Neogene palaeoceanographic changes recorded in a carbonate contourite drift (Santaren Channel, Bahamas)

Abstract

The Santaren Drift between the Great Bahama Bank and Cay Sal Bank (Bahamas) is closely linked to the development of the Gulf Stream and its shape and geometry record the local to global oceanographic, climatic and tectonic events since the Miocene. High-resolution multichannel seismic data from the Santaren Channel allow detailed insight into the growth phases of the contourite drift, and by using the stratigraphic information from Ocean Drilling Program Site 1006 to infer its sedimentation rates. The results bring new understanding to this region and to interpretation of carbonate drifts. The data document that the signatures of a bottom current flow in the Santaren Channel initiated about 12Á3 Ma, as indicated by the first occurrence of sheeted drifts and moat development at the northern part of the Santaren Channel. Narrowing and steepening of moat flanks as well as the pronounced upslope migration of the moat reflects a sustained current acceleration of the bottom currents until 5Á5 Ma, associated with a transformation into mounded elongated drifts. Between 5Á5 Ma and 3Á1 Ma, bottom current intensity reached its maximum probably caused by the final closure of the Central American Seaway. The last 3Á1 Myr were characterized by a marked increase in volume through flow reaching a maximum during the past 900 kyr. Drift growth was driven by the combined sources of export from the shallow-water carbonate factory and by pelagic rain. The Middle Miocene channel-related sheeted drift of the inner Santaren Channel is characterized by low accumulation rates, but a rapid increase of accumulation rates occurred during the Early Pliocene. The contourite drift buildup was disturbed by minor erosional phases with narrow moats in the Late Pliocene due to increasing bottom-current velocities forced by strengthened Atlantic Ocean ventilation. The Early Pleistocene was dominated by increased periplatform sedimentation and margin progradation facilitated by a reduction in along-slope current flow speed and a concurrent widening and flattening of the moats.

Carbonate drifts as marine archives of aeolian dust (Santaren Channel, Bahamas)

“…). The drift body is lined by current moats towards the slopes of GBB and CSB (Anselmetti et al ., ; Lüdmann et al ., ; Wunsch et al ., ; Paulat et al ., ). These moats form shallow sea floor depressions (up to 22 m deep) of varying width.…”

“…Here, the material mixes with carbonate from pelagic sources forming periplatform ooze redistributed by oceanic currents. As a result, large carbonate drifts develop at the foot of the platform slopes and at the bottom of the marine straits that intersect the Bahamian archipelago since the Miocene (Bergman, ; Betzler et al ., ; Lüdmann et al ., ; Paulat et al ., ). The sediment of these drifts, albeit dominated by carbonate and subordinate biogenic silica, contains a terrigenous fraction, mainly clay minerals and quartz.…”

The ichnology of carbonate drifts

“…Up to now, carbonate drifts have not been as broadly investigated as their siliciclastic equivalents (Stow et al ., ; Viana & Rebesco, ; Rebesco & Camerlenghi, ; Rebesco et al ., ). Several studies, however, document their importance in the development of tropical carbonate platform edifices (Mullins et al ., ; Anselmetti et al ., ; Isern et al ., ; Betzler et al ., , , ; Eberli et al ., ; Lüdmann et al ., , ; Mulder et al ., ; Paulat et al ., ). Studies on the ichnology of siliciclastic drifts have demonstrated that such deposits are characterized by a high degree of bioturbation (Stow et al ., , ; Wetzel et al ., ; Rebesco et al ., ; Rodríguez‐Tovar & Hernández‐Molina, ).…”

“…The Bahamas archipelago is a carbonate province consisting of several isolated platforms situated at the southern end of the eastern continental margin of the United States. In the Santaren Channel, at a water depth of ca 600 to 700 m and ca 30 km from the western platform edge of the Great Bahama Bank, there is a continuous drift sequence which is Neogene to present day in age, that interfingers with prograding carbonate‐bank deposits of the Bahamas (Eberli et al ., ; Kroon et al ., ; Anselmetti et al ., ; Bergman et al ., ; Paulat et al ., ).…”

Facies and sedimentology of a carbonate delta drift (Miocene, Maldives)

“…The external morphology and internal architecture of these deposits have been studied widely leading to a synoptic classification based predominately on siliciclastic drifts (Stow et al ., ,b; Hernández‐Molina et al ., ; Rebesco et al ., ). In contrast, the knowledge about carbonate drifts is limited and restricted to deposits either at the flanks of the banks as periplatform drifts (Mullins & Neumann, ; Mullins et al ., ; Betzler et al ., ; Chabaud et al ., ), in seaways separating carbonate banks as detached drifts (Anselmetti et al ., ; Bergman, ; Lüdmann et al ., ; Paulat et al ., ), or at the downcurrent end of shallow passages dissecting carbonate banks as delta drifts (Lüdmann et al ., , ).…”