Paddling in the Sea......

As you walk through Halifax, you may feel that here you are far away from the sea. Well, geographically you are right, but if you look about there is evidence of a sea around you. Here on John Street, at the coordinates is a large buidling which is constricted of two types of stone. The lower foundation is granite, which is an igneous rock, whilst the bulk of the building is constricted of blocks of limestone. We are here concerned with the limestone.  Limestone is a sedimentary rock.

Sedimentary rocks are types of rock  that are formed by the deposition and subsequent cementation of that material at the earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic  particles to settle in place. The particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, the sediment was formed by weathering and erosion  from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers. Sedimentation may also occur as minerals precipitate from water solution or shells of aquatic creatures settle out of suspension.

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. Most limestone is composed of skeletal fragments of marine organisms such as coral, crinoids and molluscs.

MOLLUSC SHELL FOSSILS

CRINOID FOSSILS

CORAL FOSSILS

So, we are here to look at evidence of the marine environment, you may ask - what can this building tell us. Well, sediment is deposited, but it appearance in the fossil form can tell us about the marine environment at the time. In a shallow, tropical sea, with a gentle current, sea creatures can sink to the bottom, and remain intact, though if there is a strong current / a lot of wave action, then the remains of the sea creature, will be moved about a lot, and eventually due to impact will break up. Below are some examples. 

If you look at the top of the picture there is shelly debris, as a result of wave action and current breaking up the shells, this is then deposited and forms part of the sediment that eventually became limestone. 

If you look at the fossil bivalve, it has both upper and lower shells intact, which would indicate that at the time of deposition that current and wave action was much less than in the picture above. There is still some shelly debris though. 

This being an EarthCache, in order to log it, I ask that you answer the below questions. Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile. You can also give the answers in person should you meet me. 

1. Please look at the stonework at the published co-ordinates, there is a band of broken shells in one of the blocks next to the window. How wide is this? What has caused this band to appear as it is - what would have the wave action been like?

2. Please walk down the street looking closely at the walls of the building.Please tell me where on  the street that you can find the bivalve fossil pictured above? 

3. Please measure the lenght of this fossil in cm?

4. Can you see any other fossils as you walk down the street?