Discussion of the paper

Aldinucci, M., Gandin, A. & Sandrelli, F. (2008): The Mesozoic continental rifting in the Mediterranean area: insights from the Verrucano tectofacies of Southern Tuscany (Northern Apennines, Italy). In: International Journal of Earth Sciences (Geologische Rundschau), vol. 97, pp. 1247-1269, Springer Verlag.

I regard it as necessary to comment the paper mentioned above, because I think that some facts stated there should better be rectificated.

I also studied geological formations at the stratigraphic base of the Tuscan Domain, which are interpreted in that paper as indicative of initial (middle Triassic) rifting between Adria and Europe-Corsosardinia. My comments refer essentially to the ages, geological relations and lithostratigraphy of the Civitella marittima Formation and the Monte Quoio Formation described on the pages 1252-1254 of that paper.

Page 1250, Figure 2:

- Parts of the caption and the legend of the figure providing a palaeogeographic overview - a modified excerpt from Figure 3.7 in Stampfli & Borel (2004: 66) - are not acceptable, when compared with the original:

  • The abbreviation Ap (Apulia s. str.) is not explained.
  • The abbreviation Mr (Mrzlevodice forearc) is confounded with the abbreviation Mi (Mirdita autochton); and autochton should better be spelled autochthon.
  • The abbreviations To and Ma mean according to Table 3.1 in Stampfli & Borel (2004: 58-59) Talea Ori and Mani, and not Troodos ophiolite and middle Atlas, as written in the legend of Figure 2;

It is astonishing that such confusion occurs in a paper dealing mainly with palaeogeography.

- The term Upland in the legend is of geographical meaning and seems unusual in a legend consisting of geological terms.

Page 1251, Figure 4, right part:

The arrangement of the formations in the lower part of the lithologic column of the "Verrucano-bearing successions" concerning the southern middle Tuscan Ridge is doubted according to the reasons mentioned below in detail.

Page 1252, left column:

Aldinucci et al. (2008a) write that "the Civitella marittima Formation rests unconformably upon various Permian-Lower Triassic p.p. sedimentary rocks and is referred ..... to the Early-?Middle p.p. Triassic on the basis of its stratigraphic position." Regarding the age attributions given here, a different point of view is maintained because of the following reasons:

  1. The age at the top of the stratigraphic footwall of the Civitella marittima Formation - consisting of the Poggio al Carpino Formation and the upper part of the Carpineta Formation - is considered as late Carboniferous due to the reasons explained in detail in Engelbrecht (2008: 293-296) and to the substantial age determinations given in Pasini (1980) concerning the Farma Formation (Bashkirian-Moscovian), which stratigraphically underlies the upper part of the Carpineta Formation (Engelbrecht 2008). Pasini (1980: 328: 5. paragraph) stated that because of the relative uniform middle Carboniferous age range of the microfauna found in the Farma Formation, reworking into considerable younger epochs seems contradictory (literally: "Tuttavia la relativa uniformità cronologica dei fossili nei singoli affioramenti sembra in contrasto con l’ipotesi di un rimaneggiamento in epoche significativamente successive"). It does no justice to M. Pasini, when Aldinucci et al. (2008c: 594: right column, 1. paragraph) cite him at this point as follows: "....that the possible reworking of fusulinids was supposed even by Pasini himself, although this Author finally ruled out this possibility (cf. Pasini, 1980: 328)". In addition, it is rather improbable that beside M. Pasini, also R. Redini, T. Cocozza, R. Signorini, G.-B. Vai and other geologists errored several times so fundamentally in their predominantly undivided general age classifications (Carboniferous) of the Farma- and Carpineta Formations.
  2. No Permian in-situ fauna has been detected up to now in the Farma Formation, considered as middle-late Permian by Aldinucci et al. (2008c); this datum depends exclusively on their described sporomorphs. Despite the fact that the late Permian is known as epoch of rising biotic crises (Condie, K. C. & Sloan, R. E. 1998), marine fauna assemblages from that time interval were found in the nearby subsurface of Monte Amiata (Pandeli & Pasini 1990), at Monte Facito (Ciarapica et al. 1990) as well as in Sicily (Vai 2001), Croatia-Bosnia (Pasini 1982: 180) and in Tunisia (Skinner & Wilde 1967).
  3. Pasini & Winkler Prins (1981) found late Viséan to early Namurian brachiopods in the lower part of the Carpineta Formation, which stratigraphically underlies the Farma Formation (Engelbrecht 2008), and mentioned no signs of redeposition of this macrofauna. Ferraresi & Pasini (1996) confirm the Carboniferous age attribution of the Carpineta Formation. Therefore the Carpineta Formation cannot be attributed to the late Permian as proposed by Aldinucci et al. (2008b: 570-572).
  4. The formation group (Poggio al Carpino Formation, Carpineta Formation, Farma Formation, San Antonio Limestone Formation and equivalents, Spirifer Schist Formation) considered by Engelbrecht (2008) as Carboniferous in age displays a characteristic and uniform colour spectrum: light grey, grey, dark grey, dark brown, grey black and black. This fact points to constant and persistent depositional conditions during one single period. It seems rather improbable that very similar lithologies and colours reappear after an unconformity covering ca. 40 Million years as postulated by Aldinucci et al. (2008b: 571, 576).
  5. At the San Antonio Mine area, no arguments were found which, support the hypothesis of the olistolitic origin of the San Antonio Limestone and the existence of a palaeokarst-surface at its top. A stratigraphic contact has been observed between the Spirifer Schist Formation (late Carboniferous) and the Civitella marittima Formation (Engelbrecht 2008: 295: Figure 3). This fact excludes the proposed Permian age of the Farma- and Carpineta Formations (Aldinucci et al. 2008a,b,c).
  6. At Contrada Carpineta, the stratigraphic passage between the top of the late Carboniferous Carpineta Formation and the Civitella marittima Formation is gradual and is interpreted as weak erosional unconformity (Engelbrecht 1997: 64: Fig. 52). Equivalent stratigraphic passages exist near the confluence of Fosso Cavoni and Torrente Farma, at P 183 and in the upper parts of Fosso al Verde and Fosso Pianaccia.
  7. According to U-Pb-radiometric data from detrital zircons present in metagreywackes of the Farma Formation revealed that the maximum depositional age of that formation is set to 347-371 Ma and that the depositional age of that formation cannot be considerably younger (Paoli et al. 2016).

In consequence of 1.-6., the stratigraphic footwall of the probably unfossiliferous Civitella marittima Formation is regarded as Carboniferous and not late Permian to early Triassic. Therefore the estimated age of the Civitella marittima Formation can also be Permian and may be a partly temporal equivalent of the Permian carbonate platform postulated by Pasini (1991). Because the stratigraphic hangingwall may be late Permian in age (see below), the supposed age of the Civitella marittima Formation is early Permian.

It is maintained that the Civitella marittima Formation unconformably covers the formation group mentioned above, which filled the Carboniferous Farma Basin and adjacent shelf area; and which originated very probably in an extensional or transtensional geotectonic setting.

Page 1252, right column:

  • Concerning the Monticiano-Roccastrada Area, the northward fining of the Civitella marittima Formation cannot be confirmed: Ca. 5 km to the north of the Farma Valley, identic coarse grained conglomerate- and quartz sandstone-layers are present in the Risanguigno Valley (300m SE point 332m) and in the Rifregaio Valley (500m NNW point 335m).

Pages 1253-1254: Aldinucci et al. (2008) interprete the Civitella marittima Formation as fluvial-fan deposits laid down under semiarid climate conditions. A different opinion is given here:

  • According to own observations, the colours typical of continental redbeds lack or are rare in the lower member and lower part of the intermediate member of the Civitella marittima Formation. Therefore these parts of the Formation were never or rarely exposed to atmospheric oxygen. This points to permanent subaquatic depositional conditions for these parts of the Civitella marittima Formation and excludes their fluvial sedimentation under semiaride climate conditions.

According to the palaeogeographic key position of the Civitella marittima Formation - at the turnpoint from the marine Carboniferous formation group stratigraphically below to the predominantly terrestrial redbed deposits (Verrucano in sensu stricto) stratigraphically above - the Civitella marittima Formation is interpreted as regressive, shallow marine to litoral-deltaic deposit. It is proposed that only these parts of that Formation, which contain redbeds, are constituents of the Verrucano Group.

It is astonishing that the substantial thickness-fluctuations of the Civitella marittima Formation, which are obviously caused by reworking of Civitella marittima matter into the Monte Quoio Formation and which indicate synsedimentary normal faulting (Engelbrecht 1997a: 108), were not addressed by Aldinucci et al. (2008a,b).

Page 1254 (Monte Quoio Formation):

  • It is confirmed that in the Monticiano Roccastrada Area the thickness of the Monte Quoio Formation to the south of the Farma river is reduced. Thinning and fining of the Monte Quoio Formation in the present eastward direction was observed additionally (Engelbrecht 1997a); but this is in conflict with the profiles b and c in Figure 9 on page 1262, which indicate thickening and coarsening in that direction and which obviously follow Canuti & Sagri (1974). The absence of the Monte Quoio Formation in the Monte Leoni cannot be confirmed: this Formation was mapped there by Gelmini (1969): he measured clast sizes up to 30cm within the - locally very thick bedded - conglomerates of the Monte Quoio Formation and estimated the thickness of that Formation to ca. 300-400m (including the thickness of the Civitella marittima Formation, which was not differenciated in that work).
  • The statement that "pebbles and boulders of carbonate rock are especially common in the conglomerates of the Farma Valley", is unaccepable. Instead such constituents of the coarse grained, poorly sorted, proximal fluvial conglomerates occur normally as accessories; very rarely they form discontinuous accumulations, which only in that peculiar case can be addressed as main and minor constituents within the proximal conglomerates of the Monte Quoio Formation. Such concentrates were found only at three points (Engelbrecht et al. 1989: 368) in the Farma Valley, which covers an area of ca. 30 km². One of these locations - Ferriera 263 m, which is the one and only point, where the carbonate clasts form main constituents in the conglomerates of the Monte Quoio Formation - was already described by Cocozza et al. (1975), where they found reddish fossiliferous carbonate clasts, which they attributed to the Skythian - early Anisian. Revision and repeated sampling of the same clast type - reddish carbonates - at the same location lead to the detection of another microfauna, which was determined by H. Hagn (Univ. Munich, Germany), E. Flügel (Univ. Erlangen, Germany) and M. Pasini (Univ. Siena, Italy) as latest Gzhelian - early Permian. The fossil content of other carbonate clast types sampled in addition turned out to be not age diagnostic (e.g. Spirorbis sp.). E. Flügel (pers. comm.) stated that some of the objects figured on plate 49 in Cocozza et al. (1975) might also be of Permian age. It is important to emphasize that the material for both micropalaeontological analyses in Cocozza et al. (1975) and Engelbrecht et al. (1989) was sampled at the same location (Ferriera 263m) and from the same clast-lithology (reddish, recrystallized carbonate pebbles: constituents of several m³-sized alluvial conglomerate-boulders in the Farma River). These important circumstances were explained in detail in Engelbrecht et al. (1989) and Engelbrecht (1997). It is astonishing that Aldinucci et al. (2008a) withdrew that information, which makes it rather improbable that these two fossil data differing in age about 50 Million years can coexist in the same clast-type of the same conglomerate-layer-fragment of the same formation. The irregularity concerning downstream rounding of the carbonate clasts - obvious in histogram 3 in Engelbrecht et al. (1989: 368-369), may found on different sources or different levels of one source, but more probable on the fact that the carbonate lithologies (reddish packstones, oolites and grey to yellow dolostones) were not differenciated. It is maintained that the fossiliferous reddish carbonates sampled originated most probably from one source. Therefore only one fossil datum and not both fossil data can be correct. The unfortunately worse preservation of the microfauna described in Cocozza et al. (1975) is obvious, if the plates in both publications are compared. Therefore the age determination in Cocozza et al. (1975) is regarded as deplorable misinterpretation. In consequence, the latest Carboniferous to early Permian relative age does not exclude a late Permian age of the Monte Quoio Formation, similar to that of the Alpine Verrucano. This is in conflict with the statement in Engelbrecht (2008: 298), which followed with reluctance in that point the dogmatic age attribution present in the literature since nearly 35 years. The proximal source of the reddish fusulina-carbonate-clasts probably was the latest Carboniferous - Permian carbonate platform (Pasini 1991) present above the South Tuscan Palaeozoic siliciclastics.

In consequence, the interpretations of Aldinucci et al. (2008: 1261-1263) concerning the middle Triassic rift pulses, which are thought to be represented by the Civitella marittima Formation and the Monte Quoio Formation, are not acceptable. Deposits representing equivalents of the middle Triassic failed rift fill at Punta Bianca near La Spezia (Liguria) (Martini et al. 1986), which consists of two transgressive cycles, are not present in the Monticiano Roccastrada area. Therefore the approximate synchroneity postulated by Perrone et al. (2006) for the deposition of the Verrucano Group in the central-western Mediterranean Alpine Chains is doubted.

It is maintained that the Jurassic opening of the Piedmont-Ligurian ocean between Adria and Corsosardinia-Europe had rift-precursors not only in the middle Triassic, but already in the Carboniferous, as can be deduced from the deposits of the Farma Extensional Basin.


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Dr. Hubert Engelbrecht