Climate research in the geologic past

Fig.1. Global map as published by Lyell in his "Principles of Geology" (8th edition 1850) to illustrate the past climatic changes.

The climate of a region, as experienced by daily observations of a cool morning and hot midday, was for very long time considered simply the result of the height of the sun above the horizon. This idea forced a very simple view of the distribution of climates on Earth, to the poles temperature dropped, to the equator it raised, forming so large parallel climatic belts. Such a static view of the Earth also didn’t need or even allow climate changes in the past or in the future time.
With the establishment of the deep geological time by the first geologists and naturalists it became clear that not only the distribution of sea and land changed over time, but so did climate.

Read on how Lyell explained climate change by shifting "pseudo"-continents over the globe in the post at the American Scientific Guest Blog.

Geology and Cyclicity: Milankovitch´s idea

"I do not think that's my duty to teach to the ignorant the most basic things, and I have never forced anyone to accept my theory, on so far nobody could expose something."

Milutin Milankovitch in 1950

Milutin Milankovitch (1879 - 1958) was born in a relatively wealthy Serbian family, so it was almost a kind of obligation for him to archive a higher education degree and later take over the family business. So he studied agriculture, but following a passion for natural sciences he went to Vienna, where he in 1904 concluded his studies as an engineer.
Five years later he returned to Belgrad where he found employment as professor for mathematical studies at the University. Like Croll he was in search of a scientific problem worth his efforts, and in 1911, sharing some presumably good wine with a friend, he decided to develop a mathematical theory to explain climate changes on the planets of the solar system.

He studied the work of Croll, recognized his previous achievements but also noted his insufficient data. Milankovitch also consulted the work of the German mathematician Ludwig Pilgrim, who in 1904 published exact calculations of the orbital eccentricity, earth's obliquity and the rotation of the axis of earth (change of the perihelion). Pilgrim also tried to correlate the eccentricity with the occurrence of ice ages.
Between 1912 and the beginning of World War I Milankovitch published some preliminary abstracts of his developing theory, concluding that all three factors, in contrast to previous authors, are important to explain earth's climate. At the beginning of the War, Milankovitch was arrested as Serbian officer and imprisoned in his hometown Daly, but fortunately he was carrying with him his work, and so even in the first night as prisoner he continued to work. "When after midnight I looked around in the room, I needed some time to realize where I was. The small room seemed to me like an accommodation for one night during my voyage in the Universe."
Soon after he was released and travelled back to Belgrad, where he continued his work during the entire War and published some ideas about the climate of Mars and Venus.

Finally he published his theory in 1920 "Mathematische Theorie der durch Sonneneinstrahlung ausgelösten Wärmephänomene" (Mathematical theory of thermal phenomena caused by solar radiation).

Fig.1. Variations in the Earth's orbital parameters:
1. Eccentricity: the shape of the orbit around the sun.
2. Changes in obliquity: changes in the angle that Earth's axis makes with the plane of Earth's orbit.
3. Precession: the change in the direction of the Earth's axis of rotation, i.e., the axis of rotation behaves like the spin axis of a top that is winding down; hence it traces a circle on the celestial sphere over a period of time.
Together, the periods of these orbital motions have become known as Milankovitch cycles. These parameters influence the amount of solar energy on earth´s surface, especially during summer of the northern hemisphere (55°-65°N).

In his theory he postulated:
- Glaciations are caused by variations of astronomical parameters
- The parameters influence the amount of solar energy on earth´s surface, especially during summer of the northern hemisphere (55°-65°N)
- It is possible to calculate these changes, and so calculate the climate in the past.

The German meteorologists Wladimir Köppen and Alfred Wegener supported the new theory, and noted the apparent coincidence of the calculated curve with the by Penck and Brückner postulated four European glaciations.

Fig. 2. Figure from KÖPPEN & WEGENER 1924, where they correlated the calculated cycles to the know ice ages at that time.

Fig.3. Outcrop of the Trubi-Formation at Capo Spartivento (South-Italy), a succession of Globigerina-marls from the Pliocene-Pleistocene transition. The regular stripes are caused by organic rich layers, thought to be caused by changes in the biological productivity in response of changes of the astronomical parameters - the Milankovitch cycles.

References:

CHORLTON, W. (ed) (1985): Ice Ages (Planet Earth). Time-Life Books: 176
KÖPPEN, W. & WEGENER, A. (1924): Die Klimate der geologischen Vorzeit. Borntraeger, Berlin: 256

Resources:

NASA Earth Observatory: Milutin Milankovitch (1879 - 1958). Accessed 26.06.2010

Megafauna Methane collapse

There are lots of hypothesis dealing with the extinction of the Pleistocene Megafauna. Now a research team of the University of New Mexico in Albuquerque adds a something different approach to the problem of climate change as extinction cause. SMITH et al. published a paper where they compared the production of methane of modern farm animals to extinct herbivores. Methane is a very effective green house gas. The research team observed in the geological record strong variations of the concentration of methane between the last glacial maximum, 18.000 years ago, and the Younger Dryas (13.000 years ago). Especially at the beginning of the temperature drop of the Younger Dryas the concentration of methane diminished considerable fast. The research team speculates that with the beginning extinction of large herbivores an important source of methane was removed from the climate system, destabilizing climate and environment end enforcing the extinction rate. The fast changes observed, faster than previously known variations, maybe are also related to human activity, disproving precedent research that excluded humans as triggers for the Pleistocene extinction.

References

SMITH, F.A.; ELLIOTT, S.M.. & YONS, K. (2010): Methane emissions from extinct megafauna. Nature Geoscience. Published online: 23. May 2010: doi:10.1038/ngeo877

Did volcanoes kill the Mammoth?

The cause(s) of the Pleistocene Megafauna extinction is(are) still unclear. Various explanations were proposed, ranging from human activity (hunting or disease spreading) to climate change or sea level rise, and since the last year, a possible extraterrestrial impact. But an important factor until now was less considered - volcanism. Volcanoes can have an impact on climate and ecosystems, for example ash can block the sunlight, and poison large territories.
A short, but intriguing paper by Dmitry A. Rubam summarizes and analyze the idea that intensified volcanism at the end of the last glacial period maybe triggered the biotic crisis. The volcanic activity of the last 50.000 years can be reconstructed by ash layers and geochemistry of ice cores, and compared to extinction patterns on the different continents.

The data show a higher frequency of eruptions near the end of the Pleistocene, but the demise of the fauna doesn’t coincide exactly with this period, especially the extinction in Australia happened previously. However it is possible that only a certain "sum" of volcanic events finally triggers a biotic response.

Fig. 1 - Temporal relationships between the volcanic eruption frequency and extinction events. Volcanism intensifications are highlighted by grey circles (from RUBAN 2009).

The preliminary results show that intensified volcanism cannot provide a better explanation of the crisis than other triggers; however none of the possible triggers alone provide an ultimate explanation.

The evidence makes it plausible, that an intensification of volcanism just before the end of the Pleistocene was able at least to contribute to the extinction of megafauna in America and Eurasia.

References:
RUBAN, D.A. (2009): A possible contribution of volcanism to the end-Pleistocene megafaunal etinction. Natura Nascosta 39:26-32

Darwin's rat and other strange mammals

"I had no idea at the time, to what kind of animal these remains belonged".

C. Darwin 1839

During the first two years of his voyage aboard HMS Beagle, Charles Darwin collected a considerable number of fossil mammals from various localities in Argentina and Uruguay. He recovered his first fossils at Punta Alta on September 23, 1832, and the last two years later at Puerto San Julián.
The fossils were packaged and sent to his former mentor the botanist/geologist John Stevens Henslow, deposited in the Royal College of Surgeons in London, and finally studied and named by Richard Owen between 1837 and 1845. Based on the fossil material Owen described a variety of Pleistocene mammals, including Equus curvidens, Glossotherium sp., Macrauchenia patachonica, Mylodon darwini, Scelidotherium leptocephalum and Toxodon platensis.

Unfortunately during April 10 and 11.1941 the paleontological collection of the Royal College was heavenly damaged by bombardment, almost 95% of the collection got lost. Beginning in 1946 the remaining material was transferred to the Natural History Museum in London, where it is still housed.

Fossils were known in South America since before the Spanish conquistadores, but interpreted as the remains of mythical creatures or giants annihilated by the gods. In 1774 the English Jesuit Thomas Falkner wrote:
"On the banks of the River Carcarania, or Tercero, about three or four leagues before it enters into the Parana, are found great numbers of bones, of an extraordinary bigness, which seem human. There are some greater and some less, as if they were of persons of different ages. I have seen thigh-bones, ribs, breast-bones, and pieces of skulls. I have also seen teeth, and particularly some grinders which were three inches in diameter at the base. These bones (as I have been informed) are likewise found on the banks of the Rivers Parana and Paraguay, as likewise in Peru. The Indian Historian, Garcilasso de la Vega Inga, makes mention of these bones in Peru, and tells us that the Indians have a tradition, that giants formerly inhabited those countries, and were destroyed by God for the crime of sodomy. I myself found the shell of an animal, composed of little hexagonal bones, each bone an inch in diameter at least; and the shell was near three yards over. It seemed in all respects, except it's size, to be the upper part of the shell of the armadillo; which, in these times, is not above a span in breadth."

22 years later the French naturalist George Cuvier published the first scientific work on a fossil South American mammal, and named it the giant sloth Megatherium americanum. In 1806 Cuvier described preliminary three proboscidean types, attributing them to the genus Mastodon. After these first investigations, there was almost no further research, in 1838 Owen wrote in his opening paragraph on his work on the fossil mammals collected by Darwin:
"It may be expected that the description of the osseous remains of extinct Mammalia, which rank amongst the most interesting results of Mr. Darwin's researches in South America, should be preceded by some account of the fossil mammiferous animals which have been previously discovered in that Continent. The results of such a retrospect are, however, necessarily comprised in a very brief statement; for the South American relics of extinct Mammalia, hitherto described, are limited, so far as I know, to three species of Mastodon, and the gigantic Megatherium."

The young Darwin got some of the first fossil determination wrong, so he attributed found osteoderms (regarded by Owen to belong to the giant "armadillo" Glyptodon) to Megatherium, following a reconstruction by Cuvier of an armoured ground sloth, and molars of Toxodon as remains of a giant rodent (but even Owen admitted that these teeth's bear a certain resemblance to those of rodents).
Owen by his part got the general relationship of this mammals incorrect, attributing some genera closer to existing animal-groups then they were in fact.
Influenced by the proposal of Owen, Darwin got convicted that "The most important result of this discovery, is the confirmation of the law that existing animals have a close relation in form with extinct species." (1839), surely a further clue for Darwin that species are not isolated and immutable in time.

Ironically in the error of Darwin there is a ray of truth, toxodonts are today considered highly derived native South American ungulates, distantly related phylogenetically to rodents and guanacos, whereas the large glyptodonts are not the ancestors of armadillos, but to the contrary, the latter are antecedent to the former.

Frederick Waddy: Richard Owen "Riding His Hobby" (1873)

References:

FERNICOLA; VIZCAINO & DE IULIIS (2009): The fossil mammals collected by Charles Darwin in South America during his travels on board the HMS Beagle. Revista de la Asociacon Geologica Argentina. 64(1): 147-159

Extinctions & Excrements

"dal letame nascono i fior
dai diamanti non nasce niente"
From dung flowers are born
From diamonds nothing comes
"Via del Campo", Fabrizio de André (Italian poet-musician)

Until 20.000 years ago North America showed a biodiversity of large mammals comparable with modern Africa, if not greater. 10.000 years later 34 genera with animal-species weighing more than a ton were extinct.

The extinction of the Pleistocene Megafauna is still an unsolved mystery. The proposed hypothesis range from overkill by human hunters to a meteor impact and climate change at the end of the last glacial maximum. Geologically speaking it happened suddenly, but a new study now maybe can date more precisely the extinction pattern and duration, using an unusual data source - fossil excrements and the inhabitants of this "biotope".

In 2005 and 2006 sediment cores with a complessive length of 11,7m were taken from Appleman Lake and compared with other cores of lakes in the U.S. State of Indiana.
Thirteen wood, pollen and charcoal samples, recovered from the lacustrine sediments, were dated by radiocarbon method on ages between 7.000 and 14.000 yr BP and used interpolate an age-depth model of the core.

The fungus-genus Sporomiella lives on animal dung and the spores have to pass the digestive tract of large herbivores to germinate. The spores can also accumulate in sediments along with other micro- and macrofossils like pollen and charcoal, so the presence of the fossil spores in sediments correlates with the amount of excrements - "Lots of dung means lots of spores" (JOHNSON 2009), and the amount of dung can give a hind to extrapolate the size of the population of herbivorous animals like mastodon or mammoth.

The timing of the Sporomiella decline and the first major charcoal peak are well constrained by two dates between 14.6 and 14.7ka. The wood pollen (Quercus and Pinus) increases between 10.7 and 12.2 ka.

Figure from GILL et al. 2009: Appleman Lake time series for (A to F) percent pollen abundances of selected taxa (NAP, nonarboreal pollen), (G) Sporormiella and (I) charcoal counts.

Applying this method, Gill et al. found that the amount of spores first decreases slowly, and only in 14.800 years old sediments the number of spores decreases significantly. To old for the proposed impact, and also to old for a climatic or environmental change - vegetation change, interpolated from the pollen assemblage, namely happens only after the faunal demise, and is more probable caused by the extinction of large herbivore, then the cause of extinction.

The greatest impact of humans - in form of the Clovis Culture - on the Pleistocene landscape in North American was supposed in a time interval between 13.330 and 12.900 years ago. The new data predates the Clovis, nevertheless archaeological findings support a lesser tool specialised pre-Clovis culture in the time interval of the Megafauna collapse, so human influence could not be ruled completely out.

Figure from JOHNSON 2009.

The changing environment after the Megafauna collapse, from an open savanna with scattered trees to a spruce-broadleaf woodland, was the result of ceased pasture of shrubs and trees by Mammoth and Co. The expansion of woodlands is also supported by a larger amount of charcoal in the sediments, from time to time the woodlands caught fire, and the ash was eroded, transported and finally deposited in the examined lakes.

Even if the new method con not give us the definitive answer, at least it's provide some new data to better understand the temporal progress and the environmental change of the late Pleistocene extinction event.

References:

GILL et al. (2009): Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America. Science 326: 1100-1103 http://www.sciencemag.org/cgi/content/abstract/326/5956/1100

GILL et al. (2009): Supporting Online Material for Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America. Science 326. www.sciencemag.org/cgi/content/full/326/5956/1100/DC1

JOHNSON (2009): Megafaunal Decline and Fall. Science 326: 1072 - 1073. http://www.sciencemag.org/cgi/content/short/326/5956/1072

Interview to Dr. Jacquelyn Gill by the Canadian Broadcast: mp3 (4MB)

--------- Thanks to Ole Nielson for linking to the post----------

Cool Artiodactyls

Islands seem to have own rules concerning evolution, forming unusual animals like dwarfing elephants and gigantic rats. But islands are in fact unusual habitats with limited resources and so available energy. To survive special adaptations are necessary to economize this energy. Ectotherm vertebrates, like reptiles, are specialists in coping with low levels of available energy, but doing so these animals display an inconstant growth - with times of low or ceasing growth when conditions are unfavourable. Endotherm animals, like mammals have high and steady growth rates, but the necessity of constant food - energy - input, on a confined island a possible problem. But the Pliocene-Pleistocene "cave goat" or "Mouse-goat" Myotragus balearicus after a new study by Köhler & Moyá seems to have combined the best parts of being reptile and mammal together.

Myotragus balearicus (wikipedia)

Studying fossil material of this extinct species, the researchers have noted in bone transects cyclic LAGs - lines of arrested growth. This pattern was until now unknown in mammal bones, even if single lines were known in cervids, the physiology of Myotragus seems to have used this strategy repeatedly. Myotragus grew at slow and variable rates; growth could also be arrested completely to save precious energy. With this strategy the species managed to survive on the resource poor island of Majorca for more then 5,2 million years, until humans colonized the island, and, like many times before and after, forced the species to extinction.

The mystery of Darwin's wolf

During the voyage of the Beagle, (just) one (other) of the puzzling observations by Charles Darwin was the presence of a large canid on the remote Falkland Islands - as only native mammal species. On the two islands, Darwin recognized differences between the East Falkland and West Falkland wolves (Dusicyon australis), a further clue for Darwin that species are not fixed entities.

Illustration of Dusicyon culpaeus from Zoology of the Voyage of H.M.S. Beagle (source wikipedia).

Ever since the Falklands wolf was described by Darwin, the biological origin of this now-extinct endemic canid, and how the animal reached the island, 480 kilometres distant from the South American continent, remained a mystery. Possible hypothesis about the ancestry of this enigmatic canid suggested that the Falkland wolf was related to domestic dogs, North American coyotes, or South American foxes, and was brought on the islands by human colonists.

A new study, published in "Current Biology", compared the DNA sequence of preserved museum specimens with modern canids, and helped to solve some of the riddles of this animal.
The analysed DNA sequences show that the closest living relative is actually the maned wolf-, Chrysocyon brachyurus, an unusually long-legged, fox-like South American canid - from the physical appearance very different to the wolf. The researchers also found that the four Falklands wolf samples that they examined shared a common ancestor at least 70,000 years ago, which suggests that they arrived on the islands before the end of the last ice age and appearance of humans on the American continent. This fact seam's to rule out the prevailing theory that Native Americans brought the first animals on the Falkland's.
A possible remaining explanation for the wolves' presence on the islands, which have never been connected directly to the South American mainland, is the dispersal of individuals by ice or swimming logs.
During ice ages the sea level was up to 200m lower than today. Even if this is not enough to form connecting land bridges between the mainland and the islands, the resulting sea passages were much closer, maybe facilitating significantly the surviving of animals on their "travel" to uncolonized habitats.

Topography of the South American continet and bathygraphy, note the -200m area (data source)

Mountains as only witnesses

Like islands in the sea small hills, only some dozen meters in height, rises from the flat landscape of the "Orla-valley" south of Weimar. These “mountains” consists of limestone of ancient reefs, growing once in the Permian "Zechstein - sea". Tectonic and erosion have done they dirty work since them, leaving behind only isolated “Zeugenberge” (rude translated in Witnesses mountains) from the marine deposits.

The archeological site "Gamsenberg".

In a flat landscape every vantage point, that enables a hunter to overlook a vast territory, is of strategic importance. And in fact during the last ice age early man observed from this Zeugenberge the glacial steppe in search for the big herds of mammals.

Today the summits of these hills are mostly flat, covered by dense shrubby vegetation, and the surrounding landscape is characterized by villages, fields and scattered trees.
During excavations in a depression on the summit of the “Gamsenberg” – presumably in a karst depression or a collapsed cave - underlying 1,5m thick Loess deposits from the last glacial, a fossil soil was discovered, that contained lithic artefacts, bone fragments and charcoal. This paleosoil developed under warm climatic conditions on rubble of the underlying limestone, this rubble also shows cryoturbation.

The stratigraphic section of the archeological site "Gamsenberg". The upper part consists of Loess deposits, that overlay periglacial displaced rubble and rock fragments (cryoturbation).

Dating of glacial loess samples resulted in ages between 44.700+-4.500 and 41.900+-4.600 years. Between this stratigraphic layer and the horizon with the artefacts bones of micro mammals were found, especially the remains of pika (Ochotona) and lemming (Lemmini) indicate dry, cold conditions. Dating of the layer with the artefacts gave an age of 52.500 to 70.900 years, the bone fragments in this layer belong to animals like elk (Alces), horse (Equus hydruntinus and taubachensis), stag (Cervus elaphus), deer (Capreolus capreolus), auerochs (Bos) or bison (Bison) and a undetermined proboscidean (Mammuthus ?).
This animal assemblage is indicative for a dry, continental to boreal climate, with a mosaic of tree spots and steppe areas. The paleobotanic remains are also indicative to a climate with warm summers, but an annual average temperature to low to permit the establishment of deciduous tree forests.

The only time period that coincide with the radiometric ages, and also with a change between warm to cold climate temperatures, like indicated by the sedimentological and paleontological evidences, is the Odderade interstadial between 70 to 60kyrs during the Weichsel ice age.

Humans, presumably Neanderthals, used the Zeugenberge as ideal vantage point to overlook the steppe with sparse wood spots during an interstadial of the last glacial period. Here they prepared their tools, using rocks like flintstone (found in morainic deposits 20 kilometres away), quartz, greywacke and siliceous schist. After spotting a herd of animals, and (hopefully) successful hunt, they returned and butchered their prey on this site. Then, during full glacial conditions some 50.000 years ago wind transported dust covered the abandoned site, and only today, the karst fissures return their hidden secrets.

References:

WEBER, T. (1996): Das Paläolithikum und das Mesolithikum in Mitteldeutschland. Archäologie in sachsen-Anhalt Nr.6. Archäologische Gesellschaft in Sachsen-Anhalt, Halle

Dating cave sediments

The decay chains between radioactive and a series of daughter isotopes is a useful tool to date sediments and rocks.

The radioactive decay process of uranium (238U and 235U) and thorium (in the form of either 230Th or 232Th) were investigated in 1938, but only in the 1950s and 1960s the method was applied to date lacustrine carbonates, marine sediments, corals and cave calcite deposits.

Thorium is a daughter product in the 238U decay chain. This element is much less soluble in water than uranium and is not found in groundwater, thus, speleothems (including flowstones, stalagmites and stalactites) formed in caves as a result of precipitation of calcium carbonate from aqueous solutions, will show an uranium-, but no thorium content. Thorium will be produced only as the uranium isotopes decay with time, providing a dating tool for such materials in the age range for some 100ka.

Speleothems are well suited for this dating method because their calcite crystals are usually large and have little tendency to recrystallize after deposition, forming so a "closed" system, where no contamination can "enter", and no information can "escape".
When viewed in cross section many speleothems display a prominent laminated structure (growth layers), caused by variation of the deposition conditions and so the deposited material (p.e. amount of fluid inclusions or organic matter).

The growth of speleothems depends not only from the presence of water, but also of it’s content of dissolved CO2. Before percolating through the bedrock, surface water is exposed first to atmospheric CO2 and then to soil gases enriched in biogenic CO2, from where most dissolved CO2 in groundwater comes.

The stratigraphy of the Conturines cave was recorded during the excavations conducted from 1988 to 1990, from 1996 to 1998 and in 2001. As excavation site the first encountered area with the scattered bones and skulls, where the small conduit opens in the much larger main hall of the cave – denominated conveniently “hall of skulls”- was chosen. The floor of the upper parts of the cave is covered by up to 2m thick flowstone that shows a fine lamination, maybe representing annual cycles.


It is overlain in turn by sand, fossiliferous dolomitic sand, again sand without fossil and finally large blocks.
The presence of such thick flowstone implies, that there were abundant precipitation and conditions favourable to develop soil horizons and vegetation cover in the catchment area of the cave. This limits the period of flowstone genesis to an interglacial or a warm interstadial period.
The fossils of cave bear are found only in the sand overlying the flowstones, implying that this deposit is younger. Cave bears were herbiverous animals, but today vegetation can found only 1.000m lower. During the occupation of the cave by the cave bear, vegetation was aviable in immediate vicinity, this also let´s assume that this deposits represents another warm period, with a shrub- and treebelt extending much higher then today.

So at least we need two periods were the temperatures reached higher values then today on this site – this was the case during the interglacials of the Eemian (130 to 120kyr) and the Holstein (350-300kyr). The comparation of the anatomical features of the Conturines bear with other high alpine extinct bear species seemed to confirm an minimal age between 65.000 to 30.000 years, implying a hypotetical warm and icefree period just before the glacial maximum 20.000 years ago.

So it is possible by the stratigraphy and the evolution “niveau” of the bear fossils to restrict the sedimentation phase in the cave to a period between 300kyr and 30.000 years ago.

It’s notable that the radiometric dating method confirmed in part this hypothesis. The dates of the flowstone samples resulted beyond the range of dating of 350kyr by the thorium - uranium method. The bone-bearing sands are much younger, the two oldest dates obtained by dating the bones are 87+-5kyr and 108+-8/-7kyr. Similar to the flowstone dates, the C14 method applied to the bones resulted in an age older then 39.000 years - beyond the limit of this method.
Even if this shifts the possible ages for the first sedimentation phase considerably to older ones, the flowstone still could be deposited during, or slightly before the Holstein, or – and this would be very exceptional, during the Cromer interglacial (800kyr).
Then a sedimentation phase follows, with the deposition of grey, yellow and red sand, containing no fossils, overlaid by the fossil bearing sand and rubble layer. The radiometric results seems to confirm an age for the occupation of the cave by the bear during, or just after the Eemian.
Then erosion removes and reworks in part the fossiliferous sandy layers – channels forms, which later were refilled with an grey sandy material, again lacking fossils.

This example shows how the limitations of the different dating methods can be compensated in part by careful observations and the “strengths” of other methods, and many different results are needed to reconstruct the sedimentation history in a "restricted" environments like caves.


References:

SCHWARCZ, H. Speleothems. In (ed): ELIAS, S.A. (2006): Encyclopedia of quaternary science. Elsevier : 290-300
SPÖTL et al.(2006): The last and the Penultimate Interglacial as Recorded by Speleothems From a Climatically Sensitive High-Elevation Cave Site in the Alps. In SIROCKO, F. et al. (ed): The climate of past interglacial. Developments in Quaternary Science 7.

Cave bear Cave

From the old things and old times I have heard, and I will now tell.

In August 1987 the fossil and mineral collector Willy Costamoling was exploring the area of the Conturines Mountains in the South Tyrolean Dolomites.

The Conturines mountains, the name derives from the ladinic language "con turrines", meaning "with towers". Especially the south wall of the migthy dolomite mountain are structured by numerous cliff towers.

The "Piz Taibun" (on the right), and "Piz dles Conturines" (on the left), surrounding the glacial excavated cirque of "the cave".

He was looking for calcareous concretions that form in dolomitic sands and rubble deposited in caves and fissures, denominated, after a valley where they are usual found and their sometimes unusual form “Travenanzes dolls”. Ascending to the “Piz Taibun” - a secondary summit of Conturines, he noted a cave at the very end of a glacial carved cirque.

The entrance of the cave at the end of the glacial cirque...

... and the very first meters inside it.

He decided to try his luck, and return with appropriate tools to explore the cave. On September 23. finally he stood in more then 2.700m altitude before the 5m high, and 10m broad portal. Behind the entrance a vast, empty cavity, at the first glance only some meters deep and then delimited by a rock wall, but then - on the left side a dark passage seemed to go further inside the mountain. Here the darkness, illuminated only by the headlamp, and large boulders on the cave bottom made it difficult to proceed. After 160m, and a height difference of 60m, the conduit seemed to open in a larger hall. At the entrance of this underground hall – like an old guardian- stood a bulky stalagmite.

"The guardian".


Behind it the cave bottom was covered by smooth flowstones and dolomitic sand, and scattered around … bones, a lot of large bones. The discoverer attributed them first to a recent bear, only after he showed some teeth that he brought back home to a other collector they realized that the bones were from the extinct cave bear.
And if this discovery seemed not surprisingly enough, at the very end of this mountain hall stood, some meters high, an impressing, beautiful cascade of stalagmites and stalactites.

After a legendery, secret and long lost treasure, consisting of a precious stone hidden deep inside the Dolomite mountains, it was called "Raetia" :

Introducing the cave bear

On October 22 of the year 1794 a young German medicine student submitted his “dissertatio” to the philosophical faculty of the University Leipzig. In this work, the 23 year old Johann Christian Rosenmüller described a well preserved skull of a bear discovered in a cave near the village of Burggaillenreuth in the Franconian Alb (Central Germany). Caves and fossil bones are widespread in this region, already in 1774 the german priest Johann Friedrich Esper (1732 – 1781) , recognising that the bones do not belong to a brown bear, claims – missing other material to compare - that they represent remains of a polar bear. In the following years other authors agree that the fossils can not attributed to known bear species, but only Rosenmüller describe this “unknown creature” as a new species – and because of the rich discoveries in caves – he names it “cave bear” Ursus spelaeus ROSENMÜLLER 1794.

The illustration of the holotype - skull for the species Ursus spelaeus in the work of ROSENMÜLLER 1795 from the “Zoolithenhöhle” near Burggaillenreuth (Franconian Alb). The specimen today is lost.

In 1795 Rosenmüller, after supplementary studies, publish a second description and confirmation for the new established species. He also rejects the contemporary speculations about the genesis of the bone accumulations as result of a flood catastrophe, and propose simply a slow, but consistent accumulation and deposition trough animals dying by natural causes inside the caves:

„Wir können das Dasein einer solchen Menge fossiler Knochen nicht leichter erklären, als wenn wir annehmen … daß die Tiere, von denen sie sind, in denen Höhlen gelebt, sich daselbst fortgepflanzt haben und drinnen größtenteils gestorben sind” (We can easily explain the existence of such a quantity of fossil bones, as if we assume that the animals, from which they come, have lived in those caves, have reproduced in them and have finally also died inside them).
ROSENMÜLLER 1795

250 years later the Cave bear is one of the best studied mammals of the ice age, and among others one of the best known by a broader audience. This results surely by the large number of bones found of this animal, and also the location of the remains in caves, where it maybe influenced the legends of “cave occuping dragons”.

Arnold Böcklin (1827 - 1901).

References:

ROSENMÜLLER, J.C. (1794): Quaedam de ossibus fossilibus animalis cuiusdam, historiam eius et cognitionem accuratiorem illustrantia, dissertation, quam 22. Octob. 1794 ad disputandum proposuit Ioannes Christ. Rosenmüller Heßberg-Francus, LL.AA.M. in Theatro anatomico Lipsiensi Prosector assumto socio Io. Chr. Aug. Heinroth Lips. Med. Stud. Cum tabula aenea. O.V. Leipzig
ROSENMÜLLER, J.C. (1795): Beiträge zur Geschichte und näheren Kenntniß fossiler Knochen. Georg Emil Beer. Leipzig

Fissures, holes and caves II

Bone accumulations in caves were known since antiquity – Greek sailors tell that they found the bones of Cyclops in caves on the island of Sicily. Some centuries later, the German Jesuit Athanasius Kircher visited and studied this bones, and in 1678 he published an extensive report , the “Mundus subterraneus”, on this matter, proclaiming that the remains represent at least the bones of four different kind (and sizes) of prehistoric giants. Only more centuries later the fossils were recognised to belonging to Pleistocene elephants.

In the 18th and 19th century the bones were mostly attributed to belong to victims of the biblical flood – this idea also should explained the transport and the deposition in caves of the remains.
Until 1970 bone accumulations – recognised as fossils – were mostly attributed to human activity, even if earlier observations showed how carnivores can gather and process bones in similar way as expected for human behaviour.

I have had an opportunity of seeing a Cape hyaena at Oxford...I was enabled also to observe the animal´s mode of proceeding in the destruction of bones: the shin bone of an ox being presented to this hyaena, he began to bite off with his molar teeth large fragments from its upper extremity, and swallowed them whole as fast as they were broken off. On his reaching the medullary cavity, the bone split into angular fragments...he went on cracking it till he had extracted all the marrow... this done, he left untouched the lower condyle, which contains no marrow, and is very hard. The state and form of this residuary fragment are precisely like those of similar bones at Kirkdale; the marks of teeth on it are very few...these few, however, entirely resemble the impressions we find on the bones of Kirkdale; the small splinters also in form and size, and manner of fracture, are not distinguishable from the fossil ones...there is absolutely no difference between them, except in point of age.
BUCKLAND 1823 Reliquiae Diluvianae, or, Observations on the Organic Remains attesting the Action of a Universal Deluge

The modern (re)interpretation of fossil bearing sites let conclude that the interaction between prehistoric humans and animals is complex and an ever-changing one. In the locality of Zhoukoudian (China) 42 hominid skeletal elements were found, 28 of them showing hyenid tooth marks – gnawing, biting, chewing, punctures, even regurgitation. On the other side, rhinoceros bones at the same locality show no activity by predators, but display cut marks – implying that early paleolithic humans are both predator/scavengers and preys. Nevertheless it is assumed that during later time periods humans become active and successful hunters, and lesser prey.

Fissures that act as sediment and also bone accumulation traps can develop not only in carbonates, but also in evaporitic sediments. Near the small village of Westeregeln (Thuringia, Germany) past quarrying activity for clay has exposed underlying Mesozoic gypsum and limestone formations, which in the upper part show an intensive “karst” network, refilled with Pleistocene sediments and fossils.


The uppermost part of the stratigraphic column of the infilling sediments is represented by a postglacial soil, developed on Loess – aeolian sediment deposited during the last great glacial period. These sediments cover ancient matrix supported breccias, presumably generated by partial collapse of former caves or fissures. Between these breccias, mostly on the top of the deposits, lithic artefacts, bones of ice age mammals and hyena coprolites are found exclusively in pebbly horizons.


Remarkable is - by a preliminary result - a human rib enclosed, how it seems, in a hyena coprolite. From the hyena were also discovered at least ten skulls, attributed to the ice age hyena Pachycrocuta brevirostris.

The site is still under examinations, so it is not clear if the apparent simultaneous presence in one layer of lithic artefacts/ humans bones and hyena bones mean also coexistence during the same time of this two species. Also the possible engulfed human bone can be explained by hyenas actively hunting humans, scavenging human remains, or simply -as artefact of the disturbed startigraphy and subsequent diagenesis.

The site of Westeregeln is interesting also for another “kind of fissures”. In red clays, colluvial material derived from the weathering of underlying sandstones, during the last glacial maximum an extensive ice wedge net developed. After the ice that created this wedges melted, the remaining fissure was filled by Loess. Today these ice wedges casts are easily eroding, and reveal not only loam and sand, but also lithic artefacts, that thousand of years ago felt into the open cracks and were “accumulated” and preserved trough time.


References:

BOYLE (2007): Vertebrate studies: Interactions with Hominids. In: (ed.) ELIAS: Encyclopaedia of Quaternary Science. Elsevier

Fissures, holes and caves

Most extensive cavity networks occur in water soluble lithology, like carbonatic or evaporitic formations, but smaller fissures and gorges can develop also by mechanical erosion or physical degradation of the underground, for example melting of ice (thermokarst).

Fissures can gather animals’ remains over a certain time interval simply by animals falling and/or remaining entrapped inside, and being otherwise inaccessible the bones are also protected from scavengers.

An important site of this type is represented by Pirro Nord, situated in a quarry at the north-western margin of the Gargano promontory, close to the village of Apricena in the italian province Apulia.

Here in sediments filling an extensive karst network, discovered during quarrying of limestone, a very diverse and now well-documented fossil vertebrate assemblage was discovered. This sediments returned also lithic artifacts, estimated in an interval between 1,3 and 1,7 Ma, documenting an early hominin occurrence in the older part of the Early Pleistocene, and thus now constitute the oldest record in Europe.
The karst network developed during two phases. The first, Miocene in age, extents in the mesozoic limestone of the „Sannicandro Formation“ (Cretaceous), and consists of red clays (terra rossa) in part reworked and redeposited with a hughe diversity of vertebrates remains assigned to the „Mikrotia-Fauna“, after a an endemic rodent genus.
The second phase of karst development occurred after a tectonic uplift of the Gargano peninsula during the Pliocene, extending in formerly deposited Pliocene sediments and protruding in the Sannicandro Formation. Fissures can also show in the lower part fossils attributed to the Mikrotia – Fauna, and in the upper parts of the Villafranchian mammal age (Upper Pliocene and Lower Pleistocene, 3.6–1.2 Ma ago).

The stratigraphic succession of the Apricena horst in the „Cava Passalacqua”, as seen in the vast quarry dominating the landscape near Apricena. In the lower part the quarried Mesozoic limestone’s of the “Sannicandro Formation”, truncated by Miocene red clays and karst infillings of the “Terre rosse”, covered by the yellow Pliocene deposits of the “Lago di Varano Formation” and finally sandstones of the “Serracapriola Formation”.

Detail of the “Sannicandro Formation” with extensive karst network development.

Balanus sp. occurrence in the Pliocene cover units.

The accumulation of large mammals has been due the infall or entrapment of carcasses within the wider cavities, and by subsequent transport within the karst network when it was flooded. The occurrence of a number of articulated skeletons is suggestive of accumulation of carcasses also without transport.

Karst fissure with extensive infill of red, sandy clays - "Terra Rossa", and also bones:
A teeth of Deinogaleryx, an giant hedgehog...

...and Hoplitomeryx, an endemic Miocene artiodactyl.

The abundance of bones and coprolites of Pachycrocuta brevirostris, as well as the occurrence of numerous gnawing and bite marks on fossil bones, suggests that this giant hyaenid species played an important role in local bone accumulation.

The Pirro Nord fauna mammal fauna is uncommonly diverse, until now 20 species of amphibians and reptiles, 47 species of birds and over 40 mammal species were described, some of them though to be endemic to the Gargano.
The nature of the landscape of the „catchment area“ of the ancient caves 2 Ma ago can be inferred from the composition of it´s vertebrate assemblage. The occurrence of perissodactyls, cheetah, large sized porcupine, abundant vole of the genus Allophaiomys and presence of bird species of the families Otidae, Pteroclidae and Alaudidae are all suggestive of open landscape with a basically arid climate.

Mandible with teeth from a Pleistocene bat.

References:
ARZARELLO et al. (2007): Evidence of earliest human occurrence in Europe: the site of Pirro Nord (Southern Italy). Naturwissenschaften 94: 107-112
PAVIA & ZUNINO (2009): Giornate di paleontologia IX edizione Apricena (FG), 28-31 Maggio 2009 – Guida alle escursioni 30 e 31 maggio 2009.

See part II

On the tracks of ancient mammals

Tetrapod tracks, trackways and related deformation structures can constitute an important source of paleontological and sedimentological information. Moreover, in recent times our knowledge of mammalian tracks in Holocene and Pleistocene (not only Jurassic) beach, dunes, washover fans and related environments, has been significantly increased by new discoveries. The main characteristics of sediments which play a significant role in track preservation are:

- Grain size, for example in coarse sediments anatomical features are less preserved

- Sediment macrofabric

- Sediment Cohesion

- The moisture content influences the sharpness of the shape, as well as clearly impressed or blurred tracks depend on water content

- Reworking of external agents, like waves and wind, depending on time of exposure and/or burial, can erode trackways.

- Also the tracemakers itself can prevent conservation, by further intensive trampling older tracks can be blur or destroyed, and also the slope and extent of vegetation cover during animal passing can avoid foot impressions. The behaviour gait and size of the tracemaker are also fundamental for preservation, for example deeply impress tracks by heavy individuals are more likely to be preserved.

The most suitable environment for trackways preservation are represented by tidal and flood plains, lagoons periodically subject to water level oscillations and even complete desiccation, and distal portions of washover fans, where moist, coherent, fine grained sediments are present. In areas of washover fans characterised by channels and barrens the preservation is less probable, influnced strongly by changing sedimentation dynamics.
Nevertheless mammals trampling on such a muddy to sandy sediment, still damp or wet, impress footprints that can easily be preserved if the sediment surface hardens, and then are covered by low-energy flooding, whose suspension load fills and buries tracks. During the transition Pliocene-Pleistocene, planteaters were present in coastal areas, such as beaches and dunes, where probably they were, as occurs nowadays, attracted by salt crusts.

Extraordinary examples of mammalian trackways can be found on the Italian Peninsula, ranging in age from Pliocene to Pleistocene on various sites in Sardinia, and the hill of Osoppo (North-Italy).

In Sardinia tracks and trackways attributed to the ichnogenus Bifidipes have been found on naturally exposed surface corresponding to originally stiff or firm sandy carbonate mud to pebbly sands on 6 localities. The ichnogenus Bifidipes (isp. aeolis) is also known of the Pleistocene of the Balearic Islands, where is was produced by the endemic artiodactyl Myotragus balearicus. The imprints of Sardinia where also assigned to an endemic middle-size artiodactyl -“Praemegaceros” cazioti, the only single cloven-hoofed artiodactyl present on the island during the Pleistocene.
Two main imprints associations were produced: simple tracks and, more frequentely, compound tracks. The morphology of the tracks is strongly related to the substrate conditions and to the sedimentary context, influencing the potential of preservation. Bifidipes shows similarities to tracks of modern Cervus elaphus and Dama dama, however the parameters indicates that the animal that left this tracks was slightly larger then the average fallow-deer, and smaller than adult males of C. elaphus.

Pic.1. Trackways on pebbly coarse sandstones. Porto Paglia (Gonnesa), south-west Sardinia (from FANELLI et al. 2007).

Pic.2. Trampled bedding surface showing tracks. Sediment deposited within the tracks is locally preserved. Alghero (Nurra), north-western Sardinia. Below: Compound track on damp sand. Porto Paglia (Gonnesa), south-west Sardinia (from FANELLI et al. 2007).

References: FANELLI, F.; PALOMBO, M.R.; PILLOLA, G.L. & IBBA, A. (2007): Tracks and trackways of “Praemegaceros” cazioti (Deperét 1897) (Artiodactyla, Cervidae) in Pleistocene coastal