biostratigraphy and paleoecology of cretaceous/tertiary boundary in ...

Chapter Four
Depositional Environmenment and Paleoecology
occurrence of these foraminiferal assemblages (all planktonic and most of
benthonic foraminifera) are restricted to the thin beds of shale, marl and marly
limestone intercalation within thick beds of interfingering Aqra Limestone
Formation which is famous by its components of macro and microfossils as
mentioned in Qishlagh section. Consequently the reliable bathymetry of this
unit is not greater than 30m. depth with cyclical deepening during the
deposition of shale or marly limestone intercalations.
The Aqra Limestone Formation followed by 35m. of alternation of bedded
limestone grey shale, marl, friable sandstone, marly limestone, calcareous
fossiliferous sandstone sandy limestone, with detrital fossiliferous limestone
and claystone. This interval characterized by little benthonic foraminiferal
assemblages of larger size without macrofossils growth in situ ,it is
characterized by decreasing in agglutinated percent from 20 to 10 in the upper
part of this interval. The depositional environment and paleobathymetry of this
unit may represent upper part of inner neritic shoal from 10 to 30m depth. This
interval characterized by no evidence of any porcelaneous foraminiferal
assemblages as Qishlagh section which indicates no restriction, high agitation
of watermass, and high rate of deposition which may cause the dilution of
planktonic foraminiferal survivorship.
4.4.2- Paleocene
A progressive shallowing of depositional environment started from the
Pseudoguembelina palpebra Zone (CF2) in all studied sections especially at
Gali, Qulka and Sirwan section from 65.5my upward and continued to the lower
Paleocene through Plummerita hantkeninoides Zone (CF1),Guembelitria
cretacea Zone (P0), Parvularugoglobigerina eugubina Zone (Pá),
Parvularugoglobigerina eugubina-Subbotina triloculinoides Zone (P1a) and
Subbotina triloculinoides-Praemurica inconstans (P1b). This trend of
shallowing integrated and contributed with stacking pattern of high rate
sedimentation which display extreme climax rate around Cretaceous/Tertiary
boundary with the rate of deposition about 100m/my. (Figs 4. 11, 12 & 13)
100