AAPG Bulletin, V. 83
(1999), No. 9,
Physical Property Changes as a Monitor of Pelagic
Carbonate Diagenesis: an Empirically Derived Diagenetic Model for Atlantic
Jens Grützner2 and Jürgen Mienert3
©Copyright 1999. The American Association of
Petroleum Geologists. All Rights Reserved
1Manuscript received February 5, 1998; revised manuscript
received February 2, 1999; final acceptance March 16, 1999.
2GEOMAR Forschungszentrum für marine Geowissenschaften,
Wischhofstr. 1-3, D-24148 Kiel, Germany; e-mail: [email protected]
3GEOMAR Forschungszentrum für marine Geowissenschaften,
Wischhofstr. 1-3, D-24148 Kiel, Germany. Now at Department of Geology,
University of Tromsø, Dramsveien 201,N-9037 Tromsø, Norway.
We acknowledge the financial support of the "Deutsche Forschungsgemeinschaft
(DFG)." The manuscript was improved by the comments of J. W. Schmoker,
R. E. Garrison, and one anonymous reviewer.
A new physical model of carbonate diagenesis has been derived
based on physical property measurements from 81 DSDP/ODP (Deep-Sea Drilling
Project/Ocean Drilling Project) drill sites in the Atlantic Ocean. Changing
depth gradients of porosity, bulk density, P-wave velocity (vertical and
horizontal), and acoustic impedance characterize five successive diagenetic
stages: (1) compaction of ooze, (2) breakage and dissolution of fossil
tests, (3) formation of chalk through precipitation of calcite, (4) cementation,
and (5) compaction of calcite crystals. Age-depth information from the
drill sites was used to calculate the average duration of these processes
in Atlantic Ocean basins. The model can predict carbonate sediment physical
properties down to a burial depth of 1000 m. The model is presented for
both lab and in-situ conditions and thus can serve as a standard for comparison
with lab, log, and seismic measurements. An acoustic impedance vs. age
curve derived from the model allows estimation of the initial and present-day
diagenetic potential of carbonate sediments and chalk reservoirs.