Gary R. Scott

The oldest hand-axes in Europe

Stone tools are durable reminders of the activities, skills and customs of early humans, and have distinctive morphologies that reflect the development of technological skills during the Pleistocene epoch. In Africa, large cutting tools (hand-axes and bifacial chopping tools) became part of Palaeolithic technology during the Early Pleistocene (∼1.5 Myr ago). However, in Europe this change had not been documented until the Middle Pleistocene (<0.5 Myr ago). Here we report dates for two western Mediterranean hand-axe sites that are nearly twice the age of the supposed earliest Acheulian in western Europe. Palaeomagnetic analysis of these two sites in southeastern Spain found reverse polarity magnetozones, showing that hand-axes were already in Europe as early as 0.9 Myr ago. This expanded antiquity for European hand-axe culture supports a wide geographic distribution of Palaeolithic bifacial technology outside of Africa during the Early Pleistocene.

Epitaxial relationships of clinopyroxene-hosted magnetite determined using electron backscatter diffraction (EBSD) technique

Abstract Crystallographic relationships between exsolved phases and their hosts are typically characterized using transmission electron microscopy (TEM) or single crystal X-ray diffraction (XRD). In this investigation, electron backscatter diffraction (EBSD) was used to determine the epitaxial relationships of exsolved laths of magnetite in clinopyroxenes from three sampling sites in the Cretaceous Messum Complex of Namibia. Two orientations of magnetite inclusions are found with their long axes subparallel to [100] and [001] of the host clinopyroxene. Inclusions subparallel to [100]c have [1̅10]m // [010]c, (1̅1̅1)m // (1̅01)c, and [112]m // [101]c. Inclusions subparallel to [001]c have [1̅10]m // [010]c, (111)m // (100)c, and [1̅1̅2]m // [001]c. The EBSD-derived orientation relationships agree well with previous TEM and XRD studies on similar materials. The crystallographic relationships obtained with EBSD are used in conjunction with optimal phase boundary theory to determine the exsolution temperature of the magnetite inclusions, which is of importance to paleomagnetic studies. For one sample, this temperature (840 ± 50 °C) can be compared with that (865 ± 25 °C) derived from a more widely used cation exchange geothermometer. Thus it appears clear that exsolution occurred well above the Curie temperature of pure magnetite (580 °C).

Evidence for an African-Iberian mammal dispersal during the pre-evaporitic Messinian

The accurate timing of biogeographic dispersal can be determined by examining the age of fossiliferous strata on either side of a physical barrier. Here we show that African mammals migrated to Iberia and European mammals migrated to North Africa at the same time before isolation of the Mediterranean Sea during the Messinian. The fossil site of Venta del Moro (Spain) exhibits western Europe’s most complete vertebrate fauna for the latest Miocene. Its uniquely cosmopolitan assemblage is evidence of faunal dispersals from Africa and Asia to Europe during the latest Miocene glaciation. A preliminary paleomagnetic study suggested an age of 5.8 Ma for this site, but our expanded magnetostratigraphy dates the site at 6.23 Ma. In addition, we recalibrated the paleomagnetic age of the Librilla site (Spain) and the North Africa site of Afoud-1 (Morocco) using the Astronomical Tuned Neogene Time Scale. Our results show a two-way African-Iberian mammal dispersal just before 6.2 Ma. These new ages indicate that an ephemeral land corridor existed between the two continents 250 k.y. before the onset of the Messinian Salinity Crisis, reflecting a tentative initial isolation of the Mediterranean Sea. This corridor developed after tectonics closed the Betic Seaway at 6.3 Ma and during the intensification of the latest Miocene glaciation at 6.26 Ma, when water circulation in the Mediterranean became very restricted.

New species from Ethiopia further expands Middle Pliocene hominin diversity

Middle Pliocene hominin species diversity has been a subject of debate over the past two decades, particularly after the naming of Australopithecus bahrelghazali and Kenyanthropus platyops in addition to the well-known species Australopithecus afarensis. Further analyses continue to support the proposal that several hominin species co-existed during this time period. Here we recognize a new hominin species (Australopithecus deyiremeda sp. nov.) from 3.3–3.5-million-year-old deposits in the Woranso–Mille study area, central Afar, Ethiopia. The new species from Woranso–Mille shows that there were at least two contemporaneous hominin species living in the Afar region of Ethiopia between 3.3 and 3.5 million years ago, and further confirms early hominin taxonomic diversity in eastern Africa during the Middle Pliocene epoch. The morphology of Au. deyiremeda also reinforces concerns related to dentognathic (that is, jaws and teeth) homoplasy in Plio–Pleistocene hominins, and shows that some dentognathic features traditionally associated with Paranthropus and Homo appeared in the fossil record earlier than previously thought.

40Ar/39Ar dating, paleomagnetism, and tephrochemistry of Pliocene strata of the hominid-bearing Woranso-Mille area, west-central Afar Rift, Ethiopia

(40)Ar/(39)Ar dating of tuffs and mafic lavas, tephra geochemistry, and paleomagnetic reversal stratigraphy have been used to establish the chronostratigraphy of the Pliocene hominid-bearing fossiliferous succession at Woranso-Mille, a paleontological study area in the western part of the central Afar region of Ethiopia. The succession in the northwestern part of the study area ranges in (40)Ar/(39)Ar age from 3.82-3.570 Ma, encompassed by paleomagnetic subchron C2Ar (4.187-3.596 Ma). One of the major tuff units, locally named the Kilaytoli tuff, is correlative on the basis of age and geochemistry to the Lokochot Tuff of the Turkana Basin. A hominid partial skeleton (KSD-VP-1) was found in strata whose precise stratigraphic position and age is still under investigation, but is believed to correspond to the later part of this interval. Woranso-Mille fills a significant gap in the fossil record of northeastern Africa at the time of the lower to middle Pliocene transition, when many extant species lineages of African fauna were established.

Seismically induced slump on an extremely gentle slope (<1°) of the Pleistocene Tecopa paleolake (California)

A superbly exposed ∼5 km 2 slump is developed in middle Pleistocene lacustrine deposits of the Tecopa Basin (California, United States). A subhorizontal detachment (

Discordant mid‐Cretaceous paleomagnetic pole from the Zaza Terrane of central Cuba

Thermal demagnetization of samples from five sites in mid-Cretaceous volcaniclastic and carbonate rocks of south-central Cuba reveals two or more components of magnetization. A pre-folding magnetite borne component is recognized in all, but was difficult to isolate from secondary components in many specimens. Remagnetization circle analysis, using data for 42 specimens from all five sites, yields a pole at 30.7{degree}N Lat., 193.3{degree}E Long. This pole is discordant with respect to the North American APWP, indicating 43{degree} {plus minus} 16{degree} of anticlockwise rotation and 8{degree} {plus minus} 6{degree} of northward displacement since the mid-Cretaceous. This result suggests that part or all of Cuba was transported on the Caribbean plate before accretion to North America in the Eocene.

Thermal modification of hematite-ilmenite intergrowths in the Ecstall pluton, British Columbia, Canada

Abstract In this study, we examine the effects of reheating on finely exsolved hematite-ilmenite intergrowths from the ~91 Ma Ecstall pluton using reflected light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). As a result of the emplacement of the younger adjacent ~52 Ma Quottoon pluton, samples closer to a thermal boundary have experienced greater degrees of thermal alteration. Five main microstructural features characterize hematite-ilmenite intergrowths from the Ecstall: (I) exsolution lamellae of hematite and ilmenite; (II) oxidation of ilmenite to form hematite, rutile, and other Ti-rich phases; (III) 20-50 nm magnetite precipitates in hematite; (IV) rutile blitz texture; and (V) exsolution of hematite in rutile. Based on spatial relationships, textures II through V appear to be related to reheating of the Ecstall by the Quottoon, and samples up to ~14 km from the thermal boundary intrusive contact have been affected. We propose a mechanism, similar to that of Kontny and Dietl (2001), in which reheating has driven T-ƒO₂ conditions across the hematite-magnetite buffer to lower ƒO₂ resulting in the reduction of hematite. Higher temperatures also enhanced oxidation in ilmenite. The formation of magnetite altered the bulk magnetic properties of these samples, increasing NRM intensity. This study underscores the need to consider a pluton’s post-emplacement thermal history before making tectonic interpretations based on paleomagnetic data.

The reversal test: An examination of secondary directions

Paleomagnetic data frequently display bipolar data that are not exactly antipodal. One cause of this biasing is the addition of another later (secondary) magnetization that cannot be removed by laboratory demagnetization experiments. The magnitude of this hidden secondary magnetization can be calculated when only two values are known : the non-antipodal angle (measured), and the angle between the Normal direction (measured) and secondary direction (measured or assumed). Furthermore, a minimum magnitude of the secondary magnetization can be calculated with knowledge only of the non-antipodal angle. Applied to three published data sets (sandstone, limestone and diorite intrusion) with non-antipodal angles of 11°, 28° and 11° respectively ; a secondary component is calculated at 25%, 28% and 16% of the characteristic magnetization remaining after laboratory cleaning. Near surface alteration (weathering) appears to be the source of secondary magnetization in two of these cases. A directionally consistent, biasing effect of a few degrees is made on the mean direction as compared to the conventional calculation of averaging the non-antipodal directions.

Magnetic properties of ilmenite-hematite single crystals from the Ecstall pluton near Prince Rupert, British Columbia

Paleomagnetic studies of the 91 Ma Ecstall pluton and other Cretaceous plutons of British Columbia imply large northward tectonic movements (>2000 km) may have occurred during the tectonic evolution of western North America. However, more recent studies have shown that the eastern edge of the Ecstall pluton experienced considerable mineralogical changes as younger Eocene plutons, such as the ∼58 Ma Quottoon Pluton, were emplaced along its margins. We investigated changes in the rock magnetic properties associated with this reheating event by examining isolated grains of intergrown ilmenite and hematite, the primary paleomagnetic recorder in the Ecstall pluton. Measurements of hysteresis properties, low-temperature remanence, and room temperature isothermal remanent magnetization acquisition and observations from magnetic force microscopy and off-axis electron holography indicate that samples fall into three groups. The groups are defined by the presence of mineral microstructures that are related to distance from the Quotoon plutonic complex. The two groups closest to the Quottoon Pluton contain magnetite within hematite and ilmenite lamellae. Reheating of the Ecstall pluton led to an increase in coercivity and magnetization, as well as to development of mixed phase hysteresis. These results indicate that shallow paleomagnetic directions from the western Ecstall pluton are not affected by reheating and are therefore likely to record original field conditions at the time of pluton emplacement. In the absence of structural deformation, these shallow inclinations are consistent with large-scale northward translation suggested by the Baja–British Columbia hypothesis.