Review of San Salvador Formation

1
Review of San Salvador Formation

• Geology
• Meteorology

Several diagrams in this portion adapted
from Sealey, N. 1998. Bahamian Landscapes. 2d.
ed. Media Publishing, Nassau, Bahamas.
2
Pangea Pulls Apart

• 200 MYA
• Spreading center between North American and
  African plate
• Stretches continental crust at fault with
  Caribbean plate
• Atlantic Ocean with Bahama Banks

Tethys Trench Mediterranean
North America
N
Mid-Atlantic Ridge
Africa
Gulf of Mexico Caribbean Sea
fault
South America
3
Bermuda Mount
http//topex.ucsd.edu/marine_topo/gif_topo_track/t
opo8.gif
Mid-Atlantic Ridge
San Salvador
Bahama Banks
4
Bermuda Mount
http//topex.ucsd.edu/marine_topo/gif_topo_track/t
opo8.gif
Bahama Banks
San Salvador
5
Bahamas Banks
6
North Atlantic Ocean Plate
Gulf of Mexico
San Salvador
Transition Fault Puerto Rico Trench 8,400 m
Strike-Slip Fault Cayman Trench
Caribbean Sea Plate
Subduction volcanoes
7
Neither in Gulf of Mexico Nor in Caribbean It is
in the North Atlantic Part of the Bahamas Banks
San Salvador
8
Oolitic Sedimentation
Cay Sal
Straits Of Florida
Eleuthera
Period
Age
Florida
Andros
Santeren Channel
present
recent
Tongue of the Ocean
Atlantic Ocean
35 my
Eocene
50 my
Palaeocene
5000ft1525m
Late Cretaceous
65 my
Early Cretaceous
10000ft3050m
100 my
15000ft4575m
140 my
Jurassic
20000ft6100m
Pre- Jurassic
Crust?
200 my

• Rapid Deposits
• Continental Crust Subsides
• 120 MY Young
• Cores to 20,000 ft (4mi) are surface-cemented
  limestone!!
• Crust NOT found in any cores to date

9
Biotic and Abiotic Contributions
Skeletal
Oolitic
Pelletal

• From Halimeda algae, shells, etc.

Precipitated fine particlesabiotic!
From fecal pellets of animals
10
Cementation
Mixture of Particle Types
Remaining pore space
Cementation
Aragonite Needles
Closed pore spaces

• Heat, evaporation, increases concentration of
  calcium and carbonate solutes between particles
• Aragonite limestone crystals grow outward from
  particles
• Particles cemented to form rock

11
Cementation Locking

• Aragonite crystals interdigitate and lock
• Rapid locking of particles into Beach Rock
• Slower locking into Marine Cementation

12
Bucket Model for Dune Formation
Rippled layer
Tidal flux
Bahama banks
Secondary shoal
25 ft
Atlantic Ocean
Primary shoal
Oolitic sands
Coral Reef
Skeletal sands
Limestone rock sea floor

• Coral reef edges keep oolitic particles behind
  bucket wall
• Water with fresh bicarbonate delivered by current
  to inside
• Heat, evaporation, concentration, oolitic
  precipitation
• Wind-blown particles at low tide make dunes
• Or when sea level falls at ice ages

13
Rainfall Contribution
Rippled layer
Tidal flux
Bahama banks
Secondary shoal
25 ft
Atlantic Ocean
Primary shoal
Oolitic sands
Coral Reef
Skeletal sands
Limestone rock sea floor

• Shoals of particles form at sea-level high-stands
  in interglacial periods
• At sea-level low-stands in glacial periods dunes
  are exposed
• Rainfall dissolves limestone from upper layers
• Percolates between particles to lower layers
• Concentration, crystallization, cementation
• LITHIFIED DUNES

14
The Source of Coriolis Currents
H

• Air pockets called cells with circulation
  indicated by arrows
• Arrows coming down indicate high pressure
• Arrows pointing outward indicate low pressure.
• Pattern repeated in Southern Hemisphere (not
  shown)

L
30N
H
westerlies
horse latitudes
NE trade winds
0
L
equatorial doldrums
SE trade winds
horse latitudes
westerlies
30S
Activity Making Your Own Cloud in a
Bottle Clearing Out Your Cloud
15
The Source of Coriolis Currents

• Equatorial doldrum air is heated by a shorter
  path for sunlight through atmosphere, the gas
  expands, and riseslow pressure
• Curvature and rotation of earth spins replacement
  surface air clockwise pulling it downward from
  elsewherehigh pressure
• Downdrafts are at 30 latitude from equator.

1015
1010
H
L
1020
L
1010
1015
1020
1020
H
H
Low pressure areas produce storms that must move
around the dense high pressure areassuch as the
Bermuda High over the North Atlantic Ocean
16
Coriolis Effect

• Northern Hemisphere
• Clockwise Currents
• Warm NEC
• Branches as Antilles Current and Caribbean
  Current
• CO2 Saturated Water
• Shallow water warms
• Evaporation
• Concentration
• Precipitation
• Oolitic Particles

North Atlantic Ocean
North America
Gulfstream Current
Europe
Canary Current
Sargasso Sea
Gulf of Mexico
Antilles Current
Africa
Caribbean
North Equatorial Current
South America
Equatorial Doldrums
South Atlantic Ocean
17
http//sgiot2.ssd.nesdis.noaa.gov/data_drive/produ
cts/modis/browse/MOD28L2_P2005109_1800_SE_sst.png
San Salvador
18
Annual Wind Rose
SE

• Overall annual wind rose for San Salvador
• Wind mostly out of east--mostly ocean there (but
  was this the pathway for mangrove colonization
  from Africa?)
• Wind from South East could be important for
  island hopping along the Antilles from South
  America
• 8.4 calmso sea breezes are common

19
Wind and Current Effects

• Windblown oolitic particles carried downwind
• Deposit on leeward slopes of dunes
• Current builds dune foundations down-current
• Dunes curve and form ridges
• Lithification and Island takes ultimate shape
• Was Grahams harbor once part of main island,
  eroded to just a few cays?

132,000 years
128,000 years
350 - 180,000 years
80,000 years
120,000 years
5-3,000 years
20
Ridges are Intense!
120 100 80 60 40 20 Sea Level
Grahams Harbor
Little Lake
Duck Pond
Blue Pond

• These are two cutaway transects showing how these
  lithified dune ridges can be very high!

Great Lake
Six Pack Pond
Granny Lake
South Granny Lake
Great Lake
Stouts Lake
Pigeon Creek
Snow Bay
Storrs Lake
Six Pack Pond
Fernandez Bay
Greens Bay
Little Lake
Great Lake
60 40 20 Sea Level
21
Inland Lakes Form

• Valleys between dunes fill with water
• Fresh 0.2 PPT
• Brackish 1 PPT
• Saline 2 PPT
• Sea Water 20-37 PPT
• Hypersaline 40 PPT
• Salinity depends on tidal flux, percolation,
  rainfall, elevation, etc.
• Stromatolites form in inter-dune lakes!

22
Grahams Harbor
Gerace Research Centre
23
Gerace Research Centre
Catchment Basin
Oyster Pond
24
Oyster Pond
Vent
25
Columbus and Coriolis Currents
North Atlantic Ocean

• No surprise that Columbus ships sailed south out
  of Spain toward Africa and ended up following the
  North Equatorial Current into San Salvador. The
  island is believed to be his first landfall.
  Could other Old-World species do this?

North America
Gulfstream Current
Europe
Canary Current
Sargasso Sea
Gulf of Mexico
Antilles Current
Africa
Caribbean
North Equatorial Current
South America
Equatorial Doldrums

• Clearly rafting is going to be South American
  species moving along the Antilles current to San
  Salvador.
• Flow in Florida Straight means no rafting from
  North America!

26
Pathways for Colonization
Wind flying, parachuting, hitchhiking Water
swimming, rafting
Continental Air Mass
Maritime Air Mass
Gulf stream
Tropic of Cancer
Gulf of Mexico
North-east trade winds
Antilles current
Caribbean Sea
North Equatorial Current
Tropical Air Mass

• Wind can bring organisms to an Island depending
  on direction, distance, duration, and richness of
  the source
• Currents can bring organisms to an Island
  depending upon direction, distance, richness of
  source, and ability of the organism to endure the
  passage.

27
Spain
http//www.tehrantimes.com/News/11096/09_DUST20AF
RICA.jpg
28
Dust Storms from Africa can carry mineral
particles, microorganisms and spores of organisms
across the Atlantic. Live locusts, 5 cm long,
from central Africa have arrived in the Caribbean!
http//www.theresilientearth.com/files/images/Saha
ranDustStorm.jpg
West Africa
29
http//soundwaves.usgs.gov/2002/09/sat-dust.jpg
Are microorganisms in this dust responsible for
coral decline in the Caribbean?
30
Chad
The dust is coming from Saharan Africa
http//aerosols.hamptonu.edu/images/usgs_african_d
ust.jpg
31
The sand source is Egypt and Libya The erosional
slopes into Chad are visible in satellite imagery
The the dry lake bed in Chad may be the source of
spores Satellite image from maps.google.com
32
The Bodele area is a former lake bedthe lowest
point in Chad. NE Wind from Egypt funnels sand
into the bowl of the dry lake bed. The shape of
the bowl provides the uplift to the wind flow.
The lifted lake-bottom dust joins a
westward-moving cloud.
Satellite image from maps.google.com
33
Bodele Dry Lake, Chad
250 miles
Satellite image from maps.google.com
Average winter dust lift gt700,000 metric tons
per day! Fisher, Richard. 2007. Amazon forest
relies on dust from one Saharan valley.
NewScientist Environment online. 3 Jan 2007.
34
Wind Rose
SE

• Overall annual wind rose for San Salvador
• Wind mostly out of east--mostly ocean there (but
  was this the pathway for mangrove colonization
  from Africa?)
• Wind from South East could be important
• 8.4 calmso sea breezes are common

35
Monthly Wind Roses

• Monthly wind roses show important times for
  dispersal to island
• In which months would colonizations most likely
  occur from the rest of the West
  Indies/Antilles?
• Would you expect South America to contribute much
  to the biota?
• When does North America provide organisms?

6.9
5.6
8.2
January
March
February
8.3
6.1
6.0
April
June
May
5.6
11.8
6.6
July
September
August
12.2
11.2
13.0
December
October
November
36
Hurricane Tracks
Cape Hatteras
Bermuda
Gulf of Mexico
San Salvador
Caribbean Sea

• Hurricanes break up land masses, uproot trees,
  and produce much debris that can float on
  currents for rafting.
• The path of hurricanes to San Salvador is along
  the archipelago!

37
Hurricane Frances September 2004
38
Habitats on San Salvador Island

• Reef
• Grass Beds and Sandy Bottom
• Sandy Beach and Dunes
• Mangrove Swamp
• Intertidal and Rocky Coast Headland
• Thicket or Coppice
• Lakes
• Caves

Welcome to the Podium, Dr. Idjadi!