Oceanography, sedimentology and acoustic mapping of a bryomol carbonate factory in the northern Gulf of California, Mexico
Published:January 01, 2006
J. Halfar, M. Strasser, B. Riegl, L. Godinez-Orta, 2006. "Oceanography, sedimentology and acoustic mapping of a bryomol carbonate factory in the northern Gulf of California, Mexico", Cool-Water Carbonates: Depositional Systems and Palaeoenvironmental Controls, H. M. Pedley, G. Carannante
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Bryomol carbonates, composed of bryozoans and molluscs, are found in non-tropical shelf and upper slope settings where they are sensitive indicators of oceanographic conditions. Few modern bryomol carbonate settings have been investigated to date, despite their importance in the Phanerozoic rock record. Furthermore, no detailed facies mapping and long-term oceanographic observations have been undertaken in modern bryomol settings, even though this is important for accurately interpreting facies, climate and oceanography from fossil bryomol carbonates. A bryomol carbonate factory on the western margin of the northern Gulf of California, Mexico was selected for an integrated high-resolution in situ oceanographic monitoring, acoustic seafloor mapping, sediment and bryozoan growth morphology study. Molluscan- (28%), bryozoan- (25%) and barnacle- (14%) dominated carbonate production takes place under normal saline warm-temperate eutrophic conditions, with average near sea surface temperatures of 20°C. Even though temperatures are unusually warm for the formation of bryomol carbonates, they develop as a result of prevailing eutrophic conditions (average chlorophyll-a contents of 2.2 mg chl-a m-3). Eutrophic conditions provide ample food to heterotrophic calcifiers and largely exclude faster-growing phototrophic organisms by drastically restricting the depth of the euphotic zone and, therefore, water clarity. Thus, the presence of high amounts of nutrients can generate cool-water-type carbonate assemblages at temperatures where a warm-water association would be expected.
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Cool-Water Carbonates: Depositional Systems and Palaeoenvironmental Controls
During the past decade, work on cool water carbonates has expanded to become a mainstream research area. Studies on modern and Quaternary deposits will continue to be important; however, there is increasing momentum towards unravelling sediment processes, biota-sediment interactions and diagenetic products in Cenozoic and older cool-water carbonates.
Many contributions in this book document Cenozoic and Quaternary carbonates from landlocked (microtidal) water-bodies. These carbonates display important differences in biota and fabric distributions when compared with world ocean examples. Consequently, the scientific community is now better placed to reinterpret pre-Tertiary carbonates where there is a suspicion that they have developed under microtidal conditions. Some papers in the book provide new approaches to interpreting environmental change within macrotidal regimes and others lay firm foundations for future cool-water carbonate diagenetic research
The aim of the book is to illustrate recent international contributions to cool-water carbonates research, with an emphasis on Neogene and Recent case studies. Contributions are divided into three sections: microtidal carbonates from the Mediterranean realm; macrotidal examples from New Zealand, Australia and Mexico; and early diagenetic fabrics.