The origin of carbonate mud in isolated carbonate platforms of Belize, Central America

Abstract

Carbonate mud from three small isolated carbonate platforms of Belize (Central America) is largely a product of the breakdown of skeletal grains. The composition of the 63-20-and 20-4-µm fractions of 37 samples was determined by point counting under SEM; composition of the <4-µm fraction was assessed qualitatively under SEM. The 63-4-µm fractions are dominated by fragments of mollusks, the codiacean alga Halimeda, and other skeletal types. About one-third of the particles in the 63-4-µm fractions remained unidentified, probably due to obliteration of diagnostic features by early recrystallization processes such as micritization. Nanograins (<1 µm) and short (3-5 µm) aragonite needles are most common in the <4-µm fraction. These grains are interpreted to be largely fragments of codiacean algae (Halimeda, Penicillus). The 20-4-and <4-µm sediment fractions are composed of 80 and 75% aragonite on average, respectively. Trace element composition of strontium averages 7,900 ppm in the 20-4-µm fraction and in codiacean algae samples, and 5,600 ppm in the <4-µm fraction. Geochemical (trace element) data also argue against inorganic aragonite precipitation within the water column, and favor a skeletal origin. The lower strontium contents in the <4-µm fraction as compared with the 20-4-µm fraction may also be a consequence of early recrystallization processes.

Carbon- and oxygen-isotope records of palaeoenvironmental and carbonate production changes in shallow-marine carbonates (Kimmeridgian, Swiss Jura)

“…Strontium contents in the Gorges du Pichoux and Péry-Reuchenette sections (Tables 2, 3) are very low compared to Sr contents of modern micrites (Kinsman, 1969;Andrews, Christidis & Dennis, 1997;Bosence, 1995;Gischler & Zingeler, 2002;Milliman et al 1993). However, manganese contents are close to those of modern lagoonal (brackish water) or freshwater carbonate sediments (Friedman, 1969), and lower than those measured in pelagic carbonates of Kimmeridgian successions (de Rafélis et al 2000).…”

Fish as major carbonate mud producers and missing components of the tropical carbonate factory

“…However, the origins of both aragonitic and Mg-calcite carbonate muds remains a topic of long-standing debate (2,3). Indeed, where attempts have been made to quantify sources of the fine sediment fraction a high proportion remains of unknown origin (e.g., up to 40% in Bahamian sediments and between 28 and 36% in Belize lagoon sediments) (4,5). This problem arises in part because, with the exception of inorganic carbonate precipitation (e.g., the carbonate "whiting" controversy) (3,(6)(7)(8), the processes of carbonate mud production necessarily invoke the degradation of larger bioclasts (skeletal fragments of marine organisms) to produce mud-grade carbonate, and/or grain recrystallization to produce high Mg-calcite muds (9)(10)(11).…”

The Belize margin revisited: 1. Holocene marine facies

“…There is also an in situ shelf lagoon mud contribution by coccoliths (Scholle and Kling 1972), but the magnitude of that contribution does not affect the amount of mud Matthews believed was derived from the carbonate shoals and barrier platform . Values exceeding 60% also occur in the deepest part of Glovers Reef and in the western main and northern lagoons of Turneffe Islands (Gischler and Lomando 1999) where SEM and geochemical analyses of mud also indicate a skeletal debris derivation (Gischler and Zingeler 2002).…”