Regional Geological Data on the Volturno Basin Filling and Its Relationship to the Massico Structure (Southern Tyrrhenian Sea, Italy)

Abstract

We built a regional geological section founded upon the assessment of a seismic line in the Volturno basin, which is situated on the northern Campania continental shelf of the Tyrrhenian margin of Southern Italy. This section has been integrated with multichannel seismic data of Zone E (ViDEPI project) to highlight its relationships with the Massico structure. In the Volturno basin, there are four Pleistocene to Holocene units, recognized based on seismic analysis lie above deep seismo-stratigraphic units, related to Campania Latium carbonate platform and The Frosinone Flysch. Onshore and offshore seismic data, calibrated with lithostratigraphic correlation, have displayed the seismo-stratigraphic framework, including both sedimentary and volcanic seismo-stratigraphic units. Of these, the lavas associated with the Northern Campania Volcanic Zone’s Villa Literno volcano are associated with seismic unit 2a. Seismo-stratigraphic data has shown the offshore prolongation of the Massico structure, as involved by normal faults and flower structures. The whole-data interpretation suggests that the tectonic activity acted in correspondence to normal faults, which have controlled half-graben and interposed structural highs, fitting to the regional geological setting of the continental margin.

1. Introduction

The half graben offshore basins of Southern Italy represent an important research topic in basin studies on the Campania continental margin and have been investigated in several previous studies [1,2,3,4,5]. Nonetheless, none of these studies have described in detail the stratigraphic relationships existing between the basin filling of the Volturno, one of the most important basins of the Campania continental margin, and the Massico structure. This study analyzes these relationships in detail, putting them in the regional stratigraphic context of the Campania–Latium continental margin, so contributing to the basin studies in Southern Italy.

A half-graben, in contrast to a full graben, is a geological structure surrounded by a fault on one side, whereas a full graben is surrounded by a series of parallel faults. Geological studies on half-graben are numerous and have considered the filling models and their relationships on the extensional basin development [6], their sedimentary models [7], the importance of low-angle normal faults in basin development [8], and the tectonic and bathymetric control factors on the stratigraphic sequences [9].

The half graben offshore basins of Southern Italy have been previously studied considering both the Naples Bay half-graben [3,10,11] and the Salerno Valley [1]. In Naples Bay, the Acerra–Dohrn canyon fault, a NE-SW-trending regional fault, had a significant stratigraphic control on the seismo-stratigraphic units, whose bathymetric and stratigraphic expression has been recently highlighted [12]. On the Campania–Latium margin, progressive changes in rifting directions have been suggested [4], following the key concepts on the Tyrrhenian basin development, including the continental break-up, the rifting phase and the expansion of oceanic lithosphere [13,14]. In the Tyrrhenian Sea, the rifting developed during classical subdivision of the basin filling in pre-rift, syn-rift, and post-rift stratigraphic sequences. Sartori et al. [14] have examined the very asymmetric stratigraphic relationships between the rifted margins of Sardinia and Campania, which were brought about by a low angle crustal detachment fault that dips eastward. According to this regional structure, the upper plate is outlined by the Campania margin and the one below it by the Sardinia margin [14].

Based on earlier research on the geology of the Tyrrhenian Sea, a regional geological section of the Volturno basin [2,3,15,16,17] has been constructed in this work using a deep multichannel profile taken during a seismic survey of the Southern Tyrrhenian Sea’s extensional regions [2,3,15,16,17]. The aim is to discuss the seismo-stratigraphic and regional geological data of the basin and its tectonic structure based on seismic data calibrated with the onshore seismic and well data in the Northern Campania Volcanic Zone (NCVZ) [18]. The stratigraphic relationships of the Volturno basin with the adjacent Massico structure have been analyzed in this paper based on the seismic data of the ViDEPI project [19], in the framework of the structural setting of the northern Campania continental margin, which is characterized by half-graben and structural highs. This is in contrast to previous papers on the same area that focused more on the seismo-stratigraphic reconstruction of the Volturno fan delta and on the recognition of a geometry that is characteristic of a fan complex, with a NE-SW-trending fault [2].

2. Geological Setting

The Gulf of Gaeta is located on the northern Campania continental margin, which is part of a large extensional Plio–Pleistocene basin associated with normal and strike-slip faults linked to the evolution of the eastern Tyrrhenian Sea margin (Figure 1). The extensional tectonics have been accompanied by an intense volcanic activity, among them originating from the volcanic area of Phlegraean Fields. On this margin, Plio–Quaternary basin (peri-Tyrrhenian basins) [20], including the Terracina and Gaeta basins, the Capri basin, the Naples Bay, the Salerno Valley, and the Sapri and Paola basins, are located. Below the Plio–Quaternary basin filling, the stratigraphy of the margin shows the seawards extension of the inner tectonic units of the Southern Apennines [21,22,23] (Figure 1).

The neotectonic phases that influence the tectonic uplift of the Southern Apennines commenced in the Early Pliocene and persisted through various extensional phases until the Middle to Late Pleistocene. The Quaternary marine and continental sedimentation in the Campania coastal plains, which is significantly affected by the tectonic uplift of the Southern Apennines, is characterized by considerable thickness and is frequently composed of cycles of transgressive and regressive facies [2,3,24,25,26,27].

The Campania margin’s half-graben and the intervening structural highs were formed as a result of two extensional phases that occurred during the Pleistocene. The initial phase took place in the Early Pleistocene and was characterized by NW-SE normal faults, which influenced the development of coastal depressions such as the Campania, Sele, and Volturno Plains. The subsequent phase, occurring at the transition between the Early and Middle Pleistocene, was associated with an NE-SW fault system and played a significant role in the formation of Naples Bay, leading to the development of asymmetrical structures typical of half-graben formations throughout the margin [2,3,5,28,29].

The structural setting of the Campania–Latium continental margin is characterized by structural highs and interposed basins occurring to a regional scale [2,3,5,30,31] (Figure 2). Its tectonic setting is characterized by regional normal faults, from NE-SW to NNE-SSW trending. The Massico Mount constitutes a structural elevation situated along normal faults that trend from northeast to southwest, effectively distinguishing this horst from the coastal depressions of the Garigliano and Volturno plains [32,33,34]. The down throwing of the coastal structures has been identified based on onshore and offshore seismic interpretation [2,3,32,33].

Since the Late Miocene, the Campania Plain has been significantly influenced by extensive volcanic activity. This activity, particularly along the western edge, is closely associated with NE-SW normal faults [18,35]. The volcanic deposits in this region can be categorized into two distinct cycles: the older cycle, which spans from the Miocene to the Pleistocene, consists of calcalkaline, andesitic, and basaltic lavas, represented by the Parete and Villa Literno volcanic complexes. The younger cycle is characterized by alkaline-potassic deposits and is linked to the Plio–Pleistocene extensional tectonics of the Roman co-magmatic province, which includes notable features such as Vesuvius and Campi Flegrei. Significant layers of lavas and pyroclastic materials, dating back approximately 2 million years, have been identified at the Villa Literno 2 and Parete 2 wells [2,3].

In the Northern Campania Volcanic Zone (NCVZ, the stratigraphic data obtained from 600 boreholes have allowed to construct geological sections, showing the stratigraphic architecture of the ignimbrite deposits (Figure 3 [18]. The lowermost unit is made up of marine sediments (Tyrrhenian Layer M1), whose top has been dated back at 126 ky B.P. (Figure 3) [36]. A volcanic sequence overlies the marine deposits and is constituted of massive ignimbrite deposits and lava flows. This unit is overlain by another succession of marine deposits, dated back at 55–50 ky (Tyrrhenian unit M2) [36], which is surrounded by the Campanian Ignimbrite (CI) deposits. The NYT caldera is the preeminent volcano-tectonic lineament of the intermediate Campania Volcanic Zone (CVZ; Figure 3) [18].

3. Materials and Methods

The application of a multichannel profile within the Volturno basin facilitated the development of an interpreted geological section that illustrates the stratigraphic connections among the seismo-stratigraphic units, which were previously delineated using seismo-stratigraphic criteria. The seismic profile reveals the geological framework and subsurface structure of the area under investigation, emphasizing the stratigraphic relationships between the acoustic basement and the sedimentary infill of the basin. The multichannel seismic profiles of the ViDEPI project (

Table 1. Characteristics of the seismic profiles of the Zone E (ViDEPI Project) [19].

Seismic Grid	Seismic Profile	Location
Zone E	E194	Volturno river mouth
Zone E	E196	Cuma offshore
Zone E	E198	Cuma offshore
Zone E	E200	Monte di Procida promontory
Zone E	E101SR, E109	Campania–Latium continental margin

) [19], recorded from the Western Geophysical Company (Missouri City, TX, USA), and the well lithostratigraphic data have integrated the seismic dataset. Following Italy’s Minister of Industry’s pledge to conduct a regional survey of the entire Eastern Tyrrhenian continental shelf, the Western Co. seismic grid was purchased in 1968 [19]. An Aquapulse energy source, 24-trace and 1600-m-long streamer, 2 ms sample rate, 68 m shot and group interval, 10–80 Hz filter, and a recorded length of 4 s were used to obtain these seismic data.

Seismo-stratigraphic techniques and methods have been employed for the geologic interpretation of seismic data and related stratigraphic analysis. The analysis of seismo-stratigraphy relies on recognizing regional unconformities, which in turn allows for the identification of depositional sequences. This process aids in reconstructing the original geometry of sedimentary bodies and their associated environments, as well as facilitating chrono-stratigraphic correlation. High-resolution seismic techniques and sequence stratigraphy have been thoroughly detailed as effective methods for analyzing seismic profiles and these approaches have been applied in the geological interpretation of such profiles [37,38,39,40,41,42,43].

Data processing was carried out using specialized software (Promax 2D; Landmark Ltd. (Esher, UK) and Seismic Unix SU44R28). These methods rely on complex mathematical models, enabling us to effectively reduce the impact of multiples (specifically the seabed multiples) and to achieve accurate velocity assessments in generating stacked sections for the geological interpretation. A table was constructed to display the acquisition parameters of the multi-channel seismic survey (

Table 2. Acquisition parameters of the multichannel seismic survey.

Seismic Source	n. 2 Guns GI Gun SI/Sodera (210 c.i.)
Length of the seismogram	5 s
Sampling interval	1 ms
Source distance	25 m
Hydrophone distance	12.5 m

).

The first step involved checking the quality of the data and setting up the field geometry. The purpose of editing the seismic traces was to uncover any seismic traces and spikes within the traces that could cause issues with the Fast Fourier Transform (FFT). A high-level muting was able to remove the seismic signal after the initial seismic arrivals in the seismic traces. Automatic Gain Control (AGC) enabled seismic traces to be normalized. The data processing focused on decreasing the random interference in the seismic data and enhancing the clarity of the seismic waves using deconvolution and spiking techniques.

A velocity analysis was carried out to correct the move-out of the CDP (Common Depth Point) groups, calculating the velocity of various seismic reflectors and generating a final stacked seismic section. Post-stack deconvolution was carried out to eliminate the multiple arrivals. Following deconvolution, a bandpass filter was utilized to boost the seismic signal present along the seismic section.

4. Results

4.1. Seismic Interpretation

The seismic interpretation was carried out using seismo-stratigraphic methods, which enabled the identification of various seismic units (Figure 4 and Figure 5). The lithology of the seismic units was correlated with onshore seismic sections and well lithostratigraphic data.

The lower seismic layer is distinguished by intermittent reflectors with varying amplitudes. The seismic unit’s top is found at depths ranging from 1650 m to 2025 m. Some normal faults lower this unit, with dips measuring in the range of tens of meters (Figure 5). The Meso–Cenozoic carbonate unit, identified as MC in Figure 5, is genetically related with the Campania-Lucania carbonate platform, outcropping in the adjacent sectors of the Southern Apennines [21,22,23].

The seismic layer in question is characterized by a seismic facies that exhibits acoustic transparency and is marked by a limited number of dispersed seismic reflectors. The upper boundary of this seismic unit is found at depths between 1050 m and 1350 m, with an average thickness of approximately 750 m. The presence of normal faults has resulted in a downward displacement of the continuous reflector that defines the top of the seismic unit by several tens of meters. This unit is classified as part of the Frosinone Flysch Auct. (FLS in Figure 5) and is associated with the Miocene flysch deposits of the Central Apennines. Its identification has been substantiated through both outcrop investigations and prior seismic surveys conducted in the Volturno offshore region [2,30].

The FLS unit is covered by two distinct seismo-stratigraphic units characterized by facies heterogeneity, one of which is volcanic and the other sedimentary. The volcanic unit, referred to as VC (Figure 5), is wedge-shaped and has been identified as the volcanic deposits associated with the Villa Literno volcanic complex [2,24,25]. This VC unit typically exhibits a thickness of approximately 600 m. Among the oldest volcanic deposits found in the Campania Plain are basalts and andesites, including basaltic lavas that date back 2 million years. These volcanic materials were collected in the Parete-Villa Literno region during geothermal drilling activities [24,25]. The initial unit of the Volturno basin fill (1 in Figure 5) corresponds to the sedimentary unit associated with the VC volcanic complex, with its upper boundary situated at depths between 1050 m and 1125 m.

The VC and 1 seismo-stratigraphic units are overlain by two distinct seismo-stratigraphic units (2a and 2b in Figure 5). The seismo-stratigraphic unit 2b was interpreted as an ancient prograding wedge, down lapping on the volcanic deposits of the VC unit. Moving towards the basin, it passes into the seismo-stratigraphic unit 2a, which is the second unit of the basin filling. The seismo-stratigraphic unit 3 (Figure 4 and Figure 5) is marked by high amplitude like nearly parallel seismic reflectors and is probably composed of alternating sands and clays of a deltaic environment, Pleistocene in age [33]. The seismo-stratigraphic unit 4 (Figure 4 and Figure 5) is characterized by parallel to almost parallel, discontinuous to continuous seismic reflections and has been interpreted as clays deposited in a Pleistocene coastal environment [33].

Some significant seismic profiles pertaining to the ViDEPI project [19] have been analyzed (Figure 6, Figure 7 and Figure 8). The seismic profile E101SR has shown seismo-stratigraphic units and fault trends down throwing the Meso–Cenozoic carbonates (Figure 6). The fault intersections have shown the offshore prolongation of the Massico Mt. structure. A horst has been identified, involving the seismo-stratigraphic unit correlated with the Meso–Cenozoic carbonate deposits (Figure 6 and Figure 7). Proceeding southwards, an anticline has been identified, interpreted as a positive flower structure (Figure 6). The seismo-stratigraphic 2 is characterized by discontinuous seismic reflectors and has been correlated with the Miocene flysch deposits (“Flysch di Frosinone” Auct.), outcropping in the adjacent onshore areas. An Early Pleistocene progradational unit has been recognized (unit 3a in Figure 6), representing the Volturno submerged fan. The seismo-stratigraphic unit 3b has been interpreted as Middle–Late Pleistocene marine and coastal deposits and is characterized by discontinuous and sub-parallel seismic reflectors (Figure 6), whilst the 4 one as Late Pleistocene–Holocene marine and coastal deposits.

Detailed seismic sections are provided here, showing the previously mentioned structural location and where faults intersect near the Massico structure (Figure 7 and Figure 8). Figure 7 displays the Massico horst formation, interpreted on detailed seismic profile E101 SR, where the same seismo-stratigraphic units shown in Figure 6 have been identified. Figure 8 highlights the occurrence of flower structures at the top of the Meso–Cenozoic carbonate acoustic basement.

4.2. Stratigraphic Correlation of Well Lithostratigraphic Data

A stratigraphic correlation has been established to compare the rock layers from well data drilled in the Volturno Plain with those from the offshore Phlegrean Fields (Figure 9). This correlation illustrates the distribution and thickness of pyroclastic and alluvial sediments in relation to the lavas, specifically andesites and basalts, associated with the Villa Literno volcanic complex (VC seismo-stratigraphic unit depicted in Figure 5).

Two primary categories of geological formations have been identified: pyroclastic and alluvial deposits, which constitute the sedimentary material within the Volturno Plain, alongside the volcanic lavas (andesites and basalts) originating from the Villa Literno volcanic complex. The lavas exhibit their minimum thickness at the Castelvolturno 1 and Castelvolturno 3 wells, where these deposits are located at depths of 1525 m and 1870 m, respectively (Figure 9).

A stratigraphic correlation has been conducted for the wells Castelvolturno 2, Grazzanise 1, Qualiano 1, Villa Literno 1, and Parete 2 (see Figure 9). The highest occurrence of volcanic materials was identified at depths of 600 m in Castelvolturno 2, 720 m in Grazzanise 1, 470 m in Qualiano 1, 830 m in Villa Literno 1, and 230 m in Parete 2. Notably, the thickness of the volcanic deposits exhibits an increasing trend when moving from Castelvolturno towards the towns of Parete and Villa Literno (refer to Figure 9).

The Castelvolturno 1 and Castelvolturno 3 wells have revealed sedimentary layers that transition from marine to terrestrial environments, extending to a depth of 3000 m (see Figure 9). Within these sedimentary sequences, two volcanic strata have been identified, located at depths of 1430 and 1450 m in Castelvolturno 1 and between 1800 and 1830 m in Castelvolturno 3.

At the Castelvolturno 2, Grazzanise 1, and Qualiano 1 wells, there is an observed increase in the thickness of the lava layers, which are interbedded with sand and shale deposits. The depths at which these lava formations have been encountered are 475 m, 720 m, and 500 m, respectively (see Figure 9).

At the Villa Literno 1 well, a sequence of 150 m of andesitic tuffs is situated beneath the overlying recent pyroclastic deposits. This is succeeded by 650 m of clastic deposits formed in a marine and transitional setting, along with interbedded layers of tuffs, basalts, and andesites extending from 830 m to 2980 m (Figure 9).

At the Parete 2 well, the initial 300 m consist of recent pyroclastic materials interspersed with clastic deposits. Below this layer, a sequence of alternating basaltic and andesitic lavas extends to the well’s total depth of 1800 m.

It is also important to consider in the calibration of the seismic section is the lithostratigraphic data from Mondragone 1 well. These lithostratigraphic data are crucial for the geological interpretation of the deep seismo-stratigraphic units, respectively related to the Miocene flysch deposits and to the Meso–Cenozoic carbonate acoustic basement. The Mondragone 1 well was drilled to a depth of 675 m, penetrating Quaternary deposits consisting primarily of sandy materials with volcanic components and conglomerates mixed with layers of marls (Figure 10) [44]. At depths shallower than 675 m, the well has penetrated Miocene formations, which consist of conglomerates, sandstones, and marly sandstones (Figure 10). These successions have been interpreted as post-evaporitic and interpreted in the context of the late Messinian Lago–Mare episode in the central Mediterranean Sea (Figure 10).

4.3. Calibration of the Seismic Section with the Well Data

The initial group of geological characteristics serves as a reference for calibrating the analyzed seismic data (Figure 9). The association of pyroclastic and alluvial deposits with seismo-stratigraphic units 2a, 3, and 4 elucidates the sedimentary history of the basin in the marine environment adjacent to the Volturno plain. Utilizing these significant indicators allows researchers to acquire important understanding of the geological development of the region.

The volcanic lavas, specifically andesites and basalts, originating from the Villa Literno volcanic complex (refer to Figure 9), are associated with seismic-stratigraphic unit 2a (illustrated in Figure 4 and Figure 5). The stratigraphic connections between the Villa Literno volcanic complex and the neighboring ignimbrites are depicted in Figure 3 (lower geological section).

The lithostratigraphic analysis of the Mondragone 1 well (Figure 10) suggests that the FLS unit, identified as Miocene flysch deposits, is likely comprised of a sequence of alternating shales, sandstones, conglomerates, and marly limestones. These deposits are genetically associated with the Flysch di Frosinone Auct. [21,22,23].

Geological data reveal that the ancient carbonate bedrock beneath the Campania Plain significantly deepens westward, reaching depths over 3 km. This bedrock dates back from the Miocene to the Quaternary, as confirmed by nearby oil wells (Mondragone 1 well; Figure 10). Interestingly, the Castelvolturno 1 well has uncovered Quaternary deposits extending down to 3 km, suggesting the presence of the older Miocene sequence underneath. This intriguing finding opens possibilities for further exploration and understanding of the region’s complex geological history.

5. Discussion

The seismo-stratigraphic data shown in the Volturno basin have confirmed that it represents a half-graben characterized by blocks down thrown by normal faults, mainly involving the top of the Miocene siliciclastic sequences (Figure 4 and Figure 5). The activity period of normal faults probably ranges between the end of the Late Miocene and the Early Pleistocene. Moreover, the basal seismic sequence (1 in Figure 5) has shown wedging geometries, suggesting that this unit represents a synsedimentary sequence.

The volcanic deposits in the Campania offshore exhibit a notable distinction from other sedimentary basins, as they are significantly developed and interspersed within the sedimentary fill of the basin (see Figure 5 and Figure 9). This phenomenon is exemplified by the volcanic body associated with the Villa Literno volcanic complex, which is identifiable in the interpreted seismic section (denoted as VC in Figure 5) and is correlated with the Quaternary volcanic materials encountered in the Villa Literno 1 and Parete 2 wells, with their stratigraphic relationships illustrated in Figure 9. It appears that the formation of the VC volcanic body occurred subsequent to the extensional activities within the Volturno basin. The presence of normal faults likely provided preferential conduits for the magmatic ascent associated with the VC volcanic complex.

Four distinct seismo-stratigraphic units, which align with the seismic units identified onshore [33,44], have been delineated within the Volturno basin. This classification is based on a comprehensive seismo-stratigraphic analysis of multichannel seismic profiles, with particular emphasis on the stratigraphic interactions with the Massico horst (Figure 6, Figure 7 and Figure 8). The lithological characteristics of these units have been validated through the examination of lithostratigraphic well data (Figure 9).

The initial seismo-stratigraphic unit (1 in Figure 5) is distinguished by reflectors that range from discontinuous to continuous, exhibiting both parallel and sub-parallel orientations. This unit comprises a mixture of sands, conglomerates, and shales, interspersed with pyroclastic layers, and is dated to the Early Pleistocene. This unit onlaps the side of the VC volcanic seismo-stratigraphic unit, correlating to the volcanites genetically related with the Villa Literno volcanic complex (Figure 5). The seismo-stratigraphic unit 1 is synsedimentary, as suggested by the wedging geometries observed in this unit. Similar geometries have been observed in the correlative seismic units observed onshore [33,44]. The seismo-stratigraphic data indicate that the VC volcanic unit predates the deposition of seismo-stratigraphic unit 1. This conclusion is supported by the observed onlap of unit 1 onto the concealed side of the volcanic formations, as illustrated in Figure 4 and Figure 5.

The second seismo-stratigraphic unit (2 in Figure 5) is subdivided into two primary sub-units, which are designated as occurring on the continental shelf (2a in Figure 5) and within the basin (2b in Figure 5). Sub-unit 2a is distinguished by its prograding clinoforms and is indicative of a relict prograding wedge that overlays the VC volcanic complex. In contrast, sub-unit 2b is characterized by parallel to sub-parallel reflectors and consists of alternating layers of sands and shales, indicative of a deltaic environment and dating back to the Pleistocene.

The third seismo-stratigraphic unit (3 in Figure 5) is distinguished by high-amplitude reflectors that are arranged in parallel to sub-parallel configurations. This unit consists of a succession of sands and shales indicative of a deltaic setting. In contrast, the fourth seismic sequence exhibits reflectors that range from discontinuous to continuous, maintaining a parallel to sub-parallel orientation. This sequence is primarily composed of shales that are characteristic of a coastal environment and date back to the Pleistocene.

This half-graben structure has been confirmed by the seismic profiles recorded onshore in the Garigliano plain (Figure 11) [44]. Four distinct seismic sequences can be identified by the seismic stratigraphic interpretation of these lines. Throughout the examined seismic lines, the topmost seismic horizon (horizon Q) can be easily traced; it separates the topmost seismic sequence (sequence I) from sequence II. Sequence I, the highest seismic sequence, is distinguished by irregular reflections that vary in amplitude and are occasionally parallel. Sand and clayey-sand alternate and pebbles and conglomerates (Upper Pleistocene–Holocene) are frequently intercalated. It correlates to the SP interval D. Four seismic units (U1, U2, U3, and U4 in Figure 11) have been identified within the sequence II. The external form of these seismic units is wedge-shaped at the basin scale, exhibiting an increase in thickness toward the southeast, which must be connected to the extensional syn-sedimentary activity of the fault separating the Massico Mount from the northwest. This trend of faults can be seen also offshore in the interpreted seismic profiles of Zone E (Figure 6, Figure 7 and Figure 8).

The recorded stratigraphic architecture has shown that the tectonic controls are prevalent on the eustatic ones. Normal faults have controlled the individuation of the half-graben structures and downthrown the deep seismo-stratigraphic units (Figure 5). Tectonic control prevailed on the eustatic one also regarding the first seismo-stratigraphic unit, clearly showing wedging geometries and suggesting its synsedimentary nature (Figure 5). This is in overall agreement with the previous papers in the same area, suggesting wedging geometries and synsedimentary tectonics of the seismo-stratigraphic units onshore both in the Volturno and Mondragone areas [33,44]. (Figure 11).

On the other hand, eustatic controls are prevalent in the younger seismo-stratigraphic units, where progradational geometries may have been deposited during eustatic sea-level falls, controlling phases of forced regressions [45]. This is true for the seismo-stratigraphic unit 2b, overlying the Villa Literno volcanic complex (Figure 5). A progressive deepening of the area, coupled with subsidence is suggested by the depositional geometries observed in the other seismo-stratigraphic units, where onlap geometries on both the sides of the basin prevail (Figure 5).

6. Conclusions

• A geological cross-section of the Volturno basin has been developed through the geological analysis of multichannel seismic profiles. This analysis has been combined with the multichannel seismic data from the ViDEPI project to illustrate the connections between the Volturno basin and the Massico structure.
• The seismo-stratigraphic analysis has shown four seismo-stratigraphic units, Pleistocene to Holocene in age, overlying deep seismo-stratigraphic units genetically related to the Campania–Latium carbonate platform and to the Frosinone Flysch. While the deep seismo-stratigraphic units and the first unit of the basin filling are mainly tectonically-controlled, the depositional geometries of the basin filling suggest that the eustatic controls are prevalent from the Late Pleistocene to the Holocene.
• Important volcanic seismo-stratigraphic units are interlayered in the Volturno basin filling, including the Villa Literno volcanic complex (VC), which can be framed in the volcanological evolution of the ignimbrites of the Northern Campania Volcanic Zone (NCVZ).
• Seismo-stratigraphic data have shown the offshore prolongation of the Massico structure, as involved by normal faults and flower structures, which suggest the occurrence of basin inversion in the area, according to previous literature data on the Eastern Tyrrhenian margin.
• Future tasks of this study will include further seismo-stratigraphic interpretation in the adjacent marine areas of the Eastern Tyrrhenian margin to provide detailed seismo-stratigraphic study of the half-graben offshore basins of Southern Italy.