http://hdl.handle.net/10498/6647 Thu, 05 Nov 2026 13:14:33 GMT 2026-11-05T13:14:33Z http://hdl.handle.net/10498/40234 Episodic postglacial deltaic pulses in the Gulf of Cadiz: implications for the development of a transgressive shelf and driving environmental conditions Carrión Torrente, Alvaro; Lobo, Francisco José; Puga Bernabéu, Ángel; Mendes, Isabel; Lebreiro, Susana; García, Marga; Van Rooij, David; Luján Martínez, María; Reguera, María Isabel; Antón, Laura The postglacial sea-level rise after the Last Glacial Maximum provided ideal conditions to study the transgressive sedimentary response to sudden shelf flooding driven by different rates of sea-level rise. In this study, a high-resolution seismic stratigraphic interpretation and sedimentological analysis were conducted on data from the northern Gulf of Cadiz continental shelf (SW Iberian Peninsula), in order to: 1) understand the succession of sedimentary processes during each shelf flooding episode and 2) explore the significance of variable rates of sea-level rise, sediment fluxes, and climatic conditions on the development of postglacial deposits. Four backstepping seismic postglacial transgressive units (PTUs; 4 to 1 from oldest to youngest) that are linked to the retreating mouth of the Guadiana River were interpreted. Together, these seismic units display a wedge-shape geometry, are located over the inner to middle shelf, and overlie a regional unconformity formed during the Last Glacial Maximum. Each PTU can be divided into several sub-units with distinctive seismic facies that have a similar stratigraphic organization. Each PTU contains lower sub-units that are composed of low-angle tangential-oblique clinoforms. The clinoforms are locally topped by a channelized sub-unit. The distal and/or lateral parts of the clinoforms are occasionally buried by sheet-like semitransparent subunits. The uppermost sub-units are present over the proximal and central parts of each seismic unit and are also sheet-like. PTUs can also be subdivided and described sedimentologically. Fine-grained sands with intercalated silty layers dominate the lower part of each PTU (lower clinoform sub-units). The upper part of each PTU (upper sheet-like sub-units) is characterized by reworked facies, composed of highly fragmented bioclasts within a mixture of silt and coarse to medium sand. Finally, mud deposits occur as a sediment drape over the PTUs. The internal structure of each PTU reveals several phases of development under a general process of transgressive submergence in which both coastal and marine deposits were formed and eventually preserved. The initial phase involved the development of coarse-grained deltas in shallow water, which were locally eroded by a network of distributary channels. In a transitional phase, the infilling of distributary channels and the offshore export of fine-grained sediments is related to a change in sediment sources, possibly triggered by enhanced hydrodynamic processes. The final phase involved the reworking of fluvio-deltaic sediments by shoreface processes to generate a sediment sheet. Age correlation with a suite of postglacial sea-level curves indicates that the formation of the postglacial transgressive deposits is bracketed between 14 ka and 9 ka. The studied deposits are related to a period of reduced sea-level rise, culminating in the Younger Dryas event (two oldest PTUs), and to phases of enhanced sea-level rise, such as Meltwater Pulse (MWP) 1B (two youngest PTUs). In spite of high rates of sea-level rise over MWP-1B, each PTU exhibits progradation and preservation of much of the delta. The preservation of progradational deltaic units is likely caused by increased sediment supply during progradational pulses. We suggest that those pulses of enhanced sediment fluxes during MWP-1B were strongly driven by the overall climatic conditions in the southwest of the Iberian Peninsula, probably resulting from enhanced rainfall runoff during humid periods and scarce land vegetation cover. Sat, 01 Jan 2022 00:00:00 GMT http://hdl.handle.net/10498/40234 2022-01-01T00:00:00Z http://hdl.handle.net/10498/40233 Morphology of the last subaerial unconformity on a shelf: insights into transgressive ravinement and incised valley occurrence in the Gulf of Cádiz Lobo, Francisco José; García, Margarita; Luján Martínez, María; Mendes, I.; Reguera, María Isabel; Van Rooij, David The main aim of this study is to explore the spatial patterns of the shelf-scale erosional unconformity related to the last glacial maximum (LGM), particularly in terms of the role of underlying geology and the presumed primary influence of sea-level changes. This involved a detailed mapping of the most recent and widespread erosional shelf surface in a sector of the northern margin of the Gulf of Cádiz (northeast Atlantic Ocean) located adjacent to a major fluvial source. A dense network of high resolution seismic profiles collected in the 1990s and 2013 off the Guadiana River revealed two distinct geomorphological domains on the LGM shelf-scale subaerial surface. The outer domain exhibits a widespread occurrence of erosional truncations, with a rugged, erosional pattern over the most distal shelf setting that evolves landward into a planar unconformity. The inner domain is more extensive and is characterized by the common occurrence of highly reflective, localized mounded seismic facies that laterally evolve into an irregular surface and in places may develop a channelized morphology. Significant fluvial incision is limited to a major straight valley and a secondary distributary channel. A distinct partition of the lowstand surface is documented, and attributed to a well-marked lithological change. A coarsegrained inner shelf comprises underlying lithified coastal deposits, whereas a fine grained outer shelf is regarded as the uppermost expression of regressive prodeltaic wedges. The influence of regional indurated surfaces is also expressed in (1) the pattern of erosion, this being more patchy on the inner shelf due to lateral changes of erodibility, whereas on the outer shelf it shows laterally continuous bands, owing to different modes of transgressive ravinement; (2) the spatial and temporal variability of fluvial incision. Inner shelf armoring by indurated deposits prevents reoccupation of previously incised valleys. Mon, 01 Jan 2018 00:00:00 GMT http://hdl.handle.net/10498/40233 2018-01-01T00:00:00Z http://hdl.handle.net/10498/40232 Morpho-stratigraphic features of the northern shelf of the Strait of Gibraltar: Tectonic and sedimentary processes acting at different temporal scales Luján Martínez, María; Lobo, Francisco José; Bruno Mejías, Miguel; De Castro, Sandra The northern shelf of the Strait of Gibraltar adjacent to Camarinal Sill, defined here as the Cape Paloma continental shelf, has been investigated by analyzing a set of geophysical data including multibeam bathymetric images, a side-scan sonar mosaic and high-resolution seismic profiles, and the simulation of water-mass circulation patterns along the northern coastal margin. The aim of the study was to establish the significance of factors determining the evolution of this shallow margin at different temporal scales and to assess the implications for bedform generation in strait settings, taking into account the complex tectonic evolution and the energetic hydrodynamic regime of the strait. Deformed basement rocks are part of the Betic-Rif thrust wedge, western Gibraltar Arc, mainly formed by the materials of the Flysch Complex units and covered by Pliocene to Quaternary post-orogenic deposits. A central high (Bajo de los Cabezos High) is delimited by lateral depressions, that nucleated two major depocentres with distinctive filling histories. The eastern depocentre is controlled by WNW-ESE faults cutting the Cretaceous-Miocene basement rocks; these faults generate horsts and grabens that could have contributed to the opening of the Strait of Gibraltar during the Pliocene. The largest and westernmost depocentre is related to the complete infilling of a shelf palaeovalley. The sediment cover is molded by different fields of submarine dunes and comet marks that indicate the influence of hydrodynamic processes on sediment transport at the coastal margin. The observations in the study area regarding bedform development must be placed into a wider context of strait sediment dynamics. The Cape Paloma continental shelf exhibits both erosional and depositional forms, due to its intermediate location between the strait, mostly dominated by erosional processes, and the Barbate Platform (northwest of the study area), mostly characterized by depositional forms. The long-term evolution of the sediment depocentres in the study area appears to be mainly influenced by the morpho-tectonic configuration of the margin, which in turn was established to a large extent by differential uplifting along the coast. In the shelf east of the central high, the basement horst and graben structure trapped sediments in the physiographic lows and fostered the formation of large-scale sediment banks. In the shelf west of the central high, the occurrence of a major infilled palaeovalley is in agreement with a gentle subsidence trend. The physiographic configuration is also thought to play a major role in defining short-term processes, particularly in confining a cyclonic eddy to the east of the Bajo de los Cabezos High during specific conditions of the tidal cycle. This eddy favors the recirculation of sediments in the coastal margin, as evidenced by small bedform fields that apparently show a wider distribution that the larger-scale, confined sediment banks, due to the instauration of the modern sediment dynamics after the complete shelf flooding. The sediment transport pattern established in the study area seems to be eventually captured by a submarine channel that provide an efficient mechanism for sediment export toward deep-water settings, where an extensive contourite depositional system has been documented Mon, 01 Jan 2018 00:00:00 GMT http://hdl.handle.net/10498/40232 2018-01-01T00:00:00Z http://hdl.handle.net/10498/40228 Pliocene-Quaternary Deformational Structures in the Eastern Algarve Continental Shelf, Gulf of Cadiz Luján Martínez, María; Lobo, Francisco José; Mestdagh, Thomas; Vázquez, Juan Tomás; Fernández Puga, María del Carmen; Van Rooij, David The eastern Algarve continental shelf in the northern margin of the Gulf of Cadiz has been investigated by analysing a set of high-resolution seismic reflection profiles. We examine the major structural elements affecting the upper sedimentary units. A seismo-stratigraphic interpretation and regional correlation allowed the identification of a major discontinuity that separates two main intervals, pre-Middle Pleistocene (MP) and post-MP. In addition, a number of deformation features such as ENE-WSW to NE-SW thrusts, kilometric-scale N-S to NW-SE folds and NNE-SSW to NNW-SSE sub-vertical normal faults were identified affecting the Pliocene-Quaternary sedimentary record, indicating neotectonic activity. The structures pre-dating MP are in agreement with a dominant transpressive regime along the continental shelf, under the Late Cenozoic NW-SE oblique convergence and related to the reactivation of Mesozoic diapiric structures. The structures post-dating MP induce a lower deformation of the sedimentary cover but were still active during the last glacial maximum, in agreement with the low uplift recognized in the Portuguese mainland. Wed, 01 Jan 2020 00:00:00 GMT http://hdl.handle.net/10498/40228 2020-01-01T00:00:00Z