Palynology of the Ischigualasto Formation.

Ischigualasto-perfil-gusano-montañas

Image from Ischigualasto Park (http://www.ischigualasto.gob.ar/)

Ischigualasto is an arid, sculpted valley, in northwest Argentina (San Juan Province), limiting to the north with the Talampaya National Park, in La Rioja Province. Both areas belong to the same geological formation: the Ischigualasto-Villa Unión Basin which is centered on a rift zone that accumulated thick terrestrial deposits during the Triassic. This basin preserves a complete and continuous fossiliferous succession of continental Triassic rocks.

The Ischigualasto Formation is known worldwide for its tetrapod assemblage, which included the oldest known record of dinosaurs. Adolf Stelzner in 1889 published the first data on the geology of Ischigualasto, but it was not until 1911, that Bondenbender briefly refers to the fossils of the site. Several thin volcanic ash horizons, indicates that the deposition of the Ischigualasto Formation began at the Carnian Stage (approximately 228 mya), and consists of four lithostratigraphic members which in ascending order include the La Peña Member, the Cancha de Bochas Member, the Valle de la Luna Member, and the Quebrada de la Sal Member.

1–3. Retusotriletes herbstii sp. nov; 4–5. Rogalskaisporites cicatricosus; 6. Rugulatisporites

1–3. Retusotriletes herbstii sp. nov; 4–5. Rogalskaisporites cicatricosus; 6. Rugulatisporites

During the Late Triassic two distinct microfloras have been recognised in the southern hemisphere: the Ipswich microflora and the Onslow microflora. The Ipswich province, characterized by the abundance of bisaccate pollen, monosulcate pollen and trilete spores, evolved in southern and eastern Australia, Transantarctic Mountains region, South Africa and Argentina. The Onslow province is a mixture of Gondwanan and European taxa recognized in of north-western Australia, Madagascar, East Africa, Indian, and East Antarctic (Cesari and Colombi; 2013).

The recognition of Carnian European species in the Valle de la Luna Member of the Ishchigualasto Formation expands the distribution of the Onslow-type palynofloras. This assemblage was recovered from the site known as “El Hongo” in the Provincial Park, and contain the diagnostic “Onslow” species: Samaropollenites speciosus, Enzonalasporites vigens, Patinasporites densus, Vallatisporites ignacii, Ovalipollis pseudoalatus and Cycadopites stonei. This assemblage indicates that the Valle de la Luna Member was likely deposited under more humid conditions. It also implies the existence of a latitudinal floral belt from Timor (through the Circum-Mediterranean area) to western Argentina.

 

References:

Cesari, Silvia N., Colombi, Carina, Palynology of the late Triassic ischigualasto formation, Argentina: Paleoecological and paleogeographic implications, Palaeogeography, Palaeoclimatology, Palaeoecology (2016), doi: 10.1016/j.palaeo.2016.02.023

Césari, S. N., Colombi, C. E., 2013. A new Late Triassic phytogeographical scenario in westernmost Gondwana. Nature communications, 4.

Spalletti, L. A. Artabe, A. E. & Morel, E. M. Geological factors and evolution of southwestern Gondwana Triassic plants. Gondwana Res. 6, 119–134 (2003).

 

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The Pliocene Warm Period, an analogue of a future warmer Earth.

 

Tuktoyuktuk Beach on the Arctic Ocean (From Wikipedia)

Tuktoyuktuk Beach on the Arctic Ocean (From Wikipedia)

Microfossils from deep-sea are crucial elements for our understanding of past and present oceans. Their skeletons take up chemical signals from the sea water, in particular isotopes of oxygen and carbon. Over millions of years, these skeletons accumulate in the deep ocean to become a major component of biogenic deep-sea sediments. The incorporation of Mg/Ca into the calcite of marine organisms, like foraminifera, is widely used to reconstruct the thermal evolution of the oceans throughout the Cenozoic. Planktic foraminifer Globigerinoides ruber is perhaps one of the most widely used species for reconstructing past sea-surface conditions. Additionally, Mg/Ca–oxygen isotope measurements of benthic foraminifera may be related to global ice volume and by extension, sea level (Evans et al., 2016). The importance of microfossils as tool for paleoclimate reconstruction was recognized early in the history of oceanography. John Murray, naturalist of the CHALLENGER Expedition (1872-1876) found that differences in species composition of planktonic foraminifera from ocean sediments contains clues about the temperatures in which they lived.

Scanning Electron Micrographs of Globigerinoides ruber (adapted from Thirumalai et al., 2014)

Scanning Electron Micrographs of Globigerinoides ruber (adapted from Thirumalai et al., 2014)

The most recent investigations have focused on unravelling the Pliocene Warm Period, a period proposed as a possible model for future climate. The analysis of the evolution of the major ice sheets and the temperature of the oceans indicates that during the middle part of the Pliocene epoch (3.3 Ma–3 Ma), global warmth reached temperatures similar to those projected for the end of this century, about 2°–3°C warmer globally on average than today.

The mid-Pliocene is used as an analog to a future warmer climate because it’s geologically recent and therefore similar to today in many aspects like the land-sea configuration, ocean circulation, and faunal and flora distribution. Mid- Pliocene sediments containing fossil proxies of climate are abundant worldwide, and many mid- Pliocene species are extant, making faunal and floral paleotemperature proxies based on modern calibrations possible (Robinson et al., 2012).

Surface air temperature anomalies of (top) the late 21st century and (bottom) the mid-Pliocene (from Robinson et al., 2012)

Surface air temperature anomalies of (top) the late 21st century and (bottom) the mid-Pliocene (from Robinson et al., 2012)

Foraminiferal Mg/Ca data suggest that the Pliocene tropics were the same temperature or cooler than present. At high latitudes, mid- Pliocene sea surface temperatures (SSTs) were substantially warmer than modern SSTs. These warmer temperatures were reflected in the vegetation of Iceland, Greenland, and Antarctica. Coniferous forests replaced tundra in the high latitudes of the Northern Hemisphere. Additionally, the Arctic Ocean may have been seasonally free of sea-ice, and were large fluctuations in ice cover on Greenland and West Antarctica (Dolan et al., 2011; Lunt et al., 2012).  These results highlights the importance of the Pliocene Warm Period to better understand future warm climates and their impacts.

Reference:

David Evans, Chris Brierley, Maureen E. Raymo, Jonathan Erez, Wolfgang Müller; Planktic foraminifera shell chemistry response to seawater chemistry: Pliocene–Pleistocene seawater Mg/Ca, temperature and sea level change; Earth and Planetary Science Letters, Volume 438, 15 March 2016, Pages 139-148

Jochen Knies, Patricia Cabedo-Sanz, Simon T. Belt, Soma Baranwal, Susanne Fietz, Antoni Rosell-Mel. The emergence of modern sea ice cover in the Arctic Ocean. Nature Communications, 2014; 5: 5608 DOI: 10.1038/ncomms6608

Robinson, M.; Dowsett, H. J.; Chandler, M. A. (2008). “Pliocene role in assessing future climate impacts”; Eos 89 (49): 501–502.

Dorothea Bate: cave explorer and paleontologist.

dorothea bate

Dorothea Bate excavating in Bethlehem 1935.

During the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. A good example is Barbara Hastings (1810–1858), 20th Baroness Grey de Ruthyn and Marchioness of Hastings. A special case was Mary Anning, ‘the greatest fossilist the world ever knew’. Scientists like William Buckland or Henry de la Beche owe their achievements to Mary’s work. Thanks to the pioneer work of these women, the 20th century saw the slow but firm advance of women from the periphery of science towards the center of it.

Dorothea Bate was one of these pioneer women. She was born in Carmarthen in South Wales in 1878.  She was one of the last generation of Victorians, and witnessed the significant challenge to traditional ideas about women’s submissive place within society. When Dorothea was 10 years old, her family moved to South Wales where she begins to collect insects, stones, fossils, ferns, and flowers. She also learned how to dissect birds and small mammals. Her first passion was ornithology, and when she was 19, she went to London and asked for a job at the British Museum. She was taken to the Bird Room. That was the beginning of her association with the British Museum that was to last for more than 50 years.

Dorothea Bate c. 1906, by her sister Leila Luddington.

Dorothea Bate drawing by her sister Leila Luddington (1906).

Her first paper , published by Henry Woodward in the Geological Magazine in 1901, was a report on the Wye valley fossils. In the paper, she describes the fossils of small rodents from the last ice age recovered from the “Merlin’s Cave”, a place particularly dangerous to reach. That same year, she embarked on the first of her pioneering explorations of the Mediterranean islands. She visited Cyprus and became the first paleontologist to search systematically the limestone caves of the island and discover its extinct fossil fauna. In 1904, she went to Crete, then the scene of spectacular archaeological discoveries. In Cyprus and Crete, Dorothea found the fossilized remains of dwarf elephant, Elephas cypriotes Bate and Elephas creticus Bate (Bate 1903, 1907).

In 1909, after a five-year hiatus resulting in part from her parents’ reluctance to allow her to travel abroad alone, she went to the Balearic Islands. Invited by her good friend the Reverend Robert Ashington Bullen, Dorothea started her journey in Mallorca, where she discovered and described a bizarre goat-antelope with rat-like teeth, which she named Myotragus balearicus. Between 1903 and 1914, Dorothea wrote more than 15 papers on her Mediterranean discoveries. Unfortunately, in the early 1900s, a woman could not be elected a fellow of a learned society, nor present her own paper, so Henry Woodward presented them for her.

Dorothea Bate in 1938 (Copyright Natural History Museum, London.)

Dorothea Bate in 1938 (Copyright Natural
History Museum, London.)

In 1924, although women remained ineligible for permanent staff positions, Dorothea was named Curator of Aves and Pleistocene Mammals. She worked at Mount Carmel with Cambridge archaeologist and prehistorian, Dorothy Garrod, in a pioneering work on the relationship between fauna, climate change and the environment. In 1940 she was awarded with the prestigious Wollaston Fund of the Geological Society. Shortly after, she was elected a Fellow of this Society. Eight years later, she was appointed Officer-in-Charge of the Tring Museum in Hertfordshire, an outpost where the Natural History Museum’s collections had been evacuated during World War Two.

Despite her delicate health, she continued working until her dead on 13 January 1951.

References:

SHINDLER, K. (2007): A knowledge unique: the life of the pioneering explorer and palaeontologist, Dorothea Bate (1878-1951).

BUREK, C. V. & HIGGS, B. (eds) The Role of Women in the History of Geology. Geological Society, London, Special Publications, 281, 1–8. DOI: 10.1144/SP281.1.

Bate, D.M.A. 1914. On the Pleistocene ossiferous deposits of the Balearic islands. Geological Magazine, 6: 337-345.

Wyse Jackson, Patrick N.; Mary E. Spencer Jones (2007). “The quiet workforce: the various roles of women in geological and natural history museums during the early to mid-1900s”, Geological Society of London. pp. 97–113.