Preferential dust sources: a geomorphological classification designed for use in global dust-cycle models

We present a simple theoretical land-surface classification that can be used to determine the location and temporal behaviour of preferential sources of terrestrial dust emissions. The classification also provides information about the likely nature of the sediments, their erodibility and the likelihood that they will generate emissions under given conditions. The scheme is based on the dual notions of geomorphic type and connectivity between geomorphic units. We demonstrate that the scheme can be used to map potential modern-day dust sources in the Chihuahuan Desert, the Lake Eyre Basin and the Taklamakan. Through comparison with observed dust emissions, we show that the scheme provides a reasonable prediction of areas of emission in the Chihuahuan Desert and in the Lake Eyre Basin. The classification is also applied to point source data from the Sahara to enable comparison of the relative importance of different land surfaces for dust emissions. We indicate how the scheme could be used to provide an improved characterisation of preferential dust sources in global dust-cycle models

Miocene humid intervals and establishment of drainage networks by 23 Ma in the central Sahara, southern Libya

Terrestrial and lacustrine Neogene and Quaternary sediments in the Libyan Fezzan provide key evidence for paleoclimate changes in the central Sahara, associated with Lake Megafezzan. Understanding of Holocene and late Pleistocene deposits is resolved, but the age of older sediments is not. We provide the first high-resolution chronology and stratigraphy of the Neogene deposits in the Fezzan Basin, and so also the central Sahara. The sediments are divided into three unconformity-bounded units, the oldest unit, comprising the Shabirinah and Brak formations, is dated using magnetostratigraphy. The Shabirinah Formation is a succession of lacustrine and fluvial units, locally with humid and arid paleosols, which progressively show evidence of increasing aridity up through the succession. The overlying Brak Formation is a pedogenically modified palustrine limestone at basin margin locations. All these units are dated to the early Aquitanian to late Serravallian in the early to mid-Miocene, having formed prior to major volcanic fields to the east. During the mid-late Aquitanian widespread stromatolitic lake sediments developed in SE Fezzan. In the late Burdigalian palustrine carbonate units developed that typically pass laterally into mixed clastic-paleosol-carbonate units that characterise basin margin situations. The Serravallian-aged Brak Formation is a highstand deposit developed during maximum lake extent, which formed due to restriction of basin drainage to the north and east, due to growth of the Jabal as Sawda volcanic centre and uplift of the SW shoulder of the Sirte Basin. Gradual aridification of the central Sahara occurred from the early Miocene, but this trend was periodically interrupted by humid phases during which Lake Megafezzan developed. The hyperaridity of the central Sahara must have developed after 11 Ma and the main drainage networks from the Fezzan Basin were established before 23 Ma, in the Oligocene indicating the great antiquity of major central Saharan river basins

Supplementary Information Files for "Human footprints provide snapshot of last interglacial ecology in the Arabian interior"

Supplementary Information Files for article The nature of human dispersals out of Africa has remained elusive because of the poor resolution of paleoecological data in direct association with remains of the earliest non-African people. Here, we report hominin and non-hominin mammalian tracks from an ancient lake deposit in the Arabian Peninsula, dated within the last interglacial. The findings, it is argued, likely represent the oldest securely dated evidence for Homo sapiens in Arabia. The paleoecological evidence indicates a well-watered semi-arid grassland setting during human movements into the Nefud Desert of Saudi Arabia. We conclude that visitation to the lake was transient, likely serving as a place to drink and to forage, and that late Pleistocene human and mammalian migrations and landscape use patterns in Arabia were inexorably linked.<br