José Luis Goy

Fault-generated mountain fronts in southeast Spain: geomorphologic assessment of tectonic and seismic activity

Abstract Tectonic activity of SE Spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts. The selected fronts are distributed along the two most prominent crustal-scale structures of the Mediterranean sector of Spain: The Eastern Betic Shear Zone (EBSZ) and the Valencia Trough. Geomorphic indexes used in this study are Mountain-front sinuosity index (Smf) and Valley floor/width ratio (Vf). This work is largely based on the Smf/Vf regression analysis of the studied fronts together with previous available data from SW USA. The development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios (tectonic activity classes) to be obtained. This study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis. It is demonstrated that discrete uplift rates of 0.15–0.08 m/ka are sufficient to keep relatively low Smf values down to 1.4 in Active fronts (Class 1). Taking into account the reported uplift rates and preliminary palaeoseismic data for some of the Class 1 studied fronts, recurrence periods for surface rupture events can be theoretically bracketed for SE Spain. Recurrence periods for Class 1 fronts could theoretically range between 10,000 and 12,500 years for maximum slip conditions, and 1750 and 2600 years for minimum slip conditions. Inactive fronts (Class 3) develop under uplift rates down to 0.03 m/ka, and tested recurrence intervals for rupture events range between 25,000 and 50,000 years. Class 2 fronts of intermediate characteristics and activity display uplift rates between 0.07 and 0.03 m/ka.

Depositional history of estuarine infill during the last postglacial transgression (Gulf of Cadiz, Southern Spain)

Abstract The Late Pleistocene and Holocene evolution of the estuaries in the Gulf of Cadiz is interpreted for the first time using drill cores, logs, trenches, and 38 new radiocarbon data, and the results compared with the shelf. The Odiel, Tinto and Guadalete Rivers deposited conglomerates during a highstand that did not reach the present sea level dated at ca. 25–30 ka (Isotopic Stage (IS) 3), corresponding to a relatively humid period in the area. Rivers incised these coarse-grained deposits during the last main lowstand at ca. 18 ka, when sea level dropped to −120 m and the coastline lay 14 km seawards from the present. The erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise, overlain by the valley fill deposits of the transgressive and highstand phases of the last fourth- and fifth-order depositional sequences recognised in the shelf. The first marine influence in the estuaries during the transgression occurs at −25/−30 m at ca. 10,000 years BP. According to fossil assemblages, the transgressed basins changed from brackish to more open marine as the sea rose until ca. 6500 years BP, when it reached the maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy central basins. Then, the rate of eustatic rise decreased drastically, and the estuarine filling followed a two-fold pattern governed by the progressive change from vertical accretion to lateral (centripetal) progradation. At ca. 4000 years BP the fluvial input surpassed the already negligible rate of rise, causing partial emergence of tidal flats and spit barriers in the largely filled estuarine basins. Prevalence of coastal progradation upon vertical accretion at ca. 2400 years BP caused accelerated expansion of tidal flats and rapid growth of the sandy barriers. Further changes since the 16th century reflect widespread anthropic impacts.

Pleistocene raised marine terraces of the Spanish Mediterranean and Atlantic coasts: records of coastal uplift, sea-level highstands and climate changes

Detailed geological mapping, morphostratigraphic, palaeontological and geochronological (uranium-series) analyses were undertaken on the raised marine terraces and interbedded terrestrial deposits along the Spanish peninsular and insular Atlantic and Mediterranean coasts. Several sets of Pleistocene shallow-marine to coastal deposits exposed in a staircase arrangement are interpreted as being emplaced during sea-level highstands coeval with interglacials or interstadials correlating with marine Oxygen Isotopic Stages (OIS) 5a/5c, 5e, 7, 9/11 and older. Up to three highstands have been identified in deposits formed during OIS 5e. Close to the end of OIS 5e there is a record of sudden changes in sea-surface conditions and climate marked by the disappearance of a major proportion of the warm ‘Senegalese’ fauna, switches from oolitic to non-oolitic facies, and accumulation of boulder beaches. Dating of the coral Cladocora caespitosa, found in a layer that also contains Strombus bubonius, confirms the occurrence of warm fauna in the Mediterranean basin during OIS 7, as previously suggested by Hillaire-Marcel et al. (1986), Goy et al. (1986a,b), Zazo and Goy (1989). Also the occurrence of warm faunas in deposits corresponding to an older interglacial, probably OIS 9 or 11, in the Balearic Islands suggests similar oceanographic conditions (sea-surface temperature, assuming constant salinity) during the last interglacial and at least two interglacials of the Middle Pleistocene in the western Mediterranean. A 2002 Elsevier Science B.V. All rights reserved.

A beach-ridge progradation complex reflecting periodical sea-level and climate variability during the Holocene (Gulf of Almerı́a, Western Mediterranean)

Detailed mapping based on aerial photographs at various scales, analysis of morpho-sedimentary units, and radiocarbon dating of the prograding beach-ridge complex of Campo de Dalias (Almeria) allow the differentiation of six prograding units. These are called: H1, 7400–6000 cal BP; H2, 5400–4200 cal BP; H3, 4200–3000 cal BP; H4, 2700–1900 cal BP; H5, 1900–1100 cal BP; and H6, 500 cal BP–Present. H-units are deposited during periods of high relative sea level and increased sediment input to the coast. They are bounded by large swales or erosional surfaces associated with lower sea levels and reduced input of sediment to the coast; these correspond to short periods of increased aridity inside the general arid trend recorded in the Western Mediterranean since 5.4 ka. Changes in the flux of Atlantic superficial waters into the Mediterranean Sea, and relative strength of the W/SW winds account for the recorded oscillations of relative sea level. We deduce a decadal periodicity for the deposition of a beach ridge and the adjacent swale, and suggest that it is related to fluctuations of the North Atlantic Oscillation (NAO) index and to variations of solar activity. The duration of H-units shows a quasi-millennial periodicity punctuated by short (hundred years) episodes of reduced progradation or erosion representing events of increased aridity likely to be related to Bonds Holocene cold events.

The impact of Quaternary sea-level and climatic change on coastal alluvial fans in the Cabo de Gata ranges, southeast Spain

Conventionally, a fall in base level is seen as stimulating incision into the distal zones of alluvial fans. In the Cabo de Gata ranges of southeast Spain evidence exists to the contrary. Two sets of Quaternary coastal alluvial fans demonstrate the interaction between climatically-driven variations in the supply of sediment and eustatically-driven changes in base level. The fans are supplied from Miocene volcanic terrain within which no evidence can be found for major tectonic deformation during the period of fan development. The evolution of the east-coast fans has been affected by variations in sediment supply and changes in sea level. The west-coast fans were buffered from the effects of changes in sea level by coastal barriers. Three phases of past sedimentation can be identified on the fans. These can be differentiated on the basis of field observations of soil profiles (particularly colour of the B horizons and accumulation of CaCO3), and laboratory analyses of sequential iron oxide extractions and magnetic mineral properties. The two earlier (major) sedimentation phases were coincident with global glacials (>ca. 135 ka and ca. 85–10 ka, based on the stratigraphy and uranium/thorium dating of the coastal sediments). High sea levels during the intervening interglacial and during the Holocene caused erosion of the distal zones of the east-coast fans which led to channel incision into the fan surfaces. On the west-coast fans no such incision occurred, simply proximal incision by small fanhead trenches. The youngest (relatively minor) phase of fan sedimentation has occurred during the Holocene. These contrasting contexts have produced differing styles of fans, with telescopic fan morphology on the east-coast and stacked morphology on the west-coast fans. The differences are reflected in the fan profiles, with steeper gradients dominating the east-coast fans, and extensive lower gradient distal surfaces on the west-coast fans. Fan morphometry, based on analysis of the residuals from drainage area to fan area and gradient regressions, also differentiates between the fan contexts. The fan building phases appear to be controlled proximally by climatically-driven pulses of sediment supplied to the fans. These occurred during global glacials coincident with low sea levels, and caused fan progradation onto the exposed foreshore. The intervening global interglacials were times of little fan sedimentation, and on the east coast, where high sea levels were able to erode the fan toes, deep through-fan dissection ensued.

Fan-surface dynamics and biogenic calcrete development: Interactions during ultimate phases of fan evolution in the semiarid SE Spain (Murcia)

Abstract Pleistocene alluvial fan surfaces of the Campo de Cartagena–Mar Menor Basin (Murcia, SE Spain) are capped by thick mature calcretes. Calcrete profiles consist mainly of six different horizons: prismatic, chalky, nodular, massive, laminar and coated-gravels. Petrographic study of the calcretes has shown the occurrence of features such as alveolar septal structures, calcified filaments, coated grains, spherulites, calcified root cells and calcispheres that indicate the biogenic origin of the calcretes, mainly induced by plant root related microbial activity. The calcretes studied were formed initially in the soil and represented the K horizon. Development of the calcrete profiles took place in six main stages and was driven by multiple phases of soil formation, erosion and reworking. The relationships between these processes caused the formation of different calcrete profiles in proximal and distal fan areas. In the distal areas, which are controlled by limited distal fan aggradation, episodic sediment input, buried previously developed calcretes and generated new space for calcrete growth by plants growing in the overlying unconsolidated materials. This allowed the renewal of calcrete formation and it led to the development of complex composite profiles which are thicker than in proximal areas, where surface stabilisation and/or dissection enabled calcrete reworking and brecciation. These processes of erosion, sedimentation, reworking and renewed calcrete formation initiated by vegetation were repeated through time. They explain the complex macro- and microstructures of these calcretes and indicate that calcrete development, even reaching mature stages, can start before the fan surface is completely abandoned, but it requires episodic sedimentation. Eventually, distal fan aggradation and continuous calcrete development throughout the entire fan surface, led to the ultimate fan surface induration, controlling subsequent landscape evolution. So, fan surface calcretes cannot be envisaged as simple top-surface carbonate accumulations, but as complex feedback systems in which pedogenic, biogenic and sedimentary processes interact in response to the evolving fan-surface dynamics during the terminal phases of fan development in semiarid environments.

Sequence stratigraphy of Holocene incised-valley fills and coastal evolution in the Gulf of Cádiz (southern Spain)

This first sedimentary interpretation of two incised-valley fills in the Gulf of Cádiz (southern Spain), which accumulated during the last fourth-order eustatic cycle in response to fluvial incision, changes of sea level, and correlative deposition, relates the filling of the estuarine basins and their barriers with four regional progradation phases, H1 to H4. The cases studied are the wave-dominated Guadalete, and the mixed, tide and wave-dominated Odiel-Tinto estuaries. The sequence boundary is a type-1 surface produced during the lowstand of the Last Glacial period ca. 18 000 14C yr BP. No fluvial lowstand deposits were found in the area. Due to rapid transgression the valley fills consist of transgressive and highstand sediments. The maximum landward advance of the estuarine barriers occurred ca. 6500–6000 14C yr BP during the maximum of the Flandrian transgression, but there is no evidence of sea level rising appreciably above the present. A large part of the estuaries was filled during H1 (ca. 6500–4400 14C yr BP) but ravinement by shifting tidal inlets destroyed most of the coeval barriers. During the H2 phase (ca. 4200–2550 14C yr BP) sedimentation was favoured by arid conditions and concentrated in the axial estuarine zones and the barriers. Between H2 and H3 prevailing winds changed from W to WSW, increasing spit growth to the east and south-east. Progradation of bay-head deltas and flood-plains during H3 (ca. 2300–800 14C yr BP) and H4 (500 yr ago to the present) further reduced the accommodation space in the largely-filled valleys, and sediment by-passed the estuaries and accumulated in the estuarine barriers as fast-growing spits. Arid conditions and increasing human activity have caused rapid coastal modifications.

The Last Interglacial in the Mediterranean as a model for the present interglacial

Deposits of the Last Interglacial on the south and southeastern coasts of Spain are shallow marine and coastal sediments, with a warm fauna of Strombus bubonius. These units exhibit a diversity of morpho-sedimentary models controlled by the tectonic activity of the Mediterranean area, which is closely related to the approximation of Africa and Iberia during the Quaternary. There are three well-dated peaks of maximum sea level (T-I: isotopic substage 7a, T-II: isotopic substage Se, T-III: isotopic substage 5c). A younger episode, T-IV, probably corresponds to the isotopic substage 5a. Episodes T-II, T-III and T-IV were laid down during Last Interglacial age. In addition, three Holocene peaks of maximum sea level: H1 ca. 5100 yr B.P., H2 ca. 3500 yr B.P. and H3 ca. 2400 yr B.P. were found. The three main peaks of the Last Interglacial correspond to the morpho-sedimentary Tyrrhenian units T-II, T-III and T-IV, deposited during a time span of sorne 45,000 years. Several smaller oscillations can be distinguished within each of these units as subunits separated by erosional surfaces. At least three of such mapable subunits were distinguished within the peak T-II (Se); each lasted ca. 10,500 yr. As the positive oscillations of sea level (H1, H2, and H3) recorded during the present Interglacial (Holocene) are much shorter, we infer that they are smaller-scale fluctuations (2500-1100 yr cycles) within the first oscillation (duration: ca. 10,500 yr) of the first Holocene peak of sea level which has not yet been completed. In addition to changes of sea level, the vertical and lateral arrangement of morpho-sedimentary units, which can be designated as the stratigraphic architecture, depends on tectonics and oceanography, including geoidal and steric changes and coastal dynamics. The coastal dynamics factor largely depends on the exchange of waters between the Atlantic and the Mediterranean. Maximum incursions of water coincides with warm periods (highstands) when the coastal accretion increases. The tectonic factor greatly influences and modifies the effects of sea-level changes in the coastal areas of tectonically-active regions such as the Mediterranean. Areas with tectonic uplift will be characterized by a staircase of prograding gravelly beaches, whereas sinking areas will favour the deposition of vertically stacked sequences with coastal onlap of barrier island and lagoon deposits. Rates of sea-level rise for the coming years of 1 cm/yr, have been suggested by sorne authors. These gradients greatly exceed those produced by any tectonic factor in the Spanish coast during the last 100 kyr. Shoreface erosion and transgression with landward migration of barrier islands and lagoons will occur in subsiding areas (Murcia-Alicante and Valencia), even with relatively low rates of sea-Ievel rise Oess than 0.5 cm/yr). Higher rates of sea-level rise (0.5-1 cm/yr) will increase the transgressive trend. Areas with subsidence rates higher than 7.5 cm/kyr (Mar Menor and Oval of Valencia) are prone to transgression and erosion of barrier islands and lagoons both in the cases of stable and rising sea levels. Risks are smaller in areas with lower rates of subsidence (La Mata, Santa Pola and Torrevieja lagoons) when a stable sea level is considered; however, any rise of sea level will trigger coastal erosion.

Tsunami vs. storm surge deposits: a review of the sedimentological and geomorphological records of extreme wave events (EWE) during the Holocene in the Gulf of Cadiz, Spain

The Gulf of Cadiz region of Spain has undergone many studies examining Holocene tsunami and storm deposists. Some of the studies aimed at determining recurrence intervals of events interpreted of tsunamigenic origin. A review of geomorphologic, sedimentary and paleontological features of these deposits suggests that only a few of them can be accurately ascribed to tsunami events; instead, most of them lack conclusive evidence of a tsunamigenci genesis and should be referred to as generated by extreme wave events (EWE)

Pleistocene and Holocene aeolian facies along the Huelva coast (southern Spain): climatic and neotectonic implications

The stratigraphic relationships, genesis and chronology, including radiocarbon dating, of the Quaternary sandy deposits forming the El Asperillo cliffs (Huelva) were studied with special emphasis on the influence of neotectonic activity, sea-level changes and climate upon the evolution of the coastal zone. The E-W trending normal fault of Torre del Loro separates two tectonic blocks. The oldest deposits occur in the upthrown block. They are Early to Middle Pleistocene fluviatile deposits, probably Late Pleistocene shallow-marine deposits along an E-W trending shoreline, and Late Pleistocene and Holocene aeolian sands deposited under prevailing southerly winds. Three Pleistocene and Holocene aeolian units accumulated in the downthrown block. Of these, Unit 1, is separated from the overlying Unit 2 by a supersurface that represents the end of the Last Interglacial. Accumulation of Unit 2 took place during the Last Glacial under more arid conditions than Unit 1. The supersurface separating Units 2 and 3 was formed between the Last Glacial maximum at 18 000 14C yr BP and ca. 14 000 14C yr BP, the latter age corresponding to an acceleration of the rise of sea level. Unit 3 records wet conditions. The supersurface separating Units 3 and 4 fossilised the fault and the two fault blocks. Units 4 (deposited before the 4th millennium BC), 5 (> 2700 14C yr BP to 16th century) and 6 (16th century to present) record relatively arid conditions. Prevailing wind directions changed with time from W (Units 2–4) to WSW (Unit 5) and SW (Unit 6).