Calymmian Period

Breakup of Columbia Super-continent

The Calymmian is the first period of the Mesoproterozoic, occuring after the (Statherian) Paleoproterozoic, and before the Ectasian Period

1,600–1,400 Ma
Greek word for "cover", indicating the expansion of "platform covers", which are layers of igneous or sedimentary rock that accumulate over cratons

A time of continent building, where the Earth's crust thickens due to the deposition of rock on top of older rock.
- Continental plates expand as sediments are washed into the sea and deposited along the coast, making the sea shallower.
- Movement of continents also creates shallow seas between landmasses, which are also gradually filled up due to the deposition of sediment, forming new land.
Breakup of the super-continent Columbia
- Began around 1.6 billion years ago, and continued through the Calymmian to end in the Ectasian, around 1.3-1.2 billion years ago.
- Rifts appeared along the western margin of Laurentia (the north American plate), the east margin of India, southern margin of Baltica, southeastern margin of Siberia, northwestern margin of South Africa, and the northern margin of the South China Block.
- Rifting was accompanied by volcanism along the rift sites, which led to large igneous deposits of rock in these regions.

- Globe-shaped organism, ~70 μm wide, which has wall features that may indicate that it is a representative of the green algae [Javaux et al., 2004]
Other Proterozoic acritarchs exhibit fungus-like characteristics (e.g., Trachyhystrichosphaera, Dictyosphaera, Foliomorpha), indicating that there is evidence for an extended and relatively diverse record of Proterozoic fungi.
Horodyskia is a fossilized organism dated from 1,500 - 900 mya, described as a "string of beads" connected by a very fine thread (Yochelson & Fedonkin, 2000, Fedonkin & Yochelson, 2002).
- This organism may have been an early metazoan (Fedonkin, 2003) or possibly a colonial foraminiferan (Dong et al., 2008)

Bengtson et al., 2017
Northern India dating to 1.6 Ga
Filamentous red alga about ½ millimeter long
Some cells had small holes or bumps in connecting walls. These appear to be pit connections & pit plugs, which are diagnostic of rhodophytes
Diamond-shaped structures inside the cells appear to be pyrenoids, the carbon-concentrating feature found in many algae.

Bengtson et al., 2017
Northern India dating to 1.6 Ga
Red algae fossil ranging from ~½ millimeters to over 3 mm across
It has broad, finger-like lobes radiating from the thallus’ center
Ramathallus has a pseudoparenchymatous construction
Spore-like tetrads are fossilized inside the thallus, indicating that this was the sporophyte stage of this alga

Above: Tappania plana

Below: A putative green algae acritarch named Leiosphaeridia

Above: Scanning X-Ray tomograph of Rafatazmia

Below: Image of Ramathallus