Alessandro Iannace

Triassic continental rifting of Pangaea: direct evidence from the Alpujarride carbonates, Betic Cordillera, SE Spain

Abstract: Evidence is presented for Triassic rift-related palaeo-structures from the Alpujarride Complex carbonates of the Betic Cordillera, SE Spain. Direct evidence of synsedimentary extensional tectonics is provided by macro- to meso-scale normal faults overstepped by younger strata. Most faults define domino-like horst and graben structures. The faults are associated with an expanded synrift sedimentary prism in which soft-sediment deformation, gravity-flow deposits and unconformities are widely developed. Syntectonic mafic igneous intrusions also occur. The age of this phase of extension is constrained as Ladinian–Carnian (c. 237–216 Ma). From a palaeogeographical standpoint, the thick Triassic carbonates of the Betic Internal Zone, together with comparable successions in Northern Calabria (Southern Apennines), occupied a belt with elevated subsidence connecting the Neo-Tethys to the east with the eastern North American intracontinental rift system to the west. Their carbonate facies, intermediate between classical Alpine- and Germanic-type Triassic facies, recorded the main episodes of rifting affecting Central Pangaea.

Platform margins, microbial/serpulids bioconstructions and slope-to-basin sediments in the Upper Triassic of the ‘Verbicaro Unit’ (Lucania and Calabria, southern Italy)

SummaryThe Upper Triassic carbonates of the area comprised between Maratea (Lucania) and Praia a Mare (Calabria) have been studied. They have been grouped into six facies assemblages which, in turn, define two depositional systems.1)a platform margin depositional system, comprising algae-bivalves-bearing dolomites (A1), Megalodontid-bearing limestones and dolomites (A2), dololutites and stromatolitic/bioclastic dolomites. (A3);2)a slope to basin depositional system comprising: buildup-facies, talus breccia and coarse to fine doloarenites (B1), coarse to fine doloarenites and dark laminated dololutites (B2), dark laminated dololutites (B3). The algal and bivalve dolomites represent typical peritidal platform sediments arranged in cyclical patterns formed as shoal barrier and back-reef deposits periodically emerged and deformed in tepee structures.The outer margin of the platform was colonised by peculiar bioconstructions dominated by microbialites and serpulids; little sponges occur less frequently, whereas rare corals have been found only in some turbiditic beds.Along the slope, in a distance that can be estimated in 5 or 6 km, the coarse breccias give way to coarse turbidites, then finer turbidites and finally to dark, organic-rich micrites. Most of the floatstone and associated turbidites imply a fault- controlled slope. The laminated texture and the high O.M. (Organic Matter) content of the latter facies quite obviously point to a basin with poorly oxygenated bottom waters.In the uppermost Triassic there is an indication of a regressive trend, evidenced by the progradation of the platform facies. At that time a back-reef area was characterised by Megalodontid prairies alternated to areas of sandy bioclastic transport. However, due to the poor biostratigraphic record and intense cataclasis, no definite evidence of a well-structured Rhaetian platform margin with buildups and related basinal sediments exists.These sedimentary and paleoecological features match well with those found in the intraplatform basins of the Dolomia Principale, as well as with other coeval facies in Southern Apennines, Central Apennines, Southern Alps and in Southern Spain. Altogether, this evidence suggests that in the Norian time both Southern Alps and Apennines experienced a very similar tectonic evolution and comparable paleoceanographic conditions, characterised by the formation of numerous intraplatform throughs with restricted circulation, the latter influencing the bottom conditions as well as the marginal communities. The margins of these restricted basins, differently from the typical Dachstein reefs of the Upper Triassic Tethys, were dominated by microbial-serpulid communities.

Facies and early dolomitization in Upper Albian shallow-water carbonates of the southern Apennines (Italy): paleotectonic and paleoclimatic implications

Thick successions of Cretaceous carbonates in the southern Apennines of Italy are of great economic interest since they host important aquifers and huge hydrocarbon accumulations. The reservoir of the Val d’Agri and Tempa Rossa oilfields (in the subsurface of Basilicata) consists of Upper Cretaceous rudist-rich limestones passing downward into mid-Cretaceous dolomitized limestones of restricted platform facies. Upper Albian-Lower Cenomanian dolomitized carbonates exposed in the Sorrento Peninsula and in the Cilento Promontory, part of the Apennine Carbonate Platform, represent a good surface analogue for the lower part of the reservoir. They are composed of meter-thick beds of stratabound dolomite and shallowing-upward cycles of restricted platform limestones capped by silicified evaporites and marly levels. Field relations, petrography, and geochemistry implicate the reflux of penesaline waters as the most probable dolomitization process. High-frequency climatic variability between dry and wet phases can explain the formation of evaporites, which are coeval with karstic bauxites in other sectors of the southern Apennines. The dolomitized carbonates of the Sorrento Peninsula pass laterally into dolomitized breccias, which were the result of local tectonic collapse of the platform. This is further evidence of mid-Cretaceous syn-sedimentary tectonics that in other areas of the Adria passive margin contributed to the formation of intraplatform basins where source rocks accumulated.

The Ladinian-Carnian reef facies of Monte Caramolo (Calabria, Southern Italy)

SummaryIn the Triassic of the San Donato Unit (Calabrian Apennines, Italy) a perireefal facies association of limestones and dolomites, hosting a Ladino- (?Carnian) fauna, has been recognized. This facies association is flanked by black, ostracod-bearing, calcareous marbles and evolves to peritidal dolomites, Carnian and possibly Norian in age, characterized by strong synsedimentary tectonics.The San Donato Unit has been strongly affected by alpine tectonics, resulting in pervasive deformation and metamorphic recrystallization (greenschist facies); nevertheless, careful observation on selected outcrops enabled the distinction of the following main facies:-Sponges-biogenic crusts-cement boundstone;-Reef debris rudstone;-Dasycladacean packstone-grainstone. The boundstone facies contains Sphinctozoa, biogenic crusts,Tubiphytes and minor Problematica. Inter-reefal sediments host micropeloids and rare Foraminifera. Multigeneration cements are very abundant, as radial-fibrous botryoids followed by isopachous crusts of recrystallized fibrous calcite. Among the typical building organisms should be mentioned:Colospongia catenulata catenulataOtt,Solenolmia manon manon (Münster),Uvanella irregularisOtt etc. Rare corals and isolated concentrations or whole colonies of (?)Holocoelia toulaiSteinmann are also present. The boundstone facies corresponds to deposits in various environments of a well developed reef area.The reef-debris rudstone is by far the most widespread facies. The reef detritus carry the same fauna mentioned previously. We noticed here, however, an increase in echinoderm fragments and a larger abundance ofHolocoelia fragments. The cements between the clasts are prevailingly of the isopachous and blocky types. This facies quite obviously represents the resedimentation of reworked buildups in a fore-recf environment.The Dasycladacean (Teutloporella herculea (Stoppani)) packstone/grainstone facies is relatively scarce. It sometimes contains laminated fenestrae and fibrous, isopachous cements have been often observed. This facies is interpreted as a back reef deposit because of its textural characters and for the presence ofTeutloporella herculea (Stoppani).In the basal part of the sequence grey marble with dasycladaceans ghosts occur, bearing evidence ofin situ brecciation. The whole facies succession records a regressive trend and can be interpreted as the progradation of a platform and its marginal buildups over a preexisting carbonate ramp. The overlying Scifarello tidal dolomites represent the apex of the progradational, shallowing upward trend.Compared with the reefoidal facies so far described in Southern Italy, along the margin of the Lagonegro Basin, the reef facies of Monte Caramolo record a shallower and higher energy depositional environment with no silicoclastic input. In fact, the Monte Caramolo reef association bear many affinities to the Wettersteinkalk equivalents occurring in the Northern Calcareous Alps; the Caramolo buildups probably developed as a true ecological barrier between a restricted lagoon and a yet undefined basin.

Subduction and continental collision events in the southern Apennines: constraints from two crustal cross-sections

Subduzione e collisione continentale in Appennino meridionale: vincoli da due sezioni crostali.Mediante l’integrazione di dati geologici di superficie e sottosuolo, sono state realizzate due sezioni crostali attraverso il sistema catena-avanfossa-avampaese dell’Appennino meridionale. Di tali sezioni, quella settentrionale e stata elaborata dall’interpretazione del profilo sismico a riflessione CROP 04, mentre quella meridionale attraversa i giacimenti petroliferi della Val d’Agri e di Tempa Rossa, in Basilicata. Le due sezioni mostrano la presenza, nel sottosuolo del Cilento, di unita di basamento continentale coinvolte nella strutturazione della catena appenninica. Queste evidenze suggeriscono che, dopo l’iniziale fase di subduzione oceanica, l’evoluzione tettonica dell’Appennino meridionale e stata caratterizzata da due eventi di subduzione continentale alternati a due stadi di collisione continentale.

Dolomitization impact on fracture density in pelagic carbonates: contrasting case studies from the Gargano Promontory and the Southern Apennines (Italy)

The results of combined field and laboratory analyses carried out in well bedded, partly dolomitized successions of Mesozoic pelagic carbonates outcropping in the Gargano Promontory and Southern Apennines (Italy), revealed that dolomitization can exert opposite roles in modulating fracture density of carbonate successions.The coarsely crystalline dolomites of the Gargano Promontory, which are characterized by planar-S to planar-E textures and some intercrystalline porosity (3.6-18.4%), are less densely affected by stratabound fractures (mostly joints) than the precursor micritic limestones. In contrast, the finer-crystalline, no porous dolomites outcropping in the Southern Apennines, which are dominated by non-planar-A textures, are more densely fractured than the precursor micritic limestones. Therefore, intrinsic textural parameters of dolomites, such as crystal size, texture and porosity played a prominent role in modulating stratabound fracture density. In addition, dolomites of the Gargano Promontory are thicker bedded than the precursor limestone beds due to their diagenetic homogenization, which is enhanced by absence of strongly stylolitized bed surfaces and marly interlayers. This contributed to reduce the overall density of the stratabound fractures formed later.As density of stratabound fractures is considered a prominent factor affecting the large-scale porosity of carbonate rocks, the results of this study provide new insights on how dolomitization may either increase or reduce the quality of fractured reservoirs of geofluids through its multiple controls on density of such fractures.

A new dasycladalean alga from the Middle Triassic carbonates of Northern Calabria (Southern Italy)

SummaryA new dasyclad alga—Acicularia boniae n.sp.—is discribed from Middle Triassic (?Ladinian) of the Piano del Minatore Formation, outcropping in the Cozzo del Pellegrino area (Calabria, southern Italy). The systematic position of this species, with respect to the genusAcicularia and morphogeneraAciculella andTerquemella, is discussed.RiassuntoViene descritta una nuova specie di dasicladale—Acicularia boniae—proveniente dal Triassico Medio della formazione del Piano del Minatore affiorante nel massiccio del Cozzo del Pellegrino (Calabria, Italia meridionale). Viene discussa la posizione sistematica rispetto al genereAcicularia ed ai morfogeneriTerquemella edAciculella.

The Triassic platform of the Gador-Turon unit (Alpujarride complex, Betic Cordillera, southeast Spain): climate versus tectonic factors controlling platform architecture

A litho-biostratigraphic analysis has been carried out in the Gador-Turon unit of the Sierra de Gador (Alpujarride complex, Betic Cordillera, SE Spain). The Triassic succession of this unit is composed of a lower meta-detrital formation overlain by an upper meta-carbonate formation divided in six members. In the latter, a Ladinian–Carnian-rich fossil association has been found (foraminifers, algae, bivalves, microproblematica, trace fossils). Facies analysis has enabled the recognition of 22 facies of platform origin. This succession accumulated as a subsiding margin-type carbonate platform with homoclinal ramp geometry (Anisian?–Ladinian) evolving into a fault-block-type platform with a steeper-margined geometry (Ladinian–Carnian). Slope deposits of this latter platform show a prism-like geometry with progradational patterns and include syn-sedimentary structures associated with normal faults capped by younger beds. The results of the present research indicate that the architecture of the platform studied has been controlled mainly by climate and oceanic factors during the development of the ramp, and by syn-sedimentary extensional tectonics during the development of the steeper-margined platform. The Ladinian–Carnian tectonic activity was probably also responsible for the siliciclastic input and the shift to a mixed terrigenous-carbonate platform.

The role of stratabound fractures for fluid migration pathways and storage in well-bedded carbonates

Fracture analysis, carried out on two reservoir analogues cropping out at Faito and Chianello Mts. (southern Italy) allowed us to unravel the role of stratabound joint networks for oil migration and storage within well-bedded carbonate successions. The fracture regression analysis pointed out that stratabound fracture aperture increases as a function of bed thickness according to a linear law, independently by the lithological characteristics of the analyzed rock. Furthermore, statistical results suggest that fracture aperture and spacing exhibit, for each bed thickness value, a lognormal probability distribution. The estimation of the stratabound fracture porosity allowed us to identify, in well-bedded sedimentary successions, three classes of multilayer packages: ( i ) thin beds, characterized by a dual role of permeable pathways and oil storage systems; ( ii ) medium sized beds, showing limited permeability and porosity values and ( iii ) thick beds, acting as highly permeable pathways and showing a negligible storage capacity. Our results permit a full characterization and modeling of stratabound fracture networks. In particular, they provide a powerful tool for predicting preferential fluid pathways and major oil storage systems based on bed thickness data, within the framework of an analysis that may be further enhanced by the integration of petrophysics data.

Multiscale Fracture Analysis in a Reservoir-Scale Carbonate Platform Exposure (Sorrento Peninsula, Italy): Implications for Fluid Flow

We derive the discrete fracture network (DFN) of a Lower Cretaceous carbonate platform succession exposed at Mt. Faito (Southern Apennines), which represents a good outcrop analogue of the coeval productive units of the buried Apulian Platform in the Basilicata oilfields. A stochastic distribution of joints has been derived by sampling at two different scales of observation. At the outcrop scale, we measured fracture attributes by means of scan lines. At a larger scale, we extracted fracture attributes from a 3D model. This multiscale survey showed the occurrence of an arresting bed for through-going fractures, which is characterized by a low relative permeability, determining a vertical compartmentalization. The DFN model, obtained by integrating fieldwork and numerical modelling by means of the 3D-Move® software, shows a well-defined relationship of permeability and fracture porosity with the relative connectivity of the fracture network. The latter is influenced by the length and aperture and to a lesser extent by the fracture intensity. The permeability distribution obtained for our outcrop analogue can be used to inform modelling of the Basilicata oilfield reservoirs, although the different burial history between the exposed Apennine Platform and the buried Apulian Platform must be taken into account.