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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 56 (1972)

Issue: 3. (March)

First Page: 630

Last Page: 630

Title: Stromatolitic Microfabric: Petrographic Model: ABSTRACT

Author(s): J. A. E. B. Hubbard

Article Type: Meeting abstract


Serial, stained peels, at 10-20 µ intervals, show that a combination of organic and inorganic mineral stains distinguishes between original framework and diagenetic product in a suite of carbonate stromatolites from the Bitter Springs Formation of central Australia. Five laminar microfabrics are recognized: (1) particulate (125-400 µ diameters); (2) wispy laminations (0.5-1.0 mm thick); (3) grumous aggregates with knobby surfaces; (4) mixed calcite and dolomite "brick-and-mortar" texture; (5) saccharoidal dolomite. These original textures are exaggerated by diagenesis and are comparable with recent Bahamian and Floridian microfabrics of organo-sedimentary origin. They recur both vertically and laterally within a single columnar stromatolite and between parallel ntervals in adjacent columns.

A calcite particle (125-400 µ) which preferentially absorbs organic and bacterial stains forms the basic stromatolitic unit structure. It is commonly encompassed by 10-µ dolomitic halo, and is more distinct in bedding peels than in vertical sections where it tends to aggregate with its overlying neighbor. The loose packing and aggregational tendency suggest an unconsolidated origin comparable with Holocene particulate matter of debated sedimentary/fecal/bacterial origin.

Grain-supporting algae are not found. However 2 sizes of dichotomizing transgressive dolomitic tubules (20 µ in diameter), which are reminiscent of voids left by bunches of filaments and meiobenthonic worms, commonly form the basis of the "mortar" fabric. Intrastromatolitic unconformities abound and the contact with the interstromatolitic dolomite, which comprises 400-µ detrital particles with overgrowths, is generally sharp. Periodic wispy laminated drapes outline the original stromatolite's amplitude, and an incorporated dolomitized brachiopod suggests that the interstromatolitic dolomite may have been contemporaneous shell hash.

Diagenetic rhomboidal carbonate distributions are attributed to contemporaneous migrant Mg-rich brines which are size specific and give lit par lit replacements which can be traced into intrastromatolitic faults with 2-mm displacements.

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