Dr John Murray BA., Ph.D
Carboniferous Stratigraphy & Palaeontology
I have strong interests in all aspects of Carboniferous sedimentology and palaeontology in both Ireland and further afield. The main fields of my research lie in carbonate sedimentology and palaeontology with a major focus on the Lower Carboniferous (Mississippian) of the Shannon Basin of southwest Ireland. I am particularly interested in the genesis and development of carbonate mud-mounds, microbialites and evaporites and their impacts on coeval biota.
My PhD Thesis was titled Mid to Upper Viséan facies and palaeoenvironments of the Shannon Basin, Western Ireland. This study focussed on the patterns of facies change and subsidence history of the Carboniferous (Mississippian) intracratonic Shannon Basin, based principally on detailed field and lab-based analysis of carbonate sedimentology, petrography and palaeontology (macro & micro-palaeontology and palaeoecology). A significant component of the report involved the description of a highly unusual form of calcitised evaporite ('striped limestone') which forms an 'event horizon' right across the basin.
The Carboniferous was a very important time in Earths history as the word steadily cooled and moved from Greenhouse to Icehouse conditions. The Permo-Carboniferous Glaciation [PCG] provides the closest comparable analogue for the glacial phase, which persists at present, as both cooling events saw development of ice sheets on a planet which was fully vegetated. Despite this, many uncertainties about the timing, magnitude and extent of the PCG exist. Trying to understand the broader scale patterns of environmental flux and variability during this significant time interval thus takes on an even greater significance. Sequence stratigraphy and chemostratigraphy (in particular using d18O and d13C stable isotopes) are two methods of attempting to identify and correlate events over much wider areas. Ultimately it is my intention to build up a dynamic regional model for the response of carbonate sedimentation to Carboniferous sea level fluctuations. Already, sea level fluctuations (cycles) have been reported from late Viséan (Asbian) platform carbonates due to the onset of glaciation in Gondwanaland. I've recently had a PhD student (Milo Barham) complete, who worked on shallow water carbonate sections in the NW of Ireland, which span this critical time interval. We worked in collaboration with Dr Michael Joachimsky, Universität Erlangen-Nürnberg, Germany and utilised d18O values from conodont apatite to assess the effects of climate change on sea-level oscillation.
(Collaborators: Dr Tania King (Institute of Man, Yerevan), Prof Peter Andrews (Natural History Museum London), Dr Patricio Domínguez Alonso (UCM-CSIC Madrid), Dr Yolanda Fernandez-Jalvo (Museo Nacional de Ciencias Naturales, Madrid) 0and& an international team of experts drawn from several countries).
Azokh cave is located in the Lesser Caucasus, in what is present day Nagorno Karabagh. The site is highly significant from a human evolution perspective as it lies at a major crossing ground between Africa and Eurasia. In the 1960's a jaw fragment of Homo heidelbergensis was recovered from the cave fill. Current research at the site has been ongoing since 2002. In 2003, I was invited to join an international team as the on-site geologist. Since then I have focussed on trying to gain a greater understanding of the Pleistocene and Holocene cave stratigraphy in several of the chambers at the site, as well as conducting a detailed 3-dimensional survey of the cave interior with Dr Patricio Domínguez. In addition I have begun to construct a geological map of the surrounding region, which is composed of a mixture of Mesozoic sediments and volcanics, in order to try to better understand links between geology, geomorphology and human exploitation of that particular environment over time. I’m currently also working with Dr Dave Chew (Trinity College Dublin) to produce a radiometric age for some tuffs found in the bedrock sequence west of the main cave site.
Palaeoecology of Conodonts
(Collaborators: Drs Chris Nicholas & Robbie Goodhue (both Trinity College Dublin), Prof Paul Smith (Birmingham) and Prof Phil Heckel (Iowa State)
Conodonts are an extinct group of eel-like primitive jawless vertebrates. They were extremely abundant in the seas of the Palaeozoic and possessed microscopic dental elements which are routinely recovered (disarticulated) in insoluble acid residues and used for biostratigraphic purposes. Despite their importance, details about the palaeoecology of the organisms themselves is scanty, due mainly to the paucity of complete fossil specimens. Research conducted on the isotopic composition of stable nitrogen and carbon in recent marine faunas have indicated a tiering of organisms according to their position on the food chain. Our research group has managed to obtain d15N and d13C values from c.330myo conodont elements indicating feeding at trophic levels comparable to those of modern sardines. Expansion of the area of investigation has led to fieldwork in the Carboniferous of Iowa and Illinois (US) to examine conodont rich shales there.
Comparative taphonomy and palaeobiology of Ediacaran & Phanerozoic soft-bodied fossils
Ediacarans represent the some of the earliest undisputed metazoans on earth. They predate creatures with mineralised skeletons and are a conspicuous feature of Late Neoproterozoic strata worldwide. These organisms evolved and flourished during a pivotal period in the history of life on earth; one which heralded the appearance of the first multicellular animals. The disappearance of the vast majority of these fossils at the end of the Precambrian has been attributed to the demise of ubiquitous shallow marine microbial mats, proposed to have facilitated their preservation. However, although such fossils are rare in Phanerozoic sediments, they are certainly not absent. Despite the potential significance, these occurrences have to date been very poorly studied.
In 1995 two Ediacaran disc genera were reported from upper Cambrian turbidites in County Wexford, Ireland. This was apparently the youngest find of these organisms known worldwide. We reassessed these claims through a combination of detailed analysis of sedimentology and morphology of the structures themselves as well as analogue modelling using carefully reconstructed life-sized density compensated silicon rubber replicas of one of the disc genera in a flume tank. Our work raised serious doubts over both the original taphonomic and morphological reconstructions. It is unlikely that they represent true Ediacarans; they may instead have been formed by tethered structures scraping across the seabed (‘swing-marks’).
I’m currently supervising a PhD student, Breandán MacGabhann, who is studying several Ordovician Lagerstätten sites near Erfoud in Morocco which contain abundant enigmatic soft eldonioid discoidal fossils in order to better understand both the taphonomy and biology of these organisms and also the early evolution of Palaeozoic marine ecosystems. The preservation of these soft-bodied organisms is spectacular and it is all the more remarkable as they are found in coarse siliciclastic sediments. There are obvious parallels to be drawn with the preservation styles of soft-bodied discoidal fossils from the (earlier) Neoproterozoic. At its core, this project is concerned with gaining a greater understanding of some of the oldest, most important and yet equally most controversial fossil organisms - the Ediacaran Biota.
|Fernández Jalvo, Y., Hovsepian-King, T., Moloney, N., Yepiskoposyan, L., Andrews, P., Murray, J., Safarian, V., Asryan, L., Nieto Díaz, M., Domínguez Alonso, P., Marín Monfort, Mª.D., Mkrtichyan, E., Smith, C., Bessa Correia, V., Ditchfield, P., Geigl, E.M., van der Made, J., Torres, T., Scott, L., Allué, E., Cacères, I., Sevilla, P., Hardy, K., Grün, R., Melkonyan, A., Campos, R., Sanz Martín, T., Hayrabetyan, H. & Balasanyan, G. (2009) 'Chapter XVII. Azokh Caves excavations 2002-2006. Middle upper Palaeolithic transition in Nagorno-Karabagh' In: Lobon-Cervia, J & Morales, J (eds). Notas para la historia reciente del Museo Nacional de Ciencias Naturales. Homenaje a María Dolores Soria Mayor. Madrid: Monografías del CSIC. [Details]|
Peer Reviewed Journals
|MacGabhann, B.A., Murray, J & Nicholas, C. (2007) 'Ediacaria booleyi: weeded from the Garden of Ediacara?'. Geological Society Of London,Special Publication, In Vickers-Rich, P. & Komarower, P. (eds) The Rise and Fall of the Ediacaran Biota (SP 286):277-295. [DOI] [Details]|
|MacGabhann, B.A. & Murray, J. (2010) 'Non-mineralised discoidal fossils from the Ordovician Bardahessiagh Formation, Co. Tyrone'. Irish Journal Of Earth Sciences, 28 :1-2. [DOI] [Details]|
|Fernández-Jalvo, J., King, T., Andrews, P., Yepiskoposyan, L., Moloney, N, Murray, J., Domínguez-Alonso, P., Asryan, L., Ditchfield, P., van der Made, J., Torres, T., Sevilla, P., Nieto Díaz, M., Cáceres, I., Allué, E., Marín Monfort, M.D. & Sanz Martín T. (2010) 'The Azokh Cave complex: Middle Pleistocene to Holocene human occupation in the Caucasus'. Journal Of Human Evolution, 58 :103-109. [DOI] [Details]|
|Murray, J., Domínguez-Alonso, P., Fernández-Jalvo, Y., King, T., Lynch, E.P., Andrews, P., Yepiskoposyan, L., Moloney, N., Cacères, I., Allué, E., Asryan, L., Ditchfield, P. & Williams, D.M. (2010) 'Pleistocene to Holocene stratigraphy of Azokh 1 Cave, Lesser Caucasus'. Irish Journal Of Earth Sciences, 28 :75-91. [DOI] [Details]|
|Barham, M., Joachimski, M.M., Murray, J. & Williams, D.M. (2012) 'Diagenetic alteration of the structure and δ18O signature of Palaeozoic fish apatite: potential use for corrected isotope signatures in palaeoenvironmental interpretation'. Chemical Geology, 298-299 :11-19. [DOI] [Details]|
|Barham, M., Murray, J., Joachimski, M.M. & Williams, D.M. (2012) 'The onset of the Permo-Carboniferous glaciation: reconciling global stratigraphic evidence with biogenic apatite δ18O records in the late Viséan'. Journal Of The Geological Society, London, . [Details]|