uat or Eq The Silurian Black (Hot) Shales of the Cantabrian Arc, Northern Spain: Biostratigraphy, Chemostratigraphy & Palaeoenvironmental Reconstruction Tim Ferriday. BSc. (Hons) ia s a r u Basin Dynamics Research Group, Earth Sciences and Geography, Keele University, Keele, Staffordshire, ST5 5BG What are ‘hot’ shales - Where are they found? The Silurian Black (Hot) Shale deposits of the perigondwanan region are one of the most important source rocks for hydrocarbons world-wide. Despite intensive research, questions regarding the genesis and the palaeoenvironmental, palaeogeographic factors controlling the formation of these Silurian black ‘hot’ shales are still a matter of ongoing debate. An in depth palaeoenvironmental reconstruction combined with the high-resolution biostratigraphic and chemostratiographic data will provide new insights into the genesis of the Cantabrian black ‘hot’ shale deposits. A comparison of the results of this research project with data available from other Silurian Gondwanan black ‘hot’ shale deposits will lead to a progressive, state-of-the-art genetic model and an advanced understanding of the factors controlling the deposition and genesis of the restricted black ‘hot’ shales of the Northern Gondwanan Area.nnnnnnnnnnn The 'hot' shale is termed so because of the high gamma radiation content, that of the insoluable U4+ (reduced from soluable U6+ found in seawater, as result of the anoxia). The Gamma values may exceed that of 700+ API (American Petroleum Institute) units in the 'hot' shale horizons. Yet the 'lean' shale surrounding is commonly 90-120+. In oxygenated conditions U6+ is dissolved in seawater. Under the anoxic black 'hot' shale conditions the U6+ is reduced to U4+ which is insoluble and is therefore precipitated. The enrichments in authegenic U4+ in Silurian 'hot' shales therefore coincide with high organic content and anoxic phases. The Silurian ‘hot’ shales were deposited along the majority of the northern rim of Gondwana. The palaeo-reconstructions (below) the central globe shows the locations of the ‘hot’ shale and infers where else they may have been deposited. Reasons for anoxia and genesis: Rheic O and s e sion curv s e sgr alized ations n a r t ner fluctu . Note e e n i g l mar e. A -level 1997) lobal e v Leting theugh timoic seaynolds ( s of g a Sepresen ns throalaeozand Re at time Re ressio ing P eier sis reg resent ndelm gene ) rep r Scha shale C e O ’ t t f T excess a ( ho sion ‘ n o the sgres in ntent b e r u l a C va nic co urian tran C ic ng a TO in orga irst Sil ond n a g showi rease f the f he sec the r O al peak isapid inc nesis oanian. Tds to 5) t o T e first his r he ge hudd lea l (200 Th 5%. T s to t the R c h i a n g et a of 1 espond during e Te l y Lunin m corr shales n g t h ale fro i ’ ‘hot k d u r ‘hot’ sh p e a ndary o o nd t t o sec p ) es rs cean + hales ‘Hot’ S Siberia el -lev Sea Upper Ordovician 444Ma 3. The freshwater masses may have led to fragmentation of the water column as the freshwater is less dense than the underlying saline rich water. Effectively acting as a cap to the water column nnn preventing mixing of the oxygen depleted zones thus excelling the anoxia.nnnnnnnnnnnnnnnnnnnnnnnnnnn. - n a i n vo e D 15 Equ ator ana SP %TO Gondw a 10 0M 16. 5 OC %T 3 us La pe t Ia zak sta hal ic e l a Tot ou ng s wi sho s n egio e m a C eas r a ck e ro rc hal n a bri ot s 48 nh Ma 8.3 v o d Or n a i ic an Org bo Car yr e r G G a amm R PI) A ( ay 0 20 0 10 from e s a h c k s i T Ta 000000 pid exce organ hales a . r t n the is in n the he s conte 000000 t k e e a pe betwe Henc anium 00000 r link ranium. the u )00000 f of u rms o l (2005 e in t ng et a i Lun Conclusions The project after successfully completing a number of field seasons and cataloguing/analysing a substantial data set (regarding the geochemistry and palynology) will determine whether the shales of the Cantabrian region are indeed ‘hot’ or not. If they are ‘hot’ the shales can be correlated to those of the North African basins. Modelling of the ‘hot’ shale genesis and factors controlling the formation of the shales within Cantabria will bring new insight to a topic poorly understood. If the shales of the Cantabrian region do not express the ‘hot’ shale properties, why not? 0 ) n% API ay ( API 200 nia SP a aR 0 40 ot s dda Go 0 50 h an Rhu Rh 0 60 i ych Tel nia 44 an eic Oce 0 70 S Ma 7 . 3 I t n s in ases i 700AP tent an ermed k Gaem a pe incre of n con re t m Gam n a i r vel e u L ea Sil R Gamma ganic cohere is e fixing ’ a m he or .T d th ‘hot 0 O ce ure an nti a Baltica nd wa n PI y log cornr t. The firect A ( Ra nte ay a di C 4 Ka 4. Finally the upwelling of nutrient rich water along the northern rim of Gondwana, this resulting in a high bioproductivity. This organic rich event is reflected in the high bio content in the shales. Large amounts of nutrient rich water flooded the plains of northern Africa the waters were over saturated, an excess of organic matter that could not be oxygenated. Lower Devoinian 400Ma a ani 2. Rapid transgressions as a result of the huge nnnnn amounts of fresh water released at the margins of the Hirnantian Ice Mass. This preventing thenn nnnnnn contamination of continental sediments and producing the clean shale deposits.ngggggggggggggggggggggg. st zak Ka 1. The palaeorelief generated by the Ordovician glacial processes meant that vast island belts formed as a result of the sea-level rise. The island belts acted as flow barriers in turn preventing the reoxygenation of the shelfal waters. This created a perfect environment for the anoxic phases and furthermore reduction U6+ to U4+ and the locking of organic content at the sediment-water interface.nnnnnnnnnnnnnnnnnnnnnnnn SP an UNDIFFERENTIATED PALAEOZOIC OF THE CANTABRIAN ZONE tor Baltica O ce FOLD AND NAPPE PROVINCE Equ a us PICOS DE EUROPA PROVINCE/Unit PISUERGA CARRION PROVINCE/Unit The three globes below are reconstructions of the continent configurations for the Late Ordovician, Silurian and Lower Devonian. The first globe (bottom left) represents the configuration of the Late Ordovician at the time when the Hirnantian glaciation was at its maximum. It shows the glacial maximum taken from Monod et al (2003). The central globe is of most importance as it shows the global configuration at the time of ‘hot’ shale genesis. The ‘hot’ shales are clearly marked upon the northern rim of Gondwana. Note how the Hirnantian ice masses have retreated. This lead to a massive global transgression and ultimately the genesis of the Silurian ‘hot’ shales. The third globe (top right) represents the global configuration of the Lower Devonian. Gondwana has migrated north and has collided with Laurasia leading to the closure of the Rheic Ocean and the formation of the Variscan Orogeny. Ia pe t 50km CENTRAL ASTURIAN COALFIELD PROVINCE NAPPE (PONGA NAPPE) PROVINCE/Unit Gondwana The Maps! What are they showing? tia Somiedo-Corrcillas Unit Esla-Valsurvio Unit La Sobia-Bodon Unit Aramo Unit Siberia La ure n NARCEA ANTIFORM (PRECAMBRIAN) GRANITOIDS Lower/Middle Silurian 436Ma an ce N BAY OF BISCAY MESOZOIC-TERTIARY COVER UNCONFORMABLE STEPHANIAN R ean c O heic aO Project area overview Figures from left to right. Graptolitic ‘hot’ shales from the Algerian Sahara. Silurian black shale expressing Graptolites. Finally the Algerian‘hot’ shales in weatherd form. Taken From Lunings ‘blackshale.com’ accessed 2010. La ss a la n th Pa Overview (project outline) References LÜNING, S., SHAHIN, Y., LOYDELL, D.K., AL-RABI, H.T., MASRI, A., TARAWNEH, B. and KOLONIC, S., 2005. Anatomy of a world -class source rock: Distribution and depositional model of Silurian organic rich shales in Jordan and implications for hydrocarbon potential. American Association of Petrolium Geologists, 89(10), 1397-1427. MONOD, O., KOZLU, H., GHIENNE,J.F., DEAN, W.T., GUNAY, Y., LE HERISSE, A. and PARIS, F., 2003. Late Ordovician glaciation in southern Turkey. Terra Nova, 15, 249-257.