Recent progress in plate tectonic reconstructions has seen models move beyond the classical idea of continental drift by attempting to reconstruct the full evolving configuration of tectonic plates ...and plate boundaries. A particular problem for the Neoproterozoic and Cambrian is that many existing interpretations of geological and palaeomagnetic data have remained disconnected from younger, better-constrained periods in Earth history. An important test of deep time reconstructions is therefore to demonstrate the continuous kinematic viability of tectonic motions across multiple supercontinent cycles. We present, for the first time, a continuous full-plate model spanning 1 Ga to the present-day, that includes a revised and improved model for the Neoproterozoic–Cambrian (1000–520 Ma) that connects with models of the Phanerozoic, thereby opening up pre-Gondwana times for quantitative analysis and further regional refinements. In this contribution, we first summarise methodological approaches to full-plate modelling and review the existing full-plate models in order to select appropriate models that produce a single continuous model. Our model is presented in a palaeomagnetic reference frame, with a newly-derived apparent polar wander path for Gondwana from 540 to 320 Ma, and a global apparent polar wander path from 320 to 0 Ma. We stress, though while we have used palaeomagnetic data when available, the model is also geologically constrained, based on preserved data from past-plate boundaries. This study is intended as a first step in the direction of a detailed and self-consistent tectonic reconstruction for the last billion years of Earth history, and our model files are released to facilitate community development.
The Upper Triassic to lower Middle Jurassic Shemshak Group of the Central-East-Iranian-Microcontinent is important for understanding Mesozoic geodynamics of the Middle East during and in the ...aftermath of the collision of the Cimmerian microplates with Eurasia, resulting in the massive burial of organic matter and the formation of significant coal reserves. The present study thus aims to elucidate the stratigraphic patterns, lithofacies inventory, depositional environments and geodynamic significance of the Shemshak Group in the Halvan area of the Kalmard sub-block of the northern Tabas Block where the succession is most completely developed. Lithostratigraphic studies through detailed logging resulted in a differentiation of the siliciclastic Upper Triassic Nayband and Lower Jurassic Ab-e-Haji formations, bounded at their bases by the Eo- and Main Cimmerian unconformities, respectively, and the mixed carbonate-siliciclastic Badamu Formation (upper Lower to lower Middle Jurassic). The lithofacies analysis and stacking patterns of siliciclastic strata indicate deposition in a variety of environments ranging from (proximal to distal) coastal and delta plains to delta front and prodelta settings for the Nayband and Ab-e-Haji formations. Detailed litho- and microfacies studies of the Badamu Formation revealed inner to middle parts of a mixed carbonate-siliciclastic ramp system. Careful petrographic studies indicate that sandstones of the succession are generally lithic-rich (ranging from phyllarenite to sedarenite) and, up-section, grade into quartz-rich sublitharenite, providing important information for sedimentary provenance analysis. The sandstones rich in metamorphic- and sedimentary lithic fragments indicate a proximal source on the western Yazd Block as well as rocks exposed on the Kalmad sub-block itself. The integrated studies also led to the recognition of the Eo- and Main Cimmerian orogenic phases, characterized by rapid uplift and/or subsidence phases. Late Triassic and Early Jurassic deposition took place in a back-arc extensional basin characterized by normal faulting. During the Toarcian–Aalenian, the reduced input of clastic material due to source-area denudation and/or a major transgression resulted in the development of the mixed carbonate-siliciclastic system of the lower Badamu Formation in the western part of the northern Tabas Block. This ramp system developed into an attached, ocean-facing carbonate platform with a prograding margin of ooid shoals.
•First detailed lithofacies analyses and palaeoenvironmental reconstructions of the Shemshak Group on the CEIM are presented.•Integrated studies led to the recognition of the Eo- and Main Cimmerian unconformities on the northern Tabas Block.•Litho- and microfacies analyses indicate deposition in coastal plains to delta front and prodelta settings (Nayband and Ab-e-Haji formations).•The sandstones of the succession are generally lithic-rich, indicating a proximal source on the western Yazd Block.•The mixed ramp system of the Badamu Formation developed into an attached, ocean-facing carbonate platform with a prograding margin of ooid shoals.
The Late Miocene successions of the Capo Vaticano-Monte Poro (Southern Italy) area, well exposed at Cessaniti – Cava Gentile, preserve a palaeontological record particularly relevant for phylogenetic ...studies and paleogeographic reconstructions as well as for the popular scientific divulgation and museology. The rich record of Sirenians highly contributed to the knowledge of phylogeny and intraspecific variability of Metaxytherium serresii. The exclusive terrestrial mammal association, having African and Greco-Iranian affinities, allows intriguing suggestions in the paleogeography of the Central Mediterranean. New taphonomic analyses on invertebrates and vertebrates, here presented, suggest that the good fossil preservation is due to the rapid burial of skeletons in a semipermeable mixture of sandy/muddy sediments which were quickly cemented. Late partial dissolution of the carbonate cement among particles made the fossils easy to extract from the sediment. The collaboration among palaeontology researchers, fossil collectors, and local administrators, under the direction of Superintendence and the control of Carabinieri Command for the Protection of Cultural Heritage, allowed the recovery, study, and promotion of this precious paleontological record. The area has a good flow of tourists for the pleasant seaside, and fossiliferous sites could attract cultural tourism, through educational trails and a museum network which valorize the palaeontological and archaeological heritage of the hinterland.
Sedimentary rocks preserve the geological history of a basin and play a key role in constraining the palaeogeography. The Mesozoic Kutch Basin (India) comprises a number of sub-basins representing a ...pericratonic rift formed during the break-up of Gondwanaland. It preserves sediment deposited during the rifting and drifting of the Indian subcontinent. The current study identifies evidence of provenance changes recorded in Mesozoic sandstone units using a multi-proxy approach of quantitative modal analysis, quantitative heavy-mineral analysis and garnet chemistry. The Mesozoic sedimentary successions in the sub-basins are classified as the Kutch Mainland Group (KMG), the Pachchham Island Group (PIG) and the Eastern Kutch Group (EKG). Although the sub-basins are thought to share sediment from common source areas and the sandstone units are highly mature quartz arenites, the heavy-mineral assemblages (especially the content of zircon, tourmaline, rutile, apatite and staurolite) indicate previously unreported variation in the sediment source for the PIG when compared to the KMG and EKG. Moreover, an increase in the content of staurolite and kyanite in combination with rising trends of the ratios of staurolite–kyanite and zircon–tourmaline–rutile over garnet (St + Ky/Grt and ZTR/Grt) for the Callovian and younger strata is observed in the KMG and EKG. The above indicates a change in source from the older to the younger strata in each of the two sub-basins. The absence of their coeval strata in the PIG gives credence to the previously postulated rise of a subsurface basement high, the Median High in this basin. However, the timing of the rise remained so far unspecified, mentioned as “later in Jurassic” (Biswas, 2016b). The observations made in the current study constrain the rise of the Median High in the Kutch Basin to the Callovian time. The similarities in trends of the ratio of heavy minerals and garnet chemistry as well as variations in igneous garnet suggest recycling within the Kutch Basin from the Callovian to Oxfordian–Kimmeridgian strata in the EKG to the Kimmeridgian to Albian strata in the KMG.
Besides revealing previously unknown details in the evolutionary and palaeogeographic history of the different sub-basins constituting the Kutch Basin, this multi-proxy study demonstrates the high potential of using recently developed techniques in provenance analysis i.e., the semi-automated heavy-mineral analysis by Raman spectroscopy and the state-of-the-art machine-learning aided garnet discrimination scheme. This study also provides a globally applicable workflow for other sedimentary basins, especially rift basins characterised by overall highly mature quartz arenites.
Two main groups of geological models presented over the last four decades on the palaeogeographic, paleotectonic and geodynamic eo-Alpine and neo-Alpine evolution of the central-western Mediterranean ...area were compared. The comparison was carried out mainly considering the main stratigraphic, sedimentological, petrographic, structural and plate tectonic constraints. Moreover, recent geophysical interpretations and reconstructions were also considered with an aim of presenting all the different results. The models can roughly be grouped into two main classes. First family considers the presence of the Mesozoic Tethyan Ocean, where a single oceanic basin is located between Africa and Europe and from which both eo-Alpine and neo-Alpine chains were generated during the Cretaceous to Miocene time span. Conversely, the other class considers the occurrence of at least two Tethyan oceanic branches (or with thinned continental crust) since the Jurassic, separated by one or more microcontinents. The pros and cons of both classes of models are presented. Progressive innovations and improvements to the two groups of models were proposed over the years. However, because the models are based on different data sets resulting from basic geological studies or obtained by means of other approaches, they often do not integrate easily. This caused interpretative difficulties and terminological uncertainties for their comparison, and completely different models were considered equivalent and, sometimes, the same terminology was used indifferently to identify different geological subjects. The main differences between the examined models concern the kinematic reconstructions and by hence in the palaeogeographic and paleotectonic interpretations. The discussion presented in this paper aims at contributing to clarify and update the state of knowledge on this controversial topic.
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