Aggregate Grains in Carbonates

Aggregate grains are irregularly shaped carbonate grains that consist of two or more carbonate fragments (pellets, ooids, fossil fragments) joined together by a carbonate-mud matrix that is generally dark colored and rich in organic matter. ^[1]

Grapestones

Because the shapes of the aggregate grains in some modern carbonate-forming environments, such as the Bahama Banks, resemble a bunch of grapes, they are commonly called grapestones. ^[1]

Lumps

Other aggregate grains with a somewhat smoother appearance have been referred to by the rather inelegant name of lumps. ^[1] Lumps evolve from grapestones by continued cementation and micritization of the grains. ^[1]

Mineralogy

Aggregate grains in modern carbonate environments are composed mainly of aragonite, but such grains in ancient limestones are dominantly calcite. ^[1]

Recognition and Confusion

Aggregate grains in modern environments can commonly be recognized by their botryoidal shapes and lack of internal structures; however, they can be confused with intraclasts. ^[1] In fact, they are considered a type of intraclast by some geologists. ^[1]

Preservation in Ancient Limestones

Aggregate grains are only rarely reported in ancient limestones, possibly because their shapes become distorted beyond recognition owing to compaction during diagenesis. ^[1]

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