| A prominent mid-Cretaceous sequence boundary (MCSB) divides the rock record in the Gulf of Mexico basin into two major depositional episodes and marks a major turning point in Gulf history. The nature and orgin of this boundary is still controversial. Along the deep eastern Gulf continental rise the MCSB is a prominent unconformity marked by truncation below and onlap above.
The upper part of the Lower Cretaceous section in the deep eastern Gulf is characterized by deep-sea fan systems oriented parallel to the margin. In places lying directly below the the MCSB are large southward-prograding mounds or buildups. Both of these features are interpreted to have been deposited by strong south-flowing contour currents. These currents apparently developed and intensified during the middle Cretaceous as the carbonate margins rimming the basin steepened through time, further restricting the basin. They flowed south along the base of the Lower Cretaceous carbonate margin and then out of the basin through the only deepwater outlet lying between Florida and Yucatan, possibly as part of a larger boundary current system in the Atlantic.
The overlying MCSB is characterized by major truncation of Lower Cretaceous units, probably due to extreme intensification of the currents caused by major mid-Cretaceous drops in sea level. This suggests that the MCSB represents a true erosional sequence boundary and not just regional onlap, a flooding surface or a drowning unconformity as suggested by other authors. |