The Formation of the Bahamas: San Salvador during the Ice Ages

This discussion topic submitted by Scott Wankel ( wankelsd@miamioh.edu) on 6/7/98.


Overview of last 200 Ma:
Opening of North Atlantic
Sedimentation and Subsidence (100% LS)
Gulf Stream – separation from FL and Cuba
Pleistocene:
Glaciations (4) and Interglacials (3)
Higher Sea Level:
Fossil Corals
Coastal erosion Features
Raised Beaches
Marine LS and Current Bedding
Lower Sea Level:
Wavecut platforms and Marine Terraces
Limestone Crusts and Peat
Blue Holes and caves s

The Bahamas is composed of 100% shallow marine and terrestrial facies.

Growth occurs by lateral accretion and is dependent on sea level, platform and shelf margin configuration, and the orientation of sediment transport sources.

Carbonate islands originate by shoaling during stormy periods when sediments blanket ing the platform first accumulate as shoals, and progessively emerge into beach ridges and dunes. During low stands, dune deposits indurate and form nucleation points or anchors for subsequent deposition during high sea levels.

Growth is self regulated: lateral growth on the platform means less source area for sediment production. San Salvador appears to have nearly completed its lateral growth and subsequent growth will be vertically, if accommodated by subsidence or a higher sea level in order to oversteep the high ridges surrounding the island.

Four Phases of landform development:

Phase I: (350 – 180 ka)
Deposits corners (as small ridges) of San Sal. Other phases tied to/modified by these “anchors.” Most significant cavess are within these deposits.

Phase II: (132 – 120 ka)
Early Sangamonian Interglacial (Sea Level Rising) Caternary Ridges – larger and higher farther inland. Between the “anchors”
Long smaller ridge on the north and west side. (Sandy point-Cockburntown-Sue point-Reckley point). Stable shoeline on the more tranquil side of San Sal.

Phase III: (80 ka)
Late Sangamonian (Sea Level only slightly below today) High promontories on the eastern margin of San Salvador. Lie seaward of all other ridges and form the anchors for subsequent caternary development. From 80 to 12 ka sea level retreats during the Wisconsin glacial period.

Phase IV: (5 – 3 ka)
Lower and simpler ridges around nearly the entire circumference of San Sal. Primarily on the eastern edge of San Sal and are caternary on the Phase III and older anchors.


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