Cenozoic North Research Articles

Tectonism and fracture-related dissolution induced the formation of the large-scale metamorphic granite reservoir: Implications from Bozhong 26–6 Precambrian bedrock trap, offshore Bohai Bay basin, Northern China

Crystalline rocks in basins are unconventional sites for hydrocarbon exploration. Owing to the lack of primary pores in the bedrock, it remains unclear how later tectonism and dissolution alter crystalline rock within large-scale reservoirs. Notably, the recent discovery of a 200 million-ton oil field of Precambrian metamorphic granite in the Bonan buried hill, Bohai Bay Basin, China provides an important opportunity for exploring this mechanism. Herein, the relationship between fractures and the regional tectonic evolution of this buried metamorphic granite mass, as well as the accompanying phenomena of dissolution and vein filling (which record related fluid interactions contributing to second pore formation from tight crystalline rocks) were investigated. The results indicated that the reservoir space was primarily composed of tectonic fractures and associated dissolution pores (maximum porosity ≤18%). The densely interlaced fractures with dominant NWW-trending flat surfaces indicated that the majority of Precambrian bedrock fractures were induced by Indosinian tectonic compression. The Cenozoic north–south tectonic extensional fault obliquely intersects these NWW-trending fractures, accounting for 73% of the previous dense shearing fractures transformed into open fractures. The dissolution pores were primarily distributed along the fractures and increased the porosity of these fracture-related reservoirs by ≤ 12%. The carbon and oxygen isotopes of the calcite fillings within the fractures suggested that atmospheric freshwater was the primary dissolution fluid, whereas some pores were formed by the dissolution action of deep hydrothermal and organic acid fluids. Thus, regional compressive stress is a necessary tectonic mechanism for the formation of densely interlaced fractures in tight crystalline rocks. The later extensional setting contributing to fracture release and fracture dissolution in the epi-diagenesis stage are two immediate factors in the formation of permeability and storage capacity within buried bedrock traps.

Embracing Uncertainty to Resolve Polar Wander: A Case Study of Cenozoic North America

AbstractOur understanding of Earth's paleogeography relies heavily on paleomagnetic apparent polar wander paths (APWPs), which represent the time‐dependent position of Earth's spin axis relative to a given block of lithosphere. However, conventional approaches to APWP construction have significant limitations. First, the paleomagnetic record contains substantial noise that is not integrated into APWPs. Second, parametric assumptions are adopted to represent spatial and temporal uncertainties even where the underlying data do not conform to the assumed distributions. The consequences of these limitations remain largely unknown. Here, we address these challenges with a bottom‐up Monte Carlo uncertainty propagation scheme that operates on site‐level paleomagnetic data. To demonstrate our methodology, we present an extensive compilation of site‐level Cenozoic paleomagnetic data from North America, which we use to generate a high‐resolution APWP. Our results demonstrate that even in the presence of substantial noise, polar wandering can be assessed with unprecedented temporal and spatial resolution.

Biostratigraphy and biochronology of late Cenozoic North American rodent assemblages

Biostratigraphy and biochronology of late Cenozoic North American rodent assemblages

From Left Slip to Transpression: Cenozoic Tectonic Evolution of the North Altyn Fault, NW Margin of the Tibetan Plateau

AbstractThe Cenozoic North Altyn Fault (NAF) is a major splay of the Altyn Tagh Fault along the northwestern margin of the Tibetan Plateau, but its role in the development of this plateau margin in response to the India‐Eurasia collision is highly debated. Here, we investigate fault geometry, kinematics, and shortening magnitude along the westernmost 120 km of the NAF. Seismic surveys reveal minimal Cenozoic shortening in the subsurface of the Southeast Tarim Basin and support for large‐scale (>120 km) left slip on the NAF. Based on the satellite imagery, two new faults are identified to define the northern boundary of the NAF system, which together with the NAF to the south constitute a narrow transpressional shear zone comprised of three basement‐cored, fault‐bound slivers. Fission track data and thermal modeling indicate that the NAF zone experienced broad reburial during early Cenozoic that was locally interrupted by ∼40 to 35 Ma exhumation proximal to the NAF, followed by widespread but heterogeneous exhumation since ∼17 to 15 Ma associated with ∼9 to 11 km of total shortening across the NAF system via thick‐skinned faulting. We conclude that the NAF initiated as a left‐slip fault at ∼40 to 35 Ma and then became transpressional at ∼17 to 15 Ma during the middle‐Miocene reorganization of the Altyn Tagh Fault system. We find no evidence to support prior inferences of large‐scale (∼100 km) underthrusting of the Tarim Basin beneath the Tibetan Plateau along the NAF.

Ancestral trans–North American Bell River system recorded in late Oligocene to early Miocene sediments in the Labrador Sea and Canadian Great Plains

Abstract The Bell River hypothesis proposes that an ancestral, transcontinental river occupied much of northern North America during the Cenozoic Era, transporting water and sediment from the North American Cordillera to the Saglek Basin on the eastern margin of the Labrador Sea. To explore this hypothesis and reconstruct Cenozoic North American drainage patterns, we analyzed detrital zircon grains from the Oligocene–Miocene Mokami and Saglek formations of the Saglek Basin and Oligocene–Miocene fluvial conglomerates in the Great Plains of western Canada. U-Pb detrital zircon age populations in the Mokami and Saglek formations include clusters at <250 Ma, 950–1250 Ma, 1600–2000 Ma, and 2400–3200 Ma. Detrital zircons with ages of <250 Ma were derived from the North American Cordillera, supporting the transcontinental Bell River hypothesis. Oligocene–Miocene fluvial strata in western Canada contain detrital zircon age populations similar to those in the Saglek Basin and are interpreted to represent the western headwaters of the ancient Bell River drainage. Strontium-isotope ratios of marine shell fragments from the Mokami and Saglek formations yielded ages between 25.63 and 18.08 Ma. The same shells have εNd values of −10.2 to −12.0 (average = −11.2), which are consistent with values of Paleozoic strata in western North America but are more radiogenic than the modern Labrador Current, Labrador Sea Water, and North Atlantic Deep Water values (εNd ~−12 to −25). As a freshwater source, the existence and termination of the Bell River may have been important for Labrador Sea circulation, stratification, and chemistry.

Paleotectonic and paleogeographic history of the Arctic region

Paleogeographic maps represent the ultimate synthesis of complex and extensive geologic data and express pictorially the hypothetical landscape of some region during a given time-slice of deep geologic time. Such maps, presented as paired paleogeographic and paleotectonic reconstructions, have been developed to portray the geologic history of the greater Arctic region over the past 400 million years. Collectively they depict four major episodes in the development of the Arctic region. The first episode witnessed early and middle Paleozoic terrane assembly and accretion during the Caledonian and Ellesmerian orogenies, which brought together many pieces of the Arctic collage along the northern margin of Laurussia. During the second phase, the assembly of Pangea in the late Paleozoic joined Siberia to Laurussia, an entity that became Laurasia during the subsequent break-up of Pangea. Then, Mesozoic subduction and terrane accretion constructed the Cordilleran margin and opened the Canada Basin. Finally, Cenozoic North Atlantic sea-floor spreading fully opened the Arctic Ocean.

Sixty-six million years along the road of mammalian ecomorphological specialization

The fossil record of the large terrestrial mammals of the North American Cenozoic has previously been quantitatively summarized in six sequential episodes of faunal associations-"evolutionary faunas"-that correspond well with previously proposed qualitative "Chronofaunas." Here, we investigate the ecological spectrum of these faunas by classifying their major taxonomic components into discrete ecomorphological categories of diet, locomotion, and body size. To specifically address the potential influence of long-term climatic shifts on the ecomorphological composition of these faunas, we analyze via contingency tables and detrended correspondence analyses the frequency distribution of ecomorph types within faunas. We show that each evolutionary fauna has a unique, nonrandom association of ecomorphs, and we identify a long-term trend toward greater ecomorphological specialization over successive faunas during the past 66 My. Major vegetation shifts induced by climatic changes appear to underlie the ecomorphological dynamics of these six temporal associations that summarize Cenozoic North American mammalian evolutionary history.

Cenozoic North Atlantic deep circulation history recorded in contourite drifts, offshore Newfoundland, Canada

In the North Atlantic Ocean, contour-following deep currents have created regional erosional unconformities and deposited contourite drifts that exceed 2km in thickness and extend for 100s of km. The stratigraphic records in the drifts have been used to reconstruct variations in North Atlantic deep-water circulation throughout the Cenozoic; however, uncertainties remain about certain aspects of the timing, intensity, depth distribution, and regional impact of these currents. Here, we use an integrated dataset of seismic-reflection profiles and IODP core data (lithology, biostratigraphy, and magnetostratigraphy) to document sedimentation history and the development of current effects in the Cretaceous to present sedimentary record on the J-Anomaly Ridge and Southeast Newfoundland Ridge, offshore Newfoundland, Canada. The Newfoundland ridges are in a key location, lying between well-studied areas in the northern and western North Atlantic and under the path of both the modern Deep Western Boundary Current and the Gulf Stream. Late Cretaceous through Early Eocene sedimentation on the ridges was dominated by biogenic pelagic sedimentation, but at ~47Ma, near the Early-Middle Eocene boundary, well developed contourite drifts began to accrete in paleo-water depths of ~4000–4500m, accompanied by an order-of-magnitude increase in terrigenous sediment mass accumulation rates. From this time forward, drift deposition, interrupted by brief episodes of erosion, continued unabated. This timing for the onset of persistent deep currents is coincident with reorganization of Atlantic circulation inferred from a change from biosiliceous to non-biosiliceous sedimentation in the western North Atlantic (Horizon AC) and with the current-eroded Intra-Eocene Unconformity (IEU) in the northern North Atlantic. A change in sedimentation style occurred within the Middle Eocene to upper Oligocene drift sequence, and it likely was related to a shift to deeper, more intense currents that eroded the widespread Horizon AU along the margin of eastern North America about Early Oligocene time. Beginning in the Late Oligocene (~25Ma) a thick drift exhibiting seismically laminated mudwaves was deposited in a distinct belt at ~3500–4500m paleodepth on the Southeast Newfoundland Ridge. This development correlates with widespread Late Oligocene through Miocene-Pliocene drift accumulation throughout the North Atlantic. The most recent phase of drift deposition, since Late Pliocene time (~3Ma), occurred after a shift to the ‘modern’ circulation system of deeper, swifter currents, and it includes mixed pelagic-hemipelagic sediments and ice-rafted debris that reflect glacial-interglacial influences on sedimentation.

Chilean flat slab subduction controlled by overriding plate thickness and trench rollback

How flat slab geometries are generated has been long debated. It has been suggested that trenchward motion of thick cratons in some areas of South America and Cenozoic North America progressively closed the asthenospheric wedge and induced flat subduction. Here we develop time-dependent numerical experiments to explore how trenchward motion of thick cratons may result in flat subduction. We find that as the craton approaches the trench and the wedge closes, two opposite phenomena control slab geometry: the suction between ocean and continent increases, favoring slab flattening, while the mantle confined within the closing wedge dynamically pushes the slab backward and steepens it. When the slab retreats, as in the Peru and Chile flat slabs, the wedge closure rate and dynamic push are small and suction forces generate, in some cases, flat subduction. We model the past 30 m.y. of subduction in the Chilean flat slab area and demonstrate that trenchward motion of thick lithosphere, 200–300 km, currently ∼700–800 km away from the Peru-Chile Trench, reproduces a slab geometry that fits the stress pattern, seismicity distribution, and temporal and spatial evolution of deformation and volcanism in the region. We also suggest that varying trench kinematics may explain some differing slab geometries along South America. When the trench is stationary or advances, the mantle flow within the closing wedge strongly pushes the slab backward and steepens it, possibly explaining the absence of flat subduction in the Bolivian orocline.

Quantifying crustal extension and shortening in the back‐arc region of Northeast Japan

The Northeast Japan (NEJ) arc has experienced strong extension in the early to middle Miocene time and contractive deformation since Pliocene time. We determine the amounts of the Miocene extension and Pliocene contraction along four transects across the NEJ arc by area‐balancing restoration using seismic reflection, gravity, and surface geologic data. We find that the Miocene extension is as much as 31–56 km while the Pliocene‐Quaternary contraction is only 10–15 km. The style of the Miocene extension in the back‐arc region of NEJ is highly asymmetric; the zone of concentrated extension is characterized by a breakaway fault on the west, a rollover basement anticline on the east, and abnormally deep (∼10 km) basins and strongly rotated fault blocks in between, suggesting the existence of a large‐scale detachment fault at a mid‐crustal level beneath the extended zone. We reveal that the Pliocene‐Quaternary contractive surface deformation in the back‐arc region of NEJ resulted principally from positive tectonic inversion of the underlying detachment fault. Previous works have suggested that Andean‐type orogens have often experienced negative and positive inversions alternately in their back‐arc regions. Although the former has been well documented, for example, for the Cenozoic North American Cordillera, the latter has rarely been reported because subsequent contraction has obscured the older structures. Since the NEJ arc is still at an incipient stage and hence its older structures are well preserved, our study provides an important example of positive tectonic inversion of Andean‐type orogens.

Cenozoic climate change influences mammalian evolutionary dynamics

Global climate change is having profound impacts on the natural world. However, climate influence on faunal dynamics at macroevolutionary scales remains poorly understood. In this paper we investigate the influence of climate over deep time on the diversity patterns of Cenozoic North American mammals. We use factor analysis to identify temporally correlated assemblages of taxa, or major evolutionary faunas that we can then study in relation to climatic change over the past 65 million years. These taxa can be grouped into six consecutive faunal associations that show some correspondence with the qualitative mammalian chronofaunas of previous workers. We also show that the diversity pattern of most of these chronofaunas can be correlated with the stacked deep-sea benthic foraminiferal oxygen isotope (δ(18)O) curve, which strongly suggests climatic forcing of faunal dynamics over a large macroevolutionary timescale. This study demonstrates the profound influence of climate on the diversity patterns of North American terrestrial mammals over the Cenozoic.

History of Cenozoic North American drainage basin evolution, sediment yield, and accumulation in the Gulf of Mexico basin

The Cenozoic fill of the Gulf of Mexico basin contains a continuous record of sediment supply from the North American continental interior for the past 65 million years. Regional mapping of unit thickness and paleogeography for 18 depositional episodes defines patterns of shifting entry points of continental fluvial systems and quantifies the total volume of sediment supplied during each episode. Eight fluvio-deltaic axes are present: the Rio Bravo, Rio Grande, Guadalupe, Colorado, Houston-Brazos, Red, Mississippi, and Tennessee axes. Sediment volume was calculated from digitized hand-contoured unit thickness maps using a geographic information system (GIS) algorithm to sum volumes within polygons bounding interpreted North American river contribution. General age-dependent compaction factors were used to convert calculated volume to total grain volume. Values for rate of supply range from >150 km to <10 km3/Ma. Paleogeographic maps for eleven Cenozoic time intervals display the evolving matrix of elevated source areas, intracontinental sediment repositories, known and inferred drainage elements, and depositional fluvial/deltaic depocenters along the northern Gulf of Mexico basin margin. Patterns of sediment supply in time and space record the complex interplay of intracontinental tectonism, climate change, and drainage basin evolution. Five tectono-climatic eras are differentiated: Paleocene late Laramide era; early to middle Eocene terminal Laramide era; middle Cenozoic (Late Eocene–Early Miocene) dry, volcanogenic era; middle Neogene (Middle–Late Miocene) arid, extensional era; and late Neogene (Plio–Pleistocene) monsoonal, epeirogenic uplift era. Through most of the Cenozoic, three to four independent continental-scale drainage basins have supplied sediment to the Gulf of Mexico.

Cenozoic migration of topography in the North American Cordillera

Continental topography is the result of complex interactions among mantle convection, continental dynamics, and climatic and erosional processes. Therefore, topographic evolution of mountain belts and continental interiors reflects directly upon the coupling between mantle and surface processes. It has recently been proposed that the modern topography of western North America is partly controlled by the removal of the subducting Farallon plate and replacement of lithospheric mantle by hot asthenosphere, creating surface uplift of the Colorado Plateau, the southwestern United States, and northern Mexico, while concomitant subsidence characterizes the central United States. How the topography of the Cenozoic North American Cordillera evolved in the past is largely unknown, yet currently debated tectonic models each have a predictable topographic response. Here we examine Cenozoic surface uplift patterns of western North America based on a record of ∼3000 stable isotope proxy data. This data set is consistent with Eocene north to south surface uplift in the Cordillera, culminating in the assembly of an Eocene–Oligocene highland 3–4 km in elevation. The diachronous record of surface uplift and associated magmatism further supports tectonic models calling for the convective removal of mantle lithosphere or removal of the Farallon slab by buckling along an east-west axis. The Eocene–Oligocene development of rainout patterns similar to present-day patterns along the flanks of the Cordilleran orogen is therefore unlikely to be the result of late Mesozoic crustal thickening and associated development of an Andean-style Altiplano.

Intracontinental superimposed tectonics--A case study in the Western Hills of Beijing, eastern China

Eastern China underwent structural evolution from N-S contraction to NW-SE contraction and then ESE-ward crustal thinning during Mesozoic-Cenozoic time; however, the mechanisms are still poorly understood. The Western Hills of Beijing are located at the junction among the E-W–trending Yinshan-Yanshan tectonic belt, the NNE-trending Taihang Mountain belt, and the Late Cretaceous–Cenozoic North China Basin. During Jurassic–Cretaceous time, three deformational events, including one compressional and two extensional deformation stages, were superimposed on Middle–Early Triassic south-vergent thrusts and folds in this region. These include (1) WNW-vergent thrusting and fold deformation, (2) ESE-ward crustal thinning with 110°–120°ESE stretching lineations, and (3) E-dipping, high-angle normal faulting. During these deformation stages, muscovite and sericite were produced as synkinematic minerals, and most of these micas are aligned parallel to the stretching lineation or deformed surfaces associated with contractional/extensional deformation. U-Pb zircon dating, as well as 40Ar/39Ar hornblende, muscovite, biotite, K-feldspar, and sericite dating, clearly provides the following age constraints in the Western Hills: (1) N-S contraction at ca. 250–200 Ma; (2) WNW-vergent compression at ca. 170–150 Ma; (3) granodiorite and diorite dike intrusion at ca. 136–135 Ma, followed by intrusion of the Fangshan granitic pluton at ca. 130–128 Ma; and (4) ESE-trending stretching lineation at ca. 130–110 Ma. East-dipping, high-angle normal faults developed at ca. 70–60 Ma. The N-S contraction overlaps temporally with the formation and evolution of the Inner Mongolia orogenic belt during late Paleozoic–early Mesozoic time. WNW-vergent thrusting and folding, similar to that in the Taihang Mountain belt, was controlled by the initial formation of the west Pacific plate and its westward subduction beneath the Eurasian plate. ESE-ward crustal thinning in the area was probably controlled by eastward extrusion of the northern margin of the North China craton, driven by final closure of the Mongol-Okhotsk Ocean. The E-dipping, high-angle normal faulting was related to ongoing eastern Asian detachment since Late Cretaceous time. We propose that the main mechanism for the multiple deformation events resulted from the closure of the paleo–Asian Ocean, initial formation of the paleo–Pacific plate, and its subduction, combined with closure of the Mongol-Okhotsk Ocean.

Relating Cenozoic North Sea sediments to topography in southern Norway: The interplay between tectonics and climate

About 482 000 km 3 of sediment (ca 24 m/Ma) accumulated in the North Sea during the Cenozoic. Early Cenozoic sedimentation was likely due to uplift of the circum North Atlantic landmasses related to continental break-up. Kilometre-scale transient uplift, and in some areas permanent uplift, generated sources for progradational influx of clastic sediments from Scotland, the Shetland platform and, to a lesser degree, southwestern Norway. The Eocene sedimentation pattern was similar to the Palaeocene, with lower rates of accumulation associated with flooding and tectonic quiescence. Sediment influx from the Shetland platform continued throughout the Cenozoic while supply from southern Norway increased markedly around the Eocene–Oligocene, coeval with the greenhouse–icehouse transition. Mass balance calculations of sediment and eroded rock volumes suggest that while some topography along the western margin of Norway may be pre-Cenozoic, significant uplift of the main Paleic surface in southern Norway occurred around the early Oligocene. Sedimentation rates were almost ten-fold higher than the Cenozoic average in the Plio-Pleistocene, slightly higher than the global average. Mass balance calculations indicate that Plio-Pleistocene erosion over-deepened a pre-existing topography.

Massive volcanic SO2 oxidation and sulphate aerosol deposition in Cenozoic North America

Volcanic eruptions release a large amount of sulphur dioxide (SO(2)) into the atmosphere. SO(2) is oxidized to sulphate and can subsequently form sulphate aerosol, which can affect the Earth's radiation balance, biologic productivity and high-altitude ozone concentrations, as is evident from recent volcanic eruptions. SO(2) oxidation can occur via several different pathways that depend on its flux and the atmospheric conditions. An investigation into how SO(2) is oxidized to sulphate-the oxidation product preserved in the rock record-can therefore shed light on past volcanic eruptions and atmospheric conditions. Here we use sulphur and triple oxygen isotope measurements of atmospheric sulphate extracted from tuffaceous deposits to investigate the specific oxidation pathways from which the sulphate was formed. We find that seven eruption-related sulphate aerosol deposition events have occurred during the mid-Cenozoic era (34 to 7 million years ago) in the northern High Plains, North America. Two extensively sampled ash beds display a similar sulphate mixing pattern that has two distinct atmospheric secondary sulphates. A three-dimensional atmospheric sulphur chemistry and transport model study reveals that the observed, isotopically discrete sulphates in sediments can be produced only in initially alkaline cloudwater that favours an ozone-dominated SO(2) oxidation pathway in the troposphere. Our finding suggests that, in contrast to the weakly acidic conditions today, cloudwater in the northern High Plains may frequently have been alkaline during the mid-Cenozoic era. We propose that atmospheric secondary sulphate preserved in continental deposits represents an unexploited geological archive for atmospheric SO(2) oxidation chemistry linked to volcanism and atmospheric conditions in the past.

The North Atlantic Igneous Province reconstructed and its relation to the Plume Generation Zone: the Antrim Lava Group revisited

SUMMARY Large igneous provinces (LIPs) have recently been suggested to originate at the edges of low-velocity zones on the core mantle boundary (Plume Generation Zones). If true, LIPs can potentially be used to constrain paleolongitude in plate tectonic reconstructions. To validate the hypothesis, it is essential to study LIPs of which the paleolongitude can be constrained by other methods, such as hotspot reference frames. An ideal candidate to this end is the early Cenozoic North Atlantic Igneous Province (NAIP). Despite being the largest volcanic unit of the British Tertiary Igneous Province (BTIP, part of the NAIP), the age and paleoposition of the Antrim Lava Group (ALG) in Northern Ireland, which is key to the NAIP as a whole, was hitherto poorly constrained. In this paper, we therefore present an integrated high-resolution paleomagnetic and geochronological study. The ALG is divided into three formations: the Lower Basalt Formation (LBF), Interbasaltic Formation (IBF) and the Upper Basalt Formation (UBF). The IBF is mostly lateritic and encloses the Tardree rhyolite. We offer new age constraints from all three formations using the 40 Ar/ 39 Ar method and propose that 62.6 ± 0.3, 61.3 ± 0.3 and 59.6 ± 0.3 Ma (1σ , internal uncertainties) are sound estimates of the age of emplacement of the LBF, Tardree rhyolite (IBF) and UBF, respectively. This constrains the nominal duration of emplacement of the ALG to 3 ± 0.6 Ma (1σ ). This reevaluation of the magnetic signature in the ALG revealed reverse polarity remanence in all three formations and an overall paleomagnetic north pole at latitude 78.9 ◦ N, longitude 167 ◦ E( A95= 6.3; age ∼61 Ma) in the European reference system. This appears consistent with paleomagnetic poles from the rest of the NAIP; both in Europe and Greenland, as well as predictions from modern apparent polar wander paths. The new radiometric ages span magnetochron C26r, C27n and C27r. The normal polarity chron C27n most probably occurred during the IBF hiatus, explaining why no normal polarity remanence was detected in the paleomagnetic investigation. Emplacement of the LBF falls in magnetochron C27r, making this one of the oldest lava sequence in the NAIP; older than the C27n lava pile in Western Greenland. The 60 Ma position of the NAIP in a paleomagnetic reference frame, puts it close to the northern edge of the African large low shear wave velocity anomaly at the core–mantle boundary and therefore in the line with the Plume Generation Zone hypothesis. However, the back-projected Icelandic hotspot, normally considered to have formed the NAIP, is located ∼1500 km north of the latitude at which the NAIP erupted. The northward motion of the north Atlantic lithosphere since the late Cretaceous challenging the existing correlation of the NAIP to the Icelandic hotspot, normally used to explain the observed pre- and syn-breakup North Atlantic magmatism (63–55 Ma), and either an additional plume located further south in the North Atlantic may be invoked to create the NAIP, or the Icelandic hotspot must have

NEW NEOPLAGIAULACID MULTITUBERCULATES (MAMMALIA: ALLOTHERIA) FROM THE PALEOCENE OF ALBERTA, CANADA

Neoplagiaulacid multituberculates are among the most numerous and best represented members of early Cenozoic North American mammal faunas, achieving their greatest diversity during the Paleocene. Despite their relatively dense record in the Torrejonian (middle Paleocene) and Tiffanian (late Paleocene), the study of early Cenozoic neoplagiaulacids has been limited more often than not to isolated teeth or, more rarely, incomplete skull, gnathic, or postcranial remains. The current study reports on new neoplagiaulacid multituberculates from the Paleocene Paskapoo Formation of central Alberta, Canada, at localities along the Blindman River near the City of Red Deer. The exceptionally well-preserved specimens consist of incomplete articulated and associated skull and gnathic remains, and collectively document four new species: Ectypodus elaphus, Neoplagiaulax serrator, Neoplagiaulax paskapooensis, and Neoplagiaulax cimolodontoides. Neoplagiaulax paskapooensis is the most dentally complete neoplagiaulacid so far discovered, with a single specimen documenting for the first time left and right I2 and I3 in situ with the cheek teeth, along with the associated lower dentition. Specimens of Neoplagiaulax cimolodontoides record important details of the rostrum and palate, and provide the first direct evidence of incisor replacement in Neoplagiaulax. The new neoplagiaulacids, together with other multituberculates from the Blindman River localities, document unusually high multituberculate diversity in the latter half of the Tiffanian in western Canada. Despite superficial similarity to some European species of Neoplagiaulax, the new taxa from the Paskapoo Formation apparently show no closer relationship to these than do other North American congeners, suggesting parallel evolution in endemic North America and western European clades.

The Cenozoic Lower Rhine Basin – rifting, sedimentation, and cyclic stratigraphy

In the Cenozoic, the Lower Rhine Basin formed as a rift at the southeastern terminus of the Dutch German Central Graben, while the Rhenish Massif was uplifted. The study focusses on the marginal marine and fluvial fill of the Lower Rhine Basin. A basin model is developed. Support for this study was given by extensive industry outcrop and well data, by new stratigraphical and sedimentological observations. The ingression and subsequent regression of the Cenozoic North Sea is analysed using the concept of base level cyclicity. As the geohistory of the basin was complex, a subsidence curve is constructed. Furthermore, an attempt is made to trace the simultaneous uplift of the Rhenish Massif.

Extinction and re-evolution of similar adaptive types (ecomorphs) in Cenozoic North American ungulates and carnivores reflect van der Hammen's cycles

Numerous patterns in periodicity (e.g., climate, extinction, and sedimentary cycles) and evolutionary change (e.g., chronofaunas and coordinated stasis) have been described based on aspects of the geologic record. Recently, convergent occurrences of faunal types or "repeating faunas" have received attention, but a highly specific, iterative pattern was first reported over 40 years ago. In the late 1950s, van der Hammen described climatic/floral cycles on the order of six million years based on a succession of A, B, and C pollen community types in South America. These A-B-C cycles are also seen in the replacement pattern of particular carnivore and ungulate adaptive types in Cenozoic North America as reported by Martin in the 1980s. For example, in the last 36 million years, there were four iterations of a sabertooth cat ecomorph independently evolving, dominating the niche through an A-B-C cycle, and then going extinct. Here we show further support for the existence of these cycles in the dominance turnover in hippo and dog ecomorphs in the North American Cenozoic. Shared patterns of extinction and re-evolution of adaptive types among plants and mammals across two continents suggest a global mechanism, which appears to be climatic change. Iterative climatic cycles of various scales may form a predictive framework for understanding fundamental patterns in the geologic record, such as radiations, extinction, rates of change, convergence, and sedimentary cycles.