Sedimentary Geology, 66 (1990) 135-150 135 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands Coral reefs in coarse-terrigenous sedimentary environments (Upper Tortonian, Granada Basin, southern Spain) JUAN C. BRAGA, JOSE M. MARTIN and BERTA ALCALA Departamento de Estratigrafia y Paleontologla, Universidad de Granada, Fuentenueva s / n, 18002 Granada (Spain) Received May 1, 1989; revised version accepted November 27, 1989 Abstract Braga, J.C., Martin J.M. and Alcala, B., 1990. Coral reefs in coarse-terrigenous sedimentary environments (Upper Tortonian, Granada Basin, southern Spain). Sediment. Geol., 66: 135-150. During the Upper Tortonian coral reefs developed on fan deltas and braid deltas along the active eastern edge of the Granada Basin. The corals grew in environments characterized by deposition of coarse sands and conglomerates. Frequency of sedimentation together with sea level rises controlled reef development and determined the architecture and composition of the carbonate deposits. In direct contrast to these reefs, others flourished at the same time along stable coastal margins of the basin. Their structure was influenced mainly by periodic rises in sea level. The mapping of all these reefs serves as an accurate guide to the Upper Tortonian geography of the Granada Basin. Introduction Numerous coral reefs both modern and fossil growing in areas of significant terrigenous sedi- mentation, have been described (Gvirtzman and Buchbinder, 1978; Hayward, 1982, 1985; Sellwood and Netherwood, 1984; Roberts, 1987; Purser et al., 1987; Santisteban and Taberner, 1988). The resulting sediments are generally a mixture of carbonates and siliciclastics, the varied geometries and compositions of which are determined by the interactions between the biological system of the reef itself and the dynamics of the surrounding sedimentary environment. Nevertheless, until now the processes involved in these interactions have not been the subject of detailed research. In this paper we describe the structure, com- position and palaeogeographical setting of a num- ber of Upper Tortonian coral reefs from the Granada Basin. Many of these reefs grew on fan deltas and braid deltas in areas of spasmodic sand 0037-0738/90/$03.50 © 1990 Elsevier Science Publishers B.V. and conglomerate sedimentation. These conditions are not generally considered favourable to reef growth. In fact, the type and, above all, the frequency of sedimentation did affect reef devel- opment, although the sediment supply was insuffi- cient to prevent reef building. Elsewhere in the basin reefs developed along coastlines in areas with little or no terrigenous sedimentation. At these sites their growth was controlled mainly by periodic rises in sea level. Stratigraphy and brief geological history of the Granada Basin The Granada Basin is an intramontane depres- sion situated at the boundary between the Internal and External Zones of the Betic Cordilleras (Fig. 1). Its sedimentary infilling comprises a series of units laid down from the Lower Burdigalian (Gonzalez-Donoso, 1978) to the Quaternary, each separated by unconformities (Fig. 2 ).