Siliciclastic and carbonate sedimentology, Lusitanian Basin, Portugal 2018

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BSRG goes international! The second BSRG postgraduate of 2018 took place from 26–30 November in Portugal. We visited the Jurassic and Cretaceous siliciclastic and carbonate infill of the Lusitanian rift basin, which is exposed along the west coast of Portugal. The trip was led by Matthew Watkinson, Plymouth University, and organised by Kévin Boulesteix and Maarten Heijnen, University of Manchester and NOCS/University of Southampton respectively. A diverse group of in total 24 individuals from different backgrounds, affiliations (including institutes in Poland and Thailand), age groups, and career stages, but with a common interest in sedimentology participated on the trip. Amazing outcrops, a great field guide (on paper and in person), stimulating discussions, and Portuguese cuisine made the trip a great success!

We all met on Lisbon airport at 6PM on Friday 26 November, picked up three vans and drove to Ericeira, an old, traditionally fishing village that got a make-over into a buzzing surfing town. After the usual chaos of dividing rooms, and fighting for the top bunks, we had an introduction round, followed by dinner in smaller groups, during which everybody could explore the trendy restaurants and bars of Ericeira in their own pace.

The next morning (Saturday 27 November) Matthew provided us with the geological framework of the Lusitanian Basin, needed for the trip. The basin was formed by rifting that separated Iberia and Eastern Canada and formed the Central North Atlantic. This rifting occurred in several phases spanning from the Upper Jurassic to the Lower Cretaceous, before shifting westward. The Lusitanian Basin is, besides the opening of the Atlantic, also influenced by the western Tethyan Ocean, making it an analogue to Middle Eastern petroleum systems.

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Dark organic rich shales at Portinho do Areia do Norte.

After the introduction in the hostel, it was time to study the outcrops. We drove north to the peninsula of Peniche where we started our really windy day with Jurassic pre-rift deposits. We headed to Papoa Headland, to see the inner ramp grainstones of the Coimbra Formation. These are overlain here by a textbook example of a transgressive hardground with borings and large bivalves (oysters) remains. Only a 2-minute drive brought us to Portinho do Areia do Norte, where we saw the expression of anoxic bottom waters, resulting in dark coloured shales with high organic carbon content. The rocks just above where very rich in benthic and nektonic fossils, and especially the amount of belemnites was memorable. The weather was slightly challenging this day, so we headed to Peniche to find some shelter for a comfortable lunch. After a brief visit to the GSSP for the Toarican-Pliensbachian boundary, we made several stops along the cliffs towards Cabo Corvoeiro. These sections have been interpreted as a rare example of a prograding submarine fan, but this has recently been questioned and might be a simple shallow marine succession. Several remarkable scours are visible here too and the possible interpretations of these scours and the outcrops as a whole were discussed, while being sprayed with salt water blown up onto the cliffs by heavy gusts. As the BSRG postgrad fieldtrips have already shown during last year’s storm Brian (during fieldtrip to Devon and Cornwall), a little bad weather doesn’t stop us! The field day ended at the disused quarry near Sobral de Lagoa, where the timing of a limestone cave collapse, salt tectonics, and later deposition of Upper Jurassic rocks can be very nicely discussed, using differences in bedding and detailed observation of structures. We all warmed up during the drive back and ended the day with a lovely group dinner at one of Ericeira’s nice restaurants.

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Matthew discussing the remarkable scours at the cliffs towards Cabo Corvoeiro.

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Discussing the interplay between the architecture of a channel-flood plain fill and accommodation space creation and what the implication are for reservoir connectivity at Porto Calada.

The second field day brought us to the Late Jurassic syn-rift/salt clastic deposits of the basin. We started at Praia de Santa Cruz with its iconic boulder on the beach, where we saw a broad range of deposits including a salt diaper wall, marine slope consisting of hemipelagic muds, debrites, and turbidites, and a delta front deposit on the top of this shallowing upwards sequence. This succession is interpreted to represent a progradational syn-rift to early post-rift succession in the hanging wall of a Late Jurassic half graben. We learned that in the days of the initial work, rifting was a fashionable subject in geology, and that the role of salt kinematics maybe has not been considered well enough, leading to interesting discussions. In the afternoon we visited the stunning fluvial successions at Porto Novo. This outcrop shows beautiful sedimentary structures, including lateral accretion surfaces. The last stop of the day was at Santa Rita, where we studied the Upper Lournha Formation, which is interpreted as gravelly and sand-rich fluvial deposits. This interpretation was questioned by some of the participants, leading to a good discussion.

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Lunch on a tropical Cretacous beach. The pineapple and pomegranate contributed to the tropical atmosphere. The weather didn’t.

We started the third day at Porto Calada, where we visited large-scale outcrops of channels. We discussed the interplay between the architecture of a channel-flood plain fill and accommodation space creation and what the implication are for reservoir connectivity. The rest of the day mainly focused on nearshore clastic systems of the Lower Cretaceous. We studied sequence stratigraphy on a tropical Cretaceous beach at São Lourenço, which was also an ideal lunch stop (we doesn’t want to lunch on a tropical beach?). Then we visited a beautifully 3D exposed spit with amazing sedimentary structures at Praia do Coxos. Our day ended with the transition from clastic bars into carbonate shelf with, among other fossils, beautiful nereneid gastropods. Then, we headed to a nice beach bar near Ericeira, before heading back. Since this was our last night as a complete group, we decided to have another group dinner. We ended at a nice restaurant at the old fishing harbour of Ericeira.

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Well-deserved drink after a day in the field

We visited several outcrops further south, between Ericeira and Lisbon (Cascais area) on our last day. We were back in the carbonates again. The day started at the beautiful Praia Abano, where we studied Upper Jurassic deep water carbonates, including carbonate gravity flows. Some later magmatic processes made interesting looking dyke structures through the carbonates here. On one exceptionally stunning beach we made this year’s group photo (with Miquel unfortunately missing). After a chaotic visit to the train station of Cascais to drop off one of the participants, we went to Forte Crismina. We learned the difference between elevator rudists and recumbent rudist and recognised them in the field. Also sponges and corals where plentiful. We ended the geology part of the trip by seeing the start of the Cretaceous orbitolinids (forams) bloom. We drove back to Lisbon airport where we brought back the vans. Some participants flew back in the evening, while another group explored Lisbon’s nightlife to celebrate another successful BSRG postgraduate fieldtrip.

We would like to thank the trip leader Matthew Watkinson for showing us the amazing geology of the Lusitanian Basin. Also, we would like to thank all the participants for their enthusiasm and contributions.

Maarten Heijnen and Kévin Boulesteix, BSRG representatives.

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Group photo at Praia Abano

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BSRG 2018 fieldtrip to the Permian Zechstein of Northeast England

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The first BSRG postgraduate field trip of 2018 visited Permian Zechstein outcrops of Northeast England. The trip was led by Professor Maurice Tucker and Michael Mawson of the University of Bristol and Durham University, organised by Arne Fuhrmann and Dan Tek from the universities of Manchester and Leeds and sponsored by the International Association of Sedimentologists (IAS). A diverse group of researchers from universities in Europe and North America made discussions stimulating and wide-ranging.

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Our group beside the famous Lot’s Wife sea stack at Marsden Bay

 

After an evening of introductions, we started the action packed, two-day trip on Saturday morning at Claxheugh Rock, where the basal contact of the Zechstein Raisby formation crops out. The stunning exposure shows a slide palne separating aeolian Yellow Sands from overlaying Marl Slate. Working our way up through the stratigraphy, we visited Trow Point where the uppermost Raisby Fm. is overlain by Trow Point Bed.  It consists of a 10 cm thick microbial unit equivalent to 100 m of reef carbonate just 5 km to the west, and a thin layer of residue from the dissolution of the Hartlepool Anhydrite. Above the Trow Point Bed, the concretionary Roker Formation is present as a collapse breccia.

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Maurice explaining how the succession at Trow Point was formed

 

After a nice lunch at Marsden Bay, we continued to look at the Rocker Fm. which exposes a number of primary and resedimented carbonate facies, including cross bedded, shelf-margin bioclastic oolites, and calc turbidites. The Roker Fm. also shows some spectacular secondary carbonate features such as the bizarre ‘cannonball limestones’ and oomoldic porosity. Day one ended with a look at the dolomitised reef facies of the Ford Fm. with some impressive fossil assemblages.

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Amazed looks on the faces of the participants at the wonderful cannonball limestones

In the evening, after a hearty evening meal, the group received a private tour of Durham Castle courtesy of Maurice, the former Master of Castle.

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Maurice showing the group around the great hall in Durham Castle

Day two started at Blackhall Rocks, with a jump into the weird and wonderful world of microbial carbonates. Microbial dolomites and stromatolites exposed in exceptional sections along the coast of County Durham, the most notable of which was the distinctive ‘Crinkly Bed’. Walking through the caves and past the cliffs, reefal and slope carbonates, some of them brecciated, were visible alongside these enigmatic microbialites. We finished the two fantastic days at Seaham Harbour, looking at the youngest outcropping Zechstein strata in Durham, the contact between to Rocker Fm. and the Fordon evaporates.

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Michael explaining, to the group, the geology along the coast of NE England

We would like to thank the trip leaders, Maurice Tucker and Michael Mawson for taking us to these amazing outcrops and everyone attending the trip for their valuable contribution!

Dan Tek, Postgraduate Representative

BSRG postgraduate fieldtrip 2017: Devon and North Cornwall

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The 2017 BSRG postgraduate field trip was held in North Cornwall and Devon from the 20th to the 22nd of October. The trip was led by Dr Matthew Watkinson from the University of Plymouth and EPI Geoscience and organized by Kévin Boulesteix from the University of Manchester. We were happy to be joined by 30 young researchers (PhD students, post-docs and young professionals from industry) from all over the UK and the world (including Malaysia!).

After a short introduction about the geology of the area on Friday evening, we focused on the Late Pleistocene to Devonian age strata of the North Devon Basin at Saunton Sands on Saturday morning. It was a very good opportunity to look at the impressive angular unconformity between the Late Pleistocene and the uppermost Devonian (350 Myr are missing) as well as to compare modern beach processes with the non-deltaic shelf to supratidal siliclastic facies.

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Angular unconformity between the uppermost Devonian Pilton Shales Formation and the Late Pleistocene Sandrock Formation.

 

We then spent the afternoon in Westward Ho! to study the uppermost Namurian pro-deltaic facies of the Culm Basin which are beautifully exposed along the wave cut platform. During the afternoon, the group successfully braved storm Brian while listening to Matthew’s explanations and discussing the depositional processes responsible for the deposition of this slope succession.

 

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On Sunday morning, we focused on the Culm Basin deep-water succession in Widemouth Bay near Bude in Cornwall. We mainly discussed some controversies related to this basin, such as the depositional environment of this succession (marine vs lacustrine). We also applied and discussed the recent classification of sediment gravity flow deposits.

 

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The group discussing the depositional environment of the deep-water succession exposed in Widemouth Bay.

 

We ended the trip in front of a beautifully exposed chevron fold formed during the Variscan Orogeny.

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The group in front of the chevron fold exposed in Widemouth Bay.

 

This field trip was a great success, and we would like to thank Matthew Watkinson for volunteering to lead this successful trip.

See you all next year for new events!

The BSRG postgraduate representative team