The photograph shows an exposure of sedimentary rock.  Using your powers of observation developed by your study of Block 4, Surface Processes, and honed at Summer School, what can you deduce from the photograph about the rock in this exposure and its depositional environment?  Make a list of your observations and deductions. Which graphic log in Block 4 best describes this exposure? I realize that, without a hand specimen or thin section, what you can deduce will be limited. When you have had a go a describing the exposure, click on the picture and I will tell you what it is.

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What group of animals are characterized by five-fold radial symmetry?	The echinoderms (phylum Echinodermata), which include two common groups, the class Crinoidea (crinoids or "sea lilies") and the class Echinoidea (e.g. sea urchins, starfish).  There are other major groups which are less common and which you are unlikely to encounter in your study of S260. Return to question
Did you see any examples of the animals in question 1 during Summer School?	You should have seen crinoids belonging to the genus and species Pentacrinites fossilis on the foreshore at Staithes. Return to question
Name a quick method by which you can usually tell a bivalve from a brachiopod?	In brachiopods there is a plane of bilateral symmetry that cuts through both valves at right angles.  Demonstrate this using one of the brachiopods in your Home Kit. In most bivalves there is a plane of bilateral symmetry that passes between the valves, so that each valve is a mirror image of the other.  You can see this too quite clearly using the bivalves in your Home Kit.  Refer also to Figure 9.2, p. 76. Be aware that there are some important exceptions.  Not all bivalves have shells that mirror each other.  Oysters and oyster-like fossils such as the common Jurassic forms Ostrea and Gryphaea have one valve much larger than the other, with no plane of bilateral symmetry. Return to question
Table 9.4 (p. 104) lists three classes of animals that belong to the phylum Mollusca, namely the Cephalopoda (nautiloids, ammonoids, belemnoids, octopus, squid), the Gastropoda (snails) and the Bivalvia (clams, muscles, oysters).  At Summer School during the visit to Staithes you may have seen a fossil representative of a fourth class of the Mollusca.  Can you identify it?  (Hint:  If you did not see one in the field, there is a photograph of one on the handouts.)	The Scaphopoda is a class of Molluscs known popularly as "tusk shells" because of their superficial  resemblance to elephant tusks.  The scaphopod you might have seen at Staithes is called Dentalium.  Like all molluscs, the scaphopods have a foot at the anterior end of the animal, which protrudes from the opening at the wider end of the shell. Return to question
Graptolites were pelagic colonial organisms that range in the fossil record from the Ordovician to the Carboniferous.  What is it about them that makes them useful for correlating strata?	Graptolite colonies (such as those shown in Figure 9.24, p. 105) were attached to a gas bag that acted as a flotation device.  They lived in surface waters of the oceans, where currents and winds carried them swiftly around the world.  They also evolved new forms very quickly.  So new forms were distributed around the world very rapidly and show up in sedimentary rocks all over the world.  Rocks that contain the same graptolite species are inferred to have been laid down at the same time as each other. Return to question
Taking the example of the trace fossil Cruziana (specimen P in your home kit fossils, and pp. 111-115), can you identify an important limitation to the information that trace fossils can provide?	It is usually impossible to link a trace fossil to the species of animal or plant which made it.  Cruziana is a good example, because although Cruziana fossils coincide in time with the trilobites, and are the type of trace that it is thought a trilobite would have made, they are also found in the Triassic, after the trilobites had become extinct.  So other types of animal besides trilobites must have produced Cruziana tracks, which means we cannot even be sure that all early Palaeozoic examples of Cruziana were made by trilobites (pp. 112-113). This problem is worse for many types of burrows and trails, such as Nereites, Diplocritarion and Rhizocorallium, which could have been made by any number of different creatures. The situation is somewhat less bad for vertebrate traces.  Dinosaur tracks, for example, can usually (but not always) be assigned to dinosaurs with reasonable confidence.  But to which dinosaurs?  In Wealden (early Cretaceous) rocks of the south of England, footprints assigned to Iguanodon are common.  But we can never be sure that it was a species of  Iguanodon and not some other bipedal plant-eating dinosaur that made them.  And carnivorous dinosaurs (theropods) that lived alongside Iguanodon, such as Megalosaurus and Baryonyx, were also bipedal and can be expected to have produced somewhat similar footprints! Dinosaur footprint, interpreted as probably that of a theropod, early Cretaceous, Middle Ashdown Beds, on the foreshore at Fairlight Cove, East Sussex.  Photograph © David Scarboro. Return to question
To what phylum did the trilobites belong?  Given your answer to this question, what animals living today are relatives of the trilobites?	Trilobites belong to the phylum Arthropoda.  The arthropods are an extraordinarily abundant and diverse group today, although the trilobites themselves became extinct in the Permian without leaving any descendants.  Today's arthropods include insects, spiders, crustaceans and myriapods (millipedes and centipedes).  These are all only distantly related to trilobites (alas!) even though they belong to the same phylum.  The nearest living relative is thought to be the horseshoe crab Limulus, an arachnid which is itself no more than a distant cousin to the trilobites. Return to question
Examine fossil specimen D, the ammonoid, in your home kit.  This shell has a keel.  Did all ammonoids have keeled shells?  What do you think the presence or absence of a keel may indicate?	Not all ammonoid species had keeled shells.  The keel is interpreted as an adaptation to reduce drag as the animal moved through the water by jet propulsion by expelling water from its siphuncle, in the way that living octopi, squid and Nautilus do today.  Acting rather like the bow of a ship (remember that ammonoid jet propulsion moved the animal backward) the keel, combined with the lateral flattening of the shell of specimen D, made the shell more hydrodynamic. Ammonoids lacking a keel are inferred to have been slower, probably reflecting different feeding strategies and lifestyles.  See Video Band 10. Return to question
If you find fossil corals, what can you infer about the probable environment of deposition of the rocks in which you find them?  Why can you make this inference?	You can infer that the rocks were probably deposited in warm, shallow marine waters, perhaps in a tropical sea.  We base this inference on analogy with living corals.  All living corals are marine, and have a symbiotic relationship with photosynthetic algae, which live in their tissues and produce much of the food consumed by the corals.  Therefore fossil corals, by analogy, probably also lived in the photic zone, in warm seas. But be aware of the proviso that fossil corals such as Lithostrotion, which you saw (or will see) at Hillbeck Quarry during Summer School, are not closely related to living corals.  The analogy with living corals may not, therefore, always be true. Return to question
To what extent can any living organism be termed a "living fossil"?  Can you name some examples?	The term "living fossil" refers to organisms whose morphology (form) has apparently changed very little over long periods of geological time.  Living forms can be compared closely with fossil forms.  Three examples which are frequently cited are the inarticulate brachiopod Lingula, the pearly nautilus, and the Ginkgo tree, Ginkgo biloba. Brachiopods almost indistinguishable from the living Lingula occur as fossils in Cambrian rocks more than 500 Ma.  The pearly nautilus, of which there are in fact six living species in the Pacific and Indian oceans, is a representative of the Nautiloids, a group of cephalopods with an external shell which appear in the fossil record in the Ordovician.  It should be noted that there are important morphological differences between Palaeozoic nautiloids and the modern Nautilus.  Early Palaeozoic forms, for example, frequently had uncoiled shells. Ginkgo biloba produces leaves which very closely resemble leaves found as fossils in the early Tertiary and the late Cretaceous.  Leaves somewhat less similar but still "obviously" ginkgoalean occur in the Jurassic and Triassic, and the group can be traced back to the early Permian. The examples of Nautilus and Ginkgo illustrate an important point about "living fossils".  The close morphological resemblance between living and fossil forms does not mean that no evolution has occurred, or that the group is in some way so perfectly adapted to its environments or so hardy that it is immune from natural selection.  Conservative they certainly are, but the fossil record of all "living fossils" shows evolution taking place within the constraints of the group's body plan. The carbonized impression of a leaf of Ginkgo huttoni, Middle Jurassic, Ravenscar Group, Scalby Plant Bed, Scalby Ness, North Yorkshire. Return to question
Look at Figure 9.16, p. 92.  There are two fossils in this picture.  Can you identify them?  What types of fossils are they?	One fossil is the bivalve shell.  The other is the hole!  The shell is a body fossil.  The hole is a trace fossil, produced by the action of the gastropod that presumably ate the bivalve animal by drilling through its shell to get at the soft parts. Return to question
Does the existence of bioturbation in a marine sedimentary rock, such as a sandstone, say anything important about the environment of deposition?	Yes, of course it does.  It shows that the environment within the sediments was favourable to life, which almost certainly means that it was well oxygenated.  This in turn implies that the sediment was not in deep water because the amount of oxygen in the waters of oceans, seas and lakes decreases with depth. Return to question
Cite one example of the application of the principle of uniformitarianism to the interpretation of fossils.	You can do this until the trilobites come home!  I will supply just one example from Summer School.  At Staithes you probably saw (or will see) a bivalve called Pseudopecten.  Pseudopecten looks remarkably like a living form called Pecten, which can swim by clapping its two valves together to expel water.  You may have seen this on television.  By analogy with Pecten, it is thought that Pseudopecten also could swim in the same manner. Return to question
Recall the sole structures (flute marks) that you saw during Summer School at Tebay (see also p. 48).  These were formed by a turbidity current.  Can you think of any type of fossil that might be preserved in a similar manner?	Vertebrate footprints and trackways, the most spectacular examples of trace fossils, are frequently preserved as what are called foot casts, which are a type of sole structure.  Imagine that an Iguanodon made footprints in soft mud along the shore of a Cretaceous lagoon.  The mud is baked in the sun and hardened, and some time later a storm causes the local streams to flood, and sand is deposited on top of the mud.  The sand will infill the footprints.  When the sediments are lithified long after, the original footprints will be preserved in the clay, but the sandstone above will have preserved casts of the footprints on the bottom of the sandstone layer.  When these rocks come to be eroded, the clay containing the original footprints will be eroded more easily than the sandstone, and will be removed.  This process leaves the underside of the sandstone exposed, with the foot casts on the bottom.  Examples can be seen in the coastal cliffs of East Sussex, where overhanging ledges of Wealden sandstone sometimes have huge "Iguanodon" foot casts on their undersides. Dinosaur footprints on a fallen sandstone block from the underside of an overbank deposit known as the Footprint Bed, from the Middle Jurassic, Burniston Steps, North Yorkshire.  Return to question
Are stromatolites trace fossils or body fossils?	On this topic I disagree with the course.  Section 9.5 lists stromatolites as body fossils.  But stromatolites are structures formed when sands or carbonate muds are trapped by mats formed by filamentous bacteria or algae.  They are not fossils of the bacteria or algae themselves, although fossils of the mat-forming organisms may sometimes be found within stromatolites.  I would, therefore, class stromatolites as trace fossils, i.e. evidence of the activity of the micro-organisms in creating filamentous mats. Return to question
You may have seen some belemnites at Summer School during your visit to Staithes (indeed, you should have!).  What kind of animals were belemnites?  What part of the animal is the common belemnite fossil?	Belemnites were cephalopods with an internal shell.  They resembled modern squid in appearance, although they were not especially closely related to squid (a good example of convergent evolution).  The common bullet-shaped belemnite fossil was analogous to a modern cuttlefish bone.  It was located in the rear of the animal's body, with the pointed end pointing backward.  See Figure 10.3, p. 123. Return to question
Soft tissues are occasionally preserved as fossils by pyrite (FeS2, see p. 127).  Much more commonly, fossilized hard parts such as shells and bones may be replaced by pyrite or be encrusted with it.  An example from Summer School is the crinoids found on the foreshore at Staithes, which are pyritized.  What does the presence of pyrite tell us about the conditions in which a fossil has been preserved?	The presence of pyrite implies anoxic conditions.  Burial in an anoxic environment is often favourable to the preservation of organic material, so fossils in which the hard parts have been replaced or filled in with pyrite are common.  See p. 127 for a more complete explanation. It is important to note that most organisms that are fossilized in this way did not actually live in the anoxic environment in which their remains were preserved.  Rather, their remains were transported to an anoxic depositional environment before burial and fossilization.  A good example is the small pyritized ammonites that can be found in the so-called "golden sands" (golden referring to pyrite!) on the foreshore at Charmouth, Dorset.  These ammonites lived higher in the water column, not at the bottom.  Upon death, their shells sank into deep water and were buried in the anoxic muds at the bottom. (Although these little ammonites are easy to collect, and collecting them on the beach occasions no damage to the cliffs, the bad news is that the pyrite oxidizes when exposed to the air.  You are likely to find that within a few years your specimens start to disintegrate, and one of the oxidation products is sulphuric acid!) Return to question
Why is taphonomy important?  Can you ever be certain that a fossil was preserved where the organism that made it once lived?	Most body fossils have been transported from the environment in which the animal or plant lived (and died) to a depositional site.  In some cases the remains were transported and buried, diagenetically altered (pre-fossilization, see p. 124), exhumed by erosion, transported again and re-buried somewhere else, before undergoing full fossilization.  The palaeontologist often has to work out the likely taphonomic history of a fossil before he/she can infer the environment in which it actually lived. Sometimes, however, body fossils are preserved where the organism actually lived.  A good example is the frequent preservation of infaunal bivalves in their life positions. Sedimentary trace fossils such as trails and burrows are always preserved, and nearly always found, where they were formed.  The exception refers to foot casts like those discussed in question 14; modern erosion, as along coastal cliffs, can cause foot casts to drop off from the base of the sandstone units in which they were preserved onto the beach, where they can be collected by those with sharp eyes and sturdy limbs!  But it can sometimes be difficult to trace such loose foot casts  back to the precise unit from which they came. Return to question
After working your way through these questions, you should appreciate that fossils convey two different types of information.  What are they?	Fossils are the remains of once-living organisms.  Their preservation, however, is a matter of geology.  Fossils convey palaeobiological information about the animals and plants that they once were, or that once made them, and the communities in which they once lived.  This function makes possible the science of palaeontology and all of its related sub-fields. Fossils are also geological phenomena, and may be considered to be part of the sediment in which they are found (or they may even be an integral part of the sediment itself, as in the case of chalk, oolitic limestones and coal).  A fossil burrow, for example, is a sedimentary structure, along with wave-formed ripples,  cross-stratification, dessication cracks and all the other non-biological sedimentary structures that the geologist uses to infer palaeo-environments. Return to question
It is a well-known risk that, unless the tutors are careful, geological field trips may turn into fossil hunts.  Are fossils rare?	Fossils are not at all rare in sedimentary rocks.  Indeed, some sedimentary rocks are made almost entirely of fossils; for example, the Chalk is mainly composed of  microscopic plates in their uncountable millions of phytoplanktonic algae called coccolithophores, whose shells accumulated as calcareous oozes on the floors of Cretaceous seas.  Larger body fossils such as belemnites, brachiopods and bivalves are extremely common in many formations and localities.  Trace fossils of burrowing organisms are perhaps the most common of all fossils in sedimentary rocks, to the point where individual burrowers lose their identity completely in thoroughly bioturbated sediments. Of course, certain types of fossils are much rarer.  Articulated skeletons of terrestrial vertebrates, for example, are very rare, although even these may be common at certain localities due to unusual local conditions of preservation. Return to question

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In the text that follows, observations and deductions that you might reasonably have made from the photograph are in blue.  I include a lot of information that you could not know. The photograph was taken at Athabasca Falls, in Jasper National Park, Alberta, Canada, in June 1999.  It shows the Gog Quartzite (named for Gog Lake near Mount Assiniboine) exposed in the walls of the gorge at the falls. The Gog Quartzite is late Proterozoic to early Cambrian in age, 600-525 Ma.  It was deposited as sand on the floor of a shallow sea, to the west of a landmass from which the sand was derived by erosion and transport by rivers. The units visible in the photograph are subaqueous dunes (Surface Processes, pp. 32-33), separated from one another by erosion surfaces which are clearly visible in the exposure.  These bedforms are meter-scale, which is how we can distinguish them from ripples (the scale can be estimated from the trees on top of the exposure).  The dunes indicate the action of currents. Cross stratification caused by the migration of these dunes across the sea bed is clearly visible in many areas of the exposure.  The cross stratification represents the preserved down-current slopes of the dunes (Surface Processes, p. 30).  The cross stratification consistently slopes down from right to left wherever it is visible in the exposure, indicating that the dunes were migrating from right to left.  Therefore the current was flowing from right to left. The graphic logs that most closely match the photograph are the shoreface sections of Figure 15.8 (the prograding strandplain environment) and Figure 15.9 (the barrier island environment) (Surface Processes, pp. 175-176).  Either way, this exposure of the Gog was probably deposited in the shoreface zone, not far offshore (see Figure 15.1).  Although you cannot tell this from the photograph, in many places the Gog contains casts of burrows, indicating oxic conditions on the sea bed, which reinforces the environmental interpretation of a shallow marine setting. The orange colour is caused by the presence of iron oxide derived from the weathering of pyrite crystals (FeS2), which are common in the Gog.  Pyrite is indicative of anoxic conditions (Surface Processes, p. 13) when it forms in the depositional environment.  So we might infer that the pyrite present in the Gog Quartzite was introduced diagenetically (Surface Processes, p. 58). The vertical cracks in the exposure are joints (Internal Processes, p. 85).  The rock was probably fractured by tectonic stresses at shallow depth in the crust, and the fractures were able to open as the Gog was exhumed, as erosion removed the overburden and so relieved the pressure.  The joints have been widened by weathering. The Gog Quartzite is the hardest rock in the Canadian Rockies, is therefore very resistant to erosion, and is found over a wide area, but mostly in the main ranges and the western part of the front ranges of the Canadian Rockies.  Many prominent features along the Icefield Parkway, including Mount Edith Cavell and Endless Chain Ridge, are made of Gog Quartzite. I confess to being skeptical about whether the Gog Quartzite is truly a quartzite.  That it is very hard is beyond doubt.  But is its hardness the result of metamorphism, which would turn a sandstone into a true quartzite (Earth Materials p. 92), or is it the result of pressure dissolution during compaction after burial (Surface Processes, p. 58)?  We would need to see the rock in hand specimen and thin section to decide.  Evidence in favour of pressure dissolution as opposed to metamorphism is the preservation of the cross stratification and burrows, which metamorphism might be expected to have destroyed; the jointing, which does not occur at the depths in the crust where metamorphism occurs, where rocks tend to show ductile rather than brittle deformation; and the fact that the Gog is texturally very mature, a condition which favours pressure dissolution (Surface Processes, p. 58). [Information from Ben Gadd, Handbook of the Canadian Rockies (Jasper, Alberta, Canada; Corax Press, second edition 1995), pp. 71-73]

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