Black Flysch Research Articles

Jurassic–Cretaceous controversies in the Western Carpathian Flysch: the “black flysch” case study

The age of the “black flysch” deposits in the Polish sector of the Pieniny Klippen Belt (Western Carpathians) has been a subject of a long lasting controversy. References to both the Middle Jurassic and the mid-Cretaceous have been made. The “black flysch” as well as overlying deposits, exposed in two sections located in the Slovakian and Polish segments of the Pieniny Klippen Belt (Western Carpathians), are the subject of this paper. A detailed examination of their foraminiferal and calcareous nannofossil content, carried out on 59 samples, has revealed in most samples the presence of redeposited Jurassic and Cretaceous microfossils. Analyses of our results and other published data have proved an Albian–Cenomanian age for the “black flysch” deposits and brought to light new information on the reworking processes of the Jurassic and Lower Cretaceous sediments and fossils whose presence has led to previous misinterpretations of the biostratigraphic record.

Tectono-thermal regimes and lithosphere behaviour in the External Dacides in the Upper Triassic and Jurassic Tethyan opening (Romanian Carpathians)

Traces of Mesozoic basic magmatism occur in the Romanian Carpathians in two different tectono-stratigraphic positions: (1) associated with the opening of the Tethys, and (2) associated with intracontinental basins. The latter were generated within three sedimentary basins, which are now inverted, constituting the External Dacides: the Black Flysch, Ceahlau (Eastern Carpathians) and Severin (South Carpathians) basins. Assuming a normal Jurassic lithosphere and a pure shear opening mechanism, stretching factors of 1.25 and 1.7 have been calculated for the Black Flysch and Ceahlau basins, respectively. These values were in turn used to determine the theoretical values of the syn-rift sediment thickness, and compared with those obtained by backstripping techniques. The occurrence of basic magmatism in the Black Flysch basin associated to such a low stretching factor, suggests that melt generation was possible due to ‘wet’ composition of the mantle peridotite. The thermal state was different in the Ceahlau and Severin basins, the lithosphere being affected by updoming processes prior to rifting. Upper Triassic and Jurassic thermal states of the European lithosphere are related to the coeval opening mechanism of the Tethys. There was a transition from a simple shear between Austro-Alpine (= Apuseni Mountains) and the South Carpathians, to a pure shear mechanism (accompanied by strike-slip movements) between Austro-Alpine and the northern part of the Eastern Carpathians. Related to this change in the position of the master detachment fault, an astenospheric uprise developed within the European plate. It was largest in the Severin zone, medium in the Ceahlau zone and became smaller toward the Black Flysch zone. The Dacidian Swell developed as a result of this astenospheric rise. Starting with the Lower and Middle Jurassic, the Dacidian Swell became subject of rifting.

Discussion on 'Cretaceous to Eocene volcanic arc activity in the Andes of northern Ecuador'

Dr. R. Bristow writes: Mr. Henderson is to be congratulated on the presentation of this stimulating paper. In it much new information is presented and it allows one of the first quantitative studies of are activity in Ecuador to be made. However, I have to disagree with the interpretation placed onsome of the facts contained in this paper. These are stratigraphical queries which should not detract from the author's main conclusions, but nevertheless they may have important implications concerning the timing and duration of arc activity in Ecuador. Basically, Mr. Henderson believes that there are three diachronous units-Macuchi Formation, Yunguilla Formation, and Cayo Rumi Member, which rangein age from Cretaceous to Eocene. I maintain that there is no evidence of diachronism, only that there are Eocene deposits, both marine and volcanic, which have a common lithology with Cretaceous deposits, but separated from them by a time gap of some 20 m.y. To take the Andean Yunguilla Formation, because it is the best documented, as an example: at a number of points (Loja, Cuenca, near Riobamba, and at the Yunguilla type locality in the N) the black flysch sediments of the formation are of Maastrichtian age; at one point only, near Pilaló, lithologically similar rockshave been dated as Middle Eocene in age (Bristow & Hoffstetter 1977, p. 350). Nowhere are there flysch sediments of Palaeocene or Lower Eocene age, and it is thus impossible to demonstrate that the Yunguilla Formation is diachronous from Maastrichtian to Middle Eocene.

Sur la position structurale et stratigraphique des 'gres de l'Embrunais', a l'ouest du col de Vars (Hautes-Alpes)

Abstract The Embrunais sandstone of the Crevoux peak massif, west of the Vars pass (France), is an internal, upper digitation of the Helminthoides flysch nappe of the Embrunais-Ubaye area. This digitation is characterized by its detrital facies which becomes more extensive and conglomeratic toward the northeast. The exotic sandy flysch outliers on the Brianconnais, near Briancon, are related to this digitation. West of the Vars pass the Crevoux massif overlies the basal black flysch. Southwest of the pass the black flysch has drifted over the rumpled Helminthoides flysch. The Crevoux massif therefore represents an allochthonous unit superimposed on the Saint Clement and Meyronnes folds. In this syncline the Embrunais sandstone develops progressively from south to north, emplacing itself in the basal Helminthoides flysch. Santonian-Coniacian Inoceramus species collected from the beds directly above the Embrunais sandstone date the unit as Senonian or possibly Turonian.