(Table 2) Porosity and permeability of limestones from DSDP Hole 44-392A

At sites 390 and 392 (Deep Sea Drilling Project, Leg 44) on the Blake nose, thoroughly lithified Lower Cretaceous limestone more than 250 m thick is abruptly overlain by a condensed sequence of Barremian to Eocene pelagic carbonate ooze. The Lower Cretaceous sediments consist of three units: limestone with moldic porosity (base), oolitic limestone, and fenestral limestone. Subaerial diagenesis of the limestone section is recorded by (1) caverns with vertical dimensions of up to 10 m, (2) stalactitic intergranular cement, and (3) meniscus sediment (or cement). Compatible with these subaerial features are mud cracks, fenestral fabrics, intraclasts, and cryptalgal structures. Inasmuch as these shallow-water and tidal-flat deposits are now beneath 2,607 m of sea water (plus 99 m of younger sediments), they serve to dramatize the apparent degree of Barremian and later subsidence of this part of the Atlantic outer continental shelf. Porosity and permeability are high in vuggy samples, which are common in the skelmoldic limestone. Cementation has destroyed most of the extensive primary porosity of the two younger units.在布莱克鼻（Blake Nose）的390与392站位（深海钻探计划（Deep Sea Drilling Project）第44航次），厚度逾250米的强固结下白垩统（Lower Cretaceous）灰岩之上，被一套巴列姆期（Barremian）至始新世（Eocene）远洋碳酸盐软泥（pelagic carbonate ooze）凝缩序列（condensed sequence）以突变接触关系覆盖。该下白垩统沉积物可划分为三个单元：底部为铸模孔隙（moldic porosity）灰岩、鲕粒灰岩（oolitic limestone）以及窗格灰岩（fenestral limestone）。这套灰岩段的大气成岩作用（subaerial diagenesis）证据包括：其一，垂向尺度可达10米的洞穴；其二，钟乳状粒间胶结物（stalactitic intergranular cement）；其三，新月形沉积物（或胶结物）（meniscus sediment/cement）。与上述大气成岩特征相匹配的还有泥裂（mud cracks）、窗格构造（fenestral fabrics）、内碎屑（intraclasts）以及隐藻构造（cryptalgal structures）。 鉴于此类浅水潮坪沉积（tidal-flat deposits）现今埋藏于2607米海水（叠加99米新生代沉积物）之下，它们直观展现了大西洋外大陆架该区域自巴列姆期以来的显著沉降幅度。 溶孔发育的样品（此类样品在铸模灰岩（skelmoldic limestone）中较为常见）具备较高的孔隙度与渗透率。胶结作用（cementation）已破坏了两套较年轻地层的绝大多数原生孔隙（primary porosity）。