Itsaspeko iturriak: harridurazko gueneak

1960ko hamarkadatik hona itsaspeko iturri anitz aurkitu dira munduko ozeano guztietan. Iturri hauek, agerian uzten dute lurpeko gas eta likido fluidoen eta ozeanoetako uraren artean trukaketa handia gertatzen dela. Iturrien ezaugarri fisikoak, darizkien fluidoenak (konposizioa eta tenperatura) eta, hein handi batean, bertan bizi diren komunitate biologikoenak ere, prozesu geologikoek eragindakoak dira. Hidrokarburo-iturri hotzen kasuan, kontinente-ertzetako lurpeko arroketan eta sedimentuetan dauden gasak (nagusiki metanoa) eta petrolioa dira bertatik ateratzen direnak. Iturri hidrotermalei darizkien fluidoak epelak edo beroak dira, eta konposatu kimiko anitzetan aberatsak; fluido hauek lurpeko gorputz magmatikoekin ukipenean egondako urez osatuta daude. Hidrokarburo-iturri hotzetan eta iturri hidrotermaletan izaten diren komunitate biologikoak oso antzekoak dira, inguruko hondokoenak ez bezala: izaki ugariz osatuak eta kimiosintesian oinarri dutenak. Itsaspeko iturriek gizakiarengan ere eragin handia dute, eta batzuek ondorio kaltegarriak dakarzkiotelarik ere, beste batzuk onuragarriak suertatzen zaizkio

The Role of Magmatism in Hydrocarbon Generation in Sedimented Rifts: a Nd Isotope Perspective from Mid-Cretaceous Methane-Seep Deposits of the Basque-Cantabrian Basin, Spain

Studies on the involvement of intrusive magmatism in hydrocarbon generation within sedimentary basins have gained momentum owing to increasing appraisal of the role that such processes may play in controlling global carbon cycle perturbations, and the exploration potential of the volcanic sedimentary basins. Nevertheless, for many areas the causal link between the intrusions and surrounding hydrocarbon systems remains disputed, encouraging a search for methods that could aid in identifying different hydrocarbon sources. Here, we have performed a multi-proxy geochemical study of the middle Cretaceous methane-seep deposits of the Basque-Cantabrian Basin, an early-stage, peri-cratonic rift marking the Mesozoic opening of the Bay of Biscay. Infilled by a thick sedimentary succession intruded by shallow-level igneous bodies, the basin shares analogies with modern young, sedimented rifts that sustain hydrocarbon seepage. We have applied a novel approach that uses the Nd isotope composition of the seep deposits to constrain the relationship between hydrocarbon seepage and igneous activity, and to explore the general potential of Nd isotopes to trace magmatic-influenced fluids in volcanic sedimentary basins. The Nd isotope data have been combined with rare earth element analyses and carbon and oxygen isotope measurements, providing broad insight into the former composition of the seeping fluids. For three out of four investigated seeps, the Nd isotope ratios observed in authigenic seep carbonates include signatures markedly more radiogenic than that reconstructed for background seawater-derived pore waters. The level of this Nd-143-enrichment varies both between and within individual deposits, reflecting spatial and temporal differences in fluid composition typical of seep-related environments. The radiogenic Nd isotope signals provide evidence of subseafloor interactions between the seeping fluids and mafic igneous materials, supporting the model of an igneous control on the mid-Cretaceous methane expulsion in the Basque-Cantabrian Basin. The thermogenic origin of the methane is in accord with the moderately negative delta C-13 values and paragenetic successions observed in the studied seep carbonates. For a single deposit, its relatively unradiogenic Nd isotope composition can be attributed to the smallest size and shallowest emplacement depth of the underlying intrusion, likely resulting in a short-lived character and limited hydrocarbon-generation potential of the associated contact metamorphism. The study demonstrates that Nd isotope analyses of seep carbonates offer a tool in disentangling methane fluxes from different organic matter alteration pathways for the numerous, both fossil and modern sedimented rifts for which the involvement of various methane sources remains insufficiently understood.This work was supported by the National Science Centre, Poland (grant No. 2016/23/D/ST10/00444; to MJ) , and the Eusko Jaurlaritza (Ikerketa Taldeak IT930-16) and the Spanish State Research Agency (project PID2019-105670GB-I00/AEI/10.13039/501100011033; both to LMA

The effects of astronomically forced climate change on hemipelagic carbonate sedimentation in a tectonically active setting: the Albian Mioño Formation in Castro Urdiales (Cantabria, N Spain)

Our understanding of the stratigraphic expression of astronomically driven climate-change cycles in the Milankovitch frequency band has improved significantly in recent decades. However, several aspects have been little studied to date, such as the nature of the climatically regulated environmental processes that ultimately control cyclic sedimentation. Similarly, relatively little is known about the expression of Milankovitch cycles in successions accumulated in tectonically active basins. In order to fill this knowledge gap, the Albian hemipelagic deposits of the Miono Formation exposed in Castro Urdiales (Basque-Cantabrian Basin) are studied herein. These deposits were accumulated during a rifting phase with strong tectonic activity. The sedimentological, petrographic and cyclostratigraphic analysis demonstrates that, despite the synsedimentary tectonic instabilities and some diagenetic overprinting, the hemipelagic carbonate alternation was astronomically forced 110.68-110.47 Ma. Seasonality fluctuations driven by precession cycles caused periodic (20 ky) variations in the rate of carbonate productivity (abundance of pelagic calcareous plankton and micrite exported from adjacent shallow-water areas) and/or siliceous dilution (terrestrially derived siliciclastic sediment supply and siliceous particle production by sponges). These variations resulted in the formation of marly limestone beds when annual seasonality was low (i.e., boreal summer at aphelion, winter at perihelion) and the accumulation of marlstones when seasonality increased (i.e., boreal summer at perihelion, winter at aphelion). The incidence of these processes increased and decreased in line with seasonality modulation by short-eccentricity cycles of 100 ky. In conclusion, this study shows that Milankovitch cycles can be reliably recorded in hemipelagic successions accumulated in tectonically active settings if sediment gravity flows or other disturbances do not affect autochthonous sedimentation.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Research funded by the MCIN/AEI project PID2019-105670GB-I00/AEI/10.13039/501100011033 of the Spanish Government and by the Consolidated Research Group IT160222 of the Basque Government

Itsaspeko iturriak: harridurazko gueneak

1960ko hamarkadatik hona itsaspeko iturri anitz aurkitu dira munduko ozeano guztietan. Iturri hauek, agerian uzten dute lurpeko gas eta likido fluidoen eta ozeanoetako uraren artean trukaketa handia gertatzen dela. Iturrien ezaugarri fisikoak, darizkien fluidoenak (konposizioa eta tenperatura) eta, hein handi batean, bertan bizi diren komunitate biologikoenak ere, prozesu geologikoek eragindakoak dira. Hidrokarburo-iturri hotzen kasuan, kontinente-ertzetako lurpeko arroketan eta sedimentuetan dauden gasak (nagusiki metanoa) eta petrolioa dira bertatik ateratzen direnak. Iturri hidrotermalei darizkien fluidoak epelak edo beroak dira, eta konposatu kimiko anitzetan aberatsak; fluido hauek lurpeko gorputz magmatikoekin ukipenean egondako urez osatuta daude. Hidrokarburo-iturri hotzetan eta iturri hidrotermaletan izaten diren komunitate biologikoak oso antzekoak dira, inguruko hondokoenak ez bezala: izaki ugariz osatuak eta kimiosintesian oinarri dutenak. Itsaspeko iturriek gizakiarengan ere eragin handia dute, eta batzuek ondorio kaltegarriak dakarzkiotelarik ere, beste batzuk onuragarriak suertatzen zaizkio

Interbedded mudstone slope and basin-floor sandy deposits in the Ondarooa turbidite system (Albian, Basque-Cantabrian Basin)

El sistema turbidítico de Ondarroa constituye un sistema siliciclástico confinado con forma de L, depositado en una subcuenca marina profunda de tipo pull-apart. El estudio de nuevos afloramientos correspondientes al sistema externo ha permitido caracterizar dos sistemas de dispersión coetáneos perpendiculares. Un sistema de dispersión axial de dirección ESE correspondiente a las corrientes turbidíticas siliciclásticas, y otro sistema de dispersión transversal de dirección NNE representado por potentes slumps lutíticos de talud. El confinamiento de las corrientes turbidíticas axiales y el desarrollo de depósitos de talud habrían estado causados por la actuación sinsedimentaria de la falla de Elgoibar, paralela a los flujos axiales

Gas chromatography analisis for Albian rocl<s (Black Flysch) in the Basque-Cantabrian Region

The Black Flysch Croup is a basically siliciclastic unit, constituted by thick turbiditic series of Middle Albian-Lower Cenomanian age, that were deposited in deep ocean environments from the pyrenaic domain. Using gas chromatography method, we could deduce the marine character of the organic matter from the analysed interva