Blue Beach
- For the British bridgehead during the Falklands War, codenamed Blue Beach, see San Carlos, Falkland Islands.
Blue Beach is a 2 km stretch of cliff-bordered coastline along the Avon River in the southern bight of Minas Basin, Kings County, Nova Scotia, Canada. It is best known as a globally significant fossil location for Lagerstätte of the Tournaisian Stage (Lower Carboniferous) period.
Geographic setting
Blue Beach is informally named. The name relates to the bluish-black colour of the cliffs. It stretches from a small creek to Avonport Station. The tidal range in this part of Minas Basin may be as high as 16 m. The nearest town is Hantsport, approximately 5 kilometers to the south. The beach is accessible on foot from the end of the Blue Beach Road or from Avonport Station. There is a small private museum near the parking lot before the trail to the beach. It contains numerous excellent and important examples of fossils from the beach.
The tides make for dangerous conditions because visitors can find themselves trapped. Visitors should familiarize themselves with the Hantsport tide table (see external references). In addition to the tides, the cliffs are quite fragile with rocks regularly giving way. Care should be taken when approaching the cliffs.
Geologic setting
The section is exposed in rocks of the Carboniferous Maritimes Basin. The Maritimes Basin opened and filled between ca. 360 Ma and 325 Ma.[1]
The Blue Beach cliffs consist of soft shales and sandstones of the Horton Group. They erode rapidly because of the high tides in combination with winter freeze-thaw and ice shaving conditions, thus continuously creating opportunities for new discoveries. Closer to the trail and lower in the sequence is the Blue Beach Member and further along is the Hurd Creek Member.
Blue Beach is the type locality for the apparent gap in the tetrapod fossil record known as Romer's gap. Sir William Logan, the first Director of the Geological Survey of Canada, found footprints from a tetrapod in 1841. It remains one of very few such outcrops in the world; the others are in Scotland. In recent decades, numerous tetrapod fossils dating from the earliest Carboniferous have been found.
Flora
Flora include Lepidodendron, Calamites, Aneimites,[2] Diplotnema,[2] Carpolithus,[2] Genselina.[2] In addition, countless spores can be found.
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Photograph of exposed fossil tree bases at Blue Beach, Nova Scotia. -
A well-preserved section of Lepidodendron from Blue Beach.
Fauna
Fauna includes tetrapods,[3] fish, arthropods (horseshoe crabs, trilobites and ostracods[4]) and shells. Fish material is quite common, but articulated bones are very rare. Most common are scales, small ribs and teeth. Uncommon are larger bones including fin spines, jaws, cranal material, clavicles, limb bones and pelvic bones.
Arthropods include Paleolimulus woodae, an extinct horseshoe crab. Contrary to some erroneous reports in the popular press, [5] it is not the world's oldest horseshoe crab (Order Xiphosurida), but is scientifically instead the oldest paleolimulid (Family Paleolimulidae). It is known from two examples found by visitors - including a Grade 4 student. The species name honors Sonja Wood who runs the Blue Beach Museum and has studied the fossils for many years along with her husband Chris Mansky. Trilobites are also rarely found. This is interesting because trilobites are marine, whereas the majority of the Blue Beach location is seen as a lacustrine deposit. The trilobites found thus far are restricted to a 20 cm thick layer.[2]
Fish fossils include Elonichthys,[2] Rhadinichthys,[2] Canobius,[2] Letognathus,[6] ?Ctenodus,[2] Gyracanthides,[2] Gyracanthus,[2] Acanthodidae,[2] and Bothriolepis. Letognathus was originally assigned to Rhizodus in the mid 1800s and later to Strepsodus.[6] This includes the species Rhizodus (now Letognathus) hardingi of Dawson, named after a Dr. Harding of Windsor, Nova Scotia.[6][7] Similarly, Dawson's Acrolepis is now attributed to Elonichthys and his Palaeoniscus is attributed to Canobis.[2]
Tetrapod fossils include acanthostegids, ichthyostegids, tulerpetontids, whatcheeriids, and embolomeres.[3]
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Shell -
Fish scales -
Fish jawbone with tooth -
Clavicle -
Figure of fish fossils from Dawson's Acadian Geology
Trace fossils
Trace fossils are common. Examples include tetrapod footprints,[8][9] fish fin trails, arthropod trackways,[10] wave ripples, mud cracks, rain drops, and bromolites - including coprolites.[11]
The tetrapod footprints and trackways are particularly important due to their age. They are reasonably common at Blue Beach, with over 2000 specimens known.[2] Prints of tetrapods from this era can exhibit polydactyly, or more than five digits per limb.,[12] however the specimens from Blue Beach are all pentadactyl[13] (five digits) or are at least functionally pentadactyl. Six morhotypes have been intentified so far.[13]
Several types of arthropod trace fossils are found including trackways of Diplichnites and Diplopodichnus (possibly millipedes), Rusophycus (possibly trilobites), Paleohelcura[10] (scorpions), and Arborichnus.[2]
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Photograph of trace raindrop impressions from Blue Beach. -
Fish coprolites from Blue Beach.
References
- ^ Calder, J.H. (1998) The Carboniferous evolution of Nova Scotia. In: Blundell, D.J. & Scor-r, A.C. (eds) Lyell: the Past is the Key to the Present. Geological Society, London, Special Publications, 143, 261-302. Available in The Lyell Collection.
- ^ a b c d e f g h i j k l m n o Mansky, C.F.; Lucas, S.G. (2013). "Romer's Gap Revisited: Continental Assemblages and Ichno-Assemblages from the Basal Carboniferous of Blue Beach, Nova Scotia, Canada". The Carboniferous-Permian Transition. New Mexico Museum of Natural History and Science. Bulletin 60: 244–273.
- ^ a b Anderson, J.S.; Smithson, T.; Mansky, C.F.; Meyer, T.; Clack, J. (2015). "A diverse tetrapod fauna at the base of 'Romer's Gap'". PLOS ONE. 10 (4): e0125446. doi:10.1371/journal.pone.0125446.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Tibert, N.E.; Scott, D.B. (1999). "Ostracodes and agglutinated foraminifera as indicators of paleoenvironmental change in an early Carboniferous brackish bay, Atlantic Canada". Palaios. 14: 246–260. doi:10.2307/3515437.
- ^ "World's oldest horseshoe crab finds home in Kings County museum". The Chronicle Herald. 9 May 2016. Retrieved 10 May 2016.
- ^ a b c Brazeau, M.D. (2005). "A new genus of rhizodontid (Sarcopterygii, Tetrapodomorpha) from the Lower Carboniferous Horton Bluff Formation of Nova Scotia, and the evolution of the lower jaws in this group". Canadian Journal of Earth Sciences. 42 (8): 1481–1499. doi:10.1139/e05-041.
- ^ Dawson, Sir J.W. (1891). The Geology of Nova Scotia, New Brunswick and Prince Edward Island: Or, Acadian Geology (4th ed.). London: MacMillan and Co. Retrieved 10 May 2016.
- ^ Clack, J.A. (2002). "An early tetrapod from 'Romer's Gap'". Nature. 418: 72–76. doi:10.1038/nature00824. Retrieved 9 May 2016.
- ^ Mossman, D.J.; Grantham, R.G. (2008). "Eochelysipus horni, a new vertebrate trace fossil from the Tournaisian Horton Bluff Formation, Nova Scotia". Atlantic Geology. 44: 69–77. doi:10.4138/5933. Retrieved 9 May 2016.
- ^ a b Cameron, B.; Domanski, D.; Van Dommelen, R. (1991). "Discovery of Tournaisian (Early Carboniferous) aquatic scorpion trackways in the Horton Bluff Formation". N.S. Department of Mines and Energy, 1991 Open House, Program and Abstracts: 45.
- ^ Mansky, C.F.; Lucas, S.G.; Spielmann, J.A.; Hunt, A.P. (2012). "Mississippian Bromalites from Blue Beach, Nova Scotia, Canada". Vertebrate Coprolites, New Mexico Museum of Natural History and Science, Bulletin 57: 161–170. Retrieved 9 May 2016.
- ^ Coates, M.I.; Clack, J.A. (1990). "Polydactyly in the earliest known tetrapod limbs". Nature. 347: 66–69. doi:10.1038/347066a0. Retrieved 14 May 2016.
- ^ a b Lucas, S.G.; Hunt, A.P.; Calder, J.H.; Mansky, C. (2004). "The Oldest Tetrapod Footprint Ichnofauna, from the Lower Mississippian Horton Bluff Formation, Nova Scotia, Canada" (PDF). N.S. Dept. of Resources, Report of Activities: 150. Retrieved 14 May 2016.