Deposition of fine‐grained sediments in the abyssal environment of the Algéro‐Balearic Basin, Western Mediterranean Sea

Abstract

Two depositional processes control the mud accumulation on the southern Balearic Abyssal Plain: pelagic settling at a rate of 10 cm/1000 years, and turbidity currents at an average frequency of > 3 per 2000 years. Thermo‐haline bottom flow has little effect on the abyssal sediment distribution. Just over half of the Late Quaternary section is made up of turbidite mud. Distinctive properties of turbidite mud are: structural, textural, and compositional continuity from the underlying turbidite sand‐silt layer into the overlying mud, grading within the mud layer, a ratio of carbonate percent with the underlying turbidite sand‐silt layer of about 0.5, and a proportion of sand of > 1%. Those of (hemi)pelagic mud are: bioturbation, an average of 8% of sand consisting largely of remains of foraminifera and pteropods, a grain size distribution which is virtually normal with a median around 9 φ, and very poor sorting; in general, the properties of (hemi)pelagic muds are the same in widely separated localities and depths in cores. In some instances the clay mineral ratios of the turbidite mud layer are markedly different from those of the overlying (hemi)pelagic mud layer.

Hemipelagic chalks in a clastic submarine fan sequence: Miocene SW Turkey

“…Particularly significant are the winnowed foraminifera lags, cut and fill features and biogenic silt laminations. Similar well-sorted concentrations of coarser microskeletons have been described from Recent pelagic sediments of the western Mediterranean (Rupke 1975) and from the Nova Scotian margin (Stow 1979). Table 1 compares diagnostic sedimentological features of muddy contourites, with the hemipelagic chalks of the Salir Formation.…”

“…Similar chalk beds from a clastic dominated sequence have been documented both from the ancient (Weiler 1970;Hesse 1975) and from the recent (Rupke & Stanley 1974;Rupke 1975). In most of the examples documented (both recent and ancient) the pelagic (or hemipelagic) carbonate horizons have been extensively bioturbated and any primary sedimentary structures have been destroyed.…”

“…X-ray diffraction indicates montmorillonite, illite, chlorite and serpentine are the main components of the clay fraction. The composition and sedimentary structures suggest deposition from low density turbidity currents similar to those described by Rupke (1975), Hesse (1975), Piper (1978), Stow & Shanmugam (1980) and Stow & Bowen (1980). (4) Beds of white chalk occur in association with the mudstones, they are described in detail below.…”

A mineralogical and geochemical study of turbidite sandstones and interbedded shales, Mam Tor, Derbyshire, UK

“…1). Grading has been noted in turbiditic muds, but not in hemipelagic muds (Griggs et al, 1969; Rupke, 1975) and it may therefore be suggested that shales in the Mam Tor Beds are hemipelagic rather than turbiditic. Although in the field there is a gradation from the sandstones into the shales, this gradation is not apparent on Fig.…”

“…The information presented in this paper therefore augments the petrography of Allen (1960). In general, however, the clay mineralogy of turbidites and associated sediments has received little attention, Notable exceptions are the papers by Weiler (1970), Rupke (1975) and O' Brien e t al. (1980).…”