The Jurassic rifted margins and ocean basin, offshore Guyana-Suriname-Demerara and its link with Gulf of Mexico opening

The Guyana-Suriname-Western Demerara (G-S-WD) continental margins are located at the junction of the Central Atlantic and proto-Caribbean oceanic basins as they developed in the Jurassic. The emplacement of the later Caribbean subduction partly destroyed the Jurassic record of the proto-Caribbean basin which implies that the Jurassic kinematics of this region are still debated. However, the G-S-WD margins escaped from subduction and preserve most of the Jurassic record. We investigate the architecture of the G-S-WD margins and the distribution of Jurassic oceanic crust. This allows us to determine the margins tectonic styles and gain insights into the Jurassic regional plate kinematics during the southward propagation of the Central Atlantic, the opening of the proto-Caribbean basin and its link with the development of the Gulf of Mexico (GoM).

We use 3D gravity inversion to map Moho depth, crustal basement thickness and continental lithosphere thinning factor. Input data for the gravity inversion is sediment thickness from seismic reflection grids, satellite free-air gravity data and digital bathymetry. From the resulting 3D Moho depth volume we produce margin crustal cross-sections to determine the structure and architecture of the G-S-WD margins. The Guyana segment shows a transform architecture, the Suriname segment a rift-transform architecture and the Western Demerara segment a magma-rich rifted margin with SDRs up to 20 km thick.

We also use crustal thickness mapping from gravity inversion together with regional magnetic anomaly superimposed satellite gravity anomaly data to determine the extent of Jurassic oceanic crust and delineate its boundary with Cretaceous Equatorial Atlantic oceanic crust. The boundary between Jurassic and Cretaceous oceanic crust is identified as running from the NW corner of the Demerara Plateau to Barbados. This boundary has the same orientation as the Guyana transform margin.

Plate reconstructions of crustal thickness from gravity inversion have been used to examine the relationship between the Jurassic opening of the Central Atlantic, the development and opening of the GoM and the formation of the Jurassic crust offshore G-S-WD.

A new plate reconstruction of the opening of the GoM based on transform fault small circles observed in satellite free-air gravity data shows that before the rotational opening of GoM at ~165 Ma, the early GoM and oceanic crust offshore G-S-WD formed a co-linear linked rift/sea-floor spreading system offset by a sinistral transform to the west of Florida.