Cari Zazo

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.

Interglacial sea levels

Abstract Isotopic curves have been used as approximative estimators of global sea level. Calculations of the amplitude of sea-level variations during Interglacials, especially for the last Interglacial, are based on the study of emerged coral terraces. The application of different dating methods shows great uncertainty about the length of each Interglacial and also about the number, chronology and altitude of the different highstands that occur during each Interglacial. Data of raised marine terraces from areas with different geodynamic behaviour (Bermudas, Bahamas, Peru, Chile, Italy and Spain) are summarized in order to analyze the relationships between sea level and Interglacial stages. Two Interglacials have been identified for the early Pleistocene represented by two marine terraces with different highstands. During the early-middle Pleistocene, an Interglacial with several highstands is recorded in uplifted areas. During Isotopic Stage 11 at least one highstand with sea level equal or higher than present has been recorded. Similar sea-level behaviour can be suggested for Isotopic Stage 9. All the analyzed areas record two highstands during Isotopic Stage 7, when warm equatorial fauna migrate into the Mediterranean. During Isotopic Substage 5e at least two highstands took place with evidence of lowstands between them and at least one highstand during substage 5c with similar sea-level height above present MSL, except in Barbados and Bermuda. During Substage 5a at least one highstand has been recorded.

U-series measurements in tyrrhenian deposits from mallorca — Further evidence for two last-interglacial high sea levels in the Balearic Islands

The Campo de Tiro type-section for the Tyrrhenian ecostratigraphic beds of the Balearic Islands shows four indurated littoral conglomerates and beach-rocks, unconformably superimposed. The lower two units (1 and 2) are separated by a thin layer of reddish continental silts; both contain a typical Eutyrrhenian fauna, whereas a Neotyrrhenian fauna characterizes the overlying units 3 and 4. ThU measurements by thermal ionisation mass spectrometry on mollusk shells from these deposits yielded ages of ∼135 ka (unit 1), ∼117 ka (units 2 and 3), and a scatter of ages around ∼100 ka (unit 4). The stratigraphic relationships and ThU data indicate (i) that uranium was uptaken by mollusks shells (but Arca sp.) each time during a relatively short early diagenetic interval before cementation ensured a ‘fair’ closure of the radioactive system, (ii) two high sea stands characterized the Last Interglacial (Isotopic Substage 5e) of the Balearic Islands area, (iii) the duration of this episode was ∼17 ka, and (iv) the change in faunal assemblages and disconformity observed between units 2 and 3 are due to fluctuations in sea level and surface water conditions which occurred during the second high sea level episode of the Last Interglacial.

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.

Global and regional factors controlling changes of coastlines in Southern Iberia (Spain) during the holocene

The interaction between global (glacio-eustatic sea-level rise) and regional factors (oceanographic and tectonic) has controlled the evolution of coastline during the Holocene in Southem Iberia. At ca. 10,000 14C years BP a deceleration of relative sea-level rise took place both in the Atlantic and Mediterranean littorals, with a maximum transgression at 6450 14C years BP. In subsiding areas (present tidal flats) estuaries illustrate a clear marine influence recorded both in sediments and the fauna while in uplifting areas prograding spit-bar systems developed. Two phases of major progradation are distinguished in these systems: the first one between 6450 and 3000 14C years BP, with a sedimentary gap at ca. 4000 14C years BP; and the second one from 2750 14C years BP up to present, with an intervening gap between 1200 and 1050 14C years BP. These progradation phases develop during stillstands followed by relative sea-level fall, while the sedimentary gaps represent relative high sea level. In the Mediterranean areas, with a higher uplift rate, marine terraces almost coeval to those gaps occur. The most pronounced modifications in littoral dynamics occurred at between 3000 and 2750 14C years BP represented by changes in the direction of longshore drift and prevailing winds and in the predominance of progradation over aggradation processes. At ca. 1000 14C years BP the estuaries record a greater fluvial than marine influence, and at 500 years ago an extraordinary increase in coastal progradation took place in all littoral zones. The European Medieval Warm period is characterized, at least during its initial phase, by low pressure climate conditions, while during the Little Ice Age anticyclonic conditions gave rise to a strong coastal progradation.

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.

Coastal deformation and sea-level changes in the northern Chile subduction area (23°S) during the last 330 ky

Abstract The Nazca-South American plate boundary is a subduction zone where a relatively complex pattern of vertical deformation can be inferred from the study of emerged marine terraces. Along the coasts of southern Peru and northern Chile, the vertical distribution of remnants of Pleistocene terraces suggests that a crustal, large scale uplift motion is combined with more regional/local tectonic processes. In northern Chile, the area of Hornitos (23°S) offers a remarkable sequence of well-defined marine terraces that may be dated through U-series and aminostratigraphic studies on mollusc shells. The unusual preservation of the landforms and of the shell material, which enabled the age determination of the deposits, is largely due to the lengthy history of extreme aridity in this area. The exceptional record of late Middle Pleistocene to Late Pleistocene high seastands is also favoured by the slight warping of two distinct fault blocks that have enhanced the morphostratigraphic relationships between the distinct coastal units. Detailed geomorphological, sedimentological and chronostratigraphic studies of the Hornitos area led to the identification, with reasonable confidence, of the depositional remnants of sea-level maxima coeval with the Oxygen Isotope Substages 5c, 5e, 7 (probably two episodes) and the isotope stage 9 (series of beach ridges). The coastal plain, at the foot of the major Coastal Escarpment of northern Chile, appears to have been uplifted at a mean rate of 240 mm/ky in the course of the last 330 ky. From the elevation of the older terraces and late Pliocene shorelines, it can be inferred that these steady vertical motions were much more rapid than during the Early Pleistocene.

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.