Interactive comment on “ Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins ( Ahnet and Mouydir basins , Central Sahara ) ”

Though I have been working on the Paleozoic of the Algerian Sahara for many years (1987-2006) I am only familiar with the Devonian and Carboniferous, but not with the older formations and the crystalline basement. Therefore, I can only judge these aspects of the above manuscript. Likewise, I feel not competent enough to consider some tectonic reconstructions. I hope that the other reviewer(s) are able to review these as-


Interactive comment
Printer-friendly version Discussion paper pects of the manuscript with a better competence.
The manuscript is an overview of the bio-and lithostratigraphic, sedimentologic, paleogeographic and paleotectonic evolution of the Ahnet-Mouydir area in southern Algeria based on field data from previous authors, well log analysis, satellite images and geophysical data.As such it is a good summary of the evolution of a marginal basin-andridge system which farther north in central Algeria has yielded enormous oil and gas reservoirs.

Detailed critical remarks
Title: The research areas covers a much larger area (including also the Reggane, Basin, Illizi Basin, Hoggar Shield) than expressed in the title.This should be made clear in the title.
Line 20: Pan-African orogeny.Strictly spoken this was around 600 MA, but including earlier phases it was 900-520 MA.What do you mean exactly?Line 35: "Devonian compression".I consider this as a mere speculation.According to all previously gathered data the Devonian was a period of tectonic quiescence accompanied by slight extension.
Line 61: 16 million km2.Impossible!The entire Sahara occupies about 9 million km2.Line 121 ff. and 133: It is not clear if the authors have ever been in the field; equivalent data seem to be based on previous published sources only.This should be made clear unequivocally.
Line 141: Please separate both calibration of well-logs by palynomorphs (which are poorly reliable biostratigraphic markers) and field sections by conodonts (which give by far the best time resolution), goniatites and brachiopods.Both biostratigraphic subdivisions can be only roughly be correlated.

Interactive comment
Printer-friendly version Discussion paper Line 144 (and later): "Synsedimentary extensional and compressional markers": This means during the Devonian and Carboniferous.On which evidence these important tectonic events are based?Apparently not on field data.During about 9 months of personal field work I followed typical marker levels (e.g. the upper Eifelian/Givetian limestone ridge) for tens of kilometers (walking from ridge into basin deposits), but I have never seen something like that.The observation of doubtless Hercynian faults does not automatically allow the conclusion that they are rejuvenated earlier structures.
Line 146: Outcrop sections O1-O12 cannot be detected in Figs 9 and 10.Are they personal field data?Position of well logs W1-W21 can only very roughly be located from Fig. 3A.Given the importance of these data (which apparently have never been published previously) it is absolutely necessary to indicate individual coordinates (best as an appendix) for both.
Line 152: add: major "depositional" unconformities, in order to avoid confusion with angular unconformities.
Lines 153-154: The top Pragian unconformity is diachronous (comprises also the lowermost Emsian in the Reggane Basin and on the Azel Matti ridge).Top Givetian and top mid-Frasnian are no unconformities over the entire study area.Top Quaternary is an unconformity worldwide, therefore omit.Or do you mean base Quaternary?But this would be trivial.In this list you have omitted the most important depositional unconformity, the transgression of the lower Eifelian (costatus-Zone).
Line 171: circular of oval shape of basins.This is pure imagination.Basins and ridges are capped by erosion in the south and by overlying Jurassic or Cretaceous in the north.Thus the second dimension of the paleogeographic units is unknown.
Line 174: major faults are all Hercynian.Eventual pre-Hercynian faults are inferred, but have never been documented in the field, thus are mere speculation.

Interactive comment
Printer-friendly version Discussion paper Line 178: "long" instead of "length".
After line 178: Generally, at this point there is a paragraph entitled "Previous work", but this is missing here.
Line 179: this chapter should be re-written avoiding speculations, even if they would fit well into a hypothetical and inferred depositional image.Regarding eventual "synsedimentary extensional markers" see above.

Interactive comment
Printer-friendly version Discussion paper Line 660: Which are the "Three different periods of tectonic compressional pulses"?I am aware only of one, the Hercynian.
Lines 668-1266: References: The reference list occupies almost the same space as the preceding text and should be drastically reduced, at least to one half.In order to avoid the impression that the article is nothing but a general review paper.Only articles referring to the study area should be included in the reference list.Unfortunately, the latter in its present length shows many incomplete citations (missing volume, missing pages, missing dots in abbreviations, missing editor, missing town (for books), missing capitalizing, wrong spelling), such as in lines 673,676,681,685,690,696,699,740,743,745,755,762,764,765,777,814,828,830,844,863,873,893,900,902,938,957,963,979,982,1001,1003,1013,1018,1033,1037,1041,1075,1081,1082,1095,1099,1112,1124,1129,1158,1160,1162,1169,1176,1181,1185,1186,1195,1221,1222,1226,1244,1253,1255,1257,1260.This list, however, is not complete.I did not check, if every reference in the text does also appear in the reference list and vice versa.This can be done much more accurately by a simple computer program (which I do not have).On the other hand, important local works are not cited.

Conclusion
As a whole the paper is well written, rather concise and accompanied by good illustrations (apart from the above remarks).It is an example of a modern interpretation of a basin and ridge paleogeography using all available techniques.An important contribution is the representation of well data which are difficult to obtain by non-oil geologists.Nevertheless, it cannot be overlooked that as a whole the paper appears to be based almost exclusively on pre-existing data.The personal contribution to the subject is difficult to distinguish Thus, in several aspects and conclusions the interpretations of

Line 191 :
Hercynian folding is restricted to the Reggane, Ahnet and western Mouydir Basins, but decreases markedly towards the east (eastern Mouydir and Illizi Basins) where Paleozoic strata are completely flat-lying.Lines 205-207: synsedimentary horst and graben structures -see above (lines 174 and below).What is a "synsedimentary forced fold"?A slump? Line 247: From Google Earth images it is possible to recognize faults, but it is impossible to determine their age.Please explain why the faults figures in Figs 4 and 6 are Silurian-Devonian and Middle to Late Devonian age.Line 261: "Nine facies associations" cannot be detected in Figs 9 and 10.Do you mean the depositional environments?(these are 5).I also could not find the "supplementary data".Line 291: There is no clear horizontal (gAPI) scale in Fig. 8. Thus it is impossible to check the numbers.Line 298: values range to 120, not 200 in Fig. 8D.Lines 329-330: 30-60 gAPI are low, not high.Line 346: 25-60 gAPI are low, not high.Line 366: stromatoporoids, tabulate and rugose corals are not mentioned on Tab. 1. Line 378: same as above.

Fig. 3 :
Fig.3: give exact coordinates for wells (W1-W21) and for outcrops (O1 -O9).What are the latter?Own data or previously published ones?Why there is no cross section along the O1-O9 line?

Fig. 8 :
Fig.8: Because of its tiny lettering this figure is almost unreadable.Stages and formation names should be added for each sub-figure.The accompanying sections are unreadable.I could not check the source because the equivalent reference is incomplete.In the present form this figure appears rather useless.Gamma-ray-curves often do not correspond to their interpretation in the text (see above).It would make a certain sense, if there were a comparison with equivalent well logs in each sub-figure, but it would better to omit this figure completely.

Fig. 9 :
Fig.9: Needs larger lettering!In Fig.2the Emsian is a gap (which is correct), but in Fig.9this stage is represented by strata, which is an obvious contradiction.