SOUTH ATLANTIC CARBONATE PLATFORM DURATIONS SHOW ADJACENT RIFT-SHOULDER ESCARPMENTS TO HAVE SURVIVED < 40 MY

Subaerial topographic escarpments (h~1 km) near rifted continental margins of Atlantic-type oceans are either: (a)long-term survivals since initial rifting (up to~180 Ma) or (b)Related to young (< 50 Ma) continental elevation.

Evidence supporting (a) comes largely from interpretations of onshore fission tracks while that in support of (b) is from integrated onshore and offshore information. Carbonate platforms provide key data.

Ocean floor began to form in the S.Atlantic along a length of ~8,000 km at ~128 Ma. Evaporite deposition at ~112 Ma (in then lats 10-25 S) was immediately followed by carbonate deposition itself overwhelmed by siliciclastic deposition between 7 and 22 My later.

These observations are interpreted to show: (i) that carbonate deposition dominated as long as initial escarpments were barriers to rivers carrying abundant sediment (ii) those escarpments did not survive long (iii) siliciclastic deposition has since been general.

As Bob Ginsberg has shown carbonate rocks can be used to answer a range of geological questions.