Aruba - Geological History EarthCache

The Dutch Caribbean island of Aruba owes its geologic formation to volcanic activity. Aruba’s two main landforms, rolling hills and flat coastal regions, are possibly overlooked by most visitors who gravitate toward the sunny beaches. According to Aruba.com, “Aruba attracts more than 800,000 international visitors annually and enjoys the highest return rate in the Caribbean.” Visitors who leave their beach chair in search of rewarding geological discoveries will not be disappointed. Travelers without a rental car can simply hire a taxi to get around the small island.

A tremendous flow of lava during the Upper-Cretaceous period arose from the sea floor, forming the Caribbean islands of Aruba, Bonaire and Curacao. For many years tectonic forces compressed and folded the rock, causing underwater igneous and sedimentary formations to rise from the sea. In subsequent years the islands were carved by natural erosion. Coral reefs formed around much of the islands, forming calcium-rich terraces. The resulting mix of igneous, sedimentary, metamorphic and conglomerate rocks combined to build the remarkable landforms of Aruba that we see today.

(source: http://traveltips.usatoday.com/landforms-aruba-104314.html)

Sediments

Limestones are the youngest rocks that make up Aruba and that surround the island’s older rocks. Limestone formed after and on top of the older rocks. Limestone formed very differently than the earlier rocks. Most limestone formed under water in an environment that is similar to the present-day marine environment where coral reefs grow. We know this because fossils found in the limestone are of the same organisms which live nowadays in the coral reef environment. Sediments from the breakdown of coral reefs were deposited on the seaslope, and these sediments consolidated into limestone. Other limestones are ancient sand dunes which have hardened over millions of years.

A combination of upward movements of the earths crust (known as epeirogenesis) and changes in sea level caused the limestone to be exposed above sea level. When these processes caused the earth’s crust to rise up and remain higher, some limestone stayed above sea level. This resulted in a landscape characterised by terraces. The cliffs of the terraces follow old coastlines, which are very similar to the modern coastline of Aruba. We can identify older to younger limestone in the higher, middle, and lower terraces. The older limestone (higher terrace) is best visible at Rooi Frances. Younger limestone (middle and lower terraces) can be seen here. In summary the rocks on Aruba originate from three major events, volcanism, plutonism and limestone formation. The latter is a very different process than the other two.

The rocks produced by these events differ in appearance and in the landscape they constitute. The island is nowadays mainly covered by the black and white speckled plutonic rock called quartzdiorite.

(source: http://anvilmotion.net/.Trashes/501/m2results/websites/icm_aruba/email_03/aruba_geo.pdf)

Where you step on today at the cache location was part of a large reef platform which maintained for a period of million years.
This is known because the sedimentary rock called colcarenites you can see under your feet contains fossils of the fauna that lived in lagoon.
These materials were exposed to erosion by lowering the sea level , subsequently dune systems were settled on the eroded reef. These dunes can be seen at the cliffs and near the north part of Aruba (near the lighthouse).
 

To log this Earthcache you have to mail us the answers to the following questions/ tasks:

1. To find out how high the layers  are today above the sea level, please measure the altitude with your GPS at the Cache-Location !

2. Name at least two of the corals and/ or fossils you see at the cache location (using the internet).

3. 'Upload a picture showing you or your GPS at the Cache-Location !