Cape Enrage in New Brunswick, on the north shore of the Bay of Fundy, is a popular site for visitors because of its fantastic geology. The rocks are composed of Carboniferous Period Ward Point Member sandstones and mudstones of the Enrage Formation and the Cumberland Group. The almost vertically inclined rock layers in the cliff fracture and weather to create wonderful abstract patterns. The sediments that make up the rocks are fluvial in origin, originally deposited by rivers, and the exposed cliff-section shows many in-filled river channels. Large areas of rippled surface can be seen where channels are exposed; this together with chunks of rock with cross-bedding is interpreted as point bars in which the channels were constantly migrating laterally (as in present day braided river channels before they enter the sea). Localities with conglomerate composed of sandstone with rounded pebbles represent the the centre of river channels where the flow was fastest, or where flash floods have deposited heavier loads.

5 Replies to “Cape Enrage Rocks 1”

  1. Nice photos. I love the look of this large-scale flaking. Do you know where the iron is coming from? Is pyrite (perhaps microscopic, as framboids) embedded in the sandstone or mudstone?

  2. I think that geologists are very hard workers. There are always so many things to understand before they are able to “read” the rocks. Me, I am just very curious about the rocks and grab what I can from the literature so that I can give things a name and say a little something about the context in which they developed. It is a fascinating subject and I find that I am delving deeper and deeper into thicker textbooks.

  3. I am not at all sure, Linda. I guess sometimes the iron occurs in separate nodules in the rock but other times it seems chemically bound with the sediments. I think maybe you are the expert on this one. I have had a quick look at “Sedimentology and Stratigraphy” by Gary Nichols (Wiley-Blackwell 2009 pages 38-40) 3.5 Sedimentary ironstone, in which he describes the types of iron minerals found in sediments (magnetite, haematite, goethite, limonite, pyrite, greenalite, champosite and glauconite) and how ironstones are formed – but he only says regarding pyrite (FeS) that it is a common iron sulphide material that is common in sediments where it often occurs as “finely disseminated particles” that appear black, and may give a dark coloration to sediments. And of course it occurs in larger form as crystals and nodules. Although I didn’t see any ironstone nodules at Cape Enrage in New Brunswick, I did photograph them as siderite nodules at Joggins on the opposite Nova Scotian shore of the Bay of Fundy which shares the same geology. It seems likely that they are present at Enrage too but not where I was looking. It seems that these nodules form in conditions of lowered sedimentation rate of carbonate or terrigenous clastic material and are commonly associated with deposition in freshwater reducing conditions such as non-saline marshes where sulphate ions are available from seawater so that iron sulphide forms in preference to iron carbonate. That ties in well with the type of environment in which the Ward Point Member rocks at Enrage were formed. I think that I gather from this that the pyrite is most likely found as nodules in the mudstones at the site while haematite (iron oxide) and pyrite (iron sulphide) are probably the most common form of iron in the sandstones where they occurs as a bright red to black weathering or alteration product. I may have misunderstood this – it’s a bit early in the day and I haven’t had my coffee yet. With reference to the mechanisms of the original iron deposition and the finer details of terminology I defer to you with your knowledge of iron eating bacteria.

  4. Ah, Jessica, I am no expert. Just a fan of nature who tries to research things that grab me—like the iron bacteria. Thank you for such an extensive response to my question. I learned a lot—as I do from all your postings.

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