Late Eocene Oligocene Research Articles

Characterization of Modern Turtle Death Sites for Comparison with Late Eocene and Early Oligocene Turtle Sites

Taphonomic studies of extant turtles are useful for interpreting the taphonomy of fossil turtles. In order to provide modern comparators for fossil turtle sites, we have characterized two modern turtle (Chrysemys picta) deathsites; one in northwestern Nebraska and one in southwestern South Dakota. During these studies we characterized carapace position (up or down), presence or absence of non-shell elements, relative spatial position of the turtles and presence of shell disturbances (lesions). In the Trunk Butte site (Nebraska), six turtles were in carapace up position, five were in carapace down and one was not determinable. In addition, seven of those turtles contained some non-shell elements and five had indeterminable non-shell element status. At the Buffalo Gap site (South Dakota), four were carapace down, two were carapace up and three were not determinable for that character. Six of these had non-shell elements associated with them and three had no non-shell elements. The occurrence of turtles in the carapace down position suggests either the presence of medium to large scavengers able to overturn a turtle or that the turtle died while in the water and overturned while sinking. The spatial distributions of turtles in the two modern sites were also plotted and compared to that of two Whitney (Brule Formation, White River Group) and one Chadron (White River Group) site to address the hypothesis that the fossil assemblages were associated with small ponds. The results suggest that the fossil turtle sites were not the result of death events associated with small ponds, nullifying that hypothesis.

Key issues on the post-Mesozoic Southern Caribbean Plate boundary

Abstract A lithospheric-scale, geodynamic model of the Caribbean southern boundary takes into account tectonic and stratigraphic elements previously unconsidered or not well constrained. The Falcón, Bonaire, Blanquilla and Grenada basins are parts of a former single back-arc basin associated with the migrating Mesozoic Caribbean Arc in Late Eocene–Oligocene times. Spreading of the crescent-shaped basin was triggered by declining Caribbean eastward motion in response to increased convergence between the two Americas at around 38–33 Ma. Dextral wrenching along the southern boundary started in western Venezuela at 17–15 Ma and progressed eastward to the El Pilar Fault by 12 Ma. Eastward motion of the Caribbean relative to South America was earlier accommodated by east-progressing, non-partitioned oblique subduction and collision, as illustrated today in eastern Venezuela around the Los Bajos–El Soldado fault system. Extrusion of the Maracaibo and Bonaire blocks towards the NNE started around 5 Ma, thus the dextral Boconó fault is a young feature. Total plate boundary Cenozoic dextral wrenching recorded onshore Venezuela does not exceed 100 km and is more likely to be in the order of 55 km.

Mesozoic and Cenozoic vertical movements in the Atlas system (Algeria, Morocco, Tunisia): An overview

The E–W trending Atlas System of Maghreb consists of weakly shortened, intra-continental fold belts associated with plateau areas (“Mesetas”), extending between the south-westernmost branch of the Mediterranean Alpine Belt (Rif-Tell) and the Sahara Platform. Although the Atlas system has been erected contemporaneously from Morocco to Algeria and Tunisia during the Middle Eocene to Recent, it displays a conspicuous longitudinal asymmetry, with i) Paleozoic outcrops restricted to its western part; ii) highest elevation occurring in the west, both in the Atlas System and its foreland (Anti-Atlas); iii) low elevation corridors (e.g. Hodna) and depressed foreland (Tunisian Chotts and Sahel area) in the east. We analyse the origin of these striking contrasts in relation with i) the Variscan heritage; ii) crustal vertical movements during the Mesozoic; iii) crustal shortening during the Cenozoic and finally, iv) the occurrence of a Miocene–Quaternary hot mantle anomaly in the west. The Maghreb lithosphere was affected by the Variscan orogeny, and thus thickened only in its western part. During the Late Permian–Triassic, a paleo-high formed in the west between the Central Atlantic and Alpine Tethys rift systems, giving birth to the emergent/poorly subsident West Moroccan Arch. During the late Middle Jurassic–Early Cretaceous, Morocco and western Algeria were dominantly emergent whereas rifting lasted on in eastern Algeria and Tunisia. We ascribe the uplift of the western regions to thermal doming, consistent with the Late Jurassic and Barremian gabbroic magmatism observed there. After the widespread transgression of the high stand Cenomanian–Turonian seas, the inversion of the Atlas System began during the Senonian as a consequence of the Africa–Eurasia convergence. Erosion affected three ENE-trending uplifted areas of NW Africa, which we consider as lithospheric anticlines related to the incipient Africa–Europe convergence. In contrast, in eastern Algeria and Tunisia a NW-trending rift system developed contemporaneously (Sirt rifting), normal to the general trend of the Atlas System. The general inversion and orogenesis of the Atlas System occurred during two distinct episodes, Middle–Late Eocene–Oligocene and Late Miocene–Pliocene, respectively, whereas during the intervening period, the Africa–Europe convergence was mainly accommodated in the Rif-Tell system. Inversion tectonics and crustal thickening may account for the moderate uplift of the eastern Atlas System, not for the high elevation of the western mountain ranges (Middle Atlas, High Atlas, Anti-Atlas). In line with previous authors, we ascribe part of the recent uplift of the latter regions to the occurrence of a NE-trending, high-temperature mantle anomaly, here labelled the Moroccan Hot Line (MHL), which is also marked by a strip of late Miocene–Quaternary alkaline magmatism and significant seismicity.

Structural control of the emplacement of the Portrerillos porphyry copper, central Andes of Chile

The Potrerillos porphyry is located in the Late Eocene–Oligocene metallogenic belt of porphyry copper deposits of Chile, Cordillera de Domeyko, central Andes. It is formed of a porphyritic biotite–hornblende monzonite that was emplaced at less than 1000 m depth. The intrusion has a cylindrical vertical form at depth, whereas its uppermost section resembles a mushroom whose stem is inclined 20–25° to the northwest. The location of the Potrerillos porphyry coincides with a major facies and east–west thickness change in Jurassic to Late Cretaceous marine sedimentary and Tertiary volcanic host rocks. Structurally, the porphyry was emplaced at the intersection between the northeast-oriented Potrerillos fold-and-thrust belt, and a system of northwest-trending strike-slip faults of the Ciénaga fault system. Both structural elements are related to a sinistral regional transpression that was active during the Middle to Late Eocene. The north–northeast trending Sierra Castillo-Agua Amarga fault system was trench-linked with an oblique subduction along the Peru–Chile trench in the southwestern part of South America at this time. One of the main structural elements of the Potrerillos fold-and-thrust belt is the eastward verging Potrerillos Mine reverse fault. We demonstrate a syntectonic relationship between the Potrerillos porphyry emplacement and the onset of the Potrerillos Mine fault. The control at the shallowest levels of the Potrerillos porphyry emplacement was studied by means of a structural analysis of folds, cleavage and deformed oolites in the country rock. This analysis suggests that the porphyry occupied the core of an anticline. The form of this anticline was modeled as a fault-propagation-fold taking into account a 200 m displacement along the basal fault and a local shortening of 45.5% occurred. This model is compatible with a limited displacement along the Potrerillos Mine fault under hot, ductile conditions. The remaining displacement of 1600 m would have taken place afterwards under cold, brittle conditions. The Potrerillos porphyry was emplaced during a transpressional regime within the Potrerillos fold-and-thrust belt. The fact that the cleavage does not show a concentric distribution around the Potrerillos porphyry, discounts the possibility of a forced emplacement of the porphyry, pushing aside its wall rocks. This is reinforced by the deformed oolites which do not show a strain gradient from outside towards the edge of the body. The clockwise transection of the fold axes by the cleavage and the southeast direction of displacement along the Potrerillos Mine fault are interpreted as related to the regional sinistral transpression related to the Sierra Castillo Fault movement.

Timing of tectonic emplacement of the ophiolites and terrane paleogeography in the Hellenides

The timing of tectonic emplacement of the ophiolites is analyzed in the four oceanic terranes of the Hellenides (H 2, H 4, H 6, H 8). The criteria for this analysis are based on: a) the post-emplacement sedimentary cover or intrusive rocks, b) the syn-emplacement tectonostratigraphic formations and c) the youngest rocks involved in the structure of the autochthon and the allochthon unit in each case. The timing becomes younger towards the more external tectonic units of the Hellenides with: (i) Late Eocene–Oligocene age in the external ophiolite belt of the Pindos–Cyclades oceanic terrane H 2, (ii) Late Jurassic–Early Cretaceous age in the internal ophiolite belt of the Vardar/Axios oceanic terrane H 4 , (iii) Post-Liassic–pre-Late Jurassic age in the ophiolites of Lesvos–Circum Rhodope oceanic terrane H 6 and (iv) Pre-Late Jurassic age in the ophiolites of Volvi–Eastern Rhodope terrane H 8. An ophiolite obduction model can be applied, with the ophiolitic nappes always emplaced on top of pre-Alpine continental terranes with Mesozoic shallow-water carbonate platforms. The geometry of the continental terranes drifting during the Mesozoic within the Tethys Ocean controls the number and dimensions of the Tethyan oceanic basins. Where a continental terrane dies out, the two adjacent oceanic basins merge into one larger basin. This seems to be the case of the Pelagonian terrane (H 3), which is terminated north of Skopje, where the Pindos oceanic basin (H 2) merges with the Vardar/Axios oceanic basin (H 4).

New bats (Mammalia: Chiroptera) from the late Eocene and early Oligocene, Fayum Depression, Egypt

ABSTRACT Paleogene bats from Africa are rare with only scant records from Tunisia, Egypt, and Tanzania having been described in the past. Four new genera and six new species of microchiropteran bats are described here from the late Eocene (37–34 Ma) of the Fayum Depression in northern Egypt. Included among these new taxa are the first and only African record of a fossil rhinopomatid and the earliest African records of megadermatids, emballonurids, and vespertilionids. Additionally, a new genus and two new species of the Afro-Arabian bat family Philisidae are described. The new Fayum philisids are the oldest representatives of this family, are represented by the largest species thus far recorded for the group, and include one of the largest fossil bats known. Previous biogeographic reconstructions suggest that most Old World bat families had their origin in Laurasia but several modern bat families may have diversified only after their initial dispersal into Africa. Bats and primates may have entered Africa during the same dispersal event early in the Paleogene.

Sheetflow fluvial processes in a rapidly subsiding basin, Altiplano plateau, Bolivia

AbstractAlthough facies models of braided, meandering and anastomosing rivers have provided the cornerstones of fluvial sedimentology for several decades, the depositional processes and external controls on sheetflow fluvial systems remain poorly understood. Sheetflow fluvial systems represent a volumetrically significant part of the non‐marine sedimentary record and documented here are the lithofacies, depositional processes and possible roles of rapid subsidence and arid climate in generating a sheetflow‐dominated fluvial system in the Cenozoic hinterland of the central Andes. A 6500 m thick succession comprising the Late Eocene–Oligocene Potoco Formation is exposed continuously for >100 km along the eastern limb of the Corque syncline in the high Altiplano plateau of Bolivia. Fluvial sandstone and mudstone units were deposited over an extensive region (>10 000 km2) with remarkably few incised channels or stacked‐channel complexes. The Potoco succession provides an exceptional example of rapid production of accommodation sustained over a prolonged period of time in a non‐marine setting (>0·45 mm year−1 for 14 Myr). The lower ≈4000 m of the succession coarsens upward and consists of fine‐grained to medium‐grained sandstone, mudstone and gypsum deposits with palaeocurrent indicators demonstrating eastward transport. The upper 2500 m also coarsens upward, but contains mostly fine‐grained to medium‐grained sandstone that exhibits westward palaeoflow.Three facies associations were identified from the Potoco Formation and are interpreted to represent different depositional environments in a sheetflow‐dominated system. (i) Playa lake deposits confined to the lower 750 m are composed of interbedded gypsum, gypsiferous mudstone and sandstone. (ii) Floodplain deposits occur throughout the succession and include laterally extensive (>200 m) laminated to massive mudstone and horizontally stratified and ripple cross‐stratified sandstone. Pedogenic alteration and root casts are common. (iii) Poorly confined channel and unconfined sheet sandstone deposits include laterally continuous beds (50 to >200 m) that are defined primarily by horizontally stratified and ripple cross‐stratified sandstone encased in mudstone‐rich floodplain deposits.The ubiquitous thin‐sheet geometry and spatial distribution of individual facies within channel sandstone and floodplain deposits suggest that confined to unconfined, episodic (flash) flood events were the primary mode of deposition. The laterally extensive deposition and possible distributary nature of this sheetflow‐dominated system are attributed to fluvial fan conditions in an arid to semi‐arid, possibly seasonal, environment. High rates of sediment accumulation and tectonic subsidence during early Andean orogenesis may have favoured the development and long‐term maintenance of a sheetflow system rather than a braided, meandering or anastomosing fluvial style. It is suggested here that rapidly produced accommodation space and a relatively arid, seasonal climate are critical conditions promoting the generation of sheetflow‐dominated fluvial systems.

Sedimentology of the NW margin of the Arabian plate and the SW–NE trending Nahr El-Kabir half-graben in northern Syria during the latest Cretaceous and Cenozoic

The Late Cretaceous (Maastrichtian) to Recent sedimentary record of NW Syria documents the palaeoenvironments and regional tectonic setting during a time when the Neotethys ocean to the north was closing, culminating in regional collision by mid-Miocene time. This detailed sedimentological study builds on a biostratigraphical framework established by Russian workers. During the mid-Maastrichtian the Baer-Bassit ophiolite and related melange were emplaced southwards from Neotethys onto the northern margin of the Arabian (African) plate, resulting in flexurally controlled deepening to the south. After short-lived emergence and erosion of emplaced units a renewed marine transgression ushered in shelf-depth, open-marine carbonate deposition during the Palaeocene–early Eocene. This deposition was characterized by generally westward-channelised mass flow from shallow-marine carbonate banks to the east, probably influenced by storm conditions. Flexurally controlled uplift and erosion took place during late Eocene–Oligocene, related to final closure of Neotethys. Shelf-depth carbonate deposition resumed during the Aquitanian (early Miocene), influenced by tectonic subsidence. During the Burdigalian, a SW–NE trending, narrow (up to 15 km wide), linear (∼ 60 km long) basin developed in the vicinity of the present-day Nahr-El Kabir river valley. This basin is attributed to extension or transtension along the Nahr El-Kabir Fault. This important lineament runs onshore from the southern limit of the Cyprus arc (Tartous Ridge), through NW Syria. It is then offset by the Dead Sea Transform in the Ghab Valley, before merging with the South Anatolian Transform Fault in Turkey further northeast. The basin in NW Syria developed into the asymmetrical Nahr El-Kabir half-graben during the mid-Miocene with uplift of the northern margin and rapid fault-controlled subsidence of the basin axis. Large volumes of terrigenous clastic and shallow-marine bioclastic material were redeposited from the flanks into the axis of the basin, mainly as gravity flows. Shelf-depth carbonate deposition characterized both basin flanks, especially the southern margin. Regression culminated in gypsum and marl precipitation in tectonically active local depocentres during the Messinian salinity crisis. Pliocene re-flooding established argillaceous shelf deposition within and around the pre-existing basin, coupled with local alkaline basalt volcanism and faulting in the southern, coastal area. Regional regression gave rise to prominently channelised bioclastic sedimentation by the late Pliocene. The Quaternary was marked by regional uplift and terracing, influenced by glacio-eustatic sea level change, climatic change and further movement along the Nahr El-Kabir Fault. The dominant control on basin development was thus local tectonics related to movements along the El-Kabir lineament and its interaction with regional-scale tectonic events, while eustasy played a subsidiary, modifying role.

The Variscan tectonic inheritance of the Upper Rhine Graben: evidence of reactivations in the Lias, Late Eocene–Oligocene up to the recent

Processing of gravity and magnetic maps shows that the basement of the Upper Rhine Graben area is characterized by a series of NE–SW trending discontinuities and elongated structures, identified in outcrops in the Vosges, Black Forest, and the Odenwald Mountains. They form a 40 km wide, N30–40° striking, sinistral wrench-zone that, in the Visean, shifted the Variscan and pre-Variscan structures by at least 43 km to the NE. Wrenching was associated with emplacement of several generations of plutonic bodies emplaced in the time range 340–325 Ma. The sub-vertical, NE–SW trending discontinuities in the basement acted as zones of weakness, susceptible to reactivation by subsequent tectonism. The first reactivation, marked by mineralizations and palaeomagnetic overprinting along NE–SW faults of the Vosges Mountains, results from the Liassic NW–SE extension contemporaneous with the break-up of Pangea. The major reactivation occurred during the Late Eocene N–S compression and the Early-Middle Oligocene E–W extension. The NE–SW striking basement discontinuities were successively reactivated as sinistral strike-slip faults, and as oblique normal faults. Elongated depocenters appear to form in association with reactivated Variscan wrench faults. Some of the recent earthquakes are located on NE–SW striking Variscan fault zones, and show sinistral strike-slip focal mechanisms with the same direction, suggesting also present reactivation.

Geochemistry and geodynamic setting of Late Cretaceous-Miocene basalts in the southern Korean Peninsula

Newly obtained data highlight strong geological and geochemical differences between Late Cretaceous-Paleogene and Eocene-Middle Miocene volcanic rocks in the southern Korean Peninsula. The rocks are spatially separated and differ in the proportions of acid and basic varieties. The Late Cretaceous-Paleogene basalts are similar to suprasubduction rocks in having high Al2O3, LILE, and Th contents, and low TiO2 and HFSE contents. The Miocene basalts have a composition intermediate between those of subduction and within-plate rocks. Compared to subduction rocks, they are lower in radiogenic Sr, K, LILE (Cs, Rb, Ba), and Th and higher in MgO, Ni, Ti, and HREE. A drastic change in U, Ba, Rb, Ce, Th, and 87Sr/86Sr in the basic volcanic rocks of the southern Korean Peninsula at the Late Cretaceous-Paleogene boundary suggests a decreasing sedimentary contribution to the magma. The latter testifies to a change in the direction of the motion of the oceanic and continental plates, increasing compressional forces and, finally, the cessation of subduction. The synthesis of the original authors and published data on Cenozoic volcanism of the southern Korean Peninsula and the eastern Sikhote Alin showed that the tectonic evolution of the eastern Eurasian margin occurred in four stages: Late Cretaceous-Paleogene, Eocene-Oligocene, Early, and Middle-Miocene.

Counterclockwise rotation of late Eocene–Oligocene fore‐arc deposits in southern Peru and its significance for oroclinal bending in the central Andes

The results of a paleomagnetic study along the fore arc of southern Peru (15–18°S) and northern Chile (18–19°S) are reported from middle to late Miocene ignimbrites (7 sites), late Oligocene to early Miocene ignimbrites (72 sites), Paleogene sediments (20 sites), and Mesozoic and Paleocene volcanics and intrusions (31 sites). Comparison of locality‐mean directions with expected paleomagnetic directions indicates vertical axis rotations ranging from 5.2 ± 11.3° clockwise to 55.6 ± 7.0° counterclockwise. Spatially, the magnitude of counterclockwise rotations increases northward from ∼0° within the Chilean fore arc south of 18°30′S to >45° north of 16°30′S. In southern Peru, paleomagnetic rotations recorded in Paleogene red beds decrease from late Eocene to late Oligocene, whereas Miocene ignimbrites display no evidence of rotation. These new results confirm that the rotations recorded in the fore arc of southern Peru were acquired at least before ∼15 Ma, and probably before 25 Ma, and thus prior to the late Neogene shortening of the sub‐Andes. The onset of major Andean shortening in the Eastern Cordillera during the latest Eocene–earliest Oligocene is interpreted to have triggered the bending of the Peruvian fore arc. The region of the Peruvian fore arc with the largest rotations appears to be the fore‐arc counterpart of the Abancay deflection, a remarkable NE‐SW offset in the axis of the Eastern Cordillera induced by a major regional preorogenic structure. We underline that the Abancay deflection should be seen as the northwestern boundary, and therefore as a key element, of the Bolivian Orocline.

Interaction between structural inheritance and extension direction during graben and depocentre formation: An experimental approach

Analysis of structural rift architecture shows that the graben formation is commonly controlled by the contemporaneous activity of two fault trends with an angular obliquity of approximately 40°. Inspection of the crustal basement and geophysical data reveals that these faults are parallel to inherited oblique crustal and lithospheric discrete fabrics, which are reactivated during the extension event. We conducted experiments at crustal scale to determine the role of the coeval reactivation of such oblique inherited fabrics in the graben and depocentre development. Experimentally the oblique inherited lithospheric faults were simulated by a basal discrete velocity discontinuity (VD) characterised by two different angles ( α) with respect to the extension direction at the intersection of the VDs. Our models show that besides the extension direction which induces the formation of linear or independent en-echelon grabens, the intersection of the two oblique VD segments controls the location of the depocentre and concentrates subsidence. For different stretching direction values, the depocentre geometry varies from strongly asymmetric to symmetric when the stretching direction corresponds to the bisecting line of the two VD segments. Applied to the Upper Rhine graben (central segment of the West European rift), our models allow interpretation of the development of the Late Eocene–Oligocene depocentres at the intersection of two main oblique inherited structures, as the result of a constant NW–SE extension direction. Concerning the southern East African rift, the graben geometries and the evolution of the subsidence during the Mio-Pliocene period may be explained by the reactivation of two main Pan-African inherited shear zones with an E–W direction of extension.

Asynchronous Colonization of Madagascar by the Four Endemic Clades of Primates, Tenrecs, Carnivores, and Rodents as Inferred from Nuclear Genes

Madagascar harbors four large adaptive radiations of endemic terrestrial mammals: lemurs, tenrecs, carnivorans, and rodents. These rank among the most spectacular examples of evolutionary diversification, but their monophyly and origins are debated. The lack of Tertiary fossils from Madagascar leaves molecular studies as most promising to solve these controversies. We provide a simultaneous reconstruction of phylogeny and age of the four radiations based on a 3.5-kb data set from three nuclear genes (ADRA2B, vWF, and AR). The analysis supports each as a monophyletic clade, sister to African taxa, and thereby identifies four events of colonization out of Africa. To infer the time windows for colonization, we take into account both the divergence from the closest non-insular sister group and the initial intra-insular radiation, which is a novel but conservative approach in studies of the colonization history of Madagascar. We estimate that lemurs colonized Madagascar between 60 million years ago (Mya) (split from lorises) and 50 Mya (lemur radiation) (70-41 Mya taking 95% credibility intervals into account), tenrecs between 42 and 25 Mya (50-20 Mya), carnivorans between 26 and 19 Mya (33-14 Mya), and rodents between 24 and 20 Mya (30-15 Mya). These datings suggest at least two asynchronous colonization events: by lemurs in the Late Cretaceous-Middle Eocene, and by carnivorans and rodents in the Early Oligocene-Early Miocene. The colonization by tenrecs may have taken place simultaneously with either of these two events, or in a third event in the Late Eocene-Oligocene. Colonization by at least lemurs, rodents, and carnivorans appears to have occurred by overseas rafting rather than via a land bridge hypothesized to have existed between 45 and 26 Mya, but the second scenario cannot be ruled out if credibility intervals are taken into account.

Mesozoic–Tertiary structural evolution of an extensional gneiss dome—the Kesebir–Kardamos dome, eastern Rhodope (Bulgaria–Greece)

The tectonic evolution of the Rhodope massif involves Mid-Cretaceous contractional deformation and protracted Oligocene and Miocene extension. We present structural, kinematic and strain data on the Kesebir–Kardamos dome in eastern Rhodope, which document early Tertiary extension. The dome consists of three superposed crustal units bounded by a low-angle NNE-dipping detachment on its northern flank in Bulgaria. The detachment separates footwall gneiss and migmatite in a lower unit from intermediate metamorphic and overlying upper sedimentary units in the hanging wall. The high-grade metamorphic rocks of the footwall have recorded isothermal decompression. Direct juxtaposition of the sedimentary unit onto footwall rocks is due to local extensional omission of the intermediate unit. Structural analysis and deformational/metamorphic relationships give evidence for several events. The earliest event corresponds to top-to-the SSE ductile shearing within the intermediate unit, interpreted as reflecting Mid-Late Cretaceous crustal thickening and nappe stacking. Late Cretaceous–Palaeocene/Eocene late-tectonic to post-tectonic granitoids that intruded into the intermediate unit between 70 and 53 Ma constrain at least pre-latest Late Cretaceous age for the crustal-stacking event. Subsequent extension-related deformation caused pervasive mylonitisation of the footwall, with top-to-the NNE ductile, then brittle shear. Ductile flow was dominated by non-coaxial deformation, indicated by quartz c-axis fabrics, but was nearly coaxial in the dome core. Latest events relate to brittle faulting that accommodated extension at shallow crustal levels on high-angle normal faults and additional movement along strike-slip faults. Radiometric and stratigraphic constraints bracket the ductile, then brittle, extensional events at the Kesebir–Kardamos dome between 55 and 35 Ma. Extension began in Paleocene–early Eocene time and displacement on the detachment led to unroofing of the intermediate unit, which supplied material for the syn-detachment deposits in supra-detachment basin. Subsequent cooling and exhumation of the footwall unit from beneath the detachment occurred between 42 and 37 Ma as indicated by mica cooling ages in footwall rocks, and extension proceeded at brittle levels with high-angle faulting constrained at 35 Ma by the age of hydrothermal adularia crystallized in open spaces created along the faults. This was followed by Late Eocene–Oligocene post-detachment overlap successions and volcanic activity. Crustal extension described herein is contemporaneous with the closure of the Vardar Ocean to the southwest. It has accommodated an earlier hinterland-directed unroofing of the Rhodope nappe complex, and may be pre-cursor of, and/or make a transition to the Aegean back-arc extension that further contributed to its exhumation during the Late Miocene. This study underlines the importance of crustal extension at the scale of the Rhodope massif, in particular, in the eastern Rhodope region, as it recognizes an early Tertiary extension that should be considered in future tectonic models of the Rhodope and north Aegean regions.

Bauhinia larsenii, a fossil legume from Guangxi, China

Fossil leaves and a branch with a leaf and a pod attached have been discovered from Ningming County, Guangxi Autonomous Region, China, and are described as Bauhinia larsenii sp. nov. (Leguminosae: Cercideae). The strata from which the Bauhinia fossils were collected, namely the Ningming Formation, were dated as Late Eocene–Oligocene based on a combination of pollen, fauna and flora. The affinity of the new species to Bauhinia section Micralvesia subsection Viridescentes species is also discussed. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 147, 437–440.

Variation of palaeostress patterns along the Oriente transform wrench corridor, Cuba: significance for Neogene–Quaternary tectonics of the Caribbean realm

In this study, we address the late Miocene to Recent tectonic evolution of the North Caribbean (Oriente) Transform Wrench Corridor in the southern Sierra Maestra mountain range, SE Cuba. The region has been affected by historical earthquakes and shows many features of brittle deformation in late Miocene to Pleistocene reef and other shallow water deposits as well as in pre-Neogene, late Cretaceous to Eocene basement rocks. These late Miocene to Quaternary rocks are faulted, fractured, and contain calcite- and karst-filled extension gashes. Type and orientation of the principal normal palaeostress vary along strike in accordance with observations of large-scale submarine structures at the south-eastern Cuban margin. Initial N–S extension is correlated with a transtensional regime associated with the fault, later reactivated by sinistral and/or dextral shear, mainly along E–W-oriented strike-slip faults. Sinistral shear predominated and recorded similar kinematics as historical earthquakes in the Santiago region. We correlate palaeostress changes with the kinematic evolution along the boundary between the North American and Caribbean plates. Three different tectonic regimes were distinguished for the Oriente transform wrench corridor (OTWC): compression from late Eocene–Oligocene, transtension from late Oligocene to Miocene (?) (D 1), and transpression from Pliocene to Present (D 2–D 4), when this fault became a transform system. Furthermore, present-day structures vary along strike of the Oriente transform wrench corridor (OTWC) on the south-eastern Cuban coast, with dominantly transpressional/compressional and strike-slip structures in the east and transtension in the west. The focal mechanisms of historical earthquakes are in agreement with the dominant ENE–WSW transpressional structures found on land.

Time lag of syntectonic sedimentation across an alluvial basin: theory and example from the Ebro Basin, Spain

AbstractWe propose and test a conceptual framework for evaluating the relative timing of different types of sedimentary indicators of tectonism in alluvial foreland basin settings. We take the first occurrence of a detrital grain from a newly exposed source‐area lithology to provide the best indicator of the onset of tectonic uplift in the source area. Source‐area unroofing may lag behind initial uplift because of the type, thickness and structure of rocks in the uplifted mountain block, drainage patterns and climate. However, once exposed, advective transport disperses grains quickly throughout fluvial systems. Because of increased subsidence rate from thrust belt loading, an increase in sedimentation rate begins coincident with tectonic load emplacement within the flexural half‐width of the basin. However, farther out into the basin increased sedimentation rates lag behind the composition signal because of time lags associated with propagation of the thrust load and attendant sediment loads into the basin. The progradation of syntectonic gravel lags behind all of these signals as a direct function of the relative proportion of gravel fraction within transported sediment and rates and geometry of subsidence, which selectively traps the coarsest grain‐size fractions in the most proximal parts of the basin.We demonstrate this signal attenuation in the syntectonic Horta–Gandesa alluvial system (late Eocene–Oligocene), exposed along the southeast margin of the Ebro Basin, Spain. The results demonstrate that: (1) the time spans between the compositional signal and the progradation of the gravel front can be geologically significant, on the order of more than a million years within as little as 20 km of the thrust front; and (2) time lags between the signals increase with distance away from the deformation front. No lag time was observed between the first appearance of a new clast composition and the arrival of gravel front when the thrust front was within a few tens of metres from the depositional site. In contrast, the time lag was 0.5–1 Myr when the thrust front was about 5–6 km away and it increased to >1 Myr when the deformation front was about 8 km away. At the most extreme position, when the thrust front was 15–20 km away, the gravel front never reached the study area.

Thermotectonic evolution of an extensional dome: the Cenozoic Osogovo?Lisets core complex (Kraishte zone, western Bulgaria)

The Kraishte region of Bulgaria is located at the junction of the Balkanides and Hellenides-Dinarides tectonic belts. Fission-track analysis on both apatites and zircons documents the Cenozoic exhumation of a Precambrian basement bounded by low-angle detachments. Late Eocene–Oligocene extension began prior to 47 Ma and was dominantly in a top-to-the-southwest direction, confirmed by the sense of younging of apatite and zircon ages. This crustal extension controlled the formation of half-graben sedimentary basins on the hanging walls of the detachments. Thermal modelling of these hanging wall units provides evidence for heat transfer across the detachments from a relatively warm rising footwall. From 32 to 29 Ma, pervasive magmatic activity resulted in the emplacement of rhyolitic to dacitic subvolcanic bodies and dykes, along with intrusion of the Osogovo granite. The results give evidence for extension in the southern Balkan older than, and separated from, the Miocene to Quaternary Aegean extension. This might reflect transtension during northeastward extrusion and rotation of continental fragments around the western boundary of Moesia. Eocene–Oligocene extension seems to have been controlled by the distribution of earlier thickening all around the Carpatho-Balkanic orocline, which is reflected by the Cretaceous emplacement of the Morava Nappe in the Kraishte.

Contrasting Cenozoic Lithospheric Evolution and Architecture in the Western and Eastern Sino‐Korean Craton: Constraints from Geochemistry of Basalts and Mantle Xenoliths

Abstract Cenozoic basalts from both sides of the Daxin’anling‐Taihang gravity lineament that separates the Sino‐Korean craton (SKC) into western and eastern parts have been studied. In the western SKC, magmas evolved from xenolith‐bearing alkali basalts of Late Eocene–Oligocene age to coexisting alkali and tholeiitic basalts of Late Miocene–Quaternary age. This change in basalt type is accompanied by a decrease in La/Yb and an increase in Yb content. Sr‐Nd isotopic ratios and relative abundances on incompatible elements are consistent with a prevailing asthenospheric origin, although lithospheric mantle may have also contributed to these basalts. This temporal variation in basalt geochemistry is interpreted as reflecting progressive lithospheric thinning in the western SKC during the Cenozoic. An opposite trend is observed for Cenozoic basalts from the eastern SKC, suggesting lithospheric thickening during this time period. This thickening was probably related to regional thermal decay following peak magm...

Insectivores (Mammalia) from the earliest Oligocene (MP 21) of Belgium

Abstract Insectivore remains are not common in the Lower Oligocene of Europe. For this reason, the study of the earliest Oligocene insectivore fauna (MP 21) from Boutersem and Hoogbutsel, all together yielding nine species, representing five families, constitutes an important progress in the knowledge of the Late Eocene and Early Oligocene insectivore evolution. Some of the genera discovered in Belgium are known from upper Eocene sites (Saturninia, Amphidozotherium, Euronyctia, Eotalpa), whereas others are not known before the Oligocene (Butselia, Tetracus, Heterosoricinae ind.). The co-occurrence of primitive species of Nyctitheriidae with modern forms belonging to the Plesiosoricidae, Talpidae and Erinaceidae at the Eocene-Oligocene boundary suggests a transition fauna. Between the Priabonian (Late Eocene) and the Rupelian (Early Oligocene), the endemic European insectivores were in competition with the new immigrants. This faunal turnover is generally accepted as the ‘Grande Coupure’ event (the MP 21 event).