The first questions are “what and where is it?” Both are easy to answer. It’s the ‘Sunshine Island’, at least in summer, about 30km by 20km, 1.3% of Denmark, nestling in the Baltic about 130km east of Copenhagen. Next question, how do you get there? You fly from Copenhagen to Rønne in a 45 seater. Third question, ‘Why go there?’ Because the geology is fantastic!

The island is perched on the Fennoscandian Border Zone, and is the most southerly extension of the Fennoscandian Shield, that’s the northern 2/3 of the island! The southern portion is an amazing mélange of sediments, broken into tectonic blocks by a jigsaw puzzle of faults overlying the deep crustal fault zone which can be traced from the Black Sea to the North Sea. These form a series of graben basins. The faults first developed in late Precambrian times and have been active in bursts, up to the Quaternary. It has left Bornholm with relics of their activity in the form of great hiatuses in the stratigraphic record, which means that all the sedimentary blocks are different! They are however, stuffed with trace fossils – more later in the week!

On this, our first morning, we set out in the Geobus. It was piloted by Wisty our driver and guide to the historical aspects of Bornholm, to make our greatest journey of the week. We left the converted windmill (sans sails), with Richard Bromley our excellent leader, who claimed to know nothing about granites, but knows an amazing amount about trace fossils! Fortunately, Sue Hay does know something about granites, and she had been there before! We were travelling northwestwards; to cross from the tectonised sedimentary blocks, onto the Basement – hard rocks! At first glance, Bornholm’s Basement is a single fault-bounded granite horst, that has come up through the sediments, but we were to discover that it is in reality, a composite. The Geobus took us through the great Almindingen Forest, which clothes the central part of the island, over the rather flat topography (great for cycling) which is familiar from other ‘old’ parts of the world, e.g. Anglesey, and we dropped down the winding Vang village road, to the sea. Then we bumped along the seafront track, past the old Vang Quarry, the type section of the Vang Granite, until the bus could go no further. We debussed and climbed to the new quarry, under a monumental ‘Anthony Gormley style’, rusted iron bridge, to be confronted by the usual dusty sights. Those familiar with pink Shap easily recognized at least two sets of joints; vertical, because of tectonic movement and shearing, and horizontal overburden stress release joints. At the top of the quarry, the joints and blocks were weathered enough to look like proto-tors!

What was special about the Vang granite, to distinguish it from the other three Younger Granites, (Hammer, Almindingen and Svaneke)? All these granites have characteristics of colour and texture, which means they are easy to distinguish in hand specimen. The Vang itself has a peachy-pink hue to add to its ‘high twinkle factor’. With crystals averaging between 5 and 10mm, close inspection revealed quartz, feldspar, amphibole and biotite, quite a high percentage of mafic minerals, but still a granite, in the strict sense.

Multiple phase shearing delighted us with the fabrics it had produced within the shear zones, including elongated feldspar crystals with pointed ends, up to 25mm long. Viridian green chloritization was also evident because of water influx within these zones.

The granites were penetrated at late stage by magnificent, crosscutting pegmatites with crystals up to 50mm long. The pegmatites had pinkish feldspars showing their cleavage to such advantage, that quite a few specimens were collected ‘for teaching purposes’. I think the sunshine helped emphasize their charms!

Richard decided that we needed a stone anvil, so that people need not feel inhibited and just take ‘tiny’ specimens, so a suitable sized piece was marked out and two “good strong men and true” staggered back to the Geobus with it and ‘popped’ it into the boot! Wisty then took us back to Vang Harbour, to look at the wonderful memorial to the stone workers, or ‘steinhuggerei’. The worked granite reject pieces were arranged at the harbour’s edge, outside their ‘working house’, on the place where most of the working was carried out in the open air, even in winter weather. They took it in turns to work inside in the, now restored, building. We were also delighted by smucks (the correct collective noun) of small, gently pulsing, translucent jellyfish, which were thronging the crystal clear harbour waters.

So with one Younger Granite under our belts, specimens clutched tightly for comparison with the next one, we moved off in ‘Geobus’, to see the statuesque remains of the largest castle in Scandinavia, which is perched on and partly built of the outcrop of our second Younger Granite, the ‘Hammer’. The castle is called ‘Hammershus’, the ‘House on the Rock’, and its origins in 1250 reflect the opposition of Archbishop Absolom of Lund for the King, another example of ‘Prince Bishopry’ like Durham! His castle, built of the local material, having ‘high place value’, forms the base of a wonderfully striped edifice, which is the result of its importance in the early 1500s. That was when the merchants of Lübeck, members of the Hanseatic League, refortified it using the material they knew and used at home – brick! So the Keep has brick upper storeys. The Germans left in 1576. After a brief period of Swedish rule, the local people reclaimed it by shooting the Swedish Commandant and presenting their island to the Danish King. The castle became ripe for scavenging but in 1814 further ‘quarrying’ was forbidden, and the castle forms a great tourist attraction. Three busloads of Poles, on a day trip, arrived whilst we were in the carpark!

The castle crouches on the cliff top, a fine vantage point over the sea. We visited the entrance bridge over the dry moat, the only intact Gothic bridge in Denmark, and walked down the river valley which fringed the south side of the castle. The river had been dammed and 3 mills were originally utilized there as part of the demesne of the castle. Our objective was to examine, very closely, the Hammer Granite exposed under the castle and in the valley walls, and take lunch on the fringes of the Baltic. The Hammer granite is very different from the Vang, a good job we’d taken samples for comparison! It is a much ‘rosier’ pink, with crystals, which appeared to be abraded, and floating in a matrix, it could be likened to an igneous ‘greywacke’. Quartz is present, but difficult to see. It is the feldspars which give the granite its colour, elongated amphiboles were also present, but biotite was not readily visible (we needed a thin section)! Again the crystals were large and the texture gave much room for speculation, possibly this part of the granite may have been involved in a tectonic episode, as a shear zone or fault appeared to cut the headland at this point. We enjoyed lunch, waving to the tourists bobbing about on the Baltic, bronzing the limbs and being wowed by a wonderful green frog with golden eyes, female of course, which obligingly sat still on the grasses by a small pool, to be admired.

Feeling refreshed, we set forth along the coast path, under the Hammershus, to see the Lion Rock and other geological excitements. The relationships between the Younger Granites and the Basement are best disentangled by field relationships, but dating them using modern techniques is something which needs doing. Can we find funding for a PhD?

We viewed the Rønne granite first from the quarry rim whilst Ulla smoothed the way for our entry into the quarry itself. It was a very handsome black-coloured Precambrian granite, whose feldspars are so clear that the 15% dark minerals dominate the colour. Amongst other things the quarried material is being cut into cobbles, Richard explained that they are being used on the Copenhagen streets as they last much longer than tarmac. Dramatic handsome pink stripes of dilatation pegmatites were visible at the top of the quarry, the result of late stage fluid injection. Returning to the stone yard we admired blocks of the various Bornholm basement granites and gneisses. Sue explained the formation of migmatite by the progressive metamorphism of the country rock or granite to a gneiss. Further heat and/or pressure results in the melting of the lower temperature minerals such as quartz and feldspar which form pink or white granitic stringers leaving behind the higher temperature dark minerals as restite. At this point several muffled explosions without warning suggested that we had been wise to leave the quarry face.

After driving north-east across the island we had lunch on the beach at Årnsdale (translated as Buttock Valley). This beach is composed of gravel-sized fragments of decomposed Precambrian Svaneke granite. We then journeyed slightly inland to see a Sprækkedale or fissure valley. These are narrow linear depressions with near vertical sides, probably caused by the erosion of Precambrian dolerite dykes of which there are a large number on the island. Wisti, our coach driver, explained that this one was called Cow Valley because when attacked the inhabitants would hide their cattle in the tree-filled valley before taking refuge themselves in fortified areas. Near the valley we saw the Rokkestenan, one of four rocking erratics, which in spite of years of human interference still rocks slightly. On the way back to the coach we passed a coffin stone where coffin bearers were said to rest their load.

Our next stop was a nearby recently abandoned quarry in the 1700 Ma gneiss at Praestebo, where aligned flame-like bodies of leucosome show the migmatitic nature of the rock. A few years ago an aquifer was believed to have been polluted by the quarry workings so the authorities shut all the quarries in the area. Six years later the pollution is still occurring. The experts were wrong, too late the banning order was rescinded.

On our way back to the mill we visited the Laurentund standing stones, about 50 standing stones of different rock types in an atmospheric forest glen. Finally we viewed the ruins of a Romanesque church beside the new Church at Østermarie. The latter has some wonderful ptygmatic folds in its stone walls. There is also a beautifully laid out and maintained cemetery with simple and geologically interesting head stones with no eulogies to the dear departed. Richard explained that for 25 or 99 years (dependant upon how much you pay) the plot is yours, then it is available for another burial, obviously a practical people.

DAY 3, good breakfast, clear sky and warm sun and a prospect of a long walk to the first site. John Wade and I gladly accepted a lift from our hostess, Ulla, in the bright yellow Opel named ICHNOS. So it was, having graciously waved as we passed in style, we were able to watch the brightly coloured group happily strolling to the meeting point. Mick Warren was the first of the walkers (two cyclists were thought to have had too great an advantage) but was instantly disqualified for walking too fast.

The first exposure, near a former “poor-house” at STROBY was like something out of TimeTeam. A trench some 4 metres wide and 50m long with about 1/2m of top soil removed to expose a shallow staircase of sandstone beds gently dipping to the north.

At the northern end of this immaculate scrape the gneissic basement is faulted against Cambrian sediments with the crushed zone about 1 1/2m wide. A lasting impression is of one group member standing on the crushed Nexo sandstone and bridging the melange with a walking pole in a graceful arc. Forming the majority of the exposure, down-slope and onto the floor of a quarry, the Hardeberga sandstone showed well-preserved ripple marks. These were not all parallel and initiated a variety of explanations about the environment at the time of their formation.

A small pool at the low point of the quarry was home to a green frog, possibly the EDIBLE variety Rana esculenta. It’s a good thing France is so far away.

A walk back towards the mill brought us to LIME STREET, Limensgarde which gives it’s name to the mill. Here, in a protected nature reserve, vegetation had miraculously cleared from a quarry face to expose a Lower Ordovician contact between Dictyonema shale below Komstad limestone separated by a phosphatic breccia. The walk into the quarry took over a wooden foot bridge and the “Christopher Robin’s” in the party were disappointed with the flow of water in the stream.

After lunch the geo-bus took us to a quarry at GADEBY, Ulla having gone ahead to placate an unpredictable owner. As it happened the quarry had changed hands and the new owner/manager/workman was happy for us to look around so long as we dodged his dumper truck.

Here the Nexo sandstone is a wonderful claret colour in places grading to pale cream depending on the haematite staining. The horizontal bedding showed some further ripple marks.

Our fourth location was a beach exposure at SNOGEBAEK where the claret coloured arkosic Nexo sandstone supported the creamy Hardeberga sandstone we had seen before. Here, however, we could see evidence of Skolithos and Diplocraterion as the Lower Cambrian transgression overtook this inter tidal zone. While leader Richard explained the interpretation of this exposure some people snuck away for ICE CREAMS ! !

Our final stop on a warm and sunny day was into the twilight zone. A wood named GRYET (twilight), with the largest collection (56) of standing stones on the island, brought mixed reactions from the group. Some thought it very spooky while others speculated about the “lets raise a standing stone” parties that might have been. In reality it was not a place to party unless in defiance with gallons of mead.

This was the day I had been looking forward to: Mesozoic trace fossils with Mr Trace Fossil Himself. After 3 days of brilliant sunshine we woke to a thunderstorm but Richard thought this could be beneficial so we prepared ourselves with the wet gear and set off into the woods at Stampen for our first location, spades, bark knives and all manner of other knives in hand. Under the canopy of trees we hardly noticed the rain but the stream was rather swollen making the OUGS erosion slightly harder than it might have been and giving wet feet to a few members. But it was well worth the effort. Oohs and aahs were emitted in abundance as the pallete knives scraped away the fallen debris to reveal bright green faults and a host of trace fossils in this cross-stratified greensand of Cenomanian age (early Late Cretaceous). This was the Arnager Greensand which lies above the Arnager Conglomerate. But what was that patch of rock to the top right, lying diagonally over the section? The conglomerate! Close examination revealed that the section had been overturned and the tops of the traces were truncated. Here the dominant trace was the burrow-lining, vertical Ophiomorpha and we could easily pick out the dark surrounds to burrows where pellets had been placed around the edge. Other prominent trace fossils were patches which, at first sight, I mistook for circular sections of calcium carbonate. These were not body fossils at all but the linings of Palaeophycus. Small strings of white dots were Chondrites. The trace fossils confirmed a marine origin for the rock. This was a loose sand so Richard posed the question: How could loose sand be so faulted? Brian’s answer was that under pressure even sand can behave as concrete. Richard believed that Tertiary sediments had never covered Bornholm and that these sediments had never been deeply buried. His theory was that the faulting had occurred during the ice age when the sand was frozen solid. The debate continued as to whether the green glauconite had acted as a lubricating fluid or had lined the faults at a later stage. By the time we left the section the rain had stopped and we were in for another glorious day.

At the next stop (Stampen 2) we could see the relationship with the Conglomerate much more clearly. Again, the Conglomerate overlay the Greensand, but overlying that was a brown sand of the Jydegård Formation, dated to Earliest Cretaceous age. So again, the layers had been overturned (albeit obliquely). But where exactly was the junction? A large chunk of Early Cretaceous was missing, but right at the top of the brown sand were numerous traces of Thalassinoides. The animals making these traces do not line their burrows but they have been filled with material from the overlying Greensand to form an ‘ichnoboundary’ about ½ m beneath the unconformity. The phosphatic conglomerate apparently contained ammonites of Albian age (some of the missing strata), so the hunt was on …. ‘eye of faith’ convinced someone of an ammonite fragment – not letting on who - others saw turtle droppings in every piece!

We proceeded to the beach to Korsodde headland and an exposure of the Middle Jurassic Bagå Formation. First we set to work cleaning off a section about 15 m long. Spades, brushes and knives came out again and some anxiety was expressed as a plane flew low overhead to land at Rønne airport. But our work was not finished yet. We were divided into 4 groups and while Richard and Sue had a well-earned break, the rest of us logged the section. The first group had identified occasional tangled traces that Richard identified as Bornichnus. He also spotted some small Planolites in the clays. The next group had correctly identified occasional marine Diplocraterion although none showed the diagnostic U-shape. At the top of their section 100% bioturbation was probably also caused by Diplocraterion. The third group began with a soil horizon beneath a thin coal seam, with roots protruding into underlying sand thus giving us a clue to the depositional environment. Further up their section was a return to the Diplocraterion level indicating a marginal marine environment. The fourth group found possible evidence of burrowing in disturbed clay drapes and strangely orientating iron staining, but not until close to the top did convincing traces appear. Some produced small V-shaped structures and there were others that Richard identified as Asterosoma. What some of us failed to notice was that a good 3D section had been cut by Richard on a former visit to give an excellent exposure of these beasties! We hope we’ll find a better description of this section in print before too long. The clays above contained Teichichnus – a reclining ‘J’ underlain by spreite. We should have been able to identify it as Richard had drawn it for us the night before during his evening talk. Wood fragments were associated with these upper sediments which Richard interpreted as lagoonal. The species of trace fossil were too restricted for lower shoreface described by other authors.

By now we really felt we’d earned our lunch, but after a brief stop on the cliff top we were off again. This time, a long hike around the airport perimeter took us to our next location. This was the youngest non-Quaternary deposit on Bornholm, the Bavnodde Greensand of Late Cretaceous, Senonian age. This proved to be the least interesting section of the day, but apart from the wood, it did turn up the first body fossils. Di Smith found a section of belemnite in the storm bed and there were fragments of bivalve but it was our geobus driver, Wisti who came up with the best specimens. He found a nice sponge and a wood-boring pholad, Martesia. We’ll have to come back in the spring when the section is cleaner!

We made up for it with the final geology of the day. This time buckets and brooms were employed to clean the wave-cut platform exposures at Arnager. Excellent Thalassinoides were eroded out in 3 dimensions. We were now back to the Arnager Greensand that we had seen earlier in the day, but instead of the Greensand being transported to lower layers by burrowing, in the cliffs we were seeing the white chalk from above being piped into the Greensand (this time lying horizontally, the right way up). The burrows also contained phosphatic nodules from the conglomerate layer at the base of the chalky Plattenkalk of the Arnager Limestone. As before, the phosphates signalled a hiatus in deposition. Our next scrubbed section showed Zoophycus winding in between the phosphatic nodules. This was a bit of an enigma as Zoophycus is characteristic of quiet, poorly-nutritious, deeper water sediments (probably 100-200 m during the Cretaceous) and here they were within the high-energy environment of the phosphatic conglomorate. The explanation was at hand: they had been scavenging the layers through the younger Plattenkalk, reaching the conglomerate long after it had been deposited. We finished the day with a spectacular display of sponges – well worth all the cleaning.

Today was a rare opportunity to see a wonderful display of trace fossils with not too much distraction from the body fossils. Thank-you Richard.

There was just time for another Wisti ‘mystery’ before our return to the Mill for tea and cakes. This time we visited the chambered Passage Graves at Arnager. Despite the traces of our ancestors in the form of cup marks, geology overode the mysteries of the Ancients as we admired the onion-skin weathering on the erratics used to line the tomb.

RØNNE

Today was spent mixing a bit of geology with some interesting features of the island.

First was a visit to the capital, Rønne which is the largest place with a population of about 14,500. It is linked to mainland Denmark and Sweden by ferry and to Copenhagen by air. Wisti , the driver took us on a geobus tour round the city followed by a walk in the centre and along the harbour. The houses are mostly simple wood framed buildings, very characteristic with many coloured in the distinctive “Bornholm Red”, others in bright colours. There are very few tall buildings here or indeed anywhere on the island. The commercially active harbour is quite large. One landmark within the town is a tall lighthouse, another being the church within which hangs a large model sailing ship. Wisti told us that a similar model (also in the church) is carried down to the sea once a year for a blessing ceremony. After a break for coffee and some shopping then we went on to Hasle , on the coast north of Rønne.

HASLE

At Hasle we were introduced to a common small industry in most of the seaside villages, that of fish smoking. After a look in the museum we were treated to a splendid “special” smoked fish lunch of herring, mackerel, salmon (a big thick slice of this!) and prawns, accompanied by a salad, dark bread and naturally, Bornholm Beer.

We were impressed by the finger de-smoking facilities! .

MADSEGRAV

MORE CHURCHES.

During the day we visited two more churches, that at Åkirkeby. the largest church on the island with 17th C. fittings, a decorated canopied pulpit and an extremely old sandstone font. The other church was the round church of Nylars, a most fascinating building. In times of strife, the churches doubled as forts. Of note here and at other places were the wonderfully kept graves with superb examples of all the indigenous stones of Bornholm.

THE LÆSÅ STREAM BED

An afternoon stroll of some two kilometres was undertaken along this stream bed, which is in fact a reserve – no hammering! Fossils are not plentiful although the loose material in the stream bed was examined for trilobites etc.

However , we were able to progress up the stratigraphy along the way. At the start was Lower Cambrian Broens Odde silty sandstone, well bioturbated, then a well exposed boundary with the Middle/Upper Cambrian Alum Shales, showing the thin Rispebjerg Sandstone and Exultans Limestone. The sequence up to the latter is interpreted as a single transgressive-regressive cycle which is considered to be a global sea level change. A short distance up the shales there is an outcrop of Ordovician Andrarum Limestone, in which were seen some large concretions of anthraconite. Finally in the stream bed the Komstad Limestone appears and further upstream are low cliffs of Dicellograptus Shale, named after a graptolite.

This walk was great in the sunshine and further reward was had in examining a long barrow, not to mention seeing a wonderful bright yellow bracket fungus on the way.

Another satisfying day.

This was our last day in the field, and the first stop was one of Richard’s "mystery" locations. Our geobus with Wisty at the wheel set off north to Aakirkeby and then edged its way across towards the NE coast of the island until it reached Listed, a very pretty seaside village. We finally stopped about a kilometer up the coast, and made our way down to the beach where large exposures of Svaneke granite gave way to shingle and the sea. However, Sue’s instructions were not to admire the view, but to measure Dip and Strike and to look for variations in the rock which is a "younger" granite at only 1400 M yr. We were not surprised therefore to find bands of migmatised Gneiss of mixed origin in contact with the Svaneke which itself we estimated to dip at 30 and strike 200/020. Our duty done we moved nearer to Listed to find a splendid dyke of dolerite, with very fine olivine crystals, intruding the granite, not surprisingly at 185/005. It seemed that the dyke had chilled out against granite that was already cool but the origins of the dyke were long gone so we don’t know which way it flowed. But we did recognise the "pepper and salt" sediments that occurred much later, forming a neptunian dyke, possibly in the lower Cambrian.

After the serious work, a bit of fun at Arsdale mill where the sails were whizzing round and the main shaft in amazingly silent motion. We climbed to the top enthusing over the wonders of the engineering, and then descended to the mundane matter of buying souvenirs. Off then to Østerlars Kirke, the largest round church on Bornholm, for a bout of picture taking, and finally back to the mill for lunch and to say farewell to our friend Wisty, who had other duties in the afternoon.

Refreshed by lunch we strolled down the road to Skelbro Quarry where is exposed the lower Ordovician Komstad Limestone, 5m thick and taking 5M years to form, --nothing rushes in this part of the world. We busied ourselves looking for trilobites, having been assured that 3000 had been found hereabouts, but well, perhaps it was the lunch, perhaps they had scuttled away, some of us found fragments. With a glance at the glacial striations on the uppermost surface of the exposure, we moved off to the beach once again.

Definitely lower down, but also a lot more recent, in fact Triassic, the Kagerod Formation, coloured clays and cream sandstone and occasional caliche concretions. Where the Risebaek flows down, we turn off and climb up again to the level of a waterfall, crossing a fault to arrive at Upper Ordovician exposures, the Dicellograptus Shales. Here graptolites were found by several party members, making up for the disappointments of the absent trilobites. And returning to the beach, in a sandstone boulder Richard pointed out a whacking Diplocraterion parallelum in 3 dimensions with 10cm long U-tube branches and 3/4cm spreite wonderfully preserved.

Moving N up the beach we came to Richard’s second ‘Mystery’ of the day. With the aid of trace fossils we were put to work to try and match up two small outcrops either side of a headland. What Richard hadn’t anticipated was that, well-trained as we had become in the art of surface scraping, we would uncover an outcrop of black sand with a sharp contact with the overlying white sand above. Trace fossils of the white sand had been piped down into the black, but the origin of the colour remains a mystery as the sand itself seemed to be the same. Richard had never seen this black sand before. The section was a cacophony of colours with reds and greens in a rather chaotic way and some of the white sand was soft and some hard. Looks like the whole section will need cleaning up and another paper produced …. Eventually we did get down to the exercise of the afternoon and matched the right-hand base of the section with the one we had first examined round the corner. It seems that there is a whacking great unconformity at this point, probably caused by faulting, with the white, red and black loose sediments, probably of Triassic age, overlying the green sediments with trace fossils. These were best examined in the undisturbed section where we could find excellent examples of Teichichnus. Characteristic well-cemented brown stormbeds helped date this rock to the Lower Cambrian ‘Green Shale’ (actually a sandstone also known as Broens Odde Sandstone) which we first encountered on the beach at Snogebæk (what a language).

The day finished with a reception and presentation to Richard and Ulla for their wonderful hospitality and brilliant geology. Sue had also bought a present for Line, a geology student, who had spent the week busily in the kitchen providing delicious meals. We had a splendid evening under the stars finishing with singing, vigorously conducted by Mick. Our rendering of 'The Music Man' would surely have brought the neighbours round if there had been any within a couple of kilometers!