Tectono-sedimentary evolution of the Suriname margin in the cretaceous: A sequence-stratigraphic framework

Abstract

The offshore margins of Guyana, Suriname, and French Guyana (the “Guyanas Equatorial Margin”) have become the focus of active hydrocarbon exploration over the last decade, with significant energy resources discovered since 2015 along both the Guyana and Suriname segments of the margin. Those discoveries are mainly associated with the Late Cretaceous series of the Guyana-Suriname Basin and they shed light to a rare situation where stratigraphic traps are particularly successful. To date, the tectono-stratigraphic evolution of the area has been primarily examined at margin-scale through seismic refraction, rare borehole data and sparse, regional long offset multichannel 2D seismic datasets. In this paper we combine the results from newly acquired high-resolution well data, 2D/3D seismic interpretation and 3D seismic geomorphology, to build a robust and consistent sequence stratigraphic framework and address the evolution of Cretaceous sedimentary landscapes offshore Suriname, with a particular emphasis on the Late Cretaceous strata.

The Suriname margin displays a very specific overall sequence stratigraphic evolution marked by four main phases each characterized by distinct sedimentary fluxes and related overall geometries: 1) a margin initiation phase, 2) an aggrading phase, 3) a backstepping phase and 4) a forestepping phase.

The Suriname basin initiated in the Early/Mid Jurassic after the emplacement of thick Early Jurassic volcanic series attributed to the Sierra-Leone (or Bahamas) Hotspot (phase 1). This localized early magmatic activity led to two very different configurations: a typical Volcanic Passive Margin in the east along the western border of the Demerara Plateau and a transform segment to the west (essentially along the Guyana margin). The following phase (phase 2) is characterized by the establishment of a Late Jurassic to Early Cretaceous mixed clastic‑carbonate platform with an overall aggradational stacking pattern observed until the Early Aptian. Phase 3 started by significant backstepping, that culminated during the Cenomanian-Turonian transition, coeval with widespread organic-rich marine shale deposition. This overall transgression occurred in four steps: (B) late Early Aptian flooding followed by renewed margin progradation; (C) Early Albian flooding and (D) Late Albian to Cenomanian flooding above the break-up unconformity and (E) the maximum backstep at the Cenomanian-Turonian boundary.  This long-term transgressive trend is interpreted as the combination of (1) long-term eustatic rise during the early Cretaceous; (2) high rates of margin subsidence following the Aptian to Albian opening phase of the Equatorial Atlantic, and (3) relatively limited sediment supply rates along the margin at that time.

The successive, backstepping shelf-margin wedges created a distinctive stepped profile (paleo shelf-margins) that greatly impacted the geometries of the overlying Late Cretaceous sequences. During this backstepping phase, clastic sediment delivery to the deep-water part of the Suriname basin in the Early Cretaceous was limited and mainly sourced from the large Berbice Canyon complex at the Guyana-Suriname border. The outlet of the Berbice drainage systems may have been anchored by an aborted section of the Jurassic rift and linked to the onshore Takutu graben which separates the Guyana shield in two parts.

The fourth phase of the Jurassic to Cretaceous evolution of the Suriname margin is characterized by a dramatic increase of the sediment supply during the Santonian resulting in the accumulation of thick sequences of channel-dominated turbidite fans. This renewed clastic input is linked to a major drainage reorganization on the Guyana shield and is also coeval to the change from the point-sourced Berbice system to a line-sourced input from smaller rivers and deltas along the Suriname margin. From Early Santonian to Late Maastrichtian, the offshore sedimentary systems were then characterized by an overall regression with stacked coastal clastic systems on the shelf and continued fan deposition in the slope together with abundant slope erosion and related Mass Transport Complexes. At higher frequency this long-term forestepping Late Cretaceous trend was modulated by accelerated pulses of sediment supply (and associated margin progradation) during the Middle Santonian, Middle Campanian, and the Early Maastrichtian.

From the Santonian turn-around to the Late Maastrichtian, sedimentary systems are deciphered as sequences constrained by biostratigraphic data from the latest industry wells in Block 58 in Suriname and combined with seismic interpretation of both 3D and 2D data. The multi-scale sequence stratigraphic framework built in this study highlights 1) the specific sedimentary architecture of the margin and 2) the role and the impact of external forcing on the sedimentation rate. Moreover, the results highlight the key importance of topographic inheritance (from both structural and sedimentary origin) on deep-water reservoir architecture, that led to important hydrocarbon accumulations through stratigraphic trapping in offshore Suriname.