Brankman and Aydin (2004) propose a model to explain the anomalous elevation and position of the Gargano Promontory (Southern Italy). The model in itself is absolutely consistent but is not supported by the data and is thus not really relevant for the Gargano Promontory. On the contrary, the model is often in apparent contradiction with available information. It is unfortunate that Brankman and Aydin (2004) disregard a substantial body of literature and thus reach conclusions that are not compatible with the observations. The basic idea of the paper is that the elevated position of the Gargano Promontory is related to a contractional stepover between two sinistral, E–W-trending faults. Obviously, the main ‘field’ ingredient of such a model are the two faults. Unfortunately they are not there; at least not where they are needed. Getting in some more detail and referring to Fig. 2 of Brankman and Aydin (2004), the following comments must be made. Although not stated clearly, one gathers from Fig. 2 that the fault forming the southern rail of the system is the Mattinata fault. Some observations are here relevant: – the Mattinata fault is well inside the elevated portion of the Gargano Promontory and it does not correspond to the first order change in the dip of sedimentary layers which is located a few kilometers to the south (see Fig. 4 in Bertotti et al., 1999). The statement of the authors that “.the Mattinata fault, which is located along the southern margin of the Gargano uplift” is therefore not correct. – The statement of the authors that “There is no evidence for the continuation of the Mattinata fault to the west; rather the fault appears to terminate at the southwestern corner of the of the uplifted block” disregards available observations and is therefore incorrect. Chilovi et al. (2000), using a large body of seismic data, demonstrate that the Mattinata fault does have a continuation to theW under the Apennine foredeep. The reason for the ‘disappearance’ of the Mattinata fault is simply that it is covered by Plio-Quaternary sediments. Also for this reason, the Mattinata Fault cannot be the southern ‘rail’ of the system. The northern rail of the strike-slip system is also missing. Inspection of Fig. 2 of Brankman and Aydin (2004) provides no clue as to the position of such an allegedly important fault. Some continuous lines (unspeci- fied faults) are indicated south of Lago di Varano. In reality (see detailed geological sections in Casolari et al. (2000) and Bertotti et al. (1999)), the indicated structures are SWvergent thrusts. No strike-slip fault is visible in the field. No strike-slip fault is visible in the seismic north of the Gargano Promontory either (Bertotti et al., 2001). Several additional statements contained in the article by Brankman and Aydin (2004) are incorrect: – “The Rignano fault (see Fig. 2) is .not a fault”. Themorphological cliffs (sharp break in slope according to the wording of Brankman and Aydin (2004)) correspond to the steep flank of a S-vergent fold (see geological sections in Bertotti et al., 1999). – The statement that “bedding is especially disrupted and/or dips steeply in the vicinity of faults” is in fact the product of circular reasoning. Brankman and Aydin (2004) have placed the faults there where layers are steep, but without detailed field observation. The steepest beds are encountered N of the Mattinata fault and N of what the authors call the Rignano fault. In both cases, the steep position of sedimentary layers is associated with folding. Faulting is not instrumental for their position. – That “the NW-trending lineaments .have been mapped.but not documented in detail” reflects the insuf- ficient knowledge of the authors rather than the reality. We refer to Bertotti et al. (1999) and references therein. – Contrary to what is stated by the authors these contractional structures are not in contrast with the...

G.Bertotti, V. Picotti (2004). Comment on: “Uplift and contractional deformation along a segmented strike-slip fault system: the Gargano Promontory, southern Italy” by C.M. Brankman and A. Aydin,Journal of Structural Geology, 26, 807-824. JOURNAL OF STRUCTURAL GEOLOGY, 26, 2325-2326.

Comment on: “Uplift and contractional deformation along a segmented strike-slip fault system: the Gargano Promontory, southern Italy” by C.M. Brankman and A. Aydin,Journal of Structural Geology, 26, 807-824

PICOTTI, VINCENZO
2004

Abstract

Brankman and Aydin (2004) propose a model to explain the anomalous elevation and position of the Gargano Promontory (Southern Italy). The model in itself is absolutely consistent but is not supported by the data and is thus not really relevant for the Gargano Promontory. On the contrary, the model is often in apparent contradiction with available information. It is unfortunate that Brankman and Aydin (2004) disregard a substantial body of literature and thus reach conclusions that are not compatible with the observations. The basic idea of the paper is that the elevated position of the Gargano Promontory is related to a contractional stepover between two sinistral, E–W-trending faults. Obviously, the main ‘field’ ingredient of such a model are the two faults. Unfortunately they are not there; at least not where they are needed. Getting in some more detail and referring to Fig. 2 of Brankman and Aydin (2004), the following comments must be made. Although not stated clearly, one gathers from Fig. 2 that the fault forming the southern rail of the system is the Mattinata fault. Some observations are here relevant: – the Mattinata fault is well inside the elevated portion of the Gargano Promontory and it does not correspond to the first order change in the dip of sedimentary layers which is located a few kilometers to the south (see Fig. 4 in Bertotti et al., 1999). The statement of the authors that “.the Mattinata fault, which is located along the southern margin of the Gargano uplift” is therefore not correct. – The statement of the authors that “There is no evidence for the continuation of the Mattinata fault to the west; rather the fault appears to terminate at the southwestern corner of the of the uplifted block” disregards available observations and is therefore incorrect. Chilovi et al. (2000), using a large body of seismic data, demonstrate that the Mattinata fault does have a continuation to theW under the Apennine foredeep. The reason for the ‘disappearance’ of the Mattinata fault is simply that it is covered by Plio-Quaternary sediments. Also for this reason, the Mattinata Fault cannot be the southern ‘rail’ of the system. The northern rail of the strike-slip system is also missing. Inspection of Fig. 2 of Brankman and Aydin (2004) provides no clue as to the position of such an allegedly important fault. Some continuous lines (unspeci- fied faults) are indicated south of Lago di Varano. In reality (see detailed geological sections in Casolari et al. (2000) and Bertotti et al. (1999)), the indicated structures are SWvergent thrusts. No strike-slip fault is visible in the field. No strike-slip fault is visible in the seismic north of the Gargano Promontory either (Bertotti et al., 2001). Several additional statements contained in the article by Brankman and Aydin (2004) are incorrect: – “The Rignano fault (see Fig. 2) is .not a fault”. Themorphological cliffs (sharp break in slope according to the wording of Brankman and Aydin (2004)) correspond to the steep flank of a S-vergent fold (see geological sections in Bertotti et al., 1999). – The statement that “bedding is especially disrupted and/or dips steeply in the vicinity of faults” is in fact the product of circular reasoning. Brankman and Aydin (2004) have placed the faults there where layers are steep, but without detailed field observation. The steepest beds are encountered N of the Mattinata fault and N of what the authors call the Rignano fault. In both cases, the steep position of sedimentary layers is associated with folding. Faulting is not instrumental for their position. – That “the NW-trending lineaments .have been mapped.but not documented in detail” reflects the insuf- ficient knowledge of the authors rather than the reality. We refer to Bertotti et al. (1999) and references therein. – Contrary to what is stated by the authors these contractional structures are not in contrast with the...
2004
G.Bertotti, V. Picotti (2004). Comment on: “Uplift and contractional deformation along a segmented strike-slip fault system: the Gargano Promontory, southern Italy” by C.M. Brankman and A. Aydin,Journal of Structural Geology, 26, 807-824. JOURNAL OF STRUCTURAL GEOLOGY, 26, 2325-2326.
G.Bertotti; V. Picotti
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/12492
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