Burdigalian Deposits Research Articles

Strontium stratigraphy of the Burdigalian transgression in the Western Mediterranean

Brandano, M. & Policicchio, G. 2011: Strontium stratigraphy of the Burdigalian transgression in the Western Mediterranean. Lethaia, Vol. 45, pp. 315–328. A 87Sr/86Sr analysis of selected pectinid shells has been performed to refine the stratigraphical framework of the Burdigalian transgressive event. Samples were collected from shallow water successions of the Western Mediterranean area (North-Eastern Sardinia, Southern Corsica, Central Apennines). The Western Mediterranean is the result of the interaction between the European and the African plates. Sardinia and Corsica were extended and rifted apart from the Iberian Peninsula during the opening of the Liguro-Provencal basin, between 30 and 15 Ma. In the outcrops of Northern Sardinia and Southern Corsica, Burdigalian deposits nonconformably overlie Varisican granites. In the central Apennines the Burdigalian deposits paraconformably overlie the Cretaceous platform. These are transgressive deposits, characterized by the presence of Miogypsina globulina, which points out early to middle Burdigalian age. The Sr isotope ages indicate that marine transgression in Northern Sardina and Southern Corsica took place between 18.6 and 18.3 Ma, which could correspond to the eustatic sea level rise of the Bur3 third-order sequence. In the Central Apennines the Burdigalian transgression was anticipated (18.8 Ma) by subsidence input linked to the eastward migration of the orogenic system. This input allowed the Miocene carbonate ramp to develop on the Cretaceous platform substrate, while successive eustatic rise controlled the evolution of the stratigraphical architecture. The following regressive phase is recorded in both the Apennine and Corsica successions. The end of this phase is dated between 17.6 and 17.5 Ma and corresponds to sea level drop corresponding to the occurrence of the Mi 1b event. □Burdigalian, pectinids, strontium stratigraphy, transgression, Western Mediterranean

Lower Miocene deformation in the hanging wall of the Internal-External Zone boundary of the Betic Cordillera: deformation at the edges of vertical-axis rotation domains in oblique convergent margins

Abstract In the eastern Betic Cordillera, non-cylindrical doubly plunging folds deform the Subbetic Zone (the hanging wall of the Internal-External Zone boundary). Their hinges define an arc from north-south trends in the east to ENE-WSW in the west. These folds began to form during the Early Burdigalian with a NNE-SSW trend. Middle Burdigalian rocks define progressive unconformities in the cores of the synforms, recording the tightening of the folds and an increase in the plunge of the fold hinges. All these folds experienced verticalaxis rotations during the Early Miocene, acquiring the present-day arcuate pattern. During the Middle Burdigalian, the thrusting of the External Zones over the Internal Zones occurred with a top-to-the-SE sense of movement. Upper Burdigalian deposits seal the tectonic windows eroded in these thrust surfaces. This deformational history records a constrictional deformation with area reduction in the Subbetic Zone during the Early Miocene, which can be correlated with the dextral oblique convergence between the Internal and the External Zones.

Sr-ages and grade-datings in the area of the Lower Miocene near Bordeaux (Aquitaine Basin, France)

Twelve Sr-ages, recently obtained within the Aquitanian and Burdigalian deposits near Bordeaux are consistent with the grade-dating already published from the same localities. These two interpolation methods of radiometric ages support each other.

The multistage tectonic evolution of the Gulf of Suez and northern Red Sea continental rift from field observations

Field surveys in the Gulf of Suez‐Northern Red Sea area revealed the structural pattern and evolution of this tertiary continental rift and provided constraints on the continental rifting process. The structure has been controlled, at every scale, by four major trends of faults: N0°–20°E, N100°–120°E, N140°E–160°E and N40°–60°E. Observations of sealed faults and folds and superposed structures and the detailed analysis of the fault surfaces are coherent and indicate that as least two different stages of deformation characterize the evolution of the rift. The initiation of the rift (late Oligocene‐Aquitanian) corresponds to the creation of large rhomboidal basins, weakly subsident and partly bounded by oblique strike‐slip faults. This framework, which resulted from the reactivation of inherited weakness zone in the basement, controlled the subsequent creation of large tilted blocks (upper Aquitanian‐lower Burdigalian). These structures were trangressed by the upper Burdigalian deposits. Then the blocks were sliced by a secondary horst and graben pattern, which was progressively sealed by middle Miocene units. Since the upper Miocene, the deformation has been focused along some major faults located in the central part of the rift. The determination of paleostresses from measurements of striae confirms that the initiation of the rift was controlled by a tectonic regime characterized by an horizontal compressive stress parallel to the rift, and its subsequent evolution was controlled by triaxial and radial extensional regimes with horizontal minimum stress (σ3) predominantly trending N70°–80°E. The rifting process was not induced by regional doming but by a new distribution of intraplate stresses at approximately Oligocene‐Miocene time (passive rift). Uplift of the rift shoulders began in the upper Burdigalian. Cross sections of the rift emphasize its asymmetry: large basement blocks are tilted toward the edge of the rift where a major, recently active fault and a distinct morphological unit, which we call a “banquette,” are located. Several homogeneous tilt direction provinces can be defined. They are separated by transverse hinge zones that correspond to inherited basement trends. Rifting deformation is expressed in the basement by steep faults arranged in a zig‐zag pattern and in Neogene‐Quaternary sediments by steep faults and listric faults associated with decollements. Therefore the style of shallow deformation cannot be extrapolated to deeper levels. Structures formed during the beginning of the rift show different charateristics according to their orientation, but their initial shape was generally complicated by later deformation.

Relationship of Benthic Foraminiferal Biofacies to Lithofacies in Phosphatic Miocene Sediments, Mid-Atlantic Continental Shelf: ABSTRACT

Changes in benthic foraminiferal assemblages accompany changes in total sediment texture and mineralogy (primarily percent phosphatic grains) throughout the Pungo River Formation in Onslow Bay, North Carolina. Only Burdigalian (late-early Miocene) deposits have been cored in southern Onslow Bay. Basal phosphorite sands (30% phosphate) are overlain by phosphatic (8%) muds and slightly phosphatic (4%) quartz sands. Elongate buliminaceans (Bolivina, Bulimina, Buliminella, Uvigerina) comprise over 50% of the benthic assemblage in phosphorites. They also predominate (43%) in phosphatic muds where Siphogenerina and Florilus become conspicuous faunal elements. Diverse trochospirally coiled forms (mainly Hanzawaia, also Valvulineria and Cibicides) become predominant in quartz san s; buliminaceans decline to 30% of the fauna. Pungo River deposits in northern Onslow Bay are Burdigalian, Langhian (early-middle Miocene), and Serravallian (middle Miocene) in age. Burdigalian deposits are nonphosphatic, muddy quartz sands in which Hanzawaia predominates and buliminaceans comprise only 22% of the fauna; Florilus accounts for 5%. Hanzawaia remains the dominant genus in the slightly phosphatic (4%) quartz sands of the Langhian and the phosphatic (10%) sands of the Serravallian; buliminaceans increase to 29% of the fauna, but Florilus nearly disappears. Both vertically and laterally through the Miocene of Onslow Bay, nutrient-loving buliminaceans thrive where phosphate content increases. Florilus and Siphogenerina are associated with the influx of fine-grained terrigenous ediments. The Hanzawaia-dominated assemblage thrives in clean, End_Page 529------------------------------ coarser-grained substrates. Regional trends in the distributional patterns of these taxa may aid in locating additional phosphate deposits. End_of_Article - Last_Page 530------------

A new species of fossil barbet (Aves: Piciformes) from the middle Miocene of the Nördlinger Ries (southern Germany)

ABSTRACT A new species of barbet in the Miocene genus Capitonides is described from middle Miocene lake deposits in southern Germany. This was smaller than the type species, C. europeus, from Burdigalian deposits at Wintershof, Germany. Capitonides is shown to be closely related to the extant African genus Trachyphonus, which is considered to be the most primitive genus in the family. The presence of barbets indicates that winter temperatures in the middle Miocene of southern Germany were milder than at present.

Quelques microfacies neogenes nord-aquitains

Abstract The Aquitanian and Burdigalian deposits outcropping in Villandraut and Saucats have similar microfacies, and the depositional environments of the two series appear to have been relatively uniform as evidenced by the structure of the limestone matrix. Microfacies of the Helvetian deposits exposed at Salles were deposited under different conditions, probably influenced more by coastal currents than the Aquitanian and Burdigalian sediments.