Enabling Easy Access to Analogs for Carbonate Deposition in Early Rift Settings

Driven by requests to provide carbonate analogs for exploration in rift settings like the South Atlantic Margin (SAM), we have assembled select examples into a GIS database that can be easily accessed via the company’s intranet, an in-house webpage, or locally on a PC. Each analog can be visually and quantitatively interrogated using the GIS, with hyperlinks to data folders that contain photographs, literature, and other supplemental information for each example.

The analog examples show a spectrum of sizes, shapes and styles of deposition for lacustrine and marginal marine settings, wherein the types of carbonates that have been inferred in cores from SAM reservoirs (microbialites, tufas, and travertines) can be illustrated. The examples are grouped as:

Early rift lakes using five examples from the East African Rift System: Lakes Natron-Magadi, Manyara, and Bogoria which contain microbialites (= stromatolites) and local travertines and also an outcrop record of high lake level stromatolites; Lake Turkana with extensive shoreline carbonates, local travertines, and also an outcrop record of high lake level microbialites (= stromatolites); and Lake Tanganiyka showing extensive shoreline carbonates and an outcrop record of various lake level microbialites (= stromatolites and thrombolites).

Other lakes with six diverse examples: Great Salt (and high lake level Bonneville) Lakes, Utah with shoreline carbonates including oolites, and modern and Pleistocene microbialites (= bioherms); Mono and Searles Lakes, California, and Pyramid (and high lake level Lahontan) Lake, Nevada, containing widespread spring-related tufas; and Lakes Clifton and Lake Thetis, Australia, with microbialites (= stromatolites and thrombolites).

Marginal marine basins with two examples: Shark Bay, Australia, with nearshore restricted marine microbialites (= stromatolites); and the Red Sea illustrating nearshore coral reefs and related marine carbonates.

Landsat images, DEMs, and available geological literature are used to delineate the present and past lake/basin margins - for several examples the shorelines representing different lake levels can be compared. In all cases, only a relatively small percentage of the lake area is occupied by carbonate deposition, therefore the examples are not necessarily analogs illustrating a vast extent of microbial/tufa deposits, but are intended to illustrate the location and various styles of carbonate deposition within each of the examples.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California