Angel Falls, Venezuela GSTT Geo

GSTT Geo-Tour: Angel Falls, Venezuela
‘Ultimate Orinoco experience - from Source to Sink’
May 21st – 25th, 2015
Led by Mr. Winston Awai Jr.
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Welcome!
The Geological Society of Trinidad & Tobago (GSTT) welcomes you to our Angel Falls
Geo-Tour. This new style of field trip is intended to develop our appreciation of regional
geology, whilst concurrently increase our understanding of the cultures, and natural
attractions within the Caribbean region. This Geo-Tour looks at Angel Falls (Salto
Ángel) nestled in Canaima National Park, Venezuela. It is the world's highest
uninterrupted waterfall, with a height of 979 m (3,212 ft) and a plunge of 807 m (2,648
ft). The waterfall drops over the edge of the Auyantepui mountain in the Canaima
National Park (Spanish: Parque Nacional Canaima), a UNESCO World Heritage site in
the Gran Sabana region of Bolívar State. The height figure 979 m (3,212 ft) mostly
consists of the main plunge but also includes about 400 m (0.25 mi) of sloped cascades
and rapids below the drop and a 30-metre (98 ft) high plunge downstream of the talus
rapids. The base of the falls feeds into the Kerep River (alternatively known as the Río
Gauya), which flows into the Churun River, a tributary of the Carrao River.
Topographical Map of
northern South
America
Venezuela, the Bolivarian Republic of Venezuela is located on the northern margin of
South America, with borders to Colombia to the west, Guyana to the east and Brazil to
the south. Its northern Caribbean coastline extends for 2800km, and boasts as the 33 rd
largest country in the world with an area of 916,445km2. Venezuela has a total population
in excess of 27 million, living in 23 states, of which approximately 5 million live in the
capital city - Caracas.
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Schedule Summary
Thursday 21st May - Day 1
 The GSTT shuttle buses will depart from the Hyatt
Regency heading to San Fernando.
 Depart from San Fernando at 8:00am via Ferry
(36’ Bowen) to Perdernales at 9:00am (1 hr)
 Taxi boat (1:00pm) from Perdernales to Tucupita
(3hrs)
 Arrival in Tucupita, head to hotel.
 Trip Leader will collect passports for Immigration
 Overnight at hotel – 2 persons per room.
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Friday 22nd May
- Day 2
 Breakfast at 4:45am
 Depart hotel via shuttles @ 5:00am to Ciudad
Bolivar Airport (2hrs)
 Flight to Canaima National Park (1hr).
 Drop off luggage at Hotel, collect lunches.
 Grab knapsacks and head up river via engine
powered canoes to near base of falls – (3:00pm)
 Afternoon basic hike (2.5 /5) to base of falls
 Head back to camp ~ 6-7:00pm
 Campfire dinner. Sleep in hammocks
Saturday 23rd May
- Day 3
 Morning hike to the base of falls (2.5 /5)
 Day at the falls, plunge pools
 Hike back to river, take boat back to Canaima
 Possibly visit Sapo Falls on the way back to
Canaima
 Enjoy the Canaima night life.
 Night at hotel in Canaima – rooms will be shared
between 3 or 4 persons
Sunday 24th May
- Day 4
 Breakfast at hotel in Canaima
 Optional – Helicopter ride to tepuis – view Angel
Falls and the tepuis from above
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Visit to Sapo falls and other falls within the
Canaima National Park
Head to Canaima airstrip, catch flight to Cuidad
Bolivar
Stay overnight at hotel – 2 persons per room
Monday 25th May
- Day 5
 Breakfast at hotel
 Shuttles to Tucupita
 Take water taxi from Tucupita to Perdernales
 Catch ferry from Perdernales to San Fernando
 Arrive in San Fernando at 3:00pm, Clear customs
by 4:00pm. Shuttle to Hyatt Regency.
What to bring?
Observing standard baggage policy, one should ensure to pack the following: Valid passport
 Currency ( US, £, € - large notes preferably)
 Two pairs of sneakers – the most rugged one for
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hiking and getting wet, the other for dry areas
A pair of flip flops
A jacket, hat, sun block
Mini ear plugs
Zip-lock bags for electronics
Camera, extra memory cards, at least 2 extra camera
batteries –** from Thursday night in Tucupita we
will not have electricity for charging cameras until
Saturday afternoon at Canaima
Phone and chargers
A head light
Personal Medication
Snacks and or clothes for the children along the river
Spanish-English Dictionary
Electrical outlets throughout the Bolivarian Republic of Venezuela carry the
standard North American plugs.120V/60Hz
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Exchange Rate: The current official exchange rate from US to Venezuelan Bolivares
(VEF) is:1USD = 7VEF
This rate is offered by law at banks, currency exchange bureaus, etc. However, on the
thriving black market the exchange rate can be as much as 1USD = 14VEF. For those
wishing to keep some Bolivares on hand for any local purchases Mr. Winston Awai will
facilitate to ensure that you get the best rates.
Key Information:
The GSTT Geo-Tour covers shuttle to San Fernando, flights, water transport,
accommodation, all meals, tours in Canaima, airport transfers, taxes and service charges.
Drinks apart from complimentary welcome drinks are not covered by GSTT. Personal
bills will be the responsibility of attendees and should be settled by check-out on
departing each hotel.
Contact Numbers
Tour Leader
Mr. Winston Awai
Island Hikers
Tele: 868 308-6030
CGC Convener/Field Trip Coordinator
Mr. Xavier Moonan
Centrica Energy
Eleven Albion
Corner Albion and Dere Streets
Port-of-Spain
Tele: 868 348-8035
GSTT Secretariat
Mr.Keston Brown
University of Trinidad & Tobago Campus
Ezperanza Road, Couva
Tel: 868 679-6064
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Trip Leader Profile
Field Trip Leader - Captain Winston Awai Jr.,
has led trips through the Orinoco Delta more
than a hundred times over the last 10 years. He
is affiliated with the Trinidadian based Island
Hikers, who frequently host hikes throughout
the Northern Ranges in Trinidad. His
adventures have taken him throughout the
Caribbean, the Far East and to North and South
American. Winston has a special fascination
with the country of Venezuela. At the age of
fifteen, he started his personal research into the
South American natives and their environment,
the Canaima National Park, in which resides
the highest single drop waterfall in the world. He is fluent in Spanish and the Warro
dialect and has become an accepted outsider among the Warro Indians and the secluded
Pemon Indians who presently consist of 150 members. He is formerly a Marine attached
to the Venezuelan Guardian Nacional, with over 15 years working in Venezuela, and
currently serves at the Venezuelan Embassy in Trinidad. His job primarily deals with the
handling of cross-border issues, especially with fishing boats and other water craft. He is
also member of the Venezuelan Chamber of Commerce. His love for water activities is a
major passion of his as such, he has earned the title of being one of the top extreme hikers
in the Island Hikers Club.
Xavier Moonan is a Senior Geologist at Centrica Energy,
and currently serves as the Immediate Past President of the
GSTT and the CGC Convener. Xavier coordinated the first
GSTT Geotour, which was held in Dominica in March
2012 and was quite a success, such that the Society has
continued to host such tours annually. Xavier attained a
MSc. in Structural Geology with Geophysics at the
University of Leeds, UK and was awarded a ‘Top Ten
Presentation’ by AAPG for his poster presentation on the
Penal Barrackpore Anticline at AAPG ICE Conference in
Milan, 2011.
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Day 1: Cedros, Trinidad to Pedernales , then onto Tucupita
Key Stops
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Day 2: Tucupita to Cuidad Bolivar
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Day 2: Flight from Cuidad Bolivar to Canaima
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Day 2: Boat up Charo River, hike to base of falls
Canaima National Park
Canaima National Park (Spanish:
Parque Nacional Canaima) is a 30,000
km2 (12,000 sq mi) park in southeastern Venezuela that borders Brazil
and Guyana. It is located in Bolívar
State, and roughly occupies the same
area as the Gran Sabana region. The
park was established on 12 June 1962.
It is the second largest park in the
country, after Parima-Tapirapecó, and
sixth biggest national park in the world.
Approximately 65% of the park is
occupied by plateaus of rock called
tepuis, which consists of Proterozoic sandstone rocks with vertical walls and almost flat
tops. These constitute a unique biological environment and are also of great geological
interest. Their sheer cliffs and waterfalls create spectacular landscapes. The most famous
tepuis in the park are Mount Roraima, the tallest and easiest to climb, and Auyantepui,
the site of Angel Falls. The tepuis are sandstone and date back to a time when South
America and Africa were part of a super-continent. The park is home to indigenous
Pemon Indians, part of the Carib linguistic group. The Pemon have an intimate
relationship with the tepuis, and believe they are the home of the 'Mawari' spirits. The
park is relatively remote, with only a few roads connecting towns. Most transport within
the park is done by light plane from the airstrips built by various Capuchin missions, or
by foot and canoe. Pemons have developed some basic and luxurious camps, which are
mainly visited by tourists from across the world. In 1994, the Canaima National Park was
named a World Heritage Site by UNESCO..
The Orinoco Delta is formed by the Orinoco River
as it splits into 17 main distributaries. The Orinoco
River is 2,140km long, the third longest river in South
America. It begins in the Sierra Parima, in the Guyana
Highlands, close to the border with Brazil. At its
widest point, it measures 16km and has 194
tributaries; the three largest are the Caroni, Apure and
Caura Rivers. At its mouth, the Orinoco River forms a
wide Delta that branches off into more than 300 rivers
and waterways that flow through swampy forests forming small islands and sandbanks.
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The tropical climate allows for lush vegetation and provides excellent living conditions
for a varied wildlife. The majority of the Orinoco Delta region is sparsely populated.
Nearly all of the natives belong to Warao Indian tribes who, for the most part, still live in
traditional huts on stilts built along the banks of the rivers called Palafitos
Kerepakupai Vená - the waterfall was known for most of the twentieth century by the
name "Angel Falls" after Jimmie Angel, a US aviator who was the first to fly over the
falls in a plane. The common Spanish name "Salto Ángel" derives from his surname. In
2009, President Hugo Chávez announced his intention to change the name to the original
indigenous Pemon term ("Kerepakupai Vená", meaning "waterfall of the deepest place"),
on the grounds that the nation's most famous landmark should bear an indigenous name.
Explaining the name change, Chávez was reported to have said, "This is ours, long before
Angel ever arrived there… this is indigenous property." However, he later said that he
will not decree the change of name, but only was defending the use of Kerepakupai Vená
Sir Walter Raleigh described what was possibly a tepuy (table top mountain), and he is
sometimes said to have been the first European to view the Angel Falls, but these claims
are considered far-fetched. Some historians state that the first European to visit the
waterfall was Fernando de Berrío, a Spanish explorer and governor from the 16th and
17th centuries. Later on, they were indeed spotted in 1912 by the Venezuelan explorer
Ernesto Sánchez La Cruz, but he did not publicize his discovery.
The tepuis were not known to the outside world until American aviator Jimmie Angel
flew over them on 16 November 1933 on a flight while he was searching for a valuable
ore bed. Returning on 9 October 1937, Angel tried to land his Metal Aircraft Corporation
Flamingo monoplane El Río Caroní; atop Auyan-tepui, but the plane was damaged when
the wheels sank into the marshy ground. Angel and his three companions, including his
wife Marie, were forced to descend the tepui on foot. It took them 11 days to make their
way back to civilization via the gradually sloping backside but news of their adventure
spread, and the waterfall was named Angel Falls in his honor. Angel's plane remained on
top of the tepuy for 33 years before being lifted out by helicopter. It was restored at the
Aviation Museum in Maracay and now sits outdoors on the front of the airport at Ciudad
Bolívar.
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The official height of the falls was
determined by a National Geographic
Society survey carried out by American
journalist Ruth Robertson in 1949. The
first known attempt to climb the face of the
cliff was made in 1968 during the wet
season. It failed because of slippery rock.
In 1969 a second attempt was made during
the dry season. This attempt was thwarted
by lack of water and an overhang 400 feet
from the top. The first climb to the top of
the cliff was completed on January 13,
1971. The climbers required nine and a half
days to ascend and one and a half days to
rappel down. The climbers were, John
Timo, George Bogel, David Nott, and Paul
Straub (ANGELS FOUR, Prentice-Hall
Inc. 1972) A book by David Nott, Angels
Four, chronicles the first successful climb
up the face of Auyantepui to the top of the
falls.
Angel Falls during the wet season
Tourism Angel Falls is one of Venezuela's
top tourist attractions, though a trip to the
falls is a complicated affair. The falls are
located in an isolated jungle, and a flight
from Puerto Ordaz or Ciudad Bolívar is
required to reach Canaima camp, the
starting point for river trips to the base of
the falls. River trips generally take place
from June to December, when the rivers are deep enough for the wooden curiaras used by
the Pemon guides. During the dry season (December to March) there is less water seen
than in the other months. Generally during the rainy season the falls host on average 500
tourists per day.
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Schedule Details
Thursday 21st May
The GSTT Shuttle Bus will take attendees
from the Hyatt Regency to the port at San
Fernando. We will assemble at San
Fernando immigration office at 8:00am to
catch the 9:00am ferry (36’ Bowen covered vessel) to Perdernales. Our tour
leader, Captain Winston Awai will walk us
through our check in. The GSTT, will cover
the departure taxes for all attendees.
After departure we will hug the Trinidad coastline until Cedros and then travel westward
for approximately 1hr to Pedernales. Pedernales is a city within the Venezuelan state of
Delta Amacuro. Our names will be cross checked by Immigration officers at Pedernales
and then we’ll switch to a taxi boat and travel
up the Cano Manamo distributary of the
Orinoco River delta. Manamo is a Warao word
meaning "two." As such along our route we
will note the Manamo distributary splits into
two, eventually merging into one again. Also,
along the route we will observe the Waro
Indian tribes, we will spot at local restaurants
for refreshments and a chance to mingle with
the natives. We will then disembark at
Tucupita, where we will check into our first
hotel – Hotel Saxi. Tucupita is the capital city
of the Venezuelan state Delta Amacuro.
Hotel Saxi has a total of 75 rooms, each room is fairly large ~ 14x16ft, with two beds. As
such we will have 2 persons per room at this hotel, with an optional 3 persons per room
in the case of a family. The hotel also has a swimming pool, and riverside access to the
Orinoco.
All attendees can relax, and enjoy the afternoon at the hotel. Dinner will be served at the
hotel. Mr Winston Awai will collect all passports to receive official stamping.
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It is also recommended that persons with cameras, charge their cameras and all additional
batteries on this night, since we will not be in a location to charge cameras until Saturday
afternoon. It will also be wise to pack some basic supplies in one’s knapsack since we
will be taking our knapsacks only to the camp at the falls. All heavy luggage will be left
in storage at the hotel at Canaima National Park.
Friday 22nd May
A bus will pick us up at the hotel at 5:00am
heading to Cuidad Bolivar airport. We will
be utilising either 19-seater jets or 5-seater
Cessna aircraft. Flight should take no more
than 2hrs to Canaima National Park.
Optional – for 20USD per person the flight
path can be modified so that the flight will
pass very near to Angel Falls allowing you
an early view of the wonder of the world.
At Canaima National Park we will drop off our heavy luggage for safe keeping at the
hotel – Wey Tupi, while we make our way upriver with knapsacks only to the camp near
the base of the falls. The boats will firstly drop us off on the western bank, where we will
begin our afternoon hike to the falls. Meanwhile, our boat drivers will take our knapsacks
to the eastern bank of the river – to our camps, where they will begin the makings of our
fire-side dinner. We will then return to the river, where the boat will pick us up and drop
us off on the eastern flank of the river where we will join the cooks, national park rangers
and boatsmen for dinner.
Saturday 23rd May
Today we have the entire day to enjoy Angel Falls and all that surrounds it. Persons can
choose to go on an early morning hike to the base of the falls to view it as the sunrises.
There are numerous plunge pools great for bathing – though the water is quite cold!
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After lunch we will begin our journey back down river to Canaima. Along the way we
have the option of viewing the Sapo falls. Sapo Falls (Salto El Sapo in Spanish) and
Sapito Falls (Salto El Sapito meaning "Little Sapo Falls" in Spanish) are waterfalls
tumbling into their own lagoon in an offshoot of the Carrao River (El Río Carrao). The
trail through Sapo Falls passes right behind the waterfall on its way to the other side,
where the deafening thunder of the falls can stall the faint hearted. But no need to fear,
‘runners’ or park rangers will help you along.
We will then proceed to the hotel – Wey
Tupi, have dinner and hit the ‘pubs’ to take
in the vibrant and exotic Canaima nightlife.
Hotel Wey Tupi is very basic, as are all
hotels within the national park to preserve
the environment. Rooms have in most cases
3 or 4 beds, sometimes 5 beds for a family
group. The hotel has 27 rooms with a total
bed count of 55. As such rooms will have to
be shared by 3 or 4 persons in working with
the hotel arrangement. Within our group,
sub-groups of 3 or 4 persons will be drawn
up to best work around these circumstances.
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Sunday 24th May
Since we may all not recover well from a night out partying, we’ll have a lazy breakfast,
followed by visits to falls in the near vicinity, one being the Sapo Falls. An optional this
morning is to take a helicopter ride to view Canaima from air and to fly above Angel
Falls and the tepuis. Prices will be negotiated onsite but may range from 500-800USpp.
After lunch we’ll check out of the hotel, bidding Canaima farewell, we’ll proceed by
plane back to Cuidad Bolivar, where we’ll check into Hotel Universal for the night. Hotel
Universal is located in the centre of the city of Cuidad Bolivar, so persons can venture
within the city if you so wish. The hotel has 110 rooms with two beds to a room, and
each room is approximately 15ft x 15ft. We’ll have dinner at the hotel.
Ciudad Bolívar (English: Bolivar City) is the capital of Venezuela's southeastern
Bolivar State. It was founded with the name Angostura in 1764, renamed in 1846, and, as
of 2010, had an estimated population of 350,691. The town's original name was a
contraction of its full descriptive name, Santo Tomé de Guayana de Angostura del
Orinoco (Saint Thomas of Guiana of the narrows of the Orinoco). The town also gave its
name to the Angostura tree (Cusparia febrifuga) which grows in the area. Angostura
bitters were invented there, though the company which produced them has since moved
to Trinidad and Tobago. Ciudad Bolívar's historic center is well preserved, with original
colonial buildings around the Plaza Bolívar, including a cathedral. Ciudad Bolívar lies at
a spot where the Orinoco River narrows to about 1 mile (1.6 km) in width, and is the site
of the first bridge across the river. It serves as an important port on the Orinoco River for
the eastern regions of Venezuela. One of the Orinoco Basin's chief commercial centers,
its main products include gold, iron ore, cattle, hides and rare woods.
Monday 25th May
In the morning after breakfast, we’ll be picked up by a fleet of shuttles taking us back to
Tucupita. There we’ll catch a taxi boat heading to Pedernales, where we’ll get our ferry
back to Cedros, Trinidad. We should be docking in Cedros around 5pm, checking out of
Customs around 6pm. The GSTT shuttle will pick us up and drop us off at our specified
stops.
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Geology of Eastern Venezuela
Regional Setting
Northern South America, highlighting Venezuela, Trinidad, Guyana and Angel Falls.
The island of Trinidad is located within the Eastern Venezuelan Basin, confined to the
north by the meta-sedimentary Araya/Paria/Northern Ranges rocks, which occur on the
overriding Caribbean Plate Oceanic Crust, and to the south by an open east facing
foreland basin which progressively climbs towards the Guyana Shield. Within the
foredeep, the Present Day Orinoco River flowing from the west to the east, develops a
wide wave and tide dominated delta depositing sediments derived primarily from the
interior of South America onto the South American Continental Shelf, on meeting the
Atlantic Ocean.
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Satellite imagery of Trinidad and Eastern Venezuela.
The continent of South America, as we know it today, was part of a greater landmass –
Pangaea, some 300 million years ago (Ma), during the Late Paleozoic to Early Mesozoic
eras. During the Early Jurassic (~200Ma) rifting commenced, beginning at the Tethys
Sea in the east and progressively opening to the Pacific Ocean in the west. The
supercontinent Pangaea was therefore split into two landmasses termed Laurasia and
Gondwana. It is during this time the Trinidad area began its evolution. This rifting phase,
directed to the north west, with north west to south east oriented transfer segments (such
as Bohordal, Urica and Los Bajos Fault) led to marine incursion and the deposition of the
Couva Evaporites in Trinidad. During the Early Cretaceous (150Ma-140Ma) Gondwana
began to break up into multiple continents as we know them today –South America,
Africa, India and Australia. By the Middle Cretaceous (120Ma) South America began to
move westward away from Africa opening up the South Atlantic Ocean from south to
north. It is believed that during the break up of Pangaea, the Guyana Shield and or
basement rocks to the south, were dissected and uplifted resulting in the generation of
much topographic relief within the interior of northern South America. These uplifts
remain today as the extensive array of table-top mountains termed – tepuis.
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Immediately south of the El Pilar Fault, and the Araya Paria metasedimentary rocks
within onshore north eastern Venezuela, the area is composed of heavily folded
Cretaceous rocks such as Querecual Formation (Upper Cretaceous) – time equivalent of
Naparima Hill in Trinidad. These south easterly verging fold and thrust belts form the
Serrania del Interior, and are driven by the oblique collision of the Caribbean Plate with
the northern margin of South America, and are dissected by lateral ramps namely from
west to east: Tacata, Urica and San Francisco. Each lateral ramp is complimented by a
frontal south easterly verging thrust. The relative location for these lateral ramps is
believed to be related to zones of underlying transfer faults that existing during the PostPangaea rifting phase.
Southward along the fold and thrust belt, Miocene to Recent stratigraphy onlap onto the
deformation front to the north, thickening within the asymmetric Maturin foredeep. As
such there remains many preserved anticlines completely buried by Pliocene to Recent
sediments e.g. El Furrial oilfield along the Pirital Thrust. The Maturin Basin comprises
mainly of easterly facing normal faults, especially within the younger stratigraphy due to
active loading and subsidence by the Orinoco delta. Further southward, the Pleistocene
deltaics give way to rifted- down to the north, in places inverted, heavily intruded
basement rocks (Archean-Early Proterozoic). Much of these areas occur within the
Canaima National Park.
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The National park is part of the plateau of the Guyanese shield that underlies the entirety
of the lands located in Venezuela to the south of the Orinoco, and is composed of three
main geological formations. The oldest is an underlying igneous-metamorphic basement
formed some 1.2-3.6 billion years ago whilst South America was joined to Africa as the
supercontinent Gondwanaland. Between 1.6 and 1 billion years ago, this was overlain
with a sedimentary cover. The first of these formations is too deeply buried to be visible
within the park, but second (known as the Roraima Group) forms the basis of the area's
extraordinary topography (Huber 1995). It consists of quartzite and sandstone strata
which were probably laid down in shallow seas or large inland lakes (Briceño et al. 1990)
during the Pre-Cambrian period. Lastly, during Palaeozoic and Mesozoic times magma
repeatedly penetrated the existing sediments forming intrusive rocks which are typically
diabases, and to a lesser extent granites. The tepui formations, came into being by a
process of erosion of the surrounding lands over millions of years. The tepuis are
sandstone massifs, and it is thought that what are today mountains once formed harder or
less faulted strata which were more resistant to erosion. There is an impressive array of
different soil types. The low mineral content of the parent rocks of the Guyana Shield, the
high rates of weathering that occur in tropical climates and the age of the sediments has
produced soils which are generally acid and nutrient poor.
Proterozoic (~2.5Ga - 540Ma) :- In contrast to the deep-water deposits of the Archean,
the Proterozoic features many strata that were laid down in extensive shallow
epicontinental seas, such as the Roraima Group at the Auyan tepuis at Angel Falls;
furthermore, many of these rocks are less metamorphosed than Archean-age ones, and
most are unaltered. Study of these rocks shows that the eon continued the massive
continental accretion that had begun late in the Archean, and featured the first definitive
supercontinent cycles. The first known glaciations occurred during the Proterozoic; one
began shortly after the beginning of the eon, while there were at least four during the
Neoproterozoic, climaxing with the Snowball Earth of the Sturtian and Marinoan
glaciations. One of the most important events of the Proterozoic was the gathering up of
oxygen in the Earth's atmosphere. Though oxygen was undoubtedly released by
photosynthesis well back in Archean times, it could not build up to any significant degree
until chemical sinks — unoxidized sulfur and iron — had been filled; until roughly 2.3
billion years ago, oxygen was probably only 1% to 2% of its current level. Banded iron
formations, which provide most of the world's iron ore, were also a prominent chemical
sink; most accumulation ceased after 1.9 billion years ago, either due to an increase in
oxygen or a more thorough mixing of the oceanic water column. Red beds, which are
colored by hematite, indicate an increase in atmospheric oxygen after 2 billion years ago;
they are not found in older rocks. The oxygen buildup was probably due to two factors: a
filling of the chemical sinks, and an increase in carbon burial, which sequestered organic
compounds that would have otherwise been oxidized by the atmosphere.
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Throughout the history of the Earth, there have been times when the continental mass
came together to form a supercontinent, followed by the break-up of the supercontinent
and new continents moving apart again. This repetition of tectonic events is called a
Wilson cycle. It is at least clear that, about 1,000–830 Ma, most continental mass was
united in the supercontinent Rodinia. Rodinia was not the first supercontinent; it formed
at about 1.0 Ga by accretion and collision of fragments produced by breakup of the older
supercontinent, called Nuna or Columbia, which was assembled by global-scale 2.0–1.8
Ga collisional events. This means plate tectonic processes similar to today's must have
been active during the Proterozoic. After the break-up of Rodinia about 800 Ma, it is
possible the continents joined again around 550 Ma. The hypothetical supercontinent is
sometimes referred to as Pannotia or Vendia. The evidence for it is a phase of continental
collision known as the Pan-African orogeny, which joined the continental masses of
current-day Africa, South-America, Antarctica and Australia. It is extremely likely,
however, that the aggregation of continental masses was not completed, since a continent
called Laurentia (roughly equivalent to current-day North America) had already started
breaking off around 610 Ma. It is at least certain that by the end of the Proterozoic eon,
most of the continental mass lay united in a position around the south pole.
The first advanced single-celled, eukaryotes and multi-cellular life, Francevillian Group
Fossils, roughly coincides with the start of the accumulation of free oxygen. This may
have been due to an increase in the oxidized nitrates that eukaryotes use, as opposed to
cyanobacteria. It was also during the Proterozoic that the first symbiotic relationships
between mitochondria (for nearly all eukaryotes) and chloroplasts (for plants and some
protists only) and their hosts evolved. The blossoming of eukaryotes such as acritarchs
did not preclude the expansion of cyanobacteria; in fact, stromatolites reached their
greatest abundance and diversity during the Proterozoic, peaking roughly 1.2 billion
years ago. Classically, the boundary between the Proterozoic and the Phanerozoic eons
was set at the base of the Cambrian period when the first fossils of animals including
trilobites and archeocyathids appeared. In the second half of the 20th century, a number
of fossil forms have been found in Proterozoic rocks, but the upper boundary of the
Proterozoic has remained fixed at the base of the Cambrian, which is currently placed at
542 Ma.
Roraima Group:- Sedimentary rocks of the Roraima Group were deposited in fluvial,
deltaic, shallow marine, and lacustrine or epicontinental environments on the Guyana
Shield. The Guyana Shield in Venezuela is composed of five lithotectonic provinces:
(1) an Archean amphibolite- to granulite-facies gneiss terrane
(2) an Early Proterozoic greenstone-granite terrane(s)
(3) an Early Proterozoic unmetamorphosed volcano-plutonic complex
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(4) Early to Middle Proterozoic continental sedimentary rocks
(5) Middle Proterozoic anorogenic rapakivi granite. Early to Middle Proterozoic
continental tholeiitic dikes, sills, and small intrusive bodies, and Mesozoic dykes
emplaced during the opening of the Atlantic Ocean cut all of the lithotectonic provinces
(Sidder and Mendoza, 1991).
Regional stratigraphy of the Roraima Group has been described by Reid (1972), Reid and
Bisque (1975), Ghosh (1985), Yanez (1985), and Alberdi and Contreras (1989). Four
formations are recognized in the Roraima Group by Reid (1972), which are, from oldest
to youngest: the Uairen, the Kukuenan, the Uaimapue, and the Mataui. The Uairen
Formation is an 850 m thick basal sequence of conglomerate, gravel, and pebbly
sandstone with well-rounded pebbles (-10 cm) of quartz, quartz porphyry, and quartzite
in conglomerate beds that are 30 cm to 1 m thick (Wyant and others, 1953). The
Kukuenan Formation consists of 50-100 m of fissile shale and is overlain by the
Uaimapue Formation, a 250 m section of jasper, chert, siltstone, and sandstone. The
youngest unit is the Mataui Formation, a crossbedded, massive sandstone unit of
unknown thickness with no jasper or chert.
The Uairen Formation is known for its placer gold and diamond production, and the
Mataui Formation forms prominent plateaus with vertical cliffs, or "tepuis," in the region.
Relatively unmetamorphosed Cuchivero Group and other pre-Roraima rocks are
unconformable beneath the Roraima Group. The pre Roraima rocks include deformed
quartzite, schist, and conglomerate (McCandless, 1962; Briceno, 1982; Ghosh, 1985).
Regional thickness of the Roraima Group in Venezuela, Guyana, Suriname, and northern
Brazil is estimated to be 2600 m (Dalton in Reid and Bisque, 1975). Sidder and Mendoza
(1991) have compiled dates for the Roraima Group and consider the Roraima to range
from 1.5-1.9Ga.
Sources:
www.islandhikers.com
www.sciencedirect.com
www.usgs.gov
www.tectonicanalysis.com
www.gstt.org
www.jimmieangel.org
www.lyellcollection.com
www.wikipedia.com
Google Earth
www.venezuelatuya.com
www.whc.unesco.org
www.lonelyplanet.com
Google Maps
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29
Tectonic Map of the Eastern Venezuela Basin (Pindell, 2004)
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31
Surface Geology Map of Northern Venezuela
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Surface Geology Map of Southern Venezuela
Notes
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