Submarine volcanic activity and giant amygdale formation along the Panama island arc as a precursor to 6000-year-old agate exploitation on Pedro González Island

2021 ◽  
pp. 1-16
Author(s):  
Stewart D Redwood ◽  
David M Buchs ◽  
David Edward Cavell
Keyword(s):  
Volcanic Activity ◽  
Bimodal Distribution ◽  
Island Arc ◽  
Early Miocene ◽  
Tool Manufacture ◽  
Marine Deposits ◽  
Large Size ◽  
Hydrothermal Processes ◽  
Field Evidence ◽  
Geochemical Study

Abstract An extensive deposit of agate occurs in Pedro González Island in the Gulf of Panama. Previous archaeological research showed that the agate was exploited between 6200 and 5600 cal BP to make stone tools found at the oldest known Preceramic human settlement in the Pearl Island archipelago. We constrain here the origin and geological context of the agate through a geological and geochemical study of the island. We show that it includes primary volcanic breccias, lavas, and tuffaceous marine deposits with sedimentary conglomerates and debris flow deposits, which we define as the Pedro González Formation. This formation records submarine to subaerial volcanic activity along an island arc during the Oligo-Miocene, confirming previous regional models that favour progressive emergence of the isthmus in the early Miocene. The igneous rocks have an extreme tholeiitic character that is interpreted to reflect magmatic cessation in eastern Panama during the early Miocene. The agate is hosted in andesitic lavas in unusually large amygdales up to 20–40 cm in diameter, as well as small amygdales (0.1–1.0 cm) in a bimodal distribution, and in veins. The large size of the agates made them suitable for tool manufacture. Field evidence suggests that the formation of large amygdales resulted from subaqueous lava–sediment interaction, in which water released from unconsolidated tuffaceous deposits at the base of lava flows rose through the lavas, coalesced, and accumulated below the chilled lava top, with subsequent hydrothermal mineralization. These amygdales could therefore be regarded as an unusual result of combined peperitic and hydrothermal processes.

Jarosite in Antarctic deep ice supports the ice-weathering model for jarosite formation on Mars

2021 ◽  
Author(s):  
Giovanni Baccolo ◽  
Barbara Delmonte ◽  
Paul Niles ◽  
Giannantonio Cibin ◽  
Elena Di Stefano ◽  
...  
Keyword(s):  
Low Temperature ◽  
Volcanic Activity ◽  
Liquid Water ◽  
Chemical Weathering ◽  
Ice Core ◽  
Hydrothermal Processes ◽  
Meridiani Planum ◽  
History Of ◽  
Alternative Proposal ◽  
Iron Bearing

<p>On Earth, jarosite is a weathering product forming in acidic-oxidative environments from the alteration of iron-bearing minerals in presence of liquid water. Typical settings where this iron-potassium hydrated sulphate is found, are weathering zones of pyrite-rich deposits, evaporative basins and fumaroles. Jarosite is not only known on Earth, it also occurs on Mars, where it was firstly identified by the Opportunity rover. The mineral was in fact recognized in the finely layered formations outcropping at Meridiani Planum and that were accurately investigated by the rover (Klingelhöfer et al. 2004). Since jarosite requires liquid water to form, its occurrence on Mars has been regarded as an evidence for the presence of liquid water in the geologic past of Mars (Elwood-Madden et al., 2004). Since then, many models have been proposed to describe the environments where the precipitation of Martian jarosite took place. The most accepted ones deal with evaporative basins similar to Earth’s playas, others concern volcanic activity and hydrothermal processes. An alternative proposal predicted that jarosite may have formed as a consequence of weathering of mineral dust trapped in massive ice deposits, i.e. the ice-weathering model (Niles & Michalsky, 2009). The hypothesis that jarosite formed on Mars because of low-temperature, acidic and water limited weathering, is not new (Burns, 1987), but until now no direct evidences were available to support it.</p><p>A potential Earth analogue to investigate such processes is deep Antarctic ice. We present a first investigation of deep ice samples from the Talos Dome ice core (East Antarctica) aimed at the identification of englacial jarosite, so as to support the ice-weathering model. Evidences gathered through independent techniques showed that jarosite is actually present in deep Antarctic ice and results from the weathering of dust trapped into ice. The process is controlled by the re-crystallization of ice grains and the concurrent re-location of impurities at grain-junctions, which both depend on ice depth. This study demonstrates that the deep englacial environment is suitable for jarosite precipitation. Our findings support the hypothesis that, as originally predicted by the ice-weathering model, paleo ice-related processes have been important in the geologic and geochemical history of Mars.</p><p> </p><p><strong>References</strong></p><p>Burns, R. Ferric sulfates on Mars. <em>J. Geophys. Res.</em> <strong>92</strong>, E570-E574 (1987).</p><p>Elwood-Madden et al., 2004. Jarosite as an indicator of water-limited chemical weathering on Mars. <em>Nature</em> <strong>431</strong>, 821-823 (2004).</p><p>Klingelhöfer, G. et al. Jarosite and Hematite at Meridiani Planum from Opportunity's Mössbauer Spectrometer. <em>Science</em> <strong>306</strong>, 1740-1745 (2004).</p><p>Niles, P. B. & Michalski, J. M. Meridiani Planum sediments on Mars formed through weathering in massive ice deposits. <em>Nat. Geosci.</em> <strong>2</strong>, 215-220 (2009).</p>

scholarly journals A Detailed Geochemical Study of Island Arc Crust: the Talkeetna Arc Section, South–Central Alaska

2006 ◽  
Vol 47 (6) ◽  
pp. 1051-1093 ◽  
Author(s):  
ANDREW R. GREENE ◽  
SUSAN M. DeBARI ◽  
PETER B. KELEMEN ◽  
JUREK BLUSZTAJN ◽  
PETER D. CLIFT
Keyword(s):  
Island Arc ◽  
South Central ◽  
Geochemical Study

The Numidian Sand Event in the Burdigalian Foreland Basin System of the Rif (Morocco) in a source-to-sink perspective

2021 ◽  
Author(s):  
Anas Abbassi ◽  
Paola Cipollari ◽  
Maria Giuditta Fellin ◽  
Mohamed Najib Zaghloul ◽  
Marcel Guillong ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Large Population ◽  
Foreland Basin ◽  
Source Area ◽  
Western Mediterranean ◽  
Early Miocene ◽  
Calcareous Nannofossils ◽  
External Zone ◽  
Field Evidence ◽  
Basin System

<p>During the Tertiary evolution of the Western Mediterranean subduction system, the orogenic accretion at the Maghrebian margin let the stacking of three main tectonic zones of the Rif fold-and-thrust belt: 1) the Internal Zone; 2) the “Maghrebian Flysch” Nappes; and 3) the  External Zone. In this context, a migrating foreland basin system developed between the Maghrebian orogenic belt and the adjacent African Craton. </p><p>A comprehensive reconstruction of the foreland basin system of the Rif Chain for each phase of its accretional history is still missing. In this work, by integrating field observations with quantitative biostratigraphic data from calcareous nannofossils assemblages, sandstone composition, and detrital zircon U-Pb geochronology from selected stratigraphic successions, we reconstruct the foreland basin system that in the early Miocene developed in front of the growing Rif orogen. The analyzed successions are representative of (1) the “Beliounis Facies”, made of quartz-arenites and litharenites (Numidian-like “mixed succession”), from the Predorsalian Unit; (2) the “Mérinides Facies”, made of a Numidian-like “mixed succession”, from the “Maghrebian Flysch Basin”; and (3) the classical “Numidian Facies”, exclusively made of quartzarenites, from the Intrarifian Tanger Unit.</p><p>The petrographic analyses and the detrital zircon U-Pb ages show the provenance of the quartzarenites of the “Numidian Facies” from the African Craton, whereas the sublitharenites and feldspathic litharenites, of both the “Mérinides Facies” and “Beliounis Facies”, show provenance from a cratonic area and the growing and unroofing Rif Chain, respectively. </p><p>The Alpine signature of the detrital grains sedimented into the foredeep deposits of the early Miocene orogenic system of the Rif Chain is from the feldspathic litharenites of both the Mérinides Facies and the Beni Ider Flysch. Both show Mesozoic and Cenozoic U-Pb zircon populations, with a large population of zircons centered at ca. 32 Ma. The U and Th concentration, the Th/U ratio, and the REE pattern of this population of zircons suggest a possible source area from Oligocene doleritic rock intrusions, similar to the magmatic dyke swarms (diorite) cropping out in the Malaga region ( SE Spain).</p><p>The biostratigraphic analyses pinpoint the same age for the arrival of the quartz grains in the Numidian, Mérinides, and Beliounis deposits, indicating about 1 Myr for their sedimentation (ca. 20-19 Ma, early Burdigalian). Together with field evidence, the biostratigraphic results point to an autochthonous deposition of the Numidian Sandstones on top of the Tanger Unit, allowing to delineate the early Burdigalian foreland basin system of the Rif Chain. The foreland depozone involved the Tanger Unit and received the “Numidian Facies” deposits ; the foredeep depozone hosted about 2000 m of the “Mérinides Facies” and the Beni Ider Flysch, and developed on the so-called “Flysch Basin Domain”; and, finally, the wedge-top depozone, characterized by the “Beliounis Facies”, developed on top of the Predorsalian Unit.</p><p>The Numidian Sandstones and the Numidian-like deposits analyzed in Morocco show the same age of similar deposits from Algeria, Tunisia, and Sicily, suggesting a comparable early Burdigalian tectono-sedimentary evolution along the southern branch of the Western Mediterranean subduction-related orogen.</p>

scholarly journals Upper Cretaceous volcanoclastic deposits from the Haţeg basin, south Carpathians (Romania): K-Ar ages and intrabasinal correlation

2011 ◽  
Vol 38 (2) ◽  
pp. 182-188 ◽  
Author(s):  
Ana-Voica Bojar ◽  
Stanislaw Halas ◽  
Hans-Peter Bojar ◽  
Dan Grigorescu ◽  
Stefan Vasile
Keyword(s):  
Volcanic Activity ◽  
Upper Cretaceous ◽  
The Other ◽  
Volcanic Centre ◽  
Marine Deposits ◽  
Mineral Phases ◽  
Palaeomagnetic Data ◽  
Haţeg Basin ◽  
Volcanic Bomb

AbstractIn order to constrain the age of the Upper Cretaceous continental Densuş-Ciula Formation from the Haţeg basin, South Carpathians, and correlate it with the other continental unit that occurs in the region, the Sânpetru Formation, we separated and dated by the K-Ar method biotites and amphiboles from volcanoclastic deposits. The mineral phases analysed are from two tuff layers and volcanic bombs cropping out near Rachitova village. Two tuff layers from the Densuş-Ciula Formation give early Maastrichtian ages of 69.8±1.3 and 71.3±1.6 Ma, respectively. The ages determined for the tuff layers constrain the age of deposition for the Densuş-Ciula Formation and enable further correlations with the available palaeomagnetic data from the deposits occurring along the Sibişel Valley that belong to the Sânpetru Formation. The volcanic bombs collected near to Răchitova village are andesites and dacites. The age determined by K-Ar method on hornblende separated from a volcanic bomb is 82.7±1.5 Ma, which is older than the underlying Campanian marine deposits in turbidite facies. This suggests that the volcanic bombs were re-deposited during the early Maastrichtian. Thus, the volcanics found at Răchitova have at least two origins: one type is related to an explosive synsedimentary volcanic activity, and the other type is represented by older andesitic/dacitic bombs, which most probably originate from a volcanic centre situated in the Haţeg region.

scholarly journals Natufian Settlement and Mobility: A Lithic Perspective from Saaïdé II, Lebanon

2001 ◽  
Vol 15 (1) ◽  
Author(s):  
Ildiko Horvath
Keyword(s):  
Mobility Patterns ◽  
Site Location ◽  
Human Occupation ◽  
Tool Manufacture ◽  
Large Size ◽  
Mobility Strategies ◽  
Marginal Areas ◽  
Lithic Reduction ◽  
Hunting And Gathering ◽  
Residential Camp

This study is concerned with settlement and mobility patterns from the perspective of the organization of the lithic technology. Radiating mobility patterns in the context of the Levantine Late Natufian are investigated by looking at the intensity of lithic reduction and the use of blanks for tool manufacture. By conjoining the results of the technological and morphological analysis of lithic tools with additional lines of evidence, such as site location, proximity to various resources, seasonal availability of resources, functional use of flint and non-flint artifacts, an integrated view has been reached on the intensity of human occupation at the Late Natufian site of Saaïdé II. With its large size, thick cultural deposits, varied tool kit and generalized subsistence, Saaïdé II was a residential camp for bands that subsisted on hunting and gathering. What enabled people to reside in this spot for more than one season was the overlap of seasonally available resources. The model of radiating mobility proposed for Saaïdé II illustrates that radiating mobility strategies were not abandoned with the onset of the climatic deterioration triggered by the Younger Dryas around 9,000 Be. Sites located in more marginal areas, beyond the boundaries of the Natufian "homeland", were able to sustain larger agglomerations of people and intensive human occupation.

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