011020

Compound ooid, Smackover Formation, Jurassic, Alabama, thin-section photomicrograph.

010620

Foram, Mississippian Bangor Ls, thin-section photo ~1.5 mm wide.

122919

Ooid grainstone. Note outer layers of ooids in lower part of image have popped off due to compaction before cementation. Cement has entombed those delicate curved pieces seemingly suspended above the particles they broke off from. Mississippian Bangor Limestone, thin-section photomicrograph, field-of-view 2.5 mm wide. Almost half open space at the time of deposition, this rock is now tight as a drum.

052419

Crinoid ooid bryozoan packstone, Mississippian Bangor Limestone, Alabama, thin section photomicrograph, 2.5 mm wide.

050319b

Pentagonal crinoid ossicle, thinly coated with laminated calcium carbonate, in a fossiliferous ooid grainstone, Mississippian Bangor Limestone, Alabama, thin section photomicrograph.

042619

Ooid grainstone (limestone) with prismatic pore-rimming calcite cement, probably marine. The centers of larger pores are open (white area in the upper part of the image). Jurassic Smackover Formation, Alabama, from nearly 3 miles below the surface, thin section. A tropical shallow-marine deposit.

031919

Partially dolomitized ooid grainstone. Some ooid laminae, and some cement generations, are still calcite. Bright white objects are quartz sand particles. Jurassic Smackover Formation, Alabama, thin-section photomicrograph, stained with Alizarin Red S.

031819c

Partially dolomitized limestone. Calcite is red, dolomite gray, open space light blue and white. Large spheres are ooids (made by crystallization in agitated warm water); small ones pellets (probably made by worms). Thin-section photomicrograph, Jurassic Smackover Formation, Alabama.

031819

Intraclast, thinly coated and consisting of three orids, therefore technically a compound ooid, in mixed-particle grainstone, Jurassic Smackover Formation, subsurface of south Alabama, thin-section photomicrograph.

031619

Grainstone containing numerous fossil fragments, but also a recycled ooid (center), and an intraclast, which itself contains an ooid (right). This rock includes quite a bit of material recycled from nearby pre-existing rocks. Mississippian, Bangor Limestone, Alabama, thin section photomicrograph.

What is this tiny fossil?

This is a paleontological question. The object that fills most of the image is an ooid, a concentrically laminated carbonate particle. This one is 1.4 mm in the long dimension. The inner part of the ooid is a fossil, which consists of hollow calcite objects of variable shape. The calcite consists of crystals normal to the surface of each particular object. Given the shapes visible in this cross-section through the object, they must be roughly equant. The question is, what organism made this fossil?

The rock is Mississippian in age.

Foundation of a Mississippian carbonate mound

Thin section photomicrograph (image 2.5 mm wide), part of an ancient carbonate sand shoal. Later, a small mound grew on top of the shoal. Ooid grainstone.

let's get small

An ooid, a concentrically laminated calcium carbonate spheroid, formed inorganically by wave action around a pre-existing nucleus. The nucleus in this case is the microscopic shell of an amoeba called a foraminiferan. Just so you know.

A tiny box without key or lid
inside a chambered treasure hid
its maker dead and long forgot
yet carbon saved so we aren't hot

Doggerel again, I'm afraid.