Links between Ikaite Morphology, Recrystallised Ikaite Petrography and Glendonite Pseudomorphs Determined from Polar and Deep-Sea Ikaite

Abstract

Petrography of recrystallised ikaite from Ocean Drilling Program material has been presented previously from Nankai Trough and Congo (ex-Zaire) deep-sea fan. This paper expands on the Nankai Trough ikaite observations, drawing on evidence from Laptev Sea, South Georgia, Okhotsk Sea, and coastal lagoon Point Barrow. However, even though many ikaite and glendonite sites occur at high latitudes, it cannot be that ikaite forms exclusively in polar environments, as demonstrated by the occurrences in the low latitude low temperature deep sea sediments offshore Gulf of Guinea (Angola Congo) and mid-latitude deep-sea trenches offshore Japan. Recrystallised ikaite occurs as mm large, zoned calcite crystals in all samples, along with secondary phases of calcite. Our data set is unique in that the origin, storage, and recrystallisation process of natural formed ikaite is recorded in detail and confirms that glendonite petrographic characteristics are a consequence of the structure and chemistry of recrystallising ikaite and not the physical or geochemical environment. The transformation of man-made ikaite to calcite as recorded in laboratory studies, is a process very similar to the one we have observed for natural ikaite. Most significant is that there is variation in the order of the calcite types within a single sample, leading to the conclusion that the variation is a consequence of impurities and geochemical variability in the ikaite, not the external environment. Morphological observations reveal similarities in ikaite and glendonite, this and the similarity in internal textures in glendonite and recrystallised ikaite confirms that glendonite may be used as an indicator of past presence of ikaite.

Transgression Related Holocene Coastal Glendonites from Historic Sites

“…Two different models for ikaite formation have emerged from work at Olenitsa [21,22] and the Isatkoak site [10]. The Olenitsa model involves a shallow meteoric seep in coastal regions during transgression, while the Isatkoak model requires a single forceful event, such as a storm surge.…”

“…Previous studies have reported data on single-source sediment containing diagenetic carbonate in fully marine glendonites [10,12,14]. Here, we provide a historical context in Figure 1 to coastal ikaite formation in, describe the morphology and petrology in Figure 2, and present new 14 C dating and stable isotope in analysis of carbon and oxygen for the described glendonites in Table 1.…”

“…When ikaite transforms to calcite in cave systems, it can leave behind only a few calcite preserved (CaCO 3 ) structural "relicts" [5], often in the form of zoned mm large calcite grains, termed "guttulatic", meaning little drop" [6]. Guttulatic crystals have pseudo-hexagonal or spherical cores with low Mg cores [7] formed during the recrystallisation of marine ikaite and are particularly dominant in glendonite [5,6,[8][9][10][11][12][13][14][15]. However, guttalatic structure is present in many different aquatic and terrestrial systems.…”

“…A striking similarity between ikaite and glendonites was observed, and it was tentatively concluded that ikaite is the precursor mineral of glendonite [9]. Glendonite can only have ikaite as a precursor mineral [9,10]. In marine-influenced sediments, euhedral ikaite appears to be stable above ~7 • C. Ikaite is highly unstable and rapidly breaks down into wet calcite granules within hours of retrieval [11], which has hindered traditional crystallographic investigations.…”

“…Combining with Ca and Mg ration from Table 2, we add good data to future work on a unifying theory of ikaite precipitation. [17]; † Published in Shearman and Smith [9]; ‡ Published in Schultz [10].…”