Coevolution of global brachiopod palaeobiogeography and tectonopalaeogeography during the Carboniferous

The global brachiopod palaeobiogeography of the Mississippian is divided into three realms, six regions, and eight provinces, while that of the Pennsylvanian is divided into three realms, six regions, and nine provinces. On this basis, we examined coevolutionary relationships between brachiopod palaeobiogeography and tectonopalaeogeography using a comparative approach spanning the Carboniferous. The appearance of the Boreal Realm in the Mississippian was closely related to movements of the northern plates into middle–high latitudes. From the Mississippian to the Pennsylvanian, the palaeobiogeography of Australia transitioned from the Tethys Realm to the Gondwana Realm, which is related to the southward movement of eastern Gondwana from middle to high southern latitudes. The transition of the Yukon–Pechora area from the Tethys Realm to the Boreal Realm was associated with the northward movement of Laurussia, whose northern margin entered middle–high northern latitudes then. The formation of the six palaeobiogeographic regions of Mississippian and Pennsylvanian brachiopods was directly related to “continental barriers”, which resulted in the geographical isolation of each region. The barriers resulted from the configurations of Siberia, Gondwana, and Laurussia, which supported the Boreal, Tethys, and Gondwana realms, respectively. During the late Late Devonian–Early Mississippian, the Rheic seaway closed and North America (from Laurussia) joined with South America and Africa (from Gondwana), such that the function of “continental barriers” was strengthened and the differentiation of eastern and western regions of the Tethys Realm became more distinct. In the Barents Ocean tectonic domain during the Pennsylvanian, the brachiopods on the northern margin of the Barents Ocean formed the Verkhoyansk–Taymyr Province, while those on the southern margin formed the Yukon–Pechora Province. The Mongolia–Okhotsk Province was formed by brachiopods of the Mongolia–Okhotsk Ocean tectonic domain. The Northern Margin of the Palaeo-Tethys Ocean Province and the Southern Margin of the Palaeo-Tethys Ocean Province were formed, respectively, by brachiopods on the northern and southern margins of the Palaeo-Tethys Ocean tectonic domain. South China and Southeast Asia were dissociated from the major continental blocks mentioned above, and formed the South China Province.

Reconstruction of tectonically disrupted carbonates through quantitative microfacies analyses: an example from the Middle Triassic of Southern Italy

The main goal of the paper is the reconstruction of a Middle Triassic buildup cropping out in the central part of the Southern Apennines. Middle Triassic reefs of the western Tethys realm are well known in the Northern and Southern Alps. In contrast, few studies of the Anisian–Ladinian carbonate platforms of the southern Apennines are available, due to the diagenetic alteration and tectonic disruption that hinder their paleoenvironmental and stratigraphic reconstruction. In an attempt to fill this gap, and to improve the knowledge on the Anisian–Ladinian carbonates of central Mediterranean area, this research is focused on a carbonate buildup cropping out in the “La Cerchiara” area, Sasso di Castalda (Basilicata, Southern Italy). The buildup, affected by intense tectonic deformation associated with the development of the Apennine thrust and fold belt, was studied using a statistical evaluation of the quantitative microfacies data. The research enabled a reconstruction of the original stratigraphic relationships of the various buildup fragments. A positive linear regression between the sample positions vs the percentage of autochthonous carbonates indicates an increase of the autochthons carbonate toward the top of the succession. The allochthonous fabrics (packstone/wackestone) at the base of the section (Unit IIIa) pass gradually upward into autochthonous (boundstones) facies (Units IIIb, I), consisting of microbialites (clotted peloidal micrite, microbial-derived laminae, and aphanitic micrite), microproblematica and cyanobacterial crusts, with few encrusting skeletal organisms. Statistical data suggest that units IIIa, IIIb, and I are in stratigraphic order while unit II appears to have been moved by tectonic dislocation from its original position at the base of the succession. The absence of metazoan reef framework, and the richness of micro-encrusters, autochthonous micrite and synsedimentary cements, suggest a mud-mound style of growth for the carbonate bodies of the Southern Apennine during the Anisian.

Early-Middle Jurassic stepwise deepening in the transitional facies belt between the Adriatic Carbonte Platform Basement and Neo-Tethys open shelf in northeastern Montenegro evidenced by new ammonoid data from the early Late Pliensbachian (Lavinianum Zone)

New ammonoid data prove an early Late Pliensbachian deepening event above the ?Late Hettangian-Sinemurian shallow-subtidal gray-reddish micro-oncoidal-foraminifera grainstone facies and the ?Early Pliensbachian deeper-marine micro-oncoidal-crinoidal-ammonoid wacke- to packstone facies. Based on the presence of Fuciniceras lavinianum (Fucini), Lytoceras ovimontanum Geyer and Arieticeratinae gen. indet. from a hardground above the deeper-water micro-oncoidal limestones in the Mihajlovici section (northeastern Montenegro) a Late Pliensbachian to Early Toarcian condensation horizon is proven. The Middle Toarcian ammonoid-bearing horizon also yielded species not known from previous studies: Calliphylloceras capitanii (Catullo), Harpoceras subplanatum (Oppel) and Furloceras aff. chelussii (Parisch & Viale), also described in the present paper. These new data prove a stepwise deepening of the depositional area during the Early and the Middle Jurassic reflected in detail in four sedimentary members: 1) ?Late Hettangian to Sinemurian/? earliest Pliensbachian open-marine shallow subtital micro-oncoidal limestone; 2) ?Early to Late Pliensbachian open-marine condensed limestones with few micro-oncoids and more open-marine influence; 3) Toarcian openmarine condensed red limestones with hardgrounds; and 4} condensed red nodular Bositra Limestone. These four members are separated by hardrounds representing Stratigraphie gaps in deposition. The stepwise deepening during the Early-Middle Jurassic follows the general trend of deposition as known in the whole Western Tethys Realm above the Late Triassic Dachstein Carbonate Platform.

Kinematic restoration of the southern North Atlantic and the Alpine Tethys during the Mesozoic

<p>Continental rifting preceding stable seafloor spreading is characterized by a multistage evolution during lithosphere extension. Wide regions of exhumed mantle contain linear magnetic anomalies with a strongly debated nature and origin. Contrasting information used to set up dynamic plate models has resulted in a plethora of alternative interpretations. Structural and stratigraphic records at plate boundaries show indeed variable degree of discrepancies with what expected from computed plate motions during rifting stages. The definition of robust spatial and temporal kinematic constraints using combined offshore and onshore approaches represents a major challenge to unravel rifted margins evolution.   <br> <br>In this study, we address the problem outlined above using the Mesozoic southern North Atlantic and the Alpine Tethys, west and east of the Iberian plate, as a natural laboratory. The two systems are part of the same Africa-Europe kinematic framework and record distinctive Mesozoic rift events and a subsequent Tertiary compression. While in the southern North Atlantic the kinematic framework is still preserved, in the Alpine Tethys, subsequent subduction/collision erased the paleogeographic framework. The study area is among the best investigated but also most debated geological domains on the globe.</p><p>In our analysis we (1) integrate rift domains in plate kinematic models and re-consider the nature of the magnetic anomaly J in the southern N-Atlantic; (2) discuss the results of recent studies in the northern part of the Iberian plate; and (3) show new data from the Alpine Tethys realm (Central European Alps and Southern Apennines). We discuss the implications of these observations for the geometry of the rift systems developed around Iberia.</p><p>Our robust data network radically reduces the range of possible kinematic solutions. We reconstruct thus the position of Iberia and Adria relative to Europe and Africa and we evaluate the kinematic evolution and the width of the southern North Atlantic and the Alpine Tethys domains during the Mesozoic. The analysis emphasizes (1) the stepping geometry of the plate boundary for the Atlantic-Tethys interaction, (2) the strong partitioning of deformation in time and space, and (3) the large-scale pattern of coeval compression and extension along the Africa-Europe diffuse plate boundary region.</p>