School of Earth and Environmental Sciences
Barrême Field Course EART20300 Second year, First semester
18 th September – 27 th September 2019
Course Leaders: Julian Mecklenburgh, Alison Pawley, Ian Kane, Euan Soutter and Zoë Cumberpatch
Name:
Contents
Introduction Course introduction .. …………………………………………………… ……………………. 2 Itinerary .. .…………………………………………………………………………………… .. 3 Assessment .. …………………………………………………… …………………………….. 5 Health and safety / behaviour (summary comments) .. …. ……………………………………. 5
Geolo gical Background Plate tectonic context: overview …... ……… .. ……………………………… .……………….. 9 Plate tectonic context: Pre -Alpine , Mesozoic , and Palaeocene history ……………………….. 10 Plate tectonic context: the Alpine evolution of the Barrême Basin ………………………….. 13 Qua ternary …………………………………………………………………… .………….….. 18
Field mapping skills Orienting yourself: bedding and way -up .. …………………………………………………… 21 Field notebook .. ……………………………………………………………………………… 22 Describing sedimentary unit s in the field ... .. ….. ………………………………… …………. 25 Writing descriptions of sedimentary units in reports ………………………………………… 28 Field ma p ...………… …………………………………………………………………………. 29 Cross section and stereogram ………………………………………………………………… 34 Describing folds ... ………….. ………………………………………………………………… 35 Descri bing faults …. ………..………………………………………………………………… 36 Plotting stereograms …………………………………………………………………………. 37 Stratigraphic column …………………………………………………………………………. 38 Quaternary deposits / surface processes map ………………………………………………… 39
Helpful comments for mapping u nit interpretations Les Sauzeries Formation ……………………………………………………………………… 41 La Condamine Formation ……………………………………………………………………. 50 Tartonne Formation …………………….. ……………………………………………………. 64 Bussière d’Entouart Formation ………………………………………………. ……. …………. 65 Les Cla piers Formation ………………………………………………………………………. 72 La Poste Formation / Le Château Formation .... …………… ………………………………… 73 Quaternary …. ………………………………………………………………………………… 79
Appendices References ……………………………………………………………………………………. 81 Health and Safety / b ehaviour information …………………………………………………. 83 Self -Assessment and feedback forms 86 Group Assignment 87 Peer -assessment of note book 89 Rough Stratcolumn 93
1 Course introduction
EART20300 is a 20 credit unit that comprises three residential field courses: th is one (introductory geological mapping), one at Easter 20 20 (mapping in structurally more complex areas), and one in June 20 20 (sedimentology field techniques) . Th e aim of the unit is to introduce you to geological field mapping techniques that can be app lied in a variety of different geological settings. Aims of the course
The primary emphasis of the south -east France field course is to provide introductory training in geological field mapping techniques. In doing this you will: 1. produce a geological map o f an area a few square kilometres in size that is located near the hamlet of Clumanc in the Barrême Basin; 2. illustrate the stratigraphy and structure of the mapped area using a cross section, a stereogram, and a stratigraphic column; 3. record observations tha t will allow you to write a report on the geology of the mapped area duri ng the 2 nd year autumn semester tutorials (Nov -Dec). The EART20300 package is an essential prerequisite for all who are undertaking the Independent Mapping Exercise (EART30000) in sum mer 20 20 . Intended learning outcomes At the end of the field course the student should be able to: 1. Make accurate measurements of both planar and linear geological features. 2. Record sufficient observations accurately on a field map to define geometry of area . 3. Use observations to interpret geology outside areas of observations. 4. Develop a 3D model of the geological structure of an area. 5. Record observations of the sedimentological features of the rocks seen. 6. Use this information to interpret environment of depos ition and sediment provenance. 7. Integrate structural and sedimentalogical observations to be able to fully interpret the depositional environment, sediment provenance and deformation history.
The course is 1 0 days long . T eaching will be via a range of metho ds including staff -led traverses in the mapping area, independent mapping, one -to -one interactions with staff to discuss progress and data collection strategies, and practical classwork (on one day). You will be expected to produce a geological map, a cros s-section across the mapping area with accompanying stereogram , a stratigraphic column of the mapped units, and a small map and field sketch illustrating the Quaternary geology. Note that although on some days you will work in the field with staff, and tha t throughout it is fine to discuss what you are doing with your colleagues , YOU MUST COLLECT YOUR OWN FIELD DATA . If you do not, the University deems this as COLLUSION and you will get zero for the affected piece of work.
“Education is experience, and the essence of experience is self -reliance”
2 Itinerary
The following summarizes the intended i tinerary . Each day you should be ready to depart, fully equipped with f ood, water, clothing, and equipment , by 8.40 am . E xpect to be in the field until ~ 5 pm .
Wed 18 Sept Arriv al at Nice airport at 16:0 5 am . Bus journey (~ 2 hr) to the field area Meeting to discuss logistics and expectations of field course.
Thur 19 Sept Staff -led day in the mapping area around Clumanc along the D219 road section , taking you through the mapping units, and introducing you to key data collection and data recording techniques . Evening : tidy notebooks; and draft stratigraphic column .
Fri 20 Sept Staff -led day going through geological mapping strategies and structural measurement te chniques . Evening : tidy notebooks and map. Complete peer assessment of your notebook with a friend.
Sat 21 Sept Independent mapping in the western part of the mapping area around Clumanc Evening : tidy notebooks and map , fill out self -assessment form to critically assess your progress . Meet with your tutor for the course to discuss progress.
Sun 22 Sept Staff -led traverse to key localities along the eastern part of the mapping area. Evening : ink -in field slip data; tidy notebooks; attempt a sketch se ction oriented WSW - ENE across the mapping area as a day Evening : ink -in field slip data; tidy notebooks; identify gaps in your data
Mon 23 Sept Independent m apping in the mapping area around Clumanc . Concentrate on getting as much data as close to where we will draw the cross section tomorrow. Evening : ink -in field slip data; tidy notebooks; review data collection strategy for rest of week .
Tue 24 Sept This day will be spent at the accommodation site 9-12 noon: plotting stereograms and starting the cro ss -section 1-4 pm: finishing cross -section and compiling a stratigraphic column Evening : complete the day’s work . Meet with your tutor for the course to discuss progress and set clear ta rgets for the next two days
Wed 25 Sept Independent m apping in the mapping area around Clumanc Evening : ink -in field slip data; tidy notebooks; review tomorrow’s data collection strategy
Thur 26 Sept Independent m apping in the mapping area around Clumanc Evening : complete all work ready for submission by 10 .00 am tomorrow
3 Fri 27 Sept 10 .00 am: Submission of assessed work Pack and tidy rooms ready for room inspection 12 .00 am : Depar ture from the bottom of the hill at the accommodation site 17:55 : Arri val back at Liverpool airport
4 Assessment
The course assessment will be based on the following:
Field slips of the mapping area, fully inked in, coloured, and interpreted and a n appropriately oriented, vertical cross -section with supporting stereogram show ing the structure of the mapping area (70%) A stratigraphic column drawn to scale and incorporat ing annotat ions that provide a description of each mapping unit, everyt hing to fit on to one side of paper with key on the back . The emphasis in the marking wi ll be on how well you communicate your content diagrammatically (30%)
The marking scheme will be designed to give substantially more emphasis on the quality of the work that you do in the field rather than in the evening. Note that the quali ty of your no tebook , and the extent to which you can use the information contained within it to write and illustrate a geological report of the mapping area, will be considered as part of the 2 nd year autumn semester tutorials . This may involve some evaluation of your notebook techniques by your fellow tutees. All work is to be submitted 10 .0 0am on the day of departure
Health and Safety / Behaviour
There is some advice on health and safety and on behaviour at the back of this book (p. 83.) . You must read this advice, a nd should see someone immediately if there is any part of it that you do not understand.
Key points: i n the field The weather in the field area at this time of year is mostly hot and sunny, with little opportunity for working in shade . Consequently, there is a real risk of sunburn, dehydration, and heat -related exhaustion . No -one should go into the field without adequate water (2 -3 litres), a hat, and sunscreen . You will be in hilly terrain and so sturdy walking boots are essential . You should also carry wa terproofs in case of rain. There are hunters in the area on some days – our itinerary is designed to avoid their main areas of activity but wear a high visibility jacket if in doubt. French law requires you to wear a high visibility jacket when working by the side of roads.
Key points: i n the accommodation We have been coming to the accommodation site at Font C haude for several years and we would like to continue to do so. At all times th e word of our caterers, Joseph and Fabienne, is to be followed without argument ; if you have any issues arising from that, bring the matter to the attention of one of the teaching staff. The rooms and toilet/bathroom areas should be kept clean and tidy; Joseph and Fabienne will make daily inspectio ns . Any damage/breakages sh ould be reported. There should be no talking in the accommodation blocks after 10pm except in designated areas . The personal consequences and liability arising from any inappropriate behaviour will be the sole responsibility of the offenders, and may resul t in expulsion from the field course with subsequent disciplinary action by the University authorities .
5 Above: road map showing the route that we will take between Nice and Barrême . We head north out of Nice up the Var valley on the N202 , and then continue west along this road through Entrevaux and St. André -les -Alpes to Barrême (Barrême is SE of the town of Digne -les -Bains on the western edge of the map) . Distances on the map are in kilometres.
Left: Road map at larger scale showing the field area (shaded box), the accommodation site (Font Chaude in the south - east), and the local village of Barrême. Again distances are in kilometres
6 The Geological Timescale from the start of the Carboniferous, as ratified by the International Commission on Stratigraph y. This version was ratified this year (v 201 6/0 4). See www.stratigraphy.org for future updates.
7 GEOLOGICAL BACKGROUND
Plate tectonic reconstructions Schettino A, Turco E, 2011, Tectonic history of the western Tethys since the Late Triassic. Geological Society of America Bulletin 123: 89-105 Handy MR, Schmid SM, Bousquet R, Kissling E, Bernoulli D, 2010, Reconciling plate-tectonic reconstructions of Alpine Tethys with the geological-geophysical record of spreading and subduction in the Alps. Earth Science Reviews 102: 121-158
Barrême Basin Evans MJ, Elliott T, 1999, Evolution of a thrust-sheet-top basin: the Tertiary Barrême basin, Alpes-de-Haute-Provence, France. Geological Society of America Bulletin 111: 1617-1643 Ford M, Lickorish WH, Kusznir NJ, 1999, Tertiary foreland sedimentation in the Southern Subalpine Chains, SE France: a geodynamic reappraisal. Basin Research 11: 315-336
Late Cenozoic uplift of the Alps and Quaternary Fauquette S, Bernet M, Suc J-P, Grosjean A-S, Guillot S, van der Beek P, Jourdan S, Popescu S-M, Jiménez-Moreno G, Bertini A, Pettit B, Tricart P, Dumont T, Schwartz S, Zheng Z, Roche E, Pavia G, Gardien V, 2015, Quantifying the Eocene to Pleistocene topographic evolution of the southwestern Alps, France and Italy. Earth and Planetary Science Letters 412: 220-234 Fox M, Herman F, Kissling E, Willett SD, 2015, Rapid exhumation in the Western Alps driven by slab detachment and glacial erosion. Geology 43: 379-382 Champagnac JD, Molnar P, Anderson RS, Sue C, Delacou B, 2007, Quaternary erosion-induced isostatic rebound in the western Alps. Geology 35: 195-198
8 Plate Tectonic Context
Overview The mapping area around Barrême lies in the external zone of the Alpine orogenic belt. This orogenic belt was formed during the collision of the European and Adriatic-African plates. In the early stages of collision, the weight of the units being stacked up on the margin of the European plate led to flexural subsidence of that margin and the formation of a foreland basin around the leading edge of the orogenic front. The late- Eocene and Oligocene units in the mapping area (from La Condamine Formation upwards), are sediments deposited in that foreland basin. As the collision progressed, the units underlying the foreland basin became involved in the shortening, and as they were, the sequence that had been deposited in the foreland basin was carried outwards, in piggy-back fashion, on thrust faults. In the Barrême area, the underlying thrust fault on which this movement occurred is the Digne Thrust. The movement on this fault was primarily in Late Miocene to Pliocene times and involved a displacement of the overlying units of about 10-15 km to the south-west (Lickorish & Ford, 1998). Subsequent erosion has left only isolated remnants of the Eocene- Oligocene foreland basin sediments; the Eocene-Oligocene units at Barrême are one of these remnants.
Above: SE-NW oriented cross-section across the Alpine orogenic belt (after Fossen, 2010, p.318). Barrême lies off the plane of section but its position within the overall structure of the belt is shown by the asterisk.
Right: a map of the western Alps (after Sinclair, 1997). The location of Barrême is again shown by the asterisk, and the local direction of thrust transport is shown by the thin arrow
Below: formation of a peripheral foreland basin
9 Pre-Alpine, Mesozoic and Palaeocene history The basement to the western Alps is composed of Carboniferous and older metamorphic and igneous dominated rocks that were deformed during the Variscan orogeny. These are unconformably overlain by Triassic sandstones, evaporites, and dolomitized limestones. Later, during the Alpine orogeny, the thrust faults that accommodated the crustal shortening were to localize within these Triassic units. Beginning in the Late Triassic but getting underway in earnest in the earliest Jurassic, the south-eastern French part of the European plate was subjected to a prolonged period of crustal extension related to the break-up of the supercontinent, Pangaea. The first phase of extension (Early to Mid-Jurassic) led to a series of NE-SW trending elongate, fault-bound basins in which pelagic and hemipelagic sedimentation dominated with local carbonate shoals developed over the crests of the fault blocks. A second phase of extension (Mid- Jurassic to Early Cretaceous) led to the formation, in south-eastern France, of the Vocontian Basin. This basin was located on the northern margin of the Pyrenean-Valais Ocean – a relatively narrow ocean situated between the Alpine-Tethys Ocean and the developing North Atlantic Rift. Around Barrême, the Vocontian Basin was bounded to the south, west, and north by carbonate platforms. Within the basin itself, sedimentation was dominated by calcareous hemipelagic marls intercalated with gravity-driven deposits (slumps, debris flows, turbidites, and massive sandstones). This type of sedimentation continued in the Vocontian Basin throughout the Early Cretaceous – the oldest units within the mapping area (Les Sauzeries Formation = Aptian age) come from near the end of this part of the story.
The plate configuration in Aptian (Les Sauzeries Formation) times. Left from Stampfli & Borel (2002); below from Friès & Parize (2003)
By the end of the Early Cretaceous, eastward migration and anticlockwise rotation of Iberia had begun. Consequently, although the Valais Ocean continued to spread during the Late Cretaceous, the plate margin had a strong sinistral strike-slip character, initiating folding in the Pyrenees and Provence. To the south, subduction of the Alpine-Tethys Ocean began.
10 Regional plate reconstructions for Aptian times (Les Sauzeries Formation) and for Cenomanian times (present in the mapping area only as reworked fine-grained limestone clasts incorporated into the conglomeratic base of La Condamine Formation and into the conglomerates of the Laubre Member of La Poste Formation). On the facing page are cross sections that accompany these maps. All figures from Handy et al. (2010).
11 NW SE
NW SE
In the Palaeocene and Early Eocene the rate of convergence between the European and Adriatic-African plates increased. This led to closure of the Valais Ocean and to uplift and erosion in south-eastern France.
The plate configuration in the Mid-Eocene; map right from Stampfli et al. (1998); section below from Handy et al. (2010)
NW SE
12 The Alpine evolution of the Barrême Basin By the Late Eocene (Priabonian) the effects of shortening as the European and Adriatic-African plates converged were becoming manifest in the Barrême area. As thrust sheets were stacked onto the southern margin of the European plate, a peripheral foreland basin developed around the leading edge of the orogenic belt. Subsidence associated with the formation of this basin led to a marine transgression from east to west, and around the edge of the basin a sequence of near shore nummulitic carbonates was deposited. In the literature, these carbonates are known as the Calcaires Nummulitiques; we have called them La Condamine Formation.
NW SE
Plate configuration during the Priabonian (La Condamine times). Asterisk shows the position of Barrême. Figures from Handy et al. (2010)
13 Left: position of the marine transgression through the Eocene from Lutetian (L) to Bartonian (B) to Priabonian (P) times. The sm all arrows show the source of sediment in the Grès de Ville (our Bussière d’Entouart Formation) within the va rious foreland basin remnants – the Barrême Basin is labelled Bm (after Ford et al., 1999)
In actual fact, by the time of the Calcaires Nummulitiques transgression, the Mesozoic units underlying the foreland basin were already shortening. The geometric evolution of the Barrême Basin was subsequently strongly influenced by movement on the St. Lions Thrust on the eastern margin of the basin as the whole basin was being transported to the south-west within the Digne thrust sheet.
Below: evolution of the Barrême Basin during the time span recorded by the units and structures in the mapping area (after Evans & Elliott, 1999)
14 The following provides a brief summary of the sedimentary and structural evolution of the Barrême Basin. While mapping you should see the observational evidence for many of the interpretations given here. In the Barrême Basin, the first units to be deposited im mediately prior to the Calcaires Nummulitiques transgression were a set of poorly sorted, fluvial conglomerates (Poudingues d’Argens) . As a package, these are laterally very variable in thickness – they are not exposed within the mapping area but elsewhere within the Barrême Basin they are up to 500 m thick – and are interpreted as infilling palaeovalleys. Commonly observed at the top of the Poudingues d’Argens is a horizon of cobble -sized clasts in which the clasts have been extensively bored on all sides by Lithophaga bivalves. This horizon is interpreted as a beach deposit formed during the early stages of the marine transgression. The horizon is not present in the part of the mapping area that you will map, but it is present to the west, in the part of the map that has been completed for you. You will, however, see the bored clasts – the clasts were reworked and re-deposited within the conglomerates of the younger La Poste Formation. The Calcaires Nummulitiques (= La Condamine Formation) are interpreted as marine carbonate shoreface deposits. The calcarenites of the Calcaires Nummulitiques are overlain by calcareous silty mudstones (Marnes Bleues = Tartonne Formation) . These mudstones contain a diverse marine microfossil fauna that records progressively increasing water depths. Background mudstone deposition was interrupted by an interval in which sands were brought into the basin from the south in discrete depositional events (Grès de Ville = Bussière d’Entouart Formation) . These turbidites are the lateral equivalents of the turbidites that were deposited in the Annot basin ~25 km to the west, where Bouma sequences were first defined. Following this interlude there was a return to silty mudstone deposition (Marnes Bleues = Les Clapiers Formation) . The top part of the Marnes Bleues succession contains at least three intervals in which thick packages of conglomerates were deposited (Conglomérats de Clumanc = La Poste Formation , and Conglomérats de St. Lions) . By this time, uplift to the north and east associated with the Alpine orogeny was shifting the depocentre within the Barrême Basin southwards, and these packages comprise conglomerates that were deposited in submarine channels within a fan-delta / Gilbert-type delta complex that was building out from the north into the basin. Each conglomerate package is overlain by sandstones (or in the Conglomérats de St. Lions case, by a thin coral reef) that contain evidence of shallowing and even emergence, before the background rise in relative sea level led to a return to silty mudstone deposition. Towards the end of the phase of conglomerate deposition, renewed activity on the St. Lions Thrust led to folding of the earlier Cenozoic units to form the Barrême synform. By the late Rupelian (Early Oligocene), the uplift associated with the ongoing Alpine deformation led to cessation of marine deposition in the basin. The subsequent basin fill marks the switch to continental deposition during regional uplift.
Barrême Basin in late Rupelian times (after Evans & Elliott, 1999) 15 Stratigraphy of the Tertiary units within the Barrême Basin (modified from Elliott & Evans, 1999). u/c = local unconformity (arrows indicate the more significant ones); T = transgressive flooding surface; R = forced regression surface 16 The youngest unit in the mapping area ( Le Château Formation ) is approximately contemporaneous with the Conglomérats de St. Lions. Hence the units in the mapping area predate the switch to continental deposition. However, for completeness the evolution of the basin during this phase of its history is illustrated on the diagrams below (further details of these higher units are shown on the example stratigraphic column on p.37). Analysis of the pollen from temperature sensitive trees shows that in the south-western Alps there was a period of rapid surface uplift (growth of the mountains) in the mid- Oligocene, but that since then the topography of the area has essentially been maintained, albeit with a westward propagation of the deformation front in Miocene-Pliocene times (see Fauquette et al. , 2015).
Oligocene evolution of the Barrême Basin (after Evans & Elliott, 1999)
17 The Quaternary
During the Quaternary glacial stages, the Barrême Basin lay close to, but just beyond, the limit of the Alpine ice sheet. The principal river runnin g through the mapping area (L’ Asse de Clumanc) therefore remained as a river during the glacial periods albeit within a periglacial environment. The walls of the valley show abrupt changes in slope (knick points) at several different heights above the present valley floor. There is also a well developed river terrace at a height of a few tens of metres above the valley floor. These observations suggest that during the later part of the Quaternary, the valley floor has been lowered (relatively) in step-wise fashion. The lowering of the valley floor reflects the continued uplift of the region (~ 0.5 mm/yr over the last million years). This uplift is primarily an isostatic response to the erosion of the Alps, although there is also undoubtedly a tectonic component of uplift driven by the ongoing Alpine deformation (see Fox et al. , 2015). The step-wise nature of the lowering reflects the response of the landscape to climatically-induced changes in river discharge and sediment supply through glacial / interglacial cycles – in this area the influence of base level changes (~ 100 m fluctuation in sea level during a glacial / interglacial cycle) is minor.
Cross section of a valley illustrating the formation of knick points and river terraces due
to step-wise lowering and lateral translation of the river system (t 1 is the oldest section,
t2 the next oldest, etc.). Note that the knick points may not be very obvious if there is little lateral translation, and that earlier knick points may be eliminated if the river reverses its direction of lateral translation
t 1 knick points t2 t3 ~ terrace
t4
18 The evolution in the shape of a river valley in cross section during a glacial / interglacial cycle is addressed by models of river terrace formation. Within such models, most of the change occurs during the transitionary phases (glacial → interglacial and interglacial → glacial). Both transitions may have incisional and aggradational stages so that, in principle, each cycle could record two sets of terraces / knick points. However, local controls on how climate influences discharge and sediment supply tend to favour either the warming or the cooling phase for the principal incision and aggradation. In the eastern wall of L’ Asse de Clumanc there are perhaps six knick points above the lowest river terrace (Le Puy). These are spaced at elevation intervals of about 50 m. With an uplift rate of 0.5 mm/yr, 50 m equates to ~100 kyr which is approximately the length of one glacial / interglacial cycle since the Mid- Pleistocene Transition. The implication (which must be viewed circumspectly) is that there is a record of each of the last six glacial / interglacial cycles in the valley wall.
Bridgland’s model of river terrace formation (Bridgland, 2000) applicable for valleys in temperate latitudes in areas beyond the ice limit. Note that uplift is needed to form terrace staircases, and that preservation of terraces requires river avulsion unless one is to suggest that the river channel belt narrows with time. Is the incision represented by the terrace of Le Puy in the mapping area a record of warming after the last glacial maximum?
19 FIELD MAPPING SKILLS
Further reading Lisle RJ, Brabham P, Barnes JW, 2011, Basic Geological Mapping (5 th edition), Wiley-Blackwell Coe AL (editor), 2010, Geological Field Techniques . Wiley-Blackwell
Tucker ME, 2011, Sedimentary Rocks in the Field (4 th edition), Wiley-Blackwell Stow DAV, 2005, Sedimentary Rocks in the Field: A Colour Guide , Manson Publishing Goldring R, 1999, Field Palaeontology (2 nd edition), Longman
20 Orienting yourself: bedding and way-up
When in the field the first thing you need to do, before thinking about notebooks, field slips, etc. , is to carry out a reconnaissance of the exposure. The primary focus of this is to orient yourself, and that means to establish the orientation of bedding and, if possible, to determine the younging direction (way-up) of the units. Key way-up criteria are i llustrated below – almost all of these are present in the mapping area.
Way-up criteria compiled from Bailey (1936), Stow (2005), and Nichols (2009)
21 Field notebook
The notebooks of professional geologists belong to their employer and not to the geologist who compiles them. Consequently, they must be fully intelligible to a third party, and contain all your data and any other relevant information. In principle, it should be possible to reconstruct your map and the observational part of your report using your notebook alone. The field notebook should therefore be well-presented. The notebook should be hard-backed, robust (i.e ., reasonably weather-proof), and of manageable size ( e.g. , A5). Notes should be arranged so that data are easily correlated with the field map, and they should be clearly and neatly written. Ideally, notes should be inked-in to guard against being smudged or rendered too faint to read through rubbing. There should be a regular (daily) statement of aims and a regular (after every day or two) summary of your current working hypotheses, so that the development of your ideas can be followed. Inking, editing of notes, and writing summaries are most appropriately done in the evening.
Layout You should write your name and permanent (or School) address inside the front cover as well as your local address. Provide information about the map grid and the magnetic declination used. Then leave three or four pages free at the beginning of the notebook for constructing a table of contents later. Pages should be numbered. Use a systematic layout for the notebook. The exact layout will depend on the nature of the data being collected. A commonly used layout has two 1 cm margins on each page with the central portion used for the main body of notes, the left-hand margin for locality numbers, grid references, readings, sample numbers, photo numbers, etc. , and the right-hand margin for notes made at a later date ( e.g ., minerals and fossils identified back in the laboratory).
Content You should record field observations (e.g ., detailed descriptions of lithologies, field sketches, structural readings, etc. ) and interpretations (e.g ., working hypotheses on the features that you have seen). The observations and interpretations must be kept separate from each other and be clearly distinguished. Notes should be accompanied by relevant diagrams such as sketch maps and sketch sections showing critical geological features and relationships. Each diagram should be clearly annotated and marked with an orientation and scale, and you should state whether the sketch is a map, section, or view. The following is a list of things that you should aim to record at each locality.
1. Locations. Always use an 8-figure grid reference and a locality number. Describe the position of the locality with respect to topographic / map features ( e.g ., gullies, bends in road, fence intersections, buildings, etc. ). Record compass bearings if you have used them to pin-point the locality. Describe the size and nature of the exposure at the locality.
2. Lithology. Descriptive details of the rock-types present (see the section below on how to describe sedimentary units in the field). Sub-headings should be used to organize these notes.
3. Geological structure. Position of the locality with respect to any recognized major structure in the area; description of any structurally-induced fabrics present (foliations, lineations) including their orientation
22 (strike/dip for planar features; plunge/plunge direction for linear features); description of any structures present (folds, faults, minor fractures).
4. Evidence for age relationships. If the locality contains the contact between two or more mapping units, pay particular attention to describing the nature of that contact ( e.g. , gradational, sharp, unconformable, faulted), and its orientation (strike/dip, map trend); outline any deductions about age relationships between units, and the timing of any deformation features.
Two field sketches from within the mapping area. Above: a view – note that the sketch is restricted to geologically relevant information. Left: a sketch section with bedding and fold axis readings located on it – this allows many more readings to be located in context around the structure than could be placed on a field map
23 Assessment of notebooks As a guide to the importance attached to good notebook skills, below are assessment criteria that are commonly issued when marking field notebooks.
Presentation and organization (intelligibility to a third party) General comments on neatness/condition of the notebook General comments on organization of the notebook Do the first few pages of the notebook provide adequate comment on the overall field trip dates/objectives/ etc ? Day objectives stated at the beginning of each day? Day summaries present/development of working hypotheses of the geology of the (sub-)area? Is the quality of the notebook maintained throughout the trip?
Localities Locality information (size and nature of the exposure) provided? Are the localities given grid references (generally 8 figure)? Do the grid references tally with the localities as marked on the map?
Lithological descriptions Are exposure scale features (bedding, etc. ) and hand specimen scale features (petrography) discriminated? Are the petrographic (sedimentary/metamorphic/igneous) descriptions comprehensive? Are there any interpretations of the lithological observations?
Field sketches Are there sufficient field sketches? Are the field sketches oriented and given a scale? Are the field sketches well drawn? Are the field sketches informative? Are the field sketches interpreted (labelled)?
Structural observations Are the orientation measurements correctly and fully specified: – planar features as strike/dip as, e.g. , 045/25SE – nature of the planar reading noted, e.g. , bedding (S 0), cleavage (S 1), etc. – linear features as plunge/plunge direction, e.g. , 24/230 – nature of the linear reading noted, e.g. , intersection lineation (S 1/S 0 with asymmetry) Is the geometry of the structure at each locality clearly reported and interpreted? Is there a clear sense of the map-scale geometry between localities ( e.g. , sketch cross-sections)?
24 Describing sedimentary units in the field
The description of sedimentary rocks in the field should be carried out systematically – usually working from the exposure scale to the hand specimen scale. If the variability of the rocks warrants it ( e.g. , near contacts between mapping units, and within mapping units that contain a range of lithologies and sedimentary structures), short lengths of properly measured section should be drawn to support your text. We will focus on techniques for compiling measured sections of this kind on the June 2017 field course, but some examples taken from the units in the mapping area are given in the interpretation section of this handbook. Focus on making observations that have the potential to be interpreted.
A. Exposure scale observations
1. Give a one or two sentence statement summarizing the essential features of the unit ( e.g. , thickly bedded sandstones). If the exposure is of a mapping unit that you have already described elsewhere, note its name and provide a brief comment on its similarity / differences to other occurrences of the unit 2. Give a one or two sentence account of the weathering features, including weathering colour 3. Note the strike/dip of bedding
B. Geometry of the units
1. Bed thickness ( e.g. , thick-bedded, thinly laminated) 2. Bed geometry ( e.g. , tabular, lenticular, wedge-shaped) 3. Type of bedding ( e.g. , planar, wavy, parallel) 4. Nature of contacts ( e.g. , sharp, erosive, gradational)
Terms used to describe the geometry of sedimentary units, compiled from Stow (2005) and Tucker (2011)
25 C. Sedimentary structures and trace fossils
1. Sedimentary structures that are internal to the bed ( e.g. , cross-stratification, imbrication, graded bedding, nodules) 2. Sedimentary structures on the base of beds ( e.g. , furrows, flutes, tool marks, loading and water escape structures) 3. Sedimentary structures on the top of beds ( e.g. , ripples, dessication cracks, rain imprints) 4. Trace fossils (see p.56-59) For sedimentary structures, identify the feature, describe its dimensions, and where appropriate ( e.g. , for palaeocurrent analysis) describe its orientation (see p.68-69, 76). For trace fossils, estimate % bioturbation, identify those that can be identified, for each type describe its shape/dimensions, and describe how the trace fossils vary up through the unit. Trace fossil description is described more fully on p.57.
D. Hand specimen scale: rock texture and composition
1. Grain size ( e.g. , coarse sandstone, siltstone) 2. Grain sorting ( e.g. , well-sorted, bimodal, polymodal, poorly-sorted) 3. Grain shape (sphericity, roundness, and grain form) 4. Rock fabric (clast or matrix supported) 5. Mineralogy (grain size, sorting, and shape descriptions can be applied to each individual mineral) 6. Body fossils (distribution in rock, assemblage/diversity, state of preservation – see p.53)
Rock texture terms compiled from Compton (1962), Stow (2005), Nichols (2009), and Tucker (2011). Note that on the grain size scale, phi = - log 2 d (where d is the grain size in mm).
26 Classification of siliciclastic rocks (redrawn from Nichols, 2009). Note that many prefer to use “muddy sandstone” in place of “wacke”.
For sandstones and mudstones, putting precise numbers to texture and composition terms may require thin section analysis after the fieldwork. However, for conglomerates these texture and composition terms must be described in the field (the scale of the texture is too big for thin sections). In this case, clasts are selected at random, e.g. , by lying a tape over the exposure and describing the clast that is present under the tape at set intervals (see p.74 for an example of a part analysis of clast size and shape). For conglomerates: Clast size is determined by measuring the long and short axis of the clast in the plane of section and taking the average of these two. This is an approximation of the so-called b- axis of the clast – if the clast could be extracted from the rock and its shape approximated as an ellipsoid, its b-axis is the length of the intermediate axis of that ellipsoid Clast sorting and clast shape terms can be quantified from dimensional measurements made in the field (you will meet the formal definitions in EART20121 Sediment Transport & Depositional Environments ) The proportion of clasts (grains > 2 mm) to matrix (grains < 2 mm) should be estimated The composition of the conglomerate should be described qualitatively as monomict or polymict, or better by examining 100+ clasts, the composition can be described quantitatively and illustrated with a pie-chart Ideally, the size, sorting, and shape descriptions should be given for each type of clast
In conglomerates, each clast is approximated as an ellipsoid and the dimensions of the long (a), short (c) and intermediate (b) axes determined (twice the lengths on the diagram above). If the clast cannot be extracted from the rock, b is estimated by taking the average of the (Figure from Krumbein, 1941) long and short axes in the plane of section.
27 Writing descriptions of sedimentary units in a report
The description of a sedimentary mapping unit in a report is an account of field observations and interpretations which integrates observations of the unit made at several different localities. This account should (a) be heavily focused on observations, (b) keep observation and interpretation separate as far as is practicable, and (c) be organized in something like the following way:
1. Mapping unit name plus, to serve as an introduction, a short (perhaps only one-line) description and an indication of stratigraphic context
2. Outcrop scale observations detailing the location and areal extent of the outcrop with a comment on the nature/quality of the exposure, describing any subdivisions (if any) of the unit and their locations and areal extents, and indicating the total apparent thickness and apparent thicknesses of any subdivisions
3. Exposure-scale observations primarily conveying information (quantitative whenever appropriate) on the nature of contacts, the geometry of units, and internal features ( e.g. , layering, sedimentary structures)
4. Hand specimen-scale observations primarily conveying information on mineralogy/composition and on textural features
5. Microscopic observations (if thin section work has been carried out) which augment the hand specimen scale compositional and textural observations by including features that require a microscope to be seen
6. Interpretation: a concise interpretative synthesis of the preceding observations, typically incorporating explicitly the logic flow used to deduce the interpretations.
In general, section 2 will be illustrated with a simplified map showing the outcrop of the unit and any contacts or features within it, section 3 will almost always be illustrated with a measured section to show up-stratigraphy and lateral variations, and section 4/5 will be illustrated with a synoptic sketch showing textural relationships.
28 Field map
In general, the more geological information that you can put on your map without it becoming cluttered the better; geological information is most easily assimilated and interpreted when it is located in its correct geographical position.
Precision The base maps that you will be using are at a scale of 1:10000, i.e ., 1 mm on the map = 10 m on the ground. Thus a 0.2 mm thick line on the map has a ‘ground’ thickness of 2 m. This repre sents the limit of precision of your mapping and it is this precision that you should be aiming for when locating features on the map.
Putting information on your map While working in the field, mark information on your map in pencil (sharp 2H). It will take a day or two before you establish how much data can be accommodated on the map. As a minimum, the following data must be recorded on the map while actually at the location : locality number mapping unit (using colour to show the extent of exposure) bedding and all structural readings bedding trends (form lines) contacts topographic features ( e.g. , breaks in slope) that can help to constrain the position of contacts. In the evenings, you should ink-in and colour-in all the data collected in exposed areas. It is best to leave unexposed boundaries in pencil until you have all your data. Take care when inking-in: (a) to use the recommended symbols and line colours (see below), and (b) not to obscure any areas on the map that you have not yet visited. Lettering and symbols should be neat and small, but legible.
Data to be recorded Data recorded on the map should include things actually observed in exposed rocks as well as those inferred to be there in unexposed areas.
1. Outlines of exposures at clearly defined and numbered localities. When finally inked in, locality numbers should be neat and legible but unobtrusive. You are exposure mapping and so must show the exposures that you have used to generate your map. Do this by drawing a thin green line around the limits of the exposure at each locality. This should be done accurately – no stylized circles or ellipses are. If there are large areas of unexposed ground, label these clearly ( as “NE”) ; if access to certain areas is impossible or denied ( e.g ., due to thick forest, stroppy land owner, etc. ) make this clear on the map.
2. Mapping units. The primary aim of geological mapping is to show the map distribution of lithologies. However, the units mapped should be formations , because this gives stratigraphic as well as lithological information.
A formation is a mappable stratigraphic unit that is characterized (1) by a particular group of lithologies ( e.g. , sandstone and mudstone interbeds that are interlayered on a scale too small to be mapped individually), and (2) that occurs at a particular stratigraphic position (that is, two otherwise identical units occurring in different parts of the stratigraphic column, would be assigned to different formations)
29 HELPFUL COMMENTS FOR
MAPPING UNIT INTERPRETATIONS
On this field course, we are concerned primarily with your ability to make pertinent observations rather than your ability to interpret them – you have yet to do the course units (particularly EART20121 Sediment Transport and Depositional Environments ) that will equip you with the necessary interpretative skills. However, since a ‘pertinent observation’ is generally one that can be interpreted, you need to be aware of some of the interpretations that you could make. The following pages are designed with that in mind. Note that you may find these pages useful when writing your reports in the autumn semester tutorials.
40 Les Sauzeries Formation
A notebook summary of some key observations from the D219 roadside exposure of Les Sauzeries Basse Member of Les Sauzeries Formation. Note that the unit was described more thoroughly at a different locality, and so the remarks are summary.
41 Cyclicity in Les Sauzeries Basses Member Part of Les Sauzeries Formation comprises interbedded blue-grey weathering siltstones and buff weathering siltstones (mapped as Les Sauzeries Basses Member). Apart from the weathering colour and the more resistant nature of the buff weathering units, it is difficult to see any difference between these interbeds in the field. However, by applying various geochemical / mineralogical / thin section techniques (see Tribovillard & Cotillon, 1989) it is found that:
Background composition of the formation: 50% carbonate, 30% “clays” (of which <15% chlorite, 30 - 40% ill ite, 15-25% mixed layer clays, up to 15% smectite, 20-25% kaolinite), 15% quartz, + accessory pyrite, feldspar with an average organic carbon content of 0.5% but that dark layers are richer in kaolinite+illite; light layers are richer in smectite+chlorite [clays in dark layers derived from continental weathering under warmer and more humid conditions] dark layers are enriched in carbonate; all carbonate is biogenic (microfossils) the relative abundance of different microfossil species varies with the colour of the layers: variation in the diversity : abundance ratio suggests that during dark layer deposition, conditions in the upper water body were less favourable to some forms of planktic life dark layers are less bioturbated the total organic carbon content is higher in the dark layers the ratio of total organic carbon to sulphur is smaller in the dark layers [conditions at the sediment/water interface were less oxidizing during dark layer deposition] the strontium content of the carbonates is lower in the dark layers [the water in the photic zone was fresher during dark layer deposition]
Interpretation : during dark layer deposition the climate was warmer and more humid (perhaps more monsoonal) with increased run-off from the continents. This led to increased input of nutrients and enhanced bioproductivity, and so the bottom waters became more oxygen depleted. If, at these times, the winds were stronger, wind shear on the ocean surface would have facilitated ocean upwelling from intermediate level water masses, thereby replenishing nutrients in the surface waters and enhancing bioproductivity further. Counting the number of dark-light cycles over known (from the fossils) period of time, yields a cycle of 100-140 ka suggesting orbital forcing of the climate as the root cause. The deposition-rate ~ 3.7 µm/yr.
Model of the conditions during deposition of the light- and dark-weathering units within Les Sauzeries Basses Member. (Figure from Meyers, 2006.)
42 Stratigraphic context of Les Sauzeries Formation Les Sauzeries Formation was deposited at a time when deep ocean waters periodically became oxygen depleted worldwide. The principal trigger for these Oceanic Anoxic Events (OAEs) is thought to have been enhanced volcanism → increased levels of CO 2 in the atmosphere → atmospheric warming → increased continental weathering → enhanced supply of nutrients to the oceans → increased ocean bioproductivity (+ decreased solubility of oxygen with increasing temperature) → decreased o xygen supply to deep ocean → appearance of sulphides in bottom sediments → liberation of iron -sorbed phosphate from these sediments → increased nutrient supply to surface waters further enhancing bioproductivity. Once volcanism ceased, the weathering feedback helped to remove CO 2 from the atmosphere, thereby initiating cooling.
In the mid-Cretaceous, four particularly significant OAEs occurred:
OAE2, the Bonarelli event (Cenomanian/Turonian boundary, 93.9 Ma) OAE1d, the Breistoffer event (Late Albian, ~ 101 Ma) OAE1b, the Paquier event (Early Albian, ~ 111 Ma) * OAE1a, the Goguel / Selli event (Early Aptian, ~120 Ma)
The deformation within the mapping area makes it difficult to determine exactly where Les Sauzeries Formation lies within this sequence – a tentative correlation is shown left (LSB = Les Sauzeries Basses; LSH = Les Sauzeries Haute), which locates these units between OAE1a and OAE1b. OAE1a was coeval with enhanced volcanic activity in the Ontong-Java region and OAE1b with enhanced volcanic activity in the Kerguelen Plateau area.
* This places Les Sauzeries Formation at the top of the Aptian close to the Aptian/Albian boundary. The precise position of this boundary was only formally ratified in April 2016. Historically the * boundary has been defined with reference to ammonite biozones but the provincial nature of ammonites, together with uncertainties about the systematic description of key genera (particularly Acanthohoplites and Hypacanthoplites ), mean that recent attention has focused on using planktic foraminifera instead. For a discussion of the debate (illustrating the rigour that currently goes into defining geochronological units) see Kennedy et al. (2014) – among the places suggested as the GSSP for the boundary is the section near Tartonne (2-3 km north of the mapping area), although this was not ultimately selected.
The stratigraphic column shown above left comes from Friès & Parize (2003). Asterisks show the approximate positions of horizons rich in barite nodules. These horizons are laterally persistent across large parts of the Vocontian Basin. The nodules (which are quite spectacular) were formed early in diagenesis, just below the sediment-water interface, during times when sedimentation rates were very low (see Bréhéret & Brumsack, 2000).
43 For accounts of Acanthohoplites nolani see Bulot et al (2014), and for Hypacanthoplites jacobi and Leymeriella tardefurcata see Kennedy et al. (200 0, p.693 and p. 669 respectively).
The Aptian stage is named after the village of Apt in SE France. The French have divided it into three substages (indicated righ t) but these subdivisions are only locally applied – the internationally ratified geological timescale splits the Aptian into the Early Aptian and the Late Aptian with the boundary corresponding to the traditional boundary between the “Bedoulian” and “Gargasian”
44 Fossils in Les Sauzeries Formation Les Sauzeries Formation is rich in benthic and planktic foraminifera (microfossils). It also contains horizons rich in bivalves. However, the most obvious macrofossils are ammonites and belemnites.
In principle, it is possible to infer environmental conditions from ammonite morphotypes (e.g., Batt, 1993). The figures right (after Batt, 1989) show how Cretaceous ammonite morphotypes observed in mid-western U.S.A. correlate with where the ammonites lived
If ammonites such as 8, 14, 16, and 17 are the only ones present in a given unit, it could be because the water near the sea-floor was oxygen depleted at the time when the ammonites were living (see figure left). (From Benton & Harper, 2009, but derived from Batt, 1993)
45 The ammonites are preserved as external moulds (in the lighter units of Les Sauzeries Basses) and as pyritized objects (darker units of Les Sauzeries Formation). Many of the pyritized ammonites are internal moulds that show the morphology of the suture (junction between septa and shell wall) well. The external moulds and many other pyritized examples show the external ornamentation of the shell (ribs, tubercles, etc. ), which is particularly useful for field identification.
Key dimensions used for morphometric analysis and classification
Figures adapted from Arkell et al. (1957)
Parts of ammonites other than the shell may also be fossilized. These include rhyncolites, that is, parts of the ammonite upper jaw (typically sub-millimetre to over a centimetre in size), e.g., see Riegraf & Moosleitner (2010). Illustration of fossil rhyncolites from Buckland (1837); reconstructions of ammonite jaws from Saunders et al. (1978)
46 On this and the facing page, a selection of commonly encountered ammonites in the Aptian units of SE France is shown. Examples of most of these have been found on previous field courses, particularly in the exposures on the west side of the mapping area. Many additional figures of these ammonites are shown on- line (www.cephalopodes-cretaces.com/pages/ammonites/atlas-des-ammonites-de-l-aptien). Additional details and images are given by Kennedy et al. (2000) and by Joly & Delamette (2008).
47 Figure compiled primarily from www.cephalopodes-cretaces.com/pages/ammonites/atlas-des-ammonites-de-l-aptien (original work of Gérard Thomel) but with the images of Beudanticeras convergens and the three Hypacanthoplites species from Kennedy et al. (2000) and the images of Nolaniceras nolani from Bulot et al. (2014). Note that Costidiscus, Ptychoceras and Toxoceratoides (top line of this page) are heteromorph ammonites
48 Distinguishing ammonoids and nautiloids. Note that there are exceptions to the above distinctions
In the Early Cretaceous, different types of belemnite lived in different parts of the world. The belemnite population in the Vocontian Basin was dominated by the genera Hibolites , Mesohibolites , and Duvalia . However, Hibolites disappeared prior to the Aptian and Mesohibolites and Duvalia during the Early Aptian, and these were replaced by Neohibolites and, to a lesser extent, by Parahibolites . This turnover was part of a major worldwide turnover in marine flora and fauna that occurred in the early Aptian as increased sea-floor spreading and the associated major worldwide sea level rise → replacement of restricted marginal basins by more open oceans → spread of cosmopolitan species (see Mutterlose, 1998).
Belemnite identification is primarily based on guard shape (cylindrical, conical, hastate), the shape of the transverse section, and nature and length of grooves
The belemnites in the mapping area are predominantly sp ecies of Neohibolites
49 La Condamine Formation
Recall (p.12-13) that by the mid- Eocene, flexural subsidence on the southern margin of the European plate under the weight of the advancing Alpine thrust sheets led to a marine transgression. This transgression reached the Barrême area in the latest Eocene (Priabonian). La Condamine Formation was deposited in a warm water, shallow marine setting as that transgression arrived. Mediterranean palaeogeography in the Priabonian. Dark areas are land; black areas are places of evaporite formation (after Rögl, 1998)
Near the mapping area (at Taullane), in units equivalent to La Condamine Formation, several skeletons of dugongs (sea cows) have been discovered. The species has been named Halitherium taulannense (Sagne, 2001). It seems likely that the appearance of the now extinct megatooth shark ( Otodus ) which preyed on dugongs and whales, and of the early white sharks ( Carcharodon ) which preyed on seals, together with the rapid evolutionary diversification of these prey species are connected (see Diedrich, 2013). We have found a number of shark teeth within La Condamine Formation on previous field courses to Barrême.
Above: skeleton of Halitherium – this one from northern Germany (after Lepsius, 1881)
Right teeth from the early white shark, Carcharodon auriculatus (after Diedrich, 2013)
50 Nummulites and other large benthic forminifera A diagnostic feature of La Condamine Formation is the presence of large benthic foraminifera, and most particularly those belonging to genera Nummulites , Amphigestina , Operculina , and Discocyclina . Foraminifera are single celled organisms that live either on the sea floor (benthic) or in the marine water column (plankton). Their soft tissue (protoplasm) is largely enclosed within a shell (test). The four genera named above belong to the Suborder Rotaliina which is subdivided primarily on the basis of the wall structure of the test. Foraminifera have a geological range from the early Cambrian to Recent. Large foraminifera have arisen from ordinary sized ancestors many times in the geological record, and at such times their rapid diversification and extinction makes them excellent zone fossils. Their appearance usually correlates with periods when nutrient recycling to surface waters was much reduced, that is, during periods of global warming, raised sea levels, and reduced oceanic circulation. The early Cenozoic was such a time, and in the Eocene the larger foraminifera became sufficiently abundant to become major sediment producers on the inner to mid parts of carbonate ramps. The factors that influence the morphology and distribution of the larger benthic foraminifera are only partially understood (see Beavington-Penny & Racey, 2004). However, the following interrelated factors contribute: light intensity at the sea bed, nature of the substrate, water turbidity, wa ter energy, temperature, and salinity. These combine to make large benthic foraminifera helpful indicators of water depth.
Shallow water (high light intensity, high levels of nutrients) – smaller, globular, thick-shelled foraminifera Deeper water (lower light intensity, fewer nutrients) – larger, flat, thin-shelled foraminifera Under favourable environmental conditions, foraminifera mature quickly and reproduce at small sizes (individuals are small) but when stressed by low light or low levels of nutrients, they grow more slowly and mature at large sizes (individuals large) When conditions are adequate for growth but not for reproduction ( e.g. , if a shallow-dwelling species is washed into deeper water), individuals may grow to giant size .
Illustrations (not all to the same scale) of the most commonly found large benthic foraminiferids in the Calcaires Nummulitiques (La Condamine Formation). Of these, Nummulites is by far the most common. Nummulites and Amphistegina lived in shallower water than Operculina and Discocyclina.
Nummulites is widely used in correlating Eocene rocks. The genus has a geological range of Late Palaeocene to Mid-Oligocene but nummulitid descendants are still found today in the Indo-Pacific Oceans
51 Left: two different forms of Nummulites – the A-form which is smaller, has fewer whorls, and has a large first chamber (megalosphere), and the B-form which is larger, has more whorls and has a small first chamber (microsphere). Right: patterns of imbrication that are commonly found in accumulations of Nummulites. (Figures from Racey, 2001)
Large accumulations of Nummulites are particularly common as shallow marine banks and shoals in shelf margin and carbonate ramp settings around the Tethys Ocean during the Eocene. These accumulations contain few associated micro- or macrofauna, and this has been used to suggest that deposition took place in a nutrient-poor environment and/or in an environment with significant hydrodynamic sorting. Nummulites has alternating asexual and sexual generations resulting in, respectively, small A-forms and larger B-forms (see diagram above). In Nummulites accumulations, the B-forms tend to dominate in the highest energy, bank crest locations, while the A-forms are found in the deeper water, bank flank locations. This distribution is controlled by current sorting. The extent to which these sorting processes have been active may be deduced by establishing the extent to which the tests are abraded; information on the nature (tidal, unidirectional) and energy of the currents is given by the sedimentary fabric of the deposits.
Scaphopods Benthic foraminifera have a high probability of being ingested by organisms that browse on the sea floor, e.g. , worms, crustaceans, gastropods, echinoderms, and fish. One such organism, which is usually quite rare to find as a fossil but which is quite common in the muddy units of La Condamine Formation, is the scaphopod. Scaphopods are molluscs with a tubular shell. Water currents pass in an out via the narrow posterior end, while at the anterior end the creature uses ciliated tentacles to collect detritus and small organisms from the sediment. Scaphopods spend most of their lives buried just below the sediment surface.
Left: the mode of life of a scaphopod. Right: the Eocene scaphopod, Dentalium
52 Bivalves and gastropods The muddy intervals of La Condamine Formation are very rich in bivalves and gastropods. On this field course, we are interested in these body fossils primarily because of what they can tell us about the depositional environments. In this respect, inferences of mode of life from shell morphology are significant. Gastropods show considerable diversity of form, and it is difficult to relate given morphotypes to particular life modes. However, gastropods are usually benthic (although pelagic and terrestrial forms exist). Those occupying high-energy environments have thick shells and are commonly cap-shaped or low-spired. Those with entire apertures are often herbivores ( Natica – example P below – is an exception) and live on hard substrates; those with marked siphonal canals ( e.g. , examples C, E, and Q on the diagram below) are usually carnivores and are generally found on soft substrates. Bivalves are also morphologically diverse but in this case, morphotypes can be much more clearly linked to their mode of life (see diagram facing).
A range of gastropod morphotypes: A=convolute; B=sinistral; C=fusiform; D=patelliform; E=digitate; F=turriculate; G=coeloconoid; H=pupiform; I=cyrtoconoid; J=trochiform; K=involute; L=isotrophic; M=irregularly coiled; N=turbiniform; O=discoidal and sinistral; P=naticiform; Q=biconical. Figure compiled from various sources.
53 Correlation of bivalve morphotype with mode of life (from Benton & Harper, 2009)
Key features to note when encountering body fossils in the field
A. Distribution of the fossils in the sediment 1. Fossils in life position Fossils constituting a reef: describe the growth form of colonial fossils, identify framework fossils Non-reef: are the fossils epifaunal (if so, do they have a preferred orientation reflecting currents) or infaunal (if so, is there evidence for how the organism died, e.g. , by smothering)? 2. Fossils not in life position Concentrated in lenses, concentrated particular horizons, evenly distributed through unit? Effect of transport: whole or fragmented? Delicate structures preserved? Degree of rounding? Depositional fabric: imbrication? Nature and amount of any matrix present Burial: are the fossils bored or encrusted? Relationship to bioturbation within the unit?
B. Fossil assemblage and diversity 1. Assemblage composition: estimate relative abundance of different fossil types 2. Fossil size range: for each type of fossil, note size range 3. Any lateral or up-stratigraphy variations in assemblage composition / fossil size range? 4. Life environment: do the fossil types present all tell a similar environmental story? Are certain fossil groups conspicuous by their absence?
C. Diagenesis 1. Preservation: is the original mineralogy preserved or has it been replaced? Are the fossils moulds? Do the fossils occur preferentially in nodules? 2. Deformation: are the fossils full-bodied or have they be compacted or tectonically deformed? Within La Condamine Formation there are muddy intervals that are rich in macrofossils. These are 54 indicative of a shallow marine environment. Fossils that have been identified include (Gaillard et al. , 2013):
bivalves ( Arctica plana , Chlamys biarritzensis , Cordiopsis incrassata , Glossus subtransversus , Lentipecten corneus , Panopea allonsensis , Pycnodonte gigantea , Venericardia astieri, and numerous other taxa) gastropods ( Athleta , Calyptraea , Tibia , Turritella ) scaphopods ( Dentalium castellanensis ) brachiopods ( Terebratulina ) bryozoans ( Cellepora ) echinoids ( Echinolampas , Schizaster ) solitary corals crustaceans ( Coeloma vigil ) fishes (mainly represented by shark teeth) plant remains (wood fragments)
Illustrations of the bivalves and gastropods (and the brachiopod) are shown here. The echinoids are both ‘heart urchins’ and the crustacean is a crab.
55 (Figures primarily taken from British Museum (Natural History), 1975b)
56 Trace fossils Trace fossils are present in all of the mapping units but parts of La Condamine Formation are particularly rich in identifiable ones. Trace fossils provide strong constraints on depositional environment and water depth, rates and styles of deposition, and the nature of any limiting stress factors (oxygen abundance, salinity). Consequently, it is particularly important to describe them when they are encountered in the field. The main groups of trace fossils are:
locomotion tracks and trails resting traces grazing trails made by detritus feeders or algal grazers at or just below the sediment surface feeding burrows made by detritus feeders farming structures (regularly patterned burrow systems) dwelling burrows and borings escape/adjustment structures arising as a consequence of substrate degradation or aggradation predation traces (mostly borings into hard biological materials such as shells)
From a sedimentological perspective trace fossils are usefully classified into groups of traces that each reflect a particular community of organisms – as the community changes ( e.g. , with water depth), so the particular grouping of trace fossils changes. The ten ichnofacies illustrated on the next two pages is the most widely used classification of this kind. Note that some trace fossils appear in more than one ichnofacies.
Different trace fossils (T) and body fossils (B) as a function of the substrate firmness. A=Nucula (B); B=Chondrites (T); C=Ophiomorpha (T); D=Echinocardium (T); E=Arctica (B); F=Thalassinoides (T); G=Spongeliomorpha (T); H=Petricola (B); I=Lithophaga (B); J=crinoid holdfast (T); K=Oyster (B); L=Trypanites (T); M=encrusting bryozoa and serpulids on cemented burrow wall (B,T). The ones in bold you will see in the mapping area. (Figure from Taylor et al., 2003) Bivalve = Lithophaga ; trace fossil = Gastrochaenolites
57 Trace fossil tiering: organisms occupy different depths in the sediment (left) and so one may expect the types of trace fossil to vary upwards towards the sediment-water interface (right A). The organisms adjust their position as sediment builds up (right B=continuous aggradation; right C=discontinuous aggradation). If there is a sudden change in ichnofacies (right D), a break in sedimentation and change of environment is implied. Alternatively, a gradual improving of conditions (increasing oxygenation, right E) or deterioration of conditions (decreasing oxygenation, right F) may be inferred from gradual changes in the trace fossil assemblage. (Figures from Taylor et al., 2003) An excellent introductory test on trace fossils and their interpretation is Bromley (1996).
Key features to note when describing trace fossils in the field
A. Essential characterization 1. Identify the trace fossil 2. Measure its size (width / diameter / length as appropriate) 3. Note the sedimentary context: grain size and composition, sedimentary structures / texture, presence or absence of a palaeosurface
B. For trails and tracks 1. Describe the trail pattern (regular/irregular, straight/sinuous/curved/coiled/meandering/radial) 2. Describe the trail itself (continuous ridge or furrow, appendage marks, tail marks)
C. For burrows 1. Describe the shape and orientation with respect to bedding (horizontal, subvertical, vertical, simple straight tube, simply curved, irregularly disposed tube, U-tube, branching) 2. Describe the burrow wall: lined with mud or pellets? Scratch marks? Are the laminae in the adjacent sediment deflected by the burrow? 3. Describe the burrow fill: is it compositionally or texturally different from the adjacent sediment? Is the fill pelleted? Are there curved back-fill laminae? Has the fill been mineralized 4. Look for spreite (curved laminae associated with U-shaped burrows)
D. Up-stratigraphy arrangement (tiering) 1. Describe the stacking arrangement of trace fossils with a view to constraining the position of the sediment-water interface, and whether any environmental changes up-stratigraphy were gradual or sudden
58 59 Trace fossil assemblages (ichnofacies) related to environment. (Figures from Collinson et al., 2006)
60 Facies descriptions as a rigorous basis for interpretation The various attributes of a sedimentary rock (composition, texture, sedimentary structures) combine to define a facies. Grouping observations together to define a facies is carried out so that the facies becomes the product of a particular sedimentary environment or of a process within that environment. Defining these interpretative building blocks is the key skill that is required when attempting to establish a robust interpretation of a mapping unit as a whole. The June 2020 field course will focus on this skill. However, as an example, five of the facies defined by Sinclair et al. (1998) in their study of the Eocene nummulitic limestones of the western Alps are outlined below. Their interpretation of each facies is given in square brackets:
A. Peloidal limestone: coarsening upward cycles of sand grade, cross-bedded peloidal grainstones and peloidal- foraminiferal grainstones, with local peloidal wackestones and skeletal mudstones; peloids are mostly micritized skeletal fragments. In the cross-bedded units, foraminifera and echinoid plates lie flat along the foresets. Bioclasts include Nummulites , miliolids, echinoid fragments, and serpulid worm tubes. [The peloidal nature of sediments, sparse biota, lack of carbonate mud except locally, and presence of cross bedding → scattered shoals on inner ramp above fair weather wave base; cross-bedded peloidal grainstones on shoals; peloidal-foraminiferal grainstones on more protected shoal flanks; wackestones and mudstones in back-shoal and inter-shoal settings; coarsening upward trend reflects progradation or lateral migration of the shoal bank]
B. Nummulites limestone: monospecific accumulations of Nummulites occurring as winnowed packstones and packstone-grainstones. Other bioclasts include Amphistegina , echinoids and bivalves. Foraminifera sometimes imbricated. Beds are massive with locally erosive bases and crude, large scale cross bedding. Unit passes upwards into miliolid grainstones, skeletal mudstones and foraminiferal mudstones. [Nummulite banks on inner ramp; currents sufficient to concentrate bioclasts but insufficient to abrade them or remove all of the lime mud; lack of abrasion suggests winnowed in situ by oscillatory currents; cross-beds and local grainstones imply local higher energy conditions; wackestones and mudstones are inter-shoal areas]
C. Foraminiferal limestone: intensely bioturbated wackestones and mudstones, with local packstones (with scoured bases) characterized by a diverse foraminifera assemblage ( Nummulites + Amphistegina OR Discocyclina + Operculina ). Other bioclasts include echinoid and bivalve fragments [low energy conditions on mid-ramp, the variation in foraminifera reflecting the variable water depths that occur in mid-ramp settings – Nummulites and Amphistegina → shallower water than Discocyclina and Operculina . Local packstones → storm reworking.]
D. Lime mudstone: mudstones and marls with planktic foraminifera and low diversity, flat, benthic foraminifera (Discocyclina , Operculina ) and bivalves. Locally, well burrowed [Plankt ic foraminifera → relatively deep water (outer ramp)]
E. Arenaceous limestone: quartz wackestones and quartz grainstones with abundant detrital quartz, lithic grains and glauconite. Cross lamination, cross bedding, planar lamination. Bioclasts of Amphistegina . [Bioclasts and glauconite → marine but quartz indicates a persistent terrigenous influx; sandy shoreface]
To build up a model of how these facies are interrelated, it is essential establish how they stack, that is, to draw up a measured section through the unit. Indeed facies are generally defined as one compiles a measured section because the stacking pattern may be a part of the definition of a particular facies. An example of a measured section from La Condamine Formation in the mapping area (below le Château) is shown on p.62. Note that the facies on this section are defined differently to the five above (and in more detail) because only a part of La Condamine Formation was measured. Note also that the facies on this measured section have not been fully interpreted.
61 Reconstruction of the depositional environments of the Poudingues d’Argens / Infranummulitic Formations (onshore units that are not seen in the mapping area) and La Condamine Formation (off-shore units) – a wave-dominated carbonate ramp. (Figure from Sinclair et al., 1998)
The model that Sinclair et al. (1998) developed to show how their facies are interrelated is illustrated above. Note that this diagram includes extra non-marine facies for units immediately underlying La Condamine Formation (including the Poudingues d’Argens) which are not exposed in our mapping area . They located the five facies described above in the upper to mid part of a carbonate ramp. They identified a number of shallowing upwards cycles reflecting progradation and aggradation of near shore facies, but ultimately the ramp was drowned – the units pass into deeper water mudstones (our Tartonne Formation).
62 Measured section of part of La Condamine Formation (under le Château). Note that the four facies defined here (A, B,
C, D) have been subdivided (e.g., C 1, C 2, etc.), that is, they are actually facies associations with the subdivisions being the facies. The facies descriptions need to be written up properly, and perhaps the Dunham limestone classification scheme (see p.27) could have been used profitably.
63 Tartonne Formation
There is a shortage of unweathered / unvegetated exposures of the Tartonne Formation within accessible parts of the mapping area. The best section is in the inaccessible cliffs under le Château, and so a good field sketch of those cliffs, showing the variatio n within the formation ( e.g. , the two relatively resistant units exposed in the cliffs), is essential for compilation of your stratigraphic column. Where the formation can be inspected, it is seen to be composed predominantly of grey, calcareous, silty mudstones. In the literature, the formation is noted as consisting of 50% calcite and that the clay minerals are predominantly montmorillonite with subordinate illite and kaolinite. The transition from La Condamine Formation is abrupt. The formation is rather monotonous, apart from the package of two more resistant units noted above. These more resistant units are heavily bioturbated and locally rich in nummulites, and have been reported to contain diagenetic glauconite. In the other parts of the formation the fossil content is dominated by microfossils – pelagic foraminifera ( Globigerina ) with calcareous nannoplankton appearing in the upper parts of the formation. Both the foraminifera and the calcareous nannofossils may be used to date the formation biostratigraphically to the Rupelian (see Artoni & Meckel, 1998; Joseph et al ., 2012). The foraminiferal assemblages indicate progressively increasing water depths up-stratigraphy. Biozones are missing at the level where the nummulite-rich units occur suggesting that this part of the formation is a condensed sequence. Above this condensed sequence, deposition of the mudstones was from suspension, initially on the mid ramp during fair-weather or post-storm conditions, and then subsequently on the outer ramp below the storm wave base.
Globigerina is a planktic foraminifer. The calcareous plates (coccoliths) around a coccolithophore are an example of a calcareous nannofossil. Nannofossils are usually smaller than 30 µm although, in practice, the upper size limit is taken as a fossil that will pass through a 63 µm sieve. Calcareous nannofossils include the calcareous parts from a diverse range of organisms. (Figures from Black, 1988)
64 Bussière d’Entouart Formation
Bouma sequences Care ful inspection of the sandier parts of the Bussière d’Entouart Formation shows that it is composed of fine-grained sandstones with erosive bases, that fine upward over a few centimetres into very fine-grained sandstones that are rippled, and which, in turn, are capped by laminated siltstones that drape over the ripples. These fining upward packages were formed in discrete depositional events, as sediment-charged flows, moving down the basin slope, deposited sediment of progressively finer grain size as the flow waned. Gravity-driven, turbulent mixtures of sediment temporarily suspended in water are described as turbidity currents; the exact sequence of sedimentary structures produced depends on the density of the mixture. The sequences observed in the Bussière d’Entouart Formation are Bouma sequences produced by low to medium density turbidity currents (for other sequences, see Stow, 2005, p.60).
Right: a turbidity current (after Nichols, 2009). Below: a Bouma sequence (after Collinson et al., 2006)
65 The relationship between water velocity and the transport of loose grains. Note that it is easier to move a grain in suspension than one that has previously been deposited. Note also that once deposited it is more difficult to move mud sized particles than fine sands (from Nichols, 2009, p.48)
Stability fields for subaqueous bedforms showing the influence of flow velocity and sediment particle size on the bedforms that develop. In a waning turbidity current one might expect a sequence of bedforms developed along a path from large grain size / high flow velocity to small grain size / low flow velocity. (Figure adapted from Stow, 2005, p.59)
66 During deposition of the B ussière d’Entouart Formation , the turbidity currents entered a basin containing a soft muddy substrate. Mud-sized sediment is cohesive and behaves as a deformable fluid at high water content and as a firm bed at low water content, that is, there is a range of soft sediment deformation structures that can arise from the interaction between the substrate and the base of the turbidity current.
Schematic diagram showing the flow-bed interactions for experimentally produced kaolin-rich turbidity currents flowing over a kaolin bed (adapted from Verhagen et al ., 2013)
Down flow path variation in depositional sequences for a turbidity current that penetrates the muddy substrate over which it is flowing (after Baas et al., 2014)
67 A detailed measured section of part of the Bussière d’Entouart Formation . Note that the division into facies and their interpretation is incomplete – the figure is shown as an example of what can be done
68 Palaeocurrent indicators The sandstones within the Bussière d’Entouart Formation contain good indicators of the palaeocurrent directions:
Sole marks (scours and tool marks) on the erosive bases of the fining upward packages. These mostly give only line-of-flow but some scours ( e.g. , flutes) can indicate the direction-of-flow Parting lineations which give only the line-of-flow Ripples near the tops of the fining upward packages. For straight-crested ripples the line-of-flow is at right angles to the crest and the direction-of-flow can be inferred if the ripple is asymmetric. Note, however, that many of the ripples in the Bussière d’Entouart Formation are not straight -crested.
These three palaeocurrent indicators need not give the same palaeocurrent direction if they have formed in different hydrodynamic settings ( e.g. , sole marks generated during the initial influx of sediment compared to ripples generated by subsequent wave reworking of that sediment).
Above: the distinction between scour marks (which are formed by flow turbulence) and tool marks (which are formed by objects transported at the base of the flow). (Figure from Nichols, 2009)
Left: the geometry of ripples and sedimentary features of similar form . Don’t forget to measure the wavelength and height of the ripples because these dimensions contain information about how the ripples were formed. (Figure from Stow, 2005)
69 Palaeocurrent indicators are lineations – measure them as plunge/plunge direction and note (if you can tell) whether the flow direction is up-plunge or down-plunge. Also measure bedding. To establish the palaeocurrent direction when the sediments were being deposited / reworked, it is necessary to restore bedding to horizontal. This can be done using a stereonet. If you want to know how to do this, ask one of the staff. In the Bussière d’Entouart Formation, the orientations are such that restoring the bedding to horizontal makes little difference, that is, the line-of-flow of the palaeocurrent is appoximately parallel to the measured plunge direction. However, this is not generally the case. The method of evaluating the mean and variance of several palaeocurrent direction measurements will be described in EART20121 ( Sediment Transport and Depositional Environments ) and on the June 2017 field course. Results from a few measurements in the Bussière d’Entouart Formation are shown left. The palaeocurrent direction is consistently to the north. Examination of the accessory mineral assemblage within the formation shows it to contain zircon, apatite, staurolite, kyanite, tourmaline, and garnet, with accompanying volcaniclastic apatite, titanite, biotite, augite and hornblende (see Evans & Mange-Rajetzky, 1991; Evans et al. , 2004).
These accessory minerals are consistent with the provenance for t he Bussière d’Entouart sandstones being the Permo- Triassic cover rocks of the Maures-Esterel Massif to the south. The volcanic grains are understood to be airborne products of explosive andesitic volcanoes that were active at the time of deposition.
Palae ogeographic map of the region when the Bussière d’Entouart Formation was being deposited (from Joseph & Lomas, 2004)
70 A measured section through the whole of the Bussière d’Entouart Formation as exposed on the D219 road (after Joseph et al., 2012). Note the change in palaeocurrent directions up-stratigraphy. HCS=hummocky cross stratification.
71 Up-stratigraphy and lateral variations in the formation It is clear on the D219 road section, that the relative proportion of sandstones and mudstones varies up- stratigraphy through the Bussière d’Entouart F ormation. Undoubtedly this is also true laterally. A measured section through the formation may be compiled to demonstrate this (see facing page). In the depositional setting for the Bussière d’Entouart Formation, the simplest explanation for these variations is avulsion of the channels along which the sand was brought into the basin. As the channels avulsed, the location represented by the D219 section would have been at one time close to the path of delivery (sandstone-rich intervals), and at another time well away from the path of delivery (mudstone-rich intervals).
Illustration of the idea of channel avulsion as the origin of sandstone-rich and mudstone-rich intervals within the Bussière d’Entouart Formation . (Diagram from Nichols, 2009)
Comment on trace fossils It should be noted that trace fossils are common in the Bussière d’Entouart Formation and can be used to refine the environmental interpretation (see Phillips et al. , 2011). The most common trace fossil is a deep water ( Nereites ichnofacies) variant of Ophiomorpha , which appears as vertical shafts but more commonly as horizontal tunnels on the soles of turbidite sandstones. Look for pelleted or lined burrows.
Les Clapiers Formation
Above the Bussière d’Entouart Formation there is a return to a dominantly mudstone sequence. According to the literature, the lower part of the unit contains planktic foraminifera and calcareous nannoplankton but by 40 m above the base of the formation, the planktic foraminifera disappear leaving only the calcareous nannoplankton.
72 La Poste Formation / Le Château Formation
We have divided La Poste Formation into two members: a dominantly conglomeratic package (Laubre Member) and a package of interbedded sandstones and mudstones (L’Asse Member). In actual fact , when the mapping area is extended south-west of the D219, it is clear that there are several mappable mudstone, conglomeratic, and interbedded sandstone/mudstone intervals. Consequently, had the mapping area been larger, La Poste Formation would have been subdivided into several members, not just two, and perhaps Les Clapiers Formation would have been designated as a mudstone member within this formation.
The location of the units within the mapping area on a ‘more complete’ stratigraphic column, covering the interval above Les Clapiers Formation and below Le Château Formation, is shown on the diagram left. Note that the conglomerates exposed near the 850 m contour just NE of where the coach parks each day, and the conglomerates exposed on the road by la Lèche, are two different packages of conglomerates, and that both are different to the Laubre Member conglomerates exposed on the D219. Since your mapping area is not large enough to demonstrate these differences, and even if it were, distinguishing the conglomerates would be too challenging a task for an introductory mapping exercise, we will map these conglomerates as the same unit. However, this should not stop you from making careful unit descriptions (including clast size, clast composition, etc. ) at each exposure to determine if the conglomerates could be distinguished in those terms.
Measured section through the Conglomérats de Clumanc (after Joseph et al., 2012). Correlations of the units seen within the mapping area with this section are from the map of SC-C, which has some minor differences to the work of Joseph et al.
73 Depositional setting The conglomeratic units of La Poste Formation comprise a set of amalgamated channels. They contain large boulders, often of fragile material (locally derived mudstones), suggesting short transport paths and nearby areas of relief. The grain size grading and sequences of sedimentary structures within the interbedded sandstone/mudstone units are distinctly turbiditic. In some units there is evidence for subaerial emergence (mudcracks), and the abundance of plant remains also suggests that land was nearby. Within the mudstone units that crop out immediately to the south-west of the mapping area, the lack of bioturbation suggests an intense sedimentary flux. Taken together, these observations have been interpreted as indicating that the units of La Poste Formation comprise parts of a submarine alluvial fan delta.
Two field sketches of the Laubre Member showing the internal structure within the conglomerates. Left – from the forbidden field looking ESE; below – from near the quarry above Laubre looking S.
The lateral accretion surfaces suggest that the unit prograded from the NNW to the SSE. Furrows on the base of the unit support this. Flutes and ripples in L’Asse M ember are oriented more E-W.
Depositional model for the Conglomérats de Clumanc. The different shading intensities indicate different conglomerate packages (after Joseph et al., 2012)
74 Clast composition, size, and shape Within the conglomerates of La Poste formation, the dominant clast types are carbonate mudstones of Jurassic and Cenomanian age derived from the same units that currently underlie the basin. In addition, there are clasts derive d from the Poudingues d’Argens and mudstone boulders derived from the Tartonne Formation, indicating that at least part of the basin had been uplifted and eroded by the time that La Poste Formation was being deposited. In some of the conglomerates there are intraformational sandstone clasts. However, of particular interest is the observation that the unit records the first appearance in the Barrême Basin of exotic clasts derived from internal parts of the Alpine orogenic belt (Evans & Mange-Rajetzky, 1991; Morag et al. , 2008; Schwarz et al ., 2012). These include serpentinites, dolerites, gabbros, migmatites, various granitoids, andesites, rhyolites, metamorphic quartzites, blueschists, and Jurassic radiolarites.
A clast analysis from an exposure of the Laubre Member located just outside the mapping area (at Champ Richard). Note how transforming clast size into phi units makes the class size distribution Gaussian. A simple test of whether the distribution really is Gaussian is made by plotting the data as cu mulative frequency on ‘probability’ paper – if the distribution is Gaussian it should plot as a straight line (as here) and descriptions of the distribution (mean, standard deviation, etc.) can be determined from particular phi values read off the graph.
75 The reversal of polarity of the dominant sediment transport directions in the Barrême Basin, from south to north (Bussière d’Entouart Formation) , to north to south (La Poste Formation), together with the influx of clasts derived from the internal zones of the Alps, has been linked to the emplacement of the Embrunais- Ubaye nappes and the overthrusting of the Penninic thrust front within the Alpine orogenic belt. This led to a modification of the topography of the Barrême Basin, involving uplift to the north and east of the basin, and to a southward migration of the depocentre.
SW-NE cross sections extending into the Alpine orogenic belt, showing the emplacement of Embrunais-Ubaye nappes and their emergence as a source of sediments for the units within the Barrême Basin. (Top two figures after Schwartz et al., 2012; bottom figure (the present day section) after Morag et al., 2008)
76 Pebble imbrication Do not forget the possibility of using clast imbrication as a palaeocurrent indicator.
Figure from Nichols (2009)
L’Asse Member
Field sketch of the up- stratigraphy variation in L’Asse Member, as exposed on the D219 road
Le Château Formation At le Château, Le Château Formation unconformably overlies folded Tartonne Formation. The underlying conglomerates are folded (as you will see at le Lèche). Clearly, therefore, the Barrême synform began tightening during/after the deposition of La Poste Formation but before the deposition of Le Château Formation. But is Le Château Formation also folded, that is, was it deposited while folding was still going on? The answer to this is not clear, although several authors (notably by Evans & Elliott, 1999) have asserted that it is.
A diagram showing the changing depositional environments north to south along the Barrême Basin at the time that La Poste and Le Château formations were being deposited. Note that there is a possibility that Le Château Formation was deposited subaerially. (Figure from Grosjean et al., 2012) 77 Measured section (thickness scale is in cm) through part of L’Asse Member (approximately corresponding to the middle of the three intervals shown on the field sketch facing). Compare with the 1:1 section in the Bussière d’Entouart Formation 78 Quaternary
Surface process mapping units The following surface processes may be distinguished when producing a surface process map in the area around le Château:
Bedrock : exposure good enough to obtain a bedding reading Weathered, thinly vegetated bedrock : in situ bedrock covered in thin soil and/or grassy vegetation Slope wash : weathering products slightly remobilized by rain (weathered/partly vegetated mudstone) Unconfined debris flows : gravity driven rock falls/scree which may be vegetated (steep angle of rest) Channelized debris flows : fluidized clast flows without much matrix Mass flows : more coherent slips (landslides) and matrix-controlled, unconstrained flows – large clasts carried along in fluidized mud (shallow angle of rest) Terrace / knick-point (highlight edge) Vegetated flood plain : flood reworked river and overbank deposits Active channel (dashed for seasonally dry channels)
In terms of deposits, we have alluvium (fluvial deposits), colluvium (hillslope deposits), and bedrock.
Tentative knick points (at latitude of les Roux) Q8 = modern river channel (~ 2 m of incision relative to Q7) Q7 = current flood plain (~ 840 m at the bridge over the Asse de Clumanc) Q6 ~ 850 m (Le Puy) Q5 ~ 900 m on the antiform ridge Q4 ~ 960 m Q3 ~ 1000 m Q2 ~ 1060 m Q1 ~ 1130 m Note that conventionally, terrace levels are numbered with the currently active channel being the highest number. This requires you to have identified all the terraces before you define your number system!
79 APPENDIX
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Tectonics 27, article TC2004 Mutterlose J, 1998, The Barremian-Aptian turnover of biota in northwestern Europe: evidence from belemnites. Palaeogeography, Palaeoclimatology, Palaeoecology 144: 161-173 Nichols G, 2009, Sedimentology and Stratigraphy (2nd edition), Wiley-Blackwell Phillips C, McIlroy D, Elliott T, 2011, Ichnological characterization of Eocene/Oligocene turbidites from the Grès d’Annot Ba sin, French Alps, SE France. Palaeogeography, Palaeoclimatology, Palaeoecology 300: 67-83 Racey A, 2001, A review of Eocene nummulite accumulations: structure, formation and reservoir potential. Journal of Petroleum Geology 24: 79-100 Riegraf W, Moosleitner G, 2010, Barremian rhyncolites (Lower Cretaceous Ammonoidea: calcified upper jaws) from the Serre de Bleyton (Départment Drôme, SE France). Annalen des Naturhistorischen Museums in Wien 112A: 627-658 Rögl F, 1998, Palaeogeographic considerations for the Mediterranean and Paratethys seaways (Oligocene to Miocene). Annalen des Naturhistorischen Museums in Wien 99A: 279-310 Sagne C, 2001, Halitherium taulannense , nouveau sirénien (Sirenia, Mammalia) de l’Éocène supérieur provenant du domaine Nord - Téthysien (Alpes-de-Haute-Provence, France). Comptes Rendus de l’Académie des Sciences, Paris, Sciences de la Terre et des Planètes 333: 471-476 Saunders WB, Spinosa C, Teichert C, Banks RC, 1978, The jaw apparatus of recent Nautilus and its palaeontological implications. Palaeontology 21: 129-141 Schwartz S, Guillot S, Tricart P, Bernet M, Jourdan S, Dumont T, Montagnac G, 2012, Source tracing of detrital serpentinite in the Oligocene molasses deposits from the western Alps (Barrême basin): implications for relief formation in the internal zone. Geological Magazine 149: 841-856 Sinclair HD, 1997, Tectonostratigraphic model for underfilled peripheral foreland basins: an Alpine perspective. Geological Society of America Bulletin 109: 324-346 Sinclair HD, Sayer ZR, Tucker ME, 1998, Carbonate sedimentation during early foreland basin subsidence: the Eocene succession of the French Alps. Geological Society, London, Special Publications 149: 205-227 Stampfli GM, Borel GD, 2002, A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored synthetic oceanic isochrons. Earth and Planetary Science Letters 196: 17-33 Stampfli GM, Mosar J, Marquer D, Marchant R, Baudin T, Borel G, 1998, Subduction and obduction processes in the Alps. Tectonophysics 296: 159-204 Stow DAV, 2005, Sedimentary Rocks in the Field: A Colour Guide , Manson Publishing Taylor A, Goldring R, Gowland S, 2003, Analysis and application of ichnofabrics. Earth Science Reviews 60: 227-259 Theler D, Reynard E, Bardou E, 2008, Assessing sediment dynamics from geomorphological maps: Bruchi torrential system, Swiss Alps. Journal of Maps 4: 277-289 Tribovillard N-P, Cotillion P, 1989, Relationships between climatically influenced sedimentation and salt diapirism in the French western Alps based on evidence from organic and inorganic geochemistry. Palaeogeography, Palaeoclimatology, Palaeoecology 71: 271-280 Twiss RJ, Moores EM, 2007, Structural Geology (2 nd edition), WH Freeman & Co Verhagen ITE, Baas JH, Jacinto RS, McCaffrey WD, Davies AG, 2013, A first classification scheme of flow-bed interaction for clay-laden density currents and soft substrates. Ocean Dynamics 63: 385-397
82 Health and Safety / Behaviour
Nationally agreed Code of Safety and Behaviour (relevant parts for this course)
To: All students attending a geological field course It is important that we know if you have any medical condition which may influence your work, e.g ., diabetes, epilepsy , a physical problem, so that appropriate action can be taken should you be affected while on a field course. You should therefore have indicated any such condition on the form asking for medical details that you were given prior to the field course. This will be kept by the field course leader. All information will be treated with strict confidence. If for any reason you are prevented from attending a prescribed field course, or have to withdraw during the course, please inform the course leader at the earliest opportunity. If the reasons are medical, you will be expected to produce a doctor’ s certificate as part of an application for mitigating circumstances.
I. General Geological fieldwork is an activity involving some inherent special risks and hazards, e.g ., exploring coast exposures, quarries, and mountains. Severe or dangerous weather conditions may also be encountered at any season, especially on mountains or the coast. In accordance with the Health and Safety at Work Act, leaders will have been advised by the School to take certain safety precautions and every reasonable care concerning the safety of members of their parties. It is imperative that students should cooperate by behaving reasonably in order to reduce the risk of accidents . Each individual is responsible for his or her own safety.
II. Specifically, you must: 1. Observe all safety instructions given by party leaders or field advisers. Anyone not conforming to the standards required may be dismissed from the field course (with financial and examination liabilities as a result). 2. Stay with the party, except by clear arrangement with the leaders. Assemble where requested in order to receive specific instructions regarding likely hazards. Observe instructions for reporting back after completion of work. 3. Report any injury or illness as soon as possible. 4. Carry identification of yourself and the School.
III. Equipment Note: leaders are advised by the School to refuse to allow ill-equipped students on their field courses. 1. Wear adequate clothing and footwear for the type of weather and terrain likely to be encountered. Walking boots with rubber mountaineering soles are normally essential. Sports shoes/trainers, etc. , are unsuitable for mountains, quarries or rough/wet country. 2. Always wear a safety helmet, preferably with chin strap, where there is a risk from falling objects. 3. You must wear a high visibility jacket when working on road sections – this is a legal requirement in most European countries. 4. Wear safety goggles when hammering rocks or using chisels. Do not use a geological hammer as a chisel by hitting it with another hammer; use only a soft steel chisel, preferably with a plastic guard. Avoid hammering near another person. Avoid looking towards another person hammering. 5. Carry at all times a survival bag, emergency food supplies, whistle, small first aid kit.
IV. Behaviour 1. Be aware of traffic when examining road cuttings. While there, avoid hammering, and in any event do not leave rock debris on the roadway or verges. 2. Do not climb cliffs, rock faces or crags unless this has been approved in writing as an essential part of the work. 3. Take special care near the edges of cliffs and quarries, or any other steep or sheer faces, particularly in gusting winds.
83 4. Ensure that the rocks above are safe before venturing below. Avoid working under steep overhangs. Avoid loosening rocks on steep slopes and never roll rocks down slope for amusement. Beware of landslides and mudflows occurring on clay cliffs and in clay pits, or rockfalls from any cliffs. Leaders of parties will follow the general guidance contained in: A Code for Geological Field Work issued by the Geologist s’ Association; Mountain Safety – Basic Precautions published by Climber and Rambler; Guidelines for Visits to Quarries – laid down by the British Quarrying and Slag Federation.
V. To: all students undertaking geological fieldwork alone, in pairs, or small groups (section r elevant for this field course): 1. All members of a mapping group or pair in one area must: a. Conduct a team familiarization of each mapping area and its particular risks/hazards before mapping. b. Be familiar with local rescue/medical facilities. c. Agree a formal day plan and r endezvous scheme with your ‘buddy’ which includes: o listing areas/routes to be mapped that day. o definition of meeting locations and times – an end of day rendezvous is required. d. Never carelessly b reak arrangements to meet your ‘ buddy ’; it is better to be early for a rendezvous. e. Agree a plan of action for bad weather or illness. f. Agree a scheme for rescue in the event of an accident.
Behaviour on field courses A reminder of the Code of Behaviour form that you have signed
Ordinance XIV on the admission, conduct and discipline of students, paragraph 4 states:- “Every student shall maintain at all times and in all places an acceptable standard of conduct and shall comply with such Regulations relating thereto as shall have been duly made by the University or by the authorities of any hall of residence or affiliated institution. Without prejudice to the generality of the foregoing, every student shall be liable to disciplinary action in respect of conduct which: (i) is discreditable to the University or detrimental to the discharge of the University’ s obligations under the Charter; (ii) disrupts the teaching, research or administration of the University; damages University property or obstructs or endangers the safety of officers, employees or students of the University or visitors to the University; (iii) involves the use or attempted use of unauthorized or unfair means in c onnection with any examination.”
I have read and understood Ordinance XIV.4 of the University of Manchester and fully realize that any unacceptable behaviour at any time or place while I am a member of the field course may be liable to the disciplinary action outlined therein. I also understand that financial support may be withdrawn in the event of unsatisfactory behaviour. I acknowledge that in registering as a student of the University I have undertaken to obey the regulations contained in its Charter, Statues, Ordinances and Regulations.
I also agree to use safety belts in minibuses where fitted.
84 Specific safety / behaviour advice for this field course
You must have read the material on the preceding two pages. Carry a small first aid kit with you in the field, including appropriate medication if you are particularly allergic to insect bites or other commonly encountered allergens. Students must notify staff if they have any health problems that may affect their safety and/or that of others. The vegetation in the mapping area is generally very dry – take great care to avoid doing anything that might cause a fire, e.g. , leaving litter or being careless with cigarette ends.
Topography : the mapping area is relatively low-lying with a few cliff faces and gentle hills. o Do not climb cliffs and do not walk next to the tops of cliffs. o Take care on scree covered slopes. o Take care on grassy slopes after rain.
Climate : the mapping area is on the margins of the French Alps and the weather can change very quickly. It is likely to be sunny and hot most days but it can be cold early in the morning, and afternoon thunderstorms are possible most days. o Sun is a hazard – make sure that you have a hat and sun screen with you. o Make sure that you have enough water with you (2-3 litres). o Make sure that you have full waterproof clothing with you. o Make sure that you have a warm jumper with you.
Animals : the mapping area is mixed forest and farming land, and so there are wild and domesticated animals around, plus insects, etc. o The most fearsome beasts in the area (apart from the French hunters) are wild boar – keep well clear, especially if you see a young one. o Scorpions and snakes are present within the field area – take care when picking up rocks. o Take care when passing farm animals / dogs – do not disturb them. o North of Laubre on the path up to the quarry there are several bee-hives – take care when passing and map somewhere else if the farmer is actively attending these hives.
Human : o A number of minor roads go through the mapping area and these are well used by crazy drivers, motorbikes, and farm traffic – watch out for traffic when working on road-side exposures, and do not eat road-kill. o Be especially careful on hunting days because the area is well visited by hunters – on those days make sure that you are conspicuous and avoid the woods. o A farmer has declared one part of the mapping area out-of-bounds – make sure that you know where that is and do not enter it. o Do not walk through the farm at the south-eastern part of the mapping area (at le Lèche below le Château) – there is a public right of way around the farm (over the conglomerate slopes). o Many fences are electrified – take care when working near them. o The area is well visited by other geological parties, many of whom are not well-behaved, and so the locals are easily annoyed – do not do anything that might be construed as antagonizing the locals.
Accommodation / coach All lights and appliances must be switched off before leaving each day – electricity is a significant expense. Obey Joseph at all times – he has French military training and a big dog. There is to be no smoking inside the accommodation blocks or in the coach. There is to be no consumption of alcohol inside the bedrooms or in the coach. Otherwise, the use of alcohol and tobacco must not interfere with the well-being of other students. Personal consequences and liability arising from intoxication will be the sole responsibility of those who indulge.
85 Barrême Self-Assessment and Feedback sheet Aims of Field Course Produce a geological map and cross section. Illustrate stratigraphy with a generalized vertical section (Stratigraphic column). Use stereogram and section to describe geometry of structure. Record observations both on your map and in a geological note book (not assessed here). Intended Learning Outcomes At the end of the field course the student should be able to: 1. Make accurate measurements of both planar and linear geological features. 2. Record sufficient observations accurately on a field map to define geometry of area. 3. Use observations to interpret geology outside areas of observations. 4. Develop a 3D understanding of the geological structure of an area. 5. Record observations of the sedimentological features of the rocks seen. 6. Use this information to interpret environment of deposition and sediment provenance. 7. Integrate all of the above to answer the following questions: a. How does the water depth in which the rocks in the basin were deposited change through geologic time? b. When did deformation in the area start and finish? c. How does sediment provenance change through time and how does it link to regional tectonics? Self-Assessment of Intended Learning Outcomes Criteria Bad Could do OK Great better Number of localities shown on map is consistent with number of field days ILO2: Geological information on map is recorded clearly and accurately ILO2. Geological boundaries have been attempted to be interpreted across areas of no exposure in pencil ILO3. Geological structures have been attempted to be interpreted across area ILO3. Sketch GVS accurately records the thicknesses of the sediments in the basin. ILO4 Sketch GVS accurately records the changes in sediment fill through time. ILO5 Sketch GVS shows how sediment provenance changes through time. ILO7c Have you thought about the relative time of deformation in relation to deposition is illustrated and how you could show this on your GVS. ILO7b
Field Slip Feedback
Feedback on Notebook
86 Group Assignment Last Name First Name Tutor Group Number Tutor Baker Romany 4 Zoe Cumberpatch Birch Connor 1 Julian Mecklenburgh Chowdhury Marjaan 1 Julian Mecklenburgh Colley Isabel 3 Ian Kane Conway Emma 2 Alison Pawley Emery Jake 2 Alison Pawley Frater William 4 Zoe Cumberpatch Gasques Da Cruz Ester 5 Euan Soutter Hollinrake Sophie 3 Ian Kane Howdle Thomas 2 Alison Pawley Islam Yasmine 3 Ian Kane Lewis David 2 Alison Pawley Li Xinyuan 2 Alison Pawley Mayor Benjamin 1 Julian Mecklenburgh Mustafa Wasim 5 Euan Soutter Neame Oliver 4 Zoe Cumberpatch Norshidi Fazizi Siti 5 Euan Soutter Oluwayomi Ifeoluwa 5 Euan Soutter O'Sullivan Blake 5 Euan Soutter Pardue Tom 2 Alison Pawley Parr Jamie 3 Ian Kane Samsudin Syahmi 3 Ian Kane Sefton Jordan 1 Julian Mecklenburgh Solanki Shaylen 4 Zoe Cumberpatch Subhani Baasit 1 Julian Mecklenburgh Swetnam William 1 Julian Mecklenburgh Thorley Daniel 3 Ian Kane Waters William 4 Zoe Cumberpatch Xiao Yumeng 2 Alison Pawley
87 Notebook Peer Assessment The aim of this exercise is: to develop skills of geologic note taking to give and receive feedback on a piece of work through peer review, in order to develop an understanding of what constitutes a high quality piece of work Along with the map, your notebook is the primary record of all the data you have collected in the field. The notes contained within the notebook need to be based on keen, careful observations that are systematically recorded. It is essential that your notebook is legible to a third party. Thus, is must be neat, legible, clearly written and well illustra ted. It is not your personal record and if you are employed as a geologist your notebook belongs to your employer! To emphasise these points you will each assess one of your colleagues’ notebooks as part of this tutorial exercise. At the start of the tutorial you will exchange your field notebook(s) with another student and individually answer the questions below. The aspects of the notebook that you are being asked to evaluate in this exercise are the same as those that the Examiners of your Independent Mapping notebooks will consider in assessing their quality (and grade). If you keep this handout you can use it as a checklist for your Independent Mapping! With ~15 minutes of the tutorial remaining, your tutor will instruct you to return the notebook(s) and the answer sheets to its owner for reflection and group discussion.
PRESENTATION AND ORGANIZATION (INTELLIGIBILITY TO A THIRD PARTY) Examine the first few pages of the notebook. Is the owner’s name and address clearly shown on the inside fr ont cover of the notebook (in case it is lost)? Yes/No Are the overall field trip dates specified? Yes/No Is there a table of contents at the beginning of the notebook? Yes/No Are the overall aims of the fieldwork specified? i.e. Is it clear why the author is doing the mapping? Yes/No Is the location of the study area clearly specified? i.e. Could you use the notebook to find the field area if you hadn’t been there before? If not, what is missing? Suggest one way this could be improve d. Yes/No
Now quickly scan through the whole notebook from start to finish. Can you easily read the hand writing? Is the writing too large, small, smudged and/or faded to read? Suggest one way this could be improved. Can you easily distinguish what work was done on different days? Yes/No Can you distinguish the notes for different localities? Yes/No Are there day aims/objectives stated at the beginning of each day? These should be geological in aspiration, not geographical. Comment on their frequency (e.g. are they always present, sometimes present, almost never) and usefulness.
Are day summaries present? These should be geological in nature, not travel logs of where you went. Comment on their frequency and usefulness.
88 If you read through the day summaries from start to finish, can you find evidence for the development of working hypotheses of the geology of the (sub-)area as the notebook/mapping progresses? i.e. Is there evidence that the author is trying to put together the geologic history of the study area as they map or are they simply recording observations of isolated localities throughout the whole field trip? Yes/No Is the quality of the notebook maintained throughout the trip? i.e. Does it remain unchanged, decline or does it improve? Yes/No
LOCALITIES Would you be able to use the notebook to navigate around the field area and find the locations described? Are the localities given a number in the notebooks and are these put on the map? Is there logic to the locality numbering system used? Yes/No Are the localities given grid references (you should use enough figures to get within 1mm accuracy)? Yes/No Do the grid references tally with the localities as marked on the map? Check a locality to see if you can find the location on the map using the grid references given. Yes/No Is access to the locality briefly described, either in words or with a quick sketch plan? Yes/No Is the size and nature of the exposure described? Yes/No
LITHOLOGICAL DESCRIPTIONS The lithological descriptions made at different localities in the field will form the backbone for the formation descriptions in your geological report. Thus, they must be based on careful, detailed and quantitative observations. Scan the notebook and find a locality to assess the lithological description. Make a note of the Location number. Location No.:
Is correct terminology used to describe the features observed? Yes/No Are the descriptions systematic in approach, starting with exposure scale features and working down in scale to hand specimen scale features?
Are appropriate subheadings used to organise the notes? Yes/No
Working down in scale, are the following observations made: Rock-types present and their proportions? Yes/No Is the scale, geometry and continuity of bedding described and measured? Yes/No Are primary and secondary sedimentary structures and bedforms (e.g. cross-bedding, upper plane bed, ripples, graded bedding, loading features, flute marks, mudcracks) on the top, bottom and within beds described and measured? Yes/No Comment on one thing that could be included to improve this.
Are the vertical (and lateral) relationships between the sedimentary structures described, either in words or with a sketch log/measured section? Yes/No Are any fossils (body and trace) present quantitatively described and percentages estimated? Yes/No 89 Are grain sizes and shapes described? If a conglomerate, is the matrix and sorting also described? Yes/No Are compositional descriptions comprehensive with estimated percentages for different minerals/clast types? Yes/No
Are palaeocurrent readings recorded where suitable sedimentary structures were present (e.g. crossbedding, ripple forms, pebble imbrication, flute marks)? Yes/No Is the reading correctly specified, indicating the direction of flow? Yes/No Is the feature from which the palaeocurrent direction was measured clearly specified? Yes/No Is there any consideration of how the lithology at this location may be similar or different to other localities within the same formation, within the field area? i.e. Are vertical and lateral variations within the formation being observed? Yes/No Are there any interpretations of the lithological observations? Yes/No Suggest one way these could be improved. [You may not have this information for this field course but you must have interpretation in future field notebooks]
Are there sketch stratigraphic logs for the type localities to illustrate the main features of the formations? Yes/No
NATURE OF CONTACTS The nature (primary, faulted or intrusive) and geometry of contacts between adjacent mapped units must be recorded.
Find a location in the notebook (the map should help with this) where a primary contact between two mappable units is described (e.g. the contact between the La Condamine Fm. and Les Sauzeries Fm. (Haute member) on the D219 road GR92262/20153). Is the geometric relationship between bedding either side of the contact fully described, either in words or with a sketch? (e.g., sharp, gradational, erosive, angular discordance?) Yes/No Is evidence for the age relationship between units either side of the contact clearly provided? Yes/No Is the contact interpreted? (e.g., as conformable or unconformable (using correct terminology such as disconformable/angular unconformity)) Yes/No Is the dip & strike of contact recorded? Yes/No Is the trend of contact recorded? (i.e., direction it outcrops on the erosion surface). For shallow contacts, the record should indicate which unit is on top, and for steep contacts, which unit is on which side. Yes/No Find a location in the notebook (the map should help with this) where a faulted contact between two mappable units is described (e.g. the contact where the Les Sauzeries Fm. is thrust over the La Condamine Fm. on the antiform ridge GR92410/20110).
Is evidence for faulting provided? i.e., Is the geometric/age relationships between bedding either side of the contact fully described, either in words or with a sketch? Yes/No Is there evidence for sense of movement (slickenslides, etc.) and are measurements recorded? Yes/No Is the dip & strike of contact recorded? Yes/No
90 Is the trend of contact recorded? (i.e., direction it outcrops on the erosion surface). For shallow contacts, the record should indicate which unit is on top, and for steep contacts, which unit is on which side. Yes/No
FIELD SKETCHES Field sketches may be 1-D, 2-D or 3-D and should be present on a variety of scales. These may be used to show features such as the lateral relationships and bed geometries of an exposure, the general stratigraphic section, structural relationships and geometries, the detailed vertical arrangement of sedimentary structures, the nature of contacts etc. Scan through the notebook and examine the field sketches. Are the field sketches that are present oriented and given a scale? Yes/No Are the field sketches well drawn? Yes/No Suggest one way these could be improved.
Are the field sketches informative? Yes/No Suggest one way these could be made more informative.
Are the field sketches interpreted (labelled)? Yes/No Find the sketch of Le Chateau in the notebook (drawn at GR92415/20040 looking south-east) and compare it with the example of good geological sketches provided, to give you an idea of the standard you should be aiming for. Which attributes shown in the example are present/missing from the sketch in the notebook? How could it be improved?
STRUCTURAL OBSERVATIONS Scan through the notebook and examine the structural measurements recorded. Are the orientation measurements correctly and fully specified? Yes/No Planar features as strike and dip as, e.g., 045/25SE: The nature of the planar reading noted, e.g., bedding (S0), cleavage (S1), etc.: Yes/No Linear features as plunge/plunge direction, e.g., 24/230: Yes/No The nature of the linear reading noted, e.g.., intersection lineation (S1/S0 with asymmetry noted): Yes/No Is the geometry of the structure at each locality clearly reported and interpreted? Yes/No Find a fold in the notebook (e.g. the small antiform pair in the Bussiere d’Entouart at GR92326/20193) Does the notebook specify what planar feature is being folded (i.e., bedding or cleavage)? Yes/No 91 Are sufficient bedding readings measured around the fold to constrain its geometry? Yes/No Is an annotated sketch included to locate the measurements made? Yes/No Is the geometry of the fold fully described (i.e. profile shape (e.g. hinge roundness, hinge thickening etc.), tightness (inter-limb angle), symmetrical vs. asymmetrical))? Yes/No Is the sense of asymmetry noted? (Z or S looking down plunge) Yes/No In the latter part of the notebook, as the mapping progresses, is there a clear sense of the map-scale geometry between localities i.e. how individual localities fit in with the overall structure of the field area (e.g. using sketch cross-sections)? Yes/No
FURTHER READING AND REFERENCES YOU COULD TAKE INTO THE FIELD WITH YOU Barnes, J.W. and Lyle, R.J., 2003, Basic Geological Mapping, Geological Society of London Handbook 1, WileyBlackwell, 4th edition, 196 pp. Fry, N., 1991, The Field Description of Metamorphic Rocks, Geological Society of London Handbook 3, WileyBlackwell, 128 pp. McClay, K., 2003, The Mapping of Geological Structures, Geological Society of London Handbook, John Wiley & Sons, 161pp. Stowe, D.A.V., 2005, Sedimentary Rocks in the Field, Manson Publishing, 320pp. Thorpe, R.S. and Brown, G.C., 1991, The Field Description of Igneous Rocks, Geological Society of London Handbook 4, WileyBlackwell, 160 pp. Tucker, M.E., 2003, The Field Description of Sedimentary Rocks, Geological Society of London Handbook 2, 3rd edition, John Wiley & Sons, 124 pp.
92 DATE : LOCATION : SCALE 1: SHEET of Sand PALEO- BEDDING FOSSILS
(m) Description and Interpretation CURRENTS (dip and TRENDS THICKNESS cobble
clay silt vfs fs ms cs vcs granule pebble strike)