Lacustrine formations of Late Miocene age in the Prebetic area, SE Spain, show several types of deformational structures that are interpreted as seismites. They are present in both marginal and deep lacustrine facies. Seismites formed in marginal lake environments comprise sand dikes, pillows and intruded and fractured gravels. In deep lacustrine facies, the seismites are represented by pseudonodules, mushroom-like silts protruding into laminites, mixed layers, disturbed varved lamination and loop bedding. The measured orientations of these structures are consistent with the orientations of the main faults limiting the basins, showing that their origin is clearly related to the tectonic stress field that prevailed in the region during the Late Miocene. The magnitudes of the earthquakes that deformed the sediments have been estimated after published data from both ancient and recent lake deposits accumulated in tectonic active regions elsewhere. A rank of earthquake magnitudes with two end-members, i.e. the lowest magnitudes recorded by loop bedding in laminites and the highest magnitudes represented by intruded and fractured gravels, is proposed.

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Lacustrine deposits form most of the sedimentary record accumulated throughout the Miocene in the northern part of the Teruel Graben, a landlocked basin situated in NE Spain. Three main stratigraphic units (Units I-Ill ) spanning Late Vallesian to Late Turolian in age, are distinguished in the area. The two former units comprise mainly carbonate lacustrine deposits that were deposited in a palustrine or a more permanent but shallow lacustrine setting, the latter being related mainly to periods of lake expansion under more humid and cooler climatic conditions. In contrast, deposition of Unit Ill, characterised by gypsiferous lacustrine sediments in central parts of the basin, reflects the influence of source rocks of evaporitic nature (Upper Triassic formations) that were emplaced by diapiric uplift in the eastern margin during the Middle Turolian. Carbonate lake sediments belonging to Units I and 11 consist of four main lithofacies associations: (a) distal-alluvial lake margin deposits; (b) lacustrine carbonates and pedogenically modified lacustrine carbonates; (c) carbonate fill channels; and (d ) organic-rich marlstone and carbonate (marshes).Lithofacies association (a) shows typically a sequential arrangement formed, from bottom to top, of red mudstone, carbonate palaeosols and biomicrite beds (sequence type la). These sequences are interpreted as a result of slow but continuous aggradation of the f100dplain areas and subsequent rise of the water table, probably reflecting equilibrium between subsidence and sedimentation. Lithofacies association (b) consisting of biomicrite beds passing upward into palaeosols (sequence type I b) is thought to be caused by marked pulses of tectonic subsidence that created the accommodation space required for fast development of a carbonate lake. Carbonate fill channels, showing erosive lower surfaces dig out on previous channels, marsh deposits and/or lacustrine carbonates, exhibit well-developed prismatic structure at their bed tops. The sequential arrangement suggests similar tectonic constrains than the envisaged for lithofacies lb. The comparison of depositional styles of the lake systems with the palaeoclimatic evolutionary pattern of the basin throughout the Miocene indicates that the combined effect of tectonism, climate and source rock played a major role in the stratigraphic framework of the basin during this period.

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Lacustrine laminated sediments (laminites) present in Late Miocene formations of the Hõ Âjar Basin, SE Spain, display well developed loop bedding, a structure consisting of bundles of laminae that are sharply constricted at intervals, giving a morphology of loops or links of a chain. The laminite sequences, which are interbedded with turbidite marlstones, were accumulated on the bottom of a permanently strati®ed lake developed in a rapidly subsiding basin limited by 010°and 105°normal faults. As deduced from both macro-and microdeformational analyses, the basin evolved under an extensional stress ®eld throughout the Late Miocene. Four main types of loops, simple and complex loops with subcategories, have been recognized within the laminite sequence. Simple loops of type 1 show the best de®nite pattern, quite similar to`pinch and swell structures', a type of boudinage typical of stretching of alternating beds where the competence contrast is not strongly marked. The remaining loop types display contortion and occasional breakage of laminae (microfaulted edges) indicative of microdeformation near the boundary between the ductile-brittle deformational ®elds. The distribution of the various loop types across the laminite sequence re¯ects an interplay between progressive lithi®cation of the laminites as sedimentation progressed and tectonic stresses which affected the sediment sequence. Accordingly, a mechanism of deformation under an extensional stress ®eld, ultimately related to the creep movement of the main basin faults which resulted in successive seismic shocks of low magnitude, is proposed to explain the formation of loop bedding in the laminites.

Lacustrine and alluvial carbonate facies have been investigated in Middle Miocene successions of the western side of the Madrid Basin in order to evaluate paleoenvironments in which carbonates formed. Carbonate facies are varied and include: (I) calcrete and dolocrete; (2) pond deposits; (3) lake margin dolostone; (4) mudflat carbonate; and (5) open-lake carbonate facies. The dominant mineralogy of these is dolomite and/ or low-Mg calcite. No high-Mg calcite or aragonite have been detected in any sample. 8 1 8 0-and 8 13 C-values range from-8.20 to-1.80%0 PDB and-10.25 to-0.70%0 PBD, respectively. More negative 8 18 0-and 8 13 C-values correspond to predominantly calcite calcretes and to carbonate deposited in ponds at the foot of arkosic alluvium. Higher 8 18 0-val ues are from both lacustrine carbonate and dolocrete. This latter lithofacies has strong geochemical similarities to dolostones deposited in a lake margin environment. Mudflat carbonate, deposited on shallow platforms subject to lake water oscillation, shows great heterogeneity in both stable isotope value and trace-element content. The mineralogy of these carbonates is dominated by calcite and the limestones contain molds of gypsum. Occurrence of calcitized dolomite textures in these facies suggests the influence of fresher water during expanding lacustrine cycles or further interaction with less saline groundwater. Trace-element contents are considered to be potential indicators of the different carbonate facies types, thus aiding the paleoenvironmental interpretation. However, discrimination among carbonate facies on the basis of trace-element contents appears to be dependent on the statistical method utilized for treatment of data. More information is needed to ascertain their use as paleoenvironmental indicators.