GRAINS: Skeletal Fragments: Other Micro- and Nannofossils
2003. "GRAINS: Skeletal Fragments: Other Micro- and Nannofossils", A Color Guide to the Petrography of Carbonate Rocks: Grains, textures, porosity, diagenesis, Peter A. Scholle, Dana S. Ulmer-Scholle
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Often grouped with the tintinnids (pelagic ciliate protozoans of the subclass Spirotheca), although modern tintinnids are organic-walled and calpionellids had calcareous walls. Thus, calpionellids are grouped by other workers as Protozoa incertae sedis.
Calpionellids — Late Jurassic (Tithonian) to Early Cretaceous (Valanginian; possibly into Albian)
Tintinnids — Jurassic-Recent (but with possible record extending into the Paleozoic, perhaps even to the Cambrian)
These open marine organisms are significant contributors to pelagic limestones and chalks in the Late Jurassic. Their distribution is largely restricted to the warm-water Tethyan region, within about 30-35° of the paleoequator.
All calpionellids apparently were composed of low-magnesium calcite; thus, generally well preserved. The TEM studies conducted by Fischer et al. (1967; cited at end of book’s introduction) showed that some calpionellids built two-layered tests in which the main layer incorporated carbonate detritus (including coccoliths) and was lined by an inner, secreted layer.
Small size (typically 45 to 150 μm in length and 30 to 90 μm in width), spherical to elongate, U- or V-shaped grains with a large opening rimmed, in some cases, by a narrowed, slightly thickened collar.
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