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Titolo:
LATE QUATERNARY HALIMEDA BIOHERMS AND ARAGONITIC FECAL PELLET-DOMINATED SEDIMENTS ON THE CARBONATE PLATFORM OF THE WESTERN CONTINENTAL-SHELF OF INDIA
Autore:
RAO VP; VEERAYYA M; NAIR RR; DUPEUBLE PA; LAMBOY M;
Indirizzi:
NATL INST OCEANOG PANAJI 403004 GOA INDIA UNIV ROUEN,DEPT GEOL MONT ST AIGNAN FRANCE
Titolo Testata:
Marine geology
fascicolo: 3-4, volume: 121, anno: 1994,
pagine: 293 - 315
SICI:
0025-3227(1994)121:3-4<293:LQHBAA>2.0.ZU;2-7
Fonte:
ISI
Lingua:
ENG
Soggetto:
EASTERN JAVA SEA; GREAT-BARRIER-REEF; NICARAGUAN RISE; BEACHROCK; INDONESIA; CEMENTATION; HOLOCENE; ALGAE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Science Citation Index Expanded
Science Citation Index Expanded
Citazioni:
75
Recensione:
Indirizzi per estratti:
Citazione:
V.P. Rao et al., "LATE QUATERNARY HALIMEDA BIOHERMS AND ARAGONITIC FECAL PELLET-DOMINATED SEDIMENTS ON THE CARBONATE PLATFORM OF THE WESTERN CONTINENTAL-SHELF OF INDIA", Marine geology, 121(3-4), 1994, pp. 293-315

Abstract

The Fifty Fathom Flat is a drowned carbonate platform located on the outer continental shelf of western India. It is unique because the carbonate depositional environment prevailed until Early Holocene in spite of its proximity to a major siliciclastic tidal embayment. Study of the bathymetry, seismic and sonograph data together with the petrology, mineralogy and geochemistry of the carbonate sediments and limestones recovered from the platform resulted in (a) the discovery of Late Quaternary Halimeda bioherms and (b) aragonitic faecal pellet-dominated sediments. Echograms reveal buried pinnacles between 62 and 38 m and exposed 2 to 14 m high pinnacles between 65 and; 85 m on the platform. These pinnacles occur as narrow to broad mounds (bioherms) in seismic profiles and as linear ridges and massive structures in sonographs. Seismic profiles also show a prominent reflector about 25 m below the sea bed identified by boreholes as a Late Pleistocene erosion surface. The platform consists of relict carbonate sands and limestones. Roundedand ovoid to ellipsoidal aragonite grains are predominant in the sediments. SEM studies indicate elongated parallel canals and crescent to hook-shaped canals, corresponding to faecal pellets, occur in some grains. Algal grains and pellets enclosing algal fragments are also present. The grains in the limestones are similar to those in the sediments. Halimeda and crustacean faecal pellets are abundant components, withminor echinoid, mollusc and benthic foraminifera. The limestones are characterised by abundant pores, dissolution cavities, relic aragoniteneedles, meniscus cements and drusy calcite fill the pores produced by dissolution of aragonite needles. These features indicate vadose diagenesis. The stable isotopes of the carbonate sands and limestones arealmost identical and similar to isotope values of beachrocks of the Red Sea. The limestones ages (9200-8400 yr B.P.) lie within the same age limits (10,400-8300 yr B.P.) as the surficial sediments. It appears that fluvial sediments largely accumulate in the inner shelf and did not hinder carbonate growth on the platform, lying on the outer shelf. We presume that arid climate and nutrients brought by river runoff andshelf edge currents favoured the growth of algal bioherms dominated by Halimeda between 13,700 (?) and 8300 yr B.P. The absence of Late Holocene and modern carbonates on the platform may be due to the combinedinfluence of climatic change, upwelling and neo-tectonic activity at about 9000 yr B.P. The bioherms dominated by Halimeda, produced abundant aragonite muds. Deposit feeding crustaceans and other invertebratessubsequently excreted these muds as faecal pellets. The platform thuscontains faecal pellet-dominated sediments.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 06/04/20 alle ore 23:30:02