Calcareous nannofossil biostratigraphy and sediment accumulation of turbidite sequences on the Madeira Abyssal Plain, Sites 950-952

Abstract

Drilling on the Madeira Abyssal Plain during Leg 157 penetrated deep into the sequence of interbedded turbidites and pelagic sediments that underlie the plain. The turbidites generally have abundant and well-preserved calcareous nannofossil assemblages, with the interbedded pelagic sediments having variable preservation and abundance of nannofossils dependent on CaCO 3 content. Poor preservation in pelagic sediments from the Paleogene and Miocene necessitated the use of nannofossil datums from turbidites to construct a consistent biostratigraphy.Site 950 records Neogene turbidite deposition of organic carbon-rich, volcaniclastic-rich, and highly calcareous turbidites from different sources around the plain with thin interbedded pelagic red clays, marls, and oozes. A disconformity separates the upper part of Zone CN3 from a single turbidite belonging to Zone CN2, below which a major disconformity separates Zone CN2 from Subzone CP19b, at the top of the Oligocene. Throughout the Oligocene and late Eocene, down to Subzone CP15a, the sequence comprises thin calcareous turbidites and thick pelagic red clays. Sites 951 and 952 only penetrated as deep as Zone CN3 and have similar sequences to the Neogene section of Site 951. Total sediment and pelagic sediment accumulation rates have varied dramatically with time, with low rates in the Paleogene section of Site 950 rising significantly throughout the Neogene. Sites 951 and 952 have much higher rates in the lower and middle Miocene than Site 950, above which all three sites have broadly similar rates.

Turbidite record of frequency and source of large volume (>100 km3) Canary Island landslides in the last 1.5 Ma: Implications for landslide triggers and geohazards

“…To further aid age verification of the turbidites recovered in the piston cores, previous biostratigraphic and magnetostratigraphic dates from ODP studies are utilized. A R. asanoi biostratigraphic event at 36.51–37.52 m depth at ODP Site 950, 5 cm above bed Mz, is dated at 830 ka [ Howe and Sblendorio‐Levy , ]. The top of the Jaramillo event (980 ka) occurs at 39.7 m core depth below bed Mz and above bed Mab at ODP Site 950.…”

“…Lastly, the FO of G. ericsonii is at ∼0.38 Ma, with the LO at 0.015 Ma [ Biekart , 1989]. The coccolith biostratigraphy used to date the ODP record is published and documented by Howe and Sblendorio‐Levy [].…”

“…The stratigraphy for the top 55 m of sediment recovered from ODP Sites 950, 951, and 952 is first based on position in the vertical sediment sequence, color, and magnetic susceptibility. Additional information from coccolith biostratigraphy and mudcap chemostratigraphy aided development of the 0–1.5 Ma stratigraphy, dating of the deposits and deriving potential provenances [ Howe and Sblendorio‐Levy , ; Jarvis et al ., ]. Volumetrics of the deposits were calculated from the ODP core using the method of Alibés et al .…”

“…Stratigraphic analysis of Madeira Abyssal Plain turbidites was also completed for ODP Sites 950, 951, and 952 [ Weaver et al ., ; Howe and Sblendorio‐Levy , ], with a chemostratigraphy established for Site 950 [ Jarvis et al ., ]. The upper 50 m of these ODP cores from the central basin record the same stratigraphy recovered in the piston cores from the northern basin (Figure ).…”

Northwest African Continental Margin: History of sediment accumulation, landslide deposits, and hiatuses as revealed by drilling the Madeira Abyssal Plain

“…In addition, Weaver [1994] showed that each individual turbidite contains a relatively narrow age range of sediment, typically 0.5 million years or less. Thus useful stratigraphic information can be obtained from the turbidites in the absence of data from the pelagic layers [ Howe and Sblendorio‐Levy , 1998].…”