithofacies of the Quaternary UBSUs consist of: (a) marine and coastal bioclastic calcarenites, (b) aeolian sandstones, (c) river deposits, (d) colluvial deposits, (e) talus slope deposits, (f) landslide deposits, and (g) chemical carbonates (travertines and speleothems). Quaternary environmental changes, due to tectonics, climate, and sea-level oscillations, are the causes that favoured the development of erosion/deposition processes responsible for the genesis of unconformities and deposits. As a result, through the UBSU map of the NW Sicilian coastal belt, it is possible to: (i) recognise stratigraphic units controlled by tectonic, climatic, and environmental processes (and their interplay) and (ii) detect Quaternary sedimentary evolution.

Unsung Pioneers of Sequence Stratigraphy: Eliot Blackwelder, Joseph Barrell, Amadeus Grabau, John Rich and Harry Wheeler

Few facies analysts or stratigraphers would argue against the contention that the transition to facies-driven sequence strati- graphic correlations represents one of the most important paradigm shifts in modern stratigraphy. What is less commonly appreciated is that most of the fundamental underpinnings of sequence stratigraphy were derived from a relatively small number of pioneers in the early to mid-1900s; most of them largely unknown or underappreciated by the current generation of sequence stratigraphers. Chief among these are Eliot Blackwelder, Amadeus Grabau, Joseph Barrell, John Rich, and Harry Wheeler. Blackwelder was perhaps the first to point out the presence and significance of regional unconformities in the packaging of strata in North America, which would later come to form the basis of the well-known cratonic megasequences of Larry Sloss. However, Blackwelder is best appreciated as the mentor and colleague of not only these other pioneers, but also of key workers who themselves ultimately mentored some of the most renowned sequence stratigraphers of the 1970s and 1980s. Amadeus Grabau focused his attention on expounding the law of the correlation of facies of Johannes Walther and bringing facies-driven correlations into stratigraphy; an approach at odds with the then prevailing view of lithostratigraphy as the principal physical stratigraphic framework. Grabau recognized that the rock record contains numerous temporal gaps that partition facies succes- sions, for which he defined the term “hiatus”. His Pulsation theory was used to explain the cycles of deposition and hiatal erosion/bypass, and although the mechanism is different, the net outcome of such “oscillations” is broadly similar to the effects of eustacy and tectonism that we assign to such changes today. Joseph Barrell developed the concept of base level and explored its role in controlling erosion versus deposition. Like Grabau, Barrell insisted that sedimentation was not continuous, leading to a stratigraphy that is replete with breaks of varying durations. For these he coined the term “diastems” for the small but more numerous breaks, which could be contrasted with those reflecting longer breaks which he referred to as “discontinuities”. John Rich evaluated depositional topography, for which he coined the terms clinoform, undaform and fondoform. He recognized that such depositional bodies necessarily link genetically related associations of sediment deposited from the shoreline to the basin center; what today we regard as the depositional system. The resulting architectures bounded by these surfaces form the underpinning of all systems tracts in modern sequence stratigraphy. Harry Wheeler formalized the concept of time-stratigraphy, demonstrating that temporal gaps in stratigraphy are as important in understanding the rock record as the rocks themselves. His novel approach of developing stratigraphic cross-sections with time on the vertical axis pioneered the concept of chronostratigraphy through the development of what are now referred to as Wheeler Diagrams. His resurrection of the base-level concept expounded by earlier workers was instrumental in defining sequences as unconformity-bounded units, re-establishing the concepts pio- neered by Blackwelder himself. In concert, these stratigraphic visionaries erected a stratigraphic framework focused on the understanding of the stratigraphic record as opposed to its simple lithostratigraphic mapping or biostratigraphic dating. These unsung pioneers put into place virtually all components of modern sequence stratigraphy more than two decades before its popularization in the scientific commubity.

Miocene humid intervals and establishment of drainage networks by 23 Ma in the central Sahara, southern Libya

Terrestrial and lacustrine Neogene and Quaternary sediments in the Libyan Fezzan provide key evidence for paleoclimate changes in the central Sahara, associated with Lake Megafezzan. Understanding of Holocene and late Pleistocene deposits is resolved, but the age of older sediments is not. We provide the first high-resolution chronology and stratigraphy of the Neogene deposits in the Fezzan Basin, and so also the central Sahara. The sediments are divided into three unconformity-bounded units, the oldest unit, comprising the Shabirinah and Brak formations, is dated using magnetostratigraphy. The Shabirinah Formation is a succession of lacustrine and fluvial units, locally with humid and arid paleosols, which progressively show evidence of increasing aridity up through the succession. The overlying Brak Formation is a pedogenically modified palustrine limestone at basin margin locations. All these units are dated to the early Aquitanian to late Serravallian in the early to mid-Miocene, having formed prior to major volcanic fields to the east. During the mid-late Aquitanian widespread stromatolitic lake sediments developed in SE Fezzan. In the late Burdigalian palustrine carbonate units developed that typically pass laterally into mixed clastic-paleosol-carbonate units that characterise basin margin situations. The Serravallian-aged Brak Formation is a highstand deposit developed during maximum lake extent, which formed due to restriction of basin drainage to the north and east, due to growth of the Jabal as Sawda volcanic centre and uplift of the SW shoulder of the Sirte Basin. Gradual aridification of the central Sahara occurred from the early Miocene, but this trend was periodically interrupted by humid phases during which Lake Megafezzan developed. The hyperaridity of the central Sahara must have developed after 11Ma and the main drainage networks from the Fezzan Basin were established before 23Ma, in the Oligocene indicating the great antiquity of major central Saharan river basins.

Avancées dans une réécriture de l'histoire de la transition du Jurassique au Crétacé dans le Mont Liban

The stratigraphic framework of the Upper Jurassic and Lower Cretaceous strata of Lebanon that dates back to Dubertret's publications required either consolidation or full revision. The preliminary results of our investigations in the Mount Lebanon region are presented here. We provide new micropaleontological and sedimentological information on the Salima Oolitic Limestones, which is probably an unconformity-bounded unit (possibly Early Valanginian in age), and the Gres du Liban (Barremian in age). Our revised bio- and holostratigraphic interpretations and the new age assignations lead us to emphasize the importance of the two hiatuses in the sedimentary record below and above the Salima, i.e., at the transition from the Jurassic to the Cretaceous.

Harry Eugene Wheeler (1907-1987): A Pioneer of Sequence Stratigraphy

Harry Eugene Wheeler (1907-1987) of the University of Washington was a pioneer of genetic stratigraphic principles that form the basis of our modern concept of sequence stratigraphy. Wheeler's papers on what he liked to refer to as "stratology" included the classification of stratigraphic units into lithostratigraphic and biostratigraphic entities, as well as cyclothems, unconformity-bounded units, and the analysis of base-level and its role in forming stratigraphic discontinuities. His work on unconformity-bounded "sequences" ultimately led the International Subcommission on Stratigraphic Classification to define them formally in 1987. The plots used to clarify the time-relationships of rock units are now referred to as "Wheeler diagrams". It is not uncommon that, in any scientific paradigm shift, many of the key pioneers are not fully recognized for their contributions at the time, being significantly ahead of prevailing concepts. It is also not uncommon that, by the time their points of view come into vogue, their contributions may have been largely forgotten with greater recognition given to those who synthesized or "popularized" their concepts. This is certainly true in the fields of seismic and sequence stratigraphy, where, despite the theoretical framework for sequence analysis formulated by Wheeler (1958a), little reference was made to Wheeler's work in the early formulation of these concepts in the 1970s and 1980s. Wheeler, schooled by Blackwelder, Mueller, and Schenck at Stanford and armed with the base-level concept of Joseph Barrell, was one of the first to recognize the concept of time stratigraphy. Due to his unorthodox view of stratigraphy, Wheeler was involved in one controversy after another and his views were deemed to be provocative. While the valuable contributions of latter practitioners and synthesizers are justifiably lauded, the works of original pioneers such as Harry Eugene Wheeler are largely underappreciated.

Geology of the middle and upper Pleistocene marine and continental terraces of the northern Tavoliere di Puglia plain (Apulia, southern Italy)

The Tavoliere di Puglia is a large alluvial plain located in southern Italy (Foggia Province, Apulia Region). From a geological perspective view, it represents the northern part of the Bradanic trough located between the southern Apennine Chain and the Apulian Foreland. A detailed geological survey of the middle-late Pleistocene terraces has been performed in this area and a new geologic map, at 1:150,000 scale, is here described. Criteria to distinguish these units are based on the recognition of basal unconformity surfaces: seven different synthems (UBSU, Unconformity-bounded Stratigraphic Units) have been discriminated. The data are presented in a synthesis map in which the geometrical relationships between the different sedimentary units are shown. New results for this sector of the Bradanic trough are significantly different from previous literature data. Furthermore, the map allows a reliable reconstruction of the Tavoliere di Puglia paleogeography during the Late Quaternary. Moreover, a detailed ma...

Revision of "Falaise de Blanche" (Lower Cretaceous) in Lebanon, with the definition of a Jezzinian Regional Stage

The Falaise de Blanche is a prominent cliff, consisting mostly of Lower Cretaceous limestones that extends as linear outcrops over most of the Lebanese territory and provides geologists a remarkable reference for stratigraphic studies. However, until now, this unit was lacking a clear definition. We introduce herein the Jezzinian Regional Stage, the type-locality of which is at Jezzine. It equates as an unconformity-bounded unit and, per definition, it is framed by two discontinuities. Because we identified an additional, median sequence-boundary, poorly-expressed in the type-section but better at Aazour, only 4.5 km westward of Jezzine, the new regional stage implicitly spans two sequences. The lithostratigraphic framework being properly redefined, we were able to investigate time-constrained micropaleontological assemblages, consisting mostly of benthic foraminifers and calcareous algae. Typically Southern Tethysian, these assemblages contribute to high-resolution, holostratigraphic correlations with the Persian Gulf area, on the eastern part of the Arabian Plate. The Jezzinian interval correlates with the upper part of the Kharaibian Regional Stage (also known as Thamama II reservoir unit in the oil industry). In turn, the Jezzinian is indirectly correlated with the Northern Tethysian Urgonian stratigraphic units where it corresponds to a rather short interval encompassing the standard Barremian - Bedoulian stage boundary. Locally the upper discontinuity is associated to a significant intra-Bedoulian hiatus. The macrofossil assemblages found in the Jezzinian (echinids) and above it (ammonites) support, or at least do not contradict, our micropaleontological dating.

Evaluation of carbonate diagenesis: A comparative study of minor elements, trace elements, and rare-earth elements (REE + Y) between Pleistocene corals and matrices from Grand Cayman, British West Indies

On Grand Cayman, the Pleistocene Ironshore Formation consists of six unconformity-bounded units of limestones that have been partially or completely altered to calcite by post-depositional meteoric diagenesis. In order to examine the diagenetic history from the perspective of geochemical elements, the concentrations of minor element (Sr, Na, Mg), trace elements (Ba, Fe, Mn, Al, Si), and rare-earth elements (REE) and yttrium (Y) were determined for 105 corals and 84 matrices collected from the Rogers Wreck Point (RWP), Western Onshore area (WO), and offshore George Town (GT) areas. With the transformation of aragonite to calcite, the Sr, Na, and Ba values decreased, but Mg increased, which are indicative of diagenetic alteration in an open water system. Due to intrinsic “vital effects” and the extrinsic diagenetic environment, the variations of Sr, Na, Ba, and Mg concentrations between Acropora and Montastrea from the GT area are different to those of their counterparts from RWP and WO. The signatures of Sr, Na, Ba, and Mg are in good agreement with the diagenetic history as determined from petrographic and stable isotopic criteria.The REE+Y (REY) concentrations (ΣREY) are higher in the matrices (0.2–6.9ppm, average 2.6ppm) than in the associated corals (0.1–5.4ppm, average 0.6ppm). Shale-normalized REY patterns of the Pleistocene Ironshore Formation are similar to those of oxygenated seawater, which are characterized by (1) light REE depletion relative to heavy REE (average DySN/SmSN=1.7, n=35), (2) positive La anomalies (average Pr/Pr*=1.17, n=53), and (3) negative Ce anomalies (average Ce/Ce*=0.49, n=53). The preserved seawater-like REY distribution pattern, the lack of correlation between ΣREY and mineralogy, and the lack of correlation between ΣREY and diagenesis-sensitive stable oxygen isotope (δ18O) indicate that meteoric diagenesis did not have a major impact on the REY distribution patterns. The matrices and corals in the GT area, compared to their counterparts from RWP and WO, have relatively less depleted LREE and lower Y in REY distribution pattern, suggesting contamination by minor amounts of detrital sediments. This is supported by the fact that limestones from the GT area contain abnormally high contents of detrital elements (Al, Si). The variations in ΣREY in carbonate rocks from locality to locality probably reflect variations that existed in the local depositional environments where these deposits originally formed.

High-level stratigraphic scheme for New Zealand rocks

We formally introduce 14 new high-level stratigraphic names to augment existing names and to hierarchically organise all of New Zealand's onland and offshore Cambrian–Holocene rocks and unconsolidated deposits. The two highest-level units are Austral Superprovince (new) and Zealandia Megasequence (new). These encompass all stratigraphic units of the country's Cambrian–Early Cretaceous basement rocks and Late Cretaceous–Holocene cover rocks and sediments, respectively. Most high-level constituents of the Austral Superprovince are in current and common usage: Eastern and Western Provinces consist of 12 tectonostratigraphic terranes, 10 igneous suites, 5 batholiths and Haast Schist. Ferrar, Tarpaulin and Jaquiery suites (new) have been added to existing plutonic suites to describe all known compositional variation in the Tuhua Intrusives. Zealandia Megasequence consists of five predominantly sedimentary, partly unconformity-bounded units and one igneous unit. Momotu and Haerenga supergroups (new) comprise lowermost rift to passive margin (terrestrial to marine transgressive) rock units. Waka Supergroup (new) includes rocks related to maximum marine flooding linked to passive margin culmination in the east and onset of new tectonic subsidence in the west. Māui and Pākihi supergroups (new) comprise marine to terrestrial regressive rock and sediment units deposited during Neogene plate convergence. Rūaumoko Volcanic Region (new) is introduced to include all igneous rocks of the Zealandia Megasequence and contains the geochemically differentiated Whakaari, Horomaka and Te Raupua supersuites (new). Our new scheme, Litho2014, provides a complete, high-level stratigraphic classification for the continental crust of the New Zealand region.

Cenozoic synthem stratigraphic architecture of the SE Brazilian shelf and its global eustatic context: evidence from the Pelotas Basin (offshore Brazil)

Abstract The Pelotas Basin, located on the SE Brazilian shelf, has evolved since the Aptian. Stratigraphical data from the basin can be used for delineation of the unconformity-bounded units (synthems) on the shelf, which is a first step towards a full understanding of its stratigraphic architecture, evolution, and hydrocarbon potential. Hiatuses in the Cenozoic succession of the Pelotas Basin are established with both biostratigraphic (planktonic foraminifers and calcareous nannofossils) and isotopic (87Sr/86Sr) data. The seven recognised hiatuses are dated respectively as (1) Palaeocene (Danian- Thanetian), (2) Palaeocene/Eocene boundary (Thanetian-Ypresian), (3) Eocene (Ypresian-Lutetian), (4) Eocene-Oligocene (Lutetian-Rupelian), (5) early-late Oligocene (Rupelian-Chattian), (6) early Miocene (Aquitanian-Burdigalian), and (7) middle-late Miocene (Serravallian-Tortonian). These intervals between the hiatuses are correlated with those of the Santos and Campos Basins north from the Pelotas Basin. The breaks in sedimentation that these basins have in common occurred (1) at the Palaeocene-Eocene and (2) Eocene-Oligocene transitions, (3) in the early Miocene, and (4) in the middle-late Miocene. These main unconformities outline five synthems on the SE Brazilian shelf, viz. the SEBS-1 (Palaeocene), SEBS-2 (Eocene), SEBS-3 (Oligocene), SEBS-4 (early-middle Miocene) and SEBS-5 (late Miocene-Holocene). The above unconformities are correlated with those established in the Cenozoic sedimentary successions of different regions such as Western Siberia, Arabia, NW and NE Africa, peninsular India, S Australia, the Gulf of Mexico, NW Europe, and South Africa. The only regional unconformity, near the Oligocene/Miocene boundary, coincides with the nearly-global sedimentation break. The latter was resulted from a climatic event, i.e., the ‘Mi-1 glaciation’. Thus, a eustatic origin is supposed for this regional unconformity. The other regional unconformities also correspond to global sea-level falls (probably with an exception for the Palaeocene/Eocene surface), which suggests that global eustatic movements controlled the development of the regional synthem architecture.

Heterogeneous diagenetic patterns in the Pleistocene Ironshore Formation of Grand Cayman, British West Indies

The Ironshore Formation on Grand Cayman consists of six unconformity-bounded units (A to F) that developed in response to repeated transgressive–regressive cycles during the Middle to Late Pleistocene. Corals and matrices in limestones from the Rogers Wreck Point (RWP), offshore George Town (GT), and western onshore (WO) areas are characterized by complex diagenetic fabrics that reflect marine (bioerosion, micrite envelopes, internal sediments, fibrous high-Mg calcite, acicular aragonite, isopachous prismatic calcite cements), freshwater phreatic (circumgranular cements, even/random blocky calcite cements), and vadose (meniscus calcite cements, blocky calcite cements) diagenesis. Throughout these limestones, the matrices have undergone more meteoric diagenetic alteration than the corals. Overall, however, no systematic stratigraphic patterns exist to the distribution of these diagenetic fabrics and it is generally impossible to link the different phases of diagenesis with specific unconformities that cap each unit. These heterogenous patterns of diagenetic features can be attributed to many intrinsic and extrinsic factors, including the original compositions of the different components in the limestones, the porosity and permeability of the substrate, the nature of the diagenetic fluids, climate, and the duration of exposure during each lowstand. Integration of available data, however, indicates that maximum diagenesis took place during the lowstands denoted by the unconformities at the top of Unit C (Marine Isotope Stage 7) and Unit D (Marine Isotope Stage 5e) when long periods of exposure were accompanied by wet climates with high annual rainfalls.

The Plio-Pleistocene fluvio-lacustrine Upper Valdarno Basin (central Italy): stratigraphy and Basin fill evolution

The Upper Valdarno Basin stands out from the Neogene-Quaternary basins of the Northern Apennines given its outstanding fossil mammal record, good quality of natural and artificial outcrops and remarkable chronological control on the basin-fill succession. The present paper aims to summarize the stratigraphic and sedimentological studies focused on the Upper Valdarno Basin during the past decades, and integrate them with recent investigations. The Upper Valdarno Basin is located about 35 km SE of Florence between the Chianti Mountains and the Pratomagno Ridge. It consists of a main asymmetric tectonic depression filled with 550 m of Plio-Pleistocene fluvio-lacustrine deposits (Upper Valdarno Basin s.s.) and a minor basin known as the Palazzolo sub-basin. The Upper Valdarno Basinfill is made of three unconformity-bounded units, named Castelnuovo dei Sabbioni (CSB), Montevarchi (VRC), Torrente Ciuffenna (UFF) synthems, whereas the Palazzolo sub-basin fill consists of the Fosso Salceto (OLC) and Torrente Ciuffenna (UFF) synthems. The Upper Valdarno Basin formed during Late Pliocene because of the tectonic damming of a northeastward flowing drainage. The early phase of basin development is recorded by the accumulation of fluvial gravels in vallive settings, whereas the definitive of these streams damming caused the development of lacustrine conditions at about 3.1 Ma. The accumulation of deltaic sand fed from the SW margin caused the lake filling and stopped the deposition of the CSB Synthem.Before 2.58 Ma, a tectonic phase caused uplift of the basin and partial erosion of the CSB deposits. Deposition of the lower part of the VRC Synthem occurred during a marked basin broadening and accumulation of alluvial fan successions, which were capped by aeolian-reworked alluvial sand deposited at about 2.5 Ma. At about 2.3 Ma, a new deformative phase caused further basin widening, erosion along the SW margin and development of a small lake inthe central areas. Deposition of the upper part of the Montevarchi Synthem started just after this tectonic phase and was characterized by development of axial fluvial drainage and marginal alluvial fans.During the Early Pleistocene (Olduvai Subchron, 1.95-1.78 Ma) a subsidence pulse promoted development of floodplain lakes and swamps in the axial part of the basin, where thick organic-rich mud were accumulated. During late Early Pleistocene the capture of the paleo-Arno River, which started to flow into the basin, caused the development of a marked unconformity. This unconformity was covered by fluvial and alluvial fan deposit in the axial part and along the margin respectively.

The non-marine molluscs of the Plio-Pleistocene Upper Valdarno Basin (Tuscany, central Italy): depositional environments, palaeoecology and biochronology

Since the beginning of the nineteenth century, rich non-marine molluscan faunas have been recognized in the Plio-Pleistocene Upper Valdarno Basin (Tuscany, central Italy). Further research has improved the palaeoecological and biochronological meaning of these faunas, which are often associated with significant Villafranchian vertebrate remains. The Upper Valdarno Basin fill consists of four unconformity-bounded units: Castelnuovo dei Sabbioni, Montevarchi, Fosso Salceto (occurring in the Palazzolo sub-basin) and Torrente Ciuffenna synthems. Rich molluscan assemblages of alluvial and palustrine environment are recorded from the Lower Pleistocene Montevarchi Synthem deposits. Extinct and archaic freshwater gastropods and bivalves characterising the Middle and Upper Villafranchian thermophilous assemblages of intermountain basins of central Italy, such as the Plio-Pleistocene Tiberino Basin, occur. The new record of the extinct genus Neumayria [De Stefani, 1877][1] is reported. A humid-temperate climatic phase is recognized in concomitance with the major expansion of these assemblages in the Upper Valdarno Basin. The fluvial deposits of the Torrente Ciuffenna Synthem, Middle Pleistocene in age, yielded poor mixed assemblages composed of terrestrial and freshwater species. The recorded land species, represented by Pupillidae and Vertiginidae associated with a dry exposed environment, point to an arid or semiarid cool climatic phase. [1]: #ref-18

Fault-sourced alluvial fans and their interaction with axial fluvial drainage: An example from the Plio-Pleistocene Upper Valdarno Basin (Tuscany, Italy)

The present study deals with the fault-sourced, alluvial-fan deposits of the Plio-Pleistocene Upper Valdarno Basin (Northern Apennines, Italy). Different phases of alluvial fan aggradation, progradation and backstep are discussed as possible effects of the interaction among fault-generated accommodation space, sediment supply and discharge variations affecting the axial fluvial drainage. The Upper Valdarno Basin, located about 35km SE of Florence, is filled with 550m palustrine, lacustrine and alluvial deposits forming four main unconformity-bounded units (i.e. synthems). The study alluvial-fan deposits belong to the two uppermost synthems (Montevarchi and Torrente Ciuffenna synthems) and are Early to Middle Pleistocene in age. These deposits are sourced from the fault-bounded, NE margin of the basin and interfinger with axial fluvial deposits. Alluvial fan deposits of the Montevarchi Synthem consist of three main intervals: i) a lower interval, which lacks any evidence of a depositional trend and testify balance between the subsidence rate (i.e. fault activity) and the amount of sediment provided from the margin; ii) a coarsening-upward middle interval, pointing to a decrease in subsidence rate associated with an augment in sediment supply; iii) a fining-upward, upper interval (locally preserved), documenting a phase of tectonic quiescence associated with a progressive re-equilibration of the tectonically-induced morphological profile. The basin-scale unconformity, which separates the Montevarchi and Torrente Ciuffenna synthems was due to the entrance of the Arno River into the basin as consequence of a piracy. This event caused a dramatic increase in water discharge of the axial fluvial system, and its consequent embanking. Such an erosional surface started to develop in the axial areas, and propagated along the main tributaries, triggering erosion of the alluvial fan deposits. Alluvial-fan deposits of the Torrente Ciuffenna Synthem accumulated above the unconformity during a phase of tectonic quiescence, and show a fining-upward depositional trend. This trend was generated by a progressive decrease in sediment supply stemming out from upstream migration of the knickpoints developed during the embanking of the axial system.

Chapter 5 Stratigraphic methodology for the geological mapping of volcanic areas: insights from the Aeolian archipelago (southern Italy)

Abstract A stratigraphic approach to geological fieldwork and mapping of the Aeolian archipelago is performed by primarily using unconformity-bounded units (UBUs) in addition to lithosomes and classical lithostratigraphic units, which are the basic mappable units. Lithosomes are largely used to identify the localization of eruptive vents or non-volcanic source areas through time. The UBUs display an encompassing framework of correlation on a scale from local (single islands) to regional (Aeolian archipelago), by placing particular emphasis on the stratigraphic role played by Late Quaternary marine terrace deposits and widespread tephra layers (e.g. Brown Tuffs). By establishing a direct relationship between UBUs and time-stratigraphic units, the volcanic successions are readable in terms of different and successive Eruptive Epochs (separated by prolonged non-volcanic periods), which are characterized by distinctive eruptive vents and eruption types. As such, the UBUs allow the reconstruction of the main steps of geological evolution of a volcano as the result of the interplay between volcanic activity of local and external provenance, sea-level fluctuations and volcano-tectonic or regional fault lineaments.

I vulcani nella Carta Geologica d’Italia: i risultati della sperimentazione basata sull’uso di UBSU e di altre unità stratigrafiche.

Within the framework of the national Geological Mapping Project at 1:50.000 scale (CARG), since the late 1980s the Geological Survey of Italy (GSI) financed the realization of 55 sheets where volcanic deposits are present with various extensions. The main areas interested by the 1:10.000 surveys are the active volcanic districts of Etna, Vesuvius, Phlegrean Fields and Ischia island, as well as those interested by Pleistocene volcanism. Moreover, ancient volcanism of Alps and Sardinia, also covered by the surveys, contributed to renovate this geological cartography.With the aim to produce an up-to-date, useful, innovative, official Geological Map, at the beginning of the CARG Project, GSI asked to the CNR Commission for Geological Cartography and Geomorphology (CG) to edit the Guide-books for Cartography in volcanic areas (Servizio Geologico Nazionale, 1992). In particular, referring to detailed studies by Ferrrrari et alii (1989a, b), Neri et alii (1991), Calvari et alii (1994), Coltelli et alii (1994), CG indicated the Unconformity-Bounded Stratigraphic Units (UBSU) be the stratigraphic units to be used in the cartographic representation of volcanic areas. CG indeed considered UBSU the best units to reconstruct both the eruptive history of a volcano and the geometric and stratigraphic relationships between the deposits coming from other volcanic centres, as well as the significant correlations with the adjacent different depositional environments.During the work-in-progress of the CARG Project, GSI has supported the CG's Guide-lines (APAT, 2005); however this new methodology needed an experimental application on field in order to test its potentialities and limits. So, considering the necessity of some flexibility in the application during the experimental stage, GSI allowed the Authors of the maps, to diversify this methodology, in accordance with the various volcanic contexts. Now most of the maps interesting the whole case histories of Italian volcanism are almost complete and it is possible to focus the results. As a consequence, we have more knowledge of critical expects and together with the Scientific Community we can make a careful study of the problems in order to obtain mature and, as much as possible, sharing standard methodologies, both in cartography and in terminology.In this paper we show some examples of the new official cartography in volcanic areas in which the UBS units and Lithosomes have been used for the first time, together with the traditional lithostratigraphic units, through a generally integrated approach. In the realization of the CARG sheets, the Authors of the cartography of the volcanic areas used three main stratigraphic approaches. These have been analyzed in order to evidence their advantages and good results, as well as the stratigraphic problems which need some study yet, such as the criteria of lithostratigraphic formalization of volcanic units, the criteria of both hierarchical assignment to UBS units and exportability of their unconformities among different geological contexts and, finally, the use of the lithosomes in volcanic areas.In conclusion, although some questions are still open, we point out the originality of this cultural operation that involves some key question and investigation for the future prospects.

Geological map of Mount Etna West Rift (Italy)

Please click here to download the map associated with this article. Mt Etna (3340 m a.s.l.) is the most active volcano in Europe, with more than 500 ka of geological history. In this work, a detailed structural and geological field survey of its West Rift was performed at 1:10,000 scale, by using lithostratigraphic criteria and unconformity-bounded units, in accordance with guidelines suggested by the International Stratigraphic Guide. In the studied area, lithostratigraphic units have been mapped and the eruptive fissure configuration identified. Fieldwork data were improved by highresolution orthoimages and DEM analysis, producing a map with detailed lava flow boundaries. In order to synthesize the main phases of the West Rift evolution, lithostratigraphic units were grouped into synthems. The volcanic succession starts with the oldest Etna subaerial lava flows (Adrano Synthem), unconformably covered by lavas belonging to Acireale and Concazze Synthems. Mongibello volcanic succession (Il Piano Synthem) widely crops out in the area as several superposed lava flow fields. They are generated by more than 40 eruptive fissures in the past 15,000 years forming the core of the West Rift. The eruptive fissures (strike 245° to 280°) fed several monogenetic cones located in the central sector of the western flank. Some fissures were formed in the last 2,000 years. The result of this work is a geological map at 1:15,000 scale, highlighting the geological and structural setting of the area and significantly improving the knowledge of West Rift evolution, in order to better assess the entire eruptive history and structural framework of Mt Etna.

Middle to late Pleistocene coastal deposits of Alghero, northwest Sardinia (Italy): Chronology and evolution

The shallow-marine to coastal deposits of Alghero have been dated using the Optically Stimulated Luminescence (OSL) method, and studied to define the palaeoenvironmental evolution of coastal areas in northwest Sardinia. Dating, coupled with sedimentological and stratigraphical analyses, allowed the subdivision of the succession in four unconformity-bounded units (U2, U3a, U3b, U4). Unit U2 of penultimate glacial stage (MIS 6; ca. 150 ka) is composed of dune deposits formed intermittently along rocky coastal areas under strong wind conditions. Subunit U3a is composed of cliff-bounded gravelly dominated pocket beach deposits, commonly highly fossiliferous, and is assigned to the interglacial MIS 5e (ca. 125 ka). Subunit U3b is characterized by sandy beach to coastal systems of the isotopic sub-stage MIS 5c (ca. 100 ka). The unconformity between U3b and U4 marks the initiation of last glacial regression (MIS 5a/4; ca. 77 ka) during which shelf areas were exposed and small incised valleys developed. Along the valley flanks, colluvial or sheetflood sediments were deposited and, in the central part thick reddish paleosols formed. Valleys were eventually filled by thick aeolian dune deposits (MIS 4–3) indicating persistent inland sand transport. Around Alghero, coastal carbonate-rich dunes preferentially formed and migrated inland during lowstand and falling stages when the climate is relatively cold, vegetation is quite open, winds are fairly strong and sediment supply from exposed shelf areas is high.