(Table 1) Dry bulk density and porosity of ODP Hole 165-1002C sediments, Cariaco Basin@en

Two geographically close hemipelagic deposits are compared: (1) the Pleistocene-Holocene part of the Cariaco Basin succession off Venezuela drilled in Hole 1002C and (2) the Upper Cretaceous (Cenomanian to Santonian) La Luna-Querecual Formation, which crops out in northern Venezuela from the Sierra de Perija, west of the Gulf of Maracaïbo, to the Gulf of Paria eastward. This analysis is based on thin-section descriptions, porosity data, and examination of core photographs. Despite their very different ages, these formations are similar in facies, structure, and diagenetic behavior. Their facies are calcareous black shales rich in organic matter and planktonic remains such as foraminifers, radiolarians, and diatoms. Their structures result in a high-frequency cyclic fabric with superimposed units ranging from obliquity cycles to annual varves, as well as several types of solar and pluriannual El Niño-type cycles. In the Cariaco succession, the frequencies of pluriannual cycles have been determined by a statistical study on deposits with standardized compaction and sedimentation rates to convert the thickness of cycles to a scale proportional to their duration. Their diagenetic behavior is signaled by (1) early carbonate precipitation under bacterial control leading to beige micritic layers, (2) carbonate and siliceous concretions before major compaction, (3) recrystallization, (4) deformation from compaction, and (5) dissolution. […]