GRAINS: Skeletal Fragments: Brachiopods
2003. "GRAINS: Skeletal Fragments: Brachiopods", A Color Guide to the Petrography of Carbonate Rocks: Grains, textures, porosity, diagenesis, Peter A. Scholle, Dana S. Ulmer-Scholle
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Phylum Brachiopoda — earliest Cambrian-Recent
Subphylum Linguliformea (Early Cambrian-Recent): shells lack skeletal articulation structures; shells are chitinophosphatic with laminar microstructure; pedicle usually present, emerging between valves or from opening in ventral valve.
Class Lingulata (Early Cambrian-Recent): brachiopods with chitinophosphatic shells lacking teeth and sockets; pedicle usually present emerging from shell between valves or from apex of one of the valves.
Class Paterinata (Early Cambrian-Late Ordovician): shell rounded to elliptical with straight posterior margin with pseudointerarea; delthyrium often closed by plates; pedicle reduced or absent.
Subphylum Craniiformea (Early Cambrian-Recent): calcareous shells; valves lack hinge teeth and sockets; shell usually attached to substrate by cementation of pedicle (ventral) valve.
Class Craniata (Mid. Cambrian-Recent): features as above for subphylum.
Subphylum Rhynchonelliformea (Early Cambrian-Recent): Brachiopods with calcitic shells that have endopunctate, impunctate, pseudopunctate, or tabular microstructure; crura usually present extended to form a brachidium (spiralia or loops) in some groups; articulated valves with hinge teeth and sockets are the norm, but in some forms, reduced or modified types of articulation structures are present; the vast majority of known rhynchonelliform brachiopods are included in the classes Strophomenata and Rhynchonellata.
Class Chileata (Early Cambrian only): short-lived early group, see features in Clarkson (1998, p. 181).
Class Obolellata (Early-Mid. Cambrian): short-lived early group, see features in Clarkson (1998).
Class Kutorginida (Early-Mid. Cambrian): short-lived early group, see features in Clarkson (1998).
Class Strophomenata (Mid. Cambrian-Triassic): Shell usually concavo-convex or planoconvex; shell usually pseudopunctate; straight hinge with simple teeth (often lost); some groups with spines, pedicle opening usually closed by plate(s). Includes the Orders: Strophomenida (six suborders), and Productida (two suborders).
Class Rhynchonellata (Early Cambrian-Recent): Biconvex shells with both strophic and nonstrophic hinges; impunctate and punctate shells; crura usually present; brachidium often present. Includes the orders: Orthida (shell usually impunctate); Rhynchonellida; Pentamerida; Athyrida (spiralia present, usually impunctate); Atrypida (spiralia present, impunctate); Spiriferida (spiralia present, punctate and impunctate shells); Spiriferinida (spiralia present, impunctate and punctate shells), and Terebratulida (loop present, punctate shell).
In general, brachiopods were especially abundant in the Paleozoic where they reached their peak diversity in the Devonian. In many settings, they were among the main rock-forming organisms. Although they are much less abundant in Mesozoic and Cenozoic strata, they retain considerable biostratigraphic value in those deposits.
Figures & Tables
A Color Guide to the Petrography of Carbonate Rocks: Grains, textures, porosity, diagenesis
This volume expands and improves the AAPG 1978 classic, A Color Illustrated Guide to Carbonate Rock Constituents, Textures, Cements, and Porosities(AAPG Memoir 27). Carbonate petrography can be quite complicated. Changing assemblages of organisms through time, coupled with the randomness of thin-section cuts through complex shell forms, add to the difficulty of identifying skeletal grains. Furthermore, because many primary carbonate grains are composed of unstable minerals (especially aragonite and high-Mg calcite), diagenetic alteration commonly is quite extensive in carbonate rocks. The variability of inorganic and biogenic carbonate mineralogy through time, however, complicates prediction of patterns of diagenetic alteration. This book is designed to help deal with such challenges. It includes a wide variety of examples of commonly encountered skeletal and nonskeletal grains, cements, fabrics, and porosity types. It includes extensive new tables of age distributions, mineralogy, morphologic characteristics, environmental implications and keys to grain identification. It also encompasses a number of noncarbonate grains, that occur as accessory minerals in carbonate rocks or that may provide important biostratigraphic or paleoenvironmental information in carbonate strata. With this guide, students and other workers with little formal petrographic training should be able to examine thin sections or acetate peels under the microscope and interpret the main rock constituents and their depositional and diagenetic history.
- carbonate rocks
- color imagery
- problematic fossils
- sedimentary rocks