Fossil Flora - Photographing Plant Fossils In Situ - Part Three

For the most part nature photographers strive to capture their subjects in the early morning and late afternoon when the light is lower to the horizon.  During this “golden hour” the colours are highly saturated and are much more pleasing to the eye than if the photograph was taken during the middle part of the day in full sun.  However, photographing fossils in-situ is a little different as often there was a few hours hiking to find the fossils and it wasn’t possible to wait until early morning or later afternoon to take the photograph.

Techniques

It's important to realize that photographing fossils is identical to photographing anything else - there are no set rules - only guidelines.  Use your imagination and the equipment you have on hand.  The process to photograph fossils in-situ is nothing magical; however, there are a few techniques that will improve the photographs markedly.

• Always use a quality tripod and ball head that when locked down, is tight and does not move.  A tripod that allows the ability of the head to be maneuvered to odd positions is a distinct advantage when photographing something that cannot be moved and is probably located in a relatively inaccessible location (rock crevice, overhand, etc).

• Fossil leaf photography is essential macro photography; therefore, use quality lenses and if possible a full frame camera.  Ensure you use a timer release as many of your images will be taken at slow shutter speeds to ensure adequate depth of field.  

• Use a solid board to mask your subject from the wind.  The wind is quite normal in mid latitude arid areas and can cause camera movement if shooting at a slow shutter speed.

• Use a reflector board and largish diffuser to remove stark contrasting lines that may otherwise ruin your image if you are shooting during the middle parts of the day.  

• Make use a fill flash to add, remove or change the location of shadows.  Use a wireless flash head (or similar) to avoid any camera movement that maybe caused by the flash head or cord moving.  A remote head also allows you to position the flash (s) at suitable distances and at odd angles to your subject.  

• Do not use ETTL, but use M (manual) to determine the exposure setting for the flash.  You do not want a 100% flash photograph, but an image that was taken with a subtle amount of fill flash.

• Try to use a diffuser with your flash.  I’m not discussing the small “clip on” diffusers but, a largish diffuser that can be held at varying distances from your flash head.  A diffuser will lower the starkness of the light emitted from the flash.  Using a flash as a fill light will enhance the light that may otherwise cause an object in plan-view to appear flat and uninteresting.

• Be aware of the colour of your surrounding environment; central Australia is predominately red (from iron oxides) and photographs taken will inadvertently take on a reddish colour cast.  

• Ensure you white balance your images appropriately.  Although this can be done in post processing, I prefer to take my time and white balance the images in the field; after all, the fossils are not going anywhere in a hurry…  I use a white balance card.

• Depending upon what you are attempting to achieve, position the camera lenses at the appropriate angle to the subject.  For instance, if you wish to create a scientific photograph in which the complete fossil is shown, position your camera and lenses so that the lens plane is parallel to the subject.  This will ensure that the fossil (in plan-view) will be in focus, even if using minimal depth of field.

• If your photographs look flat and lack texture because of the bright light from shooting in the middle of the day, try spraying some water from  small squeeze bottle onto the fossil.  Often, a little water will make the colours and texture of an otherwise flat object pop.

The below images are case in point.  The photograph on the left was taken without a diffuser or fill flash while that on the right was taken with a diffuser, soft fill flash and a quick spray of water on the rock.  Conditions were full sun.  Note the subtle differences in colour, texture and shadow.  Click image for larger view.

Composition

Fossil photography is often done for scientific purposes; therefore, the photographic layout must comply with certain guidelines such as the inclusion of a ruler or known size object to provide a scale.  The subject should also be photographed completely flat with all aspects of the fossil in focus.

However, if you’re not bound by these guidelines, composition is very important.  Position the fossil so it’s at an angle rather than vertical or horizontal; using angles gives your subject more visual power.  Try using minimal depth of field to add illusion to your image or attempt to place something in the image which provides scale.  

Looking at three images below, you will note the leaf in the right hand photo is at an angle forming a triangle in the image, while the center image shows part of the landscape surrounding the fossil and places the fossils in context with its surrounding environment; this creates interest.  Finally the Eucalyptus leaf I have positioned vertically with the apex of the leaf pointing downwards.  The reason for this composition is that it replicates the way extant (present day) eucalyptus leaves appear on trees – pointing downwards. 

If you navigate to the second journal post on this subject you will observe that I’ve also used minimal depth of field on one of the leaves to provide illusion.

Problems or Challenges

If you cater towards everything mentioned, you’ll almost need a mule to transport your equipment.  Carrying the gear was one of my biggest concerns on this trip.  We were walking considerable distances for most of the day in very warm temperatures.  Carrying the photographic equipment, food and other essential items such as map, compass, DGPS and 5 litres of water was tedious.

Add to this a constant wind and bright sunny conditions, and photographing fossils became an enjoyable challenge.

This is a short video I made of the trip. The reason for the relatively lengthy four wheel drive sequence is to indicate the length of time it took to reach the location.  If your computer is not powerful, click HD to remove High Definition and view at a lower resolution.

The below plate depicts a few of the fossils found and photographed in-situ.  No fossils were removed or collected; this being an illegal activity in Australia.  I have purposely not included the identification of each fossil.  Click image for larger view.

This is the final post of three dealing with this excursion.  To read the first post and second post click here.

Fossil Flora - Silcrete Plant Fossils; Evidence for Climate Change - Part Two

Hartley, 1967 stated “The past is a foreign country”

The validity of this statement becomes readily apparent looking across the vista of breakaways, dry sandy terrain, silcrete-covered ridges and dry gibber desert.  A stark contrast exists between the present day environment and the evidence presented by fossil flora of the very different conditions that prevailed here, when the fossils were deposited.  What had previously been a wet, lush, and green environment that supported a complex mosaic of tropical and temperate rainforest, is now devoid of all but the most resilient vegetation.

The content of this post, because of its scientific nature is rather specialised, however, I have attempted to succinctly explain the region’s local geology and provide evidence to how the fossils found in the area can be used to interpret climatic change.  To view an image larger, double click the image.

Geology

The region’s geology has been poorly studied, despite there being considerable interest because of the record of surface environments in the Eyre basin over the past 40 million years, and the famous silcrete floras and mammalian megafauna.  

LEFT:  A satellite view of the region (courtesy Google Maps) clearly showing the drainage lines (green), gibber plains (light brown) and breakaways (dark brown).

The geology is complex, in part because of the number of stratigraphic units involved and the interrelationship between lacustrine, fluvial, and aeolian sediments.  It’s this interrelationship and the variable development of duricrusts which has recently propelled the region’s interest, as these environments provide good scientific analogues for the surface of Mars.

The basement rock is comprised of marine deposited shale laid down during the Cretaceous Period when much of what is now inland Australia was covered in seawater.  The break-up of Gondwanaland and resultant rearrangement of tectonic plates gently deformed and duricrusted this shale, named the Bulldog Shale, to form the gibber plain uplands of the Stoney Desert.  The breakaways, prominent sentinels in today’s environment, are comprised of fluvial and lacustrine-derived sediments deposited during the Upper Triassic and Lower Tertiary, and were formed by erosion from several ephemeral streams including Coopers Creek.

Sedimentology and Palaeoenvironments   

I’ve attempted to provide a short introduction to the sedimentary units involved in the formation of the palaeochannel in which the fossils have been deposited. This interpretation is quite broad in content and further study and work needs to be done to accurately assign dates to the various stratigraphic units.  

Palaeoenvironment

The nature of the palaenvironment is well understood; a fluvial system with well-established oxbow lakes and shallow lakes surrounded by a mosaic of riparian tropical to temperate rainforest in a warm semi-tropical climate.

LEFT:  Indistinct to the untrained eye, this sandstone rock exhibits tell-tai sedimentary structures which indicate that the region was once covered in water.  The ripple marks can be used, amougst ither things, to interpreete water depth and current direction.

During the mid-Tertiary, the environment began to experience seasonality with fluctuating watertable levels; increased periods of semi-aridity began to alter the rainforest mosaic until species survived only around permanent water channels and lakes.  Eventually, as Australia and Antarctica separated and Australia moved north, aridity became more widespread and taxa became locally extinct.

The Watchie Sandstone Unit

The Watchie Sandstone is a lacustrine sequence comprising; in upwards succession, a local channel-sand facies and widespread lag deposits, a transgressive fine-grained lacustrine facies and regressive strandline deposits with a wavebase lag.  

Lag deposits indicate a low-gradient surface and strandlines incorporating pedogenic silcrete clast provide evidence of former soil horizons.    The palaeocurrent evidence is consistent with longshore processes and bar accretion onto a foreshore and larger bedforms indicate storm events.  Ridges have formed only along the eastern shoreline, indicating a strong westerly airstream and silicification and ferruginisation alternated during lacustrine regression.  

Insects (including ants and termites) lived in developing soil profiles and rhizonodules indicate that plants grew on these soils.   

The Willalinchina Sandstone Unit

This unit was deposited in a fluvial channel environment and is interpreted as a broad, shallow meandering to braided channel system which abuts a floodplain to a lacustrine palaeoenvironment.  Storm and associated flood events have also deposited bar, levee and floodplain deposits which interfinger with fluvial-derived sediments.   

LEFT:  Partly eroded to show depth of the deposit, the structures clearly are indicative of sequential mud cracks that provide evidence of a drying environment.

Field observations support this interpretation:  A thin lens of basal conglomerate has been overlain by several meters of cross-bedded fine to medium-grained sandstone containing minor lenses of course-grained sandstone.  Silicification, caused by alternating watertable levels, has occurred in several places.    

Silcrete and Silicification

Silification provides evidence of a fluctuating watertable and, in general, a marked seasonality toward aridity, which inland Australia experienced during the mid Cenozoic. 

LEFT:  Reed mould or ant's nest silcrete - a possible interpretation is reed casts or methane gas escape structures from rotting vegetation.

The silcrete is defined by closely spaced vertical structures which have been referred to in past literature as “ants nest or reed mould silcrete”.  The vertical structures have been interpreted as reed casts, however, there is no evidence of organic matter found within the Willalinchina Sandstone Unit.  A possible alternative is soft sediment deformation caused by gas escaping from rotting vegetation.  This scenario would explain why the gas escape structures are not evident throughout the sandstone unit, but are preferentially preserved. 

Another interesting sedimentary structure preserved within the silcrete are circular mound-like features (below left) which have not been successfully interpreted. One theory suggests that the features are formed when liquid silcrete bubbled its way toward the surface, akin to how artesian water bubbled to the surface in nearby artesian spring moulds.

Silcrete is an indurated soil duricrust formed when silica is dissolved and resolidifies as a cement. It is a hard and resistant material, and though different in origin and nature, appears similar to quartzite.  Silcrete is relatively common in inland Australia, often forming the resistant cap rock on features like breakaways.

Stratigraphic Analysis and Age    

Sediments from the Palaeochannel have been placed in the Watchie and Willalinchina Sandstone units although most of the palaeochannel area is located within the later.  

Preliminary palaeobotanical work suggests that the Willalinchina Sandstone correlates with the youngest phase of the Eyre Formation in the Lake Eyre Basin and is Eocene in age.  The Watchie Sandstone has been interpreted as Miocene and correlates with the Billa Kalina Basin.  However, recent stratigraphic analysis may indicate that the Willalinchina Sandstone could be Miocene to Pliocene in age.  Further investigation needs to be made in this area before a definite date can be attributed to the palaeochannel.   

Floral Record - Interpreting Climatic Change   

The Australian Tertiary plant fossil record is very poor.  Studies indicate that tropical to temperate rainforests occupied  south eastern and south western Australia for much of the early-Tertiary with a contraction of these rainforest communities in the mid to late-Tertiary.   

LEFT: One of many example of the fossil flora found in the area.  The state pf preservation is amazing and identification, in some cases, to species level is possible.

The discovery of the fossil flora confirm the palaeochannel is one of the richest, most extensive Tertiary plant fossil localities in Australia, if not globally.   

The botanical significance of silcrete fossils may be limited because silcrete formation is notoriously difficult to interpret and date with precision; however, the presence of extensive silcrete, caused by the fluctuating watertable levels does provide evidence consistent with marked climatic seasonality that occurred in inland Australia during the Cenozoic.  Therefore, floral assemblages could preserve evidence of the effect of climate change on the vegetation of inland Australia.

Initial Analysis    

Initial analysis of floral elements indicate a mosaic of plant communities dominated by sclerophyllous woodlands (Eucalypt spp.) and interspersed with riparian rainforests and deciduous marginal monsoon forests.  These plants grew along the watercourses where permanent water enabled them to survive seasonal dry periods.   

Interpretation of Fossil floras and Palaeoclimate     

Observational studies in tropical and temperate forests have demonstrated a direct relationship between leaf form (foliar physiognomy) and local climate.  For example; leaf length to leaf width and stomata number and size correlate to rainfall and ambient temperature.  

LEFT:  Ripple marks showing bifurcation of ripple crests indicate wave-formed ripples that have formed by wind blowing across shallow water.  The ripple marks are so clear, it's difficult to realize that they were formed approximately between 24 and 5 million years before present.

Mean canopy leaf size is also strongly correlated with mean annual temperature.   Palaeobotanical investigations of the botanical specimens found within the palaeochannel (Willalinchina Sandstone) provides valuable information on the mid-Tertiary distribution of Eucalyptus spp. and other plants.  

To date 245 leaf types, 47 fruit and seed types and 2 major wood types have been identified.   The sclerophyllous component (identified from linear to lanceolate leaf forms) dominated the flora and would have grown on the exposed drier plains in the more open forest areas of the floodplain.  

Many of the fossil leaves are indiscernible from extant Eucalyptus leaves and the minimal variation in leaf form suggests that Eucalyptus has existed in the area for ~15 million years.  The ecological niche of this species, based on this information, appears to be similar to that of extant Eucalyptus.    

LEFT:  An excellent example of Banklsieaeformis praegrandi.  If you open this image (double click) you can see the preserved intricate patterns of the veins that have been preserved.  The red colour is caused by iron oxide that has percolated through the sediments.

The rainforest component of the flora grew in areas that provided a permanent water resource and are not present in the area today; their absence indicative of a changing climate and environment. As the climate became increasingly drier, these plants died out to eventually become confined to the present monsoonal and tropical rainforests of northern Australia and became locally extinct.   

Ancient Eucalyptus are not the only plant fossils that have been uncovered; numerous other plant species are likely to be extinct representatives of extant genera.  As with the Eucalyptus, similarity in leaf forms between fossil leaves and extant leaves have made identification problematic and it’s highly likely that many of these species were intermediate rainforest / sclerophyllous species sandwiched between the effects of climate change.     

One species that appears to have been positively identified from its deeply incised proteaceous leaf form is Banklsieaeformis praegrandi.  This fossil plant has been found in low numbers within the palaeochannel and has been linked to the extant species Banksia chamaephyton which is restricted to a small area of heathland in Western Australia (Greenwood, 1997).  

Access  

Access to this area is STRICTLY PROHIBITED without express permission from the land owner, property station manager, and approval from an educational facility such as University or museum.   Removal of fossils or collecting is NOT ALLOWED. 

LEFT:  Preferential erosion erodes the former land surface to leave the more harder and durable silcreted surface, in a formation called a breakaway; a term uniquely Australian.  The breakaways can reveal the surface of an environment that often is completely changed to that of today.  It's often difficult to grasp that approximately 70 million years ago these surfaces were the floor of a vast inland sea.

Next Journal Post

In the final post on this topic, we'll look at a number of photographs of the fossils and discuss the best method to photograph them in situ.

References   

Krieg, G. W., Rogers, P. A., Callen, R. A., Freeman, P. J., Alley N. F. and Forbes, B. G., 1991.  Explanatory Notes Curdimurka South Australia. 1:250,000 Geological Series Geological Survey of South Australia, Peacock Publications, pp 35 – 38.  Rowett, A., 1997.  Earthwatch '96.  MESA, Journal 5, pp 27-29.