Surface features of heavy mineral grains from Palaeocene sands of the central North Sea

Abstract

Synopsis Scanning electron microscopy has revealed both mechanically and chemically produced surface textures on heavy mineral grains from Palaeocene sands of the central North Sea basin. Chemical activity initially modified irregular surfaces, producing mamillae. Further solution produced regular facets, the dimensions of which increase with intensity of etching. Variations in composition of the connate waters are thought responsible for slight variations in etching style. Mechanically-produced surface features similar to those seen on quartz grains, including breakage blocks, V-shaped indentations, grooves, upturned cleavage plates and conchoidal fractures, mostly originated in a pre-Palaeocene phase of sedimentation. The possibility of retention of pre-existing surface textures on grains during the sedimentation process must therefore be considered when using such textures in palaeoenvironmental interpretation.

Faceted garnets from sandstones of the Munising Formation (Cambrian), northern Michigan: petrographic evidence for their origin by intrastratal dissolution

“…Until more is known about the burial history and diagenetic setting of basin margin deposits like the Munising Formation, the significance of garnet etching for burial history will remain conjectural. These findings also agree with earlier work (Mackie, 1923;Bramlette, 1929;Smithson, 1941 ;Sindowski, 1949;Rahmani, 1973;Hemingway & Tamar-Agha, 1975;Morton, 1979Morton, ,1984Morton, ,1987Gravenor, 1979Gravenor, , 1980Gravenor & Gostin, 1979;Gravenor & Leavitt, 1981 ;Borg, 1986;Hansley, 1987) favouring a dissolution origin for facets on garnets. The range of stratigraphic ages, depositional facies, and geological settings in which facet formation by dissolution occurs has probably been underestimated by previous workers.…”

“…Recent papers indicate that hypotheses for the origin of faceted surface features on garnet grains remain controversial. Although most workers favour origin of faceted (positive-relief) features by intrastratal dissolution (Mackie, 1923;Bramlette, 1929;Smithson, 1941 ;Sindowski, 1949;Rahmani, 1973;Hemingway & Tamar-Agha, 1975;Morton, 1979Morton, ,1984Morton, ,1987Gravenor, 1979Gravenor, , 1980Gravenor & Gostin, 1979;Gravenor & Leavitt, 1981;Borg, 1986;Hansley, 1987), some recent workers propose that the facets are overgrowth features (e.g., Simpson, 1976;Howie et al, 1980;Mader, 1981).…”

A new approach to provenance studies: electron microprobe analysis of detrital garnets from Middle Jurassic sandstones of the northern North Sea

“…Although garnets are fairly resistant to diagenesis, strong dissolution does occur where great burial depths are involved, or where they have been subjected to percolation of acidic groundwaters in weathering (Morton, 1984a). There is every possibility that different garnet species have different stabilities : indeed, this may explain why garnet dissolution in the North Sea Palaeocene appears to begin at relatively shallow depths, although it persists throughout the sands to depths in excess of 3000m (Morton, 1979(Morton, , 1984a. The behaviour of garnet suites under intrastratal solution conditions needs to be fully elucidated before the technique is employed in areas where this is a potential problem.…”

The Chemical Composition and Surface Texture of Transparent Heavy Minerals from Core LQ24 in the Changjiang Delta

“…The corrosion signature of heavy minerals indicates different transportation, sedimentation, and burial conditions [32][33][34]. The SEM images of Core LQ24 revealed that the amphibole and epidote in the Pliocene strata were more corroded than the tourmaline mineral present in both the Pliocene and Pleistocene sediments (Figures 9-11).…”