부산대학교 도서관

The Upper Lias (Bridport) Sands contain numerous carbonate cemented layers up to a meter thick that extend continuously for over 3 km at outcrop in Dorset. These cemented layers contain bioclast-rich, clay-poor sediments and a high-energy palynofacies assemblage, and are characterized by relatively high-energy sedimentary structures. The layers are interbedded with porous, biolcast-poor, clay-rich sediments that contain a low-energy palynofacies assemblage and are characterized by extensive bioturbation. These clay-rich and bioclastic sediments were deposited by continuous fair weather and episodic storm processes, respectively, on a submerged marine shoal. Following deposition, the clay-rich fair-weather sediments are weakly cemented and compacted. Fringing cements stabilized the bioclastic storm deposits, inhibiting mechanical compaction. The resulting porous framework was subsequently cemented by calcite and dolomite supplied during dissolution of unstable aragonite and high-Mg calcite. Carbonate remobilization at elevated temperatures during burial progressively shifted oxygen isotopic compositions from Jurassic marine bioclast compositions to cement compositions of delta/sup 18/0 - 6 to - 7o/oo PDB.