Relationship between be-derived erosion rates and mean annual precipitation, vegetation type, and precipitation variability

Millenial scale erosion rates derived from cosmogenic nuclides generally suggest that a relationship between precipatation and erosion rate is absent or negligible, depite the fact that water is the main agent of erosion. Here, we acknowledge that slope has a strong primary correlation with erosion rate and examine a new 10BE compilation to determine if mean annual precipatation has significan secondary control on erosion rates

Coupled influence of precipitation and vegetation on millenial scale erosion rates derived from 10Be

Water is one of the main agent of erosion in many environmental settings, but erosion rates derived from beryllium-10 (10Be) suggests that a relationship between precipitation and erosion rate is statistically non-significant on a global scale. This might be because of the strong influence of other variables on erosion rate. In this global 10Be compilation, we examine if mean annual precipitation has a statistically significant secondary control on erosion rate. Our secondary variable assessment suggests a significant secondary influence of precipitation on erosion rate. This is the first time that the influence of precipitation on 10Be-derived erosion rate is recognized on global scale. In fact, in areas where slope is <200m/km (~11°), precipitation influences erosion rate as much as mean basin slope, which has been recognized as the most important variable in previous 10Be compilations. In areas where elevation is <1000m and slope is <11°, the correlation between precipitation and erosion rate improves considerably. These results also suggest that erosion rate responds to change in mean annual precipitation nonlinearly and in three regimes: 1) it increases with an increase in precipitation until ~1000 mm/yr; 2) erosion rate stabilizes at ~1000 mm/yr and decreases slightly with increased precipitation until ~2200 mm/yr; and 3) it increases again with further increases in precipitation. This complex relationship between erosion rate and mean annual precipitation is best explained by the interrelationship between mean annual precipitation and vegetation. Increased vegetation, particularly the presence of trees, is widely recognized to lower erosion rate. Our results suggest that tree cover of 40% or more reduces erosion rate enough to outweigh the direct erosive effects of increased rainfall. Thus, precipitation emerges as a stronger secondary control on erosion rate in hyper-arid areas, as well as in hyper-wet areas. In contrast, the regime between ~1000 and ~2200 mm/yr is dominated by opposing relationships where higher rainfall acts to increase erosion rate, but more water also increases vegetation/tree cover, which slows erosion. These results suggest that when interpreting the sedimentological record, high sediment fluxes are expected to occur when forests transition to grasslands/savannahs; however, aridification of grasslands or savannahs into deserts will result in lower sediment fluxes. This study also implies that anthropogenic deforestation, particularly in regions with high rainfall, can greatly increase erosion

Strontium and stable C and O isotopic composition of carbonates in the Ernest Henry deposit, Queensland, Australia: implications for genesis and exploration

The Ernest Henry IOCG (iron-oxide copper gold) deposit is hosted within Paleoproterozoic meta-sedimentary and meta-igneous rocks of the eastern succession of the Mt Isa inlier. The mineralization is mostly breccia-hosted, with K-feldspar altered clasts cemented by biotite-carbonate-magnetite-sulfides. The breccias grade out to crackle breccias and then veins, with the breccia/crackle breccia contact typically demarcating economic mineralization. The origin of brecciation and mineralization remains controversial, but numerous elemental enrichments suggest multiple fluids with a mixed origin including magmatic and/or saline metamorphic fluids. Foremost among the proposed mechanism for IOCG formation at Ernest Henry is that CO2 release directly from enriched mantle, or indirectly from mafic magmas, played an important role in breccia formation and in scavenging ore components from local wallrocks, particularly mafic rocks. This hypothesis is mainly based on the regional interpretation of stable C and O isotopes from carbonates within the eastern succession of the Mt Isa inlier, including limited samples from Ernest Henry

Future Understanding of Tectonics, Ores, Resources, Environment and Sustainability (FUTORES) II Conference: abstract volume

With the increasing world population and living standards the demand for mineral and energy resources continues to grow. Future exploration will need to target resources at increasing depths and in areas with cover, and will require an improved understanding of mineral and energy systems and advances in exploration methods and approaches. The Economic Geology Research Centre (EGRU) at James Cook University has organized the FUTORES II conference to summarise recent developments in the exploration and understanding of major types of mineral deposits, to examine the key issues and techniques critical to future minerals and energy exploration, and to discuss the way forward. The conference is being held in tropical Townsville, Queensland, Australia, on 4-7 June 2017. It is following on from the inaugural and highly successful FUTORES conference held in Townsville in 2013.FUTORES II will bring together researchers, explorers and government agencies to address issues related to the sustainable supply and utilisation of mineral and energy resources. The conference has three symposia: the David Groves Symposium - New Insights in Mineral Deposit Understanding, the New Technologies and Approaches in Mineral Exploration Symposium, and the Tectonics, Basins and Resources Symposium. The conference is convened by EGRU, an organisation that was established in 1982 to strengthen the links between research and exploration, to promote exploration-oriented research, and to facilitate knowledge transfer. EGRU has a track record of organising successful major conferences to facilitate the exchange of knowledge and ideas and to stimulate new ideas for cutting-edge research and exploration. The Hydrothermal Odyssey conference in 2001, and the STOMP (Structure, Tectonics and Ore Mineralization Processes) conference in 2005, both attracted over 200 participants. In 2009 EGRU collaborated with the SGA to host the tenth biennial SGA conference in Townsville - Smart Science for Exploration and Mining - which attracted over 480 delegates from around the world. In 2013 the first FUTORES conference attracted around 250 participants from 15 countries. FUTORES II is looking to be equally successful and has so far attracted around 265 registrants. This conference abstract volume contains 134 abstracts covering a wide range of topics related to mineral and energy resources, tectonics and metallogenesis. The abstracts have been reviewed and edited by the Editorial Committee and, in this volume, are organised in alphabetical order of the first author. We thank the delegates for their abstracts and the reviewers for ensuring the quality of the abstract volume

The age of homo naledi and associated sediments in the rising star cave, South Africa

New ages for flowstone, sediments and fossil bones from the Dinaledi Chamber are presented. We combined optically stimulated luminescence dating of sediments with U-Th and palaeomagnetic analyses of flowstones to establish that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity (sub-unit 3b), interpreted to be deposited between 236 ka and 414 ka. This result has been confirmed independently by dating three H. naledi teeth with combined U-series and electron spin resonance (US-ESR) dating. Two dating scenarios for the fossils were tested by varying the assumed levels of222Rn loss in the encasing sediments: a maximum age scenario provides an average age for the two least altered fossil teeth of 253 +82/-70 ka, whilst a minimum age scenario yields an average age of 200 +70/-61 ka. We consider the maximum age scenario to more closely reflect conditions in the cave, and therefore, the true age of the fossils. By combining the US-ESR maximum age estimate obtained from the teeth, with the U-Th age for the oldest flowstone overlying Homo naledi fossils, we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka. These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphologyWe would also like to thank the many funding agencies that supported various aspects of this work. In particular we would like to thank the National Geographic Society, the National Research Foundation and the Lyda Hill Foundation for significant funding of the discovery, recovery and initial analysis of this material. Further support was provided by ARC (DP140104282: PHGMD, ER, JK, HHW; FT 120100399: AH). The ESR dosimetry study undertaken by CENIEH and Griffith University has been supported by a Marie Curie International Outgoing Fellowship (under REA Grant Agreement n˚ PIOF-GA-2013–626474) of the European Union’s Seventh Framework Programme (FP7/2007-2013) and an Australian Research Council Future Fellowship (FT150100215). ESR and U-series dating undertaken at SCU were supported by ARC (DP140100919: RJB)

Stratigraphy, Geochronology and Geochemistry of Paleolakes on the Southern Bolivian Altiplano

Precise chronologies of climate events in the tropics are rare yet essential for understanding how tropical climate relates to global climate at millennial to longer time scales. An increasingly important area for understanding these interactions is the southern Bolivian Altiplano (15-22oS) which represents the waning and southeastern end of the South American Monsoon, a system that is, today, modulated by regional upper-air circulation anomalies under the influence of tropical Pacific sea-surface temperature gradients associated with El Niño/Southern Oscillation (ENSO). Mechanisms of summer rainfall variations on millennial and longer time scales are less well understood, despite well-established evidence for profound changes in hydrologic budgets on the southern Bolivian Altiplano. Large shifts in effective moisture on the southern Bolivian Altiplano produced deep lakes in the Poopo, Coipasa, and Uyuni basins, basins that are currently occupied by salt pans or very shallow lakes. We mapped shoreline stratigraphy and sampled carbonates for over 170 uranium-thorium (U-Th) and radiocarbon (14C) dates to refine paleolake history of the Southern Bolivian Altiplano. As part of this dissertation work, I helped assemble a U-Th dating facility at the University of Arizona and obtained over 90 uranium-thorium (U-Th) dates from paleolake carbonates. Carbonate textures were evaluated for potential diagenetic effects, but the principal consideration in dating such carbonates is the isotopic composition and quantity of initial Th incorporated into the carbonate. We establish criteria for statigraphically meaningful dates and strategies for successful U-Th dating of paleolake carbonates. The stable isotope, 87-strontium/86-strontium (87Sr/86Sr), and 234U/238U ratios of modern surface waters and of paleolake carbonates can be used as tracers of the region's various lake cycles and provides a test hydrologic models of these lake cycles.Volcanic tuffs provide important stratigraphic markers for paleolimnologic, geomorphic, and archeological studies. Despite the widespread occurrence of late Quaternary tuffs on the Bolivian Altiplano, few of these deposits have been previously recognized either from natural exposures or in paleolake sediment cores. We document the presence of 38 distal tuffs in Quaternary lacustrine and alluvial deposits, and determine the composition of glass and phenocrysts by electron microprobe analyses

Geochronology and stratigraphy of late Pleistocene lake cycles on the southern Bolivian Altiplano: implications for causes of tropical climate change

Large paleolakes (∼33,000–60,000 km2) that once occupied the high-altitude Poopo, Coipasa, and Uyuni Basins in southern Bolivia (18–22°S) provide evidence of major changes in low-latitude moisture. In these now-dry or oligosaline basins, extensive natural exposure reveals evidence for two deep-lake and several minor-lake cycles over the past 120 k.y. Fifty-three new U-Th and 87 new 14C dates provide a chronologic framework for changes in lake level. Deposits from the "Ouki" deep-lake cycle are extensively exposed in the Poopo Basin, but no deep lakes are apparent in the record between 98 and 18.1 ka. The Ouki lake cycle was ∼80 m deep, and nineteen U-Th dates place this deep-lake cycle between 120 and 98 ka. Shallow lakes were present in the terminal Uyuni Basin between 95 and 80 ka (Salinas lake cycle), at ca. 46 (Inca Huasi lake cycle), and between 24 and 20.5 ka (Sajsi lake cycle). The Tauca deep-lake cycle occurred between 18.1 and 14.1 ka, resulting in the deepest (∼140 m) and largest lake in the basin over the past 120 ka. Multiple 14C and U-Th dates constrain the highest stand of Lake Tauca along a topographically conspicuous shoreline between 16.4 and 14.1 ka. A probable post-Tauca lake cycle (the Coipasa) produced a ≤55-m-deep lake that is tentatively dated between 13 and 11 ka. We suggest that paleolakes on the Bolivian Altiplano expanded in response to increased moisture in the Amazon and enhanced transport of that moisture onto the Altiplano by strengthened trade winds or southward displacement of the Intertropical Convergence Zone (ITCZ). Pole-to-equator sea-surface temperature (SST) and atmospheric gradients may have influenced the position of the ITCZ, affecting moisture balance over the Altiplano and at other locations in the Amazon Basin. Links between the position of the ITCZ and the ca. 23 ka precessional solar cycle have been postulated. March insolation over the Altiplano is a relatively good fit to our lake record, but no single season or latitude of solar cycling has yet to emerge as the primary driver of climate over the entire Amazon Basin. Temperature may influence Altiplano lake levels indirectly, as potentially dry glacial periods in the Amazon Basin are linked to dry conditions on the Altiplano. Intensification of the trade winds associated with La Niña–like conditions currently brings increased precipitation on the Altiplano, and deep-lake development during the Tauca lake cycle coincided with apparently intense and persistent La Niña–like conditions in the central Pacific. This suggests that SST gradients in the Pacific are also a major influence on deep-lake development on the Altiplano

Isotopic tracers of paleohydrologic change in large lakes of the Bolivian Altiplano

We have developed an 87Sr/86Sr, 234U/238U, and δ18O data set from carbonates associated with late Quaternary paleolake cycles on the southern Bolivian Altiplano as a tool for tracking and understanding the causes of lake-level fluctuations. Distinctive groupings of 87Sr/86Sr ratios are observed. Ratios are highest for the Ouki lake cycle (120–95 ka) at 0.70932, lowest for Coipasa lake cycle (12.8–11.4 ka) at 0.70853, and intermediate at 0.70881 to 0.70884 for the Salinas (95–80 ka), Inca Huasi (~ 45 ka), Sajsi (24–20.5 ka), and Tauca (18.1–14.1 ka) lake cycles. These Sr ratios reflect variable contributions from the eastern and western Cordilleras. The Laca hydrologic divide exerts a primary influence on modern and paleolake 87Sr/86Sr ratios; waters show higher 87Sr/86Sr ratios north of this divide. Most lake cycles were sustained by slightly more rainfall north of this divide but with minimal input from Lake Titicaca. The Coipasa lake cycle appears to have been sustained mainly by rainfall south of this divide. In contrast, the Ouki lake cycle was an expansive lake, deepest in the northern (Poópo) basin, and spilling southward. These results indicate that regional variability in central Andean wet events can be reconstructed using geochemical patterns from this lake system

Geochronology and stratigraphy of late Pleistocene lake cycles on the southern Bolivian Altiplano: implications for causes of tropical climate change

Large paleolakes (∼33,000–60,000 km2) that once occupied the high-altitude Poopo, Coipasa, and Uyuni Basins in southern Bolivia (18–22°S) provide evidence of major changes in low-latitude moisture. In these now-dry or oligosaline basins, extensive natural exposure reveals evidence for two deep-lake and several minor-lake cycles over the past 120 k.y. Fifty-three new U-Th and 87 new 14C dates provide a chronologic framework for changes in lake level. Deposits from the "Ouki" deep-lake cycle are extensively exposed in the Poopo Basin, but no deep lakes are apparent in the record between 98 and 18.1 ka. The Ouki lake cycle was ∼80 m deep, and nineteen U-Th dates place this deep-lake cycle between 120 and 98 ka. Shallow lakes were present in the terminal Uyuni Basin between 95 and 80 ka (Salinas lake cycle), at ca. 46 (Inca Huasi lake cycle), and between 24 and 20.5 ka (Sajsi lake cycle). The Tauca deep-lake cycle occurred between 18.1 and 14.1 ka, resulting in the deepest (∼140 m) and largest lake in the basin over the past 120 ka. Multiple 14C and U-Th dates constrain the highest stand of Lake Tauca along a topographically conspicuous shoreline between 16.4 and 14.1 ka. A probable post-Tauca lake cycle (the Coipasa) produced a ≤55-m-deep lake that is tentatively dated between 13 and 11 ka. We suggest that paleolakes on the Bolivian Altiplano expanded in response to increased moisture in the Amazon and enhanced transport of that moisture onto the Altiplano by strengthened trade winds or southward displacement of the Intertropical Convergence Zone (ITCZ). Pole-to-equator sea-surface temperature (SST) and atmospheric gradients may have influenced the position of the ITCZ, affecting moisture balance over the Altiplano and at other locations in the Amazon Basin. Links between the position of the ITCZ and the ca. 23 ka precessional solar cycle have been postulated. March insolation over the Altiplano is a relatively good fit to our lake record, but no single season or latitude of solar cycling has yet to emerge as the primary driver of climate over the entire Amazon Basin. Temperature may influence Altiplano lake levels indirectly, as potentially dry glacial periods in the Amazon Basin are linked to dry conditions on the Altiplano. Intensification of the trade winds associated with La Niña–like conditions currently brings increased precipitation on the Altiplano, and deep-lake development during the Tauca lake cycle coincided with apparently intense and persistent La Niña–like conditions in the central Pacific. This suggests that SST gradients in the Pacific are also a major influence on deep-lake development on the Altiplano