Paleogene Time Research Articles

Age and provenance relationships between the basal Great Valley Group and its underlying basement: implications for initiation of the Great Valley forearc basin, California, U.S.A.

ABSTRACT The Great Valley forearc (GVf) basin, California, records deposition along the western margin of North America during active oceanic subduction from Jurassic through Paleogene time. Along the western GVf, its underlying basement, the Coast Range Ophiolite (CRO), is exposed as a narrow outcrop belt. CRO segments are overlain by the Great Valley Group (GVG), and locally, an ophiolitic breccia separates the CRO from basal GVG strata. New stratigraphic, petrographic, and geochronologic data (3865 detrital and 68 igneous zircon U-Pb ages) from the upper CRO, ophiolitic breccia, and basal GVG strata clarify temporal relationships among the three units, constrain maximum depositional ages (MDAs), and identify provenance signatures of the ophiolitic breccia and basal GVG strata. Gabbroic rocks from the upper CRO yield zircon U-Pb ages of 168.0 ± 1.3 Ma and 165.1 ± 1.2 Ma. Prominent detrital-zircon age populations of the ophiolitic breccia and GVG strata comprise Jurassic and Jurassic–Early Cretaceous ages, respectively, with pre-Mesozoic ages in both that are consistent with sources of North America affinity. Combined with petrographic modal analyses that show abundant volcanic grains (> 50%), we interpret the breccia to be mainly derived from the underlying CRO, with limited input from the hinterland of North America, and the basal GVG to be derived from Mesozoic igneous and volcanic rocks of the Sierra Nevada–Klamath magmatic arc and hinterland. Analysis of detrital-zircon grains from the lower and upper ophiolitic breccia yields MDAs of ∼ 166 Ma and ∼ 151 Ma, respectively. Along-strike variation in Jurassic and Cretaceous MDAs from basal GVG strata range from ∼ 148 to 141 Ma, which are interpreted to reflect diachronous deposition in segmented depocenters during early development of the forearc. The ophiolitic breccia was deposited in a forearc position proximal to North America < 4 Myr before the onset of GVG deposition. A new tectonic model for early development of the GVf highlights the role of forearc extension coeval with magmatic arc compression during the earliest stages of basin development.

Cenozoic tectono-sedimentary evolution of the external rif chain (Morocco) derived from mineralogical and geochemical analysis of mudrocks

A model of the Cenozoic tectono-sedimentary evolution of the External Rif Chain (Morocco) is provided by means of the study of the mineralogical and geochemical composition of mudrocks. To date there was a lack of homogeneous data and of a complete and extensive study of the whole External Rif Zone (ERZ). Therefore, this work shows the study of the whole ERZ where the most representative stratigraphic sections have been selected. This work provides important information about the geodynamic evolution and the variations in source-area provenance related to the growing of the Rif orogenic belt. Although there is still much work to be done, this study aims to improve the knowledge of the Cenozoic tectono-sedimentary evolution of the entire western ERZ with a homogeneous method, with a focus on the paleogeographic and paleotectonic evolution, the paleoweathering and the source areas deduced from mineralogical and geochemical data of the Cenozoic mudrocks. The bulk mineralogy is mainly characterized by the presence of calcite, quartz and dolomite plus ankerite. Feldspars have few percentages. The clay minerals are principally represented by mixed-layer illite/smectite (I/S). Illite and kaolinite are in little amount. Femic minerals, mixed-layer chlorite/smectite (C/S) and chlorite are the most abundant. The I/S features suggest a different thermal condition for the three domains. The chemical composition indicates that the mudrocks can be described as mixtures of carbonates with aluminosilicate components. The Al/Ti, Th/Cr, Th/Sc, La/Th and La/Sc ratios, the Cr/V vs. Y/Ni plot, the V-Ni-Th∗10 and La-Th-Sc ternary diagrams indicate a predominantly felsic source with a minor mafic input more evident in the Paleocene-Eocene samples of the External Intrarif and Mesorif. The External Rif Zones changed in the Cenozoic from a passive margin to a complex foreland system with the incoming of the Alpine tectonic phases. In general, the felsic contribution should be linked to the foreland area consisting in the Middle Atlas and Mesetas massifs made of a crystalline domain. This margin probably presented an intermediate narrow oceanic branch in the External Intrarif-Mesorif boundary that surprisingly should start to close during Paleogene times providing the mafic contribution. This Paleogene tectonic activity in these domains is corroborated by the thermal maturity indicating late diagenesis. The chemical weathering indices, such as the CIA (Chemical index of Alteration) and its modifications, show medium-high values and thus suggest generally moderate paleoweathering conditions in agreement with the predominant amount of I/S.

Shortening and extrusion in the East Anatolian Plateau: How was Neogene Arabia-Eurasia convergence tectonically accommodated?

Deformation in orogenic belts is typically widely distributed but may be localized to form discrete, fast-moving fault zones enclosing semi-rigid microplates. An example is the Anatolian microplate, which is extruding westwards from the East Anatolian Plateau in the Arabia-Eurasia collision zone along the North and East Anatolian Faults that cause devastating earthquakes, including those of February 6, 2023 in Southeast Anatolia. Here, we summarize the orogenic architecture of the East Anatolian Plateau and its underlying kinematic history since the Cretaceous, and use this to reconstruct the tectonic situation that existed at the onset of and during the development of the Neogene East Anatolian Plateau and the Anatolian microplate. The orogen first formed in the late Cretaceous by subduction-accretion of microcontinental lithosphere below Neotethys oceanic lithosphere. Then, in Paleogene time, the accretionary orogen underwent regional upper plate extension, causing crystalline crust exhumation and deep-marine basin formation. From early Miocene time onwards, the extended orogen shortened again and must have accommodated ∼350 km of convergence, making crust up to 45 km thick, and causing >2 km of uplift. Since the ∼13 Ma onset of North Anatolian Fault formation, microplate extrusion absorbed no more than 25 % (∼65 km) of Arabia-Eurasia convergence and even during this time alone, >200 km of convergence must have been accommodated by continued ∼N-S shortening. We highlight the need for field studies of the East Anatolian Plateau to identify where and how this major shortening was accommodated, what role it played in plateau rise and the onset and dynamics of microplate extrusion, and to better assess seismic hazards.

Linking Pacific Plate Motions to Metamorphism and Magmatism in Japan During Cretaceous to Paleogene Times

Plate reconstructions of oceanic domains are generally based on paleo-magnetic and seafloor spreading records. However, uncertainties associated with such reconstructions grow rapidly with increasing geological age because the original oceanic plates have been subducted. Here we synthesize advances in seismic tomographic mapping of subducted plates now lying within the mantle that assist plate reconstructions. Our proposed Japan–NW Pacific subduction histories incorporate tomography results and show three distinct stages comparable to those revealed by geochronology, petrology, and geochemistry. We propose major revisions to previously accepted ideas about the age, kinematics, and identity of the plates outboard of Japan during the Cretaceous–Paleogene Sanbagawa-Ryoke paired metamorphism. These revisions require updates to relevant plate convergence boundary conditions and thermo-dynamic models.

Geodynamic reconstruction of offshore eastern Tunisia during the Cretaceous and Paleogene periods and its impact on hydrocarbon exploration

The analyses of structural, seismostratigraphic patterns and seismic anomalies were conducted using borehole and two-dimensional (2-D) seismic data to reconstruct the geodynamic evolution of offshore eastern Tunisia from the Cretaceous to the Paleogene times. Thirteen third-order sequences (S1 to S13) were identified, and several hiatuses were recognized, which were most likely related to the tectonic event associated with the convergence between Eurasian and African plates. Aptian buildups have also been recognized in the outer platform margin. The growth and distribution of these reefs are controlled by the uplift of fault blocks responsible for the relative sea-level fall which led to sub-aerial exposure and the development of a karstified carbonate platform. The structural features and the major tectonic events as well as the stratigraphic pattern, recognized in offshore eastern Tunisia, are related to the geodynamic evolution of the North African and western Mediterranean basins.The identification of several undrilled reef buildups with significant hydrocarbon potential could replenish the operators' portfolio.

Insect herbivore and fungal communities on Agathis (Araucariaceae) from the latest Cretaceous to Recent.

Agathis (Araucariaceae) is a genus of broadleaved conifers that today inhabits lowland to upper montane rainforests of Australasia and Southeast Asia. A previous report showed that the earliest known fossils of the genus, from the early Paleogene and possibly latest Cretaceous of Patagonian Argentina, host diverse assemblages of insect and fungal associations, including distinctive leaf mines. Here, we provide complete documentation of the fossilized Agathis herbivore communities from Cretaceous to Recent, describing and comparing insect and fungal damage on Agathis across four latest Cretaceous to early Paleogene time slices in Patagonia with that on 15 extant species. Notable fossil associations include various types of external foliage feeding, leaf mines, galls, and a rust fungus. In addition, enigmatic structures, possibly armored scale insect (Diaspididae) covers or galls, occur on Agathis over a 16-million-year period in the early Paleogene. The extant Agathis species, throughout the range of the genus, are associated with a diverse array of mostly undescribed damage similar to the fossils, demonstrating the importance of Agathis as a host of diverse insect herbivores and pathogens and their little-known evolutionary history.

Paleogene paleogeographic reconstructions of the Kutai Basin: Refinement based on outcrop and subsurface data

The Kutai Basin is a Cenozoic sedimentary basin located in the eastern part of Borneo Island. Many studies were done on the eastern part of the basin, which is dominated by Neogene sediments. The west margin of the basin is outcropped onshore and to the east, the basin opens up to the Makassar Strait. Paleogene and older rocks outcrop in the west margin of Kutai Basin. The terrain and the access to the area are difficult and no significant hydrocarbon discovery was made in Paleogene sediments up to now.This study revisited the field works completed in the 1970s by a Shell team, which focused on the Paleogene section of the Kutai Basin. The result was integrated with later studies, and altogether were synthesized into a series of paleogeographic maps. A new set of paleogeographic maps is proposed in this paper, for Middle Eocene, Late Eocene, Early Oligocene, and Late Oligocene levels. The works included in this study comprised outcrop observations, biostratigraphy analysis of the samples and limited seismic in parts of the area. The results were integrated with other more recent work to build the new set of Paleogene paleogeographic maps.Outcrops data and well information show the distribution of shallow marine sediment in the Middle Eocene time with some fluvial input from the north and southwest of the basin. In the Late Eocene, some carbonates developed in the north of the basin. During Early Oligocene, the carbonate complex developed both in the south and in the north of the basin. In the Late Oligocene, the carbonate in the south became more stable. Through Paleogene time the center of Kutai Basin was dominated by the bathyal section.

Thermochronological constraints on the post-Variscan exhumation history of the southeastern Bohemian Massif (Waldviertel and Weinsberg Forest, Austria): palaeogeographic and geomorphologic implications

Resolving the Mesozoic and Cenozoic palaeogeography and geomorphologic development of outcropping Variscan basement is a pre-condition for the understanding of central European geodynamics. For our study, we have applied apatite fission-track (AFT) and apatite (U–Th)/He (AHe) thermochronology to surface rocks of the southeastern Bohemian Massif. 46 samples were examined by the AFT method. Additional AHe dating was applied to 8 of them. The AFT ages range from 251 ± 46 to 60.2 ± 4.8 Ma. AHe ages range from 25 to 525 Ma with rather high intra-sample scatter. On a regional scale, the AFT ages generally decrease from mainly late Variscan in the NE to Late Cretaceous and Paleocene in the SW. This regional age asymmetry relative to the NW–SE trending watershed of the Weinsberg Forest is neither compatible with regional uplift of a single block nor with large-scale lithospheric updoming. The lack of age breaks along late Variscan faults demonstrates that strong vertical offset cannot have occurred in Cretaceous and Cenozoic times. Inverse modeling of thermochronological data indicates regional Early Cretaceous cooling and subsequent reheating during the Late Cretaceous. Rocks of the present-day surface were heated up to a temperature of ca. 80 °C without full reset of the AFT system. This thermal history is compatible with the existence of a large mainland in Early Cretaceous times and a subsequent sedimentary reburial until the Campanian on the order of up to 1 km overburden. Parts of the exhumed weathering basal relief to the N and NE of the Weinsberg Forest are inherited as ‘sealed relief’ from Middle Cretaceous time. The observed regional asymmetry of AFT data is best explained by the development of a continental escarpment adjacent to the North Penninic Ocean in latest Cretaceous to Paleogene times. A final episode of accelerated cooling after ca. 20 Ma, as indicated by thermochronological modeling, is tentatively ascribed to either collisional coupling of the Alpine-Carpathian nappe pile with its northern foreland or to East-Alpine slab detachment.

Systematic Paleontology of Bartonian Larger Benthic Foraminifera from Shahrekord Region in High Zagros, Iran

The Jahrum Formation is characterized by abundant benthic Foraminifera in carbonate beds, partly marly and dolomitic limestones in the Kuh-e-Soukhteh (Shahrekord region). This formation covers a huge stretch of the Zagros Zone which is a part of the central Tethyian realm during the Paleogene time. Bio-stratigraphic analysis of the larger benthic Foraminifera distinguishes one assemblage zone assigned to the late middle Eocene (Bartonian). This new biostratigraphic range is represented by the index fossil Rhabdorites malatyaensis (Sirel) and is correlated with calcareous rocks in the Shiraz area (south Iran), Dhofar section (Oman), and Socotra Island (Yemen). The Jahrum Formation is dominated by rich miliolids-agglutinated Foraminifera with rare small rotaliids and without Nummulites Lamarck and Alveolina d'Orbigny indicating that the formation was deposited in a shallow water environment (nearshore lagoonal zone) with low energy.

Bryozoa and stratigraphy in Paleogene times through the study of Paleogene species from Europe.

The interest in Stratigraphy of Bryozoa is discussed, through the study of the Paleogene fossil species recognized in European basins (excluding the former USSR). It seems that the utility of these fossils in biostratigraphy, mainly within each basin, has been demonstrated. Their interest may be accepted given the great abundance of species found in different Paleogene chronostratigraphic units. Further research is needed to define the status of this phylum for stratigraphic analysis.

Structure and Alpine tectonic evolution of a salt canopy in the western Betic Cordillera (Spain)

Surface geology, well data, and seismic profiles confirm the occurrence of an extensive salt canopy in the western Betic Cordillera. Upper Triassic (Keuper) evaporites were emplaced allochthonously in the South-Iberian paleomargin of the Tethys during Upper Cretaceous–Paleogene time. The canopy was later deformed during the Neogene (Miocene–Pliocene) Alpine compression, overthrusting the South-Iberian Mesozoic platform and cover and the Guadalquivir foreland basin. The orogenic advance of the canopy originated a frontal open toe and an accretionary wedge (the Guadalquivir Accretionary Wedge). This wedge, which is a shaly mélange (with blocks of Triassic evaporites) deformed by foreland-directed thrusts with associated piggyback basins and syn-sedimentary listric faults. The structure of the western Betic Cordillera is described through several regional cross sections. The subsalt level involved a Jurassic–Lower Cretaceous thick section, deformed with inverted half-grabens through foreland-directed salt-detached thrusts (northwest vergence). Contraction affects previous salt structures, like Triassic half-grabens, primary minibasins, salt rollers, and a possible large salt pillow. The subsalt deformation shows a thin-skinned subsalt folded belt detached from the Paleozoic section of the Iberian Massif. The salt canopy shows pervasive basal shearing, internal evaporite flow and folding, and brittle thrusting along possible evaporite stringers and preexisting sutures. The suprasalt series consists of secondary and tertiary minibasins and carapaces or rafts. Secondary minibasins are isolated basins infilled with a deepening Upper Cretaceous–Lower Miocene marine sequence. Rotated carapaces or rafts with a condensed Jurassic–Lower Cretaceous sequence, stacked minibasins and welds are the main features of this part of the Betics. The latest stages of the Alpine contraction are accompanied by syn-tectonic (Tortonian–early Pliocene) sedimentation in slightly deformed gentle, marine–to–continental depocenters (referred to here as tertiary minibasins). This salt canopy is comparable in origin to other allochthonous shale sheets, like in the Gulf of Mexico, although as it was later deformed by Alpine compression, it complements observations in other salt-involved orogens like the western Alps, Sivas Basin or the Salina del Istmo Basin, Mexico.

Review of Geochronologic and Geochemical Data of the Greater Antilles Volcanic Arc and Implications for the Evolution of Oceanic Arcs

AbstractThe Greater Antilles islands of Cuba, Hispaniola, Puerto Rico and Jamaica plus the Virgin Islands host fragments of the fossil convergent margin that records Cretaceous subduction (operated for about 90 m.y.) of the American plates beneath the Caribbean plate and ensuing arc‐continent collision in Late Cretaceous‐Eocene time. The “soft” collision between the Greater Antilles Arc (GAA) and the Bahamas platform (and the margin of the Maya Block in western Cuba) preserved much of the convergent margin. This fossil geosystem represents an excellent natural laboratory for studying the formation and evolution of an intra‐oceanic convergent margin. We compiled geochronologic (664 ages) and geochemical data (more than 1,500 analyses) for GAA igneous and metamorphic rocks. The data was classified with a simple fourfold subdivision: fore‐arc mélange, fore‐arc ophiolite, magmatic arc, and retro‐arc to inspect the evolution of GAA through its entire lifespan. The onset of subduction recorded by fore‐arc units, together with the oldest magmatic arc sequence shows that the GAA started in Early Cretaceous time and ceased in Paleogene time. The arc was locally affected (retro‐arc region in Hispaniola) by the Caribbean Large Igneous Province (CLIP) in Early Cretaceous and strongly in Late Cretaceous time. Despite multiple biases in the database presented here, this work is intended to help overcome some of the obstacles and motivate systematic study of the GAA. Our results encourage exploration of offshore regions, especially in the east where the forearc is submerged. Offshore explorations are also encouraged in the south, to investigate relations with the CLIP.

Assessment of hydrocarbon generative potential of Late Paleocene coals from East Khasi Hills, Meghalaya, North-East India

The study area is situated in the Meghalaya state (East Khasi Hills), North-East India. The notable petroliferous basins that were formed during the Paleogene time occurred in the state of northeast India. This work focused on characterizing the source rock of Late Paleocene (Shella Formation) of Pynursla-Lynkerdem area, East Khasi Hills, Meghalaya for their hydrocarbon potential based on Rock-Eval pyrolysis and elemental data. The coals of the Pynursla-Lynkerdem area have been characterized by high total organic carbon (TOC) range between 67.2 wt% and 74.5 wt%. The remaining hydrocarbon yield (S 2) ranges from 215.5 to 294.0 mg HC/g rock. S 2 and TOC data plots entail that these coals contain Type II–III kerogen and can act as a good hydrocarbon source rock. The hydrogen index (HI) ranges from 311.1 to 405.7 mg HC/g TOC, which indicates most of the sample can generate gases. T max varies between 405 and 433 °C (less than 435 °C), revealing the immaturity of organic matter. The plot of elemental composition places these samples from sub-bituminous to high volatile bituminous in rank and furnishes these coals’ suitability for gasification.

Tromsø–Bjørnøya Composite Tectono-Sedimentary Element, Barents Sea

Abstract The Tromsø–Bjørnøya Composite Tectono-Sedimentary Element (CTSE) in the southwestern Barents Sea comprises strata of Late Paleozoic–Paleocene age. Since the Paleozoic Caledonian Orogeny, the structural evolution of the CTSE is mainly related to extension, culminating in Late Jurassic–Early Cretaceous hyperextension. Some compressive deformation observed during Late Cretaceous–Paleogene times may relate to activity in the North Atlantic prior to the Early Eocene onset of seafloor spreading between Norway and Greenland. The sedimentary succession may be up to 14 km thick. It comprises Late Paleozoic continental facies, followed by carbonates, evaporites, and eventually cherts and marine clastic material. The overlying Triassic–Paleocene succession is entirely siliciclastic, reflecting Triassic–Middle Jurassic deltaic and shallow-marine conditions followed by deeper-marine conditions during Late Jurassic–Paleocene times. Primary reservoirs are encountered in the latest Triassic–Middle Jurassic succession, with secondary reservoirs found in the Late Jurassic–Early Cretaceous synrift succession, and in Paleocene strata. The primary source rock for petroleum is of Late Jurassic–Early Cretaceous age. Other source rocks include strata of Triassic and Barremian age, and a recently observed unit of Cenomanian–Early Turonian age.

Aseismic and seismic impact on development of soft-sediment deformation structures in deep-marine sand-shaly Crocker fan in Sabah, NW Borneo

Soft-sediment deformation structures are present within the deep-marine fan of the West Crocker Formation, Sabah Basin, NW Borneo. Focus of this study is to highlight the impact of seismic and aseismic activities on the development of these structures and their distribution in deep-marine fan. Twenty-nine types of deformation structures were identified during the study of twelve exposed sections. These structures were grouped into five categories: i) water-escape structures, ii) sole marks, iii) clastic intrusions, iv) deformed laminations, and v) syn-depositional brittle and ductile deformation structures. The sediment deformation is interpreted to be caused either by aseismic processes like slope failure, gravity collapse, sediment overloading, density gradient, seismic induced mechanisms such as earthquakes, tectonic uplift, or combined effect of seismic and aseismic events. These structures are classified based on type of features developed during semi-consolidated phase of rock deposition. The seismite structures i.e., clastic intrusions, deformed laminations, and syn-depositional structures are correlated with active collisional tectonics during the Late Paleogene times in the Sabah Basin. In the present work, a generalized conceptual model has also been proposed for the development of soft-sediment deformation structures in a submarine fan environment. Dewatering structurers and rapid sedimentation features are associated with inner fan, load and flame structures are present within middle fan, while contorted layers, slumps and mass-transport deposits are linked with distal fan settings.

The Geodynamic Evolution of Iran

Iran is a remarkable geoscientific laboratory where the full range of processes that form and modify the continental crust can be studied. Iran's crustal nucleus formed as a magmatic arc above an S-dipping subduction zone on the northern margin of Gondwana 600–500 Ma. This nucleus rifted and drifted north to be accreted to SW Eurasia ∼250 Ma. A new, N-dipping subduction zone formed ∼100 Ma along ∼3,000 km of the SW Eurasian margin, including Iran's southern flank; this is when most of Iran's many ophiolites formed. Iran evolved as an extensional continental arc in Paleogene time (66–23 Ma) and began colliding with Arabia ∼25 Ma. Today, Iran is an example of a convergent plate margin in the early stages of continent-continent collision, with a waning magmatic arc behind (north of) a large and growing accretionary prism, the Zagros Fold-and-Thrust Belt. Iran's crustal evolution resulted in both significant economic resources and earthquake hazards. ▪ Iran is a natural laboratory for studying how convergent plate margins form, evolve, and behave during the early stages of continental collision. ▪ Iran formed in the past 600 million years, originating on the northern flank of Gondwana, rifting away, and accreting to SW Eurasia. ▪ Iran is actively deforming as a result of collision with the Arabian plate, but earthquakes do not outline the position of the subducting slab. ▪ The Cenozoic evolution of Iran preserves the main elements of a convergent plate margin, including foredeep (trench), accretionary prism, and magmatic arc.

(U-Th)/He Thermochronology of the Indus Group, Ladakh, Northwest India: Is Neogene Cooling a Continental-Scale Thermal Event in the India-Asia Collision Zone?

Abstract The India-Asia continental collision zone archives a sedimentary record of the tectonic, geodynamic, and erosional processes that control the thermal history of the Himalayan orogenic interior since the onset of collision in early Paleogene time. In this paper, we present new (U-Th)/He thermochronometric cooling age data from 18 detrital zircons (ZHe) and 19 detrital apatites (AHe) of the early Eocene–early Miocene (ca. 50–23 Ma) continental facies of the Indus Group along the India-Asia collision zone in Ladakh, northwest (NW) India. This along-strike regional-scale low-temperature thermochronometric data set from the Indus basin is the first report of ZHe and AHe cooling ages from western and eastern Ladakh. Thermal modeling of our ZHe and AHe cooling ages indicates a postdepositional Neogene cooling signal in the Indus Group. Cooling initiated at ca. 21–19 Ma, was operational along the ~300 km strike of the collision zone in NW India by ca. 11 Ma, and continued until ca. 3 Ma. The Miocene cooling signal, also present along the India-Asia collision zone in south Tibet, is a continental-scale cooling event likely linked to increased erosional efficiency by the Indus and Yarlung Rivers across an elevated region resulting from the subduction dynamics of the underthrusting Indian plate.

Late Cretaceous to Paleogene exhumation in central Europe – localized inversion vs. large-scale domal uplift

Abstract. Large parts of central Europe experienced exhumation in Late Cretaceous to Paleogene time. Previous studies mainly focused on thrusted basement uplifts to unravel the magnitude, processes and timing of exhumation. This study provides, for the first time, a comprehensive thermochronological dataset from mostly Permo-Triassic strata exposed adjacent to and between the basement uplifts in central Germany, comprising an area of at least some 250–300 km across. Results of apatite fission-track and (U–Th) / He analyses on > 100 new samples reveal that (i) kilometre-scale exhumation affected the entire region, (ii) thrusting of basement blocks like the Harz Mountains and the Thuringian Forest focused in the Late Cretaceous (about 90–70 Ma), while superimposed domal uplift of central Germany is slightly younger (about 75–55 Ma), and (iii) large parts of the domal uplift experienced removal of 3 to 4 km of Mesozoic strata. Using spatial extent, magnitude and timing as constraints suggests that thrusting and crustal thickening alone can account for no more than half of the domal uplift. Most likely, dynamic topography caused by upwelling asthenosphere significantly contributed to the observed pattern of exhumation in central Germany.

The Cenozoic Malaguide Basin from Sierra Espuña (Murcia, S Spain): An Example of Geological Heritage

The Cenozoic Malaguide Basin from Sierra Espuña (Internal Betic Zone, S Spain) due to the quality of outcropping, areal representation, and continuity in the sedimentation can be considered a key-basin. In the last 30 years, a large number of studies with very different methodological approaches have been done in the area. Models indicate an evolution from passive margin to wedge-top basin from Late Cretaceous to Early Miocene. Sedimentation changes from limestone platforms with scarce terrigenous inputs, during the Paleocene to Early Oligocene, to the deep basin with huge supplies of turbidite sandstones and conglomerates during the Late Oligocene to Early Miocene. The area now appears structured as an antiformal stack with evidence of synsedimentary tectonics. The Cenozoic tectono-sedimentary basin evolution is related to three phases: (1) flexural tectonics during most of the Paleogene times to create the basin; (2) fault and fold compartmentation of the basin with the creation of structural highs and subsiding areas related to blind-fault-propagation folds, deforming the basin from south to north during Late Oligocene to Early Aquitanian times; (3) thin-skin thrusting tectonics when the basin began to be eroded during the Late Aquitanian-Burdigalian. In recent times some works on the geological heritage of the area have been performed trying to diffuse different geological aspects of the sector to the general public. A review of the studies performed and the revisiting of the area allow proposing different key-outcrops to follow the tectono-sedimentary evolution of the Cenozoic basin from this area. Eight sites of geological interest have been selected (Cretaceous-Cenozoic boundary, Paleocene Mula Fm, Lower Eocene Espuña-Valdelaparra Fms, Middle Eocene Malvariche-Cánovas Fms, Lowermost Oligocene As Fm, Upper Oligocene-Lower Aquitanian Bosque Fm, Upper Oligocene-Aquitanian Río Pliego Fm, Burdigalian El Niño Fm) and an evaluation has been performed to obtain four parameters: the scientific value, the educational and touristic potential, and the degradation risk. The firsts three parameters obtained values above 50 being considered of “high” or “very high” interest (“very high” in most of the cases). The last parameter shows always values below 50 indicating a “moderate” or “low” risk of degradation. The obtained values allow us considering the tectono-sedimentary evolution of this basin worthy of being proposed as a geological heritage.

АУТИГЕННЫЕ МИНЕРАЛЫ ВУЛКАНОГЕННО-ОСАДОЧНЫХ ПОРОД ПАЛЕОЗОЙСКО-КАЙНОЗОЙСКОГО ВОЗРАСТА ЮЖНОГО ПРИМОРЬЯ

Authigenic minerals in volcanogenic-sedimentary and sedimentary rocks of Southern Primorye from Permian to Miocene time have been studied. Corrensite, rectorite, highly ordered mixed-layer differences of the chlorite-smectite (corrensite-like) and mica-smectite (rectorite-like) types, mica, vermiculite-like differences (?), chlorite, defective chlorite, kaolinite, smectite, calcite, and zeolites were found. Such a set of minerals indicates that the sedimentary layer in the studied sedimentary basins could be three to five kilometer thick, and the temperature of their formation is more than 150°C. The formation of the Lower Cretaceous and Paleocene sedimentary strata has similar features, and probably proceeded first in a shallow sea basin setting of the continental margin (rift stage), sometimes under conditions close to evaporitic (presence of corrensite?), with a frequent change of the facial situation from shallow to deep sedimentation, episodic supplies of volcanic material, and gradual deepening of sedimentation basins. It can be assumed that in Early Cretaceous and Paleogene times, a series of discrete sedimentation basins along the northeastern Asia continental margin developed in a single mineralogical, tectonic, and sedimentological regime of crustal extension: minerals accumulated in the sediments, which in the process of epigenesis transformed in the following directions: a) smectite-rectorite-mica; and b) smectite (palygorskite, sepiolite?) - corrensite-chlorite. In the studied sedimentary complexes three mineralogical «layers» are distinguished: 1) chlorite-mica – mica-chlorite (Permian - Cretaceous); 2) transitional from chlorite and mica to smectite - developed are corrensite, rectorite and highly ordered mixed-layer corrensite-like and rectorite-like minerals (Cretaceous - Paleocene-Eocene), and 3) smectite (from Oligocene to the present).