Photo Gallery of Palaeo Gas Seepages of Ailleo (2005, et al., 2001) 
‐ Western California Coast ‐

By Sutieng Ho and Jean-Philippe Blouet
Proofread by William Mackenzie
April 2017


Ailleo and  co‐workers investigated a series of magnificent examples of fossilized gas conduits – cold seep carbonates which outcrop on a sea cliff of Monterey Bay on the western Californian coast in 2001 and 2005.
These seep carbonates have different morphologies that vary from cylindrical to irregular tubular forms (Aiello, 2005; et al., 2001). They are principally parallel to stratigraphic beds or sometimes cut across beds sub-vertically. Most of the fossilised gas conduits follow the trend of fracture networks and regional faults (Aiello, 2005, et al., 2001). Some of these fossil conduits connect to form local networks. Individual carbonate conduits often have diameters which vary from ten to several tens centimetres, and have lengths that range from less than a meter to several meters. The morphologies of these fossilised car­bonate conduits are interpreted as being due to the leaking of gas through networks of fractures or faults inducing precipita­tion of cold‐seep carbonates along these zones of weakness (Aiello, 2005).
In this photo gallery, we share some pictures of these seep carbonates conduits which were photographed during our visit to the outcrop.

Picture
A cartoon drawing of the seep carbonate outcrop on a sea cliff of Monterey Bay. Modified after Aiello (2005)
Picture
The section view of the sea cliff shows the stratigraphic distributions of seep carbonate concretions. The yellow dotted contours hightlight the geometries of the carbonates.
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A close up of the seep carbonate sea cliff in the picture above.
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The plan view of the distributions of carbonate concretations on eroded stratigraphic layers.
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A close-up of seep carbonate concretions on the eroded platform.
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The most nicely exposed tubular concretion has also been called « Toilet bowl » carbonate.
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The other side of the tubular concretion in the picture above.
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A sub‐vertical tubular concretion showing concentratic inner layers. Note the parallel fracture network around the tubular on the background. See Aiello (2005) for more information.
Picture
A seep carbonate tube with a bigger diameter and a bigger central conduit.
Picture
Subvertical tubular concretion (left) and an irregular-elongate concretion (right) cross cutting stratigraphic layers.
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Flattened linear concretions parallel to the stratigraphic layer.
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Flattened sub‐circular concretions parallel to the stratigraphic layer.
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A close up of the sub‐circular concretion which is composed of several annular concretions that link together and form a chain. Each segment of the chain has a central hole.
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The continuity of the concretion chain in the picture above.
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A close up of an individual annular concretion in the picture above.
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A concretion chain with an almost regular width, showing a curving plan form on a stratigraphic layer.
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A close up of the concretion in the picture above.



More information about Aiello’s (2005, et al., 2001) studies can be found in:

Aiello, I. W., Garrison, R. E., Moore, J. C., Kastner, M., & Stakes, D. S. (2001). Anatomy and origin of carbonate
structures in a Miocene cold‐seep field. Geology, 29(12), 1111‐1114.

Aiello, I. W. (2005). Fossil seep structures of the Monterey Bay region and tectonic/structural controls on fluid flow in an active transform margin. Palaeogeography, Palaeoclimatology, Palaeoecology, 227(1), 124‐142.