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The offshore environment
Published in White David, Cassidy Mark, Offshore Geotechnical Engineering, 2017
Marine sediments are composed of detrital material from land or from the remains of marine organisms, which leads to the principal classification of sediment as either terrigenous (transported from land) or pelagic (sediments that settle through the water column). Pelagic sediments are deposited so slowly that nearshore and coastal areas are overwhelmed by terrigenous deposits.
A multi-proxy approach for delineation of ferromanganese mineralization from the West Sewell Ridge, Andaman Sea
Published in Marine Georesources & Geotechnology, 2022
Rachna Pillai, Saju Varghese, P. Durga Prasad
Seamount Fe-Mn crusts and nodules (henceforth crusts and nodules respectively) are critical submarine potential mineral resources distributed on the seamounts (Hein et al. 2000). Crust and nodules occur as pavements on hard rock substrates of submarine seamounts and ridges where sediment supply is less throughout the global ocean (Koschinsky and Halbach 1995; Koschinsky and Hein 2003). Thick crusts on seamounts commonly occur on outer-rim summit terraces and broad saddles on the summit of flat-topped seamounts (Hein and Koschinsky 2014). The exceptionally slow growth rates (1-5 mm/Myr), high porosity (> 50%) and large specific surface area (300 m2/g) of the colloidal particles allow the crusts to adsorb large quantities of economically important elements such as Cobalt (Co), Nickel (Ni), Copper (Cu), Titanium (Ti), Manganese (Mn), Rare Earth Elements (REEs) and Platinum Group Elements (PGE) (Hein et al. 2000; Koschinsky and Hein 2003). Vital geological factors influencing the distribution of crust and nodules in seamounts are calcareous pelagic sediment, carbonate sediment, and slump or debris caused by gravity (Yang et al. 2016). Therefore, establishing the relationship between spatial distributions of crusts and nodules and the distribution of sediments is critical for the exploration of crusts and nodules (Joo et al.2020).
Sr, Nd, Hf and Pb isotope geochemistry of Early Miocene shoshonitic lavas from the South Fiji Basin: note
Published in New Zealand Journal of Geology and Geophysics, 2022
Nick Mortimer, Delphine Bosch, Christine Laporte-Magoni, Erin Todd, James B. Gill
The closest SW Pacific comparison of these shoshonitic and high-K lavas is with some of the more isotopically evolved basalts and andesites in the TVZ (Figure 2) which erupted through continental crust. But even here, the overlap is not perfect, and the tectonic setting and major element composition (petrogenesis) of the suites are quite different. Our shoshonitic and high-K lavas lie on trends towards subducted pelagic sediment and/or continental basement fields on the isotope diagrams (Figure 2A–C). As is often the case in complex convergent margin tectonic settings worldwide, the lavas have likely acquired their isotope ratios by the variable mixing and melting of various components, e.g. depleted mid-ocean ridge basalt (DMM)/BABB mantle, enriched OIB mantle and subducted sediment.
Sedimentary characteristics and the implications of cobalt-rich crusts resources at Caiwei Guyot in the Western Pacific Ocean
Published in Marine Georesources & Geotechnology, 2020
Bin Zhao, Zhenquan Wei, Yong Yang, Gaowen He, Heng Zhang, Weilin Ma
According to previous studies, type I reflection is entirely lenticular in shape (thin in the middle and thick at the edges) throughout the summit, representing calcareous pelagic sediments, mainly consist of foraminiferal mud, foraminiferal sandstone, and foraminiferal mudstone deposits (He, Zhao, and Zhu 2001; Ren 2005; Yang et al. 2015; Wang et al. 2016) (Figure 3). This kind of pelagic sediment was developed widely on the Magellan Mountains, especially on guyots, indicating a typical marine deep water environment (Lee et al. 2005, 2009). To date, geological sampling at the top of Caiwei Guyot is confined to shallow surface layer, mainly from shallow drilling, dredging, and Remotely Operated Vehicle (ROV). There is no deep drilling through the sediments to the basement. However, from the reflection characteristics of existing sub-bottom profiles, it is apparent that type I reflection extends from the center to the margin until exposed (Figures 2 and 3). Outcrops on the margin are mainly volcaniclastic rock, limestone, basalt, and phosphorite (Wei et al. 2016). In addition, the DSDP drilling on the Weijia Guyot (Ita Mai Tai) of the Magellan Seamounts to the southeast of Caiwei Guyot revealed that carbonate rocks such as reef complex, reef limestone, and oolitic limestone underlay pelagic sediments (Heezen, MacGregor, and Foreman 1973a, 1973b; Hesse 1973; Lee et al. 2005). Type II deposits represent a shallow lagoon deposit environment with strong hydrodynamic activities, and were deposited near the sea level (Lee et al. 2009; Mel’nikov, Tugolesov, and Pletnev 2010; Mel’nikov et al. 2012). In summary, type I is overlying type II, and type II sediments has an unconformity on the volcanic basement (Figures 2 and 3).