No abstract

Stratigraphic relations. detailed petrography. rnicrotherrnornetry of fluid inclusions, and fine-scale iso topic analysis of diagenetic phases indicate a complex thermal history in Tithonian fluvial sandstones and lacus trine limestones of the Tera Group (North Spain). Two different thermal events have been recognized and char acterized. which are likely associated with hydrothermal events that affected the Cameros Basin during the rnid Cretaceous and the Eocene. Multiple stages of quartz cementation were identified using sealU1ing electron microscope cathodolurninescence on sandstones and frac ture fills. Primary fluid inclusions reveal homogenization temperatures (Th) from 195 to 350°C in the quartz cements of extensional fracture fillings. The high variability of Th data in each particular fluid inclusion assemblage is related to natural reequilibration of the fluid inclusions, probably due to Cretaceous hydrothermal metamorphism. Some secondary fluid inclusion assemblages show very consis tent data (Th = 281-305°C) and are considered not to have

26The early stages of intraplate extensional systems commonly are recorded by deposition of continental 27 sediments. In this context, given appropriate tectonics and eustasy, transgressions can be well recorded in 28 the areas of the basins located close to the sea, but they may be difficult to recognize in the innermost 29 landwards areas of the system. This situation occurs in the innermost Upper Jurassic-Early Cretaceous 30 Cameros Basin, part of the Iberian Extensional System (N. Spain), where a Berriasian transgression is 31 recorded. The Berriasian succession in this area consists of siliciclastic deposits (sandstone and 32 mudstone) of the Salcedal Formation and of carbonate and mixed carbonate-fine siliciclastic deposits 33 (limestone and marl) of the San Marcos Formation. The sedimentological analysis of this depositional 34 succession indicates that a Berriasian carbonate coastal wetland system occupied that sector of the 35 Cameros Basin during deposition of the San Marcos Formation. This carbonate coastal wetland system 36 consisted of shallow and quiet water bodies including some with marine influence others with no to very 37 little marine influence, and palustrine areas. A semiarid climate characterized by the seasonal alternation 38 of short wet and long dry periods caused water bodies of the system to undergo episodic desiccation and 39 subaerial exposure. Moreover, this complex mosaic of sub-environments was connected laterally with a 40 distal zone of a distributive fluvial system that was rimmed by siliciclastic tidal flats during phases of 41 greater marine influence. 42 The paleogeographic arrangement of this coastal wetland depositional system indicates that the marine 43 influence came from the Basque-Cantabrian Basin to the north. During the period of Berriasian maximum 44 marine influence, accommodation linked to the eustatic rise added to accommodation generated by 45 tectonic subsidence from the extensional reactivation of late Variscan strike-slip faults. All these factors 46 favored marine incursion into the west Cameros Basin from the Basque-Cantabrian Basin to the north.47 The example of the Berriasian transgression recorded in the W Cameros Basin by establishment of coastal 48 wetland systems matches the interpretations of previous studies in neighboring areas. In those areas, 49 complex coastal systems record transgressions in the innermost parts of the intraplate extensional basins 50 of the Iberian Plate. This observation suggests that this paleogeographic and sedimentological 51 arrangement may be common in the innermost parts of intraplate extensional basins during transgressive 52 episodes throughout the geological record.

This study confirms several inferences regarding Holocelle coastal dynamics and climate through a petrographic modal analysis of60 Holocelle sand samples recovered in seven sites along the N\V coast of the Iberian Peninsula. Fluvial sand can be discriminated from more mature intertidal and aeoliall sand according to texture and composition. Fluvial sand contains soil products and coastal sand has significant bioclasts. Quartzofeldspathic sand appears in the western area (produced by the erosion of granite and granitoid), and quartzolithic sand occurs in the eastern area (produced by the erosion of metasediment). Changes in sand composition during Holocelle deposition are manifested by an increase in modem carbonate clasts (1v1C) correlated with the Holocene transgression. Episodes of faster sea-level rise and subsequent erosion of surr ounding cliffs are indicated by the preservation of high proportions of feldspar in intertidal sand. In contrast, fl uvial sand is characterized by greater quartz enrichment. These inferences were confirmed by petrographic indices (carbonate clasts/total clasts, MClT; total feldsparsimonocrystalline quartz, FIQm; and plagioclase/total feldspars, P/F). The different maturity of intertidal and aeolian sands is revealed by their variable quartz contents, despite similar proportions of plagioclase and K-feldspar. This suggests mechanical abrasion as the main factor controlling maturity. In contrast, fl uvial sand shows depleted plagioclase contents as the result of inland weathering processes. Intertidal, beach and aeolian sands are essentially the products ofthe erosion of coastal cliffs and head deposits, with only the scarce contribution of fl uvial drainages. The long distance transport of Galician coastal sands is discarded based on the close relationship between their composition and that of local sand sources. Our findings indicate that short-distance transportof sediments from the west closed off coastal wetlands and occluded estuarine mouths during the Holocene transgression by deposition on sediment-trap zones along the irregul arly shaped Galician coast.