Structural model splicing method based on well seismic combination

The use of small blocks with model-building results for overall structural model splicing can unify fault understanding, effectively integrate existing small block model results, and form a unified and continuous overall model. This article focuses on the structural models of two small blocks in the central and western parts of a certain area, and studies the method of splicing structural models at the sedimentary unit level to lay the foundation for the precise tapping of the potential of the fault edge.

Assessing the rift to sag evolution of Parnaiba Basin, NE Brazil, through U-Pb detrital zircon geochronology and provenance

<p><strong>Assessing the rift to sag evolution of Parnaíba Basin, NE Brazil, through U-Pb detrital zircon geochronology and provenance</strong></p><p>Rodrigo I. Cerri<sup>1</sup>; Lucas V. Warren<sup>1</sup>; Mario L. Assine<sup>1<br></sup><sup>1</sup> São Paulo State University (UNESP), Institute of Geosciences and Exact Sciences, Rio Claro, Brazil.</p><p>Nowadays one of the most prolific topics in the geological sciences is the origin of intracratonic basins. Despite many Paleozoic examples in which rift systems occur under these basins, there is no consensus about how these mechanical subsidence basins influenced the origin of continental-scale intracratonic basins. Due to its inherent complexity, the understanding of this problem only comes from integrated studies based in multi-proxy analysis, placing it on the frontier of modern science. In the northeast part of Brazil, the Late-Precambrian to Early-Cambrian Jaibaras Basin is interpreted as the precursor rift of the Parnaíba intracratonic Basin, following a simple model of mechanical-to-thermal subsidence evolution. In order to assess the provenance patterns and maximum depositional ages (MDA) between the rift and cratonic phases of these basins, we present a novel detrital zircon U-Pb ages of rocks from the Aprazível and Ipu formations. The main goals of this approach is to identify provenance changes (or similarities) between the last rift related sedimentary unit of the Jaibaras Basin and the first intracratonic related sedimentary unit form the Parnaíba Basin, thus allowing to test the rift-to-sag hypothesis. The MDA for the Aprazível Formation (ca. 499 ± 5 Ma, Furongian to Miaolingian) indicates a Late Cambrian age for the upper part of the Jaibaras Basin. The Ipu Formation records a MDA of ca. 528 ± 11 Ma (Terreneuvian to Series 2, Early Cambrian). However, due to its stratigraphic position relative to the lower Aprazível (499 ± 5 Ma) and upper Tianguá (Early Silurian, Llandovery) formations, the depositional age of this unit is probably younger (Late-Cambrian to Early-Ordovician). Thus, the successions deposited in the end of the rift and the beginning of the sag phase are clearly separated by a regional unconformity (10 to 30 Ma). We also identify the complete absence of Cambrian zircons followed by a significant increase in Paleoproterozoic ones in the Ipu Formation. Although these units were significantly sourced by Neoproterozoic terrains (especially Ediacaran), this modification indicates an interesting change in provenance between the rift to sag basins. The detrital zircon provenance, helped by a consistent paleocurrent analysis, reveal local source areas for the Aprazível Formation and a consistent distal sedimentary transport towards NW for the Ipu Formation. This suggests that the primary sources for the first cratonic unit of Parnaíba Basin were located at the orogenic areas related with the Neoproterozoic Brasiliano/Pan-African Orogeny at the south/southern of Borborema Province (e.g. Rio Preto, Riacho do Pontal and Rio Grande do Norte metamorphic belts). Unlike the alluvial-related Aprazível Formation, the Ipu Formation characterizes a huge fluvial system that flowed towards NW, probably following a homoclinal ramp-like tilted and opened to the paleomargins of Gondwana.</p>

Latest Miocene Mediterranean-Atlantic gateway restriction: The Atlantic's side of the story

<p>The closure of Late Miocene Mediterranean-Atlantic gateways and the restriction of Mediterranean Outflow Water (MOW) led to the Messinian Salinity Crisis (MSC), the dynamics of which is not well understood. However, restriction of the Mediterranean-Atlantic exchange and the Mediterranean Outflow Water (MOW) is one of the prerequisites to generate hypersaline conditions for evaporitic deposition. During the Late Miocene, MOW circulation was active through a Mediterranean-Atlantic exchange of the Betic, Riffian, and possibly Gibraltar gateways. This connection is thought to have ceased or reduced with the onset of the MSC, before re-establishing through the Gibraltar gateway since the Pliocene to the present. In this study, we define the sedimentary evolution of the Neogene Basins of the Gulf of Cádiz to investigate MOW evolution during the latest Miocene. Seismic interpretation shows an Upper Messinian sedimentary unit of transparent seismic facies. It could also be found in the lower Guadalquivir and Gharb basins, and towards the West Portuguese margin. Biostratigraphic dating indicate an onset of deposition predating the MSC. Distribution of this transparent unit implicates the dominant deposition of hemipelagic/pelagic deposits during a period of quiescence in the Atlantic margins, subsequent to MOW disconnection. This suggests that weakening or cut-off of the intermediate bottom currents of the Mediterranean-Atlantic exchange through the Betic-Gibraltar-Riffian paleo-gateways precedes the onset of MSC evaporites. This work is crucial for the understanding of sedimentary, paleoceanographic and climatic implications of the Latest Miocene Mediterranean isolation in the Atlantic margins.</p>

A revised stratigraphy for the Palaeocene Agatdalen flora (Nuussuaq Peninsula, western Greenland): correlating fossiliferous outcrops, macrofossils, and palynological samples from phosphoritic nodules

The Cretaceous and Palaeogene floras of western Greenland that were initially described as part of the classical work “Flora fossilis arctica” by Oswald Heer in the 19th century are currently under revision. The Nuussuaq Basin has repeatedly been investigated by geologists and marine invertebrate palaeontologists. These studies provide a modern stratigraphic framework and a basis for revisions of various Cretaceous to Eocene floras from this region, and the correlation of fossil material to stratigraphic units and formal formations. This paper is the first in a series of papers that (i) correlate macrofossil (museum) material and fossil-rich localities with the modern lithostratigraphic framework, (ii) describe new pollen, spores, and other marine/freshwater palynomorphs, and (iii) revise the macrofossil remains from the Agatdalen area (particularly the Danian Agatdal Formation). Since the work of B. Eske Koch in the 1960s and 70s, questions emerged about the correlation of plant fossiliferous outcrops and whether the so-called Agatdalen flora, referred to the Agatdal Formation, originates from a single sedimentary unit or not. In this paper, we summarise the stratigraphy of the Agatdalen area and correlate the fossil plant-bearing outcrops described by Koch to the current lithostratigraphy. We establish which plant fossils belong to the Agatdal Formation and re-assign a great number of other plant fossils to their correct formations. New palynological material is briefly described and correlated to the macrofossil localities and the Agatdal Formation. Previous accounts on the macrofossils (leaves, fruits, seeds) are briefly discussed and directions for future revisions are outlined.

The Ankara Mélange: an indicator of Tethyan evolution of Anatolia

The Ankara Mélange is a complex formed by imbricated slices of limestone block mélanges (Karakaya and Hisarlıkaya Formations), Neotethyan ophiolites (Eldivan, Ahlat and Edige ophiolites), post-ophiolitic cover units (Mart and Kavak formations) and Tectonic Mélange Unit (Hisarköy Formation or Dereköy Mélange). The Karakaya and Hisarlıkaya formations are roughly similar and consist mainly of limestone block mélange. Nevertheless, they represent some important geological differences indicating different geological evolution. Consequently, the Karakaya and Hisarlıkaya formations are interpreted as Eurasian and Gondwanian marginal units formed by fragmentation of the Gondwanian carbonate platform during the continental rifting of the Neotethys in the Middle Triassic time. During the latest Triassic, Neotethyan lithosphere began to subduct beneath the Eurasian continent and caused intense deformation of the marginal units. The Eldivan, Ahlat and Edige ophiolites represent different fragments of the Neotethyan oceanic lithosphere emplaced onto the Gondwanian margin during the Albian–Aptian, middle Turonian and middle Campanian, respectively. The Eldivan Ophiolite is a NE–SW trending and a nearly complete assemblage composed, from bottom to top, of a volcanic-sedimentary unit, a metamorphic unit, peridotite tectonites, cumulates and sheeted dykes. The Eldivan Ophiolite is unconformably covered by Cenomanian–Lower Turonian sedimentary unit. The Eldivan Ophiolite is overthrust by the Ahlat Ophiolite in the north and Edige Ophiolite in the west. The Ahlat ophiolite is an east–west oriented assemblage comprised of volcanic-sedimentary unit, metamorphic unit, peridotite tectonites and cumulates. The Edige Ophiolite consists of a volcanic-sedimentary unit, peridotite tectonites, dunite, wherlite, pyroxenite and gabbro cumulates. The Tectonic Mélange Unit is a chaotic formation of various blocks derived from ophiolites, from the Karakaya and Hisarlıkaya formations and from post-ophiolitic sedimentary units. It was formed during the collision between Anatolian Promontory and Eurasian Continent in the middle Campanian time.

Biostratigraphy and paleoecology of an unusual palynological record from the Aquidauana Formation, Late Pennsylvanian of Paraná Basin

The Aquidauana Formation is a Permo-Carboniferous sedimentary unit, widely stratigraphicaly distributed in the northwestern and northern portions of the Paraná Basin. However, little paleontological data is available from this formation, preventing accurate biostratigraphic and paleoecological interpretations. An abundant, diversified and well preserved assemblage of palynomorphs was recognized from sampling conducted in an outcrop section in Cipolândia District of Aquidauana Municipality, state of Mato Grosso do Sul, Brazil. A total of 35 indigenous palynomorph taxa was recognized, comprising 6 species of spores (related to 5 genera), 28 species of pollen grains (14 genera) and 1 species of chlorophycean algae. Monosaccate pollen grains are exceptionally dominant, representing 90.38% of the association, particularly constituted by species of the genera Cannanoropollis (30.41% of the total assemblage), Potonieisporites (28.14%) and Plicatipollenites (19.52%). This quantitative overrepresentation is not usual from Gondwana deposits, revealing a particular plant dominance of Cordaitales in the terrestrial flora. These results are interpreted as an upland ecology characterized by plants with a moisture-independent reproduction strategy, under a glacial climate influence. Certain species of pollen allow assignment of this assemblage to the Crucisaccites monoletus Zone (Late Pennsylvanian), which had been recognized only in the middle portion of the Itararé Group at the northeastern margin of the basin.