Intense subaerial weathering of eolian sediments in Gale crater, Mars

After over 8 years of successful surface operations on Mars, the Curiosity rover has revealed much about the environment in Gale crater. Despite early observations of a lacustrine environment, few of the subsequent deposits exhibit demonstrable lacustrine character. We suggest instead that most of the stratigraphic section explored to date can be best explained as eolian and/or volcaniclastic sediments subaerially chemically weathered by acidic precipitation in a reduced atmosphere. Most of the deposits in Gale crater seemingly did not form in an ancient lake, but the results nonetheless shed considerable light on ancient climate, environmental change, and the astrobiology of Mars. Discoveries by Curiosity provide a critical piece to Mars’ global alteration puzzle.

Distinct responses of late Miocene eolian and lacustrine systems to astronomical forcing in NE Tibet

East Asian summer monsoon (EASM) and winter monsoon (EAWM) variability on orbital time scales during the late Miocene remains poorly constrained. Climate models reveal variable responses of the EASM and EAWM to astronomical forcing, but there is a lack of empirical evidence from the geological record to validate these results. In this study, we used time series analysis to reconstruct climatic changes and orbital forcing from eolian and lacustrine sediment archives from NE Tibet during the late Miocene. Analysis of magnetic susceptibility data demonstrates that lacustrine sediments in the Tianshui Basin (Yaodian section) show dominant ∼100 k.y. eccentricity forcing in the late Miocene (ca. 10.25−8 Ma). In contrast, eolian deposits in the Jianzha Basin (Jiarang section) show significant 405 k.y. eccentricity and 41 k.y. obliquity forcing over the same interval with weak evidence for ∼100 k.y. eccentricity cycles. Grain size data from the Yaodian section support a lacustrine origin of these sediments and also support previous work demonstrating aridification in NE Tibet after ca. 8.6 Ma. Taken together, our analyses highlight markedly different orbital forcing responses of lacustrine and eolian sedimentary systems during the late Miocene. We suggest that the dominant ∼100 k.y. lacustrine cycles in the Yaodian section, which were mainly controlled by EASM variability, may have been linked to Antarctic ice sheet and/or low-latitude insolation modulations related to precession amplitude modulation by eccentricity. In contrast, the orbital signature of eolian sediments in the Jiarang section was significantly influenced by the EAWM and can be linked to variability in meridional temperature/pressure gradients.

The bleaching of different K-feldspar pIRIR signals of source materials of lacustrine sediment – A case study from Bosten Lake Basin in arid central Asia

The residual ages and bleaching of K-feldspar post-IR IRSL (pIRIR) signals (pIR50IR170, pIR50IR290, and pIR200IR290) for a variety of modern sediment sources to the Bosten Lake basin in the southern Tian Shan of arid central Asia were assessed to identify the most appropriate facies to sample for ascertaining well-bleached, depositional ages associated with Quaternary paleolake development. Results indicate pIR50IR290 residual ages for pluvial fan, fluvial, and eolian sediments cluster at 40–6, 6–3, and 2–1 ka, respectively, and are depositional ages. Residual ages of pIR200IR290 signals are twice that of pIR50IR290 signals, while residual ages of pIR50IR170 signals are similar to that of pIR50IR290 signals for all samples. Eolian and fluvial samples show well-bleached, coarse-grained (90–125 μm) K-feldspar and poorly-bleached coarse grained K-feldspar from pluvial samples. High residual doses in fluvial and pluvial samples indicate it may not be advisable to apply pIRIR dating utilising different pIRIR signals to Holocene lacustrine samples. However, the residual ages measured for eolian deposits are small and can allow precise and robust assessment of paleolake development by targeting the K-feldspar pIR50IR170 signal to date Holocene samples and the pIR200IR290 and pIR50IR290 signals to date Pleistocene samples.

Geology of Nubia and Surrounding Regions

Nubia occupies a low, interior plain extending from southern Egypt to central Sudan. It is surrounded by high plateaus and mountains on all sides except the north. Across this plain flows the Nile River. The bedrock geology is dominated by metamorphic and igneous rocks of the mainly Precambrian to Paleozoic Basement Complex, and sedimentary rocks of the Cretaceous Nubian Sandstone Formation. Cataracts and rapids exist wherever the Nile River flows over Basement Complex rocks. The bedrock is blanketed in many areas by unconsolidated alluvial, lacustrine, and especially eolian sediments of mostly Quaternary age. The tectonically active Red Sea and East African rift zones are responsible for Cenozoic and still ongoing volcanism and seismicity in the Nubian region with additional tectonism resulting from uplift along the Nubian Swell in southern Egypt and northern Sudan.

ASPECTOS SEDIMENTOLÓGICOS E GEOQUÍMICOS DO TESTEMUNHO ANP 1040, DO TALUDE CONTINENTAL DA PORÇÃO OESTE DO ESTADO DO CEARÁ

The ANP 1040 core analyzed was collected at a depth of 1900 m in the Equatorial Atlantic Ocean, around 100.8 km from the coastline of the municipality of Itapipoca, Ceará. Particle size analyzes, geochemistry by X-ray fluorescence, calcium carbonate, organic matter and total nitrogen contents were performed. The data show that the ANP 1040 core contains the mud, sandy mud and muddy facies, composed of bioclastic sediments classified as limestone. The decrease of the marine influence on the sedimentation was observed in the intermediate interval of the core because it presented high levels of Ti/Ca and Fe/Ca ratios. In addition, this interval was correlated to high values of mud, organic matter, and low percentage of carbonate content. The high values of these ratios (Ti/Ca and Fe/Ca) are related to an increase of the continental sedimentary contribution, denoting a period of a greater precipitation in the region, indicating a humid tropical climate that increased the flow of the continental drainages and, consequently, the supply of terrestrial sediments to the continental slope. In addition, the high values of the Ti/Al ratio at the base of the core are related to a supply of eolian sediments, while low values of Ti/Al at the top of the core indicated a fluvial source. This work contributes to the knowledge of the Quaternary Geology of the Icaraí sub-basin, Ceará Basin, Brazilian Equatorial Margin.

The 2016 Mw 6.1 Petermann Ranges earthquake rupture, Australia: another “one-off” stable continental region earthquake

<p>The 20<sup>th</sup> May 2016 moment magnitude (M<sub>W</sub>) 6.1 Petermann earthquake was the 2<sup>nd</sup> longest single-event historic Australian surface rupture (21 km) and largest M<sub>W</sub> on-shore earthquake in 28 years. Trench logs from two hand-dug trenches show no evidence of penultimate rupture of surface eolian sediments or underlying calcrete. Available dating of eolian dunes 140 to 500 km away from the Petermann fault indicated eolian deposition during either the last glacial maximum (approximately 20 ka) or a period of aridification at approximately 180 - 200 ka. Ten <sup>10</sup>Be cosmogenic nuclide erosion rates of bedrock outcrops at 0 to 50 km from the surface rupture trace are within error of each other between 1.4 to 2.6 mMyr<sup>-1</sup>. These samples have approximate averaging times between 208 to 419 ka. Bedrock erosion rates, trenching results and interpretation of the landscape history suggest the 2016 event is the only surface rupturing earthquake on the Petermann fault in the last 200 to 400 kyrs, and possibly the first ever on this fault. This finding is consistent with a lack of evidence for penultimate rupture for all eleven historic Australian surface rupturing events, as described by either trenching and/or landscape analysis and bedrock erosion rates. These ‘one-off’ events within Precambrian cratonic Australian crust are not consistent with trenching results and geomorphology of paleo-scarps within the Flinders Ranges and Eastern Australia which indicate multiple recurrent fault offset. Variable fault recurrence behaviour highlights that uniform seismic hazard modelling approaches are not applicable across Stable Continental Regions.</p>