Dr. Jim Wright (University of Georgia, center) organized a one day trip to show the participants in the marine and landbased seismic survey of the Venezuelan margin key outcrops on the island of Aruba. From left to right: Gail Chistenson (UTIG), Alan Levander (Rice Univ.), and Jim Pindell (Tectonic Analysis, UK).

Cretaceous pillow basalts exposed east of Dos Playa beach on the north coast of Aruba. These rocks form the oldest dated rocks on Aruba and consist of amygdaloidal basalt pillow lava pictured here. The basalt is interbedded with marine sedimentary rocks containing Turonian ammonites. The geochemistry of the pillow basalts indicates their affinity to mid-oceanic ridge basalt (MORB) or ocean island tholeiites (OIT). White et al. (1999) propose that these basalts formed as part of the Caribbean oceanic plateau.

Cleaved slates well exposed in dry gulley west of Dos Playa beach. A sedimentary unit of pebbly mudstone, argillite, and basaltic tuff is interstratified with the pillow basalt. The argillite units like the one shown here contain Turonian ammonites. Both units are folded and cleaved about northwest-trending axes parallel to the present-day topography axis of the island. This folding event occurred in Turonian time and was over by the time of the emplacement of the Aruba batholith that is well dated by U-Pb dating to be 89 my old.

Cretaceous unconformity surface. A Cretaceous subaerial weathering surface characterized by these distinctive colorations around fractures separates the underlying Turonian section of pillow basalt, argillite, and diabase from an overlying late Cretaceous section of basaltic lapilli tuff and conglomerate.

East-west trending quartz diorite dike radiating outward from the Aruba batholith. The pale dike rock is slightly more resistant that the darker argillites it intrudes. These dikes extend several hundred meters in length and are 89 my old.

Cretaceous lapilli tuff. The distinctive reptile-like texture of lapilli tuff is formed as the result of explosive ejection of tuff fragments into the atmosphere following by settling and grading in a submarine environment or reworking in a subaerial environment. The lapilli tuff units are interbedded with conglomerate units.

Granite on Aruba: The Aruba batholith dated at 89 + 1 Ma (late Cretaceous) underlies most of the island. Its origin is controversial. Some propose that it formed as part of the Cretaceous, proto-Caribbean island arc (Aves ridge remnant arc); others propose that it formed as part of the Cretaceous Caribbean oceanic plateau. Dr. Jim Wright of the University of Georgia is conducting field-based mapping and geochronology to better determine the tectonic origin of the Aruba batholith.

Topography: Because the Aruba batholith weathers faster than the older Cretaceous sedimentary and volcanic rocks it intrudes, it underlies the flat central part of the island and is rimmed by low hills of the more resistant wall rocks. Prehistoric rock shelters with petroglyphs are found at the foothills of the higher rim. The extreme aridity of the island is related to its position in a rain shadow behind the high coastal ranges of northern Venezuela.