18
Gilberto Rodriguez
a
b
Fig. 2.2. Quaternary history of the Maracaibo basin. a second interglacial (Yarmouth); b second glaciation (Wisconsin) (data from GrafI969, 1972)
the Recent sediments; and a horizon of diatomite. The Recent sediments rest unconformable on the clays of the Milagro Formation. 14C determinations on the peats indicate ages of 7000-10000 years (Sarmiento and Kirby 1962).
Paleontological evidence shows that the lake throughout its Recent history has fluctuated from fresh to a brackish body of water. The maximum salinity was reached
during the rise of the sea level that accompanied the postglacial climate optimum
(Sarmiento and Kirby 1962). The date of the last opening of the estuary is given by
Redfield and Doe (1964) as 8000 years B.P. and by Sarmiento and Kirby (1962) between 4000 and 5000 years B.P. For the sea to transgrede into the lake it is necessary
a rise in sea level of 20 m, which is the value given by Sheppard (1961) for the elevation of the sea level in stable coasts during the last 9000 yr. After the connection with
the sea was established numerous islands and bars were formed at the mouth of the
estuary (Redfield 1955).
2.4
Climatology
2.4.1
Temperature
The temperature of the air in the basin is very stable. Mean annual temperature in the
north and central part of the basin (mean of 10 yr) is 28.3° C. Mean daily differences
is 7° C and mean differences between the hottest and coldest month is approximately
4° C. Surface water temperatures are very uniform throughout the inner shallow area
(12-20 m total depth) of the Gulf of Venezuela, with small seasonal and diurnal differences. The column of water is only slightly stratified or completely homogeneous;
according to Rodriguez (1973) data for March 1969, the maximum vertical temperature difference observed in 20 m was 1.4° C.
Gilberto Rodriguez
a
b
Fig. 2.2. Quaternary history of the Maracaibo basin. a second interglacial (Yarmouth); b second glaciation (Wisconsin) (data from GrafI969, 1972)
the Recent sediments; and a horizon of diatomite. The Recent sediments rest unconformable on the clays of the Milagro Formation. 14C determinations on the peats indicate ages of 7000-10000 years (Sarmiento and Kirby 1962).
Paleontological evidence shows that the lake throughout its Recent history has fluctuated from fresh to a brackish body of water. The maximum salinity was reached
during the rise of the sea level that accompanied the postglacial climate optimum
(Sarmiento and Kirby 1962). The date of the last opening of the estuary is given by
Redfield and Doe (1964) as 8000 years B.P. and by Sarmiento and Kirby (1962) between 4000 and 5000 years B.P. For the sea to transgrede into the lake it is necessary
a rise in sea level of 20 m, which is the value given by Sheppard (1961) for the elevation of the sea level in stable coasts during the last 9000 yr. After the connection with
the sea was established numerous islands and bars were formed at the mouth of the
estuary (Redfield 1955).
2.4
Climatology
2.4.1
Temperature
The temperature of the air in the basin is very stable. Mean annual temperature in the
north and central part of the basin (mean of 10 yr) is 28.3° C. Mean daily differences
is 7° C and mean differences between the hottest and coldest month is approximately
4° C. Surface water temperatures are very uniform throughout the inner shallow area
(12-20 m total depth) of the Gulf of Venezuela, with small seasonal and diurnal differences. The column of water is only slightly stratified or completely homogeneous;
according to Rodriguez (1973) data for March 1969, the maximum vertical temperature difference observed in 20 m was 1.4° C.