Comment on the paper
Aldinucci, M., Brogi, A., Spina, A. (2008a):
Middle-Late Permian sporomorphs from the Farma Formation (Monticiano-Roccastrada Ridge, southern Tuscany):
new constraints for the tectono-sedimentary history on the Tuscan Domain.- Boll. Soc. Geol. It., 127/3: 581-597, Roma

The paper deals with the geological age and deformation of the Farma Formation (Tuscan Palaeozoic), constituent of the Tertiary metamorphic core complex (MCC) of Monticiano-Roccastrada. This MCC is subdividable into several tectonostratigraphic subunits, which are supposed to be stacked in E-vergent thrust sheets. Criteria for that subdivision are zonaly distinctive degrees of deformation and metamorphism as well as the specific lithofacies of the late palaeozoic formations characterising each subunit. One specific lithofacies is the Farma Fm., element of the tectonostratigraphic Monte Leoni - Farma subunit, thought to be the easternmost and deepest one of that MCC (Lazzarotto et al. 2003).
A sedimentological log of the Farma Fm. at Contrada Carpineta is described by the authors (p. 586: Fig. 4), which displays the palynofacies content in the strata column.

- The authors use in their Fig. 1b the outline map of Lazzarotto et al. (2003). The main lineament, considered to be an E-vergent, ca. N-S striking thrust, is thought to separate the Monte Quoio - Montagnola Senese subunit from the Monte Leoni - Farma subunit. According to own observations, however, the lineament does not fulfil the criteria of separation south of river Farma: because the late palaeozoic units outcropping E of Roccastrada do not represent lithologies comparable to the Poggio al Carpino Formation, characterising the Monte Quoio - Montagnola Senese subunit. Mentioned late palaeozoic units E of Roccastrada are, however, comparable to lithologies of the Monte Leoni - Farma subunit. Therefore the strike direction of that main tectonic lineament S of river Farma should better be NE-SW (and not N-S).
In addition, it is doubted that the main tectonic lineament represents a thrust: According to own observations in the Farma valley, that section of the lineament forms, according to its bearing (that is the line formed by intersection of the terrain-surface with the plain of the lineament) a steep, E-dipping normal fault: across the Farma valley, where in that area the difference in elevation between the valley floor and the rise atop is up to 200m, a V-shaped bearing line, resulting from an E-vergent thrust, was not observed; instead, an overall NNE-SSW oriented bearing is present, which strongly indicates that the contact between both subunits must be a N-S striking steep normal fault dipping E; as already stated by Lazzarotto & Moretti (1973).

- Referring to the map presented by the authors in Fig. 3a: Despite access impeded by dense forest, despite scarce outcrops and despite the difficulty to discern similar lithologies: According to own observations, the data in Fig. 3a are, concerning mapped geological formations and their boundaries, too simplified/generalised (see confrontation below): better lithological differenciations between Monte Quoio Fm. and Civitella Fm., between Monte Quoio Fm. and Upper Verrucano as well as between Tocchi Fm. and Calcare Cavernoso should have been carried out. The formation boundaries inserted often lack precision. Examples:
- The geological structure east of Fosso Pianaccia (SE-corner of the area) is characterised by three tectonic repetitions - formed by thrusts, combined with east vergent folds with overturned flanks - consisting of the sequence Civitella Fm. - Monte Quoio Fm.; and not solely of the Civitella Fm.;
- the upper Triassic evaporites do not only consist of Tocchi Fm., but also of Calcare cavernoso and its reworked products. Moreover, the Tocchi Fm. does not consist of calcschists and phyllites (p. 584, Fig. 3a, legend), but of siltstone layers, alternating with limestone- and dolostone-layers as well as breccias consisting of the afore mentioned lithologies; accessory cm-sized gypsum fragments are present.
Before adopting this excerpt from the map (scale 1:10000) from Lazzarotto et al. (2005), the authors should have carried out their modification work - recorded in the figure-caption - thoroughly: checking, more carefulness and amending in order to obtain a better map quality.

- The minimum of geographical reference points to enable orientation during survey and to control by inspection is not present.

Confrontation of geological maps of the same area (5,3 km²): Aldinucci et al. (2008) to the left; and excerpt from Engelbrecht
(2023); legend see E. (2023). To facilitate comparison, the symbols in the map of A. et al. (2008) were adjusted.

- The authors suppose two Tertiary compressive deformational events: consisting of locally pervasive superposed tectonic foliations, related to the folding events F1 and F2. Referring to Contrada Carpineta, S1 was deformed later by F2 folds, made up of secondary parasitic folds developed in the overturned limb of a major F1 anticline. The supposed D2 event, however, did not occur solely in ductile manner, i. e. without break/fault, as sketched in Fig. 7 on p. 589: according to own observations, also brittle deformation has occurred during D2: a major fault developed during the formation of the F2 fold (see figures below). Thus a better tectonic model must be developed.

Fault accompanying an F2 fold developed in the overturned F1 fold flank in the turbidites of the Farma Fm. at Contrada Carpineta.
Left: Overview. View NE. Meter-scaled F2 fold ( b ca. 117/10) visible in the left and central part of the figure. Its strata s
0 bend as follows: 35/79 normal,
206/78 overturned, 202/63 overturned, 196/53 overturned. A fault separates the F2 fold from the strata of the F1 fold flank in the foreground:
s0 194/32 overturned. Background right above: Strata of the F1 fold flank with s0 198/67 overturned.
Right: Details at the faulted contact; view NW. At left: Strata of the F1 fold flank with s0 194/32 overturned. At right: strata of the F2 fold flank: s0 42/57 normal.

- Aldinucci et al. (2008a) describe the 10m-scaled flexure, visible in Fig. 2 (p. 583), as anticline with overturned limb (p. 590). But it is fact that both limbs - the steep inclined as well as the shallow one - are tectonically overturned. This is unusual in an open antiform. Two tectonic processes resulting in the structure of Fig. 2 are possible:
- large scale overturning of a part of the Farma Fm., followed by the formation of the flexure. It can be addressed as a synformal monocline, made up of strata overturned by a preceding tectonic event.
- Formation of an open antiformal monocline in normally oriented strata of the Farma Fm., followed by large scale tectonic overturning. The resulting structure is an open, overturned antiformal monocline.
These two processes were not distinguished by the authors. The question, which geological event - large scale overturning or the formation of the open antiformal anticline - has occurred earlier, is still open.

- The authors state that in the Monte Leoni - Farma subunit subduction related metamorphism has occurred, which attained in that zone ca. 400°C and 9-10 kbar (p. 583, Fig. 1), equivalent to the glaucophane schist metamorphic facies. However, on p. 588-590, the authors describe synkinematic very low grade metamorphism, which generated a mineral assemblage consisting of white mica (illite) / chlorite / oxides. These both predications clearly contradict each other.

- Near the transect line in Fig. 3a, not more than 10 tectonic measurements are presented by the authors. Instead, numerous asymmetric fold trains were inserted in the profile (2,5 km length) of Fig. 3b. This is disproportionate and incongruous. Much more tectonic data would be necessary to have created a reliable base for the tectonic style chosen in that profile. The other ca. 60 tectonic measurements, given in Fig. 7, refer only to the small area at the Contrada Carpineta section.

- The position of a cased exploratory CNR drill site, at ca. 198m a.s.l., a few meters beside the road to Pozzolungo - close to the boundary between the intermediate and low lying Quaternary fluvial terrace - is not present in the map of Fig. 3a. In consequence, the geological profile of Fig. 3b, running close by the CNR drill site, does not contain the data from the extracted drill core.

- In the legend of Fig. 3a (p. 584), the lithologies of the Anageniti minute Fm., the Monte Qoio Fm. and the Civitella Fm. are in unison described as "Conglomerate, sandstone, silts". This is by far a too unspecific characterisation of geological formations; the main text does not yield any further description of these formations. Similarly, the lithology of the Poggio alle Pigne Fm. is described as "Conglomerate, sandstone, phyllite".
The abbreviation SCR (Monte Quoio Fm.) in the map of Fig. 3a in confounded with SRC.

- An unconformity is postulated by the authors, separating all palaeozoic formations from the Verrucano Group, into which they include the Civitella Fm. (p. 584-585). This statement is important, but mentioned in one sentence only; a more precise explanation concerning the type of unconformity is not given. However, as already mentioned above, the palaeozoic units are always overlain by shallow marine deposits of the Civitella Fm., which effect the passage between late palaeozoic marine sediments stratigraphically below and continental red beds of the Verrucano Group above. According to own observations, the Civitella Fm. covers with slight erosive unconformity older deposits contained in the Farma Basin. The boundary layers resulting therefrom were entitled by the authors as Poggio alle Pigne Fm.. But reworking at that boundary is sparse to very sparse; so the thickness of these layers is only a few meters and therefore not mappable (Engelbrecht 1997a: 64). Consequently the Poggio alle Pigne Fm. is obsolete.
A direct stratigraphic contact between the Monte Quoio Formation and the palaeozoic formations of the Farma Valley, as suggested by the authors (Figs. 3a, 3b), was not observed.

- The authors mention two synsedimentary extensional events, supposed to have occurred during the late Palaeozoic:
- a metre-scaled listric normal fault, which is thought to have developed during the deposition of the turbidites of the Farma Fm. (p. 588 and Fig. 6). However, tilted blocks with steeper inclined stratification - created by rotational slip on the normal fault - filling the halfgraben suggested in Fig. 6b, are not present; as well as the erosive unconformity sealing the postulated extensional structure. Instead, an accomodated, slight flexure deforming one turbidite stratum is visible. Moreover, such a synsedimentary extensional structure, in so far as it had really existed, would have acted during Tertiary compressive events as zone of weakness and would have been transformed into a ramp.
- Microfossil bearing limestone pebbles - constituents of a very coarse grained debris flow of the Farma Fm. - containing calcite veins and stylolithic joints were interpreted by the authors as follows: The brittle deformation must have occurred tens of million years prior (M-Carboniferous) to the formation of the debris flow (M-L-Permian). However, this point of view is misleading: mentioned strain observed in competent limestone clasts embedded in finer grained, less competent matrix of the debris flow, might have also resulted from extensional stress, oriented perpendicular to the direction of the Tertiary compressive event. Moreover: real existing late palaeozoic - old - calcite veins in these carbonate pebbles would have been torn apart and displaced by Tertiary - young - extensional fractures, which later got filled with calcite. However, old calcite veins systematically displaced by sets of younger ones, were not mentioned by the authors.

- The authors state on p. 592 that the organic matter content in the strata of the Farma Fm. is solely of continental (terrestrial) origin. This is astonishing, because they mention several burrowed strata (p. 586, Fig. 4) in their sedimentological log. Marine microfauna has been ascertained from the Farma Fm. at Contrada Carpineta by Pasini (1979a); marine macro- and microfauna is also present in adjoining, coeval outer shelf deposits of the Carpineta Fm. (Pasini 1978, 1979b; Pasini & Winkler-Prins 1981, Pasini & Vai 1979). Ichnofauna was fotodocumented in a poster contribution by Engelbrecht (2019). Therefore organic carbon of marine origin must also be present in the turbidites.

- Spina et al. (2021) state that earlier made fossil findings in the Carpineta Fm. have occurred in its carbonate-siltitic nodules. This is incorrect, because the fossils found in that formation were present in siltitic shalestones of the Carpineta Fm. (Pasini 1978: 74).

- The authors do not give on the pages 592-594 systematic descriptions of the sporomorphs (e. g. morphological attributes, measurements, morphometric terminologies, suprageneric classifications); and no data about the spore coloration index. Their statement that the thermal alteration index is high (p. 592), is not sustained by measurements; this could have been done by determining the reflectance of the macerals.

- According to the results attained from numerous micropalaeontological analyses done in more than 400 thin sections, Pasini (1979: 328) concluded that the relative uniformity of the age attributions (E-L-Moscovian) of the fusulinids in the Farma Fm. means that their reworking has occurred soon after their lithification, but not significantly later. Despite that Aldinucci et al. (2008a) state (p. 594) that the turbidites of the Farma Fm. were deposited during M-L-Permian - ca. 45 Ma later - due to the determined ages of sporomorphs; additionally they state that no microfaunas were found in the hemipelagic interlayers of the Farma Fm.. However: no reason or assumption was given, why the interturbidite layers were reported to be barren of microfauna; the sampled interlayers were not marked in the sedimentological log of Fig. 4 (p. 586); Te is not indicated in Fig. 5a (p. 587) and no link is set from Fig. 5a to its stratigraphic position in the log of Fig. 4. Instead: more scientific value would have been gained by an integrated analysis as done in Sorci et al. (2019): a biostratigraphic comparison between the palynomorphs and coevally deposited microfauna assemblages (e. g. foraminifera, conodonts, etc.) present in the interturbidite layers.
The substantial younger age of the Farma Fm. - postulated by Aldinucci et al. (2008a) - implies that redeposited microfaunas as well as reworked microfloras, both with ages between Moscovian and M-Permian, should be present in the fossil records of that formation. But these have not been identified. One possible reason would be that the area under consideration was affected during this 45 Ma time span by permanent erosion/nondeposition; but this state is least of all probable in a continental margin setting. Another possibility would be that the referring marine area and its whole watercolumn has been sterile during that time span; but such a paleoecological state is unrealistic. So the postulated M-L-Permian age of the Farma Fm. must be rejected and the age attributions of these palynomorpha reviewed. U-Pb detrital zircon ages from the Farma Fm. revealed that its depositional age is late Early to M-Carboniferous and that it cannot be significantly younger than the maximum depositional age (Paoli et al. 2016).

- Engelbrecht (1997a,b, 2002, 2008) supposed, acccording to mapping and stratigraphic considerations that parts of the Carpineta Fm. overlie the Farma Fm.. Aldinucci et al. (2008a,b) state that the Carpineta Fm. covers stratigraphically the Farma Fm.. Spina et al. (2021) support that postulate by means of microfloral data. However, according to own mapping revision work, all these postulated stratigraphic relations made by the mentioned authors turned out to be erroneous: At several GPS-located outcrops the stratigraphic hanging walls of the Carpineta- and the Farma Fms. consist of the Civitella Fm. (?Permian); and the stratigraphic footwalls of both Farma- and Carpineta Fms. is made up of the Risanguigno Fm. (Emsian - Visean). Thus it is obvious that Farma- and Carpineta Fms. are - at least in large parts - coeval: their lithologies developed in adjacent, specific, marine areas: the Farma Fm. originated in a slope and basin margin environment and the Carpineta Fm. in an outer shelf setting, subsequent to a tectonic reorganisation of the palaeomorphology of the Risanguigno basin. In consequence, a palaeozoic normal fault, transformed during Tertiary tectogeneses, separates the Farma- from the Carpineta Fm. (Engelbrecht 2019).

- Engelbrecht (2000) stated that offshore bottom currents, which originated during tropical storms affecting the Poggio al Carpino inner shelf region, crossed the Carpineta outer shelf and triggered turbiditic input on the Farma slope and basin margin. Aldinucci et al. (2008b: 571, 575) also state that Farma Fm. and Poggio al Carpino Fm. are in part coeval. Thus, material - also including sporomorphs - mobilised in the inner shelf region, was redeposited on the slope and basin margin. In consequence it is astonishing that the Poggio al Carpino sporomorph assemblage described by Spina et al. (2001) (consisting of 11 species) is - except Punctatisporites spp. / P. fungosus - divers from the sporomorph assemblage given by the authors for the Farma Fm. (17 species listed). This point was not discussed by the authors.

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Hubert Engelbrecht