22 Sedimentation, Tectonics, and Petroleum from the Heartland to the Carribbean (Posters)

Friday, 20 March 2015
9:00 AM - 4:00 PM
Starlight Terrace

THREE TYPES OF BARBADOS BEACHROCKS

Paper number: 22-7
Program: Technical Sessions
Time: 9:00 AM – 4:00 PM

Authors

Abstract

Cemented sands were found in the intertidal zone of several beaches on Barbados. These sandstones are generally referred to as beachrock. The objective of this study is to identify similarities and differences in these sandstones. They can be classified into three types: (1) beach sandstone, (2) beach cay sandstone, and (3) pseudo-beachrock. Types 1 and 2 are from low-energy beaches along the west coast, while Type 3 is from a high-energy beach along the east coast. The low-energy rocks are subdivided into beach sandstone and beach cay sandstone based on their location to the current intertidal zone. Type 3 does not conform to the conventional definition of beachrock.

In all three locations the main clastic constituents are grains of calcite and aragonite (CaCO3), while pseudo-beachrock from the high-energy beach contains some quartz. The beachrocks from the low-energy beaches are lithified with isopachous calcite cements, while high-energy beachrocks are bound mainly by coralline algae and encrusting foraminifera, with only small, patches of calcite cement that do not appear to contribute significantly to lithification. The differences observed in cementation contribute to porosity differences between the high-energy and low-energy rocks. The pseudo-beachrock has higher porosities (up to 35%) in thin section, while the low-energy beachrocks have lower porosities (5% to 15%). The three types of cemented sandstones found in the modern intertidal zone on Barbados thus show considerable petrographic variations, derived mainly from the energy of their respective environments of deposition and early diagenetic processes.